Lesson 12 made the transportation-versus-accumulation call and picked the mechanism. This lesson answers the how-much-and-what-type it deferred: turning a buffer requirement into a zone count and a zone length, and choosing a release mode on purpose instead of trusting the default. Two outcomes every student has to leave with. First, they can size a buffer from the downstream unavailability and the arrival rate, not from the floor. Second, they never leave the release mode on default without asking what the downstream process needs. The step they'll miss on their own is the Aux I/O placement, so make "where are your Aux I/O points, and what's each one doing" an automatic question every time a student shows you a zone layout. Hold the deferrals: no merge design, no sorter pick, no final gap math.
| Segment | Min | What happens |
|---|---|---|
| A buffer is a question with a number in it | 6 | Read the hook. Put it on the board that "we need accumulation here" is a call, not a design. Ask the room what actually sets how much buffer. Steer them toward downstream unavailability and arrival rate without handing it over. |
| Sizing buffer to zones, on the board | 16 | Key teaching moment, below. Draw the multi-zone conveyor feeding the eight-second labeler, walk what each zone does through a wave, then size it: a one-minute wave at the carried-in rate becomes a zone count. Then zone length off the envelope, then run length. Make every student reason the count, not memorize it. |
| Release modes, against the sorter induction | 14 | Default singulated, then slug, then cascade. Don't define slug and cascade first. Put a sorter induction on the board and ask why one-at-a-time starves it. Let the room reach the controlled-burst answer. Name that the configuration depth is Lesson 20. |
| Back pressure and the fail-safe direction | 8 | Conceptual only. Zero-pressure isn't always zero force: ask for the failure case if a package gets pushed out of its zone. Then the release-signal direction, signal-to-stop versus signal-to-release, and why a lost signal can mean an uncontrolled release. Name it; the wiring is Lesson 20 and Lesson 23. |
| Riverside zone plan | 12 | Facilitation below. Size the pre-sorter accumulation from the 20 CPM target and the envelope, pick the induction's release mode, and run the weight-per-zone gate on the heaviest case. Do not tell them; ask. |
| Forest, close, and the Aux I/O preview | 4 | Close on the driving question, then the CONTROLS CORNER preview. Answer the Aux I/O placement on the labeler drawing: the last zone hands off to the labeler, so that's where the PLC reaches in. Full wiring is Part V. |
| Total | 60 | Baseline session. Expand with the stretch option below if you have more time. |
Accumulation is abstract until it's drawn. Put a multi-zone conveyor on the board feeding a labeler that cycles every eight seconds, and walk the room through what each zone does as the labeler falls behind during a wave. Zone one holds when zone two is full, zone two holds when zone three is full, and the buffer fills from the discharge end backward. Get them to see the buffer as time you can bank, not just steel.
Then flip to sizing. If the wave lasts a full minute at twenty a minute, that's about twenty cartons, so about twenty zones plus margin. Do the arithmetic out loud so it lands as reasoning, not a formula. Then flip to release: this labeler wants them one at a time, but a sorter induction would want a slug, and the room should say why before you confirm it. Close on the same drawing by answering the Aux I/O placement: the last zone hands off to the labeler, so that's where the PLC reaches in to command a hold and to know a package is waiting. Make them point to the spot.
Have the room size Riverside's pre-sorter accumulation from the 20 CPM design target and the four-product envelope, and pick the induction's release mode, defending both. Steer them to the slug-versus-singulate distinction themselves, against the sorter-induction requirement. Do not tell them; ask. Put the induction on the board and ask what happens when it gets product one carton at a time. Let the room reach the controlled-burst answer on its own.
Then have them run the weight-per-zone gate on the heaviest case that can stack, the Large Case at twenty-eight pounds, and say whether motor-driven roller survives it. Hold scope by name when the room drifts: the merge is Lesson 15, the sorter is Lesson 16, the final gap math is Lesson 25, and the Aux I/O wiring and fail-safe behavior are Lesson 20 and Lesson 23. Each is the right instinct at the wrong time. Today they produce one thing, an accumulation zone plan, and nothing downstream of it.
Q1. By default the line runs singulated accumulation. When the zone just downstream is occupied, the zone holds its package and waits, without pressure. When that downstream zone clears, the zone releases the package forward. And if the downstream zone is already empty when the package arrives, the package doesn't stop at all, it rides straight through. A wrong-choice application is a sorter induction, or any process that needs product delivered in a controlled burst. Fed one carton at a time, the induction starves between cartons and never holds rate; it needs the accumulated zones released as a group, a slug, or with timed spacing, a cascade, so it sees a burst instead of a trickle. Accept any downstream process that needs grouped presentation. The student has to name the need, not just the mode.
Q2. Zone count is buffer time times arrival rate: the number of packages that can arrive in the forty-five seconds the process is out. At twenty a minute that's one carton every three seconds, so about fifteen cartons, meaning about fifteen zones plus margin. Run length is zone count times zone length. Zone length is set by the longest package, its length in the direction of travel plus the gap it rides on; the two envelope dimensions to name are the longest package length and the shortest, the longest setting the minimum zone and the shortest checked so a zone still senses small product. Before assuming motor-driven roller can carry the loaded run, they check the accumulated weight in a loaded zone, and across the packed run, against the MDR's rated load per zone. If it exceeds the rating, MDR is out at that point even though it passed weight-per-foot. Full marks name the weight-per-zone gate; the exact arithmetic is Lesson 25.
The accumulation zone plan the students build today is a project-folder artifact, not a throwaway exercise. It feeds the controls architecture summary in Part V, where the Aux I/O points they placed become real I/O on a panel drawing. Reinforce the habit of writing it into the Riverside note, dated, with the zone count, zone length, release mode, and weight-per-zone result. Don't announce that payoff. Let it land when it lands. Make the zone plan feel like something a professional simply produces and files, and the student who writes it down without being told is the one you're growing.