Automating Manufacturing Systems - Process Control and ...

discrete sensors - 4.16
effective beam
effective
detector
angle
detector
emitter
effective
beam angle
alignment
is required
intensity
1
∝ ----
r 2
Figure 4.16
Beam Divergence and Alignment
If an object is smaller than the width of the light beam it will not be able to block
the beam entirely when it is in front as shown in Figure 4.17. This will create difficulties
in detection, or possibly stop detection altogether. Solutions to this problem are to use narrower
beams, or wider objects. Fiber optic cables may be used with an opposed mode optical
sensor to solve this problem, however the maximum effective distance is reduced to a
couple feet.
emitter
object
detector
the smaller beam width is good (but harder to align
Figure 4.17
The Relationship Between Beam Width and Object Size
Separated sensors can detect reflective parts using reflection as shown in Figure
4.18. The emitter and detector are positioned so that when a reflective surface is in position
the light is returned to the detector. When the surface is not present the light does not
return.