Mobile Camera Lens Position Error Compensation
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Solution Overview
Problem
Conventional auto-focusing methods using voice-coil motors in mobile terminals are inaccurate due to lens position errors caused by hysteresis characteristics and inertia, leading to longer focusing times and suboptimal image quality.
Innovation Solution
An enhanced hill-climbing search procedure with lens position error compensation, involving a three-stage process to detect focus value gradients and adjust lens positions, reduces redundant search sections and compensates for errors caused by voice-coil motor characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional hill-climbing search algorithm is used for auto-focusing, then the focusing process can be completed, but the focusing time is excessively long (2.13 seconds) and lens position accuracy is poor due to VCM hysteresis and inertia
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing compensation values for lens position errors in a lookup table during the manufacturing process. These compensation values account for VCM hysteresis and inertia characteristics, allowing the system to quickly retrieve and apply corrections during auto-focusing without performing complex real-time calculations, thus reducing focusing time while improving position accuracy
Solution Approach 2:
The patent implements feedback by using the detected focus value gradient sign change as a feedback signal to determine when to apply lens position compensation. The system continuously monitors focus values during lens movement and uses this feedback to trigger compensation at the optimal moment, ensuring accurate lens positioning while minimizing search time
2Volume of moving object
If the lens aperture is made smaller to fit the mobile terminal, then the device size is reduced, but the exposure time must be increased to pass sufficient light, complicating the focusing process
Solution Approach 1:
The patent applies self-service by enabling the auto-focusing system to automatically adapt to the constraints of small aperture and longer exposure times. The enhanced hill-climbing search procedure with lens position compensation autonomously adjusts the focusing process to work effectively within these constraints, eliminating the need for manual intervention or complex additional hardware
3Length of moving object
If lens inertia and hysteresis are present in the VCM, then the motor can provide long stroke and high-precision position control, but different focus values are generated under identical conditions and time delay occurs
Solution Approach 1:
The patent addresses focus value inconsistency caused by VCM hysteresis by pre-calculating compensation values during manufacturing and storing them in a lookup table. This preliminary action allows the system to compensate for hysteresis effects in real-time during auto-focusing, ensuring consistent focus values under identical conditions without sacrificing the long stroke capability of the VCM
Solution Approach 2:
The patent replaces the purely mechanical lens positioning approach with a hybrid system that incorporates computational compensation. By substituting mechanical precision requirements with algorithmic correction using pre-calibrated compensation values, the system maintains reliability while utilizing the VCM's mechanical advantages of long stroke and high-precision control
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 method significantly reduces auto-focusing time and improves image quality by accurately compensating for lens position errors, achieving faster and more precise focusing in mobile terminals.
Implementation Method 1
a small voice-coil motor (VCM) is preferred as an actuator
Implementation Method 2
hysteresis characteristics of the voice-coil motor and lens inertia cause a generation of different focus values under identical conditions
Implementation Method 3
several parameters such as the lens weight, lens size and lens inertia cause a time delay in the lens movement to a desired target position
Data Source
AI summary
A mobile terminal and auto-focusing method for the same are disclosed. The auto-focusing method uses a lens position error compensation and includes: detecting a target object during a photograph mode; determining a lens position at which a focus value gradient related to the detected target object changes sign while moving a lens of the camera module in units of one step size; and performing lens position compensation by moving the lens to the found lens position. As a result, the lens position errors caused by a conventional a voice coil motor are compensated, thereby providing rapid and fine auto-focusing.