Resurrection, backpedal

Jim Wilson · Mar 12, 2010

I'm being punished for bringing my lathe back to life. :bawling:

Three of four bugaboos resolved; but now a new one rears its ugly head. I guess all progress has a price. In case you haven't been following this saga, the machine is a 1993 Hardinge Conquest T51. It's had a hard life, but we can rebuild it.

The new problem is: it will no longer zero-return in X. This just started about an hour ago. Specifically, when you get to the step where you "hold down -X until the cross-slide stops on its own," it never stops. It keeps going all the way down until it hits the -X overtravel limit. This happens even if it starts way, way up high (like up to about 0.010" below the +X overtravel) and of course, despite getting a good solid 2.5" of -Z travel before starting X.

Here's my first question. It's supposed to stop when the turret reference point reaches 2.5" diameter, right? How exactly does the machine know it has reached that point? From the zero-return limit switch? That would be switch 7ALS. On the electrical schematic, that switch is labeled X AXIS DECEL, but the maintenance manual calls it the zero-return limit switch.

Anyway, the signal from that switch arrives at 13TB-10 (bit B0). As the -X movement proceeds, I can watch 13TB B0 wink out and then come back on as the dog passes the switch. So the switch is working fine. Does that mean there some other event that stops the -X travel at 2.5"? :willy_nilly:

Tonytn36 · Mar 12, 2010

Yup, once it sees the switch, it starts looking for the zero pulse on the encoder.

Jim Wilson · Mar 12, 2010

Tonytn36 said:
Yup, once it sees the switch, it starts looking for the zero pulse on the encoder.

Ok. Thanks! The "zero pulse"? I haven't had to look at the encoders yet. Don't even know if they're quadrature, optical or what.

Hole Wizard · Mar 12, 2010

Check the switches there will be two. The closest to the spindle to seek home, the second being overtravel. Chances are the home switch is gummed up with coolant and sticking. Otherwise slide the seek home switch closer to the spindle. I had an ameri-seki slant bed that gave me fits for a long time. It turned out that the home switch was on the border line of the X axis zero It was a crap shoot as to where it homed out to. Moving the seek home limit switch fixed it.

Jim Wilson · Mar 12, 2010

Hole Wizard said:
Check the switches...

I checked out the switches first. They were a little grungy, but not that bad, really. And they both are working fine. I cleaned up everything in that area, anyway, but that's not where the problem is.

Thinking back to the encoder... I found it on the schematic and on the machine; it's integrated into the drive motor assembly. The housing is cracked right where the encoder cable comes in. That may or may not be a clue, though. If the encoder were failing, wouldn't there be some indication in the X-axis position display? The display looks quite normal as the cross-slide advances.

Is there a special reference position signal (the "zero-pulse" Tonytn36 mentioned) sent out by the encoder? The schematic shows just two signals running, via twisted pairs, from the encoder to the control (called SD and REQ at the control, but those aren't very meaningful names, the exact same terms are used for the Z-axis encoder).

I haven't yet seen anything in the docs about testing the encoders, just a procedure for replacing the whole drive.

Hole Wizard · Mar 12, 2010

Slide the switch closer to X0 It might overtravel before it finds home. If memory serves the encoder is optical. If it's cracked you might need to take it apart, clean the encoder & seal the crack.

Ox · Mar 12, 2010

The new problem is: it will no longer zero-return in X. This just started about an hour ago. Specifically, when you get to the step where you "hold down -X until the cross-slide stops on its own," it never stops. It keeps going all the way down until it hits the -X overtravel limit. This happens even if it starts way, way up high (like up to about 0.010" below the +X overtravel) and of course, despite getting a good solid 2.5" of -Z travel before starting X.

Here's my first question. It's supposed to stop when the turret reference point reaches 2.5" diameter, right? How exactly does the machine know it has reached that point? From the zero-return limit switch?

I sure hope you aint moved anything already. :willy_nilly:

This machine will NOT re-home once homed!

If it has been homed - all you are dooing is jogging it.

E-STOP does NOT mean that it needs re-homed! ONLY if the control had been powered down!

As far as "X-2.5" from what point?"

It is 1.25" of travel from the possition that it was when powered up. There is NO switch used untill the trip back up.

It's had a hard life, but we can rebuild it.

I hope $6,000,000 aint involved!

edit:

ENYTIME that a CNC doesn't doo what it usta doo, power it down at case level and start over before you git too excited.

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

Think Snow Eh!
Ox

Jim Wilson · Mar 12, 2010

Ox said:
I sure hope you aint moved anything already.

Nope. Still trying to figure it out. Just lookin' so far. And cleanin'.

This machine will NOT re-home once homed! ONLY if the control had been powered down!

That's the problem. When I powered it up this afternoon. It wouldn't home.

It is 1.25" of travel from the position that it was when powered up. There is NO switch used untill the trip back up.

Ok, I was thinking it went to 1.25" radius. Never paid close attention to where it really was. So, if it's supposed to stop once it has traveled 1.25" down, why won't it stop? This is on power up, not just after an E-Stop.

I hope $6,000,000 aint involved!

Ox, yer showin' yer years! I didn't expect anyone to get the reference.

ENYTIME that a CNC doesn't doo what it usta doo, power it down at case level and start over before you git too excited.

Been there, done that. First course of action.

Jim Wilson · Mar 13, 2010

How about this for a logic puzzle:

I wondered if changing the K03.0/RTOPT bit had something to do with the machine not homing anymore. I don't see any reason why it should, but just to be sure... After all, that was the last thing changed before the machine stopped homing properly.

However, Parameter Write Enable (PWE) must be set before K03.0 can be changed. MDI mode must be selected before PWE can be set. The zero return procedure must be completed successfully before MDI mode can be selected.

What's the deal? There's no way to change parameters unless the machine has been homed? That makes no sense. :ack2:

scudzuki · Mar 13, 2010

I see, you can rebuild it.
But can you make it better than it was?
Better? Stronger? Faster?

Yeah I'm dating myself, but if you saw me you'd probably understand... who else would date me?

Joe

Oh and BTW I doubt $6 million would cover it, inflation and whatnot.

Jim Wilson · Mar 13, 2010

I found several places on the web that suggest holding P+CAN down while starting the control, to override soft overtravel limits. I don't know if that has anything to do with my problem or not, but I figure it's worth a try.

However, on my CRT/MDI panel, there isn't a 'P' key. 'P' is shift-O. Does that make any difference? Holding down O+CAN doesn't seem to do anything. :confused:

repairguy · Mar 13, 2010

I may not be any help as I've not worked on a Hardinge before but I do have a few questions, maybe it will help point you in the right direction.

I'm confused, this machine zero returns in the X minus direction? As in toward the chuck centerline?

The next question is does the axis decel when it hits the zero return limit switch. Most systems I'm used to travel to the limit switch, slow down after seeing it and then look for the encoder marker after going off the switch again.

Does this machine require you to hold the X jog button until it completes the zero return. Or can you let off the button when it first reaches the limit switch and have it continue by itself?

Final question. While homing, if you trip the limit switch by hand in the middle of the axis travel what happens?

If I'm way off in left field I apoligize. Just trying to make sense of things.

Dan

Jim Wilson · Mar 13, 2010

repairguy said:
I may not be any help as I've not worked on a Hardinge before but I do have a few questions, maybe it will help point you in the right direction.

Thank you!

this machine zero returns in the X minus direction?

No, the zero return procedure is supposed to go like this:
1. Hold down the -Z button until the carriage moves left at least one inch
2. Hold down the -X button until the cross-slide stops moving down

when this happens, the X position reads -2.5" (IIRC, maybe 2.5")

3. Press the +X key

the cross-slide goes home, X pos reads 13.25" (again, IIRC, maybe 13.5")

4. Press the +Z key

the carriage goes home, Z pos reads 23.0"

It's failing at step 2. When you hold down the -X button, the cross-slide keeps advancing until it hits the -X overtravel.

The next question is does the axis decel when it hits the zero return limit switch. Most systems I'm used to travel to the limit switch, slow down after seeing it and then look for the encoder marker after going off the switch again.

As I understand it now, after Ox's post above, this is what's supposed to happen in step 3. And I believe that is what was happening before it failed. We're not getting that far now, though.

Does this machine require you to hold the X jog button until it completes the zero return. Or can you let off the button when it first reaches the limit switch and have it continue by itself?

Not in step 3, but you do have to hold it in step 2.

Final question. While homing, if you trip the limit switch by hand in the middle of the axis travel what happens?

Dunno. I don't think it would do anything in step 2. But I bet the travel would slow if you manually tripped the decel switch (prematurely) in step 3.

If I'm way off in left field I apoligize. Just trying to make sense of things.

I sure appreciate it. I'll take any help I can get right now -- even if it's just a sounding board.

Cheers!

Jim

repairguy · Mar 13, 2010

Thanks for enlightening me. Sounds as if something in the ladder isn't satisified.

Does the machine display the position while moving? I ass-u-me it does by previous posts. So it should know it has moved the proper amount to allow the zero return.

How about the Z limit switch. If it thinks it's sitting on it will the machine allow you to zero return the X?

Again probably useless babble.

Dan

ARB · Mar 13, 2010

Are you sure about step 2?
My Hardinge is much newer but I just jog the x- about an inch then Home x then Z.

Ox · Mar 13, 2010

P/CAN is SOP for Fanuc, and will help you git past some [bogus] O/T alarms and such if all you did was power down the control. But a power down at case level trumps all 2's and one eyed jacks.

No, the zero return procedure is supposed to go like this:
1. Hold down the -Z button until the carriage moves left at least one inch
2. Hold down the -X button until the cross-slide stops moving down

We may have jist solved your issue? Z should go prox 2.5". I think you can cheat that a bit - but if you've only been moving 1" the last day - then that's quite likely your trouble ratt there.

the cross-slide goes home, X pos reads 13.25" (again, IIRC, maybe 13.5")

Mine goes out to X15.
Doo you have an X value in your G10 line that you've been MDI-ing?

edit - let me change that - WHEN you enter a G10 aggin - enter X0. X should always be zero in a G10 line in a lathe. There is an exception - but you will know when _ when you need it.

ARB - no - the X should stop in X- by itself. (as well as the sub if you have one)

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

Think Snow Eh!
Ox

Jim Wilson · Mar 13, 2010

Ox said:
P/CAN is SOP for Fanuc, and will help you git past some [bogus] O/T alarms and such if all you did was power down the control.

Ok, so it won't help me now, but how do you do a P/CAN with no P key? Just use the O key? :confused:

We may have jist solved your issue? Z should go prox 2.5".

I wish! But I usually do move it 2.5", and I have been since this problem showed up, 'cause I thought it might be that. I put the 1" in the description above because that's what the manuals say.

Mine goes out to X15.
Doo you have an X value in your G10 line that you've been MDI-ing?

That's a (nother) new issue, then. If mine really does have a 15" turn, then there's prolly another parameter wrong somewhere. But wait, there's not that much headroom between the cable raceway and the X-axis drive after homing. At least I don't think there is. Hafta check, but that's for another day.

So far, I've only ever put X0 in the G10. It's never been anything else. I sure the X work shift is 0, too. So, I dunno what's going on there.

the X should stop in X- by itself.

Do you have any clue why it stops? I mean, what gets compared to what and where? I.e., is the control looking for X == -2.5? Could I see in in the ladder? Where can I look to see what's going wrong? I can't find anything in either the Hardinge or Fanuc manuals that talks about this. It's a mystery.

Jim Wilson · Mar 13, 2010

ARB said:
Are you sure about step 2?

Well, mine at least has never homed unless it stopped on its own on the -X move. If you try just pressing +X after moving -X an inch or two, nothing happens. The cross-slide doesn't move at all.

Jim Wilson · Mar 13, 2010

repairguy said:
Sounds as if something in the ladder isn't satisfied.

That does sound reasonable, but I have no clue what, or how to find out. I've been thumbing through the ladder trying to find what signal isn't happening, but I'm empty handed so far.

Does the machine display the position while moving?

If you go the POS screen first it does.

So it should know it has moved the proper amount to allow the zero return.

My sentiment exactly. So why won't it stop?! :wall:

How about the Z limit switch. If it thinks it's sitting on it will the machine allow you to zero return the X?

I'll double check, just so's I've covered all the bases, but I don't think this is it. There's no alarm, and Z moves fine in either direction (although you do have to hold E-Stop Reset for +Z until it's homed, but that's normal).

ARB · Mar 14, 2010

It sounds like procedure is quite a bit different on the older stuff.
I'm not familiar with it.

On the newer stuff with O control
1) Jog x- about an inch
2) jog z- about an inch
3) set selector switch to Zero Return Mode
4) press x home button
5) press z home button
Done

Resurrection, backpedal

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