Dual-Modulation Scale Track for Compact Absolute Encoders
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Solution Overview
Problem
Existing absolute encoders face limitations in achieving a high range-to-resolution ratio without increasing the width of the scale or detector components, particularly in compact designs, and struggle with maintaining accuracy and reducing complexity.
Innovation Solution
The implementation of a dual-modulation scale track pattern that superimposes a long-range intensity modulation component onto a shorter-range intensity modulation component, allowing for increased absolute measuring range and range-to-resolution ratio without adding additional scale tracks, using principles that encode or superimpose a second long-range intensity modulation feature onto existing scale track patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple binary code tracks are used to achieve high range-to-resolution ratio, then the measuring range is improved, but the scale width and device complexity increase
Solution Approach 1:
The patent combines multiple functions into a single scale track by superimposing a long-range intensity modulation pattern onto the fine-wavelength binary code track. This merging eliminates the need for separate coarse tracks while maintaining both high resolution and extended measuring range, directly reducing device complexity.
Solution Approach 2:
The single scale track serves multiple functions simultaneously: it provides fine-wavelength binary code information for high-resolution measurement and long-range intensity modulation for extended measuring range. This multi-functionality allows one track to replace what would traditionally require multiple separate tracks.
2Measurement precision
If signal interpolation is used to enhance fine track resolution, then the measurement precision is improved, but the cost and device complexity increase
Solution Approach 1:
The fine-wavelength binary code track itself provides the information needed for high-resolution measurement through its inherent periodic structure. The system uses the track's own characteristics rather than requiring external interpolation components, achieving self-sufficient high-resolution measurement.
3Area of stationary object
If the scale width is reduced for compact encoder design, then the device size is improved, but the number of binary tracks and measuring range are limited
Solution Approach 1:
The patent extends the measuring range by utilizing the longitudinal dimension of the scale track through superimposed long-range intensity modulation patterns. Instead of expanding the scale width horizontally to add more tracks, the solution uses the length dimension vertically, allowing a narrow scale to provide extended measuring range through the modulation patterns that vary along the length of the track.
4Measurement precision
If additional absolute tracks with longer wavelengths are used to extend measuring range, then the range is improved, but the scale width and device complexity increase
Solution Approach 1:
The patent merges the function of separate long-wavelength absolute tracks into the existing fine-wavelength binary code track by superimposing long-range intensity modulation. This combining eliminates the need for additional physical tracks while achieving extended measuring range, directly reducing device complexity.
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 approach enables a significant extension of the absolute measuring range to 70 mm or more while maintaining high resolution and compact size, with improved robustness and cost-effectiveness, by utilizing a dual-modulation scale track pattern that integrates a second intensity modulation component to enhance measurement capabilities.
Implementation Method 1
an absolute optical encoder including a scale comprising at least a first dual-modulation scale track pattern (DMST pattern) extending along a measuring axis direction, a light source configured to illuminate the scale and the first dual-modulation scale track pattern, and a photo detector arrangement comprising a first detector track configured to receive light from the first dual-modulation scale track pattern
Implementation Method 2
a photo detector arrangement comprising a first detector track configured to receive light from the first dual-modulation scale track pattern
Data Source
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AI summary
An encoder configuration comprises a dual-modulation scale track pattern that provides a first intensity modulation component for producing periodic signals, and a second intensity modulation component for producing a long-range absolute signal. The dual-modulation scale track pattern increases the range-to-resolution ratio of the encoder without the use of additional scale tracks that would increase the width of the encoder components. The long-range signal may be encoded in the dual-modulation scale track pattern either by varying certain dimensions of pattern elements included in the scale track or by superimposing a layer including an optical density variation along on the track on pattern elements of similar areas. In either case, the net offset and/or amplitude levels of the associated signals are modified along the scale track. These modified offset and/or amplitude levels provide the basis for the long-range absolute signal.