Analytical model of the contact interaction between the components of a special percussive mechanism for planetary exploration

Special percussive mechanisms, e.g. Auto Gopher and UltraSonic/Sonic Driller/Corer (USDC) have been developed by NASA Jet Propulsion Laboratory and Honeybee Robotics Spacecraft Mechanisms, Corp. to address some of the limitations of current drilling techniques for planetary exploration. The percussive mechanism consists of an ultrasonic horn, a free mass (hammer) and the drill rod. This paper presents the analysis of the interaction between these three components. The impact between the components (i.e. ultrasonic horn and free mass, and free mass and drill rod) is analyzed using solid body collision analysis applying the principle of conservation of momentum. The drill rod is modeled for both undamped and damped cases with equivalent generalized single degree of freedom system. Various values are used for the coefficient of restitution to account for energy loss during impact. The energy transferred to the drill rod by the free mass is obtained determining the change in kinetic energy due to impact. It is observed that the free mass converts the high frequency of oscillation of the ultrasonic horn into lower frequency impacts on the drill rod. A decrease in the coefficient of restitution results in a decrease in the number of impacts, impulse imparted to the drill rod and energy transferred to the drill rod by the impact of the free mass.