You all have missed the first and most important step. You have to first adust the sensor so that it gives a 50% duty cycle square wave at all speeds. With an inductive sensor and a fast-moving gear you might not get 50% from max speed to zero in both directions.
Only after you are getting a 50% duty square wave in BOTH directions can you think about how to place the second sensor. The signal from the second sensor needs to by 90 degrees out of phase from the first. One cycle is from the leading edge of a pulse to the leading edge of the next pulse. If the sensor is "perfect" then the distance is in fact 1/2 of a tooth or 1/4 of a cycle. (remember that a cycle includes both the pulse and the low "non-pulse" that follows.) If the sensor can't by adjusted for a 50% duty cycle then you can make a "fake" quadrature sigal that only works if you look at the leading edges but this would have (1) a position error when you change direction and (2) only half the resolution, because you only look at the leading edges. You really want exactly 50% This is why optical encoders are so popular. Then can be near perfect. On Tue, Feb 18, 2020 at 1:09 AM Les Newell <les.new...@fastmail.co.uk> wrote: > Hi Jon, > > Thinking about it, you're mostly right. I didn't think it through. My > suggested spacing assumes the teeth are square, which of course they are > not. > The actual spacing is going to depend on the sensing range of the > sensors and width of the tips of the teeth. 1/4 tooth spacing is likely > a good starting point. You aren't going to get anywhere near perfect 90 > degree quadrature but there isn't much you can do about it. > > Les > > > On 18/02/2020 05:00, Jon Elson wrote: > > On 02/17/2020 03:57 PM, Les Newell wrote: > >> They should be any multiple of the tooth spacing plus half a tooth > >> spacing. > >> > > Nope, I made that mistake first time. It should be "plus 1/4 of a > > tooth space". > > > > Jon > > > > > > _______________________________________________ > > 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
