Fanuc Velocity Servos oscillating

I am working on a retrofit on a Makino FNC 74 which has a Fanuc 6m controller running Fanuc 6047 series DC drives running 10m motors. I have the following mesa hardware

6i25
7i77
7i83
(2x) 7i84
7i87

I am using the 7i77 to output the cmd signal and the 7i83 to output the velocity signal to the drives. right now it is configured for 7v/1000rpm with cmd signal and 3v/1000rpm with velocity signal. the drive is setup for pulse coder which in the manual says the velocity signal should be 3v/1000rpm

My problem is I am having a oscillation at standstill and during moving. it is very consistant on all 3 axis and has a period of about 33ms

the picture of the halscope has the following settings
7i83 analogout2 50m/div
7i77 analogout2 2m/div
encoder2 velocity 20m/div

I have also included the hal and ini files. I am not using the A axis right now. just getting things going one item at a time.

it seems like it is something with the servo drive causing this but not sure what it is. I have tried different P setting, gain settings on the drive with no success. I have tried increasing the servo-thread with no change.

I found someone else having similar issues but does not have a resolution to what was causing it

emc-users.narkive.com/RjI6FUR4/fanuc-ana...rive-linuxcnc-tuning

does anyone know what else might be causing this?

Thanks

I would first try reducing the position loop gain (P term) to say 1
to see if its a velocity loop or position loop issue.

Thanks for answering so quick


I tried changing P to 1. it makes some difference. if I give it a quick 1/2 second jog, 1/2 of the time or so the oscillation stays and seems at a smaller amplitude. but sometimes it decreases over a second or 2 to no oscillation. all three axis seem to do this. the period still seems the same

I would try reducing the velocity gain in the drive with the P loop gain set low (or 0)
I would also try increasing the servo thread rate to see if this has any effect (With P gain low or 0)
( say to 4 KHz )

If none of this works it makes me wonder if the Fanuc encoder velocity interface has some compensation
filter