On Wednesday 01 March 2017 07:42:17 Roland Jollivet wrote: > I had always assumed that machine MPG's generated one state change per > click, but following Gene's discussion, I pulled out my 1988 Fanuc > MPG, and saw that it was also 4-states per click. Obviously, one > 'pulse'/detent > > Does anyone know the rationale behind this? > I assumed one always wants one step per click, so why not use a 25ppr > encoder and use every change?
because its relaxed condition is always the same in terms of the A/B logic outputs, the detent, mechanical or magneticly derived, assures this condition by steering it to tat condition when you've let go of the wheel. Yes, the encoder does see 4 edges go by, but that is one complete detent, therefore the encoder is told to produce a count output divided by 4, so you get a 1 count advance per detent. > Used as currently is, it would have to be a software /4 to be useful. > You could also do a /2 or /1, but no-one ever wants a x2 or x4 on > their MPG It's always x10, x100 or whatever, so the count/detent would > always have to be n/4 x 1 .. or.. n/4 x10 in software. > I suspect this choice is more a force of habit, hence what I am doing give more choices, with no step being more radical than a 2.5/1 rate. The gain progression is 1,2,5,repeat for next decade, and the 1,2 sequence of the 3rd decade. 8 choices, the last being quite fast with the possibility that the joints MAXVEL may limit it depending on how furiously the knob is spun. On my machines I'd bet on it. :) > Alternatively, if I was going to make my own MPG, surely I would just > make a 25ppr encoder and make it 1 detent/change? > It's far easier for me to make, so surely it would have been for Fanuc > too? I've not dissed one of these, but since they need power, and the friction is vanishingly small, so as a CET I have to assume that they are hall effect sensors similar to the AL667's working on a 100 tooth cogwheel, with a stronger magnet actually supplying the detent force external to the bias magnets in the AL-667's. Yes, one COULD make a 25 ppr wheel, but you would have to use two cogwheels, a coarse one for the logic, and a 4x finer wheel to supply the detent. And you sure as tootin can't do it for $20 worth of your time and tooling. The hall sensors with their bias magnets do supply a small detent force too, but there is more than 1 stable condition given a low enough friction/stiction to its movements. Just the weight of the spin knob could cause it to move w/o the extra much more positive acting magnetic detent acting on another section of the rim of the same 100 tooth cogwheel. These spin dials are quite well made, and I don't believe could be made in China for a $20 bill even in 10k quantities. They have to be from a liquidation sale. So when these surplus units are gone, we'll likely never again see a competing, usable product for less than $50, likely more. If you have a potential use for them, grab a lifetime supply right now. > What am I missing? See above Roland. > Regards To you too, Roland 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) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
