Re: [CAD_CAM_EDM_DRO] Re: Geckos, Servos, VFD and twitching on Z axis

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@...> 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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