Auto-Gopher-2 - Wireline Deep Sampler Driven by Percussive Piezoelectric Actuator and Rotary EM Motors

Two of the key purposes of future NASA’s solar system exploration of planetary bodies are the search for potentially preserved bio-signatures and for habitable regions. To address these objectives, a biologically inspired wireline deep rotary-percussive drill, called Auto-Gopher, has been developed. This drill employs a piezoelectric actuated percussive mechanism for generating impulsive stresses and breaking formations, and an electric motor to rotate the bit to break material and remove the cuttings. Initially, the drill was designed as percussive mechanism for sampling ice and was demonstrated in 2005 at Lake Vida, Antarctica, reaching about 2 m depth. The lessons learned suggested there is a need to augment the percussive action with bit rotation in order to maximize the penetration rate. The first generation implementation of the rotary augmentation was focused on the demonstration of this capability. In 2012, during the 3-day field test, the drill reached a 3-meter deep in gypsum. A separate mechanism was used to break and remove the cores. The average drilling power consumption was in the range of 100-150 Watts, while the rate of penetration was approximately 2.4 m/hr. Currently under development is the second-generation drill, called Auto-Gopher 2. The drill will be fully autonomous. In this paper, the capabilities that are being integrated into the Auto-Gopher-2 are described and discussed.

Failure Analysis of Cracking on Side Tooth Gingivae of a Percussive Drill Bit

Failures of percussive drill bits have been attributed to the external mechanical force and structural design by engineers and researchers for a long time. Few attentions have been focused on the material itself. Generally, it is the unqualified material, induced by the improper metallurgy and heat treatment process, which makes the drill bits fail soon after they are put into service. Reasons of the crackings on side tooth gingivae of a drill bit, which failed prematurely at the beginning of the service, were analyzed comparatively. Scanning electron microscope, metallographic observation, mechanical performance test and chemical composition analysis were adoptedfor the failure analysis. Results show that microstructure, chemical composition and mechanic properties of the substrate were excluded from the reasons of the cracking. It is mainly the excessive inclusions and defects in the carburized layer which induced the inhomogeneity of material organization and performance. Those inclusions and defects act as stress concentrators and leading to the crack initiation. In addition, toughness of the carburized layer is also decreased due to its over-carburization. It makescracks more easily initiate from the carburized layer and then propagate into the substrate under the stress of interference fit.

Modal Analysis and Numerical Solution in Cable Drilling System

Cable percussive drill is an important drilling machine in the construction of large diameter pile foundation, and complicated dynamic system. However, the design of cable percussive drill is mainly relied on empirical methods or simplified formulas, the dynamic characteristics of coupling system has not been fully understood. Based on the special conditions, the two degrees of freedom dynamic system coupling with buffering mechanism and bit is analyzed, and the vibration differential equation is built. Finally, the modal frequency of system is obtained by numerical method, and the correlation between the modal frequency of system and the structure parameters is built. The result develops the design theory of cable percussive drill and provides valuable preferences for the optimal design.