Lasers for your sheet-of-light project

August seems to have been “sheet-of-light” month for MV4U, (“Sheet-of-Light Application”, “Sheet of light on a robot”,) so why not round it off with a discussion on where to buy machine vision-ready laser line projectors?

Four companies that I’ve dealt with are, in no particular order, ProPhotonix, Schäfter + Kirchhoff, Power Technology, and Z-laser. I should also mention that Coherent is back with a reincarnation of the old Stocker-Yale line of lasers. They all offer good products, yet I’ve always struggled with two particular aspects of laser line-based 3D scanning; line intensity and width.

Line width is always an issue because it affects resolution. If the line is wider than what you want to see the local height change tends to get drowned out. The problem though is that width is tied in to depth of focus and working distance. Essentially, a narrower line has a limited depth, which is a problem when you’re trying to measure height, and most narrow line lasers have very little standoff.

Intensity becomes an issue when scanning a surface quickly. The exposure has to be shut right down, so little light gets through, meaning that more light is needed. Most laser line projectors are in the 5 to 50 milliwatt range, which, depending on the surface being lit, is often insufficient.

I see two solutions to the intensity issue: more output (which quickly garners attention from your Laser Safety Officer (and if you don’t have one of those, you should,)) and matching wavelength to peak camera sensitivity. This last idea worked OK when cameras peaked in the red, but these days peak sensitivity is in the green region. And have you tried finding a green laser line projector? Not too many around.

So with all that said, let’s talk about Osela. This Canadian laser company doesn’t offer a green laser but they check the other boxes. They understand laser optics and can offer very thin lines, and they have some honkin’ great outputs – 3watts is enough to do some damage! So if you need an intense yet thin line, try talking to them.