Modeling, analysis and simulation of failures in a materials handling system with extended Petri nets

Abstract

This paper' models. analyzes, accommodates and simulates potential failures which may occur in a materials handling system with fitended Petri nets (EPNs). Detailed EPN based subnets are provided to study and accommodate occurred failures. The subnet structural properties and the overall system properties are preserved The Stochastic Petri Net Package (SPNP) is used for simulation studies.

Hierarchical time-extended Petri nets (H-EPNs) based error identification and recovery for multilevel systems

“…Five different types of places (shown in Figure 1a) are defined, these include: (i) Status place (s): This place is similar to a place in the original PN definition, (ii) Action place (a): This place denotes an operation (action) 'a' being performed by the system, (iii) Decision place (d): This place denotes a conflict. This definition of a decision place is different from the definition in [9,12], where a decision place essentially represents a binary switch, indicating a yes/no situation, (iv) Subnet place (su): This is similar to the subnet place defined in [9,12]. In H-EPNs, the restriction that the subnet place be a single-input single-output (SISO) place is relaxed, thereby allowing for multiple points of entry to and/or exit from the subnet.…”

“…In H-EPNs, the restriction that the subnet place be a single-input single-output (SISO) place is relaxed, thereby allowing for multiple points of entry to and/or exit from the subnet. This results in greater flexibility in the definition and usage of subnet structures, and, (v) Source-Sink place (ss): This place represents the origin and end of tokens in the net as shown in Figure 1b (this place essentially substitutes the need for separate source and sink places as in [9,12]). This implies that a complete H-EPN system model exists between the output and input arcs to this place (see Figure 1c).…”

“…PN extensions including [9,12]. However, there exists a serious disadvantage with respect to property verification with the usage of a switch place while incorporating time into the system model.…”

“…Robot R transfers parts from area INBIN to W1, or from the output of W2 to input of W3, or fixtures from W3 to INBIN. This process can be abstracted at a higher level as a robot "move" operation A detailed example of a complex system model decomposition using EPNs has been provided in [9]. The H-EPN design is shown in Figures 11, 12 and 13.…”

Failures in discrete-event systems and dealing with them by means of Petri nets

“…Failures can emerge in any device or software. It is gratifying that PN can be used [3,7,10,11,[15][16][17]19,[21][22][23]26] also for systems where failures occur. There failures can be categorized into hardware failures and software ones.…”