INTRODUCTION TO

INDUSTRIAL
AUTOMATION
MODULE II
Sensors and Actuators for Automation
Sensor
■ A sensor is a device that detects any physical quantity such as
pressure, light, heat, temperature, humidity, etc. from the outside
environment and responds according to the input to produce a desired
output in a format that is easy to read for the user.
■ The output produced by a sensor is an electric signal that can be either
converted to human readable form by a display or transmitted over a
network or supplied to a processing device, etc. Some common
examples of sensors are temperature sensor, pressure sensor, humidity
sensor, proximity sensor, photo sensor, motion sensor, etc.
Why do robots need sensors?
Characteristics of Sensors
■ Sensitivity is a measure of the change in output of the sensor relative to a unit change in the input
(the measured quantity.)
■ Linearity is determined by the calibration curve. The static calibration curve plots the output
amplitude versus the input amplitude under static conditions. Its degree of resemblance to a
straight line describes the linearity.
■ Drift is the deviation from a specific reading of the sensor when the sensor is kept at that value for
a prolonged period of time. The zero drift refers to the change in sensor output if the input is kept
steady at a level that (initially) yields a zero reading. Similarly, the full -scale drift is the drift if the
input is maintained at a value which originally yields a full scale deflection. Reasons for drift may
be extraneous, such as changes in ambient pressure, humidity, temperature etc., or due to changes
in the constituents of the sensor itself, such as aging, wear etc.
■ The range of a sensor is determined by the allowed lower and upper limits of its input or output.
Usually the range is determined by the accuracy required
■ Repeatability is defined as the deviation between measurements in a sequence when the
object under test is the same and approaches its value from the same direction each time.
The measurements have to be made under a short enough time duration so as not to
allow significant long term drift. Repeatability is usually specified as a percentage of the
sensor range.
■ Reproducibility is the same as repeatability, except it also incorporates long time lapses
between subsequent measurements. The sensor has to be operation between
measurements, but must be calibrated. Reproducibility is specified as a percentage of the
sensor range per unit of time.
Sensor Classification
 Internal Sensors
⚫ They are used to measure the internal state of a robot ie
Position, Velocity, Acceleration etc.
⚫ Depending on the quantities it measures , a sensor is termed as
position , velocity , acceleration or force sensor.

External Sensors
⚫ External Sensors are used to learn about Robot’s environment.
⚫ They can be classified as Contact type and non contact type
sensors
Position Sensors
■ Position sensors are devices that can detect the movement of an object or determine its
relative position measured from an established reference point. These types of sensors
can also be used to detect the presence of an object or its absence.
■ The overall intent of a position sensor is to detect an object and relay its position
through the generation of a signal that that provides positional feedback. This
feedback can then be used to control automated responses in a process, sound
alarms, or trigger other activity as dictated by the specific application.
■ Position sensors may be divided into three broad classes that include
linear position sensors,
rotary position sensors, and
angular position sensors.
■ There are several specific technologies that can be employed to achieve this
result, and the different types of position sensors reflect these underlying
technologies.
■ The primary types of position sensors include the following:
Potentiometric Position Sensors (resistance-based)
Inductive Position Sensors
Eddy Current-Based Position Sensors
Capacitive Position Sensors
Magnetostrictive Position Sensors
Hall Effect-Based Magnetic Position Sensors
Fiber-Optic Position Sensors
Optical Position Sensors
Ultrasonic Position Sensors
Inductive Position Sensor

Inductive sensors use currents induced by magnetic fields to detect

nearby metal objects. The inductive sensor uses a coil (an
inductor) to generate a high frequency magnetic field.
If there is a metal object near the changing magnetic field, current
will flow in the object.
This resulting current flow sets up a new magnetic field that
opposes the original magnetic field. The net effect is that it changes
the inductance of the coil in the inductive sensor.
Linear variable differential transformer (LVDT)

■ The transformer consists of a single primary winding `P' and two secondary
windings S1 and S2 wound on a cylindrical former.
■ The secondary windings have equal number of turns and are identically placed on
either side of the primary windings.
■ The primary winding is connected to an alternating current source.
■ A movable soft iron core is placed inside the former.
■ The displacement to be measured is applied to an arm attached to the soft iron
core.
■ When the core is in its normal (NULL) position equal voltages are induced in two
secondary windings.
■ A sinusoidal voltage of amplitude 3 to 15 volt and frequency 50 to 20000 Hz is
used to excite the primary.
 Linear Potentiometer
■ A linear potentiometer is a type of position sensor. This is a device which converts
mechanical displacement into an electrical output.
■ Linear potentiometers are often rod actuated and connected to an internal slider or
wiper carrier. The rod will be connected to a device or object which requires
measurement. The linear potentiometer proportionally divides an applied regulated
voltage over its operational range and provides a proportional voltage output
relevant to the position of the wiper.
■ Linear potentiometers are a contacting type of sensor which means that the moving
parts make contact with each other during use.
Principle of Working

■ Change in the position of slider leads to change in resistance of potentiometer wire and
corresponding change in output voltage generated is a measure of displacement of slider
to be measured.
■ Construction of Linear Potentiometer
Linear potentiometer consists of a stretched resistance wire and a sliding or movable contact
(wiper). The resistance element or resistance wire is made up of alloys. This resistance wire
is wound on a former in such a way that, the slider or Wiper may be moved along the
various turns axially.
Working of Linear Potentiometer
■ Linear potentiometer is a passive transducer because it required external
power source for its operation. Therefore the resistance wire is excited with
either AC or DC voltage. It is represented as input voltage (ei). When the
slider moves or slides axially along the various turns of resistance wire, the
effective resistance existing between one end of wire and slider also
changes.
■ Due to this, an output voltage (eo) is generated, which can be measured.
Alternatively, this output voltage generated can be directly calibrated to give
displacement. The output voltage generated is linear function of the
displacement to be measured.
Advantages
■ Low Cost
■ Simple to operate
■ Useful for measurement of large displacements
■ Low maintenance
Disadvantages
■ For linear potentiometer, large force is required to move the
slider. So it is not suitable for small force applications
■ Resolution is poor
■ The device has limited life due to early wear of slider or wider.
Rotary Position sensors

■ A rotary position sensor is used to measure displacement in a rotary fashion, in either a

clockwise or anti-clockwise direction.
■ The different types of rotary position sensors include contacting or non-contacting
technology. True non-contacting rotary position sensors contain no touching parts which
this gives them long mechanical life as there is no wear and tear.
■ Another way to determine a type of rotary position sensor is whether it is single turn or
multi-turn. A single turn rotary position sensor can measure angles of rotation up to 360°
whereas a multi-turn sensor can continue to rotate past 360o for larger
measurement/number of turns.
Types

■ Rotary Potentiometer
■ Rotary Variable Differential Transformer
■ Hall Effect
■ Resolver
■ Encoder
Rotary Variable Differential
Transformer (RVDT)
■ RVDT is an electro-mechanical inductive transducer that converts angular
displacement into the corresponding electrical signal. It is the most widely used
inductive sensor due to its high accuracy level.
■ Since the coil of RVDT is designed to measure an angular position, so it is also
known as an angular position sensor.
■ RVDT Construction
RVDT uses the Cam-shaped core (Rotating core) for measuring the angular
displacement.
Working Principle
■ The working principle of RVDT and LVDT both are the same and based on the mutual
induction principle.
■ When AC excitation of (5-15) Volt at a frequency of 50-400 Hz is applied to the primary
windings of RVDT then a magnetic field is produced inside the core. This magnetic field
induces a mutual current in secondary windings. Then due to transformer action, the
induced voltages in secondary windings (S1 and S2) are Es1 and Es2 respectively. Hence
the net output voltage will be the difference between both the induced secondary
voltages.
■ Hence Output will be E0 = Es1 – Es2.
■ According to the position of the core, there are three cases that arise
■ Case 1: When the core is at the Null position.
When the core is at the null position then the flux linkage with both the secondary
windings will be the same. So the induced emf (Es1 and Es2 ) in both the windings will be
the same.
Hence the Net differential output voltage E0 = Es1 – Es2 will be zero (E0 = Es1 – Es2 = 0).
It shows that no displacement of the core.
■
■ Case 2: When the core rotates in the clockwise direction.
When the core of RVDT rotates in the clockwise direction. Then, in this case, the flux
linkage with S1 will be more as compared to S2.
This means the emf induced in S1 will be more than the induced emf in S2. Hence Es1 >
Es2 and Net differential output voltage E0 = Es1 – Es2 will be positive. This means the
output voltage E0 will be in phase with the primary voltage.
■ Case 3: When the core rotates in the anti-clockwise direction.
When the core of RVDT rotates in the anti-clockwise direction. Then, in this case, the flux
linkage with S2 will be more as compared to S1.

It means the emf induced in S2 will be more than the induced emf in S1. Hence Es1 <
Es2 and Net differential output voltage E0 = Es1 – Es2 will be negative. This means the
output voltage E0 will be in phase opposition (180 degrees out of phase) with the primary
voltage.
Advantages of RVDT

• High Accuracy.
• Compact and strong construction.
• The consistency of RVDT is high.
• Long life span.
• Very high Resolution.
• Low cost.
Applications of RVDT

Actuators for controlling flight as well as engine.

Fuel valve as well as hydraulics.
Brake with a cable system.
Modern machine tools.
Nose wheel steering systems.
Robotics
Hall Effect Sensors
Hall Effect : On a thin strip of a conductor,
electrons flow in a straight line when electricity
is applied. When this charged conductor comes
in contact with the magnetic field which is in a
perpendicular direction to the motion of
electrons, the electrons get deflected. Some
electrons get collected on one side while some
on another side. Due to this, one of the
conductor’s plane behaves as negatively charged
while the other behaves as positively charged.
This creates potential difference and voltage is
generated. This voltage is called the Hall
voltage. Higher the magnetic field value, higher
the voltage level. If one provides a ring magnet,
the voltage produced is proportional to the
speed of rotation of the magnet.
Contd..

■ The working principle of a hall-effect sensor involves the voltage difference

with a magnetic field to produce output about the object's angular position.
■ The element of this sensor is a magnet, Hall element, and a rotating axis.
■ The angular displacement of any of the aspects of the sensor will result in
magnetic field changes; hence the corresponding difference in output voltage.
■ A hall-effect sensor is more suitable for applications in rugged environment
because it does not require contacting technology, unlike a potentiometer.
However, one disadvantage of a hall-effect sensor is the possible interference it
receives if there are magnets close to the device.
Resolver
■ A resolver is an electromechanical device and the main function of this
device is to change the mechanical motion to an electronic signal.
■ This device consists of three coils.
■ One of the coils rotates, while the other two remains stationary at a 90-degree
distance.
■ The two stationary coils receive current in the same manner as the rotating coil.
■ Comparing the current flow received by the fixed coil and the rotating coil
determines the angular displacement of the object.
■ A resolver also works using a magnetic field; hence also subject to sensitivity
and interference from nearby magnetic devices.
Resolver Construction
 Working
■ The resolver works on the principle of an electrical transformer. These transformers use
copper windings in stator and rotor. Based on the rotor’s angular position, the inductive
coupling of the windings will be changed. The resolver energizes by using an AC signal
and the output of this can be measured to provide an electrical signal.
■ Generally, it includes three windings like one primary and two secondaries. These are
designed with the help of copper wire on the stator. The primary winding functions like the
i/p for an AC signal whereas each of the secondary winding is used as output. In this, the
stationary part is designed with iron or steel.
■ The output signal amplitudes vary with the sine and cosine of the rotation angle, as the
inductive coupling between rotor and stator coils varies with the angular position of the
rotor.
Encoders
■ Encoder sensors are a type of mechanical motion sensor that create a digital signal from a
motion. It is an electro-mechanical device that provides users (commonly those in a motion
control capacity) with information on position, velocity and direction. There are two main types
of encoder.
■ Two types
❖ Linear type
Incremental
Absolute
❖ Rotator type
Incremental
Absolute
 Linear Encoders
■ In a linear encoder a magnetic sensor passing over a magnetic scale. As the sensor
moves along this scale, it detects changes in the magnetic field which are proportional to
the measuring speed and the displacement of the sensor. As linear sensors only detect
changes in the magnetic field, external factors such as light, debris or oil have no effect
on the sensing capabilities, and as a result they are often used in harsher environments.
Incremental linear Encoder
31
Rotary Encoders

■ Rotary Encoders are sensors that detect position and speed by converting
rotational mechanical displacements into electrical signals and processing those
signals.
Absolute Encoder

■ An absolute rotary encoder is used to maintain the positions information once

power is detached from the rotary encoder. This encoder’s position is instantly
available once power is provided.
■ This encoder includes different code rings through different binary weightings
which provide a data word for signifying the rotary encoder’s absolute position in
a single revolution. So this type of encoder is also called a parallel absolute
encoder.
Incremental Encoder

■ The incremental rotary encoder is used to provide a sequence of low & high
waves. These waves will specify the movement of position. These types of
encoders will provide a sequence of periodic signals within the pulses form
because of the shaft revolution motion.
■ An object’s speed can be measured through pulse counting for some time.
These pulses can be simply counted from a reference point to determine the
position otherwise distance covered.
■ The incremental rotary encoder generates two digital o/p signals where the
phase relationships among these two sensors will decide whether the encoder’s
shaft is revolving clockwise direction otherwise anti-clockwise. So by using this
encoder, the position can be simply determined.
 Working
■ The encoder has a disk with evenly spaced contact zones that are connected to the
common pin C and two other separate contact pins A and B, as illustrated below.
■ When the disk will start rotating step by step, pins A and B will start making contact with
the common pin and the two square wave output signals will be generated accordingly.
■ Any of the two outputs can be used for determining the rotated position if we just count
the pulses of the signal. However, if we want to determine the rotation direction as well,
we need to consider both signals at the same time.
■ We can notice that the two output signals are displaced at 90 degrees out of phase from each
other. If the encoder is rotating clockwise output A will be ahead of output B.
■ So if we count the steps each time the signal changes, from High to Low or from Low to High,
we can notice at that time the two output signals have opposite values. Vice versa, if the
encoder is rotating counter-clockwise, the output signals have equal values. So considering
this, we can easily program our controller to read the encoder position and the rotation
direction.
Applications

1. The photovoltaic cells are used in low-power devices such as light meters.
2. They are used in solar-powered scientific calculators.
3. A large set of photovoltaic cells can be connected together to form solar modules,
panels, or arrays.
Force Sensors
■ A Force Sensor is a sensor that helps in measuring the amount of force applied
to an object.
■ A spring balance is an example of a force sensor in which a force, namely, the
weight, is applied to the scale pan that causes displacement, i.e., the spring
stretches. The displacement is then a measure of the force. There exist other
types of force sensors
– Strain Gauge based force sensor
– Piezoelectric based
– Current based
 Strain Gauge based force sensor
■ The principle of this type of sensors is that the elongation of a conductor increases
its resistance. Typical resistances for strain gauges are 50-100 ohms. The increase
in resistance is due to
– Increase in the length of the conductor; and Decrease in the cross-section area of the
conductor.
■ Strain gauges are made of electrical conductors, usually wire or foil, etched on a
base material, as shown in Fig. They are glued on the surfaces where strains are to
be measured.

■ The strains cause changes in the resistances of the strain gauges, which are
measured by attaching them to the Wheatstone bridge circuit as one of the four
resistances.
Strain Gauge based force sensor
■ In order to enhance the output voltage and cancel away the resistance
changes due to the change in temperature, two strain gauges are used, as
shown in Fig, to measure the force at the end of the cantilever beam.

Cantilever beam with strain gauge Wheatstone’s bridge circuit

 Strain Gauge ref:
https://www.michsci.com/what-is-a-strain-gauge/#:~:text=A%20strain%20gauge%20is%2
0a,the%20material's%20cross%2Dsectional%20area.

■ A strain gauge is a sensor whose measured electrical resistance varies with

changes in strain.
■ Strain is the deformation or displacement of material that results from an applied
stress.
■ Stress is the force applied to a material, divided by the material’s cross-sectional
area.
Gauge Factor
Measuring Strain
Thermo-electric sensors ref:
https://www.omega.com/en-us/resources/how-thermocouples-workThermocouple

■ Thermocouple
■ RTD
■ Thermistor
■ Infra-red sensors
Thermocouple ref:
https://www.omega.com/en-us/resources/how-thermocouples-workThermocouple

■ When two wires composed of dissimilar metals are joined at both ends and one of
the ends is heated, there is a continuous current which flows in the thermoelectric
circuit. If this circuit is broken at the center, the net open circuit voltage (the
Seebeck voltage) is a function of the junction temperature and the composition of
the two metals. Which means that when the junction of the two metals is heated,
or cooled, a voltage is produced that can be correlated back to the temperature.
Resistance Temperature Detector :
https://www.omega.com/en-us/resources/rtd-resistance-elements-principles

■ Resistance Temperature Detector is a general term for any device that senses temperature by measuring the
change in resistance of a material. RTD’s come in many forms, but usually appear in sheathed form. An RTD
probe is an assembly composed of a resistance element, a sheath, lead wire and a termination or connection.
The sheath, a closed end tube, immobilizes the element, protecting it against moisture and the environment to
be measured. The sheath also provides protection and stability to the transition lead wires from the fragile
element wires.
Thermocouples vs RTDs
ref: https://www.omega.com/en-us/resources/rtd-resistance-elements-principles
 Thermistors
ref: https://www.omega.com/en-us/resources/thermistor
■ Thermistors is the contraction of term ”Thermal Resistors”.
■ They are essentially semi-conductors which behave as resistors with a high negative or
positive temperature co-efficient of resistance.
■ In some cases the resistance of a thermistor at room temperature may decrease as much
as 5 per cent for each 1o C rise in temperature.
■ This high sensitivity to temperature changes make the thermistors extremely useful for
precision temperature measurements, control and compensation.
■ Thermistors are widely used in such applications especially in the temperature range of
−60o to + 15o C. The resistance of thermistors ranges from 0·5 Ω to 0·75 Ω
 Thermistors
ref: https://www.omega.com/en-us/resources/thermistor

■ Thermistors are available in two types:

those with Negative Temperature Coefficients (NTC Thermistors) and
those with Positive Temperature Coefficients (PTC Thermistors).
■ An NTC Thermistor's resistance decreases as its temperature increases.
■ A PTC Thermistor's resistance increases as its temperature increases.

■ NTC Thermistors are more commonly used for temperature measurement

■ PTC Thermistors are primarily used for circuit protection.
 Thermistors
ref: https://www.omega.com/en-us/resources/thermistor

■ The relationship between a thermistor's temperature and its resistance is highly dependent
upon the materials from which it is composed. Thermistor manufacturers typically determine
this property with a high degree of accuracy - as this is the primary characteristic of interest
to thermistor buyers.

Thermistors are made up of metallic oxides, binders, and stabilizers pressed into wafers and
then cut to chip size, left in disc form, or made into another shape. The precise ratio of the
composite materials governs their resistance/temperature "curve". Manufacturers typically
control this ratio with great accuracy, as it determines how the thermistor will function.
Thermistors
ref: https://www.omega.com/en-us/resources/thermistor
■ Thermistors are often selected for applications where ruggedness, reliability, and
stability are important.
■ They’re well suited for use in environments with extreme conditions, or where
electronic noise is present.
■ They’re available in a variety of shapes: the ideal shape for a particular application
depends on whether the thermistor will be surface-mounted or embedded in a
system, and on the type of material being measured.
■ Thermistors are employed in a broad array of commercial and industrial applications
to measure the temperature of surfaces, liquids, and ambient gasses.
■ When sheathed in protective probes that can be reliably sanitized, they’re used in the
food and beverage industries, in scientific laboratories, and in R&D.
■ Heavy-duty probe-mounted thermistors are suitable for immersion in corrosive fluids,
and can be used in industrial processes, while vinyl-tipped thermistor mounts are used
outdoors or for biological applications. Thermistors are also available with metal or
plastic cage-style element covers for air temperature measurement.
RTD vs Thermistors
ref: https://www.omega.com/en-us/resources/rtd-vs-thermistors
 Infrared sensors
ref: https://www.manoraz.com/_Uploads/dbsAttachedFiles/MM_ENG_F_W.PDF

■ Infrared (IR) thermometry measures energy that is naturally emitted from all objects,
without actually touching them. This allows quick, safe measurement of the
temperature of objects that are moving, extremely hot, or difficult to reach. Where a
contact instrument could alter the temperature, damage, or contaminate the product, a
noncontact thermometer safely allows accurate product temperature measurement.
These sensors are also used in applications where the high temperature of the target
could damage or destroy a contact temperature sensor.
Infrared sensors
ref: https://www.sensortips.com/temperature/infrared-temperature-sensor/

■ A typical infrared temperature sensor consists of optical components,

IR detector, electronics, and a display or interface output stage. Optics
focuses IR energy onto the detector that converts the IR energy into an
electrical signal. After amplification, linearization, and temperature
stabilization, the electrical signal is converted to a value representing
the measured temperature.
 Infrared sensors
ref: https://www.sensortips.com/temperature/infrared-temperature-sensor/
■ Based on the principle of operation, IR detectors fall into one of
two categories: thermal detectors and photodetectors
(photodiodes). Thermal IR detectors absorb the incident energy,
raise the sensing element temperature, and change the
detector’s electrical properties: thermopiles generate
thermoelectric voltage, bolometers change resistance, and
pyroelectric devices change their polarization. In general, they are
slower than photodetectors.
 Infrared sensors
ref: https://www.sensortips.com/temperature/infrared-temperature-sensor/
■ A thermopile is made by connecting several thermocouples in series
and placing their hot junctions in contact with a black body that
absorbs the incident IR energy and heats the hot junctions. The cold
junctions are placed in the area of the detector with adequate heat
sinking. These detectors have fast response, broad band, large
dynamic range, and are frequently used in general-purpose,
automotive, air conditioning, and human-body thermometers.
■ Bolometers use a slab of material that changes its resistance in
response to a change of temperature. The circuit converts resistance
change to a voltage change, which is further processed by the
instrument. Bolometers are frequently used for measuring low-level
IR energy, often as an attachment to a telescope.
■ Pyroelectric devices become electrically charged when their body
temperature changes. To produce a usable signal, the incident IR
energy has to “pulse”. The output peak-to-peak AC signal is
proportional to the pulse energy. Since energy emitted by measured
objects is usually steady, thermometers that use pyroelectric
detectors have a mechanical or optical chopper in front of the sensor.
These sensors are used in many home security systems.
 Infrared sensors
ref: https://www.sensortips.com/temperature/infrared-temperature-sensor/

■ Photo detectors are built on a silicon substrate

with an IR sensitive area that releases free
electrons when impacted by the photons. The
flow of electrons produces electrical signals
proportional to the incident energy. These
detectors are often used as arrays in thermal
imaging systems.
 Infrared sensors
ref: https://www.sensortips.com/temperature/infrared-temperature-sensor/

■ Since all types of IR detectors produce signals in

the microvolt range, a high-gain amplifier should
follow the detector. Detector output vs.
temperature curves are not linear and fluctuate
greatly with a change in ambient temperature. To
remedy this a signal-conditioning circuit
stabilizes the temperature and linearizes the
signal. Many applications require an
analog-to-digital converter (ADC) to convert the
temperature reading to a digital format.
 Infrared sensors
ref: https://www.sensortips.com/temperature/infrared-temperature-sensor/

■ The key specifications and considerations for any

infrared temperature sensor application are field of
view (FOV) and distance; spectral band; response
time; accuracy and repeatability; emissivity of the
object or media being measured; media between the
object and infrared temperature sensors, such as
vacuum, air, steam, gas, glass, or other; object
temperature range; mounted or hand-held
application; and type of output signal or display.
 Actuators
■ An actuator is a hardware device that converts a controller command signal into a change in a physical
parameter.
■ The change in the physical parameter is usually mechanical, such as a position or velocity change.
■ An actuator is a transducer, because it changes one type of physical quantity, such as electric current, into
another type of physical quantity, such as rotational speed of an electric motor.
■ The controller command signal is usually low level, and so an actuator may also require an amplifier to
strengthen the signal sufficiently to drive the actuator.
■ The primary function of actuators is to control machines and allow parts to move. This motion can be any
one of hundreds of operations such as lifting, clamping, blocking and ejecting. Typically, actuators are
key parts in industrial and manufacturing operations where they activate valves, pumps, motors and
switches.
■ Most actuators can be classified into one of three categories, according to the type of amplifier:
(1) electric,
(2) hydraulic, and
(3) pneumatic.
Electric Actuators
Electric actuators are most common; they include electric motors of
various kinds, solenoids, and electromechanical relays.
Electric actuators can be either linear (output is linear displacement)
or rotational (output is angular displacement).
The function of an electric actuator is to generate mechanical power
from electricity input. Since the power source is consistent and
continuous, these actuator types offer easy maintenance and are ideal
for high-precision work. Electric actuators are common in
manufacturing, robotics and electric vehicles.
■ Most electric actuators turn an electric motor’s power into linear motion in one of three ways:
Through a linear motor … a direct-drive option
Through a belt (via a pulley mounted to the motor output)
Through a screw drive — whether ballscrew, roller screw, or roller screw
■ For linear actuation is linear motors — a technologically advanced and efficient method of directly
transmitting motor power into axis motion. These entirely omit the mechanical linkage for
rotary-to-linear conversion and instead include a moving forcer that moves along a stationary
platen.
■ Belt drive actuators are less costly, but can still move loads at fairly high linear speeds. Because
the motor is separate from the drive, the mechanical advantage can increase thrust speed. The
disadvantage of belt drives is that they wear over time and require maintenance.
■ Most screw drives take the form of either rod-style actuators or rodless cylinders. A motor
transmits power through a coupler or pulley arrangement to rotate the screw and translate a nut
along the screw axis. Attached to this nut is either the rod or saddle of the actuator. Screw drives
can use roller, ball or leadscrews.
Electrical Actuators
ref: https://journals.sagepub.com/doi/10.1177/0954406217749869

These have provisions for feedback-based corrective action

Electrical, Actuators
ref:
https://www.norgren.com/en/support/blog/what-is-an-electric-actuator#:~:text=How%20does%20an%20electric%20
actuator,in%20a%20ball%20screw%20nut.

■ An electric actuator is a device

that can create movement of a
load, or an action requiring a
force using an electric motor to
create the necessary force.

• 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 backward, 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.
• 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.
Electrical Actuator: Components
ref: https://www.elprocus.com/types-of-electric-actuators-applications/

■ An electric actuator is one kind of gear motor which can be of various voltages and
is the main torque-producing component. To stop extreme current draws, electric
actuator motors are generally set with a thermal overload sensor fixed in the motor
windings. This sensor is energetic in series with the power source and unlocks the
circuit should the motor be excited, then locks the circuit when the motor attains a
secure operating temperature.
■ An electric motor consists of an armature, an electrical winding, and a gear train.
When power is supplied to the winding, a magnetic field is generated causing the
armature to rotate. The armature will turn as long as there is a control to the
windings when the power is cut, the motor discontinues.
■ Typical end-of-travel limit switches, which are essential for an electric actuator,
handle this mission.
Electrical Actuators: Applications
ref:
https://www.norgren.com/en/support/blog/what-is-an-electric-actuator#:~:text=How%20does%20an%20electric%20
actuator,in%20a%20ball%20screw%20nut.

Electric actuators are found in a wide variety of industrial applications.

■ In the automotive industry for driverless transport vehicles, dispensing and a
selection of jointing methods – gluing, welding and riveting.
■ In the food and beverage industry, for production of PET bottles, filling and
labelling systems and robotic applications such as milking robots.
■ They are used in materials handling for operations such as servo presses and
clamping and widely used in the packaging sector.
■ Their benefits in accuracy, flexibility and low operating costs lead to use in
robotics, electronics and electronic assembly, machine tools and many other
industrial sectors.
Electrical Actuators: Advantages
ref: https://yorkpmh.com/resources/hydraulic-vs-pneumatic-vs-electric-actuators/#actuators

■ Fast: Electric actuators are directly driven. As such, they have excellent response
times that make them fast performers. For quick and light work, electric actuators are
great.
■ Precise: Electric actuators are precise devices. Whereas hydraulic and pneumatic
actuators have tolerances like slack, backlash and flex inherent in their design, that’s
not an issue with electrics. For precision control and performance, electric actuators
are a good bet.
■ Clean: Electricity is a clean energy source, meaning, there is no potential risk for
leakage.
Electrical Actuators: Disadvantages
ref: https://yorkpmh.com/resources/hydraulic-vs-pneumatic-vs-electric-actuators/#actuators

■ Weak: You can’t get the same amount of strength and power with electrics that
you can with hydraulics or pneumatics. Despite increased technology that adds
strength to actuator designs, electrics still remain relatively weak.
■ Complicated: Electric actuators tend to be complicated designs. Complications
lead to a higher risk of breakdown and downtime. This is a con you’ll want to
remember when looking at actuation systems for your site.
■ Costly: There is a significant cost attached to most electric actuation devices. On a
cost-per-strength basis, electrics are considerably higher priced.
Hydraulic Actuators

Use hydraulic fluid to amplify the controller command signal.

The available devices provide either linear or rotational motion.
Hydraulic actuators are often specified when large forces are required.
Hydraulic actuators operate with compressed fluid and control movement by
managing the amount of fluid inside. Adding fluid increases pressure while
reducing it lessens the force. These actuators are ideal for applications that
need more significant power, but you can also commonly find them in products
like exercise equipment.
Hydraulic Actuators: Principle
ref: https://electronicscoach.com/hydraulic-actuator.html

■ Hydraulic actuator system uses the concept proposed by Pascal generally known as
Pascal’s Law or Pascal’s Principle.
■ Pascal’s Law states that the pressure applied at a specific point to a confined fluid in
a container is transmitted equally in all the directions within the fluid as well as the
walls of the container without any loss.
■ Suppose, if pressure P is applied to an area A, then the resultant force due to an
applied pressure will be:
■ F=P*A
■ Now, if a certain force F is applied in a smaller area to have pressure P in a confined
fluid, then the force produced on a larger area as a result of it can be comparatively
larger than the force created by the pressure.
■ In this way, the applied pressure at a certain point is used to generate very large
forces and this principle is utilized by various hydraulic systems.
Hydraulic Actuators: Working
ref: https://electronicscoach.com/hydraulic-actuator.html

■ The major component of the unit is pilot valve also known as spool valve and main
cylinder (or power cylinder).
■ It operates in a way that difference in pressure created at the two regions of the main
cylinder leads to the occurrence of translational motion of the piston.
Hydraulic Actuators: Working
ref: https://electronicscoach.com/hydraulic-actuator.html

■ The rate with which the fluid flows inside the cylinder is controlled by the spool valve.
The spool valve has 4 ports and each port is connected to a different part of the
system.
■ Two separate ports are connected to the fluid supply and drain region respectively.
While the other two ports are connected separately to the two chambers of the main
cylinder.
Hydraulic Actuators: Working
ref: https://electronicscoach.com/hydraulic-actuator.html

■ Initially, the spool is present at the neutral position say x = 0 and at this position, there
will be no flow of fluid inside the main cylinder. The assembly of the hydraulic actuator
is such that the load will move according to the fluid flow.
■ Thus, when input displacement, x is 0 then the output displacement y will also be 0.
Hydraulic Actuators: Working
ref: https://electronicscoach.com/hydraulic-actuator.html

■ As soon as a certain input displacement is provided, then the spool moves towards
the right. The movement of spool towards the right causes the fluid from the
high-pressure source to move towards the left chamber of the main cylinder.
Hydraulic Actuators: Working
ref: https://electronicscoach.com/hydraulic-actuator.html

■ In this way, the direction in which fluid flows corresponds to the direction in which the
load moves. This acts as power amplification as discussed in operating principle
because the force supplied to displace the valve is comparatively very small than the
force generated that actually displaces the load.
Hydraulic Actuators: Advantages
ref: https://yorkpmh.com/resources/hydraulic-vs-pneumatic-vs-electric-actuators/#actuators

• Force: Hydraulic actuator motors have a high horsepower-to-weight ratio. They are
extremely forceful and produce a tremendous amount of power for their size. This
makes them economical as well as highly efficient.
• Safety: Hydraulic power is easy to contain and control. Hydraulic systems are
extremely dependable and their design has been long-proven to be safe and secure.
Many hydraulic controls are automated, but it’s simple to build manual overrides into
hydraulics that let an operator directly control the actuator.
• Mobility: Here’s where hydraulic actuators also excel. They are self-contained and
portable without needing a cumbersome and complicated support system. Hydraulics
are ideally suited for trucks and heavy equipment applications.
Hydraulic Actuators: Disadvantages
ref: https://yorkpmh.com/resources/hydraulic-vs-pneumatic-vs-electric-actuators/#actuators

• Initial investment: Because most hydraulic actuators are large and powerful, they can
be relatively expensive as initial investments. However, like other investments, you
have to consider your returns. An initial cash layout pays back over time, especially if
you require the power and performance that a hydraulic actuator delivers.
• Maintenance: Hydraulic equipment requires maintenance, and that can cost more time
and money. But, you’ll find that both pneumatic and electric actuators also need their
share of maintaining, as does any industrial product.
• Leakage: The biggest concern investors have about acquiring a hydraulic actuator is
leakage. Hydraulic oil can leak and can be challenging to clean. It's also a serious
contaminant. With proper maintenance, though, your risk of hydraulic leakage is
significantly reduced.
Pneumatic Actuators

Use compressed air (typically “shop air” in the factory) as the driving power.
Again, both linear and rotational pneumatic actuators are available.
Because of the relatively low air pressures involved, these actuators are usually
limited to relatively low-force applications compared with hydraulic actuators
The primary advantage of pneumatic systems is that they run on compressed air
or gas instead of fluid. As a result, they are involatile and require no electricity to
perform. Pneumatic actuators are versatile and affordable, making them popular
for braking systems and pressure sensors.
Pneumatic Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/

■ Pneumatic actuators have

widespread applications involving
the opening and closing of valves.
The actuators have many
applications in process control like
modulation, on/off control,
packaging machinery, fuel car
engines, and air compressors.
■ They are also common in robotics,
automobile, aviation, and the
transportation industry.
Pneumatic Actuators
ref:
https://www.electricalvolt.com/2022/02/spring-and-diaphragm-pneumatic-actuator/#:~:text=The%20linear%20pneu
matic%20diaphragm%20actuator,diaphragm%20and%20compress%20the%20spring./
■ Diaphragm actuators
– The linear pneumatic diaphragm actuator is
based on the principle that when the air
supply signal pressure passes through the
air chamber composed of the upper
diaphragm cover and the diaphragm, make
to moves the push rod down as thrust is
generated on the diaphragm and
compresses the spring.
– When the spring force becomes equal to
the thrust generated by the air supply signal
pressure on the diaphragm, the pushrod
stabilizes in a corresponding position.
Pneumatic Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/

■ Diaphragm actuators
– Diaphragm-type actuators are suitable for both modulating control and on-off service. These actuators
provide an extremely long cycle life. They are suitable for low to medium thrust requirements.

– Diaphragm Materials:
– Molded nylon reinforced oil-resistant elastomer, nylon-reinforced nitrile rubber.
Pneumatic Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/

■ Piston actuators
– The pneumatic actuator consists of a piston inside a closed
cylinder. The piston slides and transmits its movement to the
outside through a rod.
– The pneumatic cylinder is the most common actuator for the
pneumatic circuits, irrespective of their constructive form. There
are two fundamental types of pneumatic actuators.
– Single-acting cylinders
– Double-acting cylinders
Pneumatic Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/

■ Piston actuators: Single Acting

– A single-action system has only one port, which supplies air to the chamber. A
spring placed inside or outside pushes the piston into position. The inlet port
receives the air and produces a working stroke in one direction. Please note
that the single-acting cylinders can be push-type or pull-type, but, it is able to
perform any one single action. It provides inherent fail-safe action either “air
fail to close” or “air fails to open”.
Pneumatic Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/

A double-action system has two ports and is not spring-loaded. The port receives the air to move
the piston. Meanwhile, the other port supplies air on the opposite side to push the piston into place.
The concept is the same but they are different in the return method and the number of ports.
Pneumatic Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/

Rotary Pneumatic Actuators

Rotary or rotary actuators are responsible for transforming pneumatic energy into rotary mechanical
energy
Pneumatic Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/

■ Advantages
– Pneumatic actuators are relatively simple, and easy to do maintenance.
– The pneumatic actuators are relatively fast acting. As a result, the fastest cycle rate contributes to productivity
increase.
– In hot environments, Pneumatic actuators are safer than hydraulic or electrical actuators.
Pneumatic Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/
ref: https://yorkpmh.com/resources/hydraulic-vs-pneumatic-vs-electric-actuators/#actuators

■ Disadvantages
– They are best for light to medium applications because they supply limited power.
– Air compressibility and pressure losses make them less capable of producing higher forces.
– Oil or lubrication can also pollute the air.
– We should take care of monitoring the air for moisture content to avoid performance issues.
– Lesser life time than comparable hydraulic systems
 Selection: Hydraulic, Pneumatic, Electric
Actuators
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/
ref: https://yorkpmh.com/resources/hydraulic-vs-pneumatic-vs-electric-actuators/#actuators

■ Hydraulic actuators: For heavy-duty work, nothing beats hydraulic power. Compressing a fluid like oil produces
much more motion power than compressing a gas like air. Hydraulic power performance is also superior to
electrically operated actuators.
■ Pneumatic actuators: Compressed air won’t produce the power that hydraulic actuators generate, but they will be
stronger than electrically energized actuators. Pneumatic systems tend to work faster than hydraulic and electric
actuators.
■ Electric actuators: Actuators operated on electric current have their advantages and disadvantages. While generally
not producing the strength that hydraulic and pneumatic systems are capable of, they are cleaner and sometimes
more cost-effective
Important Considerations for Actuator Selection
ref: https://www.electricalvolt.com/2022/01/types-of-actuators/
ref: https://yorkpmh.com/resources/hydraulic-vs-pneumatic-vs-electric-actuators/#actuators

■ Capacity: The amount of force required

■ Voltage: Important for electric actuators or electric components
■ Stroke length: Travel measurement needed
■ Speed: The amount of operating time or rate required
■ Duty cycling: How often the actuator opens and closes
■ Orientation: Position or direction of installation
■ Special requirements: Weather, fire, or leakage concerns