| Parallel mechanism has many advantages, such as larger inflexibility, higher precision, lower inertia, higher bearing load capacity, and so on. It is proper for the parallel mechanism to be used for the high-speed or heavy-load working condition. Less DOF parallel mechanism has advantages of simple structure as well as low cost of manufacture and servicing. Especially, scholars at home and abroad have focused on the parallel mechanisms which have same branch, symmetrical structure and the trait of isotropy.Firstly, The essay utilize the helix theory to accomplish type synthesise of the branch kinematics chain whose DOF are three,four and five. Secondly, Research shifting pair’s possible layout at stationary platform when the shifting pair as drive pair of parallel mechanism according to where driving unit is installed at stationary platform, where driving unit is installed near stationary platform and the requirement of linear drive.Fanally, Select three new 3-CRU parallel mechanism in which there is a certain angle between drive pair and stationary platform and all of them meet in one point of stationary platform based on the principle that the number of kinematics branch chain’s motorial pair should be as fewer as possible.In the first, the trait of the 3-CRU mechanism is introduced and then the number and property of the degrees of freedom of the 3-CRU mechanism are given based on screw theory and the analysis correctness is verified with the help of a software Solidworks which is famous for its convenience in three-dimensional model design. The speed Jacobian matrix and acceleration Jacobian matrix are proposed based on the positive and negative position solution of the mechanism.The workspace of the mechanism is built based on the position equation and the constraint condition of the 3-CRU parallel mechanism in the form of a three-dimensional graphic model and sectional drawing of the mechanism in different angles. The relationship between the workspace cubage and the angle is obtained. The trend of the performance ragarding workspace shape and workspace cubage as quotas of the mechanism is established. The variety laws of the isotropy and the force transfer following with the changes of the angle is set up based on the speed Jacobian matrix and the force Jacobian matrix of the mechanism.The 3-CRU parallel mechanism model is established utilizing the closed-loop vector mothod and then the change regulation of the position output error under certain input error and certain error of structure parameters is found and the graphs of the output error are gotten, which is the basis of the choice of dimension and precision of the rod parts in the application design of the 3-CRU parallel mechanism.The dynamics equation is established by using virtual work principle after the speeds and accelerations of all the rod parts are caculated. The three-dimensional entity model of the 3-CRU Parallel mechanism is built utilizing Solidworks and is turned into Adams software so as to accomplish the kinematics and dynamics simulation to verify the correctness of the theoretical research and to reveal the variation of the performance of the machanism to be of guidance for designs. |
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