Machine Vision Inspection System High-Speed Z-Height Measurement

Solution Overview

Problem

Conventional machine vision inspection systems face limitations in high-speed autofocus operations due to the camera's motion through a range of Z-height positions, resulting in slower Z-height measurement capabilities compared to laser triangulation techniques, which have a lower resolution and lack comparable lateral resolution.

Innovation Solution

The implementation of a machine vision inspection system utilizing a variable focal length lens that periodically modulates focus positions at high speeds, combined with an image stack collection method where each image is exposed during strobed illumination corresponding to the focus position, allowing for high-speed Z-height measurements without the need for camera motion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the camera moves through a range of Z-height positions to capture image stacks for autofocus operations, then Z-height measurements can be obtained, but the measurement speed is limited and insufficient for high-speed applications

Engineering Contradiction:

ImproveZ-height measurement capabilityVSAvoidmeasurement speed

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent replaces the mechanical camera movement system with an optical focusing system. Instead of physically moving the camera through Z-height positions, the invention modulates the focus position of the lens optically, allowing the camera to remain stationary while still capturing images at different focal planes. This substitution enables high-speed autofocus operations without the speed limitations of mechanical movement.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent implements periodic modulation of the focus position through a defined range at a specific frequency. The focus position oscillates between maximum and minimum values, and images are captured at predetermined phases of this periodic cycle. This periodic action allows rapid acquisition of image stacks at different Z-height positions without requiring slow mechanical traversal, thereby achieving high-speed Z-height measurements.

Inventive Principle:

Principle #19Periodic action

2Measurement precision

If conventional autofocus methods are used with camera motion, then Z-height measurements can be performed, but the system cannot achieve the high speeds required for certain applications

Engineering Contradiction:

ImproveZ-height measurement capabilityVSAvoidinspection throughput

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent replaces the mechanical camera movement system with an optical focusing system. Instead of physically moving the camera through Z-height positions, the invention modulates the focus position of the lens optically, allowing the camera to remain stationary while still capturing images at different focal planes. This substitution enables high-speed autofocus operations without the speed limitations of mechanical movement.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent implements periodic modulation of the focus position through a defined range at a specific frequency. The focus position oscillates between maximum and minimum values, and images are captured at predetermined phases of this periodic cycle. This periodic action allows rapid acquisition of image stacks at different Z-height positions without requiring slow mechanical traversal, thereby achieving high-speed Z-height measurements.

Inventive Principle:

Principle #19Periodic action

3Speed

If laser triangulation techniques are used for high-speed measurements, then measurement speed improves, but resolution is limited to a lower bound of 4 μm and lateral resolution is not comparable to machine vision systems

Engineering Contradiction:

Improvemeasurement speedVSAvoidZ-height resolution

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent merges the advantages of machine vision systems (high lateral resolution) with the capability for high-speed Z-height measurements. By combining stationary camera imaging with optical focus modulation and periodic scanning, the system achieves both high lateral resolution inherent to machine vision and high measurement speed, while also achieving Z-height resolution better than the 4 μm limitation of laser triangulation.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentEP2813803B1Machine vision inspection system and method for performing high-speed focus height measurement operations

Publication Date: 2019.10.23 MITUTOYO CORP

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AI summary

A machine vision inspection system comprising an illumination source and an imaging system and a method for performing high-speed focus height measurement operations. The method comprises: placing (1010) a workpiece in a field of view of the machine vision inspection system; determining (1020) a region of interest for focus height measurement operations; operating (1030) the illumination source to illuminate the workpiece with strobed illumination; periodically modulating (1040) a focus position of the imaging system along a Z-height direction proximate to the workpiece; collecting (1050) an image stack, wherein each image of the image stack corresponds to an instance of strobed illumination matched with a phase of the modulated focus position corresponding to an appropriate Z height within the image stack; and determining (1060) a Z-height measurement for at least one portion of the region of interest.