So why is the processing world agog about laser sorters? What is a laser sorter, anyway? How does it work? What does it do?
Some basics:
As those who studied physics know, a laser is not a sensor, but simply a light source- light that is a single wavelength and phase, very dense in energy vs. projected area. Think of the laser pointer you use for presentations. It has a laser emitter inside that puts out the light, concentrated enough so that many people in a room can see the little bright spot on the screen. Lots of power even when reflected in many directions.
One of those directions is back at the laser emitter itself. And that light coming back toward the laser emitter has no trouble getting all the way back to the emitter- it is not like trying to drive the wrong way on a busy one-way street: light seems to allow lots of stuff to happen in a confined space with no collisions. In reality, the Star Wars light sabres would not work against each other like Lucas portrays!
A number of years back, some smart folks figured out that, if you could sense the reflected light coming back at the laser source, you could generate a reflected light intensity signal everywhere you pointed the laser. And if you swept the laser across a line (think about moving your laser quickly across the presentation screen from one side to the other), you could generate a line of reflection values to match- just like one line of pixels in a digital camera's picture. And if you moved that line just a bit and scanned it again and again, you could create an endless digital image, just like a linescan camera system.
In practice, just like the linescan camera, we don't move the laser spot that is flying back and forth- we move a flow of product underneath it.
So, you might ask (knowing that laser scanning assemblies are generally more costly than cameras), why use lasers if they only generate a reflected image just like cameras? Do they sense reflected color enough better than cameras to be worth the extra cost?
No.
Laser scanners have been proven time and again to be inferior to cameras when it comes to sensing reflected light. Whether you are looking for things that are green, red, yellow, blue or even different reflections in the near infrared range, cameras detect differences better. And at lower cost. If your application is to distinguish colors, camera-based systems are the tool for the job.
Next time, we will dig a bit into what laser scanners and sorting system ARE good for.
Tim
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