In today's world, where smartphones have largely replaced handheld cameras, photography has become one of the most essential use cases for users. As a core technology affecting the shooting experience, camera image stabilization not only determines image clarity but also profoundly influences how consumers record their lives and create content, making it a critical factor in smartphone purchasing decisions. This document systematically introduces the core principles, structural classifications, performance parameters, advantages, and disadvantages of piezoelectric motors, with a focus on their application scenarios in consumer electronics, precision optics, industrial manufacturing, medical devices, and other fields.
Piezoelectric Motor Applications
Piezoelectric motors are primarily used in the telephoto and macro lenses of high-end flagship smartphones, leveraging nanometer-level positioning accuracy to achieve lossless zoom and high-definition macro photography. Some high-end smart wearable devices and action cameras also employ piezoelectric motors, utilizing their non-magnetic interference characteristics to avoid affecting sensor operation and enhance shooting stability.
In addition, in the precision optics and optoelectronics industry, piezoelectric motors are the preferred core components, relying on ultra-high positioning accuracy and non-magnetic interference advantages. They are used in fiber-optic coupling calibration, optical microscope stage displacement adjustment, laser optical path fine-tuning, and spectrometer lens positioning. In the field of optical fiber communications, piezoelectric motors can precisely control fiber alignment displacement to reduce optical signal loss; in scientific optical instruments, they enable nanometer-scale optical path calibration to meet high-precision experimental testing requirements. VCM (Voice Coil Motor) motors are more commonly used in ordinary optical inspection equipment and simple optical path adjustment devices.
Working Principle of Piezoelectric Motors
The piezoelectric effect is a unique characteristic of piezoelectric materials. When a piezoelectric material deforms under external force, polarization occurs internally, and positive and negative charges related to the pressure appear on its two opposite surfaces (this characteristic can be used to detect the magnitude of external pressure), as shown in the figure below:
Figure 1 Schematic diagram of the piezoelectric effect (Image source: Toutiao @罗罗日记luoluonotes)
The core driving material of piezoelectric motors is PZT (lead zirconate titanate) piezoelectric ceramics. Utilizing the inverse piezoelectric effect, when a high-voltage alternating voltage is applied, the piezoelectric ceramic undergoes microscopic deformation. Through structural design, the microscopic deformation is amplified and combined with frictional transmission, inertial drive, or resonant drive methods to convert microscopic deformation into macroscopic continuous displacement. Unlike electromagnetic motors, piezoelectric motors have no coils and no magnetic interference, relying directly on crystal deformation for drive, with response speeds reaching the microsecond level.
Compared with VCM motors, piezoelectric motors offer significant advantages, including no electromagnetic interference, high positioning accuracy, microsecond-level fast response, power-off self-locking, and low power consumption. The following section will focus on the drive and debugging process for piezoelectric motors.
Drive Methods and Drive Process for Piezoelectric Motors
Different types of piezoelectric motors use different drive methods, including sine wave drive, sawtooth wave drive, square wave drive, etc. During actual debugging, voltage signals must be output to control motor movement according to the specifications provided by the piezoelectric motor manufacturer. The following describes the drive method and drive process for piezoelectric motors using the common PWM (square wave) approach found in the mobile phone industry.
Square wave drive involves applying different PWM signals to the terminals of the piezoelectric motor. When PWM waves of different frequencies, duty cycles, and phases are output, the motion mode of the piezoelectric motor changes accordingly.
For example, assume a piezoelectric motor with specifications provided by the manufacturer as follows:
From the figure above, it can be seen that this piezoelectric motor has two input terminals: IN1 and IN2. The drive parameters for forward and reverse motion are as follows:
Forward Motion
The PWM frequency on both IN1 and IN2 terminals is 150K; the duty cycle of IN1 is approximately 33.3%, and the duty cycle of IN2 is approximately 66.7%; the phase of IN1 is set to 0°, and the phase of IN2 is set to 120°.
Reverse Motion
The PWM frequency on both IN1 and IN2 terminals is 150K; the duty cycle of IN1 is approximately 66.7%, and the duty cycle of IN2 is approximately 33.3%; the phase of IN1 is set to 0°, and the phase of IN2 is set to 180°.
Theoretically, according to the piezoelectric specifications, after obtaining the motor, PWM signals should be output to the piezoelectric motor in cycles according to the forward and reverse waveforms described above. If the period is set to 1 second, the motor will perform open-loop motion cyclically with a 1-second period.
For
piezoelectric motor applications, awinic works closely with customers to
propose a piezoelectric motor system solution. The system block diagram is as
follows:
Figure 3 PIEZO control system solution
For hardware
circuit design, please refer to the official awinic website, search in the
Product Center -> Imaging Motion Control -> Optical Image Stabilization
Driver -> AW86102, and consult the technical documentation and product
design guidelines. After connecting the piezoelectric motor load according to
the hardware design, the firmware can be designed to drive the motor in
open-loop motion based on the characteristics of the AW86102 chip. In the
firmware driver, set the corresponding PWM frequency, duty cycle, and phase,
and map the PWM channels to the corresponding OUT drive pins. At this point,
the piezoelectric motor can achieve forward or reverse motion. The hardware
design reference is as follows:
Figure 4 AW86102 application circuit
During the operation of the piezoelectric motor, because the driver chip outputs high-frequency square waves, the high-frequency current generates electromagnetic vibrations on the coils and capacitors, producing subtle current whining noises. Additionally, sudden voltage changes can intensify voltage fluctuations and amplify noise. To address the noise issues during piezoelectric motor driving, awinic provides excellent algorithms and control schemes that can significantly reduce the noise generated at the piezoelectric terminals during motor operation.
Noise Suppression for Piezoelectric Motors
Audio noise is mainly divided into two types: one is Audio noise generated by motor motion, whose frequency points generally correspond to positions with larger FRA gain; the second is Audio noise generated by current, whose frequency generally corresponds to the loop control frequency Fs. For motor motion Audio noise, filters can be used to limit the gain at the audio noise frequency points, reducing the motor motion amplitude at those frequencies and lowering Audio noise. For current Audio noise, the loop control frequency Fs can be increased to above 20kHz to avoid the frequency range audible to the human ear, thereby reducing Audio noise. For most chips, increasing Fs means increased circuit noise. To avoid this issue, the driver drive frequency can be increased while keeping the loop Fs unchanged, without increasing circuit noise. For noisy signals, AW's noise reduction solution employs a composite filter denoising algorithm:
Figure 5 Composite filter
The composite filter can effectively suppress high-frequency noise such as motor motion noise and control signal noise. Compared with conventional low-pass filters, it offers better amplitude-frequency characteristics and reduces the impact on the phase of low-frequency signals in the control system.
In addition, in terms of control strategy, awinic also provides an advanced piezoelectric control drive mode that can resolve the sharp abnormal noise generated by the driven motor due to frequent PWM phase switching. The following shows a comparison of audio frequency spectra before and after step response of a certain AF motor. It can be seen that the overall gain is reduced by more than 10dB, and near 10kHz, the gain drops by more than 20dB, effectively suppressing high-frequency noise.
Figure 6 Comparison of left and right channels before and after abnormal noise optimization
At the same time, for autofocus and optical image stabilization applications, awinic continues to launch multiple products, covering open-loop/closed-loop focus drivers, OIS drivers, piezoelectric drivers, etc., achieving comprehensive coverage in the VCM motor driver field. This rich product portfolio provides customers with more options. awinic has been deeply engaged in the VCM product line for 10 years and is a fully domestically-manufactured producer with mass-production capabilities across open-loop, closed-loop, and OIS (integrated, discrete, and SMA) product lines. It has already achieved mass production with multiple brand customers, including vivo, Lenovo, Asus, OPPO, etc. At the same time, awinic maintains close cooperation and collaboration with motor and module manufacturers, offering a complete VCM driver total solution.
Table 2 Complete VCM driver total solution table
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