I think what you are seeing is a "speckle pattern" The laser is not making 40 small beams. it is making one nice uniform beam but remember the light is all in phase. After a reflection from a textured surface the light hitting the back your eye adds in phase and the spots you are are where the light adds in phase and the other places the wave self-cancels
see the second paragraph on this page: https://en.m.wikipedia.org/wiki/Speckle_pattern. If the pattern of the dots stay the same as you move the laser around then the "speckling" is happening on the lens and some parts of the beam are flying in a shorter or longer path length. and add the all add in phase. Even if the laser were making 40 spots and the beam as not on-axis, don't bother to fix it. You don't need to. A 1 depress misprinted beam will give only tiny error for your purpose. Down in the 2% error range. and I bet you can aim the beam by eyeball to 1/2 a degree. That is good enough. Even if there are 40 beam hitting your target, so what? Be happy not you can take 4 measurements at once and drastically reduce the signal to noise ratio. If you are using software you are like tough an autocorrelation between images and the is a peak when yu have found a match. having a complex parter makes the peak of the function more steam and you have better and more accurate results. 40 points is a Good Thing, as long as they don't change. Again, you beam is fine, it is just that most people forget the laser is 'coherent" light and all in phase. On Wed, Sep 26, 2018 at 4:24 PM Gene Heskett <ghesk...@shentel.net> wrote: > On Wednesday 26 September 2018 17:22:01 Chris Albertson wrote: > > > ---------- Forwarded message --------- > > From: Gene Heskett <ghesk...@shentel.net> > > Date: Wed, Sep 26, 2018 at 12:08 AM > > Subject: Re: [Emc-users] More on bed wear fix > > To: <emc-users@lists.sourceforge.net> > > > > > > But finding a camera chip big enough to shine these laser's on so that > > > > > the laser stays on the imaging chip cannot be found in an integrated > > > package that will plug into the 15 pin connector on a pi. The laser > > > beams are 10x the size of the imaging chips even if they're > > > perfectly aligned. > > > > What? If I buy a normal green laser pointer the green spot is about > > 1mm in dimmer. If I place a 0.01 pinhole in the path of the laser > > the spot is pretty close to 0.01. As for a camera that plugs into a > > Raspberry Pi, any USB web cam will do. But I'd use a notebook PC > > rather then the Pi. What you probably want is not to shine the beam > > on the sensor but have a glass or plastic target and use a $20 USB > > microscope to focus on the target. Glass is good because it will > > reflect 99% of the laser light away and not blind the camera. > > > > As you move the carriage the laser spot should move on the target and > > the USB microscope will image the back side of the target and you can > > measure the movement by counting pixels, Software can do better by > > doing some curve fitting. Even if the bed is very bad I doubt the > > laser spot move even 0.5mm > > > > If the laser spot looks huge, perhaps what you have is a small spot > > that overloads the sensor. > > I am looking at the spot with my eyes. I can see the individual dots, > probably 40 of them. If I could restrict it with a pinhole on the laser > to block most of the dots, that would be great, but even with edm I > don't think I could make a pinhole that small. > > > The target may need to do some serious > > amount of attenuation. > > I have a polarizing variable filter with a range from ND-2 to ND-400 > coming. > > > And while I said "USB "microscope" I bet a > > magnifier hot glued to a web cam works. But I did buy a $10 > > microscope and the image is poor but I can inspect the solder joints > > on SMT parts, A medium size SMT resister pretty much fills frame, > > these things are on eBay for $9 to $35 and they all appear to the the > > same. > > Humm, more experimentation seems in order. I have drills down to #80, and > yards of Reynolds wrap, which might get me down to a usable spot size. > > Pretty much everyone who wants to measure displacement from a line > > uses a laser. It is hard to find a better reference line > > > > If your bed where really bad Just put a steel rule in the tool holder > > and eye-ball the laser spot in the rule, maybe use a loupe to read it. > > > > Something is wrong if the laser spot is large. > > Its way too big at the source, and 2 of them (different brands) are doing > it. The pinhole at the src seems like a good starting point. > > [...] > > -- > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
