DIY Laser levelling using webcam and laser level

[John McNamara]

Hi All

Today I tested the software using a 640 x 480 VGA webcam without a lens and #2 Roslau Music wire (0.0010" thick).

Digging around the workshop I resurrected an accurate XYZ jig table I lashed up with some star linear bearings and preloaded 8mm screws some time ago, this enabled me to precisely position the webcam now stripped from it plastic housing and mounted on in an aluminium bracket securely clamped on the XY stage of the jig. Measurements were taken with a Mitutoyo 0.01mm per division dial indicator.

The wire was positioned about .0015" above the face of the Camera sensor.
Calculated resolution achieved was 130 lines used to measure 0.05m = .003846mm per pixel line 0.000151") see Excel Image below.

This was repeatable I performed the test several times. however there are some issues measuring small values. It was difficult to measure .01 increments repeatably due to the software constantly recalculating very slightly different values. the source of this error needs to be tracked down. It may not be a software issue, I suspect It may be a combination of hardware and software issues.

From various tests I have observed changing light conditions cause the measured value to change in a very substantial way. I also observed this using the laser in earlier tests although to a lesser extent.

In the image below notice the paper tent covering the sensor this is essential to reduce the effect of stray light while providing somewhat even illumination of the sensor. It is not Ideal. I need to enclose the sensor in total darkness apart from an even illumination source behind the wire. I think this light source needs to be variable intensity to provide the correct grey scale balance for the software.

Once the correct lighting conditions are achieved I will run the tests again.

The tests today have proved that the Webcam software is already capable of very good repeatable accuracy. and that there is still plenty of room for improvement. Very exciting!

Regards
John

4 images below:

[devmonkey]

Hi John,

It looks like you are using a very old version of the software, I would just download the ready to go latest version, this has the smoothing you need for actual measurements, plus a load of other enhancements, see my previous posts.

When used as a light sensor with a laser and no optics I have testing in pitch darkness and bright light and there is no variation at all, this is because the laser saturates the sensor.

When used as a camera, i.e. focused on an object such as a screen ambient light has to be completely eliminated both front and back of the sensor, you get some shine through the pcb even. I put mine in a black box.

When used as a shadow camera without optics and the shadow generator (wire in your case) very close to the sensor you should be able to just put a very intense light source behind the wire, this will saturate the sensor which is what you want, you will need some diffusion material to even out the light source as I mentioned before.

The software automatically scales the intensity plot, assuming you can generate enough contrast between the thing you are measuring and the background.

You should be able to get very repeatable measurements down to 3um, when using as a shadow camera make sure you tick the invert box in the prefs.

Keep at it!

Joe

[John McNamara]

Hi Joe

I am using the latest software

3um = 0.00011811" (Inches)

I am going to repeat the test tonight, better light control.

Regards
John

[devmonkey]

The picture you attached to the previous post was not the latest version John, the latest version has a table of measurements taken and smoothing when taking a measurement, export to csv, etc. Maybe that photo you took was from some previous experiment?

3um = 0.00011811" (Inches) --> CORRECT

FYI, this is what the latest version looks like:

[John McNamara]

Hi Joe

I ran the tests again this time using a small LED torch as a bright light source.
This gives a very sharp high contrast graph.

Strangely the scaling changed to 119.9 pixel lines with the new light source. I repeated the test a couple of times. the results were the same.

I did not change the gap between the wire and the sensor. it must be caused by the change in light source.

I used the software measure table and recorded every step between zero using 0.05mm steps see image below.

The setup I am using moves the sensor not the wire, Important for a point light source to avoid the shadow elongating like the sun in late afternoon.

This is easy to prove moving the torch by the slightest amount changes the measurement.
I really want to find an evenly dispersed light source.

I have yet to try your smoothing settings, That will be interesting.

Edit just noticed the software has changed a bit more. I will update


Regards
John

[John McNamara]

Hi Joe
Hi All

I downloaded the next version that displays a graph of the measured points. And look how nice and linear the graph is! .05mm measurement steps on the dial indicator.



I ran it 3 times to check.

While testing I moved the light a tiny bit. I had to start again, The light source will have to be rigidly mounted on the platform or you will get errors.

Will the current software work with higher resolution cameras say 1080P? I realize there would be more number crunching for he processor.

Regards
John

[devmonkey]

Hi John, Yes with your shadow camera setup you will always have to move the light source with the sensor board, they really need to be bolted together with a gap for the wire. I have used translucent white perspex for led light diffusion before, works really well, you can buy it on amazon.