I was reviewing a document from Sanyo covering AC servo motors: http://motiononline.com/PDF%20Files/Handbook/Handbook.pdf
It talked about the AC system needing absolute shaft position in order to duplicate a brushed commutator in software. It was indicated that a low resolution absolute encoder could be used to determine shaft position during motor drive initialization. Then a high resolution incremental encoder could take over for commutation and axis position feed-back. I would like to replace the encoder on a Yaskawa motor, and got to thinking about what I could use for an absolute encoder. My first thought was an optical disk encoder with N bits. Then, I realized that there will be positions between bits where the data is zero or unstable. I remembered US Digital had absolute encoders, so I looked at this one: http://www.usdigital.com/assets/general/102_mae3_datasheet_1.pdf When I saw the output graph, it showed a discontinuity at position 0, so this would not work either. Then, I envisioned a pair of sine wave outputs, which would be continuous across all possible outputs. I believe resolvers have this kind of output. I could use a pair of ADC's with Schmitt triggers to digitize the analog signals, so that I can get the data into EMC2. I had a plan for a 24 position absolute encoder for a tool changer and realized that I had the same problem. If the tool changer powers up between tool positions, I won't be able to determine the changer status without moving the carousel to scan for a valid output. I don't want to have any unsolicited changer movement or require the user to remember to manually initialize the changer, so I suppose I need a continuous encoder here too. Am I understanding the issues correctly? Anybody know of a _cheap_ way to get a non-mechanical low resolution continuous absolute position? (P. S. Maybe use two USD encoders 180 degrees apart, but this is too expensive and maybe produces two discontinuities.) -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC/EMC CNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/EMC CNC) ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
