DIY Laser levelling using webcam and laser level

[devmonkey]

Forgive me jumping in (and apologies if I've missed something) but is the geometry of the measuring setup ideal? As mentioned, the measurements are dependent both on the straightness of the rail and of the beam itself and it's not really possible to separate out the two. If you turned the sensor through 90deg so that it looked along a line parallel to the gantry, and placed the line source just off the end of the gantry but with the laser line intersecting the sensor, you would then be moving the target down the length of the beam (straight apart from gravitational bending!) rather than relying on the optical quality of the cylindrical lens generating an accurately straight line. However, you would need to get the laser line horizontal to reasonably close limits both on the roll and pitch axes (if that makes sense).

When I first started following this thread I had a picture in my mind of a point laser shooting a beam parallel to the rail being measured and striking the sensor in the middle. What I have described above is really only the same thing but using a line source to make lateral alignment less critical.

Or I might have missed the point but I do find this whole exercise very interesting to follow.

Hi Neale,

That works fine for checking something is straight, what I'm trying to do here is build a system that can check things are planar, e.g. for bringing the two X rails into plane, hence the line laser.

One idea to separate the gantry error in this test from the laser error is to run the test twice with different sections of the laser line.

I've just tried a much better detection algo, what it does is find the simple maxima of a moving average window of image rows, it then fits a gaussian to this window only, ideally it would just fit a parabola but I haven't coded that. Readings are now much more stable across the entire dynamic range and it works better with wobbly beam cross sections. Just need to migrate to the cold garage to test it.

I think a reasonable measure for success would be for the system to meet din 876 grade 1, which for a surface plate 600mm long means 16um variation in height. The cost of such a plate for my machine is £5500 !
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