Study On NNDO-based Backstepping Sliding Mode Method For Slab Thickness Correction Control Of Medium Density Fiberboard

In recent years,the throughput of medium density fiberboard is increasing year after year.In order to control slab thickness exactly,we explore effective control method to make continuous press hydraulic servo system run well.It has become the key point of study on hotpressing process slab thickness deviation rectification control.It is of overreaching importance to guarantee slab quality and improve the qualification rate of product.Continuous flat press is the main equipment in the hot-pressing technology.Hot pressboard is the critical component of heat and press transfer during the process.There are many hydraulic cylinders on the hot pressboard.Not only mechanical parameters of hydraulic cylinders but also interferences they get from externality are different during work process.As a conesequence of this,deviation of slab thickness come into being which can cause production quality of medium density fiberboard get worse.This paper introduce disturbance observer to backstepping combined sliding mode control strategy to avoid multi-hydraulic cylinders run asynchronously and thereby to achieve the deviation rectification of slab thickness of MDF continuous press.The main research work in the paper are proposed as follows:Significance of research on slab thickness deviation control of continuous flat press of medium density fiberboard and general situation of development of equipment are introduced.Each production segment of continuous press and hot press link which is the most pivotal one in the working process are expounded.Study on hydraulic cylinder which is executive component of hot press is recommended.We can set up mathematical model of servo position control system of single hydraulic cylinder by using the operating principle of hydraulic cylinder.In allusion to positioning servo system of single hydraulic cylinder,sliding mode backstepping control strategy is proposed for slab thickness deviation rectification system of medium density fiberboard which contains factors,such as interference from externality,etc.to solve position tracking control problem.The corresponding controller is designed to control deviation rectification of slab thickness.Stability of control system is proved by analysising Lyapunov theory.Simulation results show that the controller can track the given signal with no overshoot but buffet can not be removed.Backstepping sliding mode control strategy based on Neural Network Disturbance Observer(NNDO)is proposed to control single hydraulic cylinder position tracking system by injecting disturbance observer in backstepping sliding mode control strategy to weaken buffet evocabled by sliding mode backstepping method.Using universal approximation property of NNDO to estimate parameters uncertainty and interference from externality rapidly.The output of NNDO can be used in feedback compensation of disturbances.Controller can realize electric-hydraulic servo system of single hydraulic cylinder track position accurately and smoothly.So the slab thickness deviation caused by interference can be eliminated.Simulation results show the NNDO-based backstepping sliding mode controller can response quickly and tend to stabilize rapidly.The superiority of controller is evident in terms of tracing output signal steadily with no overshoot and weakening chattering.Aiming at positioning servo system of multi-hydraulic cylinders,a new control method is proposed for servo system of continuous press of medium density fiberboard during hot press process which contains different mechanical parameters and various interference from externality,etc.to avoid hydraulic cylinder array run asynchronously.Mathematical model of positioning control system of multi-hydraulic cylinders is established.Using NNDO-based backstepping sliding mode control method to control multi-hydraulic cylinders synchronization positioning system.NNDO for multi-hydraulic cylinders is designed to approach complex interference of each hydraulic cylinder subsystem and to compensate the matching control input.NNDO-based sliding mode backstepping multi-hydraulic cylinders controllers are proposed.Simulation results show that the new controller can effectively reduce synchronization error caused by complex disturbance,and then make multi-hydraulic cylinders run synchronously in a short period of time.The availabilities in terms of restraining weak buffeting and improving closed-loop dynamic performance is also proved.The controller can realize hydraulic cylinder array run synchronously,placidly and quickly.Additionally,the control goal of deviation rectification of slab thickness of MDF continuous press is achieved.