Development of a rotary-percussive ultrasonic drill for extraterrestrial rock sampling

Compared with traditional rotary-percussive drills driven by electromagnetic motors, ultrasonic drills show advantages of small size, low power, low weight on bit, and lubrication free, making them available for the extraterrestrial rock sampling, especially for the minor planet with a weak gravitational field. To solve the problem that the conventional percussive ultrasonic drills cannot remove cuttings effectively, we proposed a rotary-percussive ultrasonic drill which realizes both rotary and percussive motions of the drill bit. The conventional percussive ultrasonic drills employ the vibration energy of the front mass of the Langevin transducers to generate mechanical vibration at the bottom surface of the horn, however, the vibration energy of the back mass is not utilized. Thus, we proposed to use the vibration energy of the back mass to generate a rotary motion via a longitudinal-torsional coupler. The rotary shaft drives the drill bit to rotate continuously to deliver the cuttings out so as to increase drilling efficiency. When the diameter of the drill bit is 5 mm and the axial load is 5 N, RPUD can drill the sandstone in rotary-percussive drilling mode with a speed of 12.4 mm/min while RPUD can only drill the sandstone at a speed of 8.7 mm/min in percussive drilling mode. Contrastive experiments show that the rotary-percussive drilling can actually raise the drilling efficiency compared with percussive drilling, which indicates that the RPUD is superior to conventional percussive ultrasonic drills.