CN119309727B - Capacitive miniature six-dimensional force sensor, optimized design and six-dimensional force decoupling method - Google Patents
Capacitive miniature six-dimensional force sensor, optimized design and six-dimensional force decoupling methodInfo
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Abstract
The capacitive miniature six-dimensional force sensor comprises a three-T-shaped beam type elastic body, a lower electrode plate, an upper electrode plate and a base, wherein the three-T-shaped beam type elastic body converts external six-dimensional force into displacement change, the upper electrode plate is connected with the elastic body, the upper electrode plate and the lower electrode plate form six groups of opposite electrodes, and the electrodes comprise three groups of electrodes which are horizontally and vertically arranged to form a six-group parallel flat-plate capacitor structure. When the sensor is acted by external force, the deformation of the elastic body drives the upper electrode plate to generate displacement, the capacitance value is changed, and the force information is converted into six capacitance signals to be output. The sensor is compact in design, small in size and convenient to integrate into narrow spaces such as fingertips of the robot. Based on the capacitance measurement principle, the sensor has excellent dynamic response performance and can quickly respond to external force changes. The sensor has high sensitivity, consistent rigidity in all directions, effectively reduces the coupling effect of force, and realizes high-precision six-dimensional force decoupling by combining a decoupling algorithm.
Description
Technical Field
The invention relates to the technical field of force sensors, in particular to a capacitive small six-dimensional force sensor, an optimal design and a six-dimensional force decoupling method.
Background
In recent years, with the rapid development of robot technology, robots are increasingly used in fields of industrial manufacturing, medical care, service robots, and the like. In these applications it is often necessary to make force measurements in order to perform more advanced, more refined tasks. Particularly for humanoid robots, force sensors are an important component of humanoid energy. In each part of the robot, the finger-like joints present various force information when a tool or an object is manipulated, and the performance of the robot can be greatly improved by reasonably collecting and processing the force information, so that the force and moment perception of the finger tips of the robot becomes a key technology, and the operation flexibility, the safety and the interaction quality with the environment of the robot are directly influenced.
The six-dimensional force sensor is capable of measuring all force and moment information at a point in space, namely three orthogonal forces and three orthogonal moments. It can measure various types of force information and is therefore a force sensor suitable for robotic knuckles. The conventional force sensor can meet the operation requirement of a general robot in most cases, but for a narrow space such as a finger tip of the robot, the sensor needs to be smaller and more sensitive to realize high-precision measurement of micro force and torque. In addition, robots often need to be in contact with the environment or a person during actual operation, and for some special applications, such as medical surgical robots, high precision perception of finger tip forces is essential. However, designing such a high-performance small sensor still has difficulties in structural design, signal measurement, decoupling design, etc., which hinders practical application of the six-dimensional force sensor in robots. In recent years, a small six-dimensional force sensor for a robot knuckle has become one of hot spots for robot technology research.
It should be noted that the information disclosed in the above background section is only for understanding the background of the application and thus may include information that does not form the prior art that is already known to those of ordinary skill in the art.
Disclosure of Invention
The invention aims to overcome the defects in the background technology and provide a capacitive small six-dimensional force sensor, an optimal design and a six-dimensional force decoupling method.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
The capacitive small six-dimensional force sensor comprises a three-T-shaped beam type elastic body, a lower electrode plate, an upper electrode plate and a base, wherein the three-T-shaped beam type elastic body is used for converting external six-dimensional force into displacement change, the lower electrode plate is arranged on the base, the upper electrode plate is connected with the three-T-shaped beam type elastic body, the upper electrode plate and the electrodes of the lower electrode plate form six groups of opposite electrodes correspondingly, the six groups of opposite electrodes comprise three groups of horizontally arranged electrodes and three groups of vertically arranged electrodes to form six groups of parallel plate capacitance structures, the three-T-shaped beam type elastic body comprises an elastic beam, a flexible leaf spring and a loading round table, the three groups of elastic beam and the flexible leaf spring form a T-shaped structure and are used for bearing force, the loading round table at the center is connected with the elastic beam through the flexible leaf spring and used for transmitting torque, the upper electrode plate is connected with the three-T-shaped beam type elastic body, when the sensor is subjected to external force, the deformation of the three-T-shaped elastic body drives the upper electrode plate to generate displacement, so that six groups of parallel plate capacitance structures are formed, six groups of parallel plate capacitance signals are converted into six-dimensional force signal output signals.
Further, the lower electrode plate includes three horizontal electrodes horizontally arranged on the upper surface of the lower electrode plate, and three vertical electrodes vertically arranged at the side walls of the three grooves of the lower electrode plate, the three horizontal electrodes and the three vertical electrodes being uniformly distributed in the circumferential direction.
Further, the three horizontal electrodes and the three vertical electrodes are alternately spaced apart in the circumferential direction.
Further, the upper electrode plate includes three horizontal electrodes horizontally arranged on the lower surface of the upper electrode plate, and three vertical electrodes vertically extending downward from the lower surface of the upper electrode plate, the horizontal electrodes and the vertical electrodes of the upper electrode plate being disposed in correspondence with the horizontal electrodes and the vertical electrodes of the lower electrode plate.
Further, the lower electrode plate is based on a circuit board structure, a digital capacitor chip is arranged on the circuit board, and the six groups of opposite electrodes are all connected with the digital capacitor chip.
Further, a top cover is arranged on the three T-shaped beam type elastomer.
An optimization design method of a three-T-shaped beam type elastomer structure of a capacitive small six-dimensional force sensor comprises the following steps:
establishing a mechanical model of the three-T-shaped beam type elastomer;
The mechanical model is improved through a BP neural network, and the nonlinear fitting capacity of the BP neural network is utilized to compensate the mechanical model so as to establish a nonlinear relation between the elastomer size parameter and the mechanical model error;
Generating a group of compensation coefficients according to the results of the mechanical model and ANSYS finite element analysis, wherein a plurality of groups of data are obtained through simulation, and the simulation results and the calculation results of the mechanical model are compared to obtain the compensation coefficients;
dividing a data set consisting of the size parameters and the corresponding compensation coefficients into a training set and a testing set, training the BP neural network through the training set, and checking the compensation effect of the network by using the testing set;
Reducing the solving error of the mechanical model to be within a preset threshold value through a trained BP neural network, so as to obtain an improved mechanical model;
And carrying out the optimization design of the size of the three-T-shaped beam type elastomer by utilizing the improved mechanical model and combining a particle swarm search algorithm.
Establishing four BP neural networks with 7 inputs and 1 outputs, wherein each network corresponds to mechanical model compensation under four stress conditions, each BP neural network is configured to receive seven dimensional parameters, namely the length of an elastic beam, the width of the elastic beam, the height of the elastic beam, the length of a flexible leaf spring, the width of the flexible leaf spring, the height of the flexible leaf spring and the radius of a stressed round table, and the four stress conditions are respectively as follows:
-F z case vertical force applied along Z-axis direction;
-M x case moment of rotation around X axis;
-F y case horizontal force applied along Y-axis direction;
-M z case moment of rotation around Z axis.
Constraint conditions and fitness functions for performing the optimal design of the dimensions of the tri-T beam elastomer are:
F=ω1f1+ω2f2
Wherein L 1 denotes the length of the spring beam, b 1 denotes the width of the spring beam, h 1 denotes the height of the spring beam, L 2 denotes the length of the flexible leaf spring, b 2 denotes the width of the flexible leaf spring, h 2 denotes the height of the flexible leaf spring, r denotes the radius of the loaded round table, i=1 to n in turn denotes the six-dimensional force F x～Mz,Di denotes the maximum effective displacement caused by the force/moment, Representing the average of the maximum effective displacement caused by the six-dimensional forces, ω 1 and ω 2 represent the weights of the proximity target and the sensitivity target, respectively.
A six-dimensional force decoupling method of a three-T-shaped beam type elastomer structure of a capacitive small six-dimensional force sensor comprises the following steps:
S1, establishing a relation between capacitance and displacement, namely when the sensor receives external acting force, driving the movable polar plate to displace through deformation of the elastic body, and fixing the static polar plate on the base to form capacitance variation corresponding to each displacement, wherein three horizontal capacitances respectively correspond to normal displacement d n1,dn2,dn3 and three vertical capacitances respectively correspond to tangential displacement d s4,ds5,ds6;
s2, solving the vertical force F z, namely determining coefficients through a mechanical model by utilizing the variation of the horizontal capacitance Calculate the vertical force F z, the formula isMeanwhile, the influence of the moments M x and M y is considered, so that no coupling exists;
S3, solving a moment M x, namely determining coefficients through a mechanical model according to the change quantity of horizontal displacement The moment M x is calculated by the formulaMeanwhile, the coupling influence of force F z is considered, and decoupling is carried out;
S4, solving a moment M y, namely determining coefficients through a mechanical model by utilizing the change quantity of horizontal displacement The moment M y is calculated by the formulaMeanwhile, the coupling influence of the force F z and the moment M x is considered, and decoupling is carried out;
S5, solving a moment M z, namely determining coefficients through a mechanical model according to the variation of the vertical displacement The moment M z is calculated by the formulaSimultaneously taking the coupling influence of forces F x and F y into consideration and decoupling;
S6, solving the horizontal force F y by utilizing the variable quantity of the vertical displacement and determining the coefficient through a mechanical model Calculate the horizontal force F y as Meanwhile, the coupling influence of force F x is considered, and decoupling is carried out;
S7, solving the coefficient determined by a mechanical model according to the variation of the vertical displacement by the horizontal force F x Calculate the horizontal force F x as Meanwhile, the coupling influence of the force F y and the moment M z is considered, and decoupling is carried out;
s8, decoupling is achieved, wherein parameters in a decoupling matrix are determined through a calibration method, displacement variable delta d obtained through capacitance variable calculation is utilized, six-dimensional force decoupling is achieved through a formula F/T=Calib, wherein F and T respectively represent force and moment, and Calib is the decoupling matrix.
The invention has the following beneficial effects:
The invention provides a capacitive small six-dimensional force sensor structure, an optimal design method thereof and a six-dimensional force decoupling method. When external six-dimensional force acts on the three T-shaped beam type elastic body, the elastic body deforms to drive the upper electrode plate to displace, the electrode plate distance of the six groups of parallel plate capacitors is changed to change the capacitance value, the micro capacitance value is collected, the six-dimensional force decoupling algorithm designed by the invention is utilized to decouple the six-dimensional force, and the accurate measurement of the force and the moment in three orthogonal directions can be realized. The sensor designed by the invention has the main advantages of compact structure, small size and convenience for integration into a narrow space of a robot smart finger joint, ② is designed based on a capacitance measurement principle, so that the sensor designed by the invention has good dynamic response performance and can quickly respond to the change of external force, ③ is capable of measuring the external force of +/-30N and the external moment of +/-0.3 Nm and meeting the use requirement of a robot smart finger tip, ④ is high in structural sensitivity, similar in rigidity in all directions and capable of reducing the coupling effect of six-dimensional force, ④ is convenient for decoupling of the six-dimensional force, and can realize high-precision six-dimensional force decoupling by combining with the designed decoupling algorithm.
Other advantages of embodiments of the present invention are further described below.
Drawings
FIG. 1 is a schematic exploded view of one embodiment of a capacitive miniature six-dimensional force sensor of an embodiment of the present invention;
FIG. 2 is a schematic perspective view of a top cover structure of one embodiment of a capacitive miniature six-dimensional force sensor of an embodiment of the present invention;
FIG. 3 is a schematic perspective view of a three-T beam elastomer structure of one embodiment of a capacitive miniature six-dimensional force sensor of an embodiment of the present invention;
FIG. 4 is a schematic perspective view of the upper electrode plate structure of one embodiment of a capacitive miniature six-dimensional force sensor of an embodiment of the present invention;
FIG. 5 is a schematic diagram of the structure of a lower electrode plate (circuit board) of one embodiment of a capacitive miniature six-dimensional force sensor of an embodiment of the present invention;
FIG. 6 is a schematic diagram of a base structure of one embodiment of a capacitive miniature six-dimensional force sensor of an embodiment of the present invention.
FIG. 7 is a diagram of structural parameters of an elastomer according to an embodiment of the present invention.
FIG. 8 is a force diagram of the elastomer alone applying F_z.
FIG. 9 is a force diagram of the elastomer alone applying M_x.
FIG. 10 is a force diagram of the elastomer alone applying F_y.
FIG. 11 is a force diagram of the elastomer alone applying M_z.
Fig. 12 is a block diagram of a BP neural network built for improving a mechanical model.
Fig. 13 is a graph of the compensation effect of the neural network on the mechanical model.
Fig. 14 is a graph showing the correspondence between the capacitance of the capacitive miniature six-dimensional force sensor and the displacement of the upper electrode plate.
Detailed Description
The following describes embodiments of the present invention in detail. It should be emphasized that the following description is merely exemplary in nature and is in no way intended to limit the scope of the invention or its applications.
It will be understood that when an element is referred to as being "mounted" or "disposed" on another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element. In addition, the connection may be for both a fixing action and a coupling or communication action.
It is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are merely for convenience in describing embodiments of the invention and to simplify the description, and do not denote or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus are not to be construed as limiting the invention.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless explicitly defined otherwise.
Referring to fig. 1 to 7, the embodiment of the invention provides a capacitive small six-dimensional force sensor, which comprises a top cover 1, a three-T-shaped beam type elastic body 2, an upper electrode plate 3, a lower electrode plate 4 and a base 5, wherein the three-T-shaped beam type elastic body 2 is used for converting external six-dimensional force into displacement change, the lower electrode plate 4 is arranged on the base 5, the top cover 1 is arranged on the three-T-shaped beam type elastic body 2, the upper electrode plate 3 is connected with the three-T-shaped beam type elastic body 2, the upper electrode plate 3 and the electrodes of the lower electrode plate 4 form six groups of opposite electrodes correspondingly, the six groups of opposite electrodes comprise three groups of horizontally arranged electrodes and three groups of vertically arranged electrodes to form six groups of parallel plate capacitance structures, the three-T-shaped beam type elastic body 2 comprises an elastic beam, a flexible plate spring and a bearing plate spring, the bearing force is used for bearing the three groups of the elastic beam is connected with the elastic beam through the flexible plate bearing platform, the elastic beam is used for transmitting moment, the upper electrode plate 3 and the three-T-shaped beam type elastic body 2 is connected with the three-T-shaped beam type elastic body, and the six-dimensional plate electrode plate sensor is driven by the six-dimensional plate capacitance sensor to generate six-parallel plate capacitance structure, and the six-dimensional plate capacitance structure is deformed by the six-shaped plate capacitance plate electrode plate sensor.
As shown in fig. 1, 4 and 5, in a preferred embodiment, the lower electrode plate 4 includes three horizontal electrodes horizontally disposed on the upper surface of the lower electrode plate 4, and three vertical electrodes vertically disposed at the sidewalls of three grooves of the lower electrode plate 4, the three horizontal electrodes and the three vertical electrodes being uniformly distributed in the circumferential direction. The three horizontal electrodes and the three vertical electrodes are alternately distributed at intervals along the circumferential direction. The upper electrode plate 3 includes three horizontal electrodes horizontally arranged on the lower surface of the upper electrode plate 3, and three vertical electrodes vertically extending downward from the lower surface of the upper electrode plate 3, the horizontal electrodes and the vertical electrodes of the upper electrode plate 3 being disposed corresponding to the horizontal electrodes and the vertical electrodes of the lower electrode plate 4.
The capacitive small six-dimensional force sensor can convert the external six-dimensional force into the change amount of six groups of electrode capacitances in the sensor, and the change amount of the six groups of capacitances is decoupled, so that the external six-dimensional force is sensed by utilizing the change of an electric signal. The sensor has the advantages of small size, light weight, high sensitivity, good dynamic response, easy processing and assembly and the like, and is suitable for the smart finger tip joint of the robot.
An optimization design method of a three-T-shaped beam type elastomer structure of a capacitive small six-dimensional force sensor comprises the following steps:
establishing a mechanical model of the three-T-shaped beam type elastomer;
The mechanical model is improved through a BP neural network, and the nonlinear fitting capacity of the BP neural network is utilized to compensate the mechanical model so as to establish a nonlinear relation between the elastomer size parameter and the mechanical model error;
Generating a group of compensation coefficients according to the results of the mechanical model and ANSYS finite element analysis, wherein a plurality of groups of data are obtained through simulation, and the simulation results and the calculation results of the mechanical model are compared to obtain the compensation coefficients;
dividing a data set consisting of the size parameters and the corresponding compensation coefficients into a training set and a testing set, training the BP neural network through the training set, and checking the compensation effect of the network by using the testing set;
Reducing the solving error of the mechanical model to be within a preset threshold value through a trained BP neural network, so as to obtain an improved mechanical model;
And carrying out the optimization design of the size of the three-T-shaped beam type elastomer by utilizing the improved mechanical model and combining a particle swarm search algorithm.
Establishing four BP neural networks with 7 inputs and 1 outputs, wherein each network corresponds to mechanical model compensation under four stress conditions, each BP neural network is configured to receive seven dimensional parameters, namely the length of an elastic beam, the width of the elastic beam, the height of the elastic beam, the length of a flexible leaf spring, the width of the flexible leaf spring, the height of the flexible leaf spring and the radius of a stressed round table, and the four stress conditions are respectively as follows:
-F z case vertical force applied along Z-axis direction;
-M x case moment of rotation around X axis;
-F y case horizontal force applied along Y-axis direction;
-M z case moment of rotation around Z axis.
Constraint conditions and fitness functions for performing the optimal design of the dimensions of the tri-T beam elastomer are:
F=ω1f1+ω2f2
Wherein L 1 denotes the length of the spring beam, b 1 denotes the width of the spring beam, h 1 denotes the height of the spring beam, L 2 denotes the length of the flexible leaf spring, b 2 denotes the width of the flexible leaf spring, h 2 denotes the height of the flexible leaf spring, r denotes the radius of the loaded round table, i=1 to n in turn denotes the six-dimensional force F x～Mz,Di denotes the maximum effective displacement caused by the force/moment, Representing the average of the maximum effective displacement caused by the six-dimensional forces, ω 1 and ω 2 represent the weights of the proximity target and the sensitivity target, respectively.
Specific embodiments of the present invention are described further below.
A small capacitive six-dimensional force sensor comprises a three-T-shaped beam type elastic body 2, a lower electrode plate 4 with a specific capacitance arrangement structure, an upper electrode plate 3 with a specific structure, a top cover 1 and a base 5. The lower electrode plate 4 with a specific capacitance arrangement structure is arranged on the base 5, and the upper electrode plate 3 is connected with the three-T-shaped beam type elastic body and forms six groups of opposite electrodes with the lower electrode plate 4. The sensor can convert the external six-dimensional force into the change amount of the six groups of electrode capacitances in the sensor, and decouple the change amount of the six groups of capacitances, so that the external six-dimensional force is sensed by utilizing the change of the electric signal. Six capacitance electrodes are arranged on the lower electrode plate 4, the six capacitance electrodes are uniformly arranged on the circular circuit board, three of the six capacitance electrodes are horizontally arranged on the upper surface of the circuit board, three of the six capacitance electrodes are vertically arranged on the side walls of three grooves of the circuit board, the six capacitance electrodes are connected to a digital capacitance chip in the middle of the circuit board, and capacitance values are measured through the digital capacitance chip. The structure of the upper electrode plate 3 corresponds to that of the lower electrode plate 4, and six electrodes are uniformly arranged on the circular electrode plate, wherein three electrodes are horizontally arranged and three electrodes are vertically arranged.
When the sensor is subjected to external force, the deformation of the three T-shaped beam type elastic body 2 drives the upper electrode plate 3 to generate displacement, so that the electrode plate distance of the 6 groups of parallel plate capacitors is changed, and six-dimensional force information is converted into 6 capacitance signals to be output.
In particular embodiments, the sensor structure may be assembled as follows. The digital capacitor chip and the signal wire are welded on the lower electrode plate 4, the lower electrode plate 4 is placed on the base 5, the signal wire is led out from the lower part of the base 5, the upper electrode plate 3 is aligned with the three-T-shaped beam type elastic body 2 through the grooves and then connected with the screw, the three-T-shaped beam type elastic body 2 is positioned with the lower electrode plate 4 on the base 5 through pins, the base 5 is connected with the three-T-shaped beam type elastic body 2 through the screw after the alignment, the lower electrode plate 4 is pressed, 6 groups of opposite parallel plate capacitors are formed between the lower electrode plate electrode and the upper electrode plate electrode, the plate spacing is 0.2mm, and the top cover 1 is aligned with the three-T-shaped beam type elastic body 2 and then connected with the screw. The six-dimensional force sensor is assembled in this way.
The capacitance signal acquisition can be realized through an AD7147 digital capacitance chip, the chip can measure the capacitance of +/-8 pF, the resolution is 16 bits, the number of measurable capacitance channels is 14, and 6 capacitance signals can be measured simultaneously by using a single chip.
The sensor has the advantages of small size, light weight, high sensitivity, good dynamic response, easy processing and assembly and the like, and is suitable for the smart finger tip joint of the robot.
The mechanical model of the three-T-shaped beam type elastomer is improved through a BP neural network. The size structure of the three-T-shaped beam type elastomer is optimally designed by utilizing a particle swarm search algorithm. The specific dimensions depend on the detection requirements of the six-dimensional force sensor in all directions and the dimensional requirements of the six-dimensional force sensor.
The three-T-shaped beam type elastomer structure size is optimally designed by improving a mechanical model and a particle swarm search algorithm, wherein the BP neural network reduces the model relative error of the mechanical model to be within 5%, and the particle swarm search algorithm calculates the optimal size structure to enable the elastomer to realize high sensitivity and isotropy.
Three-T-shaped beam type elastomer structure size design method
Firstly, building a mechanical model of a three-T-shaped beam type elastomer structure, then compensating the model by utilizing a BP neural network to obtain an improved mechanical model, controlling the solving error of the model to be within 5%, and then solving the optimal size structure of the elastomer by combining the improved mechanical model and using a particle swarm search algorithm with high sensitivity and similar rigidity as targets.
Establishing a mechanical model
The total structural parameters in the mechanical model of the three-T-shaped beam type elastomer structure are 6, namely the length and width l 1,b1 of the elastic beam, the length and width l 2,b2 of the flexible plate spring, the heights h of the elastic beam and the flexible plate spring and the radius r of the bearing round table. In order to optimize the stiffness of the elastomer in all directions and to increase the designable space of the elastomer, the high of the elastic beam and the high of the flexible leaf spring are distinguished, denoted h 1 and h 2 respectively. The structural parameters of the elastomer are shown in fig. 7.
With the vertical direction noted as the Z direction, when considering that the elastomer is subjected to six-dimensional forces, it can be verified that the displacement of force F y is the same as the displacement calculation of force F x, and the displacement calculation of moment M x is the same as the displacement calculation of moment M y, since the elastomer structure is symmetrical. The elastomer displacement calculation under six-dimensional forces can thus be reduced to displacement calculations of two forces (F x and F z) and two moments (M y and M z). On the basis of the original model, since the height of the elastic beam and the height of the flexible leaf spring are distinguished, the mechanical model needs to be adjusted and improved, and the result is as follows.
1) Application of F alone z
The force applied to F z alone is shown in FIG. 8.
Recording device
l′1＝l1+b2/2,l′2＝l2-b1,k=5/6,S1＝b1h1,S2＝b2h2,(Beta is the section torsion coefficient), record
At this time F z andThe relationship of (2) can be written as
Wherein the method comprises the steps ofE is the Young's modulus of the material and G is the shear modulus of the material.
2) Separately applying M x
The force applied to M x alone is shown in FIG. 9.
The reference number lambda 1＝l′1/r,λ2＝l′2/r is given,
At this time M x andThe relationship of (2) can be written as
Wherein the method comprises the steps of
3) Application of F alone y
Fig. 10 is a force diagram of the application of F y alone.
Recording deviceRecording device
At this time F y andThe relationship of (2) can be written as
Wherein the method comprises the steps of
4) Separately applying M z
Fig. 11 is a force diagram of the application of M z alone.
Recording device
At this time M z andThe relationship of (2) can be written as
Wherein the method comprises the steps ofIs easily obtained by the symmetry of the elastomer structure
Wherein the method comprises the steps of
Improved mechanical model
By comparing the solving result of the mechanical model with the solving result of Ansys finite element analysis, the solving error of the mechanical model is about 5% -20%, and the error is larger. In order to optimize the design of the elastomeric structure, a mechanical model with high accuracy is required. The model is optimized and the method is selected by compensating with artificial neural network.
The BP neural network is a common artificial neural network model, has wide applicability and strong nonlinear fitting capability, and can introduce nonlinear mapping through an activation function so as to fit the neural network with complex nonlinear relations. These advantages of the BP neural network make it very suitable for solving the current problem, namely, establishing a nonlinear relationship between the elastomer dimensional parameters and the mechanical model errors.
For the three T-shaped beam type elastomer structure with the design, 7 dimension parameters are shared, so that 4 BP neural networks with 7 inputs and 1 outputs can be established, and the BP neural networks respectively correspond to mechanical model compensation under four conditions of F z、Mx、Fy、Mz. When the BP neural network is established, proper hidden layer number and node number are required to be selected. Because the input parameters of the designed neural network are fewer, the 1-layer hidden layer can meet the use requirement, and the number of nodes is generally twice the number of the input parameters, and the number of the nodes is 10 in order to avoid the overfitting phenomenon. The structure of the established BP neural network is shown in FIG. 12.
200 Groups of data are generated through ANSYS simulation, and the simulation result is compared with the result calculated by the existing mechanical model to obtain 200 groups of compensation coefficients. And combining 200 sets of size parameters and 200 corresponding sets of compensation coefficients into a data set, wherein the size parameters are input, and the compensation coefficients are output. 150 of them were randomly selected as training sets, and the remaining 50 were selected as test sets. After training by using the training set is finished, the test set is input into the neural network, and the compensation effect of the neural network on the mechanical model is checked, and the result is shown in fig. 13. The blue curve in the graph is the solving error of the mechanical model before the test set parameters are added to the neural network compensation, and the red curve is the solving error of the mechanical model after the neural network compensation is added. The solution error can be obviously reduced, taking F z as an example, the solution error of the mechanical model is reduced to within 5% from about 20% of the original solution error, and the error can be controlled within 5% in the rest conditions. Therefore, the neural network can show excellent performance on the test set, and the model has generalization capability on new data.
Optimal design of elastomer size and structure
Based on the optimized elastomer mechanical model, the optimization algorithm is combined to perform optimization design of the structure size of the elastomer. Common optimization algorithms include gradient descent methods, genetic algorithms, simulated annealing algorithms, particle swarm search algorithms, and the like. The particle swarm search algorithm is suitable for the multi-dimensional complex problem, is simple and convenient to realize, and is suitable for the optimization design of the elastomer structure in the invention.
The fitness function is the key of the optimization process, and the design of the function needs to embody the optimization target. In addition, certain constraints are also required to be met for the position and velocity of the particles. In this study, constraints and optimization objectives were targeted for the optimization design of the elastomer at the following four points:
Size constraints-there are stringent range requirements for each size parameter in the elastomeric structure;
deformation constraint, the phenotype of the elastomer cannot be too great or too small;
Proximity targets-the deformation caused by the elastomer when subjected to forces/moments of equal magnitude in different directions is similar;
Sensitivity targets the amount of deformation is as large as possible within the constraint range.
Based on the four points, constraint conditions and fitness functions of the optimal design are given as follows:
F=ω1f1+ω2f2#(4-8)
Wherein L 1 denotes the length of the spring beam, b 1 denotes the width of the spring beam, h 1 denotes the height of the spring beam, L 2 denotes the length of the flexible leaf spring, b 2 denotes the width of the flexible leaf spring, h 2 denotes the height of the flexible leaf spring, r denotes the radius of the loaded round table, i=1 to n in turn denotes the six-dimensional force F x～Mz,Di denotes the maximum effective displacement caused by the force/moment, Representing the average of the maximum effective displacement caused by the six-dimensional forces, ω 1 and ω 2 represent the weights of the proximity target and the sensitivity target, respectively.
Six-dimensional force decoupling method
According to the small capacitive six-dimensional force sensor, a corresponding six-dimensional force decoupling algorithm is designed according to a specific capacitance arrangement mode, and the relative error of decoupling is within 0.5%.
When the designed six-dimensional force sensor is subjected to external acting force, the elastic body is stressed to deform, the movable polar plate fixedly connected to the elastic body also moves, and the static polar plate is fixed on the base, so that the displacement of the upper polar plate can cause the change of the polar plate distance, and further the change of the capacitance. At the time of decoupling, the following procedure is performed:
C→d→F/T
under the structure designed as shown in fig. 14, each capacitor corresponds to each displacement of the upper electrode plate one by one, wherein the horizontal capacitor C 1,C2,C3 corresponds to each normal displacement d n1,dn2,dn3, and the vertical capacitor C 4,C5,C6 corresponds to each tangential displacement d s4,ds5,ds6. Therefore, the step of solving the displacement variation by the capacitance variation does not involve a coupling problem, and only the coupling problem of the displacement variation and the six-dimensional force is considered.
1) Solving F z
From the mechanical model, it can be seen that:
And further has
Consider the coupling problem caused by moment M x. When F z is applied, if M x is applied simultaneously, Δd n1、Δdn2、Δdn3 caused by M x satisfies the following relationship:
Δdn1＝-2Δdn2＝-2Δdn3
therefore, the calculation result of the formula (4-7) is not changed, i.e., no coupling exists.
Consider the coupling problem caused by moment M y. When F z is applied, if M y is applied simultaneously, Δd n1、Δdn2、Δdn3 caused by M y satisfies the following relationship:
Δdn1=0
Δdn2＝-Δdn3
therefore, the calculation result of the formula (4-7) is not changed, i.e., no coupling exists.
In addition, none of F x、Fy、Mz causes a change in Δd n1、Δdn2、Δdn3, and therefore none of the couplings are present. The formula (4-7) is the decoupling formula of F z.
2) Solving for M x
From the mechanical model, it can be seen that:
And further has
Consider the coupling problem caused by moment M y. When M x is applied, if M y is applied simultaneously, Δd n1、Δdn2、Δdn3 caused by M y satisfies the following relationship
Δdn1=0
Δdn2＝-Δdn3
Therefore, the calculation result of the formula (4-8) is not changed, i.e., no coupling exists.
Consider the coupling problem caused by force F z. When M x is applied, if F z is applied simultaneously, Δd n1、Δdn2、Δdn3 caused by F z satisfies the following relationship
Δdn1＝Δdn2＝Δdn3
This will cause the calculation of equations (4-8) to change, requiring decoupling. The method comprises calculating F z from formula (4-7), calculating the displacement change caused by F z, substituting formula (4-8), and eliminating in advance
In addition, none of F x、Fy、Mz causes a change in Δd n1、Δdn2、Δdn3, and therefore none of the couplings are present. The formula (4-9) is the decoupling formula of M x.
3) Solving for M y
From the mechanical model, it can be seen that:
And further has
Consider the coupling problem caused by force F z. When M y is applied, if F z is applied simultaneously, Δd n1、Δdn2、Δdn3 caused by F z satisfies the following relationship
Δdn1＝Δdn2＝Δdn3
Therefore, the calculation result of the formulas (4-10) is not changed, i.e., no coupling exists.
Consider the coupling problem caused by moment M x. When M y is applied, if M x is applied simultaneously, Δd n1、Δdn2、Δdn3 caused by M x satisfies the following relationship
Δdn1＝-2Δdn2＝-2Δdn3
Therefore, the calculation result of the formulas (4-10) is not changed, i.e., no coupling exists.
In addition, no change in Δd n1、Δdn2、Δdn3 is caused by F x、Fy、Mz, and thus no coupling problem exists. The formula (4-10) is the decoupling formula of M y.
4) M z solution
From the mechanical model, it can be seen that:
And further has
Consider the coupling problem caused by force F x. When M z is applied, if F x is applied simultaneously, Δd s4、Δds5、Δds6 caused by F x satisfies the following relationship
Δds6＝-2Δds4＝-2Δds5
Therefore, the calculation result of the formulas (4-11) is not changed, i.e., no coupling exists.
Consider the coupling problem caused by force F y. When M z is applied, if F y is applied simultaneously, Δd s4、Δds5、Δds6 caused by F y satisfies the following relationship
Δds4＝-Δds5
Δds6=0
Therefore, the calculation result of the formulas (4-11) is not changed, i.e., no coupling exists.
Consider the coupling problem caused by moment M x. When M z is applied, if M x is applied simultaneously, Δd s4、Δds5、Δds6 caused by M x satisfies the following relationship
Δds4＝-Δds5
Δds6=0
Therefore, the calculation result of the formulas (4-11) is not changed, i.e., no coupling exists.
Consider the coupling problem caused by moment M y. When M z is applied, if M y is applied simultaneously, Δd s4、Δds5、Δds6 caused by M y satisfies the following relationship
Δds6＝-2Δds4＝-2Δds5
Therefore, the calculation result of the formulas (4-11) is not changed, i.e., no coupling exists.
Furthermore, F z does not cause a change in Δd s4、Δds5、Δds6, and therefore there is no coupling. The formula (4-11) is the decoupling formula of M z.
5) F y solution
From the mechanical model, it can be seen that:
And further has
Consider the coupling problem caused by force F x. When F y is applied, if F x is applied simultaneously, Δd s4、Δds5、Δds6 caused by F x satisfies the following relationship
Δds6＝-2Δds4＝-2Δds5
Therefore, the calculation results of the formulas (4-12) are not changed, i.e., no coupling exists.
Consider the coupling problem caused by moment M z. When F y is applied, if M z is applied simultaneously, Δd s4、Δds5、Δds6 caused by M z satisfies the following relationship
Δds6＝Δds4＝Δds5
Therefore, the calculation results of the formulas (4-12) are not changed, i.e., no coupling exists.
Consider the coupling problem caused by moment M y. When F y is applied, if M y is applied simultaneously, Δd s4、Δds5、Δds6 caused by M y satisfies the following relationship
Δds6＝-2Δds4＝-2Δds5
Therefore, the calculation results of the formulas (4-12) are not changed, i.e., no coupling exists.
Consider the coupling problem caused by moment M x. When F y is applied, if M x is applied simultaneously, Δd s4、Δds5、Δds6 caused by M x satisfies the following relationship
Δds4＝-Δds5
Δds6=0
This will cause the calculation of equations (4-12) to change, requiring decoupling. The following relationship holds when M x is applied alone when the center-of-mass distance between the static plate and the movable plate is recorded as D
Recording deviceThen there is
In decoupling, M x is calculated from equation (4-9), and the displacement change caused by M x is calculated and substituted into equation (4-12) for elimination in advance, which comprises the following steps
Furthermore, F z does not cause a change in Δd s4、Δds5、Δds6, and therefore there is no coupling. The formula (4-15) is the decoupling formula of F y.
6) F x solution
From the mechanical model, it can be seen that:
And further has
Consider the coupling problem caused by force F y. When F x is applied, if F y is applied simultaneously, Δd s4、Δds5、Δds6 caused by F y satisfies the following relationship
Δds4＝-Δds5
Δds6=0
The calculation results of equations (4-16) are not changed, i.e. no coupling exists.
Consider the coupling problem caused by moment M z. When F x is applied, if M z is applied simultaneously, Δd s4、Δds5、Δds6 caused by M z satisfies the following relationship
Δds6＝Δds4＝Δds5
This will cause the calculation of equations (4-16) to change, requiring decoupling. The method comprises calculating M z from formula (4-11), calculating the displacement change caused by M z, substituting formula (4-16), and eliminating in advance
Consider the coupling problem caused by moment M x. When F x is applied, if M x is applied simultaneously, Δd s4、Δds5、Δds6 caused by M x satisfies the following relationship
Δds4＝-Δds5
Δds6=0
Therefore, the calculation results of the formulas (4-17) are not changed, i.e., no coupling exists.
Consider the coupling problem caused by moment M y. When F y is applied, if M y is applied simultaneously, Δd s4、Δds5、Δds6 caused by M y satisfies the following relationship
Δds6＝-2Δds4＝-2Δds5
This will also change the calculation of equations (4-17) and require decoupling. The following relationship holds when M y is applied alone
Recording deviceThen there is
In decoupling, M x and M y are calculated by the formula (4-10), and the displacement change caused by M y is calculated and substituted into the formula (4-17) for elimination in advance, wherein the method comprises the following steps
Furthermore, F z does not cause a change in Δd s4、Δds5、Δds6, and therefore there is no coupling. The formula (4-21) is the decoupling formula of F y.
In combination with the above, the decoupling algorithm for six-dimensional forces is summarized as follows:
It can also be expressed in the following form
F/T=Calib*Δd#(4-22)
In actual use, parameters in the decoupling matrix can be obtained through a calibration method. Δd can be calculated from the capacitance variation, and decoupling of six-dimensional forces can be achieved using equations (4-22).
Example
As shown in fig. 1 to 6, the sensor includes a top cover 1, a three T-beam type elastic body 2, an upper electrode plate 3, a lower electrode plate 4, and a base 5. The top cover 1 is fixed with the three-T-shaped beam type elastic body 2 through screws, the three-T-shaped beam type elastic body 2 is positioned with the upper electrode plate 3 through positioning blocks and fixed through screws, the three-T-shaped beam type elastic body 2 is positioned with the lower electrode plate 4 through pins, the lower electrode plate 4 is positioned with the base 5 through grooves, and the three-T-shaped beam type elastic body 2 is fixed with the base 5 through screws.
As shown in fig. 1 to 6, SUS304 stainless steel was selected as a material for processing the top cover 1, the upper electrode plate 3, and the base 5, and was processed by a machining method. The A212 aluminum alloy is selected as a processing material of the three-T-shaped beam type elastomer, and is processed by a mechanical processing method. And the FR-4 plate is selected as a processing plate of the lower electrode plate 4 to manufacture the PCB.
As shown in fig. 1, the top cover 1 has an overall diameter of 15mm and a thickness of 1mm;
as shown in fig. 2, the three T-beam elastomer 2 has an overall diameter of 15mm and a thickness of 4mm;
as shown in fig. 4, the overall diameter of the lower electrode plate 4 is 13.8mm, the thickness is 2mm, the capacitance electrode horizontally arranged in the lower electrode plate is processed by adopting a windowing process, and the capacitance electrode vertically arranged is processed by using 50nm copper paste paper to be stuck on the side wall;
as shown in fig. 5, the overall diameter of the base 5 is 15mm and the thickness is 5mm.
The foregoing is a further detailed description of the invention in connection with specific/preferred embodiments, and it is not intended that the invention be limited to such description. It will be apparent to those skilled in the art that several alternatives or modifications can be made to the described embodiments without departing from the spirit of the invention, and these alternatives or modifications should be considered to be within the scope of the invention. In the description of the present specification, reference to the terms "one embodiment," "some embodiments," "preferred embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Those skilled in the art may combine and combine the features of the different embodiments or examples described in this specification and of the different embodiments or examples without contradiction. Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the invention as defined by the appended claims.
Claims (7)
1. The capacitive small six-dimensional force sensor is characterized by comprising a three-T-shaped beam type elastic body, a lower electrode plate, an upper electrode plate and a base; the three-T-shaped beam type elastic body is used for converting external six-dimensional force into displacement change, the lower electrode plate is arranged on the base, the upper electrode plate is connected with the three-T-shaped beam type elastic body, the upper electrode plate and the electrodes of the lower electrode plate form six groups of opposite electrodes correspondingly, the six groups of opposite electrodes comprise three groups of horizontally arranged electrodes and three groups of vertically arranged electrodes to form a six-group parallel plate capacitance structure, the three-T-shaped beam type elastic body comprises an elastic beam, a flexible leaf spring and a stressed round table, the three groups of elastic beams and the flexible leaf spring form a T-shaped structure and are used for bearing force, the stressed round table at the center is connected with the elastic beam through the flexible leaf spring and is used for transmitting moment, the upper electrode plate is connected with the three-T-shaped beam type elastic body, when the sensor is subjected to external force, the deformation of the three-T-shaped beam type elastic body drives the upper electrode plate to generate displacement, thereby the electrode plate spacing of the six groups of parallel plate capacitances is changed, the information of the six groups of parallel plate capacitances is converted into six capacitance signals, the three capacitance signals are output, the lower electrode plate electrodes comprise three horizontally arranged on the upper electrode plates and three horizontally arranged electrodes and three horizontally arranged on the three horizontally arranged electrodes and three horizontally arranged surfaces and three horizontally arranged on the three horizontally arranged side walls, the three electrodes are vertically arranged along the circumference of the three horizontal surfaces and the three horizontally arranged side walls are vertically arranged along the three horizontal surfaces, and three vertical electrodes extending vertically downward from the lower surface of the upper electrode plate, the horizontal electrodes and the vertical electrodes of the upper electrode plate being disposed in correspondence with the horizontal electrodes and the vertical electrodes of the lower electrode plate.
2. The capacitive miniature six-dimensional force sensor of claim 1, wherein said lower electrode plate is based on a circuit board construction, a digital capacitive chip is provided on said circuit board, and said six sets of opposing electrodes are all connected to said digital capacitive chip.
3. The capacitive miniature six-dimensional force sensor of any one of claims 1-2, further comprising a top cover disposed over said tri-T beam elastomer.
4. A method of optimizing the design of a three-T beam elastomer structure of a capacitive miniature six-dimensional force sensor of any one of claims 1 to 3, comprising:
establishing a mechanical model of the three-T-shaped beam type elastomer;
The mechanical model is improved through a BP neural network, and the nonlinear fitting capacity of the BP neural network is utilized to compensate the mechanical model so as to establish a nonlinear relation between the elastomer size parameter and the mechanical model error;
Generating a group of compensation coefficients according to the results of the mechanical model and ANSYS finite element analysis, wherein a plurality of groups of data are obtained through simulation, and the simulation results and the calculation results of the mechanical model are compared to obtain the compensation coefficients;
dividing a data set consisting of the size parameters and the corresponding compensation coefficients into a training set and a testing set, training the BP neural network through the training set, and checking the compensation effect of the network by using the testing set;
Reducing the solving error of the mechanical model to be within a preset threshold value through a trained BP neural network, so as to obtain an improved mechanical model;
And carrying out the optimization design of the size of the three-T-shaped beam type elastomer by utilizing the improved mechanical model and combining a particle swarm search algorithm.
5. The method for optimally designing a three-T-shaped beam type elastomer structure of a capacitive small six-dimensional force sensor according to claim 4, wherein four BP neural networks with 7 inputs and 1 outputs are established, each network corresponds to mechanical model compensation under four stress conditions, each BP neural network is configured to receive seven dimensional parameters, specifically, the length of an elastic beam, the width of the elastic beam, the height of the elastic beam, the length of a flexible leaf spring, the width of the flexible leaf spring, the height of the flexible leaf spring and the radius of a stressed table, and a compensation coefficient is output as input, wherein the four stress conditions are as follows:
- A vertical force applied along the Z-axis direction;
- moment of rotation around X axis;
- A case where a horizontal force is applied in the Y-axis direction;
- in the case of a moment of rotation about the Z axis.
6. The method for optimally designing a three-T-beam elastomer structure for a capacitive miniature six-dimensional force sensor according to claim 4, wherein constraints and fitness functions for performing the optimal design of the dimensions of the three-T-beam elastomer are:
;
;
;
wherein, the Indicating the length of the elastic beam,Represents the width of the elastic beam,Representing the height of the elastic beam,Indicating the length of the flexible leaf spring,Indicating the width of the flexible leaf spring,The height of the flexible leaf spring is indicated,Representing the radius of the loaded round table,Sequentially express six-dimensional force,Indicating the maximum effective displacement caused by the force/moment,Represents the average of the maximum effective displacement caused by six-dimensional forces,AndThe weights of the proximity target and the sensitivity target are represented, respectively.
7. A method of six-dimensional force decoupling of a three-T-beam elastomeric structure of a capacitive miniature six-dimensional force sensor of any one of claims 1 to 3, comprising:
S1, establishing a relation between capacitance and displacement, namely when the sensor receives external force, the movable polar plate is driven to displace through deformation of the elastic body, the static polar plate is fixed on the base to form capacitance variation corresponding to each displacement, and three horizontal capacitances respectively correspond to normal displacement Three vertical capacitors respectively correspond to tangential displacement;
S2, solving the vertical forceUsing the variation of horizontal capacitance and the coefficient determined by mechanical modelCalculating vertical forceThe formula isAt the same time consider momentAndTo ensure that no coupling exists;
s3, solving moment According to the change of horizontal displacement, the coefficient determined by mechanical modelCalculating momentThe formula isAt the same time consider forceAnd perform decoupling, whereinRepresenting the radius of the loaded round table;
S4, solving moment Coefficient determined by mechanical model by using change of horizontal displacementCalculating momentThe formula isAt the same time consider forceAnd moment of forceIs coupled and decoupled;
S5, solving moment According to the variation of vertical displacement, the coefficient determined by mechanical modelCalculating momentThe formula isAt the same time consider forceAndIs coupled and decoupled;
S6, solving the horizontal force Coefficient determined by mechanical model by using variation of vertical displacementCalculating horizontal forceThe formula is
,
At the same time consider forceIs coupled and decoupled;
s7, solving the horizontal force According to the variation of vertical displacement, the coefficient determined by mechanical modelCalculating horizontal forceThe formula is
,
At the same time consider forceAnd moment of forceIs coupled and decoupled;
s8, decoupling is realized, namely parameters in a decoupling matrix are determined through a calibration method, and displacement variation obtained through calculation of capacitance variation is utilized By the formulaDecoupling of six-dimensional forces is achieved, whereinAnd T represents the force and moment respectively,Is a decoupling matrix.
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