Thursday, November 17, 2011

Application tip for IR lighting

Spotted an interesting little application story on the Vision Systems Designs website a few days back, “Smart cameras solve a pressing problem,” (Andy Wilson, November 1st, 2011.)

This relates to the use of two Dalsa BOA smart cameras for checking that a die is clear before it closes. As the story relates, closing the die with slivers of stray metal in the way can cost a lot of money.

This seems like a pretty run-of-the-mill machine vision application but there are a couple of interesting aspects. Number one is that it’s the first time I’ve read about the BOA cameras actually being put to work. Number two is the use of IR lighting.

I don’t wish to steal Andy’s thunder, (or his ad revenue,) by giving you all the details here, but trust me, the application needed infrared illumination.

Now here are two tips for when you use IR. First, remember that silicon has low quantum efficiency at wavelengths much over 750nm (and goes to zero about 1,000nm,) so you’re going to need a lot of light to make the application work.

Second, most cameras have an IR cutout filter over the sensor. You’ll need to remove this in order to detect the IR light. This might seem obvious but I have found vision engineers complaining that an IR light isn’t working when all they had to do was remove the filter!

Just a couple of points to bear in mind.

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