Design And Research Of Improved3-RPS Parallel Mechanism

Nowadays, the size of large-scale marine propeller is large and the processingequipments have many disadvantages,such as one-surface machining, propellerblade vibration, poor stiffness, repeated clamping and long processing time. Themethod of double-cutter&double-surface symmetrical machining is proposed forlarge-scale marine propeller based on the parallel-serial mechanism. The processingmethod can overcome proposed disadvantages, and improve machining efficiencyand accuracy. Hybrid mechanis m consists of serial mechanism and Lower-Mobilityparallel mechanism, the serial mechanism achieves movement in X, Y-direction andparallel mechanism achieves spindle tool movement in Z-direction and movementwith gesture. This paper mainly studies the3-RPS parallel mechanism of the hybridmechanism.Firstly, since the motion parameters of Lower-Mobility are coupled, the DOFcalculation and the motion parameters are decoupled. Then the positive and inverseof the parallel mechanism with numerical method and the analytical method arecompleted, the speed Jacobian matrix is established, the inverse and forwardsolution formula of position and velocity are derived. The statics of mechanism isanalyzed. The static balance equation is established and the force-Jacobian matrix isobtained. The mapping relationship between the external force and the driving forceand the constraint force is determined. The velocity mapping is in contrapositionwith the force mapping.Secondly, the workspace of parallel mechanism is searched by using thelimit-boundary method. The structure of each part is designed based on therequirements of the workspace. The right components of the processing equipmentare designed and selected, then the model of each part is established by using SolidWorks and assembled to a3D model of3-RPS parallel mechanism.Then by means of MSC.ADAMS, the virtual prototype of the parallelmechanis m is modeled. By this way,the degree of freedom and the positive andinverse solution are verified. The kinematics and dynamics simulation analys is areperformed based on the trajectory planning. The theoretical analysis and the designof parallel mechanism are verified, which laid a reliable foundation for optimizationdesign and motion control of the mechanism.Finally, the static stiffness of parallel mechanism model is analyzed by usingthe finite element analys is software MSC.PATRAN, the stiffness of parallelmechanis m in each direction in different moving platform position and orientation iscalculated. The design of paralle l institutions, which can meet the actual processing requirements of the stiffness,have been verified. Through the modal analys is of theparallel mechanis m,vibration characteristics have been obtained like naturalfrequencies and mode shapes, which has set up a foundation of avoiding resonancephenomena in practical applications.