> > -----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
> 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.
> > 
> > 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
> think
> > this particularly apply to DC motors since failure mode close may cause it
> to
> > 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.

Yes I think so to but other means might also be good enough. I worked at a 
quite handy machine for some time, just put a piece of wood inside and press 
the pedal. I still have all arms, hands and fingers as do the man who worked 
there before but one misstake and it would hav been gone.

> 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
> now.

I think they still are strict.

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

I think so to.

I also think some electronic devices may be approved but it's incredible hard 
to check something invisible so I think they leave this to the manufacturer.

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