Page 293 - Sensors and Control Systems in Manufacturing

The Role of Sensors and Contr ol Technology in CIM
In computer-aided manufacturing (CAM), computers are used to 251
plan and conduct production. They can correct and process data, con-
trol the manufacturing process, and provide information that can be
used in decision making. CAM can involve distributed quality con-
trol and product testing and inspection, which are built into the man-
ufacturing process to support the larger functional relationships.

5.4.2.5 Microcomputers for CIM
The integration of different elements of CIM and sensor systems can
be accomplished only with the aid of a computer. Because of the mag-
nitude of the CIM and sensor database, a mainframe (or a minicom-
puter for a small enterprise) is necessary for storage and retrieval of
information. The power of microcomputers has increased so dramat-
ically, however, that they are suitable for most other applications,
such as:
• Programmable logic controllers (PLCs). On the factory floor,
microcomputers are subject to harsh conditions. Dust, high
temperature, and high humidity can quickly destroy an ordi-
nary personal computer. Traditionally, the shop floor belongs
to the programmable logic controller. The components can
operate in extreme conditions (e.g., 55°C and 90 percent
humidity). In addition, PLCs are geared to real-time control
of factory operations. Through advances in microprocessor
technology, functions once controlled by relays and mechani-
cal switching mechanisms can now be performed by PLCs.
The ladder diagrams used to notate logic circuits can now be
programmed directly into the memory of the programmable
controller. Because of microelectronic circuitry, PLCs can
process control information quickly and shut down automat-
ically in case of emergencies. Whereas PLCs have become
commonplace on the floor of discrete product operations,
process control computers have become indispensable in the
control of process plants where conditions must be monitored
constantly. They are also used in the control of office and fac-
tory environments. For example, a PLC can turn furnaces and
air-conditioning units ON and OFF to provide suitable work-
ing conditions while optimizing energy use.
• Industrial personal computers (PCs). Until recently, PCs were
commonly found in the protected environments of offices.
Now, manufacturers have introduced rugged versions of
popular personal computers. For example, IBM has devel-
oped the 5531 and 7531/32, industrialized versions of PC/XT
and PC/AT, respectively, to withstand the environment of
the factory floor. They have the advantage of being able to
run any PC-DOS-based software, but are unable to perform
real-time control. This problem has been remedied with the