Object-oriented programming of PLC based on IEC 1131

Abstract

The software development for programmable logical controllers is usually based on low-level languages such as the instruction list or the ladder diagram. At the same time, the programmer looks at a machine or an assembly system in a bit-oriented way: he translates the operational sequences into logical and/or time based combinations of binary signals described by the means of boolean algebra. A machine, however, does not only consist of binary signals but of technical components, i.e. objects such as nc-axes, carriage systems and other facilities. These objects can be characterized by different features; their connection to a PLC being the basis of the conventional programming methods is only one of them. As these classical methods cause a lot of problems in reality they should be improved. The following report shows a way how to integrate object-oriented features into the standardized PLC-language "Sequential Function Chart".