Fault-tolerant actuators and drives—Structures, fault detection principles and applications

Abstract

As fault detection and fault diagnosis methods are more and more finding their way into modern industrial mechatronic products, it is now time to take the next step. Based on the research efforts for fault detection and diagnosis, a status report has been prepared for research on fault management, i.e. automatic reactions of the system to continue operation after the detection of faults. These reactions may employ hardware redundancy (i.e. switching from a faulty actuator to another, intact one) or analytical redundancy (i.e. switching from a faulty sensor to a “model sensor” or “soft sensor”). A total fault-tolerance concept must encompass all components of a system, i.e. the actuators and drives, the process itself, the sensors as well as the controller and communication. In many cases, a degradation of functions has to be accepted after a fault has appeared. Concentrating on some widespread actuation principles, the paper will focus on electric drives and hydraulic actuators. First, a review is given on fault-tolerance principles and general structural considerations, e.g. hot-standby and cold-standby, focusing on the scheme of an overall fault-tolerant control system. Then, fault statistics for existing actuators and drives will be presented. These fault statistics give hints on the parts of the actuators which are most susceptible to faults. Different designs of fault-tolerant actuators and drives, which have been realized as laboratory prototypes or even on an industrial scale, shall be presented and evaluated with respect to their capabilities of withstanding faults. Finally, an outlook for fault-tolerant mechatronic systems will be given.