Optical Encoder Interference Fringe Detection
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Solution Overview
Problem
Optical encoders based on the three-grating system suffer from reduced detection accuracy due to the period of the light source and light receiving gratings being set to twice the period of the scale grating, leading to lower manufacturing accuracy but also lower detection resolution when interpolation is performed.
Innovation Solution
The optical encoder design includes a light source with a scale grating of a predetermined period and a light source grating with a period twice that of the scale grating, along with interference fringe detection means that detect interference fringes with a position shift of half the period, and optionally features multiple scale gratings arranged in parallel with specific shifts and configurations to enhance detection resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the period of the light source grating and light receiving grating is set to twice the period of the scale grating, then manufacturing accuracy is improved (easier to manufacture), but detection resolution is reduced
Solution Approach 1:
The invention divides the detection function into two independent channels: a first detection channel using a first light source grating with period 2P and a first light receiving grating with period P, and a second detection channel using a second light source grating with period 2P and a second light receiving grating with period P. Each channel operates independently to detect interference fringes, and their results are combined to achieve both ease of manufacture and high detection resolution.
Solution Approach 2:
The invention extends the detection system from a single-channel to a multi-channel configuration by adding spatial redundancy. The first and second detection channels are arranged in parallel, detecting interference fringes from different optical paths. This dimensional expansion allows the system to overcome the limitation of single-channel detection where manufacturing tolerance directly impacts resolution.
2Ease of manufacture
If the period of the light source grating and light receiving grating is set to twice the period of the scale grating, then ease of manufacture is improved, but interpolation accuracy is reduced
Solution Approach 1:
The invention uses feedback from multiple detection channels to correct and refine the interpolation process. By comparing the interference fringe patterns from the first and second detection channels, the system can identify and compensate for interpolation errors that would occur in a single-channel system with doubled period gratings.
3Measurement precision
If multiple scale gratings are arranged in parallel with half-period shifts, then detection resolution is improved, but device complexity increases
Solution Approach 1:
The invention merges the functions of multiple scale gratings with the multiple detection channels in a coordinated manner. The first and second scale gratings are arranged in parallel with half-period shifts, and their light paths are combined through the optical system to produce interference fringes that are detected by the corresponding detection channels. This merging approach achieves high detection resolution while managing device complexity through systematic integration.
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 achieves a detection resolution equivalent to half the period of the scale grating, improving accuracy while maintaining ease of manufacturing, and reduces interpolation errors by ensuring uniform peak strengths in the detection signal.
Implementation Method 1
interference fringe detection means configured to be able to detect a bright part of an interference fringe with the predetermined period, the interference fringe being generated by the light source grating and the scale
Data Source
AI summary
A scale includes a scale grating formed with a period P. A light source grating includes a grating formed with a period 2P, the light source grating being disposed between a light source and the scale. Interference fringe detection means is configured to be able to detect a bright part of an interference fringe with the period P, the interference fringe being generated by the light source grating and the scale. The interference fringe detection means detects a first interference fringe formed by light coming from the scale and a second interference fringe formed by light coming from the scale, a position of a bright part of the second interference fringe being shifted from a position of a bright part of the first interference fringe by a half of the period P (i.e., P/2).