Double-channel elliptical vibration ultrasonic transducer driving control system

Abstract

The invention discloses a dual-channel elliptical vibration ultrasonic transducer driving control system, which comprises a sampling filtering module, a signal generation controller module and a power inversion amplification module which are connected in sequence, and is characterized in that the power inversion amplification module is connected with the input end of a transducer, and the output end of the transducer is connected with the sampling filtering module; the sampling filtering module samples and processes voltage and current output by the transducer, the signal generation controller module outputs frequency control signals according to the voltage and current fed back by the transducer through a Fuzzy-PID frequency tracking control method, and outputs amplitude control signals according to the current fed back by the transducer through a constant amplitude PID control method. The power inversion amplification module generates, modulates, amplifies and outputs a driving signal improvement of the transducer according to the received frequency and amplitude control signal. The problems that in ultrasonic elliptical vibration machining, the frequency tracking speed of an ultrasonic driver is low, the vibration amplitude is difficult to control, and a milling tool is seriously abraded are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic elliptical vibration machining, and particularly to a dual-channel elliptical vibration ultrasonic transducer drive system. Background Art

[0002] Ultrasonic elliptical vibration machining technology is based on the high-speed rotation of the machining spindle, and superimposes high-frequency vibration energy of ultrasonic waves on the machining tool to achieve cooperative machining of rotation and ultrasonic energy. In this system, two orthogonally arranged ultrasonic transducers respectively generate high-frequency vibrations with adjustable phase differences, which are amplified by horn structures and then transmitted to the tool. The combined motion can form an elliptical vibration trajectory of the tool tip. Among them, the ultrasonic transducer is rigidly connected to the tool through the horn structure to ensure the efficient transmission of vibration energy, which has obvious advantages for the machining of hard and brittle and difficult-to-process advanced composite materials and is widely adopted. As the core component of the ultrasonic vibration system, the ultrasonic driver has a direct decisive impact on the vibration efficiency of the machining tool and the machining surface quality.

[0003] Frequency tracking is the core function of the ultrasonic driver. Common algorithms mainly include PID control, variable step-size frequency tracking, and maximum current feedback method. However, the PID has high precision but difficult parameter adjustment and is difficult to adapt to nonlinear systems; the variable step-size frequency tracking has fast response but is easy to introduce jitter; the maximum current feedback method has high precision but is greatly affected by noise and cannot maintain stable operation in complex environments. At present, most ultrasonic drivers at home and abroad adopt single-algorithm control. For example, an existing variable step-size resonant frequency tracking method can effectively track the resonant frequency. However, due to the narrow resonant frequency band width of the ultrasonic transducer, the size of the step value has a great influence on the frequency tracking effect. If the step value is too large, it is difficult to track the resonant frequency point; if the step value is too small, the frequency tracking time will increase, resulting in slow frequency tracking speed of the device. Another existing technology estimates the amplitude and phase of ultrasonic vibration through an observer and Kalman filtering, and uses a dual-PI controller to respectively maintain the amplitude and driving frequency at the reference values. However, since this frequency tracking algorithm depends on the system model, it is sensitive to model errors and nonlinear disturbances under complex working conditions, reducing the robustness. Single frequency tracking algorithm control is simple, but the system has slow frequency tracking speed and poor adaptability under complex disturbances. Therefore, it is of great significance to study a composite frequency tracking control algorithm that simultaneously has frequency tracking speed and adaptability to nonlinear disturbances.

[0004] The constant amplitude control of the ultrasonic transducer in ultrasonic elliptical vibration machining plays a decisive role in machining effect and tool life extension, ensuring milling stability and accuracy. Common constant amplitude control algorithms include open-loop control, closed-loop amplitude control, and adaptive control. However, the open-loop control has a simple structure, poor adaptability to load changes, and difficult accuracy improvement; the closed-loop amplitude control has strong adaptability and high accuracy, but slow dynamic response; the adaptive control can adjust parameters according to working conditions, with strong flexibility, but complex algorithms and high hardware requirements. In the prior art, a driver power supply for ultrasonic vibration cutting based on a full-bridge inverter circuit has been designed, which can meet the driving requirements of high-power transducers, but only open-loop amplitude control is adopted, resulting in amplitude jitter and inconsistent machining effects on the front and back surfaces, affecting the machining effect of ultrasonic-assisted machining. This indicates that studying constant amplitude control algorithms is of great value for improving system stability and machining quality.

[0005] Therefore, it is urgent to solve the problems of slow frequency tracking speed of the ultrasonic driver frequency tracking algorithm, difficult control of vibration amplitude, and large wear of milling tools in ultrasonic elliptical vibration machining. Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] Based on the above problems, the present invention provides a dual-channel elliptical vibration ultrasonic transducer drive system to solve the problems of slow frequency tracking speed of the ultrasonic driver, difficult control of vibration amplitude, and large wear of milling tools in ultrasonic elliptical vibration machining.

[0008] (2) Technical solutions

[0009] Based on the above technical problems, the present invention provides 1. A dual-channel elliptical vibration ultrasonic transducer drive control system, characterized in that it includes a sampling and filtering module, a signal generation and controller module, and a power inverter and amplification module connected in sequence. The power inverter and amplification module is connected to the input end of the transducer, and the output end of the transducer is connected to the sampling and filtering module; the sampling and filtering module samples and processes the voltage and current output by the transducer. The signal generation and controller module outputs a frequency control signal according to the voltage and current feedback by the transducer through the Fuzzy-PID frequency tracking control method, and outputs an amplitude control signal according to the current feedback by the transducer through the constant amplitude PID control method. The power inverter and amplification module generates, modulates, amplifies, and outputs the drive signal of the transducer according to the received frequency and amplitude control signals;

[0010] The Fuzzy-PID frequency tracking control method calculates the phase difference error Δθ = |θ i according to the actual phase difference θ of the feedback voltage and current i – θ d|; When Δθ≥Δθ0, a fuzzy control method is used to track the frequency. When Δθ<Δθ0, a PID control method is used to track the frequency. The fuzzy control method or the PID control method outputs the adjustment frequency Δf; then, according to the current working frequency f and the adjustment frequency Δf, a frequency control word K is generated and input into the DDS generator. Among them, according to the target phase difference θ d being zero indicates the resonant state, and Δθ0 is the set standard threshold;

[0011] The constant amplitude PID control method calculates the current effective value I of the current according to the feedback current i , according to the current effective value I of the current i and the current difference ΔI between the current and the previous working rated current I0, and generates an amplitude control word through PID control and inputs it into the DDS generator.

[0012] (3) Beneficial effects

[0013] The above technical solutions of the present invention have the following advantages:

[0014] (1) The present invention combines software and hardware. The signal generation controller module outputs a frequency control signal according to the voltage and current feedback from the transducer through the Fuzzy-PID frequency tracking control method, enabling automatic tracking of the resonant frequency and ensuring that the transducer always operates in the resonant state. Through the constant amplitude PID control method, an amplitude control signal is output according to the current feedback from the transducer, enabling real-time adjustment of the output amplitude of the driver and ensuring the stability of the ultrasonic amplitude, thereby realizing the resonant frequency tracking of the ultrasonic transducer and the constant control of the ultrasonic amplitude; the power inverter amplification module generates, modulates, amplifies, and outputs the drive signal of the transducer according to the received frequency and amplitude control signals, enabling the transducer to synthesize the expected displacement trajectory of the ultrasonic elliptical vibration amplitude; thus, in ultrasonic elliptical vibration machining, the drive frequency tracking speed of the ultrasonic transducer is fast, and the machining vibration amplitude remains constant, thereby reducing tool wear and extending tool life;

[0015] (2) Through the Fuzzy-PID frequency tracking control method, the present invention combines fuzzy control and PID control to achieve fast frequency self-tracking and overshoot adjustment with the FPGA controller as the core. According to the phase difference relationship between the current and voltage at both ends of the transducer, it can automatically track the resonant frequency and ensure that the transducer always operates in the resonant state;

[0016] (3) The present invention adopts dual-channel drive, realizing the transmission of different vibration amplitudes in accordance with the expected phase in each direction, ensuring the formation of a circular or elliptical vibration path during the machining process, and thus effectively reducing tool wear. Description of the drawings

[0017] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings. The drawings are schematic and should not be construed as imposing any limitation on the present invention. In the drawings:

[0018] Figure 1 is the overall topological structure diagram of the hardware of the dual-channel elliptical vibration ultrasonic transducer drive control system according to an embodiment of the present invention;

[0019] Figure 2 is the principle block diagram of the Fuzzy-PID frequency tracking control method according to an embodiment of the present invention;

[0020] Figure 3 is the flowchart of the Fuzzy-PID frequency tracking control method according to an embodiment of the present invention;

[0021] Figure 4 is the principle block diagram of the fuzzy control method according to an embodiment of the present invention;

[0022] Figure 5 is the input / output characteristic surface diagram of the fuzzy control according to an embodiment of the present invention;

[0023] Figure 6 is the simulation comparison diagram between the Fuzzy-PID frequency tracking control method and the conventional PID algorithm according to an embodiment of the present invention;

[0024] Figure 7 is the flowchart of the constant amplitude PID control method according to an embodiment of the present invention;

[0025] Figure 8 is the circuit design diagram of the power inverter amplification module according to an embodiment of the present invention;

[0026] Figure 9 is the circuit design diagram of the sampling and filtering module according to an embodiment of the present invention;

[0027] Figure 10 is the overall physical diagram of the system according to an embodiment of the present invention;

[0028] Figure 11 is the output waveform diagram of the ultrasonic driver according to an embodiment of the present invention;

[0029] Figure 12 is the dual-channel signal feedback current amplitude trajectory diagram according to an embodiment of the present invention. Detailed Embodiments

[0030] The following combines the accompanying drawings and embodiments to further describe in detail the specific embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0031] An embodiment of the present invention is a dual-channel elliptical vibration ultrasonic transducer drive control system. Based on the analysis of the characteristics of piezoelectric ultrasonic transducers, when the transducer reaches the resonant state, the impedance of its equivalent circuit is minimized, the current in the circuit reaches the maximum, and the phase difference between the current and voltage signals is zero. Therefore, the overall topology diagram of its hardware is as follows Figure 1 shown, including a sampling and filtering module, a signal generation and control module, and a power inverter and amplification module connected in sequence, as well as a power supply module connected to each module. The power inverter and amplification module is connected to the input end of the transducer, and the output end of the transducer is connected to the sampling and filtering module; the sampling and filtering module samples and processes the voltage and current of the transducer. The signal generation and control module outputs a frequency control signal through the Fuzzy-PID frequency tracking control method based on the voltage and current feedback from the sampled and processed transducer, and outputs an amplitude control signal through the constant amplitude PID control method based on the feedback current. The power inverter and amplification module generates, modulates, amplifies, and outputs the drive signal of the transducer according to the received frequency and amplitude control signals, so as to enable the transducer to synthesize the expected displacement trajectory of the ultrasonic elliptical vibration amplitude.

[0032] Further, the signal generation and control module outputs a frequency control signal according to the voltage and current feedback from the transducer through the Fuzzy-PID frequency tracking control method, and outputs an amplitude control signal according to the current feedback from the transducer through the constant amplitude PID control method to achieve the resonant frequency tracking of the ultrasonic transducer and the constant control of the ultrasonic amplitude; the signal generation and control module includes a frequency tracking control module, an amplitude control module, a DDS generator, and a dual-channel ADC drive module. The input end of the dual-channel ADC drive module is connected to the sampling and filtering module, and the output end is connected to the input end of the frequency tracking control module. The input end of the amplitude control module is connected to the sampling and filtering module and the dual-channel ADC drive module. The output ends of the frequency tracking control module and the amplitude control module are both connected to the input end of the DDS generator. The output end of the DDS generator is connected to the dual-channel DAC conversion drive module of the power inverter and amplification module;

[0033] The frequency tracking control module includes a digital phase detector, a frequency sweeping module, a frequency PID controller, and a frequency fuzzy controller. The input end of the digital phase detector is connected to the dual-channel DAC conversion and drive module, and the output end is connected to the frequency sweeping module, the frequency PID controller, and the frequency fuzzy controller. The output ends of the frequency sweeping module, the frequency PID controller, and the frequency fuzzy controller generate a frequency control word through the Fuzzy-PID frequency tracking control method and connect it to the DDS generator; the digital phase detector calculates the phase difference error Δθ of the feedback X-direction voltage and current in real time; the frequency sweeping module searches for the frequency corresponding to the maximum value of the feedback X-direction current through a variable-step frequency search algorithm to determine the initial operating frequency f0; according to the feedback phase difference error, the frequency PID controller or the frequency fuzzy controller generates an adjustment frequency Δf; then, according to the initial resonance frequency f0 and the adjustment frequency Δf, the frequency control word K is cyclically generated through the Fuzzy-PID frequency tracking control method and input into the DDS generator.

[0034] The amplitude control module includes a current effective value calculation module and an amplitude PID controller connected in sequence; the current effective value calculation module calculates the current effective value I of the feedback current according to the feedback X-direction current and Y-direction current i , and then, through the constant amplitude PID control method, according to the current effective value I i , the current difference ΔI from the previous rated current I0 is input into the amplitude PID controller, and the amplitude PID controller generates an amplitude control word and inputs it into the DDS generator; the current effective value calculation module adopts a dedicated hardware pipeline structure to sequentially complete signal sampling, square operation, periodic integration, and mean value calculation, accurately obtain the current RMS value, and analyze its change trend.

[0035] The DDS generator outputs the frequency control word and the amplitude control word to the dual-channel DAC conversion and drive module of the power inverter and amplification module to realize the drive control of the output signal of the transducer, find the resonance frequency point, that is, the position where the feedback current reaches the maximum value and the phase difference between the current and the voltage is zero, can automatically track the resonance frequency, ensure that the transducer always works in the resonance state, and can realize the fast and stable control of the vibration amplitude.

[0036] Specifically, the signal generation controller module is implemented using an FPGA. The ZYNQ7020 Black Gold development board from Xilinx is selected, and a hierarchical software architecture is adopted to achieve precise control of the ultrasonic transducer. The core algorithm layer includes a frequency tracking control module, an ultrasonic amplitude PID control module, and a functional module of the DDS generator. Each module works together through a parallel pipeline architecture. Among them, the frequency sweep initialization provides a starting reference, the phase difference calculation and frequency tracking form the main control loop, and the amplitude control forms an auxiliary adjustment loop. At the same time, it interacts with the ARM processor through the AXI bus. This architecture gives full play to the parallel processing advantages of the FPGA and realizes high-precision control of the entire process from automatic frequency sweep, resonance tracking to amplitude stabilization; the dual-channel DAC conversion drive module uses the AD9226. When the signal frequency generated by the DDS generator in the FPGA is equal to the resonance frequency of the ultrasonic transducer, the transducer generates resonant vibration, the current in the circuit reaches the maximum, and the phase difference between the current and voltage signals is zero.

[0037] The software part of the signal generation controller module is implemented through the Fuzzy-PID frequency tracking control method and the constant amplitude PID control method.

[0038] Furthermore, the schematic diagram of the Fuzzy-PID frequency tracking control method is as Figure 2 shown. It combines the advantages of fuzzy control and PID control, and selects the strategies of different controllers according to the size of the error feedback value: when the phase difference error is large, the frequency fuzzy controller is used for adaptive adjustment, and when the phase difference error is small, the frequency PID controller is used for precise tracking. In the present invention, the Fuzzy-PID frequency tracking control method is used for resonance frequency tracking, and the phase difference error Δθ is used as the feedback quantity. The voltage and current signals fed back by the ultrasonic transducer are subjected to low-pass filtering, and the zero-crossing detection of the voltage and current is used to obtain the phase difference θ i , and the phase difference error Δθ is calculated according to Δθ = |θ i – θ d |. After multiple cycles, the phase difference error reaches the minimum value, realizing Fuzzy-PID frequency tracking control.

[0039] The Fuzzy-PID frequency tracking control method calculates the phase difference error Δθ = |θ i according to the actual phase difference θ of the fed-back voltage and current i – θ d |; when Δθ ≥ Δθ0, the fuzzy control method is used for frequency tracking, and when Δθ < Δθ0, the PID control method is used for frequency tracking. The fuzzy control method or the PID control method outputs the adjustment frequency Δf; then, according to the current working frequency f and the adjustment frequency Δf, a frequency control word K is generated and input into the DDS generator; the specific process is as Figure 3 shown, including the following steps:

[0040] S11. The frequency sweeping module searches for the frequency corresponding to the maximum feedback current according to the variable step frequency search algorithm, determines the initial operating frequency f0, and sets the current operating frequency f = f0.

[0041] When the driver power supply starts, first, the frequency sweeping module searches for the frequency corresponding to the maximum feedback current according to the variable step frequency search algorithm and sets it as the initial operating frequency f0 of the power inverter amplification module; the current operating frequency f after the initial state is the frequency adjusted by the frequency PID controller or the frequency fuzzy controller.

[0042] S12. The digital phase discriminator calculates the actual phase difference θ in real time according to the phase difference between the feedback X-direction voltage and current. i Then, according to the actual phase difference θ i calculate the phase difference error Δθ.

[0043] Define the phase difference error Δθ as the absolute difference between the target phase difference θ d (θ d is in the resonant state when it is zero) and the actual phase difference θ i (where i = 1, 2, 3,...), that is, Δθ = |θ i – θ d |.

[0044] S13. When Δθ ≥ Δθ0, the frequency fuzzy controller runs the fuzzy control method to chase the frequency; when Δθ < Δθ0, the frequency PID controller runs the PID control method to chase the frequency.

[0045] Select different frequency chasing algorithms according to the range of the phase difference error Δθ, and set Δθ0 = 30 degrees as the standard threshold of the deviation. When Δθ ≥ Δθ0, the system runs the fuzzy control method through the frequency fuzzy controller to chase the frequency and quickly adjusts the driving frequency of the DDS generator to make it enter the phase-locked range. When Δθ < Δθ0, the system runs the PID control method through the frequency PID controller to chase the frequency and judges whether the resonant frequency is locked through the feedback phase difference.

[0046] Furthermore, the principle block diagram of the fuzzy control method is as Figure 4 shown. The implementation steps are as follows:

[0047] 1) Determine the input and output quantities of the fuzzy control; set the input quantities of the fuzzy control as the phase difference E between the current and voltage in the transducer loop and the change rate of the phase difference EC = Δe / Δt, and the output quantity of the fuzzy control as the frequency increment DF.

[0048] Among them, the phase difference E is the phase difference θ i , Δe in EC is the phase difference error Δθ, Δt is the sampling time difference, and DF is the adjustment frequency Δf.

[0049] 2) Fuzzification of the input and output variables of the fuzzy control; According to the variation range of the phase difference, the basic domain of E is determined to be [-60, 60], the basic domain of EC is [-60, 60], and according to the variation range of the control frequency, the basic domain of the frequency increment DF is determined to be [-30, 30]. On the premise of meeting the control accuracy requirements, E is quantized into 7 levels, the fuzzy domain of E is [0, 1, 2, 3, 4, 5, 6], EC is also quantized into 7 levels, the fuzzy domain of EC is [-3, -2, -1, 0, 1, 2, 3], and DF is also quantized into 7 levels, the fuzzy domain of DF is [-3, -2, -1, 0, 1, 2, 3].

[0050] In this embodiment, the linguistic variable is assigned 7 specific linguistic values: Negative Big (NB), Negative Medium (NM), Negative Small (NS), Zero (ZO), Positive Small (PS), Positive Medium (PM), and Positive Big (PB). In the selection of the membership function, a triangular membership function is adopted. The fuzzy domains of the fuzzy variables are represented by fuzzy sets, E = {NB, NM, NS, ZO, PS, PM, PB}, EC = {NB, NM, NS, ZO, PS, PM, PB}.

[0051] 3) Establishment of fuzzy rules; According to the expert's theory and practical experience, fuzzy conditional reasoning is adopted: If E is PB and EC is PB, then DF is PB, and the obtained fuzzy inference rules are shown in Table 1.

[0052] Table 1 Fuzzy Inference Rule Table

[0053]

[0054]

[0055] 4) Calculate the fuzzy value of the output variable according to the fuzzy rules and the actual value of the input variable, and then convert the fuzzy value of the output variable into an actual value;

[0056] After completing the parameter setting of the frequency fuzzy controller, the input / output characteristic surface diagram of the whole system is as Figure 5 shown.

[0057] Furthermore, the PID control method is a classical algorithm in control theory. This algorithm calculates the proportional, integral, and differential links of the error signal and linearly combines them to form a control quantity to achieve precise regulation of the output quantity. In the present invention, the difference Δθ between the phase difference and the set value is converted into a frequency error Δf, and the frequency control word K is adjusted to effectively control the frequency of the drive signal. The classical position-type discrete PID control theory can be represented by Equation (1):

[0058]

[0059] Among them, k represents the sampling sequence, and its values are 1, 2, …; e j is the cumulative sum of errors from the 0th to the kth time; u k is the actual output value at the kth time; e k is the error between the actual output and the target value at the kth time; K p 、K i 、K d respectively represent the proportional coefficient, integral coefficient, and differential coefficient. When designing the PID algorithm, special attention needs to be paid to the possible influence of integral saturation. If the integral value is too large, it may cause disorders in the tracking system. Therefore, the present invention adopts the integral separation method for anti-integral saturation processing. When the calculated error value is greater than 1000, the integral separation enable signal is triggered, and at this time, the integral error is set to zero and no longer participates in the adjustment process. Figure 6 Shows the result of comparative simulation of the above-mentioned designed Fuzzy-PID frequency tracking control method and the conventional PID algorithm on the simulation platform.

[0060] It can be seen that the Fuzzy-PID algorithm significantly shortens the adjustment time, and the overshoot is also controlled within 10%, meeting the control requirements. After multiple parameter adjustments and simulation verifications, the optimal values of Kp, Ki, and Kd are finally determined to be 40, 1, and 2 respectively. When Fuzzy-PID responds 63 times, the error between the target value and the true value reaches 0, that is, the output value accurately equals the target value.

[0061] S14. Generate a frequency control word K and input it into the DDS generator according to the current working frequency f and the adjusted frequency Δf output by the frequency fuzzy controller or the frequency PID controller;

[0062] S15. According to the re-collected feedback signal after control, return to S12 until the phase difference error Δθ reaches the minimum threshold or actively ends the milling;

[0063] The system performs zero-crossing detection on the voltage and current signals, inputs the feedback signal output by the phase detection into the Fuzzy-PID controller and then outputs the frequency control word K. By continuously cycling and updating the frequency control word K, precise phase-locked control is achieved, thereby realizing fast and accurate frequency tracking of the system.

[0064] Furthermore, based on the principle that the input current of the ultrasonic transducer is positively correlated with the output amplitude, the constant amplitude PID control method based on the feedback current is designed. The constant amplitude PID control method calculates the current effective value I of the current according to the feedback current i , according to the current effective value I of the current iThe current difference ΔI from the previous working rated current I0 generates an amplitude control word through PID control and is input into the DDS generator; as Figure 7 shown, it includes the following steps:

[0065] S21. Take the effective value of the sampled current in the resonant state of the ultrasonic transducer under no-load as the initial working rated current I0;

[0066] S22. When the processing state and the load change, the current effective value calculation module calculates the current effective value I according to the feedback X-direction current and Y-direction current i ;

[0067] The current effective value I is calculated by calculating the root mean square RMS of the X-direction current and the Y-direction current i ;

[0068] S23. Calculate the current difference ΔI between the current effective value I i and the previous working rated current I0;

[0069] S24. Determine whether the current difference ΔI is less than the set current difference ΔI0. If so, input the current difference ΔI into the amplitude PID controller to obtain an amplitude control word and input it into the DDS generator. If not, do not update the amplitude control word;

[0070] Through the PID constant amplitude control algorithm, input the feedback current error value of the transducer loop into PID control, and use the PID output value to adjust the output amplitude of the DDS generator to achieve precise control of the power supply voltage of the ultrasonic driver, ensuring the amplitude consistency of the transducer.

[0071] S25. According to the re-acquired controlled feedback signal, return to S22 until the current difference ΔI0 reaches the minimum threshold or actively ends milling;

[0072] By continuously updating the amplitude control word in a loop, a constant amplitude output with high precision and fast response is achieved.

[0073] Furthermore, the power inverter and amplifier module is used to provide a driving signal for the transducer to ensure the stability and accuracy of the system output power. The power inverter and amplifier module adopts a multi-stage hardware architecture design, including an oscillator, a dual-channel DAC conversion and drive module, an audio IC operational amplifier module, an SPWM drive module, a MOSFET half-bridge inverter module, and a low-pass filter module. The output end of the DDS generator of the signal generation and control module is connected to the input end of the dual-channel DAC conversion and drive module. The output ends of the oscillator and the dual-channel DAC conversion and drive module are connected to the input end of the audio IC operational amplifier module. The output end of the audio IC operational amplifier module is connected to the transducer through the SPWM drive module, the MOSFET half-bridge inverter module, and the low-pass filter module in sequence. First, the oscillator generates a high-frequency triangular wave signal as the carrier reference for SPWM modulation. At the same time, the dual-channel DAC conversion and drive module receives the digital control signals of frequency and amplitude output by the signal generation and control module and outputs two independently adjustable sine wave signals (X / Y directions). Subsequently, the audio IC operational amplifier module amplifies the signals, and the SPWM drive module converts the sine wave signals into pulse width modulation signals through SPWM modulation technology. The modulated pulse width modulation signals drive the MOSFET half-bridge inverter module composed of multiple MOSFETs to complete power amplification under the power supply of the high-voltage DC power supply of the power supply module. Finally, the high-frequency components are filtered out by the low-pass filter module, and the square wave signal output by the MOSFET half-bridge inverter module is converted into a pure high-frequency sine wave signal to drive the transducer to work. The entire circuit is stably powered by the power supply module to realize a complete energy conversion link from signal generation, modulation and amplification to power output.

[0074] Specifically, the oscillator uses LTC1799, the dual-channel DAC conversion and drive module uses AD9764, the audio IC operational amplifier module uses IRS2452A, and the resonant frequency of the ultrasonic transducer driven by the ultrasonic driver is 28 kHz. Since the peak-to-peak driving voltage of the piezoelectric ceramic transducer is between 150 V and 400 V, the sine signal generated by the FPGA needs to be boosted to drive the transducer. To reduce the heating of the power transistors, a dual-MOSFET half-bridge inverter boost is designed. The IRS2452A audio IC controls the MOSFETs to conduct alternately, so that the input voltage is periodically distributed in the symmetric positive and negative half-cycles. This voltage is boosted by the high-frequency transformer and converted into a high-frequency oscillation signal with a peak-to-peak value in the range of 150 V to 400 V and transmitted to the transducer, which is converted into mechanical oscillation. Figure 8 The circuit design scheme is shown.

[0075] Furthermore, the sampling and filtering module is used to accurately sample and process the feedback voltage and current of the transducer; the sampling and filtering module includes a sampling circuit and a filtering circuit. The sampling circuit includes a voltage sampling circuit for sampling the voltage in the X direction of the transducer, two current sampling circuits for sampling the currents in the X and Y directions of the transducer, and three differential amplifier circuits connected to the voltage sampling circuit and the two current sampling circuits; the filtering circuit includes three fourth-order low-pass filters connected to the output end of the sampling circuit, a dual-channel ADC acquisition circuit for connecting the sampled voltage and current in the X direction, and an ADC acquisition circuit for connecting the sampled current in the Y direction. The output ends of the dual-channel ADC acquisition circuit and the ADC acquisition circuit are both connected to the signal generation controller module.

[0076] Specifically, the fourth-order low-pass filter uses MCP6002, the dual-channel ADC acquisition circuit uses AD9226, and the ADC acquisition circuit uses ADS8681; the loop current is converted into a voltage signal through a high-precision sampling resistor, and then a reduced signal of the voltage across the transducer is obtained through a series resistor. After passing through the filtering circuit, it is transmitted to the FPGA for AD sampling. In order to reduce interference and errors, the sampled values are subjected to multiple AD conversions and the average value is calculated. At the same time, the fourth-order low-pass filter is used to attenuate high-frequency components, and finally a smooth and accurate feedback signal is obtained to support the FPGA for transducer resonance frequency tracking control and constant amplitude control. The circuit design schematic diagram is as Figure 9 shown.

[0077] Furthermore, the power supply module provides the required voltage and current for the entire system to ensure the normal operation of each functional module; the power supply module includes a high-voltage DC power supply. The main power supply selects the JK10023 series linear voltage regulator power supply, which uses 220V AC input. After step-down, rectification, and filtering, it provides ±20V and ±5V auxiliary power supplies for the inverter power amplification circuit. The design uses LD20-23B24R2 and LHE15-20A05 power management chips to realize AC-DC conversion, and outputs 24V and ±5V DC voltages respectively. Then, a TPS5430DDAR step-down chip is used to output ±20V DC voltage; the main power supply is the JK10023 series linear voltage regulator power supply, which provides a maximum ±100V bipolar DC voltage to meet the system power supply requirements.

[0078] In this embodiment, through the hardware part and software part of the above transducer drive control system, the sine wave generated by the DDS generator control from the FPGA is power-amplified to drive the transducer to work normally, and the feedback current and voltage signals in the transducer loop are accurately collected and transmitted to the FPGA for frequency tracking and constant amplitude control. The physical diagram of the transducer drive control system is as Figure 10As shown, the effect of the frequency tracking and constant amplitude control scheme of the ultrasonic driver is verified, and the expected displacement trajectory of the ultrasonic elliptical vibration amplitude is synthesized to prove the feasibility of the design of the dual-channel ultrasonic elliptical vibration ultrasonic transducer driver.

[0079] First, use an oscilloscope to collect the waveform diagrams of the output voltage and current signals of the dual-channel ultrasonic driver, and judge the phase difference change and feedback current value change between the two signals by observing the oscilloscope waveform. The waveforms of the ultrasonic transducer collected during the debugging process of the ultrasonic driver are as Figure 11 shown. From Figure 11 the waveform diagrams of the current and voltage signals before frequency tracking in Figure (a) in Figure 11 and the waveform diagrams of the current and voltage signals after frequency tracking in Figure (b) in Figure 11 it can be seen that the dual-channel signals output by the ultrasonic driver work independently at their respective resonant frequency points. The phase difference between the current and voltage signals of each channel is basically zero within the experimental error range after frequency tracking, starting from a certain phase difference when powered on, and the amplitude of the current signal also reaches the peak value during operation, indicating that the ultrasonic driver is operating well at this time. After experimental verification, the system frequency tracking accuracy reaches 5 Hz, which is jointly confirmed by the analysis of the DDS control word K value of the FPGA and Figure 11 the steady-state phase difference data. Table 2 compares the adjustment effect parameters of the Fuzzy-PID control algorithm with those of the conventional PID, and it can be seen that the Fuzzy-PID algorithm has a faster adjustment speed and a smaller overshoot, showing certain superiority. In the constant amplitude control, the feedback current value is proportional to the amplitude of the transducer, so the current change directly reflects the vibration energy. From the analysis of Figure 11 the waveform of the current feedback value after constant amplitude control in Figure (c) in

[0080] Table 2 Fuzzy-PID and PID Transient Performance Table

[0081]

[0082] it can be obtained that the maximum value of the feedback current value is 0.87 A, the minimum value is 0.81 A, the average value is 0.85 A, and the relative range is 7.06%. When the ultrasonic amplitude changes greatly, by detecting the change amount of the feedback current and using the PID control to adjust the signal voltage value of the DDS, the relative range of the feedback current value of the ultrasonic amplitude is stabilized within 10%.

[0080] Then, by adjusting the amplitude and phase of the dual-channel drive signals, the trajectory generation ability of the ultrasonic elliptical vibration system is verified. Based on the proportional relationship between the feedback current amplitude of the ultrasonic transducer and the vibration amplitude, the synthesis trajectory of the tool tip vibration displacement is indirectly reflected by measuring the drive current values in the X and Y directions. Analyze the dynamic response, steady-state accuracy, and long-term stability of the system. The trajectories synthesized by the amplitudes of the drive current signals in the X and Y directions when setting different phase differences of the dual-channel drive signals are respectively as Figure 12As shown. The elliptical ultrasonic driver designed in this embodiment can drive the ultrasonic transducer to work by adjusting the amplitude and phase of the dual-channel drive signal to achieve different elliptical vibration trajectories. It can be seen that Figure 12 Figure (a) of Figure 12 and Figure (b) of

[0083] respectively show the drive current amplitudes of the ultrasonic transducer in the X and Y directions when the phase differences are 45 degrees and 90 degrees, forming elliptical and circular trajectories respectively. The trajectories are smooth with few burrs, meeting the precision requirements of processing.

[0084] In summary, through the above-mentioned dual-channel elliptical vibration ultrasonic transducer drive system, the following beneficial effects are obtained:

[0085] (1) The present invention combines software and hardware. The signal generation and controller module outputs a frequency control signal according to the voltage and current feedback from the transducer through the Fuzzy-PID frequency tracking control method, enabling automatic tracking of the resonant frequency to ensure that the transducer always operates in the resonant state. The amplitude control signal is output according to the current feedback from the transducer through the constant amplitude PID control method, enabling real-time adjustment of the drive amplitude output by the driver to ensure the stability of the ultrasonic amplitude. Thus, the resonant frequency tracking and constant control of the ultrasonic amplitude of the ultrasonic transducer are realized; the power inverter and amplification module generates, modulates, amplifies, and outputs the drive signal of the transducer according to the received frequency and amplitude control signals, enabling the transducer to synthesize the expected displacement trajectory of the ultrasonic elliptical vibration amplitude; thereby enabling the ultrasonic transducer drive frequency to track quickly and the processing vibration amplitude to remain constant during ultrasonic elliptical vibration processing, reducing tool wear and extending tool life.

[0086] (2) Through the Fuzzy-PID frequency tracking control method, the present invention combines fuzzy control and PID control to achieve fast frequency self-tracking and overshoot adjustment with the FPGA controller as the core. According to the phase difference relationship between the current and voltage at both ends of the transducer, it can automatically track the resonant frequency to ensure that the transducer always operates in the resonant state;

[0087] (3) The present invention adopts dual-channel drive, and realizes the transmission of different vibration amplitudes in accordance with the expected phase in all directions, ensuring that a circular or elliptical vibration path is formed during the machining process, thereby effectively reducing the wear of the tool.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the embodiments of the present invention are described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A dual-channel elliptical vibration ultrasonic transducer drive control system, characterized in that It includes a sampling and filtering module, a signal generation controller module, and a power inverter and amplification module connected in sequence. The power inverter and amplification module is connected to the input end of the transducer, and the output end of the transducer is connected to the sampling and filtering module. The sampling and filtering module samples and processes the voltage and current output by the transducer. The signal generation controller module outputs a frequency control signal according to the voltage and current fed back by the transducer through the Fuzzy-PID frequency tracking control method, and outputs an amplitude control signal according to the current fed back by the transducer through the constant amplitude PID control method. The power inverter and amplification module generates, modulates, amplifies, and outputs the drive signal of the transducer according to the received frequency and amplitude control signals. The Fuzzy-PID frequency tracking control method calculates the phase difference error Δθ = |θ i according to the actual phase difference θ of the feedback voltage and current; i – θ d |; when Δθ ≥ Δθ0, the fuzzy control method is used for frequency tracking, and when Δθ < Δθ0, the PID control method is used for frequency tracking. The fuzzy control method or the PID control method outputs the adjustment frequency Δf; then, according to the current working frequency f and the adjustment frequency Δf, a frequency control word K is generated and input into the DDS generator. Among them, when the target phase difference θ d is zero, it is in the resonance state, and Δθ0 is the set standard threshold value; The constant-amplitude PID control method calculates the current effective value I based on the feedback current. i , based on the current effective value I i and the current difference ΔI between the current effective value I and the previous working rated current I0, generates an amplitude control word through PID control and inputs it into the DDS generator.

2. The dual-channel elliptical vibration ultrasonic transducer drive control system according to claim 1, wherein The signal generation controller module includes a frequency tracking control module, an amplitude control module, a DDS generator, and a dual-channel ADC drive module. The input end of the dual-channel ADC drive module is connected to the sampling and filtering module, and the output end is connected to the input end of the frequency tracking control module. The input end of the amplitude control module is connected to the sampling and filtering module and the dual-channel ADC drive module. The output ends of the frequency tracking control module and the amplitude control module are both connected to the input end of the DDS generator. The output end of the DDS generator is connected to the dual-channel DAC conversion drive module of the power inverter and amplification module.

3. The dual-channel elliptical vibration ultrasonic transducer drive control system according to claim 2, wherein, The frequency tracking control module includes a digital phase discriminator, a frequency sweeping module, a frequency PID controller, and a frequency fuzzy controller. The input end of the digital phase discriminator is connected to the dual-channel DAC conversion drive module, and the output end is connected to the frequency sweeping module, the frequency PID controller, and the frequency fuzzy controller. The output ends of the frequency sweeping module, the frequency PID controller, and the frequency fuzzy controller generate a frequency control word through the Fuzzy-PID frequency tracking control method and are connected to the DDS generator. The digital phase discriminator calculates the phase difference error Δθ of the fed-back voltage and current in the X direction in real time. The frequency sweeping module searches for the frequency corresponding to the maximum value of the fed-back current in the X direction through a variable step frequency search algorithm to determine the initial operating frequency f0. The frequency PID controller or the frequency fuzzy controller generates an adjusted frequency Δf according to the fed-back phase difference error. Then, according to the initial resonance frequency f0 and the adjusted frequency Δf, the frequency control word K is cyclically generated through the Fuzzy-PID frequency tracking control method.

4. The drive control system of the dual-channel elliptical vibration ultrasonic transducer according to claim 2, wherein The amplitude control module includes a current effective value calculation module and an amplitude PID controller connected in sequence; the current effective value calculation module calculates the current effective value I of the feedback current according to the feedback X-direction current and Y-direction current i , and then according to the current effective value I by the constant amplitude PID control method i , the current difference ΔI between the current effective value I and the rated current I0 of the previous time is input into the amplitude PID controller, and the amplitude PID controller generates an amplitude control word.

5. The dual-channel elliptical vibration ultrasonic transducer drive control system according to claim 1, characterized in that, The power inverter and amplification module includes an oscillator, a dual-channel DAC conversion drive module, an audio IC operational amplifier module, an SPWM drive module, a MOSFET half-bridge inverter module, and a low-pass filter module. The output end of the DDS generator of the signal generation controller module is connected to the input end of the dual-channel DAC conversion drive module. The output ends of the oscillator and the dual-channel DAC conversion drive module are connected to the input end of the audio IC operational amplifier module. The output end of the audio IC operational amplifier module is connected to the transducer through the SPWM drive module, the MOSFET half-bridge inverter module, and the low-pass filter module in sequence.

6. The dual-channel elliptical vibration ultrasonic transducer drive control system according to claim 1, characterized in that, The sampling and filtering module includes a sampling circuit and a filtering circuit. The sampling circuit includes a voltage sampling circuit for sampling the voltage of the transducer in the X direction, two current sampling circuits for sampling the currents of the transducer in the X and Y directions, and three differential amplification circuits connected to the voltage sampling circuit and the two current sampling circuits. The filtering circuit includes three fourth-order low-pass filters connected to the output end of the sampling circuit, a dual-channel ADC acquisition circuit for connecting the sampled X-direction voltage and current, and an ADC acquisition circuit for connecting the sampled Y-direction current. The output ends of the dual-channel ADC acquisition circuit and the ADC acquisition circuit are both connected to the signal generation controller module.

7. The dual-channel elliptical vibration ultrasonic transducer drive control system according to claim 1, wherein It also includes a power supply module.

8. The dual-channel elliptical vibration ultrasonic transducer drive control system according to claim 1, characterized in that, The Fuzzy-PID frequency tracking control method includes: S11. The frequency sweeping module searches for the frequency corresponding to the maximum feedback current according to the variable step size frequency search algorithm, determines the initial operating frequency f0, and sets the current operating frequency f = f0. S12. The digital phase discriminator calculates the actual phase difference θ in real time based on the phase difference between the feedback X-direction voltage and current. i , and then calculates the phase difference error Δθ according to the actual phase difference θ i ; S13. When Δθ≥Δθ0, the frequency fuzzy controller runs the fuzzy control method for frequency tracking; when Δθ<Δθ0, the frequency PID controller runs the PID control method for frequency tracking. S14. Generate a frequency control word K according to the current operating frequency f and the adjusted frequency Δf output by the frequency fuzzy controller or the frequency PID controller, and input it into the DDS generator. S15. According to the re-acquired controlled feedback signal, return to S12 until the phase difference error Δθ reaches the minimum threshold or actively ends the milling.

9. The dual-channel elliptical vibration ultrasonic transducer drive control system according to claim 1, characterized in that, The constant amplitude PID control method includes: S21. Take the effective value of the sampled current in the resonant state of the ultrasonic transducer under no-load as the initial operating rated current I0. S22. When the processing state and the load change, the effective current calculation module calculates the current effective value I based on the fed-back X-direction current and Y-direction current. i ; S23. Calculate the effective value I of the current at present i and the current difference ΔI from the rated working current I0 of the previous time; S24. Judge whether the current difference ΔI is less than the set current difference ΔI0. If so, input the current difference ΔI into the amplitude PID controller to obtain an amplitude control word and input it into the DDS generator. If not, do not update the amplitude control word. S25. According to the re-acquired controlled feedback signal, return to S22 until the current difference ΔI0 reaches the minimum threshold or actively ends the milling.

10. The dual-channel elliptical vibration ultrasonic transducer drive control system according to claim 1 or 8, characterized in that, The fuzzy control method includes: 1) Determine the input and output quantities of the fuzzy control; set the input quantities of the fuzzy control as the phase difference E and the change rate of the phase difference EC = Δe / Δt, and the output quantity of the fuzzy control as the frequency increment DF. Among them, the phase difference E is the phase difference θ i , Δe in EC is the phase difference error Δθ, Δt is the sampling time difference, and DF is the adjustment frequency Δf; 2) Fuzzification of the input and output variables of the fuzzy control; Determine the basic universe of discourse of E as [-60, 60] according to the variation range of the phase difference, the basic universe of discourse of EC as [-60, 60], and the basic universe of discourse of the frequency increment DF as [-30, 30] according to the variation range of the adjustment frequency. On the premise of meeting the control accuracy requirements, quantize E into 7 levels, the fuzzy universe of discourse of E is [0, 1, 2, 3, 4, 5, 6], quantize EC into 7 levels, the fuzzy universe of discourse of EC is [-3, -2, -1, 0, 1, 2, 3], and quantize DF into 7 levels, the fuzzy universe of discourse of DF is [-3, -2, -1, 0, 1, 2, 3]; The language variable is assigned 7 specific linguistic values: Negative Big is NB, Negative Medium is NM, Negative Small is NS, Zero is ZO, Positive Small is PS, Positive Medium is PM, and Positive Big is PB; The membership function adopts the triangular membership function; Represent the fuzzy universe of discourse of the fuzzy variable with a fuzzy set, E = {NB, NM, NS, ZO, PS, PM, PB}, EC = {NB, NM, NS, ZO, PS, PM, PB}. 3) Establishment of fuzzy rules; The fuzzy rules are as follows in the table: 4) Calculate the fuzzy value of the output variable according to the said fuzzy rules and the actual value of the input variable, and then convert the fuzzy value of the output variable into an actual value.

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