Perspectives in Vision: Rubber, Plastic and Ray Charles
March 16, 2010
One of my favorite entertainers of all time was the one and only Ray Charles. Although he was an inimitable vocalist, in 1945 it was his skill with the piano that started people talking. Here was a blind 15-year-old who couldn’t see the very keys he was playing, yet just by feeling the keys, he could sit down at a piano and effortlessly produce beautiful, soulful music. Even in the twilight of his life as his voice began to falter and his body became frail and weak, his feel for the ivories was seemingly undiminished. He continued to produce incredible music until shortly before his death in 2004 at the age of 73.
I often explain the difference between 2-D and 3-D machine vision as “what you can see” compared to “what you can feel.” It sounds very Zen, but I mean this quite literally. Two-dimensional systems employ tricks of light and shadow to try and cause the features of a part to become visible. Three-dimensional systems typically use lasers and profiling to “feel” variations in the actual geometry of a part. Three-dimensional doesn’t care about the color of an object, only about its shape.
Few materials have frustrated machine vision integrators more than black (or dark) molded rubber and plastic parts. Dark materials are sponges for light, and it is often extremely challenging for conventional 2-D cameras to create enough contrast between the various features to be able to perform analyses. But laser light can be imaged even on very dark materials. Using special high-speed profiling cameras, we are able to accurately measure the geometry of even very dark items such as tires, carbon fiber and small rubber seals.
Laser light also gives us the ability to detect variations in the material properties. For example, in much the same way you can physically feel the difference in rough plastic and smooth plastic, the laser can help you identify scuffed areas or areas where clear glue has dropped onto a surface.
If you find yourself struggling to “see” a solution to your application, or if you care about the shape of your object more than its color, the solution might be to make the switch to 3-D. It’s a technique that is often under-utilized because it’s not understood by many integrators. But very often it’s a practical solution to challenging applications.