On application of precision servo mode and fault control strategies to actuator models for structural applications

The complexity of modern high precision servomechanism systems, which involve not only the tracking function of the servomechanism but also the coordinated system-level control of numerous supporting mechanical, electrical and software subsystems, is placing discrete event controller design into the industrial spotlight. The control of such systems often walks a fine line: autonomy is desirable, because the system is often not conveniently accessible; however, high reliability is also desirable, and the complex software to realize autonomous response is often unacceptable because of the cost and time required for development and verification. Using the framework of an hysteretic actuator employed in the stabilization of a structure under seismic excitation, an approach that is becoming an industry standard for a class of high precision servomechanisms is described, wherein N-squared diagrams are used to model the discrete event portion of the system. The approach practically balances the competing requirements of autonomy and reliability, and has been successfully applied in a timely and cost-effective manner on several complex systems. Additionally, it relates in a straightforward manner to the class of time-varying discrete-time state space systems.