Research On Nano Linear Motion Systems With Large Stroke And Low Velocity For Ultra-precision Fly-cutting Machining

Fly-cutting is widely used in the manufacture of complex parts such as KDP crystal,prism matrices,contact lenses,aspherical lenses and reflective gratings.It is one of the most important manufacture methods for obtaining the high-precision objects with complex surface structure,and advanced fly-cutting lathes and fly-cutting manufacture technology are widely studied in recent decades.However,high performance machining requires high performance machine tools and cutting tools.The nano linear motion systems with large stroke and low velocity in the fly-cutting lathe systems take the responsibility of the feeding action of the workpiece,which means that performance of the ultra-precision linear motion systems are crucial to the final product surface quality and production efficiency.Aiming at the design and modeling of nano linear motion systems with large stroke and low velocity for fly-cutting,this dissertation focuses on the the key technologies such as PMLSM driver,position prediction of the ultra-precision motion systems,controller design and parameter tuning of the controllers.The main research contents are as follows:Firstly,a ultra-precision air-bearing linear motion stage driven by an iron-less permanent magnet linear synchronous motor(IPMLSM)is designed.By establishing the dynamic model and performing identification experiments,the system dynamic model of the stage is calculated.A static force experiment system is build based on the motion stage,and the cable force of the stage is identified with the static force experiment system.Secondly,a simplified thrust force model of IPMLSMs including end effects is presented.Both static and dynamic identification experiments are performed to effectively identify the model.It is shown with simulations and experiments that the end effect causes velocity fluctuations under low velocities.Therefore,a feedback compensation controller based on the identified thrust force model is designed and implemented for reducing low-velocity fluctuations.Thirdly,an adaptive two-degree-of-freedom(2DoF)proportional/proportional-integral(PPI)controller is presented for ultra-precise linear motion stages driven by PMLSMs under lowvelocity and large velocity ratio conditions.To guarantee high real-time performance and high prediction accuracy,the JITL method with an improved database(JITLIDB)is presented with a layered database structure being employed and a forgetting factor being introduced.Based on the JITL predictions,a 2DoF P-PI parameter updating algorithm is designed,which is proven to guarantee that the system position errors converge to zero using the Lyapunov method.Moreover,a linear active disturbance rejection controller(LADRC)with parameter tuning algorithms based on JITL output predictions is presented for ultra-precise linear motion stages driven by PMLSMs.All the parameter tuning algorithms are proven to guarantee the convergence property of the both algorithms using the Lyapunov method.Through low-velocity uniform motion simulations and experiments,it is shown that the proposed LADRC achieves satisfying performance on rejecting disturbance and reducing the position output fluctuations caused by cutting force of fly-cutting lathe.Finally,A comprehensive comparison is made among the traditional P-PI controller,the adaptive 2Dof P-PI controller and the LADRC with parameter tuning algorithm through experiments in the presence or absence of the cutting force and the end effect compensation algorithm.Combined with the analysis and discussion of the experiments mentioned above,the instructional suggestions are given on the control algorithm design of ultra-precision air-bearing linear motion stages driven by PMLSMs.The research on nano linear motion systems with large stroke and low velocity for ultraprecision fly-cutting machining will be useful and helpful for developing nano linear motion systems with large stroke,investigating the motion control of the ultra-precision systems,studying the controller parameter tuning and predicting of the ultra-precision system outputs.