DIY Laser levelling using webcam and laser level

[devmonkey]

Hi Bert,

No nothing needs to be centred on the diagonals, the only restriction is that the device can only check a square not a rectangle, but this doesn't matter as we can always define a square ontop of the rectangle formed by our pair of rail beds.

The reference surface doesn't really exist. What we are doing is defining a square as four points on the device, call them A, B, C, and X:

AB
XC

With [A,B,C] fixed in relation to each other and X able to move up and down. Since [A,B,C] are fixed relatively to each other (in a triangle) they form a plane. The laser is fixed to this plane on the device near B pointing towards X. The camera is fixed to X.

Now define a square the same size on a table top or the machine frame or whatever, label the corners of this square 1, 2, 3, 4:

12
43

Place the device over this square such that A==1, B==2, C==3, X==4. Measure the laser height on the sensor at X. Now rotate the device 90 degrees so that say A==2, B==3, C==4 and X==1 and measure the new laser height at X which will have changed because your surface defined by [1,2,3,4] you drew on your table is not a perfect plane.

Now if you were to move X up or down so that the laser measured height is half way between the two heights measured then I think that X will be planar with A,B,C. So zero the software at the mid height between the two X heights measured and you now have a calibrated device which will read zero when placed on a true plane and a signed error when placed on an untrue plane. In other words [A,B,C,X] will be planar when the newly zero'd X is at zero. You can use this to check a machine is in plane and adjust the machine as required until it reads zero.

I haven't tested this only thought about it, I might be missing something, will draw it in CAD and check the theory is correct.

Cheers, Joe