Re: [Emc-users] Estop strategy for Hostmot2 (7i40 x 2 + 7i37)
On Mon, Apr 05, 2010 at 07:56:51AM -0700, Peter C. Wallace wrote: On Mon, 5 Apr 2010, Erik Christiansen wrote: 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?) Should be, the 7I40 has overvoltage protection, but this cannot be depended on for repeated faults (board thermal limit) That scared me off at first, but reading the manual's description of the in-built load dump protection, I'm sufficiently comforted to give it a go. [1] A good Estop system is to disconnect servo primary power and at the same time discharge the servo filter capacitors with a resistor for .5 - 1 second decay time. This will brake the motors so the voltage decay should not be too fast. Realising that the back-emf sees the parasitic FET diodes in the H-bridge as a bridge rectifier, much like the one Andy used to protect exploding relays, It finally sinks in that that provides dynamic braking of all motors with one shunt. This scheme should also keep the 7i40 powered up for the peak of the load dump, even with the supply disconnected, so I don't need an external load dump protector. Even using a FET or two (held on by a contact on the estop relay) to interrupt the total supply current (which my relays won't handle) this is neater than motor-side protection. Your at the same time advice is just sinking in. There's no need for dead-time between supply disconnection and shunt application. (It just get simpler. :-) One second decay seems a bit slow, to this novice. The motors would stop well before zero volts, but every 0.5s delay moves the hard limit switches further from the end of travel, reducing usable table area. I don't think I'd want soft limit switches even further in, then. Time to just build and try it now, I think. Many thanks for the sagacious advice. Erik [1] Found a bunch of 29mm square self-adhesive Al heatsinks, just made to stick onto each quartet of FETs on the 7i40. OK, they're only contacting the cases, but must provide some additional thermal margin. -- The advantage of a bad memory is that one enjoys several times the same good things for the first time. - Friedrich Nietzsche -- Download Intel#174; 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
Re: [Emc-users] Estop strategy for Hostmot2 (7i40 x 2 + 7i37)
A DPST will perform the function fine, unless you want DPDT for some other reason. Roland On 6 April 2010 14:39, Erik Christiansen dva...@internode.on.net wrote: On Mon, Apr 05, 2010 at 06:08:15PM +0200, Jan de Kruyf wrote: 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. I hadn't thought of that, and like it a lot. It's simple, and doesn't muck with the power supply. It does though require a DPDT relay for each motor, or an 8PDT relay for all four. Fortunately, I have a tube of 25A DPDT relays in the junkbox. Choices. :-) Erik -- An idealist is one who, on noticing that a rose smells better than a cabbage, concludes that it will also make a better soup. -- H.L. Mencken -- Download Intel#174; 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#174; 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
Re: [Emc-users] Estop strategy for Hostmot2 (7i40 x 2 + 7i37)
On Mon, Apr 05, 2010 at 07:56:51AM -0700, Peter C. Wallace wrote: A good Estop system is to disconnect servo primary power and at the same time discharge the servo filter capacitors with a resistor for .5 - 1 second decay time. This will brake the motors so the voltage decay should not be too fast. Many thanks for that solution. It needs only one SPDT relay, while motor disconnection and shorting needs four, plus 4 power resistors. 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? There is a watchdog in the FPGA. It will reset all I/O to the power up state if not accessed at the preset interval. I would not depend too much on this as a software/hardware failure of some kind might let the watchdog petting thread continue while the rest is going crazy. Yes, especially if that thread is time-sliced, like the other threads that we can specify invocation intervals for, then the watchdog is petted even if everything has ground to a halt. =8-(( Hmmm, if we were to toggle the pet output in e.g. the path planner thread, and only output the current state in the device driver which talks to the FPGA, after passing the toggling value along the chain of motion controlling threads, much like an Estop chain, then all vital threads have to be scheduled, and execute a vital section of code, or the watchdog bites. It is probably easier to have each motion-related thread notify the petting thread, via RTAPI, that it has run. The watchdog is then only petted if no needed thread has gone incommunicado. (Passing a toggling value between threads is more programming effort, and subject to greater timing variation, due to scheduling vagaries.) Even on embedded systems which controlled only telephone calls, and thereby money I'll admit, I've always been careful never to allow a single thread to pet the watchdog, because it's as unreliable as you've warned. Its watchdog will disable all I/O, (turn off all 7I37 outputs for example) so this will happen automatically on a watchdog bite but an output in series with the Estop chain is also good so EMC has an input to the chain for less severe faults/user-input Oooh, that's nifty bonus, that I hadn't expected. Thanks. Erik -- Meskimen's Law: There's never time to do it right, but always time to do it over. -- Download Intel#174; 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
Re: [Emc-users] Estop strategy for Hostmot2 (7i40 x 2 + 7i37)
Indeed, FWIW, it's called dynamic braking. Yeat another UBI (Useless Bit of Information) :) On 04/06/2010 07:39 AM, Erik Christiansen wrote: On Mon, Apr 05, 2010 at 06:08:15PM +0200, Jan de Kruyf wrote: 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. I hadn't thought of that, and like it a lot. It's simple, and doesn't muck with the power supply. It does though require a DPDT relay for each motor, or an 8PDT relay for all four. Fortunately, I have a tube of 25A DPDT relays in the junkbox. Choices. :-) Erik -- Download Intel#174; 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
Re: [Emc-users] Estop strategy for Hostmot2 (7i40 x 2 + 7i37)
On Mon, 5 Apr 2010, Erik Christiansen wrote: Date: Mon, 5 Apr 2010 23:38:59 +1000 From: Erik Christiansen dva...@internode.on.net Reply-To: emc-users@lists.sourceforge.net To: emc-users@lists.sourceforge.net Subject: [Emc-users] Estop strategy for Hostmot2 (7i40 x 2 + 7i37) 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?) Should be, the 7I40 has overvoltage protection, but this cannot be depended on for repeated faults (board thermal limit) 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.) A good Estop system is to disconnect servo primary power and at the same time discharge the servo filter capacitors with a resistor for .5 - 1 second decay time. This will brake the motors so the voltage decay should not be too fast. 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? There is a watchdog in the FPGA. It will reset all I/O to the power up state if not accessed at the preset interval. I would not depend too much on this as a software/hardware failure of some kind might let the watchdog petting thread continue while the rest is going crazy. 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? Its watchdog will disable all I/O, (turn off all 7I37 outputs for example) so this will happen automatically on a watchdog bite but an output in series with the Estop chain is also good so EMC has an input to the chain for less severe faults/user-input 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#174; 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 Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your ()_() signature to help him gain world domination. -- Download Intel#174; 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
Re: [Emc-users] Estop strategy for Hostmot2 (7i40 x 2 + 7i37)
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#174; 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#174; 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
Re: [Emc-users] Estop strategy for Hostmot2 (7i40 x 2 + 7i37)
On 5 April 2010 13:38, Erik Christiansen dva...@internode.on.net wrote: 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 don't know how relevant this is to your situation and the 7i40s but I found that an effective way to prevent relays exploding on my Robotwars robot (3 x 24V 750W motors, peak current 300A) was to wire conventional (and inexpensive) bridge-rectifier modules into the circuit with the AC terminals across the motor, and the +ve and -ve to the batteries. That way any voltage Vcc + 0.6V is shunted back into the supply lines. -- atp -- Download Intel#174; 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
