| Machining tolerance and surface quality of workpieces are greatly influenced by the servo trajectory tracking performance of ball screw feed-drive systems in machine tools.This paper focus on how to minimize the tracking error of ball screw drives,both rigid body dynamics and first order axial vibration mode dynamics are modeled,design and analyze several controllers according to different control theory,tracking performance of which are verified and compared through both software simulation and experiments.Main research contents and innovations as follows:1.General structure of a ball screw drives is introduced,then both rigid body dynamics and two freedom degree axial vibration dynamics are modeled.Two major disturbances including friction and ripple torque are modeled,identified and compensated in the control law respectively,where ripple torque disturbance curve is fitted via spectrum analysis,parameters of LuGre friction model are identified.2.Four kinds of PID,including single loop control of classical PID and fractional order PID,cascade control of P-PI and PI-PI,are analyzed and applied on ball screw drives respectively.Parameters of FOPID controller are determined through Differential Evolution Algorithm and root locus method.3.In terms of disturbances and uncertainties of ball screw drives,which are estimated through adaptive online fuzzy logical systems,combined with sliding mode control,two controllers based on rigid body dynamics and flexible body dynamics are designed to achieve high tracking performance.The experimental results show that fuzzy sliding mode control can reduce uncertainties influence.4.A modified second order sliding mode controller based super-twisting algorithm is designed for ball screw drives,compared with the controller designed with standard form,the modified control law,which considers the trajectory command information and adds integral term of table position error,greatly decreases the tracking error under higher feed velocity and load variation. |
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