ME 8843 Advanced Mechatronics Instructor Professor Charles Ume

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

Outline ME 8843 • • Introduction Hydraulic system Pneumatic system Key components – Valves – Actuators • Examples The George W. Woodruff School of Mechanical Engineering

ME 8843 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 by linear/rotary actuators The George W. Woodruff School of Mechanical Engineering

Applications ME 8843 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

ME 8843 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

ME 8843 Hydraulic Systems • Move large loads by controlling high-pressure fluid in distribution lines and pistons with mechanical or electromechanical valves • 1000 psi – 3000 psi • Closed systems, always recirculating same fluid The George W. Woodruff School of Mechanical Engineering

Hydraulic Systems ME 8843 • 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

ME 8843 Pneumatic systems • Pneumatic systems similar to hydraulic systems • Use compressed air as working fluid rather than hydraulic liquid • 70 psi - 150 psi, 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

ME 8843 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 ME 8843 • • Pump/Compressor Pressure regulator Valve Actuator The George W. Woodruff School of Mechanical Engineering

Valves ME 8843 • 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 ME 8843 • 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

ME 8843 Valve symbols Position with texts indicates initial position Valve connections Control methods Valves with controls indicated The George W. Woodruff School of Mechanical Engineering

8843 4 MEports/3 positions Solenoid Spool Valve The George W. Woodruff School of Mechanical Engineering

Example: Pneumatic lift system (analogous to car jack) ME 8843 Lift load Lower load The George W. Woodruff School of Mechanical Engineering

ME 8843 • • • 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

ME 8843 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

ME 8843 • • • Example 1: LEGO house builder Weight Stroke Speed Force Accurate positioning not required Pneumatic Lead Screw The George W. Woodruff School of Mechanical Engineering

ME 8843 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

ME 8843 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 and 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

ME 8843 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 ME 8843 • 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

ME 8843 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%27 s_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