VF6 Spindle hitting umbrella on tool change

Our old (1995) VF6 has recently started hitting the umbrella on a tool change and alarming out. We've checked limit switches and they seem to be ok. The problem does not occur on every tool change, but it is occurring daily. We've looked at the Z height tool change setting, but given that the problem is intermittent, I don't feel like this is/should be the problem. When the machine alarms out, the Z shows a negative number, but when the tool change works good, the Z reading never drops below zero. While our machine is old, it is a low hour machine and has cut a lot of aluminum, so I'm hesitant to jump to the conclusion that was suggested by our HFO that our Z ball screw may be shot.

Other than checking encoder connections, checking for chips, are there other things we should be checking before we take more drastic measures? Thanks.

Edit to the post. Here is a pic from the operators screen when running a tool change that was going to crash. During a tool change operation where the spindle is going to crash into the umbrella the spindle move's up to machine zero, when the umbrella begins to move over towards the spindle, the the spindle starts to drop (by random amounts, never the same amount) until we hit E-stop in order to prevent the crash. The machine output position always reads the same as the operator input. The manual clearly states that during an M06 tool change that the Z axis remains at zero. Why would our machine be telling the spindle to drop during a tool change? More importantly, how do I make it stop? Thanks.

Could the tool change in switch be faulty and be giving false signals that the changer is in?
The other thing that I would check is the Z axis thrust bearing. If it is the same design as my VF-1 ('91) it uses needle thrust bearings instead of the newer style angular ball bearings. My Y axis backlash was erratic and I found the needle bearing cage had broken up. The remnants of the cage were wearing into the ball screw.

magno_grail said:

Could the tool change in switch be faulty and be giving false signals that the changer is in?
The other thing that I would check is the Z axis thrust bearing. If it is the same design as my VF-1 ('91) it uses needle thrust bearings instead of the newer style angular ball bearings. My Y axis backlash was erratic and I found the needle bearing cage had broken up. The remnants of the cage were wearing into the ball screw.

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I'll re-check that we're not getting a faulty changer signal, but in any event, I don't think the spindle should be lowering as the tool changer moves in. Our other machines (roughly same vintage) all go to Z=0, and stay there as the changer moves in, then lift up once the old tool is dropped off in the umbrella. There is never any movement down from Z=0 during any part of the tool change sequence. This machine goes to Z=0 as it should, but the control is definitely giving it the signal to move down as the umbrella starts moving in now. Is it possible to have a corrupt M06?

I'm not sure about your problem, but I would not completely rule out the Z ballscrew, regardless of cutting conditions. We had a brand new machine (still under warranty), about 6 months in started getting Z servo alarms. I don't remember the exact year, 2010ish maybe. Anyways, Haas had briefly switched suppliers for the ballscrews. Ours eventually seized up and had to be replaced because of a manufacturer defect. Not saying that is your problem, but it could be related to the ballscrew. However, I would think if that were the case you would see it in your machining too, not just tool change.
You are correct in that the Z should not move anywhere until the umbrella has moved into position. Should move to zero (tool change position), umbrella comes in, spindle unclamps and moves up out of the way, umbrella indexes, z moves down....

This is really odd..
If it were the Z axis thrust bearings or screw, why the Z -0.1452?

First - Look at your program very carefully, could be post errors or mischievous effort.

Correct me if I'm wrong here..even with serious mechanical issue Z would be 0.000 even if it were actually at the table. The control gives a position command, servo moves X.XXXX encoder confirms, control goes on the next command.. the drive could be sitting on a bench - makes no difference to it.

I'm going with program error. At worst a corrupt software issue.. you'll need an old priest and a young priest.

BGL said:

This is really odd..
If it were the Z axis thrust bearings or screw, why the Z -0.1452?

First - Look at your program very carefully, could be post errors or mischievous effort.

Correct me if I'm wrong here..even with serious mechanical issue Z would be 0.000 even if it were actually at the table. The control gives a position command, servo moves X.XXXX encoder confirms, control goes on the next command.. the drive could be sitting on a bench - makes no difference to it.

I'm going with program error. At worst a corrupt software issue.. you'll need an old priest and a young priest.

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Fair comment about program error, so to rule that out here's what we went through.
1) Tool change on power up restart,
2) Tool change in MDI with ATC FWD/REV,
3) Tool change in MDI using M06 Tnn,
4) Tool change from a previously ran program using M06 Tnn

All scenarios result in the same issue, spindle gets the control signal to move down as the tool changer moves in. For these reasons we have ruled out a program issue, and think it is a control issue. Are we thinking about that correctly? If so, can we check the M06 logic somehow to see if it's corrupt? Other ideas?

Just a WAG, but can you verify the Z is moving correctly? Maybe send it to home, set an indicator somewhere, MDI it to move down .1 .2 1. 2., etc. I don't know how you would check the M06 command.... Might be worth it to have a tech just come in and figure it out.

Does this machine have a nitrogen or weighted counter balance? If nitrogen, verify that it has the proper charge.

Next, watch the "dist to go" display when performing a Z-Axis homing sequence. Whatever the value shows in the register, it should repeat each time you home that axis. Repeat the homing process several times to see if it changes. Try powering the machine off/on also

Also, check to see if you are getting good low voltages going to the pcb's; 12vdc, -12vdc, and 5vdc.

With the machine off, try resetting a bunch of the plug connectors for the motor/encoder for Z-axis along with the encoder connections at the mocon pcb.

Is it possible to tell if the Z-axis is at the negative value prior to the shuttle coming in and hitting the spindle or does the z-axis droop after the alarm is triggered resulting in the negative value?

haastec said:

Does this machine have a nitrogen or weighted counter balance? If nitrogen, verify that it has the proper charge.

Next, watch the "dist to go" display when performing a Z-Axis homing sequence. Whatever the value shows in the register, it should repeat each time you home that axis. Repeat the homing process several times to see if it changes. Try powering the machine off/on also

Also, check to see if you are getting good low voltages going to the pcb's; 12vdc, -12vdc, and 5vdc.

With the machine off, try resetting a bunch of the plug connectors for the motor/encoder for Z-axis along with the encoder connections at the mocon pcb.

Is it possible to tell if the Z-axis is at the negative value prior to the shuttle coming in and hitting the spindle or does the z-axis droop after the alarm is triggered resulting in the negative value?

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Here are pics of the counterbalance system, please let me know what this should be called, our HFO doesn't know, and it's not like our nitrogen systems on the other units. Seems to be an air counterbalance system, but I'm not sure if that's a thing.

The distance to go when performing a Z axis home seemed to work fine and was repeatable. On tool change the Z axis was at zero prior to the shuttle coming in, it was when the shuttle started to move in that the spindle moved down. I would not call it droop, as the control was telling it to move. The Z axis does not droop, it holds whatever position the control tells it.

In any event, I hope the problem has been fixed. We took the tool clamp limit switch off of one of our other machines (not me, because I was convinced that we had a computer problem, not a mechanical problem) and swapped out the limit switch on this machine. Have run 40+ tool changes without fault since swapping out the clamp limit switch this morning. Makes me feel a little dumb. Just for giggles, we hit E-stop again on a tool change just to see if the Z-axis was moving down on a tool change, and it is still moving down. I still can't understand that.

Turns out I completely mis-diagnosed the problem, and probably wasn't asking for help in the right way because of it. The machine was not technically crashing into the umbrella, but rather it was letting go of the tool, but the unclamp limit switch was telling it that it still had ahold of it, thus causing the alarm. When I packaged all of that up with watching the control move the Z-axis down to the umbrella, I created a crash that wasn't actually happening. Hopefully one more step up the learning curve.

That is just reserve air. You counter-balance should be a nitrogen based or a counter-balance weight inside the column. Check for them. That old I would guess it is a weight in the column, but could be nitrogen as in this picture. If it nitrogen, that may be your problem as it could drift down if the pressure is low. Should be about 1100 psi.



Mike

machineit2 said:

That is just reserve air. You counter-balance should be a nitrogen based or a counter-balance weight inside the column. Check for them. That old I would guess it is a weight in the column, but could be nitrogen as in this picture. If it nitrogen, that may be your problem as it could drift down if the pressure is low. Should be about 1100 psi.

View attachment 172309

Mike

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No, that tank is a surge tank for the pneumatic counterbalance system on our VF6. The grey cylinders in the photos on top of the spindle are pneumatic pistons which compress air into the surge tank as the spindle lowers, providing pressure to counterbalance the weight of the spindle. Your photo is probably off a smaller machine, and is similar to the systems on our little Haas units.

The counterweight on mine has two chains connecting it to the top of the Z axis. Very obvious.

pdexter1210 said:

The machine was not technically crashing into the umbrella, but rather it was letting go of the tool, but the unclamp limit switch was telling it that it still had ahold of it, thus causing the alarm. When I packaged all of that up with watching the control move the Z-axis down to the umbrella, I created a crash that wasn't actually happening.

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For future refrence, this would be a proper crash with the umbrella

pdexter1210 said:

No, that tank is a surge tank for the pneumatic counterbalance system on our VF6. The grey cylinders in the photos on top of the spindle are pneumatic pistons which compress air into the surge tank as the spindle lowers, providing pressure to counterbalance the weight of the spindle. Your photo is probably off a smaller machine, and is similar to the systems on our little Haas units.

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Your counterbalance system is definitely not factory and has been retrofitted at some point.

Hopefully your issues have been resolved.

haastec said:

Your counterbalance system is definitely not factory and has been retrofitted at some point.

Hopefully your issues have been resolved.

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Factory, no?

pdexter1210 said:

Factory, no?

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Although I cannot read any of the text in you attached picture (too small), I will assume that my comments are incorrect. If so, I stand corrected. That said, I personally have never seen any counterbalance on a Haas machine other than weight or nitrogen, even on machines larger than a VF-6. Can you enlarge the picture please, I have obviously not seen everything so I am curious what your document says.

haastec said:

Although I cannot read any of the text in you attached picture (too small), I will assume that my comments are incorrect. If so, I stand corrected. That said, I personally have never seen any counterbalance on a Haas machine other than weight or nitrogen, even on machines larger than a VF-6. Can you enlarge the picture please, I have obviously not seen everything so I am curious what your document says.

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Sorry, can't figure out how to make this pic work much better. Wasn't trying to be rude at all, I honestly didn't know how to describe it either. Our HFO dug it up yesterday somehow, but they knew nothing about it either. Not like anything else we have, but since it ain't broke, we're certainly not going to fix it! Machine is back in operation, so that's all we really care about. It's my own dumb fault that we even considered the counterbalance to be the problem before we checked all the limit switches. But I do love it when I hear "I've never seen that before", when we have something that's broken! I'm guessing that this was something that Haas was experimenting with, that didn't pan out.

Check G52 z offset ? Maybe you have a trickster about? Could it be something to do with that?

I've had a 98 vf5 with the problem your describing. It turned out to be the plug on the Z axis drive controller had to be disassembled and cleaned. I bought a pin removal tool at the local electronics store and used a pencil eraser to rub the carbon deposits off the connectors, slightly tightened the female pins before reassembly and haven't had a problem in 3 yrs. It did that every tool change after startup for 2 yrs before I started working there. Good luck