Hi guys, hoping someone can offer some pointers for a problem we have with a Takumi mill.
The machine uses a Fanuc 21i-MB control.
The operator had mentioned that when milling a circle, he would have tight spots (when checking for a H7 fit) at the X and Y changeover points.
I initially started to check for backlash, there was a little, but not a lot - but whilst checking against a clock I noticed that when I changed direction the axis would jump. Say I moved 0.001mm on the control, the clock would move 0.01mm. If I continued to move the axis in the same direction, the initial overshoot would be made up (i.e if I carried on moving to say 0.1mm, the clock would also show 0.1mm).
If I reduced the backlash figures in 1851, then the jump would go away, but of course I would l just be left with backlash. I read of another CNC owner who had the exact same problem and fixed it by turning the backlash acceleration function off in 2003 bit#5 - I thought this could be it as some of the backlash acceleration parameters looked to be a long way from default, but it had no effect.
Could anyone suggest what could be causing this initial overshoot? I could be wrong, but I suspect this is what is causing the problem when trying to interpolate a circle, it seems to tie up with where the tight spots are on the circle at least. I did wonder about servo tuning, but I have little experience of this so have not wanted to dive straight in!
I contacted a calibration company to have the machine checked and adjusted against a ball bar and interferometer, but they are asking me to double check for any other problems first.
Could any mechanical problems cause this overshoot?
The machine runs very well other than this, and has not had a hard life at all. Really appreciate any suggestions - thanks!
The machine uses a Fanuc 21i-MB control.
The operator had mentioned that when milling a circle, he would have tight spots (when checking for a H7 fit) at the X and Y changeover points.
I initially started to check for backlash, there was a little, but not a lot - but whilst checking against a clock I noticed that when I changed direction the axis would jump. Say I moved 0.001mm on the control, the clock would move 0.01mm. If I continued to move the axis in the same direction, the initial overshoot would be made up (i.e if I carried on moving to say 0.1mm, the clock would also show 0.1mm).
If I reduced the backlash figures in 1851, then the jump would go away, but of course I would l just be left with backlash. I read of another CNC owner who had the exact same problem and fixed it by turning the backlash acceleration function off in 2003 bit#5 - I thought this could be it as some of the backlash acceleration parameters looked to be a long way from default, but it had no effect.
Could anyone suggest what could be causing this initial overshoot? I could be wrong, but I suspect this is what is causing the problem when trying to interpolate a circle, it seems to tie up with where the tight spots are on the circle at least. I did wonder about servo tuning, but I have little experience of this so have not wanted to dive straight in!
I contacted a calibration company to have the machine checked and adjusted against a ball bar and interferometer, but they are asking me to double check for any other problems first.
Could any mechanical problems cause this overshoot?
The machine runs very well other than this, and has not had a hard life at all. Really appreciate any suggestions - thanks!