Better backlighting

I haven’t checked but I think it’s a safe bet to say that every piece of machine vision marketing material features a backlit image. (For the newcomers, backlighting is when you put a light behind the object you’re looking at so as to create a silhouette. With this black and white image it’s then straightforward to apply gauging tools to check key dimensions.)

Unfortunately, even backlighting is not as simple as it might appear. The problem is that light is emitted in all directions from the surface of the backlight, and not just towards the camera. This means that rather than appearing crisp, edges can actually be rather fuzzy, which is a problem if you need to make precise and repeatable measurements.

The answer, as discussed in this excellent article on MachineDesign.com (June 2nd, 2009) is to use telecentric backlighting, which means that that only parallel rays of light are emitted from the surface towards the camera, thus avoiding stray reflections.

As always though, there is a price to be paid: telecentric backlights typically need more space than a regular backlight, and of course, cost more. But if you need to make precise measurements you’ve got to put one on your shopping list.