On 5/1/2011 1:43 PM, Jon Elson wrote: > Well, after much fooling around, I finally found the magic recipe to > make the encoder send a report. It turns out the bit rate is 1 > Mbit/second, not 100 K bits/sec. So, the entire report can be sent in > about 80 us. That sounds a lot better. > > It seems there is an absolute position group that contains a count of > revs as well as the angular position count, and then a repeat of just > the angular part without the rev count, that would be useful for > commutation. At the end, there is likely a cyclical redundancy check. > One thing that comes to mind is how to handle encoder index. If the > angular data resets when it reaches the index pulse, then that is taken > care of. If it does, though, that means there is no angular info until > the encoder has passed its index position, and thus commutation is not > reliable until that point. > > I'm trying to get away from having to supply battery power to the > encoder as Fanuc did, but it might be necessary, but kind of messy. > > Jon > > ------------------------------------------------------------------------------ > WhatsUp Gold - Download Free Network Management Software > The most intuitive, comprehensive, and cost-effective network > management toolset available today. Delivers lowest initial > acquisition cost and overall TCO of any competing solution. > http://p.sf.net/sfu/whatsupgold-sd > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers > >
That sounds better. I have been told that all absolute encoders lose their rev position on power down. Some controllers apparently write the last rev count to flash memory on power down. Of course if the encoder is rotated through a turn it would never know that on power up since it would use the old rev count and be out of position. Battery backup might be a better option. There is likely a command that you can send to the encoder to zero or preset the encoder. Some systems call that a passive homing routine. Absolute encoder systems can be really handy on machines that are difficult to home with a conventional home switch search. If the encoder always knows where the rotor is at (since the encoder is absolute), isn't commutation pretty simple after the initial angle setting of the rotor position? Dave ------------------------------------------------------------------------------ WhatsUp Gold - Download Free Network Management Software The most intuitive, comprehensive, and cost-effective network management toolset available today. Delivers lowest initial acquisition cost and overall TCO of any competing solution. http://p.sf.net/sfu/whatsupgold-sd _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
