Dynamic Impact Force on a Special Drilling Mechanism for Planetary Exploration

Abstract

Special percussive mechanisms have been used to explore the lunar, Martian, and other planetary subsurface and extract soil (regolith)/rock samples for further study. The special type of percussive mechanisms investigated in this study, Auto-Gopher and Ultrasonic/Sonic Driller/Corer (USDC) developed by National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory and Honeybee Robotics Spacecraft Mechanisms Corporation, consists of an ultrasonic horn, a free mass (hammer), and the drill rod. This paper presents a general methodology to perform the dynamic contact analysis of the longitudinal impact of the free mass on the drill rod including the effects of structural vibration and damping of the rod. The contact force caused by impact is obtained by using Hertz force-indentation relation coupled with the structural vibration of the rod obtained by using mode superposition method and finite-element technique. Numerical solution, with equilibrium iterations, of the equations of motion is implemented. The contact force was observed to be consistent with experimental results available in the literature for similar problems. The results obtained with the model developed in this study are also verified by using a commercially available finite-element code. The magnitude of the contact force was observed to increase with increasing damping ratio, whereas the duration of the contact force slightly decreased.