Wide-field HMD Forehead Pad Tracking Eye Movement
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Solution Overview
Problem
Conventional HMDs suffer from vignetting at the pupil when the user's line of sight moves up or down, due to the fixed range of incidence of image light onto the eyeball, leading to distortion, blurring, and shadows in the observed image.
Innovation Solution
A wide-field video display device with a device main body, a forehead pad, an occipital contacting body, and a fitting member that applies a pinching force, allowing the display element and eyepiece optical system to move vertically in conjunction with the user's line of sight, thus maintaining the pupil within the exit pupil and preventing vignetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the HMD is fixed firmly to the face, then the stability of the device is improved, but the pupil becomes blocked by image light when the eyeball rotates vertically, causing vignetting
Solution Approach 1:
The patent applies the dynamics principle by making the forehead pad movable rather than fixed. The pad is positioned on the forehead at a location that allows it to move vertically when the user's line of sight moves up or down. This movement is transmitted to the device main body, causing the optical system to shift position relative to the eyeball. As a result, the exit pupil moves to track the rotating pupil, preventing image light from being blocked and eliminating vignetting while maintaining device stability through the forehead pad's strategic positioning and movement capability
2Area of stationary object
If the vertical FOV of the eyepiece optical system is increased to 23° or more, then the wide-field display capability is improved, but the range of incidence of image light onto the eyeball becomes fixed, exacerbating vignetting when the line of sight moves
Solution Approach 1:
The patent resolves this contradiction by introducing dynamic movement to the optical system. The forehead pad is positioned to engage with the forehead in a region that moves vertically when the user's line of sight changes. This movement is transmitted to the device main body, causing the eyepiece optical system with its large 23° or greater vertical FOV to shift position. Consequently, the exit pupil of the wide-field optical system tracks the rotating pupil, allowing the full wide-field view to remain accessible without vignetting even when the line of sight moves up or down
3Object-affected harmful factors
If the forehead pad is positioned 20 mm to 40 mm above the optical axis, then the device can move with eye muscle movement to suppress vignetting, but the weight distribution must be carefully controlled to ensure proper movement
Solution Approach 1:
The patent applies the parameter changes principle by precisely controlling the weight parameter of the device portion forward of the forehead pad, specifying it should be 300 gf or less. This weight constraint ensures that the forehead pad can move freely in response to forehead muscle movements when the user's line of sight changes, without being hindered by excessive weight. The specific positioning of the forehead pad 20 mm to 40 mm above the optical axis combined with this weight limitation creates the optimal conditions for the pad to track eye movements and transmit this movement to the optical system, thereby suppressing vignetting
Data Source
AI summary
A look-in type wide-field video display device (10) is fitted to the head of a user (U) by applying a pinching force thereto from front and back directions. The wide-field video display device comprises: a device main body (11) provided with a display element and an eyepiece optical system; a forehead pad (13) which is provided projecting from the device main body and which comes into contact the forehead of the user; and a fitting member (12) which applies a pinching force to the head by way of the forehead pad and an occipital contacting body. A vertical FOV of the eyepiece optical system is 23° or more. A total weight of the wide-field video display device forward of the forehead pad is 300 gf or less. All or part of a part the forehead pad that comes into contact with the forehead of the user is located in a range that is a distance 20 mm to 40 mm above an optical axis of the eyepiece optical system, and the forehead pad and the device main body move up and down in conjunction with movement of eye muscles with which the line of sight of the user is moved up and down.