Application Cases

Experiment Name: Experimental Verification of Temperature Drift Compensation Control Method for Ultrasonic Motor

Research Direction: Construction of a closed-loop experimental platform for temperature drift compensation of ultrasonic motors, speed-frequency calibration experiments, experimental verification of temperature drift compensation effectiveness

Experiment Objective: To verify the effectiveness of the "frequency tracking method for locating current minimum values based on an extremum seeking algorithm" in compensating for temperature drift in ultrasonic motors. Specifically, this involves: constructing a closed-loop experimental platform for temperature drift compensation that integrates current acquisition, control, and drive modules; completing speed-frequency calibration to establish a "speed command – initial drive frequency" parameter library; and, through long-term closed-loop experiments, verifying the compensation effectiveness of this method for temperature drift in terms of dynamic frequency tracking, speed stability, power efficiency stability, and temperature rise suppression.

Testing Equipment: NI controller, analog signal acquisition board, host computer, HIOKI power meter, ultrasonic motor, rotary encoder, hysteresis dynamometer, ATA-68020 power amplifier, multi-function I/O module board, current acquisition module, FPGA+DAC module, TIENDA T22 protocol decoding board.

Experimental Procedure: First, a closed-loop experimental platform for temperature drift compensation was constructed, integrating the current acquisition module, the NI control box as the core control system, the FPGA+DDS driver, and measurement equipment, defining the signal and data flow. Next, speed-frequency calibration was performed: with a fixed voltage, reference points were set at 10 rpm intervals between 30 and 150 rpm. Open-loop experiments recorded the frequency when the speed reached the target, establishing a parameter library. Finally, closed-loop experiments were conducted: with a fixed voltage of 130 Vrms and torque of 0.125 Nm, an initial frequency corresponding to a 150 rpm command was called from the library. After driving the motor, the current was acquired in real time, the frequency adjustment value was calculated using the algorithm and fed back to the FPGA, and parameters such as frequency and speed were monitored for 200 seconds.

Figure 1: Block Diagram of the Closed-Loop Experimental System

Figure 2: Physical Setup of the Experimental Platform

Experimental Results:

1. The drive frequency locked onto the optimal frequency within 10 seconds and stabilized. Over 200 seconds, it slowly decreased from 41.38 kHz to 41.34 kHz due to temperature drift. The extremum seeking algorithm enabled long-term dynamic tracking.

2. The closed-loop current stabilized after a brief fluctuation and increased slowly with long-term motor operation due to temperature drift characteristics.

3. The temperature rise of the motor casing was significantly suppressed, increasing by only 2.4°C over 200 seconds, much lower than the temperature rise observed in open-loop experiments.

4. The rotor speed reached above the 150 rpm command within 2 seconds and stabilized around 152 rpm over 200 seconds, achieving speed accuracy of 2.67%.

5. The drive efficiency was initially low, then increased to 23.4%, and ultimately stabilized around 22.6% due to stable speed and input power.

6. Input power rose to 16 W within the first 10 seconds, then decreased, finally stabilizing around 15.2 W, with only a slow increase during long-term operation.

Figure 3: Variation Curves of Various Performance Parameters of the Ultrasonic Motor Under Temperature Drift Compensation

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