About the control problem of the injection molding machine

Modern plastic injection molding machine is a typical system integrating machine, electricity and liquid. Because of its characteristics of complex molding, less processing, and many types of plastics processed, it has developed extremely rapidly since its inception. More than 80% of the world's engineering plastic products are processed by injection molding machines.

Conventional injection molding machines generally use simple open-loop control, which is controlled according to preset values. In the manufacturing process of the device, parameter values ​​such as clamping force, cycle time, temperature, etc. are preset in advance, and are maintained by the machine during the production process. For example, the mold temperature can be maintained by controlling the temperature of the heating fluid, which can be maintained by controlling the power of the external heating device. This control method has a simple structure, but the anti-interference ability is poor, and the control temperature is also relatively low. At present, more injection molding machines use closed-loop control, which is controlled according to the deviation between the online measured value and the set value. The closed-loop control system adopts a negative feedback loop, which has strong anti-interference ability. When the injection speed, injection pressure, cavity temperature, cavity pressure, melt temperature and oil pressure are deviated due to interference in the production process, the machine is self-applied. The control system automatically corrects the interference. This control method has strong anti-interference ability and high control precision. A more advanced control method is to use a computer to control, that is, to construct a closed-loop real-time computer control system. It includes several types of direct digital control systems, supervisory computer control systems, decentralized control systems, and multi-level control.

At present, there are three commonly used injection molding machine control systems, namely, conventional relay type, programmable controller type and microcomputer controlled type. In recent years, programmable controllers have been widely used in injection molding machine control systems due to their high reliability and high performance. In order to improve the level and quality of the injection molding machine control system, a programmable computer controller designed for small and medium-sized control systems with a higher level than the programmable controller has emerged. The programmable computer controller integrates the features of an industrial programmable computer with a standard programmable controller, has a multitasking time-sharing operating system, and is more powerful in data calculation and processing than a variable program controller. The computerized control system is composed of a programmable computer controller to realize various control processes including injection position control, speed control, temperature control, fault control and real-time display, which can greatly improve the quality of plastic products and improve the economy. benefit.

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