Why Schedule

Your problem – how long will the schedule last?

The most common tool used by schedulers is a simple planning board where work is allocated to resources in time periods such as an hour, day or week. However this is a static decision support tool trying to cope with a dynamic problem.

So how long will the schedule last?

A rush order comes in
Re-work is required
Machines break down
Demand does not meet forecast

A rush order appears, re-work is required, operators report sick, a machine breaks down, or demand does not meet forecast, & a hole is blown in the production plan, leaving schedulers to spend time re-assigning work, changing priorities or altering process routes to meet delivery dates:

Finite Capacity Scheduling

The schedulers art is to constantly try to maintain the balance between demand & capacity. On the demand side the flow of work can vary with new orders, priority changes, stock orders, leakages occur as deliveries are made, forecasts translated into demand & orders cancelled. Increased capacity can be achieved by bringing forward orders to utilise under-used resources, process routes changed, extra hours worked, sub contracted services etc

Finite Capacity Scheduling is a process whereby a production plan consisting of a sequence of operations to fulfil orders is generated based upon the capacity of resources. These can be machines, operators, tooling or anything which is a constraint on the production process.

Most planning systems assume sufficient resources are available when required, ie resources have infinite capacity. An MRP system typically takes the orders for products, breaks them down into component parts & calculates when to start making them based upon lead times. No account is taken of current available capacity of resources. At the same time that the launch time for batches are calculated, materials needed are ordered to arrive in time for work to start. If there is a delay in production upstream of a particular operation then the material will be ordered too early. With no concepts of bottlenecks available to the planning system, resources become overloaded, queues of work get longer & WIP increases. Because jobs must join the queue at each process step, orders take longer to progress, lead times become too optimistic, deliveries are late.

Using Finite Capacity Scheduling, operations are only planned when resources are available. Materials are ordered only when they are needed. Inventory levels fall & bottleneck resources are not overloaded. WIP remains relatively constant, lead times are more predictable, delivery dates more reliable.

In this way production management spend less time progress chasing & can concentrate on the everyday job of balancing often variable demand with the capacity available.

Preactor – simple to use, upgradeable

Preactor has been designed to run on standard PC’s under Windows 95, 98, ME, XP & Windows NT.

Preactor uses the ease-of-use features of Windows to the full with maximum use of the mouse to point, click, & change objects & drag & drop objects from one position on the screen to another.

Preactor has a fully configurable database & menu system. All versions use the same files to configure the system so that upgrading from say Preactor 200 to Preactor 300 does not require configuration.

Preactor – Links to other software

Preactor can be used as a stand alone application or linked to other software. All information in the Preactor database as well as schedule files generated are held in ASCII format.

Integration with other software is by ASCII file transfer or via OLE Automation techniques, ie any OLE enabled system such as excel, visual basic etc can access the Preactor database. For ASCII file transfer there are tools within Preactor for automatically changing the information in external files to be used by Preactor & in manipulating output data for use by other systems. Preactor has been successfully linked to spreadsheets, MRP systems, shop floor data collection, accountancy packages & other databases. In some applications orders (customer, order no, batch size, due date) are all downloadable from a host to Preactor & all information on product operations, routes, processing times, set-ups etc are held within the Preactor database.

In other applications the host system holds all the information required for each product & this is then passed to Preactor including routes etc. In this way only the information required by Preactor for the live products needs to be held in the Preactor database. Preactor has been used both before & after an MRP run. Before orders are loaded with product information to Preactor, which then provides a finite schedule (Fine Cut Capacity Planning). The MRP system then reads the schedule file & carries out its BOM (Bill of Materials) explosion & materials requirement plan. Preactor is then used to produce work-to-lists, route cards & reports for day to day control of the schedule & support minor changes to the sequencing of work.

Preactor – Networking

Preactor systems can be connected together in a variety of ways. A master Preactor system can be used to schedule the whole facility & work-to-list passed down to other Preactor users at cell or department level for local decision support.

The Preactor Viewer Module is designed to be used with other versions of the Preactor range of finite capacity scheduling tools over a PC network. It does not have a scheduling module as with other Preactor versions but it can be configured to read, write, & display data in a variety of ways as required by your application. Typical uses would be to provide the sales department with up to date information on the progress of orders or offer customised management reports on the performance of the business. Another is to provide an interface for sales orders to be entered remotely. The Preactor Viewer Module is also used on the shop floor PC to provide cell supervisor or machine operators with up to the minute work-to-lists generated by the master Preactor system & to log completions for use by the scheduler to monitor progress & initialise the system prior to reschedule.

Preactor – A Family of Scheduling Solutions

Preactor solutions can be selected according to the application & budget available. All versions have the same interactive features, but the scheduling engine used by Preactor to generate the schedule is different.

Preactor 200 is the entry level system. It has its own internal algorithms for sequencing work which are selected by the user. Preactor 300 has additional features for more complex manufacturing environments & uses the same method of scheduling as the 200.

Preactor APS offers the same scheduling algorithms as 200 & 300, but also offers the unique Preactor Open Planning Board

system. This is supplied with a simulation based scheduling engine with built in optimisation rules such as select shortest set up time, follow campaign sequence etc. Customised rules can be added using any ActiveX Automation compatible programming system such as visual basic. With the open planning board, Preactor APS is not limited to algorithmic, simulation, or any other fixed mechanism for generating schedules. The ActiveX Automation controls make Preactor APS a truly open system.