Abstract
In the injection moulding, it is important to control precisely injection speed in the injection process and polymer pressure in the packing process. These controlled variables mainly determine mechanical or optical properties of mouldings. Each process is essentially a distributed parameter system, and there is some variation of dynamical characteristics depending on the shape of the mould cavity, temperature of the polymer and that of the mould.
Each process is regarded as a multistage process which is a sequential series of subprocesses having different dynamical characteristics. The subprocess is modelled by a lumped parameter system. Then control system is designed as follows.
(1) state feedback control for each subprocess to make the dynamical characteristics homogeneous through the injection process or the packing process.
(2) servo compensation to improve transient characteristics of the controlled variables.
(3) repetitive control to improve steadystate characteristics and to compensate the variation of the polymer temperature and of the mould temperature.
Finally, the experimental results illustrate that this control method is effective for the improvement of the injection speed response and of the polymer pressure response.
