On Wednesday 12 February 2020 11:43:52 Chris Albertson wrote: > A sin and cos are 90 degrees apart. All you should need to do is > threshold the signal and you have A/B quadrature. Many ways to > threshold it but you want the one with least noise. > > A simple way to convert a sin wave to a square wave is to amplify then > clip it with diodes. A comparator can also convert the signal. > > The point to remember is that sin/cos is quadrature and all that is > needed is some signal conditioning. > But the sin/cos is generally per rev or at best a small multiplier. So positional accuracy is obtained by some fawncy math converting the waveforms into degrees. Which usually involves some math and therefore lag. A 1000 line (or more) quadrature encoder can give you the info your PID wants much faster. Meaning you can use Pgain by the bucketfull. I am doing that in fact.
In a pinch, one should not forget that a small stepper motor can make a good encoder driver by feeding its coils thru a high r buildout resistor in each wire, to a dual comparator setup for just enough historesis(sp?) to keep it quiet when stopped. An excellent jog dial can be constructed from old floppy drive step motors, very useable where you don't need an index pulse. Just feed the comparator output to an A/B quad decoder. Someplace in my midden heap I have box with 4 motors in it and some LM339's that I am going to finish a 4 axis jog pendent for my G0704. But I ran out of encoder inputs in my interface. A 5i25/7i76 plus a std bob. Thats only 2 decoders. And I'd also done away with the base thread, so no real way to use software encoders AND get real speeds. I could switch the 7i76 and bob out for a pair of 7i90's and a 6 pack of 7i42TA's but that would be both overkill and $400+. What would I do with another 100 gpio's after I made all that work? Boggles what little mind I have left... > On Tue, Feb 11, 2020 at 10:46 PM andrew beck > <andrewbeck0...@gmail.com> > > wrote: > > Hi guys > > > > wondering if anyone has any ideas here. > > > > I have a heidanhain spindle motor that runs up to 10000 rpm and has > > a 5v sin cos encoder on it. I am currently controlling the motor > > with a schiender vfd. I am talking to the support engineers here in > > New Zealand about buying a encoder card so I can get better low down > > torque. If I run the card in full encoder closed loop control in > > the vfd I can get 200 percent of the torque right down to 0 rpm for > > 30 seconds or so which is pretty useful. I am currently just > > running the drive in Variable frequency control which rapidly looses > > torque at low rpm. > > > > Anyway they have a bunch of cards I can use but don't have a encoder > > card that is suitable for sin cos encoders. I have no trouble > > changing the encoder but am not sure if I can get a source of > > encoders that spin up to 10k rpm. > > > > Anyone have any suggestions? > > > > regards > > > > Andrew > > > > _______________________________________________ > > 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
