A fingertip three-dimensional force measuring device based on piezoelectric sensor

Abstract

The application discloses a fingertip three-dimensional force measuring device based on a piezoelectric sensor and particularly relates to the field of sensors. The fingertip three-dimensional force measuring device comprises a force receiving block, a convex block fixed on the top of the force receiving block, a piezoelectric layer arranged on the bottom of the force receiving block, a plurality of electrodes arranged on the piezoelectric layer at intervals, a measuring circuit connected to each electrode, a protective layer covering the surface of the force receiving block, and a through hole formed on the protective layer and matched with the convex block, wherein the convex block is arranged in the through hole. The size of the force in each direction can be determined according to the output signal of the force in a single direction obtained by the measuring device, and the size and direction of the three-dimensional force in space can be recognized through the Pythagorean theorem and trigonometric function relationship, so that the measuring speed and the measuring accuracy are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sensors, in particular to a fingertip three-dimensional force measuring device based on a piezoelectric sensor. BACKGROUND

[0002] With the rapid development of bionic robots and the continuous progress of artificial intelligence, mechanical arms and intelligent robots have gradually integrated into our lives and can replace people to complete some tedious work. As the medium for mechanical arms to directly contact with the outside world, three-dimensional force sensors are crucial for improving the operation stability and reliability of mechanical arms, and play a similar role to human skin. Robots can construct the approximate shape of an object by sensing the pressure and the relative position between sensors, and can also obtain the direction of force through a three-dimensional force detection system to determine whether sliding occurs during contact. Three-dimensional force perception systems are also increasingly widely used in the field of biomedical treatment. Intelligent prostheses can improve the dexterity of prosthesis operation through the feedback information of three-dimensional force sensors, and can also rely on three-dimensional force detection systems for sliding displacement perception to better help the disabled to restore normal mobility. In summary, three-dimensional force sensors have potential application value in the fields of intelligent robots, biomedical treatment, etc.

[0003] The overall structure of a three-dimensional force sensor is generally designed based on the relevant principles of structural mechanics. By analyzing the signals generated by each array element under external force, the size and direction of the external force are obtained. Three-dimensional force sensors are mainly divided into five categories: electromagnetic, capacitive, resistive, optical, and piezoelectric. Compared with other types of sensors, piezoelectric three-dimensional force sensors are more sensitive to dynamic force perception, have a wider working frequency, and have lower power consumption. These characteristics make them more suitable for application scenarios such as bionic robots and wearable devices, so in recent years piezoelectric three-dimensional force sensors have become one of the research hotspots in the academic community. Existing fingertip three-dimensional force measuring devices are easily disturbed by forces from other action points and cannot accurately reflect the stress situation in the measurement area, resulting in poor measurement accuracy. For the data measured by the sensor, multi-dimensional force coupling is required. Currently, domestic and foreign scholars achieve multi-dimensional force coupling through linear decoupling and nonlinear decoupling. Linear decoupling algorithm mainly solves the matrix generalized inverse through the least squares principle, but this method has low decoupling efficiency and poor ability to eliminate nonlinear coupling, which further leads to inaccurate measurement results; nonlinear decoupling algorithm mainly constructs a nonlinear neural network through neural network, particle swarm optimization, etc. to achieve the purpose of eliminating nonlinear coupling, but the method based on neural network requires a large amount of labeled data and often needs to be recalibrated for different scenarios, resulting in low measurement speed. SUMMARY

[0004] The main purpose of the present application is to provide a fingertip three-dimensional force measuring device based on a piezoelectric sensor, aiming at solving the problem of poor measurement accuracy in the prior art.

[0005] To achieve the above-mentioned purpose, the present application provides a fingertip three-dimensional force measuring device based on a piezoelectric sensor, comprising: a force block, a convex block is fixed on the top; a piezoelectric layer is located at the bottom of the force block, a plurality of electrodes are arranged on the piezoelectric layer in intervals, and each electrode is connected with a measuring circuit; a protective layer is covered on the surface of the force block, and a through hole matched with the convex block is formed on the protective layer, and the convex block is located in the through hole.

[0006] Optionally, the number of electrodes is five, which are respectively a first electrode, a second electrode, a third electrode, a fourth electrode and a fifth electrode; the first electrode is located at the center position of the piezoelectric layer, and the first electrode is taken as the coordinate origin, the second electrode and the third electrode are located on the X axis and symmetric about the Y axis, and the fourth electrode and the fifth electrode are located on the Y axis and symmetric about the X axis.

[0007] Optionally, the shapes and areas of the first electrode, the second electrode, the third electrode, the fourth electrode and the fifth electrode are the same.

[0008] Optionally, the shape of the force block is hemispherical, and the shape of the piezoelectric layer is circular.

[0009] Optionally, it further comprises a supporting base located at the bottom of the piezoelectric layer and movably connected with the protective layer.

[0010] To achieve the above-mentioned purpose, the present application further provides a fingertip three-dimensional force measuring method based on a piezoelectric sensor, which adopts the above-mentioned measuring device, comprising: acquiring the output signals of the measuring circuits of the second electrode and the third electrode respectively, and differentially processing the two output signals as the X direction output signal; acquiring the output signals of the measuring circuits of the fourth electrode and the fifth electrode respectively, and differentially processing the two output signals as the Y direction output signal; acquiring the output signal of the measuring circuit of the first electrode as the Z direction output signal; respectively determining the X, Y and Z direction components according to the X, Y and Z direction output signals; and determining the size and direction of the measured three-dimensional force according to the X, Y and Z direction components and a second preset relationship.

[0011] Optionally, the determination method of the X direction component is: determined according to the X direction output signal, the sensitivity of the X direction component and a first preset relationship; the determination methods of the Y and Z direction components are the same as that of the X direction component; and the size of the measured three-dimensional force is determined according to the X, Y and Z direction components and a second preset relationship.

[0012] Optionally, the first preset relationship is:

[0013]

[0014] In the formula, V x is the output signal in the X direction, S x is the sensitivity, F x is the component force in the X direction.

[0015] Optionally, the second preset relationship is:

[0016]

[0017] In the formula, F y is the component force in the Y direction, F z is the component force in the Z direction.

[0018] Optionally, the direction of the three-dimensional force to be measured is determined according to the component forces in the X, Y and Z directions, the size of the three-dimensional force to be measured, and a third preset relationship.

[0019] Optionally, the third preset relationship is:

[0020]

[0021]

[0022] In the formula, θ is the included angle between the three-dimensional force to be measured and the positive direction of the Z axis, is the included angle between the projection of the three-dimensional force to be measured in the XOY plane and the positive direction of the X axis.

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] The fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the application can improve the sensitivity by processing the piezoelectric layer in sections, reacting the change of the force amplitude according to the change of the potential output of each section, and realizing the output signal of the single-direction force after differential processing; the piezoelectric layer output potential change is caused by the force acting on the convex block, which is shielded by the protective layer for the force not acting on the fingertip, so that the piezoelectric layer output potential change is caused by the force acting on the convex block, which is beneficial to improve the measurement accuracy; the fingertip three-dimensional force measuring method based on a piezoelectric sensor according to the application can determine the size of each directional component force for the output signal of the single-direction force obtained by the above measuring device, and can realize the identification of the size and direction of the space three-dimensional force through the Pythagorean theorem and the trigonometric function relationship, without using complex linear decoupling and nonlinear decoupling algorithms, thereby improving the measurement speed. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 FIG. 1 is a structural schematic diagram of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the application;

[0026] Figure 2 FIG. 1 is a structural schematic diagram of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the application;

[0027] Figure 3 A piezoelectric layer structure diagram of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the present application;

[0028] Figure 4 An analysis diagram of a fingertip three-dimensional force measuring method based on a piezoelectric sensor according to the present application;

[0029] Figure 5 A diagram of output signal and load relationship of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the present application when subjected to X-direction load alone;

[0030] Figure 6 A diagram of output signal and load relationship of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the present application when subjected to Y-direction load alone;

[0031] Figure 7 A diagram of output signal and load relationship of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the present application when subjected to Z-direction load alone;

[0032] Figure 8 A diagram of output signal and load relationship of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the present application when subjected to XY-direction load combined action;

[0033] Figure 9 A diagram of output signal and load relationship of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the present application when subjected to XZ-direction load combined action;

[0034] Figure 10 A diagram of output signal and load relationship of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the present application when subjected to YZ-direction load combined action;

[0035] Figure 11 A diagram of output signal and load relationship of a fingertip three-dimensional force measuring device based on a piezoelectric sensor according to the present application when subjected to non-fingertip force.

[0036] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present application more clear, the technical solutions of the present application will be described clearly and completely below with reference to the drawings in the present application. Obviously, the described embodiments are some embodiments of the present application, but not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0038] The first embodiment of the present application provides a fingertip three-dimensional force measuring device based on a piezoelectric sensor, as shown in the drawings, comprising a force receiving block 10, a piezoelectric layer 20, and a protective layer 30, wherein the top of the force receiving block 10 is fixed with a protrusion 40; the piezoelectric layer 20 is located at the bottom of the force receiving block 10, and a plurality of electrodes 50 are arranged on the piezoelectric layer 20 in intervals, and each electrode 50 is connected with a measuring circuit through a wire; the protective layer 30 covers the surface of the force receiving block 10, and a through hole is formed on the protective layer 30 and matched with the protrusion 40, and the protrusion 40 is located in the through hole. Figure 1

[0039] For example, the materials of the force receiving block 10 and the protrusion 40 are PDMS, the material of the piezoelectric layer 20 is PVDF, and the material of the protective layer 30 is alloy steel. The electrode 50 can be a planar electrode 50, and the material of the electrode 50 can be silver, gold, copper or other metal materials.

[0040] As can be understood, when the external force F acts on the protrusion 40, the external force can be decomposed into a tangential component parallel to the XOY plane and a normal component perpendicular to the XOY plane. When the normal force acts on the protrusion 40, the piezoelectric layer 20 is subjected to pressure or tension, and the closer to the bottom center, the greater the force. When the tangential force acts on the protrusion 40, one part of the piezoelectric layer 20 is subjected to upward tension, and the other part is subjected to downward pressure, and the areas of the tension and pressure are basically the same.

[0041] Based on the above analysis, when the external force F acts on the protrusion 40 (fingertip), an overturning moment will be generated on the force receiving block 10. Therefore, the present application utilizes the overturning moment to realize the measurement of the three-dimensional force in space. When the external force acts on other parts of the force receiving block 10 except the protrusion 40, a moment will also be generated on the bottom of the force receiving block 10, which will affect the output signal of the piezoelectric layer 20, so that the change of the output potential of the piezoelectric layer 20 is not caused by the force acting on the fingertip. Therefore, the present application shields the external force on the areas of the force receiving block 10 except the protrusion 40 through the protective layer 30, so as to ensure that the change of the output potential of the piezoelectric layer 20 is caused by the force acting on the fingertip, and improve the accuracy of the measurement.

[0042] In the present embodiment, the electrodes 50 are formed by silver plating on the upper and lower surfaces of the piezoelectric layer 20, and each electrode 50 is packaged with a plastic film. The change of the output potential of the two electrodes 50 reflects the change of the force amplitude, and the output signal sensitive to a single direction is realized after differential processing. The protrusion 40 is arranged on the top of the force receiving block 10 to sense the external force. When the external force acts on the protrusion 40, the external force is transmitted to the piezoelectric layer 20 through the force receiving block 10, and the change of the output signal of the electrode 50 is used to measure the external force, so as to realize the recognition of the size and direction of the fingertip three-dimensional force.

[0043] ​Exemplarily, the shape of the force-bearing block 10 is hemispherical, and the shape of the piezoelectric layer 20 is circular, which is completely compatible with the shape of the force-bearing block 10 . The piezoelectric layer 20 is fixed to the bottom surface of the force-bearing block 10 by insulating glue.

[0044] Furthermore, the device includes a support base 60, located at the bottom of the piezoelectric layer 20 and movably connected to the protective layer 30. Specifically, the support base 60 is connected to the protective layer 30 via threads and secured to the piezoelectric layer 20 via insulating adhesive. The support base 60 is provided with a plurality of fan-shaped holes for extending wires for connection to the measurement circuit.

[0045] In an exemplary embodiment, the number of electrodes 50 is five, namely the first electrode (i.e., region 5), the second electrode (i.e., region 1), the third electrode (i.e., region 2), the fourth electrode (i.e., region 3), and the fifth electrode (i.e., region 4); Figure 2 As shown, the first electrode is located at the center of the piezoelectric layer 20, with the first electrode as the coordinate origin O. The second and third electrodes are located on the X-axis and are symmetrical about the Y-axis. The fourth and fifth electrodes are located on the Y-axis and are symmetrical about the X-axis. The first, second, third, fourth, and fifth electrodes have the same shape and area.

[0046] Specifically, the first electrode is symmetrical about the center of the coordinate origin. When the tangential force acts on the bump 40, part of the piezoelectric layer 20 is subjected to an upward tensile force, and the other part is subjected to a downward pressure. It can be approximately considered that the tensile force and the pressure are equal in magnitude, the generated charges cancel each other out, and there is no output signal; when the normal force acts on the force-bearing block 10, the piezoelectric layer 20 in area 5 is subjected to tension or compression, and there is an obvious output signal; therefore, the output signal of the piezoelectric layer 20 in area 5 is not sensitive to forces in the X and Y directions, but is only sensitive to forces in the Z direction. Regions 1 and 2 are centered on the X-axis and symmetrical about the Y-axis. When the tangential force component is in the X-direction, one is subjected to tension and the other to compression. Differential processing amplifies the output signal. When the tangential force component is in the Y-direction, the areas of the piezoelectric layers 20 in regions 1 and 2 that are subjected to tension and compression are equal, and the tension and compression forces are nearly equal in magnitude. The generated charges cancel each other out, resulting in no output signal. When the normal force is applied, the piezoelectric layers 20 in regions 1 and 2 are both subjected to tension or compression. Furthermore, the piezoelectric layers 20 in regions 1 and 2 have equal areas and are at the same distance from the coordinate origin O. Therefore, they can be assumed to be subjected to the same force. Due to the identical charges generated by the piezoelectric effect, no output signal is generated after differential processing. Therefore, the output signals of the piezoelectric layers 20 in regions 1 and 2 are sensitive to forces in the X-direction but insensitive to forces in the Y and Z-directions. The output signal principle of regions 3 and 4 is essentially the same as that of regions 1 and 2, except that the output signals of the piezoelectric layers 20 in regions 3 and 4 are sensitive to forces in the Y-direction but insensitive to forces in the X and Z-directions. Based on the above analysis, the X-direction output signal only reflects the X-direction force component, the Y-direction output signal only reflects the Y-direction force component, and the Z-direction output signal only reflects the Z-direction force component.

[0047] Therefore, by the piezoelectric sensor-based fingertip three-dimensional force measuring device of the present application, the external force acting on the bump 40 (fingertip) can be measured.

[0048] The second embodiment of the present application provides a piezoelectric sensor-based fingertip three-dimensional force measuring method, by calculating the signals output by the measuring device, the size and direction of the three-dimensional force can be obtained; specifically including the following steps:

[0049] Step S1, respectively acquire the output signals of the measuring circuits of the second electrode and the third electrode, and differentially process the two output signals as the X-direction output signal; respectively acquire the output signals of the measuring circuits of the fourth electrode and the fifth electrode, and differentially process the two output signals as the Y-direction output signal; acquire the output signal of the measuring circuit of the first electrode as the Z-direction output signal; respectively determine the X, Y, Z direction components according to the X, Y, Z direction output signals;

[0050] Specifically, the X-direction component is determined according to the X-direction output signal, the sensitivity of the X-direction component, and a first preset relationship, and the first preset relationship is:

[0051]

[0052] In the formula, V x is the X-direction output signal, S x is the sensitivity, and F x is the X-direction component.

[0053] Similarly, the Y-direction component is:

[0054]

[0055] In the formula, V y is the Y-direction output signal, S y is the sensitivity, and F y is the Y-direction component.

[0056] Similarly, the Z-direction component is:

[0057]

[0058] In the formula, V z is the Z-direction output signal, S z is the sensitivity, and F y is the Z-direction component.

[0059] Step S2, determine the size of the three-dimensional force to be measured according to the X, Y, Z direction components and a second preset relationship, and the second preset relationship is:

[0060]

[0061] In the formula, F y is the component force in the Y direction, F z is the component force in the Z direction.

[0062] In step S3, the direction of the three-dimensional force to be measured is determined according to the component forces in the X, Y and Z directions, the size of the three-dimensional force to be measured, and a third preset relationship, the third preset relationship being:

[0063]

[0064]

[0065] In the formula, θ is the included angle between the three-dimensional force to be measured and the positive direction of the Z axis, is the included angle between the projection of the three-dimensional force to be measured in the XOY plane and the positive direction of the X axis.

[0066] It should be noted that in the above formula, the positive and negative of F x , F y , and F z indicate the direction, that is, when the value is greater than zero, it indicates that the component force is along the positive direction of the coordinate axis, and when the value is less than zero, it indicates that the component force is along the negative direction of the coordinate axis.

[0067] In this embodiment, compared with the conventional device, a complex decoupling algorithm is not required, the size of the component forces in the X, Y and Z directions is determined according to the output potentials in the X, Y and Z directions, and the identification of the size and direction of the three-dimensional force in space can be realized through the Pythagorean theorem and the trigonometric function relationship.

[0068] The device of the present application is verified by specific examples.

[0069] The structure of the measuring device according to the present application is modeled in the finite element software Comsol, and the sensing performance of the designed structure on the spatial three-dimensional force vector signal is verified. As shown in Figure 5 , the output signals in the X, Y and Z directions and the load relationship when the model is separately applied with the Y direction load are as shown in Figure 6 , the output signals in the X, Y and Z directions and the load relationship when the model is separately applied with the Z direction load are as shown in Figure 7 , the output signals in the X, Y and Z directions and the load relationship when the model is jointly applied with the XY direction load are as shown in Figure 8 , the output signals in the X, Y and Z directions and the load relationship when the model is jointly applied with the XZ direction load are as shown in Figure 9 , the output signals in the X, Y and Z directions and the load relationship when the model is jointly applied with the YZ direction load are as shown in Figure 10 , and Figure 8 ,Figure 9 、 Figure 10 With Figure 5 、 Figure 6 、 Figure 7 Contrast can be obtained, the output signal of force joint action and force alone when the output signal has no obvious difference, X direction output signal only reaction X direction component, Y direction output signal only reaction Y direction component, Z direction output signal only reaction Z direction component and theoretical analysis is consistent.

[0070] The force is directly applied to the stressed block 10, and the output signal of the piezoelectric layer 20 is measured, and the results are shown in Figure 11 It can be seen from the figure that the output potential does not change with the change of load, and the output potential is 0, so the output signal and the change of load when the force acts on the rest of the points, so the protective layer 30 has good shielding effect, which can realize the accurate measurement of three-dimensional force of fingertips.

[0071] The above is only the preferred embodiment of the present application, not the patent range of the present application, any equivalent structure or equivalent flow transformation using the content of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A fingertip three-dimensional force measurement device based on a piezoelectric sensor, characterized in that: include: A force-bearing block, with a protrusion fixed on the top, and the shape of the force-bearing block is hemispherical; A piezoelectric layer is located at the bottom of the force-bearing block, a plurality of electrodes are arranged on the piezoelectric layer at intervals, and each of the electrodes is connected to a measurement circuit; the piezoelectric layer is circular in shape; There are five electrodes, namely a first electrode, a second electrode, a third electrode, a fourth electrode and a fifth electrode; The first electrode is located at the center of the piezoelectric layer, with the first electrode as the coordinate origin, the second electrode and the third electrode are located on the X-axis and are symmetrical about the Y-axis, and the fourth electrode and the fifth electrode are located on the Y-axis and are symmetrical about the X-axis; A protective layer covers the surface of the force-bearing block, and a through hole adapted to the bump is opened on the protective layer, and the bump is located in the through hole; the protective layer shields the force whose action point is not on the fingertip, ensuring that the change in the output potential of the piezoelectric layer is caused by the force acting on the bump.

2. The fingertip three-dimensional force measurement device based on a piezoelectric sensor according to claim 1, characterized in that: The first electrode, the second electrode, the third electrode, the fourth electrode, and the fifth electrode have the same shape and area.

3. The fingertip three-dimensional force measurement device based on a piezoelectric sensor according to claim 1, characterized in that: Also includes: The supporting base is located at the bottom of the piezoelectric layer and is movably connected to the protective layer.

4. A method for measuring three-dimensional force of fingertips based on piezoelectric sensors, characterized in that: The measuring device according to any one of claims 1 to 3, comprising: respectively acquiring output signals of the measurement circuits of the second electrode and the third electrode, and performing differential processing on the two output signals to obtain the signals as output signals in the X direction; respectively acquiring output signals of the measurement circuits of the fourth electrode and the fifth electrode, and performing differential processing on the two output signals to obtain the signals as output signals in the Y direction; Acquire an output signal of the measurement circuit of the first electrode as a Z-direction output signal; According to the output signals in the X, Y and Z directions respectively, the component forces in the X, Y and Z directions are determined accordingly; Determine the magnitude and direction of the three-dimensional force to be measured based on the force components in the X, Y, and Z directions.

5. The method for measuring three-dimensional force of a fingertip based on a piezoelectric sensor according to claim 4, characterized in that: The X-direction force component is determined as follows: Determined according to the output signal in the X direction, the sensitivity of the component force in the X direction, and a first preset relationship; The force components in the Y and Z directions are determined in the same manner as the force component in the X direction; The magnitude of the three-dimensional force to be measured is determined according to the component forces in the X, Y, and Z directions and a second preset relationship.

6. The method for measuring three-dimensional force of a fingertip based on a piezoelectric sensor according to claim 5, characterized in that: The first preset relationship is: Where, is the output signal in the X direction, is the sensitivity, is the component force in the X direction; The second preset relationship is: Where, is the component force in the Y direction, is the component force in the Z direction.

7. The method for measuring three-dimensional force of a fingertip based on a piezoelectric sensor according to claim 4, wherein: The direction of the three-dimensional force to be measured is determined according to the component forces in the X, Y, and Z directions, the magnitude of the three-dimensional force to be measured, and a third preset relationship.

8. The method for measuring three-dimensional force of a fingertip based on a piezoelectric sensor according to claim 7, characterized in that: The third preset relationship is: Where, is the angle between the three-dimensional force to be measured and the positive direction of the Z axis, It is the angle between the projection of the three-dimensional force to be measured in the XOY plane and the positive direction of the X-axis.

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