Piezoelectric sensor electrode structure for three-dimensional force measurement and polarization method

Abstract

The invention discloses a piezoelectric sensor electrode structure for three-dimensional force measurement and a polarization method, and belongs to the technical field of mechanical arm touch. Comprising a lower sensitive layer, an isolation layer and an upper rigid-flexible mixed array which are sequentially laminated and are sealed through a packaging structure; the lower sensitive layer is composed of a first lower sensitive unit and a second lower sensitive unit which are perpendicular to each other and share the first middle sensitive layer; the first lower sensing unit comprises a first upper electrode and two independent first lower electrodes, and the electrodes are arranged in a staggered mode in the X-axis direction. The second lower sensing unit comprises a second upper electrode and two independent second lower electrodes, and the electrodes are arranged in a staggered mode in the Y-axis direction; the upper-layer rigid-flexible hybrid array is arranged above the isolation layer and comprises a third lower electrode, a second middle sensitive layer, a distributed upper electrode and a rigid column which are sequentially laminated; the packaging structure comprises a lower surface packaging layer and an upper surface packaging layer and is used for sealing the sensor. The problems that an existing sensor cannot measure three-dimensional force at the same time and interference exists are solved.

Description

Technical Field

[0001] The present invention belongs to the field of robotic arm tactile technology, and in particular relates to a piezoelectric sensor electrode structure and polarization method for three-dimensional force measurement. Background Art

[0002] Accurate, real-time acquisition of environmental information is a crucial prerequisite for ensuring safe, stable, and flexible robotic arm operation, and is crucial for protecting both humans and the robot itself. Force and tactile perception are essential inputs for contact control in robotic arms. Multi-axis force / torque sensors in the wrist and single-axis force sensors in the joints are widely used, such as the three-axis force sensor in the Curiosity rover and the six-axis force sensors in the SS-RMS and Robonaut2 arms. While these prosthetic hands closely resemble human hands and even possess degrees of freedom not found in humans, they can only perform simple manipulations. One key reason for this is the lack of in-situ attachable tactile sensors.

[0003] Tactile sensors provide support for intelligent robotic arms to achieve true human-like functionality. While other forms of perception can assist robotic arm operations, tactile sensors combine multi-modal sensing capabilities, including contact, pressure, and slip, to enhance the robotic arm's dexterity in a range of operations, including contact-grasping-holding-moving-releasing. Currently, tactile sensors primarily identify an object's contact state and other properties by in-situ detecting the positive pressure exerted by the target object on the sensor. However, in practical applications, the role of shear stress cannot be ignored in order to obtain comprehensive information about the target object. When slippage occurs or threatens to occur, relying solely on positive pressure cannot meet the robotic arm's operational requirements. Therefore, accurate three-dimensional force perception is essential for enhancing the robotic arm's operational flexibility. The ductility and flexibility of tactile sensors also enable them to operate on curved surfaces. Summary of the Invention

[0004] Technical issues to be solved:

[0005] In order to avoid the shortcomings of the prior art, the present invention provides a piezoelectric sensor electrode structure and decoupling method for three-dimensional force measurement. Based on the staggered electrode design of the lower sensitive layer combined with 60° spatial polarization, the normal force interference is shielded during shear stress measurement; based on the rigid column structure of the upper rigid-flexible hybrid array, the d 31 / d 33 The hybrid mode increases the positive pressure sensitivity to 237mV / N, which is better than the traditional 33 The mode is improved by 37%; it solves the problem that existing sensors cannot measure three-dimensional force simultaneously and there is interference.

[0006] The technical solution of the present invention is: a piezoelectric sensor electrode structure for three-dimensional force measurement, comprising a lower sensitive layer, an isolation layer, and an upper rigid-flexible hybrid array stacked in sequence, and sealed by a packaging structure;

[0007] The lower sensitive layer is composed of a first lower sensitive unit 1 and a second lower sensitive unit 2 arranged perpendicular to each other, and share a first intermediate sensitive layer 4; the first lower sensitive unit 1 includes a first upper electrode 3 and two independent first lower electrodes 5, 6, and the electrodes are staggered along the X-axis direction; the second lower sensitive unit 2 includes a second upper electrode 7 and two independent second lower electrodes 8, 9, and the electrodes are staggered along the Y-axis direction;

[0008] The isolation layer 10 covers the upper surface of the lower sensitive layer to achieve electrical isolation between the lower sensitive layer and the upper rigid-flexible hybrid array;

[0009] The upper rigid-flexible hybrid array 11 is arranged above the isolation layer 10, and includes a third lower electrode 12, a second intermediate sensitive layer 13, a distributed upper electrode 14 and a rigid column 15 stacked in sequence;

[0010] The packaging structure includes a lower surface packaging layer 16 and an upper surface packaging layer 17 for sealing the sensor.

[0011] The distributed upper electrode 14 is arranged in a 3x3 upper electrode unit array, and the rigid column 15 is set corresponding to the distributed upper electrode 14, that is, each upper electrode unit 14 corresponds to a rigid column 15, realizing the spatial distribution measurement of the positive pressure.

[0012] The technical solution of the present invention is: the rigid column 15 is located in the center of the distributed upper electrode, and the diameter of the rigid column 15 is smaller than the diameter of the distributed upper electrode 14, so that the upper sensitive layer can be completely in the d 31 with d 33 In hybrid mode, the sensor's positive pressure sensitivity is increased.

[0013] Among them, d 31 The piezoelectric film is polarized along the 3rd direction (thickness direction) and stretched along the 1st direction. 33 Indicates that the piezoelectric film is polarized in three directions and compressed in three directions. 31 with d 33 The hybrid working mode means that under the action of pressure, the second intermediate sensitive layer 13 is in a tensile and compressive working state at the same time due to the rigid-flexible hybrid structural design of the sensor assisting the lower flexible substrate.

[0014] A further technical solution of the present invention is that the intermediate sensitive layers 4, 13 are made of polyvinylidene fluoride (PVDF) film, and the electrodes are made of sputtered metal material.

[0015] A decoupling method for a piezoelectric sensor electrode structure for three-dimensional force measurement, characterized by comprising:

[0016] Spatial polarization, the steps are as follows:

[0017] A first lower electrode 5 of the first lower sensitive unit 1 and a second lower electrode 8 of the second lower sensitive unit 2 are connected to a positive high voltage, another first lower electrode 6 and another second lower electrode 9 are connected to a negative high voltage, the first upper electrode and the second upper electrode 3, 7 are grounded, and a tilted polarization vector is formed inside the first lower sensitive unit 1 at an angle of 60° to the X-axis, and a tilted polarization vector is formed inside the second lower sensitive unit 2 at an angle of 60° to the Y-axis;

[0018] The third lower electrode 12 of the upper rigid-flexible hybrid array 11 is connected to a positive high voltage, and the distributed upper electrode 14 is connected to a negative high voltage to achieve thickness direction polarization;

[0019] Signal decoupling, the steps are as follows:

[0020] When working, all lower electrodes 5, 6, 8, 9 of the lower sensitive layer are grounded, and the first upper electrode 3 outputs a signal V x , the second upper electrode 7 outputs a signal V y ;

[0021] The third lower electrode 12 of the upper rigid-flexible hybrid array 11 is grounded, and the distributed upper electrode 14 outputs a signal V z ;

[0022] Three-dimensional force decoupling, the calculation process is as follows:

[0023] Based on the signal V x , sensitivity coefficient S x and signal V y , sensitivity coefficient S y Calculate the two-dimensional shear stress amplitude F s and the two-dimensional shear stress direction θ;

[0024] Based on the Z-direction signal V z , sensitivity coefficient S z Calculate the positive pressure F z ;

[0025] Combined with the two-dimensional shear stress amplitude F s , positive pressure F z Calculate the three-dimensional force amplitude F t and three-dimensional force cone angle

[0026] A further technical solution of the present invention is: the three-dimensional force amplitude F t The calculation formula is:

[0027]

[0028] A further technical solution of the present invention is: the three-dimensional force cone angle The calculation formula is:

[0029]

[0030] Through the three-dimensional force cone angle Represents the angle between the three-dimensional force vector and the negative Z axis.

[0031] A further technical solution of the present invention is: the first lower sensitive unit 1 is only sensitive to shear stress in the X direction, the second lower sensitive unit 2 is only sensitive to shear stress in the Y direction, and the upper rigid-flexible hybrid array 14 is only sensitive to positive pressure in the Z direction.

[0032] A further technical solution of the present invention is that the arrangement of the staggered electrodes in the lower sensitive layer satisfies:

[0033] The first upper electrode 3 of the first lower sensitive unit 1 is located in the middle of the two first lower electrodes 5 and 6 in the X-axis direction;

[0034] The second upper electrode 7 of the second lower sensitive unit 2 is located in the middle of the two second lower electrodes 8 and 9 in the Y-axis direction.

[0035] A further technical solution of the present invention is that the tilted polarization vector of the lower sensitive layer is 60° so that the net charge output by the lower sensitive layer under the action of the normal force is zero, thereby achieving normal force interference shielding.

[0036] Beneficial effects

[0037] The beneficial effects of the present invention are as follows: the present invention achieves 60° tilted spatial polarization of the lower sensitive layer, so that the net charge output by the first and second lower sensitive units under the action of the normal force is zero, thereby eliminating the interference of the positive pressure on the shear stress; at the same time, the upper rigid-flexible hybrid array only responds to positive pressure due to thickness polarization and rigid column design, shielding the shear stress interference.

[0038] The present invention combines the staggered electrode arrangement of the lower sensitive layer with 60° polarization to improve the shear stress sensitivity in the X / Y direction and provide direction recognition capability.

[0039] The array rigid column design of the present invention drives the upper array to work at d 31 / d 33 Mixed mode, positive pressure sensitivity 237mV / N( Figure 6 Middle e), more traditional d 33 Mode improved by 37%.

[0040] The first and second lower sensitive units of the present invention share a middle sensitive layer, reducing interlayer interfaces. The Z-axis overlapping structure reduces overall thickness, making it easier to conform to curved surfaces. Distributed upper electrodes and rigid columns simultaneously enable spatially distributed measurement of positive pressure, making it suitable for non-uniform contact scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic diagram of the overall structure and coordinate relationship of the sensor in an embodiment of the present invention;

[0042] Figure 2 Schematic diagram of the decoupling method and operation of the lower sensitive unit 1 in an embodiment of the present invention;

[0043] Figure 3 Schematic diagram of the decoupling method and operation of the lower sensitive unit 2 in an embodiment of the present invention;

[0044] Figure 4 Figures 1 and 2 are diagrams of the polarization principle and working principle of the upper sensitive layer in an embodiment of the present invention, (a) is the polarization principle of the upper sensitive layer, and (b) is the working principle diagram of the upper sensitive layer;

[0045] Figure 5 Schematic diagram of the decomposition and coordinate relationship of three-dimensional forces in an embodiment of the present invention;

[0046] Figure 6 Schematic diagram of the sensor output voltage in an embodiment of the present invention, (a) is the sensor output voltage under positive shear stress of the X-axis, (b) is the sensor output voltage under positive shear stress of the Y-axis, (c) is the sensor output voltage under negative shear stress of the X-axis, (d) is the sensor output voltage under negative shear stress of the Y-axis, (e) is the sensor output voltage under pressure of the Z-axis, and (f) is the sensor output voltage under the simultaneous existence of positive pressure of the X-axis, positive pressure of the Y-axis, and positive pressure of the Z-axis.

[0047] Explanation of the accompanying drawings: 1. First lower sensitive unit, 2. Second lower sensitive unit, 3. First upper electrode, 4. First intermediate sensitive layer, 5 and 6. Second lower electrodes, 7. Second upper electrode, 8 and 9. Second lower electrode, 10. Isolation layer, 11. Upper rigid-flexible hybrid sensing array, 12. Third lower electrode, 13. Second intermediate sensitive layer, 14. Distributed upper electrode, 15. Rigid column, 16. Lower surface package, 17. Lower surface package. DETAILED DESCRIPTION

[0048] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0049] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0050] Based on the difficulties of existing three-dimensional force testing technology, inaccurate measurement results, and insufficient decoupling accuracy, the present invention proposes a piezoelectric sensor electrode structure for three-dimensional force measurement, comprising a lower sensitive layer, an isolation layer, and an upper rigid-flexible hybrid array stacked in sequence, and sealed by a packaging structure;

[0051] The lower sensitive layer is composed of a first lower sensitive unit 1 and a second lower sensitive unit 2 arranged perpendicular to each other, and share a first intermediate sensitive layer 4; the first lower sensitive unit 1 includes a first upper electrode 3 and two independent first lower electrodes 5, 6, and the electrodes are staggered along the X-axis direction; the second lower sensitive unit 2 includes a second upper electrode 7 and two independent second lower electrodes 8, 9, and the electrodes are staggered along the Y-axis direction;

[0052] The isolation layer 10 covers the upper surface of the lower sensitive layer to achieve electrical isolation between the lower sensitive layer and the upper rigid-flexible hybrid array;

[0053] The upper rigid-flexible hybrid array 11 is arranged above the isolation layer 10, and includes a third lower electrode 12, a second intermediate sensitive layer 13, a distributed upper electrode 14 and a rigid column 15 stacked in sequence;

[0054] The packaging structure includes a lower surface packaging layer 16 and an upper surface packaging layer 17 for sealing the sensor.

[0055] Specifically, the distributed upper electrode 14 is formed by an array of 3 x 3 upper electrode units.

[0056] Specifically, the rigid column 15 is located in the center of the distributed upper electrode, and the diameter of the rigid column 15 is smaller than the diameter of the distributed upper electrode 14, so that the upper sensitive layer can be completely in the d 31 with d 33 In the mixed mode, the positive pressure sensitivity of the sensor is improved. 31 The piezoelectric film is polarized along the 3rd direction (thickness direction) and stretched along the 1st direction. 33 Indicates that the piezoelectric film is polarized in three directions and compressed in three directions. 31 with d 33The hybrid working mode means that under the action of pressure, the second intermediate sensitive layer 13 is in a tensile and compressive working state at the same time due to the rigid-flexible hybrid structural design of the sensor assisting the lower flexible substrate.

[0057] The present invention proposes a decoupling method for the electrode structure of a piezoelectric sensor for three-dimensional force measurement, including spatial polarization, signal decoupling and three-dimensional force decoupling;

[0058] The spatial polarization steps are as follows:

[0059] A first lower electrode 5 of the first lower sensitive unit 1 and a second lower electrode 8 of the second lower sensitive unit 2 are connected to a positive high voltage, another first lower electrode 6 and another second lower electrode 9 are connected to a negative high voltage, the first upper electrode and the second upper electrode 3, 7 are grounded, and a tilted polarization vector is formed inside the first lower sensitive unit 1 at an angle of 60° to the X-axis, and a tilted polarization vector is formed inside the second lower sensitive unit 2 at an angle of 60° to the Y-axis;

[0060] The third lower electrode 12 of the upper rigid-flexible hybrid array 11 is connected to a positive high voltage, and the distributed upper electrode 14 is connected to a negative high voltage to achieve thickness direction polarization;

[0061] The signal decoupling steps are as follows:

[0062] When working, all lower electrodes 5, 6, 8, 9 of the lower sensitive layer are grounded, and the first upper electrode outputs a signal V x , the second upper electrode output signal V y ;

[0063] The third lower electrode 12 of the upper rigid-flexible hybrid array 11 is grounded, and the distributed upper electrode 14 outputs a signal V z ;

[0064] The three-dimensional force decoupling calculation process is as follows:

[0065] Based on V x , sensitivity coefficient S x and signal V y , sensitivity coefficient S y Calculate the two-dimensional shear stress amplitude F s and the two-dimensional shear stress direction θ;

[0066] Based on the Z-direction signal V z , sensitivity coefficient S z Calculate the positive pressure F z ;

[0067] Combined with the two-dimensional shear stress amplitude F s , positive pressure F z Calculate the three-dimensional force amplitude F t and three-dimensional force cone angle

[0068] The present invention can realize the measurement of two-dimensional shear stress through the arrangement of the staggered electrode structure of the lower sensitive layer and the specific spatial high-voltage decoupling method; the measurement of positive pressure can be realized through the upper rigid-flexible hybrid array, and the stacking design of the dual sensitive layers can realize the measurement and decoupling of three-dimensional force.

[0069] The above technical solution is further described below with reference to the accompanying drawings and examples:

[0070] In one embodiment, referring to Figure 1 As shown, this embodiment defines the direction perpendicular to the electrode lines of sensitive unit 1 as the X-axis direction, the direction perpendicular to the electrode lines of sensitive unit 2 as the Y-axis direction, and the direction perpendicular to the upper and lower piezoelectric sensitive layers as the Z-axis direction, establishing a Cartesian coordinate system. The three-dimensional force sensor is composed of a first lower sensitive unit 1, a second lower sensitive unit 2, an isolation layer 10, an upper rigid-flexible hybrid array 11, a lower surface encapsulation layer 16, and an upper surface encapsulation layer 17. The lower sensitive layer is composed of a first lower sensitive unit 1 and a second lower sensitive unit 2. The first lower sensitive unit 1 is composed of a first upper electrode 3, a first intermediate sensitive layer 4 and two independent second lower electrodes 5 and 6, and the upper and lower electrodes are offset along the X-axis direction; the second lower sensitive unit 2 is composed of a second upper electrode 7, a first intermediate sensitive layer 4 shared with the first lower sensitive unit 1, and two independent second lower electrodes 8 and 9, and the upper and lower electrodes are offset along the Y direction; the upper rigid-flexible hybrid array 11 is composed of a lower electrode 12, an intermediate sensitive layer 13, a distributed upper electrode 14, and a rigid column 15 corresponding to the distributed upper electrode; the isolation layer 10 is used to achieve isolation between the lower sensitive layer and the upper sensitive layer, and the lower sensitive layer and the upper rigid-flexible hybrid array together constitute a three-dimensional force piezoelectric sensor.

[0071] Before being used for testing, three-dimensional force sensors usually require high voltage polarization to improve the piezoelectric properties of the upper and lower piezoelectric sensitive layers. In one embodiment, the decoupling method of the lower sensitive layer is different from the traditional decoupling method along the thickness direction of the film. Instead, it is based on the electrode distribution of the sensitive unit 1 and the sensitive unit 2 on the surface of the sensitive layer 4, so that in the high voltage polarization stage, a spatial polarization vector is formed inside the sensitive unit 1 and the sensitive unit 2 at an angle of 60° to the X-axis and Y-axis directions respectively. The upper rigid-flexible hybrid sensing array 11 is polarized along the thickness direction. The advantage of the upper rigid-flexible hybrid array 11 is that the rigid column makes the upper sensitive layer in the d 31 with d 33 In hybrid working mode, rather than traditional d 33 In the working mode, the sensitivity of the upper piezoelectric sensitive layer to normal pressure can be improved, and three-dimensional force measurement can be achieved based on the output signals of the upper and lower sensitive layers.

[0072] In one embodiment, the lower sensitive layer 4 is first patterned on both sides using photolithography-wet etching techniques, resulting in the fabrication of a two-dimensional shear stress-sensitive film consisting of a comb-shaped lower electrode layer, an intermediate sensitive layer, and a comb-shaped upper electrode layer. Next, a metal electrode layer is sputtered onto the lower surface of the upper sensitive layer. The sputtered electrode layer on the upper surface is then patterned using photolithography-wet etching. The upper and lower sensitive layers are assembled and isolated using a 3140 silicone rubber isolation layer 10. Finally, silicone rubber is spin-coated on both sides of the upper and lower sensitive layers to achieve the packaging of the three-dimensional force sensor.

[0073] In one embodiment, high voltage spatial poling of a piezoelectric three-dimensional force sensor is performed: Figure 2 (a) and Figure 3 As shown in (a), a first lower electrode 5 of the first lower sensitive unit 1 and a second lower electrode 8 of the second lower sensitive unit 2 are connected to a positive high voltage, another first lower electrode 6 of the first lower sensitive unit 1 and another lower electrode 9 of the second lower sensitive unit 2 are connected to a negative high voltage, and the first upper electrode 3 of the first lower sensitive unit 1 and the second upper electrode 7 of the second lower sensitive unit 2 are connected to the ground. Under this connection mode, the first lower sensitive unit 1 and the second lower sensitive unit 2 are polarized simultaneously for half an hour, thereby forming a tilted polarization vector at 60° to the X-axis inside the first lower sensitive unit 1 and a tilted polarization vector at 60° to the Y-axis inside the second lower sensitive unit 2. The lower electrode 12 of the sensitive layer 13 of the upper rigid-flexible hybrid sensing array 11 is connected to a positive high voltage, and the distributed upper electrode 14 is connected to a negative high voltage, achieving thickness-direction polarization and giving the upper sensitive layer piezoelectric properties.

[0074] When working, refer to Figure 2 (b) (c) and Figure 3 As shown in (b) and (c), the lower electrodes 5 and 6 of the first lower sensitive unit 1 are grounded, and the lower electrodes 8 and 9 of the second lower sensitive unit 2 are also grounded. The difference is that the first upper electrode 3 of the first lower sensitive unit 1 serves as an independent output terminal, and the second upper electrode 7 of the second lower sensitive unit 2 serves as an independent output terminal.

[0075] Reference Figure 4 As shown in (a), the lower surface electrode 12 and the distributed upper electrode 14 of the upper rigid-flexible hybrid sensing array 11 are connected to a high voltage and ground respectively, so as to realize the polarization of the upper piezoelectric sensitive film layer 13. Figure 4 Middle (b) shows the working principle of the upper sensitive layer under positive pressure, where the lower surface electrode 12 is grounded and the upper surface distributed electrode 14 outputs a signal.

[0076] Therefore, the piezoelectric sensor designed in this embodiment has multiple output signals. The electrical signal output by the first upper electrode 3 of the first lower sensitive unit 1 is recorded as V x, reflecting the output signal of the first lower sensitive unit 1 under the action of the external load; the output signal of the second upper electrode 7 of the second lower sensitive unit 2 is recorded as V y , reflecting the output signal of the second lower sensitive unit 2 under the action of external load. The multi-channel electrical signal output by the distributed electrodes 14 on the upper surface of the upper rigid-flexible hybrid sensing array 11 is recorded as V z , reflecting the output signal of the upper rigid-flexible hybrid sensor array 11 under the action of external load.

[0077] In one embodiment, the three-dimensional force sensor electrode structure and decoupling method have the function of identifying the direction and amplitude of the three-dimensional force. Figure 2 As shown in (b), when the first lower sensitive unit 1 is subjected to positive pressure, the polarization vectors P1 and P2 inside the piezoelectric sensitive layer 4 are compressed respectively, and equal charges of opposite signs are generated on the surface of the first upper electrode 3, and the output net charge is 0; when the first lower sensitive unit 1 is subjected to shear stress in the Y-axis direction, the polarization vectors P1 and P2 are neither stretched nor compressed, so the output net charge of the first upper electrode 3 is 0; Figure 2 As shown in (c), when the first lower sensitive unit 1 is subjected to shear stress in the X-axis direction, the polarization vector P1 is stretched while the polarization vector P2 is compressed, generating charges of the same sign on the surface of the first upper electrode 3, so the output net charge is not 0. Based on the above principle, the first lower sensitive unit 1 will output charge only when subjected to X-axis shear stress, and the output charge is 0 when subjected to Z-axis pressure and Y-axis shear stress. Therefore, the first lower sensitive unit 1 has unidirectional sensitivity to X-axis shear stress. The sensitivity of the first lower sensitive unit 1 to X-axis shear stress is denoted as S x Similarly, the second lower sensitive unit 2 has a unidirectional sensitivity to the Y-axis shear stress. The sensitivity of the second lower sensitive unit 2 to the Y-axis shear stress is S y The upper rigid-flexible hybrid sensing array 11 is polarized in the thickness direction, so it is insensitive to shear stress, but highly sensitive to normal pressure. The sensitivity of the sensitive layer 11 to the Z-axis normal pressure is S z .

[0078] When the piezoelectric three-dimensional force sensor is subjected to loads in any direction, the lower sensitive layer can shield the interference of normal pressure. The first lower sensitive unit 1 and the second lower sensitive unit 2 respectively sense the shear stress along the X-axis and the shear stress along the Y-axis in the plane. And based on the output signal V x (with positive and negative) and the output signal V of the second lower sensitive unit 2 y (with positive and negative properties), the magnitude and direction of the two-dimensional shear stress vector in the plane are calculated using the Pythagorean theorem and trigonometric function relationships. The details are as follows:

[0079] Reference Figure 5As shown in the figure, the coordinate relationship and decomposition diagram of the three-dimensional force. First, the output signal V x And the corresponding sensitivity S x Calculate the shear stress F in the X direction x (Formula 1), similarly, using the output signal V of the second lower sensitive unit 2 y And the corresponding sensitivity S y Calculate the Y-direction shear stress F y (Formula 2), and then use Formula 3 to calculate the two-dimensional shear stress F s The size of the 2D shear stress is calculated using the Cartesian coordinate system established above using Formula 4. The value range of θ is [0, 2π], which is used to reflect the angle between the 2D shear stress in the plane and the positive direction of the X-axis in the counterclockwise direction. The upper rigid-flexible hybrid sensor array 11 outputs the voltage V z And the corresponding sensitivity S z Used to measure the normal pressure, use Equation 5 to calculate the normal pressure amplitude, and use Equation 6 to calculate the total three-dimensional force vector amplitude. Equation 7 can be used to calculate the cone angle of the three-dimensional force. cone angle Used to reflect the angle between the three-dimensional force vector and the negative direction of the Z axis. The value range is [0,1 / 2π].

[0080] Specifically: When V x <0 and V y When V ≤ 0, the two-dimensional shear stress vector in the plane is in the first quadrant and the angle with the X axis is less than 90°; when V x =0 and V y When V ≤ 0, the angle between the in-plane two-dimensional shear stress vector and the X-axis is 90°; when V x >0 and V y When V ≤ 0, the two-dimensional shear stress vector in the plane is in the second quadrant and the angle between it and the X-axis is greater than 90° and less than or equal to 180°; when V x >0 and V y ≥0, the two-dimensional shear stress vector in the plane is in the third quadrant and the angle with the X-axis is greater than or equal to 180° and less than 270°; when V x =0 and V y ≥0, the angle between the in-plane two-dimensional shear stress vector and the X-axis is 270°; when V x <0 and V y When ≥0, the in-plane two-dimensional shear stress vector is in the fourth quadrant and the angle between it and the X-axis is greater than 270° and less than or equal to 360°. Based on the two-dimensional shear stress vector measurement, the upper rigid-flexible hybrid sensor array 11 is used to measure the normal pressure. Combining formulas 5 to 7, the three-dimensional force measurement and decoupling can be achieved, where F z is positive pressure, F t It is a three-dimensional force.

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] According to the three-dimensional force sensor electrode structure and decoupling method proposed in the present invention, finite element simulation is used to verify that the proposed sensor has three-dimensional force measurement and decoupling capabilities. Figure 6 This is the relationship between the output voltage signal of the flexible piezoelectric three-dimensional force sensor and different loads. Figure 6 (a) shows the output voltage signals of the X-direction sensitive unit (first lower sensitive unit 1), the Y-direction sensitive unit (second lower sensitive unit 2), and the Z-upper rigid-flexible hybrid sensor array 11 under the positive shear stress of the X axis. It can be seen that under the positive shear stress of the X axis, the sensitivity of the X-direction sensitive unit is 164mV / N, and the output signal is negative, while the output voltage of the Y-direction sensitive unit and the Z-direction rigid-flexible hybrid sensor array is almost 0, which proves that only the X-direction sensitive unit is sensitive to the X-direction shear stress, while the Y-direction sensitive unit and the Z-direction rigid-flexible hybrid sensor array are not sensitive to the X-direction shear stress. Figure 6 As can be seen in (c), the output voltage of the X-direction sensitive unit is positive, which shows that the X-direction sensitive unit has the ability to identify the direction of the X-direction shear stress, verifying the rationality of the theory described above. Figure 6 As shown in (b), the sensitivity of the Y-direction sensitive unit to the Y-direction shear stress is 165mV / N, while the output voltage signal of the X-direction sensitive unit and the Z-direction rigid-flexible hybrid sensing array under the Y-direction shear stress is almost 0, which shows that the Y-direction sensitive unit has a high sensitivity to the Y-direction shear stress, but is insensitive to the X-direction and Z-direction positive pressure. Figure 6 In (d), the output voltage of the Y-direction sensitive unit is positive, which proves that the Y-direction sensitive unit has the ability to identify the direction of the Y-direction shear stress and also verifies the rationality of the theory described above. Figure 6 Figure (e) shows the relationship between the output voltage signals of the X-, Y-, and Z-direction sensitive units and pressure under positive Z-direction pressure. The sensitivity of the Z-direction rigid-flexible hybrid sensor array is 237mV / N, which is significantly greater than the sensitivity of the X- and Y-direction sensitive units. This shows that the X- and Y-direction sensitive units are not affected by positive pressure. Figure 6(f) shows the relationship between the output voltage signals of the X-axis sensitive unit, the Y-axis sensitive unit, and the Z-axis sensitive unit and the three-axis force under the conditions of the simultaneous existence of the X-axis positive shear stress, the Y-axis positive shear stress, and the Z-axis positive pressure. It can be seen that the sensitivity of the X-axis sensitive unit is 163mV / N, the sensitivity of the Y-axis sensitive unit is 164mV / N, and the sensitivity of the Z-axis rigid-flexible hybrid sensing array is 235mV / N. Figure 6 In (a), when the three-dimensional force sensor is subjected to shear stress in the X direction, the sensitivity of the X-direction sensitive unit is 164mV / N. Figure 6 In (b), when the three-dimensional force sensor is subjected to shear stress in the Y direction only, the sensitivity of the Y-direction sensitive unit is 165mV / N. Figure 6 In (e), when the three-dimensional force sensor is subjected to positive pressure in the Z direction only, the sensitivity of the Z-direction rigid-flexible hybrid sensing array is 237mV / N. It can be seen that the sensitivity change of each sensitive unit is very small, which further illustrates the high sensitivity of the X-, Y-, and Z-direction sensitive units to their respective axial loads, and the low response to loads in other directions. This shows that the designed sensor has high three-dimensional force measurement and decoupling performance, and can realize accurate measurement of three-dimensional force loads.

[0089] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A piezoelectric sensor electrode structure for three-dimensional force measurement, characterized by: It includes a lower sensitive layer, an isolation layer, and an upper rigid-flexible hybrid array stacked in sequence and sealed by a packaging structure; The lower sensitive layer is composed of a first lower sensitive unit (1) and a second lower sensitive unit (2) which are arranged perpendicular to each other and share a first intermediate sensitive layer (4); the first lower sensitive unit (1) includes a first upper electrode (3) and two independent first lower electrodes (5, 6), and the electrodes are staggered along the X-axis direction; the second lower sensitive unit (2) includes a second upper electrode (7) and two independent second lower electrodes (8, 9), and the electrodes are staggered along the Y-axis direction; The isolation layer (10) covers the upper surface of the lower sensitive layer to achieve electrical isolation between the lower sensitive layer and the upper rigid-flexible hybrid array; The upper rigid-flexible hybrid array (11) is arranged above the isolation layer (10), and includes a third lower electrode (12), a second intermediate sensitive layer (13), a distributed upper electrode (14), and a rigid column (15) stacked in sequence; The packaging structure comprises a lower surface packaging layer (16) and an upper surface packaging layer (17), which are used to seal the sensor.

2. The piezoelectric sensor electrode structure for three-dimensional force measurement according to claim 1, characterized in that: The distributed upper electrode (14) is formed by arranging a 3x3 upper electrode unit array, and the rigid column (15) is arranged corresponding to the distributed upper electrode (14), that is, each upper electrode unit corresponds to a rigid column (15), thereby realizing spatial distribution measurement of positive pressure.

3. The piezoelectric sensor electrode structure for three-dimensional force measurement according to claim 2, characterized in that: The rigid column (15) is located in the center of the distributed upper electrode, and the diameter of the rigid column (15) is smaller than the diameter of the distributed upper electrode (14), so that the upper sensitive layer can be completely located at d 31 with d 33 In hybrid mode, the sensor's positive pressure sensitivity is increased.

4. The piezoelectric sensor electrode structure for three-dimensional force measurement according to claim 1, characterized in that: The middle sensitive layer is made of polyvinylidene fluoride (PVDF) film, and the electrodes are made of sputtered metal material.

5. A decoupling method for the electrode structure of a piezoelectric sensor for three-dimensional force measurement according to any one of claims 1 to 4, characterized in that: include: Spatial polarization, the steps are as follows: A first lower electrode (5) of the first lower sensitive unit (1) and a second lower electrode (8) of the second lower sensitive unit (2) are connected to a positive high voltage, another first lower electrode (6) and another second lower electrode (9) are connected to a negative high voltage, the first upper electrode (3) and the second upper electrode (7) are grounded, a tilted polarization vector at 60° to the X-axis is formed inside the first lower sensitive unit (1), and a tilted polarization vector at 60° to the Y-axis is formed inside the second lower sensitive unit (2); The third lower electrode (12) of the upper rigid-flexible hybrid array (11) is connected to a positive high voltage, and the distributed upper electrode (14) is connected to a negative high voltage to achieve thickness direction polarization; Signal decoupling, the steps are as follows: When working, all lower electrodes (5, 6, 8, 9) of the lower sensitive layer are grounded, and the first upper electrode (3) thereof outputs a signal V x , the second upper electrode (7) outputs a signal V y ; The third lower electrode (12) of the upper rigid-flexible hybrid array (11) is grounded, and the distributed upper electrode (14) outputs a signal V z ; Three-dimensional force decoupling, the calculation process is as follows: Based on the signal V x and sensitivity coefficient S x , and signal V y and sensitivity coefficient S y Calculate the two-dimensional shear stress amplitude F s and the two-dimensional shear stress direction θ; Based on the Z-direction signal V z , sensitivity coefficient S z Calculate the positive pressure F z ; Combined with the two-dimensional shear stress amplitude F s , positive pressure F z Calculate the three-dimensional force amplitude F t and three-dimensional force cone angle 6. The decoupling method according to claim 5, characterized in that: The three-dimensional force amplitude F t The calculation formula is:

7. The decoupling method according to claim 6, characterized in that: The three-dimensional force cone angle The calculation formula is: Through the three-dimensional force cone angle Represents the angle between the three-dimensional force vector and the negative Z axis.

8. The decoupling method according to claim 5, characterized in that: The first lower sensitive unit (1) is only sensitive to shear stress in the X direction, the second lower sensitive unit (2) is only sensitive to shear stress in the Y direction, and the upper rigid-flexible hybrid array (14) is only sensitive to positive pressure in the Z direction.

9. The decoupling method according to claim 5, characterized in that: The arrangement of the staggered electrodes in the lower sensitive layer satisfies: The first upper electrode (3) of the first lower sensitive unit (1) is located in the middle of the two first lower electrodes (5, 6) in the X-axis direction; The second upper electrode (7) of the second lower sensitive unit (2) is located in the middle of the two second lower electrodes (8, 9) in the Y-axis direction.

10. The decoupling method according to claim 5, characterized in that: The tilted polarization vector of the lower sensitive layer is 60 degrees, so that the net charge output by the lower sensitive layer under the action of the normal force is zero, thereby achieving normal force interference shielding.

Images