Projection System with Concave Mirror and Negative Lens

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Solution Overview

Problem

Projection systems with shorter focal lengths tend to produce significant aberrations, requiring larger enlargement-side lenses to correct images, which increases the projector's size and diameter.

Innovation Solution

A projection system with a first optical system and a second optical system sequentially arranged from the reduction side to the enlargement side, including a diaphragm, an optical element with a concave reflection surface, and a first lens with negative power, forming an intermediate image and ensuring a telecentric portion, while satisfying specific conditional expressions to manage lens radii and numerical aperture.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If the focal length is shortened to reduce projection distance and throw ratio, then the projector size can be reduced, but aberrations increase requiring larger enlargement-side lenses which increases the projector diameter

Engineering Contradiction:

Improvefocal lengthVSAvoidaberrations

Core Design Contradiction:

Length of moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent divides the optical system into multiple segments: a first optical system (refractive lenses) and a second optical system (concave mirror + negative lens). This segmentation allows each segment to handle specific optical functions, enabling short focal length while controlling aberrations through coordinated design of both segments.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediate image formation between the first and second optical systems. This intermediate image acts as a mediator that allows the refractive system to pre-correct aberrations before the light enters the reflective system, enabling compact design with controlled aberrations.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If the effective radius of the enlargement-side lens is increased to correct aberrations, then aberration correction improves, but the amount of protrusion increases resulting in larger projector diameter

Engineering Contradiction:

Improveaberration correctionVSAvoidprojector diameter

Core Design Contradiction:

Manufacturing precisionVSArea of stationary object

Solution Approach 1:

Instead of using a positive enlargement-side lens that would require large effective radius for aberration correction, the patent uses a negative lens in combination with a concave mirror. This inverted approach achieves aberration correction with a smaller effective radius, reducing the protrusion amount and overall projector diameter.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the optical parameters by introducing a negative power lens and utilizing the reflective property of the concave mirror. This parameter change allows achieving the same aberration correction effect with different physical dimensions, specifically reducing the effective radius requirement and thus the projector diameter.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a single refractive lens is used for enlargement, then the system is simpler, but the throw ratio cannot be reduced below 0.154 with sufficient aberration correction

Engineering Contradiction:

Improveoptical system structureVSAvoidprojection distance

Core Design Contradiction:

Device complexityVSLength of moving object

Solution Approach 1:

The patent replaces part of the refractive optical system with a reflective system (concave mirror). This substitution allows achieving shorter focal length and lower throw ratio (0.114) because the reflective system can provide stronger optical power with fewer aberrations compared to purely refractive systems of equivalent power.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

The solution suppresses the increase in projector size and diameter, maintaining effective lens correction while reducing focal length, resulting in a compact and aberration-suppressed projection system.

Implementation Method 1

an optical element having a concave reflection surface

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

a first lens having negative power

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS20230367191A1Projection system and projector

Publication Date: 2023.11.16 SEIKO EPSON CORP

AI summary

A projection system includes a first optical system and a second optical system sequentially arranged from a reduction side toward an enlargement side. The second optical system includes an optical element having a concave reflection surface and a first lens having negative power, the optical element and the first lens sequentially arranged from the reduction side toward the enlargement side. The projection system satisfies Conditional Expressions (1) and (2) below.3.5≤LL+MR/imy×TR×1/NA≤6.0(1)TR≤0.2(2)