1. 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
Actuator
output
input
Electrical signal
motion
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3. SME3252: Mechatronics Lecture 3
Types
Pneumatic and hydraulic actuator (Chapter 7)
Mechanical actuator (Chapter 8)
Electrical actuator (Chapter 9)
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4. 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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5. SME3252: Mechatronics Lecture 3
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:
200 lbf
Pressure = 10 psi
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7. SME3252: Mechatronics Lecture 3
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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8. Hydraulic Power Supply
Motor
Pump
Pressure relief valve
Non-return valve
Accumulator
Oil
Sump
Return
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Figure 7.1 (a) Hydraulic power supply, (b) accumulator
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11. 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. PISTON b. GEAR c. VANE d. INTERNAL ROTOR
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14. SME3252: Mechatronics Lecture 4
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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19. SME3252: Mechatronics Lecture 3
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
Air
6 – 8 bar
motion
Compressor
Air receiver
Air regulator
Piston,
Valve,
switching
Store compressed air
Set pressure
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26. Pneumatics – Basic Principles
Pneumatics – The study of the mechanical properties of air and other gasses.
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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27. Pneumatics – Basic Principles
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30. Pneumatic Power Supply
Motor
Compressor
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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38. Application – Robotic System
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40. SME3252: Mechatronics Lecture 4
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
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