Tactile Displays

Different actuator technologies have been used to create tactile displays in our lab including linear resonant actuators, voice coil motors, piezoelectric actuators, shape memory alloy actuators and magnetorheological fluid (MRF) actuators. The latter is a joint project with collaborators at the University of Pisa. The actuators vary with respect to their bandwidth, response times, capacity to generate different waveform profiles and power requirements. Analyses of their characteristics are important to the design of tactile displays in that they indicate which motors are optimal for specific applications and how the conditions under which the motors make contact with the skin can have a profound effect on the mechanical inputs delivered.

Tactile displays have been evaluated at different locations on the body including the hand, arm, thigh and torso. We have measured the travelling waves on the skin elicited by vibration of the motors and determined how they vary at different locations and as a function of the mechanical properties of skin. There are differences among the sites tested and some features of tactile sensory processing such as tactile anisotropies influence the ability to identify tactile patterns at some locations (on the arm) but not others (the back).

Tactile patterns that are used to communicate via wearable tactile displays are often called tactons, by analogy to icons in the visual modality. As they are conceptual, the association between the tactile signal and the concept it represents must be learned. Tactons can be created by varying the frequency, waveform, intensity and duration of the vibration. Psychophysical studies have indicated that variations in the temporal profile and the location on the body stimulated are the easiest parameters for people to discriminate. Spatial cues appear to be a particularly effective dimension for creating tactons when the is distrubuted across the skin surface. We have also demonstrated that tactons can be used to convey navigational cues such as turn around, turn right or stop, and that these can be attended to and accurately identified during concurrent cognitive and physical acitivites.