We have an Amada Pega357 with Fanuc 04PC control and older style drives (look like the DC drives) that has an oscillation when it stops ONLY when moving in the -Y direction (away from the servo motor, going towards the turret). You can see the feedback oscillate in the 800 diagnostics, it starts at about plus to minus 30. It is worse at high speed and not noticeable at low speed. The operator said it developed over about a months time. Here is what I've checked so far:
Swapped the X and Y drives (identical)
Swapped the Y motor with another from another machine
Swapped the motion board
Checked the 8200 series parameters
Checked for mechanical resistance in the Y axis by disconnecting the ball nut from the yoke (takes 16 lbs to get it to move along the entire length and in either direction as compared to 25 lbs on an identical machine)
Found the Y ball screw had .012" lash so replaced ball screw, nut, and end bearings and adjusted to zero at each end with .002" sag in middle. Adjusted gear lash. No change.
Ball screw appears to deflect down at the mid point between the drive end and the ball nut but have no way to measure and not sure if it's an optical illusion.
This is a real puzzler and the boss is looking at me cross-eyed. Has anyone one seen this before? Any ideas? Is it time to sacrifice a goat and spread it's entrails across the machine? Any help would be gratefully appreciated!