This thesis describes the development of three new tactile stimulators for active
touch, i.e. devices to deliver virtual touch stimuli to the fingertip in response to
exploratory movements by the user. All three stimulators are designed to provide
spatiotemporal patterns of mechanical input to the skin via an array of contactors,
each under individual computer control. Drive mechanisms are based on
piezoelectric bimorphs in a cantilever geometry.
The first of these is a 25-contactor array (5 × 5 contactors at 2 mm spacing). It
is a rugged design with a compact drive system and is capable of producing strong
stimuli when running from low voltage supplies. Combined with a PC mouse,
it can be used for active exploration tasks. Pilot studies were performed which
demonstrated that subjects could successfully use the device for discrimination of
line orientation, simple shape identification and line following tasks.
A 24-contactor stimulator (6 × 4 contactors at 2 mm spacing) with improved
bandwidth was then developed. This features control electronics designed to transmit
arbitrary waveforms to each channel (generated on-the-fly, in real time) and
software for rapid development of experiments. It is built around a graphics tablet,
giving high precision position capability over a large 2D workspace. Experiments
using two-component stimuli (components at 40 Hz and 320 Hz) indicate that
spectral balance within active stimuli is discriminable independent of overall intensity,
and that the spatial variation (texture) within the target is easier to detect
at 320 Hz that at 40 Hz.
The third system developed (again 6 × 4 contactors at 2 mm spacing) was a lightweight modular stimulator developed for fingertip and thumb grasping tasks;
furthermore it was integrated with force-feedback on each digit and a complex
graphical display, forming a multi-modal Virtual Reality device for the display of
virtual textiles. It is capable of broadband stimulation with real-time generated
outputs derived from a physical model of the fabric surface. In an evaluation study,
virtual textiles generated from physical measurements of real textiles were ranked
in categories reflecting key mechanical and textural properties. The results were
compared with a similar study performed on the real fabrics from which the virtual
textiles had been derived. There was good agreement between the ratings of the
virtual textiles and the real textiles, indicating that the virtual textiles are a good
representation of the real textiles and that the system is delivering appropriate
cues to the user
