Head-Up Display Optical Path with Negative Lens for Luminance Uniformity
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Solution Overview
Problem
Conventional head-up display devices face challenges in maintaining high visibility of virtual images while minimizing the size of the device, as the position of the entrance pupil approaching the liquid crystal element leads to luminance differences between pixels, affecting the directivity and visibility of the displayed light.
Innovation Solution
The head-up display device incorporates a light source unit, a light condensing unit, a liquid crystal element, and an enlarging light guide unit with a positive and negative optical element, where the negative optical element is closer to the liquid crystal element, optimizing the optical path to reduce deviations and luminance differences, and using a compound lens array with collimating and deflecting surfaces to enhance directivity and reduce size expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a concave mirror is used to enlarge the virtual image, then the virtual image size is increased while the device size is reduced, but the entrance pupil position approaches the liquid crystal element causing luminance differences and visibility degradation
Solution Approach 1:
The enlarging light guide unit is divided into multiple optical elements: a concave mirror for image enlargement, a plane mirror for light direction control, and a meniscus lens for optical path correction. This segmentation allows each component to perform its specific function optimally, preventing the entrance pupil from approaching the liquid crystal element while maintaining virtual image enlargement
Solution Approach 2:
A meniscus lens is introduced as an intermediary element between the concave mirror and the liquid crystal element. This lens corrects the optical path and prevents the entrance pupil position shift that would otherwise occur with the concave mirror alone, thereby maintaining uniform luminance across the virtual image
2Device complexity
If the entrance pupil position approaches the liquid crystal element, then the device structure is simplified, but luminance differences occur between pixels reducing visibility
Solution Approach 1:
The optical system is segmented into distinct functional units: the light condensing unit, liquid crystal element, enlarging light guide unit with multiple mirrors and lenses. This segmentation maintains precise control over the optical path, preventing entrance pupil position shift while keeping the overall device compact and manageable
Solution Approach 2:
The meniscus lens acts as an intermediary that corrects the optical path between the concave mirror and liquid crystal element, preventing the entrance pupil from approaching the liquid crystal element. This intermediary element ensures uniform luminance distribution across all liquid crystal pixels
3Ease of operation
If collimated illumination light is used to enhance directivity, then the display light reaches the visible region reliably, but the device size increases due to additional optical elements
Solution Approach 1:
The light condensing unit and enlarging light guide unit are integrated into a compact configuration where the concave mirror serves dual purposes: enlarging the virtual image and helping to collimate the light. The plane mirror and meniscus lens are positioned to minimize space requirements while maintaining optical functionality
Solution Approach 2:
The optical elements are arranged in a folded optical path configuration, utilizing multiple reflections and strategic positioning to achieve collimated illumination and virtual image enlargement within a compact footprint, effectively using spatial arrangement to reduce device volume
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 high visibility of virtual images with reduced physical size expansion, as the entrance pupil is positioned further away from the liquid crystal element, allowing efficient illumination and minimizing luminance differences between pixels, thereby enhancing the visibility and directivity of the displayed light.
Implementation Method 1
a light condensing unit configured to cause condensation to collimate the illumination light
Implementation Method 2
project a display light toward a projection member of the mobile object and to cause the display light to reach a visible area in the mobile object while causing the projection member to reflect the display light
Data Source
AI summary
A head-up display device reflects a display light on a projection member to display a virtual image. A light condensing unit causes condensation and collimates an illumination light from a light source unit. A liquid crystal element includes forms an image illuminated with the illumination light. The liquid crystal element emits the display light of the image in a light flux form in an emission direction corresponding to an incident direction of the illumination light. A positive optical element has a positive refractive power. A negative optical element has a negative refractive power. Both of the optical elements are located on the optical path and guide the display light from the liquid crystal element toward the projection member to enlarge a virtual image. The negative optical element on the optical path is located closer to the liquid crystal element than the positive optical element.