Assembly line kanban
Line 2 moves to a 60 s takt. Can one water spider still keep four stations supplied, or do they stand starved waiting for bins?
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Before Line 2 moves to a 60 s takt: can one water spider keep the stations supplied, or do we add a second, more kanban cards or a faster supermarket pick?
- Who uses it
- Production engineers, line supervisors and lean and logistics planners
- How it can create value
- See whether stations starve for want of stock at the line or of the water spider’s time before hiring, buying racks or reorganising the supermarket. Here the spider is the bottleneck: more cards only delay the stops, a second person or a 25 s pick removes them. A shorter run saves money only if overtime or staffing actually fall; weigh the line-side space and stock of extra cards and the cost of a second spider against measured times.
- Bring your site data
- The takt and shift plan, parts per unit and bin quantities for every part, a time study of the water spider (collecting cards, picking and setting in bins), the route on your floor plan, station cycle times, rework rates and pallet quantities. One trip per card and all times here are assumptions.
A model you can inspect.
Line 2 at its new 60 s takt: 120 units pass four stations (42–66 s each) joined by roller buffer conveyors of 2, then inspection (40 s); 10 % are reworked (2–5 min) and inspected again. Each station takes its parts from the kanban flow rack behind it, two bins a part (brackets 12, harnesses 6, M5 screws 48, covers 6; a unit takes 2, 1, 8 and 1). An emptied bin sends its card to the kanban post and the water spider on a trip: collect the card (5 s), pick a full bin in the supermarket (45 s), set it into the rack (20 s), walk back to the base at 1 m/s. A station whose rack is empty stands starved, holding its unit, until the bin arrives; every 4 good units make a pallet the forklift takes to shipping. Each card is its own trip (no collecting several on one loop); no breakdowns, breaks, congestion in the aisles or costs. Figures are assumptions, not measured.
Change one thing
Compare 1 water spider with 2, with a third kanban card for every part and with a 25 s pick in the supermarket, on the same 120 units; then try buffers of 1 or 4, a 65 s takt or 15 % rework.
Read the consequence
Stations turning red while their rack is empty, units queuing at the line head, the water spider’s utilization and when the last pallet ships. With one spider the stations stand starved for about an hour in all and the run ends 27 minutes later; a second spider or a 25 s pick removes the stops; a third card cuts them by about 40 % but finishes no sooner, because the spider stays the bottleneck.
View the starting inputs
- Takt: a unit started every (s)
- 60
- Units in the shift
- 120
- Water spiders on the milk run
- 1
- Kanban cards (bins) for each part
- 2
- Picking a bin in the supermarket (s)
- 45
- Units a buffer conveyor holds
- 2
- Units failing inspection (%)
- 10
Agent counts, routes and resource definitions are also saved in the project JSON.
The same demand. A different capacity.
Means across 3 runs, seeds 11–13. Observation window 180 minutes. Arrivals, geometry and the seed set stay the same in every option.
| Scenario | Completed | Mean wait | Mean cycle | Blocked |
|---|---|---|---|---|
| 1 water spider · 2 cards | 230 | 6m 43s | 10m 05s | 0 |
| 2 water spiders · 2 cards | 230 | 52s | 4m 14s | 0 |
| 1 water spider · 3 cards | 230 | 4m 21s | 7m 42s | 0 |
| 1 water spider · 25 s pick | 230 | 1m 09s | 4m 24s | 0 |
Waiting averages cover arrived jobs, including unfinished waits; cycle averages cover completed jobs only. These are synthetic calculations, not measured site performance, revenue or a safety assessment.
Engine, status and output notes
process-des-2.7.0. Status: 1 water spider · 2 cards: completed; 2 water spiders · 2 cards: completed; 1 water spider · 3 cards: completed; 1 water spider · 25 s pick: completed. “Completed” is the engine run status, not success for every job. Check blocked jobs and warnings.
- No engine warnings.
Engine inputs and saved comparisons stay with the saved project. Any limited trace affects playback details, not aggregate metrics.
Articles on this example
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