What Is an Andon State in Shop Floor Monitoring?

An andon state is the single status color a work center is showing right now, chosen from a fixed set of six values: green, yellow, red, idle, blue, and white. It answers one question at a glance, which is whether this machine is doing what the schedule expects of it at this moment. EDGEBIC by User Solutions computes the state per work center for the shop floor strip on the dashboard, so a supervisor can scan a whole plant in a few seconds instead of reading a grid.

How it works

The name comes from the andon cord and lamp of the Toyota Production System, where a light above a station told the whole line whether that station was healthy. The concept generalizes to any status board. What makes an andon useful is not the color itself but the discipline of reducing a complicated situation to one honest signal.

The state is derived rather than typed in. Nobody sets a work center to yellow. The state falls out of comparing what the schedule says should be happening against what the shop floor has actually reported. The plan supplies the expected start time and expected elapsed time. The actuals supply the recorded start and the elapsed clock. The comparison produces the color.

Six values exist because three cannot carry the meaning. Under a simple running, late, stopped scheme, a machine waiting on parts and a machine with a broken spindle look the same, and so does a machine that has nothing scheduled and a machine in a maintenance window. Each of those four situations has a different owner and a different response, and collapsing them wastes the supervisor's walk.

Here is what each value means:

Note the pairs that a smaller scheme would merge. Red and idle both mean the machine is not cutting, but red is a problem and idle is not. White and red both mean nothing is running, but white was planned and red was not. Blue and red both mean a job has stalled, but blue is somebody else's fix.

A concrete example

Think of the board behind the desk on a hospital ward, where each room carries a status light. A green room is a patient resting comfortably. A yellow room is a patient whose observations are drifting. A red room needs a nurse now. An empty room is not an emergency, it is capacity. A room closed for cleaning is neither a patient problem nor free capacity. If the board only had lit and unlit, the charge nurse would walk every unlit room to find out which kind it was, and the walking is the whole cost.

A plant board behaves the same way. At 09:40 a supervisor scans twelve work centers. Nine are green. Mill-2 is yellow, so it is running but has passed its overrun threshold, and the right move is to ask the operator whether the job will still finish today. Press-1 is blue, so the material never arrived, and walking to the press would tell her nothing she does not already know. Lathe-3 is white because its planned maintenance window opened at 09:00. She has one conversation to have, at Mill-2, and she knew that within about four seconds.

Run the same board with three colors and she has three stopped machines to investigate, two of which are behaving exactly as intended.

How EDGEBIC uses it

The andon state drives the work center strip on the dashboard, which is designed to be read standing up rather than studied. The strip pairs naturally with the morning meeting view: see how to use the standup dashboard for the routine it supports, and EDGEBIC dashboards explained for the four-tab layout it sits in.

Because the state is computed from plan versus actuals, its honesty depends entirely on the timeliness of shop floor reporting. A plant that logs starts and stops as they happen gets a board that means something. A plant that keys yesterday's paper sheets in the next morning gets a wall of red. The reporting side is covered in what is a punch type and how to start a job on the kiosk.

White comes from the calendar rather than from the floor, so a maintenance window that was never entered will show as red instead: see what is a downtime event. When you want to know whether a board can be trusted at all, the companion signal is the data quality chip, and the wider daily-management framing sits in what is SQDC in manufacturing.

For the general concept outside the product, see andon and the full manufacturing glossary. To see live status colors computed against a finite capacity schedule, explore EDGEBIC.