An ultrahigh frequency control system and method for piezoelectric stack actuators

Abstract

This invention discloses an ultra-high frequency control system and method for piezoelectric stack actuators. The system includes a LabVIEW-based high sampling rate drive control system and a charge amplifier. The LabVIEW-based high sampling rate drive control system generates drive signals for the piezoelectric stack actuator, acquires displacement signals of the piezoelectric stack actuator, and processes the acquired displacement signals and drive signals to obtain control signals for the piezoelectric stack actuator. The control signals are output to the charge amplifier, which receives and amplifies the control signals. The amplified control signals are then sent to the piezoelectric stack actuator. This invention achieves high-precision trajectory tracking of the piezoelectric actuator at high operating frequencies, with tracking errors reaching the tens of nanometers level under high-frequency operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of precision actuator drive and charge drive technology, specifically relating to an ultra-high frequency control system and method for piezoelectric stack actuators. Background Technology

[0002] Piezoelectric actuators are based on the inverse piezoelectric effect of piezoelectric element materials. When an electric field is applied along the polarization direction, the dielectric will generate reversible mechanical deformation or stress in a specific direction. The deformation disappears when the electric field is removed. This effect can be used to obtain driving force to move the actuator. Since its invention, piezoelectric actuators have received long-term attention and in-depth research, leading to the improvement and maturity of piezoelectric ceramic actuators. Piezoelectric stacked actuators have advantages such as high response and high resolution, and are widely used in high-speed tool servo, precision positioning platforms, and micro-nano manipulation scenarios. Despite the many advantages of piezoelectric micro-displacement actuators, they also face several limitations and drawbacks, such as difficulty in achieving good operation at high frequencies. To address this issue, numerous experts and scholars both domestically and internationally have conducted research on their structure and control methods, achieving certain research results.

[0003] Besides external factors such as control methods and structural optimization, the hysteresis and creep effects inherent in piezoelectric materials are also major factors affecting their operating bandwidth. Due to the inherent hysteresis and creep characteristics of piezoelectric materials, there is a significant nonlinear relationship between actuator displacement and driving voltage under traditional voltage-driven methods, leading to tracking and positioning errors. This phenomenon is more pronounced at high frequencies, making it difficult to achieve good operation at high frequencies. Some researchers have proposed that piezoelectric ceramics can be regarded as nonlinear capacitors whose capacitance changes with voltage. Under voltage driving, the change in the equivalent capacitance of the piezoelectric actuator causes a change in the charge at its two ends, resulting in hysteresis and creep phenomena. If the charge (or current) at the two ends of the actuator is directly controlled to change linearly with time, the displacement of the piezoelectric actuator becomes approximately proportional to the charge at its two ends, thus proposing a charge-driven scheme. Although the charge-driven method has been proposed for decades and has gradually completed the transformation from theoretical feasibility verification to practical problem solving, its development is still constrained by many limitations. The main limiting factors include (1) limited control performance, especially in the low-frequency range, i.e., frequency dependence; (2) difficulty in matching AC and DC gains in the drive circuit, leading to output voltage drift; (3) long settling time in the circuit, affecting the system's stabilization speed; and (4) floating load configuration, which may damage the piezoelectric actuator. Due to the complex coupling relationship between these problems, it is difficult to solve them simultaneously by a single means.

[0004] To date, numerous experts and scholars both domestically and internationally have conducted research on charge-driven methods for piezoelectric actuators and achieved certain research results. However, the solutions to the problems of traditional charge-driven circuit structures are still not perfect, focusing only on addressing one or two defects. For example, Fleming et al. developed a novel circuit with active DC stabilization to address the frequency dependence characteristics of traditional charge-driven circuits (FLEMING A J. Charge drive with active DC stabilization for linearization of piezoelectric hysteresis [J].IEEE transactions on ultrasonics, ferroelectrics, and frequency control,2013, 60(8): 1630–7.). This circuit utilizes a controlled current source with voltage feedback to stabilize low-frequency behavior, but it still exhibits certain frequency dependence characteristics, and the piezoelectric actuator is configured with a floating load. In China, Yang et al. from Harbin Institute of Technology designed a nonlinear charge drive circuit (YANG C, LI C, ZHAO J. A nonlinear charge controller with tunable precision for highly linear operation of piezoelectric stack actuators [J]. IEEE Transactions on Industrial Electronics, 2017, 64(11): 8618–25.), aiming to achieve high-precision open-loop drive without using displacement sensors and without needing to establish a hysteresis model for piezoelectric materials. This scheme processes the output voltage of a traditional linear charge drive circuit as a feedback signal and sets adjustable parameters to improve the overcompensation effect of charge drive. Although it exhibits a relatively good hysteresis suppression effect, it still uses a traditional resistive DC path for charge release, which cannot avoid limited control accuracy in the low-frequency range. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, this invention proposes an ultra-high frequency control system and method for piezoelectric stack actuators, enabling the piezoelectric stack actuators to maintain good operational stability and control accuracy under ultra-high operating frequency conditions.

[0006] The technical solution adopted in this invention is:

[0007] An ultra-high frequency control system for a piezoelectric stack actuator includes a LabVIEW-based high sampling rate drive and control system and a charge amplifier. The LabVIEW-based high sampling rate drive and control system generates a drive signal for the piezoelectric stack actuator, acquires a displacement signal of the piezoelectric stack actuator, and processes the acquired displacement signal and drive signal to obtain a control signal for the piezoelectric stack actuator. The control signal is output to the charge amplifier, which receives and amplifies the control signal. The amplified control signal is then sent to the piezoelectric stack actuator.

[0008] Furthermore, the LabVIEW-based high sampling rate drive control system includes a computation processing unit, which is used to process the acquired piezoelectric stack actuator displacement signal and the piezoelectric stack actuator drive signal.

[0009] Furthermore, the processing unit includes a PID control module, a feedforward control module (FC), an adaptive feedforward cancellation control module (AFC), and an active damping control module. Loop Shaping Control Module ;

[0010] The PID control module is used to reduce static error. The PID control module is represented as follows:

[0011]

[0012] in , , These are the proportional coefficient, integral coefficient, and derivative coefficient of the PID control module, respectively.

[0013] The feedforward control module FC can compensate for phase lag and reduce amplitude attenuation. The feedforward control module FC is represented as follows:

[0014]

[0015] Where Q(s) is a low-pass filter, and G(s) is the nominal model transfer function of the system consisting of the piezoelectric stack actuator and its actuator. The nominal model transfer function is obtained by performing a small-signal frequency sweep test on the system consisting of the piezoelectric stack actuator and its actuator using a LabVIEW-based high sampling rate drive control system.

[0016] The Adaptive Feedforward Cancellation (AFC) module improves the tracking accuracy of signals at specific frequencies. It sets the frequencies corresponding to multiple harmonic signals with the piezoelectric stack actuator's drive signal as the fundamental frequency to specific frequencies. The processing unit is equipped with multiple AFC modules, effectively suppressing multi-frequency interference. The AFC module is represented as follows:

[0017]

[0018] in This is the gain coefficient. For the specific frequency set, The phase lead parameter is configured such that the nominal model transfer function of the system consisting of the piezoelectric stack actuator and its actuator is set at a specific frequency. The phase lag value at the location;

[0019] The active damping control module The active damping control module can suppress resonance by increasing system damping. Represented as:

[0020]

[0021] in For active damping control module The various coefficients;

[0022] The loop shaping control module The loop shaping control module can improve system stability and closed-loop bandwidth by correcting the open-loop system's shear frequency and stability margin. The loop shaping control module adopts a lead-lag compensator. Represented as:

[0023]

[0024] in For loop shaping control module The various coefficients, when Time indicates ( For lead compensator, when When it means ( It is a hysteresis corrector.

[0025] Furthermore, the charge amplifier includes a high-voltage amplification module HVA, a detection capacitor CS, a first voltage follower Buffer1 and a second voltage follower Buffer2, a differential operational amplifier, and a switchable charge release branch. The high-voltage amplification module HVA is a high-voltage, high-power operational amplifier, and the first voltage follower Buffer1 and the second voltage follower Buffer2 are also high-voltage, high-power operational amplifiers. The switchable charge release branch is composed of a switching element and a resistor R. The input terminal of the high-voltage amplification module HVA is connected to the polypropylene film detection capacitor. The detection capacitor CS is connected in series with the positive terminal of the piezoelectric stack actuator. The negative terminal of the piezoelectric stack actuator is connected to the reference ground. The first voltage follower Buffer1 and the second voltage follower Buffer2 are respectively connected to the two ends of the detection capacitor CS. The output terminal of the first voltage follower Buffer1 is connected to the positive port of the differential operational amplifier, and the output terminal of the second voltage follower Buffer2 is connected to the negative port of the differential operational amplifier. The output terminal of the differential operational amplifier is connected to the negative input terminal of the high-voltage amplification module HVA to complete the circuit feedback.

[0026] The positive input terminal of the high voltage amplification module HVA is used to receive the drive signal of the piezoelectric stack actuator to complete the normal movement of the predetermined trajectory.

[0027] Furthermore, the differential operational amplifier is configured as a unity-gain differential amplifier to output the voltage difference between the nodes at both ends of the detection capacitor.

[0028] Furthermore, the amplification factor of the charge amplifier for the control signal of the piezoelectric stack actuator is the ratio of the capacitance value of the detection capacitor CS to the equivalent capacitance value of the piezoelectric stack actuator.

[0029] Furthermore, both the first voltage follower Buffer1 and the second voltage follower Buffer2 are voltage follower structures in the operational amplifier, used to isolate and sample the voltage across the detection capacitor CS, so as to reduce the load effect of the differential operational amplifier input on the charge control channel.

[0030] Furthermore, the on / off charge release branch is used to conduct during the initial stage of charge amplifier operation to release the initial charge at both ends of the piezoelectric stack actuator and reset its charge. After the charge release is completed, it is disconnected to avoid forming a continuous resistive DC path and introducing frequency-dependent characteristics.

[0031] Furthermore, the detection capacitor CS is a polypropylene film capacitor.

[0032] A control method for an ultra-high frequency control system for a piezoelectric stack actuator, as described above, firstly, the LabVIEW-based high sampling rate drive control system generates a drive signal for the piezoelectric stack actuator. This drive signal is then output as a control signal to the charge amplifier. The charge amplifier receives the control signal, amplifies it, and sends it back to the piezoelectric stack actuator. Finally, the piezoelectric stack actuator receives the amplified control signal and outputs a displacement signal.

[0033] Then, the LabVIEW-based high sampling rate drive control system acquires the displacement signal of the piezoelectric stack actuator. The acquired piezoelectric stack actuator displacement signal and the piezoelectric stack actuator drive signal are processed by the arithmetic processing unit to obtain the piezoelectric stack actuator control signal. The piezoelectric stack actuator control signal is output to the charge amplifier. The charge amplifier receives the piezoelectric stack actuator control signal, amplifies it, and sends it to the piezoelectric stack actuator. The piezoelectric stack actuator receives the amplified control signal and outputs the piezoelectric stack actuator displacement signal. The LabVIEW-based high sampling rate drive control system acquires the piezoelectric stack actuator displacement signal again and processes it cyclically to complete the signal feedback control. When the LabVIEW-based high sampling rate drive control system has finished outputting all the drive signals of the piezoelectric stack actuator, the entire signal feedback process ends, and the feed motion of the piezoelectric stack actuator ends accordingly.

[0034] The signal processing procedure of the arithmetic processing unit is as follows: First, the drive signal of the piezoelectric stack actuator is subtracted from the displacement signal of the piezoelectric stack actuator to obtain an error signal. Simultaneously, the drive signal of the piezoelectric stack actuator is input to the feedforward control module FC. The drive signal of the piezoelectric stack actuator is processed by the feedforward control module FC to obtain a feedforward control signal. The error signal is then processed by the PID control module and multiple adaptive feedforward cancellation control modules AFC. All signals obtained from the PID control module and multiple adaptive feedforward cancellation control modules AFC are summed to obtain a superimposed signal. The resulting superimposed signal is then input to the loop shaping control module. The superimposed signal passes through the loop shaping control module. The calculated signal is added to the feedforward control signal to obtain the initial control signal for the piezoelectric stack actuator. Then, the displacement signal of the piezoelectric stack actuator is input to the active damping control module. The displacement signal of the piezoelectric stack actuator is processed by the active damping control module. The damping control signal is obtained through calculation. The damping control signal is then added to the initial control signal of the piezoelectric stack actuator to obtain the control signal of the piezoelectric stack actuator.

[0035] The beneficial effects of this invention are as follows: This invention addresses the problem that piezoelectric actuators are difficult to operate stably at high frequencies. By building a high sampling rate drive and control system and combining it with an improved charge amplifier to reduce the impact of hysteresis and creep on accuracy, the invention achieves high-precision trajectory tracking of piezoelectric actuators at higher operating frequencies. The tracking error under high-frequency operating conditions has reached the level of ten nanometers. Furthermore, compared with the traditional charge amplifier structure, the invention fundamentally solves the problems of frequency dependence and long settling time introduced by the continuous resistive DC path by introducing a switchable DC path. At the same time, a grounded load configuration is adopted.

[0036] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall framework of a high sampling rate drive and control system built based on LabVIEW;

[0038] Figure 2 A block diagram of the designed computational processing unit module;

[0039] Figure 3 A schematic diagram of a conventional charge amplifier with a DC path configuration;

[0040] Figure 4 This is a schematic diagram of the charge amplifier proposed in this invention;

[0041] Figure 5 This is an equivalent control block diagram of the charge amplifier proposed in this invention;

[0042] Figure 6 This is a comparison chart of the hysteresis of the present invention and that of conventional voltage drive at a frequency of 0.1Hz;

[0043] Figure 7 This is a comparison chart of the hysteresis of the present invention and that of conventional voltage drive at a frequency of 10Hz;

[0044] Figure 8 This is a comparison chart of the hysteresis of the present invention and that of conventional voltage drive at a frequency of 100Hz;

[0045] Figure 9 This is a comparison chart of the hysteresis of the present invention and that of conventional voltage drive at a frequency of 500Hz;

[0046] Figure 10 The figure shows the tracking results of different driving methods under the 1kHz sinusoidal trajectory condition of this invention. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0048] An ultra-high frequency control system for a piezoelectric stack actuator includes a LabVIEW-based high sampling rate drive control system and a charge amplifier. Figure 1 The diagram shows the overall framework of a high sampling rate drive and control system built using LabVIEW. This system generates drive signals for the piezoelectric stack actuator, acquires displacement signals from the piezoelectric stack actuator, and processes the acquired displacement and drive signals to obtain control signals. These control signals are then output to the charge amplifier. The overall high sampling rate drive and control system consists of three parts: a PC, a Real-Time interface, and an FPGA. The PC is primarily used to visualize the displacement signal data acquired from the piezoelectric stack actuator and set the parameters of each module in the computational processing unit. It also interacts with the Real-Time terminal via TCP and other communication methods. The Real-Time terminal is responsible for running computational processing tasks in a real-time environment. It communicates with the FPGA terminal through mechanisms such as FIFO (First In First Out), sending the drive signals of the piezoelectric stack actuator to the FPGA terminal and simultaneously receiving and processing the displacement signals of the piezoelectric stack actuator acquired by the FPGA terminal. The FPGA terminal is responsible for the specific implementation of the computational processing unit and completes the acquisition of the piezoelectric stack actuator displacement signals from the displacement sensor. The three components work together to achieve a closed-loop control function for the system, from signal data acquisition and signal processing to control signal output.

[0049] The Real-Time side implements core functions such as signal and data interaction between the FPGA and the host computer, as well as parameter configuration of each module in the processing unit. The host computer side handles data visualization. Together, they form the upper-level logical framework of the system. Simultaneously, the Real-Time side also needs to implement the start and stop operations of the feedback control loop to ensure the system's operational flexibility.

[0050] The FPGA side needs to implement the hardware deployment of the computing unit. By discretizing the control module and implementing it in hardware as a transfer function, the control system can operate stably at high sampling rates, thereby improving control performance and response speed. During the design process, the utilization of FPGA resources (logic slice registers, RAM blocks, and DSP48 signal processing units, etc.) needs to be fully considered to avoid the system failing to execute normally at the set sampling frequency due to program redundancy.

[0051] Combination Figure 2 The block diagram of the designed computational processing unit shown includes a PID control module, a feedforward control module (FC), an adaptive feedforward cancellation control module (AFC), and an active damping control module. and loop shaping control module A PID control module is used to reduce static error. The basic form of a PID control module can be expressed as:

[0052]

[0053] The feedforward control module (FC) can effectively compensate for phase lag and reduce amplitude attenuation. The basic form of the feedforward control module (FC) can be expressed as:

[0054]

[0055] The Adaptive Feedforward Cancellation (AFC) module can improve the tracking accuracy of signals at specific frequencies. By setting the frequencies corresponding to multiple harmonic signals with the piezoelectric stack actuator's drive signal as the fundamental frequency to specific frequencies, i.e., deploying multiple AFC modules, multi-frequency interference can be effectively suppressed. The basic form of the AFC module can be expressed as:

[0056]

[0057] Active damping control module Resonance is suppressed by increasing system damping; active damping control module. The basic form can be represented as:

[0058]

[0059] Loop Shaping Control Module The system stability and closed-loop bandwidth are improved by correcting the open-loop system's shear frequency and stability margin. This invention relates to a loop shaping control module. The loop shaping control module adopts a lead-lag compensator. The basic form can be represented as:

[0060]

[0061] The specific signal processing steps of the aforementioned processing unit are as follows: First, the drive signal of the piezoelectric stack actuator is subtracted from the displacement signal of the piezoelectric stack actuator (the initial displacement signal of the piezoelectric stack actuator is zero) to obtain an error signal. Simultaneously, the drive signal of the piezoelectric stack actuator is input to the feedforward control module FC. The drive signal of the piezoelectric stack actuator is processed by the feedforward control module FC to obtain a feedforward control signal. The error signal is then processed by the PID control module and multiple adaptive feedforward cancellation control modules AFC. All signals obtained from the PID control module and multiple adaptive feedforward cancellation control modules AFC are summed to obtain a superimposed signal. The resulting superimposed signal is then input to the loop shaping control module. The superimposed signal passes through the loop shaping control module. The calculated signal is added to the feedforward control signal to obtain the initial control signal for the piezoelectric stack actuator. Then, the displacement signal of the piezoelectric stack actuator is input to the active damping control module. The displacement signal of the piezoelectric stack actuator is processed by the active damping control module. The damping control signal is obtained through calculation. The damping control signal is added to the piezoelectric stack actuator preliminary control signal to obtain the piezoelectric stack actuator control signal. The piezoelectric stack actuator control signal is output to the charge amplifier.

[0062] Combination Figure 3 The schematic diagram shown is of a conventional charge amplifier with a DC path configuration. In this case, the voltage gain of the charge amplifier can be expressed as:

[0063]

[0064] Let the formula When this condition is met, the voltage gain in the charge amplifier remains constant and is independent of the input signal frequency. Although introducing a DC path effectively solves the charge saturation problem, the presence of the parallel resistor also forms an RC network, thus introducing undesirable dynamic characteristics. Therefore, the transition frequency of the charge amplifier is defined as:

[0065]

[0066] The transition frequency divides the charge amplifier into two modes: charge-driven dominant mode and voltage-driven dominant mode. In this situation, the charge amplifier switches to a voltage-driven operating mode, essentially equivalent to traditional voltage-driven operation. At this time, the voltage across the piezoelectric actuator is directly proportional to the input excitation voltage, making it difficult to avoid the impact of hysteresis on control. And when... At this time, the charge amplifier switches to a charge-driven operating mode, satisfying... The relationship between the charge at the actuator terminals and the input excitation voltage is linear, significantly reducing the impact of hysteresis. Therefore, the introduction of the DC path causes the drive circuit to exhibit a clear frequency-dependent characteristic. When the input signal frequency is much higher than the transition frequency, the charge amplifier operates in charge-driven mode, effectively mitigating the hysteresis effect; however, when the input signal frequency is much lower than the transition frequency, the charge amplifier degenerates into voltage-driven mode, unable to avoid the accuracy degradation caused by hysteresis.

[0067] Combination Figures 4-5As shown, the charge amplifier of the present invention includes a high-voltage amplification module HVA, a detection capacitor CS, a first voltage follower Buffer1 and a second voltage follower Buffer2, a differential operational amplifier, and a switchable charge release branch. The high-voltage amplification module is a high-voltage, high-power operational amplifier. The detection capacitor is a polypropylene film capacitor with a specified gain. The first and second voltage followers are high-voltage, high-power operational amplifiers. The switchable charge release branch is composed of a switching element and a resistor R. The input terminal of the high-voltage amplification module is connected to the polypropylene film detection capacitor. The detection capacitor is connected in series with the positive terminal of a piezoelectric stack actuator. The negative terminal of the piezoelectric stack actuator is connected to a reference ground. The first and second voltage followers are respectively connected to the two ends of the detection capacitor. The first voltage follower is connected to the positive port of the differential operational amplifier. The output terminal of the second voltage follower is connected to the negative port of the differential operational amplifier. The output terminal of the differential operational amplifier is connected to the negative input terminal of the high-voltage amplification module to complete the circuit feedback.

[0068] The positive input terminal of the high-voltage amplification module in the charge amplifier is used to receive the drive signal from the piezoelectric stack actuator to complete the normal movement along the predetermined trajectory.

[0069] The piezoelectric stack actuator interface in the charge amplifier is connected to the positive and negative terminals of the actual piezoelectric stack actuator to ensure the normal operation of the piezoelectric stack actuator.

[0070] The differential operational amplifier is configured as a unity-gain differential amplifier to output the voltage difference between the nodes at both ends of the detection capacitor.

[0071] The output voltage, i.e., the ratio of the voltage across the piezoelectric stack actuator to the input drive signal (i.e., the overall circuit gain), is determined by the ratio of the sensing capacitor to the equivalent capacitance of the piezoelectric stack actuator.

[0072] The first voltage follower Buffer1 and the second voltage follower Buffer2 are both voltage follower structures in the operational amplifier, used to isolate and sample the voltage across the detection capacitor CS to reduce the load effect of the differential operational amplifier input on the charge control channel.

[0073] The on / off charge release branch is used to conduct when the release condition is met to release the residual charge at both ends of the node piezoelectric stack actuator and reset its charge; it is disconnected when not releasing to avoid the formation of a continuous resistive DC path that could introduce frequency dependence or low-frequency degradation.

[0074] The sampling capacitor is a polypropylene film capacitor or other high-linearity capacitor to reduce the impact of nonlinear capacitance effect on charge control accuracy.

[0075] The charge amplifier described in this invention specifically uses a first voltage follower Buffer1 and a second voltage follower Buffer2 to provide low input impedance to a differential operational amplifier. The differential operational amplifier uses unity gain to calculate the voltage difference across the detection capacitor and feeds this voltage difference back to the negative input terminal of the main high-voltage, high-power amplifier HVA to complete the entire circuit loop. Figure 5 The proposed equivalent control block diagram of the charge amplifier is shown, where K represents the open-loop gain of the high-voltage amplifier module HVA. This indicates the output voltage of the high-voltage amplifier. and These represent the voltages across the detection capacitor and the piezoelectric actuator, respectively. and Let K represent the capacitive reactance values ​​of the sensing capacitor and the piezoelectric stacked actuator, respectively. Since the open-loop gain of a typical high-voltage operational amplifier is greater than 100dB, K can be considered infinite. The voltage across the sensing capacitor remains equal to the input voltage. The overall control block diagram can be represented as follows:

[0076]

[0077] As can be seen from the above formula, the proposed charge amplifier has effectively overcome frequency dependence. The overall gain of the circuit is now primarily determined by the ratio of the sensing capacitor to the equivalent capacitance of the piezoelectric stack actuator. Therefore, the value of the sensing capacitor can be selected based on the equivalent capacitance of the piezoelectric stack actuator used and the required overall gain of the charge amplifier.

[0078] To overcome the shortcomings of traditional charge amplifiers, the described charge amplifier connects a switch and a resistor in parallel across the piezoelectric stack actuator to create a temporarily controllable resistive DC path, enabling controlled charge release. In the initial stage of circuit operation, the switch is closed to release accumulated charge; subsequently, the switch is opened, allowing the circuit to enter charge-driven mode. This design effectively eliminates the influence of transition frequencies, thus maintaining consistent control performance across both high and low frequency ranges.

[0079] The charge amplifier adopts a grounded load configuration, which not only effectively protects the piezoelectric stack actuator, but also improves the applicability to different types of piezoelectric materials, such as piezoelectric stacks, piezoelectric tubes, and piezoelectric bending elements.

[0080] The actuator used in this embodiment is a single-degree-of-freedom piezoelectric-driven rapid tool servo device, mainly composed of a flexible guiding mechanism and a piezoelectric stack actuator. This device uses screws to pre-tighten the piezoelectric stack actuator, and transmits displacement to the front end of the mechanism through a flexible hinge mechanism to complete the feed motion.

[0081] A high sampling rate drive and control system built using LabVIEW was used to perform small-signal frequency sweep tests on the device to obtain the system's frequency response function and its nominal model transfer function expression. Based on this, the parameters of each control module in the arithmetic processing unit of the drive and control system were tuned. A zero-pole matching method was used for discretization, and the discretization was deployed on the FPGA of the high sampling rate drive and control system built using LabVIEW. This discretization method can maintain the system's dynamic characteristics and stability while preserving the frequency domain performance of each control module, thus achieving high-precision implementation of each control module.

[0082] In this embodiment, the equivalent capacitance of the piezoelectric stacked actuator is 3.1 μF, and the overall voltage gain of the charge amplifier is selected as 10 V / V. That is, the ratio of the detection capacitor to the equivalent capacitance of the piezoelectric stacked actuator is 10 times. The detection capacitor is a high linear polypropylene film capacitor with a capacitance of 31 μF. In contrast, if surface-mount capacitors or other devices are used, unexpected nonlinear effects are often introduced, which will adversely affect the performance of the charge amplifier.

[0083] Considering both performance requirements and cost-effectiveness, the high-voltage amplifier module HVA in this embodiment uses the APEX PA92 high-voltage operational amplifier. The PA92 is a MOSFET high-voltage operational amplifier with low quiescent current characteristics, capable of providing up to 4 A of continuous output current. By configuring appropriate current-limiting resistors, this device can adapt to various types of loads, demonstrating good versatility.

[0084] The primary function of the voltage follower Buffer1 and Buffer2 is to provide low input impedance for the differential operational amplifier, and they also need to have strong high-voltage withstand capability. However, unlike the high-voltage amplification module HVA, their output current requirements are relatively low. Based on this consideration, the embodiment uses the PA88 high-voltage operational amplifier, also from APEX, to meet the circuit's stable operation requirements under high-voltage environments. The PA88 is a high-voltage, low-quiescent-current MOSFET operational amplifier designed to output up to 100mA.

[0085] The differential operational amplifier selected must meet the high sensitivity requirement for detecting minute voltage signals. Therefore, it must possess a high common-mode rejection ratio (CMRR) and exhibit low drift and low noise characteristics to ensure the stability and accuracy of signal processing. Furthermore, its accuracy must be sufficiently high to meet the application requirements of the circuit in high-performance driving and control. In this embodiment, the AD629 high common-mode voltage differential operational amplifier is selected, allowing accurate measurement of differential signals at common-mode voltages up to ±270V. It offers advantages such as low offset, low offset drift, low gain error drift, low common-mode rejection drift, and excellent common-mode rejection ratio over a wide frequency range.

[0086] After selecting various operational amplifiers and detection capacitors, the circuit board was soldered. In this embodiment, based on the piezoelectric stack driving high-speed tool servo device, hysteresis tests were conducted under different frequency conditions using both the charge amplifier proposed in this method and the power amplifier used in traditional voltage driving. Specifically, the piezoelectric stack drive signal was directly output to the input of the charge amplifier without going through the processing unit. The piezoelectric stack drive signals used were sinusoidal trajectory signals ranging from 0.1Hz to 500Hz. Simultaneously, trajectory tracking tests were performed under high-frequency sinusoidal trajectory conditions, where the piezoelectric stack drive signal was directly output to the input of the charge amplifier through the processing unit. The piezoelectric stack drive signal used was a 1kHz sinusoidal trajectory signal.

[0087] Combination Figures 6-9 The graph shown compares the hysteresis of traditional voltage drive under different frequency conditions. Figure 6 Figure (a) shows the hysteresis plot for charge-driven hysteresis at a frequency of 0.1 Hz, and Figure (b) shows the hysteresis plot for voltage-driven hysteresis at a frequency of 0.1 Hz. Figure 7 Figure (a) shows the hysteresis diagram for charge-driven hysteresis at a frequency of 10 Hz, and Figure (b) shows the hysteresis diagram for voltage-driven hysteresis at a frequency of 10 Hz. Figure 8 Figure (a) shows the hysteresis plot for charge-driven hysteresis at 100 Hz, and Figure (b) shows the hysteresis plot for voltage-driven hysteresis at 100 Hz. Figure 9 Figure (a) shows the hysteresis diagram of charge-driven operation at 500Hz, and Figure (b) shows the hysteresis diagram of voltage-driven operation at 500Hz. The charge amplifier, while fulfilling the function of driving voltage amplification according to the designed gain, also significantly suppresses the hysteresis effect of the piezoelectric stacked actuator in the low-frequency to high-frequency range. The hysteresis can be reduced to less than 1% of the motion stroke, and it effectively solves some of the defects of traditional charge amplifiers, ensuring the consistency of control accuracy in each frequency band.

[0088] Combination Figure 10 The following figure shows the tracking results of different driving methods under a 1kHz sinusoidal trajectory condition ( Figure 10 Figure (a) shows the 1kHz tracking trajectory, Figure (b) shows a magnified view of the tracking trajectory, and Figure (c) shows the 1kHz tracking error. It can be seen that when using the charge amplifier, the tracking error result is close to the noise level of the experimental test system. Compared with the traditional voltage drive error, it is reduced by more than half, which shows the benefits and superiority of the ultra-high frequency control system for piezoelectric stack actuators proposed in this invention under ultra-high frequency working conditions.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ultra-high frequency control system for a piezoelectric stack actuator, characterized in that, The system includes a LabVIEW-based high sampling rate drive and control system and a charge amplifier. The LabVIEW-based high sampling rate drive and control system is used to generate drive signals for the piezoelectric stack actuator, acquire displacement signals of the piezoelectric stack actuator, and process the acquired displacement signals and drive signals of the piezoelectric stack actuator to obtain control signals for the piezoelectric stack actuator. The control signals of the piezoelectric stack actuator are output to the charge amplifier, which is used to receive the control signals of the piezoelectric stack actuator and amplify them. The amplified control signals of the piezoelectric stack actuator are then sent to the piezoelectric stack actuator.

2. The ultra-high frequency control system for a piezoelectric stack actuator according to claim 1, characterized in that, The LabVIEW-based high sampling rate drive control system includes a computation processing unit, which is used to process the acquired piezoelectric stack actuator displacement signal and the piezoelectric stack actuator drive signal.

3. The ultra-high frequency control system for a piezoelectric stack actuator according to claim 2, characterized in that, The processing unit includes a PID control module, a feedforward control module (FC), an adaptive feedforward cancellation control module (AFC), and an active damping control module. Loop Shaping Control Module ; The PID control module is used to reduce static error. The PID control module is represented as follows: in , , These are the proportional coefficient, integral coefficient, and derivative coefficient of the PID control module, respectively. The feedforward control module FC can compensate for phase lag and reduce amplitude attenuation. The feedforward control module FC is represented as follows: Where Q(s) is a low-pass filter, and G(s) is the nominal model transfer function of the system consisting of the piezoelectric stack actuator and its actuator. The nominal model transfer function is obtained by performing a small-signal frequency sweep test on the system consisting of the piezoelectric stack actuator and its actuator using a LabVIEW-based high sampling rate drive control system. The Adaptive Feedforward Cancellation (AFC) module improves the tracking accuracy of signals at specific frequencies. It sets the frequencies corresponding to multiple harmonic signals with the piezoelectric stack actuator's drive signal as the fundamental frequency to specific frequencies. The processing unit is equipped with multiple AFC modules, effectively suppressing multi-frequency interference. The AFC module is represented as follows: in This is the gain coefficient. For the specific frequency set, The phase lead parameter is configured such that the nominal model transfer function of the system consisting of the piezoelectric stack actuator and its actuator is set at a specific frequency. The phase lag value at the location; The active damping control module The active damping control module can suppress resonance by increasing system damping. Represented as: in For active damping control module The various coefficients; The loop shaping control module The loop shaping control module can improve system stability and closed-loop bandwidth by correcting the open-loop system's shear frequency and stability margin. The loop shaping control module adopts a lead-lag corrector. Represented as: in For loop shaping control module The various coefficients, when Time indicates ( For lead compensator, when When it means ( It is a hysteresis corrector.

4. The ultra-high frequency control system for a piezoelectric stack actuator according to claim 3, characterized in that, The charge amplifier includes a high-voltage amplification module HVA, a detection capacitor CS, a first voltage follower Buffer1 and a second voltage follower Buffer2, a differential operational amplifier, and a switchable charge release branch. The high-voltage amplification module HVA is a high-voltage, high-power operational amplifier. The first voltage follower Buffer1 and the second voltage follower Buffer2 are also high-voltage, high-power operational amplifiers. The switchable charge release branch is composed of a switching element and a resistor R. The input terminal of the high-voltage amplification module HVA is connected to the polypropylene film detection capacitor. The detection capacitor CS is connected in series with the positive terminal of the piezoelectric stack actuator. The negative terminal of the piezoelectric stack actuator is connected to a reference ground. The first voltage follower Buffer1 and the second voltage follower Buffer2 are respectively connected across the detection capacitor CS. The output terminal of the first voltage follower Buffer1 is connected to the positive port of the differential operational amplifier. The output terminal of the second voltage follower Buffer2 is connected to the negative port of the differential operational amplifier. The output terminal of the differential operational amplifier is connected to the negative input terminal of the high-voltage amplification module HVA to complete the circuit feedback. The positive input terminal of the high voltage amplification module HVA is used to receive the drive signal of the piezoelectric stack actuator to complete the normal movement of the predetermined trajectory.

5. The ultra-high frequency control system for a piezoelectric stack actuator according to claim 4, characterized in that, The differential operational amplifier is configured as a unity-gain differential amplifier to output the voltage difference between the nodes at both ends of the detection capacitor.

6. The ultra-high frequency control system for a piezoelectric stack actuator according to claim 4, characterized in that, The amplification factor of the charge amplifier for the control signal of the piezoelectric stack actuator is the ratio of the capacitance value of the detection capacitor CS to the equivalent capacitance value of the piezoelectric stack actuator.

7. The ultra-high frequency control system for a piezoelectric stack actuator according to claim 4, characterized in that, The first voltage follower Buffer1 and the second voltage follower Buffer2 are both voltage follower structures in the operational amplifier, used to isolate and sample the voltage across the detection capacitor CS to reduce the load effect of the differential operational amplifier input on the charge control channel.

8. The ultra-high frequency control system for a piezoelectric stack actuator according to claim 4, characterized in that, The on / off charge release branch is used to turn on during the initial stage of charge amplifier operation to release the initial charge at both ends of the piezoelectric stack actuator and reset its charge. After the charge release is completed, it is turned off to avoid the formation of a continuous resistive DC path and the introduction of frequency-dependent characteristics.

9. The ultra-high frequency control system for a piezoelectric stack actuator according to claim 4, characterized in that, The detection capacitor CS is a polypropylene film capacitor.

10. A control method for an ultra-high frequency control system for a piezoelectric stack actuator according to any one of claims 4-9, characterized in that, First, the LabVIEW-based high sampling rate drive control system generates a drive signal for the piezoelectric stack actuator. The drive signal of the piezoelectric stack actuator is then output as a control signal to the charge amplifier. The charge amplifier receives the control signal of the piezoelectric stack actuator, amplifies it, and sends it to the piezoelectric stack actuator. The piezoelectric stack actuator receives the amplified control signal and outputs a displacement signal. Then, the LabVIEW-based high sampling rate drive control system acquires the displacement signal of the piezoelectric stack actuator. The acquired piezoelectric stack actuator displacement signal and the piezoelectric stack actuator drive signal are processed by the arithmetic processing unit to obtain the piezoelectric stack actuator control signal. The piezoelectric stack actuator control signal is output to the charge amplifier. The charge amplifier receives the piezoelectric stack actuator control signal, amplifies it, and sends it to the piezoelectric stack actuator. The piezoelectric stack actuator receives the amplified control signal and outputs the piezoelectric stack actuator displacement signal. The LabVIEW-based high sampling rate drive control system acquires the piezoelectric stack actuator displacement signal again and processes it cyclically to complete the signal feedback control. When the LabVIEW-based high sampling rate drive control system has finished outputting all the drive signals of the piezoelectric stack actuator, the entire signal feedback process ends, and the feed motion of the piezoelectric stack actuator ends accordingly. The signal processing procedure of the arithmetic processing unit is as follows: First, the drive signal of the piezoelectric stack actuator is subtracted from the displacement signal of the piezoelectric stack actuator to obtain an error signal. Simultaneously, the drive signal of the piezoelectric stack actuator is input to the feedforward control module FC. The drive signal of the piezoelectric stack actuator is processed by the feedforward control module FC to obtain a feedforward control signal. The error signal is then processed by the PID control module and multiple adaptive feedforward cancellation control modules AFC. All signals obtained from the PID control module and multiple adaptive feedforward cancellation control modules AFC are summed to obtain a superimposed signal. The resulting superimposed signal is then input to the loop shaping control module. The superimposed signal passes through the loop shaping control module. The calculated signal is added to the feedforward control signal to obtain the initial control signal for the piezoelectric stack actuator. Then, the displacement signal of the piezoelectric stack actuator is input to the active damping control module. The displacement signal of the piezoelectric stack actuator is processed by the active damping control module. The damping control signal is obtained through calculation. The damping control signal is then added to the initial control signal of the piezoelectric stack actuator to obtain the control signal of the piezoelectric stack actuator.

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