Self-Calibrated Ringing Compensation for Camera Autofocus
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Solution Overview
Problem
Voice coil motor (VCM) based camera modules experience long autofocus convergence times due to free oscillation, which is not adequately addressed by existing technologies, as the free-oscillation frequency and damping coefficient vary among VCMs and drift over time, leading to overshooting and oscillation during lens positioning.
Innovation Solution
A self-calibrated ringing compensation method that calibrates the free-oscillation frequency and damping coefficient of the VCM using a digital-to-analog converter, filter, and current sink to generate a sink current that compensates for free oscillation, reducing settling time and enhancing autofocus rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a step sink current is applied to the VCM to rapidly position the lens, then the lens displacement speed increases, but the free oscillation amplitude increases causing longer settling time
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensation current that opposes the free oscillation before it fully develops. The compensation current is generated based on calibrated parameters (free-oscillation frequency and damping coefficient) and is applied in opposition to the oscillatory motion, thereby reducing the oscillation amplitude and settling time before the lens fully settles at the target position.
Solution Approach 2:
The patent implements feedback by using the calibrated free-oscillation frequency and damping coefficient to generate a compensation current that responds to the oscillatory behavior. The system measures or calibrates the oscillation characteristics and uses this information to adjust the compensation current, creating a closed-loop control that reduces settling time while maintaining positioning accuracy.
2Measurement precision
If the free-oscillation frequency and damping coefficient are calibrated for each VCM, then the ringing compensation accuracy improves, but the device complexity increases
Solution Approach 1:
The patent applies self-service by enabling the system to automatically calibrate its own parameters without requiring external intervention or complex external testing equipment. The calibration process uses the VCM's own oscillation response to a test signal to determine the free-oscillation frequency and damping coefficient, storing these parameters for subsequent compensation operations. This self-calibration approach reduces device complexity while maintaining high compensation accuracy.
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 self-calibrated ringing compensation method significantly reduces overshoot and settling time, allowing the lens to reach focus position in less than one oscillation cycle, thereby improving autofocus convergence time and rate in camera modules.
Implementation Method 1
When a sink current is injected to the voice coil, a Lorentz force produced by the interaction of the current in the coil and the permanent magnets causes the lens barrel to move
Implementation Method 2
The spring-loaded VCM system is modeled as a damped harmonic oscillator, and therefore, during each lens positioning sub-step in the autofocus process, the lens position is associated with overshooting and oscillation before the lens settles at the target position
Implementation Method 3
The DAC generates a voltage that may be subsequently bypassed, filtered or shaped by the filter. The voltage controls the current sink to generate a sink current
Data Source
AI summary
Various embodiments of the present invention relate to an actuator driver in a camera module, and more particularly to methods, systems and devices of employing self-calibrated ringing compensation to improve the autofocus rate of the camera module that is driven by an actuator. Oscillation characteristics of the actuator are calibrated to control a sink current that drives the actuator during an autofocus. The actuator driver comprises a digital-to-analog converter (DAC), a filter, a current sink and a self calibration module. The self calibration module calibrates the free-oscillation frequency and damping coefficient, and accordingly, the DAC generates a voltage that may be subsequently bypassed, filtered or shaped by the filter. This voltage is further converted to the sink current by the current sink. Such self-calibrated ringing compensation allows close tracking of free oscillation, and may efficiently enhance the settling time of the lens and autofocus rate of the camera module.