AC servo conversion on CNC Patriot VFD machine - Page 3

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Thread: AC servo conversion on CNC Patriot VFD machine

  1. #25
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    Default Re: AC servo conversion on CNC Patriot VFD machine

    I did the z-axis. The power cable (from drive to motor) was too short, so I lengthened it. Now machine is fully functional with 3 servo motors.

    Attached Thumbnails Attached Thumbnails AC servo conversion on CNC Patriot VFD machine-pict0638-jpg  


  2. #26
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    Default Re: AC servo conversion on CNC Patriot VFD machine

    The next step is to attempt to add an external position loop using raspberry pi 2/3 computer/board. I'm waiting for some decoder chips still for the glass-encoder-scale output signals (this is the current bottleneck). I know this coveted dual position loop can be done with kflop, but I prefer to do a custom outer position loop, and it's cheaper (just $60 for a raspberry pi). This can even be implemented with stepper motors to achieve accuracy at the resolution of the glass-scale-encoders. I don't know if the machine components are rigid enough for such a setup, but I want to try to do all 3-axis (the z-axis especially cleans up when the spindle-lock partially tightened).



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    Default Re: AC servo conversion on CNC Patriot VFD machine

    I worked night and day on this and finally finished a control system using the Raspberry Pi3 computer. It detects Mach3 step/dir control signals and encoder scale feedback signals using wiringPi interrupts on the GPIO pins and having PID output step/dir signal to the drive. It took a lot of iterations and tries, but the I managed what I think an excellent wiringPi pseudoPID code (that turned out to be short and compact) which keeps it within 2 thou over 200mm or so with super smooth motion, which I thought was pretty good. It works quite well. I'll upload the code when I get time. Some pictures too. This can be implemented in a stepper setup too. This is done solely with a $40 Raspberry Pi board and an instrument amplifier on each of the A and B encoder channels to ensure 0 to 4V signals to the Raspberry Pi board (the the feedback decoding is done in software on the Raspberry Pi (those chips never still haven't arrived)). The board also has to be grounded to the GPIO ground pins. I think the board will work for at least 2 of the axis and I may need a second for the last axis. Maybe all three will work on one board. Next, i'm going to try the position loop on the drive next to see how it compares to the Raspberry Pi board. Maybe better feedback signals to the drive will make it work.



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    Default Re: AC servo - Patriot - hi res

    Most excellent thread !
    Most excellent work !

    I highly applaud Your understanding of the electronics, signalling, developing and debugging the system.
    And most especially the persistence You have shown.

    Extremely Well Done - imho.



  5. #29
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    Default Re: AC servo conversion on CNC Patriot VFD machine

    My next post re: previous is multi-faceted.

    My interest has been making industrial "best" threads on a lathe.
    Your stuff is the only one that seems to use the glass-scale encoders for feedback ?? that I know of..

    (And I plan for very high accuracy milling results on a CNC VMC I built).

    Situation.
    I use a csmio-ip-s hw controller for motion control on the lathe.
    It supports, in theory, glass scale secondary feedback.
    Current servos are at 500 kHz and very powerful.

    I plan to, and likely will/may buy 1 micron, or 0.1 or 0.01 micron, glass scales for feedback.
    About 450 mm on z, 150-200 mm on x.

    I am looking for advice, gotchas, etc..
    As all the stuff is expensive, I really hope to get results related to costs ...



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    Default Re: AC servo conversion on CNC Patriot VFD machine

    I'll let you know what I get on the secondary feedback on my drive (CD servostar 250). So far my best solution was a Pacific Scientific SC905 drive with the positioning card. Although the Raspberry Pi is not bad how I had it setup.



  7. #31
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    Default Re: AC servo conversion on CNC Patriot VFD machine

    It looks like the CSMIO/IP-S does not accept any sort of feedback (just the CSMIO/IP-A does...and that will only work for you if your servo drives accept analog input). Your other option is secondary feedback on your servo drive itself as opposed to the motion controller.



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    Default Re: AC servo conversion on CNC Patriot VFD machine

    Two other options that you may want to look into are the kflop (Dynomotion Motion Control Boards for CNC Manufacturing and Robotics Applications) and the Galil (Galil Motion Control).



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    Default Re: AC servo conversion on CNC Patriot VFD machine

    An update! I decided to drop the dual loop for higher accuracy and use a single loop with motor encoder (or resolver) feedback. I had the raspberry pi working pretty good in a psudo-PID control as an outer position loop controller (glass-scale encoder position feedback that accepts commands from Mach3 and outputs a signal to the motor drive) but in-spite of the fact that the raspberry pi had great compact program i wrote in wiringPi (i think...it's been awhile...i think that's what it was called) and great interrupt based pins (on the raspberry) to accept the encoder signal, the raspberry would miss pulses from the glass-scale encoder and accumulate error. Because of this and the fact that motor encoders/resolvers are more robust than that on a glass-scale I decided to go with the more common single loop with motor feedback. Attached are a couple pics of the shoptask-Patriot-VFD machine working well with AC servo motors, and I learned some artcam basics to make a nice little plaque. I'm going to make a 3D lizard next and make my own 2.5D plaque great designs after that (if i can...i'll give it a try).

    Attached Thumbnails Attached Thumbnails AC servo conversion on CNC Patriot VFD machine-1-jpg   AC servo conversion on CNC Patriot VFD machine-img_0855-jpg   AC servo conversion on CNC Patriot VFD machine-pict0641-jpg   AC servo conversion on CNC Patriot VFD machine-img_0846-jpg  



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AC servo conversion on CNC Patriot VFD machine

AC servo conversion on CNC Patriot VFD machine

AC servo conversion on CNC Patriot VFD machine