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.

The disable is the same on the G250x series.  Bring it low to disable the 

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 

Lots of questions.


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