Need some help with a limit switch 1996 Bridgeport Romi EZ path !! lathe

Chevy427z · Sep 15, 2016

Hi folks.

Tried searching on this and coming up blank. Hoping some of the machine guys can chime in. I've seen Jon from H&W machine Repair commenting on a few.

I recently acquired the above mentioned lathe. It had an X Axis servo driver issue which has been solved. Now when I attempt to home it, I am getting an error message that the machine has hit a limit switch when it clearly has not. Z axis is fine ( I can jog it), the problem seems to be with the X (If I attempt to jog it, it moves a couple "thou" and quits). I have found the switch on the cross slide but am at a loss where it connects to the control. No idea if it's supposed to be open or closed and I was hoping to throw a meter on it to shed some light.

As you can tell, electricity is not my strong suit, but I get by :-) Thanks for any suggestions!

Mark

HWElecRepair · Sep 16, 2016

The switch should be on the back of the cross slide and then there is a little metal piece on the back end near the tailstock. It sounds to me like the drive or motor is causing this. What is the actual error code that pops up? The way to look and see if the switch is actually working is once you find it, get into the tuner and press the switch in. It will show on the screen that you are on the home switch.

Jon
H&W Machine Repair

Chevy427z · Sep 16, 2016

Thank you very much for your input Jon!

That is so *not* what I wanted to hear. I'll have to double check the error message (am away from the machine right now) but it is something to the effect "travel limit reached". It doesn't specify any axis, but as mentioned, the Z moves fine, X does not.

I had sent the servo drive out for repair (estimated cost: $1100) That was doable. Turns out it is irreparable and will cost $3500 to replace. That is not doable. I took a chance and bought one on Ebay for $400, very well worth the risk, to me.

Does your company troubleshoot and repair these servo drives? If so, I would love to get a quote from you.

I got a very good deal on this machine and it's in very good condition, so it's worth some investment by me, but I really need to keep the money under tight control. Thanks again.

Mark

ewlsey · Sep 16, 2016

I don't think you have a servo drive error. It's either a soft limit issue or a homing switch issue. The soft limits should not be in effect until after it is homed, so I'm not sure that's the answer. The home switch should be normally open on most machines.

Chevy427z · Sep 17, 2016

Thank you for your input!

You give me hope! I've got a call into my "machine guy", waiting to hear back. Off the top of my head, would you know where, in the system's controls, that I would find where the soft limits are set? Maybe someone set something wrong?

Mark

Edited: Just answered my own question. Just found the operator settable travel limits. Will poke around with that tomorrow.

Chevy427z · Sep 17, 2016

OK a little more information:

When I attempt to home the machine, the error msg that appears is "Following error limit exceeded". Then "power/off PC cycle" appears.

I found the page to set the soft limits. The numbers looked reasonable (i.e. x inner was 0. and x outer was 16.)and none of them were "active".

Z moves as it should. X has the issue. If I move the hand wheel ever so slowly, the cross slide will move as it should. Move too fast and it errors out.

Mark

ewlsey · Sep 17, 2016

OK. Following error is a servo or servo drive issue. Does this machine have belt drive servos? Following error means that basically the drive told the motor to move some amount and the encoder is telling the drive that it has not moved that distance in an acceptable amount of time.

There could be many causes. If it's a belt drive machine and there is a separate encoder on the ball screw and the belt is slipping or broken, you can get this error. If the ball screw or ways are seized it could cause this, though I would expect an overload error instead.

If the servo windings are bad it could be the cause. If the servo drive output is bad it could be the cause. If these are brushed servos bad brushes can cause all kinds of issues.

So, the standard way to diagnose servo issues is to swap the drives from the axis that works to the axis that doesn't and see if the issue follows. Unhook the faulty drive. Check the motor leads (should be 3 if brushless, 2 if DC brush) against each other with a multi-meter. You should see some resistance, but not a 0 which would indicate a short. If you have a short, you need a servo or a rewind.

If the motor checks out, swap the X and Z servo drives and see if the issue follows the drive. If the issue stays on the same axis, you have a servo issue. If it moves to the other axis, you have a bad drive.

Be careful though, some lathes have a larger servo and drive for the Z. It could still work, but you need to be careful.

Chevy427z · Sep 17, 2016

I understand.

It *is* a belt drive. The belt is in good condition and I can spin the gears by hand to move the cross slide. I will start by swapping the drives to see if the error follows. And I will be careful :-) I thank you very much for your time! Will report back.

Mark

amdinc · Sep 17, 2016

Following error is caused by the axis is not where the control thinks it should be.
It can be caused by a drive not moving and the control is looking for movement or it could be the drive is moving the axis but not seeing the data from the scale or rotary encoder.

I just did a repair on the z axis problem where when the axis hit the limit switch it would slow down and then take off at a fast rate into the hard E stop switch.
I reset the parameters to using no home switch so I could home it on any z,z' input from the scale. The thing would home toward the middle of the travel. The reference home pulses on the scale were about two inches apart along the scale. Ir would not home on the last pulse marks on the scale and would take off into the hard E stop. Problem was the scale was defective on the last couple of inches toward the home position. It was losing all the pulses and the control not seeing them would increase the voltage to the servo amp thinking that the servo was not moving.

John

Chevy427z · Sep 17, 2016

Worst fear realized

Swapped the drives, problem switched from the X to the Z. X axis works fine, although backwards (turn handle clockwise, cross slide moves outward). That was puzzling, but assuming it's the right way for the Z, where it came from. Now if I move the Z ever so slowly, it moves, move it too fast, error occurs.

Guessing I need someone to look at the servo drive. I used to have a contact, 3E services in Atlanta, Ga., but he's since sold his company to Radwell. Any suggestions? Still waiting to hear back from my local "machine guy" who may be away with a traveling softball team. :-)

Thank you for your time and input!

Mark

ewlsey · Sep 17, 2016

You can try Precision Zone in Chicago. They can rebuild anything they can get parts for.

Chevy427z · Sep 17, 2016

Thank you for that tip. I'll give them a shout.

I've been mulling something over in my head, maybe you can explain. Any idea why the x axis would work backwards by simply swapping out the drives? I remember you cautioning me about a size difference. Both of these drives are exactly the same physical size. In fact they are the same part number, just different serial numbers. I can get the numbers if you could use that for anything.

If the swap had shown that the problem was elsewhere, I was going to ask you if I could just leave them swapped, for no other reason than to save time.

Mark

ewlsey · Sep 17, 2016

Are they brushed servos or brushless?

I don't know exactly. The drive may have programmable parameters that set the axis step direction. Those parameters would have to be retrieved from the drive and loaded into a replacement.

Chevy427z · Sep 17, 2016

I'm not sure. I'll have to look, which will be tomorrow. Working tonight

Programmable parameters make sense. I don't even want to think about how to get that done, if necessary.

ewlsey · Sep 17, 2016

The internet seems to say you have DC brush servos. In that case I believe swapping the leads that go to the motor will reverse it's direction. If it uses quadrature encoders the drive should know it's turning the wrong way. But, maybe it's a resolver or tach or something.

isaac338 · Sep 17, 2016

Chevy427z said:
Worst fear realized

Swapped the drives, problem switched from the X to the Z. X axis works fine, although backwards (turn handle clockwise, cross slide moves outward). That was puzzling, but assuming it's the right way for the Z, where it came from. Now if I move the Z ever so slowly, it moves, move it too fast, error occurs.

Guessing I need someone to look at the servo drive. I used to have a contact, 3E services in Atlanta, Ga., but he's since sold his company to Radwell. Any suggestions? Still waiting to hear back from my local "machine guy" who may be away with a traveling softball team. :-)

Thank you for your time and input!

Mark

Are there gain pots on the drives? See if the X-axis gain is turned way down - it's a used drive so you can't guarantee someone didn't fiddle with it. Small gain means the drive isn't capable of moving the required distance in the time given, so it exceeds the following error.

Try resetting the gain pots (if present) to close to the settings of the old drive and see if you can get it to move like that, or just up the gain a bit.

HWElecRepair · Sep 19, 2016

That seems mad expensive for a drive. This is a Path II? Without verifying the part number of your drive, you would be looking at $3,300 ($1,100 refundable upon receipt of an acceptable core, so $2,200 net) It will also come pre-programmed with the parameters necessary for your Z axis. This is a re-manufactured OEM drive from the OEM. You are looking at about a 1 week lead time.

Jon

ewlsey · Sep 19, 2016

$2200 to rebuild a brush DC servo drive? That seems crazy. I can buy brand new 40 amp AC servo drives for $1500. I get 20HP vector drive inverters rebuild for $750-1000.

Chevy427z · Sep 19, 2016

My sincere thanks to everyone who contributed to this thread!

I am breathing a lot easier this morning. Special thanks go to Jon at HW Machine Repair for hooking me up with EMI who will be programming my "new/used" servo drive for $250 and shipping it back to me. Fingers crossed for dodging a bullet on this one!

Hope to be able to report back in a week and a few days with good news! Thanks again everyone!

Mark

Chevy427z · Sep 19, 2016

Isaac,

I meant to reply directly to you about your post. There *are* pots on the drives. I tried adjusting the one on the X. Didn't appear to do anything differently. Looks like I am finally on the right path. I do thank you for your time! :-)

Mark

Need some help with a limit switch 1996 Bridgeport Romi EZ path !! lathe

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