Design Of A New Locomotion System For Lunar Rover

The locomotion system is the one of the most important systems of lunar rover, and its performance decides whether the lunar rover can finish the certain tasks successfully. In addition, the locomotion system of lunar rover is an outlier system and can be see easily, which will create the comprehensiveness notice of earthling. Thus, to develop a high performance and innovative locomotion system of lunar rover not only can make lunar rover finish certain tasks successfully but also pays the lunar rover with china features.This paper is supported by China national natural science foundation and the project of locomotion system design and simulative analysis for lunar rover provided by China aviation science & technology group and mainly studies at a high performance and innovative locomotion system of lunar rover, the main content of this paper are shown as followed:Based on evolution, present a high performance and innovative suspension for lunar rover named obverse and reverse four-linkage suspension. The evolution begins with the bogie and rocker of the MARS rover Sojourner, and ends in obverse four-linkage mechanism and reverse four-linkage mechanism. The obtained mechanisms from evolution include the suspension of Sojourner, the suspension of Rocky7 and the suspension of RCL Concept-C, etc. The evolution analysis indicates that the proposed obverse and reverse four-linkage suspension has the better performance in climbing obstacle, cab stationarity, wheel load invariance and suspension stability than the suspensions of Mars rover and RCL Concept-C. In addition, The combination method of every parts of the obverse and reverse four-linkage suspension is the same as MARS rover suspension. Thus, this suspension has the better working reliability and practicality.Propose an optimization method for lunar rover suspension based on ADAMS. This method includes the contents described as followed: (1) Propose a series of performance evaluation index for lunar rover used in optimization, including effective friction coefficient. (2) Build the optimization object function and based on the character of this mechanism, choose the algorithm which is combined by one dimension search algorithm and quadratic programming algorithm. (3) Propose a new control method which can harmonize the force of every wheel in order to prevent wheels from hauling and pushing each other. Use above optimization method to optimize the obverse and reverse four-linkage suspension and the result shows that the performances, including forward climbing obstacle, backward climbing obstacle and cab stationarity, are improved. Based on the shortcoming of traditional wheel of planet rover, designed a half-walking wheel—vane-telescopic walking wheel, adapted to friable soil. It can adjust the deepness of the vane inserting into soil automatically based on the interactional relation between wheel and soil in order to adjust the wheel traction force. Thus, on the good trafficability, the vane-telescopic walking wheel possesses the advantage of short grouser wheel such as good ride comfort, low energy consumption and small resistance; on the poor ground, the vane-telescopic walking wheel possesses the better traction capability, so it make sure that the wheel can proceed on the poor ground to the utter most extend. This paper analyzes the kinematic and mechanical features of wheel and obtains the relation equation among the length of the vane inserting into soil, spring stiffness, spring initial moment and rolling resistance of wheel.Based on ensuring the traffication on slopes and minimizing energy consumption, optimize the vane-telescopic walking wheel in order to make vane stretch by need. The content includes: (1) Under the relation between the force and the length of vane out of wheel as well as the length of vane out of wheel required by trafficability, based the optimization object of the length vane out of wheel more than the length vane stretch by trafficablility need, optimize the spring stiffness and spring initial moment of front, middle and rear wheel. (2)Through Matlab, we obtain the spring stiffness and spring initial moment that can meet with above requirement. So the vane-telescopic walking wheel can pass over the all kinds of ground in the limited range with the lowest energy consumption.The new lunar rover locomotion system which this paper designs is composed of obverse and reverse four-linkage suspension and vane-telescopic walking wheel. In order to analyze the performance of new locomotion system, build a simulation system for friable soil ground based on ADAMS. The concrete progress include: (1) Deduce an equivalent force conversion model that can convert the force of friable soil giving wheel to the force of rigit ground giving wheel, because that ADMS can't simulate the relation between wheel and friable soil. (2)According to the need of model conversation, this paper adopt torque control model, its control aim includes that the speed of the locomotion system keeps at 200m/h as far as possible, and make sure it has some stationarity; On the different ground, the wheel should coordinate and cooperate; The variation range of wheel's driving torque value should limit to the adhesive ability of the ground; Locomotion system has some yaw correcting capacity. Based on above built simulation system, analyze the performance of the new locomotion system in climbing obstacle and slope. The conclusion is the same as our prevenience.Build a set of performance evaluation index for the locomotion system of lunar rover, based on it, analyze the performance of the new locomotion system through simulation and mathematical modeling. The main content includes: (1) classify locomotion performance. First of all, from the usage, it can be divided by obstacle trafficability characteristic, slope trafficability characteristic and loading platforms characteristic. Secondly, classified by the differences of affections and contents. Obstacle trafficability characteristic is divided to obstacle traction trafficability(dynamic), geometric trafficability and terrain adaptation(kinematic); Meanwhile, slope trafficability characteristic can be classified as slope traction trafficability and slope stability(including transverse and longitudinal stability). Loading platform stability can divided to pitch and vertical movement stability according to loading platform movement style. (2) analyze the specific performance in every performances. This paper uses stimulation (based on the soft terrain stimulation system that has been built) and mathematical modeling method to analyze every performances. The results shows, on the lunar surface, the new lunar rover system's obstacle trafficability characteristic mainly decided by geometric trafficability, if the obstacle which satisfies geometric trafficability, the can pass the obstacle smoothly; The new slope trafficability of the lunar rover system is decided by its traction trafficability on upslope and decided by its vertical stability on downslope, when it cross passes it is decided by slope stability, it can climb 34°slope and climb down 46.1°slope. and cross 47.5°slope; when the new lunar rover system climb 200mm height vertical obstacle, the vibration amplitude of the heart of the rover is 35 percent than the wheels. Meanwhile, in the process of passing obstacle, the biggest pitching angle of loading platform is only 8.8°, the degree of downing and upping is basically identical. Through above analysis, the performance of the new locomotion system meets the performance requirement of china lunar rover.In order to check the practicality and reliability, design a proto-type vehicle and some test is carried out, including the teat of obstacle trafficability, slope trafficability and the wheel performance. In test, the new locomotion system cross all kinds of stones and craters freely with the cab relatively stable. The most gradient that the locomotion can climb in loose soil is 27°and in compact soil is 30°. The excellent representation in test proves that the new locomotion system has the better practicality and comprehensive performance.Through theoretical analysis, simulation and test, the new locomotion has excellent comprehensive performance. Thus, it can make rover interesting to cross higher obstacles rather than to avoid. Its good cab stationarity is in favor of the on-board instruments to work. Its good wheel load invariance can decrease wheel sinkage and produce more tractive power.So far we have not found the similar locomotion system of lunar all over the world as this paper. China has determined to carry an exploring vehicle to lunar in 2012 and as a forecast, the new locomotion system will provide a valuable technical support to it.