A displacement self-sensing piezoelectric actuator based on flexoelectric effect

Abstract

A displacement self-sensing piezoelectric actuator based on the flexoelectric effect is constructed by installing a trapezoidal spring-shaped sensing element with a strong flexoelectric effect made of a special material in the diamond ring of a traditional piezoelectric ceramic actuator. Under low-amplitude vibration conditions, charge will accumulate at both ends of the element, and the amount of charge depends on the strain gradient of the spring-shaped sensing element. Therefore, by measuring the amount of charge generated, the deformation of the spring-shaped sensing element can be obtained, which also represents the output displacement of the actuator. The device integrates the output and sensing functions of the actuator, avoiding the problem of additional supporting displacement sensing devices in actual use of the actuator, thereby expanding the scope of use of the actuator. The device has a compact structure and small size, and adopts a displacement sensing device based on the flexoelectric effect, with the characteristics of high actuation accuracy and displacement sensing accuracy.

Description

Technical Field

[0001] The present invention relates to a displacement self-sensing actuating device, in particular to a displacement self-sensing piezoelectric actuator based on the flexoelectric effect. Background Art

[0002] High-precision actuators made of piezoelectric ceramics are widely used in aerospace engineering, precision machine tools, and precision medical devices due to their fast response, high precision, and compact size. However, due to the properties of piezoelectric materials and the non-linear relationship between strain and applied voltage, precise displacement output from piezoelectric ceramic actuators requires closed-loop control. Consequently, piezoelectric ceramic actuators often require additional displacement sensors. The use of displacement sensors increases the size, weight, and cost of the entire actuator mechanism. Integrating displacement sensors with piezoelectric actuators offers a novel approach to addressing this issue, as exemplified by invention patents such as CN201510116738.9, "Stepping Piezoelectric Actuator and Method with Displacement Measurement and High Push-Pull Force," and CN201810354487.1, "Linear Inertial Piezoelectric Actuator and Method with Displacement Sensing." However, these inventions still suffer from drawbacks such as large actuator size and low displacement sensing accuracy. Therefore, there is an urgent need for a piezoelectric ceramic actuator with a compact structure and high displacement sensing accuracy. Summary of the Invention

[0003] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a displacement self-sensing piezoelectric actuator based on the flexoelectric effect, which can realize real-time measurement of the actuator output displacement without the need for additional displacement sensing devices.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A displacement self-sensing piezoelectric actuator based on the flexoelectric effect, the actuator includes an outer shell, a corresponding installation space is reserved inside the outer shell, the outer shell has an opening for leading out the lead, a pre-tightening screw 2 is screwed in from the left side of the outer shell, and is used to adjust the pre-tightening force after the actuator is installed, the base 3 is located between the pre-tightening screw 2 and the gasket 4 and is tightly bonded to the gasket 4; the piezoelectric stack 6 is installed with an interference fit on the long axis of the diamond ring 8, and the spring-shaped sensor element 7 with different electrodes plated on the upper and lower side surfaces is bonded to the piezoelectric sheet 9 and installed in the diamond ring, and The piezoelectric stack 6 is installed inside the spring-shaped sensor element 7. The piezoelectric stack 6, the spring-shaped sensor element 7, the diamond ring 8 and the piezoelectric sheet 9 constitute an integrated actuating sensor mechanism. In the initial state, the spring-shaped sensor element 7 is in a compressed state. The left side of the consolidation fixture 5 is tightly bonded to the gasket 4, and the right side is fixedly connected to the left side of the long axis of the diamond ring 8. The right side of the long axis of the diamond ring 8 is consolidated with the output rod 10. The limiting ring 11 sleeved on the output rod 10 is installed in the mounting groove reserved in the external shell, and the output rod 10 is passed through the middle to ensure the linear accuracy of the displacement output.

[0006] By applying a corresponding voltage to the piezoelectric stack 6, a high-precision output of the target displacement is achieved. After the voltage is applied to the piezoelectric stack 6, the piezoelectric stack 6 stretches, causing the piezoelectric plate 9 to vibrate at a low amplitude. Electric charges are generated at both ends of the spring-shaped sensor element 7. The amount of charge is related to the strain gradient of the spring-shaped sensor element 7. By measuring the amount of charge, the strain of the spring-shaped sensor element 7 is obtained, and then the actual output displacement of the actuator is obtained. The actuator realizes the integrated function of displacement and sensing.

[0007] The displacement self-sensing piezoelectric actuator based on the flexoelectric effect has the following working principle of displacement sensing: under static load, the charge on the spring-shaped sensor element 7 is not continuously generated. Therefore, when the charge or voltage measurement is connected, the instantaneous discharge phenomenon is not conducive to accurate measurement. The measurement of the flexoelectric effect must be under the condition of vibration of the spring-shaped sensor element 7; the piezoelectric piece 9 always maintains a low-amplitude vibration, driving the vibration of the spring-shaped sensor element 7, and because the stiffness of the spring-shaped sensor element 7 is less than the stiffness of the diamond ring 8, the vibration of the piezoelectric piece 9 has a negligible effect on the output of the actuator.

[0008] The displacement sensing calibration method of the displacement self-sensing piezoelectric actuator based on the flexoelectric effect is as follows: after the actuator is installed, the spring-shaped sensor element 7 is in a compressed state. At this time, under the low-amplitude vibration of the piezoelectric piece 9, the measured charge generated is Q0; when the actuator outputs a positive displacement of x1, the compression of the spring-shaped sensor element 7 decreases, and the strain gradient decreases, and the charge generated at this time is Q1; when the actuator outputs a reverse displacement of x2, the compression of the spring-shaped sensor element 7 increases, and the strain gradient increases, and the charge generated at this time is Q2; through the calibration of the above experiment, the relationship between the displacement output x and the charge Q of the actuator can be determined.

[0009] Preferably, the material of the spring-shaped sensing element 7 is polyvinylidene fluoride (PVDF). The use of this material can enhance the flexoelectric effect of the structure and improve the accuracy of the sensing output. In addition, the material has low stiffness and has little impact on the measured structure when used.

[0010] Preferably, in order to enhance the flexoelectric effect of the spring-shaped sensing element 7 , the cross-section of the spring-shaped sensing element 7 is trapezoidal, so as to increase the strain gradient when it is subjected to force.

[0011] Preferably, the piezoelectric stack 6 is made of piezoelectric ceramics.

[0012] Preferably, the outer shell is composed of a left outer shell 1-1 and a right outer shell 1-2 fixed together, which is easy to install.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. The present invention realizes the integration of output and sensing of the actuator, avoiding the problem of the actuator needing an additional displacement sensor in actual use.

[0015] 2. The present invention has a compact structure, small size, light weight, and adopts the flexoelectric effect to achieve high displacement sensing accuracy.

[0016] 3. The present invention uses piezoelectric ceramics as the driving unit, so that the displacement output of the actuator has the characteristics of high precision and fast response. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the explosion of the actuator of the present invention.

[0018] Figure 2 This is a schematic diagram of the actuator assembly of the present invention.

[0019] Figure 3 Schematic diagram of the internal structure assembly of the actuator of the present invention.

[0020] Figure 4 Schematic diagram of the flexoelectric effect principle of the cantilever beam.

[0021] Figure 5 A spring-shaped sensing element used in the actuator of the present invention and a cross-sectional view thereof.

[0022] Figure 6 This is a calibration principle diagram of the actuator of the present invention (the curve in the figure only shows the relationship trend). DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 、 Figure 2 and Figure 3 As shown, the present invention is a displacement self-sensing piezoelectric actuator based on the flexoelectric effect. The actuator is composed of a left shell 1-1 and a right shell 1-2 fixed together to form an external shell. A corresponding installation space is reserved inside the shell, and an opening is provided on the left shell 1-1 for leading out the lead wire. The pre-tightening screw 2 is screwed in from the left side of the shell 1-1 and is used to adjust the pre-tightening force after the actuator is installed. The base 3 is located between the pre-tightening screw 2 and the gasket 4 and is tightly bonded to the gasket 4 on its right side. The piezoelectric stack 6 is installed with an interference fit with the long axis of the diamond ring 8. The spring-shaped sensor element 7 with different electrodes plated on the upper and lower side surfaces is connected to the piezoelectric After bonding, the piezoelectric stack 9 is installed in the diamond ring, and the piezoelectric stack 6 is mounted inside the spring-shaped sensor element 7. The piezoelectric stack 6, spring-shaped sensor element 7, diamond ring 8, and piezoelectric stack 9 form an integrated actuation and sensing mechanism. Initially, the spring-shaped sensor element 7 is in compression. The left side of the fixing fixture 5 is tightly bonded to the gasket 4, and the right side is screwed to the left side of the diamond ring's long axis 8. The right side of the diamond ring's long axis is fixed to the output rod 10. The limiting ring 11, which is sleeved on the output rod 10, is installed in a reserved mounting groove in the right housing 1-2, with the output rod 10 extending from the center to ensure linear accuracy of the displacement output. After the above parts are installed, the left and right housings 1-1 and 1-2 are tightened with screws.

[0025] After the installation is completed, by applying the corresponding voltage to the piezoelectric stack 6, high-precision output of the target displacement can be achieved. After the voltage is applied to the piezoelectric stack 6, the piezoelectric stack 6 stretches to cause the piezoelectric piece 9 to vibrate at a low amplitude, and electric charges will be generated at both ends of the spring-shaped sensor element 7. The amount of charge is related to the strain gradient of the spring-shaped sensor element 7. By measuring the amount of charge, the strain of the spring-shaped sensor element 7 can be obtained, and then the actual output displacement of the actuator can be obtained. The actuator realizes the integrated function of displacement and sensing.

[0026] The displacement sensing design principle of the displacement self-sensing piezoelectric actuator based on the flexoelectric effect is as follows: the flexoelectric effect is an electric polarization effect generated by strain gradient, which converts the non-uniform deformation in the material into a mechanoelectric coupling effect of voltage. It is widely present in all dielectric materials and has higher temperature stability than the piezoelectric effect. For example, Figure 4 As shown in the figure, the cantilever beam is subjected to the force F at the end, its upper surface is tensile, and its lower surface is compressed. There is a strain gradient along the y-axis direction. Under the influence of the flexoelectric effect, charges will accumulate on its upper and lower surfaces, and the amount of charge will increase as the strain gradient increases. When the two ends of the spring-shaped sensor element 7 are subjected to tension or pressure, its flexoelectric effect is similar to that of the cantilever beam, as shown in the figure. Figure 5 As shown, the upper and lower surfaces of the spring-shaped sensor element 7 are respectively plated with different electrodes, and leads for measurement are led out; in order to enhance the flexoelectric effect of the spring-shaped sensor element 7, the cross-section of the spring-shaped sensor element 7 is designed to be trapezoidal to increase the strain gradient when it is subjected to force.

[0027] The displacement self-sensing piezoelectric actuator based on the flexoelectric effect has the following working principle of displacement sensing: under static load, the charge on the spring-shaped sensor element 7 is not continuously generated. Therefore, when the charge or voltage measurement is connected, the instantaneous discharge phenomenon is not conducive to accurate measurement. The measurement of the flexoelectric effect must be under the condition of vibration of the spring-shaped sensor element 7; the piezoelectric piece 9 always maintains a low-amplitude vibration, driving the vibration of the spring-shaped sensor element 7, and because the stiffness of the spring-shaped sensor element 7 is much smaller than the stiffness of the diamond ring 8, the vibration of the piezoelectric piece 9 has a negligible effect on the output of the actuator.

[0028] The displacement sensing calibration method of the displacement self-sensing piezoelectric actuator based on the flexoelectric effect is as follows: after the actuator is installed, the spring-shaped sensor element 7 is in a compressed state. At this time, when the piezoelectric piece 9 is vibrated at a low amplitude, Figure 6 As shown, the amount of charge generated can be measured as Q0; when the output rod 10 of the actuator moves to the right, that is, when the output positive displacement is x1, the compression of the spring-shaped sensor element 7 decreases, and the strain gradient decreases. At this time, the amount of charge generated is Q1; when the output rod 10 of the actuator moves to the left, that is, when the output reverse displacement is x2, the compression of the spring-shaped sensor element 7 increases, and the strain gradient increases. At this time, the amount of charge generated is Q2; through the calibration of the above experiment, the relationship between the displacement output x and the charge Q of the actuator can be determined.

Claims

1. A displacement self-sensing piezoelectric actuator based on the flexoelectric effect, characterized by: The actuator comprises an external shell, a corresponding installation space is reserved inside the external shell, the external shell has an opening for leading out a lead, a pre-tightening screw (2) is screwed in from the left side of the external shell, and is used for adjusting the pre-tightening force after the actuator is installed, a base (3) is located between the pre-tightening screw (2) and the gasket (4) and is tightly bonded to the gasket (4); the piezoelectric stack (6) is installed with an interference fit with the long axis of the rhombus ring (8), the spring-shaped sensor element (7) with different electrodes plated on the upper and lower side surfaces is bonded to the piezoelectric sheet (9) and installed in the rhombus ring, and the piezoelectric stack (6) is installed on the spring-shaped sensor element Inside the component (7), the piezoelectric stack (6), the spring-shaped sensor element (7), the diamond ring (8) and the piezoelectric sheet (9) form an actuating sensor integrated mechanism. In the initial state, the spring-shaped sensor element (7) is in a compressed state. The left side of the consolidation fixture (5) is tightly bonded to the gasket (4), and the right side is fixedly connected to the left side of the long axis of the diamond ring (8). The right side of the long axis of the diamond ring (8) is consolidated with the output rod (10). The limiting ring (11) sleeved on the output rod (10) is installed in the mounting groove reserved in the external housing, and the output rod (10) is passed through the middle to ensure the linear accuracy of the displacement output.

2. The displacement self-sensing piezoelectric actuator based on the flexoelectric effect according to claim 1, characterized in that: By applying a corresponding voltage to the piezoelectric stack (6), a high-precision output of a target displacement is achieved. After the voltage is applied to the piezoelectric stack (6), the piezoelectric stack (6) stretches, causing the piezoelectric sheet (9) to vibrate at a low amplitude. Electric charges are generated at both ends of the spring-shaped sensing element (7), and the amount of the charge is related to the strain gradient of the spring-shaped sensing element (7). By measuring the amount of the charge, the strain of the spring-shaped sensing element (7) is obtained, and then the actual output displacement of the actuator is obtained. The actuator realizes the integrated function of displacement and sensing.

3. The displacement self-sensing piezoelectric actuator based on the flexoelectric effect according to claim 1, characterized in that: The calibration method of the displacement sensor is as follows: after the actuator is installed, the spring-shaped sensor element (7) is in a compressed state. At this time, under the low-amplitude vibration of the piezoelectric plate (9), the generated charge is measured to be Q0; when the actuator outputs a positive displacement of x1, the compression of the spring-shaped sensor element (7) decreases, the strain gradient decreases, and the generated charge is Q1; when the actuator outputs a reverse displacement of x2, the compression of the spring-shaped sensor element (7) increases, the strain gradient increases, and the generated charge is Q2; through the above-mentioned displacement sensor calibration method, the relationship between the displacement output x of the actuator and the charge Q can be determined.

4. The displacement self-sensing piezoelectric actuator based on the flexoelectric effect according to claim 1, characterized in that: The measurement of the flexoelectric effect requires that the piezoelectric piece (9) always maintains low-amplitude vibration to drive the vibration of the spring-shaped sensor element (7). Since the stiffness of the spring-shaped sensor element (7) is less than the stiffness of the diamond ring (8), the effect of the vibration of the piezoelectric piece (9) on the output of the actuator is negligible.

5. The displacement self-sensing piezoelectric actuator based on the flexoelectric effect according to claim 1, characterized in that: The material of the spring-shaped sensing element (7) is polyvinylidene fluoride (PVDF).

6. The displacement self-sensing piezoelectric actuator based on the flexoelectric effect according to claim 1, characterized in that: In order to enhance the flexoelectric effect of the spring-shaped sensing element (7), the cross section of the spring-shaped sensing element (7) is trapezoidal, so as to increase the strain gradient when the spring-shaped sensing element (7) is subjected to force.

7. The displacement self-sensing piezoelectric actuator based on the flexoelectric effect according to claim 1, characterized in that: The piezoelectric stack (6) is a piezoelectric ceramic.

8. The displacement self-sensing piezoelectric actuator based on the flexoelectric effect according to claim 1, characterized in that: The external shell is composed of a left shell (1-1) and a right shell (1-2) which are fixed together.

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