Research On Piezoelectric Actuated Mobile Systems Of Micro Lunar Robotic Rover

Deep space exploration holds exceptional significance in establishing continuous and vigorous survival environments by providing potential for exploitation of living resources and expansion of living spaces for human beings.Especially facing the contradiction between the explosive growth of the total number of human beings and the inability of other resources to continuously increase,deep space exploration becomes more and more realistic meaning.Planetary exploration,as a major part of deep space exploration,is an important approach for the exploration of extraterrestrial resources,the search for life,and investigations of the origin and evolution of the universe.Planetary rovers,acting as the executing mechanism of planetary exploration missions and the carrier of detecting instruments,are the basis to ensuring the efficient and reliable completion of planetary exploration missions.Lunar robotic rovers,the earliest planetary rovers developed,have provided a large amount of scientific data for further understanding of the moon.In order to reduce the cost of delivery via optimizing the volume and weight of the lunar robotic rover,its integration is continuously increasing,thus creating the challenge of finding the balance between the reliability and cost.With the rapid advancement of sensors and artificial intelligence technologies,lunar robotic rovers is moving towards to be micro swarm intelligent system.As multi micro lunar robotic rovers with simple functionality enable the cooperation in order to accomplish complex lunar surface exploration missions.This changes the existing individual combat mode of deep space exploration,improves the efficiency of coverage per unit time,and reduce the probability of failure due to the failure of a single rover.Simplifying the mechanism and improving the reliability are the main objectives of this dissertation.The piezoelectric excitation and friction drive principles are applied to the actuation of mobile systems of the micro lunar robotic rover.Taking into account 1)the advantages of wheeled mechanism with high maneuverability,high operating performance and high efficiency,as well as its shortcomings of the poor adaptability of movement pairs and lubricant on the lunar environment,2)the merits of a large contact area,pressure balance,adaptability to rough surface and strong obstacle-crossing ability and the drawbacks of complex gear systems and heavy weight of the tracked mechanism,a novel principle of directly driving wheel or track is proposed by constructing an integrated piezoelectric actuated frame in terms of vibration and friction.Design theory and method are expected to be established to improve the driving efficiency by investigating the factors influencing the driving efficiency and stability.Thus,as the wheeled mobile system and tracked mobile system have no movement pair,no lubricant,a light weight,and compact structure,they can be constructed in order to explore the new structure and new method of mobile systems of the micro lunar robotic rover.To conclude,the main contributions of this dissertation are as follows:1.According to the development status and trend of wheeled and tracked planetary rovers,combined with the lunar environment,a novel idea of applying swarm intelligence technology to micro planetary rovers is proposed.In terms of the research status and characteristics of the surface-bonded type and sandwich piezoelectric transducers,dynamics modeling theory and structural optimization method are analyzed.2.A new modeling approach is developed and proposed based on the classical transfer matrix method?TMM?to describe the electromechanical coupling dynamic behavior of piezoelectric transducers.Transfer matrix equations are created to describe electromechanical coupling dynamic characteristics of piezoelectric composite structures operating in the d₃₁ mode and d₃₃ mode of the piezoelectric element,respectively,when they are excited to vibrate at the pure longitudinal vibration,pure bending vibration,and longitudinal-bending coupling vibration,respectively.Taking state vectors as intermediate parameters and combining connection conditions of interfaces can be extended to the whole piezoelectric composite structure,to characterize the complete dynamic behavior of complex structures.3.A sandwich piezoelectric transducer is proposed to construct three-wheeled mobile systems.Exploiting the characteristics of high electromechanical coupling factor and excellent output performance of the piezoelectric transducer designed with the d₃₃ mode of the piezoelectric element,the double driving foot of the sandwich piezoelectric transducer can achieve synchronous actuation function by means of the multi-vibration-mode coupling,realizing a state in which the two driving wheels are directly driven by friction.An electromechanical coupling model is created for the multi-vibration-mode coupling sandwich piezoelectric transducer,in order to describe the dynamic behavior of its overall structure.Experimental results show that the maximum mean velocity of the three-wheeled mobile system reaches 99.3 mm/s and its maximum traction force is 2.6 N.4.A surface-bonded type piezoelectric transducer with a frame structure is proposed to construct a surface-bonded type piezoelectric actuated tracked mobile system.Combining the advantages of a large contact area,pressure balance,adaptability to rough surface,and strong obstacle-crossing ability of tracked mechanisms,the surface-bonded type piezoelectric transducer is designed in terms of the d₃₁mode of the piezoelectric element.It holds the characteristics of flexible structure design,easy installation and miniaturization.A novel piezoelectric actuating principle is formed for the tracked mobile system of lunar robotic rovers.This is due to the fact that in-plane bending traveling waves with the same rotational direction are simultaneously produced in the four driving rings of the surface-boned type piezoelectric transducer under the excitations of two phase different electrical signals,leading to the track driven by friction.By changing the temporal phase difference between the two excitation signals,the surface-bonded type piezoelectric actuated tracked mobile system can achieve bi-directional motion.Experimental results show that the prototype of the surface-bonded type piezoelectric actuated tracked mobile system can realize the speed of 57 mm/s.5.A sandwich piezoelectric transducer is proposed for the construction of a sandwich piezoelectric actuated tracked mobile system.Using the characteristic of the high output power of the d₃₃ mode of piezoelectric element,the track is driven by friction as two in-plane bending vibrations are coupled and superimposed to form bending traveling waves with the same rotational direction in the two driving rings of the sandwich piezoelectric transducer.By adjusting the temporal phase difference of two excitation signals,the rotational direction of traveling waves of the two driving rings can be changed,thus changing the motion direction of the sandwich piezoelectric actuated tracked mobile system.The output performance of the sandwich piezoelectric actuated tracked mobile system is greatly improved through preload optimization.Experimental results show that the maximum climbing height of the prototype system reaches 207.8 mm and the maximum traction force exceeds 6 N.The preliminary experiment of lunar simulation environment is carried out.