Absolute Position Encoder Asymmetric Detector Alignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing absolute position encoders for digital measuring instruments face limitations in accuracy and reliability due to the unfavourable positioning of the reader relative to the scale, particularly in intermediate positions between scale divisions, where the absolute position is likely to be unreliable.
Innovation Solution
The proposed absolute position encoder employs a digital scale with a sequence of discrete regions and detectors configured to select either a first or second absolute position code, ensuring no detector is aligned with transitions between regions, and utilizes an incremental track to derive a precise absolute position code, providing robustness in unfavourable positions through overlapping scale divisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a digital scale with periodic marks and a reader is used to provide relative position, then sub-pitch measuring accuracy is achieved, but the maximal unambiguous displacement range is limited to the pitch between adjacent marks
Solution Approach 1:
The patent combines a coarse absolute position track with fine relative position tracks in a single encoder system. The coarse track provides wide-range unambiguous positioning while the fine tracks deliver sub-pitch accuracy, merging both functionalities into one integrated encoder that overcomes the limitation of limited displacement range in pure incremental encoders.
Solution Approach 2:
The encoder scale is segmented into multiple functional tracks: a coarse absolute position track with larger pitch for wide-range positioning, and fine relative position tracks with smaller pitch for high-resolution measurements. This segmentation allows each track to specialize in a specific function while working together to provide both extended range and high precision.
2Reliability
If absolute position encoders with multiple tracks and zero position setting are used, then unambiguous position all along displacement range is provided, but the settings require displacement of the reader at the origin of the scale
Solution Approach 1:
The encoder system automatically performs zero position calibration and pitch counter initialization without requiring manual intervention or precise positioning by the operator. The system self-calibrates by detecting the origin mark and automatically setting the reference position, making the operation simpler and more user-friendly.
3Reliability
If absolute position encoders with multiple series of detectors are used, then robustness against unfavourable positioning is improved, but device complexity increases
Solution Approach 1:
The patent uses asymmetric positioning of detector series relative to the scale marks. Instead of symmetrically placing detectors on both sides of each mark, the detectors are positioned asymmetrically to optimize the sensing of discrete regions. This asymmetric arrangement provides robustness against positioning errors while minimizing the number of detectors needed, as each detector is strategically placed to maximize its useful sensing range.
Data Source
Figure 1~3
Figure 4~5
Figure 6a~6c
AI summary
The present invention relates to an absolute position encoder (10) for a measuring instrument, comprising a digital scale (20) and a reader (50) movable relative to the digital scale. The digital scale (20) is arranged along a travel direction of the reader (50). The digital scale comprises at least one absolute position track (30; 30a, 30b) having a sequence of discrete regions (32; 32a, 32b) sharply separated from each other by separating regions (33; 33a, 33b). The reader (50) comprises a first and a second series of detectors (70a-77a, 70b-77b) configured to sense the discrete regions (32; 32a, 32b) and separating regions (33; 33a, 33b) to detect at least one of a first and a second absolute position code. The sequence of discrete regions (32; 32a, 32b) and the first and second series of detectors (70a-77a, 70b-77b) are disposed in such a way that none of the detectors of at least one of said first and second series of detectors is aligned with a transition between a discrete region (32; 32a, 32b) and a separating region (33; 33a, 33b) at each possible position of the reader (50) relative to the digital scale (20). The position encoder (10) is configured to select the first or second absolute position code which is read by the series of detectors among which no detector is aligned with said transition.