Adding a 4th axis and have a few questions...


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    Default Adding a 4th axis and have a few questions...

    Hi Guys,

    I just ordered a 4th axis for my Fadal. Im wondering how things work with a rotary axis brake in KmotionCNC. Can i set it up to release the brake and enable axis automatically whenever it encounters a line of code with an A move in it? And clamp/disable axis again when its done moving the A axis? Or would i need to do this with an M code? The Mazak I used to use at my old shop would do it all automatically and im hoping there is some way to set it up the same.

    Also, wondering how Kmotioncnc handles multiple rotations. For example if i move to A450, and then move back to A0, does it rotate 90 degrees or 450?

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    Default Re: Adding a 4th axis and have a few questions...

    Hi mmurray70,

    Im wondering how things work with a rotary axis brake in KmotionCNC. Can i set it up to release the brake and enable axis automatically whenever it encounters a line of code with an A move in it? And clamp/disable axis again when its done moving the A axis?
    Most likely you would need an MCode before the movement to: Enable the axis, Add A to the Coordinate System, Unclamp, and delay until unclamped. Then after A movements another MCode to: Clamp, Delay, Disable, and Remove A from the Coordinate System.

    If the A Axis accelerates very slowly and the Clamp/Unclamp fast then it might be possible to detect the start and stop of A motion and automatically unclamp and clamp. But the risk would be that the motion begins before it is fully unclamped or that other motions begin before it has been fully clamped.

    Also, wondering how Kmotioncnc handles multiple rotations. For example if i move to A450, and then move back to A0, does it rotate 90 degrees or 450?
    It would rotate -450 degrees. If you only want the modulo 360degree portion you can use an MCode to convert the angle first (change 450 to 90) then the movement to A0 would be -90 degrees. See the Modulo360.c example below.

    Code:
    #include "KMotionDef.h"
    
    #define CNTS_PER_DEG 1000.0
    #define AXISA 4
    
    double modf(double, double*); // returns integer part with more than 32-bit precision
    
    double floor(double x) // truncate down toward -ininity
    {
       double y; 
       return (modf(x, &y) < 0 ? y - 1 : y);
    }
    
    main()
    {
        double dest = chan[AXISA].Dest;
        double cnts = CNTS_PER_DEG * 360.0;
        EnableAxisDest(AXISA, dest - (floor(dest/cnts)) * cnts);
    }
    Regards



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    Default Re: Adding a 4th axis and have a few questions...

    Quote Originally Posted by TomKerekes View Post
    If the A Axis accelerates very slowly and the Clamp/Unclamp fast then it might be possible to detect the start and stop of A motion and automatically unclamp and clamp. But the risk would be that the motion begins before it is fully unclamped or that other motions begin before it has been fully clamped.
    Ok yeah thats a great idea. So i could put something in the forever loop to try and catch the start of the movement and then unclamp. I could probably play around with it and get it to feedhold, wait for it to unclamp and resume when ready. I believe my 4th axis has clamp and unclamp verification sensors which I could use.

    But one question... If i have to disable the A axis and remove A from the coordinate system, will I get an error when Kmotion reads a block of code with an A value?



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    Gold Member TomKerekes's Avatar
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    Default Re: Adding a 4th axis and have a few questions...

    Hi mmurray70,

    If i have to disable the A axis and remove A from the coordinate system, will I get an error when Kmotion reads a block of code with an A value?
    Yes that would be a probleml. Do you really have to disable the A Axis? Is it open loop or closed loop? You might leave the Axis Enabled but just set the PID gains to zero and maybe the Output Gain to zero to eliminate any drive output.

    Another approach might be to use a "dummy" A axis that is always enabled and configured that just generates the trajectory. Then have another Axis be enabled/disabled and follow the dummy axis.

    Regards



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    Default Re: Adding a 4th axis and have a few questions...

    Quote Originally Posted by TomKerekes View Post
    Hi mmurray70,

    Yes that would be a probleml. Do you really have to disable the A Axis? Is it open loop or closed loop? You might leave the Axis Enabled but just set the PID gains to zero and maybe the Output Gain to zero to eliminate any drive output.

    Another approach might be to use a "dummy" A axis that is always enabled and configured that just generates the trajectory. Then have another Axis be enabled/disabled and follow the dummy axis.

    Regards
    It will be closed loop DC torque mode servo with encoder feedback to Kanalog. So I guess I will probably need to disable it each time. I supposed I could set gains to zero but what about the motor "drift" that is common with most drives?

    The dummy axis idea is great too. Seems like that should take care of it. Ill post updates and more questions when it shows up.



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    Default Re: Adding a 4th axis and have a few questions...

    Hi mmurray70,

    I supposed I could set gains to zero but what about the motor "drift" that is common with most drives?
    Actually by setting the PID gains to zero I believe the Integrator and Output will freeze wherever they are. So assuming the motor was still and under no load then the Output should be frozen at the value that generates little or no drive. Otherwise to be sure of no drive you will need to also disable the drive.

    Good luck,
    Regards



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    Default Re: Adding a 4th axis and have a few questions...

    Hi Guys,

    My 4th axis showed up today and I ran into a bit of a problem. I was 95% sure this a DC servo model but after pulling the cover i ended up getting the much less common AC version

    What do I do now?? The servo is a Yaskawa sgmg-08k3a-ya11. Specs online say 750w 200v and 4.4a continious. Is there any way to use this without spending a ton of time and money on it?

    Attached Thumbnails Attached Thumbnails Adding a 4th axis and have a few questions...-20180313_001850-jpg  


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    Default Re: Adding a 4th axis and have a few questions...

    That is a bit of an odd spec motor.
    My initial thought was just replace it, but 750W 1500RPM motors are not common.

    All I've found is that it uses a 2048CPR encoder, but not any other details. I'm guessing it outputs the full complement of ABZ and UVW, given the number of pins on the replacement encoder pictures I've found, so it could possibly be made to work with a new drive, if you can figure out the required settings.

    I think I'd be measuring the motor up, and seeing what it could be replaced with, as it's likely to be the less risky option.



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    Default Re: Adding a 4th axis and have a few questions...

    I think you'ld want your clamp and un clamp to be modal M codes, active only when your 4th axis is installed. If you're doing 4th axis continuous machining, you don't want to set and unset the brake every time you change directions. So you would have the M code for brake released prior to starting machining. If you were doing 4th axis positioning, you'ld want the M code for brake active when stopped active.



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    Default Re: Adding a 4th axis and have a few questions...

    I assume it is a 3 phase brushless. You might be able to drive it with a SnapAmp. You would need to locate the AB and index signals and the voltage would be limited to ~70V max so you would probably only be able to run it at 500RPM.

    Regards



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    Default Re: Adding a 4th axis and have a few questions...

    Quote Originally Posted by TomKerekes View Post
    I assume it is a 3 phase brushless. You might be able to drive it with a SnapAmp. You would need to locate the AB and index signals and the voltage would be limited to ~70V max so you would probably only be able to run it at 500RPM.

    Regards
    I considered SnapAmp but the DC voltage in my machine is too high at 120v, and even if I did have a suitable power supply, the loss of speed would be way too much.

    I dont understand why they used a 1500rpm (its 2000 max) motor anyway? The DC version used a 3000 rpm motor. The mechanical reduction is huge at 180:1 so even at 3000 rpm thats still pretty darn slow. If the motor was turning at 500 rpm that would be a speed of 2.7RPM which wont work for me.



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    Default Re: Adding a 4th axis and have a few questions...

    Quote Originally Posted by m_c View Post
    That is a bit of an odd spec motor.
    My initial thought was just replace it, but 750W 1500RPM motors are not common.

    All I've found is that it uses a 2048CPR encoder, but not any other details. I'm guessing it outputs the full complement of ABZ and UVW, given the number of pins on the replacement encoder pictures I've found, so it could possibly be made to work with a new drive, if you can figure out the required settings.

    I think I'd be measuring the motor up, and seeing what it could be replaced with, as it's likely to be the less risky option.
    I called Yaskawa today and got some more details on the motor. See attached. The guy i spoke with couldnt tell me anything about the encoder or what drive would work but he gave me an email address of another department, so ill see what they say. Also, I pulled the motor off today and realized the shaft end is running right in the oil bath. So if I were to look for a replacement it would need to be oil sealed, something else to worry about.

    I also called DMM-tech and they have a 750w servo with oil seal that will bolt right up. Mounting bolt pattern is the same, pilot diameter is the same, only issue is the pinion gear would need to be sleeved or replaced as they have a 14mm shaft VS the yaskawa being 16mm. Not a big deal. Torque is much less (7.1N/m peak vs 13.9) and rpm is much higher (3000/5000max vs 1500/2000max). But this might be ok for me. For some reason this perticular model 4th axis (Yuasa EUDX-280) seems to have a stupid amount of torque for the size, and i wouldnt mind trading some for a little more speed. I was debating between the 220mm or 280mm models and the 220 has 195 ft-bs of torque, and the 280 has 780 ft-lbs. Seems like a very large jump. I think I definitely have torque to spare. Yuasa seemed to realize this as well as more recent models have 120:1 gearing vs 180:1 in mine.

    What do you guys think? Is this the best way for me to go? Forgot to mention, the DMM servo and drive combo with cables is around $500.

    Attached Thumbnails Attached Thumbnails Adding a 4th axis and have a few questions...-pinion-jpg   Adding a 4th axis and have a few questions...-sgmg-08k_spec-sheet-jpg  


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Adding a 4th axis and have a few questions...

Adding a 4th axis and have a few questions...