Dynamic Focus Tracking for Gas-Suspended Workpieces
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Solution Overview
Problem
Conventional focus tracking systems in precision inspection are too complex for real-time focusing, especially when inspecting workpieces suspended above a gas platform with a limited suspension height clearance, as they cannot capture images outside their depth of field.
Innovation Solution
A dynamic automatic focus tracking system comprising an image capturing device, a driving device, and a focal length adjustment module that adjusts the position of the image capturing device based on the dimensions of a figure feature and a predefined feature, using a gas platform for suspension and an optical projector to project the feature for accurate focusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional computation processes are used for focusing, then focusing accuracy can be achieved, but the process is too complicated to achieve real-time focusing
Solution Approach 1:
The patent segments the focusing task into two independent parts: (1) using a first image capturing device to capture the workpiece image, and (2) using a second image capturing device to capture the figure feature image. This segmentation allows each device to perform its specific function with optimized simplicity, avoiding the need for complex unified computation processes while maintaining focusing accuracy through the dedicated figure feature-based distance calculation.
Solution Approach 2:
The patent introduces a figure feature (either naturally present on the workpiece or projected by an optical projector) as an intermediary element. This figure feature serves as a reference object whose image can be captured and whose known dimensions can be used to calculate the distance between the image capturing device and the workpiece. This intermediary simplifies the focusing computation by providing a direct geometric relationship rather than requiring complex image analysis of the workpiece itself.
2Measurement precision
If conventional cameras are used, then image capture is possible, but the depth of field is just 35 um and thus cannot capture images of an object not within the depth of field
Solution Approach 1:
The patent implements dynamic focus tracking by continuously monitoring the figure feature in the captured image and adjusting the image capturing device's position in real-time. Instead of relying on a fixed large depth of field, the system dynamically adapts to changes in workpiece position by calculating the required adjustment based on figure feature dimensions and actively moving the imaging system to maintain focus, thereby achieving both precision and adaptability.
Solution Approach 2:
The system employs feedback control by capturing the figure feature image, comparing the measured figure feature dimensions with the predefined standard dimensions, calculating the distance discrepancy, and using this information to adjust the image capturing device's position. This closed-loop feedback mechanism enables the system to maintain accurate focus despite variations in workpiece suspension height, effectively extending the practical depth of field through active compensation.
3Object-affected harmful factors
If a gas platform is used to suspend workpieces, then workpieces are prevented from contact with the plane below, but the suspension height clearance is limited to 300 um or so
Solution Approach 1:
The patent replaces mechanical contact-based measurement and focusing methods with optical measurement. By using an image capturing device to capture the figure feature and calculating distance based on image processing of the figure feature dimensions, the system achieves precise focusing without requiring mechanical contact or large clearance. This optical substitution enables accurate measurement and focus control within the limited 300 um suspension height clearance that the gas platform provides.
Data Source
AI summary
The present invention provides a dynamic automatic focus tracking system, comprising an image capturing device for capturing an image of a workpiece in a target picture-taking region; a driving device for adjusting a spacing between the image capturing device and the workpiece; and a focal length adjustment module coupled to the image capturing device and the driving device to generate a control signal according to a figure feature and a predefined figure feature in the image of the workpiece and send the control signal to the driving device, thereby adjusting a position of the image capturing device with the driving device.