Rotary-Percussive Ultrasonic Drill: An Effective Subsurface Penetrating Tool for Minor Planet Exploration

Compared with conventional drill, an ultrasonic drill can break into rocks under lower weight on bit and lower power, which is more suitable to sample in low gravity environment for deep-space exploration. However, the ultrasonic drill cannot remove rock cuttings effectively when drilling into a certain depth. This paper proposed a rotary-percussive ultrasonic drill (RPUD), which depends on a single piezoelectric transducer to produce rotary-percussive moment to drill into rocks and remove cuttings. The RPUD consists of four parts: a piezo-ceramics, a percussive unit, a rotary unit, and a drill tool. Percussive unit magnifies the longitudinal vibration of one side of piezo-ceramics, and delivers percussive motion to the drill tool. Rotary unit transfers the longitudinal vibration of the other side of piezo-ceramics into longitudinal-torsional vibration to drive the drill tool to rotate. Percussive motion and rotary motion of drill tools are relatively independent, and thus their parameters can be adjusted separately. Finite element method is adopted to assist the design of the RPUD. Modal analysis is employed to tune the resonance frequencies of the percussive unit and rotary unit to be close. After the fabrication of a RPUD prototype, contrastive test of rotary percussive drilling and percussive drilling was carried out based on the RPUD prototype. Test results show that the RPUD can drill into the rocks and improve the efficiency of cutting removal.