2004: stator of USR60

2004: Prehistoric time.

First prototype of StimTac used a free stator of an Ultrasonic Motor called USR60. This ring shaped resonator can provide 3µm vibrations at 40kHz. A plastic tape was bonded to level the touched surface, and eliminate the effect of the teeth machined on the original stator. A Linear Variable Differential Transformer (LVDT) was used to detect fingertip's position. This solution wasn't optimal: it's one dimension, with contact, and doesn't measure touch area's position acurately.

2007: made at the lab

2007: First prototypes made at the lab.

The idea of StimTac was to produce a tactile device which can render good tactile stimulation, and which can be as small as possible in the same time. « Squeeze film effect » was found to be the interaction process between the vibrating plate and the fingertip. A specific prototype was then manufactured. The design results in a plate, on which a stationary wave propagates. Width and length have been chosen in order to favour squeeze film.

2008: Stimtac becomes a portable tactile stimulator

2008: A portable tactile stimulator.

To operate, Stimtac need an accurate finger position sensor.In order to remove the LVDT, a custom-made optical sensor is thus used to locate the user’s finger. The sensor was built from two white LEDs, a set of mirrors and a linear 200 dpi CCD array. An on-board DSP computes the centroids of two shadow images created by the user’s finger and sends them on a serial line as absolute (x; y) coordinates at a rate of 120 Hz. The final resolution of the sensor is 170 dpi due to optical constraints and post-treatments.

2010: improvement in power consumption

2010: Stimtac is thin, lightweight and sobre.

A more convenient design of Stimtac could cut the power losses down by 90%. Consequently, the tactile plate doesn't get warm, allowing the user to play a long time with the device. Moreover, the rated power (0.5W) is sufficiently small to allow a power supply from a lightweight power source, or directly from an USB port for example.