Re: [CAD_CAM_EDM_DRO] Re: z axis drive question

bitnick78 wrote:

>Jon Elson wrote:
>
>
>>A properly designed servo motor has no detectable "cogging" due to
>>individual
>>windings, commutator segments and pole pieces. (Yes, badly designed
>>motors, or those for high-speed operation only, may have significant
>>torque ripple, velocity ripple or reluctance cogging, but these are
>>
>>
>NOT
>
>
>>servo motors.)
>>
>>Jon
>>
>>
>
>Can one detect cogging by turning the motor by hand? The reason I ask
>is that I recently bought a used servo motor, and when I rotate the
>motor by hand I can clearly feel a "stepping" sensation; that is, the
>motor favors some positions over others.
>

Hmm, this is not real good. That clearly is cogging, probably due to
changes
in the magnetic circuit as the magnets in the rotor pass the stator poles.

> I think it has 8 steps/rev,
>and some steps are a bit weaker than the others. They are not very
>distinct (nothing like a stepper), but quite strong - when left in
>the middle of a step the motor turns so that it sits between steps...
>if you get what I mean.
>
>This is the same 3-ph PM Yaskawa servo motor I asked about in an
>earlier message.
>
>

Well, in low speed movement, it requires the servo system to compensate
for these errors in the motor. For the cogging to overcome bearing
friction,
it is pretty strong. Still, compared to the motor's torque output, it
is probably
small.

Jon