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.
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_W0QQite >>>>>mZ >>>>> 140200200097QQihZ004QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewIte >>>>>m >>>>> >>>>> (7 hours to go, $22.50) >>>> >>>>Another couple sets: >>>> >>>>http://cgi.ebay.com/INSIDE-MICROMETER-AND-END-MEASURE-SET_W0QQitemZ3500173 >>>>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_W0QQ >>>>it >>>> emZ330206299195QQihZ014QQcategoryZ41937QQssPageNameZWDVWQQrdZ1QQcmdZViewI >>>>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
