Research On Mechanical Modeling And Control Strategy Of Drilling And Coring In Lunar Soil Simulant

With the rapid development of space technology, the mankind continues the further exploration of the universe. The exploration of extraterrestrial celestial bodies has become the research focus around the world in the new round of space exploration. The drilling and coring device is the main equipment for planetary subsurface sampling. Although the United States and the former Soviet Union have successfully landed their spacecrafts on the Moon and Mars, our research on designing autonomous drilling and coring used in planetary exploration is still in its infancy, and there are a number of key technologies require breakthroughs. This dissertation study is supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China to carry out research on drilling and coring mechanism characteristics and related key technologies to provide essential theoretical foundations that support unmanned planetary exploration.Interactions between the sampling drill and lunar soil simulant must be investigated in advance to evaluate the drilling load and coring rate on th e Earth. It is necessary to measure the mechanical properties that are distributed in a longitudinal direction during the preparation of the lunar soil simulant. Until now, there is a lack of research on reporting systematic method for measurement estimation in the literature. The flat dilatometer test(DMT) is an in situ civil empirical method for soil type identification and settlement prediction that analyzes the test results by depth. Because the empirical formulas used in the standard DMT method aim to cover various soil types, the accuracy of mechanical properties estimation for a specific soil type is limited, especially for well-distributed artificial soil, such as lunar soil simulant. This paper proposed a modified DMT method that considered relations of compressibility, shear strength and bulk density as additional information for the DMT result analys es. Based on the relationship between the DMT constrained modulus(MDMT) and depth, the distributions of bulk density and shear strength could be derived accurately from the subsurface lunar soil simulant. The test results were consistent with both theoretical analysis and Apollo estimation in bulk density. The contribution of this dissertation study is to provide a feasible approach to obtain the longitudinal distribution of the mechanical properties for the subsurface lunar soil simulant.The interaction between drill tools and lunar soil played an important role in the field of structure designing, performance evaluation, dynamic control and simulation of lunar automatic sampler. However, research on the interaction between drill tools and lunar soil was not sufficient to reveal the source of drilling load. Based on the theory of passive earth pressure, this paper proposed that the soil on the rake face of blade was composed of deposition zone and failure zone on different cutting phases. According to the analyses of the contribution from deposition zone and failure zone to the total drilling load, a drilling load model of penetrating loosened lunar soil simulant was established. In the end, the drilling load model was verified based on the experimental results of HIT-LS1# lunar soil simulant and HIT-2 drill bit.During the design of drilling and coring mechanism for lunar exploration, a coring method based on a flexible tube can obtain slim continuous sample core, which enables high coring rate and preserves the stratification information of the subsurface samples. Since the complex movement of lunar soil particles during the flexible tube coring, there is no systemic method to analyze factors that determine the coring quantity. This paper analyzed the flowage of the lunar soil particles in flexible tube and established the coring model of the flexible tube based on the theory of limit equilibrium. The mechanical boundary conditions of the model were interactions between lunar soil and coring drill tools and among each part of lunar soil. The coring model described the dynamic process of lunar soil flowing from the outside of coring drill tools into the flexible tube. A numerical prediction method for coring rate was proposed based on the coring model. Drilling parameters, lunar soil properties and drill tool structures were analyzed as key factors of coring rate. A verifying experiment with simulant of lunar soil HIT-LS1# and drill tools HIT-2 was implemented on a simulated drill test bed. The average error between the experimental results and the predicted results was less than 5%.In lunar drilling and coring missions, it is found that the lunar soil and the lunar rock differ from each other in mechanical properties. The stratification of the landing zone varies in a large scale along vertical direction, which causes the task full of risks. To meet the requirements of sampling mission on lunar surface unde r the load safety conditions, the drill control strategy should adapt to the complex environments. Therefore, the online recognition of drill medium should be employed to achieve real-time drilling parameters adjustment. This paper analyzed the characteristics of signals in the process of blades contacting and penetrating rock block and proposed an online recognition method based on safety drilling parameters. This method employed artificial neural networks to recognize typical drilling medium under safety drilling parameters and employed continuous wavelet transform methods to recognize interfaces. An autonomous drilling process was proposed based on online recognition, which provide a foundation to improve the environmental adaptability of autonomous drilling.According to the 3 drilling states of interface detection, initiating DPR and drilling medium recognition with initiating DP, appropriate drilling parameters for each drilling state were analyzed to propose a multi-state autonomous drilling control method based on finite state machine. A drilling and coring experimental system was developed and validation experiments with multi-layered drilling simulated environments constructed by lunar soil simulant and lunar rock simulant and experimental drilling tools were implemented. The experimental results revealed that the multi-state autonomous drilling control method is capable of detecting drilling state variation and adjusting drilling parameters timely to adapt to different drilling loads and vibration interferences. This provided a feasible reference for the control of extraterrestrial autonomous drilling.