Integrated Scale Reference Markings for Misalignment-Tolerant Position Sensing
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Solution Overview
Problem
Position-measuring devices with high-precision scales face inaccuracies due to non-optimal alignment, as the 1-out-of-8 gap in incremental tracks can cause phase shifts and measurement deviations when the scale and detector are not perfectly aligned.
Innovation Solution
A scale with integrated reference markings, featuring two P-periodic graduation tracks offset transversely and staggered reference markings, combined with a patterned detector with specific sensor gaps, allows for accurate position value formation even when the device is not optimally aligned by canceling out measuring errors through suitable correlation of position values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If reference markings are integrated into the incremental track at regular intervals, then the assignment of absolute track is simplified and susceptibility to moiré errors is reduced, but measurement inaccuracies arise when the scale and detector are not optimally aligned due to phase shifts
Solution Approach 1:
The scale is divided into multiple incremental tracks (e.g., four tracks with different orientations). Each track independently provides position information, and the combination of multiple tracks cancels out alignment-induced phase errors, thereby maintaining measurement precision while preserving the benefits of integrated reference markings
Solution Approach 2:
The incremental tracks are designed with different orientations (e.g., 0°, 45°, 90°, 135°) rather than identical parallel tracks. This asymmetric arrangement ensures that alignment errors affect each track differently, allowing error cancellation through signal combination and improving measurement accuracy under non-optimal alignment conditions
2Measurement precision
If a 1-out-of-8 gap is introduced in the incremental track, then absolute position determination is enabled, but phase shifts occur when illuminating optics do not supply ideally parallel ray trajectory or photodetector is shifted radially
Solution Approach 1:
The position measurement function is segmented across multiple independent incremental tracks. Each track provides redundant position information, and the combination of signals from multiple tracks eliminates the reliability issues caused by alignment-induced phase shifts in any single track
Solution Approach 2:
The system changes the orientation parameter of incremental tracks (using different angles) to create diversity in how alignment errors manifest across tracks. This parameter variation allows the system to maintain reliable absolute position determination even when individual tracks experience phase shifts due to non-ideal alignment
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 configuration significantly reduces measurement inaccuracies by averaging shifted periodic errors, resulting in more precise position measurements and improved alignment tolerance.
Implementation Method 1
a patterned photodetector having numerous sensor fields, which detects many periods of the scale simultaneously
Data Source
AI summary
A scale and a position-measuring device include the shifting of reference markings in graduation tracks, offset transversely with respect to the measuring direction, by fractions of the interval of the reference markings within a graduation track. It is thus possible to eliminate, or at least to markedly reduce, negative effects of the disturbance of the periodicity of a graduation track by the reference markings.