A Study of Industrial Logic Control Programming using Library Components

In this paper a study of logic control programming practices and use of library components at two European car manufacturers, is presented. The research provides results important to consider for researchers and PLC vendors when developing frameworks for control program generation, to cope with new requirements of flexible manufacturing systems. The main observations are: the programs, written mainly in Ladder Diagrams and Sequential Function Charts, frequently reuse pre-developed function blocks; it is important that the control programs can be understood and used for trouble-shooting by the operators; and finally, the code handles, besides automatic control, also safety and supervision, human machine interface, product data, communication etc., the code for automatic control is a minor part of the total code.