What will influence the accuracy of the encoder！

Speaking of dust and debris, they are a huge problem for all optical encoders, no matter what the disk type.  They can block the light just like a line on a rotary encoder disk, fooling the encoder sensor system.  This creates velocity errors for incremental encoders, and position errors for absolute encoders.

Water? Did someone say liquids?  A single droplet of liquid on the rotary encoder disk acts like a lens, bending the light.  Now the encoder position is not measured accurately.  To make matters worse, if the optical encoder heats up, the moisture can evaporate!  Now the quadrature encoder that was malfunctioning starts working again!

Now let's look at what happens on the other side of the rotary encoder disk.

On this side of the encoder disk in most optical rotary encoders is a "mask", which is a pattern of lines that closely match the disk.  By passing the light through the encoder mask, the on/off transitions are sharpened.  (Again, the goal of optical encoders is to clearly differentiate between light and dark areas to measure movement accurately).  

The light then falls on a set of encoder photo-detectors.  These are typically silicon semiconductor cells closely related to solar cells.  More light allows more electrons to flow; darkness prevents electron flow.  Here's a picture of a photocell; unfortunately in this rotary encoder, the spinning disk contacted the encoder sensor, destroying it and leaving a visible mark.

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