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

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" <pete@v...>
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" <da-mack@e...>
> 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.