Look at the Pulse Coder Feedback Cable First, This Place Is the Most Likely to Play Tricks
After 416 comes out the first thing I'd go and look at is that pulse coder feedback cable. Is the plug loose? Are the pins in the connector oxidised? Is the wire crushed or stretched? Is the signal line shorted? All of those will prevent the CNC from getting proper position feedback. Particularly on a machine that has just had the servo motor replaced, the coder removed and reinstalled, the electrical cabinet repaired or the feedback cable changed you have to be even more vigilant.
Sometimes the plug appears to be properly plugged in but in fact it's not all the way in; the jacket of the wire may look fine but the core could already be damaged. Don't just look at it with your eyes, you have to check that the plug is actually all the way in and that the wire hasn't been pinched or pulled at some stage during the installation.
If the feedback line checks out perfectly then your thinking should turn to the pulse coder itself. A genuinely bad built in coder could well be producing a non-standard position signal. All you can do with a 416 is bite your lip and insist the coder is the problem.
The external sensor and circuit on the CNC side could well be the cause of the same alarm.
Especially on machines with full closed loop control (apart from the pulse coder at the back end of the motor there's also a separate position detector mounted externally, something like a linear scale, directly measuring the position of the table). On such a machine there are two position feedback paths, one via the motor's built in coder and one via the external detector. If the external detector or its lead is at fault and you only check the motor coder the actual fault could well go completely unnoticed.
Diagnostic Number 0201, Don't Wait Until the Power Is Off to Remember to Look
For the Fanuc Series 16/18/160/180 Model C systems, diagnostic number 0201 is very useful in that it can assist the technician in further determining the disconnection associated with 416.
Inside there are these states ALD and EXP. They can be used to distinguish:
- Whether it's related to the built-in pulse coder
- Whether it's related to the external position detector
- Or whether it's a disconnection judged by software
Don't go rushing off and tearing the motor to pieces or ordering a coder. Just write down the actual state of diagnostic 0201 first.
Then combine the alarm axis number with the full alarm information and the machine's feedback system configuration. The range is going to be considerably reduced.
But it has to be stated quite clearly. What ALD and EXP actually mean and what the diagnostic conditions are you have to refer to the maintenance manual for the relevant Fanuc control system.
Different CNC series and different position detection configurations are not quite the same. You can't just take a diagnostic state that you've seen on one system and apply that directly to all Fanuc machines.
- If the diagnostic indicates the built-in pulse coder then look at the motor coder and its feedback.
- If it's pointing to an independent position detector then follow the signal path of the external detector and keep checking.
This is vastly more reliable than replacing the servo motor the moment you see 416.
From Feedback Cable to Position Detector, Which Places Are Prone to Hiding Faults
When looking at the feedback system, the best thing to do is to pull out the machine's electrical drawings and then go right along the signal path from the detector to the relevant control hardware.
What to check depends on the configuration:
- If it's using a built in pulse coder then check the feedback leads at both ends (motor end and control system end).
- If it's full closed loop control then the test range also has to incorporate the external position detector, the plug and the associated signal lines.
If you've got cable damage, a loose plug or a short, deal with the actual fault first, then go back and see if the alarm has cleared.
Checks involving electrical measurement have to be carried out by a qualified person in accordance with the specific requirements of the Fanuc system. You must not just go around measuring and pulling plugs at random without first confirming the circuit and the test conditions.
Once the cable, the connections, the power supply and all the associated conditions have been checked and confirmed to be normal and the position detector is still not giving a valid signal you then have to go on and test the pulse coder or the external position detector.
At this stage the decision as to whether to replace any parts is going to be based on the actual test results. Don't put all the communication issues and all the feedback problems down to the coder's head.
Coder and Wire Both Normal, Keep an Eye on the CNC Hardware Too
For the relevant
Fanuc systems the associated repair materials also list the servo control module and certain of the CNC control boards as potential fault sources.
If the feedback line and coder have both been checked and the state of diagnostic number 0201 is still incorrect then you have to go on to look at the servo interface and the CNC side circuit.
The CNC board really shouldn't be in the first batch of parts that you just blindly replace.
A more reasonable path is:
1. Firstly use the diagnostic information and carry out the relevant tests to isolate the fault area.
2. Then decide whether the control board needs repairing or replacing.
If you absolutely need to replace the CNC board then back up the required NC data in accordance with the relevant repair procedure and ensure the new board is the same as the original board in the machine.
After Replacing the Pulse Coder, the Job Isn't Done
If in the end the pulse coder or external position detector is confirmed as bad then when replacing it be absolutely sure to check the exact model and the actual system configuration. Don't just look at the servo motor series or the way it looks and go for a replacement.
After replacing, do these checks:
- Confirm according to the machine builder's requirements that position feedback has returned to normal
- Confirm whether the machine reference position is correct
Some repairs may require the reference point to be re-established. The exact requirements will of course depend on the machine configuration and the particular Fanuc system repair procedure.
Before the positional relationship is established, don't go rushing to re-enable the automatic machining.
Especially in the case of full closed loop systems. You have to go through the procedure to verify the sensor feedback and the machine position state are all normal prior to restarting production.
Don't Only Stare at the Motor for 416, SongWei CNC Can Help You Narrow the Range
We supply Fanuc servo motors, pulse coders,
servo amplifiers, CNC boards and all the associated parts. We also provide testing, repair and replacement.
If you've got Fanuc alarm 416 then please can you send over the CNC model, the alarm axis number, the full alarm info, the full model of the servo motor or pulse coder and the state of diagnostic number 0201. If it's full closed loop then please let us know if you have a separate position coder and whether the alarm only occurred after the motor, coder, feedback cable or CNC board had been replaced.
This will help us determine whether the fault is with the built in pulse coder, the external position detector, the feedback line or the associated CNC hardware. First we eliminate the possibilities, then we can go on to select the correct replacement part.
Final
Fanuc alarm 416 is a servo alarm relating to a disconnection or connection abnormality of the position detection system. Causes could be a feedback cable disconnection or short, a pulse coder fault, the external position detector not being normal or the related servo or CNC control hardware having a problem.
Don't replace the servo motor or servo amplifier just based on a 416. First find accurately which section of the position feedback system has the problem, then decide whether to repair or replace. Before resuming production, confirm the machine reference position well. This way you can both spend less wasted parts money and stop the machine for a few days less.
