Inductive Stylus Position Detection via Asymmetric Coil Arrays
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Solution Overview
Problem
Existing inductive sensing configurations for coordinate measurement machines (CMMs) face challenges such as inaccuracies, signal non-linearities, position errors due to assembly and alignment issues, and environmental effects like temperature changes, which limit their precision and reliability.
Innovation Solution
A scanning probe with a stylus suspension portion and a stylus position detection system using a coil board configuration with top and bottom axial sensing coils, rotary sensing coils, and a disruptor element, which generates a changing magnetic flux to provide accurate three-dimensional position information through signal processing and control circuitry, minimizing signal errors and cross-coupling errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional LVDT sensors are used for position detection, then measurement accuracy is improved, but device size and complexity increase
Solution Approach 1:
The sensor system is divided into multiple independent planar coil assemblies arranged in specific spatial configurations. Each coil assembly detects specific components of the magnetic field, and their outputs are combined to provide complete three-dimensional position information, replacing the monolithic LVDT structure.
Solution Approach 2:
The mechanical LVDT sensor system is replaced with an electromagnetic field-based detection system using planar coils. This substitution eliminates mechanical contact and moving parts, reducing device complexity while maintaining measurement capability through inductive sensing principles.
2Measurement precision
If complex inductive sensor configurations are used, then measurement precision is improved, but susceptibility to cross-coupling errors increases
Solution Approach 1:
The planar coils are intentionally positioned asymmetrically relative to the disruptor element, with different coil areas and orientations. This asymmetric configuration creates distinct magnetic coupling characteristics for each coil, enabling the system to resolve cross-coupling errors through differential measurement and signal processing.
Solution Approach 2:
The system uses multiple coils providing redundant measurement information that feeds into a unified position calculation algorithm. The combined signals from multiple coils allow real-time compensation and correction of cross-coupling errors through mathematical processing, improving reliability.
3Adaptability or versatility
If multiple sensing coils are used to detect three-dimensional position, then measurement capability is improved, but signal non-linearities and position errors increase
Solution Approach 1:
The system varies the effective magnetic coupling parameters by changing the relative positions and orientations of the planar coils and disruptor element. By carefully designing the geometric parameters and spatial relationships, the system achieves linear response characteristics across the measurement range despite using multiple coils.
Solution Approach 2:
The problem of signal non-linearity in three-dimensional space is solved by introducing a fourth dimension through temporal variation. The system uses time-varying magnetic fields and processes signals in the frequency domain, transforming spatial non-linearities into manageable temporal signals that can be processed linearly.
4Reliability
If inductive sensors are used in CMM probes, then environmental robustness is improved, but signal drift due to environmental effects increases
Solution Approach 1:
The system incorporates reference coils and uses differential measurement techniques where environmental effects appear equally in all channels and are subtracted out during signal processing. This feedback mechanism continuously compensates for temperature drift and environmental variations, maintaining signal stability.
Solution Approach 2:
The planar coil configuration acts as an intermediary that transforms environmental disturbances into measurable signals that can be mathematically separated from the actual position information. The specific geometric arrangement of coils provides a reference framework that distinguishes environmental effects from positional changes.
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, reducing signal errors and environmental influences, thereby enhancing the precision and reliability of CMMs.
Implementation Method 1
the field generating coil configuration generates a changing magnetic flux generally along the axial direction in the disruptor motion volume in response to a coil drive signal
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 that surrounds a hole in the coil board configuration, a top axial sensing coil configuration and a bottom axial sensing coil configuration, and N top rotary sensing coils and N bottom rotary sensing coils. A stylus-coupled disruptor configuration includes a cylindrical disruptor element that is configured to move and fit within the hole of the coil board configuration, and moves along Z (axial) and X-Y (rotary) directions in a motion volume. The field generating coil configuration generates a changing magnetic flux (e.g., encompassing all or at least part of the cylindrical disruptor element), and coil signals indicate the cylindrical disruptor element and/or stylus positions.