Production in time
Production in time (PIT) is a method for order generation, order release and capacity control as part of production planning and control . It aims to a high degree to optimize adherence to deadlines by creating a constant flow of production. It differs significantly from known planning and control methods, especially in the processing logic. They are used in complex productions with a multidirectional material flow and a large number of variants.
Compared to many other methods, it consciously relies on a coarser planning (here in particular the scheduling) in order to achieve both a simplification and a reduction in the effort of planning and control. Its main features were developed by Löllmann and Färber.
Functional logic of PIT
Figure 1 visualizes the functional logic of PIT. Each resource is represented by a planning pot with a specific cycle duration. A resource can hide one or more capacity units that can be reasonably aggregated.
As part of lead time scheduling, the planning run of the PPS system assigns identical start and end dates to several orders for each resource, depending on the planned pot capacity and cycle duration. As a result, at the beginning of a cycle at each resource several jobs are available for processing, each of which can be selected without jeopardizing the dates of the scheduled jobs. The time between the start and end date of a pot is called the cycle duration.
After the cycle has expired, the work content of each cycle moves to the next resource. Now, depending on the material flow, there are again several orders to be processed. This logic is repeated after each cycle has elapsed. The cycle times of the individual resources can differ from one another. However, they should represent integer multiples of each other in order to avoid jobs that are not in a cycle that is available for processing.
Order generation
Lead time scheduling
The lead time scheduling takes place primarily as backward scheduling, in which, based on the customer's requested date, each work process of an order is planned into the pool of resources required for processing. This takes place for all orders with a similar customer request date until the capacity of individual resources in the order cycle is exhausted. The subsequent orders are then postponed into the future until the bottleneck cycle has free capacity again. All operations in a cycle have the same start and end dates. As a result, the cycle-specific cycle time results from the cycle duration of each resource, whereas the order-specific cycle time is derived from the sum of all cycle times of each resource required for order processing. Due to the coarsening of the schedule, this procedure results in a very simple and efficient capacity planning.
Capacity planning
The capacity planning within the scope of the scheduling does not take place, as in known methods, against rigid capacity, but against partially flexible capacities. These flexible capacities are represented by a capacity utilization traffic light as in Figure 2 for each resource. As long as the traffic light is in the green, it is always possible to schedule each order without further coordination. The green area of the traffic light implies the normal capacity of the resource in question.
If, on the other hand, the traffic light is in the yellow area, planning requires coordination between the planner and production. The yellow area indicates the planning of individual resources in a defined flexibility corridor. For example, capacities can be withdrawn from other areas that are currently less busy or capacities can be provided by Springer or the like. be mobilized. This has the advantage that there is no need to change the shift model in the planning system used.
Scheduling in the red area, however, is not possible because the capacity reserves of the production resource are exceeded here.
Order approval
The order release can be characterized as order release according to a deadline. It occurs cyclically for all resources after each cycle has expired. Since it is not event-oriented, this significantly reduces the effort. Not every single order or work step has to be tracked and approved, but rather entire bundles of orders with identical start and end dates.
Capacity control
Depending on the size of the backlog, capacity control can take place in several ways, whereby these differ in the effort they induce.
In the case of small residues, coordination takes place between those responsible for the resource under consideration and those of the successors. It must be clarified whether the backlog can be made up in the following periods without negative consequences for the following production program. In the positive case, time-consuming rescheduling and return of the backlog to the planning can be avoided.
In the case of larger residues, it must be checked whether capacities can be mobilized to reduce the residue after the end of the cycle. For example, in single-shift operation, the backlog can be processed directly in the next shift with cycles lasting one shift. Depending on the company agreements on the mobilization of overtime or weekend work and the current workload situation, it must be checked whether this is possible.
If this proves not to be feasible or if the backlog turns out to be too great for the measures mentioned, the current planning results must be re-planned.
Processing logic
Due to the scheduling logic with identical resource-specific basic dates for several orders or work processes, all orders or work processes with the same deadlines can be processed in any order. The logic therefore has the advantage that the processing people can determine their sequence themselves, for example depending on the required set-up restrictions, without endangering the deadline situation. This significantly promotes the acceptance of the production plan at the execution level.
Differences between production in takt and normal lead time scheduling
- There are significantly fewer basic deadlines than with normal lead time scheduling.
- The planning and control effort is considerably reduced by the decreasing number of appointments to be coordinated.
- All jobs in one cycle can be processed in any order.
- The jobs to be processed in any order result in a decoupling of the jobs between the resources. This promotes the robustness of the planning against postponements.
Individual evidence
- ↑ H. Lödding: method of production control. Springer-Verlag, Berlin 2005.
- ↑ Günther Schuh (Ed.): Production planning and control: "Basics, design and concepts" 3rd edition. Springer-Verlag, Berlin 2006.
- ↑ http://www.lfconsult.de/files/upload/ARTIKEL/Artikel%20Wt-online.pdf (PDF; 393 kB)
- ↑ Ulrich Färber, Pit Löllmann: PIT approach - PIT production in time. In: www.lfconsult.de. LF CONSULT GmbH, January 1, 2017, accessed on January 23, 2017 .