HMD Varifocal Guidance to Minimize Parasitic Motion Errors
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) struggle to compensate for vergence and accommodation conflicts, leading to visual fatigue and nausea in users due to the inability to adjust the focal distance dynamically.
Innovation Solution
A guidance system is integrated into the HMD to adjust the location of the image plane by moving the electronic display and optical elements, using a varifocal actuation mechanism and eye tracking to minimize parasitic motion errors, thereby aligning the vergence and accommodation distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the focal distance is fixed in conventional HMDs, then the device structure is simple, but visual fatigue and nausea occur due to vergence-accommodation conflict
Solution Approach 1:
The patent implements dynamic adjustment of the image plane location through a guidance system with movable carriages that can shift the display along the optical axis. This allows the focal distance to change dynamically based on vergence requirements, resolving the vergence-accommodation conflict while maintaining a relatively compact form factor through precision mechanical guidance.
Solution Approach 2:
The patent introduces a guidance system as an intermediary mechanism between the fixed HMD structure and the variable focal distance requirement. This guidance system with carriages and guidance configurations acts as a mediator that enables smooth, controlled movement of the image plane without requiring complete redesign of the entire display system.
2Reliability
If the image plane location is adjusted dynamically, then vergence and accommodation distances are aligned, but parasitic motion errors occur
Solution Approach 1:
The patent employs encoder feedback mechanisms that continuously monitor the position of the movable carriage and provide real-time position data. This feedback allows the system to detect and correct parasitic motion errors, ensuring accurate image plane positioning despite the dynamic adjustment process.
Solution Approach 2:
The guidance system is pre-configured with precise guidance configurations and retaining mechanisms that constrain movement to the intended linear path along the optical axis. This preliminary structuring prevents parasitic motions before they occur, maintaining positioning accuracy during dynamic adjustment.
3Adaptability or versatility
If a guidance system with movable carriages is used, then the focal distance can be adjusted, but the device complexity increases
Solution Approach 1:
The patent divides the adjustment mechanism into separate modular components: a fixed carriage, a movable carriage, and a guidance system connecting them. This segmentation allows each component to be optimized independently and simplifies the overall structure by distributing functions across multiple manageable modules rather than requiring a monolithic complex mechanism.
Data Source
AI summary
In some embodiments, a head-mounted display device includes an optics block and a varifocal actuation system coupled to the optics block. The varifocal actuation system utilizes at least one of a tandem retaining configuration, a tandem guidance system, and a tandem preload configuration to minimize parasitic motion errors associated with the head-mounted display device. In some embodiments, the tandem retaining configuration includes a hooking structure or a washer-based structure, the tandem guidance system includes an anti-creep system, and the tandem preload configuration includes a preload magnet and a preload target.