On the design of a fault-tolerant flight controller

Autonomous manipulators can be used in a wide range of applications, especially to complete dangerous tasks in remote or hazard environment such as planetary exploration, cleanup of toxic waste, fire fighting, etc. When an error occurs (e.g., a sensor fails to provide correct measurement), it is desirable that the mobile manipulator is capable of compensating this failure without the need of human presence to fix the problem. A fault-tolerant system is the one that can continue its operation without significant impact on performance in the presence of hardware and/or software errors. The studies of fault-tolerant system started in late 50s, when the first electronic computer was developed. To overcome the low reliability of the electronic parts, some of the early computers had two duplicated Arithmetic Logic Units (ALUs). Since 1970s, research on fault-tolerance systems has led to a variety of applications, including robotics, nuclear power plants, computer architecture and industrial process control. In this paper, the design of a fault-tolerant flight controller to control the lateral motion of an aircraft is investigated. A fifth-order state space representation of the airplane lateral motion dynamics is derived; then a nominal feedback controller is designed, without considering faults that may occur on the system. There are two sets of sensors; one set measures the (yaw and roll) angles and the other set measures the corresponding angular velocities. If one of the sensors fails, the controller identifies the failure and uses the measurements from other sensors to compensate the measurement of the malfunctioned sensor.