Absolute Encoder Sectioning for Accurate Multi-Cycle Position Detection
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Solution Overview
Problem
Conventional absolute encoders face challenges in accurately detecting the absolute position, especially near the boundaries of M-sequence patterns, leading to potential errors in positioning control.
Innovation Solution
The proposed absolute encoder includes a scale with an optical pattern featuring code patterns for multiple cycles, an illumination unit, a light detection unit, a section determination unit, and an absolute position calculation unit. This configuration allows for precise determination of the section to which a code string belongs, enabling accurate calculation of the absolute position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pattern region is extended to increase the number of detectable bits, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The optical pattern is divided into multiple code patterns arranged in a circular direction, with each code pattern representing a specific angular range. This segmentation allows the encoder to cover a full 360-degree range without increasing the radial or axial dimensions of the scale, thereby maintaining compact device complexity while improving measurement precision through increased bit detection capability.
Solution Approach 2:
Instead of extending the pattern region radially or axially, the patent utilizes the circular direction (angular dimension) to arrange multiple code patterns. This dimensional transition from linear extension to circular arrangement enables the encoder to detect more bits without increasing the overall configuration size, resolving the contradiction between measurement precision and device complexity.
2Reliability
If the order of the M-sequence pattern is increased to improve error correction capability, then the reliability is improved, but the measurement precision deteriorates due to similar pattern arrays
Solution Approach 1:
Each code pattern is assigned a specific local angular range (e.g., first code pattern for 0-180 degrees, second code pattern for 180-360 degrees). This local quality assignment ensures that even when similar M-sequence patterns are used for error correction, the absolute position can be uniquely determined by identifying which local angular range the detected pattern corresponds to, thereby maintaining measurement precision while improving reliability.
Solution Approach 2:
The patent introduces an intermediary mechanism (the section determination unit and identification patterns) that mediates between the similar M-sequence patterns. By detecting which angular section the current position falls into, the system can distinguish between similar patterns from different cycles, preventing erroneous absolute position detection while maintaining high error correction capability.
3Reliability
If identification patterns are added to distinguish M-sequence patterns, then the reliability is improved, but the device complexity increases due to additional patterns
Solution Approach 1:
The patent merges the identification function with the existing code patterns by arranging them in a circular sequence. Rather than adding separate identification patterns, the system uses the sequential arrangement of code patterns themselves as identifiers, where the position in the circular sequence serves as the identification mechanism. This merging approach improves reliability without significantly increasing device complexity.
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 absolute encoder achieves high accuracy in detecting the absolute position, reducing errors near pattern boundaries and maintaining high error correction capability without increasing the encoder's configuration size.
Implementation Method 1
an illumination unit (11) to output light for illuminating the scale (10); a light detection unit (12) to detect light from the scale (10) receiving the light from the illumination unit (11)
Data Source
AI summary
An absolute encoder includes: a scale including an optical pattern that includes code patterns for a plurality of cycles; an illumination unit that outputs light for illuminating the scale; a light detection unit that detects light from the scale; a section determination unit that determines, for a region of the optical pattern divided into a plurality of sections, the section to which a code string belongs; and an absolute position calculation unit that obtains an absolute position of the scale on the basis of the section determined and the code string. When N is the number of the cycles of the code patterns on the scale, in a case where N is equal to two, the number of the sections is three or more, and in a case where N is equal to three or more, the number of the sections is N or more.