mv40 z axis jumping up & down

[DAVID SHELL]

if any body can help? the z movement stutters mostly when traveling at 25% override in the plus direction.I removed the belt and ran the motor with the hand wheel seemed smooth. when the jerking starts the pulley on the motor jumps back & forth as it turns. could this be an incoder problem? feedback?or amplifier problem? this machine has been running fine up until it started breaking taps. because the movement was not steady. seems to be losing position.

[underthetire]

MV40 what. Mv40-m, Mv40-E, MV40B MV40/40. What control ? My guess is you blew the rectifier for the Z axis brake, or the brake is hanging up. Z axis motor does not move, so I doubt its cables. It could be a shot motor or amplifier.

[DAVID SHELL]

my tech guy sugest the bearings or ball screw. the motor does run smoothly when not under load. but your sugestion on the brake makes since. thanks for the imput

[underthetire]

It could be bearings, but usually Z bearings last a long time. Is it noisy in rapid mode? Bearings / screw will always make noise if they are bad.

[dtmach]

My '83 MV50 had very similar symptoms as you are describing only it would do so violently that it would alarm out. Actually now that I think back it would be sitting still and start jumping a bit and alarm out. Ok so it was in my case the mother board. There are the three axis input cables into your main board and I forget what the real name the guys at Fanuc called each channel but they had me swap x axis for z axis on the board via the cam plug and see if the jumping transfered to the other axis. It did and after replacing the board it has been trouble free for 4 years since.
Yes of coarse I looked at the brake and everything else and in my Mori's case it was none of them. good luck and call FanucUS as they are a great help. David

[dertsap]

does that mv40 have a z break ? the two i used to work on didn't , and if I over traveled , hit e stop or there was a power outage the z would drop about .15

[underthetire]

All MV40's have a brake of some sort. Some are on the motor, some are on the ballscrew, and some very early MV35 or 45's had hydraulic counterbalance. .15 drop is normal for those, it takes a few milliseconds for the brakes to engage, especially when they get older. The new machines will actually lift the spindle ever so much during a power outage.

[B Godard]

Sound like the brake to me as well. Put a block of wood under the z axis so that it has to travel about 4 inches to hit the block of wood.. Have the machine in estop so the servos are off. Follow your schematics in the cabinet, and locate the rectifier and a terminal point for the Z axis brake in the cabinet. Sometimes it can be hard to spot. It is not very big. Jump power from the rectifier to the brake. If you hear the brake click and the Z axis falls down to the block of wood then the brake is fine.

[egvdw]

I have the same machine. Had them come in and replace the cable and the problem went away. We took the cable apart and found two wires that where broken so when it hit certin positions it would jump. Try taking the cable off and testing end to end with a meter. When the cable bends it seperates.

[underthetire]

Z axis cable does not bend. Spindle, and x on some, spindle, x,y on others.