Compact Inductive Position Encoder Using Pseudorandom Code
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Solution Overview
Problem
Existing absolute position encoders using inductive sensing technology face challenges in achieving compact size, high resolution, and reduced electronic complexity while maintaining operational robustness and cost-effectiveness, particularly in applications with small spatial wavelengths and large absolute ranges.
Innovation Solution
The design incorporates a scale with a periodic pattern and an absolute position code pattern, where the code bit length (Wcode) is larger than the spatial wavelength (Wf) of the periodic pattern, utilizing multiple sets of code pattern sensing elements to achieve a resolution finer than the code bit length by analyzing signals from these elements, allowing for accurate position determination with a coarse resolution at least as fine as Wf and a fine resolution of 0.1*Wf.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the code bit length (Wcode) is made equal to or smaller than the periodic wavelength (Wf) to avoid position ambiguity, then position measurement reliability is improved, but the scale width transverse to the measuring axis increases
Solution Approach 1:
The patent transitions from parallel binary code tracks arranged transverse to the measuring axis to a serial pseudorandom code track arranged along the measuring axis direction. This dimensional reorganization allows the code to be read sequentially along the axis of motion rather than requiring multiple parallel tracks across the width, thereby reducing the transverse scale width while maintaining position measurement reliability through the pseudorandom code's unique properties
Solution Approach 2:
The patent divides the code reading process into multiple segments by using M sets of code pattern sensing elements spaced along the measuring axis direction. Each set reads a portion of the pseudorandom code sequence, and the combined information from all M sets reconstructs the complete position information. This segmentation allows the use of a longer code bit length (Wcode > Wf) without increasing scale width, as the code is effectively distributed along the measuring axis rather than requiring parallel transverse arrangement
2Measurement precision
If multiple sets of code pattern sensing elements are used to achieve fine resolution (0.1*Wf) with Wcode > Wf, then position determination accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes the code pattern sensing elements multi-functional by having them serve dual purposes: they detect the pseudorandom code pattern for absolute position identification while simultaneously providing fine resolution measurements through their spatial arrangement. The M sets of sensing elements are positioned at specific intervals (at most Wf apart) along the measuring axis, allowing them to read the code sequence at different positions and enable both coarse code-based positioning and fine interpolated positioning within a unified detector structure
Solution Approach 2:
The patent changes the spatial parameter arrangement by positioning M sets of code pattern sensing elements at specific intervals along the measuring axis direction, with each successive alignment interval being at most Wf. This parameter optimization allows the system to achieve fine resolution (0.1*Wf) without proportionally increasing detector complexity, as the sensing elements are strategically positioned to maximize information extraction from the pseudorandom code sequence while minimizing redundant elements
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 provides improved resolution and accuracy in position determination, overcoming position ambiguity issues and enabling reliable operation in compact applications with small spatial wavelengths and large absolute ranges, while reducing detector dimensions and processing complexity.
Implementation Method 1
a field generating configuration comprising at least one conductive loop that generates a changing magnetic field
Implementation Method 2
sensing elements that comprise respective conductive loops that receive at least a portion of the changing magnetic field and generate a corresponding signal
Data Source
AI summary
An absolute position encoder comprises a scale and a detector overlaying the scale. The scale includes a periodic pattern of wavelength Wf and a code pattern having bit length Wcode. The detector includes a set of periodic pattern sensors and M sets of code pattern sensors. M is at least two. The configuration principles include: a) Wcode is larger than Wf and at most M*Wf, and b) the sets of code pattern sensors are located along the measuring axis at respective alignment positions configured such that as the code pattern moves in a single direction it moves by successive alignment intervals that are each at most Wf to align with successive alignment positions. Signal processing is provided to determine the absolute position based on the M respective sets of code detector signals and on spatially periodic signals arising in the periodic pattern sensing elements due to the periodic pattern.