ME8843
ME 8843
Advanced Mechatronics
Instructor: Professor Charles Ume
Introduction to Hydraulic and Pneumatic Systems
The George W. Woodruff School of Mechanical Engineering
Outline
ME8843
•
•
•
•
Introduction
Hydraulic system
Pneumatic system
Key components
– Valves
– Actuators
• Examples
The George W. Woodruff School of Mechanical Engineering
ME8843
Hydraulic/Pneumatic Systems
• Use fluids as working media
• Convert electrical/mechanical energy into
potential energy of fluids (pump, compressor)
• Transmit power through distribution lines
(pipes, air hoses)
• Convert potential energy of fluids/compressed
gas into mechanical energy that turns
linear/rotary actuators
The George W. Woodruff School of Mechanical Engineering
Applications
ME8843
Air Conveyor
• Advantages
–
–
–
–
adaptable power distribution
constant force actuators
power amplification
inexpensive
Impact Wrench
Hydraulic Jack
• Disadvantages
– difficult to control position
– leaks and contamination of working
fluid
The George W. Woodruff School of Mechanical Engineering
ME8843
Pascal’s Law
• Pascal's law states that:
"a change in the pressure of an
enclosed incompressible fluid is
conveyed undiminished to every part
of the fluid and to the surfaces of its
container.“
– Force determined by pressure
– Speed determined by flow rate
The George W. Woodruff School of Mechanical Engineering
ME8843
Hydraulic Systems
• Move large loads by controlling high-pressure fluid in
distribution lines and pistons with mechanical or
electromechanical valves
• 1000psi – 3000psi
• Closed systems, always recirculating same fluid
The George W. Woodruff School of Mechanical Engineering
Hydraulic Systems
ME8843
• Advantage:
– Able to generate extremely large forces from compact actuators
– Easy to control speed
– Easy to implement linear motion
• Disadvantage:
–
–
–
–
–
–
Large infrastructure (high-pressure pump, tank, distribution lines)
Potential fluid leaks
Noisy operation
Vibration
Maintenance requirements, expensive
Characteristics of working fluids change with temperature and moisture
The George W. Woodruff School of Mechanical Engineering
ME8843
Pneumatic systems
• Pneumatic systems similar to hydraulic systems
• Use compressed air as working fluid rather than hydraulic liquid
• 70psi - 150psi, much lower than hydraulic system pressures, much lower
forces than hydraulic actuators
• Energy can be stored in high pressure tanks
• Open systems, always processing new air
The George W. Woodruff School of Mechanical Engineering
ME8843
Pneumatic systems
• Advantage:
–
–
–
–
–
–
Constant force
Clean (food industry)
No return lines needed
Adaptable infrastructure
Possible light, mobile pneumatic systems
Fast system response
• Disadvantage:
– Difficult to achieve position control (compressible air)
– Noisy
The George W. Woodruff School of Mechanical Engineering
Key components of Hydraulic and
Pneumatic
ME8843
•
•
•
•
Pump/Compressor
Pressure regulator
Valve
Actuator
The George W. Woodruff School of Mechanical Engineering
Valves
ME8843
• Infinite position valve as shown in figure on right:
– allows any position between open and closed to modulate
flow or pressure
• Finite position valve:
– has discrete positions, usually just open and closed,
providing different pressure and flow condition
• Ports: inlet and outlet connections to valve
• Finite position valve usually specified as “x/y valve”
Pressure regulator
– x: number of ports (sum of inlets and outlets)
– y: number of positions
– 4/3 valve: 4 ports and 3 positions
The George W. Woodruff School of Mechanical Engineering
Types of Valves
ME8843
• Type: Spool, poppet, ball, butterfly valves, etc.
Poppet valve
Spool valve
Ball valve
Check valve (One directional flow)
Butterfly valve
The George W. Woodruff School of Mechanical Engineering
ME8843
Valve symbols
Position with texts
indicates initial position
Valve connections
Control methods
Valves with controls indicated
The George W. Woodruff School of Mechanical Engineering
4ME8843
ports/3 positions Solenoid Spool Valve
The George W. Woodruff School of Mechanical Engineering
Example:
Pneumatic lift system (analogous to car jack)
ME8843
Lift load
Lower load
The George W. Woodruff School of Mechanical Engineering
ME8843
•
•
•
•
•
Hydraulic/Pneumatic actuators
Cylinders with piston driven by pressurized fluid
Single acting cylinder (SAC)
Double acting cylinder (DAC)
Two well-defined endpoints
Rotary
The George W. Woodruff School of Mechanical Engineering
ME8843 parameters in choosing air cylinders
Key
•
•
•
•
•
Stroke length
Bore size
Force
Pressure rating
Mounting style
Return type (SAC vs. DAC)
– Spring force in SAC
•
•
•
•
Loads
Temperature range
Lubrication
Material Compatibility
The George W. Woodruff School of Mechanical Engineering
ME8843
•
•
•
•
•
Example 1: LEGO house builder
Weight
Stroke
Speed
Force
Accurate
positioning
not required
Pneumatic
Lead Screw
The George W. Woodruff School of Mechanical Engineering
ME8843
Example 2: Anti-Lock Braking System
Regular Automobile Breaking System Includes:
•Hydraulic actuation
•Pneumatic power assist
ABS includes additional features:
–
–
–
–
sensors
valves
hydraulic pump
control unit
The George W. Woodruff School of Mechanical Engineering
ME8843
Hydraulic System
fluid reservoir
Supplies the main
braking force to the
pistons at the wheels
actuated by brake pedal
Front
circuit
Rear
circuit
•Proportioning Valves – control the pressure provided to the front and rear
• Can change pressure distribution according to vehicle weight distribution
•Metering Valves- engage the rear breaks before the front
The George W. Woodruff School of Mechanical Engineering
ME8843
Vacuum from engine
Pneumatic Power Assist
Brake Released
Brake Applied
Bi-directional check valve
•
•
Brakes applied
• Opens check valve to pressurize one side of diaphragm
• Pressure difference assist in applying braking force
• Pushes pistons in master cylinder
Brakes released
• Check valve closes and engine vacuum is again applied to both chambers
The George W. Woodruff School of Mechanical Engineering
Anti-lock Breaking System
ME8843
• Wheel speed sensor
• Electric hydraulic pump
– Stores fluid in pressurized chamber
nitrogen
pressurized
fluid
• Solenoid valves
– Open: braking pressure supplied directly from master cylinder (under normal
conditions)
– Closed: isolate master cylinder pressure line (modulation)
– Release: applies stored pressure to blocked break lines (modulation)
The George W. Woodruff School of Mechanical Engineering
ME8843
Reference
• Mechatronics, by Sabri Cetinkunt, published by Wiley
• Introduction to Mechatronics and Measurement Systems, Second Edition,
by David G. Alciatore and Michael B. Histand
• Mechatronics: Electronic Control Systems in Mechanical Engineering, by
W. Bolton
• http://en.wikipedia.org/wiki/Pascal%27s_law
• http://en.wikipedia.org/wiki/Pneumatic_cylinder
• http://www.bimba.com
• http://www.tpub.com/content/engine/14105
The George W. Woodruff School of Mechanical Engineering