I've been mulling over how to use later Fanuc brushless motors that have the serial encoder. I have gotten just a little bit of data about them. Apparently, they send a 77-bit string at 100K bits/second. So, the readout takes almost a ms. Now, a lot of people would want to convert this to quadrature. One problem shows up immediately, they have 65K and 1 million count/rev versions. At 1800 RPM, the million count encoder would need to send 30 million quadrature counts/second, even the 65K version would send 2 million cts/sec. The encoders take a request command to initiate reading and sending the position. I can see a way to synchronize the readout of the encoder with EMC's reading of the position count, but at a 1 ms servo thread, the first servo cycle would read out the encoder, then during the second servo cycle, a converter board would send the quadrature counts in a burst.
Now, the dilemma. I'm not a controls guru, but it seems to me that having a 2 servo cycle delay between position changes and the availability of that position data to the PID component might make tuning really messy. I can also envision making a board that would read the Fanuc serial code directly and make the data available to EMC. At the start of every servo cycle, it would command the encoder to take a reading. Thsi way, there would be an exact one-cycle delay to the data. That should make the PID work a lot better. So, does anyone have any comments on this, especially from a control law perspective? Thanks, 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
