Absolute Optical Encoder Scale with Misalignment-Tolerant Detector
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Solution Overview
Problem
Existing absolute encoders face limitations in achieving a high range-to-resolution ratio, compact size, and cost-effectiveness, particularly when requiring sub-micron resolution, due to challenges with signal interpolation and sinusoidal fidelity in narrow scales.
Innovation Solution
The proposed configuration includes an absolute optical encoder with a fine track pattern and at least one absolute track pattern, where the absolute track pattern is designed with geometrically congruent subtrack portions and detector areas that allow for misalignment tolerance, maintaining sinusoidal fidelity and reducing the size of detector elements for economic and compact devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal interpolation is used to enhance resolution, then measurement precision is improved, but device complexity and cost increase significantly
Solution Approach 1:
The scale track is divided into multiple independent binary code tracks (first through fourth tracks) with different wavelengths. Each track provides independent resolution information, allowing the system to achieve high measurement precision through parallel processing of multiple segmented signals rather than relying on complex interpolation of a single signal.
Solution Approach 2:
The patent transitions from single-track interpolation to multi-track parallel measurement by adding a temporal dimension - multiple tracks are read sequentially in a predetermined sequence. This dimensional expansion allows the system to achieve high resolution through the combination of multiple simpler tracks rather than complex processing of a single track.
2Length of moving object
If multiple binary code tracks are used to increase range, then measuring range is improved, but the scale width increases limiting compactness
Solution Approach 1:
The patent utilizes the temporal dimension by reading multiple binary code tracks in a predetermined sequence rather than requiring all tracks to be read simultaneously. This allows multiple tracks to be packed into a narrow scale width while still achieving extended measuring range through sequential processing, effectively using time to multiply the range capability without proportionally increasing spatial footprint.
3Measurement precision
If fine wavelength tracks are used for high resolution, then measurement precision is improved, but the number of additional binary tracks required increases
Solution Approach 1:
Each binary code track serves multiple functions: it provides absolute position information, contributes to resolution through its specific wavelength, and enables range extension when combined with other tracks. The tracks are designed with different wavelengths (first track: 40-80 microns, second track: 80-160 microns, etc.) so that each track contributes differently to the overall performance metrics, maximizing the utility of each additional track.
4Measurement precision
If detector areas are made larger to improve signal quality, then measurement precision is improved, but device size and cost increase
Solution Approach 1:
The patent combines signals from multiple binary code tracks and their corresponding detector portions through signal processing. By merging the information from multiple tracks read in sequence, the system achieves improved measurement precision and signal quality without requiring each individual detector to have large area, thus reducing overall device size and cost.
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 provides an improved range-to-resolution ratio and sinusoidal fidelity, enabling high-resolution absolute position sensing in a compact and economical manner, suitable for applications like linear gauges and rotary encoders.
Implementation Method 1
an illumination portion, a scale element including an absolute scale pattern comprising a fine track pattern and at least a first absolute track pattern, and the detector electronics. The track patterns are arranged to receive light from the illumination portion and output respective spatially modulated light patterns along respective light paths to various corresponding detector portions
Data Source
AI summary
An encoder configuration comprises an illumination portion, absolute scale pattern comprising absolute tracks, and a detector having a width dimension YDETABS. An absolute track pattern comprises geometrically congruent sub tracks, and the congruent sub tracks are arranged such that if one is translated by the width dimension YDETABS, then they will nominally coincide. The congruent sub tracks may be separated by a dimension YCENT that is less than YDETABS, and may each have a dimension YTOL, such that [YCENT+2(YTOL)] is greater than YDETABS. Thus, the detector may be narrower than the absolute track pattern, but because the detector edges are each nominally located over congruent sub tracks the detected signal is not sensitive to lateral misalignment of the detector within the pattern. These principles provide great freedom in configuring advantageous individual pattern features in the absolute track, even though the detector is narrower than the absolute track.