Fingertip three-dimensional force measuring device based on piezoelectric sensor

Abstract

The invention discloses a fingertip three-dimensional force measuring device based on a piezoelectric sensor, and particularly relates to the field of sensors. Comprising a stress block, a spring and a spring, the piezoelectric layer is located at the bottom of the stress block, a plurality of electrodes are arranged on the piezoelectric layer at intervals, and each electrode is connected with a measuring circuit; and the protective layer covers the surface of the stress block, through holes matched with the convex blocks are formed in the protective layer, and the convex blocks are located in the through holes. For the output signal of the single-direction force obtained by the measuring device, the magnitude of the component force in each direction is determined, and the magnitude and the direction of the spatial three-dimensional force can be identified through the Pythagorean theorem and the 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, and in particular to a fingertip three-dimensional force measurement device based on a piezoelectric sensor. Background Art

[0002] With the rapid development of bionic robots and the continuous progress of artificial intelligence, robotic arms and intelligent robots have gradually been integrated into our lives and can replace people to complete some tedious tasks. As a medium for direct contact between the robotic arm and the outside world, the three-dimensional force sensor is crucial to improving the operational stability and reliability of the robotic arm, playing a role similar to that of human skin. The robot can construct the approximate shape of the object through the pressure it feels and the relative position between the sensors. It can also obtain the direction of the force with the help of the three-dimensional force detection system to determine whether sliding occurs during the contact process. The application of three-dimensional force sensing systems in the field of biomedicine is also becoming more and more extensive. Intelligent prostheses can improve the dexterity of prosthetic operation through the information feedback from the three-dimensional force sensor. The three-dimensional force detection system can also sense the sliding displacement and better help the disabled to restore their normal mobility. In summary, three-dimensional force sensors have potential application value in the fields of intelligent robots, biomedicine, 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 the action of external force, the magnitude and direction of the external force can be 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 operating frequency, and lower power consumption. These characteristics make them more suitable for application scenarios such as bionic robots and wearable devices. Therefore, piezoelectric three-dimensional force sensors have become one of the research hotspots in academia in recent years. Existing fingertip three-dimensional force measurement devices are easily disturbed by forces from other points of action, and cannot accurately reflect the force conditions in the measurement area, resulting in poor measurement accuracy. For the data measured by the sensor, multi-dimensional force coupling must be performed. At present, domestic and foreign scholars have achieved multi-dimensional force coupling through linear decoupling and nonlinear decoupling. The linear decoupling algorithm mainly solves the generalized inverse of the matrix through the least squares principle, but this method has problems such as low decoupling efficiency and poor ability to eliminate nonlinear coupling, which leads to inaccurate measurement results; the nonlinear decoupling algorithm mainly constructs nonlinear neural networks through algorithms such as neural mesh particles and particle swarm optimization to achieve the purpose of eliminating nonlinear coupling, but the neural network-based method requires a large amount of labeled data and often needs to be recalibrated for different scenarios, resulting in low measurement speed. Summary of the invention

[0004] The main purpose of the present application is to provide a fingertip three-dimensional force measurement device based on a piezoelectric sensor, aiming to solve 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 measurement device based on a piezoelectric sensor, comprising: a force-bearing block with a protrusion fixed on the top; a piezoelectric layer located at the bottom of the force-bearing block, with multiple electrodes arranged at intervals on the piezoelectric layer, and each electrode is connected to a measurement circuit; a protective layer covering the surface of the force-bearing block, and the protective layer is provided with a through hole adapted to the protrusion, and the protrusion is located in the through hole.

[0006] Optionally, the number of electrodes is five, namely the first electrode, the second electrode, the third electrode, the fourth electrode and the 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.

[0007] Optionally, the first electrode, the second electrode, the third electrode, the fourth electrode and the fifth electrode are all the same in shape and area.

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

[0009] Optionally, it also includes: a supporting base, which is located at the bottom of the piezoelectric layer and is movably connected to the protective layer.

[0010] To achieve the above-mentioned purpose, the present application also provides a fingertip three-dimensional force measurement method based on a piezoelectric sensor, using the above-mentioned measurement device, including: respectively obtaining the output signals of the measurement circuits of the second electrode and the third electrode, and differentially processing the two output signals as the X-direction output signal; respectively obtaining the output signals of the measurement circuits of the fourth electrode and the fifth electrode, and differentially processing the two output signals as the Y-direction output signal; obtaining the output signal of the measurement circuit of the first electrode as the Z-direction output signal; respectively determining the component forces in the X, Y, and Z directions according to the output signals in the X, Y, and Z directions; and determining the magnitude and direction of the three-dimensional force to be measured according to the component forces in the X, Y, and Z directions.

[0011] Optionally, the force component in the X direction is determined according to the output signal in the X direction, the sensitivity of the force component in the X direction, and a first preset relationship; the force components in the Y and Z directions are determined in the same way as the force component in the X direction; and the magnitude of the three-dimensional force to be measured is determined according to the force components in the X, Y, and Z directions, and a second preset relationship.

[0012] Optionally, the first preset relationship is:

[0013]

[0014] Where 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 force component 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 magnitude 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 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.

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

[0024] The piezoelectric sensor-based fingertip three-dimensional force measurement device of the present invention, through the zoning processing of the piezoelectric layer, reflects the change of the force amplitude according to the change of the output potential of each area, and obtains the output signal of the single-direction force after differential processing, which can improve the sensitivity; the force whose action point is not on the fingertip is shielded by the protective layer, ensuring that the change of the output potential of the piezoelectric layer is caused by the force acting on the bump, which is conducive to improving the measurement accuracy; the piezoelectric sensor-based fingertip three-dimensional force measurement method of the present invention, for the output signal of the single-direction force obtained by the above-mentioned measuring device, determines the size of each directional component force, and can realize the recognition of the size and direction of the three-dimensional force in space through the Pythagorean theorem and trigonometric function relationship, without the need to adopt complex linear decoupling and nonlinear decoupling algorithms, thereby improving the measurement speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of a fingertip three-dimensional force measurement device based on a piezoelectric sensor in this application;

[0026] Figure 2 A cross-sectional view of a fingertip three-dimensional force measurement device based on a piezoelectric sensor according to the present application;

[0027] Figure 3 This is a schematic diagram of the structure of a piezoelectric layer of a fingertip three-dimensional force measurement device based on a piezoelectric sensor in the present application;

[0028] Figure 4 This is a schematic diagram of an analysis of a fingertip three-dimensional force measurement method based on a piezoelectric sensor in this application;

[0029] Figure 5 This is a graph showing the relationship between the output signal and the load of a fingertip three-dimensional force measurement device based on a piezoelectric sensor when subjected to a single X-direction load;

[0030] Figure 6 This is a graph showing the relationship between the output signal and the load of a fingertip three-dimensional force measurement device based on a piezoelectric sensor when subjected to a Y-direction load alone;

[0031] Figure 7 This is a graph showing the relationship between the output signal and the load of a fingertip three-dimensional force measurement device based on a piezoelectric sensor when it is subjected to a Z-direction load alone;

[0032] Figure 8 This is a graph showing the relationship between the output signal and the load of a fingertip three-dimensional force measurement device based on a piezoelectric sensor when subjected to a combined XY direction load;

[0033] Fig. 9 This is a graph showing the relationship between the output signal and the load of a fingertip three-dimensional force measurement device based on a piezoelectric sensor when subjected to a combined XZ direction load;

[0034] Fig.10 This is a graph showing the relationship between the output signal and the load of a fingertip three-dimensional force measurement device based on a piezoelectric sensor when subjected to a combined load in the Y and Z directions;

[0035] Fig.11 This application discloses a diagram showing the relationship between the output signal and the load of a fingertip three-dimensional force measurement device based on a piezoelectric sensor when the device is subjected to a non-fingertip force.

[0036] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] The first embodiment of the present invention provides a fingertip three-dimensional force measurement device based on a piezoelectric sensor, such as Figure 1 As shown, it includes a force-bearing block 10, a piezoelectric layer 20, and a protective layer 30, wherein a bump 40 is fixed on the top of the force-bearing block 10; the piezoelectric layer 20 is located at the bottom of the force-bearing block 10, and a plurality of electrodes 50 are arranged at intervals on the piezoelectric layer 20, and each electrode 50 is connected to a measuring circuit through a wire; the protective layer 30 covers the surface of the force-bearing block 10, and a through hole adapted to the bump 40 is opened on the protective layer 30, and the bump 40 is located in the through hole.

[0039] Exemplarily, the material of the force bearing block 10 and the bump 40 is PDMS, the material of the piezoelectric layer 20 is PVDF, and the material of the protective layer 30 is alloy steel. The electrode 50 may be a planar electrode 50, and the material of the electrode 50 may be a metal material such as silver, gold, and copper.

[0040] It can be understood that when the external force F acts on the bump 40, the external force can be decomposed into a tangential force parallel to the XOY plane and a normal force perpendicular to the XOY plane. When the normal force acts on the bump 40, the piezoelectric layer 20 is subjected to pressure or tension, and the part closer to the center of the bottom surface is subjected to greater force; when the tangential force acts on the bump 40, a part of the piezoelectric layer 20 is subjected to upward tension, and the other part is subjected to downward pressure, and the area of ​​the tension and compression regions is substantially the same.

[0041] Based on the above analysis, it can be known that when the external force F acts on the bump 40 (fingertip), an overturning moment will be generated on the force-bearing block 10. Therefore, the present invention uses the overturning moment to achieve the measurement of three-dimensional force in space. When the external force acts on other parts of the force-bearing block 10 except the bump 40, a torque will also be generated at the bottom of the force-bearing block 10, affecting the output signal of the piezoelectric layer 20, so that the change in the output potential of the piezoelectric layer 20 is not entirely caused by the force acting on the fingertips. Therefore, the present invention shields the external force of the area other than the bump 40 on the force-bearing block 10 through the protective layer 30, thereby ensuring that the change in the output potential of the piezoelectric layer 20 is caused by the force acting on the fingertips, thereby improving the accuracy of the measurement.

[0042] In this embodiment, electrodes 50 are formed by silver plating on the upper and lower surfaces of the piezoelectric layer 20, and each electrode 50 is encapsulated with a plastic film. The change in the output potential of the two electrodes 50 reflects the change in the force amplitude, and an output signal sensitive to a single-direction force is realized after differential processing. A protrusion 40 is provided on the top of the force-bearing block 10 for sensing external force. When the external force acts on the protrusion 40, the external force is transmitted to the piezoelectric layer 20 through the force-bearing block 10, and then the external force is measured through the change in the output signal of the electrode 50, thereby realizing the recognition of the size and direction of the three-dimensional force of the fingertip.

[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, it also includes a support base 60, which is located at the bottom of the piezoelectric layer 20 and is movably connected to the protective layer 30. Specifically, the support base 60 is connected to the protective layer 30 through a thread, and is fixed to the piezoelectric layer 20 through an insulating glue. A plurality of fan-shaped holes are provided on the support base 60 for leading out wires to connect to the measurement circuit.

[0045] In an exemplary embodiment, the number of electrodes 50 is five, namely, a first electrode (i.e., region 5), a second electrode (i.e., region 1), a third electrode (i.e., region 2), a fourth electrode (i.e., region 3), and a 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 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. The first electrode, the second electrode, the third electrode, the fourth electrode and the fifth electrode are all the same in 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, a 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. The centers of regions 1 and 2 are on the X-axis and symmetrical about the Y-axis. When the tangential force is along the X-direction, one is under tension and the other is under compression. After differential processing, the output signal is amplified; when the tangential force is along the Y-direction, the areas of the piezoelectric layer 20 in regions 1 and 2 under tension and compression are equal, the tension and pressure are almost equal, the generated charges cancel each other out, and there is no output signal; when the normal force acts, the piezoelectric layer 20 in regions 1 and 2 are both under tension or compression, and the areas of the piezoelectric layer 20 in regions 1 and 2 are equal, and the distances to the coordinate origin O are the same. It can be approximately considered that the forces are consistent. Since the charges generated by the piezoelectric effect are the same, there is no output signal after differential processing. Therefore, the output signal of the piezoelectric layer 20 in regions 1 and 2 is sensitive to the force in the X-direction, but not to the forces in the Y and Z-directions. The output signal principle of regions 3 and 4 is basically the same as that of regions 1 and 2, except that the output signal of the piezoelectric layer 20 in regions 3 and 4 is sensitive to the force in the Y-direction, but not to the 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, the external force acting on the bump 40 (fingertip) can be measured by the fingertip three-dimensional force measurement device based on the piezoelectric sensor of the present invention.

[0048] The second embodiment of the present invention provides a method for measuring the three-dimensional force of a fingertip based on a piezoelectric sensor. By calculating the signal output by the above-mentioned measuring device, the magnitude and direction of the three-dimensional force can be obtained. The method specifically includes the following steps:

[0049] Step S1, respectively obtaining output signals of the measurement circuits of the second electrode and the third electrode, and performing differential processing on the two output signals as output signals in the X direction; respectively obtaining output signals of the measurement circuits of the fourth electrode and the fifth electrode, and performing differential processing on the two output signals as output signals in the Y direction; obtaining the output signal of the measurement circuit of the first electrode as an output signal in the Z direction; and respectively determining the component forces in the X, Y, and Z directions according to the output signals in the X, Y, and Z directions;

[0050] Specifically, the component force in the X direction is 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, and the first preset relationship is:

[0051]

[0052] Where 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.

[0053] Similarly, the component force in the Y direction is:

[0054]

[0055] Where V y is the output signal in the Y direction, S y is the sensitivity, F y is the component force in the Y direction.

[0056] Similarly, the component force in the Z direction is:

[0057]

[0058] Where V z is the output signal in the Z direction, S z is the sensitivity, F y is the force component in the Z direction.

[0059] Step S2, determining the magnitude of the three-dimensional force to be measured according to the component forces in the X, Y, and Z directions and a second preset relationship, the second preset relationship being:

[0060]

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

[0062] Step S3, determining the direction of the three-dimensional force to be measured 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, wherein the third preset relationship is:

[0063]

[0064]

[0065] In the formula, θ 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.

[0066] It is worth noting that in the above formula, F x 、F y 、F z The positive or negative value indicates the direction, that is, when the value is greater than zero, it means that the component force is along the positive direction of the coordinate axis, and when the value is less than zero, it means that the component force is along the negative direction of the coordinate axis.

[0067] In this embodiment, compared with traditional devices, no complex decoupling algorithm is required. The magnitude of the component forces in the X, Y, and Z directions is determined by the output potentials in the X, Y, and Z directions, and the magnitude and direction of the three-dimensional force in space can be identified through the Pythagorean theorem and trigonometric function relationships.

[0068] The device of the present invention is verified by using specific examples below.

[0069] The structure of the measuring device according to the present invention was modeled in the finite element software Comsol, and the sensing performance of the designed structure for the three-dimensional force vector signal was verified. The X-direction load was applied to the model alone, and the relationship between the output signal and the load in the X, Y, and Z directions was as follows: Figure 5 As shown, a Y-direction load is applied to the model alone. The relationship between the output signals in the X, Y, and Z directions and the load is as follows: Figure 6 As shown, a Z-direction load is applied to the model alone. The relationship between the output signals in the X, Y, and Z directions and the load is as follows: Figure 7 As shown; the XY direction load is applied to the model jointly, and the relationship between the output signal and the load in the X, Y, and Z directions is as follows Figure 8 As shown, the XZ direction load is applied to the model jointly. The relationship between the output signal and the load in the X, Y, and Z directions is as follows Fig. 9 As shown, the YZ direction load is applied to the model jointly. The relationship between the output signal and the load in the X, Y, and Z directions is as follows Fig.10 As shown; Figure 8 , Fig. 9 , Fig.10 and Figure 5 , Figure 6 , Figure 7 By comparison, there is no obvious difference between the output signal of the combined force and the output signal of the single force, which means that the output signal in the X direction only reflects the force component in the X direction, the output signal in the Y direction only reflects the force component in the Y direction, and the output signal in the Z direction only reflects the force component in the Z direction, which is consistent with the theoretical analysis.

[0070] A force is directly applied to the force bearing block 10, and the output signal of the piezoelectric layer 20 is measured. The result is as follows: Fig.11 As shown in the figure, it can be seen that the output potential does not change with the change of load, and the output potential is 0. From this, it can be seen that when the force acts on the other points, the relationship between the output signal and the load changes. From this, it can be seen that the protective layer 30 has a good shielding effect and can realize the accurate measurement of the three-dimensional force of the fingertip.

[0071] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied 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 convex block fixed on the top; 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 measuring circuit; The protective layer covers the surface of the force-bearing block, and the protective layer is provided with a through hole matched with the convex block, and the convex block is located in the through hole.

2. The fingertip three-dimensional force measurement device based on piezoelectric sensor according to claim 1 is characterized in that: The number of the electrodes is five, 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. Taking 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. The fourth electrode and the fifth electrode are located on the Y-axis and are symmetrical about the X-axis.

3. The fingertip three-dimensional force measurement device based on piezoelectric sensor according to claim 2 is 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.

4. The fingertip three-dimensional force measurement device based on piezoelectric sensor according to claim 2, characterized in that: The force-bearing block is hemispherical in shape, and the piezoelectric layer is circular in shape.

5. The fingertip three-dimensional force measurement device based on piezoelectric sensor according to claim 2, 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.

6. 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 2 to 5 comprises: respectively acquiring output signals of the measuring circuits of the second electrode and the third electrode, and performing differential processing on the two output signals as output signals in the X direction; respectively acquiring output signals of the measuring circuits of the fourth electrode and the fifth electrode, and performing differential processing on the two output signals as output signals in the Y direction; Acquire an output signal of a measuring 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 components of force in the X, Y and Z directions are determined accordingly; According to the force components in the X, Y, and Z directions, the magnitude and direction of the three-dimensional force to be measured are determined.

7. The method for measuring three-dimensional force of fingertips based on piezoelectric sensors according to claim 6, 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 the 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.

8. The fingertip three-dimensional force measurement method based on piezoelectric sensor according to claim 7 is characterized in that: The first preset relationship is: Where 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. The second preset relationship is: In the formula, F y is the component force in the Y direction, F z is the force component in the Z direction.

9. The method for measuring three-dimensional force of fingertips based on piezoelectric sensors according to claim 6, characterized in that: 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.

10. The fingertip three-dimensional force measurement method based on piezoelectric sensor according to claim 9, characterized in that: The third preset relationship is: In the formula, θ 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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