Projection Lens Unit Thermal Focal Correction
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Solution Overview
Problem
Existing projection lens systems for large-screen projectors face challenges in maintaining image quality due to temperature-induced changes in focal point, as lenses expand and shift, leading to issues like digging into the lens barrel, deformation, and complex constructions that are difficult to manufacture, especially with glass lenses, and only allow for partial correction of focal point fluctuations.
Innovation Solution
A projection lens unit with a movable lens barrel and a thermal deformation member that moves the lens barrel in the optical axis direction to correct focal point shifts caused by temperature increases, rather than moving the lens itself, using a bimetal member or thermal expansion member to maintain lens alignment and prevent deformation, allowing for effective correction of focal length changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lens is made to move through thermal expansion of a flange on the lens or by a thermal-expansion member, then the focal point can be corrected for temperature increases, but the lens may dig into the lens barrel due to radial expansion, causing deformation and insufficient movement
Solution Approach 1:
The invention separates the lens from the thermal expansion mechanism by introducing a lens holder as an intermediate component. The lens holder contains the flange with thermal expansion properties, while the lens itself remains separate and is prevented from direct contact with the lens barrel. This segmentation allows the flange to expand radially without causing the lens to dig into the barrel.
Solution Approach 2:
The lens holder acts as an intermediary between the thermal-expanding flange and the lens barrel. It receives the radial expansion force from the flange and transmits only the axial movement component to the lens, while preventing the harmful radial digging-in effect. The lens holder thus mediates the thermal expansion to achieve beneficial focal correction without detrimental side effects.
2Object-affected harmful factors
If the gap between lens barrel and lens is increased to prevent digging-in, then lens deformation is avoided, but lens inclination and eccentricity increase
Solution Approach 1:
The lens holder serves as a precision intermediary that maintains proper lens alignment while accommodating thermal expansion. It provides a controlled interface between the expanding flange and the lens barrel, ensuring the lens remains properly positioned without inclination or eccentricity even when the gap is sufficient to prevent digging-in.
Solution Approach 2:
The lens holder provides localized precision support at critical contact points with the lens, while allowing radial expansion elsewhere. This localized quality control ensures that the lens maintains proper alignment and orientation despite the presence of gaps necessary to prevent thermal digging-in.
3Reliability
If a flange is added to the lens to enable thermal expansion movement, then focal point correction is achieved, but the lens becomes complex and difficult to manufacture, especially glass lenses
Solution Approach 1:
The invention divides the thermal correction function from the lens itself by placing the flange in a separate lens holder component. This segmentation allows the lens to remain simple and easy to manufacture (especially glass lenses), while the flange with its thermal expansion properties resides in the holder that can be manufactured separately and assembled.
Solution Approach 2:
The lens holder acts as an intermediary carrier that contains the flange and holds the lens. This intermediary structure enables the flange to provide thermal expansion-based focal correction without requiring the lens itself to have a complex flanged structure, thereby simplifying lens manufacturing while achieving the desired correction function.
4Device complexity
If only one lens is made movable among multiple lenses, then the construction remains relatively simple, but effective correction of focal point fluctuations is difficult to achieve
Solution Approach 1:
The invention achieves effective focal point correction by strategically selecting which lens to make movable based on optical parameters. By choosing the lens with positive power closest to the image formation device as the movable element, and by adjusting the focal length of this lens according to specific mathematical relationships, the system achieves effective correction without requiring multiple movable lenses, thus maintaining simple construction while ensuring correction effectiveness.
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 effectively corrects focal point shifts due to temperature changes with a simple design, maintaining lens alignment and preventing deformation, thus ensuring high image quality without the need for complex manufacturing or irregular lens shapes.
Implementation Method 1
a thermal deformation member which, by means of thermal deformation upon an increase in temperature, causes movement of the movable lens barrel in the optical axis direction so as to recede from the image formation device
Data Source
AI summary
A projection lens system 1A enlarges and projects onto a screen 8, via a plurality of lenses G1 to G16, image light emitted from, a light source 4 and modulated by DMDs 3r to 3b. A movable lens barrel 25 holds the lens G16, having positive power, which is positioned closest to the DMDs 3r to 3b. An outer tube 24 holds the movable lens barrel 25 to enable movement in the optical axis direction. Through thermal deformation at the time of an increase in temperature, the bimetal member 27 moves the movable lens barrel 25 in the optical axis direction so as to recede from the image formation devices which are the DMDs 3r to 3b.