Advanced planning and scheduling

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Advanced planning and scheduling systems (APS systems) are used in production management to support the planning functions according to the MRP-II method, for example the currently usual ERP systems and many PPS systems . Usually the systems aim at solving the lead time syndrome . A generally recognized and exact definition, for example by the American Production and Inventory Control Society APICS or the REFA Association , does not currently exist.

Finite Capacity Scheduling

Finite Capacity Scheduling (FCS) modules are APS modules for the simultaneous planning of resources (material, machines, personnel and tools) and for the calculation of production start dates.

In contrast to FCS is MRP II , which uses backward scheduling to calculate the start time for production orders from primary and secondary requirements . This calculation is based on a fixed lead time , i.e. the time to manufacture a component is always assumed to be the same, regardless of this

This results in a strongly distorted picture of the expected completion dates, which cannot be corrected by changing the planning parameters.

FCS systems (modules) come into play at this point. You calculate the expected order time from the planned times for set-up and production, examine whether production capacities are available and create a plan for the start times of the individual orders.

Are being introduced heuristic optimization methods ( constraint programming , evolutionary algorithms ), set up to improve plans. The calculation is usually carried out iteratively, that is, one order is planned, then the next ... until the “planning board” slowly fills up. The calculations when adding an order are comparatively quick. A recalculation of the entire planning board can take a considerable amount of time, depending on the priority rules, limitations, planning rules, etc. used.

High demands are placed on an FCS system in the case of varied single and small series production. Mechanical engineering, in particular, often has to struggle with missing parts in assemblies and unsatisfactory adherence to deadlines with a large variety of parts and medium and small batch sizes. The biggest problem is the variance in the calculated order times. If this fluctuates by only 5% per order, the probability of a statement drops below 50% after the fourteenth order, so that a coin can just as easily be tossed for the next order.

Suitable FCS systems must have high-performance synchronization and coordination properties, which in turn requires high standards for the optimization algorithms used and at the same time means a lot of effort for data acquisition. Only a few FCS systems then carry out a simultaneous comparison of the material availability.

Other APS systems

Further software modules are available for other areas of ERP planning. There are rule-based systems for forecasts (forecasting), available-to-promise (ATP ~ availability forecasts ), capable-to-promise (CTP ~ delivery capability forecast), distribution planning (loading space planning, transport time, etc.), demand control, warehouse control (storage, removal , etc. with optimized path / time characteristics) and pretty much every other area of ​​the supply chain .

criticism

APS systems are an attempt to use mathematical models with refined data to achieve a more precise prediction of the future. The calculated results are based on assumptions, for example an “average production time per part”, which can change if the raw material changes, depending on the machine condition, production temperature, etc. Often the quantities are far from being reached at which a statistical compensation would result. APS systems often reduce the gap between plan and target, but do not completely close the gap.

Alternative processes, for example JIT , reduce the need for planning through systematic control of the production environment, but only partially solve the problems of workshop control in the long term .

Compared to the classic MRP-II calculation, FCS systems offer advantages that are paid for with the maintenance and procurement costs for the data, etc. So far, however, it has also been shown that people are just as indispensable in planning as they were before the introduction of APS.

literature

  • Hans-Otto Günther, Horst Tempelmeier: Production and Logistics . 8th edition. Springer-Verlag, Berlin 2007, ISBN 978-3-642-00379-0 .
  • Hartmut Stadtler, Christoph Kilger (Eds.): Supply Chain Management and Advanced Planning - Concepts, Models, Software and Case Studies . Springer-Verlag, Heidelberg 2010, ISBN 978-3-540-67682-9 .

Individual evidence

  1. ^ A b Wallace J. Hopp, Mark L. Spearman: Factory Physics: foundations of manufacturing management . 2nd edition, McGraw-Hill Higher Education, 2000, ISBN 0-256-24795-1