Measuring Rotational Inertia in HMDs: Calculation of Torque as an Unobtrusive Indicator of Expended Effort in Virtual Environments

In this paper, we detail a novel method for calculating torque levels generated by users wearing a head-mounted display (HMD). This method considers not only the movement from a given user but also the weight characteristics of the specific configured headset. In this way, we can calculate a user's expended effort during a specific time frame to better understand the effort expended, as well as the risk of fatigue or injury, while using augmented and virtual reality HMDs. To illustrate the applicability of the method, we apply it in an initial user study analyzing torque and force during a basic target selection task and determined that (1) both force and torque decrease significantly over time as participants tire, and (2) the lighter HMD incurred lower levels of force and torque throughout the various trials. This research substantially furthers the practice of human factors and usability in augmented and virtual reality and fills a need within the community by adding to the extant literature an easy to use and well-documented method that can determine the effect of the total HMD system (HMD hardware, HMD interface, and task elements) on end users over both long- and short-duration tasks.