DIY Laser levelling using webcam and laser level

[devmonkey]

Afternoon all.

I've finally got back to my machine project. I gave up with trying to create a planar surface in one shot and as the weather had warmed up I poured epoxy, this looks like it has worked well and made a very close surface for final levelling using the laser and shimming if required.

Anyway the purpose of this post is to describe a new app I put together today for laying the master rail straight. I decided it would be easier to use a taut wire rather than the laser for this and a cheap USB microscope.

So armed with some 0.28mm black fishing line I found in the garage and a club hammer I tensioned a wire parallel to where the master rail will sit. I used some white insulation tape on the machine frame below the wire to provide good contrast for the software and the wire runs over a couple of bolts that run through angle iron supports clamped to the ends of the machine frame. The wire is anchored at one end and the club hammer suspended from the other, the fishing line stretches out quite a bit and you can see the nylon flowing under the microscope, I waited for it to stop flowing before doing anything else.

The microscope is attached to a hiwin carriage and the new app accurately locates the wire allowing you to zero the tool then reports the error as you slide the carriage back and forth. A 3D printed clamp allows the microscope to the rigidly attached to the magnetic base.

Nothing new in the process that other people have performed other than the app that lets you achieve excellent accuracy with little effort. The resolution is roughly 3um per pixel repeatable down to less than 1um (relative to the straightness of the taut wire obviously).

The wire locating algo is quite different from the laser gausian model and seems extremely robust. For those interested it locates the two edges of the wire using a median gradient threshold down each column of pixels, regresses lines down these edges and auto tunes the threshold until it has exactly two lines that completely cross the image from left->right. It then bisects the two edge lines to locate the wire centre. This removes any error from tapering of the wire due to stretching under tension. You hit zero then the app will will show you the relative error to this point as you move the rail and/or carriage about.

Anyway I captured this video showing the app working on the machine frame:


I will use this tool to set the master rail over the next day or so.

Cheers, Joe

[Michael Gilligan]

Afternoon all.

[...]

Anyway the purpose of this post is to describe a new app I put together today for laying the master rail straight. I decided it would be easier to use a taut wire rather than the laser for this and a cheap USB microscope.
[...]

The microscope is attached to a hiwin carriage and the new app accurately locates the wire allowing you to zero the tool then reports the error as you slide the carriage back and forth.
[...]

Nothing new in the process that other people have performed other than the app that lets you achieve excellent accuracy with little effort.
[...]

The wire locating algo is quite different from the laser gausian model and seems extremely robust.
[...]

Cheers, Joe

.

With apologies for absence ... it's been a while since I was here :

That sounds like a great development, Joe
I obviously need to read the next couple of pages, but please let me join those requesting that you share the App

MichaelG.
.

Edit: Just off to grab that code

[devmonkey]

.

With apologies for absence ... it's been a while since I was here :

That sounds like a great development, Joe
I obviously need to read the next couple of pages, but please let me join those requesting that you share the App

MichaelG.
.

Edit: Just off to grab that code

Hi Michael,

I actually wrote a different app for the taut wire method, I don't think I uploaded it anywhere. It has been a while but I think it made use of the wire not crossing the sensor exactly parallel to the pixel rows to gain excellent sub-pixel resolution and it also took a bisector of the line edges as the line shadow is not gaussian when lit from above by a microscope. This also takes care of the converging or diverging wire edges which you can see under high magnification and are caused by the wire stretching more in the centre of the span than at the edges as it flows.

Unfortunately I wont have access to the machine with the code on for a few weeks. Thanks for the offer of some wire but I don't really need it, I found that black fishing line worked perfectly since the app is tolerant of an imperfect wire as described above.

Edit:
Actually it turns out I did upload the code, fill ya boots!
https://github.com/betzuka/laserleve...uilds/wire.zip

Cheers, Joe