Nachi FD/CFD Controller — Errors, Alarms & Reset

Nachi · beginner · 20 min

A Nachi FD/CFD controller separates faults into Errors (E) that stop the robot and turn the servo off, and Alarms (A) that stop it temporarily. Learn to read the code on the pendant, clear it, and recover from the common "step number not designated" alarm.

ℹ️ On a Nachi FD/CFD controller an E (Error) prohibits further operation until the cause is removed and, in auto, turns the servo off; an A (Alarm) stops the robot temporarily with the servo still on. Read which one you have before you touch anything.

Errors vs alarms

Nachi FD/CFD controllers classify faults into two families, and the letter tells you how serious it is:

• E — Error. Operation is prohibited until the cause is eliminated. If it happens during auto operation, the robot servo turns off. These are the ones that drop power to the motors.
• A — Alarm. A condition that may lead to a future error or needs attention. In auto operation the servo stays on and the robot stops temporarily. Fix the flagged condition and you can continue.

Knowing the family before you react tells you whether power was cut (E) or the robot merely paused (A).

Read the fault on the teach pendant

When a fault trips, the teach pendant shows the message. Before resetting, note the details the controller gives you — you'll need them to find the true cause (and to give them to a Nachi service engineer if you have to escalate):

• Error Code — the E/A number.
• Flag, Address, and Stack — the extra fields shown alongside the code.
• What you were doing and the operating situation when it happened.

Common causes behind an E-code include motor over-temperature, encoder serial-data errors, collision-sensor trips, and safety/interlock conditions — the code text points you at which.

Clear an error and re-enable the servo

1. Read the code and its message on the pendant; identify E vs A.
2. Remove the physical cause — clear a collision, let an over-temp motor cool, fix the tripped interlock or wiring the message points to. An E-code will not stay cleared while the cause is still present.
3. Reset the error from the pendant (error-reset), then turn the servo back on — for an E-code in auto the servo was dropped, so you re-engage it.
4. Recover the motion task and resume per your workflow.

The "step number not designated" alarm

A frequently seen recovery case is the alarm that appears when the robot can't restart the motion task after an interruption — it reports that the step number is not designated. To clear it:

1. Activate the E-Stop on the teach pendant or controller.
2. Use Clear Robot Error on the pendant (or your cell HMI).
3. On the pendant, select the step-number field in the top bar to open its menu.
4. Set the designated step to 0 (or re-enter it if it's already 0) and confirm with Enter.
5. Release the E-Stop — motors and motion execution resume.

Never do this

Don't clear a safety- or collision-related E-code and re-run without finding why it tripped — an over-temp or collision code is telling you something in the cell is wrong. Fix the cause, then reset. Never defeat a safety interlock to get a stubborn error to clear.