Research On Contour Tracking Control Algorithm In Network Environment

Contour tracking control is a common task of multi-axis motion control in manufacturing processing,such as welding,spraying,grinding,cutting,engraving,etc.Contour accuracy is one of the key technical indicators to measure production quality.At present,contour-tracking control systems in centralized or point-to-point structure have been developed relatively well.The controller products mostly use the ‘PC + motion-control card' architecture and can achieve high-precision contour tracking control.However,this architecture of motion controllers has the disadvantages of complicated wiring,poor scalability,limited transmission,and poor interconnectivity,which becomes difficult to meet the requirements of data sharing and intelligent manufacturing in modern manufacturing.Aim at this issue,Ethernet communication technology is introduced into the multi-axis motion control system.Therefore,it is of great theoretical and practical significance to study the problem of contour tracking control in the network environment.With the rapid development of network communication technology and the growing demand for networked motion controllers,a variety of industrial-Ethernet protocols have emerged,such as EtherCAT,EtherNet/IP,EPA,etc.,and are widely used in motion control systems.However,most industrial Ethernet-based motion control systems require additional hardware support,and the associated products are expensive,which limits their development to some extent.Relatively speaking,the general-purpose Ethernet has lower network cost and better network interconnection,and with the continuous increase of network transmission rate,it is possible to apply it to motion control systems.In addition,if we use the personal computer(PC)as a control center,which has a powerful computing ability,the versatility of the control system will be greatly increased without adding hardware modules.Therefore,based on a PC control center,the development of a networked motion control system based on general-purpose Ethernet has certain application value.However,the introduction of the Ethernet technology into the motion control system brings new problems.Among them,network induced delay is one of the main problems,which will lead to the degradation of multi-axis contour tracking control performance.At the same time,the actuator is often affected by various external disturbances during the machining process.The effect of time-varying aperiodic disturbances on the repetitive machining process cannot be ignored.According to the above,this dissertation studies the contour tracking control algorithm in the general-purpose Ethernet environment.The purpose is to achieve high-precision contour tracking control for contour processing tasks with repetitive properties while considering the effect of system time-varying delay and external disturbance.The main research contents and results are as follows:(1)Based on the research requirements of the contour tracking control algorithm,an experimental setup of a multi-axis contour tracking control system based on general-purpose Ethernet is constructed.Then,it is very convenient to carry out the experiments of various contour tracking control algorithms,therefore to verify the effectiveness and feasibility of the algorithms.At the same time,the model of the contour tracking control system in a network environment is established.The system time-varying delay is treated as a delay-induced disturbance(DID),whose mathematical expression is listed.Thus,the system delay and disturbance are normalized,which is well prepared for subsequent algorithm research.The experimental setup has good versatility and can be used for experimental verification of various motion control algorithms.(2)A contour tracking control algorithm based on active disturbance rejection control(ADRC)and iterative learning cross-coupling control(ILCCC)is proposed for a class of simple contour trajectories.The ADRC is used to estimate the system total disturbance(including DID and external disturbances)to eliminate its effect on the system.Since the system tasks are repetitive,an ILCCC contour-error-compensation controller is designed,which continuously optimizes the control performance though the learning mechanism,to further improve the contour tracking accuracy.This contour controller doesn't need system model information and has a simple structure,which can be widely used for tracking control of simple contour trajectories.(3)In order to consider the individual-axis tracking control performance and contour tracking control performance at the same time,a contour tracking control algorithm based on iterative learning control(ILC),ESO and cross-coupling control(CCC)is proposed.The ESO is used to estimate the system total disturbance,and the ILC-based control law is designed,which can achieve high-precision individual-axis tracking control while compensating the disturbance.Subsequently,a CCC contour-error-compensation controller based on iterative-domain fuzzy control is designed,where the fuzzy controller is applied to self-tuning CCC gains.Thus,the contour-error-compensation controller is prevented from overcompensating the individual-axis tracking controller during the first few iteration trials,which ensures individual-axis tracking control performance.This algorithm guarantees the stability of the system and can be used for high-precision tracking control of various contour trajectories in the network environment.(4)Considering mismatched disturbances in the system,a contour tracking control algorithm based on ILC,equivalent input disturbance(EID)and CCC is proposed for a class of continuous contour trajectories.First,an improved EID(IEID)control method is proposed,which can effectively suppress the effect of system matched and mismatched disturbances,and combined with ILC to achieve high-precision individual-axis tracking control.Subsequently,CCC is used to further improve contour tracking control performance.The IEID can effectively improve the accuracy of disturbance estimation without bringing any other constraints,which can widely replace the application of EID.At the same time,the control algorithm based on ILC and IEID can be used to attenuate various kinds of disturbances including periodic/aperiodic and matched/mismatched ones,and also have good algorithm portability.Simulations and experiments were carried out to verify the effectiveness and feasibility of the proposed control algorithms.Finally,the dissertation is summarized and the issues to be further studied are looked into.