Parameters Optimization And Reliability Analysis Of Lunar Drilling Sampling Mechanism

Based on the Chinese lunar exploration project phase three drilling sampling as the background and the full analysis of research status of mechanism of lunar drilling sampling in domestic and foreign, to carry out parameters optimization and reliability analysis of lunar drilling sampling mechanism.First, in respect of the sampling process of the hollow–external–screw drill stem for automatic drilling sampling mechanism, the mathematical models between the cohesive force, friction coefficient of lunar-soil and the lunar-soil depth are built separately; and the relationships between drill stem kinematic parameters(drill stem drilling speed and rotary speed) and the structural parameters(drill stem spiral angle, outside diameter, groove width ratio and spiral grooved depth in the drilling process) are also established. These models take into account not only characteristics of lunar-soil physical and mechanical parameters changing with drilling depth, drill stem drilling convected velocity, but also the shear resistance among lunar-soil infinitesimals. Such approach subjects the drill stem’s parameters to the job requirement of lunar drilling sampling. The effectiveness of the model is validated, and the analysis of the influence of the drill stem structural parameters on its kinematic parameters is conducted with the models. As a result, the influence law of the drill stem structure parameters on its kinematic parameters is revealed, and the best value range of drill stem structure parameters is obtained. Taking the minimum value of the ratio between the drill stem rotary speed and drilling speed as optimal object, the structural parameters as design variables, and based on genetic algorithm, the structural parameters of drill stem are optimized. Before and after, the ratio between the drill stem rotary speed and drilling speed is reduced by 13.8%. The research results will reduce the energy consumption and improve efficiency, which provide theoretical basis for design of automatic drilling sampling mechanism.Second, based on the analysis of the output of lunar soil principle and the(resistance moment) output of lunar soil resistance of spiral drill stem, the impact of lunar soil in the spiral groove regolith on drill stem driving torque, the valued field of helix angle and axial drilling power drill stem are considered, and models of drill stem driving torque, axial loading force and power consumption model are established, then effects of structural parameters such as the outer diameter of drill stem, the depth of spiral groove, groove width ratio and helix angle on the driving torque and the axially loading force of drill stem are analyzed by using the above models, and the rule of effect of structure parameters on the driving torque and the loading axially force of drill stem is obtained. Both mass and power consumption of drill stem are selected to be two-objective optimization, outer diameter of drill stem, depth of spiral groove, groove width ratio, helix angle and other parameters are taken as design variables, and the structure parameters of drill stem are optimized by using Genetic Algorithm. The power consumption is reduced by 31.8% and the mass of drill stem is reduced by 23.3% after optimizations, thus reducing the risk of drilling and providing a theory basis for the design of automatic drill sampling mechanism.Based on the analysis of output of lunar soil resistance,driving torque and lunar failure field of spiral drill bit, the mechanical models of drill bit are established, considered the pressure and frictional force between the lateral surface of cutter and lunar, and considered the effect of the surface load of lateral failure surface on circumferential torque, total power consumption of drill bit and drilling power drill stem are considered, and models of drill bit driving torque, axial loading force and power c and lunar soil failure distance, the model are established by simulation and trial(the maximum error less than 10.63%). Deep soil constitutive relation of Mohr-Coulomb model is adopted in simulation process, which makes the simulation more accord with actual situation that internal friction angle, is more than 22°. The rule of effect of structure parameters of drill bit on the power consumption and failure distance of cutter is obtained by using the models. power consumption of drill bit are selected to be objective optimization, and the structure parameters of drill stem are optimized by using Genetic Algorithm. The power consumption is reduced by 34.8% after optimizations, thus reducing the risk of drilling and system energy consumption, providing a theory basis for the design of drill bit of automatic drill sampling mechanism.This paper proposes a hierarchical modeling approach of mechanical and physical properties of rock and soil with the change of depth, and the constitutive law of rock and soil is established by this method, which is more close to the real situation of the lunar soil. The movement process of drilling into lunar soil of drilling sample mechanism is simulated, relationship between drilling resistance, peripheral driving torque of lunar soil of drilling automatic sampling mechanism and drilling depth is analyzed respectively, and make the comparison between theoretical and experimental data to verify the correctness of the mode, and provided a favorable basis for correction and design of the test of drilling automatic sampling mechanism.At last, the establishment of fault tree model for drilling automatic mechanism is established, and analyze the fault tree, one or two order minimum cut sets list for failure of drilling sampling is given, which provide guidance for reliability design of drilling automatic sampling mechanism.