Pre-tightening force automatic loading control method for piezoelectric stack driver based on capacitance feedback

Abstract

The application discloses a pre-tightening force automatic loading control method of a piezoelectric stack driver based on a capacitor feedback, characterized in that a capacitor value-pre-tightening force mapping model of the piezoelectric stack driver is first established; a pre-tightening force automatic loading mechanism is installed on an application device of the piezoelectric stack driver to automatically load an initial pre-tightening force; the capacitor value of the piezoelectric stack driver is automatically detected in a gap of a working cycle, and the pre-tightening force value of the piezoelectric stack driver in the gap of the working cycle is obtained through the mapping model; whether the pre-tightening force value is in a normal range is judged, if the pre-tightening force value deviates from the normal range and is in a pre-warning range, the pre-tightening force is automatically adjusted until the pre-tightening force is in the normal range; if the pre-tightening force value deviates from the normal range and is in a dangerous range, an alarm is given and the piezoelectric stack driver is stopped; the method has the advantages that the measurement result of the pre-tightening force is accurate and reliable, the control of the pre-tightening force is accurate and reliable, the piezoelectric stack driver is prevented from being damaged due to improper pre-tightening force, the service life of the piezoelectric stack driver is prolonged, and the stability of each cycle in long-term operation is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of piezoelectric precision drive control, and particularly relates to a pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitance feedback. BACKGROUND

[0002] The piezoelectric stack driver is a driving element composed of multiple layers of piezoelectric ceramic sheets connected in series or parallel through electrodes. Its working is based on the inverse piezoelectric effect of piezoelectric materials: when an alternating electric field is applied, the piezoelectric ceramic sheet produces a slight expansion along the polarization direction, and the output displacement can be amplified through the superposition of multiple layers. In the field of precision driving, the output accuracy, response speed and reliability of the piezoelectric stack driver directly determine the system performance. In order to make the piezoelectric stack driver achieve the best mechanical performance and ensure long service life, it is very important to apply appropriate pre-tightening force to the piezoelectric stack driver during assembly. Only under the action of appropriate pre-tightening force, the piezoelectric stack driver can achieve high-precision displacement output, fast response and long-term stable operation. The appropriate pre-tightening force not only ensures that the piezoelectric stack driver can quickly achieve accurate displacement output after the next start, but also effectively avoids performance degradation or structural damage caused by pre-tightening force deviation. If the pre-tightening force state of the piezoelectric stack driver is not checked in time and adjusted in time, the deviation caused by external factors (such as mechanical vibration leading to loosening of the connecting parts and making the pre-tightening force smaller, or environmental temperature rising and making the structure expand and squeeze the stack to make the pre-tightening force larger) will directly affect the next cycle performance of the piezoelectric stack driver: when the pre-tightening force is too small, the piezoelectric stack driver is prone to delamination or gap under dynamic loading next time, resulting in nonlinear relationship between displacement output and voltage, actual displacement significantly smaller than theoretical value, and positioning accuracy decreased; when the pre-tightening force is too large, the internal lattice of the piezoelectric ceramic sheet is excessively compressed, the conversion rate of the inverse piezoelectric effect is reduced, the displacement output is significantly attenuated after the next start, and even the piezoelectric ceramic sheet is broken, shortening the service life of the device.

[0003] Currently, the initial pre-tightening force loading of the piezoelectric stack driver mainly relies on manual experience adjustment, and the pre-tightening force is indirectly estimated by static measurement means such as torque wrench. This method has low loading accuracy and poor repeatability, and cannot achieve precise and automatic loading of the pre-tightening force. In the running and maintenance stage of the piezoelectric stack driver, the pre-tightening force is mainly monitored by the external force sensor, but the force sensor needs to be installed inside the device, occupying additional axial space, which conflicts with the demand for compact design of precision equipment. At the same time, the signal of the force sensor is easily affected by electromagnetic interference, and in high-frequency driving scenarios, zero drift may occur, affecting the measurement accuracy. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitor feedback, which can realize automatic and accurate loading of initial pre-tightening force, dynamic monitoring and compensation of pre-tightening force in the working cycle gap of the piezoelectric stack driver, has strong anti-interference ability, and realizes accurate pre-tightening force control.

[0005] The technical solution adopted by the present application to solve the above technical problem is a pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitor feedback, comprising the following specific steps:

[0006] (1) Establishing a capacitor value-pre-tightening force mapping model of the piezoelectric stack driver;

[0007] (2) Installing a pre-tightening force automatic loading mechanism on the application device of the piezoelectric stack driver, and automatically loading the initial pre-tightening force of the piezoelectric stack driver through the capacitor value-pre-tightening force mapping model;

[0008] (3) Automatically detecting the capacitor value of the piezoelectric stack driver in the gap of the working cycle, and obtaining the pre-tightening force value of the piezoelectric stack driver in the gap of the working cycle through the capacitor value-pre-tightening force mapping model;

[0009] (4) Judging whether the pre-tightening force value of the piezoelectric stack driver in the gap of the working cycle is within a normal range, if it deviates from the normal range and is within a pre-warning range, automatically adjusting the pre-tightening force through the pre-tightening force automatic loading mechanism until it is within the normal range, if the pre-tightening force value deviates from the normal range and is within a dangerous range, alarming and stopping.

[0010] Further, in step (1), before establishing the capacitor value-pre-tightening force mapping model, a pre-tightening force manual loading mechanism is constructed, specifically: at least two vertical fixed screw rods are arranged on a vibration isolation table, a force sensor is arranged or fixed between the screw rods, then the piezoelectric stack driver to be measured is placed on the force sensor, a pressure plate is sleeved on the screw rods, the pressure plate is pressed on the upper end of the piezoelectric stack driver, a pre-tightening nut is screwed on the screw rod, the pre-tightening nut abuts against the upper end surface of the pressure plate, and a capacitor measurement module is electrically connected to the piezoelectric stack driver, and the pre-tightening force applied by the pressure plate on the piezoelectric stack driver can be adjusted by manually rotating the pre-tightening nut.

[0011] Further, in step (1), the establishment process of the capacitor value-pre-tightening force mapping model is as follows:

[0012] (1.1) Manually rotating the pre-tightening nut and applying pre-tightening force on the piezoelectric stack driver by the pressure plate at the same interval value, while the force sensor detects the pre-tightening force received by the piezoelectric stack driver in real time;

[0013] (1.2) when the force sensor detects that the pre-tightening force of the first interval point remains unchanged, the capacitance value of the piezoelectric stack driver corresponding to the pre-tightening force of the interval point is measured by the capacitance measurement module;

[0014] (1.3) repeating step (1.2) to sequentially measure the capacitance value of the piezoelectric stack driver corresponding to the pre-tightening force of each interval point;

[0015] (1.4) establishing a capacitance value-pre-tightening force mapping model of the piezoelectric stack driver by function fitting.

[0016] Further, the function fitting adopts a five-order polynomial fitting, and the correlation coefficient R of the capacitance value-pre-tightening force mapping model is greater than or equal to 0.995. 2

[0017] Further, in step (2), the pre-tightening force automatic loading mechanism is an electric push rod fixed on an application device of the piezoelectric stack driver, and the capacitance measurement module is electrically connected with the piezoelectric stack driver in the application device, the electric push rod automatically applies an initial pre-tightening force to the piezoelectric stack driver, the capacitance measurement module synchronously and real-timely measures the capacitance value of the piezoelectric stack driver, and the corresponding initial pre-tightening force value is obtained through the capacitance value-pre-tightening force mapping model in step (1), when the initial pre-tightening force value reaches a predetermined value, the electric push rod stops working, and the initial pre-tightening force of the piezoelectric stack driver is automatically loaded.

[0018] Further, in step (3), the capacitance value of the piezoelectric stack driver in the working cycle interval is real-timely measured by the capacitance measurement module.

[0019] Further, the capacitance measurement module used in steps (1)-(3) all adopts an LCR tester.

[0020] Further, in step (4), when the pre-tightening force value of the piezoelectric stack driver in the working cycle interval is in a pre-warning range, the electric push rod is extended or retracted to increase or decrease the pre-tightening force applied to the piezoelectric stack driver until the pre-tightening force value corresponding to the capacitance value of the piezoelectric stack driver measured by the capacitance measurement module is in a normal range, and the electric push rod stops working.

[0021] Further, in step (4), when the pre-tightening force value of the piezoelectric stack driver in the working cycle interval is in a pre-warning range, the adjustment amount of the electric push rod required to make the pre-tightening force value of the piezoelectric stack driver in a normal range is calculated through a PID closed-loop control algorithm, and the electric push rod adjusts the pre-tightening force applied to the piezoelectric stack driver according to the adjustment amount, so that the pre-tightening force value of the piezoelectric stack driver is in the normal range.

[0022] Compared with the prior art, the application has the following advantages: ​

[0023] (1), the pre-established piezoelectric stack driver capacitance value-tightness mapping model, so that in the piezoelectric stack driver application device without additional installation of force sensor to measure the piezoelectric stack driver pre-tightness, avoid the force sensor in the application device in the axial space occupation, meet the needs of some precision equipment compact design; At the same time, fundamentally avoid the problem that the force sensor signal is easy to be disturbed by electromagnetic interference, so that the measurement result of pre-tightness is accurate and reliable, so that the control of pre-tightness is accurate and reliable;

[0024] (2), the pre-tightness automatic loading mechanism is used to automatically and accurately load the piezoelectric stack driver before work, so as to avoid damage to the piezoelectric stack driver due to improper pre-tightness; And the pre-tightness of the piezoelectric stack driver is monitored and adjusted in real time during the working cycle gap, so as to prevent the continuous damage to the piezoelectric stack driver caused by excessive or insufficient pre-tightness, prolong the service life of the piezoelectric stack driver, and ensure the stability of each cycle in long-term operation;

[0025] (3), the adjustment of pre-tightness is limited to the working cycle gap of the piezoelectric stack driver, which ensures the absolute stability of the piezoelectric driving process;

[0026] (4), compared with the traditional pre-tightness manual loading and adjustment, the method is more convenient and controllable in precision, and avoids the influence of the next cycle operation due to the delay of manual operation. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is the structure diagram of the pre-tightness manual loading mechanism of the present application;

[0028] Figure 2 is the fitting curve of the piezoelectric stack driver capacitance value-pre-tightness obtained by five-order polynomial fitting of the present application;

[0029] Figure 3 is the installation schematic diagram of the pre-tightness automatic loading mechanism of the present application on the piezoelectric injection valve;

[0030] Figure 4 is the flow chart of the present application. DETAILED DESCRIPTION

[0031] The present application is further described in detail in the following embodiment combined with the drawings.

[0032] As Figures 1-4 shown, the pre-tightness automatic loading control method of piezoelectric stack driver based on capacitance feedback includes the following specific steps:

[0033] (1), first, construct a pre-tightness manual loading mechanism, as Figure 1As shown, specifically: on the vibration isolation platform 1, two screw rods 2 are vertically fixed, a force sensor 3 is placed or fixed between the screw rods 2, then the piezoelectric stack driver 4 to be measured is placed on the force sensor 3, a pressing plate 5 is sleeved on the screw rods 2, the pressing plate 5 is pressed on the upper end of the piezoelectric stack driver 4, a pre-tightening nut 6 is screwed on the screw rod 2, the pre-tightening nut 6 abuts against the upper end surface of the pressing plate 5, and the piezoelectric stack driver 4 is electrically connected with an LCR tester 7; after the pre-tightening force manual loading mechanism is constructed, the piezoelectric stack driver's capacitance value-pre-tightening force mapping model is established according to the following process:

[0034] (1.1), manually screw the pre-tightening nut 6 and apply pre-tightening force to the piezoelectric stack driver 4 by the pressing plate 5 at the same interval value (for example: interval value is 100N), while the force sensor 3 detects the pre-tightening force received by the piezoelectric stack driver 4 in real time;

[0035] (1.2), when the force sensor 3 detects that the pre-tightening force at the first interval point (for example: 0N or 100N) remains unchanged, the capacitance value of the piezoelectric stack driver 4 corresponding to the pre-tightening force at the interval point is measured by the LCR tester 7;

[0036] (1.3), repeat step (1.2) to sequentially measure the capacitance value of the piezoelectric stack driver 4 corresponding to the pre-tightening force at each interval point (200N, 300N, …);

[0037] (1.4), the capacitance value-pre-tightening force mapping model of the piezoelectric stack driver 4 is established by fitting the above measured pre-tightening force and the corresponding capacitance value by a five-order polynomial, that is:

[0038] ,

[0039] Wherein: F represents the pre-tightening force of the piezoelectric stack driver 4, C represents the capacitance value corresponding to the pre-tightening force F received by the piezoelectric stack driver 4, a 0、 a 1、 a 2、 a 3、 a 4、 a 5 represents the fitting coefficient of the capacitance value-pre-tightening force mapping model, and the correlation coefficient R 2 ≥0.995 of the capacitance value-pre-tightening force mapping model;

[0040] (2), the piezoelectric stack driver 4 that has been measured in step (1) is disassembled and installed in an application device 9 (such as a piezoelectric injection valve), then an electric push rod 8 is fixedly installed on the application device, other linear driving mechanisms can also be used instead of the electric push rod 8, and the LCR tester 7 is electrically connected with the piezoelectric stack driver 4 in the application device, such as Figure 3As shown, the electric push rod 8 extends to automatically apply the initial preload force to the piezoelectric stack driver 4, the LCR tester 7 synchronously measures the capacitance value of the piezoelectric stack driver 4 in real time, and the corresponding initial preload force value is calculated through the capacitance value-preload force mapping model in step (1), when the initial preload force value reaches the predetermined value, the electric push rod 8 stops working, and the initial preload force of the piezoelectric stack driver 4 is automatically loaded;

[0041] (3) When the piezoelectric stack driver 4 completes a working cycle and stops (i.e. the gap of the working cycle), the LCR tester 7 automatically detects the capacitance value in real time, and the preload force value of the piezoelectric stack driver 4 in the working cycle gap is calculated through the capacitance value-preload force mapping model;

[0042] (4) Determine whether the preload force value of the piezoelectric stack driver 4 in the working cycle gap is within the normal range, if it deviates from the normal range and is within the warning range, the electric push rod 8 extends or retracts to increase or decrease the preload force applied to the piezoelectric stack driver 4, until the capacitance value of the piezoelectric stack driver 4 measured by the LCR tester 7 corresponds to the preload force value within the normal range, and the electric push rod 8 stops working; if the preload force value deviates from the normal range and is within the dangerous range, an alarm is given and the machine is stopped.

[0043] In step (4) of the above embodiment, when the preload force value of the piezoelectric stack driver 4 in the working cycle gap is within the warning range, other methods can also be used to adjust the preload force of the piezoelectric stack driver 4, such as: first calculating the adjustment amount of the electric push rod 8 required to make the preload force value of the piezoelectric stack driver 4 within the normal range through the PID closed-loop control algorithm, and adjusting the preload force applied to the piezoelectric stack driver 4 by the electric push rod 8 can make it within the normal range.

[0044] In addition, in order to avoid excessive adjustment caused by small fluctuations in preload force, while ensuring the necessity of adjustment, in steps (3)-(4) above, in the gap of the working cycle of the piezoelectric stack driver 4, the electric push rod 8 only automatically adjusts the preload force or stops and alarms after the preload force values corresponding to the capacitance values detected by the LCR tester 7 for two consecutive times exceed the normal range.

[0045] In order to realize the automatic loading control of the pre-tightening force of the piezoelectric stack driver 4, the predetermined value of the initial pre-tightening force of the piezoelectric stack driver 4 and the normal range of the pre-tightening force of the working cycle gap can be preset in the comparison module, the LCR tester 7 sends the measured capacitance value to the controller, the controller calculates the corresponding pre-tightening force value through the capacitance value-pre-tightening force mapping model, and then sends the pre-tightening force value to the comparison module and compares it with the predetermined value of the initial pre-tightening force or the normal range of the pre-tightening force of the working cycle gap, if not reached, the controller controls the electric push rod 8 to work according to the requirements in the corresponding steps; if reached, the controller controls the electric push rod 8 to stop working.

[0046] The protection scope of the present application includes but is not limited to the above embodiments, and the protection scope is subject to the claims, and any replacement, deformation, improvement of the present technology that can be easily thought of by those skilled in the art falls within the protection scope of the present application.

Claims

1. A method of pre-tension automatic loading control of a piezoelectric stack driver based on capacitive feedback, characterized by The method comprises the following specific steps: (1) first, construct a pre-tightening force manual loading mechanism, specifically: at least two vertical fixed screw on the vibration isolation platform, between the screw placed or fixed force sensor, then the piezoelectric stack driver to be measured is placed on the force sensor, and the pressure plate is sleeved on the screw, the pressure plate is pressed on the upper end of the piezoelectric stack driver, the screw is screwed with a pre-tightening nut, the pre-tightening nut is pressed against the upper end surface of the pressure plate, the piezoelectric stack driver is electrically connected with the capacitance measurement module, the pre-tightening force of the pressure plate on the piezoelectric stack driver can be adjusted by manually rotating the pre-tightening nut; then the capacitance value-pre-tightening force mapping model of the piezoelectric stack driver is established; (2) install the pre-tightening force automatic loading mechanism on the application device of the piezoelectric stack driver, and automatically load the initial pre-tightening force of the piezoelectric stack driver through the capacitance value-pre-tightening force mapping model; (3) automatically detect the capacitance value of the piezoelectric stack driver in the working cycle gap, and obtain the pre-tightening force value of the piezoelectric stack driver in the working cycle gap through the capacitance value-pre-tightening force mapping model; (4) judge whether the pre-tightening force value of the piezoelectric stack driver in the working cycle gap is in the normal range, if it deviates from the normal range and is in the warning range, the pre-tightening force is automatically adjusted through the pre-tightening force automatic loading mechanism until it is in the normal range; if the pre-tightening force value deviates from the normal range and is in the dangerous range, an alarm is given and the machine is stopped.

2. The pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitance feedback according to claim 1, characterized by: In the step (1), the establishment process of the capacitance value-pre-tightening force mapping model is as follows: (1.1) manually rotate the pre-tightening nut and make the pressure plate apply pre-tightening force to the piezoelectric stack driver at the same interval value, while the force sensor detects the pre-tightening force received by the piezoelectric stack driver in real time; (1.2) when the force sensor detects that the pre-tightening force of the first interval point remains unchanged, measure the capacitance value of the piezoelectric stack driver corresponding to the pre-tightening force of the interval point through the capacitance measurement module; (1.3) repeat step (1.2) to measure the capacitance value of the piezoelectric stack driver corresponding to the pre-tightening force of each interval point; (1.4) establish the capacitance value-pre-tightening force mapping model of the piezoelectric stack driver through function fitting.

3. The pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitance feedback according to claim 2, characterized by: The function fitting adopts a fifth-order polynomial fitting, and the correlation coefficient R of the capacitance value-pre-tightening force mapping model is ≥0.

995. 2 ≥0.

995.

4. The pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitance feedback according to claim 1, characterized by: In the step (2), the pre-tightening force automatic loading mechanism is an electric push rod fixed on the application device of the piezoelectric stack driver, and the capacitance measurement module is electrically connected with the piezoelectric stack driver in the application device, the electric push rod automatically applies initial pre-tightening force to the piezoelectric stack driver, the capacitance measurement module synchronously measures the capacitance value of the piezoelectric stack driver in real time, and the corresponding initial pre-tightening force value is obtained through the capacitance value-pre-tightening force mapping model of step (1), when the initial pre-tightening force value reaches the predetermined value, the electric push rod stops working, and the initial pre-tightening force of the piezoelectric stack driver is automatically loaded.

5. The pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitance feedback according to claim 4, characterized by: In the step (3), the capacitance value of the piezoelectric stack driver in the working cycle gap is measured in real time through the capacitance measurement module.

6. The pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitance feedback according to claim 5, characterized by: The capacitance measurement module adopts an LCR tester.

7. The pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitance feedback according to claim 4, characterized by: In the step (4), when the pre-tightening force value of the piezoelectric stack actuator is in the pre-warning range during the working cycle gap, the electric push rod is extended or retracted to increase or decrease the pre-tightening force applied to the piezoelectric stack actuator until the pre-tightening force value corresponding to the capacitance value of the piezoelectric stack actuator measured by the capacitance measurement module is in the normal range, and the electric push rod stops working.

8. The pre-tightening force automatic loading control method of a piezoelectric stack driver based on capacitance feedback according to claim 4, characterized by: In the step (4), when the pre-tightening force value of the piezoelectric stack actuator is in the pre-warning range during the working cycle gap, the adjustment amount of the electric push rod required to make the pre-tightening force value of the piezoelectric stack actuator be in the normal range is calculated through a PID closed-loop control algorithm, and the electric push rod adjusts the pre-tightening force applied to the piezoelectric stack actuator according to the adjustment amount, so that the pre-tightening force value of the piezoelectric stack actuator is in the normal range.

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