Practice of Industrial Control Logic Programming using Library Components
Oscar Ljungkrantz, Knut �kesson, Martin Fabi · InTech eBooks · 2010
In this chapter a study of PLC programming and use of library components at two Swedish car manufacturers is presented. Both companies used several programs for each PLC, implemented mainly in LD and SFC. These programs included lots of instances of reusable function blocks, FBs. Some of the most frequent FBs were used for automatic control of actuators and conveyors but in total only a minor part of the used FB instances was for automatic control; the majority was for HMI, safety, supervision, production data, communication etc. This is important to consider when developing or modifying frameworks for control program generation, to cope with the new requirements of flexible manufacturing systems. Integrating industrial FBs with new frameworks for generating control sequences is an interesting direction for future research. It is also interesting to consider that although the FBs were frequently reused, their behaviours were only informally specified. In our opinion the FB reuse can be made more efficient by also using tools and methods for formal specification and verification. This is demonstrated by an example component, in which an error of the first implementation attempt is discovered and solved. For formal specifications to be used in industry it is important that the development of relevant specifications is not too troublesome or time consuming. We therefore currently research into developing guidelines for formal specification of PLC program components.