Inductive Encoder Scale and Detector Configuration for Pitch Error Compensation
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Solution Overview
Problem
Existing inductive position encoders face challenges in achieving a combination of compact size, high resolution, cost-effectiveness, robustness to contamination, and practical layout and fabrication constraints, while also addressing signal offset and dynamic pitch errors.
Innovation Solution
The design incorporates a scale with interleaved field attenuating and sustaining elements, a detector portion with non-symmetrical sensing coil configurations, and a signal processing configuration that allows for flexible layout and fabrication, using conventional or unconventional scales, and mitigates signal asymmetries and dynamic pitch effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional inductive encoder configurations are used, then manufacturing is simpler and cost is lower, but signal strength is weaker and measurement precision is reduced
Solution Approach 1:
The scale is divided into multiple track segments (first track and second track) with different pattern offsets. Each track segment interacts with corresponding sensing coil segments to generate distinct signal components. This segmentation allows the system to combine multiple signal components to achieve stronger overall signal strength and better measurement precision while managing coil configuration complexity through modular design.
Solution Approach 2:
The patent introduces a second track dimension parallel to the first track, creating a two-dimensional scale structure. The sensing coil configuration similarly extends into a second dimension with coils positioned above and below the scale plane. This dimensional expansion enables the system to generate multiple signal components that can be combined for enhanced signal strength and precision.
2Measurement precision
If symmetrical sensing coil configurations are used, then fabrication is easier and layout is simpler, but signal offset errors increase due to dynamic pitch effects
Solution Approach 1:
The sensing coil configuration deliberately uses asymmetrical positioning relative to the scale tracks. The first sensing coil segment is positioned at a different distance from the first track than the second sensing coil segment is from the second track. This asymmetrical configuration, when combined with the offset track patterns, generates signal components with opposite polarity that can be summed to eliminate signal offset errors caused by dynamic pitch effects.
Solution Approach 2:
The patent changes the geometric parameters of the coil-s scale arrangement, specifically the distances between sensing coils and scale tracks, and the offsets between track patterns. By optimizing these parameters, the system achieves cancellation of signal offset errors while maintaining manufacturability through defined geometric relationships.
3Measurement precision
If high resolution is achieved through conventional means, then measurement precision improves, but device size increases and compactness is reduced
Solution Approach 1:
The patent achieves high resolution within a compact volume by utilizing three-dimensional coil positioning. Sensing coils are placed both above and below the scale plane, effectively using the z-dimension to increase the sensing aperture without increasing the x-y footprint. This allows high-resolution measurement in a compact detector portion suitable for minimally invasive applications.
Solution Approach 2:
The detector portion is segmented into multiple sensing coil segments positioned at different locations and orientations. This segmentation allows the system to achieve high resolution through the combined output of multiple smaller sensing elements rather than requiring a single large sensing element, thus maintaining compact overall device size.
4Reliability
If robustness to contamination is required, then inductive transducer design is used, but signal strength and measurement precision are compromised
Solution Approach 1:
The patent merges multiple signal generation mechanisms within the inductive transducer framework. By combining the effects of multiple scale tracks with different patterns and multiple sensing coils at different positions, the system creates a composite signal that is both strong and robust to contamination. The redundant signal paths ensure reliable operation in contaminated environments while maintaining measurement precision.
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 configuration enhances signal strength, reduces signal offset and dynamic pitch errors, and allows for more practical and cost-effective production of high-resolution position encoders robust to contamination.
Implementation Method 1
The field generating coil configuration comprises at least one field generating loop configured to provide a changing first magnetic flux in a first interior area aligned with the first pattern track and to provide a changing second magnetic flux in a second interior area aligned with the second pattern track
Implementation Method 2
The sensing coil configuration comprises a first spatial phase signal sensing coil configuration arranged in the first interior area and a second spatial phase signal sensing coil configuration arranged in the second interior area
Data Source
AI summary
A pitch compensated inductive position encoder includes a scale comprising first and second tracks including periodic patterns having a wavelength W, a detector, and signal processing. The second track pattern may be shifted along the measuring direction by a pattern offset STO relative to the first track pattern. In the detector, first-track and second-track field generating coil portions generate fields in first and second interior areas aligned with the first and second pattern tracks, respectively. First and second sensing coil configurations that are aligned with the first and second tracks, respectively, are offset relative to one another by STO+/â0.5*W along the measuring direction. In various embodiments, the first and second sensing coil configurations may have the same sequence of individual coil polarities if the generated field polarities are different, and may have inverted or opposite sequences if the generated field polarities are the same.