DIY Laser levelling using webcam and laser level

[devmonkey]

Hi Joe

I wish I knew more about optics.

Cylinder lenses appear to be the cheapest.
I wonder if a piece of glass rod would suffice?

I don't think they are round, rather half round, I maybe wrong. The better ones are made out of something called K9 glass, again I don't know what this is. Maybe Andy can jump in here?

[AndyUK]

I don't think they are round, rather half round, I maybe wrong. The better ones are made out of something called K9 glass, again I don't know what this is. Maybe Andy can jump in here?

Watching the thread with interest, but unfortunately its been many years since I studied optics, and I'm not massively useful at this point! But I whole-heartedly agree that you want to keep the guassian characteristic where possible, as its a nice structure to fit to. You could use the FWHM from a flat-top profile, but I'd trust the guassian fit better as the regression uses the entire curve, rather than just the penumbras.

Re. lenses; It all depends on the incoming beam width, the radius of the rod/lens, and the refractive index of the material being used; in general I'd guesstimate that given a beam focused to infinity, you're likely to get a wider output spread by using a full rod, but there are so many variables here to play with, i'd be tempted to just go with an off the shelf lens designed for the job which will also guarantee clarity of the beam to a certain extent.

[John McNamara]

A number of sites show what appears to be a plain cylinder.

https://www.google.com/search?q=line...%3Apinterest.*

[Kitwn]

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

[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]

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