WO2024251498A1 - Touch sensor in the form of a ring and associated human-machine interface - Google Patents

Abstract

The invention relates to a sensor assembly (R) in the form of a ring, the assembly comprising an annular element (ANN) having a substantially cylindrical shape; at least two deformation sensors (SENS₁, SENS₂, SENS₃) mounted on the annular element on at least two radii thereof, respectively, the two radii being angularly separate from one another, so that the at least two sensors are sensitive to an overall deformation of the annular element; and an electronic module (EL) configured so as to produce a detection signal representative of the overall deformation of the annular element in response to the step of processing at least two signals transmitted by the at least two deformation sensors (SENS₁, SENS₂, SENS₃), respectively.

Description

RING-SHAPED TOUCH SENSOR AND ASSOCIATED HUMAN-MACHINE INTERFACE TECHNICAL FIELD OF THE INVENTION

The invention relates to a ring-shaped sensor, and extends to human-machine interfaces, systems allowing a user to control interactive systems, and is therefore in the field of human-machine interactions sometimes designated by the acronym HMI.

TECHNOLOGICAL BACKGROUND

Human-machine interfaces come in many forms that allow a user to interact with an electronic system, whether it is in the form of a computer, a robot, a television, a sound reproduction system, or a game console. These interfaces are designed to i) generate control signals from a user action, and then ii) transmit these signals to the electronic system.

The wide variety of possible actions for a user for the purpose of controlling the electronic system has been used to design various types of interfaces: it can be a keyboard, a mouse, a touch screen, an optical detection system, a microphone or even a controller, all equipped with sensors (contact, infrared, magnetometer, optical, camera, accelerometer, gyroscope, etc.) whose function is to detect a specific action by the user (movement, gesture, speech, actuation, etc.).

Among these various types of interfaces, development efforts have focused on devices in the form of a ring, generally intended to be worn around a user's finger, as described in US patent 9,582,076 B2 and in patent application US 2017/0242496 A1. Such devices have the advantage of minimal bulk, being able to be worn without bothering the user, but require complex sensors such as cameras intended to analyze the immediate environment of the ring and generating signals whose processing involves heavy calculations, requiring high-performance electronics, expensive and compromising the autonomy of these interfaces. In addition, this complexity negatively impacts the reliability of the control.

Still regarding ring-shaped devices, there are simpler design schemes, such as an eight-sided ring described in the paper by Hyunchul Lim et al., “OctaRing: Examining pressure-sensitive multi-touch input on a finger ring device,” UIST 2016 Adjunct - Proceedings of the 29th Annual Symposium on User Interface Software and Technology, Association for Computing Machinery, Inc, pages 223-224. Each of the eight faces is equipped with a pressure sensor to be directly pressed by the user. Various control signals can be generated depending on which pressure sensors are pressed simultaneously.

Along the same lines, patent application US 2020/0150715 A1 describes ring-shaped systems intended to be worn on a finger. Each of these systems is equipped with one or more sensors that may be intended to detect an action of the wearer of the ring performed by the hand wearing it or to detect an action that would be applied to it by the wearer's other hand.

Another device, a ring intended to be grasped with two hands by the user at two diametrically opposed areas, is described in patent application US 2022/0212112 A1. It comprises a flexible ring mounted on a base provided with a deformation sensor, the assembly being configured to generate a signal representative of the amplitude of deformation of the flexible ring when the user deforms the ring by bringing his hands closer together.

However, a human-machine interface having a general ring shape, of simple design while allowing the generation of varied control signals from equally varied user actions remains to be defined.

The applicant's objective is to propose, on the one hand, a ring-shaped deformation sensor and, on the other hand, an application of this deformation sensor to a human-machine interaction device taking the form of a ring sensitive to the deformation of an annular element of the ring caused by a user.

In order to achieve this aim, a first aspect of the invention is a sensor assembly in the form of a ring, comprising an annular element of substantially cylindrical shape, at least two deformation sensors mounted on the annular element at levels of at least two radii thereof, respectively, the two radii being angularly distinct from each other, such that the at least two sensors are sensitive to an overall deformation of the annular element, and an electronic module configured so as to generate a detection signal representative of the overall deformation of the annular element, in response to processing of at least two signals respectively emitted by the at least two deformation sensors.

Such a sensor assembly allows the detection of a wide variety of actions on the annular element forming its mechanical structure. More specifically, mechanical actions such as pressures, taps or frictions applied to the annular element itself cause its deformation and, thanks to the presence of at least two sensors, this deformation can be characterized spatially and followed over time. The annular element is not a simple passive support for the sensors, but participates, through its deformation, in the detection of a user action, more specifically a mechanical action causing a deformation of the annular element.

Thus, this sensor assembly allows the detection and characterization of a large number of actions, in a manner not limited to a binary detection logic of an action or to a measurement of a one-dimensional deformation amplitude. This sensor indeed makes possible the spatio-temporal monitoring of a deformation imposed on the annular element, as will be developed in more detail in the rest of the description.

It is notable that the actions do not have to be applied directly to the sensors, but can be applied at any point of the annular element, possibly at a plurality of points of this element, regardless of the presence or absence of sensors at this or these points. Furthermore, the point or points of application of the action on the annular element do not have to be fixed, but can be movable on the surface of this annular element.

The structure of the sensor assembly itself, with essentially sensors permanently fixed on an annular element, remains simple and does not include any moving parts, guaranteeing the reliability and robustness of the assembly.

According to additional non-limiting characteristics of the sensor according to the invention, considered individually or in any technically feasible combination:

- the annular element can have a monolithic structure;

- the annular element may be formed of metal;

- the at least two distinct rays may be angularly spaced apart from each other by an angle of between 20° and 160°;

- the at least two deformation sensors may be piezoelectric type sensors;

- the at least two strain sensors may comprise at least one thin monocrystalline piezoelectric element in the form of a plate extending in an extension plane defined by a first direction and a second direction normal to the first direction, with dimensions in the first direction and the second direction each greater than 100 µm and with a thickness of less than 50 µm, a ratio of the thickness to the dimension in the first direction or the dimension in the second direction being less than 0.1.

A second object of the invention is a human-machine interface comprising the sensor assembly according to the invention, the electronic module being further configured so as to generate a control signal from a device external to the human-machine interface in response to the detection signal.

Such an interface makes it possible to characterize in a simple, precise and time-monitored manner, a global or localized deformation of the annular element on the basis of local deformations measured by the sensors. Various control signals from an external device can be associated with the occurrences and variations in time of the deformation, which allows great flexibility of use compared to the simplicity of the device.

In fact, the deformations of the annular element are not evaluated using a single sensor, or using a single sensor independently of any other sensors, but using at least two sensors, a minimum number sufficient to detect and characterize a wide variety of deformations of the annular element.

The deformations can in particular be deformations considered as global, that is to say that they can be detected by all the sensors. The deformation amplitudes detected by each of the sensors, of relative values and respective temporal evolutions specific to each of the sensors, depend on the deformation actually applied to the annular element and allow a very fine characterization of the deformation and to associate it with an action applied on the annular element by the user. Thus, very diverse mechanical actions of the user on the annular element can be associated with as many control signals from the external device. This gives a very versatile control interface, capable of generating a very large number of control signals despite a very simple hardware architecture: a ring, two sensors and measurement and control electronics.

It is also an interface that does not infringe on the user's privacy since it does not rely on the acquisition and processing of video or sound signals, which may contain personal information. This interface is very suitable for integration into classic-looking jewelry, including small ones.

According to additional non-limiting characteristics of the sensor according to the invention, considered individually or in any technically feasible combination:

- the interface can be configured to keep awake only a first part of the acquisition module associated with the detection and to activate second parts of the acquisition module only when it is determined that respective activations of these second parts are necessary for an analysis of the signals emitted by the at least two deformation sensors;

- the calculator can be configured to (i) classify events represented by the signals emitted by the at least two deformation sensors and (ii) generate the control signal of a device external to the human-machine interface in response to this classification;

- the control signal may be representative of at least one action chosen from a tightening, a short tightening or a long tightening of the annular element between two fingers or between three fingers, repeated or not, in a centripetal direction to the annular element; a tightening of the annular element, repeated or not, parallel to an axis of revolution of the annular element; a closing of a hand with one finger carrying the annular element or the closing of a finger carrying the annular element; and a rotation of the annular element between two fingers of a first amplitude belonging to an angular interval or of a second amplitude greater than an upper limit of the angular interval;

- the control signal may be representative of at least one action selected from a touch of the annular element by a finger; a tap of a surface by a finger carrying the annular element; a tap of a surface directly with the annular element; the application of pressure to the annular element at a point moving on the annular element around a finger carrying the annular element; a sliding of the annular element on a surface, a sliding of a finger of a first hand on the annular element in a direction parallel to a finger of a second hand carrying the annular element; a localization of any one of the preceding actions; and a snap of a finger carrying the annular element;

- the acquisition module can be configured to detect a rotation of the annular element on the basis of the signals emitted by the at least two deformation sensors; and in response to the detection step, generate a signal representative of the occurrence of a rotation of the annular element;

- the signal is representative of a rotation having exceeded an incremental angular value;

- the interface may further comprise a wireless transmission module configured to transmit signals generated by the acquisition module to the external device and a source of electrical energy supply to the wireless transmission module and the acquisition module;

- the interface may further comprise a feedback device configured to signal to a user a generation of a detection signal by the acquisition module; and

- the interface may be configured to be threaded onto a part of a user or a rod of a control device of the external appliance.

The interface according to the invention can be compact, passive when piezoelectric type deformation sensors are used, and the processing of the signals generated by these sensors can be simple and light from the point of view of computational intensity, resulting in a high autonomy of the device. In addition, the detection of deformation of the ring, or, more specifically, of the annular element, can be of high sensitivity and can therefore operate without difficulty even with very rigid rings such as thick metal rings, such as commonly worn jewelry.

The invention extends to a kit comprising a human-machine interface according to the invention as well as an external device configured to be controlled by means of the human-machine interface.

BRIEF DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

There represents a human-machine interface according to the invention, taking the form of a ring equipped with sensors;

There represents ways of using the ring;

There represents structural features of the ring;

There is a functional diagram of elements constituting the ring;

There illustrates signals generated by the ring in response to pressure on a first sensor of the ring;

There illustrates signals generated by the ring in response to pressure on a second sensor on the ring;

There illustrates signals generated by the ring in response to pressure on a third sensor on the ring;

There illustrates signals generated by the ring in response to two successive presses on the ring sensors;

There represents signals generated by the ring in response to long and short ring clamps;

There illustrates signals generated by the ring during rotational actions in opposite directions;

There is a representation of signals generated by the ring during a rotation action;

There illustrates signals generated by the ring in response to a tap of a finger wearing the ring on a table;

There illustrates signals generated by the ring in response to a strike of the ring on a table;

There represents signals generated by the ring in response to taps at the sensors;

There represents a first and a second block of a ring usage algorithm;

There illustrates the location of a point on the ring;

There represents a third block of the ring usage algorithm;

There represents a fourth block of the ring usage algorithm; and

There represents variations in the structure of the human-machine interface of the .

There illustrates a variance curve taken from signals emitted by the sensors of the ;

There illustrates a step of determining the occurrence of an event from sensor signals;

There illustrates a method of controlling the human-machine interface;

There represents a table gathering test results of the process of the ;

There represents a table gathering test results of the process of the ;

There illustrates actions applied to the ring of the and recognized by the process of ;

There illustrates the determination of the amplitude of a rotation of the ring;

There represents various variance profiles depending on the type of actions applied to the ring;

There represents a thin piezoelectric element; and

There illustrates a strain sensor incorporating a thin piezoelectric element;

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention is described by means of Figures 1 to 19 and the associated passages below. Figures 1 to 4 and 19 provide information on the structure, usage and operating principle of the human-machine interaction ring.

Figures 5 to 18 detail a first option for exploiting the signals generated by the deformation sensors following manipulation of the ring by a user.

Figures 20 to 27 detail a second option for exploiting the signals generated by the deformation sensors following manipulation of the ring by the user.

Figures 28 and 29 illustrate a piezoelectric element that can be used to form a deformation sensor integrated into the human-machine interface according to the invention.

There illustrates the structure and the general operating principle of the ring according to the invention, with in (A) a perspective view of a sensor assembly R according to the invention, comprising an annular element ANN instrumented by three sensors SENS ₁ , SENS ₂ and SENS ₃ . The sensor assembly R may subsequently also be designated as the ring R. The sensors may be conventional deformation sensors, for example resistive gauges, the electrical resistance of which varies with their deformation, or piezoelectric type sensors. The latter are deformation sensors based on a piezoelectric measuring element, that is to say taking advantage of the piezoelectric behavior of a material to transform into an electrical signal a deformation that it undergoes under the effect of external forces, for example when it is stuck to a surface and the latter deforms. The annular element ANN may be made of any material capable of forming a self-supporting structure capable of being passed around a finger or a rod. The annular element may have a composite structure. Preferably, the annular element has a monolithic structure, i.e. formed from a single piece and a single material. Thus, the annular element may be formed from a metal piece. This latter configuration has the advantages of a simple, robust and reliable structure.

This instrumentation of the annular element, and therefore of the ring, makes it possible to couple it with an electronic module EL to form a human/machine interface in order to control, for example, an electronic device such as a computer, a smartphone, a television or a multimedia player. In this example, three piezoelectric deformation sensors SENS ₁ to SENS ₃ are glued to the annular element, on which the electronic module EL is mounted, configured to measure the electrical charges or the electrical voltage generated by the sensors, analyze them, and return, using a wireless technique, the information to an external device such as those mentioned above.

As illustrated in (B) of the , when the ring R is taken between two fingers F1 and F2, a pressure force F is applied on either side of the ring by the fingers (the pressure force therefore being applied to the annular element ANN), which will create an overall deformation of the ring that can be characterized using the three sensors SENS ₁ to SENS ₃ . More generally, and as will be detailed below, the detection of this deformation, single or repeated, and the profile of this deformation, corresponding for example to pressure between the fingers or to a strike, can be used to generate a control signal for an external device APP. Indeed, the sensors make it possible to detect the locations of the support points on the annular element, the temporal evolution of these locations, as well as the temporal evolution of the amplitude of the force applied.

As illustrated in (C) of the , when the ring is rolled between the fingers in a rotational movement Rot caused by the combination of the pressure force F and the displacements Dplt of the fingers F1 and F2, the position at which this force is applied to the annular element moves significantly, and this displacement can be measured by comparing the signals from the three sensors.

Various user actions on the ring can thus be detected and associated with predetermined actions, such as (i) a single squeeze between the fingers associated with a validation action, (ii) a double press associated with a back-up action in a menu of an application controlled by the ring, (iii) a rotation in one direction or the other associated with controlling scrolling up or down in a list or controlling the volume of a music player, and (iv) a tap of the finger wearing the ring on a hard surface such as a table or (v) a direct tap of the ring on a hard surface such as the table associated with validation actions equivalent to a single click or a double click of a computer mouse. The intensity of the squeeze or taps, or the speed of rotation can also be associated with particular commands to control the external device. Other actions can be considered, such as those listed in the table Tab. 1 below. In this document, when rotations are mentioned, and unless otherwise indicated, it is a rotation of the ring around its axis of revolution Ax, illustrated by the . A direction of rotation may be that of the trigonometric direction around this axis of revolution, or a direction opposite to the trigonometric direction. An axis of revolution is here considered as an axis of revolution making it possible to describe the general shape of the annular element, which extends parallel to the axis of revolution and has an overall shape having a symmetry of revolution around this axis, which includes the examples of figures 1, 3 and 19.

It should be noted that the ring taken as an example in this embodiment is equipped with three sensors, but a ring equipped with two sensors, the minimum number to spatially characterize the deformation of the ring, would also work. Using three sensors brings redundancy and an additional measurement allowing discrimination in the event of an ambiguous situation. It is also possible to use a greater number of sensors, with the disadvantages of an increase in the integration and cost of the ring, as well as a complexity of the electronic processing system to be integrated on the annular element, with an increase in the electrical contact tracks and signal processing paths, and as an advantage a better robustness of the event detections. An event is understood here as a deliberate action of the user on the ring in order to produce a control signal of an external device, the sensors generating signals in response to this action.

Also, the sensors SENS ₁ , SENS ₂ and SENS ₃ are illustrated located on the outer surface of the ring, but they could also be located on its inner surface, or even integrated into the volume of the annular element, for example by being sandwiched between two concentric rings.

In (C), the illustrates a ring equipped with two sensors SENS ₁ and SENS ₂ arranged on the inner surface of the ring, substantially at 90° to each other (the respective radii r1 and r2 make an angle of substantially 90° to each other).

The respective positions of the sensors on the ring are identified by means of rays, the center of one of the sensors defining a reference radius, the positions of the other sensors being identified by the angles made by the rays passing through their respective centers (in a sectional view along the axis of revolution Ax of the ring) with the initial radius. In the example of the in (A), the three sensors are arranged substantially homogeneously around the ring, at angular intervals of approximately 120°. In this case, the radius r1 associated with the SENS ₁ sensor can be considered as the reference ray, the radii r2 and r3 associated respectively with the SENS ₂ and SENS ₃ sensors being located respectively at approximately 120° and 240° from the radius r1.

There is no strict requirement to respect in the relative positioning of the sensors, except that it is advisable to avoid placing two sensors at diametrically opposed positions if one wishes to spatially characterize the deformation linked to a pressure exerted at two diametrically opposed points, for example between two fingers of the user: such a symmetrical positioning of the two sensors limits the spatial characterization capabilities of the deformation. It is also preferable to space two sensors sufficiently apart from each other to facilitate this spatial characterization, which is all the easier since the deformations measured by the sensors will have different amplitudes.

Thus, it is preferable that the rays defining the positions of the sensors are angularly spaced at angles between 20° and 160°, more preferably between 40° and 140°. Of course, the angles chosen may depend on the number of sensors integrated on the ring.

The ring may also be provided with a feedback device FB, or feedback in English terminology, informing the user that his manipulation of the ring by tightening, tapping or rotating has been taken into account. The FB device may be of any type conventionally used for this purpose, such as a light, sound or haptic device.

The ring can be manipulated while it is threaded onto a part of a user, and in particular onto a finger F6 of a hand H as illustrated in (A) of the , or threaded onto a rod or RD wand of an external device control system as in (B) of the . It is of course possible to construct the ring so that it can be worn, for example, on the user's wrist, arm or leg. Alternatively, the ring can be used "free" without being threaded onto any element, as illustrated by the .

The ring preferably has dimensions making it suitable for being put on a finger as would be a piece of jewelry such as a ring, with for example for the annular element ANN an internal diameter f _in , illustrated in (A) of the , between 1 and 3 cm and a length L, illustrated in (B) of the , along its axis of revolution Ax between 2 mm and 2 cm. The radial thickness Thck of the annular element, defined for example by (f _in - f _ext )/2 for a perfectly cylindrical annular element of external diameter f _ext , as illustrated in (A) and (B) of the , may be greater than 0.1 mm, preferably 0.4 mm, and less than 3 mm, preferably 1 mm. Such thicknesses provide sufficient rigidity for the annular element to be self-supporting while allowing deformations imposed manually by the user to be detectable, even if the annular element is formed of metal. Among the metals in which the annular element can be formed, a metal that is not very susceptible to corrosion and is hypoallergenic will preferably be chosen. For example, it may be a metal conventionally used in jewelry such as gold, silver, stainless steel, brass, titanium, solid or plated.

Furthermore, the ring is not necessarily a closed ring, but can also be an open ring with a cut C, as shown in (C) of the . Even without symmetry of revolution in the strict sense, we consider that the ring has an axis Ax oriented by revolution, illustrated in (B) of the and perpendicular to the plane of the page in (B) and (C) of the , located at the center of the ring and along which the ring extends. The orientation of the axis Ax is indicated by the arrowhead in the figure.

The ring element is considered to be substantially cylindrical in shape in the sense that it is capable of being slipped onto a finger. However, the substantially cylindrical shape of the ring element may encompass a variety of shapes, the important thing being that it can be comfortably worn on a finger by a user and that sensors can be integrated therein.

There illustrates the elements integrated on a ring R and the functional relationships between the elements composing it and with an external device. Thus, the ring R comprises, in a two-sensor configuration, two sensors SENS ₁ and SENS ₂ connected to an electronic module EL for processing the signals from the sensors.

The electronic module EL comprises an acquisition module ACQ in which an analog-to-digital converter CONV receives the analog signals from the sensors SENS ₁ and SENS ₂ and converts them into digital signals processed by a digital computer CALC. The digital computer processes the digital signals, generates detection signals in response to the digital signals, generates control signals S _Con of an external device APP on the basis of the detection signals, and sends these control signals to a communication module COM. The communication module COM has the function of transmitting according to conventional methods, preferably wirelessly, the generated control signals to the external device APP, remote from the ring R.

The CALC calculator is also configured to, if necessary, control the FB feedback device and trigger an action indicating to the user of the ring that his action on the ring has been taken into account to send a control signal to the external device APP.

A BAT battery provides the energy needed to operate the analog-to-digital converter CONV, the digital calculator CALC, the communication module COM and the feedback device FB. If the sensors are resistive gauges, the battery can also be used to supply them with electrical current.

Optionally, the battery may be charged by means of an energy harvesting device EH, or “Energy Harvesting” in English terminology, such as a miniature electromechanical device configured to conventionally harvest energy from ambient vibrations or movements of the user of the ring R.

As for the structure of the sensor assembly, the invention is not limited to the examples mentioned above and the annular element and the sensors can be implemented in different ways, illustrated by FIGS. 1, 3 and 19 as described below.

Thus, the sensor assembly or ring R may comprise an open or closed annular element ANN formed from a block as illustrated in A) of the , an annular element formed of two coaxial elements ANN _1/2C and ANN _2/2C as illustrated in B) of the , or formed from two angularly complementary parts ANN _1/2A and ANN _2/2A connected by assembly elements AE, preferably rigidly to each other so as to transmit a deformation applied to one element to the other, as illustrated in C) of the .

The sensors can be mounted on the same surface, either inside or outside the ring as illustrated in Figures 1 and 3, or they can be mounted on different surfaces of the ring. illustrates in A) a configuration where the SENS ₁ and SENS ₃ sensors are mounted on an external surface S _ext of the annular element and the SENS ₂ sensor on an internal surface S _int of this annular element, in B) a configuration where the SENS ₁ and SENS ₃ sensors are mounted on an external surface of the annular element and the SENS ₂ sensor is positioned between a first coaxial element ANN _1/2C and a second coaxial element ANN _2/2C of the annular element, in D) a configuration similar to the configuration illustrated in A), except that the sensors are mounted in recesses or notches formed on the annular element. Placing the sensors in recesses has the advantage of protecting them from external aggression when they are directly accessible from the outside or making the ring more comfortable to wear by the user when they are located on the internal surface in contact with the skin.

The sensors may also be mounted on other parts of the annular element than its outer or inner surfaces. thus illustrates in E) a configuration where the sensors are mounted on a surface S _t of the edge of the ring, so as to be positioned according to a plane intersecting the longitudinal axis of the ring.

The sensors are mounted on the annular element so as to be integral with its deformations and thus generate signals representative of these deformations. They can be glued to a surface of the annular element, crimped between two elements of the annular element, or integrated in any other manner considered adequate for a person skilled in the art.

Any combination of the sensor implementations illustrated in Figures 1, 3 and 19 is acceptable and falls within the scope of the invention described herein.

I. Analytical option for event detection

Several types of user actions can be applied to the ring, each type of action being associated with a given command of the external device allowing it to be controlled. Each action results in a deformation event of the ring, which results in the generation of signals by the sensors. Each episode of signal generation corresponds to an event that we seek to characterize and which makes it possible to go back to the type of action exerted on the ring: tightening, rotation, tapping, or other.

Analytical methods for detecting these types of actions through the signals generated by the sensors are explained below, using the ring illustrated by the , therefore equipped with 3 sensors distributed evenly around the periphery of the ring. Similar results would be obtained with a different number of sensors or sensors distributed differently. The explanations below are intended to explain the principles on which the practitioner can base himself to implement the ring according to the invention with sensor configurations varied in number and location.

In the figures mentioned below, the references S1, S2 and S3 are associated respectively with the signals generated by the three sensors Sens ₁ , Sens ₂ and Sens ₃ in response to an action S00 applied to the annular element by a user. The reference "S" represents the signals S2 and S3, the reference T represents the time. The references S, S1 and T are expressed respectively mV, mV and s.

I.1 Tightening

Here we call "tightening" the action which consists of squeezing the ring between two fingers, as illustrated by the in (B). This figure illustrates a situation in which the SENS ₂ sensor undergoes elongation and the SENS ₁ and SENS ₃ sensors undergo compression.

A clamping action can be detected by exceeding a detection threshold THR ₀ by the amplitudes of the signals generated by the sensors.

It is also possible to detect not only the occurrence of the application of a tightening, but also its angular location on the ring. Indeed, depending on the location of the tightening applied, the three sensors will provide different signals. An analysis of the relationships between the signals makes it possible to go back to the location of the tightening applied, either by ab initio simulation of the ring or by a calibration of the latter. By tightening location, we mean the determination of an angle between 0° and 180° defining the position of one of the two fingers applying the tightening pressures relative to a reference angle, for example defined by the radius r1 of the SENS ₁ sensor. It is assumed that the second applies a pressure at a location diametrically opposite that of the first finger.

Figures 5, 6 and 7 illustrate the results of three experimental situations in which the ring is tightened so that one of the two fingers exerting the tightening is located at, respectively, the sensors SENS ₁ , SENS ₂ and SENS ₃ , the other finger being located diametrically opposite the first finger. In (A) are represented graphs of the amplitudes of the signals S2 and S3 generated respectively by the sensors SENS ₂ and SENS ₃ as a function of the amplitude of the signal S1 generated by the sensor SENS ₁ . In (B) are represented graphs of the amplitudes of the signals generated by the sensors SENS ₁ , SENS ₂ and SENS ₃ from the same data as the corresponding graphs in (A), but this time expressed as a function of time T.

When, as in , one of the fingers exerting the tightening is located on the SENS ₁ sensor, the two curves illustrated in (A) trace approximately straight lines of the same slope. This is due to the symmetry of the ring, which means that the mechanical load is distributed symmetrically at the levels of the SENS ₂ and SENS ₃ sensors.

When, as in , one of the fingers exerting the tightening is located on the SENS ₂ sensor, the curve corresponding to the SENS ₂ sensor approximately forms a straight line with a negative slope while the curve corresponding to the SENS ₃ sensor approximately forms a straight line with a positive slope.

When, as in , one of the fingers exerting the tightening is located on the SENS ₃ sensor, the curve corresponding to the SENS ₂ sensor approximately forms a straight line with a positive slope while the curve corresponding to the SENS ₃ sensor approximately forms a straight line with a negative slope.

The fact that the amplitudes of the signals generated by the SENS ₂ and SENS ₃ sensors expressed as a function of the amplitude of the signal generated by the SENS ₁ sensor substantially form straight lines is representative of the fact that the ratios of the amplitudes of the signals generated by the SENS ₂ and SENS ₃ sensors to the amplitude of the signal generated by the SENS ₁ sensor are substantially constant. This characteristic is due to the fact that the pressure application zones on the ring remain stationary during the application of the pressure.

Also, as illustrated in (B) of Figures 5, 7 and 6, the maximum amplitude among the signals generated by the three sensors is found in the signal generated by the sensor at which one of the user's fingers is located when tightening, indicating that this location of the ring has a greater deformation than the locations of the other two sensors.

A tightening action produces two peaks in absolute value in the signals generated by the sensors: a first peak caused by the application of tightening pressure to the ring, and a second peak due to the release of this pressure, identified respectively by Max1 and Max2 in (B) of the for signal S1. The first peak and the second peak have opposite signs.

The analysis of curves such as those in figures 5, 6 and 7 makes it possible to trace back to the occurrence of a tightening action as well as a characterization of this tightening action, a characterization which is a function of the areas of application of the tightening forces.

For example, a tightening action without significant displacement of the pressure application zones can be considered to have been applied to the ring if a criterion is met, according to which a ratio between the amplitudes of two of the signals is constant to within 20% of the average value of the ratio during the duration of the action. The percentage can be adjusted by the user. The detection of an action of this type makes it possible to rule out the possibility that an action involving a significant displacement of the pressure zones on the ring, such as rotation or sliding, has been applied. In other words, compliance with this criterion implies that a pressure action of substantially constant localization has been applied to the ring by a user. In order to improve the reliability of the application of the criterion, it can be applied only to signal amplitude values exceeding a certain level, in order to avoid the effect of relative noise which becomes very significant for small amplitude values and/or adjust the percentage.

Thus, it is important to note that an analysis of the relationships between the signals generated by the different sensors makes it possible to characterize the tightening action according to a criterion linked to a location of the fingers applying the tightening, not only at a particular sensor, but also at an arbitrary position varying continuously between two sensors. The straight lines obtained by tightening actions gradually shifting from the situation of the to that of the would show a corresponding continuous variation of the slopes of the curves. To each slope or grouping of slopes, and therefore to each ratio of amplitudes of signals generated by two sensors, it is possible to associate a particular location of the action exerted on the ring and to associate with this location a particular command of the external device.

I.2 Double tightening

Double-clamping is a variation of the clamping action described above, in which the clamping action is repeated within a predefined time interval, like double-clicking a computer mouse.

This action is detected by counting for each sensor the number of maximums taking place during the predefined time interval. illustrates in (A), (B) and (C) the signals S (in mV) generated by the sensors in response to the double clamping actions at the levels of the sensors SENS ₁ , SENS ₂ and SENS ₃ , respectively, expressed as a function of time T (in s). The amplitude maxima (in absolute value) clearly show four maxima identified Max1 to Max4 in (A) of the for the S1 signal. We can thus associate the occurrence of a double clamping with the detection of four maxima in absolute value in the signal generated by a sensor over a given time interval, preferably of the order of a second or less.

I.3 Long tightening

A long tightening is distinguished from a tightening that can be described as short, such as those illustrated in Figures 5 to 7, in that the tightening is maintained for a certain duration exceeding a predetermined duration threshold value THR ₄ .

During a tightening action, the signals generated by the sensors each comprise a first maximum Max1 in the form of a peak at the start of tightening and a second maximum Max2 of opposite sign to Max1 in the form of a peak of opposite orientation when tightening is released. An event corresponds to a long tightening action when two maximums are detected, each exceeding a predetermined threshold level, which are spaced apart by a duration exceeding the predetermined threshold value THR ₄ , as illustrated in B) of the .

The profile of the curves in B) is explained by the fact that the voltage generated by a piezoelectric sensor will gradually return to zero after application of the deformation, even without the sensor returning to its initial physical state, according to a characteristic time depending on the sensor itself and the acquisition system, i.e. approximately 0.2 s for the system having generated the signals represented here.

I.4 Rotation – Method 1

Here, we call "rotation" the action of rotating the ring between two fingers while applying a tightening to it using the two fingers. This action by the user results in a deformation of the ring moving with the rotation. It is a rotation of the ring according to this principle which makes it possible to move from configuration (B) to configuration (C) of the . Sensors can characterize this deformation and its movement, and therefore the rotation imposed on the ring, as described below.

There shows graphs representing signals S1, S2 and S3 (in mV) experimentally generated by the piezoelectric sensors SENS ₁ , SENS ₂ and SENS ₃ of the ring of the , respectively, as a function of time T (in s), in (A) for a rotation Rot in one direction going from the SENS ₁ sensor to the SENS ₂ sensor then the SENS ₃ sensor (direction 1-2-3) and in (B) for a rotation in the opposite direction going from the SENS ₃ sensor to the SENS ₂ sensor then the SENS ₁ sensor (direction 3-2-1), by rotating the ring between two fingers.

It is found that the sensor signals oscillate in an approximately sinusoidal pattern. The oscillation maxima, which correspond to deformation maxima at the three sensors, appear in an order imposed by the direction of rotation. The latter can therefore be deduced from the analysis of the signals generated by the sensors, by finding the maxima and determining their order of appearance. Thus, it is possible to characterize the rotation in direction, angular amplitude and speed.

I.5 Rotation – Method 2

The first method of characterizing a ring rotation is based on the order of appearance of the maxima in the deformation amplitude. A second method, based on the same signals generated by the sensors, can be considered.

There shows in A) and B) graphs in which the signals S (in mV) generated by the sensors SENS ₂ and SENS ₃ are expressed as a function of the signal S1 (in mV) generated by the sensor SENS ₁ , forming two distinct curves in the plane (S ₁ , S) defined by the signal S1 and one or other of the signals S2 and S3. In these two graphs, the progress of the curves is followed over time by moving on them in the directions indicated by the arrows.

As regards the graph in A), in a ZSq-Start zone of the graph corresponding to the start of the application of the tightening using the two fingers of the , we observe that the two curves move away from the origin of the graph along straight lines until they exceed a threshold level Thr represented by a circle centered on the origin of the graph. The ratios of the amplitudes of the signals remain substantially constant, due to the fact that the pressure application zones on the ring remain immobile: this is for the moment a simple tightening action, already described above. The distance of each curve from the origin of the graph is defined by the root of the quadratic sum of the amplitudes of the signals concerned: either a first pair of signals consisting of the signals from the SENS ₁ and SENS ₂ sensors, or a second pair of signals consisting of signals from the SENS ₁ and SENS ₃ sensors. The distance of each point of these curves from the origin point (0,0) of the graph represents the root of the quadratic sum of the coordinates of the curve at this point.

In a second step, the ring is rolled between the two fingers, the amplitudes of the signal pairs remaining such that the roots of their quadratic sums remain greater than the threshold value, if not constant. This behavior is representative of a tightening exerted on the ring by a human being: it is difficult to maintain a constant tightening on the ring while rolling it between two fingers, but it is possible to maintain a certain level of tightening. The rolling results in displacements over time in opposite directions of rotation along the two curves, clockwise for the SENS sensor₂, counterclockwise for the SENS sensor₃, these two directions depending on the direction of rotation imposed on the ring. The ratios between the amplitudes of the signals generated by the SENS sensors₂and MEANING₃and the amplitude of the signal generated by the SENS sensor₁change continuously due to the continuous displacement of the pressure zones applied to the ring. The detection of these changes is indicative of the occurrence of a rotation action. The amplitude of these changes is representative of the angle of rotation. The curve can be followed and an angular amplitude of rotation W between two given instants can be matched to it, by calibration or ab initio calculations.

At the end of rotation, the finger grip is released, the signal amplitudes return to zero, which results in the curves simultaneously returning to the perimeter defined by the threshold level Thr then falling back to the point of origin of the graph, at the levels of the ZSq-End ₂ and Zsq-End ₃ zones of release of the grip, for the curves resulting from the signals generated by the Sens ₂ and Sens ₃ sensors, respectively. At the time of release of the grip, the rotation is stopped, the pressure application points are fixed, the curves form straight lines, as for the case of a grip described above using figures 5 to 7.

Analysis of the graph in A) of the , whether we consider a single curve or both curves, allows us to go back to the detection of a rotation action of the ring and to the characteristics (angle, duration) of this rotation by correspondence between the points of crossing of the threshold level by these curves at the beginning and end of the rotation action and a rotation of the ring, correspondence determined by simulation calculations or calibrations of the ring.

In practice, it may be advantageous to initiate an analysis of the curve as soon as the Thr threshold level is reached, analyze the curve continuously, generate a rotation detection signal each time the rotation angle exceeds one of a series of thresholds (e.g. spaced at intervals of 10° or any other predetermined value), and stop the analysis when the curves fall back below the Thr threshold.

This is illustrated by the in B), with the tracking of the curve representing the signal S2 expressed as a function of the signal S1, signals respectively generated by the sensors Sens2 and Sens1. The curve representing the signal S2 leaves the Thr threshold visualization circle at a point A, turns clockwise around the origin point of the graph while remaining outside the circle, then crosses it at a point B. Points A and B are angularly separated by a total rotation angle W _tot . During rotation, the increase in the rotation angle exceeded several thresholds indicated by the values W ₁ and W ₂ .

I.6 Finger tap

Tapping the finger wearing the ring, preferably on a hard surface such as a table, generates a signal of higher frequency content than the actions of squeezing or rotating the ring. illustrates the signals S1, S2 and S3 detected during a tap of the finger wearing the ring. The frequency components of the signals generated during a tap of the finger therefore make it possible to distinguish this action from a tightening or rotation action.

A method for detecting a tap of the finger wearing the ring may comprise as a first step a sum of the signals generated by the sensors during an event to obtain a sum signal. A high-pass filter is applied to the sum signal, then a first RMS effective value _H of this filtered sum signal is calculated. A low-pass filter is applied to the same sum signal, then a second RMS effective value _L of this filtered sum signal is calculated. The ratio of these two effective values is then compared to a predetermined threshold value THR ₁ . The cut-off frequencies of the filters applied may be for example 10 Hz. If the RMS _H /RMS _L ratio is greater than or equal to the threshold value THR ₁ , then the ring deformation event is considered to have been generated by a tap of the finger. If the RMS _H /RMS _L ratio is less than the threshold value THR ₁ , then the event is classified as a clamping. The sum of the signals may be a weighted sum, each signal being associated with a given weighting coefficient. It is thus possible to choose the coefficients in order to choose the sensor(s) used for detection. An effective value can be defined as the square root of the mean of the square of the signal value over a period of time.

I.7 Ring Tape

The approach taken for the finger tap can be applied to the ring when it is tapped directly on a surface, preferably hard, such as a table. The difference is that the signals generated by the sensors have a higher frequency component content than when only the finger wearing the ring is tapped on the hard surface. For example, we can compare the curves of the signals S1, S2 and S3 of the , generated when directly tapping the ring on a table at the . Thus, this time we can compare the RMS _H /RMS _L ratio to a threshold value THR ₂ preferably greater than THR ₁ . If the RMS _H /RMS _L ratio is greater than or equal to the threshold value THR ₂ , then the event is considered to have been generated by a tap of the ring.

I.8 Tap on a sensor

Tapping a sensor is an action that involves directly tapping the ring at the location of one of the sensors with a finger. The difference with tightening is that the force is applied to only one side of the ring, not both sides. In the case of the configuration illustrated by the , the sensors are tapped directly and the measured amplitudes of the S signals (in mV) generated in response by the sensors are illustrated by means of the graphs of the , with in (A), (B) and (C) the measurement results for taps on the SENS1, SENS2 and SENS3 sensors, respectively.

For each of the situations (A), (B) and (C), we note that the maximum amplitude among all the signals generated by the sensors is that corresponding to the sensor at which the tap is made, and that it corresponds to the maximum amplitude of a peak.

Thus, a tap event on a given sensor can be identified by identifying the sensor whose generated signal has a peak with the highest amplitude, calculating the ratio of this amplitude to the maximum amplitudes of each of the other sensors, and, if these ratios are all greater than a threshold value THR ₃ , considering the event as having been generated by a tap at the sensor having generated the signal having the peak with the highest amplitude, therefore the maximum amplitude.

I.9 Example of algorithm

As illustrated above, several types of ring deformation events can be detected by analyzing the signals from the sensors mounted on it.

Figures 15 to 18 illustrate a method of using a ring R equipped with at least two sensors SENS ₁ and SENS ₂ , according to an algorithm allowing the detection of several types of events each characterized by the signals generated by the sensors following an action by the user on the ring.

Upon user action on the ring, two digital signals S1 and S2 are generated by the two sensors SENS ₁ and SENS ₂ , respectively, and the analog-to-digital converter CONV, according to the algorithm illustrated by the .

A first calculation block Bl ₁ has the function of discriminating background noise or accidental or purposeless manipulations from a voluntary action by the user. In the first calculation block Bl ₁ , the CALC calculator performs the quadratic sum of the amplitudes of the signals S1 and S2 during a summation operation Bl _1-10 . During a test operation Bl _1-15 , the calculator determines whether the quadratic sum Q of the amplitudes of the signals exceeds a predetermined threshold value Thr, indicating that an action has been deliberately performed on the ring. This test operation has a function of detecting an event measured by the sensors of the ring. In response to this determination, in the event that the sum exceeds the threshold value, an action detection signal S _Act is generated and, in response to this signal, a second calculation block Bl ₂ is implemented and the signals S1 and S2 are recorded in a computer memory MEM in functional communication with the computer CALC during an operation Bl _1-20 . The recorded signals will be used in the following operations. The recording is stopped when the quadratic sum falls below the threshold value THR again.

More generally, the amplitude of a signal representative of a sum of unaveraged signals generated by the sensors or the amplitude of a single signal, averaged or not, representative of a signal generated by a single sensor, could be used as the amplitude of the signal Q and compared to the threshold value to determine the occurrence of a voluntary action. In all cases, it is a question of comparing the amplitude of a signal or a combination of signals, reprocessed or not, representative of a deformation of the ring, to a predefined threshold and of determining that a voluntary action has been exerted on the ring when this amplitude exceeds this predefined threshold, such as the threshold level Thr represented on the . Averaging over a combination (a sum in particular) of several signals representative of signals generated by the sensors allows for better reliability in this determination.

Alternatively, in order to discriminate background noise or accidental or purposeless manipulations from a voluntary action by the user, the test operation Bl _1-10 could relate to a variance of the amplitudes of the signals emitted by the sensors. This variance can for example be calculated over a sliding period of a signal or of the sum, weighted or not, of several signals generated by the sensors, and can be considered as an event detection signal when it exceeds a predetermined threshold, set for example by a user: the variance of the signals indeed becomes greater when the user initiates an action on the ring.

The test step Bl _1-15 thus has the function of detecting an exceedance of a threshold by a quantity representative of an amplitude of a signal or of a combination of signals each representative of a deformation of the annular element and generated by one or more of the deformation sensors mounted on the annular element in response to an action of the user, whether the quantity in question is derived directly from the amplitudes of the signal(s) considered, from a variance of this or these signals, or is representative of any other information derived from the signal(s) considered.

Block Bl ₁ is advantageous from the point of view of the autonomy of the human-machine interface: except for the detection of an event exceeding a certain threshold level, only part of the ACQ acquisition module associated with block Bl ₁ needs to be supplied with voltage, which greatly limits the electrical consumption of the entire device. Indeed, a comparator, an electronic device consuming very little energy, may be sufficient to implement block Bl ₁ , in particular when piezoelectric sensors are used, the voltages they generate being sufficient to operate the comparator without requiring amplification.

The second calculation block Bl ₂ has the function of performing a first analysis of the signals S1 and S2, intended to detect whether or not a rotation is exerted by the user on the ring and to characterize this rotation, if applicable. When the block Bl ₂ is implemented, the CALC calculator performs the operations described below. In preliminary steps, (i) a counter of the CALC calculator initializes to 0 a rotation increment counting variable n, at a step Bl _{2-1 0} , and the CALC calculator determines and assigns, to a rotation angle variable W ₀ , the exit angle of the circle of radius Thr in the plane (S1, S2) by the signal S2 as determined according to method 2 for characterizing a rotation on the basis of the signals S1 and S2, at a step Bl _{2- 15} . For illustration, reference may be made to the zone ZSq-Start in A) of the . In the graph in B) of the , this exit angle corresponds to the orientation of the line passing through the origin of the graph and point A located on the circle of radius Thr.

A test operation Bl _2-20 ensures that as long as the quadratic sum of the signals remains greater than the threshold Thr, as indicated by the filled test condition indicator Y, the following calculation loop is continuously implemented by the calculator. A current rotation angle W is calculated on the basis of the signals S1 and S2 according to method 2 during an operation Bl _2-25 . A difference WW ₀ is calculated at an operation Bl _2-30 , and the result of this difference is compared during two test operations Bl _2-35 and Bl _2-45 to a positive angular threshold value Thr _Ang and its opposite -Thr _Ang , respectively. If the test operation Bl _2-35 returns a positive result, indicated by Y in the figure, then an event determination signal ROT- is generated, representative of the fact that i) there has been rotation of the ring by an angle defined by the value of Thr _Ang , and ii) this rotation is in a direction defined as negative. Conversely, if the test operation Bl _2-45 returns a positive result, indicated by Y in the figure, then an event determination signal ROT+ is generated, representative of the fact that i) there has been rotation of the ring by an angle defined by the value of Thr _Ang , and ii) this rotation is in a direction defined as positive. The signals ROT- and ROT+ can be generated in succession when the user continues a rotation. Each of these signals is generated in response to an incremental increase in this rotation imposed on the ring by the user, each of which can be associated with a control signal from the external device APP.

In response to positive results of the test operations Bl _2-35 and Bl _2-45 , the rotation increment count variable n is incremented by 1 during a Bl _2-55 operation and the current rotation angle W is assigned to the rotation angle variable W ₀ . The count value n therefore indicates the number of times the ring has been rotated by a value Thr _Ang during the rotation being analyzed and is therefore representative of a total rotation amplitude, corresponding to the sum of the n rotation increments. By repeating these operations, rotations can be tracked in both directions, according to amplitude increments defined by the value of Thr _Ang .

This algorithm implements method 2 of characterizing a ring rotation, but method 1 could be applied, or any other suitable method.

If the test operation Bl _{2- 2 0} returns a result N, indicative of the fact that the quadratic sum of the signals S1 and S2 has fallen below the value Thr, then another test operation Bl _2-70 is performed in order to check whether the count value n is at 0, indicative of the fact that the analyzed event is not representative of a rotation. If this is the case, then a signal S _No.Rot for detecting the absence of rotation is generated and, in response, a third calculation block Bl ₃ is implemented during a step Bl _2-75 .

Alternatively, the test operation Bl _2-70 could be implemented independently of the counting value n, by implementing the test principle described in the "Clamping" section. Thus, the test operation Bl _2-70 could consist in testing whether a ratio between the signals S1 and S2 is substantially constant over the duration of the analyzed event, i.e. within an interval defined by XX% around the mean value of the ratio over the duration of the recorded event, XX% representing a percentage of the mean value defined by the user, 20% for example, which constitutes a value allowing a relevant discrimination of the constancy of the ratio.

The third calculation block Bl ₃ , illustrated by the , has the function of analyzing the signals generated by the sensors when it has been determined that this event is not generated by a rotation. More specifically, the Bl ₃ block has the function of discriminating the type of action among the ring tightening, finger tapping and ring tapping actions, and of characterizing the tightening actions. For these purposes, the computer implements the operations of the Bl ₃ block, the principles of which are explained in the Tightening, Finger Tapping and Ring Tapping sections described above.

First, the digitized signal S1 is filtered in parallel according to two filtering operations Bl _3-10 and Bl _{3 -15} employing a high-pass filter and a low-pass filter, respectively, so as to obtain two filtered signals. Each of the two signals filtered by the filtering operations Bl _3-10 and Bl _2-15 are averaged during averaging operations Bl _3-15 and Bl _3-25 to obtain the RMS _H and RMS _H averages of the two averaged filtered signals, respectively. The averaging period can be selected by the user according to his preference.

According to the principle explained above in the sections "Finger tap" and "Ring tap", a first test operation Bl _3-35 checks whether the value of the RMS _H /RMS _L ratio is greater than a high threshold value ThrH. If a positive response, indicated by Y in the figure, is returned, then a detection signal Hit(R) is generated, representative of the fact that the event was caused by a tapping action of the ring on a rigid surface.

If a negative response to test operation Bl _3-35 , indicated by N in the figure, is returned, then a test operation Bl _3-40 is implemented, checking whether the value of the RMS _H /RMS _L ratio is greater than a low threshold value ThrL, with ThrL < ThrH.

If a positive response, indicated by Y in the figure, is returned, then a Hit(F) detection signal is generated, representative of the fact that the event was caused by a tapping action of the finger (F6) bringing the ring to a rigid surface.

If a negative response to test operation Bl _3-40 , indicated by N in the figure, is returned, then it is determined that the event was caused by a clamping action, and a fourth calculation block Bl ₄ is implemented during operation Bl _3-45 .

The operations Bl _3-10 to Bl _3-40 constitute as a whole an operation Bl _3-FA for analyzing the frequency content of the signals emitted by the sensors, analysis on the basis of which is carried out a detection of the actions of tapping a finger Hit(F) and tapping the ring Hit(R), and a detection of the fact that the user's action is a tightening action, the latter being characterized more finely by the block Bl ₄ described below. The principle used is that the energy of a signal or a sum of signals is distributed more predominantly in the high frequencies for the action Hit(R) than for the action Hit(F), and more predominantly in the low frequencies for tightening actions of the ring than for the action Hit(F). The block Bl ₃ of the illustrates a particular implementation of this principle, but other implementations may be considered by those skilled in the art to implement this principle.

Basically, this involves carrying out an analysis of the energy distribution of the detected signals according to the frequencies. For example, it would be possible to carry out a Fourier transformation of the signals and analyse the energy distribution in the frequency domain, for example by comparing the energy contained in the signals for frequencies above 10Hz and the energy contained in these same signals for frequencies below 10Hz.

The fourth calculation block Bl ₄ , illustrated by the , has the function of analyzing the signals generated by the sensors when it has been determined that the event detected by block Bl ₁ is not caused by a rotation, nor by either a tap of the ring or a tap of the finger, as determined at the levels of blocks Bl ₂ and Bl ₃ . More specifically, block Bl ₄ has the function of characterizing the type of tightening applied to the ring by the user: short tightening, long tightening, double tightening, and the location of the tightening. For these purposes, the calculator performs the operations of block Bl ₄ described in the sections Tightening, Finger Tap and Ring Tap described above.

Bl _4-10 , Bl _4-15 and Bl _4-20 operations of block Bl ₄ are used to spatially characterize the event being analyzed. Operation Bl _4-10 consists of calculating the ratio of signals S1 and S2, then averaging this ratio during an averaging operation Bl _4-20 over the entire duration of the detected event. This average is compared to a calibration table prepared in advance and establishing a correspondence between averaged ratio values and a location of a tightening applied to the ring. The calibration table can be stored in the MEM memory. On the basis of this comparison, a signal Loc representative of the location of the event being analyzed is generated.

There illustrates the Local localization of the application of pressure (tightening, tapping) by a finger F1 on a ring R equipped with sensors SENS ₁ and SENS ₂ . A table prepared in advance by calibrating the ring can indicate a correspondence between the ratio of the amplitudes of the signals generated respectively by the sensors SENS ₁ and SENS ₂ and a Local localization identified by a radius r _Loc angularly offset from a reference radius r _ref . The same table, or a similar table taking into account the two diametrically opposed support zones existing during a tightening between two fingers, can be used to locate the start and end of the tightening illustrated by the and therefore evaluate the angular amplitude of the rotation applied to the ring during a rotation action of the latter. Generally speaking, any action (tightening, rotation, tap) can be associated with a localization signal Loc representative of a Local localization of the action considered, on the basis of a ratio of the amplitudes of two signals generated simultaneously by two sensors located on two distinct radii of the ring.

Operations Bl _4-30 to Bl _4-50 of block _{Bl 4 are} used to determine the type of tightening applied to the ring and having caused the generation of signals S1 and S2.

Operation Bl _4-30 consists of detecting the number of peaks, i.e. the number of amplitude maxima, in absolute value, for each of the signals S1 and S2 and averaging the number of peaks detected. Alternatively, one can simply count the number of peaks detected for a signal. However, averaging over multiple signals makes the detection more robust.

Based on the Bl _4-30 operation, the Bl _4-35 test operation returns a positive response when the number of detected peaks is close to 4, for example in an interval from 3.5 to 4.5 encompassing four to account for the averaging effect, as indicated by Y in the figure. In response to a positive response to the Bl _4-35 test operation, a detection signal D.Sq is generated, representative of a double clamping action (2 peaks per clamping action, therefore 4 peaks for a double clamping action, as explained in the “Double Clamping” section above).

Based on the Bl _4-30 operation, the Bl _4-40 test operation returns a positive response when the number of detected peaks is 2, as indicated by Y in the figure. In response to this detection, the time interval ΔT separating the two detected peaks is determined during the Bl _4-45 operation. During a Bl _4-50 test operation, the time interval ΔT is compared to the predetermined duration threshold value THR ₄ as explained in the “Long Clamp” section above.

If it is determined that ΔT is greater than THR ₄ , as indicated by Y in the figure, then a signal L.Sq representative of a long clamping action is generated.

If it is determined that ΔT is not greater than THR ₄ , as indicated by N in the figure, then a signal S.Sq representative of a short clamping action, or clamp, is generated.

Blocks Bl1 and Bl2 directly process the signals S1 and S2 generated by the sensors. Blocks Bl3 and Bl4 process the version of these signals recorded in the MEM memory during step Bl _1-20 .

An advantage of this algorithm is that it consumes only minimal energy, with the parts of the ACQ acquisition module associated with blocks Bl ₂ and Bl ₃ of the algorithm only being activated when it has been determined that it is necessary to use their respective functionalities.

When averaging operations are mentioned in this description, it will be understood that, unless otherwise indicated, this is averaging over time, over a duration that can be chosen by the user or the manufacturer of the human-machine interface according to the behavior desired for this interface. However, these may be durations of the order of a few tenths of a second.

Also, when we talk about a signal generated by the sensors, it could be a converted or processed signal and not only directly from the sensor, as long as it can be considered representative of a deformation applied to the ring, that is to say as being able to be used to characterize this deformation.

Of course, those skilled in the art will be able to develop similar algorithms to enable the user to benefit from all of the types of action described in this description.

In addition, it is quite possible to detect actions other than those described above, such as a three-finger press, sliding a finger on the ring without rotating it (“swipe” in English terminology), flexing the finger, extending the hand, clenching the fist, rotating around the finger without moving the pressure zones applied to the ring, etc.

Furthermore, those skilled in the art will understand that it is possible to implement algorithms other than those described here to exploit the signals generated by the sensors, including a so-called artificial intelligence approach, making it possible to classify the detected signals into different categories previously defined by carrying out automatic learning based on a database of signals measured during realistic actions by a user wearing the ring.

In response to the detection of events and therefore to the generation of signals representative of particular actions applied to the ring, the calculator can be configured to transmit these signals to the external device via the communication module COM in the form of a control signal S _Con . Alternatively, the control signal S _Con can be a signal of a command associated with the type of action applied to the ring.

II. Learning option for event detection

The previous section presents a first option for the detection of actions applied to the ring, of an analytical type: each action applied to the ring causes a deformation of the latter, deformation resulting in the generation of signals by the sensors, which can be analyzed in order to determine the action exerted and therefore the control signal to be generated.

A second option for determining the type of action exerted on the ring is based on the classification of the event generated by this action by a computer system that has benefited from automatic learning, often referred to as "machine learning", or "deep learning" in the case of a neural network, in English terminology.

This approach can for example be based on the use of a neural network trained to classify events detected by sensors into different categories defined by a user or an agent responsible for the preparation and configuration of the ring. Alternatively, methods other than those of neural networks could be used, such as those of the K-nearest neighbor algorithm (sometimes abbreviated to k-NN) or decision tree forests, respectively "k-nearest neighbors" and "random decision forest" in English terminology.

For illustration purposes, this description will be based on the use of a neural network for processing sensor data. In the context of using neural networks for gesture detection, the following references can be referred to: (1) Nguyen-Trong, K., Vu, H. N., Trung, N. N., & Pham, C. (2021), Gesture Recognition Using Wearable Sensors With Bi-Long Short-Term Memory Convolutional Neural Networks. IEEE Sensors Journal, 21(13), 15065-15079; (2) Kim, M., Cho, J., Lee, S., & Jung, Y. (2019), IMU Sensor-Based Hand Gesture Recognition for Human-Machine Interfaces. Sensors (Basel, Switzerland), 19(18), 3827; (3) Chuang, W.-C., Hwang, W.-J., Tai, T.-M., Huang, D.-R., & Jhang, Y.-J. (2019), Continuous Finger Gesture Recognition Based on Flex Sensors. Sensors (Basel, Switzerland), 19(18), 3986.

Figures 20, 21 and 22 illustrate the implementation of such an approach based on the use of a neural network, for the particular case where three sensors SENS1, SENS2 and SENS3 are used and deliver signals S1, S2 and S3, respectively. The approach consists in (i) detecting the occurrence of an event and (ii) classifying this event among a list of event classes prepared in advance. The classification is supported by the CALC calculator of the , which includes a neural network that has been previously trained to classify events based on the profile of the signals delivered by the sensors.

II.1 Detection and isolation of an event

Before even considering the classification of an event, considered here as resulting from a deliberate action by the user on the ring with a view to generating a control signal from an external device, it is appropriate to detect and isolate this event in a continuous flow of signals generated by the sensors in response, or not, to a deliberate action by the user.

There is a graph representing the temporal evolution of the sum Var of the variances on a sliding window of the three signals S1, S2 and S3 in the form of a curve: the abscissa axis represents time and the ordinate axis the amplitude of the sum of the variances. In the present case, the signals and the sum of their variances are representative of a deformation of the ring in response to a double tightening action, i.e. two brief tightening actions of the ring close together in time, carried out for example by the right hand of a user wearing the ring on his left hand. Each peak P1 and P2 of the curve is representative of an individual tightening action.

The graph shows two variance threshold values: V _S and V _E , which can be the same or different. Here, V _S is greater than V _E , but V _S could be less than V _E .

The first variance threshold V _S is used to determine the start of the event: when the Var curve reaches and then exceeds the threshold value V _S , an event is considered to have already started. Time T ₀ indicates the moment when the curve reaches the threshold V _S . The event is considered to have started at a time T _S = T ₀ -dT _S , dT _S representing a safety duration determined by the practitioner in order to include a part of the curve with an amplitude lower than the threshold value V _S , but which may be significant for the classification of the event.

Symmetrically, the second variance threshold V _E is used to determine the end of the event: when the Var curve falls below the threshold value V _E , the event is considered to end. Time T ₂ indicates the moment when the curve reaches the threshold V _E . The event is considered to end at a time T _E = T ₀ + dT _E on the condition that the curve remains below the threshold value for a duration dT _E , dT _E representing a safety duration determined by the practitioner in order to include a part of the curve with an amplitude lower than the threshold value V _E , but which may be significant for the classification of the event, and which also makes it possible to include in the same event two parts of a Var curve separated by a portion of the curve with an amplitude lower than the threshold V _E .

Thus, in the case where the curve passes below the threshold value V _E , at time T1 on the , for a duration less than the duration dT _E , we consider that we have only a single event. The application here is to consider an event consisting of a double clamping, with two peaks of variance amplitude close together in time but separated by a brief period where the variance of the sum of the signals is low.

An advantage of choosing V _S > V _E is to combine a good level of selectivity regarding the detection of an event, selectivity conditioned by a relatively high V _S value, with consideration of the entire event, consideration favored by a relatively low V _E value.

Of course, this principle applies to any event including brief phases of ring release, during which no mechanical force is applied to the ring, or a mechanical force too weak for the curve of the sum of the variances of the signals to exceed the threshold V _E .

From a practical point of view, the sensor signals can be kept in a buffer memory, possibly a part of the MEM memory, for a duration at least equal to dT _S , then, in case of detection of the occurrence of an event, the signals generated by the sensors from the beginning to the end of the event can be stored in the MEM memory for processing. The width of the variance calculation window, dT _S and dT _E can take identical or distinct values adjustable by the practitioner, 50 ms for example.

By proceeding as explained above, the start and end times of an event are determined from the signals generated by the sensors.

There represents a diagram summarizing the above explanations. The diagram represents a step S00 of applying an action by the user to a ring R, causing an event at the level of the detection signals S1, S2 and S3 generated by the sensors integrated into the ring. The step S00 of generating the signals is followed by a step S10 of determining the start times Start and end times End of the event, this step comprising steps S12, S14, 16 and S18.

At a step S12, the variances Var1, Var2 and Var3 of the three signals S1, S2 and S3 generated respectively by the three sensors Sens1, Sens2 and Sens3 are calculated on a sliding window.

At step S14, the variances are summed to give the summed variance Var illustrated by the .

At a step S16, the computer determines that the summed variance Var exceeds a given threshold and generates a Trig command to trigger the recording in memory MEM of the sensor signals. The recording of data predating the generation of the Trig command can be obtained by using a buffer memory recording the data according to a sliding window. Step 16 can also be used to exit a standby phase of the parts of the acquisition module, in a manner similar to the test step Bl _1-15 written above in relation to the algorithm of the .

At step S18, the calculator determines that the event has ended, and returns the start times Start and the end times End of this event.

II.2 Actions to detect

Preparing a training program for a neural network involves first listing the classes into which this network will be tasked with classifying the data submitted to it.

Table Tab. 1 below lists action types that may be interesting to identify from the recorded data of ring deformation events. Action Description Direction Variants Squeeze Squeeze the ring between two fingers Single, Double, Triple Short, Long 3 Fingers
squeeze Squeeze the ring between three fingers Single, Double, Triple Short, Long Lat Squeeze Squeeze the ring taken between two fingers along its axis of revolution Single, Double, Triple Short, Long Rot Spin the ring Positive, Negative Short, Long, Small, Large Fast, Slow Touch Touching the ring worn with a finger Single, Double, Triple Short, Long Knock Tap a surface with a finger wearing the ring Single, Double, Triple Ring Toc Tap a surface directly with the ring Single, Double, Triple Slide Apply pressure to a point moving on the ring around the finger Positive, Negative Fast, Slow Surf Slide Slide the ring placed on a surface Right, Left Fast, Slow Up, Down Short, Long Swipe Slide a finger across the ring in a direction parallel to the finger wearing the ring Right, left Hand Closure Close the hand with the ring on one finger Single, Double, Triple Finger only Finger Snap Snap your finger Trash

Tab. 1

The SQ “Squeeze” action corresponds to a radial tightening of the ring between two fingers, as illustrated in (B) of the .

The 3FS “3 Fingers Squeeze” action corresponds to a radial tightening of the ring between three fingers, as illustrated in (B) of the .

The “Lat Squeeze” action LS corresponds to a tightening of the ring R between two fingers F1 and F2 which apply forces F in a direction parallel to its axis of revolution, as illustrated in (C) of the .

The “Rot” action ROT corresponds to a rotation of the ring around the finger wearing it, as illustrated in (C) of the . To identify the direction of rotation, we consider that, when observing the ring with the axis oriented Ax directed towards the observer, the trigonometric direction, that is to say the counterclockwise direction of rotation, is the positive direction of rotation.

The “Touch” action TCH corresponds to the support of a finger F1 of one hand of the user exerting a force F on the ring R worn around a finger of the other hand of the user, as illustrated in (A) of the .

The “Knock” action corresponds to striking a rigid surface with a finger wearing the ring.

The “Ring Toc” action corresponds to tapping a rigid surface directly with the ring worn around a finger.

The “Slide” action SL corresponds to a radial centripetal force F applied at least partially towards the inside of the ring R at a point P moving on the periphery of the ring along a trajectory Traj so as to rotate around the finger F6 carrying the ring, as illustrated in (D) of the .

The action "Surf Slide" SS corresponds to the sliding of the ring R placed on a rigid surface Surf, such as the top of a table, for example in four directions Left, Right, Up and Down parallel to the rigid surface, opposed two by two, the directions Left and Right being normal to the directions Up and Down, as illustrated in (E) of the .

The action "Swipe" SW corresponds to a friction of the ring in a direction parallel to the finger wearing the ring. This situation can be described as the displacement of a point of application of a centripetal force F to the ring and/or to the finger wearing it along a trajectory Traj substantially parallel to the axis Ax of revolution of the ring, as illustrated in (F) of the .

The action "Hand closure" corresponds to the formation of a fist with a hand with one finger wearing the ring. Alternatively, only the finger wearing the ring can be bent. The ring is deformed by the expansion of the finger wearing it due to the muscular contraction of the latter, which results in a centrifugal force applied from the inside of the ring to the outside.

The “finger snap” action corresponds to a snap of the finger wearing the ring.

The “Trash” action corresponds to user actions not related to the intention of the external device to execute a command: for example, it could be a gesture such as grabbing a pen or a cup. These actions can be considered as parasitic actions that should not be taken into account for the control of the external device, and the events that they generate involuntarily can be classified as such so as not to cause the generation of control signals by the CALC calculator.

Some of the actions listed above may have characteristic directions or meanings and/or variations.

The Slide and Rot actions, involving an angular displacement around the axis of revolution of the ring, can be applied in the trigonometric direction (positive direction) or in the opposite direction (negative direction).

The Rot action can have two variants: Small and Large, which are characterized by the angular amplitude α of the rotation imposed on the ring, illustrated by the . For example, we can consider that a rotation of an angle α included in an angular interval between 20° and 40° is a rotation of small amplitude, therefore corresponding to the Small variant. Similarly, we can consider, for example, that a rotation of an angle α greater than the upper limit (40°) of the angular interval, for example greater than 90°, is a rotation of large amplitude, therefore corresponding to the Large variant.

The Swipe and Surf Slide actions can be performed by moving (either a finger applying pressure for slide or the ring itself for Surf Slide) from left to right (right direction) or from right to left (left direction), from the user's point of view.

The Surf Slide action can be performed in any direction, but the right and left directions described above and the forward (Up) and backward (Down) directions can be considered first.

The Slide, Surf Slide and Rot actions can respectively have more or less high speeds of movement of a finger on the ring, of the ring on a surface, or of rotation, corresponding to relatively slow or relatively fast movements corresponding respectively to Slow and Fast variants.

Furthermore, with the exception of the inherently brief actions (Toc, Ring Toc, Swipe, Finger Snap), each of the actions in the table can have a relatively short duration or a relatively long duration. These durations can be illustrated for example by means of the variances of the corresponding events, as illustrated by the graphs in (A) and (C) of the (we can refer to the explanations concerning the graph of the ). A short action corresponds to an applied force amplitude exhibiting a peak and will therefore generate only a peak in the variance Var as in (A) whereas a long action will generate a variance remaining of relatively large amplitude over a certain duration before falling back close to zero at the end of the event, illustrated in (C) by a plateau.

Also, the actions Touch, Toc, Ring Toc, Squeeze, 3 Fingers Squeeze, Lat Squeeze, Click and Hand Closure can be repeated during the same event (see the example of the which represents a double action), thus creating variations of the basic event, as illustrated in (A), (B) and (D) of the (we can refer to the explanations concerning the graph of the ). One, two and three occurrences of a basic action correspond respectively to the Single, Double and Triple variants of this action, for example repeating three times in rapid succession the action Toc corresponds to the Triple variant of this action Toc.

The curves in Figures 20 and 26 are of course simplified curves in order to explain the principle. Curves obtained during real measurements will generally have much less regular profiles, or even very irregular ones.

Of course, each action, direction of action and variant of action can be associated with a respective control signal to an external device to be controlled by means of the human-machine interface constituted by the ring R. A high speed or a high amplitude of an action can be used to perform to generate a command of a control signal of the same type as the same action having a lower amplitude or speed, or a command of another type.

A first application example is the navigation within a drop-down menu of a computer interface by means of rotation actions. A low amplitude Rot rotation can allow you to move to an element of the menu immediately adjacent before or after the current element, depending on the direction of rotation, while a high amplitude rotation will move to a more distant element of the menu.

A second application example, still concerning rotations, is that of listening to a piece of music in a list. A low amplitude rotation can be associated with volume control while a high amplitude rotation can be associated with the choice of the piece of the list to play: piece of the list following or preceding the piece currently playing, depending on the direction of the rotation.

Among the actions detailed above, some will tend to globally deform the annular element, this is particularly the case for the so-called "global" actions of tightening, rotation and closing of a hand or finger wearing the ring. The detection of these actions by the sensors distributed on the annular element will be particularly effective.

Other actions will tend to deform the annular element more locally, less globally than the actions listed in the previous paragraph, such as the so-called "local" actions of touching, pressing, tapping, and sliding. However, the detection of these local actions remains possible, and this with the same sensor system as for global actions, which allows increased integration and simplification of the sensor and the human-machine interface described in this document.

Of course, it remains possible to combine (i) the sensor assembly described here in order to detect global actions and (ii) contact sensors (piezoelectric, capacitive or other) or actuation buttons in order to generate control signals sensitive to global deformations of the ring, local actions on it, and/or combinations thereof.

II.3 Training the neural network

Training the neural network involves providing it, during a learning phase, with a set of training data corresponding to events of identified classes, the classes being transmitted to the neural network associated with the corresponding data. Based on the data and associations provided, the neural network then “learns” to recognize the events and to associate each of them with a given class, which correspond to an action of the user on the ring. Ideally, each action of the user on the ring corresponds uniquely to a particular class of events which can be determined from the signals generated by the sensors and recorded in the memory.

Once the actions generating the events that the neural network must be able to process and classify have been defined, it is necessary to produce the corresponding training data. The actions can be chosen from the table Tab. 1 presented above. One solution to produce the training data for the chosen actions is to use the ring by applying these actions to it and recording the events generated in response.

Training data can thus be obtained by recording the signals generated by the sensors for, for example, 100 repetitions of a ring deformation event caused by a given user action, and performing this operation for each type of action to be identified.

Steps S00, S10, S20 and S30 of the diagram of the can be used to illustrate this process of producing training data.

In step S10, detailed above, the calculator CALC determines the start and end of an event defined by the signals S1, S2 and S3 generated in response to an action by the user of the ring in step S00.

In a step S20, the signals generated during the duration of the event are sampled and recorded in the memory MEM during a recording operation Rec. It is preferable that the same number of measurements be associated with each detected event. If, for example, the sampling of the measurement signals is done at a frequency of 100 Hz and the number of samples of each of the signals S1, S2 and S3 is set to 100 for a given event, the signals are recorded for a duration of one second. If the event lasts less than one second, the data is completed with zeros to maintain the number of 100 samples.

At a step S30, the recorded data are preferably normalized by a conditioning Cond implemented by the calculation unit: the amplitude of this signal averaged over the duration of the event can be subtracted from each sample of a signal, then the result can be divided by the variance of the signal during the event.

This data conditioning allows to have data sets in the same format, facilitating their processing and classification by means of the neural network. In this example, each event is associated with a matrix of 3x100 samples.

Data conditioning can be adapted to the number of sensors, to the use of the ring which can influence the length of the events to be recorded, to the desired sampling rate, or even to the processing capacity by the computer integrated into the ring.

Steps S00 to S30 are repeated until event recordings are obtained in a number and diversity considered sufficient by the practitioner.

The recorded data here is the training data of the neural network: each data recording is associated with the corresponding action. We can use part of the data for the training itself, and another part for the validation of the training, we will speak for the latter of validation data.

Training a neural network conventionally involves providing the training data and expected results, the class of each event in the training data, as input to the neural network. At the end of the training phase, the processing of data by the neural network is assumed to be sufficiently reliable for it to be used in real conditions. The level of reliability is estimated using validation data, which allows testing the network's performance.

The tables in Figures 23 and 24 illustrate the results of training a neural network. For each of these examples, a neural network was trained to classify events into a number of classes corresponding to given user actions. Following training, a test was performed, the table allowing a comparison between the classifications made by the neural network and the known classes of the validation data. The training and validation data consisted of a few dozen recordings of each action that were collected from about ten different users.

The table of the shows the classification test results for the following actions: Touch, Toc, Squeeze, Slide_pos and Slide_neg (Slide actions in a positive and opposite negative direction, respectively), Rot_pos and Rot_neg (Rot actions in the counterclockwise and opposite direction, respectively), Surf_slide_rl and Surf_slide_lr (Surf Slide actions to the left and to the right, respectively), and Swipe_rl and Swipe_lr (Swipe action to the left and to the right, respectively).

The table of the shows the classification test results for the following actions: Single_squeeze and Double_squeeze (occurrence and two occurrences of the Squeeze action during one event, respectively), Rot_neg_small and Rot_neg_large (rot actions in the opposite direction to the counterclockwise direction for small and large amplitude rotations, respectively), Rot_pos_small and Rot_pos_large (rot actions in the counterclockwise direction for small and large amplitude rotations, respectively), and Trash.

The rows of the tables correspond to the true (known) classes of the validation data and the columns to the classifications of these data by the neural network. In an ideal case, the main diagonal of the tables would only include “1”s and the other boxes would only include “0”. Preliminary results show a classification reliability of 86% and 91% respectively for the tables in Figures 23 and 24. These scores largely validate the relevance of this approach to determine user actions on the ring from sensor measurement signals.

II.4 Event classification by the neural network

Once the neural network is trained, it can be used for practical use of the human-machine interface in the form of a ring illustrated for example by the .

There is a diagram summarizing the control process of an external APP device by means of the R ring.

Steps S00 to S30 are performed in the same way as for the production of training data in the previous section.

Following the conditioning of the data in step S30, the conditioned data associated with an event are provided as input to the neural network of the CALC calculator, which performs a Class classification of the event in a step S40, which makes it possible to determine the type of action that generated this event and generate a signal S _Class representative of the class of the event and the type of action that generated it. Each signal S _Class can be considered as a signal for detecting an action applied to the annular element, more specifically a mechanical action leading to an overall deformation of the annular element. The neural network determines during this step to which class the event belongs. Step S40 can be considered as a step for detecting a particular event, and the signal S _Class is also a signal for detecting a given event and therefore the action that generated it.

At a step S50, the CALC calculator of the ACQ acquisition module generates a control signal S _Con in response to the signal S _Class and therefore to the classification of the data by the neural network. This operation can be carried out for example by searching in a table for a command associated with the class of the event, contained in the control signal. Alternatively, the signal S _Class , can be used as the signal S _Con . The signal S _Con can be sent to the external device APP via the communication module Com.

An advantage of using a neural network is that the user, provided that the network is trained, will be able to adapt the response of the interface to his own gestures, and will even be able to add new detection classes to the “vocabulary” understood by the interface. Thus, unlike the analytical option I, any type of action applied to the ring and leading to reproducible events in the deformation measurement signals of the annular element can be used to control the external device. A user could thus “educate” the ring R to recognize a given manipulation of the ring, regardless of whether or not this manipulation was envisaged by its designer.

III. Piezoelectric type strain sensors

Strain sensors are used to estimate the surface deformation undergone by an element of any mechanical system when it is subjected to external forces (force and moments of force applied to it by external elements).

A sensor particularly suited to the ring-shaped human-machine interface described above is a thin monocrystalline piezoelectric element in the form of a plate extending in an extension plane defined by a first direction and a second direction normal to the first direction, with dimensions in the first direction and the second direction each greater than 100 µm and a thickness of less than 50 µm, a ratio of the thickness to the dimension in the first direction or the dimension in the second direction being less than 0.1. The piezoelectric element may have a first sensitivity S _x to deformation in the first direction and a second sensitivity S _y to deformation in the second direction, a crystalline orientation of the element may be such that abs(S _y /S _x ) < 0.1, corresponding to a so-called “unidirectional” sensitivity, abs((S _y +S _x )/S _x ) < 0.1, corresponding to a so-called “bidirectional” sensitivity, or for at least two first directions of the extension plane making an angle between them of between 30° and 60°, abs((S _x -S _y )/S _x ) < 0.1, corresponding to a so-called “omnidirectional” sensitivity.

Such a thin piezoelectric element is suitable for forming the basis of a passive strain sensor, which can combine precision, sensitivity, conformability, flexibility, lightness, stability, linearity, directivity and applicability to wide strain ranges, as described in detail in French patent application FR2303635.

Thus, this piezoelectric element can measure deformations greater than 5000 micrometers per meter with a resolution of the order of 1 nanometer of deformation per meter. These figures compare with those of conventional resistive gauges which can measure deformations of up to 12000 micrometers per meter but with a much lower resolution, of the order of 1 micrometer of deformation per meter, or with those of piezoelectric gauges in a box which are only capable of measuring deformations limited to approximately 300 micrometers per meter with a resolution of 1 nanometer per meter.

This thin piezoelectric element may be provided with a pair of electrically conductive layers located respectively on two opposite faces of the thin piezoelectric element.

A strain sensor may include at least one thin piezoelectric element as described above, located on a flexible sheet.

According to additional characteristics, considered individually or in any technically feasible combination:

- the at least one thin piezoelectric element may be encapsulated between the flexible sheet and another flexible sheet;

- the sensor may comprise at least one charge amplifier connected to the at least one thin piezoelectric element;

- at least one charge amplifier can be integrated on the flexible sheet;

- the sensor may comprise a plurality of thin piezoelectric elements as described above, oriented in different directions having at least a 30° separation between them;

- the sensor may comprise a first, a second and a third piezoelectric thin elements, each having the characteristic abs(S _y /S _x ) < 0.1, the first direction of the second piezoelectric thin element being able to make an angle of 90° with the first direction of the first piezoelectric thin element, the first direction of the third piezoelectric thin element being able to make an angle of 45° with the first direction of the first piezoelectric thin element;

- the sensor may comprise a first, a second and a third piezoelectric thin elements, each of which may have the characteristic abs(S _y /S _x ) < 0.1, the first direction of the second piezoelectric thin element being able to make an angle of 120° with the first direction of the first piezoelectric thin element, the first direction of the third piezoelectric thin element being able to make an angle of 240° with the first direction of the first piezoelectric thin element;

- the sensor may comprise a plurality of charge amplifiers each connected to a respective one of the thin piezoelectric elements; and

- a sensor can combine at least two sensors according to the invention electrically connected in parallel.

Each of the sensors integrated into the R ring, such as the Sens1, Sens2 and Sens3 sensors, can consist of a sensor combining one or more of the characteristics listed above.

Indeed, the human-machine interface in the form of a ring, equipped with sensors sensitive to the deformation of the annular element as a whole, can advantageously use deformation sensors having as a sensitive element the thin monocrystalline piezoelectric element described above. Its advantages are multiple, we can in particular cite the sensitivity and, possibly if it is sought, the directivity of a sensor based on such an element, but also the precision, conformability, flexibility, lightness, integrability and reduced dimensions, stability, linearity, directivity and applicability to wide ranges of deformations.

The R ring will benefit in particular from the integrability and sensitivity of the thin piezoelectric element. The sensitivity allows for example to form the ANN annular element in conventional materials and dimensions for manufacturing rings: lower sensitivities would require the use of more deformable and/or thinner materials, reducing their robustness and wearing comfort.

Indeed, a classic ring, made of metal, is rigid and deforms little under the action of forces applied by fingers, (usually of amplitudes less than 10 N. Such forces generate deformations of the order of 5 µdef, which are difficult to measure using conventional strain gauges.

Resistive gauges, for example, have insufficient sensitivity for the application targeted here. Even if they were mounted on a sufficiently flexible annular element so that they could measure the deformations caused by the user, their power consumption would disqualify them for the intended application. In addition, reducing the noise of the gauges by filtering to keep only the low frequencies of the measurement signals would induce a prohibitive delay for a control interface.

It is better to consider sensors with low energy consumption, or even passive sensors. Piezoelectric sensors meet this criterion.

A first type of piezoelectric deformation sensors is based on the use of a crystal of piezoelectric material with relatively good sensitivity to deformation and stable over time, but thick and rigid, often housed in a metal case to which it is mechanically attached, these latter characteristics making it difficult to integrate into a structure having the dimensions of the ring R and poorly suited to installation on a curved surface such as that of the annular element ANN.

A second type of piezoelectric strain sensors is based on the use of composite structures comprising PZT (or lead zirconate titanate) bars located between sheets of polymer materials, or on polymer piezoelectric films called "PVDF" for poly(vinylidene fluoride) in English terminology.

These structures are relatively flexible, but too unstable over time and sensitive to temperature for an application such as those targeted for the R ring, intended among other things to be worn around a user's finger.

On the other hand, the thin monocrystalline piezoelectric element described above meets all the criteria necessary for good integration into the ring and good functionalities for it: dimensions, flexibility and sensitivity. The integrability of the piezoelectric element (ease of placing it in intimate contact with a rounded structure such as the annular element) is essential here, and its sensitivity makes it possible to detect deformations even simply applied to the finger to an annular element of comparable rigidity to a traditional metal ring.

The piezoelectric element can be formed from lithium tantalate LiTaO3 in monocrystalline form, which belongs to the 3m space group, but also from lithium niobate LiNbO3 (group 3m), lead magnesium niobate MgNb2(PbO3)3 (group P1), aluminum nitride AlN (group P6 _3mc ), barium titanate BaTiO3, potassium niobate KNbO3 or lead titanate TiPbO3 (all three from the P4mm group).

Sensors

There illustrates in (A) a cross-sectional view of a SENS piezoelectric sensor based on a thin piezoelectric element PIEZO of extension plane chosen to exhibit a particular behavior, unidirectional, omnidirectional or bidirectional to a unidirectional deformation applied to it in its extension plane. The sensitivity behavior of the thin piezoelectric element (unidirectional, omnidirectional or bidirectional) is transferred to the sensor integrating this thin piezoelectric element. Such sensors can be particularly adapted to specific situations as illustrated by figures 10 to 12 commented below, but they can also be used in the context of more general applications, as will become apparent later.

In order to benefit from the thinness and therefore the flexibility and conformability of the thin PIEZO element, the SENS sensor comprises a flexible SH1 sheet on which the thin PIEZO element is fixed. The sheets are preferably made of flexible materials chosen according to the intended application, and may be, for example, made of metal, polyvinyl chloride (PVC), polyimide (PI), polyethylene terephthalate (PET), biaxially oriented polyethylene terephthalate (Mylar®) or a composite material of epoxy resin and glass fibers. The thin PIEZO element may be fixed to the SH1 sheet by means of a flexible adhesive such as an anisotropic conductive film (ACF) which also allows electrical contact as described in patent document FR 3 122 985. In use, the SENS sensor may be fixed to a surface to be characterized by means of an adhesive, for example a cyanoacrylate glue or an epoxy resin.

In addition to the thin PIEZO element, in the example of the , a charge amplifier C.AMP is also fixed on the sheet SH1 and functionally connected to two conductive layers EL1 and EL2 acting as electrodes, respectively formed on two opposite faces of the thin PIEZO element. The function of the charge amplifier is to produce a voltage corresponding to the charge applied at the input and which corresponds to the charge generated by the PIEZO element during its deformation, for the purposes of electronic processing of the generated electrical potential and to carry out an effective measurement of the deformation of the PIEZO element. Although not shown, a wire connection element, such as a ribbon cord, is connected to the charge amplifier to connect the sensor to an external measuring device.

There illustrates in (B) a sensor similar to that of the configuration illustrated in (A), but further comprising a second sheet SH2, which may be of the same nature as the sheet SH1, which makes it possible to encapsulate the thin PIEZO element and charge amplifier C.AMP by sandwiching it between the sheets SH1 and SH2.

The thin piezoelectric element PIEZO preferably has a thickness of less than 50 µm, more preferably less than 25 µm, even more preferably less than 10 µm. Considering a piezoelectric element defined as illustrated in the , a ratio of the thickness of the PIEZO element to its dimension L _X in a first direction of its extension plane, and/or of a dimension Ly in a second dimension of its extension plane normal to the Lx direction, is less than 0.1, preferably less than 0.05, more preferably less than 0.01.

The SH1 sheet and, where applicable, the SH2 sheet, may have a thickness between 5 and 300 µm.

However, it is preferable that the SENS piezoelectric sensor considered as a whole is sufficiently flexible to fit the surface of the annular element to which it is to be fixed and capable of following its deformations. The practitioner will be able to decide for each application the characteristics of the thin piezoelectric element PIEZO, its support, and other elements such as the electrode layers or the means of making electrical contacts.

The flexibility of the thin piezoelectric element is advantageously exploited to fix the entirety of one of its faces in intimate contact with the curved surface of the annular element ANN (through an electrode and a possible adhesive film). In this way, this piezoelectric element is integral with the annular element, undergoes the same deformations as those undergone by the annular element where the piezoelectric element is fixed, and its deformation is therefore representative of that of the annular element.

The SH1 sheet may be made of or replaced by a flexible support such as a flexible printed circuit called "flex PCB", composed of layers of electrically insulating polymer and layers of copper, making it possible to route signals between the different components of an electronic circuit. Each sensor assembly may comprise a plurality of piezoelectric PIEZO elements, each having its own support, as may the electronic module controlling them. Alternatively, a single flex PCB support may accommodate all of the PIEZO elements and the electronic module controlling these elements. Alternatively, a first flex PCB support may be common to all of the PIEZO elements and a second flex PCB support may be dedicated to the electronic control module.

The exact type of sensor(s) to be integrated into the ANN annular element will depend on the type of action to be detected and the constraints imposed (autonomy, sensitivity, etc.), according to the designers' intentions.

The invention is not limited to the method of implementation described above and variant embodiments may be made without departing from the scope of the invention as defined by the claims.

Claims (17)

Sensor assembly (R) in the form of a ring, comprising:
- an annular element (ANN) of substantially cylindrical shape;
- at least two deformation sensors (SENS ₁ , SENS ₂ , SENS ₃ ) mounted on the annular element at levels of at least two radii (r1, r2, r3) thereof, respectively, the two radii being angularly distinct from each other, such that the at least two sensors are sensitive to an overall deformation of the annular element; and
an electronic module (EL) configured to generate a detection signal (ROT-, ROT+, Loc, S.Sq, L.Sq, D.Sq, Hit(F), Hit(R), S _Class ) representative of the overall deformation of the annular element, in response to processing of at least two signals (S1, S2, S3) respectively emitted by the at least two deformation sensors (SENS ₁ , SENS ₂ , SENS ₃ ). Sensor assembly (R) according to claim 1, in which the annular element (ANN) has a monolithic structure. Sensor assembly (R) according to claim 2, in which the annular element (ANN) is formed of metal. Sensor assembly (R) according to any one of claims 1 to 3, in which the at least two distinct rays (r1, r2, r3) are angularly spaced apart from each other by an angle of between 20° and 160°. Sensor assembly (R) according to any one of claims 1 to 4, in which the at least two deformation sensors (SENS ₁ , SENS ₂ , SENS ₃ ) are piezoelectric type sensors. The sensor assembly (R) according to claim 5, in which the at least two deformation sensors (SENS ₁ , SENS ₂ , SENS ₃ ) comprise at least one thin monocrystalline piezoelectric element (PIEZO) in the form of a plate extending in an extension plane (xy) defined by a first direction (x) and a second direction (y) normal to the first direction, with dimensions (L _X , L _Y ) in the first direction and the second direction each greater than 100 µm and with a thickness (L _Z ) less than 50 µm, a ratio of the thickness to the dimension (L _X ) in the first direction or the dimension (L _y ) in the second direction being less than 0.1. Human-machine interface (R) comprising the sensor assembly according to any one of claims 1 to 6, the electronic module (EL) being further configured to generate a control signal (S _Con ) of a device (APP) external to the human-machine interface (R) in response to the detection signal (ROT-, ROT+, Loc, S.Sq, L.Sq, D.Sq, Hit(F), Hit(R), S _Class ). Human-machine interface (R) according to claim 7, configured to keep awake only a first part of the acquisition module (ACQ) associated with the detection (Bl _1-15 ) and to activate second parts of the acquisition module only when it is determined that respective activations of these second parts are necessary for an analysis of the signals (S1, S2) emitted by the at least two deformation sensors (SENS ₁ , SENS ₂ , SENS ₃ ). Human-machine interface (R) according to claim 7 or 8, in which the electronic module (EL) comprises a calculator (CALC) configured to (i) classify (S40) events represented by the signals (S1, S2, S3) emitted by the at least two deformation sensors (SENS ₁ , SENS ₂ , SENS ₃ ) and (ii) generate (S50) the control signal (S _Con ) of a device (APP) external to the human-machine interface (R) in response to this classification. Human-machine interface (R) according to any one of claims 7 to 9, in which the control signal is representative of at least one action (S00) chosen from a tightening (SQ, 3SQ), a short tightening or a long tightening of the annular element (ANN) between two fingers (F1, F2) or between three fingers (F1, F2, F3), repeated or not, in a centripetal direction to the annular element (ANN); a tightening (LS) of the annular element (ANN), repeated or not, parallel to an axis (Ax) of revolution of the annular element (ANN); a closing of a hand of which one finger carries the annular element (ANN) or the closing of a finger carrying the annular element (ANN); and a rotation (ROT) of the annular element (ANN) between two fingers (F1, F2) of a first amplitude (α) belonging to an angular interval or of a second amplitude greater than an upper limit of the angular interval. Human-machine interface (R) according to any one of claims 7 to 9, in which the control signal (S _Con ) is representative of at least one action (S00) chosen from a touch (TCH) of the annular element (ANN) by a finger (F1); a tap of a surface by a finger carrying the annular element (ANN); a tap of a surface directly with the annular element (ANN); the application (SL) of pressure on the annular element (ANN) at a point moving on the annular element (ANN) around a finger (F6) carrying the annular element (ANN); a sliding (SS) of the annular element (ANN) on a surface (Surf), a sliding of a finger of a first hand on the annular element (ANN) in a direction parallel to a finger of a second hand carrying the annular element (ANN); a localization of any one of the preceding actions; and a snap of a finger carrying the annular element (ANN). Human-machine interface (R) according to any one of claims 7 to 11, in which the acquisition module is configured to:
- detecting (Bl _2-35 , Bl _2-45 , S40) a rotation (Rot, Rot_pos, Rot_neg, Rot_pos_small, Rot_pos_large, Rot_neg_small, Rot_neg_large) of the annular element on the basis of the signals (S1, S2) emitted by the at least two deformation sensors (SENS ₁ , SENS ₂ , SENS ₃ ); and
- in response to the detection step, generate a signal (ROT-, ROT+, S _Class ) representative of the occurrence of a rotation of the annular element (ANN). Human-machine interface (R) according to claim 12, in which the signal (ROT-, ROT+) is representative of a rotation having exceeded an incremental angular value (-Thr _Ang , Thr _Ang ). Human-machine interface (R) according to any one of claims 7 to 13, further comprising a wireless transmission module (COM) configured to transmit signals generated by the acquisition module (ACQ) to the external device (APP) and a power source (BAT) for supplying electrical energy to the wireless transmission module (COM) and the acquisition module (ACQ). Human-machine interface (R) according to any one of claims 7 to 14, further comprising a feedback device (FB) configured to signal to a user a generation of a detection signal (ROT-, ROT+, Hit(R), Hit(R), Loc, S.Sq, L.Sq, D.Sq, S _Class ) by the acquisition module (ACQ). Human-machine interface (R) according to any one of claims 7 to 15, configured to be threaded onto a part (F6) of a user or a rod (RD) of an external appliance control device (APP). Kit comprising a human-machine interface (R) according to any one of claims 7 to 16 as well as an external device (APP) configured to be controlled by means of the human-machine interface (R).