DIY Laser levelling using webcam and laser level

[John McNamara]

Hi Devmonkey

Your comment.....
"or the laser line is using a diffraction pattern rather than a cylindrical lens."

Yes I think there is a problem with the laser source.

Without the lens the graph is far worse with multiple peaks. Upon opening the case there is a shaped plastic stepped prism that limits the beam to 90 degrees of coverage. the step is in the middle of the laser. (There are actually 2 similar laser sources in the unit) both are the same. it is not a tubular lens.

I will have to source a good quality line laser. not sure where yet?

The camera sensor appears to be closer to 3.5mm wide including the border so I guess the active area to be about 3mm wide. Its a fairly old unit but it works well.

Regards
John

[devmonkey]

Hi John,

I'm just using a bog standard Dewalt laser level, part number DW088.

I'm curious, the laser you have, how thick is the line at 2 and 5 or more meters? If it is still a nice narrow line 2-4mm thick it could still be usable, try moving it further away from the sensor. Also try using the laser without the case on, maybe the window is distorting it as well?

The £3 diffraction based lasers I have that are total rubbish but still work but can only be focused to a fine line line at a specific distance making them useless for any actual measurement we need.

This is what the crap lasers look like looking into the lens:


This is what a cylindrical lens looks like on the DW088


I haven't tried one but this looks like it might work well:
https://banggood.app.link/AAvDRpISpZ
Cheers, Joe

[devmonkey]

Software should work on most platforms, that is the point of java. However the native component that talks to the webcam doesn't work on the RPI without some changes, see here from the author.

http://webcam-capture.sarxos.pl/

[devmonkey]

John, it would be trivial to extend the software to write the resolved beam location down a com port to your arduino. On the arduino you would run a closed loop to move the sensor to get the beam central.

Let me know if you want this added, and also what format to send the data in.

[John McNamara]

Gee Joe.

So many minds around the planet working on a problem generously sharing their ideas.

I Ordered a PI 4 today and will start thinking on the software.

Regards
John

[devmonkey]

Gee Joe.

So many minds around the planet working on a problem generously sharing their ideas.

I Ordered a PI 4 today and will start thinking on the software.

Regards
John

See what I said above about it not working on a PI by default.

[Kitwn]

Hi Kit,

At the moment the app is only performing a gaussian fit in 2D, i.e. one spatial dimension say Z and intensity. I could probably add a 3D fit which would allow you to use a dot laser.

I wasn't thinking of measuring in two dimensions at once, just wondering if the software would cope with just a spot, treating it rather like a short line segment covering only part of the sensor. I would always expect to rotate the sensor to select between horizontal and vertical error measurements. Please don't do even more work just to suit my whims! This was more to do with removing the problems associated with the line-laser lenses. As you would only ever be working with the same central area of the laser line anyway if used as I was thinking, it probably makes no difference.

The camera I've ordered is this one, it looks suitably flimsy at the front and is even cheaper than yours!

[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:

[driftspin]

Hey guys,

I have been following this thread with great interest. Really great work.

I really like they way the camera + software is used for this purpose. It smells like a commercial oppertunity in my opinion.

Anyway, Since i bought a new house i am about to move my cnc machine in about a month or two.

I think i could use a laser level device for some of the needed remodelling work so that one could pass investment committee.

I would like to use this technique for a check on my machine after transport.

Actually.. it would be the first time and method i could set up for a half decent check on my machine.



So i would like to buy a new laser device with this in mind.

I only have an 8 mm umbilical type usb HD cam atm. So a really small chip.. i guess not usable for this pupose.

Maybe it could be with the indirect method putting the camera behind the screen.
Is that idea abandoned?

Are you guys using 640x480 on purpose?
Do low res low cost chips have the wanted size / resolution / pixels per mm.
So no need/advantage for throwing a few extra pecunia?

So does a laser level loc in position after setup?

Or do you have to trust the deviation is constant / repeatable.

Greetings Bert


Verstuurd vanaf mijn SM-A320FL met Tapatalk

[devmonkey]

Hey guys,

I have been following this thread with great interest. Really great work.

I really like they way the camera + software is used for this purpose. It smells like a commercial oppertunity in my opinion.

Anyway, Since i bought a new house i am about to move my cnc machine in about a month or two.

I think i could use a laser level device for some of the needed remodelling work so that one could pass investment committee.

I would like to use this technique for a check on my machine after transport.

Actually.. it would be the first time and method i could set up for a half decent check on my machine.



So i would like to buy a new laser device with this in mind.

I only have an 8 mm umbilical type usb HD cam atm. So a really small chip.. i guess not usable for this pupose.

Maybe it could be with the indirect method putting the camera behind the screen.
Is that idea abandoned?

Are you guys using 640x480 on purpose?
Do low res low cost chips have the wanted size / resolution / pixels per mm.
So no need/advantage for throwing a few extra pecunia?

So does a laser level loc in position after setup?

Or do you have to trust the deviation is constant / repeatable.

Greetings Bert


Verstuurd vanaf mijn SM-A320FL met Tapatalk

Hi Bert,

The sensor in your cam is probably fine, although if the overall dimension of the camera is only 8mm it maybe harder to work with. The VGA sensors we are using are 2mm across.

It seems most of the cheap cameras are vga even though they are sold as HD. It is difficult to determine what the actual resolution of the sensors are without a part number, some are probably higher resolution sensor that are binned to get VGA output. We want a reasonable frame rate for averaging so given the bandwidth constraints of USB2 which most of the cameras talk, VGA can be give us 30FPS.

If you take a 2mm sensor with 640 columns of pixels you get 3um per row which is plenty small enough for what we are doing.

My laser doesn't lock in position, but once allowed to stabalise it doesn't move unless knocked. I only need the laser to not move for one measurement run, as I'm not trying to align to the laser rather to get the errors between the laser and whatever i'm measuring to lie in a straight line. From my initial experiments the laser doesn't move at all over say a 10min session. The Dewalt laser I'm using is damped with a magnet, this probably helps. The laser doesn't even need to be self leveling, this just helps getting it setup.

So the process would be switch on the laser (this moves it a bit), wait for a few seconds for it to stabalise, take N measurements along a rail, switch the laser off, shim the rail, repeat. It doesn't matter if the laser moves between runs.

Cheers, Joe