P6.8 - Ultrasonic Piezoelectric Motor with Intrinsic Torque Measurement – First Results

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
P6 - Technology, Materials
P. Pott, S. Matich, H. Schlaak - Technische Universität Darmstadt (Germany)
827 - 830


In many technical applications the actual torque provided by an actuator is of interest. Torque sensing, however, tends to be costly and complex. When it comes to small-sized high-torque but low velocity actuation systems ultrasonic piezoelectric actuators can be used. Here, high power density and noise-less operation can be provided.
Here, we present an ultrasonic piezoelectric motor with intrinsic force sensing capabilities that provides high power density, high torque and a signal linearly correlated to the torque output, without the need of an additional sensor element. The actuator consists of a metal bar that is forced to resonant longitudinal vibration by a pre-stressed piezo element at 22.3 kHz. The rotor is mounted in a way that the bar can be tangentially pressed to the rotor by a second piezo stack. By applying a two-phase signal to the piezo elements the friction contact is forced into an elliptic movement and drives the rotor.
An external torque applied to the rotor leads to an axial force in the resonator bar and finally in the driving piezo element. Here, the piezoelectric effect causes a charge transfer and thus a voltage that is proportional to the force applied. This can be measured by a capacitive bridge circuit. So a signal proportional to the torque provided by the resonant actuator can be derived.
The frequency of the torque signal correlates with the rotations. So, it can be also seen, that for each load step six rotations were measured. Future work will comprise the optimization of the electromechanical set-up (signal quality and mechanical wear) and the build-up of an embedded system for signal analysis and force/velocitycontrol of the actuator.