Do you need a sharp rise and fall time? I think a sine wave would work well enough.
The bigger question is how many slots to cut per revolution. The number has to "work" at the slowest speed the shaft will be used. The high end of the range is "easy" but the slow end requires some thinking... Those C-shape sensors are easy to use. Typically, the detection electronic uses an op-amp wired as a voltage comparator with hysteresis. It is just an op-amp with a little POSITIVE feedback. Hysteresis provides a small dead-band that eliminates noise. The beam diameter of the IR sensor is not a geometric point but has some diameter so the interrupter disk wipes a shadow across the detector and the output voltage depends on the fraction of the beam that is being cut. The output is always a voltage ramp. The positive feedback detector moves the "trip" and "untrip" points far enough apart on the ramp, so there is no ambiguity. On Fri, Jul 2, 2021 at 12:01 AM John Dammeyer <[email protected]> wrote: > > From: Gene Heskett [mailto:[email protected]] > > Subject: Re: [Emc-users] Mounting spindle sensors. > > > > On Friday 02 July 2021 01:42:25 John Dammeyer wrote: > > > > > Progress. This will ultimately be metal since I don't trust the > > > plastic to be stable and the encoder disk is perhaps a tad thick for > > > the slotted sensors. > > > With regard to the comment about disk thickness, its a small effect, but > > the thicker disk has more effect of the edge diffraction, so you would > > get sharper rise and fall times from a thinner disk. One way to reduce > > the rise & fall time if it is a problem would be to cut the disk with an > > engraving tool, because the 60 degree v would leave a single sharp edge > > but that would also tend to give small errors if your z depth is shakey > > or the disk isn't optically flat. If using the engraving tool, turn the > > disk over to put the sharp edge, narrower opening towad the led in the > > interruptor, less chance of an errant reflection from the angled face > > that way. > > > > Cheers, Gene Heskett > > Thanks Gene. Good suggestions. > > I started with a front panel from an old S-100 computer. Used the mill > to cut the complete part. Then after I realized it was too thick I milled > it thinner. I should have started with thinner aluminium to start with. > Or some thinner steel sheet. > > Live and learn. Just a do over. Project #42. In fact all my projects > are #42. > > BTW, in case you missed that from the book "Hitchhiker's Guide To the > Galaxy" the #42 is the answer to Life, the Universe and Everything. And > more interesting, although there are claims that it's a coincidence, if you > take the letters of the alphabet and assign a number to each. > A=1, B=2, C=3, ... Z=26 > and add but the numbers for the word "MATH" you get 42. > > So in fact MATH is the answer to Life, the Universe and Everything! > > Some trivia for the last 3 minutes of Canada Day. > John > > > > > > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
