A methodology to evaluate the availability of reconfigurable conveyor systems

Networked sensor-actuator systemspsila technologies significantly impact the design of future automation systems. Since the automation domain is critical, there is a need to ensure high availability of the system. A model-based approach to evaluate system availability offers systematic, quantitative guidance on the effectiveness of different topologies and failure recovery mechanisms. We present a methodology to evaluate the availability of a simple class of automation systems, namely reconfigurable conveyor systems in which each conveyor unit is regulated by a local micro-controller. Microcontrollers in different units interact via wireless communications. The availability of the conveyor system depends on the correct functioning of each unit in the system. We assume that only the sensors, actuators and mechanical components of units can fail, i.e., the microcontrollers and radio transceivers do not fail. Because the Stochastic Reward Nets (SRN) paradigm provides the capability to integrate notions of performance and service value, we use this paradigm as the basis of our methodology. At the lowest level, the operational and failure states of each unit are considered to model unit-level availability. Next, the states of units are combined to provide path metrics and states. Finally, at the third level path metrics and states are composed to obtain system-level metrics. We illustrate how the methodology provides key design guidance and operational guidance using an example of an Inspection Station (IS) conveyor system.