Re: [CAD_CAM_EDM_DRO] Servo issue

Jon,

I have stripped everything down and have my servo's running on a bench. I
have swapped the axies over but have not been able to replicate the problem
I had on the mill.

One thing I did notice however, is that the motor which was over heated
seems to be weak when I try to turn the shaft anti-clockwise. When the servo
is holding position I am able by hand to turn the shaft about 1degree anti
clockwise, this requires some strength, it then get a slow pulsation going.
I cannot turn the shaft by hand clockwise. And this happens regardless of
the g320 I use. What could be causing this weakness and could it somehow
relate to my machine going crazy?

Thanks Jon.

Jason.

----- Original Message -----
From: Jon Elson <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, August 13, 2003 3:32 AM
Subject: Re: [CAD_CAM_EDM_DRO] Servo issue


>
>
> Jason Cox wrote:
>
> >Hi everyone,
> >
> >I have a retrofitted rf-45 mill/drill, using ametek servo's with us
digital encoders fitted. All is driven by gecko 320's and cncPro.
> >
> >I havent got around to fitting limit switches yet and the other day
somehow the machine was bumped and the x axis driven to the right into its
stop, it stayed that way for some time until i noticed smoke from the x axis
motor.
> >
> >I stipped everything down and concluded that the smoke was from the resin
in the motors windings, however the motor seems to run perfectly with no
issues.
> >
> >I hooked everything back up an switched on, the g320's resetted and held
position. a few minutes later the thing started driving to the right by
itself, just like when a g320 breaks its lock range.
> >
> >Its unpredictable when this will happen, and I can jog the x axis fine
but then all of a sudden, bang it starts going to the right, sometimes after
2 seconds sometimes after 10mins.
> >
> >
> I have a client in my area who has the same thing happen last night. I
> am going to
> see him tonight. He has Gecko 320's and the same Ametek/US Digital
motors.
>
> >What could this problem be, maybe the encoder? or have I damaged the g320
through heat? I thought the g320 would fault if there were problem.
> >
> >
> No, don't depend on the 320 to protect itself. It has no overtemp
> sensor, just an
> overcurrent trip. The high resistance of these motors may prevent the
> overcurrent
> trip from activating. My guess is that there may be a weak power
> transistor in
> your gecko, and it is going to the shorted condition after it heats up.
> You might
> also check your encoder cable carefully for any loose connections. If
> it only fails
> while moving, that is a much stronger indication of a bad connection on
the
> encoder wires. You might also swap both the motor and encoder connections
> between two axes, and see where the problem goes. If it stays with the
> motor/encoder,
> then it is there (motor, encoder, wires). If it moves to another axis,
> it must be
> in the Gecko drive. If you have not put a cover over your encoders, you
> might want to do that. A speck of dust in the wrong place could block the
> light and disable the encoder. And, that could be intermittent.
>
> I will let you know what I find with my client tonight. His doesn't
> wait to go
> flying, it does this as soon as you power on. He said it stayed with the
> motor/encoder in his case, but I want to verify it.
>
> >Any help would be greatly appreciated, Im off to install some limit
switches!
> >
> >
> >
> Limit switches may not help you, unless you have them set to cause an
> E-stop.
>
> Jon
>
>
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