I intend to do a linear measuring tool like digital calliper. And I'm searching for reflective optical encoder from Avago Tech. However, there are some points I’m not clear about the code strip for the reflective optical technology.

The reflective stripe and non-reflective stripe are built from different materials which have different reflectance ? If not, how can the reflectance difference between these two kinds of stripes be created ?

Hope you light me up. Thank you.

 

hi.
The optical encoder reflector strip is composed of alternate high and low reflectivity stripes.
The stripes are 'illuminated' by an LED emitter, the reflected light detectors are arranged to give a Quadrature signal output.
Is this what you are asking.?
E

https://www.google.co.uk/search?client=firefox-a&hs=NTV&rls=org.mozilla:en-USfficial&channel=sb&tbm=isch&source=univ&sa=X&ei=CR9jVKahI8eV7AbssIHACA&ved=0CEYQsAQ&biw=1439&bih=926&q=linear optical encoder material

 

There are a few basic principles in use, the LED and glass graticule method which is further divided by some options, a basic LED is only capable of reading a very coarse resolution, in the order of 1/10th's of an inch, due to the closeness of the lines at very small resolution, in order to combat this, a method known as the Moiré effect is used where a small portion of the scale is carried with the head in front of the LED to greatly increase the resolution.
Another way of increasing the resolution is to read the two basic quadrature sine waves received by the LED/Photocell and use the arc-tangent calculation.
In the inductive/capacitive methods such as used by micrometer's etc, also use the arc-tangent method to increase the quadrature sine wave.
You may notice the Avago site shows relatively low resolution of their encoders indicating they may make use of the simple individual graduations.
Max.