Re: [CAD_CAM_EDM_DRO] Servo Dynamics 1525 servo drive noise

shawncd2001 wrote:

>I recently purchased an older Milltronics Partner mill. This
>particular unit uses the older Servo Dynamics 1525 servo drives.
>I have tuned the drives to where they perform the way I want them,
>but there is an ear piercing whine or whistling sonund coming from
>the boards. Anybody out there have the same problem? Any ideas on a
>fix? Any information would be much appreciated.
>
>
>

Yup, these older drives have very low frequency PWM cycles, and so
produce lots of audible tone. Looking in the book, it says it is 16 KHz.
Most people past their 20's can't hear much up there anymore. This would
be the same pitch as the horizontal output of a TV set.

I'm wondering if what you are getting is a subharmonic or unrelated
lower frequency than the 16 KHz? Can you make the pitch or loudness
of the tone change by moving the axis to a different position, or
manually damping the shafts (motor, encoder, tach) with your hands?
Can you make a guess at the frequency of the tone? Are you sure it
is coming from the servo amp, and not the motor?

You might also disconnect or disable all but one amp at a time to see
if it is one particular amp, or all of them emit this tone. If you can
disconnect the velocity command signal from the CNC control to
the amps, you can see if this is a positioning loop oscillation, or
just in the servo amp.

The Servo Dynamics does have inductors on the output. They appear
to be quite small, so it doesn't seem likely they are emitting much
sound. There is a large transformer (T3) on the circuit board. I have
only partial schematics of this amp, but I assume this is a DC-DC
converter that provides isolated power to floating circuits in the
amp. It may be running at an abnormally low frequency. Without
diagrams, I can't go much further. You could try wrapping foam
around this transformer, but if it already runs hot, that might not
be a good idea.

Jon