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Thread: Z-axis overshooting sometimes

  1. #37
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    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by dazp1976 View Post
    If I ever get that far where I'm using a VFD I'll be putting it in it's own separate case as far as poss from both the PC and controller case.
    Good idea.... When I put mine in I didn't read about it anywhere and tried to mimic other cases that I had seen that apparently didn't have issues. I am actually beginning to wonder if my old nema23 steppers were not an issue and were powerful enough, but because of the added drives in the enclosure I was getting random EMI issues with lost steps...



  2. #38
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    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by dazp1976 View Post
    If I ever get that far where I'm using a VFD I'll be putting it in it's own separate case as far as poss from both the PC and controller case.
    It is not a problem if everything is wired correctly, a separate cabinet does not always solve an EMI problem, so using a separate cabinet in most cases it can create other problems

    Mactec54


  3. #39
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    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by mactec54 View Post
    It is not a problem if everything is wired correctly, a separate cabinet does not always solve an EMI problem, so using a separate cabinet in most cases it can create other problems
    When you say wired correctly, what do you mean exactly? Shielded cables, no disconnects to the case but emi shields instead, all grounds go to one spot, keep shields on wires inside case especially low power signal cables. What else am I missing? Is there a picture of a perfectly wired control panel with a VFD out there to reference?



  4. #40
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    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by drxlcarfreak View Post
    Good idea.... When I put mine in I didn't read about it anywhere and tried to mimic other cases that I had seen that apparently didn't have issues. I am actually beginning to wonder if my old nema23 steppers were not an issue and were powerful enough, but because of the added drives in the enclosure I was getting random EMI issues with lost steps...
    Most likely where not the problem as many use steppers without problems, it all come's down to wiring in most cases, steppers also are noisy and need shielded cables and good Grounding practice for Shields and Ground wires

    Simple Aluminum shields around noisy parts like stepper drives , VFD Drives low voltage Electronics can save the day, the Shield needs to be Grounded

    Attached Thumbnails Attached Thumbnails Z-axis overshooting sometimes-working-principle-grounded-shield-png  
    Mactec54


  5. #41
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    Default Re: Z-axis overshooting sometimes

    I wouldn’t randomly add cabinets because cabinets do little t address conducted EMI, they might not impact radiated EMI as much as you would think.

    Years ago, (decades? Yikes) I was trying to debug a custom lathe with an old Bandit come controller. We would loose position in the submicrons every cycle of the machine. After realizing that this happened a in conjunction with spindle usage we decided to look into the third party spindle controllers eventually we traced the problem to a relay in the packaged controller. The controller is as a bit of a distance away from the bandit card rack and the rest of the machine control os and the I/O was isolated. Some how the spike from that relay switching each cycle screwed up position maintenance in the Bandit. A snubbing diode (a few cents per drive) ended up solving the problem after the organization suffered for weeks.

    Lesson to be learned here 1. Solve noise issues at the generator. 2. Finding the cause can sometimes be extremely difficult. 3. Hand coding G-Code is very valuable in CNC maintenance as we eventually where able to minimize the G-Code until the problem went away and then created a little routine to test our fix.



    Quote Originally Posted by drxlcarfreak View Post
    Good idea.... When I put mine in I didn't read about it anywhere and tried to mimic other cases that I had seen that apparently didn't have issues. I am actually beginning to wonder if my old nema23 steppers were not an issue and were powerful enough, but because of the added drives in the enclosure I was getting random EMI issues with lost steps...




  6. #42
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    Default Re: Z-axis overshooting sometimes

    So I messed with it last night. I tried doing one item at a time to see what had an impact. I tried the EMI filter first and that immediately cleared up the spindle requiring a debounce to not trip the limits. When doing this I did notice that the non shielded output of the VFD wiring ran right between the non-shielded limit switch wiring and servo wiring. So I wrapped all of the limit switches with emi shielding and copper tape, and grounded the partially shielded servo motors. I also replaced the VFD wiring with the 16/4 shielded wire from automation direct in the case and the entire length making sure that both sides of the shield were grounded to the case and the spindle. It looks like I must have grounded a wire on one of the limit switches because it is showing permanently switched, so I need to address that, but I am hopeful that this will lick my issues.

    I do have a couple more questions about grounding though. I never grounded my case or the cnc itself. I am not sure the reason, but I am guessing that was what I had read in a couple threads most likely. The closest I had is a pin on the BOB on the CNC chassis and another on a touch plate. The only ground from actual panel ground in the case went directly to the VFD which is in a plastic case so there wasn't a chance for the case to be grounded thorough the VFD. Now that I added the EMI filter with it's metal baseplate I noticed that the chassis does now have continuity to ground. Would it be beneficial to ground both sides of the EMI Filter, the VFD and the earth ground all to one spot, or is this sufficient? The 60v, 12v and 5v DC rail grounds now all seem to be grounded, would I want to add them to a star ground as well, or leave them as is? Would it be beneficial to ground the CNC Chassis to the case, or would this add a potential ground loop issue?



  7. #43
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    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by drxlcarfreak View Post
    So I messed with it last night. I tried doing one item at a time to see what had an impact. I tried the EMI filter first and that immediately cleared up the spindle requiring a debounce to not trip the limits. When doing this I did notice that the non shielded output of the VFD wiring ran right between the non-shielded limit switch wiring and servo wiring. So I wrapped all of the limit switches with emi shielding and copper tape, and grounded the partially shielded servo motors. I also replaced the VFD wiring with the 16/4 shielded wire from automation direct in the case and the entire length making sure that both sides of the shield were grounded to the case and the spindle. It looks like I must have grounded a wire on one of the limit switches because it is showing permanently switched, so I need to address that, but I am hopeful that this will lick my issues.

    I do have a couple more questions about grounding though. I never grounded my case or the cnc itself. I am not sure the reason, but I am guessing that was what I had read in a couple threads most likely. The closest I had is a pin on the BOB on the CNC chassis and another on a touch plate. The only ground from actual panel ground in the case went directly to the VFD which is in a plastic case so there wasn't a chance for the case to be grounded thorough the VFD. Now that I added the EMI filter with it's metal baseplate I noticed that the chassis does now have continuity to ground. Would it be beneficial to ground both sides of the EMI Filter, the VFD and the earth ground all to one spot, or is this sufficient? The 60v, 12v and 5v DC rail grounds now all seem to be grounded, would I want to add them to a star ground as well, or leave them as is? Would it be beneficial to ground the CNC Chassis to the case, or would this add a potential ground loop issue?
    It sounds like you are almost there

    You don't want anything to do with the Bob and Mains Power Grounding

    As the Filter is the supply to the VFD Drive the Ground should go to the VFD Drive then the VFD Drive Ground to the Spindle Ground

    The main input Power Ground to the Filter and to the Star Point Ground, for all your other Ground connections Power Supply Etc

    All your equipment Grounds should all go to ( 1 ) Point ( Star Ground ) so you add a Bus or a Stud and mount all Grounds to that in to your Cabinet or a Ground Plane Plate

    I don't like wrapping cables leaving the foil exposed, as that wrapping can carry EMI and spread it every where

    Any of the methods attached will work for Star Point Grounding

    Attached Thumbnails Attached Thumbnails Z-axis overshooting sometimes-gounding-post-case-png   Z-axis overshooting sometimes-ground-buss-png   Z-axis overshooting sometimes-grounding-bar-png  
    Mactec54


  8. #44
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    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by mactec54 View Post
    It sounds like you are almost there

    You don't want anything to do with the Bob and Mains Power Grounding

    As the Filter is the supply to the VFD Drive the Ground should go to the VFD Drive then the VFD Drive Ground to the Spindle Ground

    The main input Power Ground to the Filter and to the Star Point Ground, for all your other Ground connections Power Supply Etc

    All your equipment Grounds should all go to ( 1 ) Point ( Star Ground ) so you add a Bus or a Stud and mount all Grounds to that in to your Cabinet or a Ground Plane Plate

    I don't like wrapping cables leaving the foil exposed, as that wrapping can carry EMI and spread it every where

    Any of the methods attached will work for Star Point Grounding
    Fair enough. Sounds like one more ground to go then!

    Yeah, I wasn't a fan of it being exposed so I wrapped most of it in electrical tape just so it wouldn't accidentally short into something. Is there something better to use?



  9. #45
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    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by drxlcarfreak View Post
    Fair enough. Sounds like one more ground to go then!

    Yeah, I wasn't a fan of it being exposed so I wrapped most of it in electrical tape just so it wouldn't accidentally short into something. Is there something better to use?
    Other than better cable to start with, yes shorting is the main problem when using exposed foil or braid

    Mactec54


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