EMC2 Dependability

[baden0001]

Hello all,

I have been lurking around cnczones forums for a while, trying to gather information about EMC2 and CamSoft.

From what I gather EMC2 closes the servo loop at the CPU processor, while CamSoft can close the loop at a PCI based motion controller. So if the CPU crashes the PCI card will finish its commands but not continue on after that.

My question is this. For those people that have used EMC2, have you ever experienced a CPU failure and what was the effects on the machine that was being ran with it?

Thanks,
Will Baden

[samco]

If the computer/hadware is setup correctly.. The second the watchdog/charge pump circuit detects that the computer isn't there anymore - the machine will go into estop.

That being said. I can't think of one time that emc 'crashed' on me and or caused a bad part (that wasn't caused by me ).

sam

[baden0001]

Sam

How do you have the watchdog timer setup? Is it watching power to the pc, or actually watching a thread in the pc?

You say it is a charge pump, so I am guessing that you have the pc send an output to the charge circuit to drain the cap, but if the cap isn't discharged in time the cap will charge and possibly activate or deactivate a relay that is tied into the E-Stop circuit. Something along those lines?

Thanks for the fast response,
Will Baden

[Seb]

Originally Posted by baden0001 How do you have the watchdog timer setup? Is it watching power to the pc, or actually watching a thread in the pc?

The watchdog setup is dependent on the control hardware you're using.

I'm most familiar with Mesa's Anything I/O boards, which connect to the host PC via PCI or EPP. On these boards (with the hostmot2 firmware), the watchdog runs on the FPGA on the AnyIO board. The emc2 servo loop resets the watchdog each time it runs. The watchdog timeout is configurable from microseconds up to about four seconds. A watchdog timeout of a few times the servo period is normal.

With this setup, if emc2's servo loop stops communicating with the AnyIO board (due to the PC crashing, or emc2 crashing or locking up, etc), the watchdog will bite. When it bites, the watchdog safes the system by switching all the I/O pins to high-impedance mode, weakly pulled high.

The motor amplifiers "downstream" should use an active-low enable, so that the pulled-high "NotEnable" pin causes the motor to shut off.

Hope this makes sense...

[cadmonkey]

Originally Posted by baden0001 You say it is a charge pump, so I am guessing that you have the pc send an output to the charge circuit to drain the cap, but if the cap isn't discharged in time the cap will charge and possibly activate or deactivate a relay that is tied into the E-Stop circuit. Something along those lines?

A charge pump is really simple - it's a relay or solid state switch that is stand alone from the computer and all the other controls (ie it's its own device) and monitors a single pin on the interface for a certain pulse rate. If EMC is running properly that pin will continue to output the pulse rate you've setup in the configuration file (documentation is a bit sketchy on exactly what you get but typically the commercially available CP's aren't that tight on the frequency) and keep the relay (or SS switch) energized powering the drives. If EMC "gets lost" (which I have never had happen - my system specs P3 650MHz, 384MB, on board LPT for motion control and the CP, add on PCI LPT card for limit & homes, a sound card [hey, sometimes you want some tunes when you're doing maintenance...], and a PCI 10/100 card, driving 3 Gecko G203V drives through a DIY high speed opto isolating BOB) the CP signal will stop and the charge pump will in turn shut down the contactor which supplies power to the drives and the spindle, effectively stopping any motion. I've tested it by doing things like pulling a stick of memory, shorting the pin, disconnecting the pin, etc. and it worked each time.

It's nice to be able to boot the computer and do maintenance on the computer (updates, backups, playing some tunes, etc) and not having to worry about the mill being powered up. As soon as EMC starts, the mill is live and ready. Some people choose to have the CP also part of the E-Stop chain - such that if E-stop is pressed, then the CP shuts down also. If I were running big iron - I would too. But on my X3 I feel my sequence of operation is safe.

HTH - YMMV

Greg

edit - forgot I have onboard video too (typically a no-no but the bios on this machine won't let me turn it off so even if I put in a different card it still runs the onboard video.

And in case you got overloaded with my windy explanation I'll answer the thread question - EMC has NEVER died on me during a run or at idle, as long as the computer boots, it runs. Never had to hard reset or pull the plug - this is steppers not servos, but EMC is still counting pulses like an encoder, just instead of an encoder being used, the stepper configurations tie the step pulse generator to the counter so as far as the internal code goes, it's not a big difference.
/edit

[baden0001]

Thanks seb and cadmonkey, you guys answered my question about the watchdog timer. Both ways seem logical to me.

Also, cadmonkey, knowing that you havent had the operating system crash is what I was looking for in this thread. Thanks.

Right now the company I am working for is looking to retrofit an old Okuma LS-N possibly. We are looking for any and all options and trying to weigh them against safety, ease of use and how fixable in case of cpu failure.

Thanks,
Will Baden

[baden0001]

Originally Posted by Seb I'm most familiar with Mesa's Anything I/O boards, which connect to the host PC via PCI or EPP. On these boards (with the hostmot2 firmware), the watchdog runs on the FPGA on the AnyIO board. The emc2 servo loop resets the watchdog each time it runs. The watchdog timeout is configurable from microseconds up to about four seconds. A watchdog timeout of a few times the servo period is normal.

Seb,
I have been looking into this setup a little more and wonder what all drivers are needed for these cards (particularly 5i20) to run with EMC2?

Thanks,
Will Baden

[Seb]

There are two things called "drivers". One is software that runs on the PC and talks to the motion control hardware, and the other is electronics that provides power to the motors.

There are currently two software drivers in emc2 for talking to the 5i20. The older, more stable one is called m5i20. This one has been widely used for a long time, but it's somewhat limited in its capabilities. The other one is called hostmot2. This one is pretty new, but working well for lots of people.

These two drivers let emc2 talk to the 5i20 (hostmot2 supports all the other AnyIO boards as well). But the AnyIO boards by themselves can't drive motors, you need the other kind of driver for that: a power amplifier.

There are tons of options here, and your needs will dictate which you choose. Mesa sells amps for both steppers (7i32) and servos (7i33, 7i29, etc). Lots of other hardware manufacturers sell power amps, Gecko being perhaps the most well-known.

[baden0001]

Originally Posted by Seb There are two things called "drivers". One is software that runs on the PC and talks to the motion control hardware, and the other is electronics that provides power to the motors.

Sorry for being loose with my terms. I was looking for software drivers.

But since you did bring up Amplifier drivers for the servos, which did you end up using?

We are looking to use possibly the OKUMA drivers but that is looking like it wont work out. May end up using Advanced Motion Control Servo Drives.

Thanks,
Will Baden

[Seb]

Originally Posted by baden0001 But since you did bring up Amplifier drivers for the servos, which did you end up using?

My machine is still a work in progress... I haven't selected a servo amp yet.

I'm leaning towards the Mesa 7i29.

[samco]

the mesa hardware can do pwm+dir or +/-10v depending on the interface. That really covers the bulk of drives that are out there.

The new mesa driver (hostmot2) will also do hardware step/direction. (I would not use this though for servos as encoder feedback to emc is a much better solution)

[baden0001]

Originally Posted by Seb My machine is still a work in progress... I haven't selected a servo amp yet. I'm leaning towards the Mesa 7i29.

Good luck on the build! The 7i29 looks like a good way to go.

Will Baden