Haptic Performance Using Voltage-Mode Motor Control

Haptic devices driven by dc motors are usually controlled in current mode due to the direct relationship between current and torque. This paper analyzes the performance of voltage-mode controllers whose main drawback is that the torque of the actuator depends on its electrical dynamics. However, the electrical dynamics of the motor add the viscosity generated by the back electromotive force. Since the motor damping seen from the handle of the interface is increased by the square of the transmission ratio, the physical damping of the mechanism can be very high, maintaining low inertia. As a result, very high performance in terms of critical stiffness can be achieved, even using cost-effective electronics. There is a tradeoff between the achievable virtual stiffness during the haptic interaction and the backdrivability in free movement, if the damping is set too high. To investigate the benefits of this motor control strategy, CEIT's haptic gearshift is used as a testbed. The experimental results confirm that a very high critical stiffness can be achieved using this strategy.