As do all modeling projects, manufacturing and material-handling simulation projects need to address• the issues of scope and level of detail.

Consider scope as analogous to breadth and level of detail as analogous to depth. Scope describes the boundaries of the project: what's in the model, and what’s not for a subsystem, process, machine, or other component, the project scope determines whether the object is in the model.

Then, once a component or subsystem is treated as part of a model, often it can be simulated at many different levels of detail.

The proper scope and level of detail should be determined by the objectives of the study and the questions being asked.

On the other hand, level of detail could be constrained by the availability of input data" and the knowledge of how system components work. For new, nonexistent systems, data availability might be limited, and system knowledge might be based on assumptions.

Some general guidelines can be provided, but the judgment of experienced simulation analysts working with the customer to define, early in the project, the questions the model is being designed to address provides the most effective basis for selecting a proper scope and a proper level of detail.

Should the model simulate each conveyor section or vehicle movement, or can some be replaced by a simple time delay?

Should the model simulate auxiliary parts, or the handling of purchased parts, or can the model assume that such parts are always available at the right location when needed for assembly?

At what level of detail does the control system need to be simulated? Many modern manufacturing facilities, distribution centers, baggage-handling systems, and other material-handling systems are computer controlled by a management-control software system.

The algorithms built into such control software play a key role in system performance. Simulation is often used to evaluate and compare the effectiveness of competing control schemes and to evaluate suggested improvements.

It can be used to debug and fine-tune the logic of a control system before it is installed.

These questions are representative of the issues that need to be addressed in choosing the correct level of model detail and scope of a project In turn, the scope and level of model detail limit the type of questions that can be addressed by the model.

In addition, models can be developed in an iterative fashion, adding detail for peripheral operations at later stages if such operations are later judged to affect the main operation significantly.

It is good advice to start as simple as possible and add detail only as needed.