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Function documentationExtended Backward Planning

 

The heuristic SAP_DS_02 performs a multistep backward scheduling to thus create a production plan with balanced capacities in which the order dates/times orientate themselves on the customer's desired dates/times. The heuristic does not create sequences but primarily searches for free capacities for the orders to be scheduled.

The heuristic is based on the algorithm /SAPAPO/SFW_HEUR_BW_EXT.

The heuristic is stable, that is, based on the same starting data, it delivers the same results even if it is executed twice in a row.

You can invoke the heuristic interactively in the Detailed Scheduling Planning Board and the Resource Planning Board or integrate it in a Production Planning Run. The objects to be scheduled can be resources or orders/operations.

The heuristic can be used for the following planning processes:

  • Creation of a feasible production plan following an infinite MRP run.

    You can use the heuristic for scenarios with one to three finitely scheduled resources. To achieve a good result, you must not have created any maximum values for relationships or any setup matrixes (or only simple ones) and must have created only a few production stages.

  • Analysis of capacity problems

    After executing the heuristic, the planner can check which sales order dates/times have been violated and which resources (with the highest capacity load) caused these date/time violations.

    To be able to create this analysis, you must execute the heuristic several times with different finiteness levels one after the other and save the planning results in different simulation versions. After this, you can compare the different simulation versions with each other.

  • Use in a CTP or CTP/MRP process

    You can use the heuristic in the CTP process or in a combined process in which some products are scheduled with CTP and some with the MRP run. In this way, you achieve a smoothing of the production schedule - i.e. you can reduce the number of small gaps in utilized capacity by using the heuristic to produce a smaller total number of gaps which, on the other hand, are larger in size. These gaps can subsequently be filled with new orders more easily during further CTP checks. Note that you can only schedule resources with time-continuous capacity using this heuristic. The use of resources with finite PP/DS bucket capacity is not possible.

Restrictions

  • The heuristic does not create an optimal production schedule

  • The heuristic cannot perform compact scheduling

  • Maximum intervals are disregarded

  • CDP blocks are disregarded

Integration

Together with the relationships, the pegging forms the basis for setting up the network of operations to be rescheduled. In complex scenarios, the use of fixed pegging is recommended because in this case, the assignments between the requirement and receipt elements are retained even after execution of the heuristic. If dynamic pegging is used, on the other hand, the network of operations is only fixed for the execution of the heuristic. After this, the assignments can dynamically change again. For the planner, it is therefore more difficult to understand the planning results of the heuristic if dynamic pegging is used.

The assignments of the pegging constitute the basis for determining the requirement dates/times. The latter, on the other hand, are the basis for sorting the activities that that heuristic carries out.

In the case of orders that are not assigned to a requirement, the system uses the end date/time of the order as the requirement date/time. This approach ensures that these orders are not scheduled at the end of the planning horizon.

Note Note

You can create fixed pegging relationships following an infinite MRP run using the heuristic SAP_PP_019, for example.

End of the note.

Prerequisites

You have made the following heuristic settings:

  • Treatment of deallocated operations

  • Selection of alternative modes

  • Setup sequence taken into account

  • ATP categories taken into account

    You can specify ATP categories for independent requirements. Orders that are assigned to these ATP categories via pegging are then rescheduled. All other orders are deallocated. This setting works like a filter to limit the number of of orders to be rescheduled.

  • Order priorities taken into account

    You can set priorities for independent requirements. In the heuristic settings, you can also specify an order priority as filter criterion. The system then determines the orders (receipt elements) that are assigned to the independent requirement via pegging. If you stipulate an order priority of 2, for example, the system filters out those orders that have an order priority of 2 or less. The system can then reschedule just those orders with the relevant order priorities. The others are deallocated.

Features

This heuristic enables you to schedule on a multilevel finite basis. The system determines all relevant orders/operations and resources on the basis of the relationships and pegging relationships and builds up the network of operations that are to be rescheduled from them. If, for example, you select a resource on the detailed scheduling planning board and invoke the heuristic, the system automatically determines all operations at the resource and all dependent operations at the super- and subordinate production stages that are connected with one of the selected operations via pegging. At resources that are intended for finite planning, the operations are scheduled taking the available capacity into consideration. If necessary, the system carries out a mode selection process and chooses a suitable resource. Infinite resources are scheduled infinitely accordingly.

The heuristic schedules the operations in the planning direction 'backward' and fills the finitely scheduled resources as completely as possible with operations. In the process, the operations can also be scheduled in the past. Only when the available capacity of the resource in the past has been exhausted does the system deallocate the remaining operations. To reschedule the backlog, you can then execute the heuristic Stable Forward Scheduling (SAP_DS_01). This heuristic schedules all operations in the future without switching the mode and without changing the existing order sequence at the resource. This can lead to date/time violations in the future. Frequently, these date/time violations lie within the far distant future, so that you are still able to reschedule them through later planning runs.

Activities

The heuristic runs through the following individual processing steps:

  1. The system filters the activities to be rescheduled in accordance with the filter criteria you have specified for the requirements in the heuristic settings. Activities that do not satisfy the specified criteria, because they have a lower order priority for example, are deallocated.

  2. The system sorts the activities involved in the backward scheduling to arrange them in a sequence. The most important sort criteria are the requirement date/time and the ATP category of the pegged requirement, and whether a confirmed or unconfirmed sales order is involved. See also: Sorting of Activities.

  3. The system chooses a mode whose resource still has free capacity for the activities See also: Selection of Mode.

  4. The system resorts the activities prior to scheduling to determine a setup sequence in which the setup times are as short as possible.

  5. The system schedules the operations. In the process, the dependent operations are also shifted and their dates/times adjusted accordingly.