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  1. #25
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    Default Re: Retrofit CNC to this saw with kflop?

    The deadband was left in from my previous tinkering... I will rerun with it disabled. But yes it was originally put in to help with dithering, one of the "features" of the VFD is that it supports +-10v in something they call "joystick" mode. With this feature enabled there doesn't seem to be a deadband on the VFD itself. For a 0-10+v analog input the VFD allows you to scale the input so it will treat voltages near 0 as meaning stopped. This doesn't happen in joystick mode and the VFD is always on, commanding very low rpm for near 0v input. I haven't found a setting yet on the VFD that works around this. My plan was to have my forever loop monitor velocity/command/position and when "close enough to zero speed +- some error" disable the VFD. Disabling the VFD (vs 0 rpm output) is desirable in this case since the AC motors don't like to be on with 0 (or near 0) rpm for extended periods of time. That might be desirable if I needed holding torque but my axis are self braking so the motors don't need to be on when not moving.

    10 counts @ 46.12 counts/mm = 0.22mm ~ 0.009 in < 1/64... if that translates directly to accuracy then YES!

    Yes that is probably backlash, I did some work to remove what I could but remember the axis is made up of an old automotive lift and a 900:1 gearbox. I think I lucked out a bit with the gearbox being a well made Japanese unit.

    Moving on to the Y axis: That VFD doesn't support +-10V, only 0-10+V, but it does support "joystick" mode as well, so 0V is full speed reverse*, 5v stopped, 10v full speed. I'm assuming I can handle that using the output gain/offset on the axis Configuration screen? Using vout = vin*scale + offset, I'd have 10v/20v = 0.5 gain, and an offset of 5. This sound right?

    FYI. There is a bug in the plotting when saving data, it adds an extra \n new line to every line and then if you try to read that data back in it fails... I've fixed this but haven't checked in the change yet.

    Thanks again.

    *the VFD has it's own input scaling setting so the range it operates over is some positive voltage-10V. So 0v doesn't command full speed reverse in the event of losing analog input.



  2. #26
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    Default Re: Retrofit CNC to this saw with kflop?

    Hi,

    OK reran the x axis tuning with no dead band and turned down I gain to 0.01 and got a much "flatter" error curve. These are my final settings:
    Code:
            ch0->Vel=40;
    	ch0->Accel=3;
    	ch0->Jerk=50;
    	ch0->P=170;
    	ch0->I=0.01;
    	ch0->D=0;
    	ch0->FFAccel=0;
    	ch0->FFVel=0;
    	ch0->MaxI=2000;
    	ch0->MaxErr=200;
    	ch0->MaxOutput=2047;
    	ch0->DeadBandGain=0;
    	ch0->DeadBandRange=0;
    Moving to the Y Axis, as mentioned above this VFD only accepts 0 to 10V+. I configured the VFD for "joystick" mode with a range of 1v-10v, so 0v doesn't result in full reverse. 9v/20v = 0.45 gain, offset 5.5v, converted to DAC counts 5.5v x 2048/10v = 1126.4. I had to set the Output Channel gain and offset to -0.45 and -1126.4. Otherwise the output voltages were negative.

    This axis can move much faster however I've tuned it with lower velocity and acceleration than it's capable of. If there are disadvantages to doing that I can go back and refine the higher speed tuning. For now I've tuned it using the same V and A as the x axis. Resulting plots show similar characteristics to the X-Axis... perhaps it's a setting in the VFD that I can eventually figure out to get the change in direction to occur nicer.
    Retrofit CNC to this saw with kflop?-y_axis_v40a3j50p60i0-005maxi2000maxerr200maxoutput2047_cpo-jpg

    Final settings:
    Code:
    	ch1->Vel=40;
    	ch1->Accel=3;
    	ch1->Jerk=50;
    	ch1->P=60;
    	ch1->I=0.005;
    	ch1->D=0;
    	ch1->FFAccel=0;
    	ch1->FFVel=0;
    	ch1->MaxI=2000;
    	ch1->MaxErr=200;
    	ch1->MaxOutput=2047;
    	ch1->DeadBandGain=1;
    	ch1->DeadBandRange=0;
    	ch1->InputChan0=1;
    	ch1->InputChan1=0;
    	ch1->OutputChan0=1;
    	ch1->OutputChan1=0;
    	ch1->MasterAxis=-1;
    	ch1->LimitSwitchOptions=0x100;
    	ch1->LimitSwitchNegBit=0;
    	ch1->LimitSwitchPosBit=0;
    	ch1->SoftLimitPos=1e+09;
    	ch1->SoftLimitNeg=-1e+09;
    	ch1->InputGain0=-1;
    	ch1->InputGain1=1;
    	ch1->InputOffset0=0;
    	ch1->InputOffset1=0;
    	ch1->OutputGain=-0.45;
    	ch1->OutputOffset=-1126.4;
    The one thing that came up is that this axis is moved via cables, occasionally the cable may bind a bit as it is wrapping around the winch drum. This results in a bit of vibration, seen here at ~ 44 & 50 seconds:
    Retrofit CNC to this saw with kflop?-y_axis_v40a3j50p60i0maxi2000maxerr200maxoutput2047_cpo-jpg

    Is there any way to filter this out without affecting the overall accuracy? I've done the tuning without the main motor running, once it is there is a bit of vibration as the big wheels are not balanced as well as they should be. Hopefully this doesn't end up being a problem.

    My next step was to rig up a pen to trace the movement and then begin testing with KmotionCnC.

    Thanks again.

    Attached Thumbnails Attached Thumbnails Retrofit CNC to this saw with kflop?-x_axis_v40a3j50p170i0-01maxi2000maxerr200maxoutput2047_nodeadband_error-jpg   Retrofit CNC to this saw with kflop?-x_axis_v40a3j50p170i0-01maxi2000maxerr200maxoutput2047_nodeadband-jpg   Retrofit CNC to this saw with kflop?-y_axis_v40a3j50p60i0-005maxi2000maxerr200maxoutput2047_error-jpg   Retrofit CNC to this saw with kflop?-y_axis_v40a3j50p60i0maxi2000maxerr200maxoutput2047_error-jpg  

    Attached Files Attached Files


  3. #27
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    Default Re: Retrofit CNC to this saw with kflop?

    Hi Greg,

    It all looks good to me. I don't think there is any way to dampen those "shocks" caused by the cable binding or whatever is going on the system just doesn't have the bandwidth.

    Regards



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    Default Re: Retrofit CNC to this saw with kflop?

    Hi,
    Quick update... video to follow but will take me a few days to put together. Here are some pictures. I didn't work on this too much last summer and started back at it this summer. Cut this today.

    Not perfect, but I'm pretty happy with it. Where it did have problems was where the wire had already passed close to the current path, in a few places the wire 'jumps' to the previous cut path. You can see this in the attached pictures on the P and the back side of the L. There could be a few reasons for this. My small guide wheels do not rotate to follow the path of the cut they remain vertical, or feed rate too low, or I'll have to always leave more than twice the kerf thickness between two adjacent cut paths.

    This is the cad file. I used a program called devFoam meant for foam block cutting for the drawing and GCode generation. It has kerf compensation and the ability to add G4 dwell at large angle changes:
    Retrofit CNC to this saw with kflop?-kflop_cad-jpg

    Cut letters approximately 15"x5"

    Retrofit CNC to this saw with kflop?-kflop_cut_002-jpg

    Retrofit CNC to this saw with kflop?-kflop_cut_003-jpg

    Retrofit CNC to this saw with kflop?-kflop_cut_007-jpg

    Retrofit CNC to this saw with kflop?-kflop_cut_008-jpg

    Retrofit CNC to this saw with kflop?-kflop_cut_011-jpg

    Retrofit CNC to this saw with kflop?-kflop_cut_012-jpg



  5. #29
    Gold Member TomKerekes's Avatar
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    Default Re: Retrofit CNC to this saw with kflop?

    Hi Gred,

    That is awesome! Can't wait for the Video. How long did it take to run?

    Looks like the kerf compensation worked well. Maybe cutting the straight lines first might work out better?

    Thanks



  6. #30
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    Default Re: Retrofit CNC to this saw with kflop?

    Hi Tom,

    I was running at a very conservative 1"/min feed rate. Which had a 'spindle' load of 5.5 amps on a motor that draws 10 amps at full load. During the cut I upped the feed rate to as high as 1.4 (so 1.4 in/min), the spindle load was still low but I turned it back down because this caused too much dust for my water to keep up with (have to keep my neighbours happy). I'm ordering some more coolant nozzles this week so I can try to go faster. It was around a 2 hour run time.

    Yes I think if I would have went anti-clockwise that might have helped, looking at the letters it cut from right to left, clockwise, starting at the bottom long horizontal run. I think it maybe just something I have to be aware of and try not to have two cut paths come too close. The wire 'twists' as it runs so the beads wear evenly, this causes lots of vibration in the wire. Maybe something I have to live with.

    FWIW the beads on the wire have an 8.8mm diameter (0.346") and the kerf left measures to about 0.373" so that is what I used.

    Random info: I able to keep within +/- a few counts of error on the Y axis. Which I think is pretty amazing as it's suspended from a cable, moved by a 60 year old winch with worm gear, then chain driven by a 100:1 gearmotor... none of which were designed for any type of position accuracy. All the while the Y axis moves 5' diameter wheels spinning at 330 rpm. The X axis is even better +/- 1 count (1171 counts/inch both axis).

    This is a plot from the cut:

    Retrofit CNC to this saw with kflop?-y-axis-position-error-output_kflopcut-jpg

    Retrofit CNC to this saw with kflop?-x-axis-position-error-output_kflopcut-jpg


    Hard to see the error series, but it pretty much follows the output series, just different scale.

    Oh and those spikes in the plots from the post on 10-26-2016 above were caused by chain slipping on the drive... fixed that.



  7. #31
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    Default Re: Retrofit CNC to this saw with kflop?

    Nice work!



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    Default Re: Retrofit CNC to this saw with kflop?

    Thanks mmurray70!
    Tom the video is up, hopefully I didn't say anything incorrect about kflop/kmotoinCNC. Video is kind of long, I do eventually get to the cutting and show a time lapse of it.





  9. #33
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    Default Re: Retrofit CNC to this saw with kflop?

    Hi Greg,

    Well done. Loved every minute of it!

    Thanks



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Retrofit CNC to this saw with kflop?

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