Study Of Position Tracking Control Of MDF Continuous Hot-press Plank Thickness Control Hydraulic System

In recent years, with the development of continuous hot-press and technical improvement, continuous hot-press is gradually taking the place of intermittent multilayer hot-press, and has becoming the main production equipment of Medium Density Fiberboard (MDF). In the stage of keeping thickness, realizing rapid and accurate thickness control is the prerequisite to produce high-quality MDF. However, continuous hot-press plank thickness control hydraulic system contains nonlinear factors, internal parameter perturbations and external load disturbance, so it is highly challenging to realize rapid and accurate thickness control. For this reason, aiming at improving the dynamic performance of the closed-loop system and the robustness with respect to internal parameter perturbations and external load disturbance, based on backstepping sliding mode control method, this paper will deeply study on the position tracking control method of continuous hot-press plank thickness control hydraulic system.(1) According to the structure of continuous hot-press plank thickness control system and the principle of hydraulic position control system, the mathematical model of plank thickness control hydraulic system is established by analyzing the power-mechanism of the valve-controlled hydraulic cylinder, and in order to provide a data basis for simulation verification, the nominal values of the main parameters of the system are given.(2) Aiming at the position tracking control problem of MDF continuous hot-press plank thickness control hydraulic system, and fully taking the internal parameter perturbations and external load disturbance into account, in order to realize rapid and accurate position tracking for eliminating the thickness deviation of slab, the adaptive backstepping sliding mode controller is designed. The designed controller can ensure the asymptotic stability of the system and the asymptotic convergence of the tracking error. Simulation results show that the adaptive backstepping sliding mode controller has better control performance than PID controller.(3) In order to simplify the design process of the adaptive backstepping sliding mode controller, and to improve the dynamic performance of the closed-loop system and the robustness with respect to internal parameter perturbations and external load disturbance, disturbance observer technology is introduced in this paper, and fuzzy disturbance observer (FDO)-based adaptive backstepping sliding mode control strategy is presented. Considering that the conventional FDO has a slow estimation speed when the disturbance observation error is very small and the fast fuzzy disturbance observer (FFDO) has a larger disturbance estimation steady-state error, inspired by fast terminal sliding mode thought, a novel FDO is designed, moreover, the proof is given to prove that the disturbance observation error is uniformly ultimately bounded, and then an adaptive backstepping sliding mode controller is designed based on the novel FDO. Simulation results show that the novel FDO is superior to the conventional FDO and the FFDO; compared with adaptive backstepping sliding mode controller and PID controller, the designed controller has a better control performance.(4) Considering that the design process of FDO is complex, a sliding mode disturbance observer (SMDO) is designed based on adaptive super-twisting algorithm, meanwhile, in order to further improve the dynamic performance of the closed-loop system, the SMDO-based backstepping terminal sliding mode control strategy is presented, terminal sliding mode control is combined at the last step of backstepping method, and a continuous finite time controller is designed. The designed controller not only can realize the finite time convergence of the tracking error of the third subsystem, but also can fundamentally avoid the control singularity problem, and the control input is continuous and chattering-free. Simulation results show that the designed SMDO can accurately estimate the composite disturbance of the system in finite time, and the designed controller can guarantee the closed-loop system have a better dynamic performance.In this paper, the position tracking control problem of continuous hot-press plank thickness control hydraulic system is deeply studied. The theoretical research achievements have significant engineering reference value for producing high-quality MDF.