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SCM Scheduling

Nature of Scheduling Problems

Scheduling is the process of developing a list of tasks for some system, e.g. the sequence of activities on some machine. Scheduling problems arise in all areas of manufacturing, transport and distribution and also in less obvious areas such as broadcasting and advertising.

Scheduling problems tend to have these characteristics:
  • they relate to the near future (1 day - 1 month ahead);
  • there is an enormous number of potential solutions;
  • they exist within a hierarchy of related problems over different timescales;
  • they recur in slightly different form as the solution to one scheduling problem is implemented and the next arises.

Spectrum of Planning and Scheduling

The entire spectrum of planning and scheduling problems may be considered as a spiral in which decisions made at one level determine the scope of what happens at the next:
At the outermost level there is strategic planning. This takes place over a timescale of years and is undertaken by the entire corporation. It is concerned with investments and determines what facilities are made available and where.

Next there is planning. This may take place every month and is typically concerned with individual sites. The facilities which can be used are effectively fixed and the aim is to develop a plan of what activities will be undertaken over the next month. This in turn may be reflected in a product offering, set of prices and availability.

Customers respond to the product offering by placing orders. In aggregate these are unlikely to match exactly what the plant had been planning to produce. Scheduling is concerned with working out the details of exactly what will be produced and when. Its focus is typically the next few days and the actual orders which have been placed rather than forecasts of orders.

Schedules are rarely implemented exactly as planned. Things go wrong; sometimes they work out better than planned. In either case the next schedule needs to reflect what has happened as well as orders which are new to the schedule.

Software Systems

Corresponding to these different stages there are different software systems:
  • strategic planning models: company-wide with a timescale of years ;
  • planning models: individual plants with a timescale of a month;
  • scheduling models: individual plants with a timescale of a few days.
Complementing these systems there may be further systems which interact directly with customers:
  • order-handling systems (sometimes known as AtP, Available-to-Promise), which respond to prospective orders by quoting a date when the order can be supplied;
  • yield-management systems, which manage the taking of orders and vary the price according to the demand and the remaining availability of resources.

Aspen SCM and Scheduling Systems

The original focus of Aspen SCM Scheduling was scheduling models but it is also used in order-handling (AtP) systems. Its particular strength is its ability to make use of an assortment of in-built and custom mathematical techniques and integrate these into a system with a rich user interface:

Many planning models are based on Linear and Integer Programming and Aspen SCM Scheduling contains algorithms to disaggregate the solution from such a model into the first draft of a schedule. In this way Aspen SCM Scheduling is able to make use of the results of a planning model to develop a detailed schedule automatically.