Self-validating actuators

Actuators can contain significant internal nonlinearities, such as hysteresis and dead-band caused by static and dynamic friction. One function of the embedded controller is to overcome such undesirable inherent characteristics, as far as it is capable. Actuators are frequently critical items in a control loop, complete failure leading to plant or process shutdown. A more common fault, however, is a degraded level of performance which requires external corrective action to be taken to mitigate the effect. Common examples of this are when operators take manual control of automatic loops or when technicians de-tune control loops to make them less demanding of the actuator performance. Future control systems that can intelligently process the data from the self-validating sensors and self-validating actuators will lead to plants and processes with efficient, condition-based preventative maintenance, optimum ´limp-home´ strategies resulting in a minimum number of unscheduled breakdowns and greater overall plant availability. This paper discusses an intelligent self-validating actuator, with reference to an example of a position control actuator in the presence of significant friction.