To be honest, at least half of the 401 alarms we encountered were not because the drive was bad, but because the peripheral conditions were not met. You first run through those simplest and most easily overlooked places, than come up to dismantle the drive to save a lot of work.
1. Emergency stop or safety circuit is not closed (this is the most wanted)
This is the number one cause. Emergency stop button is not reset, the safety gate is still open, an axis travel limit is triggered, or somewhere in the safety circuit is disconnected - as long as the safety link is not completely closed, the servo is not allowed to start. No start, naturally no VRDY, and then 401. often you do not even need to check the schematic, see if the emergency stop is still pressed, the door is not closed, the problem is solved.
This is also a common occurrence. Performance is a drive panel lights are not lit, with the same dead. The reason may be that the power supply is not given on the insurance burned, loose wire. Simply put, that is, the CNC side of the shouting throat, drive this side of the "sleep too dead simply did not wake up.
3. The contactor called MCC did not engage
This detail will be ignored by many newcomers. There is a key role in the machine called the main contactor, which is responsible for the entire servo system power. Listen carefully when the power is on, there is no "snap” a clear sound of suction. If there is no such sound, the drive is dead, and VRDY will naturally go down. Check the contactor coil, control its circuit, there are often surprises.
4. Power Supply Module (PSM) abandoned the work
PSM is the core module that supplies DC power to the servo. If it hangs, the entire servo system can not get up, may be all axes flush report 401, and usually with a few other alarms. At this time, just look at a 401 is not enough.
5. Communication problems (fiber optic or signal lines)
Many Fanuc systems now use fiber optic communication. Fiber optic head loose, dirty interface, optical module is not very good, the CNC will not receive drive status information, VRDY will not receive. This problem is quite common on older equipment with high vibration.
6. Drive internal failure (but definitely not the primary object of suspicion)
This situation does exist, the drive inside a component is bad, can not enter the ready state. However, it is recommended that you make sure that all those simple and easy to check the previous links are cleaned up, and then come back to consider it at the end. Do not come up to spend a lot of money to replace the drive, and then find that the replacement is still reported 401, it would be embarrassing.
7. 401 "brought out” by other alarms
This is especially critical. Many times an axis first reported other servo alarms, the drive out of self-protection directly stopped, the VRDY signal followed by the disappearance of the system immediately after the report 401. So you must make a habit - first turn over the alarm history, see if there is something else popped up before the 401. It's easy to get sidetracked by just staring at 401.
And by the way, make a distinction between 401, 400, and 402
A lot of people are always confused with these codes, so let's talk briefly:
- 400: servo abnormality, the range is broader.
- 401: servo is not ready, that is, we talk about this VRDY OFF. 402: more specific servo alarm.
- 402: more specific servo alarm, more directional.
So 401 is characterized by - the machine is not yet moving it, in the startup phase to stop you.
How do I get the 401 to come around less often in the future?
To be honest, a lot of this alarm is caused by human factors or small oversights.
A couple of solid suggestions:
- Check the emergency stop circuit regularly, especially the buttons that are always activated.
- Make sure that the wiring in the cabinet is secure, and don't make false connections.
- Keep the fiber optic connectors clean, don't just pull them apart.
- Keep a record of alarms and parameter changes, so that problems can be traced back.
Look at all the small things, but the time saved is really more troubleshooting. If you can't do it yourself, you can find a professional team like
Songwei CNC.
The essence of the Fanuc 401 alarm is not "which part is broken”, but that there is a link in the chain of servo startup that is not open. If you come up to run to replace the drive to go, the probability is that it is a waste of time, but also ride in a lot of money. The real efficient way is to start from the root of "can start”, step by step backward. Connect the broken link, and the 401 will be eliminated by itself.
