[pquerro]

I have a Sabre 1500 with an A2100 control. BDS4 Servo Drives. I can move the Y and Z axes just fine. The X axis however jerks, I'm guessing a servo oscillation. The control then errors out with a Foldback error. I can move it very slowly for a bit with the MPG but any speed at all and it begins jerking. Anyone have any ideas - Drive? Motor? Feedback? Thanks

[maver1ck]

Although you didn't mention it, I'm assuming you have scale feedback on the x-axis. If so, the first thing I would do is check is x-axis bearings and ballscrew for looseness. I recently worked on a similar problem on a 1250, and it turned out to be the x-axis thrust bearings were installed incorrectly.

[pquerro]

Yes, It has scale feedback. Also, I didn't mention the fact that it was running fine until this occurence. It was mid cycle and all of a sudden started jerking and errored out. I will definetely check the bearings and screw. Can I swap the x and y drives to eliminate that from the equation?

[maver1ck]

On the smaller machines, the X and Y drives are identical and can be swapped, but you should perform the drive setup procedure if you plan to leave them swapped for any actual production.

On the larger models, they started using different amp drives for the axes. From my experience, you can swap any of the drives short term as a test, but if they are different amp drives, obviously you'll want to put them back as soon as the test is over.

[mike_Kilroy]

drive? motor? feedback?

maver1ck gave u some good checks. if drives & motors r the same on x&y then swappking drive will check that part. ditto swap motors if same. did u ck the feedback? mounting head screws come loose?

did u try at different table location? sometimes a cable or scale problem will only happen at one spot on table so try other spots to verify not location dependent.

usually last thing we do b4 a failure is cause. u were machining.... so sounds like something BROKE rather than is slowly wearing out. what can break? cable? scale looseness? I had a scale glass come unglued inside one time and it moved back and forth 1/2 in and caused this result....

u can learn a lot from ur 2100 screen: commanded position & actual position..... can u push table by hand? does actual pos display move as expected or is it 'dead' for a bit then move like the backlash maver1ck was trying to help find?

handcrank .001 and what does actual pos display show? no movement? or if u go 5 + then try minus .001 does it show unusually large backlash? ur description sounds like hmmmmm guess.... .010" backlash problem.

btw, when our bds4 drives (or any) go into foldback, that is an effect not a cause; drive is just telling u that jerking back and forth in that oscillation is pulling too much current so drive folds it back to protect stuff; result is the 2100 sees excess position error and faults out.

so sounds like something broke, bang, all of a sudden. it usually results in excess backlash between the scale and motor shaft and the result is what u describe. call us tomorrow if u poke around more and want to ask questions; we try to keep these motors and drives in stock for quick turn around/exchange while/if we repair the broke ones. bet u find mechanical issue creating the backlash tho.

[pquerro]

Thanks for the info. I dove under the way covers. Is the scale difficult to remove? Any tips?

[mike_Kilroy]

I cant help; don't recall whats under the hood - we normally just work on the motors, spindles, and drives off the machine or thru internet connection to them on the machine.

[pquerro]

Mike, you mentioned to call. Can you PM me your phone #

[mike_Kilroy]

i tried all morning before I left the office but ur mailbox was full. i tried again just now and it went. sorry for delay. i will be in office tom morning again.

[pquerro]

Mike,
I will call Monday.
I powered it up again to check a few of the things you listed and with the way cover back there is a noticable "hiss" coming from the motor. Almost sounds like an air leak does.

The actual position display updates when I push on the table before I power on the servos. After the servos are powered on it does not change when I push on the table. No noticable backlash either.

The commanded position vs. actual position seems to be operating properly when using the mpg.

I jogged it a few rotations of the moter very slowly using the mpg and the "hiss" changes volume and tone as the motor changes position.

[mike_Kilroy]

I have a Sabre 1500 with an A2100 control. BDS4 Servo Drives. I can move the Y and Z axes just fine. The X axis however jerks, I'm guessing a servo oscillation. The control then errors out with a Foldback error. I can move it very slowly for a bit with the MPG but any speed at all and it begins jerking. Anyone have any ideas - Drive? Motor? Feedback? Thanks

back to basics again; what is the problem?

is it when you move it moves the right way and the right amount but not smoothly (jerky) then stops where it is supposed to stop and sits still?

or by oscillation do you mean you tell it to move and then it begins to oscillate back and forth and does not stop until you turn off power?

these are not the same thing.

perhaps a better description would help point the right direction?

[Al_The_Man]

As Maver1ck suggested, I would see if the drives are the same size and swap them if so, just to see the difference.
If the problem follows the axis, I would be tempted to remove the motor mechanically, leave it connected and see if you still have the problem.
Al.

[pquerro]

For example - if I'm using the mpg and have it set on .01. If I move 4 or 5 clicks at anything but a snails pace it will begin to oscillate "jump back and forth". I can jog it back the other direction and it will stop oscillating.
It will also start jerking even at a snails pace intermittently but it will settle down when jogged back the other way.
We moved the axis by hand and everything moves very nicely so I don't think it's mechanical.

[pquerro]

Al,
I thought about doing that. Since it has scales, if I remove the motor and jog it, what will happen? Will it just error out due to a following error?

[mike_Kilroy]

backlash will not necessarily feel bad moving by hand.... doesnt take much.

AL, the pos feedback is a scale on the axis so he cannot remove motor from slide and try it.

swapping drive and motor of course is good option to verify the problem is indeed mechanical as it sounds.

[Al_The_Man]

I have seen drives with those symptoms, especially the BDS4's.
Al.

[pquerro]

I will swap the drives and see what happens. what would the new "hiss" sound from the motor be if it was mechanical??

[Al_The_Man]

Even with scales I have tested this type of problem by disconnecting the motor and moving by MPG very slowly, you should have a fair bit of movement before it registers a following error, If the following error occurs around .25 to .375, I have even advanced the table by turning the BS in tandem so that the following error does not register, this way you can test the motor with no load.
Or even oscillate the MPG within the range of the following error.
Al.

[mike_Kilroy]

Al, the integral gain on these machines are so high that just a couple counts of error will generate saturated full output torque in much less than 1 sec. a handful of counts will saturate the 10v speed command to the drive too. it is not an issue of exceeding the controls max following error, it is an issue of instant run away at full speed and torque; often the operator cannot react fast enough to hit the estop button and prevent damage in the crash. Of course with the motor off the machine, it can be tried and no damage will happen; but by the same token, the motor will likely be inherently unstable just by removing the axis inertial load.

the new 'hiss' will come from backlash. this is an example of the rule of thumb of keep the load inertia to 5x the motor max; these machines are probably around 25:1 so if you get backlash, the velocity loop will become unstable and buzz or hiss when in the backlash since the motor sees no inertia load while in the backlash. so the new hiss sound makes sense if you have backlash that has shown up. a few of these machines had such an issue with this hiss and buzz that there was is a tech note that said to replace the motor with a special high inertia version of it to fix it - we made the same motor about 2" longer and added a hunk of solid steel to the rotor to increaase its inertia approx 7x; hence this 25:1 problem became only 3:1 and the hiss/buss when backlash got into the axis go away.

[greg b]

Im not sure this will be of any use or not but on the cincinatti lathes they have on the x axis both slide and motor feedback so if your trying to take the scale out of the equation you may be able to switch to motor feed back in the configuration menu to elaminate the scale as being a problem,also they purge the scale on the lathes with very light air pressure to stop contamination,could that be the hissing noise your hearing.Hope this is of some use regards Greg.