A Simple Method for Tuning the Temperature Control Parameters for an Extruder

SATO Akira, KONO Toshiaki

doi:10.4325/seikeikakou.6.740

A simple method for tuning the temperature control parameters for the die and cylinder of a plastics extruder is investigated. This method is based on a fuzzy control system. Recently, an increasing demand for small lot size manufacturing has led to frequent and rapid changes in the manufacturing process. This requires temperature controllers to find the appropriate control parameters quickly with an auto-tuning method. Unfortunately, most commercially based PID controllers apply the so called “Limit cycle method” to tune the appropriate control parameters. This method takes a relatively long time to find the parameters, because it requires several on/off cycles of heater output to form a temperature wave in order to idenify the process characteristics. Furthermore, this method discards the first peak of the temperataure wave, thus wasting time. The first peak is usually higher in magnitude than succeeding waves, but this characteristic can not be explained as long as we assume that the process is a first-order system plus a transportation lag. In this paper, assuming that the process is a second order system, we can explain the characteristics of the wave form theoretically. We find that the magnitude of the peak at an appropriate set temperature can be estimated using the magnitude of the peak of the tuning temperature, regardless of the value of the time constant and gain of the process. We also generate a simple fuzzy rule that can utilize the magnitude of the first peak as a control parameter. Experimental results show that this method is practical enough for its accuracy and robustness, and can decrease the tuning time by one third compared to that of conventional PID controllers.

A Simple Method for Tuning the Temperature Control Parameters for an Extruder

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