The encoder read head has three major components: a light source, a
mask and a detector (
Figure 5.28). The mask is a small scale-like
piece, having identically spaced transparent and opaque lines.
Figure 5.28: Optical Encoder Read Head
Combining the scale with the read head, when one moves relative to
another, the light will pass through where the transparent areas line up
or blocked when they do not line up (
Figure 5.29).
The detector signal is similar to a sine wave. Converting it to a digital
waveform, the user will get the desired encoder signal. But, this is only
one phase, only half of the signal needed to get position information.
The second channel is obtained the same way but from a mask that is
placed 90% out of phase relative to the first one (
Figure 5.30).
Figure 5.29: Single-Channel Optical Encoder Scale and Read Head Assembly
5-24 Section 5 – Motion Control Tutorial
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