Optical Encoder Lens Fixing Mechanism for Thermal Stability
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Solution Overview
Problem
Optical encoders face challenges in maintaining assembly accuracy and stability due to temperature variations, which cause stress and distortion in plastic lenses, leading to reduced signal efficiency and accuracy.
Innovation Solution
The optical encoder employs a lens fixing mechanism with bosses and reference pins arranged on a central symmetry plane, allowing for precise assembly and adjustment of the optical axis, and a fixing surface on a plane bisecting the lens volume to mitigate thermal expansion effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If plastic lenses are used to reduce size and simplify manufacturing, then ease of manufacture and compactness are improved, but thermal expansion causes stress and distortion leading to reduced measurement precision
Solution Approach 1:
The patent positions the adhesive layer exactly at the center thickness of the lens (at the optical axis), creating a symmetric bonding configuration. This parameter change in adhesive placement ensures that thermal expansion occurs uniformly in all directions from the center, preventing asymmetric stress and distortion that would otherwise degrade measurement precision while maintaining the ease of using plastic lenses.
2Device complexity
If lenses are fixed to housing with adhesive, then assembly is simplified, but temperature variation causes stress on lens surface leading to curvature variation
Solution Approach 1:
The patent strategically places the adhesive layer at the center thickness of the lens beforehand, creating a pre-positioned stress distribution pattern. This prior cushioning approach ensures that when temperature varies, the adhesive bond at the center allows the lens to expand or contract uniformly without creating unexpected stress concentrations, thereby maintaining lens curvature stability despite temperature fluctuations.
Solution Approach 2:
By changing the critical parameter of adhesive layer position from conventional edge or surface bonding to center-thickness bonding at the optical axis, the patent transforms the stress distribution pattern during thermal cycling. This parameter change reduces the moment arm for thermal stress, minimizing curvature variation while keeping the adhesive fixation method simple.
3Manufacturing precision
If reference surfaces are used for assembling optical elements, then assembly accuracy is improved, but manufacturing and adjusting the reference surfaces becomes more complex
Solution Approach 1:
The patent makes the lens itself serve multiple functions: it acts as both the optical element and the reference surface for positioning the aperture plate and other components. The outer surface of the lens becomes a universal reference that simplifies assembly procedures while maintaining high accuracy, eliminating the need for separate complex reference surfaces and reducing overall device complexity.
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 solution ensures high-accuracy assembly and stability of the optical system, preventing distortion and maintaining signal quality across temperature changes, thereby enhancing the encoder's performance and reducing inter-track errors.
Implementation Method 1
an imaging optics including a lens and an aperture plate, and a light-receiving element, wherein the imaging optics forms an image of the track on the light-receiving element
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An optical encoder includes a detection head (20). The detection head includes an optical system including a lens (22, 24) including a pair of bosses (22A, 24A) integrally formed with the lens (22, 24) and disposed with an optical axis of the lens (22, 24) therebetween, and an aperture plate (28) having a pair of reference-pin-insertion holes (28A, 28B) disposed with an aperture therebetween; a housing (26) including a pair of attachment portions (26D) and having a pair of lens-boss-insertion holes (26A, 26B) and a pair of reference-pin-insertion holes (26A, 26B) disposed on a central symmetry plane (P1); a lens holder (30) having a pair of lens-boss-insertion holes (30A, 30B) and a pair of reference-pin-insertion holes (30C, 30D) disposed on the central symmetry plane (P1); and a pair of reference pins (32) for positioning the lens holder (30) and the aperture plate (28) relative to the housing (26). An optical axis of the optical system is adjusted with respect to the bosses (22A, 24A) and the reference pins (32).