Page 318 - Sensors and Control Systems in Manufacturing

CHAPTER 6

Advanced Sensor

Technology

in Precision

Manufacturing

Applications

6.1 Identification of Manufactured Components
In an automated manufacturing operation, one should be able to
monitor the identification of moving parts. The most common means
of automatic identification is bar-code technology, but other approaches
offer advantages under certain conditions.
6.1.1 Bar-Code Identification Systems
The universal product code (UPC) used in retail stores is a standard
12-digit code. Five of the digits represent the manufacturer and five
the item being scanned. The first digit identifies the type of number
system being decoded (a standard supermarket item, for example)
and the second is a parity digit to determine the correctness of the
reading. The first six digits are represented by code in an alternating
pattern of light and dark bars. Figure 6.1 shows two encodings of the
binary string 100111000. In both cases, the minimum printed width is
the same. The delta code requires nine such widths (the number of
bits), while the width code requires 13 such widths (if a wide element
is twice the width of the narrow element). Different bar widths allow
for many character combinations. The remaining six digits are formed
by dark alternating with light bars reversing the sequence of the first
six digits. This allows backward scanning detection (Fig. 6.2).

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