To maximize user experience in VR environments, optimizing the comfortability of head-mounted displays (HMDs) is essential. To date, few studies have investigated the fatigue induced by wearing commercially available HMDs. Here, we focus on the effects of HMD weight and balance on the physical load experienced by the user. We conducted an experiment in which participants completed a shooting game while wearing differently weighted and balanced HMDs. Afterwards, the participants completed questionnaires to assess levels of discomfort and fatigue. The results clarify that the weight of the HMD affects user fatigue, with the degree of fatigue varying depending on the center of mass position. Additionally, they suggest that the torque at the neck joint corresponds to the physical load imparted by the HMD. Therefore, our results provide valuable insights, demonstrating that, to improve HMD comfortability, it is necessary to consider both the balance and reduction of weight during HMD design.

We propose Transtiff, a stick-shaped device that can display various stiffness for stick-based haptic interaction. The device has a stiffness-changing joint replicating an artificial muscle mechanism in the relay portion of the stick to change its stiffness. Transtiff can be applied to touch interaction of the screen, augmenting the haptic experience of operating with a stylus pen, which is usually felt uniform. As applications, users can experience the sensation of pen and brush writing on a single device. In addition, it is possible to change the stiffness of the device for each object on the screen to reproduce the tactile feel of that object.