Ultrasonic crack detection in glass bottles

[dc878787]

I'm working on a project for a bottling plant that is trying to make a vision-based machine to detect cracked glass bottles before they attempt to fill them.

It seems that the vision & backlight approach is the standard way to do this in the industry, but the shape of the bottle in this application makes this a tricky/expensive machine.

I'm wondering if anyone has any experience with some type of ultrasonic crack detection methodology? I'm just going on a hunch here, but I think that at least some cracks should change the resonate frequency of a bottle enough to detect the change..

 

[NascentOxygen]

Can you provide a pic of the bottle's shape?

 

[Bystander]

vision & backlight approach

Shows a lot of flaws --- laser plus beam expander (cylindrical lens in front of laser level light source) and a diode array looking for reflections, or reduced transmission.

 

[Baluncore]

Support a bottle by one point, say by the cap, then tap the bottle so it rings like a bell at a fundamental frequency. If there is a fracture in a bottle it will sound dull and generate a short burst of harmonics of the fundamental frequency. I expect the harmonics generated to be even because the crack opens for part of the cycle but is closed on the other half cycle. With a good bottle the ringing will continue for longer at the fundamental frequency and there will be less 2'nd harmonic generated.

 

[dc878787]

Can you provide a pic of the bottle's shape?

This is not the actual bottle, but the shape is simmilar to a typical "fifth" of alcohol. See: http://img0127.popscreencdn.com/181451910_vtg-1962-seagrams-crown-royal-fifth-empty-bottle.jpg

There are four sides to the bottle, so vision inspection will require multiple cameras, or rotating the bottle with some kind of turntable to check all four sides.