Displacement Encoder Light-Receiving Unit Design

Solution Overview

Problem

Existing optical displacement encoders require additional optical elements like index gratings, lenses, and spatial filters to remove 0th order diffracted light, leading to increased size and complexity, and restricted optical design due to the need for precise separation of diffracted light orders.

Innovation Solution

A displacement encoder with a detection unit featuring a light-receiving unit with an even number of elements arranged at odd multiples of the fundamental period, where each element's width is not an integral multiple of the period, effectively removing the effect of 0th order diffracted light without additional optical elements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If additional optical elements (index grating, spatial filter) are added to remove 0th order diffracted light, then position detection accuracy is improved, but device complexity and size increase

Engineering Contradiction:

Improveposition detection accuracyVSAvoidoptical structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the harmful 0th order diffracted light component from the optical path by using a detection unit that selectively receives only +1st and -1st order diffracted light, removing the need for additional filtering elements

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent combines the functions of multiple optical elements (index grating, spatial filter, diffraction grating) into a single integrated detection unit that achieves the same effect of separating and selecting diffracted light orders without requiring separate components

Inventive Principle:

Principle #5Merging (Combining)

2Measurement precision

If additional optical elements are added to remove 0th order diffracted light, then position detection accuracy is improved, but the size of the encoder increases

Engineering Contradiction:

Improveposition detection accuracyVSAvoidencoder size

Core Design Contradiction:

Measurement precisionVSVolume of moving object

Solution Approach 1:

The patent extracts and eliminates the harmful 0th order diffracted light component from the optical path by using a detection unit that selectively receives only +1st and -1st order diffracted light, removing the need for additional filtering elements that would increase size

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent combines the functions of multiple optical elements (index grating, spatial filter, diffraction grating) into a single integrated detection unit, significantly reducing the overall volume of the encoder while maintaining the ability to filter unwanted diffracted light

Inventive Principle:

Principle #5Merging (Combining)

3Measurement precision

If optical elements are added to separate diffracted light orders, then position detection accuracy is improved, but the optical design becomes more restricted and complex

Engineering Contradiction:

Improveposition detection accuracyVSAvoidoptical design flexibility

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent extracts and eliminates the harmful 0th order diffracted light component from the optical path by using a detection unit that selectively receives only +1st and -1st order diffracted light, removing the need for additional filtering elements

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent combines the functions of multiple optical elements (index grating, spatial filter, diffraction grating) into a single integrated detection unit, significantly reducing the overall volume of the encoder while maintaining the ability to filter unwanted diffracted light

Inventive Principle:

Principle #5Merging (Combining)

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 improves position detection accuracy by eliminating unwanted diffracted light effects, maintaining a compact design and simplifying the optical structure.

Implementation Method 1

light applied from a light source to the incremental pattern on the scale, resultant diffracted light of various orders

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

interference fringes formed on the detection unit by +1st order diffracted light and −1st order diffracted light

Methodology Applied

Scientific EffectInterference: Interference

Data Source

PatentUS10274344B2Displacement encoder

Publication Date: 2019.04.30 MITUTOYO CORP

AI summary

A detection head movable relative to a scale detects diffracted light and outputs a detection result. The diffracted light is diffracted by an incremental pattern. A signal processing unit calculates a relative displacement between the scale and the detection head. The detection head includes: a light source emitting the light to the scale; and a detection unit including a light-receiving unit receiving the diffracted light through an optical element, in which the light-receiving elements outputting detection signals are periodically arranged with a predetermined period. The number of the plurality of light-receiving elements is an even number. The predetermined period is a value obtained by multiplying a fundamental period by an odd-number. The fundamental period is a period of interference fringes formed on the light-receiving unit by +1st and −1st order diffracted lights. A width of the light-receiving element is not equal to an integral multiple of the fundamental period.