-Basic Concepts of Actuators -Type of actuators -Example of actuators

1. Mechanicalactuators
Basic Concepts of Actuators
An actuator is something that actuates or moves something. More
specifically, an actuator is a device that coverts energy into motion
or mechanical energy. Therefore, an actuator is a specific type of a
transducer
An actuator requires a control signal and a source of energy. The
control signal is relatively low energy and may be electric voltage or
current, pneumatic or hydraulic pressure, or even human power. Its
main energy source may be an electric current, hydraulic fluid
pressure, or pneumatic pressure. When it receives a control signal,
an actuator responds by converting the signal's energy into
mechanical motion.

2. Type of actuators:
 Hydraulic actuators
 Pneumatic actuators
 Electric actuators

3.  thermal or magnetic
 Mechanical actuator

4. Example of actuators:
• Comb drive.
• Digital micro mirror device.
• Electric motor.
• Electroactive polymer.
• Hydraulic cylinder.
• Piezoelectric actuator.
• Pneumatic actuator.
• Screw jack.
• Servomechanism.
• Solenoid.
• Stepper motor.
• Shape-memory alloy.
• Thermal bimorph.
• Hydraulic actuators.

5. Hydraulic cylinder : ( linear hydraulic motor)
Is a mechanical actuator that is used to give a unidirectional
force through a unidirectional stroke. It has many applications,
notably in construction equipment (engineering vehicles),
manufacturing machinery, and civil engineering

6. 1. Pins & retainers
2. Ports
3. Piston nut
4. Piston
5. Piston nut
6. Piston
7. Piston seal
8. Tie – Rods
9. Cylinder shaft
10. Tube
11. Tube seal
12. Rod seal
13. Rod Cap & Clevis Cap
14. Rod Wiper
15. Threadad shaft (on ASAE cylinders )
16. Rod Clevis

7. Basic parts:
• Cylinder barrel
The main function of the cylinder body is to hold cylinder
pressure. The cylinder barrel is mostly made from a seamless
tube. The cylinder barrel is ground and/or honed internally with
a typical surface finish of 4 to 16 microinch,honing process and
Skiving & Roller burnishing (SRB) process are the two main types
of processes for manufacturing cylinder tube.[3] The piston
reciprocates in the cylinder.
• Cylinder base or cap
The main function of the cap is to enclose the pressure
chamber at one end. The cap is connected to the body by
means of welding, threading, bolts, or tie rod. Caps also
perform as cylinder mounting components [cap flange, cap
trunnion, cap clevis]. Cap size is determined based on the
bending stress. A static seal / o-ring is used in between cap and
barrel (except welded construction).

8. • Cylinder head
The main function of the head is to enclose the pressure
chamber from the other end. The head contains an integrated
rod sealing arrangement or the option to accept a seal gland.
The head is connected to the body by means of threading,
bolts, or tie rod. A static seal / o-ring is used in between head
and barrel.
• Piston
The main function of the piston is to separate the pressure
zones inside the barrel. The piston is machined with grooves to
fit elastomeric or metal seals and bearing elements. These
seals can be single acting or double acting. The difference in
pressure between the two sides of the piston causes the
cylinder to extend and retract. The piston is attached with the
piston rod by means of threads, bolts, or nuts to transfer the
linear motion.

9. • Piston rod
The piston rod is typically a hard chrome-plated piece
of cold-rolled steel which attaches to the piston and
extends from the cylinder through the rod-end head. In
Seal gland
• Seals
Attaches to the piston and extends from the cylinder
through the rod-end head. In double rod-end cylinders,
the actuator has a rod extending from both sides of the
piston and out both ends of the barrel. The piston rod
connects the hydraulic actuator to the machine
component doing the work. This connection can be in
the form of a machine thread or a mounting attachment.
The piston rod is highly ground and polished so as to
provide a reliable seal and prevent leakage.

10. Hydraulic cylinder
Application for hydraulic actuators :

11. This circuit is designed as shown in Figure 10.2.
When the four-way valve is in its spring-centered position, the cylinder is hydraulically locked.
Also the pump is loaded back to the tank at atmospheric pressure.
When the four-way valve is actuated into the flow path configuration of the left envelope, the
cylinder is extended against its force load (Flood) as oil flows from port P through port A. The
oil at the rod end of the cylinder is free to flow back into the reservoir through the four-way
valve from port B through port T. The cylinder will not extend if the oil in the rod end is not
allowed to flow back to the reservoir.
When the four-way valve is de-activated, the spring-centered envelope prevails, and the
cylinder is once again hydraulically locked.
When the four-way valve is actuated in the right envelope configuration, the cylinder retracts,
as oil flows from port P through port B. Oil in the blank end is allowed to flow back to the
reservoir from port A through port T of the four-way valve. At the end of the stroke, there is no
system demand for oil. Therefore the pump flow goes through the relief valve at its set
pressure, unless the four-way valve is de-activated. In any event, the system is protected from
cylinder overloads.

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