Page 39 - Modern Control Systems

Section 1.3 Examples of Control Systems 13

Table 1.2 Task Difficulty: Human Versus Automatic Machine
Tasks Difficult for a Machine Tasks Difficult for a Human
Inspect seedlings in a nursery. Inspect a system in a hot, toxic
Drive a vehicle through rugged terrain. environment.
Identify the most expensive jewels on Repetitively assemble a clock.
a tray of jewels. Land an airliner at night, in bad weather.

A three-axis control system for inspecting individual semiconductor wafers is
shown in Figure 1.12. This system uses a specific motor to drive each axis to the de-
sired position in the x-y-z-axis, respectively. The goal is to achieve smooth, accurate
movement in each axis. This control system is an important one for the semiconductor
manufacturing industry.
There has been considerable discussion recently concerning the gap between
practice and theory in control engineering. However, it is natural that theory pre-
cedes the applications in many fields of control engineering. Nonetheless, it is inter-
esting to note that in the electric power industry, the largest industry in the United
States, the gap is relatively insignificant. The electric power industry is primarily

v-axis motor
FIGURE 1.12 A three-axis control system for inspecting individual semiconductor wafers with a
highly sensitive camera.