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Fanuc SPC 350 Alarm on 16M control with glass scales?

huleo

Hot Rolled
Joined
Feb 12, 2014
Location
UT
Was going to put a call in to Fanuc Monday but would really like to keep moving on this. Machine is a horizontal machining center and has been powered down for a while. It was most certainly just fine last time it was run. I was going to stretch it's legs and swap some batteries.

Anywho, it fired up just fine and even warmed the spindle. However, as soon as I attempted to Jog the Y, it threw the alarm and shut down power to the servos. There are no amplifier alarms and nothing blown. All appears well.

Because this machine has scales and I can be very certain they are active, I am not quite sure how to troubleshoot the alarm, which is (Y axis encoder fault). I guess I am not sure if that is a scale fault or what but I can verify once power iss removed from servos, I can slightly move the Y and I have a reaction on the position screen so I doubt it is scale related.

When I first experienced the issue, it would not fault until I tried to move, so I moved carefully and it would take about two .001" steps before it faulted. I decided to reseat the connector to the Y servo encoder and now have an alarm as soon as I power up. I am pretty certain the Y has a brake in it because there is otherwise no ballast and I am a little surprised with that.

After pulling that encoder plug, I started to wonder if the control was also using the absolute encoders and I just made it lose it's mind by pulling the cable?

I will have to check schematics but these are Alpha drives and I need to know if servo encoder cables just go to control or hit the servo first?

I am just trying to come up with some cross checks to narrow down where the issue is. I know people will say "check your cable" but that is pretty easy to say from the couch. I honestly don't think a wire broke itself while sitting, but I do suspect some terminations. However, I just don't want to lose my home position and have to deal with that. This machine can be a nightmare to tune. It took me weeks to figure out how to set home position on the tool changer and its NOT fun.
 
Check your parameters in 1815 and see if it uses bit four(APZ) and five(APC) for absolute encoder on y axis. You can also see if bit one(OPT) is on for separate feedback(Scale), one = uses scale. I have turned bit one off to troubleshoot if it is an encoder or scale issue. You don't want to jog very far as the flex gear will likely not be correct but it will help diagnose a scale/encoder issue. You will also have to reference the slide after changing this bit.

I think you are on the right track of a brake hanging up and a brake relay not releasing when power is on. If it uses the old ice-cube relays the coils go bad in the brake relays and the points will also stick together, and this will cause servo alarms.

Hit the system button, right expansion arrow until you see the soft-key servo, spindle etc and select servo tune, then page down to y-axis. You want the smallest increment in handle mode and jog one click down and watch the position error. If the error immediately goes crazy like 6 digit numbers and faults out you probably have a bad encoder or scale. If it goes to around 3 digit numbers and then finds the position with 0 error every time, just slowly, it is probably a stuck brake relay.

You can also use diagnostic 202 and 204 to help troubleshoot this. Hit the system button, then diagnostic button, page down to 202/204 and see what bits are on when the alarm is active.

If 1815.5 is a "1" you lost your Y axis home position when you unplugged the encoder but that should give you a 300 alarm saying the axis needs to be zero returned. The Y axis home position needs to be set-up especially due to the tool change position.

That is how I would go about troubleshooting this issue. Daryl
 
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What I can tell you so far.
1. I replaced batteries in ONE of the packs yesterday. Thought it was for scales but now second guessing.
2. 1815 bit 1 is set for XYZ and no other bits set EXCEPT B axis, which does have bit 4/5 set for absolute.
3. I would assume this will all be verified if I first fire machine and check 1815 bit 4 for XYZ. if a 1, something is holding position. 0 means no position held?
3. Diag param 202 indicated a 1 for PHA, which indication there is phase issues from encoder, which probably means it lost one of the 3 feeds. I will have to verify if these have sine or TTL output (book shows both) but I have troubleshot them before.

I do know Mori could not even answer the question if the machine had absolutes in it because I know for sure it wants referenced when firing up, which is a hallmark for incrementals.

Questions---
1. This is a stupid one....Where the hell is the parameter screen? Used to seeing "par or param" as key option. I stood there for 30min trying to find them!
2. What do the encoders on the fanuc servos do? It was my understanding they go back to the servo amp to relay motor performance. They are certainly plugged in to something but I can't tell what yet. One book clearly shows encoders going to control only, but another diagram shows them hitting the amp first.


All in all, I am inclined to think I have a scale issue with Y, and not the encoder on the servo. The alarm is generic but is indicating a positional error in that axis and scales are what give position. I agree about testing by switching off scales on Y but I should probably check with Mori just to see if there is something loopy. I want the scales functional on the machine.

The wrench here is the scales.
 
UPDATE:
Here is where I am and now. Confirmed at machine that Absolute encoders are not set in par 1815, only in B axis. So I reseated all plugs for Y, confirmed wire routing, and tried to narrow things. All connectors by Heidenhain are just badass! Their wire quality, pin connectors, etc, are perfect. However, there is not a plug on the Y scale and I am not sure how that comes apart, and I don't want to attempt that until I am damn convinced that is it.

I also confirmed a hard and soft limit in Y which IMO means the machine will set itself on those so as long as the limits don't get messed with, I don't have concerns messing with scales as far as my home position, etc.

Here are the facts and tests.

1. When control fires up, it will now immediately flag the 350 alarm and not reset so I cannot power servos.
2. When control is active, because servos are not hot, I can push up/down on spindle and can get .00001" movement both positive and negative so the display most certainly responds to motion.
3. Scales are analog with mV signal outputs. 3 channels, appears 2 channels are 90% from each other so machine can tell direction and confirm position, 3rd appears to be a tach. Everything works off 5V.
4. Scales have ADCs (analog digital converters) mounted on the door so Fanuc control gets 5V digital input from scales.
5. Servo tuning screen for Y indicates position error to hover around 0-1 even when trying to move axis by hand. Gain pops up with some big number momentarily but to fast to even read.
6. I attempted to disable the scales by just making the bit in par 1815 a 0 and turned control pwr switch off and back on. Alarm remained and control was still displaying values from the Y scale.
7. Confirmed Alarm diag still shows in 202.4 a PHA error which is some sort of signal error but not necessarily a disconnection. Something would have to stand out for control to flag it immediately.


What I would like to do is figure out more test procedures for the scale system. I really would like to test the wiring but with no certainty how scale connects, I don't want to contaminate anything until I know more. I can be pretty certain the scale is getting 5V power and sending enough data to control that it is displayed so I don't think it's dead. If I had to guess right now, I would say the scale needs cleaned or sat too long and just needs to move. The Fanuc control is seeing digital input from the scale ADC so I really should be able to see those signals 'somewhere', buy where?

Ultimately I would like to disable the scale long enough to move the axis to a different position and try again. I think if the scale is dirty, it will probably act different in a new position. This probably moves me to my next question of, how much does it suck to realign a scale? Am I overthinking this?
 
I injured my hand, hard to type. But if you turned off the scale and now the alarm is present immediately I would say bad encoder. Swap encoders with x-axis if they are the same, if it follows the encoder bingo, if not it is probably the drive. You don't have any alarm on the drive?
 
Then I find out from Fanuc that even though there are scales, that alarm is for the encoder on the servo motor......LOL Talk about chasing my tail.

At least it answers a few questions. I am now on a mission to examine wiring between the Y servo encoder and amp.
 








 
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