On Friday 20 March 2020 14:24:32 Sam Sokolik wrote: > You guys think too much.. 38 tooth gear..
152 edges. Thats less than any of my machines are using. Now, I need to make or find a boreing bit small enough to do that for an 0-80 nut, that would just the ticket to make my encoder much more quadrature precise because i could adjust a ats667's location from the outside face of the encoder bracket, something I can't do now. But I think first I have to get a hoist rigged to lift my new BS-1 onto my g0704's table, then find out if that 80+ kg's is too much for the table to move. I might have bit off more that it can chew with the 470 oz nema 23 motors I put on it all those years ago. :( Waiting for a warm. low wind day so I can weld up brackets to fit merican iron to a chinese hoist with a MIG setup on a wire welder. Nice temps, and almost reasonable wind but too much precip today. > https://youtu.be/E2t0y2EsSO8?t=487 > > On Fri, Mar 20, 2020, 1:13 PM Gene Heskett <[email protected]> wrote: > > On Friday 20 March 2020 12:12:06 John Dammeyer wrote: > > > > > But what happens when someone has a 2500 line encoder on the > > > > > spindle creating 10,000 edges per rev. or 200,000 edges per > > > > > second at 1200 RPM. Now that 8 threads deep hole is > > > > > 1.6million. Again, not an issue with a 32 bit signed counter > > > > > but a problem with a 16 bit. > > > > > > > > Not an issue, the 16 bit hardware count is extended to 64 bits > > > > in the driver (every servo thread) this does limit you to a 16 > > > > MHz maximum count rate at a 1 KHz servo thread but thats way > > > > above the capabilities of most encoders... > > > > > > So let's see if I have the math right. At 16MHz we have an edge > > > every 0.063 MicroSeconds. At most then we'd see 16,000 in a > > > hardware 16 bit register ever 1 millisecond (the 1 khZ servo > > > rate). This value is added to a 64 bit integer. Is the hardware > > > counter cleared again? If not 1 mS later it would be 32,000 which > > > is still positive. But on the next 1 mS check it's now 48,000 > > > which is -17536 as a signed number and adding that > > > > > > There are probably hardware quadrature encoder counters that can > > > be set to latch the value on command and clear the counter? I > > > haven't checked the encoder on the BeagleBone for example to see > > > if it has that feature. Certainly your FPGA stuff can be set up > > > to do that. > > > > > > As the spindle reverses that counter value drops and eventually > > > becomes negative when B now leads A. > > > > > > Have I got that right? > > > > > > And if so, is there a minimum number of encoder pulses one can > > > have per revolution before the tracking becomes flaky? > > > > > > John > > > > I have heard of usable threads being cut with one, but i'd have to > > assume it was being done on machinery with otherwise very stiff > > spindle speeds that were stiff enough to ignore the taps loading. > > Probably a synchronous motor on a vfd and not all are by any means. > > Far more are induction mode with a load dependent slip angle, and > > that categorically won't work without an encoder accuracy of 2 > > degrees or better. > > > > > > > Finally, at that speed, and an edge every 5 micro seconds, how > > > > > does the software ever figure out that the spindle is varying > > > > > in speed? Or is one of the real time threads running maybe > > > > > only 1 kHz actually look at the spindle counter and compare it > > > > > to what they expect every 1mS and then adjust the speed of the > > > > > Z axis? > > > > > > > > Yes, the Z axis is "geared" to the spindle position > > > > More precisely to the spindles rotational position > > > > With my Sheldon turning 300 rpms, thats 5 rps. its a 60 tooth or 240 > > edges gear. 1200 edges a second=a new position 1200x a second. A new > > position every .8333333 miliseconds thats accurate to 1.5 degrees of > > spindle rotation. > > > > > > > Thanks > > > > > > > > > > John > > > > > > > > Peter Wallace > > > > Mesa Electronics > > > > 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 > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > Emc-users mailing list > [email protected] > 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
