JPH073379B2 - Touch sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tactile sensor that is mounted on, for example, a hand of a robot and detects a force received from a grasped object.

[Prior Art] In recent years, technological progress of industrial robots has been remarkable. In particular, there is an increasing tendency to attach a touch sensor to a robot hand to make the robot intelligent.

The following are the performances and conditions required of the touch sensor.

High sensitivity: High sensitivity to detect force. It is desirable to be able to detect several grams with one element.

High resolution: The sensor elements are desired to be small and have high density.

Wide dynamic range: A wide operating range is possible.

High reliability and durability: Withstands harsh environments and long-term use.

Linearity and Hysteresis: Pressure and output are proportional and have no hysteresis.

Response speed: When the object is grasped, the signal is transmitted to the control section quickly.

Flexibility: It is preferable that it is as soft as the skin of a human hand.

Slip sensation: Detecting slip as well as pressure.

Small size and low price: Thin, small and inexpensive.

Various touch sensors satisfying some of these have been proposed or developed. For example, there is a touch sensor such as a push button type or a conductive rubber type. A push-button type touch sensor normally turns off electrically when the metal push button supported by the coil spring is normally not pressed, but when it is pressed, the contact closes and turns on. Is. However, there is a drawback that the lump method only knows the ON and OFF states and is not suitable for continuous force detection.

On the other hand, the conductive rubber type contact sensor uses the fact that both sides of a conductive rubber sheet are sandwiched by electrodes, and the electric resistance (conductivity) of the conductive rubber decreases when force is applied to the sensor surface. However, this method also has a problem that nonlinearity and hysteresis occur between the force and the conductivity of rubber.

In addition to these, the various types of contact sensors that have been proposed have their respective merits and demerits, and not only are they not sufficiently satisfied, but also the pressure direction is unidirectional, that is, only the direction perpendicular to the contact surface is felt. However, at present, there are very few that also detect a force parallel to the contact surface.

[Problems to be Solved by the Invention] Recently, there is a tendency to develop a touch sensor capable of detecting a three-minute force. For example, Japanese Patent Application No. Sho 62, which is a prior application proposed by the applicant.
For example, −049996. However, in such a conventional touch sensor, sufficient consideration has not been given in terms of sensitivity and wiring reliability. That is, the conventional touch sensor has low sensitivity and there is a fear of disconnection due to crossover (overlapping of wiring), so that it is not possible to satisfy all of the above requirements.

The present invention eliminates the above-mentioned conventional drawbacks and has a thin structure,
Moreover, it is an object of the present invention to provide a highly reliable contact sensor that detects forces in three directions with higher sensitivity and does not cause crossover on wiring.

[Means for Solving the Problems] In order to achieve the above object, according to the present invention, pressure is received in the central portion of a sensor cell in which three sets of strain sensing elements are arranged corresponding to forces in three directions. A column is provided, and the dimension of the pressure receiving column is set so that a high stress is generated in the three sets of strain detecting elements by the action of a moment when a force is applied to the upper surface of the pressure receiving column, and the column is arranged in the sensor cell. In addition, the contact sensation sensor configured such that the wirings of the three sets of strain detection elements do not overlap and do not cross each other, and the height of the pressure receiving column is set to be 2 to 3 times the diameter of the pressure receiving column. The strain detecting element corresponding to the force in the three directions is a half bridge using two sets of strain gauges and the other one is a full bridge using four strain gauges. And

[Operation] According to the present invention, three-component forces F _X , F _Y , and
Strain gauges are arranged with a simple structure corresponding to F _Z , and the height of the pressure receiving column protruding in the center of the sensor cell is made twice or more its diameter, and F _X , Since a moment due to F _Y and F _Z is applied, when a horizontal force is applied to the upper surface of the pressure receiving column, a large strain is generated in the strain gauge due to the action of the moment, and the detection sensitivity can be increased. Since the wiring is small and thin, capable of detecting 3 minutes force with high sensitivity, and has no crossover, there is no need to worry about disconnection.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

1 (A) to 1 (C) are views for explaining the basic operation of the touch sensor according to the present invention, and FIG. 1 (A) is a top view,
(B) is a sectional view and (C) is a stress distribution diagram of the strain gauge. Here, 1 is a sensor cell (contact sensor cell), the outer shape of which is square, and a cylindrical pressure-receiving column 3 is integrally formed at the center of the cell. Reference numeral 4 denotes a fixing portion that projects along the entire circumference of the outer edge portion of the sensor cell 1, and reference numeral 5 denotes an annular groove-shaped thin portion formed between the pressure receiving column 3 and the fixing portion 4. Strain gauges 2A and 2B are formed in the thin portion 5 at two positions in the diametrical direction as shown in the figure by some method such as a semiconductor wafer process.

When a force F parallel to the upper surface (pressure receiving surface) of the pressure receiving column 3 is applied, a moment F × l acts on the pressure receiving column 3 due to the arm length l of the pressure receiving column 3. By this moment,
Compressive stress (−δ) acts on one strain gauge 2A, and tensile stress (+ δ) acts on the other strain gauge 2B. Therefore, the stress distributions of the strain gauges 2A and 2B on both sides at this time are as shown in FIG. 1 (C).

FIG. 2 shows an arrangement example of strain gauges for detecting forces F _X , F _Y and F _Z in three directions in the touch sensor according to the present invention, and a stress distribution of each strain gauge. X ₁ and X ₂ are strain gauges for detecting the force F _{X in the} X direction, which are on the same diameter of the thin portion 5 and whose longitudinal directions are aligned in the radial direction. Y ₁ and Y ₂
Is a strain gauge for detecting the force F _{Y in the} Y direction.
It is arranged in the direction orthogonal to X ₁ and X ₂ . Z ₁ and Z ₂ are strain gauges for detecting the force F _{Z in the} vertical direction, and are arranged at 45 ° with respect to X ₁ , X ₂ , Y ₁ , and Y ₂ .

Now, _{assuming that} the force of F _X acts in the X direction of the arrow in this figure in FIG. 2 (A), the stress distribution on the center lines of X ₁ and X ₂ is as shown in FIG. It becomes like C). That acts tensile stress (+ [delta]) is a strain gauge X ₁ side, compressive stress (- [delta) acts on a strain gauge X ₂ side. Similarly, in FIG. 2A, when the force F _Y acts in the Y direction of the arrow in this figure, the strain gauges Y ₁ and Y ₂ have a stress distribution as shown in this figure (D). Furthermore, the force of F _Z is _Z in the arrow in FIG. 2 (B).
When acting in the direction (vertical direction), the strain gauges Z ₁ and Z ₂ have a stress distribution as shown in FIG. 2 (E).

However, in both cases, the stress in the pressure receiving column 3 and the fixed portion 4 is relatively extremely smaller than that in the strain gauge, and thus is displayed as zero. If the strain gauges X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , and Z ₂ are arranged at the maximum points of such stress distribution, the maximum detection sensitivity can be obtained.

Next, the wiring and the like in the case of being concretely implemented based on the above principle will be described below. In particular, as shown in FIG. 2 (A), three pairs of strain gauges X ₁ ,
Since X ₂ , Y ₁ , Y ₂ , Z ₁ , and Z ₂ coexist, there is a problem of mutual interference. In order to solve this problem, how to separate the force applied to the touch sensor and how to make the wiring are described.

First, a detection method when the above-mentioned forces of F _X , F _Y , and F _Z act independently will be described. Fig. 3 (A),
(B), (C) is a figure explaining the detection of force F _{X in} the X direction. Of the strain gauges shown in FIG. 2A, FIG.
The wiring of X ₁ and X ₂ is shown. The figure (B) shows the force shown in the figure (A).
The change in gauge resistance at each strain gauge (X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z ₂ ) caused by F _X acting on the pressure receiving column 3 is shown. An equivalent circuit of a half-brush composed of gauges X ₁ and X ₂ is shown. The sensor cell 1 is made of semiconductor silicon, and each strain gauge is formed by a semiconductor wafer process. The electrode (connection terminal) 6, 7, 9 are formed in nodular solder, wire 8 connecting the respective electrodes 6, 7, 9 a strain gauge X _1, X ₂ may be formed of aluminum. Electrode 6 is an electrode of output electrode V _X , electrode 7 is an electrode of ground (earth) G, and electrode 9 is an electrode of bridge voltage (input voltage) E.

FIG. 3B shows a change in resistance value of each strain gauge when the force F _{X in the} X direction shown in FIG. 3A acts on the pressure receiving column 3. As a matter of course, the strain gauge X ₁ in the X direction undergoes a resistance value change F _X1 corresponding to the tensile stress + δ applied in the longitudinal direction, and the strain gauge X ₂ in the X direction has a compressive stress applied in the longitudinal direction. A resistance change corresponding to −δ −F _X2 occurs. At this time, the resistance values of the strain gauges Y ₁ and Y ₂ in the Y direction hardly change. However, the vertical strain gauges Z ₁ and Z ₂ show an apparent change in resistance value due to F _X , that is, + F _Z1 and −F _Z2 .

In order to read that the force F _{X in the} X direction is generated from such a change in the resistance value, it suffices to simply detect the change in the resistance value of + F _X1 and −F _X2 . On the other hand, apparent resistance change + F
_{Since Z1} and −F _Z2 are F _Z1 = F _Z2 , (+ F _Z1 ) and (−
The sum of F _Z2 ) cancels each other out to zero, and the apparent F _Z due to F _X is not detected.

To change the resistance value as described above, for example, in a half bridge circuit as shown in FIG. 3 (C), a voltage (input voltage) E is applied and the resistance values of the strain gauges X ₁ and X ₂ are changed. If it changes, the output voltage V _X changes, so that it can be detected from the change of the output voltage V _X.

4 (A), (B), and (C) are diagrams for explaining the detection of the force F _{Y in} the Y direction. Note that FIGS. 3A and 3C have the same configurations as those in FIGS. 3A and 3C described above, and therefore description thereof will be omitted. In FIG. 4B, the resistance values of the strain gauges X ₁ and X ₂ in the X direction hardly change. As a matter of course, the strain gauges Y ₁ and Y ₂ in the Y direction undergo remarkable resistance value changes of + F _Y1 and −F _Y2 , respectively. At this time, the resistance values of + F _Z1 and −F _Z2 also change in the strain gauges Z ₁ and Z ₂ in the vertical direction, but (+ F _Z1 ) and (−F _Z2 ) cancel each other out, so the vertical force F _Z is apparently not detected. Therefore, the force F _{Y in} the Y direction can be detected only by measuring the voltage V _Y between the contacts of the strain gauges Y ₁ and Y ₂ and the ground G.

FIGS. 5 (A), (B), and (C) are diagrams for explaining detection when a force F _Z perpendicular to the surface of the pressure receiving column 3 (perpendicular to the strain gauge installation surface) acts. FIG. 3A shows the arrangement and connection of strain gauges. In addition to the strain gauges Z ₁ and Z ₂ described in FIG. ₂ , dummy gauges Z ₃ and Z ₄ having a longitudinal direction in the circumferential direction are arranged. Is
In each gauge Z ₁ to Z ₄ constitute a full bridge circuit as shown in FIG. (C). Reference numeral 9 is an input voltage E electrode, and 11 is an output voltage V _Z electrode. The strain gauges Z ₁ and Z ₂ show changes in resistance value in the same direction. The strain gauges Z ₃ and Z ₄ also serve as temperature compensation,
And no distortion occurs. That is, the dummy gauge has no change in resistance value.

The stress distribution when the vertical force F _Z acts is as shown in FIG. That is, each strain gauge X ₁ ,
_{X 2, Y 1, Y 2} , Z 1, Z 2 denotes a resistance value change of equal magnitude in the same direction. However, strain gauges X ₁ and X ₂ in the X direction and Y
The resistance value changes of the strain gauges Y ₁ and Y _{2 in} the direction may be canceled out to zero. This is because, if able to work force F _YX and Y direction force F _Y in the X direction, strain gauges X ₁ and X _2, and strain gauge Y ₁ and Y ₂ is because show different directions of the change in resistance value, respectively. Therefore,
Vertical strain gauge Z ₁ when vertical force F _Z is applied
And Z ₂ resistance changes, that is, the output voltage V _Z shown by the bridge circuit in FIG.

Next, detection of F _X , F _Y , and F _Z when two or more forces act on the surface of the pressure receiving column 3 at the same time will be described.

FIGS. 6A to 6D show changes in resistance value of each strain gauge when two or more forces act on the surface of the pressure receiving column 3 at the same time. The figure (A) is F _X and F _Y , the figure (B) is F _Y and F _Z , the figure (C) is F _Z and F _X , and the figure (D) is F _X , F _Y and F _Z. Is when they act simultaneously.

First, in FIG. 6 (A), since the forces F _X and F _Z act simultaneously, resistance value changes F _X1 and F _X2 appear on the strain gauges X ₁ and X ₂ , respectively. F _X1 and F with bridge
_The force F _X is obtained from the sum of _X2 . At the same time, strain gauges Y ₁ and Y ₂
Resistance changes F _Y1 and F _Y2 appear in Fig. 4 (C).
The force F _Y can be calculated from the sum of F _Y1 and F _Y2 using the half bridge of. The resistance change of strain gauges Z ₁ and Z ₂ is F _Z1 and F
_{Since it is Z2} and the output direction is different, the output is zero, that is, the force F _Z is apparently not detected if F _Z1 and F _Z2 are canceled by using the bridge of FIG. 5 (C). In addition,
In FIG. 7A, the shaded portion means the original true output, and the white frame portion means the apparent output due to the influence of other forces. This also applies to FIGS. 7B, 7C and 7D.

Since the forces F _Y and F _Z act simultaneously in FIG. 6 (B), the influence of the force F _Z in the vertical direction appears on the strain gauges X ₁ and X ₂ in the X direction. The half bridge in Fig. 3 (C) cancels it out to zero. The original true output (F _Y1 and F _Y2 ) and the apparent output F _Z appear on the strain gauges Y ₁ and Y ₂ in the Y direction, but the Y ₁ side value is the F _Y1 + F _Z , Y ₂ side value. Is calculated as F _Y2 −F _Z, and the sum of the two is calculated, the sum = (F _Y1 + F _Z ) + (F _Y2 −F _Z ).
= F _Y1 + F _Y2 and the term of F _Z disappears, so Fig. 4 (C)
It is possible to detect F _Y1 and F _Y2 purely with the half bridge. The same applies to the strain gauges Z ₁ and Z _{2 in the} vertical direction, and the resistance value change on the Z ₁ side F _Z1 + F _Y and the resistance value change on the Z ₂ side F _Z2 −
If the sum of F _Y is taken, the sum = (F _Z1 + F _Y ) + (F _Z2 −F _Y ) = F _Z1
It becomes + F _Z2 and F _Y disappears, and F _Y and F _Z can be detected purely by the full bridge in FIG. 5 (C).

Furthermore, since Figure 6 (C) shows a case where the force F _Z and F _X is applied simultaneously, in the same way that the above-mentioned F _Z and F _X acts simultaneously detect forces F _Z and F _X, respectively can do.
That is, strain gauges X ₁ and X ₂ in the X direction are F _X1 + F
_{Since Z} and F _X2 −F _Z are generated, if the sum of these is taken by the half bridge of FIG. 3 (C), the sum = (F _X1 + F _Z ) + (F _X2 −
F _Z ) = F _X1 + F _X2 and F _X is detected. Further, the strain gauges Y ₁ and Y ₂ in the Y direction are affected in the same direction by the force F _{Z in the} vertical direction, so that they can be canceled out by the half bridge in FIG. 4 (C) to zero. The strain gauges Z ₁ and Z ₂ in the vertical direction have F _Z1 + F _X and F _Z2 −F _X , respectively. Therefore, if these are summed with the full bridge in FIG. 5 (C), the sum = (F
_Z1 + F _X ) + (F _Z2 −F _X ) = F _Z1 + F _Z2 and only F _{Z in} the vertical direction can be detected.

Finally, FIG. 6 (D) shows a change in resistance value when three forces, F _{X in the X} direction, F _{Y in the Y} direction, and F _{Z in} the vertical direction, act on the surface of the pressure receiving column 3 at the same time. Also in this case, the three forces of F _X , F _Y and F _Z can be detected separately as follows.

For strain gauges X ₁ and X ₂ in the X direction, (F _X1 + F _Z ) and (F _X2
Since the resistance value change of −F _Z ) is occurring, take the sum and
Sum = (F _X1 + F _Z ) + (F _X2 −F _Z ) = F _X1 + F _X2
The direction force F _X is obtained. In this case, the effect of F _Y does not appear.

Similarly, in the strain gauges Y ₁ and Y ₂ in the Y direction, since the influence of F _X does not appear, the resistance change (F _Y1 + F _Z ) and (F _Y2 −
Taking the sum of F _Z), the sum _{= (F Y1 + F Z)} + (F Y2 -F Z) = F
It becomes _Y1 + F _Y2 and only the force F _{Y in the} Y direction can be detected.

The strain gauges Z ₁ and Z _{2 in the} vertical direction are similar, but since F _X and F _Y affect at the same time, (F _Z1 + F _Y
+ F _X ) and (F _Z2 −F _X −F _Y ), the sum = (F _Z1 + F _Y
+ F _X ) + (F _Z2 −F _X −F _Y ) = F _Z1 + F _Z2 , and only the vertical force F _Z can be detected.

In short, in any case, if you consider the sign (plus and minus) indicating the output direction and take the sum of the signals output from the strain gauge as the bridge voltage (output voltage), unnecessary parts (influence other forces) Since the apparent signal that is generated and appears) is removed, even if two or more forces are applied at the same time, they can be detected separately.

Fig. 7 shows three directions of forces F _X , F _Y and F _{Z in} one sensor cell.
2 shows a structure of a touch sensor of an embodiment of the present invention having a strain gauge corresponding to the above. The sensor cell 1 is formed from a semiconductor silicon wafer, and the above-mentioned X ₁ ,
Strain gauges 2 of X ₂ , Y ₁ , Y ₂ , Z _{1 to} Z ₄ are formed. Also,
When the above-mentioned electrodes 6, 7, 9, 10, 11 are represented by the symbol 13 as a representative, the solder bumps 12 for connecting the wiring 8 and the voltage 13 can also be formed by a plating process of a semiconductor process.
The pressure receiving column 3 is obtained by forming an annular groove in the above-mentioned semiconductor silicon wafer by dry etching or wet etching.

In this case, since the pressure receiving column 3 is made of hard and brittle silicon, the coating 16 for protecting the surface of the pressure receiving column 3 is necessary. The coating 16 can be applied by a known coating processing method such as vapor deposition or sputtering of metal or ceramic. Further, the entire surface of the sensor cell 1 needs to be covered with the skin 15 except for the pressure receiving column 3, and therefore the thickness of the fixing portion 4 of the sensor cell 1 is made slightly thinner than that of the pressure receiving column 3. Then, the skin 15 and the fixing portion 4 of the sensor cell 1 are bonded together by the adhesive layer 17.

On the other hand, the solder bumps 12 are connected to the respective aluminum wirings 8 by soldering so as to correspond to the positions of the respective electrodes 13 on the wiring substrate 14, whereby signals from the strain gauge bridge of the sensor cell 1 are transferred to the solder bumps 12. Wiring board 14 through the joint
Configure to send to. In the gap between the upper surface of the wiring board 14 and the lower surface of the sensor cell 1, a soft bonding layer is formed by a known manufacturing method.
18 is filled, and the force acting on the pressure receiving column 3 is supported by the bonding layer 18.

Here, the length of the pressure receiving column 3 is l, and the diameter of the pressure receiving column 3 is d.
Then, the pressure receiving column 3 is regulated by the ratio of 1 / d. That is, for high sensitivity, it is desirable that the length 1 be as large as possible and the diameter d be as small as possible. However, since the pressure receiving column 3 is made of semiconductor silicon together with the thin portion 5 and the fixing portion 4, In practice, it is regulated within the range of 3 ≧ l / d ≧ 2. Because when l / d> 3, the pressure receiving column 3 is likely to break at the root. Also, when l / d <2, the effect of the moment becomes weak.

FIG. 8 shows the arrangement of wirings and terminals in the sensor cell 1 of FIG. This wiring pattern is also one of the features of the present invention. Two sets of half bridges and one set of full bridges coexist, and 3 to 4 electrodes are required for each, but the bridge voltage E and the ground G are The electrodes 7 and 9 are commonly used so that V _X , V _Y and V _Z can be taken out from the electrodes 6, 10 and 11 as output voltages. Further, the wiring 8 is arranged so as not to cross over the wirings while wrapping around these electrodes 6, 7, 9, 10, 11. In other words, one of the major features of the present invention is that the wiring does not cause crossover, and this makes it possible to eliminate the decrease in the reliability of the electrical characteristics when crossover occurs. FIG. 9 shows an equivalent circuit corresponding to the wiring of FIG.

[Effects of the Invention] As described above, according to the present invention, the strain gauges are arranged in a simple structure corresponding to the three-component forces F _X , F _Y , and F _Z in the tactile sensor cell, and Since the pressure receiving column is made twice or more longer than its diameter, the action of force due to the moment occurs in the strain gauge, and as a result, it is possible to detect the three-component force with high sensitivity. Also, by eliminating crossover in the cell wiring, the concern about disconnection has been eliminated. For this reason, it is small, thin, high-density, highly sensitive, and has improved reliability in wiring. Therefore, if this contact sensor is attached to the robot hand, it will be extremely useful for making the robot intelligent. It becomes effective.

[Brief description of drawings]

1 (A) and 1 (B) are a top view and a sectional view showing the basic principle of the touch sensor of the present invention, FIG. 1 (C) is a view showing the stress distribution of the strain sensor, and FIG. 2 (A). (E) is a figure for demonstrating the basic operation | movement of this invention with respect to 3 component force, (A) and (B) of this figure shows 3.
The bottom view and the cross-sectional view showing the disposition position of the strain gauge corresponding to the component force, the figures (C) to (E) are diagrams showing the stress distribution of each strain gauge, and FIGS. 3 (A), (B), ( C) is for detecting the force in the X direction, FIGS. 4 (A), (B), and (C) are for detecting the force in the Y direction, and FIG.
Figures (A), (B), and (C) are diagrams for explaining the detection of force in the Z direction, and Figs. 3 (A), 4 (A), and 5 (A) show strain gauges. FIG. 3 (B), FIG. 4 (B) and FIG. 5 (B) showing arrangement and connection, and FIG. 3 (C) and FIG. 4 showing changes in resistance value of each strain gauge. (C) and FIG. 5 (C) are Wheatstone bridge circuit diagrams composed of strain gauges, and FIGS. 6 (A), (B), (C) and (D) are X-direction, Y-direction and Y-direction, respectively. The figure which shows the change of the resistance value of each strain gauge when the force of Z direction, Z direction and X direction, and X direction, Y direction, and Z direction is applied. FIG. 7: of the contact sensor of the Example of this invention. FIG. 8 is a sectional view showing the structure, FIG. 8 is a bottom view of the sensor cell showing the arrangement and connection of strain gauges in the cell of FIG. 7, and FIG. 9 is an equivalent circuit diagram of the configuration of FIG. 1 ...... sensor cell, 2, 2A, 2B ...... strain _{gauges, X 1, X 2, Y} 1, Y 2, Z 1, Z 2, Z 3, Z 4 ...... strain gauges, 3 ...... pressure column, 4 ...... Fixed part, 5 ...... Thin part, 6,7,9,10,11,13 ...... Electrode, 8 …… Wiring, 12 …… Solder bump, 14 …… Wiring board, 15 …… Skin, 16… … Coating, 17 …… Adhesive layer, 18 …… Joining layer.

Claims (1)

[Claims] 1. A pressure-receiving column is provided in the center of a sensor cell in which three sets of strain detecting elements are arranged corresponding to forces in three directions, and when a force acts on the upper surface of the pressure-receiving column, a force is applied by a moment. The dimensions of the pressure-receiving columns are set so as to generate high stress in the three sets of strain sensing elements, and the wirings of the three sets of strain sensing elements arranged in the sensor cell do not overlap and cross each other. In the contact sensation sensor configured as described above, the height of the pressure receiving column is 2 times or more to 3 times or less the diameter of the pressure receiving column, and the strain detecting element corresponding to the force in the three directions is 2 A tactile sensor characterized in that a set is made up of a half bridge by using two strain gauges, and another set is made up as a full bridge by using four strain gauges.