Solver constraints

The options are available to ignore some constraints that are normally used or add additional constraints to provide more flexibility for identifying a (feasible) schedule.

Network-related constraints are constraints owned by batches that are not selected automatically, however these are connected by flows to the batch-selection. The current position of these batches constrain the position of the selected batches. It is possible to ignore the properties of these connected batches as limiting the degrees of freedom of the selected batches are not required.

These are the types of solver constraints:

• enabling batches

  If this check box is selected, the searched solution must meet these requirements:

  • The constraints for the process batches, the tank batches, and the enabling batches
  • The allocated resources for these batches.

  If this check box is cleared, the allocation of the enabling batches to resources and in time is not considered during the search.

• utilities

  If this check box is selected, the searched solution must meet the availability constraints of all critical utilities every time. The requirements must always consider the minimum and maximum capacity of the utilities.

  If this check box is cleared, these constraints are not considered account during the search.

• inventory constraint

  If this check box is selected, the constraints that originate from inventory points are not considered.

• ignore resource availability

  If this check box is selected, availability on all resources for all selected batches is not considered. The availability is defined by timetable, time period, and availability exception; however the occupation of the resource, as defined by batches and downtime is also considered. This check box is used when a schedule is very stringent and almost fits within the availability profile.

• ignore time constraints related network

  If this check box is selected, the related network batches are not fixed in time. As a result, flows into or out of the selected batches are not bound in time. Hence, the selected batches can move in horizontal direction. This is useful when the primary concern of the user is not the related network, except for the routing constraints.

• ignore routing constraints related network

  If this check box is selected, the related network batches are not allocated to the current resource. As a result, flows into or out of the selected batches can now be routed. Hence, the selected batches can move in vertical direction. This is useful when a routing problem is identified that prevents the solver from finding a feasible schedule.

• allocate equal products to same resource

  If this check box is selected, the solver tries to schedule all batches with the same product on a separate resource. If the number of products in the selection does not exceed the number of available resources in the Choice group, this works effectively. In many cases, this check box can be used to minimize changeovers.

• cycle

  Select this check box, if you require to retain a batch within the current cycle and limit the extent the Solver can move a batch. The options corresponding to the check box lists all user-defined cycles. The cycle check box is disabled if no cycles are defined. The cycle list and the keep within cycle options are disabled when the cycle check box is cleared or disabled.

• automatically relax constraints

  If this check box is selected, the solver automatically relax the constraints in a predefined order, when a partial or no feasible solution is found during the search.

  This table shows the order in which the constraints are relaxed:

  ASAP	JIT
  Batch not before fixed time constraint	Batch not after fixed time constraint
  Batch not before current start time constraint	Batch not after current end time constraint
  Batch not before first batch constraint	Batch not after last batch constraint
  Batch not before earliest start time	Batch not after latest end time
  Batch not before start of work area constraint	Batch not after end of work area constraint
  Inventory constraint	Inventory constraint
  Utilities constraint	Utilities constraint
  Enabling batches constraint	Enabling batches constraint