Planning for Control Points and Disposition Decisions

Many processes require that a "disposition" decision be made for each item produced.  The disposition decision may involve simply accepting or rejecting a batch or lot, or it may also involve changing the "routing," or path the product will take through the plant.

In the process disposition, decisions that will be made are known as "control points" and are configured as Production Units within the Plant Model.  Control points may represent physical pieces of equipment, or may simply be a logical point in the process where quality decisions must be made.

Do you want manual or automatic disposition?

Manual disposition can be achieved from a variety of clients by simply changing the status of a Product Event.  Automatic disposition can be driven by the Disposition Model defined by the Production Event properties on a given Unit.  The standard Disposition Model watches for any variables to fall outside of Reject limits and automatically Rejects the Production Event without user intervention.

Which variables can affect disposition?

Any variable whether manually entered or calculated may have specification limits, therefore may affect disposition.  The general strategy to associate certain variables with the disposition decision is to make sure those variables have Reject Limits defined as part of the Product specification.  Any variables that do not affect disposition should not have Reject Limits defined.

Who needs to be aware of a disposition change?

Whenever a Disposition Event occurs, the status of the Production Event changes and is be automatically updated on any Displays where that Production Event is shown.  In addition, the Disposition Event may trigger alarms and calculations.  These alarms and calculations may be on the Unit where the Disposition Event occurred, or may be on upstream or downstream Units.  This provides a variety of ways to highlight an issue with product that may need to be dealt with upstream or downstream in the process.

Changing the disposition may also affect how Production Events can be routed through the process.  Each Unit has one or more "Inputs" defined.  For each Input, the "legal" statuses available for a move into the Input are defined.  Through this configuration, rejected statuses can be prevented from moving further in the process.  Likewise, this may be used to prevent the movement of Production Events before a Disposition Event occurs.

What is the upstream and downstream affect of disposition?

As discussed above, changing the status of a Production Event can affect its potential paths through the process.  The case that is potentially more important to consider is, what should happen when disposition is changed after a Production Event has already moved forward in the process.  Sometimes the output of the next Unit in line needs to be automatically rejected, other times the process may need to be shut down.  Both can be achieved through Alarms and Calculations.

Specifically, a type of calculation known as a "Genealogy Calculation"  may be employed.  Genealogy calculations model genealogy to perform calculations that cross Units. Through a Genealogy calculation, changes in the data or the status of a Production Event can fire calculations upstream and downstream in the process, which can in-turn provide alarming or automatic disposition at that point in the process.