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Hardinge Conquest T51 X-axis hardware overtravel - my fault, but how to recover?

Jim Wilson

Aluminum
Joined
Mar 25, 2007
Location
Tucson, AZ, USA
I posted this in the Hardinge forum and received the suggestion to post here, since it's a CNC issue. Hope that's ok.

Short Story:

Please help me correctly recover from a severe X-axis hardware overtravel.

I powered up my lathe with the X- and A-axis motor leads disconnected at the servo amp. With no support under the carriage. Wham! The carriage fell from its top position all the way down against the hard stop at the bottom.

Unsurprisingly, I now have a 501 X-axis hardware overtravel alarm. What is the right way to recover from this?

The lathe is a Hardinge Conquest T51 with a Fanuc 18T control.

Long Story:

This machine has been running fine, very light duty, for quite a few years. The other day, we got a surprise on startup: 400 alarm and 414's on both X and A (turret) axes.

The servo amp motor leads all read > 25 Mohm against each other and GND for both X and A (turret) axes. The fact that both X and A alarms appeared at the same time suggested to me that maybe the servo amp is to blame.

Powering up (motor leads re-attached), I noticed the servo amp LED Status display only briefly flashed a 2 before going blank. The servo amp fuse checked good. I guessed maybe the 5V leg of the power supply is failing, so I opened up the servo amp. It was quite dirty and sticky. I wondered if maybe a cap or power resistor had released its magic smoke, but there was no clear localization of overheating or soot. I removed the power supply and inspected it carefully but did not find any obvious signs of failure. I thoroughly cleaned it, and at the same time, all of rest of the servo amp's electronics, as well. (One of the things we make here is electronic PCBs, so we have the supplies and equipment to do that properly.)

I then rough bench-tested the power supply with no load. Most of the outputs appeared nominal, including the 5V. However, the 24V was sagging to about 17V with no load. This raised suspicion, but I'm not familiar with this particular power supply. I am aware of others that do not provide nominal power without some specified minimal load. Since I was focused on the 5V anyway, I decided to reinstall the PS and give it a final whirl before ordering a new servo amp.

Surprise! Amazingly, the servo amp now appeared to start up normally, with the Status LED display no longer blank, but reading "-" (not ready), as expected. However, on E-Stop reset, Status LED became 8 and the 414 alarms reappeared.

I disconnected the X-axis motor leads from the servo amp, thinking if there truly is an overcurrent through the motor, this would clear it. But on startup, the alarms and Status appeared the same as before. I then disconnected the A-axis (turret) motor leads, and tried starting again.

This time, though, as soon as I hit E-Stop Reset, the carriage, which had been sitting at home, suddenly fell all the way to the bottom of its travel, slamming into whatever prevents it from falling out of the machine. I should have propped up the carriage with a piece of wood before trying these no-power to the motor tests.

That's where I am now. Obviously, I need to get the carriage back to within it's normal operating range. What's the correct procedure for this?
 
Not sure how hard the hard stop got hit. Damage to the ball screw, screw jammed? If not maybe all you need to do is reset the zeros. I have done this several times on my GT but the procedure will be entirely different for your machine. I requested instructions from Hardinge on 2 different occasions and 2 different pages were sent. Seems like each set is incomplete and by using both sets I get the job done.

If this is not helpful at least it will bump it to the top where someone else might have better answers.
 
IDK if your machine normally gets HOMED at start up or not, so that may make a difference, but if it does require HOMING, then - as you seem to already ass_u_me by the title of another thread - you will need to reboot with holding down the P/CAN buttons the whole time. You use whatever button has a P on it.

Then with the E-stop Reset button held down (and possibly the e-stop button pulled up at the same time- depending on the year) you will be able to jog it up above the O/T switch.

However - with the type of crash that you say - it would be expected that you also likely tripped the X torque limiter - simply from the inertia of the screw at bottom out.

In this case you will need to push the X agginst something to pop the trq limiter back in. Whether you put a 2by between the turret and the tailstock, or you go and push agginst the spindle, whatever. But only if you are getting that alarm, or ... if you hear it ratcheting when you start running parts (in the case of a possible bad prox).

You will then need to reboot while again holding down the P/Can buttons, and then when you re-home it - all should be right with the world.

All this after you figger out the drive/motor problem.


---------------------

Think Snow Eh!
Ox
 
Thanks, Fred. Your questions mirror mine. I have the manuals for this machine, but didn't find an appropriate procedure. I probably just haven't looked in the right place.

Also, thanks again, Ox. As usual, you bring up the useful points.

My machine does get homed at startup, but we have been unable to home it since the initial 400-series alarms appeared. However, it was homed prior to the last shutdown before the alarms, because all of our parts programs send the machine home at the end.

The 501 alarm clearly says the overtravel is in -X (which is physically correct), not +X. Dunno how much that matters.

I was unaware of the torque limiter, and have no idea how to deal with that. I will start educating myself about it today. Glad you brought it up. I do know it sounded terrible when it fell.

I think you are right about first resolving the 400-series alarms. I feared that the X-axis crash-to-bottom might prevent troubleshooting the drive problem, by inhibiting power to the motor, or whatnot. But now I think rather the reverse; I can't move the carriage off the bottom stop without drive power.

I followed "How to diagnose a Fanuc 414 Servo Alarm". Got all the way to the final step, which I can't do, because I don't have a proper 1000-volt "megger" (yet). Amazon says it will be here in a couple of hours. But, my gut expects it will only confirm the motor and cabling are ok. My multimeter shows, with the motor connected, all motor leads are 1.6 ohms to the other phases and >25 megohm to ground. With the motor disconnected, every lead is >25 megohm to anything else. All of that looks normal to me.

Apparently that leaves the servo amp as the only remaining possible culprit. I've already ordered a "pre-owned" replacement from eBay. It's gotta cross an ocean, so I won't see it for another 2-4 weeks.

We did another test which also suggests a failed X-axis amp:

1. Prop up the carriage with a 2x4 or something, to prevent it falling by gravity when the brake is released!!!
2. Disconnect the motor leads from the servo amp
3. Provide compressed air, and turn on the main Power switch
4. Observe the servo amp Status LED indicates "-"
5. Press the green power button on the Control Panel, and wait for it to finish its startup routine
6. Ensure E-Stop is released
7. Verify door switch
8. Press E-Stop Reset (starts hydraulics, etc.)
At this point, all alarms except my incidental X-axis overtravel are cleared.​
9. Observe the servo amp Status LED still indicates "-"

These next steps require an assistant; someone needs to be at the control panel and someone at the back of the machine.

10. Hold down E-Stop Reset until a relay clicks in the back, and
while continuing to hold down E-Stop Reset, observe the servo amp Status LED display.
On my machine, the amp always indicates "0" after the relay clicks.​
11. Still continuing to hold down E-Stop Reset, press and release the +X or -Z jog button
On my machine, after -Z, the Z-axis amp continues to indicate "0", but upon +X, the X-axis amp changes to "8".​

Thereafter, upon releasing E-Stop Reset, the Z-axis amp returns to "-", but the X-axis amp continues to display "8" and the machine must be powered down to clear that error. If E-Stop Reset is released before pressing the +X jog button, i.e., while the "0" is still showing, that amp also returns to "-". I imagine this is because of the overtravel alarm, and that without the alarm, the "0" would remain. But I'm not sure of this, since I have yet to watch for it without the overtravel condition present.

Bottom line, with the motor leads disconnected from the amp, there should be no way for an excessive current to flow, but the "8" tells me my X-axis servo amp thinks there is. From that, I think I have to conclude the amp is bad.

Incidentally, in P/CAN, the only alarm is
1011 X-AXIS HARDWARE OVERTRAVEL​
but without P/CAN, there are two:
1011 X-AXIS HARDWARE OVERTRAVEL
501 OVER TRAVEL : -X
So, I can see that P/CAN does indeed appear to work on my machine. Didn't notice that detail until this morning.

I will chime in here again after the amp is replaced or if anything different pops up, just to give the issue proper closure. I hate when a thread on a subject I'm interested in just dies without a clear resolution!

Thanks again.

Jim
 
You said that it made bad sounds when it hit bottom, and that Sir was your motor/screw having inertia when the carriage hit bedrock.
It popped and ratcheted several times likely before coming to a stop.
It may, or may not, be engaged at this point.

It is a mechanical spring loaded gizmo that will pop during a crash and keep from creating excessive damage to the machine.
They are a very nice feature to have!

A popped trq gizmo will not inhibit the motor or control, but it seems that the brakes like to drag on this machine until you git it latched in.
You can likely hear the brake screech while initially moving both X and/or Z.


----------------------

Think Snow Eh!
Ox
 
So, I'm not the first one to witness this? :D

Yes, as it fell, it sounded briefly like the motor was being "spun up"--this happened quite rapidly--and then it seemed to travel the rest of the way at essentially a constant speed. At or near the end of its journey, I heard a few or maybe several distinct loud clicks (the ratcheting you mentioned?), but I'm not sure whether that happened before the big bump, during, or just after. The whole event was over in less than a second, so pretty hard to make out/recall the details. And I'd like to avoid hearing it again. :D :D

I confess to some surprise that the carriage can turn the ball screw like that. I imagined it to be more like a worm, where it's quite hard for the load to turn the drive (and likely to break something).

I don't think Z was affected; it moves normally.

However, a couple of times during the tests I elaborated on above, I did notice a brief screech-like sound when trying to jog the carriage off the X-axis stop. This was when I was simultaneously applying mechanical upward force, first with a pry bar, and then later with a jack. It never moved significantly, though, despite the sound. Maybe I wasn't pushing hard enough; I don't know. I am leery of breaking something.
 
I see no reason to push it up.
When you git the amp werking, it will go on it's own.

I guess I wasn't thinking this through...
The X will likely squeak the brake when the Z trq limiter is compromised, but I doubt that the Z axis has a brake at all anyhow, so it's not likely to squawk with sympathy pains when the X is tripped.

Lead screw likely has 10mm lead, which will roll under gravity on it's own.
Yeah, I did it recently when testing a drive as well.
I unhooked the motor leads, and when I powered it up, it let the brake loose, and down she came.

WOOPS!
Look around - "did anyone else see/hear that?" :o


-------------------

Think Snow Eh!
Ox
 
Yes, I think you are right about no need to push. I was hoping to move it up out of the limit, to troubleshoot the other issue without any concern that the presence of the overtravel alarm or the ball-screw being jammed, or whatever, would affect test results.

Something occurred to me. I went over to the machine to confirm it, and double-checked my memory, my notes and pictures, to make sure I'm not fooling myself. But now, I'm more confused than before.

The X-axis 414 alarm is only ever raised if the A-axis motor (turret) is connected to the amp.​

The carriage fell when I disconnected the A-axis motor leads and restarted the machine. It did not fall when I only disconnected the X-axis motor leads and restarted. This is a 2-axis amp, and the error always shows both 414 X and 414 A.

This is what I just retested (the test I detailed up above, post #4):

When both A- and X-axis motor leads are disconnected, the end status is "0" (no error).
It also ends with "0" if A is disconnected and X is connected (but the carriage does not move).
In other words, the test always ends with "0" if A is disconnected, regardless of whether X is connected or not.
Likewise, it always ends with "8" (X-axis overcurrent) when A is connected, regardless of whether X is connected or not.

I double-checked and did not forget to re-attach any motor connectors after testing the cables. So, the X-axis never works, but the servo amp only ever reports an error condition, and the 414 alarms are only ever raised, when the A-axis motor leads are connected and an attempt is made to move the carriage in X. :confused:

By the way, the megger arrived and the motor conductors and windings are all >4000 megohm @ 1000V for both X- and A- axes. So, there is little doubt that the servo amp is faulty, as previously concluded. What's actually wrong it is a mystery, though. I guess some things just aren't meant to be understood. :D
 
Yes, I think you are right about no need to push. I was hoping to move it up out of the limit, to troubleshoot the other issue without any concern that the presence of the overtravel alarm or the ball-screw being jammed, or whatever, would affect test results.

Something occurred to me. I went over to the machine to confirm it, and double-checked my memory, my notes and pictures, to make sure I'm not fooling myself. But now, I'm more confused than before.
The X-axis 414 alarm is only ever raised if the A-axis motor (turret) is connected to the amp.

The carriage fell when I disconnected the A-axis motor leads and restarted the machine. It did not fall when I only disconnected the X-axis motor leads and restarted. This is a 2-axis amp, and the error always shows both 414 X and 414 A.

This is what I just retested (the test I detailed up above, post #4):

When both A- and X-axis motor leads are disconnected, the end status is "0" (no error).
It also ends with "0" if A is disconnected and X is connected (but the carriage does not move).
In other words, the test always ends with "0" if A is disconnected, regardless of whether X is connected or not.
Likewise, it always ends with "8" (X-axis overcurrent) when A is connected, regardless of whether X is connected or not.

I double-checked and did not forget to re-attach any motor connectors after testing the cables. So, the X-axis never works, but the servo amp only ever reports an error condition, and the 414 alarms are only ever raised, when the A-axis motor leads are connected and an attempt is made to move the carriage in X. :confused:

By the way, the megger arrived and the motor conductors and windings are all >4000 megohm @ 1000V for both X- and A- axes. So, there is little doubt that the servo amp is faulty, as previously concluded. What's actually wrong it is a mystery, though. I guess some things just aren't meant to be understood. :D

If you are all fired up about getting the X off the O/T, then just scurry on to the RH side of the machine and yank the big door off the end.
Wretch in there and unbolt the O/T L/S enough to git it to not be depressed. Depression is hard on machine tools as well.

BTW - I keep stock of those little switches inside that housing.
If you doo bother to take it off, I suggest looking at it and buying a spare - so that you don't need it.

... or I could just go look and see what I have and tell you, but where would the fun be in that?
... but I should dbl; check that I doo still have a spare. :scratchchin:


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Think Snow Eh!
Ox
 
Last edited:
Eh, I think I will remain in bliss on this a bit longer... :D

If it proves to be an issue--I'm takin' your word that it shouldn't be!--then I'll have a stab at tricking it.

Cheers!
 








 
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