On Thursday 19 March 2020 23:08:52 John Dammeyer wrote: > > -----Original Message----- > > From: Jon Elson [mailto:el...@pico-systems.com] > > Sent: March-19-20 4:13 PM > > To: Enhanced Machine Controller (EMC) > > Subject: Re: [Emc-users] A hal question? > > > > On 03/19/2020 04:02 PM, Gene Heskett wrote: > > > Greetings; I am trying to reduce the f/r error in an ATS667 based > > > encoder. > > > > > > The index pulse is turned upside down by a reversal of spindel > > > direction. Tts the nature of the beast to remain in this stable > > > state until the approach of the triggering ferrous metal causes > > > the first reversal which the edge ignores, and then goes back true > > > or false as the ferrous piece crosses the center. > > > > > > > > > > > > Does anyone see any problems with that? > > > > The index pulse is only used during the initial synch to the > > spindle, then the encoder is counted > > up and down during reversals, without looking at the index > > again. So, rigid tapping doesn't care > > that the index signal from the encoder does something > > different when the spindle is running in > > reverse. It has been this way since I did the first ATS667 > > encoder hack some years ago. > > > > Jon > > So can you tell me something more about that? I could see that first > encoder index edge clearing a a quadrature counter attached to the A/B > pins. After that the index is ignored. > > But it's here where I become a bit confused. A 60 tooth gear at 1200 > RPM produces 7200 edges per second or 1 about every 139 microseconds. > Say we're rigid tapping 8 threads which means a total of 57600 > pulses. If the hardware counter is 16 bit signed that's larger than > the 32767 before the counter rolls over. If it's a 32 bit counter > it's not an issue. > I doubt if that would be a problem at 1200 because it would following error out from Z not being able to move that fast. Probably before the tap ever touched metal going in. Another problem would also rear its ugly heard is that the overshoot at the bottom of the hole would likely exceed the length of the tap at 1200. I got concerned about blind holes, and despite the belts yelping like michelin tires on hot blacktop, the overshoot at the bottom of the hole was over 3 turns at 300 rpms when swinging an 8" 40 lb chuck with a workpiece in it. Trade my 1hp motor for a 10 and a bigger vfd might speed up the turnaround but my place isn't wired for that kind of power.
So I have modified most of my rigid tap routines to tell me how many turns and how far the overshoot is at that taps pitch and show me in the gui. So I can cut clear to the bottom of the blind hole w/o breaking the tap. > 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. > > 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? > > Thanks > John > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > 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
