Modeling Activities

An activity is defined by an activity time that is either a constant value or a probability distribution (normal, triangular, etc).

In this solution, the activity time or other activity action is based on the value of a particular attribute. (For routings based on activity attributes see conditional routings.) For example, moldings entering an inspect and clean operation are either defective or non-defective. The activity time for defective molds is normally distributed with a mean of 2 minutes and a standard deviation of .5 minutes. Non-defective molds have a mean activity time of .6 minutes with a std. dev. of .2 minutes.

In this solution, one or more entities are attached to a base entity at an activity. For example: In the final assembly operation for a bicycle, two pedals and a seat are assembled to the bike.

This solution shows how two or more entities are batched or consolidated at an activity. For example, in the final collector inventory buffer of a process sequence, entities are batched into quantities of 20 and then sent to shipping.

You can consolidate entities into a batch and accumulated them until a condition becomes true (e.g., until a resource is available or until a truck has arrived). For example, 10, but no more than 20 completed parts are accumulated in a Buffer and then placed as a batch in an Oven for heat treatment, whenever the Oven has completed a previous batch.

A bicycle rental shop rents bikes to customers who return them when they are finished. It takes 10 minutes to check in the bike upon return. This solution shows how to model that type of activity. One or more entities are detached from a base entity at an activity. It is assumed that the entities to be detached have been previously attached to the base entity (see assembly activities). If you want to detach entities that weren't previously attached at some activity in the model, you must create them as new entities (See Creating Entities How-To).

The activity time or other activity action (JOIN, SPLIT, ASSIGN, etc.) is based on the type of entity being processed. For example: two types of orders (A and B) must go through a review activity. A orders take .5 minute to review and B orders take 1.2 minutes. Solution A is typically used If only the activity time is a function of the entity type. Solution B is used for specifying any activity action-not just a time-as a function of the entity type.

Sometimes one or more new entities are created as a result of an entity activity. The modeler can decide whether the incoming entity is to persist or disappear after the new entities are created. For example, incoming shipments arrive in containerized cartons with 100 cartons to a container. At an unload activity the cartons are removed ("created") from the container and stored. The empty containers are then routed to shipping to go back to the supplier.

In this solution, sometimes different products are assembled at the same activity requiring different components to complete the assembly. For example, two different products are assembled at a particular assembly station. Product A has 2 Component A's attached to it while Product B has 1 Component B attached to it. The component parts are fed from two separate inventories and you want to ensure that the right component parts and quantities get assembled to the right product. The Attach routings designate the specific product that each component is to assemble to and the quantity to be assembled.

For a given activity, a different activity time or activity action should occur a certain percentage of the time. For example, 20% of those who get a flu vaccination at a certain health facility also get a pneumonia vaccination at the same time. It takes only 1 minute to get a flu vaccination but 2 minutes if both are obtained. Solution A shows how to do this with two possible percentages. Solution B demonstrates situations with more than two possible percentages, testing on the cumulative percentages of interest.

In this solution, entities move from activity to activity as a batch, but are processed at each activity individually. For example, a stack of to 20 loan approval documents of quantity N(15, 5) are processed through three activities for approval, recording and filing. Documents are processed individually at each step, but are moved as a batch. Because you want to track individual statistics on each document, you have decided you want to model each individual document being processed at each step.

One or more new entities are created by an entity and later rejoined to the parent entity. For example: customers enter a fast-food restaurant, place (i.e., create) an order and receive a number for their order. While the order gets filled, customers wait in a Pickup area for their number to be called.

You can also consolidate entities into a batch that has accumulated only for a specific amount of time (e.g., consolidate accumulated entities every 15 minutes). Here's how:

1. Set up a recurring timer that sets a variable (e.g., vGo) to 1 (see Defining a One-time or Recurring Timer).

2. Follow the same procedure used to define "Condition-dependent Batching"

You can unbatch a previously batched group of entities at an activity. For example, an entity batch of documents was moved from review to the input buffer of a Process activity where they are to be unbatched and processed individually.

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