Inductive Stylus Position Detection with Coil Misalignment Compensation
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Solution Overview
Problem
Existing inductive sensing configurations for coordinate measuring machines (CMMs) face challenges such as inaccuracies, susceptibility to cross-coupling errors, and environmental factors like temperature changes, which affect the precision and cost-effectiveness of displacement detection in CMM probes.
Innovation Solution
A scanning probe with a stylus position detection system utilizing a coil board configuration, misalignment compensation elements, and a disruptor configuration, which includes a field generating coil and multiple sensing coils, provides robust and accurate three-dimensional position detection by compensating signal offsets and reducing 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 inductive sensor is segmented into multiple independent coil assemblies arranged in a planar configuration. Each coil assembly measures a specific displacement component, allowing the sensor to achieve three-dimensional measurement capability without requiring a single large volumetric sensor. This segmentation enables compact integration into CMM probes while maintaining measurement accuracy.
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 uses planar coil assemblies that can be manufactured using standard PCB fabrication techniques, effectively copying the simplicity and cost-effectiveness of printed circuit board manufacturing. This approach replaces expensive, custom-wound LVDT sensors with replicated coil patterns that can be mass-produced using conventional manufacturing processes, significantly reducing unit costs while maintaining measurement capability.
3Device complexity
If simple planar inductive sensor configurations are used, then device complexity and cost are reduced, but measurement accuracy decreases due to cross-coupling errors
Solution Approach 1:
The patent implements local quality by assigning specific functional characteristics to different regions of the planar coil assembly. Each coil is positioned and oriented to optimally sense specific displacement components, with compensation coils strategically placed to cancel cross-coupling errors in their local measurement zones. This localized optimization maintains overall system simplicity while improving measurement accuracy through targeted error compensation.
4Ease of operation
If known inductive sensing systems are used in CMM probes, then basic position detection is achieved, but signal accuracy deteriorates due to non-linearities, misalignment errors, and environmental effects
Solution Approach 1:
The patent incorporates compensation coils that provide feedback signals to counteract measurement errors. These compensation coils are configured to detect cross-coupling effects and environmental disturbances, generating correction signals that are subtracted from the primary measurement signals. This feedback mechanism continuously compensates for non-linearities and misalignment errors, maintaining high signal accuracy throughout the measurement range.
5Reliability
If traditional inductive sensors are used in CMM probes, then displacement measurement is possible, but reliability decreases due to susceptibility to temperature changes and environmental effects
Solution Approach 1:
The patent uses compensation coils as intermediary elements that mediate between the primary sensing coils and the measurement output. These intermediary coils specifically detect temperature-induced drift and environmental disturbances, allowing the system to distinguish between actual displacement measurements and environmental artifacts. This intermediary measurement approach isolates the primary measurement function from environmental interference, improving reliability.
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 the accuracy and reliability of position detection in CMMs by eliminating signal errors and improving precision, while being more cost-effective and less susceptible to environmental influences.
Implementation Method 1
A CMM employing a mechanical contact probe is also described in U.S. Patent No. 6,971,183. The probe disclosed therein includes a stylus having a surface contact portion, an axial motion mechanism, and a rotary motion mechanism.
Data Source
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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).