DIY Laser levelling using webcam and laser level

[devmonkey]

Kitwn, about using it for tramming I would attach my sensor block to a T-bar in the spindle as if I was tramming a mill with a single dial indicator. Rotate the spindle and take sensor height readings at 0, 120 and 240 degrees rotation. Take plane described by these 3 3D points, calculate the plane normal and determine the error to the plane normal of your x axis plane, then shim the z axis until the normals are the same.

I will have a think about squaring but this is usually easy to do with dual x axis machines after skimming the bed by drilling 4 corners of a large square and checking diagonals using a stick with an indicator on the end, adjust home proximity sensors, re-home, repeat.

If at any point after initially bringing the x rails into plane you need to re-establish this plane in order to do something like tramming, it is unlikely the laser can be put back where it was initially. However since the rails are still planar the laser can be setup again and 3 points measured 2 from one rail, one from the other and the x plane normal established relative to the new laser normal. This is similar to moving between machine and workpiece coordinate systems in a CAM programme. For tramming we would align the spindle normal to the x plane normal via the laser normal, i.e. When the two errors are the same the spindle is trammed.

[Kitwn]

I'm very interested to look at your software on github. I'm no great programmer but have an unused Raspeberry Pi and a Pi camera which my brother -in-law sent me. I've been trying to work out what to do with them so this might be a possibility.This is exactly the sort of application he'd enjoy seeing it used for. It would be a large sensor block though with the Pi included as the camera attaches directly to it.
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Part of my concern with working out an exact series of measurements is separating the possible sources of a given error and being able to align the machine in a systematic way. There's no point making the axis of the spindle exactly vertical until after you've ensured the axis along which the Z assembly moves is vertical and that can't be done until the Y rails and gantry mountings are set up and so on.
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Some assumptions might be possible if your mechanical construction is very accurate but my machine is built using welded steel construction, a drill press and hand tools without access to a milling machine or other precision machining, so it's accuracy will only ever depend on being able to make measurements and correct errors with shims. I designed the whole thing with that requirement in mind but it's being able to make accurate measurements without spending more on a variety of gauges than on the machine itself that has made this thread so interesting. Like many hobbyists I have more spare time than spare money and there's great satisfaction in following Arthur Wellesley's maxim.
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Kit

[John McNamara]

Hi Devmonkey

I downloaded and set up the camera software from Github.
setting up is quite a process, a mate who is a far better programmer than me led me through the environment variables setup. I am not used to this sort of programming environment.
Once installed correctly the software compiled without an issue.

I was only using the webcam on my laptop and a hand held laser line (not point) generator. It worked very well.

A logitech webcam was also tried it worked but there were strange fresnel like circles produced with the laser. The logitech camera had a quite large lens. The laptop camera did not display the same aberrations. its camera is tiny.

I also tried a fuzzy pencil line drawn on paper that worked OK too.
A piece of wire should be no problem.

Over the weekend when I have time I will set up a test on a granite surface plate with some precision gauges. and a proper camera with and without a lens on a stand.

It will be very interesting to get a better idea of repeatable accuracy. I am sure it will be very good.

Congratulations Joe, great job.

Regards
John

PS:
I have started to draw up the flat surface generator I described,
I want to make it 90% from Laser cut 5mm steel plate. Using a single universal beam as the main frame (100ub 23) I know that that profile is available in Australia and the UK Hopefully Europe and the US too. It will hold an up to 100x100mm RHS Workpiece. To be used as linear rail support beams for routers and mills.
I hope it works! There is only one way to find out.

[devmonkey]

Hi Devmonkey

A logitech webcam was also tried it worked but there were strange fresnel like circles produced with the laser. The logitech camera had a quite large lens. The laptop camera did not display the same aberrations. its camera is tiny.

I also tried a fuzzy pencil line drawn on paper that worked OK too.
A piece of wire should be no problem.

If you are using a laser with the (crap) optics of a webcam then you will get all sorts of weird patterns and probably more problematic non-linearity meaning each pixel will register slightly different height errors, best to get an old or cheap webcam and rip the sensor out and bin the optics. If you want to stick with optics then use a piece of white paper as a screen between the laser and the camera, focus the camera on the screen.

With the pencil line did the gaussian detection work? I would be surprised if it did as the pencil line would be lower intensity than the paper. I would need to invert the intensity I would think for this to work properly with a pencil line or wire. Also to use as a shadow camera you will need to flood the background with an even light source, maybe a white led behind a piece of diffusion perspex (the translucent white stuff). This is to eliminate false triggering from the otherwise random background intensity of your workshop wherever the camera is pointing.

[John McNamara]

Hi Devmonkey

Yes the line did produce a gaussian plot. It was a crude test. I just placed the paper in front of the Logitec camera about 150mm away no backlighting just ambient fluorescent (Its night time) I did get the curve plot. it was all hand held testing lots of movement. I really want to test it properly. It will be interesting to try inverting greyscale?.

Cheers
John

[devmonkey]

To invert the greyscale add the following line to FrameAnalyzer.analyzeNextFrame() below where the rotation is performed:
Core.rotate(mat, mat, Core.ROTATE_90_CLOCKWISE);
Core.bitwise_not(mat, mat); <-- Add this line

[John McNamara]

Hi Devmonkey
Hi All

First tests!

Today I set up a quick test to determine what sort of accuracy might be achieved using a Webcam and laser.

I mounted the webcam on a linear rail slide, I was going to use gauge blocks against a stop to measure the resolution of the device using a cheap laser that I picked up from Aldi one day. it is the only line laser I have. That did not work because the hard plastic ends on the linear rails were too flexible, I could not get constant results.....

The Webcam is a 640 x 480 resolution Microsoft LifeCam VX -1000. It has an adjustable lens that I was unable to remove quickly so I just used it as is! Pointing the laser directly at the camera produced horrible flare. However angling the camera did work! I am not sure why? Probably something to do with the lens. The next tests will be done without a lens.

I think you could say that the tests were a bit of a comedy of errors!

Fortunately I has also set a magnetic base 0.01mm indicator on the rail. It saved the day. By simply pressing on the linear slide I was able to move the slide laterally about 0.04mm with medium pressure. when i released the pressure the indicator went back to zero. This is all I needed...

Now for the exciting part; Hidden at the bottom of the Gaussian graph there is a tiny numeric value, It followed my indicator movement when I moved the slide. very roughly a value of 1 to 4 on the graph value to 1 to 4 ticks on the 0.01mm indicator. I assume this correlation may not have been planned however with the particular camera I used it was very convenient.

I ran the test several times and it was repeatable.
0.01mm is equal to .00039" (about 4 tenths)
A very good result from a crude setup.

The following improvements will no doubt greatly improve the results.

A better camera with the lens removed.

Controlled ambient light. moving around the room can move the graph also sunlight entering the room moved the graph.
The sensor needs to be shaded as much as possible.

The numeric values at the bottom of the screen needs to be enlarged. Optional rounding and time averaging settings that can be applied to the displayed number would help to reduce the flicker.

I have yet to test the device with wire.

Regards
John

Three images below:

Homage to Johann Carl Friedrich Gauss https://en.wikipedia.org/wiki/Carl_Friedrich_Gauss

And the measurement principal of reversal. https://www.google.com/search?q=meas...%3Apinterest.*