Touch Probe Anisotropy Reduction via Optical Sensing
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Solution Overview
Problem
Existing touch probes for coordinate measurement machines suffer from directional sensitivity variations, leading to anisotropy and reduced repeatability and quality of measurements due to their sensitivity to external forces, which is not constant across different directions.
Innovation Solution
A touch probe with a stylus holder elastically connected to a fixed member, equipped with sensors generating displacement signals and a digital processor that generates directional displacement signals and trigger signals based on amplitude thresholds, ensuring direction-independent triggering and noise filtering to improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional pin-based isostatic connection is used, then structural simplicity and reliability are improved, but directional sensitivity uniformity deteriorates due to three-lobed anisotropy
Solution Approach 1:
The patent replaces the traditional mechanical pin-based trigger mechanism with an optical sensing system. The optical sensor detects stylus position and contact events through light field changes, eliminating the mechanical pins that caused directional sensitivity variations. This substitution maintains reliability while achieving uniform sensitivity in all directions.
Solution Approach 2:
The patent changes the fundamental operating parameter from mechanical contact force detection to optical position detection. By measuring light field changes rather than mechanical pin displacement, the system achieves direction-independent sensitivity while maintaining the reliability of contact detection.
2Device complexity
If mechanical pin trigger mechanism is used, then device complexity is reduced, but measurement repeatability deteriorates due to variable sensitivity to external forces
Solution Approach 1:
The patent replaces the mechanical pin trigger mechanism with an optical sensing system. The optical sensor detects stylus position and contact events through light field changes, eliminating the mechanical pins that caused directional sensitivity variations. This substitution maintains reliability while achieving uniform sensitivity in all directions.
3Measurement precision
If optical sensor with image processing is used, then directional sensitivity uniformity is improved, but device complexity increases
Solution Approach 1:
The patent uses a single optical sensor system that serves multiple functions: detecting stylus position, detecting contact events, and providing directional information. This multi-functionality achieves uniform directional sensitivity without proportionally increasing device complexity, as one sensor system replaces what would otherwise require multiple specialized components.
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
The solution achieves low or no anisotropy, enhancing the repeatability and quality of dimensional measurements by providing consistent sensitivity across different directions and reducing false triggers through advanced signal processing and filtering techniques.
Implementation Method 1
a stylus holder, elastically connected to the fixed member and comprising a reference element
Data Source
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AI summary
A touch probe for a coordinate measuring machine with a processor which is programmed to generate a trigger signal signalling a contact between a stylus of the probe and a workpiece, whenever one of a plurality displacement signals exceeds a corresponding threshold. In addition, or in alternative, a delayed trigger is generated based on a processing a plurality of samples of displacement signals that are stored in a buffer. The processor is programmed to minimize anisotropy of the probe response. Furthermore, the thresholds can be modified during operations based on commands received from the CMM controller.