Rockwell Automation FactoryTalk Scheduler Users Guide - Manual (Page 55)

5 • S CHEDULING C ONCEPTS
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and selects the desired operation using any appropriate logic. This type of rule gives
complete flexibility in the selection of the next operation to load. In essence, if you can
logically describe how an operation is selected, then you should be able to transform that
logic into a user-coded logic rule.
Although the primary purpose of a given rule is to make a selection, the rule can be coded
to perform other logic based on the selection. For example, the rule could both select a job
and change the priority of the selected job from 2 to 1 by using the OLE Automation
interface to write to the FactoryTalk Scheduler database.
R
ESOURCE SELECTION RULES
Resource selection rules, RSR’s, are invoked in FactoryTalk Scheduler whenever an
operation is being loaded onto a resource group and two or more eligible resources within
the group are idle. The rule selects the resource within the group on which the operation is
to be loaded. There are two basic types of resource selection rules: standard and user-
coded logic.
Standard resource selection rules are hard-coded in FactoryTalk Scheduler. The user
simply selects one of these rules from the menu of available rules.
User-coded resource selection rules are also supported. These rules are coded by the user
in Visual Basic and provide complete flexibility in selecting a resource. Although the RSR
Visual Basic procedure’s primary purpose is to select a resource, it can also perform
manipulation of the FactoryTalk Scheduler database using the OLE Automation interface.
For example, if the operation is assigned to a specific machine, the state of the system
could be modified in some way to account for this selection.
Picking the correct rule
The primary consideration in determining the operation and resource selection rules for an
application is the criteria by which you measure a good schedule. For example, is your
primary objective to create a schedule that meets the specified due date for all jobs or are
you focused on improving facility utilization by reducing the non-productive time (e.g.,
setup time and equipment maintenance)?
Determining the fundamental scheduling objective is a prerequisite to selecting the
appropriate rules to use. Once you have determined your objective, you select an
operation and resource selection rule to accomplish that objective. Generally, this is done
by first selecting an operation selection rule and then selecting an appropriate companion
resource selection rule. In some cases, the associated resource selection rule is determined
by the operation selection rule.
To help with this task, we have categorized the standard FactoryTalk Scheduler operation
selection rules into four main categories that correspond to four distinct scheduling
objectives. These categories include Predefined Job Preferences, Minimum Job