ERT 457 DESIGN OF AUTOMATION SYSTEMS Powerpoint Templates

ERT 457 DESIGN OF AUTOMATION SYSTEMS Powerpoint Templates Munira Mohamed Nazari PPK Bioproses Uni. MAP

Lecture 3: Actuators and Drivers

Course Outcome CO 2 Ability to design (C 5) automation system for agricultural and biological production system.

Course Outline • • Introduction Pneumatic & Hydraulic Actuation Systems Electrical Actuation Systems Mechanical Actuation Systems

INTRODUCTION

Why we automated systems in agricultural area? • To fulfill requirement of modern farming. – Reduce labor work and cost. – Reduce time. • Help you to improve your agricultural application to be even more productive and comfortable to use.

Actuators in agriculture • Actuator solutions in spreaders adjusting the amount of fertilizers. • Sprayer, actuator control height and angle of outlet nozzle. • In chopper, actuator used to adjust the outlet direction. • Electric actuators – used to improve ergonomics and comfort in a number of applications such as adjustment of steering wheels, seats and ventilation.

Sensor vs Actuator • A sensor – monitors the variable such as pressure and temperature and send a signal to a transmitter or indicator. • An actuator – Hardware devices that convert a controller command signal into a change in a physical parameter. – The change is usually mechanical (eg: position or velocity). – An actuator is a transducer because it changes one type of physical quantity into some alternative form. – An actuator is usually activated by a low-level command signal, so an amplifier may be required to provide sufficient power to drive the actuator.

Actuation Systems • Practically every industrial process requires objects to be moved, manipulated, held, or subjected to some type of force. • The most commonly employed methods for producing the required forces/motions are: – – Air – Pneumatics Liquids – Hydraulics Electrical – motors, solenoids. Mechanical

A Brief System Comparison • The task considered is how to lift a body by a distance x mm. such tasks are common in manufacturing industries.

Electric Actuators - motor

Drives & Control Engineering for Actutors Energy (Medium) Control Drive Actuator Type Electrical - Electrical current Contactor and relay Power control contactor Digital and analog control -Wired program -Freely programmable system DC motor AC motor Stepper motor Solenoid Pneumatics - Compressed air from compressor Digital control Conventional valve technology Solenoid Pneumatic logic Directional valve Flow control valve Motors Cylinders Tools-gripper Hydraulics - Hydraulic fluids using pump Mechanical driven Manual driven Solenoid Directional valve Flow control valve Special valve Motors Cylinders

PNEUMATIC & HYDRAULIC ACTUATION SYSTEMS

Actuate large valve & highpower control device PNEUMATIC SIGNALS Compressibility of air More high-power control device - expensive HYDRAULIC SYSTEMS Oil leaks – causes hazard

Pneumatic Vs Hydraulic • Application – Hydraulics are used for power and precision. – Pneumatics are used for light weight and speedy applications. • Material used in the construction of the components. – Hydraulic components are mainly made from steel. – Pneumatic components are made from plastic and mom-ferrous materials. • However, the materials used in the system may have to withstand some of the following conditions: – – – Heat Cold Mechanical damage Dust Chemical attack

Pneumatic Vs Hydraulic • When either pneumatic or hydraulic systems are equally for an application the following should be considered. – Hydraulics generally calls for a greater capital outlay. – Hydraulic power generally cheaper on an energy basis. – Installation of hydraulic equipment generally requires a power pack for each machine. – Hydraulics with multiple machines generally requires a power pack for each machine. – Pneumatic machinery can be plugged into a ring main.

Pneumatic Vs Hydraulic Comparison Table HYDRAULIC PNEUMATIC ENERGY SOURCE Electric motor Int. combustion engine ENERGY STORAGE Accumulator Air receiver DISTRIBUTION SYSTEM Very localized Ring main Not easy to expand Easy to modify and change CAPITAL COST High Lower ENERGY COST Medium Higher ROTARY ACTUATOR Low speed Good control High speed Control - difficult LINEAR ACTUATOR High force Medium force FLEXIBILITY

Pneumatic Vs Hydraulic Comparison Table (con’t…) HYDRAULIC PNEUMATIC CONTROLLABLE FORCE High degree of control and precision with high forces. Control difficult with high forces. MAINTENANCE Expansive Fluid replacement/top up Cheaper No fluid replacement SAFETY Oil may leak Fire hazard Chemical/environment al Explosive failure Noisy

Hydraulics Definition • Is the science of transmitting force and/or motion through the medium of a confined liquid. • Power is transmitted by pushing on a confined liquid.

Hydraulic Systems • Hydraulic systems schematic diagram. Prevent the oil being back to the pump Smooth out any short term fluctuations – output oil pressure Release pressure – rise about safe level.

Hydraulic Systems • Hydraulic pumps. ØGear pump – two close meshing gear rotated. ØVane pump – spring loaded sliding vanes. ØPiston pump • Radial piston pump - cylinder block is rotate. • Axial piston pump – move axially.

Hydraulic Systems • Gear pump • Advantages – Widely used – Low cost – Robust • Weaknesses – Leakage – Limit efficiency §Gear wheels rotate in opposite direction. §Fluid forces through pump, become trapped between gear teeth. §Fluid transferred fro the inlet port to be discharged at the outlet port.

Hydraulic Systems • Vane pump §Spring loaded sliding vanes slotted in a driven motor. §Rotor rotates – vanes follow contours of the casing. §Fluid trapped between successive vanes and casing. §Transported round from inlet to outlet. • Advantage – Leakage less than gear pump.

Hydraulic Systems • Radial piston pump §Cylinder block rotates – hollow pistons with spring return, to move in and out. §Fluid drawn from inlet port. §Fluid transported round for ejection from the discharge port. • Axial piston pump §Piston move axially in a rotating cylinder block – move by contact with the swash plate. §Shaft rotates – move the pistons. §Air sucks (piston opposite the inlet), air expelled (opposite the discharge port.

Hydraulic Systems • Piston pump advantages. – High efficiency – Can be used at higher hydraulic pressures than gear (below 15 MPa) or vane pumps.

Pneumatic Systems • Pneumatic systems schematic diagram Drive a compressor To reduce noise level To reduce temperature Provide protection against pressure in the system. Increase volume of air Remove contamination and water

Pneumatic Systems • Types of an air compressors. • Are ones in which successive volumes of air are isolated and then compressed. ØSingle acting, single stage, vertical, reciprocating compressor. ØRotary vane compressor. ØScrew compressor.

Pneumatic Systems • Single acting, single stage, vertical, reciprocating compressor Piston Spring loaded inlet valve §The descending piston causes air to be sucked into the chamber. §Piston rise again – trapped air forces the inlet valve to close – become compressed. §Air pressure risen sufficiently – spring loaded outlet valve open – trapped air flows into the compressed air system. §After the piston has reached the top dead centre it then begins to descend and the cycle repeat itself.

Pneumatic Systems • Rotary vane compressor. §Has a rotor mounted eccentrically in a cylindrical chamber. §Rotation causing the vanes to be driven outwards against the walls of the cylinder. §Air is trapped in pockets formed by the vanes – rotor rotates – pockets become smaller and the air is compressed. §Compressed packets of air thus discharged from the discharge port.

Pneumatic Systems • Screw compressor. §Screw rotate – air drawn into the space between the screws. §Air trapped – move along the length of the screws and compressed (space progressively smaller), emerging from the discharge port.

Valves • Are used with hydraulics and pneumatics systems to direct and regulate the fluid flow. • Two types: – Finite position • To allow or block fluid flow and so can be used to switch actuators on or off. • Can be used for directional control to switch the flow from one path to another and so from one actuator to another. – Infinite position • Able to control flow anywhere between fully on and fully off, • Are used to control varying actuator forces or the rate of fluid flow for a process control situation.

Directional Control Valves • To direct the flow of fluid through a system. • Not intended to vary the rate of fluid flow but are either completely open or completely closed. – Example: on/off devices. • widely used to develop sequenced control systems. • Might be activated to switch the fluid flow direction by means of mechanical, electric or fluid pressure signals. • Common types: – Spool valve – Poppet valve

Directional Control Valves • Spool valve.

Directional Control Valves • Poppet valve.

Directional Control Valves • Valve symbols – Consists of a square for each of its switching positions. (eg: poppet valve – two position valve – two squares) Flow path Port labels: 1 or P = pressure supply 3 or T = hydraulic return 3 (R) or 5 (S) = pneumatic exhaust 2 (B) or 5 (A) = output Initial connections ( 4 ports) Flow shut-off

Directional Control Valves • Valve actuation symbols.

Directional Control Valves • Symbol for two port, two position poppet valve. • Can be describe as a 2/2 valve. Number of ports Number of positions Output port Push button Spring Pressure supply port

Directional Control Valves • Single-solenoid valve. How many port and position? ? Answer: 3/2

Directional Control Valves • Symbol for a 4/2 valve. Output port Solenoid Spring Pressure supply port Pneumatic exhaust

Directional Control Valves • Lift system. • A simple example of an application of valves in a pneumatic lift system.

Directional Control Valves • Pilot-operated Valve – To overcome a problem of too large force required to move the ball or shuttle in a valve for manual or solenoid operation. One valve (pilot valve) is used to control a second valve (main valve). Pilot pressure line Small capacity & can be operated manually or by a solenoid.

Directional Control Valves • Directional Valves – Free flow can only occur in one direction through the valve. – The ball being pressed against the spring. Flow in other direction is blocked by the spring forcing the ball against its seat.

Pressure Control Valves • 3 main types. – Pressure-regulating valves • To control the operating pressure in a circuit and maintain it at a constant value. – Pressure-limiting valves • As safety device. • The valve opens and vents to the atmosphere, or back to the sump if the pressure rises above the set safe value.

Pressure Control Valves – Pressure sequence valves. – used to sense the pressure of an external line and give a signal when it reaches some preset value. The valve switching on when the inlet pressure reaches a particular value and allowing the pressure to be applied to the system that follow.

Cylinders • Pneumatic and hydraulic cylinder is an example of linear actuator. • Same principles, differences in term of size as hydraulic required high pressure. • Consists of a cylindrical tube along which a piston/ram cam slide. • 2 basic types: – single acting cylinder and – double acting cylinder.

Cylinders • Single acting cylinder. – Used when the control pressure is applied to just one side of the piston, a spring often being used to provide the opposition to the movement of the piston. The other side is open to the atmosphere.

Cylinders Control of a single-acting cylinder with (a) no current through solenoid, (b) a current through the solenoid. When a current passes through the solenoid, the valve switches position and pressure is applied to move the piston along the cylinder. When the current ceases, the valve reverts to its initial position and the air is vented from the cylinder.

Cylinders • Double acting cylinder. – Used when the control pressure applied to each side of the piston. A differences in pressure between the 2 sides, results in motion of the piston. The piston being able to move in either direction along the cylinder as a result of high-pressure signals.

Cylinders Control of a double-acting cylinder with solenoid, (a) not activated, (b) activated. Current through one solenoid causes the piston to move in one direction with current through the other solenoid reversing the direction of motion.

Cylinders • The choice of cylinder, determined by force required to move the load and speed required. – Hydraulic – capable larger force – Pneumatic – capable greater speed FORCE Force produced by cylinder Working pressure F = Aρ Cross-sectional area of cylinder HYDRAULIC FLUID FLOW Q = Av Speed Can’t use for pneumatic !! -since its speed depends on the rate at which air can be vented ahead of the advancing piston.

Cylinders • Cylinder Sequencing – Used as a sequential control of extensions and retractions of the cylinder. • Cylinder – reference letter A, B, C, D, … • State of cylinder – ‘+’ sign = extended, ‘-’ sign = retracted. • So sequence of operation = A+, A-, B+, B-

Cylinders • Cylinder Sequencing – Valve 1 is pressed – applied pressure to valve 2 – activated limit switch b- - valve 3 is switched to apply pressure to cylinder A for extension. – Cylinder A extends – releasing limit switch a- - cylinder A fully extended – limit switch a+ operates – switches valve 5 – pressure applied to valve 6 – apply pressure to cylinder B – piston extend. – Cylinder B extends – releasing limit switch b- - cylinder B fully extended – limit switch b+ operates – switches valve 4 – pressure applied to valve 3 – applies pressure to cylinder A – piston retracting. – Cylinder A retract – releasing limit switch a+ - cylinder A fully retracted – limit switch a- operates – switches valve 7 – pressure applied to valve 5 – applies pressure to cylinder B – piston retracting. – Cylinder B retracts – releasing limit switch b+ - cylinder B fully retracted – limit switch b- operates to complete the cycle.

Servo and Proportional Control Valve • Are both infinite position valves which give a valve spool displacement proportional to the current supplied to a solenoid. • Servo : – – have a torque motor to move the spool within a valve. High precision Costly Used in a closed-loop control system.

Servo and Proportional Control Valve • Proportional control valve: – Less expensive – Have the spool position directly controlled by the size of current to the valve solenoid. – Used in open-loop control systems.

Process Control Valve • Used to control the rate of fluid flow. • Common form of pneumatic actuator used with process control valves is the diaphragm actuator. • Consists of a diaphragm with the input pressure signal from the controller on one side and atmospheric pressure on the other. Differences in pressure being termed the gauge pressure. • The diaphragm is made of rubber which is sandwiched in its centre between two circular steel discs.

Process Control Valve • Effect of changes in the input pressure.

Process Control Valve • If the shaft moves through a distance x, and compression of spring is proportional to the force, F = kx • and, displacement of the shaft is proportional to the gauge pressure. kx = PA • So, pressure P, P=F/A Diaphragm area

Process Control Valve • Control Valve Sizing – Procedure of determining correct size of valve body. Flow rate Q = Av √ (∆P / ρ) Valve flow coefficient Density of the fluid Pressure drop across the valve Valve size (mm) Flow coefficient 480 640 800 960 1260 1600 1920 2560 Cv 8 14 22 30 50 75 110 200 Av x 10 -5 19 33 52 71 119 178 261 474 Table 7. 1

Process Control Valve • Example: – Consider the problem of diaphragm actuator to be used to open a control valve if a force of 500 N must be applied to the valve. What diaphragm are is required for a control gauge pressure of 100 k. PA. A=F/P = 500 / (100 x 10³) = 0. 005 m²

Process Control Valve • Example: – Consider the problem of determining the valve size for a valve that is required to control the flow of water when the maximum flow required is 0. 012 m³/s and the permissible pressure drop across the valve at this flow rate is 300 k. Pa. Density of water is 1000 kg/m³ Q = Av √ (∆P / ρ) Av = Q√ (ρ /∆P) = 0. 012√ (1000 / 300 x 10³) = 69. 3 x 10 -5 m² So, the valve size is 960 mm.

Problem 7. 9 • A hydraulic cylinder is to be used to move a workpiece in a manufacturing operation through a distance of 50 mm in 10 s. A force of 10 k. N is required to move the workpiece. Determine the required working pressure and hydraulic liquid flow rate if a cylinder with a piston diameter of 100 mm is available. P = 1. 27 Mpa & Q = 3. 93 x 10 -5 m³/s

Problem 7. 12 • What is the process control valve size for a valve that is required to control the flow of water when the maximum flow required is 0. 002 m³/s and the permissible pressure drop across the valve at this flow rate is 100 k. Pa? The density of water is 1000 kg/m³. The process control valve size = 480 mm

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