Model resources and transfers
Represent zones, merges, diversions, identification points and accumulation areas. Define usable capacity, direction, load restrictions and availability for each resource. The model must reflect what the installation can observe and control.
PLCs usually execute local transport sequences; WCS coordinates destinations and admission at the agreed boundary. Do not move deterministic local or safety decisions into a network-dependent application.
Reserve approaching capacity
Observed occupancy is not available capacity: released loads may still be approaching. Specify when reservations begin, expire, become occupied or are released after failure.
At merges, balance priorities without starving one input. Circular waits can arise when every zone waits for space in another. Admission limits and escape capacity may prevent this, depending on topology.
Tracking and manual removal
Identity must follow transfers. A sensor event without reliable identification can update occupancy but cannot invent identity. Manual intervention requires reconciliation before releasing the task.
Monitor occupancy age and lack of progress. Distinguish legitimate destination waiting from transfer failure. An operational alarm should explain what blocks the next step.
Worked finite-buffer scenario
A buffer holds 20 cartons, with 14 present and four released toward it. Only two more positions are available, not six. If the outlet stops, restricting admission preserves the limit. Recovery must account for valid reservations and manual removals.
The average relation L = λ × W is a consistency check under appropriate stable conditions and units, not a complete peak-capacity model. Test bursts and blockages, measuring maximum occupancy and clearing time.
Project verification criteria
- Compare occupancy plus approaching reservations with capacity.
- Test merges under continuous competing demand.
- Reconcile manual removal without completing the wrong load.
Examples describe engineering decisions and test scenarios. Implemented interfaces, limits and features are defined by each project’s scope.