1. Unit III
Actuator: An actuator is a part of a
device or machine that helps it to
achieve physical movements by
converting energy, often electrical, air,
or hydraulic, into mechanical force.
Simply put, it is the component in any
machine that enables movement.
2. • Sometimes, to answer the question of what
does an actuator do, the process is compared
to the functioning of a human body. Like
muscles in a body that enable energy to be
converted to some form of motion like the
movement of arms or legs, actuators work in a
machine to perform a mechanical action.
3. • Actuators are present in almost every machine
around us, from simple electronic access
control systems, the vibrator on your mobile
phone and household appliances to vehicles,
industrial devices, and robots. Common
examples of actuators include electric motors,
stepper motors, jackscrews, electric muscular
stimulators in robots, etc.
4. • Mechanical actuators are mechanisms that
use a source of power to achieve physical
movement. These are essential and can be
found on nearly every automated machine.
• The three main types of actuators are
pneumatic (air pressure), hydraulic (fluid
pressure) and electric.
5. Electric Actuators
Electric actuators convert energy from an
electrical power source into mechanical
energy.
A variety of uses include valve operation,
cutting equipment, food and beverage
manufacturing, and material handling. They
are generally easy to maintain compared to
hydraulic and offer a high level of precision.
Electric actuator diagram
6. • An electric motor will create rotary motion as the
spindle, or rotor, rotates. The motor spindle is
directly coupled to a helical screw, via the drive
shaft, which in turn rotates in a ball screw nut.
• As the spindle rotates the ball screw nut is driven
forwards, or backwards, along the helical screw.
• A hollow piston rod is attached to the ball screw
nut and this creates the linear motion out of, or into
the linear actuator as the motor rotates clockwise or
anti-clockwise.
7. • The motor is controlled by an electric drive,
which allows the rotation speed to be varied and,
hence, the linear speed of the actuator.
• A feedback mechanism gives positional
information and the linear actuator can be
programmed to move to a certain position, stop
and then move on, or return to its rest position.
• The power of the motor will determine the
torque that can be generated and hence the force
that can be put to useful motion through the
actuator.
8. Electrical systems:
In any discussion of electrical systems used as as actuators
for control, the discussion has to include
• 1. Switching devices such as mechanical switches ex: relays,
or solid switches ex: diodes,thyristors, and transistors, where
the control signal switches on or off some electrical device,
perhaps a heater or a motor.
• 2. Solenoid type devices where a current through a solenoid
is used to actuate a soft iron core, as for example,the solenoid
operated hydraulic/pneumatic valve where a control current
through a solenoid is used to actuate a hydraulic/pneumatic
flow.
• 3. Drive systems, such as d.c and a.c motors, where a current
a motor is used to produce rotation.
9. • Mechanical switches are elements which are
often used as sensors to give input to systems
eg. Keyboard. In this chapter we are
concerned with their use as actuators to
perhaps switch on electric motors or heating
elements, or switch on the current to actuate
solenoid valves controlling hydraulic or
pneumatic cylinders. The electrical relay is an
example of a mechanical switch used in
control systems as an actuator.
10. • Relays: Relays are electrically operated switches in which
changing a current in one electrical circuit switches a current on or
off in another circuit.
• For the relay shown in fig , when there is a current through the
solenoid of the relay, magnetic field is produced with attracts the
iron armature, moves the push rod, and so closes the normally
open (NO) switch contacts and opens the normally closed (NC)
switch contacts.
• Relays are often used in control systems; the output from the
controller is a relatively small current and a much larger current is
needed to switch on or off the final correction element , eg. The
current required by an electrical heater in a temperature control
system or a motor.
• In such a situation they are likely to be used in conjunction with
transistors and fig b) shows the type of circuit that might be used.
13. • Solid –state switches : There are a number ofsolid-
state devices which can be used to electronically switch
circuits.
• These include
• 1. Diodes
• 2. Thyristors and triacs
14. • Diodes: The diode has the characteristics
shown in fig and so allows a significant
current in one direction only.
• A diode can thus be regarded as ‘directional
element’ , only passing a current when
forward biased. i.e. with the anode being
positive with respect to the cathode. If the
diode is sufficiently reverse biased, i.e. a very
high voltage , it will breakdown.
15.
16. • Thyristors and triacs The thyristor, or silicon-
controlled rectifier (SCR), can be regarded as a diode
which has agate controlling the conditions under which
the diode can be switched on.
• Fig shows the thyristor characteristic. With the gate
current zero, the thyristor passes negligible current
when reverse biased when forward biased the current
is also negligible until the forward breakdown voltage
is exceeded. When this occurs the voltage across the
diode falls to a level, about 1V to 2V and the current is
then only limited by the external resistance in a circuit.
17.
18. • Triacs The triac is similar to thyristor and is equivalent to a
pair of thyristors connected in reverse parallel on the same
chip.
• The triac can be turned on in either the forward or reverse
direction. Fig shows the characteristic.
• Triacs are simple, relatively inexpensive ,method of controlling
a.c. power.
• Fig 7.8shows the type of effect that occurs when a sinsusoidal
alternating voltage is applied across a) Thyristor and b) a triac
19. • BJT and FET
• BJTs and FETs are two different kind of transistors and also
known as active semiconductor devices. The acronym of the
BJT is Bipolar Junction Transistor and FET stands for Field
Effect Transistor.
• BJTS and FETS are available in a variety of packages based
on the operating frequency, current, voltage, and power
ratings.
• These types of devices allow a greater degree of control over
their work.
• BJTS and FETs can be used as switches and amplifiers in
electrical and electronic circuits.
• The major difference between BJT and FET is that in a field
effect transistor only majority charge carries flows, whereas in
BJT both majority and minority charge carriers flow.
21. DC Motors
DC Motors are electromechanical devices which use the
interaction of magnetic fields and conductors to convert the
electrical energy into rotary mechanical energy
22. • The DC Motor or Direct Current Motor to give it its full
title, is the most commonly used actuator for producing
continuous movement and whose speed of rotation can easily
be controlled, making them ideal for use in applications were
speed control, servo type control, and/or positioning is
required.
• A DC motor consists of two parts, a “Stator” which is the
stationary part and a “Rotor” which is the rotating part. The
result is that there are basically three types of DC Motor
available.
• 1. Brushed motor 2.Brushless motor 3. Servomotor
23. • Servomotor: This type of motor is basically a brushed DC
motor with some form of positional feedback control
connected to the rotor shaft. They are connected to and
controlled by a PWM type controller and are mainly used in
positional control systems and radio controlled models.
The Servomotor control scheme. Notice how the motor itself is only a small part of the system.
24. • BLDC Motor (Brushless DC Motor)
• When it comes to speed control, you may think the choice is
between an inverter driven three-phase motor or servo
motor, but did you know that brushless DC motors specialize
in speed control? The brushless DC motor is growing in
popularity in the world of speed control.
• BLDC’s are replacing brushed DC motors due to their
“superior efficiency, long life, smooth torque delivery, and
high speed operation.”
• While they have been successfully applied in the automotive,
HVAC, electronic, computer, semiconductor and medical
industries, BLDC motors have long been used in industrial
applications such as actuators, feed drives for CNC machines,
industrial robots, extruder drives, among others.
26. • AC Motor
AC motors are electrical devices that convert
electrical current into mechanical rotational
energy, or torque, by using alternating current
(AC) from an electrical power grid or electrical
generator. The stator and the rotor are important
parts of AC motors.
The stator is the stationary part of the motor, and
the rotor is the rotating part of the motor. The AC
motor may be single-phase or three-phase
27. • Pneumatic Actuators
• Pneumatic actuators use compressed air or pressurized gas to
create a controlled movement.
•
• Pneumatic actuators are versatile and can be customized to fit
any project. On top of being cost effective, pneumatic
actuators are simple to use and are a safe alternative to both
electric and hydraulic actuators since they do not require
ignition or electricity to operate.
• One disadvantage of the pneumatic actuator is that
a compressor must continuously run to maintain operating
pressure whether the device is in use or not.
29. • Some disadvantages of electrical actuators
are they are not suited for all environments
and need supervision for overheating
tendencies.
• Taking into consideration their need for
constant power, electrical actuators have no
fail-safe position if there is a power loss and
have an average failure rate that is higher than
that of a pneumatic actuator.
30. •
Hydraulic Actuators
• Hydraulic actuators use fluid pressure to facilitate
mechanical movement.
• These are used when a considerable amount of power
is needed for a machine or system to operate. Most
commonly seen in heavy machinery, hydraulic power is
controlled by the amount of fluid in a cylinder. Pressure
is created by increasing fluid and lessened by
decreasing fluid.
• Although hydraulic actuators are useful when high-
powered energy is needed, they are volatile in nature
and require highly trained mechanics to operate and
maintain.
33. • Directional Control Valves-1
– Pneumatic and hydraulic systems use directional
control valves to direct the flow of fluid through a
system; its ON/OFF devices either completely
open or closed
– They might be activated to switch the fluid flow
direction by means of mechanical, electrical or
fluid pressure signal
•
34. Spool Valve
1-Spool valve:
Move horizontally within the valve body to control flow
2-Rotary spool valve: have the same idea,
when rotates opens and closes ports
Directional control valves-2
35. Directional control valve- 3
Poppet valve
This valve is normally in closed condition.
In this valve, balls, discs or cones
are used in conjunction with valve seats
to control the flow.
38. • Cylinder sequencing
• Many pneumatic or hydraulic control systems may require a sequence of
extension and retraction of cylinders to occur. e.g
• Suppose we have two cylinders: A and B If the start button pressed;
• { piston A extends;
• If fully extended then piston B extends; If both A and B fully extended then
• Piston A retracts;
• If A is fully retracted have piston B retract}
• If both A and B fully extended then Piston A retracts
40. Piezoelectric actuators
A piezoelectric actuator is a transducer, used to change an
electrical signal into an accurately controlled physical
displacement
The working principle of a piezoelectric actuator is, once the
voltage is applied to piezoelectric actuators then they
generate a small displacement through a high force capacity,
so these are used in many applications like ultra-precise
positioning, in high forces handling & generation in
stationary or dynamic conditions.
A piezoelectric actuator is used to adjust different types of
equipment like lenses, machining tools, mirrors, etc.
42. • Advantages of piezoelectric actuators
• The advantages of the piezoelectric actuator include the
following.
• Simple design
• Least moving parts,
• High-reliability characteristics
• These are simply optimized for particular applications like a
non-magnetic, cryogenic, ultra-high vacuum & high stiffness.
• High force for each unit areaResolution is unlimited
• Vacuum &Clean Room Compatible
• Generation of High Force
• No Wear & Tear
• Energy consumption is low
• No Magnetic Fields
• Quick Response and Operates at Cryogenic Temperatures
43. Advantages of electric,pneumatic and hydraullic
actuators
Electric Pneumatic Hydraulic
Easy to maintain
high level of
precision
Versatile and
customizable
Cost-effective
Safe
Very high force /
power
44. Disadvantages
Electric Pneumatic Hydraulic
Less cost effective
than pneumatic
Strict working
environment
No fail-safe position
if power is lost
Compressor must
run continuously
Volatile nature
Requires highly
trained mechanics
45. • Shape-memory alloy (SMA) is an alloy that can
be deformed when cold but returns to its pre-
deformed ("remembered") shape when heated. It may
also be called memory metal, memory alloy, smart
metal, smart alloy, or muscle wire.
• Parts made of shape-memory alloys can be lightweight,
solid-state alternatives to conventional actuators such
as hydraulic, pneumatic, and motor-based systems.
They can also be used to make hermetic joints in metal
tubing.
