In this project an MRI-compatible haptic interface will be implemented and optimal control parameters for the device will be derived. The haptic device has three degrees of freedom and it is actuated using ultrasonic motors. The actuation principle of the ultrasonic motors are based on friction: the stator and rotor of the motor are pressed against each other. A travelor wave is excited by the stator to create rolling movement of the rotor and generates the motor actuation. Haptic applications require also a wide range of velocities as control inputs. In order to achieve smooth behaviour at low velocities, the motors should be controlled with a hybrid controller (changing the input frequency or the phase). The optimal switching point and the optimal control parameters for each control mode should be determined experimentally. Using the derived control parameters a position based admittance controller should be implemented on the haptic interface and several objects with certain stiffness values should be rendered to verify the effectiveness of the implemented control algorithms.

Tasks:

• Literature review
• Determination of motor characteristics with and without load
• Implementation of the hybrid control
• Controller parameterization
• Implementation of the admittance controller
• Experimental verification of the motor characterization

Prerequisites:

• Good programming skills in C or C++
• Experience in Matlab/Simulink

Supervisor:

• Mehmet Alper Ergin

Literature:

1. Position control of ultrasonic motors with adaptive dead-zone compensation
   Senjyu, T. Yokoda, S. Gushiken, Y. Uezato, K.
   In Industry Applications Conference, Thirty-Third IAS
   Annual Meeting, vol. 1, pp.506-512,1998
2. High-performance load-adaptive speed control for ultrasonic motors
   Ferreira, A. and Minotti, P.
   In Control Engineering Practice, vol. 6, number 1, pp. 1-13, 1998,Elsevier
3. Development of a 3 dof mr-compatible haptic interface for pointing and reaching movements
   Klare, S. Peer, A. Buss, M.
   In Proceedings of EuroHaptics’10, pages 211–218, 2010.