| With the progress of various types of missions in lunar exploration engineering,our country has now put its eyes on the permanent shadow of the South Pole of the moon,and plans to carry out the lunar polar resource exploration mission,requiring the collection and detection of lunar soil on the spot.The collection and transfer of lunar soil is planned to be accomplished by a sampling robot arm,which relies on the end-effector to carry the absorbing slice to realize the circumferential sampling and axial push out the slice delivery.Based on the extreme vacuum and low temperature working environment,the transmission accuracy and characteristics of the screw drive mechanism of the end-effector was studied.According to the task requirements of the sampling manipulator,the overall scheme of the end-effector,namely the sampling tube,is designed.The two functions of rotary sampling and axial feeding are integrated.Only a single motor is needed to drive,and the two actions are decoupled by a double ratchet reversing mechanism.The axial feeding plate is realized by the axial movement of the screw drive mechanism nut.Considering the thermal deformation errors caused by temperature,the precision model of screw drive was established based on various errors,which were divided into macro and micro temperature errors.The accuracy design is carried out for the given tolerance,the transmission error distribution is analyzed by Monte Carlo simulation,and the transmission error under different temperature gradients was analyzed.It showed that the reasonable selection of material linear expansion coefficient can play a certain role in compensating the error.The model of load spring group of screw pair was established,which can calculate load percentage of thread in each turn theoretically,and the parameters in the model were optimized by finite element simulation.The load model of screw pair at low temperature was established by introducing the difference of thermal deformation clearance.The critical load conditions of each coil of spiral pair were deduced.The critical load varies with temperature,and the critical load was verified by finite element simulation.Based on the sliding friction model of screw pair,the efficiency of screw transmission was deduced,the influencing factors of transmission efficiency were analyzed,and the solid lubrication method suitable for deep space exploration was studied.The transmission efficiency of screw pair under different load,friction coefficient and number of meshing turns was studied by ADAMS simulation.The equivalent thermal deformation and the nut opening of the dust tank were also simulated.On the whole,the reduction of the thread contact surface would improve the transmission efficiency.The experiment platform of screw transmission efficiency was built,and the experiment of transmission efficiency of different screw pairs was carried out,which was basically consistent with the simulation results.The transmission efficiency experiments under the interference of lunar dust showed that the dust tank can adapt to the lunar dust and improve the transmission efficiency.In addition,for a small amount of lunar dust,the dual-capacity dust tank has stronger adaptability,while for a large amount of lunar dust,the four-capacity dust tank has stronger adaptability. |
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