Which is the best material to use for laser scanner exit windows?
Glass? Plastic? Which Plastic?
When building your data acquisition product using a laser reader scanner, especially mobile computing units, you are faced with an important design decision: Which material do I select for the exit window through which the transmitting and receiving information passes?
Lets first look at what features are important for an optimum functioning exit window:
Readability
High transmission in descrete wavelengths,
low transmission in all others
Low reflectance
High optical clarity
Low distortion
Durability
Low susceptibility to break upon impact or when dropped
Scratch or mar resistant
Long usage life
Design flexibility
Ease of manufacture into more complex 2D geometries
Available in 3D shapes
Cost effectiveness
Inexpensive
Not volume sensitive
Glass vs. Plastic: How do they compare?
The following chart shows how we feel glass and various plastics compare on these critical criteria:
| | Glass | Cast Acrylic* | CR39 | Polycarbonate* |
|---|
| Readability | very good
excellent (w/ AR) | very good
excellent (w/ AR**) | very good | fair (wavefront distortion) |
| Durability | poor (breakage) | fair (breakage)
very good (scratches*) | fair (breakage)
fair (scratches) | very good (breakage)
poor (scratches)
very good (hardcoated*) |
| Design flexibility | poor | very good (2D) | good | excellent (2D & 3D) |
| Cost effectiveness | very good (non AR)
fair (w/ AR) | good/very good
fair (w/ AR**) | good | good |
| | * with TSP's DURAVUE®1000 optically clear scratch resistant hardcoat
** with TSP's DURAVUE®7000 high resolution anti-reflective hardcoat |
As you can see from the chart, while glass begins with slight advantages in readability and base cost, it is not suitable for most applications due to breakage, and also is too limiting for many of today's more elaborate window designs/shapes. Of the optical plastics, cast acrylic and CR39 can deliver most if not all of the readability of glass, particularily when an anti-reflective coating like TSP's DURAVUE® 7000 is added. However, once you consider all four performance factors - readability, durability, design flexibility and cost - we believe nothing stacks up as well as optical grade cast acrylic with TSP's DURAVUE® 1000 scratch resistant hardcoat.
Before you select a material for your exit windows, we encourage you to talk to a TSP Sales Engineer to help you pick the option best for you. Contact us today!