Rockwell Automation FactoryTalk Scheduler Users Guide - Manual (Page 53)

5 • S CHEDULING C ONCEPTS
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Selection rules
In a simulation-based sequencer, there are two types of selection rules that can be applied
each time an operation is scheduled: an operation selection rule or a resource selection
rule. If a resource becomes available and there are several available operations that
require that resource, the operation selection rule is used to determine which operation is
scheduled. If an operation becomes available and it can be scheduled on more than one
resource, the resource selection rule is used to determine that resource. If both multiple
operations and multiple resources are available, the operation rule is applied to select an
operation, and then the resource rule is applied to select the resource.
Simulation-based sequencing can be set up so there is a single operation selection rule
used to select all operations and a single resource selection rule to select all resources, or
separate rules can be applied. If separate rules are used, they are associated with specific
resource groups. For example, you may want to use a minimize setup rule for one group
of resources and a due date rule for another.
Types of rules
There are two types of rules: independent and dependent. The use of independent rules
allows different rules to be applied to the selection of operations and the selection of
resources. Dependent rules require that the same rule be applied to the selection of both
the operation and the resource. You can also develop and include your own rules. These
are referred to as user rules, which will be included automatically on the list of available
rules.
Although the operation-at-a-time loading scheme used by a simulation-based sequencer
provides great flexibility in schedule generation, the key to tapping this flexibility is the
development of rules for selecting the next operation to load or the resource on which it
will be loaded. We discuss this in the following section.
Sequencing rules: The key to good schedules
The key to tapping the power and flexibility of simulation-based scheduling is the
development of rules for guiding this two-step process. There are two basic categories of
rules: operation selection rules (OSR’s) and resource selection rules (RSR’s). This
section describes the basic concepts for incorporating rules into the FactoryTalk Scheduler
simulation-based sequencer. One of the key advantages of a simulation-based sequencer is
the ability to incorporate decision logic in the scheduling process based on rules for
selecting operations and resources.
Operation selection rules
Operation selection rules, OSR’s, are invoked in FactoryTalk Scheduler whenever at least
one resource is idle and two or more operations can be loaded on that resource. The rule