Closed-loop control of gas pressure in the gas-assisted injection molding process

Abstract

This paper is concerned with the practical application of closed‐loop control on the gas pressure during the gas‐assisted injection molding process. In principle, the gas‐injection process can be treated as a valve‐controlled tank charging. One of the critical factors for the successful application of the process is the obtaining and maintaining of a desired gas injection pressure within the polymer melt in the mold cavity. Most of the currently available commercial gas‐injection machines operate either in an open‐loop manner or with closed‐loop control, relying upon manual tuning of the associated controllers. This is not only time consuming but also lacking in measurable performance. To improve the controller tuning problem while retaining the currently used controller structure, this study implements a control method which combines system identification and optimal linear quadratic regulator theory into an analytic approach. To demonstrate and verify the proposed method, several experiments were conducted. The results of these experiments show that the approach has excellent potential for designing a control system for regulating gas pressure variation during the gas‐assisted injection molding process. © 1999 John Wiley & Sons, Inc. Adv Polym Techn 18: 137–145, 1999

Self-Organizing Fuzzy Controller for Gas-Assisted Injection Molding Combination Systems

“…However, the mathematical model of the gas system is highly nonlinear and complex. According to the assumption that the gas-injection process can be considered to be a valve-controlled tank charging, Chen and Chao [20] simplified the work of Chao et al [19] that was concerned with the model of the gas pressure dynamics, and proposed a linear transfer function to describe it (1) where denotes the open-loop gain of the process, represents the open-loop time constant, is the desired pressure setting of the regulator valve, and denotes the gas-injection pressure. The parameters in this transfer function can be determined using a system identification technology [21]- [23].…”