Page 342 - The Mechatronics Handbook

TABLE 16.2 Type of Actuators and Their Features (Continued)
Actuator Features
Magnetostrictive High frequency with small motion
Low voltage with high current excitation
Shape Memory Alloy Low voltage with high current excitation
Low frequency with large motion
Electrorheological fluids Very high voltage excitation
Good resistance to mechanical shock and vibration
Low frequency with large force

Micro- and Nanoactuators
Micromotors Suitable for micromechanical system
Microvalves Can use available silicon processing technology, such as
electrostatic motor
Micropumps Can use any smart material

Power
Supply

Source
Controller
Gate
Drain

Load

FIGURE 16.8 n-channel power MOSFET.

voltage and varying the voltage can easily control their speed. They are widely used in applications ranging
from thousands of horsepower motors used in rolling mills to fractional horsepower motors used in
automobiles (starter motors, fan motors, windshield wiper motors, etc.). Although they are costlier, they
need DC power supply and require more maintenance compared to AC motors.
The governing equation of motion of a DC motor can be written as:

dω
T = J ------- + T L + T loss
dt

where T is torque, J is the total inertia, ω is the angular mechanical speed of the rotor, T L is the torque
applied to the motor shaft, and T loss is the internal mechanical losses such as friction.
AC motors are the most popular since they use standard AC power, do not require brushes and commu-
tator, and are therefore less expensive. AC motors can be further classified as the induction motors, synchro-
nous motors, and universal motors according to their physical construction. The induction motor is simple,
rugged, and maintenance free. They are available in many sizes and shapes based on number of phases
used. For example, a three-phase induction motor is used in large-horsepower applications, such as pump
drives, steel mill drives, hoist drives, and vehicle drives. The two-phase servomotor is used extensively in
position control systems. Single-phase induction motors are widely used in many household appliances.
The synchronous motor is one of the most efficient electrical motors in industry, so it is used in industry
to reduce the cost of electrical power. In addition, synchronous motors rotate at synchronous speed, so they
are also used in applications that require synchronous operations. The universal motors operate with either

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