Autofocus Lighting Optimization for Z-Height Measurement Precision
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Solution Overview
Problem
Existing machine vision inspection systems face challenges in achieving high accuracy and repeatability for Z-height measurements due to suboptimal autofocus lighting, which is not reliably integrated with autofocus tools, leading to degraded measurement precision and increased pixel saturation.
Innovation Solution
A method for optimized autofocus lighting is introduced, where an initial quantitative autofocus is performed using an initial lighting configuration, followed by a refined lighting configuration determination to enhance image focus metrics, ensuring fewer saturated pixels and improved focus curve accuracy, allowing for more precise Z-height determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional autofocus methods are used with fixed lighting configuration, then the system operation is simple, but the measurement precision and repeatability of Z-height measurements are degraded
Solution Approach 1:
The system performs preliminary autofocus operations with an initial lighting configuration to obtain a preliminary focused image, then uses this image to determine optimized lighting parameters before performing the final precision autofocus measurement. This preliminary action prepares the optimal conditions for the subsequent high-precision measurement.
Solution Approach 2:
The system uses the preliminary focused image as feedback to determine refined lighting parameters, then applies these refined parameters to improve the quality of the final autofocus images. This feedback loop ensures that the lighting is optimized based on actual image quality assessment.
2Measurement precision
If lighting is increased to improve image quality, then signal-to-noise ratio improves, but pixel saturation increases which degrades measurement accuracy
Solution Approach 1:
The system changes lighting parameters dynamically - first using an initial lighting configuration for preliminary autofocus, then determining refined lighting parameters based on the preliminary image characteristics, and finally using these refined parameters for the precision measurement. This parameter optimization balances signal-to-noise ratio with saturation avoidance.
3Measurement precision
If multiple autofocus operations are performed with refined lighting, then measurement accuracy improves, but inspection time increases
Solution Approach 1:
The system performs a preliminary autofocus operation with initial lighting to establish a preliminary focused image, then uses this image to determine optimized lighting parameters. This preliminary action enables subsequent high-precision measurements to be performed more efficiently with the optimized lighting, reducing the need for repeated trial-and-error adjustments.
Solution Approach 2:
The system maintains continuous useful action by performing the preliminary autofocus and lighting optimization in sequence without interruption, then immediately using the refined parameters for the precision measurement. This continuous process minimizes idle time and ensures that each operation builds on the previous one.
Data Source
AI summary
A refined autofocus method provides optimized lighting between iterative autofocus operations, to reliably provide the best possible autofocus Z-height precision. The method includes a quantitative initial focus Z-height determination based on initial focus curve data from initial autofocus images acquired using initial light control parameters. Then, the camera is set at that initial focus Z-height such that well focused images are provided. Refined (optimized) light control parameters are then determined based on at least one respective image acquired using respective light control parameters at that Z-height, such that an image acquired using the refined light control parameters provides a near-optimum value for a contrast-related metric (e.g., a focus metric) at that Z-height. Then, refined autofocus images are acquired using the refined light control parameters and a refined precise Z-height is quantitatively determined base on the resulting focus curve.