Originally Posted by
MadTooler
Well, I did a lot of tuning at various speeds and was able to make some improvement. I also was able to map the range of velocity on my X that was nastiest. However, I couldn't find a tune that entirely made the oscillation go away.
A new project came in the door that really needs to be cut without the extra chatter. I thought I would do some inspection of the angular contact bearings and maybe get lucky with a simple replacement if they were running rough and the source of the noise injection into the control loop. Well, they were fine, but I found the ballnuts were a bit crunchy. Possibly just dirt in there, but it seemed like the right time to replace the 25 year old screws with better and try to remove some of the poorly designed components with as close to decently designed as possible without a full gantry rebuild. I am optimistic this will at least greatly reduce the problem, if not fully remove it.
Part of what I am thinking of improving is the pulleys and belt from my DC servos to the ball screw. They were type L with 0.375" pitch at a 1:1 ratio. Since I am only running my servos at about 1,200 rpm, due to critical speed on the ball screws, I was thinking it would be good to reduce backlash and introduce a gear reduction with GT2 pulleys and a GT3 belt at either 1.4:1 or 1.5:1 to gain resolution and torque which may better smooth out mechanical issues that have tendency to inject noise into the control loop. Currently, I am at 20,000 encoder counts per inch and running a max of 240ipm. Gearing down at 1.4:1, I would have the increased resolution of 28,000 encoder counts per inch while still maxing out at either 240 or 250ipm at most. If this is a good thing, I would also switch to GT2 pulleys on my Y with a 1.5:1 reduction for 30,000 encoder counts and same ipm as the X. Am I thinking correctly that this would be beneficial for the control loop?
Thanks.