Re: [CAD_CAM_EDM_DRO] Slight Servo Problem

mmurray701 wrote:

>I'm having a slight problem with my Z axis servo. Everything is
>running fine but it oscilates (buzzes) MUCH more than the other 2.
>Its also running hotter, over 50 degrees C when the other two
>actually feel cool to the touch.
>
>The servos are all Electrocraft E543's with renco encoders.
>
>The Z axis is almost always buzzing. And at a much higher frequency
>than the other two. The Gecko 340s are all set exactly the same.
>Factory settings on Gain/damening and current limit set to about
>half. I've tried playing with the gain/dampening knobs, even to the
>point of having gain at the minimium and it still seems to buzz much
>the same way.
>
>And the problem is not related to the constant Z axis weight. The
>machine isnt using ball screws and the z axis probably only weights
>20 lbs anyway (mini mill). And i've tried moving the handwheels
>slighly to move it past the neutral position but it still buzzes.
>
>One other weird thing I noticed is that the other motors are
>perfectly silent when running. No noise at all, and just some very
>slight noise when stopped as any servo has. The Z servo, on the
>other hand, makes the same "stepping sound" as a stepper during
>average cutting speeds (~10IPM).
>
>I cant get the same speed out of the Z axis either. It oscilates
>heavily and even causes the drive to fault before 3000 RPM when the
>others can go to 4000 no problem.
>
>

Hmm... I guess you should open up the Gecko box and make sure the
anti-dither mode is activated on that Z drive. I think that means the
jumper
should be missing in that location.

The other possible problem is feedback on the encoder wires. Do you have
the encoder wires strapped to the motor wires? That is not a good idea,
as the
Gecko drives send a lot of fast rise-time pulses out the motor cable.
You likely
need shielded cables for the encoder, if you aren't using them.

Do you have the same number of steps (encoder counts) per inch for all the
axes? Does the axis still buzz when in estop-off mode (assuming EMC is
the control program, you don't say)? There are some combinations of
resolution that cause a lot of hunting of the simulated servo in freqmod,
and a deadband setting of about 1-2 encoder counts helps immensely.

Jon