On Tuesday 11 April 2017 14:53:10 Peter C. Wallace wrote:
> On Tue, 11 Apr 2017, Valerio Bellizzomi wrote:
> > Date: Tue, 11 Apr 2017 20:25:04 +0200
> > From: Valerio Bellizzomi <vale...@selnet.org>
> > Reply-To: "Enhanced Machine Controller (EMC)"
> > <emc-users@lists.sourceforge.net>
> > To: EMC Users <emc-users@lists.sourceforge.net>
> > Subject: [Emc-users] mesa setup
> >
> > Hello,
> > I am looking at the 7i76 manual and at the TB2 connector pinout
> > (page 5), it is evident where to connect the step and dir wires, it
> > is less evident where to connect the enable+ and enable- wires for
> > each motor driver.
> >
> > What is the usual setup ?
>
> Normally Step drive "enable" pins are actually disable pins
> so the drive functions normally without these being connected
>
> In addition typically step drives are fairly safe in that unlike servo
> drives, they will not move without step pulses
>
> So its most common that these pins are just ignored
>
> If they are actually enable pins (powered to enable drive),
> they can be driven by a spare step/dir pin or 7I76 field output
>
> If your enable pins are actually disable pins (and you must power them
> to disable the drive), and you feel you need to disble them for things
> like emergency stop, perhaps the best solution is to drive them with a
> normally closed relay contact so the drives are disabled until the
> relay is energized
I do not disable a stepper driver with anything but the main power
switch. Using it for an emergency stop will if its moving when the stop
is activated, allow it to continue to move/coasting, at the very least
unhoming the axis. That is not what you want to do for an emergency
stop, you want it to stop under controlled deceleration as fast as the
stepper driver can stop it, under which conditions you have not lost
your home, while at the same time stopping it as rapidly as it can be
stopped.
The exception to that was a calculated risk in the case of my Sheldon
lathe, as I wanted to be able to effectively shut down the power hogs,
without having a jungle of power strips to turn on and off, while
leaving the pi and the interface powered up 24/7 so amanda can back it
up every night along with the rest of my machines, so I used a couple 40
amp ssr's to switch motor and spindle power on and of with the machine
enable, so power is killed when there is a fault. That reduces the power
drain to about 15 watts once the dpms has powered down the 11 watt
monitor.
But both steppers are powered from conventional transformers, bridge
rectifiers and a good sized filter capacitor type power supply's, so the
supplies hold up for that fraction of a second it takes to bring the
motors to a halt. However, that still means it will be un-homed by the
fraction of a step where it lost power, and the step condition the
driver powers back up, a potential half a full step positioning error,
so I should net that in the hal file so as to unhome on a fault. Belt
and suspenders theory. ;-)
Anyway thats my theory on un-powering a stepper with the drivers disable,
generally, I don't do it.
> Peter Wallace
> Mesa Electronics
>
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