Development of a switchable system for longitudinal and longitudinal-torsional vibration extraction

High-frequency/low-frequency drilling is an attractive technology for planetary exploration tools, and one which has seen considerable innovation in the techniques used to ensure rotation of the front-end cutting bit. This rotation is essential to prevent tooth imprintation in hard materials, and extracting the rotation from the high-frequency or ultrasonic system has obvious benefits in terms of simplicity and robustness. However, extracting the rotation from an ultrasonic horn raises the possibility of bit-walk if it is used to operate a coring device and the authors therefore propose an ultrasonic horn which uses an excitation applied to a single input surface to yield torsional and longitudinal vibration on two physically separated output surfaces. By engaging with the two output surfaces, longitudinal vibration can be extracted to achieve initial percussive drilling, even where a coring bit is applied, and the torsional output can subsequently be added to prevent tooth imprintation once the coring bit has settled into the site in question. In this manner, the horn provides a mechanism whereby high-frequency/low-frequency drilling technique can be applied to coring operations without the need for an exceptionally robust drill structure capable of resisting bit-walk forces

Optimisation of an ultrasonic drill horn for planetary subsurface sample retrieval

Ultrasonic tools can cut through foodstuffs, biological material and other soft matter with relative ease. However, when attempts are made to cut through harder material, the rate of progress markedly declines. Under such circumstances it is sometimes necessary to reduce the frequency of the blows delivered to the target, in order to ensure that each blow exceeds the compressive strength of the material, but for space applications the small size of high-frequency ultrasonic horns is extremely attractive. This paper therefore considers the optimization of horns for exploitation of the high-frequency/low-frequency drilling technique, whereby a free-mass oscillating between the horn and the target is employed to reduce the frequency at which impulse events are delivered to the target

Full and half-wavelength ultrasonic percussive drills

Ultrasonic-percussive drills are a leading technology for small rock drilling applications where power and weight-on-bit are at a premium. The concept uses ultrasonic vibrations to excite an oscillatory motion in a free-mass, which then delivers impulsive blows to a drilling-bit. This is a relatively complex dynamic problem involving the transducer, the free-mass, the drilling-bit and, to a certain extent, the rock surface itself. This paper examines the performance of a full-wavelength transducer compared to a half-wavelength system, which may be more attractive due to mass and dimensional drivers. To compare the two approaches, three-dimensional finite element models of the ultrasonic-percussive stacks using full and half wavelength ultrasonic transducers are created to assess delivered impulse at similar power settings. In addition, impact-induced stress levels are evaluated to optimize the design of drill tools at a range of internal spring rates before, finally, experimental drilling is conducted. The results suggest that full-wavelength systems will yield much more effective impulse but, interestingly, their actual drilling performance was only marginally better than half-wavelength equivalents

Optimisation of the longitudinal-torsional output of a half-wavelength Langevin transducer

Numerous ultrasonic applications, such as high-frequency/low frequency drilling, require or can benefit from the inclusion of some torsional vibration behaviour within a primarily longitudinal pattern. Producing longitudinal-torsional (LT) vibration in a Langevin transducer using the mode degeneration method tends to give more robust results than the competing mode-coupling approach, and this work is concerned with optimizing the relative strengths of the longitudinal and torsional responses within the context of a half-wavelength Langevin transducer. Using numerical and experimental techniques, the output of such a system is predicted across a range of geometries and compared to experimental results obtained through laser vibrometry

A generalised approach to torsionality maximisation in longitudinal-torsional ultrasonic devices

A longitudinal-torsional vibration mode has many applications in ultrasonic systems. Obtaining this behaviour could be achieved either by coupling the longitudinal and torsional modes or by degenerating the longitudinal mode, but the results may be unsatisfactory. These methods have many disadvantages including the expense and complexity in operation, the possibility of coupling unwanted bending modes, and the low responsiveness and torsionality. In this work, we employed a geometric modification to a traditional Langevin transducer to overcome these disadvantages. This was achieved by incorporating helical slits and exponential geometry features in the front mass of the transducer. Finite element analysis and vibration response measurements show that this strategy prevents coupling of bending modes, increases responsiveness, reduces energy losses, and produces high torsionality

Drill Tools for Earth and space design of a novel longitudinal-torsional ultrasonic transducer

Measurement of complex combinations of different vibration modes operating together at ultrasonic frequencies can be carried out using 3-D laser vibrometry

A parametric study for the design of an optimized ultrasonic-percussive planetary drill tool

Traditional rotary drilling for planetary rock sampling, in situ analysis, and sample return are challenging because the axial force and holding torque requirements are not necessarily compatible with lightweight spacecraft architectures in low-gravity environments. This paper seeks to optimize an ultrasonic percussive drill tool to achieve rock penetration with lower reacted force requirements, with a strategic view toward building an ultrasonic planetary core drill (UPCD) device. The UPCD is a descendant of the ultrasonic/sonic driller/corer technique. In these concepts, a transducer and horn (typically resonant at around 20 kHz) are used to excite a toroidal free mass that oscillates chaotically between the horn tip and drill base at lower frequencies (generally between 10 Hz and 1 kHz). This creates a series of stress pulses that is 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, it causes 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, the drill bit and transducer have been varied and compared in both computer simulation and 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

The European Ultrasonic Planetary Core Drill: Preliminary Results from Field Trials at the Haughton Mars Project

This paper presents the findings of a recent field trip by the Ultrasonic Planetary Core Drill team to the Mars analog site at the Haughton Mars Project. Results of this trip are compared to results obtained drilling permafrost simulant in the lab

Ultrasonic Planetary Core Drill: Overview and Results from Field Trial

In the effort to explore the subsurface of terrestrial bodies, we seek to obtain better samples from ever greater depths. Many organisations are working towards technologies that can achieve this goal whilst ensuring compatibility with the likely requirements of planetary landers in terms of mass, power, and dimensions. The Ultrasonic Planetary Core Drill (UPCD) was an FP7 funded project which aimed to develop such a planetary sub-surface sample acquisition system, developing the required drill hardware and testing it in a Mars analogue environment in Antarctica. The objective was to reach 30cm and containerise the samples using the least possible power, while operating at low weight-on-bit. This has been broadly achieved within a conceptually-deployable package