ADVANCED TRANSFER TEMPLATE PANEL

13.1 ADVANCED TRANSFER TEMPLATE PANEL

Thus far, entity transfers were implemented via Arena connections (for instantaneous transfer) and Delay modules (for time-lapse transfer). The Advanced Transfer template panel provides additional mechanisms of time-lapse transfer of entities among sets of modules or geographic locations. This section briefly reviews the facilities provided by this template panel.

The Advanced Transfer template panel implements a worldview in which entities are transported among Station modules. The simplest transfer mechanism uses Route modules as dispatch points and Station modules as destination points. Additionally, the Enter and Leave modules may be used to transfer entities into and out of physical or logical locations. The PickStation module allows entities to select a destination Station module using a selection criterion, such as the minimal or maximal queue size, number of busy resource units, or an arbitrary expression. Alternatively, an entity can be endowed with an itinerary using the Sequence module to specify a sequence of Station modules (referred to as Step objects). The Sequence module also supports assignment of variables or attributes at each Step object.

Station and Route modules are the most fundamental components of the Advanced Transfer template panel. A Station module is used to designate a physical location in the model (e.g., a milling workstation that physically houses milling machines). It may also be used to designate a logical location in the model comprised of a set of modules that perform some logical function (e.g., inventory control logic). Entities are trans- ferred among Station modules using Route modules, where the modeler specifies a Station module destination and duration for entity transfers. The destination Station module may be specified in an attribute, as an expression, as a Station module name, or as part of an itinerary defined in a Sequence module (see Section 13.5). Note that Route modules are not graphically connected to destination Station modules. Consequently, these modules arrange for entity transfer without animation.

The Advanced Transfer template panel also provides specialized transportation facilities for material handling in manufacturing-related systems. The Transporter module is used to model vehicles, such as trucks, forklifts, container carriers, and similar transport vehicles that move material in discrete parcels. These are collectively referred to as transporters. The Conveyor module is used to model continuous-mode conveyance facilities, such as conveyor belts. These are collectively referred to as conveyors.

In order to implement transporters or conveyors, the modeler specifies a transporta- tion network consisting of locations (Station modules) and topology (distances among

Modeling Transportation Systems 315 locations). Network topology is specified in Distance modules (for transporters) and

Segment modules (for conveyors). Thus, once the velocities of transporters and con- veyors are known, Arena will automatically compute the corresponding travel times. When an entity gets hold of a transporter, the entity enters a Transport module for the duration of the transportation activity. In fact, the two (entity and transporter) move together as a group. When the group arrives at its destination Station module, the entity frees the transporter (possibly after a delay for unloading) and exits the Transport module. The transporter will stay at that Station module until requested again. Similarly, when an entity accesses a conveyor, it enters a Convey module for the duration of the conveyance activity, during which it occupies a number of cells on the conveyor. On arrival at its destination Station module, it exits the conveyor and releases the conveyor cells that it had previously occupied, and then exits the Convey module.

A number of modules regulate the operation of transporters and conveyors. The Free module is used to release a transporter engaged by an entity, while the Exit module

is used to release a conveyor in a similar way. The Activate and Halt modules are used to start and stop transporters (e.g., to model scheduled and unscheduled maintenance), while the Stop and Start modules provide the analogous functionality for conveyors. The Move module is used to advance a transporter among stations. The assignment of various transportation facilities to requesting entities is handled by a separate set of modules. The Allocate and Request modules assign a transporter to an entity, with or without moving it, respectively. Similarly, the Access module is used to allocate conveyor cells to an entity.

In this chapter, we illustrate the use of most transporter-related modules in a number of examples. Because conveyor implementation is similar to that of transporters, we will not discuss such models here, but encourage the reader to experiment with them.