On Sat, 8 Aug 2015, Nicholas Mc Guire wrote: > Date: Sat, 8 Aug 2015 10:02:00 +0200 > From: Nicholas Mc Guire <der.h...@hofr.at> > Reply-To: EMC developers <emc-developers@lists.sourceforge.net> > To: EMC developers <emc-developers@lists.sourceforge.net> > Subject: Re: [Emc-developers] research on optical encoders > > 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 >
I think the trick the Resolute encoder uses is this: the image is captured in a perhaps sub microsecond flash of the LED, and then the "image" can be shifted out of the sensor at a leisurely rate. The specifications sort of suggests this (very fast capture (ns) time, but only multi KHz maximum update rate) Peter Wallace Mesa Electronics ------------------------------------------------------------------------------ _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
