Absolute Position Encoder With Pseudo-Random Track Coding
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Solution Overview
Problem
Existing encoders face challenges in determining the absolute position of a readhead relative to a scale graduation element without initial displacement and are susceptible to dirt and material imperfections, which affect accuracy.
Innovation Solution
The encoder incorporates an absolute track with a pseudo-random sequence of marks disposed between periodic marks, generating additional electrical signals with multiple transitions, allowing robust absolute position determination immune to dirt and material imperfections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference mark or absolute track is added to determine absolute position, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the incremental track and absolute track into a single scale graduation element, with both tracks sharing the same physical substrate. This merging approach allows absolute position determination without requiring separate independent structures, thereby improving measurement precision while controlling device complexity.
Solution Approach 2:
The scale graduation element serves multiple functions simultaneously: it provides both incremental position information through the incremental track and absolute position information through the absolute track. This multi-functionality eliminates the need for separate reference marks or additional structures, resolving the contradiction between measurement precision and device complexity.
2Reliability
If a pseudo-random sequence code is used on the absolute track, then immunity to dirt and material imperfections is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses a pseudo-random sequence code with specific parameters (mark spacing, mark width, sequence pattern) that are optimized to provide robustness against dirt and material imperfections. The code is designed with inherent error-detection capabilities that maintain reliability even with manufacturing variations, thus improving reliability while managing manufacturing precision requirements.
3Measurement precision
If the absolute period is made larger than the incremental period, then resolution is improved, but the length of the scale graduation element increases
Solution Approach 1:
The patent resolves the contradiction by using a pseudo-random sequence code that encodes absolute position information in a compact manner. Instead of requiring a long periodic pattern, the pseudo-random code achieves high resolution through its unique sequence properties within a shorter length, effectively utilizing the dimensional space more efficiently.
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 design enhances the encoder's immunity to dirt and material imperfections, providing a more robust and accurate absolute position measurement with increased resolution and ability to detect dirt presence.
Implementation Method 1
The readhead comprises at least one light emitter for lighting up the scale graduation element, and an analyser that receives the light that passes through or is reflected on said scale graduation element, said analyser comprising some photodetector means adapted to generate electrical signals representative of the light they receive
Data Source
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AI summary
Encoder which comprises a scale (2) and a readhead that may be displaced in relation to the scale graduation element (2), said scale (2) comprising an incremental track (23) with a plurality of periodic marks (20) distributed with an incremental period and an absolute track comprising a pseudo-random sequence of marks (21 a) and a periodic sequence of marks (21b) distributed with an absolute period greater than the incremental period. A maximum of one mark (21 a) of the pseudo-random sequence is disposed between every two marks (21 b) of the periodic sequence, separated from both marks (21 b) of said periodic sequence, the presence or absence of said marks (21a) of the pseudo-random sequence defining a pseudo-random code. The readhead comprises a light emitter for lightting the scale (2) and an analyser which generates an additional electrical signal representative of the light it receives after being reflected on the absolute track (21).