DIY Laser levelling using webcam and laser level

[Kitwn]

Joe,
It's all working, giving a good display even with the B&D laser which I thought might be a problem. The only issue I have now is that my not-quite-full-HD 768 line laptop monitor can't show me the table of results which wants to be at the bottom of the screen rather than the side as in your picture. Looks a treat on the desktop monitor though. I wonder what the chances are of my wife lending me her swanky new full-HD touch-screen hybrid laptop for use in the shed? I could fold it over into tablet mode, put it keyboard down on top of a pile of sharp, greasy tools and then enjoy a slow, painfull death

[devmonkey]

Hi guys,

Fixed some UI issues so it should work on a 1024x768 laptop screen (just for you Kit). I've also added linear regression to the measurements taken. This is because the best way to use this imho is not to try to align to the reference plane (the laser) rather to calculate the error to the reference plane and then to shim or scrape such that these errors lie in a straight line. Please let me know if this makes sense to you. It is kind of a fudge and only works because given our vertical resolution is only +/-1mm and we are using it over a range of over 1000mm (or however long your x rail is) giving a worst case divergence angle of ~0.1degrees, i.e. the laser and the linear regression are very nearly paralllel. This implies a worst case vertical error of the residual caused by the divergence of the regression line from the laser is a rather small 1 nanometer, 1000x smaller than our sensor resolution.

The app now plots both the absolute and residual errors and tells you how much to shim or scrape at each point. So this is everything we need to level a rail, and when operated with a vertical laser line everything we need to straighten a rail. When I get around to it I will add two further measurement types, one for getting two rails planar, the other for tramming the spindle.

https://github.com/betzuka/laserleve...r.zip?raw=true


Cheers, Joe

[Kitwn]

And he does all this whilst standing on one leg and juggling with knives.

Kit

[devmonkey]

Just for fun I tried the system out with the very cheap line lasers you can get on Amazon and ebay for £3. These don't use a glass cylindrical lens, rather a plastic ridged grating with multiple ridges. Although the software was able to get a solid lock on the beam I personally wouldn't trust this, the lens seems to create multiple lines that when focused land on top of each other, giving us multiple guassians. The depth of focus is also not good. See the pictures:

[John McNamara]

Hi Joe

I wish I knew more about optics.

Cylinder lenses appear to be the cheapest.
I wonder if a piece of glass rod would suffice?

So many choices........

Powel lenses are more expensive,

https://www.laserlineoptics.com/powell_primer.html

https://www.google.com/search?q=powe...=powell%20lens

General searches .

https://www.google.com/search?q=line...%3Apinterest.*

https://www.dhgate.com/product/2pcs-...397472227.html

https://www.ebay.com/itm/2pcs-Optica...-/180869393128


EDIT:

Added
https://www.coherent.com/assets/pdf/..._FORMFIRST.pdf

https://www.alibaba.com/showroom/powell-lens.html

Regards
John

[devmonkey]

The cheapest are definitely these plastic grate things, the glass cylinders are much more, then the powel lens are about twice as much again. I think the cylinder is the best choice as the powel is designed to remove the gaussian beam intensity which for our purposes is extremely useful.

The self levelling laser i'm using is 1.3mW and has two lasers each with a cylindrical glass lens. 1.3mW is very weak compared to what you can buy online. Probably wants to be low power to avoid potentially damaging the cmos camera sensor.

If you want something that definitely works pick up a broken Dewalt DW088 on ebay. These seem to fail whereby one or other of the lasers becomes very dim, this is down to the driver board failing, so I would expect the lasers still work perfectly and can be scavenged.

[devmonkey]

Hi Joe

I wish I knew more about optics.

Cylinder lenses appear to be the cheapest.
I wonder if a piece of glass rod would suffice?

I don't think they are round, rather half round, I maybe wrong. The better ones are made out of something called K9 glass, again I don't know what this is. Maybe Andy can jump in here?

[AndyUK]

I don't think they are round, rather half round, I maybe wrong. The better ones are made out of something called K9 glass, again I don't know what this is. Maybe Andy can jump in here?

Watching the thread with interest, but unfortunately its been many years since I studied optics, and I'm not massively useful at this point! But I whole-heartedly agree that you want to keep the guassian characteristic where possible, as its a nice structure to fit to. You could use the FWHM from a flat-top profile, but I'd trust the guassian fit better as the regression uses the entire curve, rather than just the penumbras.

Re. lenses; It all depends on the incoming beam width, the radius of the rod/lens, and the refractive index of the material being used; in general I'd guesstimate that given a beam focused to infinity, you're likely to get a wider output spread by using a full rod, but there are so many variables here to play with, i'd be tempted to just go with an off the shelf lens designed for the job which will also guarantee clarity of the beam to a certain extent.

[John McNamara]

A number of sites show what appears to be a plain cylinder.

https://www.google.com/search?q=line...%3Apinterest.*

[Kitwn]

Joe,
The latest software version works perfectly and can be resized to fit nicely on my 'old' laptop. Thanks for all your effort.

Does the software work with a lens-less camera pointed directly at a laser pointer? I'm thinking you could arrange the pointer to provide a straight beam at a set height above a rail and detect how the spot moves around on the sensor as the camera backs away from the source on a carriage. Turning the camera 90 degrees allows measurement of horizontal and vertical errors. This is the quantum version of John's taught wire and requires a rigid, adjustable mount for the laser on the bed of the machine under test.

All,
I advise against trying to remove the optics from your cylindrically shaped, metal bodied, Mircosoft, auto-focus webcam. They're actually very solidly put together and mine is now a small pile of mangled bin-fodder. I've ordered a much more flimsy looking manual focus version from eBay (and a laser pointer).

Kit