Hallo, The accepted wisdom with commutator d.c. servo motors was always to have a contactor break the motor wires and short the motor armature through a resistor. The shorting of the armature works as a brake to stop the motors reasonably quick. The resistor in series is needed so the armature shorting current does not become greater than the demagnetizing current of the permanent magnets. 2 or 3 times maximum stall current should be ok.
On modern 3 phase servos this arrangement has fallen away since a rotating field is needed to move the motor. I am not familiar with the exact arrangement in those installations. Jan de Kruyf. On Mon, Apr 5, 2010 at 3:38 PM, Erik Christiansen <dva...@internode.on.net> wrote: > I'm about to wire in an NVR (No-Volt Release), i.e. a latching relay, > set by a momentary pushbutton [1], but have a couple of questions: > > A) Is it safe to interrupt Motor Power to my 7i40s, with hairy great > inductive motors on their outputs? (OK, mostly resistive under load, > but then back EMF might also be deadly if V+ is open-circuited?) > > I can't use the 7i40's active low enable inputs, because they're in > the ribbon cable to the 5i20. > > That means we have to go via the 7i37 inputs and the EMC2 software, > if we're to avoid potentially stressing the 7i40s. > > Ah ... maybe interrupt Motor Power before the filter capacitors? That > leaves somewhere to dump back EMF, and should be gentler on the > H-bridges. (A bit rough on a relay though, with zero volts on the > capacitors at start-up. A fat MOSFET would handle it better.) > > B) What about a charge-pump? i.e. Estop if the controller goes down or > loses the plot. Or does the 5i20 do that in the FPGA? > > I've read the "5i20 Anything I/O Manual", but the Hostmot2 section is > a bit thin. (Re the wiki, see below.) > > But even if the 5i20 does disable the 4 H-bridges, that still leaves > the spindle whirring away. Does it tell EMC, so that I can > "net estop-out => some_7i30_output", to interrupt the Estop chain, > and cut spindle power as well? > > Finding only http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?EstopChain in > the wiki, which just points to > http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?MazakEstopChain , I wonder > if: > > C) Is the HAL "estop latch" mentioned there just FYI? Point 26 raises > the issue of ESTOP_RESET, but point 27 says "ESTOP_RESET comes from > the core of EMC, and is asserted when the machine is taken out of > ESTOP (by hitting F1)." > > So there appears to be no physical input needed for that. (But maybe > I should spraypaint F1 green.) > > D) Have I missed (in the wiki) a concise schematic showing a typical > Estop chain, useful relay contacts, and estop-in & estop-out wiring > and HAL config? Or is that a ToDo that I'm cheerfully walking into? > ;-) > > I hope that I'm expressing all that clearly, it's nearly midnight here. > > Erik > > [1] I'll try to use the existing Big Red Button on the mill, even if I > have to add a relay in the control box, to gain a free pair of > output contacts to go to the Estop chain. > > -- > You really HAVE to have a hardware E-stop! > - Jon Elson on emc-users, 14 Jun 2008. > > ------------------------------------------------------------------------------ > Download Intel® Parallel Studio Eval > Try the new software tools for yourself. Speed compiling, find bugs > proactively, and fine-tune applications for parallel performance. > See why Intel Parallel Studio got high marks during beta. > http://p.sf.net/sfu/intel-sw-dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
