On Wed, 4 Apr 2018, John Dammeyer wrote:
Date: Wed, 4 Apr 2018 12:57:03 -0700
From: John Dammeyer <jo...@autoartisans.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "'Enhanced Machine Controller (EMC)'" <emc-users@lists.sourceforge.net>
Subject: [Emc-users] ESTOP and Drive Enable handling.
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
I think low cost/low power/not so dangerous drives (Gecko, Leadshine, etc step
drives ) use a disable pin rather than an enable pin because a large number of
users ignore the drive enable/disable so they will "just work" when
unconnected.
Some older analog servo drives have disable pins also (which is a quite bad
idea) If you want to use drive with a disable input and you want to disable it
with EStop or a LinuxCNC signal I would use a relay (or a form B OPTO) to
disable the drive until EStop and LinuxCNC give the go-ahead.
LinuxCNC has an enable signal (axis/joint.n.amp-enable-out) thats useful for
this function, but drive enable should be guaranteed to revert to the disabled
state if LinuxCNC or the host PC crashes or loses power so also requires a
watchdog or chargepump circuit.
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Peter Wallace
Mesa Electronics
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