Automatic diagnosis on sequential machine control

In the factory automation (FA) area of the manufacturing industry, maintenance management for improving the operational efficiency of equipment is very important. The production line, which is highly automated and is operated by a small number of staff, is very sensitive to unexpected troubles. If there is little information about the troubles, diagnosis and repair of equipment will take time and production efficiency will fall as a result. A programmable controller (PC) is adopted as machine control of a production line in many manufacturing industries. Generally the ladder diagram, which imitates the electric circuit, is used for the PC program. If equipment is highly automated, the volume of a ladder diagram increases, and it becomes complicated and it is impossible to maintain. This paper proposes automatic diagnosis (AD) for PC, which supports maintenance powerfully at the time of equipment failure. The AD features a simple and standard expression, it can be applied to any PCs, has been independent of an application program, and is not influenced by program change. The authors found out many advantages compared with the conventional troubleshooting, as a result of applying AD to actual equipment.