Page 321 - Sensors and Control Systems in Manufacturing

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number, and so on. This same scanning station can also be set up
using bar-code information; however, with magnetic striping, the
information can be read even if the stripe becomes coated with dirt or
grease. A disadvantage of magnetic striping is that the reader has to
contact the stripe in order to recall the information.
6.1.4 Surface Acoustic Waves
A process similar to RF identification is surface acoustic waves (SAW).
With this process, part identification is triggered by a radar-type sig-
nal that can be transmitted over greater distances than in RF systems.

6.1.5 Optical Character Recognition
Another form of automatic identification is optical character recognition
(OCR). Alphanumeric characters form the information, which the
OCR reader can “read.” In mail processing centers, high-speed sorting
by the U.S. Postal Service is accomplished using OCR. The potential
application to manufacturing information determination is obvious.
Other means of part identification abound, such as vision sys-
tems and voice recognition systems. Vision systems utilize TV cameras
to read alphanumeric data and transmit the information to a digital
converter. OCR data can be read with such devices, as can conven-
tionally typed characters. Voice recognition systems have potential
where an individual’s arms and hands are utilized in some function
that is not conducive to reporting information. Such an application
might be the inspection of parts by an operator who has to make
physical measurements on the same parts.
In laser scanning applications, a laser beam scans and identifies
objects at a constant speed. The object being scanned interrupts the
beam for a time proportional to its diameter or thickness. Resolutions
of less than 1 mm are possible.
In linear array applications, parallel light beams are emitted from
one side of the object to be measured to a photooptical diode array on
the opposite side. Diameters are measured by the number of array ele-
ments that are blocked. Resolutions of 5 mm or greater are possible.
In TV camera applications, a TV camera is used in the digitizing of
the image of an object and the result is compared to the stored
image. Dimensions can be measured, part orientation can be deter-
mined, and feature presence can be checked. Some exploratory
work is being accomplished with cameras that can fit in a tool
changer mechanism. The camera can be brought to the part like a
tool and verify part characteristics.

6.2 Digital Encoder Sensors
Digital encoder sensors provide an output directly in a digital form
and thus require only simple signal conditioning. They are also less