You guys think too much.. 38 tooth gear.. 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
