Dynamic Modeling And Applications Of Excavation For Lunar Regolith

With a successfully development of deep space exploration mission, especially for the stage III of Chang E project, the excavation of lunar regolith becomes the focus of the current research. It is difficult to simulate or test the dynamics of the lunar regolith excavation on earth environment, because of the influence of1/6gravity and lunar regolith’s adhensive sand type. Moreover, the difference between lunar regolith and earth soil in Marco physical properties will make it hard to use the traditional empirical resistance formula for lunar surface environment. Therefore, to get a grip on the dynamics of the lunar regolith sampler, and for further improvement of the excavation control accuracy, the dynamics modeling of lunar regolith excavation is been researched based on the domestic and foreign research results and the correcting of resistance coefficient and rheometry parameters.To counteract the problems of simulation and analysis of lunar regolith’s mechanical properties in1/6gravity environment, a viscosity-elastic contact model with adhension is established using discrete element method (DEM). By using multiple-output Least Squares Support Vector Machines, self-adaptor Genetic Algorithms (AGA) and real lunar regolith trixial testing data, the sphere particle equivalent micro parameters which can describe lunar regolith’s macroscopic mechanical properties is standardized.Penetration is an important phenomenon in lunar regolith excavation. It can separate the sample from lunar regolith in suit by the bucket’s penetration action. In order to predict the penetration resistance of lunar regolith, a penetration resistance model in1/6gravity environment is established by combining the static earth pressure theory and Kostritsyn resistance formula. According to the relevance between porosity, grandation and lunar regolith mechanical properties, the earth pressure coefficient and the specific resistance are corrected by DEM confined compression simulation, and the friction coefficient is corrected by DEM friction testing simulation. On this basis, By comparison an example’s penetration resistance which is calculated respectively by prediction model and discrete element model, the correctness and accuracy of penetration model are verified.Cutting is the other important phenomenon in lunar regolith excavation. It can make the lunar regolith moved as an entire substance in cutting action. In order to predict the cutting resistance of lunar regolith, a cutting resistance model,which is suitable for the translation motion and top rotation motion, is establish by using the mothod of level layer element. According to the feature of the non global convergence in the cutting model, a new solving method which integrated the DFP and genetic algorithms is proposed, and it realizes the solution of the resistance distribution. According to the relevance between lunar regolith basic properties and shear strength, the lunar regolith conhesion and internal friction angle are corrected by DEM triaxial testing simulation. On this basis, By comparison the cutting distribution which is calculated respectively by prediction model and discrete element model, the correctness and accuracy of cutting model are verified.The actual excavation process is very complicated, the bucket shape and the lunar regolith accumulation influence the excavation resistance. Therefore, an excavation resistance model considing penetration and cutting action is established based on Hemami excavation theory. On this basis, using the excavation resistance model in optimization of bucket penetration angle, calculating the specified lunar regolith’s excavation resistance in condition of the rotation action and shoveling action, and then analyze the optimal structure parameters in minimum resistance using AGA.Meanwhile, according to the soil rheological theory, a variable excavation force makes the lunar regolith vibrate. So a lunar regolith’s parallel connection Iwan model is established, and the Iwan parameters are calculated by DEM dynamic trixial testing. Finally, a lunar regolith simple substance2-DOF vibration equation which is used in soil-tool interaction is established by using this Iwan model. On this basis, using the excavation dynamics model in control algorithm design of sample manipulator. With this object, a4-DOF flexible manipulator model is created using modal synthesis method, an excavation strategy is designed, and an excavation controller based on computed torque method is achieved. In view of the characteristic that different lunar regolith owns differnet marco parameters, this paper estimates the regolith in suit in early stage of the excavation, making use of Newton-Raphson method, then corrects the controller parameters by this estimation value, to improve the excavation control accuracy.