Study Of Refiner Grinding Gap On Electro- Hydraulic Servo Control System

The size of the gap between grinds of a refiner has a great effect on the fiber dissociation quality of the wood pieces, and it’s the base of the constant load control and constant energy consumption rate. Usually, the size of the gap between grinds of a refiner should be controlled within the range of 0.2-0.5mm, and the control accuracy is 0.01mm. The gap which is set before fiber separation changes easily due to the load changes in grinding process, uneven loading on the gap and the moving disc, and the abrasion of the grinds. The size of the gap usually controlled by mechanical adjustment and hydraulic adjustment, but they cause deviations more or less. The preparation of high quality fibers needs the accurate fine-tuning ability on the size of the gap. Based on its excellent performance, a servo control system on controlling the size of the gap is designed, and this has a role in promoting the technology on the gap size control.The main factors affecting the stability of the grinding gap and the structure and theory of the typical gap control system of a refiner are studied based on the description of a refiner structure and working principles. The proper function and control requirements of a grinding gap size control system of the refiner is summarized. Based on the hydraulic servo control principles, a design of control scheme is put forward with the features of grinding gap control of a refiner. The servo control system structure is determined and the work principles are elaborated.The parameters of the system are determined with the structure reference of 54 inches diameters grinds refiner. After determining the control parameters, the valve controlled hydraulic cylinder is designed and some key parts are chosen. The mathematical models of each system sectors are established and the open-loop transfer functions are exported, and the parameters of each sector are solved. The transfer functions of the system are exported and the mathematical model is established. And it’s the mathematical basis of the system performance analysis.The stability of the system and time-domain response characteristics are analyzed by using Matlab to grasp the steady-state errors and inadequate of time-domain response. Based on the errors and inadequate, a forward correction is finished by using PID control method. Using the critical ratio method, a set of the PID controller parameters is made by Matlab/Simulink which makes the control performance can meet the requirements of grinding gap controls.A simulation of the system control performance is made, a physical model is established and the parameters are set by using AMESim. The Loaded status is simulated by utilizing standard signal. A simulation under changing loading and abrasion of the grinding circumstances is made to analyze the refiner working situation. The result of the test to the dynamic characteristic shows that the servo control system is stable and accurate. It meet the requirements of the controlling the size of the refiner grindings.