On Sunday 27 January 2008, Kenneth Lerman wrote: >Mounting two detectors in quadrature will be a bit of a problem since the >distance betweeen them will need to change depending on the temperature >(although off hand, I haven't checked to seem how much). At any rate, >though, that's just a matter of engineering.
I wouldn't think I'd need to Ken, just drive the carrier input of a 4 quad detector with the tx signal suitably attenuated. Count zero crossings as it moves for the major divisions. Two of them with a 90 degree lag would give the equ of step/dir or a/b signals to count. I don't intend to try and take an absolute position other than zeroing the counter at some repeatable arbitrary point & everything else is measured relative to there. I think I'd probably generate the carrier digitally at 4x operating, and get my drive phases from a shift register driven by the 4x, and clocking in the /4 output. All cmos for cool operation etc. Details, details. Doable in wire wrap for the breadboard model. A milled pcb for production. :-) >Every once and a while, I check ebay for interferometers. The dual frequency >laser sources go for around $1000, I believe. Sam's laser FAQ does have some >info on making your own, though. So far, I haven't been that committed. > >This is not something I need. But, it is something I'd like to have. > >Ken > >----- Original Message ----- >From: "Gene Heskett" <[EMAIL PROTECTED]> >To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> >Sent: Sunday, January 27, 2008 4:15 PM >Subject: Re: [Emc-users] Ball screws + error compensation > >> On Sunday 27 January 2008, Kenneth Lerman wrote: >>>At 1080 feet per second, one wavlength of sound at 50 KHz is 1/50 foot or >>>about 1/4 inch. I think you want way more resolution than that. >>> >>>Ken >> >> I had in mind one of the 200 khz+ models, Ken. Furinstance, 200 khz >> gives .067" per wavelength according to kcalc using Massa's formula's and >> converting to inches, and a quadrature phase detector can surely break >> that >> down to one or 2 degree increments. 2 degrees would give us .0003" >> accuracy >> that wouldn't be subject to cyclic errors in the screws and such. For my >> little mill, that is, as an ex bro-in-law used to say, "close enough for >> the >> girls I go with". Heck just having a known zero point every 0.067" would >> beat the pants off the dial indicators I have. >> >> There is also some even higher frequency stuff out there. I've sent for >> P&A >> on the 420khz devices from the link in my reply below. And google turned >> up >> one that claims megahertz plus stuff. That's probably out due to air >> attenuation factors but TBT I haven't looked. >> >> This is something I may be able to knock up a breadboard proof of concept >> model that I'd never take a picture of, else somebody would pull my >> tinkers >> license, in a price range I can afford. If it shows promise even if my >> breadboard model has trouble nailing jelly to a tree cuz its not very >> rigid, >> well... Ya never know, but I do like to think out loud. Others picking >> holes in my theory are always welcome to comment. :-) >> >> The sheer cost of a laser src pure enough to do this prices it well out of >> my >> range, and I suspect out of range for anybody but GM & Toy. I *think* >> this >> is doable in a 3.2 USD price range. >> >>>----- Original Message ----- >>>From: "Gene Heskett" <[EMAIL PROTECTED]> >>>To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> >>>Sent: Sunday, January 27, 2008 3:03 PM >>>Subject: Re: [Emc-users] Ball screws + error compensation >>> >>>> On Sunday 27 January 2008, John Kasunich wrote: >>>>>John Kasunich wrote: >>>>>> For measurements every inch, you can often find jig-borer micrometer >>>>>> sets on ebay or other surplus places, often mis-listed as inside mics >>>>>> like this one: >>>>>> >>>>>> http://cgi.ebay.com/PRATT-WHITNEY-10-PIECE-INSIDE-MICROMETER-SET_W0QQi >>>>>>te mZ >>>>>> 140200200097QQihZ004QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewI >>>>>>te m >>>>>> >>>>>> (7 hours to go, $22.50) >>>>> >>>>>Another couple sets: >>>>> >>>>>http://cgi.ebay.com/INSIDE-MICROMETER-AND-END-MEASURE-SET_W0QQitemZ35001 >>>>>73 55 826QQihZ022QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewItem >>>>> >>>>>Missing a few parts, makes it less interesting to most buyers, but it >>>>>has three 12" standards, so it can do 1" to 51" in steps of 1". No bids >>>>>so far, with less than one day to go, and an asking price of $20. >>>>> >>>>>http://cgi.ebay.com/PRATT-WHITNEY-11-PIECE-INSIDE-MICROMETER-SET-0001_W0 >>>>>QQ it >>>>> emZ330206299195QQihZ014QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZVie >>>>>wI tem >>>>> >>>>>This set is complete, has 3 bids ($10.50) so far, and will probably go >>>>>up a bit. >>>>> >>>>>There are a few more as well. >>>>> >>>>>Even cheaper would be a set that is missing the micrometer head. >>>>>However, they'll be harder to find because they're more likely to be >>>>>mis-listed as something else. Perhaps search for Pratt & Whitney or >>>>>Lufkin, since the rods are usually marked with the makers name. >>>>> >>>>>Like anything, its possible that the rods are worn and no longer >>>>>accurate. You can do some testing, by comparing for instance a 12" rod >>>>>to another 12" rod, or to the sum of a 6" and two 3", etc. In general >>>>>though, people tended to use those things gently. >>>>> >>>>>Regards, >>>>> >>>>>John Kasunich >>>> >>>> Interesting John. But the whole idea has threads about interferometer >>>> based >>>> methods going around in my head, and the thought of the single frequency >>>> coherence required to make that work keeps backing away from the >>>> relatively >>>> expensive he-neon lasers that still require some filters to achieve a >>>> reasonable facsimile of single frequency output, plus the fact that the >>>> accuracy level with an IR source is 10x overkill for this, and thinking >>>> in >>>> terms of ultrasound in the 50khz plus ranges. >>>> >>>> First, single frequency is easily achieved, and second, given a phase >>>> detector, wouldn't the accuracy be more than sufficient for uses such as >>>> this >>>> over distance ranges up to say 4 feet? Speed of sound in air vs >>>> pressure >>>> and >>>> temp would need to be taken into account, but what other problems might >>>> there >>>> be? I have in mind a peizo mic on both ends, one carried by the table >>>> and >>>> the other fixed, with the table mounted one being the mover, and the >>>> stationary one being the pickup and detector driver. >>>> >>>> Can anyone throw a wrench into this and debunk the basic idea? The >>>> medical >>>> field is awash with suitable transducers I believe. >>>> >>>> At <http://parsonicscorp.com/ultrasonics.html> is one that operates at: >>>> Model Number 42005 >>>> Frequency kHz 420 >>>> Capacitance pf 650 >>>> Insertion Loss db at range listed -80 8" >>>> Maximum Drive Volts p-p 150 >>>> Rise Time Microseconds 100 >>>> Temperature Range Degrees F 0 - 135 >>>> Beam Angle Total -6bd Pulse Echo Mode Degrees 6 >>>> Bandwidth -6 db in kHz 20 >>>> Power Input at rated Voltage Watts RMS 4 >>>> Typical Range* 3" - 18" >>>> Housing Material ABS >>>> Transmission Window ABS >>>> >>>> For longer distances than 18" additional gain would be needed in the >>>> path >>>> of >>>> the one used for a microphone, but a quadrature detector should be able >>>> to >>>> count ok. Side shielding for ambient noise control might be in order >>>> some >>>> some environments due to the 20 khz bandwidth spec, but I can't see any >>>> reason it couldn't work at least as accurately as any mechanical method >>>> could. One would want to scope the output and adjust the driver >>>> oscillator >>>> to center it on the individual pairs most sensitive frequency which >>>> would >>>> help in the ambient noise cases. This is however, well above the shops >>>> local >>>> crickets I'd bet... >>>> >>>> I'll email them for a quote just for grins & giggles. >>>> >>>> -- >>>> 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) >>>> We are what we are. >>>> >>>> ------------------------------------------------------------------------ >>>>- This SF.net email is sponsored by: Microsoft >>>> Defy all challenges. Microsoft(R) Visual Studio 2008. >>>> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >>>> _______________________________________________ >>>> Emc-users mailing list >>>> Emc-users@lists.sourceforge.net >>>> https://lists.sourceforge.net/lists/listinfo/emc-users >>> >>>------------------------------------------------------------------------- >>>This SF.net email is sponsored by: Microsoft >>>Defy all challenges. Microsoft(R) Visual Studio 2008. >>>http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >>>_______________________________________________ >>>Emc-users mailing list >>>Emc-users@lists.sourceforge.net >>>https://lists.sourceforge.net/lists/listinfo/emc-users >> >> -- >> 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) >> The scum also rises. >> -- Dr. Hunter S. Thompson >> >> ------------------------------------------------------------------------- >> This SF.net email is sponsored by: Microsoft >> Defy all challenges. Microsoft(R) Visual Studio 2008. >> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > >------------------------------------------------------------------------- >This SF.net email is sponsored by: Microsoft >Defy all challenges. Microsoft(R) Visual Studio 2008. >http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >_______________________________________________ >Emc-users mailing list >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users -- 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) Westheimer's Discovery: A couple of months in the laboratory can frequently save a couple of hours in the library. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
