Newbie question about USB & EMC
06 Nov 2010 15:49 #5112
by billooms
Newbie question about USB & EMC was created by billooms
I'm new to this forum. After searching a lot, I see that there apparently is no USB interface for EMC. I read the information about the timing model at wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Emc2HardwareDesign and I see a few threads here that talk about the problem with latency in USB being too much.
I understand the latency concern if the computer is in the loop controlling servo motors. However, if you have an open loop system such as with stepper motors, why the issue? I see USB being used for digital audio (which is very sensitive to timing in a real-time application) at sample rates up to 192KHz. So if USB timing is adequate for something like digital audio, why is it not appropriate for CNC applications with open-loop stepper motors?
I understand the latency concern if the computer is in the loop controlling servo motors. However, if you have an open loop system such as with stepper motors, why the issue? I see USB being used for digital audio (which is very sensitive to timing in a real-time application) at sample rates up to 192KHz. So if USB timing is adequate for something like digital audio, why is it not appropriate for CNC applications with open-loop stepper motors?
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06 Nov 2010 16:57 #5115
by PCW
Replied by PCW on topic Re:Newbie question about USB & EMC
The problem is that even a step motor system is not truly open loop, as there are real time
requirements for various feedback devices including home and limit switches, spindle encoders for
rigid tapping and threading, touch off probes etc.
requirements for various feedback devices including home and limit switches, spindle encoders for
rigid tapping and threading, touch off probes etc.
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07 Nov 2010 00:38 #5124
by billooms
Replied by billooms on topic Re:Newbie question about USB & EMC
Thanks for the reply. OK, I can see that on the limit switches, etc.
I take it there's no way, then, to run EMC on a laptop or other computer without PCI card capability?
I take it there's no way, then, to run EMC on a laptop or other computer without PCI card capability?
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07 Nov 2010 01:16 #5126
by BigJohnT
Replied by BigJohnT on topic Re:Newbie question about USB & EMC
A laptop introduces other issues with hardware in the laptop itself trying to outsmart the system and power down just when your trying to cut something... in general a laptop is only useful for running the sims due to the design of a laptop trying to conserve battery even if your plugged in.
John
John
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17 Nov 2010 10:47 #5365
by KenC
Replied by KenC on topic Re:Newbie question about USB & EMC
I can't remember where I read it, there are those who use laptop & notebook . They disable the power management of the notebook. but I have no idea how to.
It will be cool & slick with an used P3 notebook siting beside the CNC machine.
It will be cool & slick with an used P3 notebook siting beside the CNC machine.
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17 Nov 2010 14:40 #5366
by andypugh
Replied by andypugh on topic Re:Newbie question about USB & EMC
billooms wrote:
You can use the parallel port (if the laptop has one) either directly or to drive one of the EMC-supported parallel-port interfaces.
Examples include:
Mesa 7i43: 48 IO ports configurable as hardware step generators, encoder counters, PWM generators, brushless motor drivers....
www.mesanet.com/fpgacardinfo.html
Pico PPMC: A more "focussed" motion control system than the Mesa one, equally well supported by EMC2
pico-systems.com/motion.html
There is also EMC2 support for the Pluto Parallel port device (both stepper and servo firmwares) but basically don't bother. The 7i43 is very nearly the same price but actually works.
USB to parallel is not an option, but a PCMCIA parallel port should work fine if you get the right one. (You might also find that there is a set of parallel port pins in the laptop dock connector even if there is not one on the back of the machine)
I take it there's no way, then, to run EMC on a laptop or other computer without PCI card capability?
You can use the parallel port (if the laptop has one) either directly or to drive one of the EMC-supported parallel-port interfaces.
Examples include:
Mesa 7i43: 48 IO ports configurable as hardware step generators, encoder counters, PWM generators, brushless motor drivers....
www.mesanet.com/fpgacardinfo.html
Pico PPMC: A more "focussed" motion control system than the Mesa one, equally well supported by EMC2
pico-systems.com/motion.html
There is also EMC2 support for the Pluto Parallel port device (both stepper and servo firmwares) but basically don't bother. The 7i43 is very nearly the same price but actually works.
USB to parallel is not an option, but a PCMCIA parallel port should work fine if you get the right one. (You might also find that there is a set of parallel port pins in the laptop dock connector even if there is not one on the back of the machine)
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18 Nov 2010 14:33 #5405
by dab77
Replied by dab77 on topic Re:Newbie question about USB & EMC
KenC wrote:
for example i'm using a p4 notebook, without problems. just check in the bios for some 'smart' powermanagement settings, and disable in ubuntu all screensavers and monitor/harddisk powersavings.
@andy
the pcmcia to parallel port would be a great thing for me!! can you tell me which one would work? thanks..
I can't remember where I read it, there are those who use laptop & notebook . They disable the power management of the notebook. but I have no idea how to.
It will be cool & slick with an used P3 notebook siting beside the CNC machine.
for example i'm using a p4 notebook, without problems. just check in the bios for some 'smart' powermanagement settings, and disable in ubuntu all screensavers and monitor/harddisk powersavings.
@andy
the pcmcia to parallel port would be a great thing for me!! can you tell me which one would work? thanks..
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18 Nov 2010 14:57 #5406
by andypugh
Replied by andypugh on topic Re:Newbie question about USB & EMC
I have absolutely no experience with them, so you would have to judge from the description.
This one here sounds hopeful though:
www.dpie.com/pcmcia/spp100.html
This one here sounds hopeful though:
www.dpie.com/pcmcia/spp100.html
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