Structural Synthesis And Analysis Of Folded-deployable Locomotion System For Wheeled Planetary Rover

To better implement planetary exploration missions, various rovers withdifferent configurations are presented to obtain detailed topography, geology andother related information with the help of scientific instruments. Now manyresearchers mainly focus on various performances of one specific rover and fewtheories or methods are employed to guide the design from function to structure.Constrainted by transport capacity of current rockets, planetary rover having foldingfunction has recently become a research focus. However, how to instruct designersin realizing folding function is still an unsolved problem. For deep spaceexploration, it will be a promotion if one folding method is proposed.Considering the effect of wheel grousers, mathematic model of single wheel isestablished using wheel-soil interaction terramechanics, and the relationshipbetween sinkage and drive efficience caused by soil is obtained while wheel width,wheel radius and height of wheel grouser all locate in certain range, and then oneapproach is presented to determine reasonable numbers of wheels. DOFs requiredfor single, double and three wheel suspension systems with self-adaptiveperformance are analyzed, and structural synthesis of rover suspension is carriedout based on single-open chain method. A new isomorphism identification methodis presented and used in the synthesis process using incident matrixes of topologicalgraph with identification rules and steps. After obtaining vertice combinations ofsix-wheel rover suspension topology, lots of new suspension configurations arecreated by direct synthesis and combination synthesis methods.Ideal suspension mechanism has been studied and MCQS (Muti-constraintquadrilateral suspension) is chosen for further research from all synthesizedconfigurations. Mathematic models of step-climbing performance, ditch-crossingperformance and the stability of the rover are established, and the relationshipbetween motion performances and structural parameters is achieved. Someconstraint conditions are goven to realize rover perfprmances well. For lowingenergy consuming and safing instruments, resultant torque provided by wheels andsmooth performance of rover mass center are used as the optimization objective.Muti-objective function is established in ADAMS to optimize the structural parameters of MCQS rover for optimal structure size.MCQS is decomposed and three basic kinematic chains are obtained. Based onstructure change in metamorphic mechanisms and cell fusion and variation theory inbiology, fusion and variation manners of some basic units are studied. Three basicchains with various variation manners have been fused into one suspensionaccording to the permutation and combination mode. Thus one is determined forfurther research by optimal selection in all obtained15folding schemes.For general mechanisms, mathematical models of kinetic and potential energyare established and dynamic equations used for unfolding course of deployablemechanisms are developed. Especially for the unfolding process, three collisionclassifications are given followed by velocity change expressions. Model mass andinertia of changed links and the matrix transformations for velocity and position ofmass center are given. Two unfolding modes of MCQS are presented and dynamicanalysis of collided links in the unfolding process are carried out to determine theimpact time and force. The result shows that impact force has little influence on thesafety of rover structure.Lunar terrain and parameter settings for simulation are introduced, virtual3DMCQS rover is built in ADAMS and then is simulated to determine whether foldedrover can unfold successfully or not. Simulating some lunar obstacles and relatedlocomotion performances of MCQS rover under two different connection modes areanalyzed. Based on simulation results and optimized structure size, the structuraldesign of rover sample is completed. Unfolding and some locomotion performanceexperiments are carried out, these results show MCQS rover can unfold well withmeeting the required folding ratio and can also pass over step-obstacle whose heightis larger than wheel radius and slope with25°inclination angle.