Light Guide Positioning for Image Reading Apparatus Thermal Stability
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Solution Overview
Problem
The existing image reading apparatuses face issues with light guide warping due to thermal expansion differences between the circuit board and light guide, leading to misalignment and decreased light efficiency.
Innovation Solution
The image reading apparatus incorporates a light guide with positioning surfaces and flexible pressing portions that abut against the circuit board, allowing for stable positioning and alignment without adhesives, enabling the circuit board to thermally expand without warping and maintaining efficient light distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If adhesive members are used to fix the light guide to the circuit board, then assembly is simplified, but the light guide warps due to thermal expansion differences causing misalignment
Solution Approach 1:
The light guide is divided into a first light guide portion and a second light guide portion, with the circuit board positioned between them. This segmentation allows the first portion to be positioned by the positioning surface while the second portion extends freely, accommodating thermal expansion without causing warp-induced misalignment of the LED mounting surface.
Solution Approach 2:
The light guide has different structural properties in different regions: the first light guide portion has a positioning surface with high rigidity for precise positioning, while the second light guide portion has lower rigidity to allow thermal expansion. This local differentiation resolves the contradiction between assembly simplicity and alignment precision.
2Stability of the object's composition
If the light guide is rigidly fixed to the circuit board, then positioning stability is improved, but thermal expansion causes warping and misalignment
Solution Approach 1:
The light guide structure transitions from a fully rigid configuration to a dynamic system where the first light guide portion is rigidly positioned on the circuit board while the second light guide portion remains flexible to accommodate thermal expansion. This dynamic design maintains positioning stability while preventing warping-induced misalignment.
Solution Approach 2:
The second light guide portion is designed with reduced rigidity, acting as a flexible element that can expand and contract with temperature changes without transmitting stress to the LED mounting surface, thus preventing warping while maintaining overall structure integrity.
3Productivity
If adhesive members are used to join the light guide and circuit board, then assembly efficiency is improved, but adhesive-related issues affect light efficiency during thermal expansion
Solution Approach 1:
The invention extracts and removes the adhesive members from the light guide-circuit board joint, replacing them with a mechanical positioning structure. The first light guide portion is positioned by the positioning surface on the circuit board, eliminating adhesive-related reliability issues while maintaining assembly efficiency through the simplified positioning mechanism.
Solution Approach 2:
The positioning surface acts as an intermediary mechanical feature between the light guide and circuit board, providing precise positioning without requiring adhesives. This intermediary structure ensures reliable light efficiency consistency during thermal expansion while maintaining high assembly efficiency.
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 prevents warping and misalignment, enhancing assembly efficiency and maintaining light efficiency by allowing the circuit board to thermally expand without adhesive-related issues, ensuring consistent illumination.
Implementation Method 1
the linear expansion coefficient of the circuit board and that of the light guide differ. Accordingly, the amount of expansion of the circuit board and that of the light guide differ during increase in temperature such that the light guide, disadvantageously, becomes warped with respect to the circuit board
Implementation Method 2
a pressing portion that abuts against a second surface of the circuit board on an opposite side of the first surface and that presses the circuit board against the positioning surface
Implementation Method 3
a light guide that guides light, emitted from the light emitting element, to a sheet read surface
Data Source
AI summary
An image reading apparatus includes an illumination unit that illuminates light on an image surface of a sheet, and a photoelectric conversion element that converts reflected light from the sheet illuminated by the illumination unit into an electric signal. The illumination unit includes a circuit board including a light emitting element, and a light guide that guides light, emitted from the light emitting element, to a sheet read surface. In the image reading apparatus, the light guide includes a positioning surface that abuts against a first surface of the circuit board and that performs positioning of the light guide and the circuit board, and a pressing portion that abuts against a second surface of the circuit board on an opposite side of the first surface and that presses the circuit board against the positioning surface.