Application Cases

Experiment Name: Performance Testing of Impact Rotary Piezoelectric Motors Based on Helical Electrode Torsional Actuators

Test Purpose:
To measure the mechanical characteristics of the piezoelectric motor, we designed an experimental measurement setup and mechanism. The primary measurements include the relationship between motor speed and voltage, the relationship between speed and frequency, and other mechanical properties of the piezoelectric motor.

Test Equipment:
High-voltage amplifier, digital oscilloscope, signal generator, laser Doppler vibrometer, laser micrometer, etc.

Experimental Process:

Figure 1: Piezoelectric Motor Speed Measurement Setup

The speed measurement setup for the piezoelectric motor is shown in Figure 1. A digital synthesized signal generator produces a sawtooth drive signal, which can output waveforms ranging from triangular to sawtooth waves with adjustable amplitudes of -10V to 10V and the required frequency. The signal generator allows for easy configuration of the output signal. The sawtooth signal is amplified by a high-voltage amplifier that meets the driving requirements of the piezoelectric ceramic fiber torsional actuator. The amplified sawtooth signal is then used to drive the piezoelectric ceramic fiber torsional actuator.

The stepper characteristics of the piezoelectric motor are measured using a laser Doppler vibrometer. The vibrometer consists of five parts: an optical detection unit, an observation unit, a sample stage, a velocity signal processing unit, and a frequency-stabilized laser. It can measure the motion velocity of the target object along the Z-axis and X-axis. For measuring the stepper characteristics of the piezoelectric motor, the X-axis measurement is used. As shown in Figure 1, the laser head is vertically incident on the load shaft, with the focal point on the shaft surface. When the load shaft is rotated by the piezoelectric motor, it can be considered as a plane moving along the X-axis. The collected data is processed by the velocity signal processing unit and input to a computer, enabling the acquisition of stepper characteristic data for the piezoelectric motor.

The X-axis measurement resolution has two settings: 4 nm and 40 nm, with maximum measurement speeds of 40 mm/s and 400 mm/s, respectively. During measurements, the 4 nm resolution is selected. Since the laser Doppler vibrometer requires a certain surface smoothness for lateral velocity measurements, the load shaft must be polished before measurement. However, the measured surface should not be too smooth, as the vibrometer detects scattered light from the surface, and overly smooth surfaces may result in no signal.

During measurement, the piezoelectric motor is placed on a micro-motion stage, and the laser head of the vibrometer is adjusted to ensure vertical incidence on the load shaft surface. By fine-tuning the instrument parameters, the stepper characteristics of the piezoelectric motor can be accurately measured. The measured signals are collected, stored, and processed by a computer to generate curves representing the stepper characteristics of the piezoelectric motor.

Experimental Results:

(A) Frequency-Modulated Stepper Characteristics

Figure 2: Frequency-Modulated Stepper Characteristic Curve

Figure 2 shows a set of torsional angle characteristic curves of the piezoelectric motor measured by the laser Doppler vibrometer at Vpp = 600V under different driving frequencies, reflecting the frequency-modulated stepper characteristics of the motor. The measured frequency points are f = 1 Hz, 10 Hz, 100 Hz, and 1 kHz. Each step is divided into forward and backward processes, and the step angle is calculated as the difference between the forward and backward angles. The results indicate that the step angle remains consistent across different frequencies, with each step measuring approximately 0.063°.

(B) Amplitude-Modulated Characteristics

Figure 3: Amplitude-Modulated Stepper Characteristic Curve

Figure 3 shows a set of torsional angle characteristic curves of the piezoelectric motor measured by the laser Doppler vibrometer at f = 30 Hz under different driving voltages, reflecting the amplitude-modulated stepper characteristics of the motor. The measured voltage points are Vpp = 400V, 600V, 800V, and 1 kV. The curves clearly demonstrate that higher driving voltages result in larger step angles. After eight steps, the motor rotates by angles of 0.317°, 0.913°, 1.689°, and 2.231°, respectively. The difference in driving voltage amplitudes shows a linear relationship with the difference in rotation angles, with a proportionality factor of 4×10⁻⁴ °/V. Additionally, it was observed that the piezoelectric motor fails to operate properly when the peak-to-peak driving voltage is below 360V. Overcoming bearing resistance is likely the main reason for the motor's inability to function under low voltage conditions.

Recommended High-Voltage Amplifier: ATA-7015

Figure: ATA-7015 High-Voltage Amplifier Specifications

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