| Lunar rover, named planet detect robot, can proceed long-term practical exploration in place of the astronaut. But lunar rover do not hold enough traversing ability to ensure its normal work,when driving in the lax road. Generally, it can cross obstacles which height of these is smaller than the diameter of carwheel, and only step over the deep ditch which width of it do not exceed the diameter of wheel.Thus it can be seen, the performance of the lunar rover depends mostly on the performance of the lunar rover's wheel.So it is important to study the mechanical performance of the wheel of lunar rover. Now some universities and institutes of China have made some samples of the lunar rovers and theirs wheels, but until now the wheel's mechanical performance is seldom researched and tested. The paper is organized as follows:Firstly , introducing various index of describing its physical characteristic then the mechanical characters of the soil are separated to press-sinkage character and shear character based on Bekker's theory, and common press- sinkage and shear models are introduced. These basic theories are helpful to construct the rigid wheel with sandy soil model. Some parameters of soil used for experiments are measured by shear experiments .By passing to check against, its various parameter indexs are close to lunar soil, it can be used for experimenting.The tractive trust is one of the key factors of vehicle moving. Based on the confirming drawbar pull of lunar rover, using related theories of the ground mechanics and the soil mechanics, I analyze various resistance and driving force of its subjecting to when the lunar rover driving on the surface of the moon. Finally I build the lunar rover dynamics model, then I have a conclusion that drawbar pull relate to the ratio of diameter to width of wheel.To study the performance of the wheel further, we design a test-bed. This test system can measure the followed mechanics parameters: drawbar pull,torgue and sinkage etc. at the same time try to imitate the lunar rover have the ability of crossing obstacle and come through various ground and geography normally, under the moon environment.This system has the function of the changed angle.It can measure the biggest angle of the slope that the lunar rover overcome upgrades.According to above design request, we have chosen the electrical motor and the direction electrical motor. Based on displacement and drawbar pull, we select displacement sensor and pull/press sensor and checked the driving capability and the distance demand .Experiment shows that the sensor can satisfy the performance requirement.Orthogonal test optimization is adopted in the rigid wheel passing ability test, which the primary and secondary factor is the ratio of diameter to width of wheel, the level speed and the load. I get the optimal combination is ratio of diameter to width of wheel is 3, speed at 3.6m/min and plumb load is 30N. One equation was obtained based on the one factor regression experiment. The rigid wheel equation between ratio of diameter to width of wheel and drawbar pull is: y = -11.758x2 + 81.729x - 58.512. Concluded by the orthogonal experiment, the quadratic equation between drawbar pull and these three factors was: y=-2.39+1.882Z1-0.03Z2+0.053Z3-0.006Z1Z2 -0.003Z1Z3-0.001Z2Z3-0.33Z12+0.001Z22Using ANSYS software to analyze three dimensional finite element model of rigid wheel and sandy soil contacting process. This method cannot only provide physical parameters that cannot be measured in experiments, but also modify the parameters of structure and movement conveniently. The method can shorten the development period of lunar rover and improve the testing technique. ANSYS simulation involves three parts: modeling, solution and analysis. The model of the contact of the rigid wheel with sandy soil was established after Studying on the interaction between rigid wheel and sandy soil. Element type, material and same parameters were defined. The model was meshed, limited conditions were added and resolution parameters were setup. Afterwards, the procedure of the contact of the rigid wheel with sandy soil was simulated. The simulation result was analyzed through powerful postprocess functions. 3D stress nephogram and Y direction stress curve through the path node for the driving soil were obtained. The simulating results showed that: the average stress on 200x100 rigid wheel surface was 0.251 KPa, the average stress on 250x200 rigid wheel surface was 0.267 KPa and the average stress on 300x100 rigid wheel surface was 0.238 KPa. The stress of the bigger rigid wheel with ratio of diameter to width of wheel reduced 10%coKParing with the smaller one. This shows the bigger rigid wheel can decrease rolling resistance and be helpful to lead sandy soil movement under moving lunar rover, which is useful to improve lunar rover trafficability. |
PDF Full Text Request