Capacitive small six-dimensional force sensor, optimization design and six-dimensional force decoupling method

Abstract

The invention discloses a capacitive small six-dimensional force sensor, an optimization design method and a six-dimensional force decoupling method.The sensor comprises 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 converts external six-dimensional force into displacement changes, the upper electrode plate is connected with the elastic body, the upper electrode plate and the lower electrode plate form six sets of opposite electrodes, and the three-T-shaped beam type elastic body is connected with the base. Comprising three groups of horizontally arranged electrodes and three groups of vertically arranged electrodes to form six groups of parallel plate capacitor structures. When the sensor is subjected to external force, deformation of the elastic body drives the upper electrode plate to generate displacement, a capacitance value is changed, and force information is converted into six capacitance signals to be output. The sensor is compact in design and small in size, and can be conveniently integrated into narrow spaces such as robot fingertips. Based on a capacitance measurement principle, the sensor has excellent dynamic response performance and can quickly respond to external force change. The sensor has high sensitivity, rigidity in all directions is consistent, the coupling effect of force is effectively reduced, and high-precision six-dimensional force decoupling is achieved by combining a decoupling algorithm.

Description

Technical Field

[0001] The present invention relates to the technical field of force sensors, and in particular to a capacitive small six-dimensional force sensor, an optimized design and a six-dimensional force decoupling method. Background Art

[0002] In recent years, with the rapid development of robotics technology, robots are increasingly used in industrial manufacturing, medical care, service robots and other fields. In these applications, force measurement is often required in order to perform more advanced and sophisticated tasks. Especially for humanoid robots, force sensors are an important part of humanoid performance. Among the various components of the robot, humanoid finger joints present a variety of force information when manipulating tools or objects. Reasonable collection and processing of this force information can greatly improve the performance of the robot. Therefore, the force and torque perception of the robot's fingertips has become a key technology, which directly affects the robot's operational flexibility, safety and interaction quality with the environment in complex environments.

[0003] The six-dimensional force sensor can measure all the force and torque information at a certain point in space, namely three orthogonal forces and three orthogonal moments. It can measure various types of force information, so it is a force sensor suitable for robot finger joints. Traditional force sensors can meet the needs of general robot operations in most cases, but for small spaces such as robot fingertips, sensors need to be smaller and more sensitive to achieve high-precision measurement of tiny forces and torques. In addition, robots often need to contact the environment or people in actual work. For some special applications, such as medical surgical robots, high-precision perception of fingertip force is even more essential. However, there are still difficulties in designing such high-performance small sensors in terms of structural design, signal measurement, and decoupling design, which hinders the practical application of six-dimensional force sensors in robots. In recent years, small six-dimensional force sensors for robot finger joints have become one of the hot spots in robotics research.

[0004] It should be noted that the information disclosed in the above background technology section is only used for understanding the background of the present application, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the invention

[0005] The main purpose of the present invention is to overcome the defects existing in the above-mentioned background technology and provide a capacitive small six-axis force sensor, an optimized design and a six-axis force decoupling method.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A capacitive small six-dimensional force sensor, comprising a three-T-beam elastic body, a lower electrode plate, an upper electrode plate and a base; the three-T-beam elastic body is used to convert an external six-dimensional force into a displacement change, the lower electrode plate is placed on the base, the upper electrode plate is connected to the three-T-beam elastic body, and the electrodes of the upper electrode plate and the lower electrode plate correspond to form six groups of facing electrodes; the six groups of facing electrodes include three groups of horizontally arranged electrodes and three groups of vertically arranged electrodes, forming six groups of parallel flat plate capacitor structures; the three-T-beam elastic body includes an elastic The sensor comprises a three-T-beam elastic body, a flexible leaf spring and a loaded truncated table, wherein the three groups of the elastic beams and the flexible leaf springs form a T-shaped structure for bearing the action of force, and the loaded truncated table located in the center is connected to the elastic beams through the flexible leaf springs for transmitting torque; the upper electrode plate is connected to the three-T-beam elastic body; wherein, when the sensor is subjected to external force, the deformation of the three-T-beam elastic body drives the upper electrode plate to displace, thereby causing the plate spacing of the six groups of parallel flat plate capacitors to change, and then converting the six-dimensional force information into six capacitance signal outputs.

[0008] Furthermore, 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, and the three horizontal electrodes and the three vertical electrodes are evenly distributed along the circumferential direction.

[0009] Furthermore, the three horizontal electrodes and the three vertical electrodes are alternately spaced and distributed along the circumferential direction.

[0010] Furthermore, the upper electrode plate includes three horizontal electrodes horizontally arranged on the lower surface of the upper electrode plate, and three vertical electrodes extending vertically downward from the lower surface of the upper electrode plate, and the horizontal electrodes and vertical electrodes of the upper electrode plate are arranged corresponding to the horizontal electrodes and vertical electrodes of the lower electrode plate.

[0011] Furthermore, the lower electrode plate is constructed based on a circuit board, a digital capacitor chip is arranged on the circuit board, and the six groups of facing electrodes are all connected to the digital capacitor chip.

[0012] Furthermore, it also includes a top cover placed on the three T-beam elastic body.

[0013] An optimization design method for a three-T-beam elastic body structure of a capacitive small six-dimensional force sensor includes:

[0014] Establishing a mechanical model of the three-T-beam elastic body;

[0015] The mechanical model is improved by using a BP neural network, and the nonlinear fitting ability of the BP neural network is used to compensate the mechanical model so as to establish a nonlinear relationship between the size parameters of the elastic body and the error of the mechanical model;

[0016] wherein, a set of compensation coefficients is generated according to the mechanical model and the results of ANSYS finite element analysis, wherein multiple sets of data are obtained through simulation, and the simulation results are compared with the calculation results of the mechanical model to obtain the compensation coefficients;

[0017] The data set consisting of the size parameters and the corresponding compensation coefficients is divided into a training set and a test set, the BP neural network is trained by the training set, and the compensation effect of the network is tested by the test set;

[0018] By using the trained BP neural network, the solution error of the mechanical model is reduced to within a preset threshold, thereby obtaining an improved mechanical model;

[0019] The improved mechanical model is used in combination with a particle swarm search algorithm to optimize the size of the three-T-beam elastic body.

[0020] Four BP neural networks with 7 inputs and 1 output are established, each network corresponding to the mechanical model compensation under four stress conditions; each BP neural network is configured to receive seven size parameters, specifically the length of the elastic beam, the width of the elastic beam, the height of the elastic beam, the length of the flexible leaf spring, the width of the flexible leaf spring, the height of the flexible leaf spring and the radius of the loaded truncated cone, as input, and output a compensation coefficient; the four stress conditions are respectively:

[0021] -F z Situation: vertical force applied along the Z axis;

[0022] -M x Situation: torque about the X axis;

[0023] -F y Situation: Horizontal force applied along the Y-axis;

[0024] -M z Situation: Torque about the Z axis.

[0025] The constraint conditions and fitness function for the optimal design of the size of the three T-beam elastic body are:

[0026]

[0027] F=ω1f1+ω2f2

[0028] Wherein, L1 represents the length of the elastic beam, b1 represents the width of the elastic beam, h1 represents the height of the elastic beam, L2 represents the length of the flexible leaf spring, b2 represents the width of the flexible leaf spring, h2 represents the height of the flexible leaf spring, r represents the radius of the loaded cone, and i=1~n represents the six-dimensional force F in turn. x ~Mz , D i represents the maximum effective displacement caused by the force / torque, represents the average value of the maximum effective displacement caused by the six-dimensional force, ω1 and ω2 represent the weights of the proximity target and the sensitivity target, respectively.

[0029] A six-dimensional force decoupling method of a three-T-beam elastic body structure of a capacitive small six-dimensional force sensor comprises:

[0030] S1. Establish the relationship between capacitance and displacement: When the sensor is subjected to external force, the deformation of the elastic body drives the moving plate to move, and the static plate is fixed to the base, forming a capacitance change corresponding to the displacement in each direction, where the three horizontal capacitances correspond to the normal displacement d n1 ,d n2 ,d n3 , the three vertical capacitors correspond to the tangential displacement d s4 ,d s5 ,d s6 ;

[0031] S2. Solve for the vertical force F z : Using the change in horizontal capacitance, the coefficient determined by the mechanical model Calculate the vertical force F z , the formula is Considering the moment M x and M y to ensure that there is no coupling;

[0032] S3. Solve the moment M x : The coefficient determined by the mechanical model according to the change in horizontal displacement Calculate the moment M x , the formula is Considering the force F z The coupling influence of and decoupling;

[0033] S4. Solve the moment M y :Use the change in horizontal displacement to determine the coefficients through the mechanical model Calculate the moment M y , the formula is Considering the force F z and moment M x The coupling influence of and decoupling;

[0034] S5. Solve the moment M z : The coefficient determined by the mechanical model according to the change in vertical displacement Calculate the moment M z , the formula is Considering the force F xand F y The coupling influence of and decoupling;

[0035] S6. Solve for the horizontal force F y :Using the change in vertical displacement, the coefficient determined by the mechanical model Calculate the horizontal force F y , the formula is Considering the force F x The coupling influence of and decoupling;

[0036] S7. Solve for the horizontal force F x : The coefficient determined by the mechanical model according to the change in vertical displacement Calculate the horizontal force F x , the formula is Considering the force F y and moment M z The coupling influence of and decoupling;

[0037] S8. Realize decoupling: Determine the parameters in the decoupling matrix through calibration method, use the displacement change Δd calculated by the capacitance change, and realize the decoupling of six-dimensional force through the formula F / T=Calib*Δd, where F and T represent force and torque respectively, and Calib is the decoupling matrix.

[0038] The present invention has the following beneficial effects:

[0039] The present invention proposes a capacitive small six-dimensional force sensor structure and its optimization design method and six-dimensional force decoupling method. When the external six-dimensional force acts on the three T-beam elastic body, the elastic body deforms to drive the upper electrode plate to displace, thereby changing the plate spacing of the six sets of parallel plate capacitors and causing the capacitance value to change. The tiny capacitance value is collected, and the six-dimensional force is decoupled using the six-dimensional force decoupling algorithm designed by the present invention, which can realize accurate measurement of forces and moments in three orthogonal directions. The main advantages of the present invention are: ① The sensor designed by the present invention has a compact structure and a small size, and is easy to be integrated into the narrow space of the robot's dexterous finger joints; ② The sensor designed by the present invention is designed based on the capacitive measurement principle, so it has good dynamic response performance and can quickly respond to changes in external force; ③ The sensor designed by the present invention can measure ±30N external force and ±0.3Nm external torque, which can meet the use requirements of the robot's dexterous fingertips; ④ The three-T-beam elastomer structure designed by the present invention has high sensitivity and similar stiffness in all directions, which can reduce the coupling effect of six-dimensional force; ④ The capacitor arrangement structure designed by the present invention is convenient for the decoupling of six-dimensional force, and the coupling effect is small. Combined with the designed decoupling algorithm, high-precision six-dimensional force decoupling can be achieved.

[0040] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the structure explosion of an embodiment of a capacitive small six-dimensional force sensor according to an embodiment of the present invention;

[0042] Figure 2 It is a three-dimensional schematic diagram of a top cover structure of an embodiment of a capacitive small six-dimensional force sensor according to an embodiment of the present invention;

[0043] Figure 3 It is a three-dimensional schematic diagram of a three-T-beam elastic body structure of an embodiment of a capacitive small six-dimensional force sensor according to an embodiment of the present invention;

[0044] Figure 4 It is a three-dimensional schematic diagram of the upper electrode plate structure of an embodiment of a capacitive small six-dimensional force sensor according to an embodiment of the present invention;

[0045] Figure 5 1 is a schematic diagram of the structure of a lower electrode plate (circuit board) of an embodiment of a capacitive small six-dimensional force sensor according to an embodiment of the present invention;

[0046] Figure 6 It is a schematic diagram of the base structure of an embodiment of a capacitive small six-dimensional force sensor according to an embodiment of the present invention.

[0047] Figure 7 4 is a structural parameter diagram of the elastomer according to an embodiment of the present invention.

[0048] Figure 8 It is a schematic diagram of the force applied by the elastic body alone with F_z.

[0049] Fig. 9 It is a schematic diagram of the force M_x exerted on the elastic body alone.

[0050] Fig.10 It is a schematic diagram of the force F_y exerted by the elastic body alone.

[0051] Fig.11 It is a schematic diagram of the force M_z exerted on the elastic body alone.

[0052] Fig.12 This is the structural diagram of the BP neural network established to improve the mechanical model.

[0053] Fig.13 This is a diagram showing the compensation effect of the neural network on the mechanical model.

[0054] Fig.14 This is a graph showing the corresponding relationship between the capacitance and displacement of the upper electrode plate of a capacitive small six-dimensional force sensor. DETAILED DESCRIPTION

[0055] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.

[0056] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or 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 indirectly connected to the other element. In addition, connection can be used for fixing as well as for coupling or communication.

[0057] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0058] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0059] See also Figures 1 to 7The embodiment of the present invention provides a capacitive small six-dimensional force sensor, including a top cover 1, a three-T-beam elastic body 2, an upper electrode plate 3, a lower electrode plate 4 and a base 5; the three-T-beam elastic body 2 is used to convert the external six-dimensional force into displacement changes, the lower electrode plate 4 is placed on the base 5, the top cover 1 is placed on the three-T-beam elastic body 2, the upper electrode plate 3 is connected to the three-T-beam elastic body 2, and the electrodes of the upper electrode plate 3 and the lower electrode plate 4 correspond to form six groups of facing electrodes; the six groups of facing electrodes include three groups of horizontally arranged electrodes and three groups of vertically arranged electrodes, forming six groups of parallel plate capacitors Structure; the three T-beam elastomer 2 includes an elastic beam, a flexible leaf spring and a loaded truncated cone, wherein the three groups of the elastic beams and the flexible leaf springs constitute a T-shaped structure for bearing the action of force, and the loaded truncated cone located in the center is connected to the elastic beam through the flexible leaf spring for transmitting torque; the upper electrode plate 3 is connected to the three T-beam elastomer 2; wherein, when the sensor is subjected to external force, the deformation of the three T-beam elastomer 2 drives the upper electrode plate 3 to displace, thereby causing the plate spacing of the six groups of parallel flat plate capacitors to change, and then converting the six-dimensional force information into six capacitance signal outputs.

[0060] like Figure 1 , Figure 4 and Figure 5 As shown, in a preferred embodiment, the lower electrode plate 4 includes three horizontal electrodes horizontally arranged on the upper surface of the lower electrode plate 4, and three vertical electrodes vertically arranged at the side walls of the three grooves of the lower electrode plate 4, and the three horizontal electrodes and the three vertical electrodes are evenly distributed along the circumferential direction. The three horizontal electrodes and the three vertical electrodes are alternately spaced and distributed 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 extending vertically downward from the lower surface of the upper electrode plate 3, and the horizontal electrodes and vertical electrodes of the upper electrode plate 3 are arranged corresponding to the horizontal electrodes and vertical electrodes of the lower electrode plate 4.

[0061] This small capacitive six-dimensional force sensor can convert the size of the external six-dimensional force into the change in the capacitance of the six groups of electrodes in the sensor, decouple the change in the six groups of capacitance, and thus use the change in electrical signals to sense the size of the external six-dimensional force. The sensor has the advantages of small size, light weight, high sensitivity, good dynamic response, and easy processing and assembly, and is suitable for the dexterous fingertip joints of robots.

[0062] An optimization design method for a three-T-beam elastic body structure of a capacitive small six-dimensional force sensor includes:

[0063] Establishing a mechanical model of the three-T-beam elastic body;

[0064] The mechanical model is improved by using a BP neural network, and the nonlinear fitting ability of the BP neural network is used to compensate the mechanical model so as to establish a nonlinear relationship between the size parameters of the elastic body and the error of the mechanical model;

[0065] wherein, a set of compensation coefficients is generated according to the mechanical model and the results of ANSYS finite element analysis, wherein multiple sets of data are obtained through simulation, and the simulation results are compared with the calculation results of the mechanical model to obtain the compensation coefficients;

[0066] The data set consisting of the size parameters and the corresponding compensation coefficients is divided into a training set and a test set, the BP neural network is trained by the training set, and the compensation effect of the network is tested by the test set;

[0067] By using the trained BP neural network, the solution error of the mechanical model is reduced to within a preset threshold, thereby obtaining an improved mechanical model;

[0068] The improved mechanical model is used in combination with a particle swarm search algorithm to optimize the size of the three-T-beam elastic body.

[0069] Four BP neural networks with 7 inputs and 1 output are established, each network corresponding to the mechanical model compensation under four stress conditions; each BP neural network is configured to receive seven size parameters, specifically the length of the elastic beam, the width of the elastic beam, the height of the elastic beam, the length of the flexible leaf spring, the width of the flexible leaf spring, the height of the flexible leaf spring and the radius of the loaded truncated cone, as input, and output a compensation coefficient; the four stress conditions are respectively:

[0070] -F z Situation: vertical force applied along the Z axis;

[0071] -M x Situation: torque about the X axis;

[0072] -F y Situation: Horizontal force applied along the Y-axis;

[0073] -M z Situation: Torque about the Z axis.

[0074] The constraint conditions and fitness function for the optimal design of the size of the three T-beam elastic body are:

[0075]

[0076] F=ω1f1+ω2f2

[0077] Wherein, L1 represents the length of the elastic beam, b1 represents the width of the elastic beam, h1 represents the height of the elastic beam, L2 represents the length of the flexible leaf spring, b2 represents the width of the flexible leaf spring, h2 represents the height of the flexible leaf spring, r represents the radius of the loaded cone, and i=1~n represents the six-dimensional force F in turn. x ~M z , D i represents the maximum effective displacement caused by the force / torque, represents the average value of the maximum effective displacement caused by the six-dimensional force, ω1 and ω2 represent the weights of the proximity target and the sensitivity target, respectively.

[0078] The specific embodiments of the present invention are further described below.

[0079] A small capacitive six-dimensional force sensor comprises a three-T-beam elastic body 2, a lower electrode plate 4 with a specific capacitor 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 capacitor arrangement structure is placed on the base 5, and the upper electrode plate 3 is connected to the three-T-beam elastic body and forms six groups of electrodes facing each other with the lower electrode plate 4. The sensor can convert the size of the external six-dimensional force into the change in the capacitance of the six groups of electrodes in the sensor, decouple the change in the six groups of capacitance, and thus realize the use of the change in electrical signals to sense the size of the external six-dimensional force. The lower electrode plate 4 is arranged with six capacitor electrodes, and the six electrodes are evenly arranged on a circular circuit board, of which three are arranged horizontally on the upper surface of the circuit board, and three are arranged vertically on the side walls of the three grooves of the circuit board. The six electrodes are all connected to a digital capacitor chip in the middle of the circuit board, and the capacitance value is measured by the digital capacitor chip. The structure of the upper electrode plate 3 corresponds to that of the lower electrode plate 4, and the six electrodes are evenly arranged on the circular plate, of which three are arranged horizontally and three are arranged vertically.

[0080] When the sensor is subjected to external force, the deformation of the three T-beam elastic bodies 2 drives the upper electrode plate 3 to displace, thereby causing the plate spacing of the six sets of parallel plate capacitors to change, and then converting the six-dimensional force information into six capacitance signal outputs.

[0081] In a specific embodiment, the sensor structure can be assembled in the following manner. A digital capacitor chip and a signal line are welded on the lower electrode plate 4, the lower electrode plate 4 is placed on the base 5, and the signal line is led out from the lower part of the base 5; the upper electrode plate 3 is aligned with the three T-beam elastic body 2 through the groove and connected with screws; the three T-beam elastic body 2 is positioned with the lower electrode plate 4 on the base 5 with pins, and the base 5 is connected with the three T-beam elastic body 2 with screws after alignment, so that the lower electrode plate 4 is pressed tightly, and the lower electrode plate electrode and the upper electrode plate electrode form 6 groups of parallel plate capacitors facing each other, and the plate spacing is 0.2mm; the top cover 1 is aligned with the three T-beam elastic body 2 and connected with screws. The six-dimensional force sensor is assembled in this way.

[0082] Capacitance signal acquisition can be achieved through the AD7147 digital capacitance chip, which can measure ±8pF capacitance, has a resolution of 16 bits, and can measure 14 capacitance channels. A single chip can measure 6 capacitance signals simultaneously.

[0083] The sensor has the advantages of small size, light weight, high sensitivity, good dynamic response, and easy processing and assembly. It is suitable for the dexterous fingertip joints of robots.

[0084] The mechanical model of the three-T beam elastic body is improved by BP neural network. The size structure of the three-T beam elastic body is optimally designed by particle swarm search algorithm. The specific size depends on the detection requirements of the six-dimensional force sensor in each direction and the size requirements of the six-dimensional force sensor.

[0085] The structural dimensions of the three-T-beam elastomer are optimally designed by an improved mechanical model and a particle swarm search algorithm, wherein the BP neural network reduces the relative error of the mechanical model to less than 5%, and the particle swarm search algorithm calculates the optimal dimension structure to enable the elastomer to achieve high sensitivity and isotropy.

[0086] Design method of three-T-beam elastic structure size

[0087] Firstly, a mechanical model of a three-T-beam elastic body structure is established. Then, the BP neural network is used to compensate the model to obtain an improved mechanical model, the solution error of which can be controlled within 5%. Then, combined with the improved mechanical model, a particle swarm search algorithm is used to solve the optimal size structure of the elastomer with the goal of high sensitivity and similar stiffness.

[0088] Establishing the mechanical model

[0089] There are 6 structural parameters in the mechanical model of the three-T-beam elastic body structure, which are the length and width of the elastic beam l1, b1, the length and width of the flexible leaf spring l2, b2, the height h of the elastic beam and the flexible leaf spring, and the radius r of the loaded cone. In order to optimize the stiffness of the elastic body in all directions and increase the design space of the elastic body, the height of the elastic beam and the height of the flexible leaf spring are separated and recorded as h1 and h2 respectively. The structural parameters of the elastic body are as follows Figure 7 shown.

[0090] The vertical direction is recorded as the Z direction. When considering the elastic body subjected to six-dimensional force, since the elastic body structure is symmetrical, it can be verified that the force F y Displacement and force F x The displacement calculation is the same as that of x Displacement calculation and moment M y Therefore, the displacement calculation of the elastic body under the action of six-dimensional force can be simplified to two forces (F x and F z ) and two moments (M y and M z ) displacement calculation. Based on 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 results are as follows.

[0091] 1) Apply F alone z

[0092] Apply F alone z The force Figure 8 shown.

[0093] remember

[0094] l′1=l1+b2 / 2, l′2=l2-b1, k=5 / 6, S1=b1h1,S2=b2h2, (β is the cross-sectional torsion coefficient),

[0095] At this time F z and The relationship can be written as

[0096]

[0097] in E is the Young's modulus of the material, and G is the shear modulus of the material.

[0098] 2) Apply M alone x

[0099] Apply M alone x The force Fig. 9 shown.

[0100] Remember λ1=l′1 / r, λ2=l′2 / r,

[0101] At this time M x and The relationship can be written as

[0102]

[0103] in

[0104] 3) Apply F alone y

[0105] Fig.10 For applying F y Force diagram of .

[0106] remember remember

[0107]

[0108] At this time F y and The relationship can be written as

[0109]

[0110] in

[0111] 4) Apply M alone z

[0112] Fig.11 For applying M alone z Force diagram of .

[0113] remember

[0114] At this time M z and The relationship can be written as

[0115]

[0116] in According to the symmetry of the elastic structure, it is easy to get

[0117]

[0118] in

[0119] Improved mechanical model

[0120] By comparing the solution results of the above mechanical model with the solution results of Ansys finite element analysis, it can be seen that the solution error of the above mechanical model is about 5% to 20%, which is relatively large. In order to optimize the design of the elastic structure, a mechanical model with higher accuracy is required. To optimize the model, the method selected is to use artificial neural network for compensation.

[0121] BP neural network is a common artificial neural network model. It has a wide range of applicability and strong nonlinear fitting ability. It can introduce nonlinear mapping through activation function, so that the neural network can fit complex nonlinear relationships. These advantages of BP neural network make it very suitable for solving the current problem, that is, establishing the nonlinear relationship between the size parameters of the elastic body and the error of the mechanical model.

[0122] For the three-T-beam elastic body structure shown in the design, there are a total of 7 size parameters, so 4 "7-input-1-output" BP neural networks can be established, corresponding to F z 、M x 、F y 、M z Mechanical model compensation in four cases. When establishing a BP neural network, it is necessary to select the appropriate number of hidden layers and nodes. Since the designed neural network has fewer input parameters, one hidden layer can meet the use requirements. Usually, the number of nodes is twice the number of input parameters. To avoid overfitting, the number of nodes is set to 10. The structure of the established BP neural network is as follows: Fig.12 shown.

[0123] 200 sets of data were generated through ANSYS simulation, and the simulation results were compared with the results calculated by the existing mechanical model to obtain 200 sets of compensation coefficients. The 200 sets of dimensional parameters and the corresponding 200 sets of compensation coefficients were combined into a data set, in which the dimensional parameters were input and the compensation coefficients were output. 150 sets were randomly selected as training sets, and the remaining 50 sets were used as test sets. After the training with the training set was completed, the test set was input into the neural network to test the compensation effect of the neural network on the mechanical model. The results are shown in Figure 2. Fig.13 As shown in the figure. The blue curve in the figure is the solution error of the mechanical model before the test set parameters are added with neural network compensation, and the red curve is the solution error of the mechanical model after adding neural network compensation. It can be seen that the solution error has decreased significantly, with F z For example, the error of solving the mechanical model was reduced from about 20% to less than 5%. Similarly, the error of other cases was also controlled within 5%. Therefore, the neural network can show excellent performance on the test set, indicating that the model has the ability to generalize on new data.

[0124] Optimal design of elastic body size and structure

[0125] Based on the elastic body mechanical model optimized in the above text, the optimization design of the elastic body structure size can be carried out in combination with the optimization algorithm. Common optimization algorithms include gradient descent method, genetic algorithm, simulated annealing algorithm, particle swarm search algorithm, etc. Among them, the particle swarm search algorithm is suitable for complex problems in multiple dimensions, is easy to implement, and is suitable for the optimization design of the elastic body structure in the present invention.

[0126] The fitness function is the key to the optimization process, and the design of the function needs to reflect the optimization goal. In addition, the position and speed of the particles also need to meet certain constraints. In this study, the constraints and optimization goals for the optimization design of the elastomer are set as the following four points:

[0127] Dimensional constraints: There are strict range requirements for each dimensional parameter in the elastomer structure;

[0128] Deformation constraints: The shape of the elastic body cannot be too large or too small;

[0129] Proximity goal: When an elastic body is subjected to forces / torques of equal magnitude in different directions, the deformation caused is similar;

[0130] Sensitivity target: The deformation is as large as possible within the constraints.

[0131] Based on the above four points, the constraints and fitness function of the optimization design are given as follows:

[0132]

[0133] F=ω1f1+ω2f2#(4-8)

[0134] Wherein, L1 represents the length of the elastic beam, b1 represents the width of the elastic beam, h1 represents the height of the elastic beam, L2 represents the length of the flexible leaf spring, b2 represents the width of the flexible leaf spring, h2 represents the height of the flexible leaf spring, r represents the radius of the loaded cone, and i=1~n represents the six-dimensional force F in turn. x ~M z , D i represents the maximum effective displacement caused by the force / torque, represents the average value of the maximum effective displacement caused by the six-dimensional force, ω1 and ω2 represent the weights of the proximity target and the sensitivity target, respectively.

[0135] Six-dimensional force decoupling method

[0136] The small capacitive six-dimensional force sensor is designed with a corresponding six-dimensional force decoupling algorithm according to its specific capacitor arrangement, and the relative error of the decoupling is within 0.5%.

[0137] When the designed six-dimensional force sensor is subjected to external force, the elastic body is deformed, and the moving electrode plate fixed to the elastic body also moves accordingly, while the static electrode plate is fixed on the base. Therefore, the displacement of the upper electrode plate will cause the change of the distance between the electrodes, and then cause the change of capacitance. When decoupling, follow the following sequence:

[0138] C→d→F / T

[0139] In such Fig.14 Under the designed structure, each capacitor corresponds to the displacement of each location on the upper electrode plate, where the horizontal capacitors C1, C2, and C3 correspond to the normal displacement d at each location. n1 , d n2 , d n3 , the vertical capacitors C4, C5, and C6 correspond to the tangential displacement d at each location s4 , d s5 , d s6 Therefore, the step of solving the displacement change from the capacitance change does not involve coupling problems, and only the coupling problem between the displacement change and the six-dimensional force needs to be considered.

[0140] 1) Solve for F z

[0141] From the mechanical model, we know that:

[0142]

[0143] Furthermore,

[0144]

[0145] Consider the moment M x Coupling problems caused: When F is applied z When M is applied at the same time x , by M x The Δd caused n1 , Δd n2 , Δd n3 The following relations are satisfied:

[0146] Δd n1 =-2Δd n2 =-2Δd n3

[0147] Therefore, the calculation result of formula (4-7) will not change, that is, there is no coupling.

[0148] Consider the moment M y Coupling problems caused: When F is applied z When M is applied at the same time y , by M y The Δd caused n1 , Δdn2 , Δd n3 The following relations are satisfied:

[0149] Δd n1 =0

[0150] Δd n2 =-Δd n3

[0151] Therefore, the calculation result of formula (4-7) will not change, that is, there is no coupling.

[0152] In addition, F x 、F y 、M z Will not cause Δd n1 , Δd n2 , Δd n3 changes, so there is no coupling. Formula (4-7) is F z Decoupled type.

[0153] 2) Solve for M x

[0154] From the mechanical model, we know that:

[0155]

[0156] Furthermore,

[0157]

[0158] Consider the moment M y Coupling problem caused: When M is applied x When M is applied at the same time y , by M y Δd caused n1 , Δd n2 , Δd n3 Satisfies the following relationship

[0159] Δd n1 =0

[0160] Δd n2 =-Δd n3

[0161] Therefore, the calculation result of formula (4-8) will not change, that is, there is no coupling.

[0162] Consideration F z Coupling problem caused: When M is applied x When F is applied at the same time z , by F z Δd caused n1 , Δd n2, Δd n3 Satisfies the following relationship

[0163] Δd n1 =Δd n2 =Δd n3

[0164] This will change the calculation result of formula (4-8), and decoupling is required. The method is to first calculate F from formula (4-7) z , then F z The displacement change caused by is calculated and substituted into formula (4-8) to eliminate it in advance. The specific process is as follows:

[0165]

[0166] In addition, F x 、F y 、M z Will not cause Δd n1 , Δd n2 , Δd n3 changes, so there is no coupling. Formula (4-9) is M x Decoupled type.

[0167] 3) Solve for M y

[0168] From the mechanical model, we know that:

[0169]

[0170] Furthermore,

[0171]

[0172] Consideration F z Coupling problem caused: When M is applied y When F is applied at the same time z , by F z The Δd caused n1 , Δd n2 , Δd n3 Satisfies the following relationship

[0173] Δd n1 =Δd n2 =Δd n3

[0174] Therefore, the calculation result of formula (4-10) will not change, that is, there is no coupling.

[0175] Consider the moment M x Coupling problem caused: When M is applied y When M is applied at the same time x , by Mx The Δd caused n1 , Δd n2 , Δd n3 Satisfies the following relationship

[0176] Δd n1 =-2Δd n2 =-2Δd n3

[0177] Therefore, the calculation result of formula (4-10) will not change, that is, there is no coupling.

[0178] In addition, F x 、F y 、M z Will not cause Δd n1 , Δd n2 , Δd n3 changes, so there is no coupling problem. Formula (4-10) is M y Decoupled type.

[0179] 4)M z Solution

[0180] From the mechanical model, we know that:

[0181]

[0182] Furthermore,

[0183]

[0184] Consideration F x Coupling problem caused: When M is applied z When F is applied at the same time x , by F x The Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0185] Δd s6 =-2Δd s4 =-2Δd s5

[0186] Therefore, the calculation result of formula (4-11) will not change, that is, there is no coupling.

[0187] Consideration F y Coupling problem caused: When M is applied z When F is applied at the same time y , by F y The Δd caused s4 , Δd s5 , Δds6 Satisfies the following relationship

[0188] Δd s4 =-Δd s5

[0189] Δd s6 =0

[0190] Therefore, the calculation result of formula (4-11) will not change, that is, there is no coupling.

[0191] Consider the moment M x Coupling problem caused: When M is applied z When M is applied at the same time x , by M x Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0192] Δd s4 =-Δd s5

[0193] Δd s6 =0

[0194] Therefore, the calculation result of formula (4-11) will not change, that is, there is no coupling.

[0195] Consider the moment M y Coupling problem caused: When M is applied z When M is applied at the same time y , by M y Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0196] Δd s6 =-2Δd s4 =-2Δd s5

[0197] Therefore, the calculation result of formula (4-11) will not change, that is, there is no coupling.

[0198] In addition, F z Will not cause Δd s4 , Δd s5 , Δd s6 , so there is no coupling. Equation (4-11) is M z Decoupled type.

[0199] 5) F y Solution

[0200] From the mechanical model, we know that:

[0201]

[0202] Furthermore,

[0203]

[0204] Consideration F x Coupling problems caused: When F is applied y When F is applied at the same time x , by F x The Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0205] Δd s6 =-2Δd s4 =-2Δd s5

[0206] Therefore, the calculation result of formula (4-12) will not change, that is, there is no coupling.

[0207] Consider the moment M z Coupling problems caused: When F is applied y When M is applied at the same time z , by M z The Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0208] Δd s6 =Δd s4 =Δd s5

[0209] Therefore, the calculation result of formula (4-12) will not change, that is, there is no coupling.

[0210] Consider the moment M y Coupling problems caused: When F is applied y When M is applied at the same time y , by M y The Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0211] Δd s6 =-2Δd s4 =-2Δd s5

[0212] Therefore, the calculation result of formula (4-12) will not change, that is, there is no coupling.

[0213] Consider the moment M x Coupling problems caused: When F is applied y When M is applied at the same time x , by M x The Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0214] Δd s4 =-Δd s5

[0215] Δd s6 =0

[0216] This will change the calculation result of formula (4-12), and decoupling is required. Let the distance between the center of mass of the static plate and the moving plate be D, then apply M x The following relationship holds

[0217]

[0218] remember Then there is

[0219]

[0220] When decoupling, first calculate M by formula (4-9) x , and then M x The displacement change caused by is calculated and substituted into formula (4-12) to eliminate it in advance. The specific process is as follows:

[0221]

[0222] In addition, F z Will not cause Δd s4 , Δd s5 , Δd s6 , so there is no coupling. Formula (4-15) is F y Decoupled type.

[0223] 6) F x Solution

[0224] From the mechanical model, we know that:

[0225]

[0226] Furthermore,

[0227]

[0228] Consideration F y Coupling problems caused: When F is appliedx When F is applied at the same time y , by F y Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0229] Δd s4 =-Δd s5

[0230] Δd s6 =0

[0231] Therefore, the calculation result of formula (4-16) will not change, that is, there is no coupling.

[0232] Consider the moment M z Coupling problems caused: When F is applied x When M is applied at the same time z , by M z Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0233] Δd s6 =Δd s4 =Δd s5

[0234] This will change the calculation result of formula (4-16), and decoupling is required. The method is to first calculate M from formula (4-11): z , then M z The displacement change caused by is calculated and substituted into formula (4-16) to eliminate it in advance. The specific process is as follows:

[0235]

[0236] Consider the moment M x Coupling problems caused: When F is applied x When M is applied at the same time x , by M x Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0237] Δd s4 =-Δd s5

[0238] Δd s6 =0

[0239] Therefore, the calculation result of formula (4-17) will not change, that is, there is no coupling.

[0240] Consider the moment M y Coupling problems caused: When F is applied y When M is applied at the same time y , by M y The Δd caused s4 , Δd s5 , Δd s6 Satisfies the following relationship

[0241] Δd s6 =-2Δd s4 =-2Δd s5

[0242] This will also change the calculation result of formula (4-17), and decoupling is required. y The following relationship holds

[0243]

[0244] remember Then there is

[0245]

[0246] When decoupling, first calculate M by formula (4-10) x and M y , and then M y The displacement change caused by is calculated and substituted into formula (4-17) to eliminate it in advance. The specific process is as follows:

[0247]

[0248] In addition, F z Will not cause Δd s4 , Δd s5 , Δd s6 , so there is no coupling. Formula (4-21) is F y Decoupled type.

[0249] Based on the above, the decoupling algorithm of the six-dimensional force is summarized as follows:

[0250]

[0251] It can also be expressed as follows

[0252] F / T=Calib*Δd#(4-22)

[0253] In actual use, the parameters in the decoupling matrix can be obtained by calibration. Δd can be calculated from the capacitance change, and the decoupling of the six-dimensional force can be achieved by using formula (4-22).

[0254] Example

[0255] like Figures 1 to 6 As shown, the sensor includes a top cover 1, a three-T-beam elastic body 2, an upper electrode plate 3, a lower electrode plate 4, and a base 5. The top cover 1 and the three-T-beam elastic body 2 are fixed by screws, the three-T-beam elastic body 2 and the upper electrode plate 3 are positioned by a positioning block and fixed by screws, the three-T-beam elastic body 2 and the lower electrode plate 4 are positioned by pins, the lower electrode plate 4 and the base 5 are positioned by grooves, and the three-T-beam elastic body 2 and the base 5 are fixed by screws.

[0256] like Figures 1 to 6 As shown, SUS304 stainless steel is selected as the processing material of the top cover 1, the upper electrode plate 3, and the base 5, and is processed by mechanical processing. A212 aluminum alloy is selected as the processing material of the three-T beam elastic body, and is processed by mechanical processing. FR-4 sheet is selected as the processing sheet of the lower electrode plate 4 to make the PCB.

[0257] like Figure 1 As shown, the overall diameter of the top cover 1 is 15 mm and the thickness is 1 mm;

[0258] like Figure 2 As shown, the overall diameter of the three-T-beam elastic body 2 is 15 mm and the thickness is 4 mm;

[0259] like Figure 4 As shown, the overall diameter of the lower electrode plate 4 is 13.8 mm and the thickness is 2 mm. The horizontally arranged capacitor electrodes in the lower electrode plate are processed by a window opening process, and the vertically arranged capacitor electrodes are processed by pasting 50 nm copper stickers on the side walls.

[0260] like Figure 5 As shown, the overall diameter of the base 5 is 15 mm and the thickness is 5 mm.

[0261] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of the reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A capacitive small six-dimensional force sensor, characterized in that: It includes three T-beam elastic bodies, a lower electrode plate, an upper electrode plate and a base; the three T-beam elastic bodies are used to convert external six-dimensional forces into displacement changes, the lower electrode plate is placed on the base, the upper electrode plate is connected to the three T-beam elastic bodies, and the electrodes of the upper electrode plate and the lower electrode plate correspond to form six groups of facing electrodes; the six groups of facing electrodes include three groups of horizontally arranged electrodes and three groups of vertically arranged electrodes, forming six groups of parallel flat plate capacitor structures; the three T-beam elastic bodies include elastic beams, flexible leaf springs and loaded truncated tables, wherein the three groups of elastic beams and the flexible leaf springs form a T-shaped structure for bearing the action of force, and the loaded truncated table located in the center is connected to the elastic beams through the flexible leaf springs for transmitting torque; the upper electrode plate is connected to the three T-beam elastic bodies; wherein, when the sensor is subjected to external force, the deformation of the three T-beam elastic bodies drives the upper electrode plate to produce displacement, thereby causing the plate spacing of the six groups of parallel flat plate capacitors to change, and then converting the information of the six-dimensional force into six capacitor signal outputs.

2. The capacitive small six-dimensional force sensor according to claim 1, characterized in that: 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 three grooves of the lower electrode plate. The three horizontal electrodes and the three vertical electrodes are evenly distributed along the circumferential direction.

3. The capacitive small six-dimensional force sensor as claimed in claim 2, characterized in that: The three horizontal electrodes and the three vertical electrodes are alternately spaced and distributed along the circumferential direction.

4. The capacitive small six-dimensional force sensor according to claim 2 or 3, characterized in that: The upper electrode plate includes three horizontal electrodes arranged horizontally on the lower surface of the upper electrode plate, and three vertical electrodes extending vertically downward from the lower surface of the upper electrode plate. The horizontal electrodes and vertical electrodes of the upper electrode plate are arranged corresponding to the horizontal electrodes and vertical electrodes of the lower electrode plate.

5. The capacitive small six-axis force sensor according to any one of claims 1 to 4, characterized in that: The lower electrode plate is constructed based on a circuit board, a digital capacitor chip is arranged on the circuit board, and the six groups of facing electrodes are all connected to the digital capacitor chip.

6. The capacitive small six-dimensional force sensor according to any one of claims 1 to 5, characterized in that: Also included is a top cover placed on the three-T-beam elastic body.

7. An optimization design method for a three-T-beam elastic body structure of a capacitive small six-axis force sensor according to any one of claims 1 to 6, characterized in that: include: Establishing a mechanical model of the three-T-beam elastic body; The mechanical model is improved by using a BP neural network, and the nonlinear fitting ability of the BP neural network is used to compensate the mechanical model so as to establish a nonlinear relationship between the size parameters of the elastic body and the error of the mechanical model; wherein, a set of compensation coefficients is generated according to the mechanical model and the results of ANSYS finite element analysis, wherein multiple sets of data are obtained through simulation, and the simulation results are compared with the calculation results of the mechanical model to obtain the compensation coefficients; The data set consisting of the size parameters and the corresponding compensation coefficients is divided into a training set and a test set, the BP neural network is trained by the training set, and the compensation effect of the network is tested by the test set; By using the trained BP neural network, the solution error of the mechanical model is reduced to within a preset threshold, thereby obtaining an improved mechanical model; The improved mechanical model is used in combination with a particle swarm search algorithm to optimize the size of the three-T-beam elastic body.

8. The optimization design method of the three-T-beam elastic body structure of the capacitive small six-dimensional force sensor as claimed in claim 7, characterized in that: Four BP neural networks with 7 inputs and 1 output are established, each network corresponding to the mechanical model compensation under four stress conditions; each BP neural network is configured to receive seven size parameters, specifically the length of the elastic beam, the width of the elastic beam, the height of the elastic beam, the length of the flexible leaf spring, the width of the flexible leaf spring, the height of the flexible leaf spring and the radius of the loaded truncated cone, as input, and output a compensation coefficient; the four stress conditions are respectively: -F z Situation: vertical force applied along the Z axis; -M x Situation: torque about the X axis; -F y Situation: Horizontal force applied along the Y-axis; -M z Situation: Torque about the Z axis.

9. The optimization design method of the three-T-beam elastic body structure of the capacitive small six-dimensional force sensor according to claim 7, characterized in that: The constraint conditions and fitness function for the optimal design of the size of the three T-beam elastic body are: F=ω1f1+ω2f2 Wherein, L1 represents the length of the elastic beam, b1 represents the width of the elastic beam, h1 represents the height of the elastic beam, L2 represents the length of the flexible leaf spring, b2 represents the width of the flexible leaf spring, h2 represents the height of the flexible leaf spring, r represents the radius of the loaded cone, and i=1~n represents the six-dimensional force F in turn. x ~M z , D i represents the maximum effective displacement caused by the force / torque, represents the average value of the maximum effective displacement caused by the six-dimensional force, ω1 and ω2 represent the weights of the proximity target and the sensitivity target, respectively.

10. A six-dimensional force decoupling method for a three-T-beam elastic body structure of a capacitive small six-dimensional force sensor according to any one of claims 1 to 6, characterized in that: include: S1. Establish the relationship between capacitance and displacement: When the sensor is subjected to external force, the deformation of the elastic body drives the moving plate to move, and the static plate is fixed to the base, forming a capacitance change corresponding to the displacement in each direction, where the three horizontal capacitances correspond to the normal displacement d n1 ,d n2 ,d n3 , the three vertical capacitors correspond to the tangential displacement d s4 ,d s5 ,d s6 ; S2. Solve for the vertical force F z : Using the change in horizontal capacitance, the coefficient determined by the mechanical model Calculate the vertical force F z , the formula is Considering the moment M x and M y to ensure that there is no coupling; S3. Solve the moment M x : The coefficient determined by the mechanical model according to the change in horizontal displacement Calculate the moment M x , the formula is Considering the force F z The coupling influence of and decoupling; S4. Solve the moment M y :Use the change in horizontal displacement to determine the coefficients through the mechanical model Calculate the moment M y , the formula is Considering the force F z and moment M x The coupling influence of and decoupling; S5. Solve the moment M z : The coefficient determined by the mechanical model according to the change in vertical displacement Calculate the moment M z , the formula is Considering the force F x and F y The coupling influence of and decoupling; S6. Solve for the horizontal force F y :Using the change in vertical displacement, the coefficient determined by the mechanical model Calculate the horizontal force F y , the formula is Considering the force F x The coupling influence of and decoupling; S7. Solve for the horizontal force F x : The coefficient determined by the mechanical model according to the change in vertical displacement Calculate the horizontal force F x , the formula is Considering the force F y and moment M z The coupling influence of and decoupling; S8. Realize decoupling: Determine the parameters in the decoupling matrix through calibration method, use the displacement change Δd calculated by the capacitance change, and realize the decoupling of six-dimensional force through the formula F / T=Calib*Δd, where F and T represent force and torque respectively, and Calib is the decoupling matrix.

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