On Sunday 12 August 2018 05:08:37 andy pugh wrote: > On 12 August 2018 at 02:01, Gene Heskett <ghesk...@shentel.net> wrote: > >> Resolvers are absolute and much tougher. > > > > It appears that Omron's use of precision bearings seems to > > addressing the toughness aspect. > > Now fill your optical encoder with coolant and see how it goes. > > I may be sounding like a bit of a resolver fanboi, but that is because > I am. I have even taken off an encoder to fit a resolver on one of my > lathe servos. > > With a resolver that perfectly matches the motor it makes BLDC > commutation very easy too. On the Z servo of my lathe absolutely all > that is needed is: > > net z-angle hm2_5i24.0.resover.01.angle => hm2_5i24.0.8i20.0.1.angle > net z-pid pid.1.out => hm2_5i25.0.8i20.0.1.current
I am probably a poor judge of that as my servo experience is not in the machine shop. I've quite some experience tuning servo's in broadcast gear, intending to play a tape while keeping the output within 5 ns of house time. Ampex, in the VR-1200, was the only maker that "got it right" so that could be done in about half an hour on a totalled diddled with machine. But they only tried for about 2 u-sec mechanical accuracy at the video out, the rest was done electronicly with varactor controlled delay lines which could get the off tape color burst to within 5ns by the 3rd of 8 cycles of color burst. There were still some mechanical residual errors that could cause the colors to shift in phase from the just corrected left side of the screen to the right side of the screen 50 some u-secs later, but that was eventually solved on later machines by servoing the shoe height based on the initial error of the next color burst. The shoe is a vacuum pumped tape holder that brought to tape to presumably the exact same radius of the head tips as they wore in service. A rate of wear highly determined by the environment, cooler and drier were better. Heads could wear about 1.75 thou, and head hardness determined how much they charged an hour. Nebraska ETV, (where I spent about 8 years of my broadcasting time) since they have 2 time zones, built their delay center with 3 such machines (sold for about $125k/ea in those days, late 60's) in a clean room whose air was both dried and cooled to about 50F and precipitron cleaned, and a roll of blank tape went in and was continually reused until trimming the damaged ends made it too short to use anymore. Those machines were initially setup with soft heads rated for 500 hours use, so the projected cost/hour was around $1.50 US. But with cold dry clean air, the first head failure was at just over 7000 hours, and was a solder joint in the internal rotary transformer, (the head wheel has 4 tips, and is spun at 14400 rpms) which was fixed N.C. and returned as there was still a nearly a thou of tip left. So a 500 hour head actually ran for just under 10k hours. Over the life of those machines that saved 3x the cost of the clean room including the energy bill. There's a lesson in that. No, I don't know much about servo's in dirty shops. -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
