E1C12 09/14/2010
13:54:12 Page 534
12.3 ACTUATORS
Linear Actuators
The task of a linear actuator is to provide motion in a straight line. We discuss three ways to achieve
linear motion:
1. Conversion of rotary motion into linear motion. This can be accomplished using a linkage, as
in the slider-crank mechanism, or using screw threads coupled to a rotary motion source.
2. Use of a fluid pressure to move a piston in a cylinder. When air or another gas is used as the
working fluid, the system is called a pneumatic system. When a fluid such as oil is used as the
working fluid, the system is termed hydraulic.
3. Electromagnetic
Slider–Crank Mechanism
A common means of generating a reciprocating linear motion, or converting linear motion to rotary
motion, is the slider–crank mechanism, as illustrated in Figure 12.30. Such a mechanism is the basis
of transforming the reciprocating motion of the piston in an internal combustion engine. This or
similar linkages could also be applied in pick-and-place operations, or in a variety of automation
applications.
Screw-drive linear motion
A common means for translating rotary motion into linear motion is a lead screw. A lead screw has
helical threads that are designed for minimum backlash to allow precise positioning. Numerous
designs exist for such actuating threads. The basic principle is illustrated in Figure 12.31. The rotary
motion of the lead screw is translated into linear motion of the nut, with the torque required to drive
the lead screw directly related to the thrust the particular application requires.
Figure 12.30 Slider–crank mechanism.
Thrust
output
Torque
input
Thrust
output
Nut
Figure 12.31 Linear actuation using a lead
screw.
534 Chapter 12 Mechatronics: Sensors, Actuators, and Controls
13:54:12 Page 534
12.3 ACTUATORS
Linear Actuators
The task of a linear actuator is to provide motion in a straight line. We discuss three ways to achieve
linear motion:
1. Conversion of rotary motion into linear motion. This can be accomplished using a linkage, as
in the slider-crank mechanism, or using screw threads coupled to a rotary motion source.
2. Use of a fluid pressure to move a piston in a cylinder. When air or another gas is used as the
working fluid, the system is called a pneumatic system. When a fluid such as oil is used as the
working fluid, the system is termed hydraulic.
3. Electromagnetic
Slider–Crank Mechanism
A common means of generating a reciprocating linear motion, or converting linear motion to rotary
motion, is the slider–crank mechanism, as illustrated in Figure 12.30. Such a mechanism is the basis
of transforming the reciprocating motion of the piston in an internal combustion engine. This or
similar linkages could also be applied in pick-and-place operations, or in a variety of automation
applications.
Screw-drive linear motion
A common means for translating rotary motion into linear motion is a lead screw. A lead screw has
helical threads that are designed for minimum backlash to allow precise positioning. Numerous
designs exist for such actuating threads. The basic principle is illustrated in Figure 12.31. The rotary
motion of the lead screw is translated into linear motion of the nut, with the torque required to drive
the lead screw directly related to the thrust the particular application requires.
Figure 12.30 Slider–crank mechanism.
Thrust
output
Torque
input
Thrust
output
Nut
Figure 12.31 Linear actuation using a lead
screw.
534 Chapter 12 Mechatronics: Sensors, Actuators, and Controls