Research On Kinematic Performance And Simulation Of 3-DOF Parallel Mechanism With Spherical Pair In Limbs

Parallel mechanism has the advantages of good stiffness, high precision, stable structure,strong bearing capacity, low movement inertia and easy driving control. It is widely used in many fields, which includes machine tools, aerospace, robotics, positioning assembly,recreational facilities, biological medicine and machinery processing, etc.This paper discusses three kinds of 3-DOF parallel mechanisms with spherical pair S in limbs. 3-PSR 3-DOF parallel mechanism with the prismatic pair P, the spherical pair S and the revolute pair R in limbs is studied, and the main research contents are as follows:Firstly, according to different arrangements of kinematic pairs in limbs, three kinds of parallel mechanism configurations with prismatic pair, spherical pair and revolute pair in limbs are synthesized, they are 3-RPS, 3-PRS and 3-PSR parallel mechanisms respectively.Their main application situations are summarized. Then, the first configuration, i.e. 3-PSR parallel mechanism, is mainly analyzed. The degree of freedom is calculated. The movement form of the end-effector output is analyzed by using screw theory. Therefore the motion form with 2R1 T outputted by the end-effector platform of this mechanism is obtained.Secondly, the kinematics of 3-PSR parallel mechanism is analyzed. The inverse positions solution constraint equation is established by closed loop vector method. According to the structure characteristics of the mechanism, the positive position solution is solved in auxiliary by adding three structural constraint equations. Through solving the equations by mathematical software Maple, the numerical verifications of position and inverse solution are conducted, and both results are consistent. According to reciprocal screw theory, the global Jacobian matrix expression is derived, which provides the basis for velocity and acceleration analysis of the mechanism.Thirdly, the workspace of the 3-PSR parallel mechanism is studied. According to the position constraint equations and joint structure constraints, using numerical search method,the reachable workspace of the mechanism is researched. The location set of satisfied end platform reference points are searched, the workspace diagrams of the mechanism with detailed analysis are exported.Finally, the virtual prototype simulation of 3-PSR parallel mechanism is analyzed. By Solid Works software, the 3Dmodel of the mechanism is created, and the 3D model of the mechanism is imported in Adams. Then its kinematics and dynamic are simulated. The change rule of the position, velocity and acceleration of output reference point with respect to time are analyzed by adding the output curve to the end-effector, meanwhile, the change of input with time can be obtained. When a certain external load is applied on the end-effector,the dynamic characteristic change is analyzed. Power consumptions are compared with the situation of zero load and external load. The effect of the load to the mechanism driving force change is analyzed. It is found that the force of driving joint after forced changed smoothly and no mutation. Due to the influence of direction of the force, the power consumption of the second motor is more than the others. The results provide theoretical guidance for the selection of the driver motor, optimization of links and control.