Modelling approaches for an ultrasonic percussion drill

This work deals with a novel piezoelectrically driven vibro-impact drilling tool which is designed to drill holes and take rock samples in NASA's future space missions. The drilling device consists of an ultrasonic transducer with a piezoelectric stack, a free flying mass and a drill stem. Excited by the high-frequency vibration of the transducer the free mass oscillates between the horn tip of the transducer and the drill stem. The shock waves in the drill stem caused by the impacts with the free mass affect hard and brittle materials so effectively that small holes can be performed with extremely low additional downforce and low power consumption. This paper provides measurements with a modified actuator which show an irregular motion of the free mass. For further optimization two model approaches are investigated: the finite element method and a discrete lumped parameter model. Each model is capable of predicting actuator's parts motion similar to measurements.