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  1. #13
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    Default Re: Adding a 4th axis and have a few questions...

    Hi guys, heres a little update on my 4th axis. I went ahead and bought the DMM 750w servo and drive, I think the extra speed with less torque will be better overall for my application. Servo bolted right up after making a sleeve for the gear. I got busy with other things and put the project on hold for a while but back at it again now. I mounted the drive today and started to wire everything up.

    So question of the day is how to control the 24v solenoid for the brake. Specs say it uses 270ma (see pic) and i was hoping to control it with Konnect optical ouputs which are rated at 0.25a. Im just a hair over the limit. Do you think this will be ok Tom? If it were to damage it, would i just loose that one output or damage the whole konnect board?

    My relay drivers are all used, i could move things around but another problem is i dont have a proper 24v power supply. Only have +12v and -12v so relay drivers switching to ground wouldnt work.

    Attached Thumbnails Attached Thumbnails Adding a 4th axis and have a few questions...-solenoid-specs-jpg  


  2. #14
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    Default Re: Adding a 4th axis and have a few questions...

    Hi mmurray70,

    270ma should be ok. The transistor on Konnect DSS4240T-7 is rated for 2A cont. and 600mw power dissipation. The power at 270ma should be:

    0.27A x 0.8V = 136mw

    If the transistor is damaged it is unlikely to damage anything else as it is opto isolated.

    Regards

    TK
    http://dynomotion.com


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

    Ok great, thats quite a safety factor you have there.

    Im trying to decide how to control this. Dmm reccomends step/direction, and a few months back Troy had best results with step/direction Closed loop on his hurco. How exactly do I use step/direction when using Kanlog? I read something about using JP5 on kflop and loosing half the encoder inputs on kanalog. Is there any way to avoid this? I will have 5 encoder inputs now (4 axis plus spindle) so I wont have enough if i loose all the jp2 inputs. Is there any other way to do it or will i have to do analog with 5 encoders?



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

    Also if I use analog, should i use Speed or Torque mode? Seems like the DMM drives still adjusts acceleration and have a smoothing filter in speed mode. Torque mode appears like it would give kmotion full control. Any suggestions?

    My other axes all run in torque mode and they work very well, but the tuning was done by previous owner. Not sure if i will be able to get the same results, no experience with tuning yet.



  5. #17
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    Default Re: Adding a 4th axis and have a few questions...

    Hi mmurray70,

    Im trying to decide how to control this. Dmm reccomends step/direction, and a few months back Troy had best results with step/direction Closed loop on his hurco. How exactly do I use step/direction when using Kanlog? I read something about using JP5 on kflop and loosing half the encoder inputs on kanalog. Is there any way to avoid this? I will have 5 encoder inputs now (4 axis plus spindle) so I wont have enough if i loose all the jp2 inputs. Is there any other way to do it or will i have to do analog with 5 encoders?
    Yes see faqs here.

    Also if I use analog, should i use Speed or Torque mode? Seems like the DMM drives still adjusts acceleration and have a smoothing filter in speed mode. Torque mode appears like it would give kmotion full control. Any suggestions?
    Not really. Both approaches should work. It depends on your preference of doing more tuning in KFLOP or the Drives. Unless the Drives have any quirks in any particular mode.

    Regards

    TK
    http://dynomotion.com


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

    mmurray, I got a batch of PCBs made to breakout the JP5/9 cable, and provide the ability to select between the encoder signals passing through from the Kanalog, or outputting the step/dir signals via differential drivers.
    This yahoo group thread has the details - https://groups.yahoo.com/neo/groups/...s/topics/13790

    If you want, I can send you one, but the only problem might be is I designed it for surface mount driver chips. I would offer to solder one up, but I don't think I've currently got any usable solder.



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

    Ok great, looks like i have some options. Thats a neat board m_c, so i would be able to use pins 4 and 5 as encoder inputs and 5 and 6 as step direction output right? Thats exatly what i was hoping for.

    Im going to try analog first and see how it goes. Hoping to get it connected tonight or tomorrow. Ill post the results. Thanks again guys



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

    Yes.
    They use 8 jumpers, that allow you to select for each wire, to change between either pass through from Kanalog, or outputting to the differential drivers.

    If you do want one, just let me know.



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

    m_c, sounds like a great setup. Ill let you know if i need one. Thanks for the offer again.

    Made some progress tonight. Got it wired up with analog control and got it moving in Kmotion! Started off in speed mode and couldnt get any good results at all. Tried switching to torque mode and things got better. Starting getting better results but had to use very high D numbers. Not sure if this is ok or not. At first glance the graphs look good, but error is still very high, over 1000 counts. Servo is 8192 counts per turn so this is not that great. Considering its a rotary axis with 180:1 reduction it might actually be usable as it is but Id like to try and do better. I tried adding I gain but it didnt help error at all before going unstable. Tried less P and more I, but no improvement.

    Here are my results. What filters should i be using? I added a 500hz low pass simply because my other axes have it. Any suggestions?

    Attached Thumbnails Attached Thumbnails Adding a 4th axis and have a few questions...-move-jpg   Adding a 4th axis and have a few questions...-moveerror-jpg   Adding a 4th axis and have a few questions...-rapid-jpg   Adding a 4th axis and have a few questions...-rapiderror-jpg  



  10. #22
    Gold Member TomKerekes's Avatar
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    Default Re: Adding a 4th axis and have a few questions...

    Hi mmurray,

    Looks like a good start.

    You might try adding Velocity Feed Forward to compensate for drag caused by the high D gain. Start at D x 90us = 40 x 90us = 0.0036

    I would have thought I Gain would have helped also. But you have it limited to Max 200 DAC counts. That would prevent it from doing much.

    2nd order Low pass filter at 500Hz and Q=1.4 is probably helpful.

    I'm guessing the oscillation might be due to some once per rev friction, wobble, unbalance of something such as the worm screw? You might try different speeds and see if it follows a period of time or distance.

    3662RPM is pretty high. Would you be cutting while moving? If so what speed?

    HTH
    Regards

    TK
    http://dynomotion.com


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

    Spent some more time tuning today and have it working very nice now. I played around with the PID numbers a little more and also tried second order low pass filter without much improvement. And out of curiosity I tried using a pole zero filter like my other axes use. I dont really know what numbers are best so i just copied my other axes exactly, used 45 and 180 hz. This seems to work much better. Im down to around 50 counts of error now and not much more even on rapid at over 5000 rpm. I rounded off encoder count output to 8000 counts/rev so this is like 0.01 of a degree which is awesome! I also doubled max integrator, and the I gain did help in this configuration with the pole zero filter.

    I think the oscillation i had before was as least partly due to tuning since you could see the oscillating error fading while at constant speed in the 4th pic from last night, and also fading in reverse direction. But your right, I do have some once per turn friction. I adjusted the gear mesh tighter when i bought this and the worm shaft does go a shade tighter once per turn, which is actually once per 2 servo turns (gear driven). If you look at the slower move from today, the servo makes 31 revoloutions, which is 15.5 worm gear rotations, and thats approximately how many oscillating cycles are in each move so Id say your exactly right again Tom.

    I might not need to go quite that fast. Honestly, 90% of the time this wont be doing any cutting at all. Will just be indexing and then clamped with brake. But occasionally it will be used for cutting as jobs come up that require it. And when you do cut with a 4th axis the servo speed does tend to go through the roof. If I were trying to cut 100 IPM for example on top of a piece of 2" stock that would be 15.9 RPM or 2866 RPM at the servo in my case. Occasionally at my old shop we would do 4 axis surfacing and rotary axis speed was the limiting factor.

    So everything look good here? Not missing anything am I? Also take a look at the step move, seems to settle out pretty quick. Im guessing this should be stable enough right?

    Attached Thumbnails Attached Thumbnails Adding a 4th axis and have a few questions...-rapid3-jpg   Adding a 4th axis and have a few questions...-rapid2-jpg   Adding a 4th axis and have a few questions...-filters-jpg   Adding a 4th axis and have a few questions...-step-jpg  

    Adding a 4th axis and have a few questions...-move2-jpg  


  12. #24
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    Default Re: Adding a 4th axis and have a few questions...

    Hi mmurray70,

    That looks reasonable to me. Except the Integrator limit might be still set low at 400 DAC counts when sometimes 1200 DAC counts is required to do the motion.

    I normally use a 2nd order low pass filter with Q=1.4

    Nice. Waiting for the Video

    Regards

    TK
    http://dynomotion.com


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

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