VCM Auto Focusing Method Using Hysteresis Table Compensation
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Solution Overview
Problem
The existing auto focusing methods using Voice Coil Motor (VCM) actuators in cameras face challenges due to hysteresis characteristics and lens inertia, resulting in different focus values when moving the lens upward and downward, which hinders accurate focus adjustment.
Innovation Solution
An auto focusing method that compensates for lens position errors by determining the difference between upward and downward position values and using a hysteresis table to select the most appropriate code value for downward position adjustment, ensuring accurate focus adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a VCM actuator is used to move the lens, then the response time is reduced and position control precision is improved, but hysteresis characteristics cause different focus values under identical conditions
Solution Approach 1:
The patent implements a feedback mechanism by detecting the actual focus value through image signal analysis and comparing it with the expected focus value from the VCM position. The controller adjusts the lens position based on this feedback to compensate for hysteresis effects, ensuring consistent focus values despite the nonlinear VCM characteristics.
Solution Approach 2:
The patent changes the control parameter from direct VCM position commands to corrected position values that account for hysteresis. By pre-characterizing the hysteresis behavior and using lookup tables or compensation algorithms, the system transforms the nonlinear VCM output into accurate lens position information for reliable auto-focusing.
2Productivity
If the lens is moved upward and downward to find the maximum focus value, then the auto-focusing search is performed, but the upward and downward position values differ due to VCM hysteresis
Solution Approach 1:
The patent performs preliminary characterization of the VCM's hysteresis behavior during system setup or calibration. By pre-measuring the upward and downward position differences and storing them in lookup tables, the system can quickly compensate for hysteresis during normal auto-focusing operation without repeating the characterization process.
Solution Approach 2:
The patent introduces an intermediary correction mechanism between the VCM position measurement and the final focus value determination. This intermediary layer (lookup tables, compensation algorithms, or corrected position calculations) mediates the hysteresis effect, allowing the system to achieve accurate focus values despite the upward-downward position differences.
3Extent of automation
If a hill-climbing search algorithm is used to find the maximum focus value, then the focus adjustment is automated, but the nonlinear and time-varying characteristics of the VCM degrade control performance
Solution Approach 1:
The patent enhances the automated hill-climbing search by incorporating feedback from actual focus value measurement. The controller monitors the focus quality through image signals and adjusts the search algorithm's behavior based on this feedback, compensating for VCM nonlinearities and time-varying characteristics to maintain reliable control performance.
Solution Approach 2:
The patent makes the control system dynamic by adapting the hill-climbing search parameters in real-time based on detected focus conditions and VCM response characteristics. The controller dynamically adjusts search step sizes, direction, and speed to account for changing VCM behavior, maintaining effective automation despite nonlinear and time-varying characteristics.
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 method enables rapid and accurate lens focusing by minimizing the difference between upward and downward position values, improving the overall precision of the auto focusing process.
Implementation Method 1
A voice coil motor (VCM) is an actuator that uses Lorentz force generated by electromagnetic force of a coil in a magnetic field of a permanent magnet to linearly move a lens
Data Source
AI summary
The present disclosure relates to an auto focusing method using a VCM (voice coil motor) actuator, the method of using the VCM actuator to upwardly move a lens position, to obtain a most-focused upward position value, and downwardly move the lens position to automatically adjust the lens focus, the method comprising: obtaining an auto focus (AF) upward position value, which is an upward position value of a lens when the lens is most focused by upwardly moving the lens to capture an image; determining whether a difference between the AF upward position value and an AF downward position value of a code value which is a bit value corresponding to the AF upward position value is smaller than a pre-set level; and implementing the auto focusing the code value if the difference is smaller than the pre-set level, and using a hysteresis table of the VCM actuator to select a code value corresponding to a downward position value most approximate to the AF upward position value in a downward position value column and to implement the auto focusing adjustment using the corrected code value, if the difference is not smaller than the pre-set level.