Model Based Fault Isolation for Object-Oriented Control Systems
Magnus Larsson, Inger Erlander Klein, Dan Lawesson, Ulf Nilsson · 1999
This report addresses the problem of fault propagation between software modules in a large industrial control system with anobject oriented architecture. There exists a conflict between object-oriented design goals such as encapsulation and modularity, and the possibility to suppress propagating error conditions. When an object detects an error condition, it is not desirable toperform the extensive querying of other objects that would be necessary to decide how close to the real fault the object is and hence whether it should report to the user. The fault propagation manifests itself as many irrelevant error messages thus causing problems for system operators and service personnel trying to quickly isolate the real fault. A system developer with insight in the system design, can, of course, often easily interpret the multitude of error messages from a fault scenario and isolate the primary cause. The key observation is thatt his can often be done using high-level models of the system and the fault propagation. We have made an effort to automate this procedure, and we propose a fault isolation scheme as an extra layer between the operator and the core control system. In the fault isolation layer, post-processing of the fault information from the system is performed, to achieve clear and concise fault information to the operator without violating encapsulation and modularity. A high-level and informal explanation model for the fault propagation is presented and a taxonomy for error conditions in an object oriented system is proposed. We outline algorithms and methods that use the explanation model and the error condition taxonomy together with a structural system model to form a cause-effect relation on the error messages, that can be used to find the most significant error message(s) in a fault scenario.The approach is illustrated by means of several examples. The approach has been implemented and tested on a commercial control system for industrial robots developed by ABB Robotics. A patent claim has also been filed with the Swedish Patent Office (PRV).