Order Sequencing Using Operation Numbers to Link Operations Within an Order
When sequencing orders linked together using operation numbers, the sequencer engine groups all of the operations of the order together and places them on the planning board according to their operation number sequence.In a simple sequence of three operations: 10, 20, and 30, operation 10 is placed first, operation 20 is placed so that it starts after operation 10 has finished, and finally operation 30 is placed after operation 20.
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If there are multiple operations that have the same operation number, then all operations with that number will be considered as a whole when determining the times that subsequent operations are placed on the planning board. Where only a simple relationship exists, for example 2 operations 20s this is usually adequate.
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If the operation relationship is more complex, then the desired relationship may not be obtained. If there were 2 operation 20s and two operation 30s, the operation 30s may be only dependent on their preceding operation 20s. The sequence generated may be sub-optimal if the operation 20’s do not finish at the same time.
Sequencing Using MADE FROM Relationships to Link Operations in the Same or Different Orders
When using MADE FROM each operation has a defined set of relationships, there are no implied relationships as with Operation numbers.
The sequencer generates sets of operations based on their subsequent and previous operations. After each set has been sequenced, the next unallocated operation is found and another set is built. For example, with the data set above with a single disassembly point, the following operation sets will be created and sequenced:
Op 10, Previous operations, None; Subsequent operations, Op 20a, Op 20b.
Op 20a, Previous operations, Op 10; Subsequent operations, Op30a.
Op 20b, Previous operations, Op 10; Subsequent operations, Op 30b.
Op 30a, Previous operations, Op 20a; Subsequent operations, None.
Op 30b, Previous operations, Op 20b; Subsequent operations, None.
The sequence on the planning board is built up in the following way:
Op 10 and its dependents are sequenced
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As Op 20a and Op 20b are now sequenced, these are not used as a base operation for the next set. Op 30a is the next operation not on the planning board, so it is used to create the set Op 20a and Op 30a. Op 20a is already on the planning board, Op 10 and Op 20b are also on the planning board but not included when determining the operation relationships for Op 30a.
Next, Op 30b and its dependents are sequenced. Op 20b is already on the planning board, Op 10, Op 20a and Op 30a are also on the planning board, but are not included when determining theoperation relationships of Op 30b.
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As operations 30a and 30b have no dependents that are not on the planning board, so sequencing is complete. Operation 30a is now scheduled independently to operation 20b.
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Sequencing Features that May Not Work as Expected with MADE FROM
Due to the small sub sets of operations that are scheduled together, sequencing features that cause links between non-contiguous operations may not work as expected.
SUBSEQUENT RESOURCE CONSTRAINT
If a SUBSEQUENT RESOURCE CONSTRAINT is set by an Operation, then with Operations 10, 20 and 30 the constraint set by Op 10 will not have any effect on Op 30 as Op 10 and Op 30 are never included in the same operation set.
Op 10 and its dependents are sequenced
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Op 20 is already on the planning board, so Op 30 and its dependents are sequenced
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The operation set when sequencing Op 30 only contains Op 20 and Op 30. The constraints set by Op 10 are not considered.
INTER OPERATION INTERVAL
If two or more contiguous operations are linked using an INTER OPERATION INTERVAL, that is to say Op 10 is linked to Op 20 and Op 20 is linked to Op 30, then the first link may be violated if the second link requires Op 20 to be moved.
Op 10 and Op 20 are sequenced first, the interval is not violated
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The next operation that is not on the planning board is Op 30, so the operation set Op 20 and Op 30 is sequenced, on the first attempt the INTER OPERATION INTERVAL is violated.
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The sequencer now adjusts Op 20 to satisfy the INTER OPERATION INTERVAL between Op 20 and Op 30, but in doing so exceeds the INTER OPERATION INTERVAL between Op 10 and Op 20. However, as the operation set only includes Op 20 and Op 30 this violation is not detected.
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Using Secondary Constraint Across Multiple Operations
If the usage of a secondary constraint is incremented or decremented by one operation, then decremented or incremented by a subsequent operation, the results may not be as expected. If the secondary constraint is used by another operation on the planning board or has a shift pattern then it may exceed its capacity while scheduling one operation set.
For example, if we have three linked operations, the first of which increments a secondary constraint and the last decrements the secondary constraint by the same amount. If the secondary constraint has a capacity of 1 and the operations increment and decrement the usage by 1, an unexpected violation may occur if another operation that uses the secondary constraint is already placed on the planning board at any point in the future.
If the initial state of the planning board is:
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Giving secondary constraint usage of:![]()
When sequencing the new order, we might expect the following result
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However, the actual result will be
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To understand this result we need to examine the individual steps in placing the operations on the planning board. The first step is to sequence the operation set created by Op 10, this contains Op 10 and Op 20. The first sequencing parse generates the following
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The secondary constraint is violated because the combination of the operation on the planning board and the increment by the newly sequenced operation, exceed the capacity. The operation that decrements the secondary constraint has not yet been placed on the planning board.
Due to the constraint violation the operations are moved to a time when the violation no longer occurs.
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Even though the constraint is never decremented, it does not exceed its limits.
Sequencing the final operation set related to Op 30 causes the constraint to decrement again to produce the final sequence.
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Using LINK COMPLETE ORDER to Increase the Size of Operation Sets
In order to limit the impact of the Operations sets, the classification LINK COMPLETE ORDER can be set on a TOGGLE type field. When the LINK COMPLETE ORDER toggle is set, then the sequencing engine will increase the size of the operation set for both previous and subsequent operations up to the point at which assembly or disassembly occurs. The LINK COMPLETE ORDER toggle can only be set on the PARENT field of an Order.
SUBSEQUENT RESOURCE CONSTRAINT
In a configuration using MADE FROM with an order that has a simple linear flow of 3 operations, Op 10, 20 and 30, but with a SUBSEQUENT RESOURCE CONSTRAINT set by Op 10, LINK COMPLETE ORDER can be used to enable any SUBSEQUENT RESOURCE CONSTRAINT applied by Op 10 to effect Op 30.
The LINK COMPLETE ORDER option enables all three operations, Op 10, 20 and 30, to be part of the same operation set. Thus if Op 10 has set a SUBSEQUENT RESOURCE CONSTRAINT both Op 20 and Op 30 will respect that constraint when testing which resources they can be processed on.
INTER OPERATION INTERVAL
In a configuration using MADE FROM with an order that has a simple linear flow of 3 operations, Op 10, 20 and 30, but with an INTER OPERATION INTERVAL set between both Op 10 and Op 20 and between Op 20 and Op 30, LINK COMPLETE ORDER can be used to prevent the INTER OPERATION INTERVAL between Op 10 and Op 20 being violated.
The LINK COMPLETE ORDER option enables all three operations, Op 10, 20 and 30, to be part of the same operation set. Thus if Op 20 has to be adjusted due to the INTER OPERATION INTERVAL between Op 20 and Op 30, the INTER OPERATION INTERVAL between Op 10 and Op 20 will also be taken into account and Op 10 moved if required.
Using Secondary Constraint Across Multiple Operations
In a configuration using MADE FROM with an order that has a simple linear flow of 3 operations, Op 10, 20 and 30, but with a secondary constraint increment on Op 10 and a decrement on Op 30, LINK COMPLETE ORDER can be used to prevent the increment on Op 10 causing the constraint to be violated outside the total span of the 3 operations.
The LINK COMPLETE ORDER option enables all three operations, Op 10, 20 and 30, to be part of the same operation set. Thus if Op 10 has incremented a secondary constraint, the decrement by Op 30 will be considered before any final checks are performed.
Assembly and Disassembly
Consider the following operation relationships
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If there were, for example, a secondary constraint Increment on Op 30 which was decremented at Op 50 then there would be the potential for this to fail due to the creation of the operation sets as follows:
Op 10, Op 20a and Op 20b
Op 20a and Op 30
Op 30 and Op 40
Op 40 and Op 50
Op 50, Op 60a and Op 60b.
The operations that increment and decrement the secondary constraint are never considered together.
If all these operations are part of the same Preactor order, with Op 10 being the PARENT, LINK COMPLETE ORDER will have no effect at all. The First disassembly point is after Op 10, this will prevent LINK COMPLETE ORDER progressing past Op 10. If however the order were split into two Preactor Orders, with Op 10 and Op 30 being the PARENTs, LINK COMPLETE ORDER would affect the operation sets.
Order 1 Order 2
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The operation sets will now become:
Op 10, Op 20a and Op 20b
Op 20a and Op 30
Op 30, Op 40 and Op 50
Op 50, Op 60a and Op 60b.
Setting LINK COMPLETE ORDER on the PARENT Op 30 has now caused Op 30, 40 and 50 to be included in the same operation set. The operations that increment and decrement the secondary constraint are now in the same operation set, which will ensure that the constraint is handled correctly.