VCM Driver Input Shaping for Fast Camera Lens Focus
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Solution Overview
Problem
Existing motor control systems for camera lenses with under-damped voice coil motors (VCMs) face challenges in achieving fast focus times due to mechanical oscillations, which are difficult to eliminate without increasing power consumption or complicating driver device designs.
Innovation Solution
The implementation of higher-order input shaping signals, such as second, third, and fourth-order impulse signals, is used to drive the VCM, canceling oscillations by adjusting the input signal to match the natural frequency and damping ratio of the system, thereby reducing settling time and simplifying driver design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If higher-order input shaping signals are used to drive the VCM, then focus time is reduced and oscillation is canceled, but driver device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing shaping signal parameters (amplitudes and time intervals) for different focus distances before actual operation. The driver device stores multiple sets of shaping signal parameters corresponding to different object distances, and selects the appropriate parameters in advance based on the desired focus distance, thereby reducing real-time computational complexity while achieving fast focus.
Solution Approach 2:
The patent implements dynamics by making the driver device adaptable to different VCM characteristics. The system can dynamically select from multiple pre-stored shaping signal parameter sets based on the specific VCM's natural frequency and damping ratio, allowing the driver to optimize performance for each individual actuator without requiring complex real-time parameter identification.
2Reliability
If shaping signal parameters are precisely matched to natural frequency and damping ratio, then oscillation cancellation is improved, but measurement precision requirements increase
Solution Approach 1:
The patent applies partial action by using a family of shaping signal parameter sets with slightly different natural frequency and damping ratio values rather than requiring precise single-point matching. The system selects the closest matching parameters from the pre-stored sets, which is sufficient to achieve effective oscillation cancellation without demanding ultra-precise measurement.
Solution Approach 2:
The patent implements parameter changes by providing multiple discrete sets of shaping signal parameters with varying natural frequency and damping ratio values. Instead of requiring continuous precise adjustment, the system selects from predetermined parameter sets, transforming the continuous parameter matching problem into a discrete selection problem that is less sensitive to measurement precision.
3Device complexity
If traditional step signals are used to drive the VCM, then driver design is simple, but mechanical oscillation occurs and focus time increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing multiple sets of shaping signal parameters (amplitudes and time intervals) corresponding to different focus distances and VCM characteristics before operation. This allows the driver to achieve fast focus with oscillation cancellation using simple parameter selection and signal generation, avoiding complex real-time computation while maintaining simple driver architecture.
Solution Approach 2:
The patent implements periodic action through the use of shaped impulse signals with specific time intervals and amplitudes. The shaping signals consist of multiple periodic impulses whose amplitudes and intervals are carefully designed to counteract the natural oscillation frequency of the VCM, thereby canceling mechanical oscillation while maintaining simple driver implementation.
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
This approach significantly reduces focus time from hundreds of milliseconds to a few milliseconds, while also reducing sensitivity to natural frequency and damping ratio errors, thereby simplifying system design and reducing power consumption.
Implementation Method 1
When a driving current applied to the coil of VCM, the Lorentz force generated by electromagnetic force of the coil in a magnetic field from a permanent magnet moves lens linearly.
Data Source
AI summary
The present invention relates to a device and method for driving an under damped voice coil motor (VCM) actuator of a camera lens. In one embodiment, the device for driving an under damped VCM actuator comprises a first generator operable to read a first manufacture data from an image signal processor (ISP) and to generate a half natural period, ½ Td, of the VCM actuator by selecting a value approximate to the first data in a first table of the device, a second generator operable to read a second manufacture data from the ISP and to generate the maximum overshoot, K, of the VCM actuator by selecting a value approximate to the second data in a second table of the device, an input shaping signal generator operable to read an input signal corresponding to a desired camera lens moving distance from the ISP and to generate a shaping signal according to the value of the half natural period and the maximum overshoot. The input shaping signal may be produced from second order, third order and fourth order input shaping function. The present invention also provides a simple implementation of a driver configuration to achieve a fast camera lens focus speed, yet robust to tolerate actual system deviation from a manufacture design.