Friend and colleague Joe Malloch blogs about a very interesting project in which he uses a pipe with an accelerometer in both ends and a vibration actuator in the middle to create a haptic illusion of a rolling ball inside the pipe. From his technical report about the device:
Since the controller already contains five channels of acceleration sensing, it is simple to link this to virtual physical dynamics consistent with real-life gravity and user interaction. The acceleration signal is integrated to approximate velocity, and the resulting signal is used to control the frequency of a periodic signal mimicking the rolling of a ball of a set circumference. By varying the scaling of acceleration data and the scaling of velocity data, the mass and circumference of the virtual ball may be altered. Performing waveshaping of the final signal (or altering the stored waveform if look-up tables are used) alters the perception of the interaction between the virtual ball and the inside of the tube, creating the impression that the motion is smooth or bumpy, or that the inside of the pipe is ribbed. Integrating a second time approximates the position of the ball; this data is used to stop the virtual motion and set the velocity back to zero when the ball reaches the end of the modeled pipe…
Even lacking appropriate amplification and using somewhat un-physical coefficients, people trying the demonstration were convinced by the model â€“ some would not believe that there was actually nothing rolling inside. Observation of users showed that their gaze would often follow the apparent position of the virtual ball, and perception of mass distribution would change depending on which end of the controller â€œcontainedâ€ the virtual ball.
The altered perception of mass distribution shows that vibrotaction can give rise to illusions of force. I think there’s a lot of potential for this concept to be exploited for PxD.