Page 96 - Sensors and Control Systems in Manufacturing

Classification and Types of Sensors

FIGURE 2.27 Over/ 57
under-speed of rotating
FIGURE 2.26 Web fl aw detection. disk.

In a web flaw detection application, a web passes over an array of
retroreflectors (Fig. 2.26). When light is returned to the sensor head,
the output is energized and the web shuts down. High web speeds
can be maintained because of the superior response time of the con-
trol unit.
A reflex photoelectric sensor with a motion control module counts
the revolutions of a wheel to monitor over/underspeed of a rotating
object. Speed is controlled by a programmable controller. The rate
ranges from 2.4 to 12,000 counts per minute (Fig. 2.27).
When the two through-beam photoelectric sensors in Fig. 2.28
observe the same signal strength, the output is zero. When the capacity
of the web changes, as in a splice, the signal strengths are thrown out of
balance and the output is energized. This system can be used on webs
of different colors and opacities with no system reconfiguration.
Understanding the environment is important to effective imple-
mentation of an error-free environment. An awareness of the charac-
teristics of photoelectric controls and the different ways in which they

FIGURE 2.28 Web splice detection.