Re: safety

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> mariss92705 wrote:
>
> > Hi,
> >
> > The only sure-fire way to E-stop a DC brush servomotor is to kill
the
> > power supply to it. Unlike step motors/drives where if anything
> > breaks, the motor stops, most anything that breaks in a servomotor
> > drive makes the motor take off full tilt.
>
> Quite so, and in a system with a DC tach, there's just one more
thing
> to go wrong (but I like the performance of a tach-equipped servo).
> I have high-side current sensing on mmy servo amps, so a grounded
> motor will also be detected as a fault condition. Generally, if any
> of the control loops goes open (loses the signal) then the motor
> will accelerate without control. The small inductance of the
current
> sense resistor magnifies this sharp current rise, and makes the
> amp trip earlier. I've been able to set the current limit and fault
> trip limits such that the amp will not trip even when applying
current
> up to the limit to move a stuck axis, but will trip before the motor
> moves more than a few degrees when the loop is open. I'm not
> sure you can set up other amps like this.
>
> Jon