Research On Rotary Percussive Ultrasonic Drill With Bidirectional Drive And Its Performance

The acquisition of geological samples on the surface or underground of extraterrestrial bodies is of great significance to the analysis of mineral composition of stars,the study of the evolution process of celestial bodies and the detection of the existence of life signs.In planetary exploration missions to obtain soil or rock samples,drilling is often the method of choice.However,the challenges facing conventional drilling devices driven by electromagnetic motors are the large axial forces and holding torques needed,which means that a probe should have a relatively large mass.During drilling rocks,the weight on bit applied on the drilling devices is usually provided by the gravity of the lander.When the carrier samples in a weak gravitational field environment,the carrier provides a limited weight on bit for the drills,which limits the application of the conventional drilling devices.To address these challenges,ultrasonic drills that employ the high frequency longitudinal vibration of a piezoelectric actuator to fracture rocks were developed.Compared with conventional drilling devices,the ultrasonic drills have the advantages of having a small size,low power,low axial force,and small holding torque.Based on the engineering background of rock drilling sampling in the outer body detection,a Rotary-Percussive Ultrasonic Drill(RPUD)driven by a single piezoelectric ceramic stack is proposed in this paper.The vibration energy of one end of the piezoelectric stack is used to drive the drilling tool to make a percussive motion,and the vibration energy of the other end drives the drilling tool to make a rotary motion.Around the research of the RPUD,the following work was carried out: 1)Design and research of longitudinal & longitudinal-torsional transducer for the RPUD;2)Dynamics model and energy transfer characteristics analysis of the RPUD;3)Study on vibration characteristics of the transducer direct drive drill;4)Experimental study on drilling performance of the RPUD.A stepped horn is used to amplify the longitudinal vibration of one end of the piezoelectric stack,and a high-frequency simple harmonic vibration is generated at the bottom of the horn.A longitudinal–torsional convertor is used to convert part of the longitudinal vibration of the other end of the piezoelectric stack into torsional vibration,and elliptical motion trajectories are formed at the output ends of the convertor.The modal analysis of the transducer is performed by means of a finite element simulation method to determine the first-order longitudinal mode and resonant frequency of the transducer.A harmonic response analysis is performed on the transducer to estimate the amplitudes of the vibration displacements at the outputs of the transducer.A transient analysis of the transducer is carried out to draw the elliptical motion trajectories of the transducer's rotary output s.The influences of the structural size parameters of the stepped horn and the longitudinal–torsional convertor on the vibration displacement amplitudes of the transducer outputs are simulated.The acoustic impedance equivalent network model of the piezoelectric transducer is established,and the corresponding relationship between the acoustic impedance and the frequency of the transducer is analyzed.Structural design of the RPUD is completed.According to the vibration characteristics of the RPUD before rock drilling and during rock drilling,reasonable assumptions are made to establish the vibration model before rock drilling and the vibration model during rock drilling.Two collisions(the collision between the transducer and the free mass and the collision between the free mass and the drill tool)are analyzed.The numerical simulation analysis of the vibration model of the RPUD is carried out to study the influence of parameters such as weight on bit,free mass and restoring force on the vibration characteristics of the RPUD.Structural design of the transducer direct drive drill is finished.According to the working characteristics of the drill under no load and under load,the vibration models of the drill are established on the basis of reasonable assumptions.The contact collisions between the transducer and the drill tool in two working conditions are analyzed.The numerical simulation analysis of the vibration model of the transducer direct drive drill under no load and under load is carried out.According to the test requirements of the drilling performance of ultrasonic drills,the drilling performance testing platform for ultrasonic drills is developed.Using a laser displacement sensing system and an impedance analyzer,the influences of the tightening torque on the amplitude of the longitudinal vibration and the resonant frequency are experimentally studied to determine the optimal tightening torque of the transducer.Several experiments are conducted to investigate the effect of excitation voltage frequency and amplitude on the drive characteristics of the transducer to determine the optimum excitation frequency.Comparison test for percussive drilling and rotary-percussive drilling is carried out to verify the superiority of the rotary-percussive drill to percussive drilling.The drilling performance tests are carried out on the RPUD,and the influence of weight on bit,free mass,restoring force,et al on the drilling performance of the drills are obtained.Aiming at rock drilling sampling on the surface of extraterrestrial bodies in deep space exploration,this paper presents a bidirectional driving rotary-percussive ultrasonic drill.The drill has the advantages of small size,light weight,low power consumption,low weight on bit and wide temperature resistance.It can provide a feasible technical reference for rock sampling of extraterrestrial bodies such as Mars and asteroids.