Defect free?

Using machine vision for gauging is not too hard. Yes, resolution and repeatability can have you tearing out those gray hairs, but at least the requirements are pretty specific. But set out to do defect detection and you'll have an uphill struggle to understand the requirements.

In my experience, most inspection standards were written for human inspectors. That means a level of intelligence was assumed which machine vision systems just don't have. As a result, the standard usually includes the phrase “all surfaces must be defect free” or something similar.

When you see this I suggest you start by asking, “At what magnification?” After all, if you put any surface under a high-powered microscope you'll see all sorts of things that weren't evident to the naked eye.

Don't forget that you'll want at least three pixels to detect any flaw. For blob detection a three by three matrix is an absolute minimum, so what does this mean for resolution?

Check back for my next post on this subject