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AbstractThis article proposes a newtype of suspension forlunar rover. The suspension is mainlyconstructed bya positivequadrilateral levers mechanism and a negative quadrilaterallevers mechanism. The suspension is designed based onfollowing factors: Climbing up obstacles, adapting terrain,traveling smoothly, and distributing equally the load of cab towheels. In the article, firstly the structure of the newsuspension is described, secondly the kinematics of the leversis analyzed, and the relational equations of the suspensionlevers are established, so the distortion capability of thesuspension is known. In order to test the capability ofsuspension, we design a prototype rover with the newsuspension and take a test of climbing obstacles, and the resultindicates that the prototype rover with new type of suspensionhas excellent capability to climb up obstacles with keeping cabsmooth. Based on the shortcoming found in test, we optimizethe levers mechanism, and then establish the rover modelswith the new type of suspension and with Rocker-Bogiesuspension based on ADAMS, and then the capability compareon simulation is followed. The further researching work forthis newdeveloped suspension is being carried out now so as toimprove its overall performances. China has been determinedto carry out the lunar exploration project in the near future.The proposed newtype of suspension would provide a valuabletechnical support to it.I. INTRODUCTIONhina expects to send a lunar rover to the moon toimplement themenologyexploration in 2012. Therefore,some of research institutes and universities are activelyengaged in related areas of the lunar rover. Since thelocomotion systemofthelunar rover isloaded with detectioninstruments, it is important to move smoothly. In order todevelop menology exploration technology in china, JilinUniversity china invents a new type of suspension for lunarrover in 2004. The suspension is mainly constructed by apositive quadrilateral levers mechanism and a negativequadrilateral levers mechanism. The test results indicatethat the new type of suspension has excellent capability toclimb up obstacles with keeping cab smoothness. Theproposed new type of suspension would provide a valuabletechnical support to the moon exploration in the future.Manuscript receivedSeptember 30, 2006. This work was supported in partby the National Natural Science Foundation of China (No.50675086).Chen Bai-chao is with the Transportation College, Jilin University,Changchun,130025,China.(Phone:0086-431-85095461;Fax:0086-431-85095461; Email: ).Wang Rong-ben is with the Transportation College, Jilin University,Changchun, 130025, China. (Email: wrb)II.OBSTACLESANALYSISThe force loaded in suspension lever is shown partly infigure 1 when a wheel encounters the obstacle.Gwis the gravity of single wheel. Fmis the resultant forceactedtosuspension lever bywheel. is theanglebetween Fmand horizon. G is the weight of whole rover. is theadhesion coefficient between road and wheel. is roadresistance coefficient. Defining f is a coefficient and takingf=-. It is assumed that thelunar rover is driven by sixwheels, threewheels on each side,and the load of weight is equallydistributed to six wheels. Sowhen a single wheel encountersthe obstacle, there is:=36arctanf/G-GG/w(1)Considering the characteristics of menology soil, takefmax=0.451. Considering the structure and weight of rover,take Gw=G/602. Sothrough theequation (1), theconclusionis =45. It means the direction of the force acting tosuspension lever by wheel is 45 to horizon.III. DESIGN OF THE NEW TYPE OFSUSPENSIONA. Design principles of SuspensionThe following factors are considered when suspension isdesigned.1) Excellent capability of climbing up the obstaclesWe known from above analyses, when wheel encounterobstacles, thedirection offorceacting tosuspension lever bywheel is 45 to horizon.When the levers mechanism is designed, the directions ofsome levers to joint wheel should be vertical to directions ofthe forces acted in them as much as possible in order toincrease the torque to make lever turn in the directionbeneficial to climb up the obstacles. So we should make therelevant levers sloped with reverse 45 to horizon.2) Excellent capability of traveling smoothlySuspension should have the capability of automaticadapting terrain when traversing obstacles, which couldeliminate the influence of uneven ground and keep the cabsmooth.Design and Simulation Research on a New Type of Suspension forLunar RoverCHEN Bai-chao, WANG Rong-ben, YANG Lu, JIN Li-sheng, GUO LieCFigure.1 Force of suspension leverProceedings of the 2007 IEEE International Symposium onComputational Intelligence in Robotics and AutomationJacksonville, FL, USA, June 20-23, 2007ThBT3.51-4244-0790-7/07/$20.00 2007 IEEE.1733) Distributing equally the load of cab to every wheel4)Excellentabilityoffoldingandunfolding in order to becarried easilyB. Structure of the positive and negative quadrilateralsuspensionAccording to the suspension design principles above, wedesigna new type of suspension, which is mainlyconstructed by a positive quadrilateral levers mechanismand a negative quadrilateral lever mechanism,shown in Figure2. Thesuspension is composed ofsix levers,and theends ofthelever 1, lever 3 and lever 6 are connectedseparately with front-wheel 15, middle-wheel 16 andrear-wheel 17. The lever 1 and lever 2 are hinged at point 8,thesamehinged is alsothelever 1 and lever 3 at point 7, thelever 2andlever 4atpoint10, thelever 3 and lever 4 at point9, the lever 2 and lever 5 at point 12, the lever 4 and lever 6atpoint14, andthelever 5andlever 6at point 13. Both sidesof the positive and negative quadrilateral levers mechanismareconnectedwith cabthrough differentialshaftin lever 4 atpoint 11. So yaw angle of cab is the average yaw angle ofboth side lever4.Figure 2 Positive and negative quadrilateral suspensionIV. ABILITY OF ADAPTING TERRAINA. Kinematics equations of the suspension leversIn order to analyze the movement relation among thelevers easily, an assistant line is made from the center of thefront-wheel and 45 to the lever 1, shown in Figure 3. Theangles among three branch levers of lever 4 are respective135, 135, and 90.Thelever 1isparalleltoabranch lever oflever 4, thelever2 is parallel to lever 3, and the assistant line is parallel toanother branch lever of lever 4. The lengths of every leverare respective L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, and L11,shown in Figure3. And a is the distance between the centersoffront-wheel and middle-wheel along horizontal direction,b is the distance between the center of middle -wheel andrear-wheel along horizontal direction, c is the distancebetween the assistant line and the center of rear-wheel, d isthe distance betweenthe centerof front-wheel andrear-wheel along the assistant line, h is the height betweenthe centers of climbing-wheel and other wheels, is theanglebetween lever 3 and lever 1, is between assistant lineand lever 1, is the angle between lever 5 and the verticallineoftheassistant line, is between lever 6 and the verticallineoftheassistant line, is the angle between assistant lineand horizontal, is between lever 3 and horizontal, isbetween lever 6 and horizontal, is between lever 1 andhorizontal, is the angle between the vertical line of lever 6and lever 5, is between thevertical lineoflever 2 and lever5, and is a medial- variable. The angle unit is all degree.Figure 3 Geometric parameters of the suspensionIt is assumed that every wheel does not depart fromground when climbing up the obstacles. The kinematicsequationsoflevers areshown as belowwhen thefront-wheelclimbing up obstacle.( )( )( )()()2911765135cossinsincos-LL-LLLL=+o( )( )( )()()29765135sincoscossinLLLLL=+o()()( ) ()()( )c-L-LLLLL=+cos135sinsin45sin829321oo()()( )()()( )dLLLLLLL=+sin135coscos45cos82911321oo()() ()431sin45sinLLLh+=+o()( ) ()431cos45cosLLLa+=o( )( )achb+=cotcos( )( )/dchsincos=+o90+=+=o45( )( )/coscos=+=o90=o135Theequations ofthemiddle-wheel and the rear-wheel areestablished in the same way.B. Height of obstacle wheel climbing upConsidering the whole structure of rover, the followingparameters are initialized:L1=400mm, L2=50mm, L3=250mm,L4=150mm, L5=100mm, L6=250mm, L7=100mm, L8=250mm, L9=100mm, L10=50mm, L11=282.8mm.What height obstacle wheel can climb up can be gainedThBT3.5174through the value of h. However, the equations above arenonlinear and there are15equations for16variables, theanalytic solutions of h cant be got. The numerical methodmust be applied here to solve the problem. As can expressthe corresponding relation to positive and negativeFigure 4 Corresponding relations between the heights ofclimbing up in the front, middle, rear wheels and angle quadrilaterals, is selected as independent variable. Thedifferent values of between-20-100are taken into theequations, and then corresponding values of h can beobtained. Figure4show the conclusion of calculationthrough curves. The x coordinate represents angle , the ycoordinate represents the height of wheel raising, and thecurves ofright, left and middlesides correspond to the front,middle, rear wheels. Obviously, the maximum height ofwheel climbing is about220mm.V. TRAVELING EXPERIMENTS OF PROTOTYPE LUNAR ROVERIn order to validate the characteristics of the suspension,the suspension is installed on a prototype lunar rover. Whentesting, a block with height of250mm, and theobstacleangleof 75 is placed at the front of the lunar rover. It is shown inFigure 5. The testing results indicate that the lunar roverwith thenewtypeofsuspension hasexcellentabilitytoclimbup obstacles with keeping cab smooth.VI.SIMULATION ANALYSISThetestingresultsindicatethatthelocomotion systemhasthe following advantages: Excellent capability of climbingup the obstacles forward and excellent capability of keepingcab smooth. But it also has some disadvantages: Unequalwheel loads and bad capability of climbing up the obstaclesbackward.So, this suspension is optimized so as to improve aboveshortcomings. The simulation is followed in order to verifythe optimizing results, the rocker-bogie suspension used insojourner mar rover34is taken as comparable modelduring simulation.A. Simulation environmentWe make the Rocker-Bogie suspension rover model (thefollowing shortened form: Rover) and the positive andnegativequadrilateralsuspensionrovermodel(thefollowing shortened form: CJ-1) the same size models onADAMS for justice. Only in suspension form is the twomodels different, the characters of other parts are the same.The same is that mass of the two rover is 200 kg, center ofmass is 515mm to the ground, mass of a single wheel is4.5kg ,diameter and width of the wheels are 330mm and200mm, wheeltrack is the same, and the wheelbase betweenfront-wheel and rear-wheel is also the same. During thesimulation the gravity acceleration is 9.8m/s2, the frictionalcoefficient is 0.5, and the velocity of the driving wheels is0.3rad/s. Figure 6(a) show the outline sizes of CJ-1, figure6(b) show the outline sizes of Rover.Figure 6(a) the outline sizes of CJ-1Figure 6(b) the outline sizes of RoverB. Simulation and comparisonIn the following simulation, the cab of CJ-1 is blue, andthe cab of Rover is green.Figure 5 Experiments of climbing blockThBT3.51751) Wheel Load equalityThe results: the load of CJ-1 is close to the one of Rover.2) Capability of climbing up the obstacles forwardThe heights of vertical obstacles are respective 135mm,137mm, and 280mm.The results: CJ-1 can climbup theheight of 280mm, andRover cant climb up the height of 137mm.3) Capability of climbing up the obstacles backwardTheheights ofvertical obstacles arerespective 95mm and97mm.The results: CJ-1 and Rover can get across the obstacleof 95mm, but neither can get across the obstacle of 97mm.4) Yaw angle of cab when acrossing obstacles forwardThe height of vertical obstacles is 135mm.The results: when acrossing the vertical obstacles of135mm, themaximum yawangleofCJ-1 is 6.7 and theoneof Rover is 8.7.5) Roll angle of cab when one side wheels acrossingobstacles forwardThe height of vertical obstacles is 135mm.The results: when acrossing the obstacles, the roll angleof CJ-1 is 2.4, and the one of Rover 3.3.6) Roll angle of cab when one side wheels acrossingobstacles backwardThe height of vertical obstacles is 95mm.The results: when acrossing the obstacles, the roll angleof CJ-1 is 5.8 and the one of Rover is 4.3.7) Capability of climbing up the slopeTheangles ofslopes arerespective25, 26, 27, and 28.The results: the two models are skidding at the slope of26-27.8) Capability of climbing down the slopeTheanglesofslopesarerespective25, 27, 29, 31, 33,and 35.ThBT3.5176The results: when climbing down, CJ-1 climbs down the31 slop and turn over at 33 slope, and Rover turns over at31 slope.9) Radial force at pivotWhen CJ-1 and Rover across the obstacle of 135 mm, thecurvesofradialforcesathingedpointsareshown in Figure7and 8. There are 7 hinged points in CJ-1, and two of thosepoints are same