| As a robot mechanism, moving platform being an output actuator of the parallelmechanism has the characteristics of high exactitude, high structure rigidity and highspeed. There remain some key technologies to be solved for the parallel mechanismwith six degrees of freedom (DOF) which is difficult to control and owns acomplicated structure. Therefore, it has not been widely used in engineering practice.Compared to the general6-DOF parallel mechanism, the lower mobility parallelmechanism has become a focus in the field of robotics, which has simpler structureand lower cost in design, manufacturing and control. In view of this, a5-DOF parallelmechanism called4UPS+UPU was proposed in this paper which includes threerotational DOF and two translational DOF. Regarding4UPS+UPU parallelmechanism as research object, the thesis focused on theoretical analysis of kinematics,singular configurations, workspace and dynamics of the mechanism. The mainresearch contents and conclusions are presented as follows:Based on the characteristics of constrained force/torque, the motion freedoms of4UPS+UPU parallel mechanism were analyzed. According to Euler transform method,kinematics analytical formulae were derived including the poses, velocities, andaccelerations, as well as Jacobian and Hessian matrixes. Lengths, velocities andaccelerations of branched-chains were acquired by numerical simulation according tothe practical motion law of the parallel mechanism.The statics equilibrium equation of4UPS+UPU parallel mechanism wasestablished. Six spatial lines were obtained by plǜcker coordinate expression of thestatic mechanical transformation matrix. On the basis of Grassmann line geometrytheory accompanied by linear correlation of the six spatial lines, singularconfiguration of the parallel mechanism was studied. By analyzing the spatialdistribution characteristics of different linear varieties, singular configurations withdifferent variety ranks were obtained and the corresponding constraint equations ofthe singularities were established in closed forms. By numerical simulation, singulartrajectories corresponding to different singularities were obtained, as well as thecorresponding variation laws of cosine parameters.To ensure better motion ability of4UPS+UPU parallel mechanism, it isnecessary to analyze the position/orientation workspace performance. The volume ofthe whole workspace was selected as an evaluation index for the workplace, and the responding optimized structure parameters were derived. In order to obtain the motionability in the entire workspace and avoid the inconvenience that the dimensions werenot unified, the evaluation indices of motion ability of the position/orientationworkspace were established. Furthermore, the condition number in the entireposition/orientation workspace was studied according to the variations of structureparameters, and the workspace corresponding to different condition number was alsoobtained.According to the rigid model of4UPS+UPU parallel mechanism, the analyticalexpressions of the velocity and acceleration of all branched-chains were built, and thelink Jacobian matrices were derived as well. The forces and torques of the parallelmechanism were obtained based on the results of kinematic analysis, which provideda basis for later dynamics analysis. Based on the principle of virtual work, the inversedynamics was studied and the inverse dynamics model of the parallel mechanism wasestablished. On this basis, the dynamics performance indices with different physicalmeanings were derived and the dynamics composite performance index was built,which contains the velocity, acceleration and gravity terms of all branched-chains.Meanwhile the global performance index evaluating the average performance of theparallel mechanism was established. By numerical simulation, the variation curves ofthe active forces and the dynamics performance index along with the angle variationof the moving platform and the geometric parameters were obtained. |
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