Hydraulic and Pneumatic Actuators

ME407
MECHATRONICS
SUKESH O P
Assistant Professor
Dept. of Mechanical Engineering
JECC
10/16/18
1SUKESH O P/ APME/ME407- MR-2018
SUKESH O P/ APME/ME407- MR-2018

ME407 MECHATRONICS
 Course Objectives:
 To introduce the features of various sensors used in CNC machines and
robots
 To study the fabrication and functioning of MEMS pressure and inertial
sensors
 To enable development of hydraulic/pneumatic circuit and PLC
programs for simple applications
10/16/18
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SUKESH O P/ APME/ME407- MR-2018SUKESH O P/ APME/ME407- MR-2018

Expected outcome:
The students will be able to
i. Know the mechanical systems used in mechatronics ii. Integrate
mechanical, electronics, control and computer engineering in the
design of mechatronics systems
ME407 MECHATRONICS
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Expected outcome:
The students will be able to
i. Know the mechanical systems used in mechatronics ii. Integrate
mechanical, electronics, control and computer engineering in the
design of mechatronics systems
ME407 MECHATRONICS
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SYLLABUS
 Introduction to Mechatronics, sensors, Actuators, Micro Electro
Mechanical Systems (MEMS), Mechatronics in Computer Numerical
Control (CNC) machines, Mechatronics in Robotics-Electrical drives,
Force and tactile sensors, Image processing techniques, Case studies
of Mechatronics systems.
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MODULE-II
 Actuators: Hydraulic and Pneumatic actuators - Directional control
valves, pressure control valves, process control valves. Rotary
actuators. Development of simple hydraulic and pneumatic circuits
using standard Symbols.
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MODULE-II
Actuators: Hydraulic and Pneumatic actuators
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WHAT IS AN ACTUATOR?
 Actuators are devices used to produce action or motion.
 Input(mainly electrical signal , air, fluids)
 Electrical signal can be low power or high power.
 Actuators output can be position or rate i.e. linear displacement or
velocity.
 Actuation can be from few microns to few meters
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FLOWDIAGRAMOF AN
ACTUATOR
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TYPES OF ACTUATORS
 Hydraulic Actuators
 Pneumatic actuators
 Mechanical Actuators
 Electrical Actuators
 Linear actuator: solenoid, Hydraulic/Pneumatic.
 Rotary actuator: motor, Hydraulic/Pneumatic.
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 Devices which can be considered to be motion converters in that
they transform motion from one form to some other required
form.
 Eg: Transform linear motion into rotational motion and vice versa.
 Mechanical elements can include the use of linkages, cams, gears,
rack-and-pinion, chains, belt drives, etc.
 Eg: rack-and-pinion can be used to convert rotational motion to linear
motion.
 Many of the actions which previously were obtained by the use of
mechanism are, however, often nowadays being obtained, as a
result of a mechatronics approach by the use of microprocessor
systems.

 Mechanisms still, however, have a role in mechatronics systems.
For example, the mechatronics system in use in an automatic
camera for adjusting the aperture for correct exposures involves a
mechanism for adjusting the size of diaphragm.
 Others function:
 Force amplification – given by levers.
 Change of speed – given by gears.
 Transfer of rotation about one axis to rotation about another – timing belt.
 The term kinematics is used for the study of motion without
regard to forces. When we consider just the motions without any
consideration of the forces or energy involved then we are
carrying out a kinematic analysis of the mechanism.

Translation motion Rotational motion
Movement which can be
resolved into components
along one or more of the 3
Movement which can be
resolved into components
along one or more of the 3
Rotation which has
components rotating about
one or more of the axes.
Rotation which has
components rotating about
one or more of the axes.SUKESH O P/ APME/ME407- MR-2018

 Each part of a mechanism which has motion relative to some
other part is termed a link.
 A rigid body which has two or more points of attachment to other
links is termed nodes.
 Each link is capable of moving relative to its neighboring links.
 A joint is a connection between the connected links at their nodes
and which allows some motion between the connected links.
 Levers, cranks, connecting rods and pistons, sliders, pulleys, belts
and shafts are all examples of links.
(a) with two nodes (c) with four nodes(b) with three nodesSUKESH O P/ APME/ME407- MR-2018

 A sequence of joints and links is
known as kinematic chain.
 For a kinematic chain to transmit
motion, one link must be fixed.
Movement of one link will then
produce predictable relative
movements of the others.
 It is possible to obtain from one
kinematic chain a number of
different mechanisms by having a
different link as the fixed one.
 The design of many mechanisms
are based on two basic forms of
kinematic chains, the four-bar
chain and the slider-crank chain. The reciprocating motion of a piston
is transformed into rotational motion
of a crankshaft on bearings mounted
in a fixed frame.
The reciprocating motion of a piston
is transformed into rotational motion
of a crankshaft on bearings mounted
in a fixed frame.
Slider
Crankshaft
Connecting
rod
Fixed frame

Double-lever mechanism Lever-crank mechanism Double-crank mechanism

Cine film advance mechanismSUKESH O P/ APME/ME407- MR-2018

The position sequence for the
links in a slider-crank mechanismSUKESH O P/ APME/ME407- MR-2018

 Cam is a body which rotates or oscillates and in doing so imparts a
reciprocating motion to a second body called follower, with which
it is in contact.
 The length of times spent for the rotation is depending on the
shape of the cam.
Part that lowers the
follower, its profile
determining how
quickly the cam
follower will fall.
Part that lowers the
follower, its profile
determining how
quickly the cam
follower will fall.
Part that allows the
follower to remain at
the same lever for a
significant period of
time and where its
circular with a radius
Part that allows the
follower to remain at
the same lever for a
significant period of
time and where its
circular with a radius
that does not change.
Part that drives the
follower upwards, its
profile determining
how quickly the cam
follower will lifted.
Part that drives the
follower upwards, its
profile determining
how quickly the cam
follower will lifted.

 The cam shape required to produce a particular motion of the
follower will depend on the shape of the cam and the type of
follower used.
Displacement diagram for an eccentric camSUKESH O P/ APME/ME407- MR-2018

 Figure below shows the types of follower displacement diagrams
that can be produced with two other different shaped cams and
either point or knife followers.
Heart
shape
Heart
shape
Pear
shape
Pear
shape
(constant rate,
uniform speed)
(constant rate,
uniform speed)
(rise and fall
symmetrically)
(rise and fall
symmetrically)

 Figure below shows a number of examples of different types of
cam followers.
Point RollerKnife
Lower friction than
sliding contact but
can be more
expensive
Lower friction than
sliding contact but
can be more
expensive

 Figure below shows a number of examples of different types of
cam followers.
Often used
because –
cheaper and can
be made smaller
than roller
follower.
Often used
because –
cheaper and can
be made smaller
than roller
follower.
Sliding and oscillating Flat Mushroom

 Gear trains are mechanisms which are very widely used to
transfer and transform rotational motion. They are used when a
change in speed or torque of a rotating device is needed. For
example, the car gearbox enables the driver to match the speed
and torque requirements of the terrain with the engine power
available.
(a) Parallel gear axes, (b) axes inclined to one another, (c) axial teeth,
(d) helical teeth, (e) double helical teethSUKESH O P/ APME/ME407- MR-2018

 Two meshed gears.
 Gear ratio,
ωA = number of teeth on B = dB
ωB number of teeth on A dA
ωA = number of teeth on B = dB
ωB number of teeth on A dA
Angular velocity Diameter

G = ωA = ωA ωB
ωC ωB ωC
G = ωA = ωA ωB
ωC ωB ωC
x

 Compound gears trains – two wheels are mounted on a common
shaft.
 Ratio of the angular velocities,
 For the input and output shafts to be in line, we must also have for the
radii of the gears.
G = ωA = ωA ωB ωC = ωA ωC
ωD ωB ωC ωD ωB ωD
G = ωA = ωA ωB ωC = ωA ωC
ωD ωB ωC ωD ωB ωDxx x
rA + rB = rD + rCrA + rB = rD + rCSUKESH O P/ APME/ME407- MR-2018

v = nL / t = fLv = nL / t = fL
Time
Distance moved parallel to the screw axis
Revolution

 Pair of rolling cylinders with the motion of one cylinder being transferred to
the other by a belt.
 Belt drives use the friction that develops between the pulleys attached to
the shaft and the belt around the arc of contact in order to transmit a
torque.
 The transmitted torque is due to the differences in tension that occur in the
belt during operation. This difference results in a tight side and a slack side
for the belt.

 If the tension on the tight side is T1, and a slack side is T2, then with pulley
A as a driver,
 Pulley B as a driver,
 Since the power transmitted is the produce of the torque and the angular
velocity, and since the angular velocity is v/rA for pulley A and v/rB for
pulley B, then for either pulley we have
Torque on A = (T1 – T2) rATorque on A = (T1 – T2) rA
Power = (T1 –
T2) v
Power = (T1 –
T2) v
Torque on B = (T1 – T2) rBTorque on B = (T1 – T2) rB

 As a method of transmitting power between two shafts, belt drives have
the advantage that the length of the belt can easily be adjusted to suit a
wide range of shaft to shaft distance and the system is automatically
protected against overload because slipping occurs if the loading exceeds
the maximum tension that can be sustained by frictional forces.
 If the distance between shafts is large, a belt drive is more suitable than
gears, but over small distances gears are to be preferred.
 Different size pulleys can be used to give a gearing effect. However, the
gear ratio is limited to about 3 because of the need to maintain an
adequate arc of contact between the belt and pulleys.

 Figure below shows two types of reversing drives.
 With both forms of drive, both side of the belt comes into contact with the
wheels and so V-belts or timing belts cannot be used.
Cross belt
Open belt

 V
 V – belts are used with grooved pulleys and are less efficient that flat belts
but a number of them can be used on a single wheel and so give multiple
drive.
 Timing.
 Require toothed wheels, having teeth which fit into the grooves on the
wheel.
 Unlike the other belts, timing belt does not stretch or slip and consequently
transmits power at a constant angular velocity ratio.
 The teeth make it possible for the belt to be run at slow or fast speeds.

 Whenever there is relative motion of one surface in contact with another,
either by rotating or sliding, the resulting frictional forces generate heat
which wastes energy and results in wear.
 The function of bearing is to guide with minimum friction and maximum
accuracy the movement of one part relative to another.
 Give suitable support to rotating shaft.
 The term thrust bearing is used for bearings that are designed to withstand
forces along the axis of a shaft when the relative motion is primarily
rotation.

a) Deep-groove
b) Filling-slot
c) Angular contact
a) Deep-groove
b) Filling-slot
c) Angular contact
d) double-row
e) Self-aligning
e) Thrust, grooved
race
d) double-row
e) Self-aligning
e) Thrust, grooved
race

a) Straight roller
b) Taper roller
c) Needle roller
a) Straight roller
b) Taper roller
c) Needle roller

Electrical Actuators
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An actuator receiving electrical energy for motion is called
an electrical actuator.
1.Switching devices
1. Mechanical switches
1. Solenoids
2. Relays
2. Solid state switches
1. Diodes
2. Tyristors
3. Transistors
2.Drive system
1. DC motors
2. AC motors

Hydraulics and Pneumatics
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Hydraulics
 An actuator wherein hydraulic energy is used to impart motion is
called an hydraulic actuator.
 Hydraulic systems are power-transmitting assemblies employing
pressurized liquid as a fluid
for transmitting energy from an energy-generating source to an
energy-using point to
accomplish useful work.
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HYDRAULIC SYSTEM
 The basic rule of using hydraulic power is Pascal's Principle.
 Pascal's Principle: pressure exerted on a fluid is distributed
equally throughout the fluid.
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Hydraulics uses incompresible liquids so the applied pressure from one end
(small arrow) is equal to the desired pressure on the other end (big arrow).

Hydraulics
1. Hydraulic pump unit : in an actual hydraulic system a pump converts
mechanical power into fluid power.
2. Control valve : the flow of pressurized liquid discharge by the pump is
controlled by valves.
 Pressure control valves- control the liquid pressure .
 Flow control valves : control the liquid flow rate.
 Directional control valve : control the direction of flow of the liquid.
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Hydraulics
3. hydraulic motor/cylinder
 The liquid discharged by the pump is directed to hydraulic motors or
cylinders by control valves.
 Motors are used where rotory motion is desired and cylinders are
used where linear motion is necessary.
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HYDRAULIC ACTUATOR
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Hydraulic systems are used to control & transmit power.
•A pump driven by prime mover (electric motor) creates flow of fluid

Hydraulic system
50

51

Functions of the components
1. The hydraulic actuator is a device used to
convert the fluid power into mechanical
power to do useful work. The actuator may be
of the linear type (e.g., hydraulic
cylinder) or rotary type(e.g., hydraulic motor)
to provide linear or rotary motion,
respectively.
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2. The hydraulic pump is used to force the fluid from the reservoir to
rest of the
hydraulic circuit by converting mechanical energy into hydraulic
energy.
3. Valves are used to control the direction, pressure and flow rate of a
fluid flowing
through the circuit.
4. External power supply (motor) is required to drive the pump.
5. Reservoir is used to hold the hydraulic liquid, usually hydraulic oil.
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6. Piping system carries the hydraulic oil from one place to another.
7. Filters are used to remove any foreign particles so as keep the fluid
system clean and
efficient, as well as avoid damage to the actuator and valves.
8. Pressure regulator regulates (i.e., maintains) the required level of
pressure in the
hydraulic fluid.
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- Economic
- Reliable
- Resistant to overloads
- Able to support heavy loads
Hydraulic actuators
- Low working speed
- Hydraulic group noisy in operation
- Possible oil leakage

Pneumatics
Uses pressurised air to transmit and control power.
Air is used as the fluid because:-
 It is safe.
 It is less expensive and readily available
 It can be inducted and exhausted directly to the atmosphere and
return line is not necessary as with hydraulics.
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Pneumatics System
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58

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Pneumatic systems are systems always
processing new air (where as hydraulic
systems are closed systems always
returning the oil)

Pneumatic actuators (cylinders)
- Economic
- Reliable
- High operation speed
- Resistant to overloads
- Operation at constant force
- No speed control
- Poor position speed
- Noisy operation

Comparison between Hydraulic and Pneumatic system
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S.
No.
Hydraulic System Pneumatic System
1. It employs a pressurized liquid as a
fluid
It employs a compressed gas,
usually air, as a fluid
2. An oil hydraulic system operates at
pressures up to 700 bar
A pneumatic system usually
operates at 5–10 bar
3. Generally designed as closed system Usually designed as open system
4. The system slows down when leakage
occurs
Leakage does not affect the system
much
5. Valve operations are difficult Valve operations are easy
6. Heavier in weight Lighter in weight
7. Pumps are used to provide
pressurized liquids
Compressors are used to provide
compressed gases
8. The system is unsafe to fire hazards The system is free from fire
hazards
9. Automatic lubrication is provided Special arrangements for
lubrication are neededSUKESH O P/ APME/ME407- MR-2018

HYDRAULIC ACTUATOR
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Linear Actuators - CYLINDERS
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Parts of linear actuator
 Cylinder barrel Piston
 Cylinder base or cap Piston rod
 Cylinder head Rod gland
 Other parts : Cylinder base connection - Seals-Cushions
64

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Single acting cylinder
 In the case of a single acting cylinder, only the piston side is
pressurized with hydraulic fluid. The cylinder can thus carry out work
only in one direction.
 The fluid which flows into the piston chamber causes a pressure to
build up the surface of the piston.
 The piston travels into its forward end position. The return stroke is
effected by a spring, the dead eight of the piston rod or an external
load.
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PLUNGER TYPE SINGLE
ACTING CYLINDER
 In the case of plunger cylinders, the piston and rod form a single
component.
 Due to the design of the cylinder, the return stroke can only be
effected by external forces.
 The cylinders can therefore generally be installed only vertically.
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DOUBLE ACTING CYLINDER
WITH
END POSITION CUSHIONING Cylinder with end position cushioning are used to brake high stroke
speeds smoothly and prevent hard impacts at the end of the stroke.
Shortly before the end position is reached, the cross- section for the
outflow of fluid is reduced by the built-in cushioning pistons and then
finally closed. The hydraulic fluid is then forced to escape through a
flow control valve.
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Cylinder cushioning
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Through rod cylinder
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tandem cylinder
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ROTARYACTUATORS
 ASSIGNMENT QUESTION
HYDRAULICS & PNEUMATICS: :
 Gear motor
 Vane motor
 Piston motor
 Turbine motors
 Gerotor type motors
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Module-II
 Directional control valves, pressure control valves, process
control valves.
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Control valves
 Fluid power is controlled primarily through the
use of control devices called valves.
 Hydraulic and pneumatic systems require
control valves to direct and regulate the flow of
fluid and regulate the flow of fluid from pump(or
compressor) to hydraulic cylinders or motors.
1. Direction control valves
2. Pressure control valves
3. Process control valves (flow)
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Flow control valves
 These valves are used to control the speed
of hydraulic actuator by controlling the flow
rate or discharge
1. Needle valve
2. Gate and globe valve

1. Needle valve
 It is the most common hydraulic flow control
device.
 It consists of a needle or pointed threaded
stem that can be adjusted manually to control
the flow or discharge through the valve. It is
made of steel.
 This valve can also be used as a stop valve to
prevent the flow of fluid from one part of the
hydraulic circuit to another.

Needle valves

Globe valve
 In this valve the flow area is larger than that of a
needle valve. Hence globe valve will have a larger
flow capacity at a lower pressure drop than a
needle valve of the same size.
 Globe valves have a round disk to control or stop
the fluid flow.
 Needle valves are suitable for throttling i.e., the
flow area is slowly reduced as the valve is closed,
gradually reducing the quantity of fluid passing
through the valve. But the globe valves are not so
suitable for throttling function.SUKESH O P/ APME/ME407- MR-2018

Gate valve
 Gate valves are not normally used as flow control
valves. Most of the gate valves are used as stops
to shutoff fluid flow (or) to open the line to full
flow.
 Gate valves provides a opening with minimum
pressure drop.

Pressure control valvesPressure control valves
 These valves control the pressure of flow medium
required by the system..
 To regulate or reduce oil pressure in certain portions of
the circuit
 to unload system pressure.
 To limit maximum system pressure as a safety
measure.
 To assist sequential operation of actuators in a circuit
by pressure control.
 To perform any other pressure related functions by
virtue of pressure control.SUKESH O P/ APME/ME407- MR-2018

Types
1. Pressure relief valve.
2. Pressure sequencing valve.
3. Pressure reducing or regulating valve.
4. Pressure unloading valve.
5. Pressure brake valve.

1. Pressure relief valves
 These valves are found in every hydraulic system.
 It is normally closed valve, connected between
the pressure line and the oil reservoir.
 Its main purpose is to limit the presure in a system
to a prescribed maximum by diverting some or all
of the pump output to the tanks, when the desired
set pressure is reached.

PRV

2. Pressure sequencing valve
 Sequence valve is used to direct the flow to more
than one portion of a fluid circuit in sequence.

3.Pressure reducing valve
 This type of valves are normally open
pressure control valves used to maintain
reduced pressures in certain portions of the
hydraulic system.
 These are actuated by the pressure sensed
in the branch circuit and tend to close as it
reaches the pressure of the valve setting
preventing further buildup of pressure.

4. Pressure unloading valve
 This type of valves is used to unload the
energy in a system of a lower pressure.
 This valve allows pressure to build up to an
adjustable setting and then bypasses the flow
as long as a remote source maintains the
preset pressure on the pilot port.
 Unloading valves are normally used in double
pump applications. When the high speed and
more flow are not required.
SUKESHOP/APME/ME407- MR-2018

Direction control valves
 The direction control valvea start, stop and control the
direction of flow for reversing the direction of motion of
the actuator.

Dcv

1. Check valve
 Check valve is a one way valve because it permits
flow in only one direction and prevents any flow in
the opposite direction.

Pilot operated check valve
 The pilot operated check valve always permits free
flow in one direction but permits flow in the
normally blocked opposite direction only if pilot
pressure pushes the pilot piston sownward.


2. Poppet valve
 It is a check valve that can be forced open to allow
reverse flow.

3. Spool valve
 It consists of a cylindrical spool with multiple lobes
moving within a cylindrical casing containing
multiple ports.
 The spool can be moved back and fourth to align
spaces between the spool lobes with input and
output ports in the housing to direct high pressure
flow to different circuits in the system.

Spool valve

4. Shuttle valve
 This is the another type of direction control valve.
 It allows a system to operate from either of two
fluid power sources.
 It is also known as a double check valve. It is
mostly used in pneumatic device and is rarely
used in hydraulic circuits.

Shuttle valve

Two way valve
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(Normally Closed)
(Normally opened)

Two-way two-position
directional control valve
 Gate valve is example of 2W/2P directional control
valve which either turns on or off the flow in
normal or working positions depending on need of
application.
 Here arrow indicates that fluid flow is taking place
whereas other position shows cut-off position.

Three way valve
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Three-Way Direction Control
3/2-Way DCV
(Normally Closed)
(Normally opened)

Four way valves

Four-way two-position
 4/2 valve has four connections to it and two valve
positions. Normally, one port is open to flow from
the pump.

Four-way three-position
 It has one way for pump (P), one for reservoir (R)
or tank (T) and two for the inlet to the actuator.
And it has 3 positions: one normal, one cross way,
and one straight way.

 2POSITION , 2WAY DCV
SINGLE ACTING HYDRAULIC
CYLINDER CIRCUIT

 Three position, four way DCV
Double ACTING HYDRAULIC
CYLINDER CIRCUIT

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Hydraulic and Pneumatic Actuators

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Hydraulic and Pneumatic Actuators