Help with motor tuning

[harrisam]

Hello all,

I just joined CNC zone and I am hoping to get a little help with my machine. I have a question about motor tuning/velocity/acceleration. I have a 4x4 table from DynaCNC with servo motors. I have played around a little bit with the tuning but I do not seem to get much results. The problem I am getting is when I am cutting an arc or curve I am getting very jagged edges. My straight line cuts look great and when I cut manually they look pretty good. This is why I thought it might be in the motor tuning part of Mach 3. I would appreciate any feedback you might have to offer.

Thanks for your time.
harrisam

[mc-motorsports]

are the servo's jerking or wandering? I'm guessing it's a plasma machine?

[harrisam]

Yes, it is a plasma machine. I would have to say more of a jerky appearance in the cut. I have attached a couple of pictures to show what it looks like. These are just some random arcs and curves I drew to use a test pieces. The arcs have all of the "jerky" looking divets instead of being smooth. If I increase the feed rate (currently at 90 ipm) my accuracy of cut goes out the window. It starts lopping off the corners and such. The first picture shows where on the right bottom side it comes off the curve and then should be 3 angled straight lines and then a straight cut along the bottom. The bottom is straight but the other are not.

Again, thanks for any suggestions and your time.
harrisam

[Al_The_Man]

Too high a gain?
On my systems I use the following,
I set the KP, KI & KD by starting with low or zero KI, set proportional gain KP to a low value = 1 and KD =100.
Test a move and increase KD until motor vibrates, then reduce slightly, next increase the value of KP, the error on the test move will reduce untill the motor starts to vibrate, then back off.
Finally KI is increased to improve the in-position error.
You may need to go back and forth with minor adjustments, before it is complete.
But if you have a system where the motor/load inertia is not matched properly, you may find you only get satisfactory results at low accel/decel settings.
I use this pattern to really put the motion commands to the limit.
Servo Test pattern
Al.

[mc-motorsports]

That's your arc wandering. It has more to do with the plasma machine and torch/torch height.

[mc-motorsports]

BTW, the bottom is straight because your arc if following in a straight line, but whipping out around corners and curves.

[DynaCNC]

I don't know which machine you have. Why not email me directly and I think I can help you with this.

Dave Cress
DynaCNC

[DISCONNECTED]

Sounds to me like you are running your machine in exact stop mode instead of constant velocity mode(MACH 3).Or your artwork is really bad.

[harrisam]

Hey all,

Thanks so much for all of your suggestions. I have also been in contact with Dave Cress from DynaCNC and he has gone out of his way to try and help me get this fixed. I figured I would try both directions and see what feedback I would get. As users of the machine, there is always a lot of helpful input to be learned from those with the experience. But let me just tell you I would give DynaCNC and Dave Cress their 5-star rating in their diligence to try and fix my problem. I have read of a lot of the other threads with some seriously ugly things being said about him and his company so I was a little skeptical as to what response I would get.

I had a reponse back within 12 hours and he has been nothing but helpful since.

To the best of what I can tell, the setting that seemed to have fixed most of the problem was that the backlash was turned on. Once that was turned off the arcs smoothed out considerably. (Thanks, Dave!)