| Large stroke and high precision micro feed technology has become one of the main bottlenecks restricting the further development of precision and ultra-precision machining.The feed system based on conventional rolling contact components is difficult to achieve high-precision micro-displacement control due to the shortcomings of high-frequency vibration,low-speed crawling and contact wear.Although the feed technology driven by macro-micro composite can meet the requirements of large stroke feed,the micro-motion platform driven by electric,magnetic,thermal,optical and acoustic effects of intelligent materials has obvious defects such as nonlinearity,creep,small stroke and small rigidity.The conventional hydrostatic lead screw feed system can make up for the shortcomings of the rolling transmission components due to its high precision,high stiffness and high vibration resistance,but the low-speed crawling problem at the drive end is still difficult to avoid.Therefore,based on the principle of ’differential’ synthesis and spiral transmission of hydrostatic lead screw,a new method of realizing large stroke micro feed is proposed to overcome the bottleneck of existing technology.In this dissertation,the proposed dual-drive hydrostatic lead screw micro-feed technology is systematically investigated.The design and optimization of the dual-drive hydrostatic lead screw,the static and dynamic characteristics of the micro-feed system under the influence of boundary slip and variable load,the thermal characteristics of micro-feed system and the friction modeling,identification,compensation control are explored.The specific investigation in this work is as follows:First of all,based on the proposed dual-drive hydrostatic lead screw,the static and dynamic characteristics under different motion modes are investigated considering the influence of boundary slip.The structure of dual-drive hydrostatic lead screw is designed,which reduces the manufacturing difficulty of nut-driven hydrostatic lead screw.Based on the equivalent sector theory of helical surface,Reynolds equation and flow continuity equation,the oil film flow model of double-drive hydrostatic lead screw is proposed.The Navier slip model boundary condition is introduced into the modified Reynolds equation in the oil film flow equation of the double-drive hydrostatic lead screw.The finite difference method is used to reveal the influence of boundary slip on the axial bearing capacity,axial stiffness and damping coefficient of the oil film of the hydrostatic lead screw under the conventional screw single-drive feed mode and dual-drive differential feed mode.After that,the transmission mechanism of the double-drive hydrostatic lead screw,the nut displacement fluctuation characteristics under variable load and extremely-low feed speed,and the method of reducing the displacement fluctuation are investigated.It is proposed to use the dual-drive differential composite principle and the wedge oil film gap to greatly enhance the hydrodynamic effect of the lubricating oil film while ensuring the extremely low speed feed of the workbench.The oil film Reynolds equation including pitch error and nut pose error is derived.The transient motion of hydrostatic nut under ultra-low speed and variable load is studied by combining the motion equation and Euler equation.The nut displacement fluctuation curve and the corresponding oil film characteristics distribution of the dual-drive hydrostatic lead screw feed system under different loads and synthetic speeds at extremely low feed speeds are explored.The combined dual-drive hydrostatic lead screw is developed,and the micro-feeding experimental platform of the dual-drive hydrostatic lead screw is built.The experiment confirmed that the dual-drive hydrostatic lead screw,a key functional component,can greatly improve the stability of the conventional hydrostatic lead screw under extreme conditions such as extremely low speed and variable load.Then,the thermal performance of dual-drive hydrostatic lead screw micro-feed system is investigated.The theoretical model of heat generation and heat dissipation of the dual-drive hydrostatic screw micro-feeding system is established.The threedimensional multi-physical field(flow-heat-solid)coupled thermal characteristic analysis model of the system is constructed by finite element method.Considering the variable viscosity of the oil film and the heat dissipation conditions in the oil film region,the steady-state temperature field distribution of the micro-feed system and the axial thermal error of the screw under different combined speeds are simulated and calculated.The validity and accuracy of the simulation model are verified by experiments.By comparing with the two-axis differential feed system based on rolling functional components,it is proved that the thermal performance of the micro feed system proposed in this study is superior.In addition,an optimized heat dissipation scheme is proposed for the dual-drive hydrostatic lead screw.The simulation results show that the proposed optimization scheme can effectively suppress the thermal impact of the hydrostatic nut assembly on the screw.Finally,the friction modeling,identification and compensation control technology of the novel dual-drive hydrostatic lead screw micro-feed system are investigated.Aiming at the micro control requirements of feed system,a dynamic friction calculation model of oil film is established based on the theory of variable viscosity of oil film.According to the special transmission structure and oil film damping characteristics of the dual-drive hydrostatic lead screw micro-feed system,the all-component refinement friction identification method is proposed based on the LuGre friction model.Based on Backstepping method,the all-component adaptive compensation control algorithm considering the influence of external disturbances such as temperature rise and mechanical vibration/shock is designed.The effectiveness of the oil film dynamic damping calculation method and the all-component adaptive compensation control algorithm is proved by experiments.At the same time,it is also verified that the developed dual-drive hydrostatic lead screw micro feed system is superior to the conventional servo system at extreme-low speed and large stroke. |
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