Dual-Modulation Optical Encoder Scale for Long-Range Absolute Position

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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, which is essential for compact and cost-effective designs, especially in applications requiring long-range measurement capabilities.

Innovation Solution

The implementation of a dual-modulation scale track pattern that includes a first periodic intensity modulation component and a long-range intensity modulation component, allowing for an extended absolute measuring range without adding additional scale tracks, by varying the dimensions of pattern elements on the scale to encode both medium and long-range signals.

Engineering Contradictions & Design Principles

VSEngineering 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 increases

Engineering Contradiction:

Improverange-to-resolution ratioVSAvoidscale width

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent combines multiple functions into a single scale track by superimposing a long-range intensity modulation pattern onto the traditional fine wavelength binary code track. This merging allows the track to simultaneously provide both fine resolution measurements and long-range absolute positioning information, eliminating the need for multiple separate tracks and reducing the overall scale width.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The dual-modulation scale track pattern serves multiple functions: it provides fine wavelength binary code information for high-resolution measurements, long-range intensity modulation for extended measuring range, and absolute position encoding. This multi-functionality allows a single track to replace what would traditionally require multiple separate tracks, thereby reducing scale width while maintaining or improving range-to-resolution ratio.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If additional absolute scale tracks are added to extend measuring range, then the range-to-resolution ratio is improved, but the device complexity increases

Engineering Contradiction:

Improverange-to-resolution ratioVSAvoidnumber of scale tracks

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges the functions of fine wavelength binary code tracks and long-range absolute scale tracks into a single dual-modulation track pattern. By combining these previously separate components into one integrated structure, the device complexity is reduced while the range-to-resolution ratio is improved through the extended measuring range capability.

Inventive Principle:

Principle #5Merging (Combining)

3Area of stationary object

If the scale width is reduced for compact design, then the device size is improved, but the range-to-resolution ratio deteriorates

Engineering Contradiction:

Improvescale widthVSAvoidrange-to-resolution ratio

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The patent introduces a temporal or functional dimension by using dual modulation frequencies on the same spatial track. Instead of requiring additional spatial tracks to achieve long-range measurement, the invention encodes long-range information through a second modulation dimension (intensity modulation at a different frequency), allowing compact scale width while maintaining high range-to-resolution ratio.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 enhances the range-to-resolution ratio significantly, enabling absolute measuring ranges of up to 70 mm or more with micron-level resolution in a compact and economical encoder configuration, while maintaining accurate signal processing and minimizing errors.

Implementation Method 1

Each scale track pattern is configured to provide a first intensity modulation component in light from that scale track pattern

Methodology Applied

Scientific EffectLight modulation:

Implementation Method 2

a photo detector arrangement configured to receive light from the first dual-modulation scale track pattern

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS20110304482A1Absolute optical encoder with long range intensity modulation on scale

Publication Date: 2011.12.15 MITUTOYO CORP

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.