Projection Lens Shift Limit Detection Using a Shift Allowance Plate
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Solution Overview
Problem
Projectors with lens shift functions face vignetting issues when the projection lens is displaced beyond its horizontal or vertical displacement limits, and existing detection methods using pulse motors can lose synchronism, leading to inaccurate positioning.
Innovation Solution
A projector configuration using a pulse motor with a shift allowance plate and a single photosensor to detect lens displacement limits, ensuring the projection lens remains within permissible bounds by employing a shift allowance plate with a through hole and a detector that senses contact with the plate's edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pulse motor is used to displace the projection lens, then the lens can be positioned within displacement limits, but the system may lose synchronism and fail to detect accurate position
Solution Approach 1:
The patent replaces the pulse motor's electrical control system with a mechanical detection system using a photosensor and light blocking member. The light blocking member mechanically follows the lens displacement and blocks light from reaching the photosensor when the lens reaches the displacement limit, providing reliable mechanical position detection that cannot lose synchronism like electrical pulse counting systems.
Solution Approach 2:
The patent introduces a light blocking member as an intermediary between the projection lens and the photosensor. This intermediary mechanically couples to the lens displacement mechanism and translates lens position into light blockage events, enabling accurate position detection without directly measuring the lens itself or relying on pulse motor feedback.
2Adaptability or versatility
If the projection lens is displaced beyond the displacement limit, then more flexible positioning is achieved, but vignetting occurs in projected image light
Solution Approach 1:
The patent implements preliminary action by detecting the lens displacement limit before the lens actually reaches a position that would cause vignetting. The light blocking member is positioned to block light from the light emitting part to the photosensor slightly before the lens displacement would exceed acceptable limits, allowing the system to stop displacement in advance and prevent vignetting from occurring.
Solution Approach 2:
The patent establishes a feedback mechanism where the photosensor continuously monitors the position of the light blocking member, which is mechanically linked to the lens displacement. When the lens approaches the displacement limit, the light blocking member blocks the light path, causing the photosensor to detect this condition and provide feedback to stop further displacement, thereby preventing vignetting.
3Measurement precision
If a complex detection system is used to prevent vignetting, then position accuracy is improved, but device complexity increases
Solution Approach 1:
The patent extracts the detection function from complex electronic systems and implements it through a simple optical-mechanical subsystem. The detection system consists of only three main components: a light emitting part, a photosensor, and a light blocking member. This extracted minimal system provides sufficient detection accuracy without the complexity of electronic feedback loops, pulse counting systems, or multiple sensors.
Solution Approach 2:
The patent employs simple, inexpensive optical components (light emitting diode, photosensor, and light blocking member) rather than expensive precision measurement devices. These simple components achieve the required detection function through their basic optical properties, providing a cost-effective solution that avoids complex and expensive position sensing systems.
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
Prevents vignetting by accurately detecting and stopping lens displacement at limits, using a simple and cost-effective setup with a single photosensor, ensuring clear projection without exceeding displacement boundaries.
Implementation Method 1
a photosensor including a light emitting part and a light receiving part
Implementation Method 2
a detector configured to detect that the projection lens has been displaced to a limit position, based on a change from a state in which the light receiving part does not receive light emitted from the light emitting part to a state in which the light receiving part receives light emitted from the light emitting part
Data Source
AI summary
A shift tolerance is defined as a range in which a projection lens can be displaced in any direction without causing vignetting of image light projected by the projection lens. A shift allowance plate has an opening that is similar in shape to the shift tolerance and has a size equal to or smaller than the shift tolerance, and has a through hole. When the projection lens displaces in any direction and displaces the shift allowance plate, a light receiving part receives light, and a detector detects that the projection lens has been displaced to a limit position.