Light Guide Positioning for Uniform Illumination

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Solution Overview

Problem

Conventional light projection units in image reading devices face challenges in accurately positioning the light guide relative to the LED array substrate, leading to inefficient light distribution and insufficient light intensity at the document edges due to internal reflection issues and uneven light distribution.

Innovation Solution

A light projection unit with a substrate, light emitting elements, and a holder, where the light guide has positioning pins between the centers of adjacent light emitting elements, ensuring proper alignment and minimizing light leakage, and the holder engages these pins to maintain precise positioning, optimizing light distribution across the document area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If the light guide is fixed to the LED array substrate using double-sided tape or adhesive agent without a positioning mechanism, then the device complexity is reduced, but the manufacturing precision of light guide positioning deteriorates

Engineering Contradiction:

Improvepositioning mechanism complexityVSAvoidlight guide positioning precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The light guide structure itself provides positioning functionality through its geometric features (positioning protrusions and grooves), eliminating the need for separate positioning mechanisms. The positioning is achieved through the inherent structure of the light guide rather than external devices.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The positioning function is segmented into discrete geometric features (protrusions and grooves) integrated into the light guide structure, allowing precise positioning through modular geometric interfaces between the light guide and substrate.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the light guide extends beyond the document area to accommodate positioning holes outside the document area, then the positioning reliability is improved, but the loss of energy increases due to light being projected outside the document area

Engineering Contradiction:

Improvepositioning reliabilityVSAvoidlight energy loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The light guide has different functional zones: the main body within the document area for light transmission, and extended portions with positioning features outside the document area. The positioning protrusions are strategically located to engage with substrate features while minimizing light loss.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The extended light guide portions that would normally cause light loss are converted into beneficial positioning features. The positioning protrusions engage with corresponding grooves on the substrate, ensuring accurate alignment while the geometric design minimizes unnecessary light projection outside the document area.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Ease of operation

If the light guide is positioned with ends separated from the document area ends, then the positioning ease is improved, but the illumination intensity at document edges deteriorates

Engineering Contradiction:

Improvepositioning easeVSAvoidedge illumination intensity

Core Design Contradiction:

Ease of operationVSIllumination intensity

Solution Approach 1:

The positioning system uses a third dimension (vertical engagement through protrusions and grooves) to achieve precise positioning, allowing the light guide to be accurately positioned within the document area without requiring extensions beyond it. This enables both accurate positioning and optimal edge illumination.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 ensures even light illumination across the document area, preventing light loss and maintaining sufficient intensity at the edges, thereby enhancing image reading accuracy and consistency.

Implementation Method 1

The light guide reflects and concentrates light radially emitted from the light source

Methodology Applied

Scientific EffectLight reflection: Reflection

Implementation Method 2

The light guide is longer than a document area F in the main scanning direction, in order to accommodate positioning holes 604a for positioning the light guide 603 formed at both ends of the holding member 605 outside the document area F

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS8643917B2Light projection unit, image reading device including same, and image forming apparatus including the image reading device

Publication Date: 2014.02.04 RICOH CO LTD

AI summary

A light projection unit includes a substrate, a plurality of light emitting elements arrayed on the substrate in a main scanning direction and including light emitting surfaces, a light guide facing the light emitting surfaces to direct light projected from the light emitting elements onto an illumination target and including a first positioning portion, and a holder including a second positioning portion that engages the first positioning portion of the light guide to position the light guide on the holder. The first positioning portion of the light guide is positioned between centers of light emission of adjacent light emitting elements in the main scanning direction of the substrate when the first positioning portion engages the second positioning portion of the holder.