Compact HUD Optical System Using Nested Beam Splitters
Solution Overview
Problem
There is a need for a compact, lightweight, and cost-effective Head-Up Display (HUD) system for small aircraft that provides a wide field of view while addressing stowage, break-away, and ingress/egress issues, and avoiding the complexities of off-axis components.
Innovation Solution
A compact HUD system comprising an image source, a first lens, a polarizing beam splitter, a mirror, a first beam splitter, and a combiner with a curved partially reflective surface, which operates as a rotationally symmetric relaying and collimating optical system, allowing for easy adaptation to cockpit geometries and efficient optical correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a traditional HUD system is used, then the field of view is adequate, but the system size and weight are too large for small aircraft cockpits
Solution Approach 1:
The patent implements a nested optical architecture where the beam splitter is positioned within the combiner assembly, and optical components are arranged in a compact nested configuration. This nesting allows multiple optical elements to occupy overlapping spatial volumes, dramatically reducing the overall HUD system size while preserving the complete optical path for wide field of view performance.
Solution Approach 2:
The patent transitions from a conventional planar optical layout to a three-dimensional folded optical path. By using the beam splitter to fold the optical path and positioning components at different depths along the optical axis, the system achieves a compact footprint in the cockpit plane while maintaining adequate optical path lengths for wide field of view.
2Loss of information
If off-axis components are used, then the field of view can be expanded, but the optical correction requirements increase significantly
Solution Approach 1:
The patent deliberately introduces asymmetric optical elements, specifically a cylindrical lens with different focal lengths in orthogonal directions. This asymmetric component corrects for the asymmetric distortion introduced by the folded optical path and off-axis viewing angles, providing wide field of view while managing optical correction requirements through targeted asymmetric compensation rather than requiring complex symmetric correction systems.
3Volume of moving object
If a compact HUD design is implemented, then space is saved in the cockpit, but stowage and break-away issues arise
Solution Approach 1:
The patent divides the combiner assembly into separable components, including a beam splitter portion and a combiner portion that can be detached from each other. This segmentation allows the optical components to be easily removed for stowage in compact configurations and facilitates quick installation and removal during aircraft maintenance or pilot access, resolving the contradiction between compact design and operational ease.
4Loss of information
If more optical components are added to expand field of view, then the field of view increases, but the system cost and complexity increase
Solution Approach 1:
The patent designs the beam splitter to serve multiple functions simultaneously: it acts as a partial reflector for the HUD image path, a partial transmitter for the outside view, and an optical folding element to compact the system. The combiner assembly similarly performs multiple functions including image projection, pilot view transmission, and structural mounting. This multi-functionality achieves wide field of view without proportionally increasing component count or system complexity.
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 system provides a wide field of view of 24×30 degrees, is simple, inexpensive, and easy to stow, with minimal optical correction requirements, ensuring clear vision and easy installation in small cockpits without obscuration, while allowing for easy pilot access.
Implementation Method 1
a polarizing beam splitter and a mirror, a first beam splitter and a combiner. The first lens is disposed between the image source and polarizing beam splitter
Implementation Method 2
The combiner has a curved, partially reflective surface positioned to receive light from the first beam splitter
Implementation Method 3
The first lens is disposed between the image source and polarizing beam splitter. The second lens is disposed between the polarizing beam splitter and the first beam splitter
Data Source
AI summary
A head up display (HUD) includes an image source, a first lens, a second lens, a focusing mirror, a polarizing beam splitter, a second beam splitter and a combiner. The first lens is disposed between the image source and polarizing beam splitter. The second lens is disposed between the polarizing beam splitter and the second beam splitter. The polarizing beam splitter is disposed between the first lens, the mirror, and the second lens. The optical system for the HUD forms an intermediate image between the second lens and the second beam splitter. The intermediate image is located at the focal point of the curved combiner, and therefore the curved combiner collimates the display light upon reflection. The HUD can be compact and have a wide field of view.