On Thu, Aug 09, 2007 at 06:32:45PM -0700, Kirk Wallace wrote: > What are the major points for choosing a lathe spindle encoder > resolution? My controller has a count limit of 300k counts per second. > Currently, my encoder has 10k pulses per revolution, so I will have an > RPM limit of 1800 RPM. So, obviously there is an upper limit. Is there a > lower limit too?
I think the lower limit would be in the low hundreds. I think for a while I had 256 counts per revolution and could cut nice threads. That was before CSS/FPR though. I wouldn't want to go lower (it was so low because I was counting with software on the parport). > I get the impression that for threading, the index pulse is used, so the > resolution is not important here. For Constant Surface Speed, the higher > the resolution, the finer the granularity in the feedback signal. But I > don't think accuracy is a big issue with CSS. The only time I would > think high resolution would be needed would be for live tooling milling > operations, where the spindle location is very important. > > I would like to have an RPM limit of 3k RPM. So, should I reduce the > current encoder resolution by one half, or not worry about it because > the encoder is only used at lower RPM? I think you should pick a highish resolution that your encoder counters can count at your intended highest RPM. In this situation more can't hurt, and you're right that your velocity estimate is better as the resolution goes up. The quality of the velocity output depends on which encoder counter you're using. I think the 'encoder' block is currently the best, pluto is adequate (integer number of counts), and ppmc doesn't have any at all (but I bet you can use ddt). I don't know about mesa/motenc/etc. The problem with using ddt is it will go briefly nuts when the count resets at an index or wraps around. This is why the driver should give a velocity output that has these cases handled. (On a lathe spindle, though, you won't be relying on index and velocity at the same time.) Hmm, that was fairly rambling. Hope it helps a bit anyway. Chris ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
