I have a 1999 Bridgeport VMC800 with Fanuc 18i control. I've been getting an over-current alarm 436 - Soft Thermal occasionally on the X-axis and I've figured that it only seems to happen when I have left the table sitting near the travel limits of the X-axis for a minute or so. I'm not sure how long this has been a problem as the machine has only been used occasionally for the last couple years and I don't remember if I was getting this alarm before.
I turned on the current monitor page and can watch the X-axis servo current climb over 100% when I jog to either the far right or the far left of X-axis. When at rest in the middle of the table the motor is typically drawing 40 - 50% current. As I jog towards either end the current slowly climbs and will go above 100% for the last 4 inches of travel.
One interesting thing is that if I switch directions and turn the jog-wheel 0.0001" in the opposite direction the current will drop to ~5% and stay there. Reverse back 0.0001" in the original direction and current returns to 100%+. It doesn't matter which direction I and traveling, as long as I am near the extents of travel my current remains over 100%.
My initial thought was that the ballscrew nut is not exactly colinear with the ballscrew. The closer I get to the middle of travel the ballscrew can bend slightly and it doesn't load too much. The closer to the edge of travel the ballscrew is much stiffer and resists more. I'm not sure this is true however because the ballscrew mounts are pinned in place after being factory aligned and don't seem able to be shifted. Also, I loosened the ball nut from it's bracket under the table and jog it to the end of travel and the problem persists. There is plenty of play in the screw holes and the bracket for the nut to shift in any direction it wants to but no reduction in current occurs even if I remove all four mounting screws.
If I jog the ball nut to the extent of travel when not attached to the table current stays ~5% always.
I loosened up the gibbs significantly to see if it had any effect and it did decrease the current draws at the extents a bit but still goes above 100% near the ends. Machine is level.
Any ideas what could be wrong?
Thanks,
Aaron
I turned on the current monitor page and can watch the X-axis servo current climb over 100% when I jog to either the far right or the far left of X-axis. When at rest in the middle of the table the motor is typically drawing 40 - 50% current. As I jog towards either end the current slowly climbs and will go above 100% for the last 4 inches of travel.
One interesting thing is that if I switch directions and turn the jog-wheel 0.0001" in the opposite direction the current will drop to ~5% and stay there. Reverse back 0.0001" in the original direction and current returns to 100%+. It doesn't matter which direction I and traveling, as long as I am near the extents of travel my current remains over 100%.
My initial thought was that the ballscrew nut is not exactly colinear with the ballscrew. The closer I get to the middle of travel the ballscrew can bend slightly and it doesn't load too much. The closer to the edge of travel the ballscrew is much stiffer and resists more. I'm not sure this is true however because the ballscrew mounts are pinned in place after being factory aligned and don't seem able to be shifted. Also, I loosened the ball nut from it's bracket under the table and jog it to the end of travel and the problem persists. There is plenty of play in the screw holes and the bracket for the nut to shift in any direction it wants to but no reduction in current occurs even if I remove all four mounting screws.
If I jog the ball nut to the extent of travel when not attached to the table current stays ~5% always.
I loosened up the gibbs significantly to see if it had any effect and it did decrease the current draws at the extents a bit but still goes above 100% near the ends. Machine is level.
Any ideas what could be wrong?
Thanks,
Aaron