The effect of damping on the perception of hardness

In controlling teleoperation systems subject to communication delays, unstable behavior is often prevented by injecting damping. A proper perception of hardness is required to efficiently interact with an object, but it is unknown if and how this injected damping influences the perceived hardness of objects. To investigate the effect of damping on the perceived hardness of an object, 12 participants compared the hardnesses of lightly and heavily damped objects in a two-alternative forced choice experiment. Two tasks were investigated: an in-contact and a contact-transition task. For each task, 3 reference stiffnesses were used. Both force and position data were recorded. The results show that adding damping increases the perceived hardness of an object for an in-contact task, while it decreases perceived hardness for a contact-transition task. Movement and force data show that object indentation, mean and maximum velocity and adjusted rate-hardness, a new parameter defined in this paper, correlate with perceived object hardness. From a fundamental perspective, the results show that perceived hardness is influenced by damping in a task- specific way. Moreover, for designers of teleoperation systems the results provide insights for tuning and designing control architectures that properly reflect the desired hardness.