Thats my first time here! Thank you for accepting me.
We have here a big and old machine that has been retrofitted but the guys didn't tuned the servo, so I decided to try fix it... ( I know how bad can be it!!!)
The machine is not doing circle interpolation properly and I have played already with acc/dec. times and loop gain, so I think it will not be the biggest problem.
The main thing is that there's a big jerk on the X axis. This axis is equipped with a gearbox and it goes to a 10 meters rack.
The machine is working well when cutting straight and in one direction, but when it changes direction in X, you can fell the problem.
The control is 32i-Model A and I can use servo guide. I have tried already almost everything related to backlash, load inertia ration, feed-forward, etc and no solution.
I will attach a picture about the problem if someone feels that can help me, I much appreciate!!
The circular graph shows an almost exact opposite when switching from forward to reverse on a particular axis. Not sure which way the diagram reads but it almost certainly looks like mechanical backlash in one axis.
Other folks may be more familiar with those diagrams. How did you generate them?
Hi! I took the graphs from servo guide. The strange thing is that we have checked already the backlash, and it seems to be ok. I also played with backlash values and the results are the same. I also tried correct the backlash more than 2 mm, step by step, only to see if something change and I end up with the same results.
the backlash as you talking is a combination from the ballscrew nut backlash+end bearings of the ballscrew backlash.
also you can have a side backlash on guideways too.
So the backlash compensation parameter will adjust it only if exist in the ballscrew nut,untill 0.5mm maximum,if it is more you can not do more from parameters.
i suggest you to:
-move the axis in one direction and mount a dial guage in the opposite direction and try to push the axis in the other side(opposite side of the moving by handwheel) and see if it is mechanical moving checking the dial gauge.
----if it is moving try to mount the dial gauge first on the end of the ballscrew(opposite to motor side) and also on one point of the axis itself to determinate if the moving is from the ballscrew nut or from bearings from the end of the ballscrew.
-mount the dial gauge on the perpendicular direction of the initial moving of the axis(look for a very good surface plane to touch it with dial gauge) and move the axis back and foward quick and see if you have a side move of the axis when this is changing direction.
make all this checking and then come and say the results and i can make a conclusion.
PS:before you start make a paint mark on the coulping between the motor of the axis and the ballscrew ,it happens sometimes that there is a little slide of the coupling while change direction so you have to check that the coupling is strong enough tighten.
Also take out the covers of the slideways that keeps the lubrification oil inside and check and be sure you have enough oil on the guideways.
Good luck.
Hi! I have taken some tests already on the machine using dial and moving with handwheel. I got practically 0 of backlash.
Like I said before, the machine has no ballscrew. It's a rack, gearbox, coupling and the servo motor. We have recently opened the gearbox, and checked all the mechanical stuffs.
The most strange is that the motor start the movement, the speed of the servo motor and the velocity of the load increse proportionally, but after some milliseconds the servo motor increases the torque and speed suddenly. You can see that on the graphs.
Hi!! Yes. The machine has separate position detector. We use Heidenhain. Fanuc has a function for dual position feedback but it has not helped as well.
In servo guide have you ran the auto tuning tests?
Not just the frequency response, but all of them.
If the interpolation is not adjusted you will not cut a circle, it may look like an egg, as I have had in the past. If it is not mechanical this should take care of the jerking ad well.
Hi Bill4807!
Yes, I run the servo guide auto tuning, but I got some issues with some codes and parameters. For example the parameter 2448 that is related backlash's acceleration, doesn't appear on no one FANUC manuals. The other thing is the G code 5.8 and 5.7 that servo guide uses, these codes practically doesn't exist in any manual as well.
Servo TUNING
Re: Servo TUNING
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