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Pneumatic and hydraulic actuation systems

Lecture 4

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7.1: Actuation system• Transform output of control system (i.e.

µprocessor) into action (controlling) on device / machine

• Examples are:• Electrical output from controller to a

linear motion to move a load• Electrical output from controller to control

amount of liquid passing through a pipe

Controller Actuatorinput

Electrical signal

output

motion

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Types

• Pneumatic and hydraulic actuator (Chapter 7)

• Mechanical actuator (Chapter 8)

• Electrical actuator (Chapter 9)

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7.2: Pneumatic and hydraulic systems

• Pneumatic signals – to control final control elements

• The electrical signal – actuate large valve and high power control devices

• Drawbacks – compressibility of air• Hydraulic signals – higher power

control devices• Drawbacks – expensive, hazards due

to oil leaks

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PSI (lb/in2)

Pounds per Square Inch

•determines amount of force

GPM

Gallons per Minute

•determines speed of action

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PRESSURE = FORCE/AREA

Find Pressure, F2:

F2 =

F1 = 20 lbf

A1 = 2 in2

A1 = 20 in2

Pressure = 10 psi

200 lbf

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7.2.1: Hydraulic Actuator

• Tool or equipment powered by the movement of fluid under pressure.

• Pressurized hydraulic oil - sump• Heavy duty - brakes, jacks & tractor

lifts.

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Hydraulic Power Supply

Motor

Pump

Pressure relief valveNon-

return valve

Accumulator

Oil

Sump

Return

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Figure 7.1 (a) Hydraulic power supply, (b) accumulator

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Parts of a Hydraulic System

• Pump - pressurize and move fluid from one part of the system to another

• Valves• Ball• Check• Solenoid / power transfer• Relief

• Filters– Remove impurities in oil

• Heat exchangers– Remove heat created by high pressure and

moving parts

• Accumulators

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Hydraulic Pump

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Hydraulic pumps are usually one of four types:

a. PISTONb. GEARc. VANEd. INTERNAL ROTOR

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a. Piston Pumps• Work well at PSI’s of 2000 or more• Single piston pump used in bottle

jacks• Require several pistons working

together to generate enough volume for tractor applications

• Necessarily involve many moving parts

• Refer to Figure 7.2c for radial piston pump and 7.2d for axial piston pump

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b. Gear Pumps•Work well at 1500 PSI and

below•Work with a minimum of

moving parts•Less expensive to

manufacture than piston type pumps

•Disadv. – leakage occurs

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Gear Pump driven gear

idler gear

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c. Vane Pump

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ACCUMULATORS

• Dampens hydraulic shock

• Supply of pressure if pump fails

• Maintain pressure without continuous pump operation

• Demand changes

• Make-up• Three types

– Piston– Bladder– Direct contact

-

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Figure 7.2 (a) Gear pump, (b) vane pump, (c) radial piston pump, (d) axial piston pump with swash plate

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Application

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HYDRAULIC SYSTEMS

• ADVANTAGES– Long distances– Great flexibility

(any shape or form)– Variable speed

control– Reliability

• DISADVANTAGES– Need for positive

confinement– Oil is flammable– High pressure

(typically 3000 psi)– Need for filtration

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Pneumatic Actuator

• Compressed air• Light duty

Compressor

Air receiver

Air regulator

Air

6 – 8 bar

Store compressed air

Set pressure

Piston,

Valve,

switching

motion

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Pneumatics – Basic Principles

o Pneumatics – The study of the mechanical properties of air and other gasses.

o A gas under pressure has the ability to exert a force

Pascal’s Law states that a compressed gas will exert pressure equally in all directions

A pressure acting over an area will result in a net force being applied

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Pneumatics – Basic Principles

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Pneumatic Power Supply

MotorCompressor

Silencer

Filter

Pressure relief valve Cooler

Filter and water trap

-dry and dust free

Air receiver

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Figure 7.3 Pneumatic power supply

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Compressor

• To compress air• Three types:

– Piston– Screw– Diaphragm

• Air receiver to store compressed air• Regulator to regulate the pressure• Automatic power cut-off above set

pressure• Pressure relief valve

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Compressor

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Figure 7.4 (a) Single-acting, single stage, vertical, reciprocating compressor,(b) rotary vane compressor, (c) screw compressor

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Pneumatic Circuit

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Application – Robotic System

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Exercises

• Power supply components for hydraulic system and pneumatic system – explain with diagram and identify difference

• Examples of application for both system

• Advantages and disadvantages of each system

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End of Lecture 4