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Design and analysis of ultrasonic horn for USDC (ultrasonic/sonic driller/corer)

In-situ sampling and analysis is one of the major objectives of future NASA exploration missions. Existing drilling techniques are limited by the need for large axial forces, holding torques, and high power consumption. Lightweight robots and rovers have difficulties accommodating these requirements. These requirements are becoming increasingly tougher to meet as the need for drilling techniques is expanding to reach deeper into the subsurface. To address these key challenges to the NASA objective of planetary in-situ rock sampling and analysis, a drilling technology called ultrasonic/sonic driller/corer (USDC) was developed. The USDC uses a novel driving mechanism, transferring ultrasonic vibration to sonic frequency impacts with the aid of a free-flying mass block (free-mass). The free mass then drives the drill bit. The actuator consists of a stack of piezoelectric disks with a horn that amplifies the induced vibration amplitudes. To meet the need for deep driller the USDC was modified to form the Ultrasonic/Sonic Gopher. Drilling to the depth of several meters in ice or hard rocks requires the optimization of the amplification of the vibration displacement and velocity that are generated by the piezoelectric materials. For this purpose, various horn designs were examined analytically. Conventional and new designs of the horn were analyzed using finite element modeling and the results allow for the determination of the control parameters that can enhance the tip displacement and velocity. The results of the modeling are described and discussed in this paper.