Stepping Motor Lens Control with Virtual Target Position
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Solution Overview
Problem
Conventional lens control systems using stepping motors face challenges in achieving accurate positioning due to non-linear relationships between rotational and optical axis positions, resulting in offset errors and complex drive control processes.
Innovation Solution
A lens control device and method that incorporate a stepping motor, position detection circuit, and memory to determine a virtual target rotational position based on input target information, retrieving a corresponding rotational position within a given range to simplify the control process and correct for offset errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If closed loop control with drive current correction processing is used to improve positioning accuracy, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent pre-calculates and stores correction values for the non-linear relationship between rotational position and optical axis position in a lookup table during system initialization. During operation, the controller simply retrieves the appropriate correction value from the table based on the current position, avoiding complex real-time calculations and achieving both high positioning accuracy and simple control processing.
2Manufacturing precision
If closed loop control with drive current correction processing is used to improve positioning accuracy, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
The correction data for the non-linear positional relationship is pre-computed and stored in a lookup table during system initialization. During actual lens positioning operations, the controller performs a simple table lookup operation to retrieve the correction value, which takes minimal time compared to performing complex drive current correction calculations in real-time, thus achieving high positioning accuracy without significant processing time penalty.
3Ease of operation
If a stepping motor is used to move the lens, then ease of operation is improved, but manufacturing precision deteriorates due to non-linear relationship and offset errors
Solution Approach 1:
The patent employs a feedback mechanism where the actual rotational position of the stepping motor is detected and fed back to the controller. The controller then retrieves the corresponding correction value from the pre-stored lookup table and applies it to adjust the drive pulses, compensating for the non-linear relationship and offset errors between rotational position and optical axis position, thereby maintaining both ease of operation and positioning precision.
Solution Approach 2:
The patent changes the control parameter from direct rotational position to corrected rotational position by applying a correction value retrieved from a lookup table. This correction value compensates for the non-linear relationship and offset errors inherent in the stepping motor system, allowing the simple stepping motor control to achieve high positioning accuracy without complex real-time calculations.
Data Source
AI summary
A lens control device that moves a lens in an optical axis direction comprises a stepping motor that drives the lens, a position detection circuit that detects position of the lens in an optical axis direction, a memory that stores data relating to a relationship between rotational position of the stepping motor and detected position of the position detection circuit, and a controller that designates rotational position of the stepping motor based on target information that is input, determines a virtual target rotational position based on a target position corresponding to detected position of the position detection circuit corresponding to the target information that has been input, and, based on the virtual target rotational position, searches for a rotational position that corresponds to the target position, within a range of given rotational positions of the data.