Bowing virtual strings with realistic haptic feedback

We present a music interface implementing a bowed string. The bow is realised using a commercially available haptic device, consisting of a stylus attached to a robotic arm. While playing the virtual strings with the stylus reproducing the bow, users feel both the elastic force from the strings and the friction resulting from the interaction with their surfaces. The audio-haptic feedback is obtained by a physical model: four stiff strings are simulated using a finite difference time domain method, modelled as 1-D elements in the virtual 3-D space. The bow is simply modelled as a rigid cylinder that can move free in this space, and interact with the strings. Finally, the frictional interaction between such elements is modelled by a nonlinear friction model capable of reproducing the characteristic stick-slip phenomenon observed during string bowing. Moreover, the model can be dynamically controlled in one parameter so as to become more sticky or slippery. By turning on and off the frictional feedback, users can appreciate the significance of this interaction. A real-time visualisation of the bowed strings complements the audio-haptic display.