4.1 Digital andon systems

A traditional Andon system (lights on a pole) serves as a passive request for help; a Digital Andon system acts as an active subpoena for support. In a high-speed manufacturing environment, a “Red Light” that goes unnoticed for 10 minutes equates to 10 minutes of lost capacity that can never be recovered. The core objective of a Digital Andon system is to convert “Line Down” events into Workflow Tickets governed by enforceable Service Level Agreements (SLAs).

The taxonomy of stops

Not all stops are equal. The system must classify the “Ask” immediately to route it to the correct department. It is recommended to avoid broadcasting generic “Help” messages to everyone.

Material call (logistics)

Trigger: Operator scans “Low Level” or Machine throws “Feeder Empty” alarm.
Routing: Warehouse / Water Spider.

Maintenance call (equipment)

Trigger: Machine Error Code (e.g. “Motor Fault”) or Operator “Broken Tool” button.
Routing: Maintenance Technician.

Quality call (process)

Trigger: Consecutive Failures at Automated Optical Inspection (AOI) or Operator visual doubt.
Routing: Quality Engineer / Line Lead.

Process call (bottleneck)

Trigger: Cycle time exceeds target by > 15%.
Routing: Shift Supervisor.

The escalation logic (the timer)

The Digital Andon functions as a “Dead Man’s Switch.” When the primary responder does not react within the allotted time, the system automatically escalates the issue to the next tier of management. This design removes the social friction of operators feeling like they are “tattling” on a coworker; the system initiates the escalation, not the operator.

Severity & SLA matrix

These rules must be defined in the MES configuration:

Tier 1 (Responder): The Technician or Lead assigned to the line.
- Response SLA: 5 Minutes.
- Action: They must “Acknowledge” the alert (e.g. Scan Badge) at the station.
Tier 2 (Manager): The Area Manager or Engineer.
- Trigger: When the Tier 1 Status remains “Open” for more than 15 minutes.
- Action: The system sends a Push Notification or SMS to this tier.
Tier 3 (Executive): Plant Manager or Director.
- Trigger: When the Tier 1 Status remains “Open” for more than 60 minutes.
- Action: The system generates and sends an Email Report. (This acts as the “nuclear option”).

Pro-Tip: Avoid conflating “Response Time” with “Fix Time.” It is better to measure two distinct metrics: “Time to Acknowledge” (Reaction speed) and “Time to Resolve” (Technical capability).

The workflow state machine

An Andon event is a ticket. It must traverse a defined lifecycle.

Open (red state)

Start: Event Triggered.
Clock: Ticking. Line is likely Down.
Andon Board: Flashing Red.

Acknowledged (yellow state)

Action: Responder scans badge at the terminal.
Meaning: “I am here working on it.”
Clock: Escalation Timer pauses; Resolution Timer continues.
Andon Board: Solid Yellow.

Resolved (green state)

Action: Responder selects Root Cause Code and closes ticket.
Meaning: Production has resumed.
Clock: Stopped.

Closure rules & reason codes

We cannot effectively improve what we do not accurately categorize. Closing an Andon ticket requires a “Confession”—a mandatory data entry step where the responder explains exactly why the line stopped.

The “other” category

Rule: “Other” or “Miscellaneous” must be removed from the dropdown menu.
Why: “Other” creates a data black hole. The system must be designed to guide users to select a specific category (e.g. “Feeder Jam,” “Software Crash,” “Missing Part”).

Validation logic

When the duration exceeds 10 minutes and the comment field is empty, the system should block closure, prompting the technician to type a brief explanation.
When the Responder ID matches the Operator ID, the system should flag the ticket for review. Operators generally should not be closing their own maintenance tickets.

Automatic vs. manual triggers

Automatic (Hard Down): The machine state (DI/O or OPC-UA) must be connected directly to the Andon framework.
- Logic: When the Machine State registers “Error” for more than 30 seconds, the system should auto-create a Maintenance Ticket.
Manual (Soft Stop): A touchscreen interface must be provided for the operator.
- Logic: When the operator presses “Quality Check,” the line continues running (if safe to do so), but the system immediately summons a Quality Engineer.

Final Checkout: Digital andon systems

Category	Metric / Control	Threshold / Rule
Routing	Targeted Alerts	Alerts go only to the relevant department (Logistics vs. Maintenance).
SLA	Auto-Escalation	When a Ticket remains unacknowledged > 15 mins, the system auto-alerts the Manager.
States	Acknowledgement	Establish distinct visual states for “Help Requested” (Red) vs “Help Arrived” (Yellow).
Data	Taxonomy	The “Other” category is removed. Responders select a Specific Root Cause for closure.
Input	Friction	Implement one-touch activation for operators to avoid complex menus during a crisis.
Governance	Ghost Calls	When an Auto-Andon triggers but the Operator clears it instantly, log it as a “Micro-stop” for analysis.
Visibility	Displays	Large overhead screens must refresh status in < 5 seconds.