Encoder Readhead Sensor Weighting for Lower Position Jitter
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Solution Overview
Problem
Existing encoder designs suffer from noise-induced position jitter (jitter error) due to the influence of sensor elements on the position signal, particularly when the scale and readhead are stationary relative to each other, which affects the accuracy of position measurement.
Innovation Solution
The encoder readhead incorporates a primary sensor with a continuous array of sensor elements whose influence on the position signal varies along the measuring dimension according to a multimodal distribution that tapers towards its ends, and a secondary sensor positioned between the ends, allowing for improved signal noise reduction and reduced jitter error.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the primary sensor uses a continuous array of sensor elements with uniform influence, then the sensor can detect the full scale signal, but noise-induced position jitter increases
Solution Approach 1:
The patent applies local quality by varying the influence of different sensor elements along the measuring dimension. The sensor array is configured such that sensor elements near the center have higher influence weights while those toward the ends have lower influence weights. This non-uniform weighting reduces the impact of noise from edge sensor elements, thereby reducing position jitter while maintaining measurement accuracy through the central region's dominant contribution.
2Device complexity
If the primary sensor elements have uniform influence on the position signal, then the sensor structure is simple, but position jitter error increases due to noise
Solution Approach 1:
The patent implements parameter changes by modifying the influence weight parameter of sensor elements along the measuring dimension. Instead of uniform weighting, the system uses a tapering weight distribution where the influence parameter decreases from the center toward the ends. This parameter variation stabilizes the position signal by reducing the relative impact of noise in the sensor array, improving reliability without requiring complex additional hardware.
3Measurement precision
If a secondary sensor is added between the ends of the primary sensor, then position jitter is reduced, but device complexity increases
Solution Approach 1:
The patent merges the functions of the primary and secondary sensors into a unified sensor array structure. The secondary sensor elements are integrated within the same physical array as the primary sensor elements, sharing the same substrate and readout circuitry. This merging approach reduces device complexity compared to having separate sensor assemblies, while still achieving position jitter reduction through the combined signal processing of both sensor types.
Data Source
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AI summary
A position encoder readhead for reading a scale member, the readhead comprising: a primary sensor comprising a substantially continuous array of primary sensor elements for detecting a primary scale signal falling thereon, said array extending along a measuring dimension, the primary sensor configured to output a signal that is dependent on the relative position of the readhead and a scale along the measuring dimension; a secondary sensor comprising at least a first secondary sensor element positioned along the measuring dimension at a location between the ends of the primary sensor, for detecting a secondary scale signal falling thereon; configured such that: i) the influence of the primary sensor elements on the position signal output by the primary sensor varies along the measuring dimension, according to a multimodal distribution that tapers toward its ends; and ii) a first notional line can be identified that extends parallel to the measuring dimension and that passes through the at least first secondary sensor element and, on either side of the at least first secondary sensor element, passes through at least one primary sensor element.