Study Of The Motion Characteristics Of The New Parallel Machine Tool

A structure design scheme for a new type parallel machine tool (PMT) is proposed in this thesis. A 4dof spatial parallel mechanism is utilized as main feed mechanism,with assistance of a dual direction movable worktable,multi-coordinates number control machining can be realized.The theory of structure design, displacement analysis , workspace analysis, trajectory planning, kinematic and dynamic model for the main feed mechanism of parallel machine tool is studied extensively and systematically. A kinematic simulation system for the parallel machine tool is implemented in virtual environment based on above research,3D MAX software and MAXScrip language desktop.The typical structure of PMT is mostly based on the Stewart platform and its evolving style till now,this type PMT possesses advantages of high precision, good vibration_resistance_ability and good machining_steady_ability etc., on the other hand, this type PMT possesses disadvantages of small workspace and small orientation angle etc. A 4-DOF spatial parallel mechanism,which realize one-dimension movement and three-dimension rotation, is proposed in the thesis. The PMT which consist of a 4-DOF spatial parallel mechanism and a dual direction movable worktable can meet the need of multi coordinate NC machining.This type PMT enjoys some advantages over its conventional counterparts: large workspace,good dexterity,position decouples with orientation etc.Method for inverse displacement analysis of main feed mechanism of PMT is given,the closed form solution for forward displacement analysis of main feed mechanism of PMT is derived based on resultant elimination method.A new trajectory planning method is proposed in thesis. This method plans trajectory in parameter space fist, then the trajectory of parameter space is mapped into joint space. The redundant DOF of Parallel Machine Tool is optimized with genetic algorithm, and the condition number of Jacobian matrix is chosen as adaptation degree function.The fuzzy neural network(FNN) model for dynamic equation of the PMT is established.The model is divided into six sub-models, and the generalized coordinates are chosen as input variables.Sub_models of dynamic equation are established respectively,then the output result which represent the joint drive force is gained through the sum manipulation. This FNN model can improve the on_line calculation efficiency greatly.A kinematic simulation system for the parallel machine tool is implemented in virtual environment based on 3D MAX software and MAXScrip language desktop.This simulation system can implement precise positioning of solid model in each frame and integrating data of trajectory planning.