Interferometric Touch Probe for Soft Part Measurement
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Solution Overview
Problem
Existing touch probes for coordinate measuring machines require significant force to detect contact, which can be excessive for soft or flexible parts, and previous interferometric solutions are complex and expensive.
Innovation Solution
A touch probe design using a flexible reflective element, a semitransparent element, and a coherent light source to create interference fringes, allowing for minimal force detection with a simple and sensitive optical system, featuring a kinematic joint for repeatable positioning and auto-resetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If mechanical spring systems are used to detect probe contact, then contact detection is achieved, but the force required is excessive for soft or flexible parts
Solution Approach 1:
The patent replaces the mechanical spring system with an optical interferometric system. Instead of using mechanical springs that require significant force to deflect and trigger contact detection, the invention uses a laser interferometer to detect minute displacements of the probe stylus. The interferometric system measures the position of a reflective element on the probe by detecting interference patterns of light, enabling contact detection with forces measured in micro-Newtons rather than the milli-Newtons required by mechanical springs.
2Force
If traditional interferometric optical systems are used to reduce contact force, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines the interferometric measurement function and the probe structure into a single integrated unit. The reflective element is directly mounted on the probe stylus, and the interferometer is positioned within the probe housing, eliminating the need for separate external optical systems. This integration simplifies the overall system while maintaining the low-force measurement capability.
Solution Approach 2:
The probe design incorporates multiple functions into a single device: the interferometric system serves both as the measurement instrument and as part of the probe structure itself. The reflective element serves dual purposes as both a mechanical component of the probe and as the optical reference for interferometric measurement, reducing the total number of components required.
3Force
If complex interferometric systems are implemented for minimal force detection, then measurement precision on soft parts is improved, but measurement time increases due to threshold adjustments
Solution Approach 1:
The interferometric system provides continuous real-time feedback on the position of the probe stylus through continuous monitoring of interference fringe patterns. This allows the system to immediately detect when contact occurs and automatically reset to the pre-contact position, eliminating the need for manual threshold adjustments and enabling rapid sequential measurements.
Solution Approach 2:
The system automatically returns the probe stylus to its pre-contact position immediately after each measurement, preparing it for the next contact detection. This auto-resetting function is performed automatically without requiring manual intervention, maintaining measurement readiness and reducing idle time between measurements.
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
Enables high-accuracy contact detection with minimal transients and productivity, avoiding the need for threshold adjustments and reducing measurement time between contacts.
Implementation Method 1
light reflected from the reflective surface can constructively or destructively interfere with the internally reflected light in the semitransparent element and create interference fringes over the first area dependent upon separation distances between the reflective surface of the flexible reflective element and the opposing surface of the semitransparent element
Data Source
Figure 1
Figure 2
AI summary
A touch probe for sensing the position of a surface, having a housing and a moving assembly supported within the housing and including a flexible reflective element, a spacer element, and a semitransparent element, wherein a reflective surface of the flexible reflective element and a surface of the semitransparent element opposing the reflective surface are separated by the spacer element, and a stylus connected to the flexible reflective element. The moving assembly and stylus are configured such that movement of the stylus responsive to a force on the stylus causes the flexible reflective element to flex and change distances between points on the reflective surface of the flexible reflective element and on the opposing surface of the semitransparent element. A coherent light source provides coherent light incident upon the semitransparent element and directed through the semitransparent element towards the reflective surface of the flexible reflective element, such that interference fringes are created dependent upon separation distances between the reflective surface of the reflective element and the opposing surface of the semitransparent element. A detector senses changes in the interference fringes patterns in response to flexing of the flexible element.