Page 497 - Sensors and Control Systems in Manufacturing

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Ni ne
Cha p te r

9.5.3 Process Computer
The process computer is constructed from components similar to
those used in a microcomputer system, with the difference that these
components are considerably more powerful because of their pro-
cessing speed and memory capacity. The supporting operating sys-
tems are also more powerful, meaning that many control tasks can be
processed in parallel. For this reason, the process computer is used in
places where it is necessary to solve extensive and complicated auto-
matic control tasks. In such cases, it has the responsibility of control-
ling a complete process (such as a power station), which is made of a
large number of subprocesses. Many smaller control systems, which
operate peripherally, are often subordinated to a process computer. In
such cases, the process computer assumes the role of a coordinating
master computer.

9.6 The NC Controller
Numerical control systems are the most widely used control in
machine tools. A blank or preworked workpiece is machined by NC
machine tools in accordance with specifications given in a technical
drawing and other processing data. Two-, three-, or multiple-axis
machines may be used, depending on the shape of the workpiece and
the processing technology. A two-axis machine tool might be an NC
lathe, for example. A milling machine is an example of a three-axis
machine tool.
In NC machines, sensors and actuators are connected to the pro-
cessor by the manufacturer. The operator or programmer needs to
know the operational principle and the interplay between the con-
troller and machine.
Figure 9.10 illustrates the location of holes to be drilled in a work-
piece. The skilled machinist needs to know the material from which
the workpiece has been made so that suitable drills and feed values
can be selected for machining. A drilling machine is equipped with a
work table which is adjustable in two directions. The adjustment is

FIGURE 9.10
Location of holes
to be drilled in a
workpiece.