Virtual Image Display Optics for Compact Double-Image Suppression
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Solution Overview
Problem
Existing virtual image display devices, such as head-up displays, face challenges in downsizing due to the need for the display unit to be positioned at the focal point of the optical system to prevent double images caused by positional displacement of light rays reflected from the front and back surfaces of the windshield, limiting their compactness.
Innovation Solution
A virtual image display device configuration that includes a convex lens between the display surface and a transparent member with a front and back surface, where the optical path of light rays reflected from both surfaces coincides through refraction in the convex lens, and the display surface is positioned closer to the convex lens than its focal point, allowing for downsizing while preventing double images by adjusting the lens's eccentricity and tilt.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the display unit is positioned at the focal point of the optical system to prevent double images, then image quality is improved, but the device size increases
Solution Approach 1:
The patent introduces asymmetric positioning of the display unit relative to the focal point, placing it at a specific distance shorter than the focal length. This asymmetric arrangement, combined with tilted transparent members at different angles, creates a non-conventional optical path that eliminates double images without requiring the display unit to be at the focal point, thereby reducing device size while maintaining image quality
Solution Approach 2:
The patent utilizes the tilt angle dimension of the transparent members as an additional degree of freedom to control light ray paths. By tilting the first and second transparent members at different angles relative to the optical axis, the system can compensate for the displaced display unit position and prevent double image formation in a different dimensional parameter space
2Volume of moving object
If the display unit is positioned closer to the convex lens than the focal point to downsize the device, then device size is reduced, but double images occur due to positional displacement of reflected light rays
Solution Approach 1:
The patent changes multiple parameters simultaneously: the display unit position (distance from lens shorter than focal length), the tilt angles of the first and second transparent members, and their relative positions. By adjusting these parameters together, the system achieves optimal light ray coincidence from both front and back surface reflections, preventing double images while maintaining compact dimensions
Solution Approach 2:
The patent introduces transparent members as intermediary elements between the displaced display unit and the observer's eye. These intermediaries actively manipulate the light ray paths through refraction and reflection, redirecting rays from both front and back surface reflections to coincide at the observer's position, thereby compensating for the non-focal display unit placement
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 enables the downsizing of virtual image display devices while maintaining image quality by ensuring that the optical paths of light rays reflected from both surfaces coincide, thereby eliminating double images and allowing for a more compact design.
Implementation Method 1
An optical path of a first light ray, which is emitted from one point on the display surface, penetrates the convex lens, and is reflected by the front surface of the transparent member, after the reflection by the front surface coincides with an optical path of a second light ray, which is emitted from the one point, penetrates the convex lens, is reflected by the back surface of the transparent member, and is emitted from the front surface of the transparent member, after the emission from the front surface, due to refraction in the convex lens.
Data Source
AI summary
A virtual image display device includes a display surface and a projection optical system that projects a light ray from the display surface toward a transparent member. The projection optical system includes a convex lens. An optical path of a first light ray, which is emitted from one point on the display surface and is reflected by the front surface of the transparent member coincides with an optical path of a second light ray, which is emitted from the one point and is reflected by the back surface of the transparent member, due to refraction in the convex lens. The center of the convex lens is displaced from a reference axis Z that passes through the one point and extends in a direction perpendicular to the display surface. The display surface is positioned closer to the convex lens than a focal point of the projection optical system.