Fault diagnosis and fault tolerance of drive systems - Status and research

Mechatronic components allow to design systems with many new functionalities and to turn away from classical design paradigms which had been required for purely mechanical designs. However, the increase in complexity and the renunciation from purely mechanical to electro-mechanical designs goes along with an increase in the possibility of unpredictable faults. Therefore, the design paradigm also has to increase from fault detection and diagnosis to fault-tolerance by redundancy at least for safety related applications. The idea for this paradigm change is that faults cannot entirely be avoided in complex systems. Rather, the occurrence of faults is accepted and measures are taken as to limit the implications of the fault and maintain the operability despite these impairments caused by the fault. The paper at hand will first introduce the overall setup of a component respectively system with integrated fault management. Fault detection and diagnosis are compactly sketched before fault tolerance principles are introduced. The paper looks at both hardware tolerance and analytical tolerance. As the reaction to the fault can cause a functional degradation even in the presence of redundancy, the different degradation steps are also introduced. Then, different designs of fault tolerant electric and hydraulic actuators as well as sensors are presented. An essential requirement for the inclusion of the designs into this paper was at least an experimental realization of the concept. A total of 11 different designs is presented. Finally, the different designs are compared and future developments are shortly discussed.