DIY Laser levelling using webcam and laser level

[John McNamara]

Hi Joe and Kit

I have been working on automating the positioning of the sensor to the wire.
To do that it really needs a micro to do the hardware housekeeping, control step motors and limits etc. It also removes the need to lug a PC around.

A mate tried running the cam software on a laptop that runs Debian Linux. It Ran!
He is also into Rasberry PI micros. as said that the software should be fairly easy to port over to a PI. Best a PI 4 for speed. it may be slower than a PC that has to be tested.

I am going to order one and we will try it.

To automate the software will it to address some output registers to hold the current position of the wire or laser relative to the centre point of the camera sensor.

The more I work on this project the more excited I get. Great work Joe.

Regards
John

[Kitwn]

John,
I have a Pi 4 and a matching touch screen waiting for something useful to do so will be very interested to see your results.

Kit

[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]

Joe,
The latest software version works perfectly and can be resized to fit nicely on my 'old' laptop. Thanks for all your effort.

Does the software work with a lens-less camera pointed directly at a laser pointer? I'm thinking you could arrange the pointer to provide a straight beam at a set height above a rail and detect how the spot moves around on the sensor as the camera backs away from the source on a carriage. Turning the camera 90 degrees allows measurement of horizontal and vertical errors. This is the quantum version of John's taught wire and requires a rigid, adjustable mount for the laser on the bed of the machine under test.

All,
I advise against trying to remove the optics from your cylindrically shaped, metal bodied, Mircosoft, auto-focus webcam. They're actually very solidly put together and mine is now a small pile of mangled bin-fodder. I've ordered a much more flimsy looking manual focus version from eBay (and a laser pointer).

Kit

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.

The method I'm going to use will not require this as I think it is considerably easier to straighten in one dimension at a time having done some shimming and scraping in the past. I will use the laser horizontally to flatten the rail in Z with shims then rotate the laser and camera and straighten it in X, trying to do both at once is a nightmare in my experience, not from a measurement perspective but from an adjustment perspective. Since i'm only getting the errors in a straight line rather than trying to get the rail parallel with the laser it doesn't matter if the laser and camera move relatively to each other all over the place when you rotate them, the two operations (flatten then straighten) are entirely independent.

This is the camera I'm currently using, very easy to take apart and remount and only £7, works superbly.
https://www.amazon.co.uk/gp/product/B01L1XAQAS

Cheers, Joe

[John McNamara]

Hi All

A mate and I made this device a while back, The test device searches for and senses the position of a wire electrically to .0001" The stepper and 3:1 timing belt driven screw attached to a Flexure hinged 10:1 ratio lever provided repeatable accuracy. The only variable was the contact resistance of the wire. It sensed on the break of contact naturally. This occasionally led to false readings, I left the test running for hours.

This is where the non contact camera is very attractive.

Automating positioning using a webcam the laser or wire sensing requires accurate mechanicals. This test machine was bulky It was designed to move a cutting head with an attached sensor, it cost very little.

I guess a ball screw would be the obvious answer. surprisingly small ones are not inexpensive. That is why I used a flexure for the first stage of amplification, Flexures have effectively no backlash. Have to think on this.....



It was driven by a baby Arduino with a small attached display for settings.

Regards
John

[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: