Variable Speed Autofocus for Lens Group Overshoot
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Solution Overview
Problem
Existing autofocus methods for large-focal length electrical driven lenses, whether using stepper motors or DC motors, face challenges in achieving fast and accurate focusing due to the large stroke and inertia of the lens group, leading to either prolonged focusing times or inaccurate positioning caused by overshoot.
Innovation Solution
An automatic focusing method that controls the lens group to move at a first speed for coarse focusing and then reduces speed to a second speed for fine focusing, with image photography at preset frequencies, and decelerates to return to the initial position of the highest definition image, dividing the focusing process into quick coarse and slow fine stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a stepper motor is used to move the lens group for a long distance, then the lens group can be driven stepwise with fixed angle per step, but the moving process will take a long time and fast focusing cannot be achieved
Solution Approach 1:
The patent applies dynamics by switching from a static stepwise motor control approach to a dynamic multi-speed control strategy. The system uses a first speed for coarse focusing to cover long distances quickly, then transitions to a second speed for fine focusing to achieve precise positioning. This dynamic speed adjustment resolves the contradiction between fast movement and precise positioning.
Solution Approach 2:
The patent segments the focusing process into two distinct stages: coarse focusing and fine focusing. Coarse focusing uses a higher speed to cover the majority of the movement distance, while fine focusing uses a lower speed to achieve precise positioning. This segmentation allows the system to optimize for both speed and precision in different phases of the same operation.
2Loss of time
If a DC motor is used to move the lens group for a long distance, then the moving process will take a shorter time, but overshoot tends to occur leading to inaccurate position and low auto focus accuracy
Solution Approach 1:
The patent applies dynamics by implementing variable speed control with two distinct speeds. The first speed enables fast movement to reduce focusing time, while the second speed allows for precise positioning without overshoot. The system dynamically switches between these speeds based on the focusing stage, resolving the contradiction between speed and positioning accuracy.
Solution Approach 2:
The patent segments the focusing operation into coarse focusing (using first speed) and fine focusing (using second speed). This segmentation allows the system to use high speed when precision requirements are lower, and switch to low speed when precise positioning is needed, thereby avoiding overshoot while maintaining fast overall focusing.
3Productivity
If the lens group moves at high speed for coarse focusing, then the focusing process is faster, but the positioning accuracy decreases
Solution Approach 1:
The patent segments the focusing process into two speed modes: first speed for coarse focusing to maximize productivity, and second speed for fine focusing to ensure positioning accuracy. This segmentation allows the system to achieve both high overall focusing speed and precise final positioning by optimizing each segment for its specific goal.
Solution Approach 2:
The patent applies dynamics through multi-speed control, where the system transitions from a dynamic high-speed phase (coarse focusing) to a dynamic low-speed phase (fine focusing). This dynamic speed adjustment allows the system to maintain high productivity during the majority of the focusing process while ensuring accurate positioning at the end.
Data Source
AI summary
Autofocus methods and devices are provided. The method includes: controlling a lens group to move at a first speed, and photographing an image at a preset photographing frequency when the lens group moves at the first speed; when a definition of the image photographed by the lens group in a state of moving at the first speed satisfies a preset condition, reducing a moving speed of the lens group to a second speed, and photographing images at the preset photographing frequency when the lens group moves at the second speed; and when a first image with a highest definition is determined in the images photographed by the lens group in a state of moving at the second speed, controlling the lens group to decelerate, and controlling, when the lens group stops moving, the lens group to return to a position of the lens group where the first image was photographed.