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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
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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.
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| 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.
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| 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.
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| 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.
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| 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. |
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