andy pugh wrote: > On 15 July 2012 22:14, Gene Heskett <ghesk...@wdtv.com> wrote: > > >> Sure there is Jon. Timestamp the last 4 edges so you can develop an >> average speed over the total time period of those 4 stamps. >> > > That's quite a lot like putting a lowpass on the velocity output. > No, it is not a lot LIKE a lowpass, I think it is EXACTLY a type of lowpass filter. In a steady-state system, it might be a reasonable thing to do, assuming you are never losing any encoder counts. But, it is papering over a problem, whatever it may be. In a non-steady state system, where loads on the motor change and maybe even the spindle reverses while a tap is in the work, it is a REALLY bad thing to do. > I know you want a more satisfactory solution, and so would I after > spending so long making the encoder so perfect, but pragmatically a > filter will probably work. > > I actually get a whole lot of dither from my lathe encoder, and I have > never really figured out why. I just assume it isn't a great encoder. I have a 324 count/rev encoder that uses an 81-tooth bull gear in my Bridgeport, and three gear tooth sensors from Avago. Details are at http://pico-systems.com/bridge_spindle.html
This works great. The Z servos do not grumble at all, although I will mention that almost all threading I have done with it has been fine thread, such as 4-40 to 10-32. The spindle speed display, however, DID jump all over the place, so I put a lowpass filter on the DISPLAYED speed only, not in the feedback path to the CNC control. So, I'm not sure how this 324 count/rev compares to the systems that are giving problems. I do NOT have encoder time stamping on that system, by the way. Jon ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
