Variable Focal Lens Modulation for Extended Depth of Field Imaging
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Solution Overview
Problem
Current machine vision inspection systems face challenges in achieving extended depth-of-field imaging efficiently, as existing methods are either slow or mechanically complex, and may compromise accuracy and repeatability for precision measurements.
Innovation Solution
The implementation of a variable focal length lens that modulates focus position rapidly without mechanical adjustments, combined with computational deconvolution using a point spread function, to provide an extended depth-of-field image that is clear and stable for high-speed imaging applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If image stacking method is used to collect extended depth of field images, then depth of field is extended, but imaging speed becomes slow
Solution Approach 1:
The patent applies periodic action by modulating the focus position of the imaging system at a high frequency (e.g., 300 Hz or higher) during a single image exposure. This rapid periodic focusing allows the system to capture light from multiple focal planes within the exposure time, effectively extending the depth of field while maintaining high imaging speed, thus resolving the contradiction between extended depth of field and fast imaging.
2Volume of moving object
If detector position is altered to change focal distance, then extended depth of field is achieved, but mechanical complexity increases and accuracy/repeatability deteriorates
Solution Approach 1:
The patent replaces the mechanical detector translation system with an optical focusing modulation approach. Instead of physically moving the detector along the optical axis to change focal distance, the system modulates the focus position of the imaging system optically at high frequency. This substitution eliminates the need for mechanical translation components, reducing mechanical complexity while maintaining the ability to achieve extended depth of field, and preserving accuracy and repeatability for precision measurements.
Data Source
AI summary
A method for operating an imaging system of a machine vision inspection system to provide an extended depth of field (EDOF) image. The method comprises (a) placing a workpiece in a field of view; (b) periodically modulating a focus position of the imaging system without macroscopically adjusting the spacing between elements in the imaging system, the focus position is periodically modulated over a plurality of positions along a focus axis direction in a focus range including a workpiece surface height; (c) exposing a first preliminary image during an image integration time while modulating the focus position in the focus range; and (d) processing the first preliminary image to remove blurred image contributions occurring in the focus range during the image integration time to provide an EDOF image that is focused throughout a larger depth of field than the imaging system provides at a single focal position.