Optical Encoder Lens Array Pitch Asymmetry for Aberration Control
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Solution Overview
Problem
Optical linear encoders face challenges in accurately determining the pitch of lens arrays due to material expansion/contraction with temperature fluctuations, leading to lens aberrations that affect the accuracy of interference fringe detection, especially when the pattern period is short and the use of glass material increases costs.
Innovation Solution
Implementing an optical system with a 1-power or reducing erect-image optical configuration using multiple lens arrays with specific pitch relationships and focal lengths, and employing an erect-image optical system to average aberration effects across interference fringes, allowing for flexible lens array pitch settings that are not integral multiples of the grating pattern pitch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the lens array pitch is set to an integral multiple of the grating pattern pitch for synchronization, then the image formation is improved, but lens aberrations are periodically repeated and affect detection accuracy
Solution Approach 1:
The patent applies asymmetry by deliberately setting the lens array pitch to a non-integer multiple of the grating pattern pitch. This asymmetric relationship breaks the periodic repetition of lens aberrations that occurs with integer multiples, thereby eliminating the harmful periodic interference in the interference fringes while maintaining adequate image formation quality.
2Stability of the object's composition
If glass material is used for the lens array to reduce thermal expansion, then the pitch stability is improved, but the material cost and manufacturing cost increase
Solution Approach 1:
The patent applies parameter changes by modifying the relationship between lens array pitch and grating pattern pitch from an integer multiple to a non-integer multiple. This parameter change makes the system less sensitive to absolute pitch stability, allowing the use of cost-effective plastic materials with higher thermal expansion coefficients without compromising detection accuracy, thereby reducing material and manufacturing costs.
3Measurement precision
If the lens array pitch is precisely manufactured to account for thermal expansion, then the detection accuracy is improved, but the manufacturing complexity increases
Solution Approach 1:
By using a non-integer multiple relationship between lens array pitch and grating pattern pitch, the patent creates an asymmetric configuration that averages out the effects of pitch variations due to thermal expansion. This reduces the manufacturing precision requirements compared to synchronized integer multiple configurations, where any pitch error directly translates to detection errors.
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 reduces the impact of lens aberrations on interference fringe detection, improves manufacturing tolerance, and maintains detection accuracy even with pitch fluctuations, while minimizing material and manufacturing costs.
Implementation Method 1
an optical system configured as an erect-image optical system, the erect-image optical system being configured to form light from the scale into interference fringes on a light-receiving surface of the light-receiving unit by using a lens array
Implementation Method 2
a light-receiving element array arranged in the measurement direction and configured to output a result of detection of the irradiation light applied to the light-receiving element array
Data Source
AI summary
A scale includes a grating pattern arranged in a measurement direction. A detection head can be moved relative to the scale in the measurement direction and outputs an electric signal indicating a result of detection of the pattern. An operation unit calculates a relative displacement of the detection head relative to the scale. The detection head irradiates the scale with light. A light-receiving unit includes a light-receiving element array arranged in the measurement direction and outputs a result of detection of the irradiation light applied to the light-receiving element array as the electric signal. An optical system forms light from the scale into interference fringes on a light-receiving surface of the light-receiving unit by using lens arrays arranged in the measurement direction. A lens array pitch between neighboring lenses of the lens arrays is not equal to an integral multiple of a pitch of the grating pattern.