16.2: Points Made in the Case Study

This case study deals with modeling issues concerning conveyors. A conveyor is viewed as consisting of multiple segments. Certain segments, such as the exit points for work stations, are key. Key segments are modeled as resources with the number of units equal to the capacity of the segment. When all resources with the number of units equal to the capacity of the segment. When all resources units are busy, the key segment is full and other items "back up" along preceding segments of the conveyor. The non-key segments are modeled as time delays only.

Key segments and operations are modeled similarly. A scarce system object is modeled as a resource constraining the movement of an entity. An entity uses this object for a length of time and then releases it for use by other entities.

Package travel time on a conveyor is determined from specifications of the speed of the conveyor and the distance the package must travel.

Many simulation languages have special modeling constructs for representing conveyor systems in a model. These constructs contain the logic for modeling key and other segments. Thus, this logic can be included in a model transparently to its developer.

In some cases, an operation may be performed by any of several workers or machines. In the model, this implies a choice between resources. The logic for making this choice must be specified.

Multiple individually distinguishable resources may be identified by the same name. The individual resources each have a unique ID number or index. For example a model could represent 10 workers with the resource WORKER and worker 7 could be referenced by WORKER(7).

Ergonomic considerations can be included in a model. In this case, worker walking time as well as allowances for rest and other personal time are taken into account.

Performance measures can be computed from other performance measures. In this case, the average utilization for a group of workers is computed from the utilization of each individual worker.

---