tuning problem or what am I missing.

[REVCAM_Bob]

I have a 150 inch pound servo motor set up with Galil controller
hooked to a vertically oriented ball screw with 1/2 inch pitch, supporting
approximately 500 pound load. When moveing straight down at about 400 to
500 inches per minute, it "bangs" like the servo is suddenly trying to change
directions and the drives fault out. It only does it on the down stroke.
It does it while jogging down and more often after releasing the jog key.
It does it more so when I increase the weight it is moveing with a load of
approximately 75 pounds. It does not seem like the system should be overloaded because when going down, if I don't stop the system it has
enough force to bow a solid wooden table of 2 x 6 construction by 1 to 2 inches. I know thats not very scientific, but it appears to have the ability
to exert hundreds of pounds of force. I think I may have a tuning issue.

Any thoughts?

[HuFlungDung]

What kind of slides are you using? I'm wondering if the load is quite offset, that maybe you are getting some degree of 'stick-slip' jamming of the ways?

[Al_The_Man]

From all the symptoms, I would say you are seeing an overhauling load and the motor is trying to control the accel/decel rate and the motor is trying to correct, normally you would have a following error, but this may be a leading error due to the large weight attempting to backfeed the ballscrew.
On a vertical axis like this, it is usual to see a hydraulic or other type of balancer arrangement.
Al.

[REVCAM_Bob]

The way system is cam roller followers against the edges of a cold rolled steel
bar stock. There is some vibration in the system that could be causing the
moving part to hit the stationary part which would possibly cause this stick slip friction..... I'll take a closer look. Could it be that sudden outside forces,
although relatively small could really throw this thing for a loop?