Synthesis And Analysis Of TPM With Closed-loop In Each Chain

Parallel mechanism compared with traditional series mechanism has someadvantages of better stiffness and capacity, smaller accumulated error, and smallerinertia. Especially, three translational freedom parallel mechanisms (TPM) withsymmetrical structure have more advantages. In addition, the closed-loop structurehas advantages of small friction, easily manufacturing, and proving good stiffness.Moreover, with the requirement of high speed and precision is put forward, the errorcaused by the joint clearance cannot be neglected. Therefore, systematic typesynthesis and analysis to TPM with closed-loop structures has great significance.This paper’s contents is mainly about that the type synthesis of the TPM withclosed-loop structures, and dimension synthesis of a chosen TPM, and the stiffnessanalysis pose error analysis considering joint clearance of this mechanism. The maincontent of the research includes:The degree of freedom of four novel closed-loop structures is analyzed byintroducing the screw theory, and type synthesis of TPM considering closed-loopstructure is completed,and some novel mechanisms is obtained, and a furtheranalysis object is chosen.Based on the analysis of the structure of the mechanism, the positive and inversekinematics are solved and Jacobian matrix is obtained, and the dimension synthesisis completed to get the size of the mechanism based on the condition number of theJacobian matrix.The global Jacobian matrix is calculated and the stiffness matrix based on theglobal Jacobian matrix is obtained. The distribution of the stiffness of mechanism inwork space is analyzed by introducing the CSV approach. Some significantconclusions are obtained from the results of stiffness analysis.By analyzing the mapping relations between the load on the platform and thejoint forces, the joint forces and joint local displacement, joint local displacementand the pose error of the platform, the mapping relation between the load on theplatform and the pose error of the platform is obtained, and the distribution of thepose error of the platform in work space is calculated in using a given magnitude ofthe mechanism, and then the results is analyzed.