Reply with QuoteLubrication or way wear? Maybe the lube is a bit gummed up out at the ends from sitting. Maybe try to lube it up a bit with some Dexron ATF and flush it out.
VMC X-axis motor draws too much current near the extents of travel
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 am 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
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Re: VMC X-axis motor draws too much current near the extents of travel
Lubrication or way wear? Maybe the lube is a bit gummed up out at the ends from sitting. Maybe try to lube it up a bit with some Dexron ATF and flush it out.
Jim Dawson
Sandy, Oregon, USA
It seems well lubed with vactra no. 2 and I've been lubing extra as I've been investigating this problem. What's special about the Dexron ATF? I'm happy to give it a try.Originally Posted by Jim Dawson
Re: VMC X-axis motor draws too much current near the extents of travel
It seems that Dexron ATF is a bit of a solvent as well as a lubricant. It seems to dissolve dried up oil and grease.
Jim Dawson
Sandy, Oregon, USA
Re: VMC X-axis motor draws too much current near the extents of travel
If this happens at the two extremes it is most likely some kind of binding. Disconnect motor and move by hand and see if you detect binding. Ballscrew might be dirty at the end or ballscrew and rails are not running in parallel
Russ
Re: VMC X-axis motor draws too much current near the extents of travel
That is a false alarm. That machine uses Yaskawa axis drives: they dont talk Fanuc, and Fanuc doesnt talk Yaskawa. The only feedback from the drive to the control is 'Drive Fault'.
The problem is the FSSB module, yellow module in upper left of electrical cabinet. It is the interface between Fanuc Optical Drive Control and Yaskawa analog voltage control.
No fixing these, even Fanuc doesnt bother, Its disposable, especially in the Bridgeport. Anyone advertising repair is bs. Its all Fanuc proprietary chips that cannot be obtained. And unless they test it with a Fanuc Control and Yaskawa Drives they dont know good or bad.
Order a new one from Fanuc. Or from anyone else advertising 'New'. No Pulled from working.
