Inductive Stylus Position Detection with Coil Misalignment Compensation
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Solution Overview
Problem
Existing inductive sensing technologies for coordinate measurement machines (CMMs) are inaccurate, prone to signal non-linearities, and susceptible to errors due to cross-coupling and environmental factors, making them unsuitable for precision metrology applications.
Innovation Solution
A scanning probe with a stylus position detection system using a coil board configuration with multiple sensing coils and a disruptor element, along with misalignment compensation elements, to provide accurate three-dimensional position information, reducing signal offsets and cross-coupling errors through advanced signal processing and control circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LVDTs or known inductive type sensors are used to measure displacements in CMM probes, then measurement accuracy is improved, but device size increases and cost increases
Solution Approach 1:
The patent replaces traditional mechanical LVDT sensors with an inductive sensing system using coils and a conductive target. The inductive sensing configuration uses electromagnetic fields instead of mechanical contact to detect stylus position, eliminating the need for bulky mechanical components while maintaining measurement accuracy. The coil assembly with top and bottom coils creates an electromagnetic field that interacts with the conductive target on the stylus, providing precise position detection without mechanical complexity.
2Measurement precision
If LVDTs or known inductive type sensors are used to measure displacements in CMM probes, then measurement accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive mechanical LVDT sensors with an inductive sensing system using coils and a conductive target. The inductive sensing configuration uses electromagnetic fields instead of mechanical contact to detect stylus position, eliminating the need for bulky mechanical components while maintaining measurement accuracy. The coil assembly with top and bottom coils creates an electromagnetic field that interacts with the conductive target on the stylus, providing precise position detection without mechanical complexity.
3Device complexity
If known inductive sensing configurations are used, then device complexity is reduced, but measurement precision deteriorates due to cross-coupling errors and signal non-linearities
Solution Approach 1:
The patent segments the sensing system into distinct functional components: top coils for detecting axial position, bottom coils for detecting rotary position, and a conductive target on the stylus. This segmentation allows each coil set to specialize in detecting specific motion components, reducing cross-coupling errors. The top coils are positioned to primarily sense axial displacement while the bottom coils sense rotary displacement, and the signal processing system combines these segmented measurements to achieve high precision three-dimensional position detection.
4Device complexity
If known inductive sensing configurations are used, then device complexity is reduced, but reliability deteriorates due to susceptibility to environmental effects
Solution Approach 1:
The patent implements signal processing that continuously monitors and corrects for environmental effects on the inductive sensing signals. The system processes signals from both top and bottom coils to detect axial and rotary positions, using feedback mechanisms to compensate for temperature drift and other environmental variations. This feedback approach maintains reliable measurements even when environmental conditions change, without requiring complex environmental control systems.
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 provides robust and highly accurate three-dimensional position indications, eliminating or correcting signal errors and cross-coupling issues, enabling precise measurements in CMMs.
Implementation Method 1
A CMM employing a mechanical contact probe is also described in U.S. Pat. No. 6,971,183, which is hereby incorporated herein by reference in its entirety. The probe disclosed therein includes a stylus having a surface contact portion, an axial motion mechanism, and a rotary motion mechanism.
Data Source
AI summary
An inductive position detector for stylus position measurement in a scanning probe comprises a coil board configuration located along a central axis in the probe. The coil board configuration includes a field generating coil configuration and top and bottom axial and rotary sensing coil configurations. The field generating coil configuration generates a changing magnetic flux, and coil signals indicate conductive disruptor element and/or stylus positions. At least one misalignment compensation element is configured to reduce a signal offset that results from a misalignment of at least one coil of the coil board configuration (e.g., the coil board configuration may comprise a printed circuit board with a plurality of layers in which the coils are located and the misalignment of the at least one coil may result from a registration error, such as within manufacturing tolerances, in a layer to layer registration as part of a fabrication process).