For a variety of reasons, some manufacturers prefer to schedule jobs according to the limitation of resources and capacity found within their system. Scheduling processes that, from the outset, take the limited capacity of a plant to produce are said to be using a finite approach to scheduling management. For the manufacturer, this approach works a schedule according to capacity criteria set in advance of production. The criteria can include any number of factors such as job due dates, job importance, and even the very importance of the customer to the manufacturer. Finite scheduling means that you are more often than not running your most important jobs first, getting them out as close to the promised delivery due date as possible, while hoping to return to less vital jobs in due time.
There are a number of ways to determine this concept of “importance" when it comes to finite job scheduling. In the most simplest terms, a manufacturer can schedule merely according to how much a plant is capable of producing in any one average workday. That is to say, how much can be produced without the need for additional machinery, manpower, or other resources? Often, this technique employs electronic scheduling boards, which tend to copy the old card-based loading boards and calculate time and machinery automatically so that no two jobs are loaded on the same machine at the same time. In this way, production is limited through finite scheduling that recognizes limited capacity.
On the other hand, scheduling can be done based upon priority criteria. Finite techniques such as order-based scheduling produce tasking lists on the basis of order priority. The router sequence for individual resources is determined by the overall priority of the order for which the parts are destined. Here, jobs may be deemed “important" by their relationship to other jobs in assembly modes, the sudden availability of usually limited materials, and/or the customer value to the company of the client placing the order. While this technique can prove to be a more accurate way of producing scheduling algorithms, the concept does open up the possibility for some work centers to go under utilized due to gaps in the schedule to accommodate idiosyncratic router sequencing.
Finally, constraint-based scheduling is a finite method that works through a Master Production Schedule to locate the bottleneck in the line and continue to load it. In short, constraint-based scheduling will try to synchronize, or “balance", the bottleneck with non-bottlenecks along the line and in this way have a more accurate determination of when bottleneck items will be ready. As a finite concept used in enterprise resource planning (ERP) software, constraint-based scheduling has become interesting as a form of modeling and solving scheduling problems. With a robust ERP system, it is now possible to run constraint-based schedulers on-line for any number of parts and assemblies.
Dusty Alexander is the President of Global Shop Solutions. Global Shop Solutions is the largest privately held ERP software company in the United States.
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