Sunday, February 27, 2011

The Layer of PLC Programming Environment

The architecture of PLC programming environment consists of two layers, a model layer, and an application layer. The model layer has three models, a PLC program (control model), a plant model (virtual factory model), and an I/O mapping model. The plant model includes all manufacturing devices of the production system as well as the corresponding device programs to perform their tasks in the production system, and the PLC program consist the control logic for the plant model. It is necessary to define the mapping between the plant model and the PLC program, which is described by the I/O mapping model for the integration of the plant model and the PLC program. The application layer provides two interfaces simultaneously to users.

The ‘PLC Simulator’ performs the control program simulation, and the ‘plant model visualizer’ shows the corresponding plant model (3D graphic models) reflecting the changing states of the production system during the PLC simulation. Thus, it becomes much easier for users to verify the PLC program though the visualizer plant model.

Among the three models of the model layer, the plant model plays a key role in the proposed environment of PLC programming. As mentioned earlier, the plant model should consist all devices as well as the device control programs. The plant model contains of manufacturing devices with their positions in the layout.

This article employs the concept of a virtual device: a digital model imitating the physical and logical aspects of a real device to represent such a manufacturing device. A virtual device needs to maintain its relationships with PLC programs or other devices as well as the inherent attributes of the device, such as the kinematics and geometric shape. To do so, a virtual device is split into two parts; a shell and a core. The shell part can adapt to the different configurations of production systems, and the core part undertakes the inherent properties of the device.

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