Optical Encoder Scale Grating Displacement
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Solution Overview
Problem
Existing optical encoders using the three-grating principle face challenges in achieving precise detection signals with a period of P/2 due to interference fringe characteristics and manufacturing limitations, leading to interpolation errors.
Innovation Solution
The optical encoder design includes two or more scale gratings with the same pitch, displaced by a half period, and an interference fringe detector to generate and detect interference fringes simultaneously, allowing for precise detection signals with a period of P/2, and can be arranged in multiple rows for enhanced resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single scale grating is used in the three-grating principle, then the structure is simple, but the detection precision is insufficient due to interference fringe characteristics and manufacturing limitations
Solution Approach 1:
The scale grating is divided into multiple scale gratings (first scale grating and second scale grating) that are disposed side by side in the measurement direction. Each scale grating generates interference fringes independently, and their signals are combined to achieve higher detection precision while maintaining manageable structural complexity through modular segmentation.
Solution Approach 2:
The multiple scale gratings are arranged in the measurement direction (spatial dimension), creating additional measurement channels. This dimensional arrangement allows simultaneous generation of multiple interference fringe patterns that can be processed to eliminate errors and improve precision beyond what a single grating can achieve.
2Measurement precision
If multiple scale gratings are used to improve precision, then detection precision increases, but the device complexity increases
Solution Approach 1:
The interference fringe signals from multiple scale gratings are merged and processed together through signal processing circuits. By combining the measurement results from multiple gratings disposed side by side, the system achieves enhanced detection precision while managing device complexity through integrated signal processing that consolidates the output from multiple channels.
3Manufacturing precision
If scale gratings are disposed side by side in measurement direction, then resolution is enhanced, but manufacturing precision requirements increase
Solution Approach 1:
The scale grating structure is segmented into multiple independent gratings that can be manufactured separately with standard precision tolerances. By dividing the overall measurement function across multiple segments rather than requiring one extremely precise grating, the manufacturing difficulty is reduced while the combined resolution is enhanced through the multiplicity of measurement channels.
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 enables precise detection signals with a period of P/2, reducing interpolation errors and improving resolution, while maintaining consistency in signal intensity peaks.
Implementation Method 1
an interference fringe detector (150) that detects an interference fringe generated by the light source grating and the scale
Data Source
AI summary
An optical encoder according to the present invention includes a light source that emits light; a scale including scale gratings each having a predetermined pitch; a light source grating disposed between the light source and the scale and having a predetermined pitch; and an interference fringe detector that detects an interference fringe generated by the light source grating and the scale. The scale gratings are disposed side by side, and the adjacent scale gratings are displaced from each other by a ½ period.