| In the transition phase of the lunar exploration phase IV mission objective "Survey,Build,Use",the focus is on the formation of the lunar research station,which is also to lay the foundation for the subsequent lunar base construction as a pavement.The rotary drilling of pile holes for building foundations in microgravity environment is undoubtedly one of the key points of research and exploration.The design and manufacture of rotary drilling equipment can provide constructive guidance and reference for the construction of the lunar base foundations and even the deep space exploration missions in the future.Based on the microgravity environment,this paper takes the lunar soil drilling device as the object,considers the interaction between the drill head and the lunar soil,and investigates the dynamic characteristics of the device during the drilling process.First of all,for the special external environment and the project requirments of the overall structure of the device,the NGWN-type planetary gear reducer in the power head is selected for structural design and analysis;the transmission and pressure device on the drilling mast is replaced by the planetary roller screw system,and the structural design and some dynamic characteristics are analyzed.Finally,based on the discrete element method,a multi-body dynamics coupling model between the particle dynamics of the lunar soil and the device is established,and the dynamic characteristics of the coupled device are analyzed by combining the displacement,force and torque of the reducer output to the drill bit.Observed the difference between the force and moment of the drill bit in the two cases of coupling and uncoupling and the two cases of gravitational acceleration of the earth and moon and the force and torque of the lunar soil feedback to the device.The main contents are as follows:1.Analyzed the project requirements of the target foundation pile and based on the soil micro-element method the summary of the forces and moments on the drilling device is made.According to these general estimation of the total forces and moments on the drilling and the obtained power demand,the NGWN-type planetary gear is selected as the object and the structural design of the gear is completed.Based the concentrated mass method,the kinetic equations of the planetary gear system are established and Newmark-β is used to solve the kinetic equations to obtain the displacement,force and moment of the device during the drilling process to provide feedback input for subsequent coupling.2.Considering the practicality of pneumatic and hydraulic devices in microgravity environment,the planetary roller screw system is used to provide driving and pressuring function for the power head.The target structure is designed with the standard planetary roller screw as the object,and the target structure is initially matched with the parameters to complete the displacement modification of the roller end teeth.Based on the Lagrangian method,the dynamics equations of the standard planetary roller screw are established and solved.The friction coefficient,screw speed and nut load are selected and changed to investigate the dynamic characteristics of the system.A three-dimensional model of the system is established and dynamic simulation is done.3.The dynamics equations of the drilling device based on the discrete unit method coupled with system dynamics is established.The forces and moments of the lunar soil in the drilling process by the commercial software EDEM is calculated,which are used as input datas to the dynamics equations.And then obtained the displacements,forces and moments from dynamics solution,the datas are feeded back to the discrete element calculation of EDEM as input datas,so the discrete element method and system dynamics coupled dynamics is establish to solve this.Through the design and verification of the important structure of the rotary drilling device in microgravity environment and the simulation of the drilling process,a set of design and simulation process are obtained,which will provide a reference for China’s extraterrestrial exploration space career. |
