Absolute Position Encoder Using Focused Laser Beam

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Solution Overview

Problem

Existing absolute position encoders face challenges in achieving small size, high accuracy, and contamination tolerance while determining the absolute position relative to a scale.

Innovation Solution

The system comprises an optical source, optics subsystem, and code word decoder, with a position location medium patterned to form position identifier code words, allowing for precise focus adjustment and error correction, enabling accurate position detection through optical radiation interaction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional absolute position encoder designs are used, then position measurement functionality is achieved, but the device size is large and contamination tolerance is poor

Engineering Contradiction:

Improvecontamination toleranceVSAvoidencoder size

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The patent replaces traditional mechanical encoder components with an optical system consisting of a laser source, optics subsystem, and photodetector array. The optical beam interacts with position code words patterned on a scale, enabling non-contact measurement that is inherently more contamination-tolerant and allows for compact integration.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses focused laser beams to read position code words in three-dimensional space, with the ability to adjust focus along the optical axis (z-direction) and scan transverse to the code word direction (y-direction). This multi-dimensional optical approach enables compact encoder design while maintaining measurement accuracy.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If high measurement accuracy is achieved through precise optical focusing, then position detection precision improves, but device complexity increases

Engineering Contradiction:

Improveposition detection accuracyVSAvoidoptics subsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent implements dynamic focus adjustment through a focus lens that can move along the optical axis, and dynamic scanning through a scanning lens that can move transverse to the code word direction. These dynamic elements allow the system to maintain measurement accuracy across varying conditions while using relatively simple optical components.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent employs feedback control where the position of the focused beam is detected by the photodetector array, and this information is used to adjust the scanning actuator and transverse actuator positions. This closed-loop feedback enables high measurement precision without requiring overly complex optical systems.

Inventive Principle:

Principle #23Feedback

3Reliability

If multiple redundant position code words are used for error correction, then reliability improves, but the area required on the scale increases

Engineering Contradiction:

Improveerror correction capabilityVSAvoidscale area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent uses the same optical beam and photodetector array to read multiple redundant position code words that are spatially separated on the scale. This multi-functional approach allows error correction through redundancy without requiring separate detection systems, thereby minimizing the additional area required on the scale.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 solution provides a compact, accurate, and contamination-tolerant absolute position encoder capable of maintaining focus and detecting code words effectively, ensuring precise position determination.

Implementation Method 1

an optical source, configured and operative to generate a source beam of optical radiation

Methodology Applied

Scientific EffectLight emission: Light

Implementation Method 2

an optics subsystem configured and operative to focus the source beam onto the position location medium at the interrogation location

Methodology Applied

Scientific EffectOptical focusing: Focusing

Implementation Method 3

an optical detector configured and operative to convert a return beam of optical radiation to a corresponding electrical detector signal

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS10963724B2Absolute position encoder using a focused laser beam to detect position code words

Publication Date: 2021.03.30 NOVANTA CORP

AI summary

An absolute position encoder includes a position location medium containing position identifier code words providing absolute position indications, and an optical source, an optical detector, an optics subsystem and a code word decoder. The optics subsystem focuses a source beam onto the position location medium and directs a return beam to the optical detector, detects a focus condition from the return beam, and automatically adjusts focus of the source beam to maintain a predetermined focus condition during operation. The code word decoder responds to the detector signal to detect a code word and generate a decoder output indicative of a corresponding code word value and corresponding detected position.