I am building AS we mail ;-) On 8. August 2015 15:28:06 MESZ, Kenneth Lerman <ler...@se-ltd.com> wrote: >Here's an interesting experiment. > >Mount one of these so it tracks the circumference of a rotary table -- >say >a 12 inch diameter one. Setup a camera or laser or other means to >determine >when the table has rotated a full revolution. > >Then rotate the table a full revolution and see how many counts you >get. Do >this again. Does the number of counts repeat? How large is the error. > >If so, we've just made a rotary table with a resolution of a few tenths >(1/8200 of an inch) at the circumference. That's .00116 degrees. or 4.2 >seconds of arc. > >Ken > > >On Sat, Aug 8, 2015 at 6:37 AM, Julian WIngert <julian.wing...@web.de> >wrote: > >> Reading the datasheet: >> >> http://datasheet.octopart.com/ADNS-9800-Avago-datasheet-10666463.pdf >> >> Page 13: Path deaviation >> >> It seems that a homogenous surface puts down the error to ~1.25 / >1600 >> inch / inch with an optimum @~0.8 /1600 inch / inch with photopaper >and >> a sensing distance of 2.25mm. >> All at a relatively low speed (6ips) >> >> Combined with a rough syncing (every 2mm) - using a frame capture of >the >> sensor - you shall be able to get pretty high resolution with a >minimum >> of effort. >> The sensor itself works up to 150ips and 30g, what the resolution and >> deviation there may be... I dont know. >> >> It is - not recommended for new designs, but I am sure there is >> equivalent stuff out there. >> >> best regards >> julian >> >> >> On Sat, 08 Aug 2015, Julian WIngert wrote: >> >>> Am 08.08.2015 um 04:00 schrieb EBo: >> >>>> On Aug 7 2015 5:32 PM, Peter C. Wallace wrote: >> >>>>> On Fri, 7 Aug 2015, EBo wrote: >> >>>>> >> >>>>>> Date: Fri, 07 Aug 2015 17:13:25 -0600 >> >>>>>> From: EBo <e...@sandien.com> >> >>>>>> Reply-To: EMC developers ><emc-developers@lists.sourceforge.net> >> >>>>>> To: emc-developers@lists.sourceforge.net >> >>>>>> Subject: Re: [Emc-developers] research on optical encoders >> >>>>>> >> >>>>>> On Aug 7 2015 4:16 PM, andy pugh wrote: >> >>>>>>> On 7 August 2015 at 12:23, EBo <e...@sandien.com> wrote: >> >>>>>>>> Possibly, but I cannot tell from the information Renishaw >> >>>>>>>> published >> >>>>>>>> in >> >>>>>>>> that brochure. >> >>>>>>> I think that the target is a barcode. The head can see enough >> >>>>>>> barcode >> >>>>>>> to tell exactly where it is on the code sequence to within >one >> >> bar, >> >>>>>>> then looks at the absolute position of the bars in the >viewing >> >> area >> >>>>>>> to work out the rest of the bits of data. >> >>>>>> I think it is following on the same idea roughly. Looking at >the >> >>>>>> renshaw they claim it can give you 1nm (1e-9m) or 3.9e-8 >inches >> >>>>>> precision. I have no idea how they are pulling that off >besides >> >>>>>> laser >> >>>>>> interferometry and ring counting. Can you suggest another >method >> >>>>>> that >> >>>>>> would work? >> >>>>> AFAIK they dont use a laser, just a bright LED thats pulsed to >> >> take a >> >>>>> snapshot >> >>>>> of the barcode, probably with a rather high resolution linear >> >> sensor >> >>>>> array (or >> >>>>> multiple arrays with pixel interleaving) >> >>>>> >> >>>>> Quite high-sub pixel interpolation should possible with such a >> >> setup >> >>>>> because >> >>>>> of all the duplicated edges >> >>>> agreed with the laser/LED. I would have to study sub pixel >> >>>> interpolation to see how much additional interpolation you could >> >> get. >> >>> You can get really fine results on a theoretical perfect >black/white >> >>> change and the imaging sensor mounted 45deg. of an almost >unlimited >> >>> degree of subsampling. >> >>> Even with a cheap camera and optics there should be no problem to >> >>> resolve down to the uM scale. Problem is the speed of such a >> >> construct. >> >>> Even with high performance camera systems you have a delay that >makes >> >> it >> >>> imho unusable in realtime positioning. >> >>> >> >>> If you are able to interface the sensor with an FPGA doing the >> >> realtime >> >>> analysis - well then you have what renishaw probably has build... >> >>> >> >>> What should "relatively" easy to be doable is to add such a slow >> >> scale >> >>> to recalibrate the machine position regularly. >> >>> >> >>> My first idea was to use a laser mouse sensor, which is easily >> >>> interfaceable even with MESA cards - there are ones with SPI >> >> interface - >> >>> but my application is the calibration of my astronomic mount - >which >> >>> hardly moves more than 1RPD (Rounds per DAY)... >> >>> >> >> maybe a somewhat naive question - but how would you deal with >vibration >> >> >> >> of the cameras/sensors ? gut feeling - if you try to deduce 10E-9 >m >> >> then >> >> even just environment noise would become a problem or is there >some way >> >> to eliminate that in practice ? >> >> >> >> thx! >> >> hofrat >> >> >> >> >> >------------------------------------------------------------------------------ >> >> _______________________________________________ >> >> Emc-developers mailing list >> >> Emc-developers@lists.sourceforge.net >> >> https://lists.sourceforge.net/lists/listinfo/emc-developers >> >> >> -- >> Mit freundlichen Grüßen aus Pinneberg >> Julian Wingert >> >> Hellenkamp 8 >> 25421 Pinneberg >> >> Phone: 0170/4516094 >> Mail: julian.wing...@web.de >> >> USt-IdNr.: DE272503212 >> >> >> >> >------------------------------------------------------------------------------ >> _______________________________________________ >> Emc-developers mailing list >> Emc-developers@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-developers >> > > > >-- >Kenneth Lerman >55 Main Street >Newtown, CT 06470 >------------------------------------------------------------------------------ >_______________________________________________ >Emc-developers mailing list >Emc-developers@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-developers
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