A feeding buffer is extra time added to the routing step that feeds directly into the bottleneck, giving that critical hand-off enough slack to absorb upstream variation so the constraint is never left starved and idle. In Theory of Constraints scheduling, the bottleneck sets the pace of the entire plant, so protecting the moment work arrives at it protects everything downstream: it is arriving at the airport early to protect the one part of the trip you cannot rush.
This entry is part of the EDGEBIC by User Solutions glossary; the broader dictionary lives in the manufacturing glossary.
Why the Constraint Needs Protecting
The Theory of Constraints says a plant's throughput is limited by its single weakest link. Every hour the bottleneck runs is an hour of plant output; every hour it sits idle is output the plant can never recover, because nothing downstream can outrun it.
That makes the bottleneck's start time sacred. If the operation that feeds it slips even slightly, the constraint waits with nothing to work on, and the whole plan loses that hour. Upstream variation is normal (a late material, a slow prior step), so the feeder step needs a cushion. That cushion is the feeding buffer.
How It Works
Anchor scheduling treats the bottleneck as the fixed point of the plan and schedules around it. Three buffers can protect the constraint, and the feeding buffer is the one aimed at the direct feeder:
- The constraint buffer is a pause inserted between the last upstream step and the bottleneck's start: a general safety gap before the constraint.
- The feeding buffer is extra duration added to the step that feeds the bottleneck directly, giving that specific hand-off more protection.
- The shipping buffer protects the customer due date from variation after the constraint.
The feeding buffer is applied only to the direct feeder step, not to every upstream step. It effectively widens that step's planned window so a small delay in it does not push the constraint's start.
How It Is Sized
Buffer sizing runs only when buffer calculation is enabled. With it off, all three anchor buffers are zero and the schedule is tight, with no planned slack.
When enabled, sizing depends on whether the anchor is a true bottleneck:
| Anchor type | Feeding buffer |
|---|---|
| True bottleneck work center | About 10 percent of total upstream time, applied only to the direct feeder step |
| Non-bottleneck anchor | A flat 1 hour on the direct feeder step |
For context, the sibling buffers on a true bottleneck are sized larger: the constraint buffer at about 50 percent of upstream time (minimum 1 hour) and the shipping buffer at about 25 percent of downstream time (minimum 2 hours). The feeding buffer is the smaller, targeted top-up on the single feeder step.
A Concrete Example
A job's routing feeds a heat-treat oven that is flagged as the bottleneck. The upstream steps total 20 hours of work. Buffer calculation is enabled.
The feeding buffer is roughly 10 percent of that upstream time, so about 2 hours, added to the step that feeds the oven directly. When the engine schedules the pre-oven steps backward from the oven's protected start, the feeder step's window carries that extra 2 hours of cushion. If the feeder runs a little long on the day, the oven still has parts ready when its protected start arrives. The constraint keeps running, and the plan holds.
How EDGEBIC Uses It
In EDGEBIC, the feeding buffer is one of three anchor scheduling buffers that activate when a work center is flagged as the bottleneck and buffer calculation is turned on. The engine schedules pre-anchor steps backward from the constraint, and when it reaches the direct feeder step, it adds the feeding buffer to that step's duration before placing it, so the feeder finishes with margin ahead of the constraint's protected start.
Anchor scheduling itself is distinct from plain backward scheduling: the anchor pins the plan to the constraint, whereas backward scheduling right-aligns a whole job to its due date (see anchor scheduling versus plain backward scheduling). The feeding buffer works alongside the constraint buffer and shipping buffer to keep the bottleneck fed, exploited, and never starved. For how direction and buffers interact, see TOC buffers and direction precedence.
A feeding buffer is extra time added to the routing step that feeds directly into the bottleneck, protecting the constraint from upstream variation so it is never left starved and idle. In Theory of Constraints scheduling, the bottleneck sets the pace of the whole plant, so an hour lost there is an hour lost for everyone. The feeding buffer pads the direct feeder step's window so a small upstream delay does not leave the constraint waiting for work.
They protect the same bottleneck from different angles. The constraint buffer is a pause inserted between the last upstream step and the bottleneck's start, a general safety zone before the constraint. The feeding buffer is extra duration added specifically to the step that feeds the bottleneck directly, giving that one critical hand-off more protection. One is a gap before the constraint; the other is padding on the feeder step itself.
For a true bottleneck work center, the feeding buffer is sized at about 10 percent of the total upstream time, applied only to the step that feeds the constraint directly. For a non-bottleneck anchor, a flat one-hour feeding buffer is used. Buffer sizing runs only when buffer calculation is enabled; with it off, all the anchor buffers are zero and the schedule is tight with no padding.
Expert Q&A: Deep Dive
Q: Our heat-treat oven is the constraint and it keeps sitting idle waiting for the prior operation. Would a feeding buffer fix that?
A: That is exactly what it targets. When the oven is flagged as the bottleneck, anchor scheduling protects it, and enabling buffer calculation adds a feeding buffer to the step that feeds the oven directly, sized at roughly 10 percent of the total upstream time. That padding absorbs small upstream slips so the oven has work ready when it is due to start. It does not create capacity out of thin air; it front-loads a little protection onto the critical hand-off so the constraint stops starving on ordinary variation.
Q: If buffers add time, do they make every job later? Why would we turn them on?
A: Buffers move time around rather than simply adding it: the feeding buffer front-loads protection onto the feeder step so the constraint starts on schedule, which protects the due date more than a tight, fragile plan would. They are also optional. Buffer sizing runs only when you enable it; left off, the anchor buffers are all zero and the schedule is packed tight. You turn buffers on when the cost of the bottleneck starving is higher than the cost of a little planned slack, which is the usual case for an expensive, plant-pacing constraint.
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