Ideally the e-stop would be fail safe.   This means if a wire comes
loose, something gets shorted or whatever the machine stops.    It is
designed so that some positive action is required to make the motors
spin.

Alarm systems are like this to.  The normal signal is a "hot" wire so
that if the cable is cut the dead wire triggers the alarm.   The alarm
is actively held off.


There is also the question of where to place the e-stop.   Should the
e-stop signal go to the control computer, the drivers or the motors.?
  I think the closer to the motors you can get the more reliable it
is.  Certainly a relay that requires power to keep the DC motor power
connected is going to be very reliable.  But it is also a big
expensive device that must be mounted close to the machine.

But I just started design of a wireless hand controller and thought it
would be nice to have a stop button on it.   After all my thumb would
be just inches away and I could press stop quickly if needed.  But the
problem is that a LOT has to be working for this stop button to work.
 It would not have high reliability especially during development and
debugging.

My thinking is that a layered approach might be good.   The reliable
e-stop is mounted on the machine but a less reliable stop that is
physically close to the operator might be very useful.

In one case I have a 3D printer soon to be moved to a remove location.
It will have a webcam to show me what is going on.  I could get to the
printer in about 3 minutes and stop it or I could send a "stop" over
the WiFi network and stop it in seconds.   Think it is best to have
both methods.

On Wed, Apr 4, 2018 at 12:57 PM, John Dammeyer <jo...@autoartisans.com> wrote:
> In the past ESTOP appeared to be pretty simple a 12V or 24V control signal 
> was routed through any number of Normally Closed (NC) switches and then run 
> into relays and or opto-isolated inputs. Any ESTOP even would then interrupt 
> the control voltage and relays would open dropping all power.
>
> However things have changed a bit.  With PCs in the mix, rules changed and 
> PCs and control systems could stay active but anything in hardware dangerous 
> to humans was now switched off by the signal interruption.
>
> Enter a wide variety of motor controllers.  The HP_UHU has an active low 
> ESTOP IN/OUT signal.   A low on the ESTOP input shuts off power to the drive 
> control logic.  If the drive has  a fault, it brings this line low too and 
> any other HP_UHU drives are also then pulled into ESTOP mode.   I think this 
> would be better identified as ENABLE rather than ESTOP.
>
> The STMBL AC Servo drive I'm currently working with has an ENABLE high input. 
>  So when Low it's disabled and stepping pulses can't move the motor.
>
> The Gecko Servo drive is disabled by bringing Terminal 5 ERR/RES low.
> http://www.geckodrive.com/support/motor-control-manuals/dc-servo-drives/g320-rev-7.html
>
> The disable is the same on the G250x series.  Bring it low to disable the 
> drive.
>
> So it seems the various drives all use a logic low or contact to ground to 
> disable the drive and let the input float or bring it high to enable the 
> drive.
>
> So where does the ESTOP fit into these systems?  Are people still wiring up 
> an ESTOP to remove driver power (up to 80V for GECKO, as much as 100V or more 
> for DC/AC Servos).
>
> And if the drives enable pin is something controlled by the PC or CNC 
> controller, when is it allowed to be valid?  Should all DC voltages be there 
> first for a given amount of time or should the drives power up and function 
> if the enable pin is already active even if the supply lags behind the enable 
> signal?
>
> Lots of questions.
>
> Thanks
> John
>
>
>
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-- 

Chris Albertson
Redondo Beach, California

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