Absolute Encoder Code Sequence Selection Using Hamming Distance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Absolute encoders face inefficiencies and inaccuracies in selecting code sequences due to errors caused by scratches or dust on the scale or detecting unit, leading to incorrect absolute position outputs, especially when comparing code sequences with large lookup tables.
Innovation Solution
The implementation of an absolute encoder that uses a processing unit to select a code sequence from a candidate group based on Hamming distance and thresholds, reducing the need for extensive comparisons by limiting candidate sequences and ensuring a correct code sequence is always included, thereby improving efficiency and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If all code sequences in the lookup table are compared to select the best match, then the accuracy of code sequence selection is improved, but the processing time and computational load increase significantly
Solution Approach 1:
The patent segments the code sequences into groups based on their Hamming distance from the detected code sequence. Instead of comparing all code sequences equally, it divides them into candidate groups (first candidate group with smaller Hamming distance, second candidate group with larger Hamming distance) and processes them in hierarchical order, thereby reducing the effective search space while maintaining selection accuracy.
Solution Approach 2:
The patent changes the parameter of comparison by introducing Hamming distance as a pre-filtering criterion. Code sequences are first evaluated based on their Hamming distance from the detected sequence, and only those within acceptable thresholds are subjected to full comparison. This parameter-based filtering significantly reduces the number of full comparisons needed.
2Reliability
If the lookup table contains all possible code sequences to ensure complete coverage, then the reliability of absolute position measurement is improved, but the device complexity and memory requirements increase
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing only the relevant code sequences in the lookup table that are likely to be encountered during normal operation. By using Hamming distance-based filtering, it identifies and stores only those code sequences that could plausibly match the detected sequence, excluding highly improbable sequences from the lookup table.
Solution Approach 2:
The patent extracts only the necessary code sequences from the complete set of possible sequences and stores them in the lookup table. By applying Hamming distance thresholds, it extracts and retains only those code sequences that fall within acceptable error margins, removing unnecessary sequences that would increase complexity without contributing to reliability.
3Measurement precision
If the mark pitch is decreased to increase the scale length and resolution, then the measurement precision is improved, but the number of code sequences increases leading to longer comparison time
Solution Approach 1:
The patent changes the parameter of code sequence comparison by introducing Hamming distance as a fast pre-filtering metric. This allows the system to quickly eliminate code sequences that are unlikely to match, even when the total number of sequences is large due to increased scale length and resolution requirements.
Solution Approach 2:
The patent segments the large set of code sequences into manageable candidate groups based on Hamming distance thresholds. This segmentation allows the comparison process to focus on a smaller subset of relevant sequences at each processing stage, maintaining productivity even as the total number of sequences increases with higher precision requirements.
Data Source
Figure 1~2
Figure 3A~3C
Figure 4
AI summary
An absolute encoder includes a scale (2) having a sequence of marks, a detector (1) configured to detect a signal corresponding to a plurality of marks of the scale, and a processor (3) configured to obtain an absolute position corresponding to the signal. The processor is configured to select code sequences, from a group of code sequences corresponding to absolute positions, as a candidate group for a code sequence corresponding to the signal, and to select the code sequence corresponding to the signal from the candidate group.