Adaptive Motor Control for Voice Coil Actuators
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Solution Overview
Problem
Motor driven mechanical systems, such as autofocus cameras, experience overshoot and ringing due to variations in resonant frequency with position, temperature, and orientation, making it challenging to achieve rapid and accurate movement between positions without excessive oscillation.
Innovation Solution
A method involving calculating a change in drive signal value and dividing it into stepped signals, with the update period adjusted based on resonant frequency, which varies as a function of position, temperature, and orientation, to minimize overshoot and ringing, using a controller that can adapt the drive signal update rate to match the mechanical system's changing characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the drive signal is updated continuously to achieve fast positioning, then the positioning speed is improved, but overshoot and ringing occur due to resonant frequency variations
Solution Approach 1:
The patent applies dynamics by making the drive signal update period variable rather than fixed. The update period adapts dynamically based on the resonant frequency of the mechanical system, which changes with position, temperature, and orientation. This allows the system to maintain optimal control across varying operating conditions, reducing overshoot and ringing while preserving fast positioning capability.
Solution Approach 2:
The patent changes the parameter of drive signal update period (tu) based on resonant frequency variations. By adjusting tu as a function of resonant frequency, which itself varies with position, temperature, and orientation, the system optimizes its response to minimize oscillations while maintaining speed. This is implemented through calibration steps that store tu values for different operating conditions.
2Device complexity
If the resonant frequency is assumed constant for simplified control, then the control complexity is reduced, but positioning accuracy deteriorates due to frequency variations with position and environmental conditions
Solution Approach 1:
The patent applies preliminary action by performing calibration steps before normal operation to establish the relationship between resonant frequency and operating conditions (position, temperature, orientation). The results are stored in lookup tables or calibration data, allowing the controller to quickly retrieve appropriate update periods without complex real-time calculations. This reduces runtime complexity while maintaining high positioning precision.
Solution Approach 2:
The patent uses feedback by periodically updating the drive signal based on the actual resonant frequency of the system. The controller monitors system response and adjusts the update period accordingly, creating a closed-loop control system that adapts to frequency variations. This feedback mechanism maintains positioning accuracy without requiring overly complex control algorithms.
3Stability of the object's composition
If the drive signal update period is fixed at a standard value, then the system response is predictable, but overshoot and ringing increase when resonant frequency varies with operating conditions
Solution Approach 1:
The patent makes the drive signal update period dynamic rather than fixed. The update period tu is adjusted based on the actual resonant frequency, which varies with position, temperature, and orientation. This dynamic adaptation maintains system stability across different operating conditions while preventing overshoot and ringing that would occur with a fixed update period.
Solution Approach 2:
The patent applies preliminary anti-action by pre-calibrating the relationship between operating conditions and optimal update periods. During calibration, the system learns the appropriate tu values for different resonant frequency conditions and stores this information for later use. This preliminary preparation allows the system to counteract resonant frequency variations before they cause overshoot or ringing during normal operation.
Data Source
AI summary
Actuators are used to move a variety of objects to desired positions. It is generally desirable that they can do this quickly without exhibiting overshoot or ringing. Some actuators are required to respond very quickly and examples of these are voice coil drivers used to move lenses in autofocus cameras provided in everyday devices such as smart phones and tablets. A rapid two step controller scheme had already been disclosed by Analog Devices Inc. While the scheme works well, it can only be used reliably if the resonant frequency of the actuator is known to within 2 or 3%. The inventors have discovered that the resonant frequency of an actuator unexpectedly changes as a function of position. This disclosure provides ways of modifying the control scheme to cope with changes in resonant frequency.