* Lost absolute position data is the most direct cause
The absolute position system uses stored position data to let the CNC know the relationship between each axis and the machine reference point. Once this data is lost, the system becomes confused and no longer knows exactly where the X-axis is.
When is the data likely to be lost? It can happen after repair work, a power interruption, work on the absolute position system, or the removal of related electronic parts. This is especially common on older machines. If the battery voltage becomes low, the connection is poor, or the battery is replaced in the wrong way, the position data can disappear just like that.
Sometimes the machine seems to run normally. Then the power is disconnected or some maintenance is carried out. When the machine is powered on again, alarm 310 appears.
So when you see alarm 310, do not rush to remove the motor. First think back to what happened before the alarm. Was the machine powered off? Was maintenance just carried out? Was the battery replaced? Was the encoder or
servo motor removed? The timing of these events is especially important.
* Pulse encoder battery problems are very common on older machines
Fanuc systems that use absolute position encoders normally have a battery to keep the absolute position information stored. Low battery power, poor connector contact, or incorrect battery replacement can all cause the position data to be lost.
But one point needs to be made clear: Alarm 310 does not mean that the battery is definitely faulty. The battery is only one possible cause. If the battery tests normal, you still need to check the feedback cable, encoder, parameters, main board, and other related parts. Do not treat alarm 310 as meaning "replace the battery and everything will be fine."
* Feedback cables, connectors, and encoders often cause trouble after a motor is replaced
The X-axis gets its position feedback from the pulse encoder or another related absolute position detection system. If the encoder cable is broken, a connector is loose, or a plug is not fully inserted, the CNC cannot receive accurate position data. This is especially common after servo motor repair work.
For example, if alarm 310 appears immediately after replacing the servo motor, pulse encoder, or encoder cable, or after repairing the electrical cabinet or removing and reinstalling the servo system, the first thing you should do is go back and check the feedback cable.
Do not only check whether the cable is broken. Check whether the connector is fully inserted, whether any pins are damaged, whether the cable has been crushed or pulled, and whether it was connected to the wrong position. Sometimes a small contact problem is enough to stop the CNC from recognizing the absolute position.
* Replacing the main board or restoring parameters can also cause alarm 310
There is another situation that is also fairly common in actual repair work. If the CNC board, CPU board, or related hardware has been replaced, but the original parameters were not properly restored, the configuration of the absolute position system may be wrong.
Some people do not have the original machine parameter backup, so they copy a set of parameters from another Fanuc machine of the "same model." The CNC models may look the same, but the servo motors, pulse encoders, axis travel, and reference point settings of the two machines may be completely different. Once the parameters are wrong, alarm 310 appears.
When you see alarm 310, it is best to compare the parameters with the original machine backup and check them against the repair manual for that particular Fanuc system. Do not change parameters randomly just because you see alarm 310. More importantly, do not overwrite a large group of parameters using data from another machine.
* Sometimes nothing is broken. The X-axis simply needs to return to zero
The words NEED ZRN already make the meaning fairly clear: The X-axis needs to return to its reference point. If you cannot find any problem with the absolute position detection system, feedback cable, battery, or parameters, the machine may really just need an X-axis reference point return.
But there is a catch. The zero return method may be different for different Fanuc series, machine builders, and machine configurations. You cannot simply search online for "Fanuc zero return procedure" and follow whatever steps you find.
You need to check the actual CNC model and the machine builder's operation and maintenance manual. Establishing the reference point for an absolute position system is not exactly the same as an ordinary zero return. If the procedure is wrong, the position data still may not be established.
First, do not rush to touch anything. Write down the complete alarm shown on the screen. Do not only write "Fanuc 310." Record the full message: 310 APC ALARM: X-AXIS NEED ZRN.
Also record the CNC model, which axis has the alarm, whether there are any other alarms, whether it appears immediately after power-on or only after repair work, and whether the motor, encoder, main board, or battery was recently replaced.
Then think about what was worked on recently. Was the X-axis servo motor replaced? Was the pulse encoder replaced? Was the feedback cable replaced? Was the electrical cabinet repaired? Were the parameters restored? If any of these things were done, check the places that were recently touched first.
Next, check the pulse encoder battery and feedback connections. Go through the battery voltage, battery box connector, encoder plug, and cable condition. Then check the absolute position parameters and compare them with the original machine backup.
If there is no obvious problem with any of these, perform an X-axis reference point return using the procedure specified for that Fanuc system. If alarm 310 disappears afterward, the most likely cause was lost absolute position data or a reference relationship that had not been properly established.
If the alarm remains after the procedure, continue checking the pulse encoder, servo motor, and related CNC hardware.
