Section: New Results

Advances in the control of piezo-electric actuators used in for force-feedback devices.

Participants : Frédéric Giraud, Betty Lemaire-Semail, Zheng Dai.

As a solution to the lack of compactness and simplicity often encountered in haptic interfaces, we propose a device based on friction coefficient control principle. This device includes polarised piezoceramics well adjusted and glued to a 64x38x3 mm copper-beryllium plate supported by four legs. Then, properly energised around a resonant frequency, with legs at antinodes, a stationary wave is created in the plate. Variable friction forces between the legs and the plane substrate are created by the control of the wave amplitude, according to electro-active lubrication. So the user obtains force feedback by holding the plate, and moving it on a plane substrate, as he could do with a mouse interface. Preliminary psychophysical evaluation trends to assess the validity of the device as a force feedback interface[21] [20] .

Moreover, Using Travelling Wave Ultrasonic Motors needs specific control algorithms in order to allow force feedback operations. For example, mechanical overload on the shaft of a traveling-wave ultrasonic motor often results in the motor suddenly stalling. To avoid this drawback, one can increase the supply voltage or add a control loop in the rotating reference frame of the traveling wave. The consequences are extra power losses or lower dynamic performances. We proposed a method which combines the advantages of classical controls and controls in a rotating frame: both stability and dynamic performances are obtained at low supply-voltage levels. Experimental runs are presented, showing performances of a position control of the motor[14] .