Re: [CAD_CAM_EDM_DRO] Re: z axis drive question

Dave Fisher wrote:

>I can see the calculation gives 0.0005", which I am sure would be fine for
>my
>needs, but I can't seem to visualise how the DC servo motor can move such a
>SMALL amount - is the motor not governed by its commutators and magnetic
>pole
>pieces ?
>
>

No, it is governed by the encoder. With a Gecko drive, for instance, the
drive reads the encoder position 25,000 times a second and decides if motion
is needed to correct the position, and if so, how much power to apply.
This is far faster than the motor can respond, so it maintains tight control
on motor position and velocity. Any attempt to move the motor off course
is detected and responded to in a fraction of a millisecond.

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