Communication Delay Compensation Technology Of Full-closed Position Control For Milling Machine Feed System

CNC machine tool is an important tool of equipment manufacturing industry,the cornerstone of advanced manufacturing and modern manufacturing,and the key link of realizing high-end technology and national defense modernization.The milling machine is an important part of CNC machine tools.It can not only process simple surfaces such as plane and groove,but also process complex surfaces such as revolving body surface and spline shaft.It is widely used in mechanical manufacturing.High speed and high precision machining is always the development direction of milling machine feed system.In order to achieve high-precision control,the traditional semi closed-loop control method is no longer applicable.Generally,the full closed-loop control method using the actual load position for position closed-loop control is adopted.However,the full closed-loop control loop is long and contains a large number of mechanical nonlinear links.It is difficult to achieve high stiffness control,which will sacrifice the dynamic response of the feed system and limit the high-speed machining ability.In addition,the modern CNC system often adopts the structural concept that the NC device is responsible for the calculation and the servo driver is responsible for the execution.The data interaction between the two is conducted through the bus,and there is inevitably a communication delay.And the existence of the delay will further deteriorate the response performance of the system,which is no different from adding insult to injury for high-speed machining.The optimization of full closed-loop control strategy and communication delay compensation become particularly important.In this paper,firstly,the mechanical transmission mechanism is modeled,and the structure of mechanical transmission is divided one by one,which is equivalent to a multi inertia model.Then,from the actual mechanical structure stiffness and the connection between them,the mechanical transmission link is approximately reduced to a dual inertia model.At last,the full closed-loop feed system model is established based on the equivalent model of the electrical control part.In the next two chapters,the elastic resonance problem and the communication delay problem are separated and analyzed one by one.In the first chapter,the influence of the elastic link on the full closed-loop system is analyzed,and the transfer function of the full closed-loop control is derived.The existence of the elastic link introduces the resonance point to the system.The sudden change of the amplitude and phase frequency at the resonance point seriously affects the gain margin of the system at that point,and then the oscillation problem occurs.In order to suppress the oscillation phenomenon of full closed-loop,a position control strategy of double position feedback is proposed.Through simulation and experiment,the effectiveness of double position feedback control in suppressing oscillation is verified to ensure the position gain of the system.In the second chapter,the communication delay is introduced and analyzed on the premise of adopting the double position feedback control strategy.The existence of time delay makes it difficult for the system to respond to the input signal in time.Taking the linear positioning as an example,the end is prone to overshoot,which is strictly avoided in machining.Firstly,from the perspective of frequency-domain root locus,we get that the delay will reduce the gain of stable root locus of the system.Secondly,we propose Smith predictor and communication disturbance observer(CDOB)to compensate for the delay.To solve the problem that the method is sensitive to the accuracy of the model,we propose two improved strategies,robust Smith predictor and communication disturbance observer(CDOB).The effectiveness of the algorithm is verified by simulation and experiment.