Study Of Lunar Soil Excavation Acquisition And Mechanical Parameters Identification Based On Robot Arm

Exploring the unknown domain, such as universe, might be the eternalmotivation of human advancement. United States, the former Soviet Union,Russia and etc. have done some exploration and sampling analysis ofextraterrestrial planets. As a budding rising space powers, China, is also planning“circling”,“landing” and “returning” as the three-stage of the lunar explorationprogram. In the exploration process, energy comsumption and plantary soilparameter identification are two major focus. With the support of “surfacesampling mechanism and plantary soil parameters identification” for the ChineseLunar Exploration Plan Stage III, this disserstion aims to design a set of robotarm end-effecot which can complete the plantary exploration, sampling,acquisition and return tasks, develop a reliable plantary parameters identificationalgorithm and optimize the excavation strategy which based on the parametersidentification results to reduce the energy consumption.Due to the uncertainty of the lunar surface and unpredictability of theparticle movement in the low-gravity environment, the simulation analysis wascarried out via EDEM software aiming at the fluidity of lunar soil particle underlow-gravity environment. The influence rule of inner frction angle and soil-toolfriction angle on the fluidity of lunar particle was acquired as well as the theoptimal percussion frequency and direction of the percussion mechanism on theend-effector. Meanwhile, applying the bionic design theory, the shape of diggingshovel on the end-effector was optimized to ensure the lowest excavationresistance. Based on these studies, a highly integrated end-effector with multi-funtions, such as acquisition, cathing, locking and percussion, was designed.This paper took the soil mechanics of soil-bucket as the foundation oftheoretical analysis. Based on this theory, this paper analyzed the determinationmethod of the plantary soil strength failure, the force stauts of retaining wallpressure distribution and soil limit equilibrium and quantitative analyzed the soilshear slip under the ideal conditions to make sure the location of slip surfaceunder the initiative and passive soil pressure, in order to establish the soil-bucketdigging force model. Different from the common bucket, the shape of this bionic designed bucket is curved. Consequently, a method which based on the micro-element method to analyze the isolated body limit equilibrium force was appliedin this paper. Through the two-dimensional stress analysis of the micro-elementmodel, the earth pressure force calculation model under the initiative and passiveearth pressure conditions were established to obtain the function between thepeak digging resistive force and the plantary soil parameters. Based on the aboveoutcomes, a Newton Accelerate the iterative algorithm based plantary soilparameters identification algorithm was introduced to achieve the identificationof the soil density, the soil internal friction angle and the friction angle betweensoil and bucket.This paper established a mathematical model which contains the excavationvelocity effect, the bucket edge effect and bucket shape effect, quantitativelyanalyzed the key excavation parameters, obtained the effect of angle of attackand excavation velocity on excavation resistance. Also, based on the analysis ofthe three stage of excavation process, penetrate, drag and curl, this paperintroduced the thought of hierarchical optimization that contains the outer andinner layers. The outerlayer set the excavation energy consumption as target tooptimize the excavation path. The inner layer set the digging force as target tooptimize the angle of attack. The double layers were calculated by the geneticalgorithm. Then, an objective function was established which takes theexcavation time and energy consumption as the comprehensive specification.Continuous nonlinear optimization problem was transformed to a standarddiscrete convex optimization problem by the variable transformation to calculate.After this, the optimal excavation trajectory that based on the time-energyconsumption could be achieved.Finally, this paper used the existing equipments of the laboratory to bulid upa testbed to verify the feasibility and reliability of the end-effector function, thesoil parameters identification algorithm and optimal excavation strategy.