On Wednesday 15 January 2020 13:18:09 Brent Loschen wrote: > Thanks for your reply Andy, and yes, PWM would be odd choice for the > BP. I chose PWM for this "lab" project, because in addition to the BP > mill, I have a LCNC router with an analog controlled VFD which is next > in line for a conversion. Getting an analog controlled PWM to work > properly seemed the most challenging, and it forces me to dig a little > deeper into hal. I feel much of what I learn here is applicable to > the Bridgeport, even though I won't be using PWM there. > > The Bridgeport does have the split sheave/air motor "vari-speed" > setup. I've removed the pot used by the BOSS control, and fabricated > an encoder wheel with I/R sensor that sits inside a 3D printed housing > which bolts to existing tapped holes in the top of the spindle > housing. As much as I would like to have rigid tapping, I feel the > mechanics of that old BP aren't up to the task, which is why I have > just a single encoder and no index.
I should probably interject here that with a good high-res encoder, it won't care about the wobbly speed mechanics as long as it keeps on turning under load. The z axis rigid tapping motion is 100% controlled by the spindle position as it turns. Since the Z is typically the slowest axis, you will have maximum spindle speeds to deal with because Z can't keep up. My G0704 can reverse directions much faster than Z, so I have some hal trickery in the form of a limit3 to shape the reversal decel/accel's into something resembling what the tv folks call a "sine squared" signal, where the peak of the delta in speed matches the zero speed and the z motor _can_ keep up because it has maximum torque at zero speed. This "shaping" of the reversal of the spindle has almost no effect on the actual reversal times. Hi rez in the encoder allows much higher Pgain in the spindle motors PID, and with the speed being helped by the air drive if its wired up to the high.on.low signals and fast enough in reaction times, rigid tapping should not be a problem. Haveing some experience with split sheeves needing several revs to adjust, I can see that being a problem, but it would be an educational experiment to see how big a problem. > I've seen a couple of posts from > others who have used various combinations of spindle-at-speed plus > others to control the air motor which I hope to leverage. > > Brent > > On 1/15/2020 3:06 AM, andy pugh wrote: > > On Wed, 15 Jan 2020 at 03:09, Brent Loschen <brent.losc...@gmail.com> wrote: > >> The DC motor speed is > >> currently controlled with a pot wiper on a small PWM driver board. > >> The goals of this test bed are to show spindle RPM , control the DC > >> motor with 0-5vdc from the 7i76 , and use knowledge gained to > >> convert the BP. > > > > Are you planning to use a VFD and control spindle motor speed, or > > use a mechanical variable speed? > > > > If you have a 7i76 then using PWM seems a bit odd, as the 7i76 has a > > built-in digital potentiometer for spindle speed control. > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
