On 4/28/2011 11:39 AM, Jon Elson wrote: > 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 >
Jon, Are those serial encoders clocked by the attached device like a SSI encoder? If that is the case, perhaps you can clock them faster than 100K per second. I was just working with some new Heidenhain SSI encoders that are attached to an Allen Bradley PLC and the specs say it can be clocked from about 60 khz to just over a megahertz. These encoders came attached to some SEW motors and we had some problems reading the encoder position. Turns out the AB card was defective out of the box. The AB servo card can clock the encoder at 208 khz or about 600 khz and use it to close a servo loop. These SSI encoders are absolute. I have no idea how long the message string is, but looking at it on an O-scope, it doesn't look nearly 77 bits long. The only critical setup parameter was the number of significant bits per revolution and for these encoders the magic number was 13 bits even though the encoders only report 4096 counts per rev. I was setting up a test system with a Siemens servo drive and motor that also had an absolute SSI encoder attached but that was communicating back to the drive controller via Siemens Drive Click protocol. The Drive Click setup allows the drive controller to simply read out all of the encoder and motor parameters directly, so the setup between the drive controller and the motor/encoder is pretty much automatic. SEW does something similar on their servo drive systems also. I wonder if those Fanuc encoders aren't passing a lot more than just encoder data? A millisecond for an encoder reading seems like a very long time. Siemens has brand labeled Heidenhain two bearing encoders for years, and obviously SEW uses them also. I wonder if Fanuc makes their own or ? Dave 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
