Definition
A pull system is a production control method where downstream processes withdraw (pull) only what they need from upstream processes, and the act of withdrawal is the signal to replenish. Nothing is produced upstream until a downstream process consumes and signals.
This is the opposite of push production, where upstream processes produce based on forecasts and schedules, pushing output forward regardless of whether downstream needs it. Push creates overproduction, excess inventory, and disconnection from actual demand. Pull connects every process to actual consumption.
The full Toyota term is 後工程引き取り (atokoutei hikitori) — “subsequent process withdrawal” — which precisely describes the mechanism: the next process in line reaches back and takes what it needs.
Japanese Origin
The word hikitori (引き取り) combines 引き (hiki, “to pull”) and 取り (tori, “to take”). It is a common Japanese word meaning to withdraw, retrieve, or take back. In the TPS context, it refers to the downstream process “pulling and taking” parts from the upstream process — the customer reaches back to the shelf.
History at Toyota
The supermarket inspiration, 1954 — Toyota’s 75-year corporate history documents the origin precisely. The “supermarket method” was introduced at Toyota inspired by a report on a Lockheed aircraft plant and the American supermarket concept. The key insight: “The subsequent process is the ‘customer’ and the prior process is the ‘supermarket.’” Customers take what they need, and the store replenishes what was taken.
The problem pull solved: Before the pull system, Toyota suffered severe production imbalances. Parts accumulated excessively at assembly plants. Assembly could only proceed with whatever parts happened to be available. Early-month production ran at roughly 50% of targets, followed by frantic end-of-month acceleration with excess workers and faster conveyor speeds.
Kanban as the mechanism — The supermarket method evolved through the addition of kanban cards indicating product name, number, and quantity. Kanban became the operational tool controlling pull, ultimately developing into the full Just-in-Time system.
Expansion, 1950s-1960s — Taiichi Ohno systematically expanded pull from engine manufacturing across all of Toyota’s operations, then to the supplier network by the late 1960s.
How It Actually Works
There are three types of pull systems:
Supermarket pull (Type A) — Each process maintains a small inventory “supermarket” of finished items. When a downstream process withdraws items, that consumption triggers a kanban signal to replenish. Best for high-volume, repeating parts.
Sequential pull (Type B) — Products are made to order with no supermarket inventory. A scheduling department places production instructions based on actual downstream orders. Best for high-variety, low-volume, or expensive items.
Mixed pull (Type C) — Combines both: supermarket logic for high-volume parts (perhaps 80% of volume) and sequential logic for low-volume items (20%).
Toyota’s actual kanban flow is far more sophisticated than most descriptions suggest. Art Smalley has documented the real process:
- On the assembly line, a worker pulls a kanban card upon using the first item from a container
- Cards are collected on a timed basis, signaled by the andon board
- Cards are fed into an automatic sorting machine that reads bar-coded information and relieves inventory
- Scanned information triggers payment to the supplier
- Consumed parts data is evaluated by Production Control
- Electronic transfer to the supplier triggers a printer at the supplier facility to print the supplier kanban
- The supplier kanban goes into a heijunka box for scheduling
The key observation: many lean observers focus only on the paper kanban and manual heijunka board. The sophisticated IT integration in the middle — bar-code scanning, automatic sorting, electronic supplier signaling, automated payment — is often missed. This was Toyota’s process over 20 years ago; today it is even more automated.
Implementation Guidance
Do not implement pull without its prerequisites:
- Heijunka (leveled production) — pull without leveling creates wild demand fluctuations upstream
- Reliable equipment — a pull system on unreliable machines creates constant shortages
- Quality at the source — pulling defective parts downstream amplifies waste
- Standardized work — operators must follow standardized sequences for kanban handling
Start with a supermarket between two processes. Pick a high-volume, repeating part. Install a small buffer (supermarket) between the producing process and the consuming process. Use kanban cards to signal replenishment. Get this working before expanding.
Expect problems. Pull systems expose problems that push systems hide. When you reduce inventory buffers, equipment breakdowns, quality issues, and changeover delays become immediately visible. This is a feature, not a bug — solve these problems to make the system more capable.
Integrate technology appropriately. Art Smalley has explicitly criticized the vocal lean segment that implies “the only answer is to unplug computers and do things entirely manually.” Toyota has integrated IT into their pull system for decades. Use technology where it adds value — bar-code scanning, electronic kanban, demand analytics.
Common Mistakes
Implementing pull without leveling. This is the most common failure. Without heijunka to smooth the demand signal, pull amplifies variation rather than reducing it. Upstream processes get hit with lumpy, unpredictable demand that is worse than the forecast-driven system it replaced.
Confusing pull with zero inventory. Pull systems require inventory — the supermarket buffers are essential. They provide the decoupling between processes that allows each to operate at its own pace while still being connected to actual demand. The goal is controlled, minimal inventory — not zero.
Thinking pull means “no computers.” Toyota’s pull system is deeply integrated with IT systems — bar-coded kanban, automatic sorting, electronic supplier communication, payment triggering. The physical kanban card is the visible part; the digital infrastructure underneath is equally important.
Implementing pull as a standalone tool. Pull (kanban) is one of four elements that comprise the JIT pillar of TPS: flow, takt time, kanban, and leveling. Implementing kanban alone without the other three produces a scheduling tool, not a lean production system.
Skipping the response to exposed problems. Pull exposes problems by design. When companies encounter the disruptions that come from reduced buffers and respond by adding inventory back, they have defeated the purpose. The correct response is to solve the problem that was exposed.