Event Driven Activity

The event driven activities focuses upon precedence resources or constraints of the activities and is robust to disturbances. Specific precedence constraints or resources in between any two operations usually exist because of the need of completion of single activity before other.

Timed Petri nets are termed to behave in two ways: one where time is related with places or timed place Petri nets and the other where it is related with transitions or timed transition Petri nets. Usually a timed transition removes tokens from its input places and takes several times before introduction of a new token to the output place. Therefore the marking of the state remains unconfident between termination and initiation of firing. In case of timed transitions, firing transitions or multiple initiations are allowed for presenting the concurrency of activities. Hence the time related with each initiated transition should be tracked in order to update the marking or state properly. Because the initiated transitions may not be tracked in applications of Petri net modelling, so an additional tracking method is needed.

While employing timed transitions, multiple marked places present the concurrency of transitions naturally and merely a track of time for the marked places is essential to be maintained. Suppose a situation when time is associated only along with places and every transition is immediate. Now we consider every part or partially ended products that enters and moves inside a Flexible Manufacturing Systems is termed as a part. Resource needs are not considered in the procedures. Each product is the conclusion of sequence of procedures according to the needs that require to be fulfilled. Furthermore, a sequence of processes is explained to be a job type or sequence type. A Flexible Manufacturing Systems is designed to generate a multiple product of the similar product type. There might be more than single way to carry out one process. As an illustration consider two machines M₁, M₂, a robot R, and a part. To acquire a deeper insight to the entire operating scenario, we arbitrarily suppose a rule like a part can be either treated at M₁, or M₂ along with R providing the similar result. Here treating a part at M₁ and M₂ is explained as an operation. Thus, resource needs are an integral part of an operation.