Triple Grating Optical Encoder Segmentation for Displacement Detection
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Solution Overview
Problem
Conventional optical encoders face challenges in achieving stable performance, high reliability, and cost-effective mass production due to issues with signal amplitude dispersion and manufacturing accuracy, particularly when reducing encoder size and using resin molding, which can lead to defects like cracks and reduced signal strength.
Innovation Solution
The optical encoder design features separate first and third gratings on distinct members, with optimized effective widths and pitches, and refractive indices to maintain signal amplitude and reliability, allowing for precise alignment and reduced manufacturing tolerances, enabling stable and cost-effective production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the thickness of glass is reduced to reduce encoder size, then the size is reduced, but cracks and breaking occur due to stress from resin molding
Solution Approach 1:
The encoder is divided into separate modules: a first encoder module containing the first grating and light source, and a second encoder module containing the third grating and photodetector. These modules are attached to opposite surfaces of the scale, eliminating the need for a single thick glass substrate and preventing stress-induced cracking in thin glass.
Solution Approach 2:
The scale acts as an intermediary substrate between the first and third gratings. By attaching encoder components to opposite surfaces of the scale, the design distributes mechanical stress and avoids concentrating stress in thin glass, thereby preventing cracks while maintaining compact size.
2Manufacturing precision
If the first grating and third grating are formed on the same transparent member to suppress misalignment, then height alignment is improved, but the structure becomes complex and costly
Solution Approach 1:
The encoder is segmented into separate first and second encoder modules that can be manufactured independently with standard tolerances. The scale serves as the mounting substrate, and the separation of gratings into different modules eliminates the need for complex integrated structures while maintaining alignment through the scale's rigid substrate.
Solution Approach 2:
Instead of aligning gratings in the vertical dimension on a single substrate, the design transitions to a three-dimensional arrangement where gratings are positioned on opposite surfaces of the scale. This dimensional change allows standard manufacturing tolerances to achieve sufficient alignment without complex integration.
3Ease of manufacture
If separate members are used for first and third gratings to reduce size and cost, then manufacturing cost is reduced, but signal amplitude decreases due to alignment dispersion
Solution Approach 1:
The design optimizes the effective widths of the first and third gratings and the optical distances between them to compensate for separation effects. By adjusting these parameters, the signal amplitude is maintained at effective levels even with separate modules, achieving both cost reduction and performance preservation.
Solution Approach 2:
The system is designed to accommodate manufacturing variations through optimized optical parameters rather than requiring tight tolerances. The effective widths and optical distances are tuned to provide robustness against alignment dispersion, maintaining signal quality across production batches.
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 achieves stable performance, high reliability, and cost-effective mass production by maintaining signal amplitude and reducing manufacturing tolerances, while minimizing defects and improving signal strength.
Implementation Method 1
Light emerged from the first grating 14 is diffracted at the second grating 12
Implementation Method 2
a photodetector which is disposed immediately after the third grating
Data Source
AI summary
In a triple slit optical encoder, a first grating and a third grating are formed on separate members, and values of a first effective width W1 and a first pitch p1 of an optical pattern on the first grating, and a third effective width W3 and a third pitch p3 of an optical pattern on the third grating are set to values such that a periodic signal having the amplitude effective for detection of a relative displacement of a scale is achieved based on periodicity of the self-image, refractive indices of substances of substances and/or spaces interposed in the optical path from a bare LED up to a photodetector, and the thickness of those substances and/or spaces in a direction substantially perpendicular to a plane on which the second grating is formed.