Vibration Feedback

Excerpt from: Joseph Malloch, “Adding vibrotactile feedback to the T-Stick digital musical instrument”. Technical Report MUMT-IDMIL-07-11, Music Technology Area, McGill University, 2007.

The actuator was constructed by hand-winding electromagnet wire on a purpose-build plastic sleeve featuring 2 recessed sections as seen in figure [below]. The direction of winding was reversed when passing the wire from one side of the sleeve to the other. A cylindrical rare-earth magnet was suspended inside the sleeve using flexible rubber discs. As described in [Yao 2004], the actuator is constructed such that the field lines escaping the rare earth magnet cross the two coils at right angles, so that when current flows in the coils, a Lorentz force develops between the magnet and the sleeve.

Constructing a vibration actuator

Constructing a vibration actuator as designed by Hsin-Yun Yao and Vincent Hayward. (H.-Y. Yoa and V. Hayward. An experiment on length perception with a virtual rolling stone. In Proceedings of Eurohaptics 2006, pages 325–330, 2006.)

 

The actuator was encased in shrink-tubing for protection and bonded strongly to the interior of the T-Stick using epoxy adhesive, in order to ensure coupling between the actuator and the instrument. It was decided to use the same actuator orientation as that used for the MicroTactus and the rolling-ball experiment, in which the actuator is driven in the axis corresponding to the length of the tube. This makes difference in placement of the actuator negligible: the stiffness of the ABS plastic pipe means that vibrations are not noticeably damped from one end of the pipe to the other.

The actuator was driven with audio signal generated by software running on a laptop computer (see figure [below])…

The set-up used for driving the actuated T-Stick.

The set-up used for driving the actuated T-Stick.

The actuator exhibits impedance similar to that of an audio speaker, and for this initial investigation a simple 1W 5V audio amplifier circuit was used, using a Philips TDA7052 mono amplifier IC. More powerful amplifiers may be used for future work with the actuated T-Sticks.