Smart Materials and New Technologies Through-beam
Manufacturing
Doors
Reflective
Reflective
Manufacturing
Doors
s Figure 5-9 Applications of different sensors in manufacturing and other contexts (detection of presence, counting, etc.)
mance can be hampered when there is dust or moisture in their operating environment. There are other light-based proximity sensors as well and many different kinds of applications. Of particular interest is the ‘light curtain’. Here an array of parallel infrared beams is projected across a space to a receiving unit. When the light is interrupted by any solid object, including a human, the light curtain controller sends out a signal activating some other operation. These devices are often used around hazardous equipment. Ultrasonic position sensors find use in large-scale applications. They are often used as ‘obstacle detection’ systems. They can be small and relatively inexpensive. They find use in everything from robotic devices to consumer devices such as digital cameras. A typical ultrasonic ranging system sends out a short pulse of high frequency sound waves in a cone towards the object. The sound reflects back causing a responding voltage output in a transducer that is a direct analog to the distance to the object. The cone of vision can be varied, but is an important design factor. Ultrasonic sensors of this general type can normally function in environments where there is heavy dust and moisture. Thus, they have been used in automated ‘car washes’. Surrounding high noise levels can sometimes be problematic. Inductive and capacitance sensors, by contrast, are used in short range situations, but can be very reliable and also detect the presence of something without physical contact.
s Figure 5-10 Light curtains based on infrared light can be used for sensing movements through openings. Machines can be cut off, for example, if something interrupts the infrared light curtain
120
Elements and control systems