Page 320 - Sensors and Control Systems in Manufacturing

Advanced Sensors in Pr ecision Manufacturing
follows: three of nine bars (light and dark) form wide characters; the 277
rest are narrow.
Bar-code labels are simple to produce. Code 39, for example, can
be generated by a personal computer. Such labels are ideal for inven-
tory identifications and other types of fixed-information gathering.
Bar codes are not necessarily placed on labels. Tools, for example,
have had the code etched on their surfaces to allow for tool tracking.
Techniques have been developed for molding bar codes onto rubber
tires. Holographic scanners allow reading around corners so that
parts need not be oriented perpendicular to the reader as they feed
down a processing line.
A difficulty with bar coding has been the fact that it cannot be
read if the bars become obscured by dirt, grease, or other substances.
Infrared scanners are used to read codes coated with black substances
to prevent secrecy violations through reproduction of the codes. One
way to generally offset the problem of a dirty environment is to use
magnetic-stripe-encoded information.

6.1.2 Transponders
While bar-code labels and magnetic stripes are very effective on the
shop floor, shop circumstances may require more information to be
gathered about a product than can be realistically handled with
encoded media. For instance, with automobiles being assembled to
order in many plants, significant amounts of information are neces-
sary to indicate the options for a particular assembly. Radio-frequency
(RF) devices are used in many cases. An RF device, often called a tran-
sponder, is fixed to the chassis of a car during assembly. It contains a
chip that can store a great amount of information. A radio signal at
specific assembly stations causes the transponder to emit information
that can be understood by a local receiver. The transponder can be
coated with grease and still function. Its potential in any assembly
operation is readily apparent. Several advanced transponders have
read/write capability, thus supporting local decision making.

6.1.3 Electromagnetic Identification of Manufactured
Components
Many other possible electronic schemes can be employed to identify
manufactured parts in motion. Information can be coded on a mag-
netic stripe in much the same way that bars represent information on
a bar-code label, since the light and dark bars are just a form of binary
coding.
Operator identification data are often coded on magnetic stripes
that are imprinted on the operators’ badges. Magnetic stripe informa-
tion can be fed into a computer. Such information might include the
following: (1) the task is complete, (2) x number of units have been
produced, (3) the unit part numbers, (4) the operator’s identification