Coordinate Measurement Probe Directional Sensitivity
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Solution Overview
Problem
Dimensional measurement probes used in coordinate measurement machines face issues with stylus bending due to side loading, leading to inaccurate measurements and false triggers, as the trigger signal depends on the relative position of the object surface and the stylus axis, and existing solutions like calibration or sensitive sensors have limitations such as requiring time-consuming calibration or producing false triggers.
Innovation Solution
A measurement probe with a stylus and sensor elements that combines the outputs of multiple sensor elements using a processor to generate a trigger signal based on predefined displacement, independent of the approach direction, ensuring consistent sensitivity in all directions by using an algorithm or data comparison to account for stylus bending and strain gauge outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensitive sensors are used to detect stylus contact, then measurement precision is improved, but false trigger signals occur due to vibration and rapid acceleration
Solution Approach 1:
The sensor system is divided into multiple independent sensor elements (e.g., strain gauges) positioned at different locations on the stylus. Each sensor detects different aspects of stylus deformation, and their outputs are processed separately before being combined to generate the trigger signal, allowing discrimination between genuine contact and vibration
Solution Approach 2:
The processor analyzes the outputs from multiple sensor elements and applies algorithms (such as sum of squares combination) to determine when a genuine contact has occurred. The system uses feedback from the pattern of sensor responses to distinguish between false triggers caused by vibration and genuine object contact, adjusting the trigger decision based on the consistency of signals across multiple sensors
2Reliability
If less sensitive sensors are used to avoid false triggers, then reliability is improved, but measurement precision deteriorates due to lag between initial contact and trigger signal
Solution Approach 1:
Multiple sensor elements are distributed along the stylus stem to detect contact forces at different locations. This segmentation allows the system to use less sensitive individual sensors while still achieving reliable contact detection through the combined information from all sensors, reducing the lag between initial contact and trigger signal
Solution Approach 2:
The outputs from multiple less-sensitive sensor elements are merged and processed by the processor using algorithms such as sum of squares combination or neural network analysis. This combining effect effectively increases the sensitivity of the overall system while maintaining the reliability benefits of using less sensitive individual sensors, eliminating the lag problem
3Measurement precision
If calibration with correction factors is applied to account for stylus bending, then measurement precision is improved, but productivity deteriorates due to time-consuming calibration process
Solution Approach 1:
The probe system performs self-calibration by automatically analyzing the patterns of deformation detected by multiple sensor elements during normal operation. The processor identifies characteristic deformation patterns and applies correction algorithms in real-time without requiring external calibration artifacts or manual intervention, making the system self-calibrating and eliminating time-consuming calibration procedures
Solution Approach 2:
The system dynamically adjusts processing parameters and sensitivity thresholds based on real-time analysis of sensor output patterns. By changing the processing parameters adaptively rather than using fixed calibration factors, the system maintains measurement precision without requiring time-consuming calibration procedures
4Measurement precision
If mechanical solutions like resilient members are used to compensate for stylus bending, then measurement precision is improved, but device complexity increases due to manufacturing complexity and vibration
Solution Approach 1:
The patent replaces complex mechanical compensation mechanisms (such as resilient members positioned along the stem) with an electronic sensing and processing system. Multiple sensor elements detect stylus deformation, and a processor applies algorithms to compensate for bending effects, eliminating the need for complex mechanical structures while maintaining measurement precision and reducing vibration issues
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 approach provides a consistent trigger signal independent of the contact direction, reducing the impact of stylus bending and improving measurement accuracy by ensuring the same predefined displacement triggers the signal regardless of the approach direction, thus minimizing directional dependence and false triggers.
Implementation Method 1
a strain sensing element in the form of three strain gauges arranged radially on to the stylus stem
Data Source
Figure 1a~6
Figure 2~3
Figure 4
AI summary
A probe for measuring the dimensions of objects on a coordinate positioning machine such as a machine tool has a workpiece-contacting stylus 20. This is suspended via a sensor mechanism 30, including strain gauges 34 which provide an output when the stylus contacts a workpiece. A processor 16 processes the strain gauge outputs to produce a trigger signal. It does so in accordance with an algorithm or equation or look-up table which ensures equal sensitivity in all possible directions of approach to the workpiece in the three dimensions X,Y,Z.