Application of fuzzy control to start-up of twin screw extruder

For the improvement of existing control method which used a simple method of comparison of torque with main screw rpm in start-up of extruder, the fuzzy control algorithm was applied based on the expert principles of extrusion. The first step of the start-up in extrusion of corn grits was that water input rate is maintained at three times higher than an operating set point. Then, as bulk feed rate increases to its set point stepwise, the main screw rpm is controlled by fuzzy reasoning to prevent a blockage phenomena. In the fuzzy reasoning, input variables were torque% and main screw rpm (n)%, and the main screw rpm was estimated to keep the main screw rpm% at higher level than the torque% in excess of about 18% and 26%, respectively. After the bulk feed rate reaches at its set point, the water input rate sequentially decreases back to its set point, during which the main screw rpm is also controlled by fuzzy reasoning in the same manner. Finally, the main screw rpm is also adjusted to its set point after the water input rate reaches at its set point. To manipulate the temperatures of the barrel and the die, PID algorithm for heating and on/off control for cooling were used. Consequently, the successful automation was achieved reproducibly without blockage.