On Sunday 15 July 2012 17:01:22 Jon Elson did opine: > andy pugh wrote: > > On 15 July 2012 14:45, Gene Heskett <ghesk...@wdtv.com> wrote: > >> But the internal calculations for velocity etc are done at the servo > >> threads granularity of nominally 1 millisecond. So there is no > >> chance of the figures being accurate when the count may be up to a > >> millisecond old. > > > > The counts shouldn't be more than a thread-dither old (10uS or so). > > The calculation function reads the latest count from the base thread > > functions (possibly a base-thread old). > > > > The FPGA in the Pico card being discussed here ought to make an even > > better job at being up-to-date. > > The Pico Systems USC does not have this feature (timestamping of encoder > count arrival). The UPC does. The position CAN be thought of as > "stale" as the encoder gives no info between counts. So, if it crossed > the boundary to a new position a while ago, you have no way to know how > close it is to crossing the next boundary. > > Jon
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. Then add the last few digits for the position it is expected to be at the servo threads time. The only thing to complicate that would be a motion reversal within that 4 sample period. Or maybe I don't fully appreciate the problem. No explanation offered so far seems to explain why the encoders rps output, at a mechanical speed of 20 rps, has +- 3.xxx or more from the 20 its actually doing, flickering in the halmeter output. And this 'noise' does not seem to be all that much effected by the actual speed regardless of the speed as long as its over about 1 rps. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! A synonym is a word you use when you can't spell the word you first thought of. -- Burt Bacharach ------------------------------------------------------------------------------ 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
