Re: Geckos, Servos, VFD and twitching on Z axis

Could be the electrical interference from the VFD but
have you try'd to tune the Servo?
There should be 2 places to make adjustments to the
Servos for proper tuning.
A miss adjusted servo would likely twich a little at
standstill.
Check the documentation of the geckos.
You would not notice a difference just switching the motor.
Good Luck


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "yethdear0" <da-mack@e...>
wrote:

>
> We tried the wire separation and isolation, we even swapped motors
> and encoders with the Y axis. We are at the mercy of the machine's
> construction. The Z axis servo is mounted right up front of the
> spindle head. The spindle motor is directly behind that about 10"
> away from the servo and encoder. The VFD we wanted mounted to the
> side of the spindle head for ease of use. We could have mounted the
> VFD in a cabinet behind the machine and rigged up a remote keypad
> for operation but we didn't realize that it would cause such noise.
>
> The noise would result in a slight "twitch" of the Z axis usually
> causing a .005-.010 jump or error in the Z axis motion. As for now,
> everything seems to be working and repeating fine. I ran a program
> over and over and there were no position errors or twitches. As for
> other noises, the machine is located in a high school machine shop.
> It is surrounded by other machines, 3 phase and single phase and
> machines powered from the some bus. We also have quite a few
> machines with VFDs on them as well. So far, we have no noise

showing

> up. We are going to try some 3D contouring tomorrow. Any noise
> produced by any of the axii will definitely show up then as a divot
> in the surface of the part. We have our fingers crossed.
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
> wrote:
> > I had the same crosstalk issues when I retrofitted my Bridgeport.
> I was able to just seperate the motor leads and encoder cables to
> rectify. It seems there should be a standard to eliminate cross-

talk

> and interference issues with encoders, or at least a more absolute
> fix and safeguard. I'm wondering what difference moving the 10 uf
> cap on the encoder current a few inches away from the Gecko made. I
> dont have any caps on my encoder wiring and wondering if I need

any.

> Once I see a servo act extremely erradical and resolve it by just
> moving wires, It's not a very secure feeling for future operation.
> What else could possibly make it happen? Arcing in the spindle
> motor? Noise from another piece of equiptment coming through the
> line? Cell phone? The kids RC car? I think about this when I have a
> 1.25"dia. X .875"dia. shank Reamer buried 10" deep in a large
> workpiece. Having 5hp at the ballscrews from the servos, that would
> be a disaster.
> >
> > Ron
> >
> > yethdear0 <da-mack@e...> wrote:
> >
> >
> > Everything is shielded.
> >
> > By chance, we installed a 10 microfarad capacitor on the 5 volt
> power
> > wire that powers up our encoder and "Bigo!" all is great in the
> > universe. We also found out that the capacitor had to be

installed

> > within a few inches of the encoder. If we installed it at the
> Gecko,
> > it wouldn't help. All 3 axis repeat now on a travle indicator
> > within .0005in.
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "vavaroutsos"
> >
> > wrote:
> > >
> > > Sounds to me like you are getting noise on your Z encoder. Are
> you
> > > running single ended encoders, or differential with converters?
> Are
> > > the encoder cables shielded? Did you use shielded VFD cable

from

> > the
> > > VFD to the spindle motor? How are your ground connections
> oriented?
> > >
> > > ~petev
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "yethdear0"
> > > wrote:
> > > >
> > > > Hiya,
> > > >
> > > > We have an old Hurco knee mill that we have stripped and

retro-

> ed
> > > > with a pc, CNCPro, Geckos and a Baldor VFD for the spindle
> motor.
> > > We
> > > > just got it all up and running but have a problem with the Z
> axis
> > > > servo or controller. Using a travel indicator on the Z axis,
> the
> > > > movement is smooth and exact. We have the machine running a
> > program
> > > > that move Z -.100" pauses for 1 second and then moves Z

+.100"

> > and
> > > > then runs in a loop. When we turn on the VFD and the spindle,
> the
> > Z
> > > > axis seems noisy and the travel on the indicator will start

to

> > > > drift .001" to .005" each time the program cycles. The drift
> is
> > > > random, sometimes positive and sometimes negative but

positive

> > the
> > > > majority of the time. When we slowed the motion to 1 ipm, you
> can
> > > > see the motion twitch at random during the movement. This

only

> > > > happens when the spindle is running and only the on the Z
> axis.
> > We
> > > > swapped out the servo motors with the Y axis and the problem
> > stayed
> > > > with the Z axis controller. On the machine, the Z axis servo
> is
> > > > mounted on the front of the spindle head of the machine, the
> > motor
> > > > (5hp, 230V, 3ph,) is on the back of the head. The VFD (a new
> > > Baldor)
> > > > is mounted on the side of the head about 6in from the Z

servo.

> We
> > > > also dismounted the Z servo and located it away from the

motor

> > and
> > > > VFD to test for magnetic flux or noise and it still twitches.
> We
> > > > have also played with the gain and damping adjustment but
> nothing
> > > > there would correct the problem. The twitching is only in Z,
> all
> > 3
> > > > Geckos are getting their power from the same DC power source
> > which
> > > > baffles us why the twitching is only on the Z axis. We are
> also
> > > > using new US Digital encoders. When we swapped servos though,
> we
> > > > also swapped encoders and the twitching stays on the Z axis.
> We
> > > also
> > > > rerouted cables as far from our VFD and motor as possible but
> > still
> > > > have the problem.
> > > >
> > > > Any suggestions or input will be greatly appreciated, thanks.
> >
> >
> >
> >
> >
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