Speed and position feedback system suitable for linear ultrasonic motor driving control

Abstract

The invention discloses a speed and position feedback system suitable for linear ultrasonic motor driving control, which adopts a blue light reflection type grating to collect rotor displacement in real time, outputs TTL pulse signals, carries out subdivision and filtering and then processes the TTL pulse signals by a single-chip microcomputer, and generates closed-loop feedback signals to adjust driving parameters. The problem of speed position misalignment caused by frequency drift and friction loss of the ultrasonic motor is effectively solved, and the method is suitable for the fields of high-precision industrial automation and aerospace.

Description

Technical Field

[0001] The present invention relates to the field of ultrasonic motor control technology, and in particular to a speed position feedback system suitable for linear ultrasonic motor drive control, for solving the frequency drift and speed position deviation problems of the linear ultrasonic motor caused by long-term high-frequency and high-voltage operation. Background Art

[0002] Ultrasonic motors are based on the inverse piezoelectric effect. They drive the rotor by generating microscopic elliptical motions of particles on the stator surface. They have the advantages of compact structure, fast response, and self-locking when power is off. They are widely used in precision instruments, aerospace, and other fields. However, when ultrasonic motors are operated at high frequency and high voltage for a long time, the friction between the stator and the rotor will cause the temperature of the contact surface to rise. At the same time, the frequency drift of the driving signal will cause the optimal working point to shift, resulting in a downward shift in the actual speed and position values, affecting the control accuracy. Traditional open-loop control schemes are difficult to compensate for such deviations in real time, and a high-precision, high-response closed-loop feedback system is urgently needed. Summary of the invention

[0003] Purpose of the Invention Aiming at the speed and position misalignment problem of ultrasonic motor caused by frequency drift and friction loss, the present invention proposes a speed and position feedback system suitable for linear ultrasonic motor drive control. The speed and position signals are collected in real time and fed back to the controller, and the drive parameters are dynamically adjusted to ensure the stability and accuracy of the motor operation.

[0004] A speed position feedback system suitable for linear ultrasonic motor drive control, comprising: Blue light reflective grating ruler reading head, wavelength range is 400-410nm, output differential TTL square wave pulse signal, positioning resolution ≤0.5μm; Dynamically adjustable subdivision circuit, 4× or 8× subdivision mode switching can be realized through FPGA programming, and the input port is connected to the grating ruler reading head; Second-order Butterworth low-pass filter circuit, with the cut-off frequency set to 1.2 times the grating ruler signal frequency, the input end is connected to the subdivision circuit, and the output end is connected to the microcontroller timer; The 5V power supply module of the single-chip microcomputer drives the grating ruler reading head and processes the filtered pulse signal to generate closed-loop compensation instructions; Photoelectric isolation module, set between the single chip microcomputer and the ultrasonic motor controller, shielding effectiveness ≥ 60dB; The grating ruler reading head is attached to the surface of the ultrasonic motor stator, and its differential signal output end is connected to the subdivision circuit through a twisted pair shielded line to form a closed-loop feedback system to suppress the displacement deviation caused by frequency drift.

[0005] The resolution of the blue light reflective grating ruler is achieved through the FPGA dynamic subdivision mode, and the positioning error is ≤±2μm when 4× subdivision is performed, and the positioning error is ≤±0.5μm when 8× subdivision is performed.

[0006] The cut-off frequency of the second-order Butterworth filter is 80kHz, which matches the base frequency of the ultrasonic motor drive signal, and the response delay is ≤20μs.

[0007] The photoelectric isolation module adopts a magnetic coupling isolation chip, the isolation voltage is ≥2500Vrms, and the signal transmission delay is ≤1μs.

[0008] The single chip microcomputer generates a frequency compensation signal through a fuzzy PID algorithm, and the drive controller adjusts the step length ≤0.1Hz and the voltage amplitude adjustment step length ≤1V.

[0009] The shielding layer of the twisted shielded pair cable is connected to the metal housing of the motor through a multi-point grounding method, and the common mode rejection ratio is ≥80dB.

[0010] The ultrasonic motor, power amplifier driver and host computer are all carriers of the entire feedback system.

[0011] The present invention proposes an innovative closed-loop feedback solution to the frequency drift problem of ultrasonic motors when they run for a long time at high frequency and high voltage. Through the coordinated optimization of hardware design and control strategy, the system performance is significantly improved. The beneficial effects are as follows: Traditional ultrasonic motor closed-loop systems mostly use red light gratings or piezoelectric sensors. Due to the wavelength of the light source, the positioning accuracy is usually around ±2μm. The blue light reflective grating (wavelength 405nm) used in the present invention improves the resolution to ±0.5μm through a denser optical grating design. For example, in the joint control scenario of a medical robot, this accuracy can reduce the positioning error of the end of the surgical instrument to the cellular level (about 5-10μm), meeting the needs of minimally invasive surgery. At the same time, the system automatically switches to high-resolution mode under heavy load conditions through dynamic subdivision technology (4× / 8× mode switching), avoiding the loss of accuracy caused by load mutations in traditional fixed subdivision circuits, and achieving high precision and stability.

[0012] The ultrasonic motor drive signal is usually a 60-100kHz high-voltage sine wave, which is easy to cause electromagnetic interference to the feedback system. The present invention solves this problem through three key technologies. ① Through differential signal transmission, the positive / negative phase TTL signal output by the grating is transmitted through a twisted pair shielded line to suppress common mode interference; ② A Butterworth filter with adjustable cutoff frequency is used to dynamically adjust the filter parameters according to the noise spectrum collected in real time; ③ A magnetic coupling isolation chip is added to the control system to achieve 2500Vrms electrical isolation, block ground loop interference, and achieve enhanced photoelectric isolation.

[0013] Aiming at the core problem of frequency drift, the system integrates hardware feedback and intelligent control algorithms to optimize dynamic compensation capabilities: ① The position loop (grating feedback) and the frequency loop (phase detection) work together. When the grating detects position deviation, the drive frequency and voltage amplitude are adjusted synchronously. ② The fuzzy PID algorithm is used to dynamically adjust the control parameters by learning parameters such as motor temperature rise and load changes in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural block diagram of the speed position feedback system of the present invention. DETAILED DESCRIPTION

[0015] Reference Figure 1 , a speed position feedback system suitable for linear ultrasonic motor drive control, comprising: Blue light reflective grating ruler reading head, wavelength range is 400-410nm, output differential TTL square wave pulse signal, positioning resolution ≤0.5μm; Dynamically adjustable subdivision circuit, 4× or 8× subdivision mode switching can be realized through FPGA programming, and the input port is connected to the grating ruler reading head; Second-order Butterworth low-pass filter circuit, with the cut-off frequency set to 1.2 times the grating ruler signal frequency, the input end is connected to the subdivision circuit, and the output end is connected to the microcontroller timer; The 5V power supply module of the single-chip microcomputer drives the grating ruler reading head and processes the filtered pulse signal to generate closed-loop compensation instructions; Photoelectric isolation module, set between the single chip microcomputer and the ultrasonic motor controller, shielding effectiveness ≥ 60dB; The grating ruler reading head is attached to the surface of the ultrasonic motor stator, and its differential signal output end is connected to the subdivision circuit through a twisted pair shielded line to form a closed-loop feedback system to suppress the displacement deviation caused by frequency drift.

[0016] The resolution of the blue light reflective grating ruler is achieved through the FPGA dynamic subdivision mode, and the positioning error is ≤±2μm when 4× subdivision is performed, and the positioning error is ≤±0.5μm when 8× subdivision is performed.

[0017] The cut-off frequency of the second-order Butterworth filter is 80kHz, which matches the base frequency of the ultrasonic motor drive signal, and the response delay is ≤20μs.

[0018] The photoelectric isolation module adopts a magnetic coupling isolation chip, the isolation voltage is ≥2500Vrms, and the signal transmission delay is ≤1μs.

[0019] The single chip microcomputer generates a frequency compensation signal through a fuzzy PID algorithm, and the drive controller adjusts the step length ≤0.1Hz and the voltage amplitude adjustment step length ≤1V.

[0020] The shielding layer of the twisted shielded pair cable is connected to the metal housing of the motor through a multi-point grounding method, and the common mode rejection ratio is ≥80dB.

[0021] The ultrasonic motor, power amplifier driver and host computer are all carriers of the entire feedback system.

[0022] The speed position feedback system of the present invention realizes high-precision control of the ultrasonic motor through the following steps to ensure its stability under long-term high-frequency and high-voltage operation: First, install the blue light reflective grating ruler: attach the blue light reflective grating ruler reading head (wavelength 405nm±5nm) to the surface of the ultrasonic motor stator, and fix the grating grid sheet on the mover. When the mover moves, the grating ruler detects displacement through the change of light and dark fringes (Moiré fringes) formed by light reflection, and outputs a differential TTL square wave pulse signal.

[0023] The signal dynamically selects the subdivision mode through the FPGA chip as follows: 4× subdivision mode: used when light load is used, each pulse corresponds to a displacement of 0.125μm, and the positioning error is ≤±2μm; 8× subdivision mode: automatically switches when heavy load or high precision is required, each pulse corresponds to a displacement of 0.0625μm, and the positioning error is ≤±0.5μm.

[0024] The differential signal is transmitted through twisted-pair shielded cables, and the shielding layer is connected to the metal casing of the motor through three-point grounding, which suppresses external electromagnetic interference by more than 80% and achieves anti-interference transmission.

[0025] Then, signal filtering and noise elimination are performed. The filter circuit sets the cutoff frequency to 80kHz (1.2 times the fundamental frequency of the ultrasonic motor drive signal) to filter out high-frequency noise above 160kHz; the signal delay after filtering is ≤20μs to ensure real-time performance.

[0026] The pulse signal waveform after filtering is clearer, which can reduce the misjudgment of the microcontroller.

[0027] Then, the 100MHz high-speed timer of the microcontroller (STM32H7 series) counts the filtered pulses at four times the frequency, calculates the displacement deviation in real time, dynamically adjusts the PID parameters according to the displacement deviation and temperature sensor data, and generates compensation instructions: Frequency compensation: drive signal frequency is fine-tuned from 80.00kHz to 80.05kHz (step size ≤ 0.1Hz); Voltage compensation: The power amplifier output voltage is adjusted from 150Vpp to 151Vpp (step size ≤ 1V).

[0028] Then, the compensation command is transmitted to the ultrasonic motor controller through the magnetic coupling isolation chip. The isolation voltage is ≥2500Vrms, which avoids the interference of high-voltage drive signals on the single-chip microcomputer circuit and realizes photoelectric isolation protection. The controller adjusts the DDS signal source and the power amplifier module in real time, so that the motor operating frequency is always close to the optimal resonance point, eliminating the frequency drift caused by temperature rise.

[0029] Finally, the entire closed loop is continuously optimized and monitored, and the system continuously executes the above-mentioned "signal acquisition → filtering → calculation → feedback" process in a period of 30μs to ensure real-time correction.

[0030] The displacement, speed and compensation parameters are transmitted to the host computer interface through RS485 communication. The operator can manually switch the subdivision mode or view historical data and realize monitoring through the host computer.

Claims

1. A speed position feedback system suitable for linear ultrasonic motor drive control, characterized in that: include: Blue light reflective grating ruler reading head, wavelength range is 400-410nm, output differential TTL square wave pulse signal, positioning resolution ≤0.5μm; Dynamically adjustable subdivision circuit, 4× or 8× subdivision mode switching can be realized through FPGA programming, and the input port is connected to the grating ruler reading head; Second-order Butterworth low-pass filter circuit, with the cut-off frequency set to 1.2 times the grating ruler signal frequency, the input end is connected to the subdivision circuit, and the output end is connected to the microcontroller timer; The 5V power supply module of the single-chip microcomputer drives the grating ruler reading head and processes the filtered pulse signal to generate closed-loop compensation instructions; Photoelectric isolation module, set between the single chip microcomputer and the ultrasonic motor controller, shielding effectiveness ≥ 60dB; The grating ruler reading head is attached to the surface of the ultrasonic motor stator, and its differential signal output end is connected to the subdivision circuit through a twisted pair shielded line to form a closed-loop feedback system to suppress the displacement deviation caused by frequency drift.

2. The speed position feedback system for linear ultrasonic motor drive control according to claim 1, characterized in that: The resolution of the blue light reflective grating ruler is achieved through the FPGA dynamic subdivision mode, and the positioning error is ≤±2μm when 4× subdivision is performed, and the positioning error is ≤±0.5μm when 8× subdivision is performed.

3. The speed position feedback system for linear ultrasonic motor drive control according to claim 1, characterized in that: The cut-off frequency of the second-order Butterworth filter is 80kHz, which matches the base frequency of the ultrasonic motor drive signal, and the response delay is ≤20μs.

4. The speed position feedback system for linear ultrasonic motor drive control according to claim 1, characterized in that: The photoelectric isolation module adopts a magnetic coupling isolation chip, the isolation voltage is ≥2500Vrms, and the signal transmission delay is ≤1μs.

5. The speed position feedback system for linear ultrasonic motor drive control according to claim 1, characterized in that: The single chip microcomputer generates a frequency compensation signal through a fuzzy PID algorithm, and the drive controller adjusts the step length ≤0.1Hz and the voltage amplitude adjustment step length ≤1V.

6. The speed position feedback system for linear ultrasonic motor drive control according to claim 1, characterized in that: The shielding layer of the twisted shielded pair cable is connected to the metal housing of the motor through a multi-point grounding method, and the common mode rejection ratio is ≥80dB.

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