Rockwell Automation FactoryTalk Scheduler Users Guide - Manual (Page 35)

4 • S CHEDULING F EATURES
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Sequencing constraints
Sequencing constraints are normally a part of the product or job routing and determine the
sequence in which operations can be performed. Many systems have simple or straight
routings where the sequence is simply determined by the order in which the operations are
listed. The first operation must be completed before the second one can start, the second
completed before the third can start, and so on. Other systems allow parallel or concurrent
operations in their routings. These types of systems often include assembly or disassem-
bly operations. The most difficult sequencing constraints are found in systems where rout-
ings are represented as networks. These types of routings are most frequently found in
maintenance operations.
FactoryTalk Scheduler provides complete support for all types and combinations of
sequencing constraints. There are two different ways to describe sequencing constraints:
using an operation sequence numbering scheme or using an immediate successor
operation(s) scheme. The two methods cannot be used together in the same application.
All sequencing constraints for a given application must be described using the same
scheme.
The operation sequence numbering scheme
The operation sequence numbering scheme has the following format:
XX.YY.YY.YY…
where:
XX is the standard integer operation sequence number and will be referred to as the
root operation number
YY is the integer suffix that can be appended to the basic number, separated by the
decimal character “.”
You can append as many suffixes as needed to represent your routings accurately. The
rules used by FactoryTalk Scheduler to determine the sequence of operations are:
1. If the operation sequence number consists of only a root operation number (only XX),
then all operations with lower root numbers (ignoring all suffixes) must precede that
operation. Conversely, all operations with higher root numbers (ignoring all suffixes)
must succeed that operation. Note that it is possible to have one or more operations
with the same root number, with or without suffixes.
2. If the operation sequence number consists of a root operation number and one or more
suffixes, then:
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all operations with lower root numbers and the same exact suffixes must precede
that operation,