DIY Laser levelling using webcam and laser level

[Michael Gilligan]

Greetings from NorthWest England

I was alerted to this very interesting project by John McNamara [many thanks, John] and have joined the forum to participate in this discussion. ... Hopefully I can be of some help on the optical side of things, but this first post concerns the software:

I have tried running the current version on my 2009 MacBook Pro, under el Capitan, and everything seemed fine except that I could not close the application ... it did not even respond to ‘Force Quit’ and I was obliged to re-boot the machine.

Windows users have a .bat file; so I am wondering if some ‘initialisation’ might be required before Java is happy running the application under OS X

I would be most grateful if anyone can advise.

MichaelG.

[devmonkey]

Hi Michael,

Welcome! I haven't tried it under OSX, but I'm pretty sure someone in this thread did.

It might well be a driver issue with it not unloading properly, unfortunately I don't have a mac book pro old enough to replicate your system.

Joe

[Michael Gilligan]

Thanks for the prompt reply, Joe

Hopefully there is someone else out there, limping along with a much-loved but obsolete Mac !

MichaelG.

.

Edit: I’ve just tried a little ‘self-help’ and found this:
https://apple.stackexchange.com/ques...vents-shutdown

Unfortunately it is beyond my comprehension.

[AndyUK]

Edit: I’ve just tried a little ‘self-help’ and found this:
https://apple.stackexchange.com/ques...vents-shutdown
Unfortunately it is beyond my comprehension.

As far as I can see, that's just talking about the issue and other ways to force quit the application.

I'd try uninstalling and reinstalling java on your Mac.

Failing that, you could try running Linux in a virtual machine, and download Java onto that. I'm a fan of Oracle's Virtualbox.

[Michael Gilligan]

Thanks, Andy

I will try a clean install of Java this evening
... There have been several versions on my Mac over the years, so perhaps there is something unnecessary lurking.

MichaelG.

.

Edit:
I removed all trace of Java from the machine [following Oracle's instructions], and installed afresh:
____ You have the recommended Java installed (Version 8 Update 231) ____

For whatever reason: The application now closes as it should. ... Thanks again, Andy

[John McNamara]

Hi Michael :)

I am glad you have popped in here to shed a little light on the optical side of these experiments.

Regards
John

[Michael Gilligan]

I think it worth sharing this FAQ answer from Edmund Optics:

Frequently Asked Question
Question

What is the difference between refractive and diffractive line generators?

Answer

A refractive line generator uses a cylinder or rod lens to focus a laser in only one axis only (drop-moved placement) in order to create a line of light. A diffractive line generator uses a flat optic with an etched microstructure that breaks apart a laser beam and forms an interference pattern in the shape of a laser line. Refractive optics do not correct for the inherent Gaussian profile of a laser beam and form a line with a "hot spot" in the center and fading edges. Diffractive optics will create a line that is uniform in thickness over its length, but is segmented. Diffractive line generators also cause a small portion of the light to be redirected into different diffractive orders, which causes additional faint lines to appear. Some laser line generators use a unique patented Powell glass lens design in order to achieve a continuous (not segmented) line with an even distribution along the length of the line.

Here is Powell’s patent:
https://worldwide.espacenet.com/publ...C&locale=en_EP

and a more comprehensible description:
https://www.laserlineoptics.com/powell_primer.html

MichaelG.

[John McNamara]

Hi Michael

Buying A Powell lens from Laserline, Edmund or other big optical equipment suppliers is pretty expensive starting at around $250 USD. I did a little google search and found a few from Ebay etc. at a more reasonable cost for an amateur experimenter. The question is which one?

I have not yet got my head around what would be the ideal angle for the Powell lens assuming that the l operating range is from 100 to say 3000mm.

The laser driving the unit also is also a consideration I nice clean spot is required.

Regards
John

https://www.google.com/search?q=powe...l%20lens#spd=0

[Michael Gilligan]

You’re quite right, John ... they are pricey, ‘though It’s encouraging to see better prices on ebay

My post was really just for technical information.

For what you are are doing [with the wire shadow and very small displacements], I don’t think you need worry about laser lines anyway: Unless I am very much mistaken, you could use any collimated light-source that filled the area of the sensor.

As for laser spot quality ... the classic solution is to use ‘Spatial Filtering’ ... but that’s another potentially costly and bulky solution to a problem that might not exist.

My impression is that this project is all about leveraging the precision of mass-market sensors with ingenious software.

MichaelG.

[devmonkey]

Hi Michael,

Do you have a view on how flat the projected plane of a cylindrical lens laser line is likely to be? This is something I still haven't measured as I have no large enough reference plane.
Along a given ray it should be absolutely straight but will it undulate across 'rays'? By ray I mean a line from laser source to sensor.

My latest thoughts on how to measure this was to place four pillars in a square on a reasonably flat stable surface (concrete floor). Place the laser so that it projects across the tops of the four pillars and use height readings from 3 of them (as any 3 points will be planar) to bring the fourth into plane with some shimming. Now move the laser around the room and have it cast a different area of the beam over the pillars and measure again, check if all 4 pillars are still planar, repeat this a few times.

Thanks, Joe