Control of injection velocity using a fuzzy logic rule-based controller for thermoplastics injection molding

Injection velocity to a large degree determines the melt injection rate dur ing the injection phase, and it has critical impact on the molded part qual ity, such as shrinkage, warpage, and impact strength. An injection molding machine operates with different injection velocity profiles, barrel tempera tures, molds, and materials. These strongly different molding conditions ca use the injection velocity dynamics to vary significantly and to make the c ontrol performance of the injection velocity poor with a typical PID contro ller. A real-time, closed-loop feedback and feedforward control system base d on fuzzy logic has been designed, developed, and implemented to control t he injection velocity. The fuzzy logic rules of the controller are optimize d by analyzing phase plane characteristics. The controller output membershi p functions are optimized based on a 2(k) factorial design technique. The e xperimental results reveal that the fuzzy logic-based controller works well with different molds, materials, barrel temperatures, and injection veloci ty profiles, indicating that the fuzzy logic controller has superior perfor mance over the conventional PID controller in response speed, set-point tra cking ability, noise rejection, and robustness.