Absolute Position Encoder With Chirped Scale Pattern

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Solution Overview

Problem

Existing absolute position encoders face limitations in achieving a combination of compact size, high resolution, robustness to contamination, and robustness to unintended gap variations between the read head and scale, while also providing power conservation and low power consumption.

Innovation Solution

An electronic absolute position encoder system featuring a scale with a pattern of signal modulating elements whose spatial characteristics, such as spatial frequency, progressively change along the measuring axis, and a detector portion with sensing elements that provide signals for processing to determine absolute position using Fourier transform processing, ensuring unique spatial characteristics at each position and robustness against contamination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a scale with progressively changing spatial characteristics is used, then measurement precision is improved, but device complexity increases due to the need for Fourier transform processing

Engineering Contradiction:

Improveposition determination precisionVSAvoidsignal processing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies parameter changes by progressively modifying the spatial characteristics (spatial frequency or wavelength) of signal modulating elements along the measuring axis. This creates a chirped scale pattern where parameters change systematically, enabling unique position identification through Fourier transform analysis of the detector signals.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces traditional mechanical or optical reading mechanisms with electrical signal processing. Instead of mechanically reading scale markings or using complex optical systems, the invention uses sensing elements to generate electrical signals that are processed through Fourier transform algorithms, substituting mechanical/optical complexity with electrical computation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Use of energy by moving object

If an absolute position encoder is used instead of incremental, then power conservation is achieved, but measurement precision may be compromised due to lack of continuous tracking

Engineering Contradiction:

Improvepower consumptionVSAvoidposition measurement accuracy

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The patent implements preliminary action by pre-encoding position information in the spatial characteristics of signal modulating elements along the entire measuring range. Each position has a unique spatial signature encoded in advance, allowing the system to determine absolute position without continuous power or tracking, as the position information is inherently embedded in the scale structure itself.

Inventive Principle:

Principle #10Preliminary action

3Ease of operation

If the read head and scale are separated to allow movement, then ease of operation is improved, but reliability decreases due to gap variations and contamination risk

Engineering Contradiction:

Improveread head movement capabilityVSAvoidmeasurement stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent uses parameter changes in the spatial frequency or wavelength of signal modulating elements to create position-dependent signal characteristics. This allows the system to maintain reliable position determination despite variations in gap distance, as the changing spatial parameters provide a robust signal signature that can be distinguished through Fourier transform processing even when gap conditions vary.

Inventive Principle:

Principle #35Parameter changes

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

The system achieves high resolution and robustness to contamination and gap variations, enabling efficient power use and precise position determination across the absolute measuring range.

Implementation Method 1

the signal processing configuration may utilize Fourier transform processing (e.g., utilizing a fast Fourier transform) and/or other processing for determining the absolute position

Methodology Applied

Scientific EffectFourier transform:

Data Source

PatentUS9958294B2Absolute position encoder including scale with varying spatial characteristic and utilizing Fourier transform or other signal processing

Publication Date: 2018.05.01 MITUTOYO CORP

AI summary

An electronic absolute position encoder is provided including a scale, a detector portion and a signal processing configuration. The scale includes a first scale pattern of signal modulating elements, wherein the first scale pattern includes a spatial characteristic of the signal modulating elements which progressively changes as a function of position along a measuring axis direction and defines an absolute measuring range. The spatial characteristic includes at least one of a spatial wavelength or a spatial frequency of the signal modulating elements and is unique at each unique position in the absolute measuring range. The detector portion includes a group of sensing elements, and the signal processing configuration determines an absolute position of the sensing elements relative to the scale within the absolute measuring range. In various implementations, the signal processing configuration may utilize Fourier transform processing and/or other processing for determining the absolute position.