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
