Re: Question on Power Supply - regulated notes

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Alan Marconett"
<KM6VV@a...> wrote:

> HI Dave,
>
> I wonder if there isn't a difference between a servo motor and a

stepper in

> decelerating. Mariss has measured back EMF on the steppers, so we

know it's

> there, but we still have to step the stepper motor. Probably a

smaller

> current "drink" from the power supply. But as the windings still

get

> energized, then I'd think we would still have drive power to

cancel back

> EMF.
>
> Now on servos it's obvious that there is EMF. We actually drop

the drive

> from a motor (small peristaltic pump) for a short bit of time in

order to

> measure the back EMF, and use it to control the speed (servo loop).

Back emf is a factor of the ability of a machine tool to "coast". A
machine with a v thread leadscrew like a Taig or Sherline will NOT
experience any sizable( or significant) back emf because the machine
screw acts as a brake when changing directions.

A machine with a ball screws is the most likely to produce sizable
back emf because they are free wheeling. The knee on some
bridgeports with an acme screw will also free wheel, but generally
the X and Y axis are not nearly as free wheeling without a ball
screw.

Fred Smith - IMService
http://www.cadcamcadcam.com/hobby