Research On High Rigidity Technology Of Hydrostatic Guideway System In High-Precision Lathe And Turning Center

High-precision digital controlled lathes or turning centers are referred as automatic lathes that have high precision and efficiency.They play a critical role in quantity production of complex parts.Guideway system,as an important part of these machines,must satisfy such requirements such as high static and kineticstraightness accuracy,strong stiffness,large damping,and steady motion(no creeping)in low velocity.Therefore,this research analyzes the guideway systems in literature and proposes a novel concept that employs closed hydrostatic guide way as supporting part of X and Z direction feed shaft.In addition,lathe beds are made of resin concrete in order to get good vibration damping performance and heat stability.In order to build the system,we design differential rectangle chamber with double thin-film feedback for Z shaft.We also calculate its static stiffness and kinetic damping of the hydrostatic supporting system.We obtain differential equations of the guideway system by establishing kinematic equations of the guideway and double thin film,and flow equations.Next,the system transfer function is obtained by performing Laplace transform.The effects of load size and frequency on the system precision are further investigated.The guideway system needs not only thin film to have high static and kinetic stiffness,but also mechanical structure does.This research establishes the models of clip and base and analyzes their static force and deformation by ANSYS.In addition,we also implement modal analysis and obtain their vibration mode of first four orders and corresponding frequencies in order to avoid resonance during production.In order to study the micro flow in chamber and the effects of each part,we establish the model of different rectangle chambers.The effects of chamber depth,four circular bead and supporting surface velocity on static pressure distribution,flow distribution and temperature distribution are investigated by defining different boundary conditions and system parameters.We obtain the range of these parameters which are used for designing cooling systems.The static and kinetic stiffness of hydrostatic supporting with double thin-film feedback is high in ideal conditions,which satisfies requirements of high-precision guideway system.However,in practice the stiffness may be low or even the system is not steady because of the effects of guide gap,film thickness and throttling gap,and oil compressibility.In order to control the gap of guideway,this research employs servo valve as control element and calculates the corresponding transfer function.In order to improve the performance,PSO,LDIWPSO,CLPSO and MMAPSO algorithms are used to optimize PID parameters.Results show that MMAPSO algorithm could reduce the settling time greatly and has fastest convergence rate and precision.To test the rigidity and bearing capacity of the guide way system adopted the servo position closed-loop control theory,which the test bench was modelled on the topic of Z axis machine tool guideway structure and parameters.Only the one side position was controlled by servo valve in the guideway system due to some constraints.Considering the servo valve and interference factors,a good control effect was achieved and the great stiffness requirement was satisfied.At the same time,the system has a strong ability to resist the overload.