Design and Psychophysical Evaluation of the HapSticks: A Novel Non-Grounded Mechanism for Presenting Tool-Mediated Vertical Forces

Force feedback in tool-mediated interactions with the environment is important for the successful performance of complex tasks in daily life as well as in specialized fields such as medicine. Most stylus-based haptic devices require either grounding or attachment to the user's body. Recently, non-grounded haptic devices have attracted a growing interest. In this study, we propose a non-grounded rotation mechanism to represent the vertical forces applied on the tip of a tool by mimicking the cutaneous sensations that are caused by such forces. As an example of an application of our method, we developed a non-grounded haptic device called HapSticks, which mimicked the sensation of manipulating objects using chopsticks. First, using an adjustment paradigm, we directly compared a virtual weight rendered by our device and a real weight to investigate the relation of real weight and virtual weight. Next, we used a forced choice constant stimuli paradigm in a virtual and a real weight discrimination task. We conclude that our novel device renders a reliable illusion of sensed weight that leads to a discrimination ability that is typical of virtual-reality applications but worse than the discrimination between real weights.