Capacitive Touch Trigger Probe for Isotropic 3D Measurement
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Solution Overview
Problem
Conventional touch trigger probes suffer from sensitivity anisotropy and pre-travel errors, leading to reduced measurement accuracy and repeatability due to varying sensitivity with direction and displacement, especially when used in CNC machines for 3D coordinate measurement.
Innovation Solution
A capacitive touch trigger probe with a flexible suspension allowing three degrees of freedom, featuring a sensor base and head capacitively coupled, providing isotropic mechanical stiffness and a mechanical interface for safety decoupling, which enables precise measurement by minimizing fringe capacitances and optimizing trigger sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional touch trigger probes use radial pins arranged symmetrically on spheres, then the probe structure is simple and reliable, but the sensitivity varies with direction (anisotropy) causing reduced measurement repeatability
Solution Approach 1:
The patent replaces the mechanical pin-sphere contact system with a capacitive sensing system. The capacitive sensor detects stylus deflection through electrical field changes rather than mechanical contact, eliminating the anisotropy inherent in directional mechanical pins while maintaining structural simplicity. This substitution provides isotropic sensitivity in all directions.
Solution Approach 2:
The patent changes the detection parameter from mechanical contact force to capacitive coupling. By measuring changes in electrical capacitance as the stylus deflects, the system achieves direction-independent sensitivity while maintaining the simple probe structure. The capacitive parameter provides uniform response regardless of deflection direction.
2Productivity
If the probe measures coordinates while in motion, then productivity is improved, but pre-travel errors vary with speed and direction causing reduced measurement accuracy
Solution Approach 1:
The capacitive sensing system responds instantaneously to stylus position changes during motion, providing real-time feedback without the mechanical lag and pre-travel errors characteristic of contact-based systems. This enables accurate coordinate measurement while maintaining high measurement speed and productivity.
Solution Approach 2:
The capacitive sensor provides continuous feedback on stylus deflection during motion, allowing the system to dynamically compensate for speed and direction variations. This feedback mechanism eliminates the fixed pre-travel errors that plague conventional systems operating at different speeds.
3Reliability
If the probe uses mechanical contact detection, then the trigger signal is reliable, but the pre-travel displacement between contact and signal triggering reduces measurement accuracy
Solution Approach 1:
The capacitive sensing system detects stylus deflection through electrical field changes that occur at the same instant as physical contact, eliminating the pre-travel displacement inherent in mechanical systems. The capacitive signal triggers immediately upon contact while maintaining reliable signal generation.
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 enhances measurement accuracy by ensuring consistent sensitivity across all directions and reducing pre-travel errors, achieving high precision below 500 nm with low power consumption and improved repeatability.
Implementation Method 1
The capacitive sensor comprises a sensor base and a sensor head which is spaced to the sensor base (in an axial direction or z-direction) by a suspension and can be capacitively coupled to the sensor base, whereby the sensor head follows a displacement of the probe tip center when contacting the object with the probe tip
Data Source
AI summary
A touch trigger probe with a capacitive sensor for measuring three degrees of freedom with a sensor base and a sensor head which is spaced to the sensor base by a flexible suspension and can be capacitively coupled to the sensor base, whereby the suspension enables a relative movement in three degrees of freedom of the sensor head with respect to the sensor base following a displacement (d) of a probe tip when contacting the object with the probe tip. The suspension and the sensor are adapted to each other in such a way that there is a bijective map between the three degrees of freedom measured by the sensor and all three translational degrees of freedom of the displacement (d) of the probe tip center (C).