ME8843 The George W. Woodruff School of Mechanical Engineering ME 8843 Advanced Mechatronics Instructor: Professor Charles Ume Introduction to Hydraulic and Pneumatic Systems

ME8843 The George W. Woodruff School of Mechanical Engineering Outline Introduction Hydraulic system Pneumatic system Key components –Valves –Actuators Examples

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering Applications Advantages –adaptable power distribution –constant force actuators –power amplification –inexpensive Disadvantages –difficult to control position –leaks and contamination of working fluid Air ConveyorImpact WrenchHydraulic Jack

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering Key components of Hydraulic and Pneumatic Pump/Compressor Pressure regulator Valve Actuator

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering Types of Valves Type: Spool, poppet, ball, butterfly valves, etc. Check valve (One directional flow) Poppet valve Spool valve Ball valve Butterfly valve

ME8843 The George W. Woodruff School of Mechanical Engineering Valve symbols Control methods Valve connections Valves with controls indicated Position with texts indicates initial position

ME8843 The George W. Woodruff School of Mechanical Engineering 4 ports/3 positions Solenoid Spool Valve

ME8843 The George W. Woodruff School of Mechanical Engineering Example: Pneumatic lift system (analogous to car jack) Lift load Lower load

ME8843 The George W. Woodruff School of Mechanical Engineering Hydraulic/Pneumatic actuators Cylinders with piston driven by pressurized fluid Single acting cylinder (SAC) Double acting cylinder (DAC) Two well-defined endpoints Rotary

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering Example 1: LEGO house builder Weight Stroke Speed Force Accurate positioning not required Lead ScrewPneumatic

ME8843 The George W. Woodruff School of Mechanical Engineering 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

ME8843 The George W. Woodruff School of Mechanical Engineering Hydraulic System Supplies the main braking force to the pistons at the wheels 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 Front circuit Rear circuit actuated by brake pedal fluid reservoir

ME8843 The George W. Woodruff School of Mechanical Engineering Pneumatic Power Assist Brake Applied Vacuum from engine Brake Released 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 Bi-directional check valve

ME8843 The George W. Woodruff School of Mechanical Engineering 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) nitrogen pressurized fluid

ME8843 The George W. Woodruff School of Mechanical Engineering 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