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Thread: fanuc 15b X axis osc.

  1. #1
    DWH Guest

    Default fanuc 15b X axis osc.

    We have removed X axis ball screw to repair the way surface on machine. Everything is put back together and all mechanical adjustments have been made. We are getting a strange oscillation in the axis as it is hunting for position. We are oscillating .0004". We have proven out the following: end play in ball screw, gear box, ball nut adj., motor coupling, and hydrostatic lift. It has an MP scale for feedback and the signal is clean on both the scale and readhead. I have played drastically with the drive tuning without success. We can trace the signal and what we see is the following error looking like a perfect sign wave with the current trace the same while holding position. All other axes have a flat trace with normal position holding characteristics. I cant figure out where the sign wave is coming from as I have never seen this before.
    We are working with a Fanuc 15 B control and have an @40/2000 motor (ID# 30), we are using an AD converter for the MP scale.

  2. #2
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    How does the ballscrew feel when turning by hand?? maybe Compare to another axis. Also can you turn the scale off and just use the pulse coder to see if the problem goes away?? When you had the ballscrew out did you turn the nut on the screw? You should have some resistance approx 6 lbs. to turn. If it is less then the ballscew lost its preload and there may be play in the nut that is causing the scale to constantly oscillate. If you are able to turn off the scale and everything is ok then the odds are it is to much backlash either in the nut, ballscrew or bearings. Does it oscillate throughout the entire stroke of the axis. This could tell you if there is a bind or some wear.
    Programming is like ***: one mistake and you have to support it for the rest of your life

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    DWH

    Your machine has an table yo put values of backlash ??? You said that adjust all, but you correct the backlash table ???

    Daniel

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    DHW,

    I had this type of situation years ago with a scale feedback. It turned out to be the lack of preload on the ball screw bearings. Some systems like this react funny to lost motion, and in my case again it was do to bad bearings. Since you had the slide off you may want to go back and check the ball screw bearings nuts again.

    RRL

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