On Sunday, 27 March 2022 15:40:35 EDT andrew beck wrote: > Chris just reading your email again and looks like the sensors you > linked are good up to 1 mhz so I'm good to go. > > How wide a slot do you think they need to read the light through? > > If they could read 0.5mm that would be great > > But I probably don't need that accuracy. > > I just want it as good as I can get as I know I'll be tapping several > thousand holes. > > 400 PPR x4 is 1600 PPR. > > M12 tap pitch is 1.75mm > > 1.75/1600=0.001mm > > Which is plenty lol. > > Maybe I'll try this. > > Can I use halscope to check the sensors are making good quadrature >
Yes and no. The halscope quantizes the time according to which thread it is being clocked with, and that can, except at quite low speeds, lie like a rug. Since those come into linuxcnc from hardware, you'd be much closer to seeing the truth with an external scope. Even with a 10mhz scope. This is a case of all the scope bandwidth the budget will buy. > > On Mon, 28 Mar 2022, 06:06 Chris Albertson, <albertson.ch...@gmail.com> > wrote: > > THis goes to 10K RPM? that is 167 revolutions per second. 400 > > slots > > means 70 KHz signal. > > > > Can you design an inductive sensor that does 70KHz but is also > > sensitive enough for near zero RPM? Optical sensors can work up to > > 1MHz with no problem as they don't have any inductanve. You can > > buy a "C" space sensor for a few dollars > > > > In either case, optical of inductive, you want a 50% "slot" where > > there is as much metal left as cut away Then the "edges" of the > > square wave are the same in either direction. The 50% duty cycle > > in effect doubles the sensor resolution. > > > > Why? Think about the signal when the direction changes. You have > > two sensors in quadrature and lets say one is being blocked and one > > is not, I think you want the turnaround to take as long for each > > sensor.> > > On Sun, Mar 27, 2022 at 2:22 AM Andy Pugh <bodge...@gmail.com> wrote: > > > > On 27 Mar 2022, at 08:09, andrew beck <andrewbeck0...@gmail.com> > > > > wrote: > > > > And is bigger dia better for higher resolution? > > > > > > Probably not, as it will perhaps have more scope to oscillate at > > > 10,000 rpm. > > > > > > Don’t neglect the purely mechanical design of this fast-spinning > > > part. > > > > > > Have you considered optical sensors rather than inductive? > > > > > > What will be counting the pulses? > > > > > > LinuxCNC can lathe-thread with one sensor. > > > But rigid-tapping is different as it needs to accurately detect the > > > reversal point. So you need three channels for index and full > > > quadrature. > > > > > > Work out what error you can accept in the reversal point detection > > > (as a fraction of thread pitch) and you can get a feel for how > > > many slots you need. > > > > > > > > > > > > > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > 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, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
