Absolute Position Encoder with Reference Track for Alignment
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Solution Overview
Problem
Existing absolute position length-measurement type encoders face difficulties in forming minute absolute patterns without positional errors, especially as the scale length increases, due to the need for precise alignment with incremental patterns, which limits the accuracy and feasibility of smaller encoders.
Innovation Solution
Incorporating a reference position track with patterns formed at longer intervals than incremental patterns, allowing absolute patterns to have larger position errors, thus enabling more accurate and minute incremental patterns without requiring precise alignment, and using a photodetector and signal processing circuit to detect absolute positions based on both incremental and reference patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If absolute patterns are formed with minute intervals to match incremental patterns, then measurement precision is improved, but manufacturing precision deteriorates due to difficulty in maintaining positional accuracy
Solution Approach 1:
The patent introduces reference position patterns as an intermediary element between absolute patterns and incremental patterns. The reference position patterns serve as a mediator that simplifies the formation process: absolute patterns only need to be aligned with reference position patterns (which have larger intervals and are easier to manufacture), rather than requiring direct precise alignment with minute incremental patterns. This intermediary structure resolves the contradiction by decoupling the stringent alignment requirements while maintaining measurement precision.
2Productivity
If the scale length is increased to improve measurement range, then productivity is improved, but manufacturing precision deteriorates due to difficulty in maintaining relative phase relation throughout the scale
Solution Approach 1:
The patent segments the scale into distinct functional tracks: absolute tracks with absolute patterns, reference position tracks with reference position patterns, and incremental tracks with incremental patterns. This segmentation allows each track to be optimized independently - the reference position track provides periodic alignment references throughout the extended scale length, breaking down the continuous alignment requirement into manageable segments. This enables the scale to be extended for greater measurement range while maintaining manufacturing precision through periodic reference points.
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 approach enhances the accuracy of absolute position measurements by allowing larger position errors in absolute patterns relative to incremental patterns, resulting in improved encoder accuracy and feasibility for smaller encoders.
Implementation Method 1
a photodetector for receiving the measurement light reflected at or transmitted through the scale
Implementation Method 2
a photodetector for receiving the measurement light reflected at or transmitted through the scale
Data Source
AI summary
An absolute position length-measurement type encoder includes a scale having an incremental track, an absolute track, and a reference position track. The incremental track has incremental patterns including first light and dark patterns formed at equal intervals in first periods. The absolute track has absolute patterns representing an absolute position. The reference position track has reference position patterns including second light and dark patterns formed at equal intervals in second periods longer than the first periods. A light source emits a measurement light to the scale. A photodetector receives the measurement light reflected at or transmitted through the scale. A signal processing circuit processes the received light signal of the photodetector to detect an absolute position of the scale.