A Parametric Study for the Design of an Optimized Ultrasonic Percussive Planetary Drill Tool

Abstract

Abstract-Traditional rotary drilling for planetary rock sampling, in-situ analysis and sample return, is challenging because the axial force and holding torque requirements are not necessarily compatible with lightweight spacecraft architectures in low-gravity environments. This article seeks to optimize an ultrasonic-percussive drill tool to achieve rock penetration with lower reacted force requirements, with a strategic view towards building an Ultrasonic Planetary Core Drill (UPCD) device. The UPCD is a descendant of the Ultrasonic/Sonic Driller/Corer (USDC) technique. In these concepts, a transducer and horn (typically resonant at around 20kHz) is used to excite a toroidal free-mass which oscillates chaotically between the horn tip and drill base at lower frequencies (generally between 10Hz to 1kHz). This creates a series of stress pulses which are transferred through the drill-bit to the rock surface and, while the stress at the drill-bit tip/rock interface exceeds the compressive strength of the rock, cause fractures that result in fragmentation of the rock. This facilitates augering and downward progress. In order to ensure that the drill-bit tip delivers the greatest effective impulse (the time-integral of the drill-bit tip/rock pressure curve exceeding the strength of the rock), parameters such as the spring rates and the mass of the free-mass, drill-bit and transducer have been varied and compared in both computer simulation and in practical experiment. The most interesting findings, and those of particular relevance to deep drilling, indicate that increasing the mass of the drill-bit has a limited (or even positive) influence on the rate of effective impulse delivered.

Full and Half-Wavelength Ultrasonic Percussive Drills

“…In previous research [9], the ultrasonic transducer was 0885-3010 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.…”

“…Previous research [9] on the full wavelength drill tool suggested that a minor change in the mass of the free-mass, within a specified range, will not significantly affect the delivered impulse to the impact plate, and consequently a 6g toroidal free-mass is selected. For the drill-bit, it was found that a similar level of impulse was delivered to the impact plate using one drill-bit or multiple connected drillbits, and therefore a single drill-bit element (80g) is used throughout.…”

UPCD: Field Trial Results and Further Work

“…The drill uses the ultrasonic-percussive technique, where the transducer assembly is free to travel as a sprung mass (via front and back springs) over several mm in order to deliver recurring percussive interactions with a free-mass, which then goes on to hammer against the drill string. This concept is covered further in Li, et al, (2017). The travel range is additionally exploited to permit the relative vertical movement needed to connect and disconnect the drillstring elements.…”

A Novel Fast Resonance Frequency Tracking Method Based on the Admittance Circle for Ultrasonic Transducers

“…Generally, a PT can be equivalent to a simple circuit shown consisting of two arms as shown in Fig. 1 [11,12]. The first arm is the electric arm containing a parallel capacitor and a dielectric resistance .…”