The Study Of Dynamical Modeling And Mobility Performance On The Four-Wheel-Rhombus-Arranged (FWRA) Mobility System

The lunar exploration tasks require that the mobility system of a lunar rover must have the capability to carry up the payload for large-area and long-term exploration. The environment of the lunar surface is severe and unpredictable such that the high mobility performance is the key technique for the mobility system.The mobility performance of the four-wheel-rhombus-arranged mobility system (FWRA) of a new concept lunar rover is investigated and some new modeling methodologies are developed in this dissertation. The main works are summarized as follows:(1) The structure properties of the four-wheel-rhombus-arranged (FWRA) mobility system are analyzed and the physical prototype is developed. In order to possess the characteristic of high obstacle-climbing capability and turning maneuverability, the mobility system integrates the indepENDent active suspension with the passive rotary link structure and is equipped with the offset steering mechanism. The active suspension with swing arms improves the rover’s capacity to escape from trapped environment and the passive rotary link structure guarantees the continuous contact between the four wheels and the terrain. Using the suspensions and the offset steering mechanism, the off-road performance of FWRA mobility system can be improved considerably.(2) In order to investigate the obstacle-crossing capability, the mechanical judging method is put forward based on quasi-static theory. The obstacle-crossing capability can be judged by the road adhesive coefficient in this method. According to this method, the quasi-static equations of the FWRA mobility system are developed to compute the road adhesive coefficient while the wheels cross the dIFferent obstacles. THEN, the obstacle-climbing capability of FWRA mobility system is analyzed. Due to the adjustable property of the swing arms, the influence of swing arms on the climbing-capability is studied. Besides, the minimum value of the turning radial is considered to be the judging criterion on turning quality. The influence of the steering mechanism on the turning performance of the mobility system is investigated according to this criterion. In comparison with a six-wheel rocker-bogie mobility system in theory, the FWRA mobility system shows the higher mobility performance.(3) A new modeling method for dynamic interactive behavior of rigid wheel traveling on the loose soil is put forward. Using this method, the surface and grousers of the wheel are both divided into finite elements. According to the sinkage-pressure theory and Jacce theory, the forces acting at the elements are discrete and computed separately. Thus, the distribution of the normal and shear stresses at the interface between wheel and soil can be analyzed and the drawbar pull and torque of the wheel can be predicted. In order to validate this model, the virtual simulation is developed to study the drawbar pull and the torque of the wheel. The analytical comparison between the predicted values and the measured values indicates that this modeling method has the capability to predict the performance of the wheels traveling on the loose soil with high accuracy.(4) Based on the new modeling method, the wheel-soil contact model is integrated into the six-wheel six-wheel rocker-bogie mobility system. The dynamical model of the six-wheel rocker-bogie mobility system is developed to investigate the off-road mobility performance while the rover travels on the loose soil. Using this model, the distribution of the stress acting on the interface between the wheel and soil and the drawbar pull and torque of the wheel can be predicted. In order to validate this model, the test bed and the physical prototype of the six-wheel rocker-bogie mobility system are both developed. The accuracy and reliability of the model are verIFied by some experiments. The comparison between the measured results and the simulation results indicates that this model can be used to investigate the performance of the multi-wheel rover traveling on the loose soil.(5) The dynamical model of the FWRA mobility system traveling on the lunar surface is developed. Using this model, the correlations between the wheels of FWRA mobility system are analyzed. The obstacle-crossing capability and the grade-climbing ability are predicted while the FWRA mobility system travels on the lunar surface. The influence of swing-arms on the mobility capability is investigated. The results indicate that the swing arms can greatly improve the obstacle-crosing and grade-climbing capability. From the previous analysis, it can be seen that this dynamical model is useful to investigate the performance of the FWRA mobility system traveling on the lunar surface.