Kinematic Analysis And Structural Parameters Design Of Novel Five Axes Serial-parallel Machine Tool

The pure parallel mechanisms have lots of the merits in structural configuration and kinematic characteristics compared with the traditional serial mechanisms, such as larger carrying capability, higher location accuracy, the great ratio of stiffness over weight, simple structure and agile mobile ability, etc. However, parallel mechanism has the following disadvantages, such as small workspace, complicated control system, difficulties in kinematic calibration, etc. Compared with six Degrees-Of-Freedom(DOFs) parallel mechanisms represented by Stewart platform, the research of the limit-DOF parallel mechanisms has been highly focused by academia and indutry, the outsdanding merits of the mechanism include the simple structure, the larger workspace and the lower cost, etc. A novel kind of 4-DOF parallel mechanism of 2-TPR/2-TPS is proposed in this thesis. The analysis of the concerned mechanism is investigated in details. Based on that mechanism a novel five axes serial-parallel machine tool is developed by combining a serial rotational axis. The kinamatic analysis and structural parameters design the concerned machine tool are investigated.The structural layout features of 2-TPR/2-TPS parallel mechanism are discussed. Moving character of the concerned mechanism is analyzed by using the theory of screws, and then the movements of the mechanism are determined. The decoupling equation of position and posture parameters are formulated on the basis of structural constraint of the concerned mechanism. The inverse kinematic solution of this mechanism is deduced by analytical method and the forward kinematic solution of this mechanism is achieved by numerical method. A novel approach of analying singularity for parallel mechanism, instantaneous coordinate system method, is presented based on the theory of screws, and then three possible types of singular configuration of this mechanism are achieved by this method.Based on the 2-TPR/2-TPS parallel mechanism, a novel five axes serial-parallel machine tool is proposed by combining a serial rotational axis on the moving platform of the mechanism. The structural characteristics of this machine tool is discussed. The inverse kinematic solution and forward kinematic solution of this machine tool are achieved. The first-order kinematic influence coefficient matrix and the sencond-order kinematic influence coefficient matrix can be obtained by using vector geometry approach, and then the ananlysis of the velocity and acceleration is carried out based on the influence coefficient matrixs. On the basis of the inverse kinematic solution of this machine tool, the shape of the reachable workspace of the cutter of this machine tool with given the maximum cutter dip is described by numerical method of spatial three dimensions alternating search. The characteristics of workspace for this machine tool is discussed. The volume of the workspace for this machine tool is calculated by numerical method. The effect of the change on the cutter dip to the workspace of the machine tool is analyzed. The effects of the change on structural parameterts to the workspace are investigated, it povides a theoretical basis for the selecting design parameters of structure of this machine tool.The dexterity of machine tool is resolved baesd on the first-order kinematic influence coefficient matrix of the 2-TPR/2-TPS parallel mechanism. The distribution in the workspace of position dexterity index and posture dexterity index for machine tool is discussed. The effects of the change on structural parameterts to the dexterity index of machine tool are investigated, it can serve as a theoretical basis for the selecting design parameters of structure of this machine tool .The specified representation of working space for machine tool is represented, and then the inverse analysis of workspace is investigated. The structure design for this machine tool according to a given workspace is achieved. The three-dimensional solid model of the machine tool is established in ADAMS. The kinematic simulation of machine tool is carried out in the ADAMS simulation module. On the basis of the kinematic simulation of the machine tool, The results of the previous theoretical analysis are verified , including the number of degrees of freedom and redundant constraints, inverse kinematic solution and forward kinematic solution, the calculation of the velocity and acceleration.