Experimental Investigation of an Ultrasonic Motor for the Rotary Action of an Ultrasonic/Sonic Planetary Drill Dimitris Drazinos Introduction It has been suggested that lightweight rotary-hammer drills, that require low preload and power input, are ideal for remote planetary drilling operations. The hammering action of the drill is provided by an ultrasonic/sonic drill that incorporates a free-mass between the horn tip and the drill bit. The free-mass converts ultrasonic to sonic energy through continuous impacts with the horn tip and drill bit’s head, generating a stress at the bit’s rock interface [1]. When that stress exceeds the rock’s strength, the rock fractures. Ultrasonic motors could be potential rotary actuators for planetary hammer drills, as they require low power input, they are able to operate in extreme conditions and they weigh much less than conventional electric and electromagnetic motors [2]. The Ultrasonic Motor It has been proposed that ultrasonic motors with longitudinal- torsional converter horns generate higher torque compared to other types [3]. Such a horn has the same shape as a standard ½ wavelength step horn, tuned to a resonant longitudinal frequency, with the only difference being the 45̊ angle diagonal slits machined on the nodal point. The diagonal slits generate vibrations of elliptical trajectory on the surface of the step, and when a hollow cylinder (rotor) is in contact with it, it rotates. The horn’s tip vibrates longitudinally. Ultrasonic motor with longitudinal-torsional converter horn Test Rig and Methods A test rig was designed and manufactured in order to mount the transducer and motor assembly as well as a force transducer so that the driving force could be measured under various loads. The design included two arms bolted to the rotor, that provided a flat surface to contact the force transducer as well as a uniform load. CAD model and set-up of the test rig Once a steady state driving force was measured by the force transducer, the torque, τ, was calculated. τ=F∗r Then rpm of the rotor was measured by using a laser tachometer while the resultant power output and efficiency, η, of the motor were calculated. Power Output = τ ∗ rpm ∗ 2π 60 η= Power Output Power Input ∗ 100% The average power input was 53.5W (52-55W) and the excitation input amplitude was 2μm, while the loads varied from 0N to 9N. The motor was driven at resonance, approximately 20kHz. Results The maximum rpm measured was 890rpm under 9N of load on the rotor, at a torque of 0.058Nm and efficiency of 10.15%. Torque against various loads on rotor RPM against various loads on rotor. It was observed that the rpm, torque and efficiency were increasing while the load was increasing. Efficiency against torque When the loads were placed on the arms, the rpm measured was significantly higher, 1455rpm under 4N of load on each arm (8N in total). Due to experimental limitations though, it was not possible to measure the driving force and calculate the torque. Rpm response under loads on arms. References [1] P. Harkness, M. Lucas, A.Cardoni, ’’Maximization of the effective impulse by a High-Frequency/Low Frequency Planetary Drill Tool,’’ IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol. 58, No. 11, 2011. [2] S. Sherrit, L. Domn, X. Bao, Y. Bar-Cohen, Z. Chang, M. Badescu, ‘’Single Piezo-Actuator Rotary-Hammering (SPARH) Drill,’’ Proceedings of SPIE Smart Structures and Materials, San Diego, paper # 8345-79, 2012. [3] J. Tsujino, R. Suzuki, M. Takeuchi, ‘’Load characteristics of ultrasonic rotary motor using a longitudinal-torsional vibration converter with diagonal slits. Large torque ultrasonic rotary motor,’’ Ultrasonics 34, 265-269, 1996. University of Glasgow, charity number SC004401 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 1 2 3 4 5 6 7 8 9 10 Calculated Torque (Nm) Load on Rotor (N) Torque 0 100 200 300 400 500 600 700 800 900 1000 1 2 3 4 5 6 7 8 9 10 RPM Load on Rotor RPM 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.00% 2.00% 4.00% 6.00% 8.00% 10.00% 12.00% Torque (Nm) Efficiency, η 0 200 400 600 800 1000 1200 1400 1600 0N 2N 4N 6N 8N RPM Load on Arms (N) RPM