Properties of the travelling Wave Ultrasonic Motor (TWUM) -among which we find a high-torque to mass ratio, locking without supply, ultrasonic operation -are very attractive for embedded application, such as human prothesis for example. But unfortunately, its control for high precision or high dynamic motion is not easy to achieve because of many non linearities induced by its particular energy conversion process. This is why this paper deals with the modelling of a TWUM, based on a causal approach. According to the inversion principle, control strategies are deduced as well as a novel torque estimation structure. A mechanical claw control using this torque estimator is then achieved and experimental results check the accuracy of the proposed control scheme.