[CDennyRun]

For about a year now we've been having problems with our Z axis on a Kval CNC machine (Edge STS). This machine is basically a router for the "style" of wood doors. The Z axis drives the spindle in towards the product. It's really hit or miss for the overspeed error (no consistencies to it what so ever). Sometimes it happens 20 times in an eight hour shift, and every once in a while it'll go a month without problems.

The drive is a Lenze E94R040Y2NRX and the servo is a Parker MPM892BSG7G1N.

Things I've don to try and resolve the problem:

-Replaced the drive twice

-Replaced the servo

-Replaced the ball screw and nut

-Made sure the ball rail bearings associated with the Z axis are in good shape

-Reduced the weight of the head unit by at least 40+ lbs

-Ran auxiliary encoder cable

When we get this error, it's not usually under much of a load. I'll kill the machine to reset the drive, and there doesn't seem to be any mechanical issues upon inspection. It doesn't error out in the same spot at any time.

Do you guys have any ideas as to what would cause this problem? It's been going on for too long, and we've lost TONS of hours to it. Not to mention the ass-o-nine amount of money we've thrown at it.

Any ideas and opinions will be very much appreciated!

Regards,

Chris Denny

[mike_Kilroy]

OK, I'll take a stab at it.....

basics: overspeed is a fault that happens when a motors feedback tells drive it is going faster than a max speed setting in the drive. As I do not know this drive, I cannot say if it is a POT setting or a DIGITAL setting in software. But it is one or the other.

What can cause this fault?

1) actually going FASTER than this setting
2) Wild wonderful electrical NOISE that we all know and love
3) Defective motor, feedback, or drive.

- You replaced drive & motor so not it.
- how is the overspeed setting done on YOUR drive? pot? turn it up? digital? communicate to drive and ask it and turn it up?
- you do not say if the fault happens while moving or sitting still; if sitting still it is likely noise, if while moving could still be any of the 3 listed above.
- if fault while moving? is it going really really fast? ie., does it seem to be a REAL overspeed issue? very important distinguisher.....
- when something fails, it usually can be traced back to something that happened or at least a given time; you did not state if the machine EVER worked right, I assume from 'for the last year' it used to work right.... a year ago when it began happening, did the machine get a bad crash? lightning strike your shop? grounding changed? etc?

Can you turn a speed rate overide pot down to some low speed to see if that stops the faults?

Is grounding good?

[CDennyRun]

Thanks for the reply!

It has errored out while in motion, not in motion, and I've never seen it move faster than any other servo in it's application on our other machines. When it throws a error, it does store it. The motion controller (Galil) says its a position error, and the drive program states it has encountered a overspeed. I know those a re two separate entities, and two separate problems, but they happen simultaneously. At the moment the machine is running, but we'll get this error 10-20 times in a shift, and we have to power down to reset the drives, home and the whole nine yards. It's very taxing on production.

I don't think we've had any lightning strikes lately. It could be possible I suppose. We have had instances where we had three or four drives go bad within a week of each other, which raised that same question in the past.

I'm not too familiar with setting parameters in the drive, and probably shouldn't mess with it! Ha ha. We can hook up online with the manufacturer and have them do it (waiting on a call back from them now to do that)

We are also going to get spare power and encoder cables on the way to see if it's a noise thing. We've replaced them in the past, but they do wear out from constant movement inside the chaseway.

Thanks again for the response! I really appreciate it.

Regards,

Chris Denny

[mike_Kilroy]

not sure where you are Chris - maybe you should put a city/st on your settings; if I knew where you were there is a fair chance I and others could give you names of some local folks to help you out! So tell us if you want.

Since u get the error when motor is NOT moving, that pretty much says it is a noise issue or bad drive. since u replaced drive more than once w/no effect, that leaves noise.

The 2 errors ARE ONE AND THE SAME; the drive stops moving on fault, so the Galil says "dude, you are not moving and are getting behind where I want u to be, so after a predetermined (programmed in galil) maxPE distance, it too faults.

So u got noise. why? what happened 1 yr ago? SOMETHING LIKELY DID. These things don't go goofy on noise for no reason: something happened 1 year ago.

Did u buy a new arc welder then? Is it sitting right next to this machine? Did the power company change your plant's main transformer? Did a cable go bad, get replaced but the grounding done differently now? something CHANGED 1 yr ago to cause this. Murphy found you.

THAT all said, can u test by running only 1 drive? power down the others on the machine? and see if the fault still happens? it could very well be ANOTHER motor/drive on the machine outputing a zillion times normal (starting 1 yr ago) noise and this particular axis is the most susceptible....

If you wanna try to tell us how you ground the cables (motor cable and feedback cable), and or include a machine wiring diagram, there are those here who can look at them and offer comments.

For instance, depending on the age of this machine, quite a few manufactures using servos 2-3-4-5+ years ago did not know how to properly ground the cables! They used ancient methods, like grounding only 1 side of the feedback and motor shield, maybe not even having a ground wire (4rth wire) going to the motor CASE, and/or the shield grounding was done by taping/soldering a 20" long #16 wire to the cable shield and running that to some obscure ground point - all wrong stuff.

Wiring diagrams so we can see if there is any basic design flaw; it is not as uncommon as u might think; folks using galil for motion controllers can be notorious for using single ended encoder inputs - really bad for this kind of issue.

[CDennyRun]

I'm pretty sure you're onto something with this. We ran a ground from the motor to the main box to see if we can get rid of noise, if there is any. Hopefully that's the case. You are spot on about grounding both ends. The equipment manufacturer confirmed this about 20 minutes after you posted. Ha ha, it's almost as if he read you post right before we called, and quoted it.

I really appreciate you're insight and time. Thank you very much!

I'll update if anything changes.

Regards,

Chris

[mike_Kilroy]

ok, go next step.... ground both ends but how?

strip back the pvc cover over shield. do not disturb shield. just push it up against bare cabinet metal close to end by drive. use plastic tie wrap to hold it against it. if u use ANY wire extension, it becomes NO GROUND.

ditto the feedback cable.

at motor, tie as best u can to motor case or connector.

[chrishogan]

You can find all the info about PositionServo at the following page.

Lenze PositionServo 940/941 Servo Drives & Controllers Distributors