Abstract-We are developing haptic interfaces compatible with functional Magnetic Resonance Imaging (fMRI) for neuroscience studies. The presented prototype with one rotary degree of freedom is actuated by a traveling wave ultrasonic motor operating under admittance control. Torque is sensed from the deflection of an elastic polymer probe via light intensity measurement over optical fibers. This concept allows us to place all electronic components outside the shielded MR room. Hence, the device can be used in conjunction with fMRI, providing torque and motion feedback simultaneously with imaging. Its compactness and simplicity facilitate the construction of multiple degree of freedom systems.

Piezoelectric ultrasonic motors are superior to electromagnetic micromotors, because their efficiency remains theoretically constant during miniaturization. However, the still relatively recent technology has a considerable unexploited optimization potential. Numerical structural analysis by the means of the finite element method (FEM) is a common approach for dimensioning piezoelectric motors. Consequently, there is a need for efficient optimization procedures fitted to the FEM simulation. We developped a dedicated design methodology to first well understand the influence of the geometrical parameters on the movement of the motor. The parameters with the strongest influence on the objective function, the vibration amplitude of the resonator, were used in a following optimization stage. The operation of the optimized motor was proofed on a test bench. Interferometrical measurements validated quantitatively the FEM model along with the suggested design methodology.

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Abstract-Ultrasonic motors are a good alternative to electromagnetic motors in medical robotics, since they are electromagnetically compatible. Estimating speed instead of using encoders reduces cost and dimension of the robot on the one hand and increases reliability on the other hand. However, no sensorless speed controller is yet industrialized. Analytical models of the traveling wave ultrasonic motor being too complex to be exploited for sensorless control purpose, we suggest speed estimation based on artificial neural networks. The artificial neural network is designed based on a sensitivity analysis using design of experiments methods. Factorial designs have been chosen to find out the effects of each input factor, but also the effect of their interactions. First results show that speed estimation using artificial neural networks is a promising approach. The artificial neural network optimized with design of experiments methods is a valid model of the traveling wave ultrasonic motor to estimate speed.

Abstract-In this study, a hollow cylinder ultrasonic motor has been designed in order to be integrated into mechatronic devices where the bore is either occupied for functional reasons or must remain free. The design approach consists in performing a FE modelling of the motor structure. After finding the different vibration modes, it is possible to find out the axial and tangential deformation amplitudes of the resonator allowing the motor rotation when a pre-stressing force is applied to the rotor. Using an optimisation methodology based on a sensitivity analysis using in particular the design of experiments method and then a FE optimisation, it is possible to maximize the deformation amplitudes in both directions to obtain higher torque and speed of the motor. Along with this process, functional models are built in order to validate the adopted design methodology and verify if the chosen motor concept is appropriate.