CMM Conformance Test Artifact with Convex Illumination
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Solution Overview
Problem
Coordinate measuring machines (CMMs) face challenges in calibrating optical sensors due to the difficulty in creating a suitable test artifact that can effectively produce a silhouette for precise measurement, especially with traditional spheres, which can be obscured by illumination issues.
Innovation Solution
A conformance test artifact is introduced, featuring a calibrated standard, such as a sphere or hemisphere, paired with a convex or concave background illumination surface that creates a silhouette within the vision sensor's field of view, allowing for precise measurement and assessment of sensor accuracy and associativity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a traditional sphere is used as a calibration artifact for optical sensors, then the artifact structure is simple, but illumination issues obscure the silhouette and reduce measurement precision
Solution Approach 1:
A background illuminator is introduced as an intermediary element between the calibration artifact and the environment. This illuminator projects light onto a background surface to create a high-contrast silhouette of the artifact, mediating the interaction between light and the artifact to eliminate illumination problems that previously obscured measurement precision
Solution Approach 2:
The invention utilizes contrast changes through illumination - by projecting light onto a background surface, the system creates a high-contrast silhouette effect where the artifact appears as a dark shape against a bright background. This contrast enhancement allows the vision sensor to clearly detect edges and contours regardless of ambient lighting conditions
2Measurement precision
If a calibrated sphere is used for vision CMM calibration, then the artifact can be measured, but the video sensor cannot clearly detect edges due to lack of contrast
Solution Approach 1:
The background illuminator serves as an intermediary that transforms the lighting conditions. Instead of relying on ambient light or direct illumination of the artifact, the system uses a controlled light projection onto a background surface to create optimal contrast conditions for edge detection by the vision sensor
Solution Approach 2:
The system creates artificial contrast by illuminating the background surface, causing the artifact to appear as a dark silhouette against a bright background. This contrast transformation provides the vision sensor with clear edge information that would otherwise be lost in uniform or poor lighting conditions
3Reliability
If multiple sensors are calibrated without a standardized artifact, then calibration can be performed, but associativity between sensors cannot be verified
Solution Approach 1:
The calibration artifact is designed as a universal standard that can be used with multiple different sensor types (tactile, video, laser, etc.). The artifact's standardized geometry and the background illuminator's universal illumination approach enable any sensor to measure the same reference features, allowing associativity verification across different sensing technologies
Solution Approach 2:
The system allows for controlled changes in measurement parameters while maintaining a constant reference standard. By keeping the artifact geometry and illumination conditions standardized, the system can vary sensor types and measurement approaches to verify that all sensors report consistent data within tolerance zones, thus verifying associativity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the calibration and verification of CMMs by improving the accuracy of vision sensors and other measuring sensors, ensuring that different sensors at various orientations can measure the same artifact within a specified tolerance zone, thereby improving measurement reliability and consistency.
Implementation Method 1
the convex background illumination surface is reflective (and may be a passive reflector), and creates the silhouette by reflecting light towards the vision sensor
Data Source
Figure 1A
Figure 1B~1D
Figure 2A~2B
AI summary
A test artifact for a coordinate measuring machine includes a calibrated standard and a convex background illumination surface. The calibrated standard, the convex background illumination surface and a vision sensor are positionable relative to one another so as to create a silhouette of the calibrated sphere in the vision sensor's field of view. The test artifact may thus be used to calibrate the coordinate measuring machine, and/or to assess the associativity between the vision sensor and another measuring sensor.