Deen Bai

Development of a rotary-percussive ultrasonic drill for extraterrestrial rock sampling

Compared with traditional rotary-percussive drills driven by electromagnetic motors, ultrasonic drills show advantages of small size, low power, low weight on bit, and lubrication free, making them available for the extraterrestrial rock sampling, especially for the minor planet with a weak gravitational field. To solve the problem that the conventional percussive ultrasonic drills cannot remove cuttings effectively, we proposed a rotary-percussive ultrasonic drill which realizes both rotary and percussive motions of the drill bit. The conventional percussive ultrasonic drills employ the vibration energy of the front mass of the Langevin transducers to generate mechanical vibration at the bottom surface of the horn, however, the vibration energy of the back mass is not utilized. Thus, we proposed to use the vibration energy of the back mass to generate a rotary motion via a longitudinal-torsional coupler. The rotary shaft drives the drill bit to rotate continuously to deliver the cuttings out so as to increase drilling efficiency. When the diameter of the drill bit is 5 mm and the axial load is 5 N, RPUD can drill the sandstone in rotary-percussive drilling mode with a speed of 12.4 mm/min while RPUD can only drill the sandstone at a speed of 8.7 mm/min in percussive drilling mode. Contrastive experiments show that the rotary-percussive drilling can actually raise the drilling efficiency compared with percussive drilling, which indicates that the RPUD is superior to conventional percussive ultrasonic drills.

On the modeling of levitation force for ultrasonic journal bearings actuated by piezoelectric transducers

Different from conventional hydrostatic or hydrodynamic journal bearings, an ultrasonic journal bearing provides carrying force by air squeeze film generated by high-frequency vibration of bearing bush surfaces. Detailed investigation indicates that studies on levitating force modeling based on fluid dynamics for ultrasonic journal bearings are rarely conducted, and the existing theoretical models generally neglect some significant contributors to levitating force such as gas inertia, surface topography, rarefaction effect, or boundary effect. A modified Reynolds-type equation considering these factors is put forward in this study to predict the ultrasonic journal bearing’s carrying capacity. The numerical solving results can interpret the experimental data well. The proposed model will provide theoretical reference for the design of ultrasonic journal bearings.

A Rotary-Percussive Ultrasonic Drill for planetary rock sampling

Conventional ultrasonic drills can drill into rocks using high frequency axial vibration, which feature lower power and lower preload force, thus they could become a very attractive solution for future deep-space exploration. However, drill cuttings cannot be removed effectively with the increase of drilling depth by conventional ultrasonic drills that only driven by longitudinal vibration. To address this issue, a Rotary-Percussive Ultrasonic Drill (RPUD) is proposed, which employs one single PZT transducer to generate rotary-percussive motion for rock fracturing. RPUD is composed of a PZT transducer, a percussive unit, a rotary unit, and a drill tool. The percussive unit enlarges the longitudinal vibration of front part of PZT transducer, and provides a reciprocating percussion to the drill tool. The rotary unit transforms longitudinal vibration of rear part of PZT transducer into longitudinal-torsional vibration to drive the drill tool to rotate continuously. The rotary and percussive motions are independent of each other, and can be adjusted separately. To make the rotary and percussive motions move synchronously, finite element method is employed to tune the resonance frequencies of the rotary unit and percussive unit to be close by transient analysis. Experimental results show that RPUD can improve removal efficiency of the drill cuttings due to its rotary motion, compared with conventional ultrasonic drills.

A Piezoelectric-Driven Rock-Drilling Device for Extraterrestrial Subsurface Exploration

The rocks on extraterrestrial objects contain plenty of original geological and biological information. Drilling and sampling are an essential task in lunar exploration or future explorations of other planets like mars. Due to the limitation of payloads, energies, and drill pressure, the investigation of a lightweight and low-powered rock-drilling device is crucial for explorations of distant celestial bodies. The ultrasonic drill driven by piezoelectric ceramics is a new drilling device that can adapt to the arduous space rock-drilling tasks in weak gravitational fields. An ultrasonic drill suitable for mounting on a planetary rover’s robotic arm is developed. The ultrasonic transducer’s energy conversion from electric energy to acoustic energy and the energy transmission from the horn’s high-frequency vibration to the drill stem’s low-frequency impact motion are analyzed to guide the design of the drill. To deeply understand the percussive drilling mechanism under high-speed impact, the interaction between the drill stem and the rock is simulated using LS-DYNA software. Drilling experiments on rocks with different hardness grades are conducted. The experiment results illustrate that the ultrasonic drill can penetrate into the hard rocks only taking a force of 6 N and a power consumption of 15 W. The study of ultrasonic drill will provide a reference method for sample collection of extraterrestrial rocks.

Experimental evaluating approach to a suitable Martian coaxial rotorcraft blade

This paper presents a detailed experimental approach for understanding and optimizing the hover performance of Martian UAV rotor, including a systematic discussion about several coefficients for hover characteristics and a detailed design approach for rotor blades of Martian UAV at Reynolds numbers lower than 50000. The discussed hover performance coefficients include figure of merit, thrust coefficient, thrust weighted solidity, power loading and disk loading, and these coefficients are also used to evaluate the hover performance of a specific rotor configuration. In addition, rotor parameters are investigated and analyzed in this experimental approach, including airfoil, camber, solidity, blade chord, number of blades and blade twist. These parameters are the major factors significantly influence the rotor hover performance. A detailed rotor design approach is proposed based on the experimental result by optimizing the hover performance coefficients and rotor parameters.

Design of experimental setups for evaluating hover performance of a Martian coaxial rotorcraft

In order to verify whether a small-scale rotorcraft can fly on Mars, this paper is proposed to establish a Martian atmosphere simulator and to design a hover test stand for coaxial rotorcraft rotor. Since the ultra-low air density of Mars is approximately 1/70 of that on the Earth, it is difficult to obtain enough thrust to lift the rotorcraft against Mars gravity. The proposed Martian Atmosphere Simulator (MAS) is composed of an evacuation chamber, a roots pumping system, vacuum gages, and an atmospheric pressure control unit. The seesawed hover stand mounted in the center of MAS, is employed to acquire the thrust and power characteristics with respect to blade collective pitch angle and rotational speeds. Experimental approach is proposed to evaluate the rotorcraft hover performance and endurance on Mars. The experimental setups provide a fundamental platform for further aerodynamics research of different types of blades and rotorcraft hover performance evaluation.

Impact Dynamics of a Percussive System Based on Rotary-Percussive Ultrasonic Drill

This paper presents an impact dynamic analysis of a percussive system based on rotary-percussive ultrasonic drill (RPUD). The RPUD employs vibrations on two sides of one single piezoelectric stack to achieve rotary-percussive motion, which improves drilling efficiency. The RPUD’s percussive system is composed of a percussive horn, a free mass, and a drill tool. The percussive horn enlarges longitudinal vibration from piezoelectric stack and delivers the vibration to the drill tool through the free mass, which forms the percussive motion. Based on the theory of conservation of momentum and Newton’s impact law, collision process of the percussive system under no-load condition is analyzed to establish the collision model between the percussive horn, the free mass, and the drill tool. The collision model shows that free mass transfers high-frequency small-amplitude vibration of percussive horn into low-frequency large-amplitude vibration of drill tool through impact. As an important parameter of free mass, the greater the weight of the free mass, the higher the kinetic energy obtained by drill tool after collision. High-speed camera system and drilling experiments are employed to validate the inference results of collision model by using a prototype of the RPUD.