Re: E-Stop Revisited (PS on sherline auto changer)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo <ballendo@y...>"
<ballendo@y...> wrote:

> Peter,
>
> On small "desktop" machines, here's what I do:
>
> As soon as the estop is pressed; I cut spindle power(with a
> "hockey puck" SSR), drop power to the optos so the steps stop
> getting to the drives, begin a timing circuit set to the worst
> case spindle run down time, and raise the voltage to a "1" on
> the estop signal line going to the computer.
>
> Now the spindle is winding down, held in place by the still
> active drives, and the computer has been "notified" that we
> have a problem out here...
>
> When the timer times out, I can assume the spindle is no longer
> turning, so the enable for the drives is turned off, allowing
> free movement of the motors.

A very well thought out system. I just want to point out that
this system should only be used for stepper based machines.
With servo motors there are failure modes that would cause the
motors to run away at full speed even though the step inputs
are blocked. If using servos, cut the servo motor power right
away, don't just block the step pulses.

John Kasunich