04269864.pdf

AbstractThis article proposes a newtype of suspension for lunar rover. The suspension is mainlyconstructed bya positive quadrilateral levers mechanism and a negative quadrilateral levers mechanism. The suspension is designed based on following factors: Climbing up obstacles, adapting terrain, traveling smoothly, and distributing equally the load of cab to wheels. In the article, firstly the structure of the new suspension is described, secondly the kinematics of the levers is analyzed, and the relational equations of the suspension levers are established, so the distortion capability of the suspension is known. In order to test the capability of suspension, we design a prototype rover with the new suspension and take a test of climbing obstacles, and the result indicates that the prototype rover with new type of suspension has excellent capability to climb up obstacles with keeping cab smooth. Based on the shortcoming found in test, we optimize the levers mechanism, and then establish the rover models with the new type of suspension and with Rocker-Bogie suspension based on ADAMS, and then the capability compare on simulation is followed. The further researching work for this newdeveloped suspension is being carried out now so as to improve its overall performances. China has been determined to carry out the lunar exploration project in the near future. The proposed newtype of suspension would provide a valuable technical support to it. I. INTRODUCTION hina expects to send a lunar rover to the moon to implement themenologyexploration in 2012. Therefore, some of research institutes and universities are actively engaged in related areas of the lunar rover. Since the locomotion systemofthelunar rover isloaded with detection instruments, it is important to move smoothly. In order to develop menology exploration technology in china, Jilin University china invents a new type of suspension for lunar rover in 2004. The suspension is mainly constructed by a positive quadrilateral levers mechanism and a negative quadrilateral levers mechanism. The test results indicate that the new type of suspension has excellent capability to climb up obstacles with keeping cab smoothness. The proposed new type of suspension would provide a valuable technical support to the moon exploration in the future. Manuscript receivedSeptember 30, 2006. This work was supported in part by 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: cbc2009). Wang Rong-ben is with the Transportation College, Jilin University, Changchun, 130025, China. (Email: wrb) II.OBSTACLESANALYSIS The force loaded in suspension lever is shown partly in figure 1 when a wheel encounters the obstacle. Gwis the gravity of single wheel. Fmis the resultant force actedtosuspension lever bywheel. is theanglebetween Fm and horizon. G is the weight of whole rover. is the adhesion coefficient between road and wheel. is road resistance coefficient. Defining f is a coefficient and taking f=-. It is assumed that the lunar rover is driven by six wheels, threewheels on each side, and the load of weight is equally distributed to six wheels. So when a single wheel encounters the obstacle, there is: = 3 6 arctan f/G -GG/ w (1) Considering the characteristics of menology soil, take fmax=0.451. Considering the structure and weight of rover, take Gw=G/602. Sothrough theequation (1), theconclusion is =45. It means the direction of the force acting to suspension lever by wheel is 45 to horizon. III. DESIGN OF THE NEW TYPE OFSUSPENSION A. Design principles of Suspension The following factors are considered when suspension is designed. 1) Excellent capability of climbing up the obstacles We known from above analyses, when wheel encounter obstacles, thedirection offorceacting tosuspension lever by wheel is 45 to horizon. When the levers mechanism is designed, the directions of some levers to joint wheel should be vertical to directions of the forces acted in them as much as possible in order to increase the torque to make lever turn in the direction beneficial to climb up the obstacles. So we should make the relevant levers sloped with reverse 45 to horizon. 2) Excellent capability of traveling smoothly Suspension should have the capability of automatic adapting terrain when traversing obstacles, which could eliminate the influence of uneven ground and keep the cab smooth. Design and Simulation Research on a New Type of Suspension for Lunar Rover CHEN Bai-chao, WANG Rong-ben, YANG Lu, JIN Li-sheng, GUO Lie C Figure.1 Force of suspension lever Proceedings of the 2007 IEEE International Symposium on Computational Intelligence in Robotics and Automation Jacksonville, FL, USA, June 20-23, 2007 ThBT3.5 1-4244-0790-7/07/$20.00 2007 IEEE.173 3) Distributing equally the load of cab to every wheel 4)Excellentabilityoffoldingandunfolding in order to be carried easily B. Structure of the positive and negative quadrilateral suspension According to the suspension design principles above, we designa new type of suspension, which is mainly constructed by a positive quadrilateral levers mechanism and a negative quadrilateral lever mechanism, shown in Figure2. Thesuspension is composed ofsix levers, and theends ofthelever 1, lever 3 and lever 6 are connected separately with front-wheel 15, middle-wheel 16 and rear-wheel 17. The lever 1 and lever 2 are hinged at point 8, thesamehinged is alsothelever 1 and lever 3 at point 7, the lever 2andlever 4atpoint10, thelever 3 and lever 4 at point 9, the lever 2 and lever 5 at point 12, the lever 4 and lever 6 atpoint14, andthelever 5andlever 6at point 13. Both sides of the positive and negative quadrilateral levers mechanism areconnectedwith cabthrough differentialshaftin lever 4 at point 11. So yaw angle of cab is the average yaw angle of both side lever4. Figure 2 Positive and negative quadrilateral suspension IV. ABILITY OF ADAPTING TERRAIN A. Kinematics equations of the suspension levers In order to analyze the movement relation among the levers easily, an assistant line is made from the center of the front-wheel and 45 to the lever 1, shown in Figure 3. The angles among three branch levers of lever 4 are respective 135, 135, and 90. Thelever 1isparalleltoabranch lever oflever 4, thelever 2 is parallel to lever 3, and the assistant line is parallel to another branch lever of lever 4. The lengths of every lever are respective L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, and L11, shown in Figure3. And a is the distance between the centers offront-wheel and middle-wheel along horizontal direction, b is the distance between the center of middle -wheel and rear-wheel along horizontal direction, c is the distance between the assistant line and the center of rear-wheel, d is the distance betweenthe centerof front-wheel and rear-wheel along the assistant line, h is the height between the centers of climbing-wheel and other wheels, is the anglebetween lever 3 and lever 1, is between assistant line and lever 1, is the angle between lever 5 and the vertical lineoftheassistant line, is between lever 6 and the vertical lineoftheassistant line, is the angle between assistant line and horizontal, is between lever 3 and horizontal, is between lever 6 and horizontal, is between lever 1 and horizontal, is the angle between the vertical line of lever 6 and lever 5, is between thevertical lineoflever 2 and lever 5, and is a medial- variable. The angle unit is all degree. Figure 3 Geometric parameters of the suspension It is assumed that every wheel does not depart from ground when climbing up the obstacles. The kinematics equationsoflevers areshown as belowwhen thefront-wheel climbing up obstacle. ( )( )( )()()2911765135cossinsincos-LL-LLLL=+ o ( )( )( )()()29765135sincoscossinLLLLL=+ o ()()( ) ()()( )c-L-LLLLL=+cos135sinsin45sin829321 oo ()()( )()()( )dLLLLLLL=+sin135coscos45cos82911321 oo ()() ()431sin45sinLLLh+=+ o ()( ) ()431cos45cosLLLa+= o ( )( )achb+=cotcos ( )( )/dchsincos=+ o 90+= = += = o 45 ( )( )/coscos= += o 90 = o 135 Theequations ofthemiddle-wheel and the rear-wheel are established in the same way. B. Height of obstacle wheel climbing up Considering the whole structure of rover, the following parameters 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 gained ThBT3.5 174 through the value of h. However, the equations above are nonlinear and there are15equations for16variables, the analytic solutions of h cant be got. The numerical method must be applied here to solve the problem. As can express the corresponding relation to positive and negative Figure 4 Corresponding relations between the heights of climbing up in the front, middle, rear wheels and angle quadrilaterals, is selected as independent variable. The different values of between-20-100are taken into the equations, and then corresponding values of h can be obtained. Figure4show the conclusion of calculation through curves. The x coordinate represents angle , the y coordinate represents the height of wheel raising, and the curves ofright, left and middlesides correspond to the front, middle, rear wheels. Obviously, the maximum height of wheel climbing is about220mm. V. TRAVELING EXPERIMENTS OF PROTOTYPE LUNAR ROVER In order to validate the characteristics of the suspension, the suspension is installed on a prototype lunar rover. When testing, a block with height of250mm, and theobstacleangle of 75 is placed at the front of the lunar rover. It is shown in Figure 5. The testing results indicate that the lunar rover with thenewtypeofsuspension hasexcellentabilitytoclimb up obstacles with keeping cab smooth. VI.SIMULATION ANALYSIS Thetestingresultsindicatethatthelocomotion systemhas the following advantages: Excellent capability of climbing up the obstacles forward and excellent capability of keeping cab smooth. But it also has some disadvantages: Unequal wheel loads and bad capability of climbing up the obstacles backward. So, this suspension is optimized so as to improve above shortcomings. The simulation is followed in order to verify the optimizing results, the rocker-bogie suspension used in sojourner mar rover34is taken as comparable model during simulation. A. Simulation environment We make the Rocker-Bogie suspension rover model (the following shortened form: Rover) and the positive and negativequadrilateralsuspensionrovermodel(the following shortened form: CJ-1) the same size models on ADAMS for justice. Only in suspension form is the two models different, the characters of other parts are the same. The same is that mass of the two rover is 200 kg, center of mass is 515mm to the ground, mass of a single wheel is 4.5kg ,diameter and width of the wheels are 330mm and 200mm, wheeltrack is the same, and the wheelbase between front-wheel and rear-wheel is also the same. During the simulation the gravity acceleration is 9.8m/s2, the frictional coefficient is 0.5, and the velocity of the driving wheels is 0.3rad/s. Figure 6(a) show the outline sizes of CJ-1, figure 6(b) show the outline sizes of Rover. Figure 6(a) the outline sizes of CJ-1 Figure 6(b) the outline sizes of Rover B. Simulation and comparison In the following simulation, the cab of CJ-1 is blue, and the cab of Rover is green. Figure 5 Experiments of climbing block ThBT3.5 175 1) Wheel Load equality The results: the load of CJ-1 is close to the one of Rover. 2) Capability of climbing up the obstacles forward The heights of vertical obstacles are respective 135mm, 137mm, and 280mm. The results: CJ-1 can climbup theheight of 280mm, and Rover cant climb up the height of 137mm. 3) Capability of climbing up the obstacles backward Theheights ofvertical obstacles arerespective 95mm and 97mm. The results: CJ-1 and Rover can get across the obstacle of 95mm, but neither can get across the obstacle of 97mm. 4) Yaw angle of cab when acrossing obstacles forward The height of vertical obstacles is 135mm. The results: when acrossing the vertical obstacles of 135mm, themaximum yawangleofCJ-1 is 6.7 and theone of Rover is 8.7. 5) Roll angle of cab when one side wheels acrossing obstacles forward The height of vertical obstacles is 135mm. The results: when acrossing the obstacles, the roll angle of CJ-1 is 2.4, and the one of Rover 3.3. 6) Roll angle of cab when one side wheels acrossing obstacles backward The height of vertical obstacles is 95mm. The results: when acrossing the obstacles, the roll angle of CJ-1 is 5.8 and the one of Rover is 4.3. 7) Capability of climbing up the slope Theangles ofslopes arerespective25, 26, 27, and 28. The results: the two models are skidding at the slope of 26-27. 8) Capability of climbing down the slope Theanglesofslopesarerespective25, 27, 29, 31, 33, and 35. ThBT3.5 176 The results: when climbing down, CJ-1 climbs down the 31 slop and turn over at 33 slope, and Rover turns over at 31 slope. 9) Radial force at pivot When CJ-1 and Rover across the obstacle of 135 mm, the curvesofradialforcesathingedpointsareshown in Figure7 and 8. There are 7 hinged points in CJ-1, and two of those points are sam