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  1. #1
    Member Lizmet's Avatar
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    Default Renew old plasma table

    Hi

    Got my hands to old plasma CNC. Its like 30 year old, but mechanical part does not look that bad. Software and controller side, well, things have changed with 30 years
    Company who owned it 30 years said they renewed motors and gearboxes (hope that's true) two years ago.

    Controller needs to be new, think that's not a question.
    But maybe servos are usable?


    At the moment:
    Controller - NUM720
    Controllers - PWME 140x8/16
    X axle motor - BAUMULLER GSF 45-M
    Y axle motor - SOPREL ROS6D20/12A2

    Any good ideas are welcome


    Added also some pictures.

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    Renew old plasma table-plasma_002-jpg   Renew old plasma table-plasma_005-jpg   Renew old plasma table-plasma_009-jpg   Renew old plasma table-plasma_011-jpg  



  2. #2
    Community Moderator Jim Dawson's Avatar
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    Default Re: Renew old plasma table

    That looks like a substantial old machine, but as you say the controls were made when the dinosaurs still roamed the earth.

    Those drives appear to be analog DC drives. And as such are a bit more difficult and expensive to interface than step & direction drives. But depending on your skills and budget they are a very robust system, I still have 30 year old DC drives on my mill and am running modern controls. Having said that, there are some relatively inexpensive modern DC drives that do take a step & direction input that might be worth looking at.

    The alternative would be to replace the motors and drives with modern AC servos.

    If you have the original electrical documentation for the machine it would make the transition easier.

    Jim Dawson
    Sandy, Oregon, USA


  3. #3
    Member Lizmet's Avatar
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    Default Re: Renew old plasma table

    I have some documentation.
    From pictures I can understand whats what in servo controllers.

    In big picture I would like to keep motors and their controllers, those are most expensive parts. If they are bad, then I need to go with with new ones of course. At the moment I just have to figure out, how to feed them step and dir signals. So any ideas and thought are welcome.
    Z axle at the moment works on compressed air, but this is also big no go. I haven't decided jet will I buy new one or add servo/stepper to existing mechanics.


    Plan is to go with those.
    https://www.poscope.com/product/pokeys57cnc/
    https://www.poscope.com/product/plasmasensout/

    Attached Thumbnails Attached Thumbnails Renew old plasma table-plasma_012-jpg   Renew old plasma table-plasma_013-jpg  


  4. #4
    Community Moderator Jim Dawson's Avatar
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    Default Re: Renew old plasma table

    I am not aware of any device that can convert step & direction to +/- 10V analog. You might look into a Dynomotion Kflop/Kanalog as an analog controller, or replace the drives with inexpensive step & direction input DC drives.

    Jim Dawson
    Sandy, Oregon, USA


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    Member Lizmet's Avatar
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    Default Re: Renew old plasma table

    Thank you, signal change is again no go


    Looks like those can to what needed. Just have to check encoders if those are ok for those drives.

    https://www.geckodrive.com/g320x-dig...rvo-drive.html

    And they have reseller in Germany, which is only some thousands kilometres away



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    Default Re: Renew old plasma table

    Have you considered using LinuxCNC+PlasmaC?

    This would allow re-using your existing drives and having full feedback to the controller
    (which you lose if you go to a step/dir system)



  7. #7
    Member Lizmet's Avatar
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    Default Re: Renew old plasma table

    Quote Originally Posted by PCW_MESA View Post
    Have you considered using LinuxCNC+PlasmaC?

    This would allow re-using your existing drives and having full feedback to the controller
    (which you lose if you go to a step/dir system)
    No I haven't. Mostly because for me (not a lot experience in this area) it looks more complicated, but like always, never say never

    Just for curiosity, do "big and famous" machine building companies use full feedback? How big problem it can be for plasma table?



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    Community Moderator Jim Dawson's Avatar
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    Default Re: Renew old plasma table

    I don't know specifically about plasma tables, but all modern ''big & famous'' machine tools use full feedback. The plasma table I am currently building will have feedback.

    Jim Dawson
    Sandy, Oregon, USA


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    Member Lizmet's Avatar
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    Default Re: Renew old plasma table

    I hope that this feedback is not a big problem. Servo and controller should take care of lost step. Computer doesn't know about that, but hope for the best.
    Same time many users have build their plasma tables with steppers without any feedback and looks like they also run those, of course I don't know quality of those.

    To improve all those things and also stability will change all cabling to shielded ones.



  10. #10
    Member Lizmet's Avatar
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    Default Re: Renew old plasma table

    I have been Googeling around and saw of course some Chinese motors and controllers, is this total waste of money and time or have someone had luck with those?

    Also looks like fixing bolts of my old DC motors doesn't match newer AC motors, can it be like this?

    Last edited by Lizmet; 11-28-2020 at 03:02 PM.


  11. #11
    Community Moderator Jim Dawson's Avatar
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    Default Re: Renew old plasma table

    Like anything else, there is some good Chinese equipment and some not so good. Delta servos seem to be OK, as is Wantai equipment. As far as controllers go, they seem to be hit & miss based on some of the threads I have seen, and support seems to be a bit lacking. I would stick with Mach3/4, Centroid, or Dynomotion. All are well supported by either user groups or the manufacturer.

    Jim Dawson
    Sandy, Oregon, USA


  12. #12
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    Default Re: Renew old plasma table

    Have spent some more time in Google and reached to point where every CNC builder in some point reaches - steppers. To be exact, closed loop HV steppers.

    I removed old servo motors, to count how many turns is how much linear movement. For 100 mm linear movement both axes did 8 (more like 7,5) rounds. So one round was ~12,5 mm linear movement.

    Object reference not set to an instance of an object. - it has max 20 nm - for Y
    Object reference not set to an instance of an object. - it has max 12 nm - for X
    Object reference not set to an instance of an object. - controller

    Both have 1.2 degree one step. One turn will then be 300 steps. And from that we will get that with one step it will move 0,0417 mm linear.

    From Hypertherm website got information that cutting speed for 3 mm mild steel 6000 mm/min and for 10 mm mild steel 1500 mm/min.

    So for 3 mm mild steel stepper has to do 480 RPM and for 10 mm mild it has to do 120 RPM.

    20 nm stepper has in 600 RPM ~17 nm
    12 nm stepper has in 600 RPM ~9 nm

    That looks like enough torque. If I calculated everything correctly.

    But is that a good idea???

    Price with matching controllers will be ~1000EUR.

    Last edited by Lizmet; 11-29-2020 at 10:04 AM.


  13. #13
    Community Moderator Jim Dawson's Avatar
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    Default Re: Renew old plasma table

    It looks like those specifications would run your machine.

    I am a bit confused by the description of the motors, they appear to be brushless DC motors, but are advertised as 3 phase steppers. I have seen both 3 phase steppers, and 3 phase brushless DC motors, but the description in the specification is confusing.

    A 1000 line encoder should give you 4000 discrete ''steps'' per revolution.

    You might also look at the servo motors and drives from DMM Technologies. DMM | AC SERVO DRIVE | AC SERVO MOTOR | ROTARY ENCODER I have used several of their systems and have been very happy with the result. Very good documentation, and very good tech support.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Renew old plasma table

    Quote Originally Posted by Jim Dawson View Post
    You might also look at the servo motors and drives from DMM Technologies. DMM | AC SERVO DRIVE | AC SERVO MOTOR | ROTARY ENCODER I have used several of their systems and have been very happy with the result. Very good documentation, and very good tech support.
    Will check those also, price in their store really fine. But with transport and taxes to Europe probably not anymore.

    As I have been reading and looking for this CNC stuff, looks like in Europe there aren't that much builders. Most of the good stuff looks to be over the big ocean



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    Default Re: Renew old plasma table

    Quote Originally Posted by PCW_MESA View Post
    Have you considered using LinuxCNC+PlasmaC?

    This would allow re-using your existing drives and having full feedback to the controller
    (which you lose if you go to a step/dir system)
    This really is the way forward for your machine. As said, retaining the analog motors you have is a robust solution. They can be controlled with a Mesa 7i77 card.

    In Europe contact https://eusurplus.com/ for the hardware. Linuxcnc's Plasmac plasma controller runs rings around other thc's as its a full blown plasma controller integrated to the motion controller.

    If you want to go down this path, ask some questions and share photos of motors on the Linuxcnc forum. https://forum.linuxcnc.org/forum/index
    You will be amazed with the support users will offer.

    Rod Webster
    www.vmn.com.au


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    Default Re: Renew old plasma table

    Quote Originally Posted by rodw View Post
    This really is the way forward for your machine. As said, retaining the analog motors you have is a robust solution. They can be controlled with a Mesa 7i77 card.

    In Europe contact https://eusurplus.com/ for the hardware. Linuxcnc's Plasmac plasma controller runs rings around other thc's as its a full blown plasma controller integrated to the motion controller.

    If you want to go down this path, ask some questions and share photos of motors on the Linuxcnc forum. https://forum.linuxcnc.org/forum/index
    You will be amazed with the support users will offer.

    I will do some reading about that. That's totally new thing for me

    Any same set up users here? Any feedback? Or thoughts why this is bad solution?



  17. #17
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    Default Re: Renew old plasma table

    I'm sure that I'm not the only one who thinks how big issue this full feedback is?

    As I understand from motor drives, then there can't be any lost steps or is that just nice talk and in real life there are lost steps!?!!



  18. #18
    Community Moderator Jim Dawson's Avatar
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    Default Re: Renew old plasma table

    Quote Originally Posted by Lizmet View Post
    I'm sure that I'm not the only one who thinks how big issue this full feedback is?

    As I understand from motor drives, then there can't be any lost steps or is that just nice talk and in real life there are lost steps!?!!

    Closing the loop is what actually makes a servo system. The controller commands the motor to some position, and the feedback makes sure that the motor gets to where it is supposed to go.

    In an analog system, there are no steps to lose. As long as the feedback device (encoder) is working correctly, the analog system will keep trying to achieve the commanded position.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Renew old plasma table

    Quote Originally Posted by Lizmet View Post
    I'm sure that I'm not the only one who thinks how big issue this full feedback is?

    As I understand from motor drives, then there can't be any lost steps or is that just nice talk and in real life there are lost steps!?!!
    With your motors, there are no lost steps becasue they are not step and direction drives. Position feedback is provided an encoder (or sometimes a resolver). The motion controller (eg Linuxcnc) will track the following error (the difference between commanded position and actual position) from the encoder feedback via a PID loop and adjust the position to minimise the following error. This implies you need to tune the servo wen you rebuild your machine.

    Linuxcnc includes the tools to allow you to do that. Here is a simple tutorial which may help you to understand the process. https://gnipsel.com/linuxcnc/tuning/servo.html
    I don't expect you to understand it all but if you look at the Linuxcnc halscope plots, it shows Commanded position (As a velocity) in Green and the following error due to mistuning in light blue.
    You can see the first plots have a classic PID induced following error overrun at the start and finish and after a couple of tweaks, the following error is eliminated.

    So you do have hardware capable of really accurate position control, but you need a motion controller (like CNC) and the appropriate hardware interface (like a Mesa Card - but there are other hardware options). You just need to forget about step and direction for your velocity controlled servos.

    Rod Webster
    www.vmn.com.au


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    Default Re: Renew old plasma table

    According to IEC 60228 there one or two options for moving cables:
    Class 5: Flexible conductor
    Class 6: Very Flexible conductor

    One cable selling company says that class 5 is enough but other says that must be class 6. Price difference is 3 times.

    Any ideas with that?



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