On Friday 14 February 2020 07:29:53 Gene Heskett wrote: > On Friday 14 February 2020 02:01:08 andrew beck wrote: > > Chris. I'm still learning electronics. Could you expand a bit on > > this please. > > > > Maybe draw a napkin sketch of it. Sorry to be a bit slow on the > > uptake > > I'm not Chris, but the word quadrature means two signals that change > state like this at a steady speed > > ---- ---- ---- ---- ---- logic + > ____ ____ ____ ____ ____signal A, logic - > > ---- ---- ---- ---- ---- logic + > __ ____ ____ ____ ____ __signal B. logic - > > time is left to right if clockwise, or right to left if > counterclockwise. poor ascii image of oscilloscope trace sorry. > > From this train of pulses coming out of the encoder the edges per time > unit can be very accurately turned into an rpm scale to be displayed. > > Also the direction its moving is available at the output, freshly > determined at the instant of any change in status of these two > signals. > > Now add a 3rd signal, call it I for index, which has only a narrow > pulse that probably is identical to just one of the above but is only > sent by the encoder once per revolution. This tells the decoder, > called an encoder for some reason I don't control, that it has > moved|turned one full turn. linear scales may or may not have this > last signal but rotary encoders nearly always do. If present, this > allows a scale to be measured and established with which you can the > measure how far something has moved down to sub-micron accuracy. > Applied to a spindle, it allows linuxcnc to know exactly where in its > rotation the spindle is and that in turn allows linuxcnc to drive a > tap into a predrilled hole, and back out at the exact pitch of the > tap. We call that rigid tapping and taps last a loooong time time > because they are not being bent or otherwise stressed by hand tapping. > > There are conditions in driveing a stepper motor faster than it can > track that same format of driving signal to the coils of a stepper, > and keeping that slow enough the stepper can keep up becomes that > axis's speed limit. But thats a whole different critter and subject. > > This type of encoder signal never skips a count even after millions of > direction changes. And its cheap to build in hardware or software but > the software version will have a speed limit much slower than the > hardware version, but even that can work on a smallish mill at up to > 30 or so inches a minute, with only a parport breakout board driving > the machines motors.
correction here, that should say "the machines motor drivers, which for stepper motors is normally done by step and step direction signals." > I hope this helps explain it. Introducing the element of time often > causes some confusion to the idea of drawing a vertical line thru the > above accii drawing to mark the instant of time to what happens next. > > > Cheers, Gene Heskett 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
