Synchronization Error Analysis And Experimental Study Of The Dual-drive Feed System Of CNC Machine Tools

Double screw driven system is widely used in feed system with high speed,heavy load and gantry machine tools.The main problem of dual drive systems is synchronization.In this paper,the dual screw feed system is taken as the research object.The influences of dual drive feed table geometry error,thermal deformation of ball screws and feed system structure parameters on the synchronization error were analyzed.And a control scheme of synchronization error was proposed.Firstly,the feed system friction and axial stiffness was identified.The friction of the two axes of feed system under different feed rates was measured by experiments.The parameters in Stribeck friction model were solved by genetic algorithm.Through theoretical analysis,the relationship between axial stiffness and damping with natural frequency and damping ratio is obtained.The curves of amplitude-frequency and phase-frequency characteristic of two axes were measured by experiments.And the axial stiffness and damping of the two axes were calculated.Secondly,the influence of thermal deformation on synchronization error was studied.The temperature field,thermal equilibrium time and temperature difference between the two feed axes were analyzed by finite element analysis and experiment.At the same time,the variation of synchronization error with feed speed,running time and thermal equilibrium time was analyzed.And the prediction model of synchronization error was established.Then,a mathematical model of synchronization error was established with the change of the parameters of the feed system.The influences of feed speed,axial stiffness and load position on the synchronization error were analyzed.Taking the feed system of MCH63 machining center as the research object,the laser interferometer was used to measure the synchronization error under different feed rates.The accuracy of the mathematical model of synchronization error was verified.Finally,the characteristics of three synchronous control modes were analyzed.And the control scheme of fuzzy PID is proposed.The simulation results shew that the fuzzy PID controller has better stability and control ability of synchronization than the ordinary PID.