Rotary Encoder Absolute Positioning Using Dual Readhead Reference Marks
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Solution Overview
Problem
Rotary encoders with multiple readheads still suffer from absolute angular errors when determining position using reference marks, despite mitigating bearing wander effects, due to the complexity and cost of existing dual readhead systems.
Innovation Solution
A rotary encoder system that combines incremental measurements with absolute angular orientation determination using reference mark signals from two readheads, separated by a time or angular interval, to establish a reliable absolute position unaffected by bearing wander, employing a reference position setter and incremental signal blending to generate a resultant incremental count resistant to bearing wander.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single readhead is used to read reference marks for determining absolute position, then the device complexity is low, but bearing wander introduces errors in the incremental count and absolute position measurement
Solution Approach 1:
The patent combines incremental position measurement and absolute reference mark detection functions into a single readhead, eliminating the need for separate readheads while maintaining both measurement capabilities through integrated sensors and processing logic
Solution Approach 2:
The system dynamically switches between incremental measurement mode and absolute reference mark detection mode based on operational requirements, allowing the readhead to adapt its function rather than requiring fixed dual readhead configuration
2Measurement precision
If dual readheads are provided at diametrically opposed locations to eliminate bearing wander effects, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The patent merges the functions of two diametrically opposed readheads into a single integrated readhead that performs both incremental measurement and reference mark detection, achieving bearing wander compensation without requiring physical duplication of readhead components
Solution Approach 2:
The single readhead is designed with multi-functionality to perform both incremental position measurement and absolute reference mark detection, replacing the specialized functions previously requiring separate readheads
3Measurement precision
If CCD-based absolute encoder systems are used to determine absolute angular position, then measurement precision improves, but device complexity and cost increase significantly
Solution Approach 1:
The patent replaces expensive, complex CCD-based absolute encoding systems with a simpler, more economical approach using standard sensors and software-based reference mark detection, achieving comparable accuracy at lower cost and complexity
Solution Approach 2:
The system substitutes complex optical CCD detection mechanisms with a simpler sensor-based approach that uses signal processing and reference mark patterns to achieve absolute position determination without requiring sophisticated detector arrays
Data Source
Figure 1A~2B
Figure 3A~6
Figure 4
AI summary
Rotary encoder apparatus (2) is described that comprises an encoder scale or ring (30) and an encoder scale reader. The encoder scale includes an incremental scale and one or more reference marks (32,34). The encoder scale reader comprises at least a first readhead (4) and a second readhead (6) that each produce a reference mark signal when passed over a reference mark of the encoder scale. The apparatus also comprises a reference position setter (40) for determining, as the encoder scale reader is rotated relative to the encoder scale, at least one angularly repeatable reference position of the encoder scale relative to the encoder scale reader using a first reference mark signal produced by the first readhead and a second reference mark signal subsequently produced by the second readhead.