Three-degree-of-freedom ultrasonic motor driving control method

Abstract

The invention discloses a three-degree-of-freedom ultrasonic motor driving control method. A three-degree-of-freedom ultrasonic motor comprises a signal generation module, a key control module, a power amplification module, a communication module, a grating ruler analysis module, a control algorithm, a data processing module, a power amplification circuit, a matching circuit and a voltage and current sampling circuit. The signal generation module outputs six paths of PWM waves with adjustable frequencies, phases and duty ratios, the control algorithm module performs adjustment through a control algorithm according to operation parameters of an ultrasonic motor fed back by a grating ruler, the key module is used for manual control, and the communication module is composed of USART logic and DMA logic. A control algorithm and data processing are generated by a single-chip microcomputer, detection and servo control are carried out through a communication USART module, and real-time monitoring, power amplification and matching are carried out on a serial port assistant of an upper computer, and a voltage and current sampling circuit drives and stabilizes operation of the ultrasonic motor. According to the invention, the amplitude modulation precision is below 4mv, and the stability is higher through a closed-loop control algorithm.

Description

Technical Field

[0001] The present invention relates to the field of ultrasonic drive technology, and more particularly to a high-speed, high-precision, amplitude-modulated drive three-degree-of-freedom ultrasonic motor drive circuit based on a single-chip microcomputer and a control method thereof. Background Art

[0002] Ultrasonic motors (USMs) are a new type of motor. Compared to traditional motors, they offer advantages such as simple structure, small size and light weight, fast response, low noise, high torque at low speed, excellent control characteristics, self-locking upon power failure, immunity to magnetic field interference, and precise motion. Furthermore, they are resistant to low temperatures and vacuum environments, making them suitable for space environments. Therefore, they are widely used in various fields. Ultrasonic motors utilize the inverse piezoelectric effect to generate micromechanical motion in the stator within the ultrasonic frequency band (above 20 kHz). This motion, driven by a certain preload, drives the rotor. In other words, the stator generates traveling waves that drive the rotor through friction. Friction increases the temperature of the contact surface, which can affect control performance, necessitating the development of a feedback loop. Based on the principles of ultrasonic motor motion, the following control methods exist: 1. Amplitude modulation, which varies the voltage of the signal; 2. Frequency modulation, which varies the frequency of the output signal; and 3. Phase modulation, which varies the phase difference between the two output signals.

[0003] Currently, PWM signals are primarily generated using microcontrollers and FPGAs. Compared to FPGAs, microcontrollers are lower cost and simpler to operate. However, the current ultrasonic motor drive structure is complex, the speed is slow, and the control accuracy is limited. This fails to meet the demands for high integration, high speed, high precision, and ease of operation required for ultrasonic motors. Summary of the Invention

[0004] In order to overcome technical deficiencies such as complex structure, low motion speed, low precision, low efficiency and poor stability, the purpose of the present invention is to provide a three-degree-of-freedom ultrasonic motor drive control method, which solves the existing problems by configuring advanced timers and ordinary timers, constructing multi-channel frequency modulation, phase modulation and duty cycle modulation PWM signals, configuring encoder analysis modules, configuring communication modules, control algorithm modules, power amplifier modules, matching modules and combining with a drive control board with small size, high integration and high efficiency transmission and an algorithm combining feedforward and closed loop.

[0005] To achieve the above object, the present invention adopts the following method: A three-degree-of-freedom ultrasonic motor drive control method, the control system includes a signal generation module, a communication module, a GPIO button control module, a grating ruler analysis module, a control algorithm and a data processing module, the communication module is used to realize communication between a single-chip microcomputer chip and a PC host computer, the signal generation module is used to output six-channel high-precision PWM waves with amplitude modulation, frequency modulation, phase modulation and duty cycle modulation, and the output waveform is connected to a drive circuit to drive a three-degree-of-freedom ultrasonic motor; the GPIO button control module is used to manually control the single-chip microcomputer chip; the grating ruler analysis module is connected to the three-degree-of-freedom ultrasonic motor and is used to feedback the operating parameters and status of the three-degree-of-freedom ultrasonic motor, and the parameters analyzed by the grating ruler are passed through the control algorithm to optimize the drive control of the three-degree-of-freedom ultrasonic motor.

[0006] Furthermore, the signal generating module realizes the output of PWM wave by configuring various parameters of the advanced timer or ordinary timer in the single-chip microcomputer chip, wherein: the various parameters are determined by the automatic reload register ARR, the comparison register CRR, the pre-scaling PSC and the configuration of each channel.

[0007] After further determining the clock frequency of the advanced timer or ordinary timer of the single-chip microcomputer, the pre-scaling parameter value PSC of the timer and the automatic reload register ARR are configured to change the frequency of the output waveform; The automatic reload register ARR determines the duty cycle interval, and then adjusts the size of the pulse in the timer output channel to change the duty cycle of the waveform within the range of 0-ARR; The output comparison module compares the value of the counter CNT with the capture comparison register CRR. When the CNT value is equal to the CRR value, the output level is flipped to achieve phase adjustment of the output PWM wave.

[0008] Furthermore, the control algorithm module transmits the obtained three-degree-of-freedom ultrasonic motor operating parameters to the single-chip microcomputer, and performs algorithm optimization control after data processing to adjust the output PWM to realize a complete closed-loop system.

[0009] Furthermore, the grating ruler analysis module supports multiple protocol types of absolute and incremental encoders.

[0010] Furthermore, the USART protocol enables real-time communication between the single-chip microcomputer and the host computer PC, thereby optimizing the control system.

[0011] Furthermore, the voltage and current sampling module feeds back the obtained signal to the controller to adjust and compensate the output signal voltage and current, thereby improving the performance of the drive control system.

[0012] Beneficial effects of the present invention: The present invention can achieve rapid adjustment of the phase difference, frequency and duty cycle of the main driving parameters of the three-degree-of-freedom ultrasonic motor by outputting six-channel PWM through a single-chip microcomputer, wherein amplitude modulation with an accuracy of less than 4mV and various drive and control signals can be realized. Through real-time communication with a PC host computer via a serial port, the FPGA can be modified and optimized online by the host computer. The timer encoder mode is set, and the structure is simple. Through a grating ruler, the characteristics of the three-degree-of-freedom ultrasonic motor can be measured in real time, the obtained data can be fed back in real time, and the algorithm can be optimized to achieve full closed-loop control of the three-degree-of-freedom ultrasonic motor and enhance the stability of the motor operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a diagram of the three-degree-of-freedom ultrasonic motor control system; Figure 2 This is a configuration diagram where the PWM duty cycle is determined by auto-reload and Pulse; Figure 3 This is the PWM working mode diagram; Figure 4 This is a diagram of the timer master-slave mode; Figure 5 This is the master-slave relationship diagram of the microcontroller timer; Figure 6 This is the circuit diagram of the ultrasonic motor driver chip; Figure 7 This is the USART serial port configuration diagram. DETAILED DESCRIPTION

[0014] The technical solutions of the present invention will be described in more detail below in conjunction with the accompanying drawings in the embodiments of the present invention. The present invention can be implemented in many different forms and should not be considered to be limited to the embodiments described herein. On the contrary, these embodiments are provided to make this disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0015] like Figure 1 As shown, the present invention is a high-speed, high-precision amplitude modulation driven multi-parameter feedback three-degree-of-freedom ultrasonic motor control system based on a single-chip microcomputer, including an encoder module, a communication module, a signal generation module, a key control module, a control algorithm module, a power amplifier module, a matching module, etc., wherein the signal generation module mainly controls the frequency of the PWM output by setting an advanced timer or an ordinary timer, and the PWM control part mainly controls the duty cycle of the PWM output.

[0016] like Figure 2 In this example, when the auto-reload value is 9999, every time the PWM output channel Pulse increases by 1, the duty cycle increases by 0.0001 and the amplitude increases by 3.571mV.

[0017] like Figure 3 , in PWM working mode, a register CCR1 is introduced. This register is used to control the effective level length (duty cycle) of the PWM output wave. Assume the timer works in the up - counting PWM mode. When CNT < CCR1, the output is 0, and when CNT >= CCR1, the output is 1. When CNT reaches the ARR value, it resets to zero and then starts up - counting again, cycling in turn. By changing the value of CCRx, the duty cycle of the PWM output can be changed, and by changing the value of ARR, the frequency of the PWM output can be changed.

[0018] The PWM phase difference adjustment can be changed through the master - slave mode of the timer, such as Figure 4 , the main timer TIM1 outputs two PWM signals. Among them, channel 1 (CH1) is used for tube driving, and channel 2 (CH2) sets the comparison value to half of the period (to achieve a fixed phase difference between channel 1 of the main timer TIM1 and channel 1 of the slave timer TIM2). Configure the MMS register as 100, and set its comparison valid signal OC2REF as the output of the main timer TIM1, which is used to trigger the slave timer TIM2 to reset. The timer TIM2 is set to the slave mode (SMS) reset mode (100), and the trigger signal TS is set to the internal trigger ITRx.

[0019] In the example, such as Figure 5 , TIM1 is the main timer, TIM2 is the slave timer, and TIM3 is the secondary slave timer. The PWM formed by TIM1 and TIM3 is the one we finally need, and TIM2 plays a role in phase adjustment. When TIM1 generates a rising edge, TIM2 starts timing. When TIM2 counts to 3 / 4 of the period (which is 90° phase value, or in other words, a time difference, here the time difference is 3 / 4 of the period, that is, TIM2 generates a PWM with a duty cycle of 75%), it generates a PWM. After the rising edge of TIM2 is detected by TIM3, TIM3 starts to generate a PWM with an arbitrary duty cycle. In this way, two PWMs with arbitrary phases and arbitrary duty cycles can be achieved. Similarly for the other four PWMs.

[0020] After the six - channel PWM waves pass through the drive circuit, two sine signals are output to drive the ultrasonic motor, and the operating parameters of the ultrasonic motor are obtained through the grating scale encoder module. One of the phase drive circuits is as Figure 6 shown. <​​​​​As shown, the grating scale encoder parsing module obtains the parameters of the grating scale and transmits them serially to the microcontroller for data processing. The processed data is optimized for the control algorithm and fed back to the signal generator through the communication decoding module, so that the ultrasonic motor can be controlled with high performance.

[0023] Depend on Figure 7 As shown, the USART interface is connected to other devices through three pins. Any USART bidirectional communication requires at least two pins: receive data input pin (RX: receive data input pin is the serial data input pin. Oversampling technology can distinguish between valid input data and noise, thereby used to recover data.) and transmit data pin output (TX: transmit data output pin. If the transmitter is turned off, the output pin mode is determined by the I / O port configuration. If the transmitter is enabled but there is no data to be sent, the TX pin is at a high level. In single-wire and smart card modes, this I / O port is used to send and receive data (at the USART level, then receive data on SW_RX).

[0024] In normal USART mode, serial data is sent and received in frames via these pins: ● Keep the line idle before sending or receiving ●Start bit ●Data (word length 8 or 9 bits), least significant bit first ● 0.5, 1, 1.5, or 2 stop bits to indicate frame transmission completion ●This interface uses a fractional baud rate generator - with 12-bit mantissa and 4-bit decimal Status register (USART_SR) Data register (USART_DR) ● Baud Rate Register (USART_BRR) - 12-bit mantissa and 4-bit fractional number.

[0025] ●Guard Time Register (USART_GTPR) in smart card mode.

[0026] The following pins are required when connecting in synchronous mode: SCLK: Transmitter Clock Output. This pin outputs the transmitter data clock for synchronous transmission in SPI master mode (no clock pulses are provided for the start and stop bits; a clock pulse can be provided for the last data bit via software). The RX pin can also synchronously receive parallel data. This can be used to control peripherals with shift registers, such as LCD drivers. The clock phase and polarity are software programmable. In smart card mode, SCLK provides the clock to the smart card.

[0027] The following pins are required in hardware flow control mode: nCTS: “Clear to Send” is used to prevent data from being sent when the current transmission ends (when high) nRTS: “Request to Send” is used to indicate that the USART is ready to receive data (when low) The PC can communicate with the MCU via the USART protocol, transferring the ultrasonic motor drive parameter data stored in the MCU to facilitate further theoretical analysis. Online debugging can also be used to optimize the MCU control algorithm module to achieve high-performance control of the ultrasonic motor drive controller.

[0028] The key module uses an external keyboard array as input to perform real-time control of the communication module, encoder analysis, and control algorithm data processing, which can be used to ensure the safe and stable operation of the ultrasonic motor.

[0029] The present invention relates to a high-speed, high-precision amplitude modulation driven three-degree-of-freedom ultrasonic motor drive and control system based on a single-chip microcomputer. The system adopts a single-chip microcomputer as a main control chip, a driving power amplifier circuit and a grating scale encoder. The single-chip microcomputer outputs a PWM signal which is output to the three-degree-of-freedom ultrasonic motor through the driving power amplifier circuit. The grating scale encoder reads multiple parameters of the three-degree-of-freedom ultrasonic motor. Then, the various parameters are fed back into the control algorithm for optimized control, thereby realizing full closed-loop control of the three-degree-of-freedom ultrasonic motor, achieving a minimum step length of 3um for the three-degree-of-freedom ultrasonic motor, and enhancing the stability of the motor operation.

Claims

1. A three-degree-of-freedom ultrasonic motor drive control method, characterized in that: The motor controller includes a communication module, a signal generation module, a GPIO button control module, a grating scale analysis module, a control algorithm and a data processing module as well as a power amplifier, matching, and voltage and current sampling circuits; the communication module is used to realize communication between the single-chip microcomputer chip and the PC host computer, and the signal generation module is used to output six-channel PWM waves with high precision amplitude modulation, frequency modulation, phase modulation and duty cycle modulation. The output waveform is connected to the drive circuit to drive the three-degree-of-freedom ultrasonic motor; the GPIO button control module is used to manually control the single-chip microcomputer chip; the grating scale analysis module is connected to the three-degree-of-freedom ultrasonic motor to feedback the operating parameters and status of the three-degree-of-freedom ultrasonic motor, and the parameters after grating scale analysis are passed through the control algorithm. The matching and voltage and current sampling module samples the voltage and current signals of the ultrasonic motor and feeds them back to the controller, adjusts and compensates the output signal voltage and current, thereby improving the performance of the drive control system and optimizing the drive control of the three-degree-of-freedom ultrasonic motor.

2. The three-degree-of-freedom ultrasonic motor drive control method according to claim 1, characterized in that: The signal generation module includes the timer's pre-scaling PSC value, timer clock frequency, automatic reload ARR, output comparison, etc. The frequency of the output PWM is determined by configuring the timer's automatic reload register ARR, the pre-scaling value PSC and the timer's clock frequency. The automatic reload register ARR is used to determine the duty cycle interval size of the output PWM. The output comparison is used to set the CNT value and compare it with the capture comparison register CRR to achieve phase adjustment.

3. The three-degree-of-freedom ultrasonic motor drive control method according to claim 2, characterized in that: The duty cycle, frequency and phase difference are adjusted in the following ways: (1) When the value of the timer's automatic reload register ARR is determined, the duty cycle of the PWM wave is adjusted by setting the parameters in the timer's PWM output channel in the range of 0-ARR; (2) By changing the value of the timer's automatic reload register ARR and the value of the prescaler PSC, the output PWM wave frequency can be adjusted; (3) The output comparison module compares the value of the counter CNT with the capture comparison register CRR. When the CNT value is equal to the CRR value, the output level is flipped to achieve phase adjustment of the output PWM wave.

4. The three-degree-of-freedom ultrasonic motor drive control method according to claim 1, characterized in that: The control algorithm module transmits the obtained three-degree-of-freedom ultrasonic motor operating parameters to the single-chip microcomputer, and after data processing, performs algorithm optimization control to adjust the output PWM to realize a complete closed-loop system.

5. The three-degree-of-freedom ultrasonic motor drive control method according to claim 3, characterized in that : The grating ruler analysis module supports multiple protocol types of absolute and incremental encoders.

6. The three-degree-of-freedom ultrasonic motor drive control method according to claim 3, characterized in that: Through the USART protocol, the microcontroller and the host PC can achieve real-time communication and optimize the control system.

7. The three-degree-of-freedom ultrasonic motor drive control method according to claim 3, characterized in that : Monitor voltage and current, feed the obtained signal back to the controller, adjust and compensate the output signal voltage and current, and improve the performance of the drive control system.

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