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ERT 457 DESIGN OF AUTOMATION SYSTEMS

Munira Mohamed NazariPPK BioprosesUniMAP

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Lecture 3:Actuators and Drivers

Course OutcomeCourse Outcome

CO 2

Ability to design (C5) automation system for agricultural and biological production system.

Course OutlineCourse Outline

• Introduction

• Pneumatic & Hydraulic Actuation Systems

• Electrical Actuation Systems

• Mechanical Actuation Systems

INTRODUCTION

Why we automated systems in Why we automated systems in agricultural area?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 agricultureActuators 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 ActuatorSensor 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 SystemsActuation 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 controlDigital and analog control-Wired program-Freely programmable system

Power contactor

DC motorAC motorStepper motorSolenoid

Pneumatics- Compressed air from compressor

Digital controlConventional valve technologySolenoidPneumatic logic

Directional valveFlow control valve

MotorsCylindersTools-gripper

Hydraulics- Hydraulic fluids using pump

Mechanical drivenManual drivenSolenoid

Directional valveFlow control valveSpecial valve

MotorsCylinders

PNEUMATIC & HYDRAULIC ACTUATION SYSTEMS

PNEUMATICSIGNALS

HYDRAULICSYSTEMS

Actuate large valve & high-power control device

Compressibility of air

More high-power control device - expensive

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.

Comparison Table

Pneumatic Vs Hydraulic

HYDRAULIC PNEUMATIC

ENERGY SOURCEElectric motorInt. combustion engine

Electric motorInt. combustion engine

ENERGY STORAGE Accumulator Air receiver

DISTRIBUTION SYSTEM Very localized Ring main

FLEXIBILITYNot easy to expand Easy to modify and

change

CAPITAL COST High Lower

ENERGY COST Medium Higher

ROTARY ACTUATORLow speedGood control

High speedControl - difficult

LINEAR ACTUATOR High force Medium force

Comparison Table (con’t…)

Pneumatic Vs Hydraulic

HYDRAULIC PNEUMATIC

CONTROLLABLE FORCEHigh degree of control and precision with high forces.

Control difficult with high forces.

MAINTENANCEExpansive Fluid replacement/top up

CheaperNo fluid replacement

SAFETY

Oil may leakFire hazardChemical/environmental

Explosive failureNoisy

Hydraulics DefinitionHydraulics 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 SystemsHydraulic 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 SystemsHydraulic Systems

• Hydraulic pumps.Gear pump – two close meshing gear rotated.

Vane pump – spring loaded sliding vanes.

Piston pump • Radial piston pump - cylinder block is rotate.• Axial piston pump – move axially.

Hydraulic SystemsHydraulic 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.

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.

• Vane pump


• Advantage– Leakage less than

gear 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.

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.

• Radial piston pump • Axial piston pumpHydraulic SystemsHydraulic Systems

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.

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.

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.

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.

• Piston pump advantages.– High efficiency– Can be used at higher hydraulic pressures

than gear (below 15 MPa) or vane pumps.


Pneumatic SystemsPneumatic Systems• Pneumatic systems schematic diagram

To reduce noise level

Provide protection against pressure

in the system.

To reduce temperature

Remove contamination

and water

Increase volume of air

Drive a compressor

Pneumatic SystemsPneumatic Systems

• Types of an air compressors.• Are ones in which successive volumes of air are isolated

and then compressed.

Single acting, single stage, vertical, reciprocating compressor.

Rotary vane compressor.

Screw compressor.

• Single acting, single stage, vertical, reciprocating compressor


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.

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.

Piston

Spring loaded inlet valve

• 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.

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.

• 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.

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.

ValvesValves • 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

• Spool valve.


• Poppet valve.


• Valve symbolsValve symbols– Consists of a square for each of its switching positions.

(eg: poppet valve – two position valve – two squares)


Flow path

Flow shut-off

Initial connections ( 4ports)

Port labels:1 or P = pressure supply3 or T = hydraulic return 3 (R) or 5 (S) = pneumatic exhaust2 (B) or 5 (A) = output

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 portsNumber of positions

Output port

Spring Push button

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.

Solenoid Spring

Output port

Pneumatic exhaust

Output port

Pressure supply port

Directional Control Valves• Lift system.

• A simple example of an application of valves in a pneumatic lift system.

• Pilot-operated ValvePilot-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 pressureline

Small capacity & can be operated manually or by a

solenoid.

• Directional ValvesDirectional 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.

CylindersCylinders

• 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.

• 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.

CylindersCylinders

CylindersCylinders 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.

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.

CylindersCylinders • Double acting cylinder.

– Used when the control pressure are 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.

CylindersCylinders 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.Current through one solenoid causes the piston to move in one direction with current through the other solenoid reversing the direction of motion.

• The choice of cylinder, determined by force required to move the load and speed required.– Hydraulic – capable larger force– Pneumatic – capable greater speed

CylindersCylinders

F = AρF = Aρ

Force produced by cylinder

Cross-sectional area of cylinder

Working pressureFORCEFORCE

HYDRAULICHYDRAULICFLUID FLOWFLUID FLOW Q = AvQ = 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.

Can’t use for pneumatic !!-since its speed depends on the rate at which air can be vented ahead of the advancing piston.

• 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-

CylindersCylinders

• 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.

CylindersCylinders

• 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 ValveServo 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.

Servo and Proportional Control ValveServo and Proportional 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 ValveProcess Control Valve

• Effect of changes in the input pressure.


• If the shaft moves through a distance x, and compression of spring is proportional to the force,

• and, displacement of the shaft is proportional to the gauge pressure.

• So, pressure P,


F = kx

kx = PA

P = F / A

Diaphragm area

• Control Valve Sizing– Procedure of determining correct size of valve body.


Q = Av √ (∆P / ρ)Flow rate

Pressure drop across the valveValve flow coefficient

Density of the fluid

Flow coefficientValve size (mm)

480 640 800 960 1260 1600 1920 2560

Cv 8 14 22 30 50 75 110 200

Av x 10 19 33 52 71 119 178 261 474-5

Table 7.1

Flow rate

• 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 kPA.


A = F / P = 500 / (100 x 10³) = 0.005 m²

• 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 kPa. 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 m²

So, the valve size is 960 mm.

-5

Problem 7.9• A hydraulic cylinder is to be used to move a

workpiece in a manufacturing operation through a distance of 50mm in 10 s. A force of 10 kN is required to move the workpiece. Determine the required working pressure and hydraulic liquid flow rate if a cylinder with a piston diameter of 100mm is available.

P = 1.27 Mpa & Q = 3.93 x 10 m³/s-5

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 kPa? The density of water is 1000 kg/m³.

The process control valve size = 480 mm

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