ME 8843

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ME 8843

• Advanced Mechatronics
• Instructor Professor Charles Ume
• Introduction to Hydraulic and Pneumatic Systems

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Outline

• Introduction
• Hydraulic system
• Pneumatic system
• Key components
• Valves
• Actuators
• Examples

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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

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Applications
Air Conveyor
Impact Wrench
Hydraulic Jack

• Advantages
• adaptable power distribution
• constant force actuators
• power amplification
• inexpensive

• Disadvantages
• difficult to control position
• leaks and contamination of working fluid

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Pascals 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

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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

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Hydraulic Systems

• 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

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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

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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

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Key components of Hydraulic and Pneumatic

• Pump/Compressor
• Pressure regulator
• Valve
• Actuator

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Valves

• 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
• x number of ports (sum of inlets and outlets)
• y number of positions
• 4/3 valve 4 ports and 3 positions

Pressure regulator
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Types of Valves

• Type Spool, poppet, ball, butterfly valves, etc.

Poppet valve
Spool valve
Check valve (One directional flow)
Ball valve
Butterfly valve
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Valve symbols
Position with texts indicates initial position
Valve connections
Valves with controls indicated
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4 ports/3 positions Solenoid Spool Valve
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Example Pneumatic lift system (analogous to car
jack)
Lift load
Lower load
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Hydraulic/Pneumatic actuators

• Cylinders with piston driven by pressurized fluid
• Single acting cylinder (SAC)
• Double acting cylinder (DAC)
• Two well-defined endpoints
• Rotary

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Key parameters in choosing air cylinders

• Stroke length
• Bore size
• Pressure rating
• Mounting style
• Return type (SAC vs. DAC)
• Spring force in SAC
• Loads
• Temperature range
• Lubrication
• Material Compatibility

Force
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Example 1 LEGO house builder

• Weight
• Stroke
• Speed
• Force
• Accurate positioning not required

Lead Screw
Pneumatic
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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

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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

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Pneumatic Power Assist
Brake Applied
Brake Released
Vacuum from engine
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

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Anti-lock Breaking System

• Wheel speed sensor
• Electric hydraulic pump
• Stores fluid in pressurized chamber
• 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)

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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/Pascal27s_law
• http//en.wikipedia.org/wiki/Pneumatic_cylinder
• http//www.bimba.com
• http//www.tpub.com/content/engine/14105