Supermarket Systems are controlled inventory points that support pull replenishment between processes with different timing, locations, or flow constraints.
Definition
A Supermarket System is a controlled inventory buffer used in Lean pull systems. Downstream consumption from the supermarket triggers upstream replenishment through kanban or other signals. The supermarket defines what is stored, how much, where, and under what replenishment rules.
It is not just storage. It is an intentional control point that connects flow where continuous one-piece flow is not yet practical.
History
The term comes from the way retail supermarkets replenish shelves based on customer consumption. Toyota adapted this logic into production control, enabling replenishment based on actual downstream use rather than forecast push.
When to Use
Use a Supermarket System when adjacent processes cannot be directly connected due to cycle-time differences, distance, batch constraints, shared equipment, or supplier replenishment limits. It works best with stable part families and disciplined replenishment rules.
Step-by-Step
- Define the items, customers, and supplying process.
- Measure demand, replenishment lead time, container size, and variation.
- Set maximum and minimum inventory levels.
- Design visual locations, labels, FIFO rules, and kanban signals.
- Define replenishment frequency and responsibilities.
- Train users on withdrawal and replenishment rules.
- Audit accuracy, shortages, excess, and signal discipline.
- Adjust levels based on usage, lead time, and improvement.
Examples
- Assembly: A parts supermarket feeds multiple cells based on kanban withdrawal.
- Healthcare: Supply rooms replenish procedure carts based on used quantities.
- Office: Standard forms or kits are replenished when minimum levels are reached.
Common Pitfalls
- Calling any storage area a supermarket.
- No calculated inventory levels.
- Broken kanban or replenishment discipline.
- Excess obsolete inventory hidden in the system.
- No FIFO control.
- Ignoring quality issues that create shortages.