Position Encoder Extrapolation for Dirty Scale Reliability
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Solution Overview
Problem
Existing position measurement encoders face reliability issues due to spurious readings caused by external factors like dirt on the scale, leading to incorrect position data, which can result in machine shutdowns even at low error rates.
Innovation Solution
A method that calculates extrapolated position information by combining coarse and fine position data, allowing for the use of extrapolated positions instead of actual readings, and maintains a record of discrepancies to differentiate between extrapolation failures and reading errors, ensuring more reliable position feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous phase measuring and counting is used, then measurement speed is maintained, but reliability deteriorates due to spurious readings from external factors like dirt
Solution Approach 1:
The system performs preliminary action by calculating extrapolated position information based on previously determined absolute positions before actual scale reading is performed. This allows the system to have a predicted position value ready, which can be used when reading errors occur. The extrapolated position serves as a fallback that maintains measurement continuity even when the scale reading is corrupted by external factors like dirt.
Solution Approach 2:
The system implements feedback by comparing the extrapolated position with the actual scale reading and using this comparison to detect reading errors. When a discrepancy is detected (indicating a spurious reading), the system switches to using the extrapolated position instead. This feedback mechanism allows the system to maintain high reliability by automatically correcting for reading errors without sacrificing measurement speed.
2Reliability
If snapshot reading is used, then reliability improves by reducing noise floor, but measurement speed deteriorates due to discrete sampling
Solution Approach 1:
The system merges two different measurement approaches by combining snapshot reading (for reliability) with extrapolation based on previous absolute positions (for speed). The snapshot reading provides accurate, low-noise position data at discrete moments, while the extrapolation fills in the gaps between snapshots, effectively combining the advantages of both methods to achieve both high reliability and high operating velocity.
3Reliability
If extrapolated position is used, then reliability improves by reducing incorrect readings, but device complexity increases due to additional calculation requirements
Solution Approach 1:
The system applies partial action by using extrapolation selectively rather than continuously. It performs extrapolation and comparison only when needed to detect or correct reading errors, not for every single measurement. This selective application reduces the overall computational burden while still providing the reliability benefits of error detection and correction where necessary.
Data Source
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AI summary
A method of operating a position encoder apparatus, comprising a scale having features defining position information and a readhead for reading the scale. The method comprises: calculating extrapolated position information from calculating extrapolated position information from at least one previous reading of the scale using i) a coarse position extrapolated from at least one previously determined absolute position and ii) fine position information calculated from a current reading of the scale.