0195136047.pdf

16.3 DIGITAL CONTROL SYSTEMS 811

Memory and

instructions

Computer

Digital

processor

Drill-motor

drive Drilling operation

Drill position

Drill

position

mechanism

Position

feedback

network

(Electromechanical drive)

Sampled-data position-control system

Input

numeric

data

Figure 16.3.6Simplified block diagram of a digitally controlled drill press.

Digital computer Sequencer Drive circuit Step motor

Digital position

encoder

Read–write head

Figure 16.3.7Step-motor control system for read–write head positioning on a disk drive.

when a conductive surface, such as an airplane, appears in the signal path. While the antenna
is continuously rotated in search of a target, the antenna is stopped when the target is located.
It is pointed toward the target by varying its angular direction until a maximum echo is heard.
The position coordinateθ(t) of the antenna is usually controlled through a gear train by a dc
servomotor. The motor torque is varied in both magnitude and direction by means of a control
voltage obtained from the amplifier output. The control problem is then to command the motor
such that the outputθ(t) is nearly the same as the reference angular positionθr(t). The closed
loop can be controlled by a digital controller.

Microprocessor Control

The microprocessor, which has rapidly become a key component in digital control systems, and
its associated circuits function as the digital processor. It is often used as a dedicated computer

Transducer (amplifier)Controller Motor andantenna

Transducer

Position

command

θr(t)

Position θ(t)

Figure 16.3.8Plant model of a position servo in a radar system.