Aspherical Visor Curvature for HMD Astigmatism Reduction
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Solution Overview
Problem
Conventional head-mounted display devices for aircraft struggle to provide a wide visual field with high visibility due to astigmatism issues, limiting the expansion of the display image's visual field.
Innovation Solution
The head-mounted display device features an aspherical visor reflecting surface with curvature differences in the Y'-Z' and X'-Z' planes to equalize optical power, reducing astigmatism, and incorporates a projection optical system with aspherical surfaces and lenses to correct asymmetrical blurring, allowing for a wider visual field and improved visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a spherical visor is used to ensure dimensional accuracy and strength, then manufacturing ease and structural strength are improved, but astigmatism increases causing image blurring and limiting visual field expansion
Solution Approach 1:
The patent applies an aspherical visor design where the curvature radius in the vertical direction (Y'-Z' plane) is made larger than in the horizontal direction (X'-Z' plane). This asymmetric curvature configuration corrects astigmatism by equalizing optical power across different meridians, thereby improving image quality and expanding the visual field while maintaining the spherical-like protective function of the visor
2Area of moving object
If the visual field of the display image is expanded, then the useful information coverage is improved, but astigmatism increases causing the image to blur
Solution Approach 1:
The aspherical visor with different curvature radii in vertical and horizontal directions enables expansion of the visual field while correcting astigmatism. The specific curvature configuration ensures that optical power is equalized across the expanded field of view, allowing wider information coverage without image blurring
3Ease of operation
If the upper portion of the visor is inclined toward the external world to match helmet design, then aerodynamic performance and helmet integration are improved, but asymmetrical blurring increases
Solution Approach 1:
The patent intentionally introduces asymmetry in the visor's curvature configuration, with the vertical curvature radius being larger than the horizontal curvature radius. This asymmetric design compensates for the inclined positioning of the visor on the helmet, correcting the asymmetrical blurring caused by the non-orthogonal incident angles of display light
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 reduces astigmatism, enabling a wider visual field for both vertical and horizontal directions, enhancing visibility of the display image and external scenes while reducing device size and weight.
Implementation Method 1
the reflecting surface of the visor has an aspherical shape whose curvature in the Y'-Z' plane is smaller than the curvature in the X'-Z' plane by an amount corresponding to the difference in optical power due to a difference in the incident angle of the display light to the reflecting surface
Implementation Method 2
The display light emitted from an image display section 101 which creates a display image is projected through a projection optical system 102 onto a predetermined area of the reflection surface 100a of the visor 100. The thereby reflected light reaches the eyes EL and ER of the user H.
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The purpose of the present invention is to provide a head mounted display for aircraft in which astigmatism is reduced so that a display image with a wide visual field can be observed. A reflection surface (10a) of a visor (10), onto which display light is projected from a projection optical system (12), does not have a spherical shape but an aspherical shape whose curvature in the vertical direction is smaller than in the horizontal direction. This difference in curvature eliminates the difference in optical power due to a difference in the incident angle on the reflection surface (10a) and reduces the amount of astigmatism. An intermediate image is formed in both the vertical and horizontal directions within the projection optical system (12) or in the middle of an optical path from the projection optical system (12) to the reflection surface (10a). This increases the degree of freedom of the arrangement of optical elements and allows for the reduction in size and weight of the device.