> -----Original Message-----
> From: Nicklas Karlsson [mailto:nicklas.karlsso...@gmail.com]
> Sent: April-08-18 9:52 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] ESTOP and Drive Enable handling. (SAFE OFF)
> On Wed, 4 Apr 2018 12:57:03 -0700
> "John Dammeyer" <jo...@autoartisans.com> wrote:
> > In the past ESTOP appeared to be pretty simple a 12V or 24V control
> 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
> Then working with frequency inverters I come upon the term "safe torque
> off" and are pretty sure there are special requirements on this signal. I
> this particularly apply to DC motors since failure mode close may cause it
> run at full speed.

I believe that the ESTOP signal should remove power to relays that supply
energy to anything that could hurt a human.  That means, motor voltage,
heater voltage, lasers and pneumatics.   Once the ESTOP is released that
same set of relays must require a separate action to re-enable them.   SO
that someone doesn't just release the ESTOP and a motor starts up cutting
through the rest of a man's arm for example.

Keeping the ENABLE as a switch that must be cycled off and then on allows
the software to also disengage all motion.  Then, if safety warrants it, the
drives can be re-enabled and JOG feature used to pull back our out or away
from the human pinned by it.  Way back when I worked in The Netherlands
there were pretty strict rules about what ESTOP did and how equipment
behaved after ESTOP was released.  I don't know what the regulations are

And ideally the separate ESTOP circuit must be Normally closed so a broken
wire has the same effect.


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