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Automating Manufacturing Systems - Process Control and ...

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discrete sensors - 4.18<br />

The optical reflectivity of objects varies from material to material as shown in Figemitter<br />

lens<br />

distance 1 distance 2<br />

detector 2<br />

detector 1<br />

lens<br />

Figure 4.20<br />

Multiple Point Detection Using Optics<br />

Some applications do not permit full sized photooptic sensors to be used. Fiber<br />

optics can be used to separate the emitters <strong>and</strong> detectors from the application. Some vendors<br />

also sell photosensors that have the phototransistors <strong>and</strong> LEDs separated from the<br />

electronics.<br />

Light curtains are an array of beams, set up as shown in Figure 4.21. If any of the<br />

beams are broken it indicates that somebody has entered a workcell <strong>and</strong> the machine needs<br />

to be shut down. This is an inexpensive replacement for some mechanical cages <strong>and</strong> barriers.<br />

Figure 4.21<br />

A Light Curtain

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