2015-03-25 21:12 GMT-03:00 Gene Heskett <ghesk...@wdtv.com>: > If I can butt in here Leonardo, when I was setting up the spindle speed > servo in my toy lathe after switching from a non-linear and failure > prone driver to drive the 1hp treadmill motor my 7x12 now sports, to a > slightly modified version of the Pico Systems servo driver, and keeping > in mind I am using one of Peters 5i25 interfaces, which means I no > longer needed a base thread in the setup. But the speed servo was > hunting badly enough to keep the back gears in the headstock rattling > pretty good when the servo thread was running at nominally 1 kilohertz. > > I had to reduce the P in the pid to the point it was essentially > worthless at sub 300 rev speeds. So for S&G, thinking the control was > too slow, I did a rockhopper diagram and re-arranged the hal file so > that I was doing a straight fall thru of the control path so it was not > wasting a period or more because it was out of order when the modules > were in the wrong order. That helped but the amount of P seemed to be > limited yet, so the only other way to get a faster control loop was to > raise the servo thread speed. Nominally 2 kilohertz made an obvious > difference, and at 4 kilohertz, it was lots quieter. So that is where > it has been running at for several months now. P in the speed PID is > now high enough that I can peel off a pretty good sized string of blued > steel at 150 revs, or even a dimly glowing string at 500 revs, which > gives a "more better" finish. >
Hello Gene! I always like to here from your experiences. >From what I've been doing I got really good results but I don't recall trying to raise the speed of the servo thread to make any difference so I'll be trying tomorrow. The idea that was spinning in my head is if it will make any difference (if possible) first to close a speed loop and then feed with that the position loop all using the same encoders for the two feedbacks. Here's an example picture: http://s23.postimg.org/6xyj2q0zf/reductor.jpg That's the rotary axis, the picture is before I mounted the encoder but you can see how it works. I know It would be the best to have another encoder on the main shaft to really know the exact position but, since this is not thar critical and the worm and gear have almost none backlash we decided this setup would be ok. What I'm doing here is to sense directly on the shaft of the motor (this would give me a really accurate reading of the speed). But It would be great if this same encoder could feed also the position loop in LinuxCNC. -- *Leonardo Marsaglia*. ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
