Automating Manufacturing Systems - Process Control and ...

discrete sensors - 4.15
emitter
object
detector
Note: with diffuse reflection the light is scattered. This reduces the quantity of light
returned. As a result the light needs to be amplified using lenses.
Figure 4.15
Diffuse Optical Sensor
Diffuse sensors use light focused over a given range, and a sensitivity adjustment
is used to select a distance. These sensors are the easiest to set up, but they require well
controlled conditions. For example if it is to pick up light and dark colored objects problems
would result.
When using opposed mode sensors the emitter and detector must be aligned so that
the emitter beam and detector window overlap, as shown in Figure 4.16. Emitter beams
normally have a cone shape with a small angle of divergence (a few degrees of less).
Detectors also have a cone shaped volume of detection. Therefore when aligning opposed
mode sensor care is required not just to point the emitter at the detector, but also the detector
at the emitter. Another factor that must be considered with this and other sensors is that
the light intensity decreases over distance, so the sensors will have a limit to separation
distance.