Re: [CAD_CAM_EDM_DRO] Re: safety

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