Dynamic Performance Analysis Of Planar Parallel Mechanism And Motorized Spindle Coupling System

Parallel machine tool which is also called virtual axis machine tool, is a new kind of machine tool. Parallel machine tool gets breakthrough development in machine tool structure and technique in resent years. The substance of parallel machine tools is the combination of robot technology and machine tool structure technology. The machining precision is one of the main indices of parallel machine tool performances, people have higher demand to the machining precision with the development of the modern manufactory, and machining precision has become the key factor that parallel machine tool can be applied to actual process. Therefore, studying the affecting factors on the parallel machine tool machining precision, analyzing the dynamic performances of the parallel machine tool are of great importance to the improvement of parallel machine tool machining precision.After a summary on the research actualities of the parallel machine tool both at home and aboard, the dynamic performances of the planar parallel machine tool are studied. First, problems such as kinematics solution, machine error, and error model are discussed based on the kinematics fundamental theory. Second, the dynamic model of the coupling system is obtained through building the dynamic model of the planar parallel mechanism and the motorized spindle unit by means of extended order method. Meantime, the vibration responses of the coupling system under the action of several typical excitations are analyzed. Finally, the dynamic performances of the planar parallel mechanism and motorized spindle coupling system are analyzed and evaluated. The main work and the results obtained are as follows:(1) The basic classification and the main source of the parallel machine tool error are analyzed. It is pointed out that the key of dynamic performance analysis of the planar parallel machine tools is to reflect the characteristics of both the vibration of planar parallel mechanism and motorized spindle unit. Therefore, the dynamic model of the planar parallel mechanism and the motorized spindle unit is built based on the Finite Element Method and rotor dynamics theory respectively, and then the dynamic model of the coupling system is obtained by means of extended order method. (2) The steady-state responses of the key nodes of the coupling system under the action of sinusoidal excitation are analyzed based on the dynamic model of the coupling system, and the magnitude-frequency characteristic curves are obtained. Then, the dynamic performances of the planar parallel machine tool are preliminary described from the simulation data. The results show that the parallel mechanism becomes deformed obviously under the action of excitation at frequencies greater than 20Hz, which causes the motorized spindle vibrate excessively, and lowers the dynamic performances of the planar parallel machine tool obviously.(3) The transient responses of the motorized spindle under the action of the impulse, step, pitch and simple harmonic excitation are respectively analyzed in two cases of the planar parallel machine tool is rigid and elastic, and the systematic evaluation of the dynamic performances of the coupling system is made. The results show that the elastic deformation of the planar parallel machine tool leads to remarkable increase of the motorized spindle amplitude, and the vibration range of the motorized spindle is much greater than that the parallel mechanism is rigid.(4) The influences of planar parallel mechanism and motorized spindle dynamic parameters on the planar parallel machine tool and motorized spindle coupling system are studied respectively. The results show that the vibration responses of the coupling system are mainly affected by the stiffness and damping of the planar parallel mechanism, the larger the stiffness and damping of the parallel mechanisms are, the higher the machining precision of the planar parallel machine tool is. In contrast, the influences of motorized spindle stiffness and damping on the machining precision are not obvious.(5) The time-domain responses of the planar parallel mechanism are measured, and the amplitude-frequency characteristics of the parallel mechanism are obtained by analyzing and processing the experiment data. The correctness of theoretical modeling and simulation analysis is verified by comparing experimental results with the simulation ones.The creative points are as follows: First, the conceive to take the planar parallel mechanism and motorized spindle as a dynamic coupling system is raised in the study of machine tool dynamic performances. Second, the dynamic model of planar parallel mechanism and motorized spindle coupling system is established by means of extended order method.