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  1. #1
    Join Date
    Jul 2004
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    79

    Mach3 or EMC for servos

    I'm working on designing a cnc controller for a knee mill (bridgeport clone).

    I want a closed loop servo system. However, I have some confusion about the software.

    I've read elsewhere that Mach 3, while great for steppers, is not capable of running a true closed loop servo system. I'm not sure that this is true because I've seen many machines described on this site that use Mach 3 with Gecko or Viper servo drivers.
    Can anyone provide any more details on this?

    In addition, there is also the EMC software. At this point, I haven't done too much research on the EMC. Is there any advantages to this software?

    Thanks in advance for any input.

    mtechserv

  2. #2
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    I don't know about viper, but the Gecko servo drives close the loop at the drive not in the control software. So, with a Gecko servo drive, as far as Mach or EMC are concerned you are running a stepper system. If you want to have the loop closed in the control software, you will choose EMC2, if you want to allow the drive itself to close the loop you can choose either EMC2 or Mach.

    Alan

  3. #3
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    Also mach with a Galil option card should close the loop.
    In this case you can use non-intelligent drives with analogue input.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  4. #4
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    You can also run Mach3 closed loop with this.
    http://www.vitalsystem.com/web/motion/dspmc.php
    Gerry

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  5. #5
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    Al and Gerry,

    Correct me if I am wrong, but aren't both of those options closing the loop in the external controller and not in the control software (Mach).

    Alan

  6. #6
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    Yes, but why does it matter? I would think that letting the hardware do it would allow much higher encoder counts and higher speeds.
    Gerry

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    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  7. #7
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    Jul 2004
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    Thanks for all of the feedback so far.

    This brings up a couple more questions:

    Alan mentioned that when using Mach with servos, the software still works as though it is driving steppers. So, what would I be gaining anything by using Gecko servo drives (or Vipers or any other Servo drive) with Mach3?
    What happens if the servo starts to lose position for some reason?

    mtechserv

  8. #8
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    Quote Originally Posted by mtechserv View Post
    This brings up a couple more questions:

    Alan mentioned that when using Mach with servos, the software still works as though it is driving steppers.
    With the Galil and DSPMC devices, it does not. The external devices handle all the motion and feedback.

    Regardless of what servo drives or methods you use, if position is lost, either the drives will fault or the motion controller will stop motion. With Geckos this happens at 128 encoder counts. The other devices probably give you more control over what happens and when. But I'm not sure on that.
    Gerry

    UCCNC 2017 Screenset
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  9. #9
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    Quote Originally Posted by mtechserv View Post
    So, what would I be gaining anything by using Gecko servo drives (or Vipers or any other Servo drive) with Mach3?
    Do you mean vs steppers? Servos can give you more resolution, more power, and higher speeds. And with a step/direction drive like the Gecko or Viper, they will stop if something goes wrong, where a stepper will keep going.

    But, keep in mind that you'll need to build a circuit to stop all the drives when one faults, otherwise the other axis will continue to move while the one has stopped.
    Gerry

    UCCNC 2017 Screenset
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    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  10. #10
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    Jul 2004
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    Gerry,

    Thanks for the feedback.

    I didn't word my questions very well.
    I am aware of the resolution and power advantages of servos. I was more confused about positional errors with this type of setup. But your answer cleared it up.

    I have other commercially produced CNC machinery in my shop, but this is my first experience with designing / building my own controller. My only related experience in this area is wiring / programming PLC's, but I've never done much with servo or stepper controllers.

    Thanks for the help.

    mtechserv

  11. #11
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    Jul 2003
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    1753
    with inexpensive cards from mesa, pico systems, vital systems.. ( http://wiki.linuxcnc.org/cgi-bin/emc...orted_Hardware ) Some for under $100 allow for very high encoder counts. The hardware is dumb and just counts the encoder and sends the count to emc. Also outputs pwm +/-10v or whatever to control the servo amps. (so emc closes the loop)

    sam

    Quote Originally Posted by ger21 View Post
    Yes, but why does it matter? I would think that letting the hardware do it would allow much higher encoder counts and higher speeds.

  12. #12
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    Gerry, you asked, Yes, but why does it matter?

    Quote Originally Posted by ger21 View Post
    With a step/direction drive like the Gecko or Viper, they will stop if something goes wrong, where a stepper will keep going.

    But, keep in mind that you'll need to build a circuit to stop all the drives when one faults, otherwise the other axis will continue to move while the one has stopped.
    Gerry,

    I think that you just answered you own question.

    Alan

  13. #13
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    With Galil all the motion trajectory, interpolation and PID control is done in the PCI card, Mach acts as front end operator software only, if a fault is detected via one axis feedback, all axis can be shut down within the card.
    With all axis feedback closed back to the card, features like electronic gearing, electronic cam, constant surface feed, threading and feed/rev can be done with encoder count gearing.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  14. #14
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    Quote Originally Posted by Al_The_Man View Post
    With Galil all the motion trajectory, interpolation and PID control is done in the PCI card, Mach acts as front end operator software only, if a fault is detected via one axis feedback, all axis can be shut down within the card.
    With all axis feedback closed back to the card, features like electronic gearing, electronic cam, constant surface feed, threading and feed/rev can be done with encoder count gearing.
    Al.
    Al,

    That was what I expected. So, basically Mach is just a GUI for the card. Just curious what is the cost for a Galil controller card?

    Alan

  15. #15
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    Quote Originally Posted by mtechserv View Post
    I'm working on designing a cnc controller for a knee mill (bridgeport clone).
    mtechserv
    Not to confuse things more here, but unless you are already an electronics tech or want to learn to be one, you might want to consider a integrated controller approach. We use the Gecko drives and MACH3 but our interface cards and "Smart" power supply remove the disadvantages of a DIY controller project. You can get 3, 4 or 5 axis servo systems (or steppers) and the central shutdown on drive fault is standard. So is softstart (AC side) power off to all motors on fault, and protection against overload, overvoltage or overtemp. Out of hundreds of Gecko servo drives we had seen less than a 1% failure rate in our controllers.

    We use differential signaling for the encoders to make them reliable in noisy conditions.

    Motors come with 20 ft power cables (can be shortened) plug type power connectors, and 25ft color coded encoder cables.

    We ship every product with MACH3 custom profiles and custom screens. The Interface that connects to the PC can be upgraded to support controlling a VFD for Spindle speed from the g-code or operators screen.

    The Gecko Servo drive monitors the motor shaft position VS the commanded position from the software and develops an error voltage that it uses to correct minor position anomalies. If it falls outside the 128 count limit it indicates that even if your motor could catch up (or slow down) to get back on toolpath it may leave you with a bad cut. Typically you get drive faults for one of 3 reasons: You asked the motor to provide acceleration faster than it can, you ran past what the motor drive can furnish in power (amps) or you hit an obstacle and it can't move the load fast enough. In the final one you want something that will turn things off BEFORE it ruins expensive electronics.

    In our system any drive fault (for any reason) shuts down everything (including stopping MACH) and reports via the screen what shut things down and which Gecko Faulted.

    We use a 5 axis servo table in daily production (Actually 4 axis with a dual gantry drive setup.). We have managed to ram it into the hard stops numerous times. In each case the Smart power controller shut things down before there was any damage to man or beast (gecko).


    TOM Caudle
    www.CandCNC.com
    Totally Modular CNC Electronics
    http://www.CandCNC.com/RouterPakPriceChart.htm

  16. #16
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    Dec 2003
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    Quote Originally Posted by acondit View Post
    Al,

    That was what I expected. So, basically Mach is just a GUI for the card. Just curious what is the cost for a Galil controller card?

    Alan
    The Galil cards run from anywhere from $1,500.00 to $3,500.00, not cheap, but ebay is a good source, the legacy cards I use, I have picked up for as low as $50.00.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  17. #17
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    Jul 2004
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    Thanks again for all of the input.

    Torchhead,

    I have seen your products before, when I initially started doing some research on this project. I am impressed with some of the equipment you have. The prices seem to be very reasonable as well.
    I'm not an electronics tech, but I am trying to learn more. I own a small machine shop and design service. Currently I design and build a lot of manufacturing tooling and small machines. Most of the machines I build are simple, with basic motor starters, VFD's, pnuematics, and sometimes small logic controllers. I've been filling my spare time by taking motor control and PLC classes at some local schools.
    So, I'm really doing the "build from scratch" approach for the educational value. I don't expect it to be easy, but I will definetely learn a lot from it.
    I've never worked with the small stepper / servo drives or Mach software. So, that's why I was a bit confused over the exact functionality / capabilties of the Gecko type drives.

    Al,

    Thanks for the recomendation on the Galil mc option. I've had some experience with Galil equipment a couple years ago. Just curious, what "non-intelligent" drives would you recommend?

    I've seen several, but have no way of knowing the reliability of any of them.



    Thanks again,

    Brian

  18. #18
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    Dec 2003
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    24216
    Quote Originally Posted by mtechserv View Post
    Al,

    Thanks for the recomendation on the Galil mc option. I've had some experience with Galil equipment a couple years ago. Just curious, what "non-intelligent" drives would you recommend?
    I've seen several, but have no way of knowing the reliability of any of them.
    Thanks again,
    Brian
    I have mainly used Advanced Motion Controls, they also have a helpful technical design section.
    Other makes are Copley Controls and Aerotech, both also make nice easy to use products.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  19. #19
    Join Date
    Feb 2007
    Posts
    77
    The Mach/Galil combination works very well. I happen to know this because I wrote the current encarnation of the Galil Plugin for Mach. On the Mach forum, there is a list of compatible Galil controllers in the "Galil" section. I like the Ethernet Econo models (DMC-21x3). They provide a great bang for the buck if you are not needing analog inputs. The remote nature of Ethernet means that you only have one cable from the Mach host PC to the machine control cabinet.

    I'm also writing Plugins for the Mesa 5i20, 5i22, 5i23, and 7i43 boards. So pretty soon, there will be lots of choices to run analog servos with Mach. Galil, Vital, and Mesa.

    Steve

  20. #20
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    Quote Originally Posted by smurph View Post

    I'm also writing Plugins for the Mesa 5i20, 5i22, 5i23, and 7i43 boards. So pretty soon, there will be lots of choices to run analog servos with Mach. Galil, Vital, and Mesa.

    Steve
    Good news.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

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