Ultrasonic motor positioning control method and control system based on beat traveling waves

Abstract

The invention relates to an ultrasonic motor positioning control method and system based on beat traveling waves, and the method achieves the deceleration stage before positioning through the strict control of the output duration of a beat traveling wave signal, and achieves the gradient micro-stepping motion through the pulse driving of different duty ratios of the beat traveling waves. According to the method, the positioning time is shortened through large-step stepping when the distance from the target position is large, the positioning precision is guaranteed through high-precision stepping when the distance is close to the target position, and the purpose of short-time high-precision positioning is achieved by combining an ultrasonic motor positioning control system based on an FPGA, generating required traveling wave signals and beat traveling wave signals and switching different stages in the positioning process. And the control requirement of short-time high-precision positioning of the ultrasonic motor can be met.

Description

Technical Field

[0001] The present invention relates to a positioning control method and a control system of an ultrasonic motor based on beat waves, and belongs to the technical field of ultrasonic motor positioning control. Background Art

[0002] The unique electrical properties of semiconductors make them the foundation of electronic devices and the core of the development of the electronics industry. Semiconductor packaging plays a vital role in protecting chips, supporting and fixing chips, connecting chips to external circuits, and enhancing thermal conductivity. During the packaging process, the need to ensure the accurate position of the chip and install the housing and lead out the pins requires short-term, high-precision positioning control of the semiconductor packaging machine drive unit. As a new type of actuator, ultrasonic motors have the advantages of fast response, low speed and high torque, no electromagnetic interference, and self-locking when power is off. They use the inverse piezoelectric effect of piezoelectric ceramics to generate high-frequency ultrasonic vibrations in the stator elastomer, and convert microscopic vibrations into macroscopic motion through friction between the stator and rotor, realizing the conversion of electrical energy into mechanical energy. It can achieve high-resolution stepping to complete high-precision positioning requirements.

[0003] However, the significant nonlinear motion characteristics of ultrasonic motors present significant challenges for positioning control. Currently, most ultrasonic motor positioning control methods are difficult to develop in engineering applications due to complex control and poor robustness. Furthermore, these methods are subject to certain limitations on the structure and type of ultrasonic motors, as well as the operating environment. Therefore, a control method that is universal, simple, and efficient, while achieving short-term, high-precision positioning is urgently needed.

[0004] For example, application publication number CN1109325977A discloses a variable-frequency vibration method and vibration actuator that can shorten response time, combining a beat wave signal with a novel ultrasonic motor structure. Application publication number CN117792146A discloses a high-stiffness drive method and system for ultrasonic motors based on beat wave pulses, using beat wave pulse drive to achieve high-stiffness, ultra-low-speed stepping motion in ultrasonic motors. These two different applications of beat waves in ultrasonic motors fail to address or solve the positioning problem of ultrasonic motors. Application publication number CN116111876A discloses a positioning method and drive system for ultrasonic motors based on frequency difference signal control. This method utilizes variable drive frequency and beat wave switching to decelerate the motor, then power it off, and then performs microstepping compensation to complete the positioning process. The application of beat waves is limited to the deceleration process prior to positioning, and this process is regulated by position advance, which does not achieve optimal deceleration. Furthermore, its positioning accuracy is primarily dependent on the accuracy of microstepping compensation.

[0005] Therefore, it is necessary to design a new ultrasonic motor positioning method to solve the above problems. Summary of the Invention

[0006] The present invention provides an ultrasonic motor positioning control method and control system based on beat waves, which can meet the control requirements of short-time high-precision positioning of the ultrasonic motor.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A positioning control method for an ultrasonic motor based on a beat wave, comprising the following steps:

[0009] Step S1, setting the target position according to the ultrasonic motor positioning requirements;

[0010] Step S2, starting the control system, outputting a continuous traveling wave signal to drive the ultrasonic motor, setting a switching position close to the target position, and continuously operating the ultrasonic motor until the switching position is reached, and then proceeding to step S3. If the switching position has not been reached, continuously outputting a continuous traveling wave signal to drive the ultrasonic motor;

[0011] Step S3: After the ultrasonic motor reaches the switching position, the control system outputs a beat wave continuous signal to drive the ultrasonic motor to decelerate.

[0012] Step S4, setting a preset duration for outputting the continuous beat wave signal, stopping the output after the preset duration, and stopping the ultrasonic motor to complete the fuzzy positioning process;

[0013] Step S5: Start the control system, output a beat wave pulse signal to drive the ultrasonic motor to perform gradient micro-stepping motion, and adjust the step size according to the distance to the target position. If the distance to the target position is far, a large step size is used; if the distance to the target position is close, an ultra-high resolution step size is used. If the distance to the target position is greater than 100 μrad, the distance is defined as far, and if the distance to the target position is less than 100 μrad, the distance is defined as close.

[0014] Step S6: After the ultrasonic motor reaches the target position, the control system stops outputting signals, and the ultrasonic motor stops micro-stepping motion, completing the precise positioning process and ending the positioning;

[0015] Furthermore, the traveling wave continuous signal output by the control system is a sinusoidal continuous signal with the same frequency, a phase difference of 90° and the same amplitude in two phases; the beat wave continuous signal output by the control system is a sinusoidal continuous signal with a frequency difference, an initial phase difference of 90° and the same amplitude in two phases; the beat wave pulse signal output by the control system is a sinusoidal pulse signal with a frequency difference, an initial phase difference of nearly 180° and the same amplitude in two phases;

[0016] Furthermore, define the target position as P, the switching position as P1, and the preset duration as T.

[0017] In step S4, set T≤0.25 / Δf, where Δf is the frequency difference of the beat wave;

[0018] Furthermore, the position value range of the switching position P1 ahead of the target position P is 0°-2°, and the distance between the switching position P1 and the target position P is less than 10% of the total positioning stroke;

[0019] The control system used for the ultrasonic motor positioning control method based on beat wave is an FPGA-based ultrasonic motor control system, including a control module, a signal generation module, a power amplification module, a data acquisition module, a communication module and a power supply module;

[0020] The control module uses the host computer to set the target position and drive the output and switching of the ultrasonic motor operation signal;

[0021] The signal generation module uses FPGA to realize the DDS signal generation function, outputs two-phase frequency and phase high-resolution adjustable sine wave digital signals, and at the same time, two high-speed D / A converters are installed at the back to convert the digital signals into low-voltage analog signals;

[0022] The power amplifier module includes a pre-power amplifier and a secondary push-pull amplifier, and performs voltage boost processing on the operating signal of the driving ultrasonic motor;

[0023] The data acquisition module uses FPGA to collect data from the high-precision encoder installed on the ultrasonic motor in real time;

[0024] The communication module uses the UART bus to connect the host computer and FPGA to achieve real-time data transmission;

[0025] The power supply module provides direct current power to the FPGA, D / A digital-to-analog converter, pre-power amplifier, secondary push-pull amplifier, and high-precision encoder;

[0026] Furthermore, the FPGA uses the XC7A35T chip of the Xilinx Artix7 series;

[0027] The two high-speed D / A converters use AD9767 chips.

[0028] The pre-power amplifier adopts an operational amplifier of model ACF2101BU;

[0029] The high-precision encoder adopts the ID1102C model of the Positive series;

[0030] The power supply module adopts a high-precision digital display DC power supply with an adjustable 40V 8A and a programmable regulated power supply with an output power of 320W.

[0031] Through the above technical solution, compared with the existing technology, the present invention has the following beneficial effects:

[0032] 1. The beat-wave-based ultrasonic motor positioning control method provided by the present invention employs switching between a continuous traveling wave signal and a continuous beat-wave signal, or between a continuous beat-wave signal and a beat-wave pulse signal, and uses the control parameters in each switching as the key to control. This simplifies the implementation of the entire positioning control method and facilitates engineering applications.

[0033] 2. The beat-wave-based ultrasonic motor positioning control method provided by the present invention utilizes the special motion form of the beat-wave-driven ultrasonic motor to drive reciprocating motion, achieving continuous deceleration and ultra-high-resolution stepping motion, completing high-precision positioning, and broadening the application of ultrasonic motors in the engineering field.

[0034] 3. The beat-wave-based ultrasonic motor positioning control method provided by the present invention realizes the analysis of the ultrasonic motor's "fuzzy positioning + precise positioning" process through the design of three stages: the traveling wave approach stage, the beat-wave deceleration stage, and the beat-wave gradient micro-stepping stage during the ultrasonic motor positioning process;

[0035] 4. The control system of the ultrasonic motor positioning control method based on beat waves provided by the present invention has various modules that cooperate with each other to provide accurate signal generation, power amplification, data acquisition and control capabilities for the ultrasonic motor positioning control method based on beat waves, making the positioning process more efficient, accurate and stable, and achieving a closed-loop control effect of high-precision positioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described below with reference to the accompanying drawings and examples.

[0037] Figure 1 This is a flow chart of the ultrasonic motor positioning control method based on beat wave provided by the present invention;

[0038] Figure 2 Schematic diagram of the principle of the ultrasonic motor positioning control method based on beat wave provided by the present invention;

[0039] Figure 3 1 is a schematic diagram of a process for implementing a beat wave-based ultrasonic motor positioning control method provided by the present invention;

[0040] Figure 4 1 is a schematic diagram of a speed and displacement curve when implementing the ultrasonic motor positioning control method based on beat wave provided by the present invention;

[0041] Figure 5 Schematic diagram of the operating principle of the control system of the ultrasonic motor positioning control method based on beat wave provided by the present invention;

[0042] Figure 6It is a schematic diagram of positioning error results of a positioning test when three target positions are set according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "left side", "right side", "upper", "lower", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are intended only to facilitate the description of the present invention and simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second", etc. do not indicate the importance of the components and therefore should not be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrative purposes only and do not limit the scope of protection of the present invention.

[0044] As explained in the background technology, the currently widely used ultrasonic motors have obvious motion nonlinearity and complex driving control conditions. Therefore, this application first provides an ultrasonic motor positioning control method based on beat waves, which ensures a sufficiently small positioning error to achieve high-precision positioning, while shortening the positioning time to achieve a short-time positioning process.

[0045] The whole process principle is as follows Figure 1 As shown, this method divides the positioning process into two stages: fuzzy positioning and precise positioning. The ultrasonic motor is driven by a continuous traveling wave signal to quickly approach the target position. The beat wave continuous signal with a duration of T drives the motor to continuously decelerate until it is close to zero, and then the power is cut off and the fuzzy positioning is completed. This process allows the motor to quickly approach the target position and smoothly transition to the deceleration state. The gradient micro-stepping motion of the ultrasonic motor is realized by controlling the parameters of the beat wave pulse signal through the feedback of the position value, ensuring that the target position is reached by ultra-high resolution stepping and then stopped to ensure high positioning accuracy, complete precise positioning, and greatly improve positioning accuracy. Compared with the existing technology that may only use a single signal drive, it can take into account the effects of rapid arrival and precise stopping.

[0046] Next, the ultrasonic motor positioning control method is specifically described, including the following steps:

[0047] Step S1: Set a target position based on the ultrasonic motor (USM) positioning requirements. The target position, defined as P, should be determined based on the specific USM application system and positioning requirements, and can range from 0° to 360°. The entire positioning process begins after outputting the target position P.

[0048] Step S2: Start the control system and output a continuous traveling wave signal to drive the ultrasonic motor. The continuous traveling wave signal output by the control system is a continuous sinusoidal signal with two phases of the same frequency, a 90° phase difference, and the same amplitude. Because the target positioning range is large, the positioning time at different target positions is significantly affected by the speed of the traveling wave during the approach phase. Therefore, it is necessary to change the frequency of the continuous traveling wave signal to increase or decrease the motor speed during this phase to quickly approach the target position.

[0049] Furthermore, a switching position P1 is set near the target position P, and the ultrasonic motor continues to run until it reaches the switching position P1, and then proceeds to the next step. If the switching position is not reached, the traveling wave continuous signal is continuously output to drive the ultrasonic motor to run.

[0050] Switching position P1 should be set ahead of target position P. This is because its specific value is related to the control parameters of the beat wave deceleration phase and the beat wave gradient microstepping phase. If the switch position lead value is too large, the positioning time will be longer. If the switch position lead value is too small, the deceleration and microstepping effects cannot be achieved, affecting the positioning accuracy and system stiffness of the entire positioning process. Therefore, it needs to be set according to the actual movement of the ultrasonic motor. The range of the switch position P1 ahead of the target position P is usually set to 0°-2°, and the distance between the switch position P1 and the target position P is less than 10% of the total positioning stroke.

[0051] In step S3, after the ultrasonic motor runs to the switching position P1, the control system outputs a beat wave continuous signal to drive the ultrasonic motor to decelerate; this avoids the impact caused by the ultrasonic motor suddenly stopping when running at high speed, and reduces the mechanical wear and electrical loss of the ultrasonic motor. Figure 2 As shown, when driven by traveling waves, the ultrasonic motor's speed undergoes a rapid response followed by continuous operation at a stable speed. However, when driven by beat waves with a constant frequency difference and zero initial phase difference, the speed varies sinusoidally, following a pattern of "forward acceleration-forward deceleration-reverse acceleration-reverse deceleration." During the beat wave deceleration phase, the control system outputs continuous beat wave signals with a constant frequency difference and an initial phase difference of 90°, causing the ultrasonic motor to continuously decelerate from its maximum stable speed.

[0052] In step S4, the beat wave continuous signal output is set to a preset duration, T. After the preset duration, the output stops, the ultrasonic motor stops running, and the fuzzy positioning process is completed. Research and testing have shown that setting T ≤ 0.25 / Δf (Δf is the frequency difference of the beat wave) can rapidly reduce the ultrasonic motor speed and shut down when it approaches zero.

[0053] Continue to step S5, start the control system, output a beat wave pulse signal with a certain frequency difference and an initial phase difference of nearly 180° to drive the ultrasonic motor to perform gradient micro-stepping motion, adjust the step length according to the distance to the target position, ensure that the target position is quickly approached while reaching the target position with ultra-high resolution stepping, and thus complete the positioning process.

[0054] When outputting a traveling wave pulse signal for micro-stepping motion, the step length is dynamically adjusted according to the distance from the target position. If the distance to the target position is far, a large step length step can quickly shorten the gap with the target position. If the distance to the target position is close, an ultra-high resolution step can achieve high-precision positioning. Compared with the existing stepping method using a fixed step length, this method of optimizing positioning accuracy by using gradient micro-stepping motion avoids the problem that the fixed step length may be too large when approaching the target position, resulting in the inability to accurately reach the target position. At the same time, it avoids the problem of low efficiency of the positioning process caused by the use of small step length steps throughout the entire process. Preferably, in this application, if the distance to the target position is greater than 100 μrad, it is defined as far away, and if the distance to the target position is less than 100 μrad, it is defined as close.

[0055] Step S6: After the ultrasonic motor reaches the target position, the control system stops outputting signals, and the ultrasonic motor stops micro-stepping motion, completing the precise positioning process and ending the positioning.

[0056] In summary, the present application provides a positioning control method for an ultrasonic motor based on a beat wave, such as Figure 3 As shown, the entire positioning process is divided into three stages according to the output signal of the control system and the motion state of the ultrasonic motor. The first stage is the traveling wave approach stage. In this stage, the ultrasonic motor, driven by the continuous traveling wave signal, performs a fast response start and then approaches the target position at high speed. In this process, the ultrasonic motor moves most of the displacement toward the target position. The switching between the first and second stages is divided by reaching the switching position P1. The second stage is the beat wave deceleration stage. After the ultrasonic motor reaches the switching position, the control system switches to output the beat wave continuous signal at time T. In this stage, the ultrasonic motor continues to decelerate until the speed is close to zero and stops moving. In this process, the ultrasonic motor moves a small amount of displacement toward the target position. The switching between the second and third stages is divided by whether the beat wave continuous signal at time T is output. The third stage is the beat wave gradient microstepping stage. In this stage, the ultrasonic motor performs gradient microstepping motion under the drive of the beat wave pulse signal, which can ensure positioning accuracy. The gradient microstepping motion process continuously adjusts the pulse signal duty cycle according to the position feedback of the ultrasonic motor, thereby achieving large stepping when far away from the target position, and ultra-high resolution stepping when close enough to the target position to achieve high-precision positioning. In this process, the ultrasonic motor stops after reaching the target position with gradient microstepping, completing the entire positioning process.

[0057] The ultrasonic motor's rapid approach using traveling waves in the first phase and its gradient microstepping using beat-wave motion in the third phase are both designed to shorten positioning time and maximize short-term positioning capabilities. The beat-wave deceleration process in the second phase ensures strong positioning stiffness and reduces nonlinearity in ultrasonic motor control.

[0058] As the biggest innovation of this application, Figure 4 Figure 2 is a schematic diagram of the speed and displacement curves used when implementing a beat-wave-based ultrasonic motor positioning control method. During the first and second stages, the traveling wave approach phase and the beat-wave deceleration phase, the ultrasonic motor completes the majority of its displacement toward the target position P, completing the fuzzy positioning process. During the third stage, the beat-wave gradient microstepping phase, the ultrasonic motor completes the remaining displacement from the target position P using gradient microstepping, completing the precise positioning process.

[0059] During actual experiments and tests, developing this phased, multi-signal combined control strategy places high demands on the control system hardware, including a signal generator that can accurately generate continuous traveling wave signals, continuous beat wave signals, and pulsed beat wave signals, as well as a controller that can monitor the motor position in real time and adjust the signal output based on the position information.

[0060] Therefore, the present application also provides a control system for an ultrasonic motor positioning control method based on a beat wave, which is an ultrasonic motor control system based on FPGA. Preferably, the FPGA uses the XC7A35T chip of the Xilinx Artix7 series, and the crystal oscillator frequency is 50MHz. The ultrasonic motor control system mainly includes a control module, a signal generation module, a power amplifier module, a data acquisition module, a communication module, and a power supply module. The principle diagram of the control system is shown in FIG. Figure 5As shown, the control module uses the host computer to set the target position. The communication module connects the host computer to the FPGA via a UART bus, enabling real-time data transmission. The signal generation module utilizes the FPGA to implement DDS (Direct Digital Synthesis) signal generation, outputting two-phase sinusoidal digital signals with high-resolution adjustable frequency and phase. The principle is to digitize the required analog signal and store it in ROM. The ROM module is instantiated using the FPGA's IP core. Accumulator registers are used to control the frequency of the digital signal and output it. Address offsets are used to control the phase of the output signal, and counters are used to control the pulse and continuous nature of the signal, as well as the duty cycle. Two high-speed D / A converters are then used to convert the digital signal into a low-voltage analog signal. This enables the system to accurately generate a continuous traveling wave signal. The signal frequency and phase can be flexibly adjusted according to the characteristics and operating requirements of the ultrasonic motor, achieving precise control of the ultrasonic motor's speed and direction, ensuring that the motor can quickly and stably reach the switching position. Furthermore, based on the FPGA's DDS signal generation function, the signal generation module can quickly and accurately switch from outputting a continuous traveling wave signal to outputting a continuous traveling wave signal. By precisely adjusting the frequency and phase of the signal, a continuous beat wave signal that meets the requirements is generated, thereby achieving deceleration control of the ultrasonic motor. This flexible signal switching and adjustment capability is the key to achieving staged positioning control.

[0061] The power amplifier module, consisting of a preamplifier and a secondary push-pull amplifier, boosts the signal driving the ultrasonic motor. The boosted signal has sufficient power to drive the ultrasonic motor, ensuring sufficient power during operation and preventing unstable operation or failure to achieve the desired speed due to insufficient signal power. The data acquisition module utilizes an FPGA to collect data from a high-precision encoder mounted on the ultrasonic motor in real time. During fuzzy positioning, the encoder data monitors the motor's position and operating status in real time within a preset duration of the continuous beat wave signal output. When the preset duration is reached, the control system accurately determines whether the motor has stopped at the appropriate position based on the collected position information, thus completing the fuzzy positioning process. This real-time monitoring and feedback mechanism improves positioning accuracy and reliability. During precise positioning, the data acquisition module continuously collects real-time motor position information, and the control module uses this information to determine whether the motor has reached the target position. When the ultrasonic motor reaches the target position, the control module immediately stops the signal output from the signal generation module, causing the motor to stop microstepping motion, completing the precise positioning process. This real-time monitoring and precise control capability ensures high positioning accuracy.

[0062] The power supply module preferably adopts a high-precision digital display DC power supply with an adjustable 40V 8A and an output power of 320W. It provides DC power supply for FPGA, D / A digital-to-analog converter, pre-power amplifier (preferably, ACF2101BU operational amplifier), secondary push-pull amplifier and high-precision encoder (preferably, ID1102C model of Posic series). When powering, the distribution of each component is as follows: FPGA, D / A digital-to-analog converter, and high-precision encoder are all powered by 5V, and the pre-power amplifier circuit and secondary power amplifier are powered by 12V, which ensures the stable operation of each module of the entire control system.

[0063] The FPGA chip receives the control word sent to its corresponding control word register, accumulates and calls the digitized signal instantiated in the ROM module based on table lookup, converts the digital signal to analog after passing through the D / A converter, and outputs two stable sine and cosine current signals with a frequency difference, with a maximum output amplitude of approximately 500mVp-p. The output current signal of approximately 500mVp-p is then input into a preamplifier and a secondary power amplifier for two-stage amplification. The D / A converter preferably uses the AD9767 DAC series digital-to-analog converter, which features high performance and low power consumption, supports independent dual-channel output, has a 14-bit digital-to-analog conversion bit, and a maximum conversion speed of 125MSPS.

[0064] Finally, in order to verify the superiority of the provided method and system, this application provides three embodiments, setting the target positions to 5°, 15°, and 30° respectively. Positioning tests are performed under these three working conditions, using the Poic series ID1102C model incremental encoder, whose single-turn pulse number is 2949120 lines. Figure 6 It can be seen that under the three different positioning target positions, the positioning error can be stabilized within the minimum resolution of the encoder (approximately 2.13 μrad). Where 1° = π / 180 rad, which is approximately equal to 17453.3 μrad.

[0065] Therefore, the present application provides a positioning control method for an ultrasonic motor based on a beat wave, which uses strict control of the output duration of the beat wave signal to complete the deceleration stage before positioning and uses pulse drive with different duty cycles of the beat wave to achieve gradient micro-stepping motion. When the distance from the target position is far, large step length steps are used to shorten the positioning duration, and when the target position is close, high-precision steps are used to ensure positioning accuracy. Combined with multiple signal drives, the positioning efficiency and accuracy are improved, and the gradient micro-stepping motion optimizes the positioning accuracy while reducing the loss of the ultrasonic motor. Equipped with a corresponding FPGA-based ultrasonic motor control system, it realizes switching between traveling wave / beat wave and continuous signal / pulse signal, achieving a two-level positioning effect of "fuzzy positioning + precise positioning". The control method of the present invention is simple and efficient, and can achieve short-term high-precision positioning of the ultrasonic motor.

[0066] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such herein, will not be interpreted in an idealized or overly formal sense.

[0067] The meaning of "and / or" in this application means that both situations where each exists alone or both exist at the same time are included.

[0068] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0069] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A positioning control method for an ultrasonic motor based on a beat wave, characterized in that: The specific steps include: Step S1, setting the target position according to the ultrasonic motor positioning requirements; Step S2, starting the control system, outputting a continuous traveling wave signal to drive the ultrasonic motor, setting a switching position close to the target position, and continuously operating the ultrasonic motor until the switching position is reached, and then proceeding to step S3. If the switching position has not been reached, continuously outputting a continuous traveling wave signal to drive the ultrasonic motor; Step S3: After the ultrasonic motor reaches the switching position, the control system outputs a beat wave continuous signal to drive the ultrasonic motor to decelerate. Step S4, setting a preset duration for outputting the continuous beat wave signal, stopping the output after the preset duration, and stopping the ultrasonic motor to complete the fuzzy positioning process; Step S5: Start the control system, output a beat wave pulse signal to drive the ultrasonic motor to perform gradient micro-stepping motion, and adjust the step size according to the distance to the target position. If the distance to the target position is far, a large step size is used; if the distance to the target position is close, an ultra-high resolution step size is used. If the distance to the target position is greater than 100 μrad, the distance is defined as far, and if the distance to the target position is less than 100 μrad, the distance is defined as close. Step S6: After the ultrasonic motor reaches the target position, the control system stops outputting signals, and the ultrasonic motor stops micro-stepping motion, completing the precise positioning process and ending the positioning.

2. The ultrasonic motor positioning control method based on beat waves according to claim 1, characterized in that: The traveling wave continuous signal output by the control system is a sinusoidal continuous signal with the same frequency, a phase difference of 90° and the same amplitude in two phases; the beat wave continuous signal output by the control system is a sinusoidal continuous signal with a frequency difference, an initial phase difference of 90° and the same amplitude in two phases; the beat wave pulse signal output by the control system is a sinusoidal pulse signal with a frequency difference, an initial phase difference of nearly 180° and the same amplitude in two phases.

3. The ultrasonic motor positioning control method based on beat waves according to claim 1, characterized in that: Define the target position as P, the switching position as P1, and the preset duration as T. In step S4 , T is set to ≤ 0.25 / Δf, where Δf is the frequency difference of the beat wave.

4. The ultrasonic motor positioning control method based on beat waves according to claim 3, characterized in that: The position value range of the switching position P1 ahead of the target position P is 0°-2°, and the distance between the switching position P1 and the target position P is less than 10% of the total positioning stroke.

5. A control system for the beat wave-based ultrasonic motor positioning control method according to any one of claims 1 to 4, characterized in that: It is an FPGA-based ultrasonic motor control system, including a control module, a signal generation module, a power amplifier module, a data acquisition module, a communication module, and a power supply module; The control module uses the host computer to set the target position and drive the output and switching of the ultrasonic motor operation signal; the signal generation module uses FPGA to realize the DDS signal generation function, outputting a two-phase sinusoidal digital signal with high-resolution adjustable frequency and phase, and at the same time, two high-speed D / A converters are installed at the back to convert the digital signal into a low-voltage analog signal; The power amplifier module includes a pre-power amplifier and a secondary push-pull amplifier, and performs voltage boost processing on the operating signal of the driving ultrasonic motor; The data acquisition module uses FPGA to collect data from the high-precision encoder installed on the ultrasonic motor in real time; the communication module uses the UART bus to connect the host computer and FPGA to achieve real-time data transmission; The power supply module provides direct current power to the FPGA, D / A digital-to-analog converter, pre-power amplifier, secondary push-pull amplifier and high-precision encoder.

6. The control system of the ultrasonic motor positioning control method based on beat wave according to claim 5, characterized in that: The FPGA uses the XC7A35T chip of the Xilinx Artix7 series; The two high-speed D / A converters use AD9767 chips. The pre-power amplifier adopts an operational amplifier of model ACF2101BU; The high-precision encoder adopts the ID1102C model of the Positive series; The power supply module adopts a high-precision digital display DC power supply with an adjustable 40V 8A and a programmable regulated power supply with an output power of 320W.

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