Research On Theory And Methodology Of Adaptive Constant Force Control In The Milling Process

In the traditional Numerical Control(NC)machining,because the shape of the workpiece is complex and changeable,the selection of machining parameters tends to be conservative and results in the low efficiency,which cannot meet the need of the production requirements of high speed machining in large quantities.At present,since the adaptive control technology for machining processes can solve this problem well,the research into this topic is of great importance.This thesis researches the application of adaptive control of cutting force in milling processes.Focus on the design of adaptive control system of milling force,the following main work is completed in this paper.The quadratic mathematical model,which can describe the dynamic characteristics of machining processes,is set up based on the deep-going research on the cutting process modeling.Furthermore,the improved recursive least squares algorithm for estimating the time-varying parameters of the dynamic system is studied by using the least squares system identification principle.Aiming at quadratic model of machining process,an improved model reference adaptive control algorithm is put forward,and the designed adaptive controller is validated by the simulation analysis.Based on the analysis of the influence of cutting force and variable parameter milling tests,the experiential formula for calculating average milling force is adopted to modelling fitting in good effect.Considering the influence of cyclical adaptive adjustment of feed speed on the dynamic characteristics of machine feed system,the identification method of working mode of feed system is studied.Two methods,machine motion self-excitation and force hammer excitation,are used to process the modal identification test,and the range of adaptive instruction sending cycle is determined on the basis of the experimental results.Based on PMAC numerical control system,the software development of the adaptive control system in milling processes is completed by using VB.net programming language.Furthermore,this paper then makes programming technology analysis on the software components in modular,and verifies the effectiveness of the online parameter identification,adaptive control algorithm and software design through the milling experiment of variable cutting width T-shape workpiece.The research results show that the adaptive control system can achieve effective cutting force control in milling process.When the cutting width of workpiece is changed,the cyclical average cutting force of principal axis can keep near the expected constraint by adjusting feed speed automatically so as to improve machine efficiency and protect machine tools and cutters at the same time.Meanwhile it also indicates that the machining process control has little impact on the dynamic characteristics of machine feed system and can satisfy the demands of processing and use.