Piezo-Actuated Varifocal Head-Mounted Displays for Virtual and Augmented Reality

A fundamental cause of visual discomfort in traditional head-mounted displays (HMDs) for Virtual and Augmented Reality (VR/AR) is the vergence-accommodation conflict (VAC). We propose and develop a novel headset prototype based on the Verifocal (TM) platform to eliminate VAC by dynamically adjusting the focal plane of the display. The developed headset employs an eye tracking system to track the user's gaze and determine the virtual object being observed by the user. The varifocal display then moves the focal plane of the display to dynamically match the depth of the observed object, providing correct focus cues to the user. We achieve the focal plane adjustment by moving the headset's stereo displays independently using small, lightweight and low-power piezoelectric actuators. Such actuators offer a very low response time with high positional accuracy, while operating at a high speed and virtually silently. Furthermore, our headset prototype has a large adjustable dioptric range for each eye and thus provides the capability for also correcting myopia and anisometropia, allowing vision-impaired users to use the headset without the need for eyeglasses. In conclusion, our approach makes it possible for the user to observe close or far objects in the virtual environment with reduced eye strain by providing consistent depth cues for all viewing distances.