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Author Topic: Lathe Problems with Mach Motion Wizards, Is this Gcode Good?  (Read 1775 times)

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Re: Lathe Problems with Mach Motion Wizards, Is this Gcode Good?
« Reply #10 on: August 01, 2018, 10:53:35 AM »
Hi,
what sort of servos?

Old style brushed servos with DC drives don't have a 'following error window' but detect large deviation between commanded position and
actual position by measuring armature current. If the deviation is large then the servo will attempt to accelerate quickly ( high current) to the
correct position.

AC Step/Direction servos have a commanded input position and compare that to the actual position as indicated by the encoder. Ideally they would be
the same but they aren't. The servo position and therefore the encoder position will always lag a little.

I have an Allen Bradley servo for a spindle motor. It has an 8000 count per rev encoder. I have it programmed with a following error window of 20
counts, ie 0.9 degrees. If it gets more than 0.9 degrees from where it should be then it will fault, signal Mach, and if I wish it, have Mach stop.
I could make the error window smaller but then I would have to use less aggressive moves so that the servo can keep up or it would fault all the time.
Alternately I could make the error window wider and therefore drive the servo harder with a greater difference between commanded position and
actual position but with the wider tolerance or window still not fault.

Understanding how following error is handled is an important part of understanding your machine.

Craig
« Last Edit: August 01, 2018, 10:56:02 AM by joeaverage »
My wife left with my best friend...
     and I miss him!
Re: Lathe Problems with Mach Motion Wizards, Is this Gcode Good?
« Reply #11 on: August 01, 2018, 11:49:47 AM »
I'm using new DMM. Also I remember when the servos have stalled, I forget the problem, that the servo would fault and I'd have to reset it on the driver.
Re: Lathe Problems with Mach Motion Wizards, Is this Gcode Good?
« Reply #12 on: August 01, 2018, 02:47:11 PM »
Hi,
I suspect DMMs have a very similar set up to the Allen Bradley drive. There will be a programmable register for following error, or whatever DMM
call it.

I suspect also that you can program what the fault signal includes. The Allen Bradley has alarms for over voltage, over current, over heat, following error.
They can be combined into one fault line or over several lines. Such line would be hooked to Mach and then you program Mach how to handle them.
There is also an alarm reset, if memory serves its a distinct input on the Allen Bradley but with many drives it a pulse Mach applies to the fault line
that resets the drive.

Time to look at the manual.

Does DMM have servo setup software that you install as an application on your PC? If it does you might use the software scope to observe your servo while
doing a Gcode job and detect a loss of position. It would give you valuable insight as to how servos work and following errors.

Craig
My wife left with my best friend...
     and I miss him!
Re: Lathe Problems with Mach Motion Wizards, Is this Gcode Good?
« Reply #13 on: August 01, 2018, 03:13:36 PM »
Yes it has setup software. Great advise thanks. I'll see if I can monitor while it's running.