Optical Stylus for CMM Rigidity-Accuracy Trade-off
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Solution Overview
Problem
Existing surface sensing devices for position determining apparatus, such as CMMs, face accuracy issues due to the lack of rigidity in stylus probes, which leads to bending under contact forces and inertial forces during high-speed scanning, limiting the precision of surface profile measurements.
Innovation Solution
A surface sensing device with an elongate stylus featuring a workpiece-sensing tip, an optical element, and an optical transducer system that measures both lateral and longitudinal displacements of the stylus, utilizing a flexible carbon fibre or solid transparent material stylus with integrated laser diodes and position sensitive detectors to provide precise three-dimensional position data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the stylus is made sufficiently rigid to ensure measurement accuracy, then measurement precision is improved, but the device complexity and manufacturing difficulty increase significantly
Solution Approach 1:
The patent replaces the traditional rigid mechanical stylus with a flexible optical measurement system. Instead of relying on mechanical rigidity to maintain measurement accuracy, the invention uses optical transducers (such as capacitive, inductive, or optical sensors) to detect stylus tip position and compensate for flexure effects, thereby achieving high measurement precision without requiring a rigid stylus structure.
Solution Approach 2:
The invention changes the measurement parameters by introducing optical or electromagnetic sensing parameters alongside mechanical position data. By measuring additional parameters such as stylus deflection, orientation, and position through optical transducers, the system can compensate for flexure and achieve accurate measurements even with a flexible stylus, thus resolving the contradiction between rigidity requirements and measurement accuracy.
2Device complexity
If the stylus is made flexible to reduce device complexity, then device complexity is reduced, but measurement precision deteriorates due to bending under contact and inertial forces
Solution Approach 1:
The patent implements feedback mechanisms through optical transducers that continuously monitor the stylus tip position and orientation. The measured data from these transducers is fed back to the measurement system, allowing real-time compensation for stylus flexure caused by contact forces and inertial effects during high-speed scanning, thereby maintaining measurement precision despite using a flexible stylus.
Solution Approach 2:
The invention substitutes mechanical rigidity with an optical measurement and compensation system. Instead of relying on the mechanical property of rigidity to prevent measurement errors, the system uses optical transducers to detect and measure stylus deflection, then compensates for these deflections through computational methods, achieving accurate measurements with a flexible stylus.
3Device complexity
If traditional transducers are used to measure stylus position, then device complexity is low, but the ability to measure lateral and longitudinal displacements accurately is limited
Solution Approach 1:
The patent employs optical transducer systems that serve multiple measurement functions simultaneously. A single optical transducer assembly can measure lateral displacements, longitudinal displacements, and stylus orientation, providing comprehensive three-dimensional position data. This multi-functional approach enhances measurement precision without proportionally increasing device complexity, as the optical system integrates multiple sensing capabilities.
Solution Approach 2:
The invention replaces traditional mechanical transducers with optical transducer systems. These optical transducers use light-based sensing mechanisms (such as interferometry, triangulation, or capacitive sensing) to measure stylus position and orientation with higher precision than mechanical transducers, enabling accurate three-dimensional position measurement while maintaining reasonable device complexity through integrated optical designs.
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 enables accurate measurement of three-dimensional positions of the stylus tip relative to the workpiece, enhancing the precision and dynamic performance of surface scanning operations by accounting for both lateral and vertical movements, thus overcoming the rigidity limitations of previous designs.
Implementation Method 1
an optical transducer system which projects a light beam between the optical element and a detector, thereby to measure said lateral displacements of the tip
Data Source
AI summary
A surface sensing device for use in position determining apparatus has an elongate stylus (74) with a tip (82) for scanning the surface of a workpiece to be measured. Lateral displacements of the stylus tip are detected by a light beam which passes along the stylus from a light source (66) to a retroreflector (78). This reflects the beam back via a beamsplitter (70) to a position sensitive detector (76). The stylus is mounted for longitudinal displacement on a carriage (72). The longitudinal displacement is measured by another light beam projected by the beamsplitter (70) onto a second position sensitive detector (84).