Voice Coil Motor Actuator Driver Vibration Suppression
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Solution Overview
Problem
Voice coil motor (VCM) actuators in camera modules experience significant vibrations and oscillations during position adjustment, leading to extended settling times and undesirable image artifacts due to the natural vibration frequency of the VCM actuator.
Innovation Solution
An actuator driver system that includes a digital converter, a digital-to-analog converter, and a current amplifier, which converts a VCM driving control code into a series of conversion codes to generate an analog signal that incrementally adjusts the driving current, adhering to specific difference code relationships to suppress vibrations, thereby quickly stabilizing the lens at the target position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a VCM actuator is driven by a driving current to adjust the lens position, then the lens position adjustment function is achieved, but significant vibrations and oscillations occur during position adjustment
Solution Approach 1:
The driving current waveform is segmented into multiple discrete current levels (e.g., 5 levels: 0, 100mA, 200mA, 300mA, 400mA) instead of using a continuous current change. The digital-to-analog converter sequentially outputs conversion codes corresponding to these discrete levels, dividing the current adjustment process into staged segments that reduce vibration excitation.
Solution Approach 2:
The VCM actuator is driven using periodic pulse signals with specific duty cycles corresponding to different current levels. The driving signal applies current in periodic pulses rather than continuously, allowing the actuator to settle between pulses and reducing oscillation amplitude. The period and duty cycle are carefully controlled to minimize resonance excitation.
2Loss of time
If the driving current is continuously adjusted to reach the target position quickly, then the settling time is reduced, but vibrations and oscillations are exacerbated
Solution Approach 1:
The system pre-calculates and stores optimal driving waveforms for different target positions and movement distances. Before actual lens adjustment, the controller selects the appropriate pre-computed waveform from memory, which has been optimized to minimize vibrations. This preliminary preparation allows the system to execute vibration-reduced waveforms without real-time computation delays.
Solution Approach 2:
The driving current waveform is made dynamic and adaptive based on the lens movement distance and target position. The system adjusts the number of current levels, the duration at each level, and the pulse timing dynamically according to the specific adjustment requirements. For short movements, fewer current levels are used; for long movements, more levels are employed, optimizing both speed and vibration reduction for each scenario.
3Device complexity
If a simple driving current waveform is used, then the control system is simple, but the lens exhibits extended settling time due to vibrations
Solution Approach 1:
The system incorporates feedback from position detection circuits that monitor the lens position in real-time. This feedback is fed back to the controller, which automatically adjusts the driving current waveform to dampen vibrations and accelerate settling. The system serves itself by using its own position information to optimize its driving strategy, eliminating the need for external complex control systems.
Solution Approach 2:
The system changes multiple parameters of the driving waveform including current amplitude levels, pulse width, pulse frequency, and duty cycle to optimize performance. The digital-to-analog converter transforms digital control codes into analog current levels with specific relationships between consecutive levels. These parameter changes are coordinated to reduce vibrations while maintaining reasonable settling time, balancing complexity and performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution effectively reduces the output transient characteristics of the VCM actuator, allowing the lens to settle quickly and stably at the target position, minimizing vibrations and improving auto-focus performance in camera modules.
Implementation Method 1
Voice coil motors (VCMs) may be used for auto focusing in a camera module included in a mobile electronic device, such as a mobile phone, or the like. VCMs may be driven by an electric current
Data Source
AI summary
An actuator driver for a voice coil motor (VCM) includes a digital converter configured to convert a VCM driving control code into a plurality of conversion codes including at least a first to nth conversion codes, during a predetermined period of time, a digital-to-analog converter configured to sequentially generate an analog signal according to each of the plurality of conversion codes during the predetermined time to actuate a VCM actuator to a target position, and a current amplifier configured amplify the analog signal to generate a driving signal and provide the driving signal to the VCM actuator, wherein the sequential generation of the analog signal includes increasing a level of the analog signal in response to one of the conversion codes and decreasing a level of the analog signal in response to another one of the conversion codes.