pneumatics

INTRODUCTIONTO

PNEUMATICS

• Technology of Pneumatics deals with the study of the behavior and application of compressed air

• Science of air is known to man for centuries• Not used in industry before the beginning of the Second World war

(1939-44)• Many industries all over the developed western countries started

switching over to more & more automatic equipment and machineries• Origin of Pneumatics – Manufacturing & other activities to meet the

sudden need of enhanced production of war commodities under the tremendous shortage of skilled manpower (concept of automation)

• Cheaper medium of Industrial automation• Maximum application of pneumatics – Construction (power hammers,

drills, riveting hammers, pneumatic cranes, air brakes, printing presses etc.)

PNEUMATICS

• Wide availability of air

• Compressibility of air

• Easy transportability

• Explosion proof characteristics of the medium

• Simple construction of pneumatic elements and easy handling

• High degree of controllability of pressure, speed and force

• Possibility of easy but reasonably reliable remote controlling

• Easier maintenance

• Comparatively cheaper in cost than other systems

PNEUMATICS – Notable Features

• Earth is surrounded by air up to a height of approximately 1600 km above the top surface of the earth

• Gaseous layer of air around the earth is known as atmosphere

• Main constituents of air by volume –- Nitrogen : 78%- Oxygen : 21 %- Carbon dioxide & other gases : 1%

• Air which is a mixture of various chemical elements follows the gas laws.

PNEUMATICS – Physical Principles

GAS LAWS

PNEUMATICS REVIEW• Played an important role as a Technology in the performance of

Mechanical Work• In the majority of applications compressed Air is used for one or more

of the following functions- To determine status of the processor (sensor)- Information processing (processors)- Switching of actuators by means of final control elements- Carrying out work (actuators)

• Interaction of all the above governs installation and control ofmachinery

PNEUMATICS REVIEW

APPLICATIONS

APPLICATIONS

Pneumatic Bending device

USAGE OF PNEUMATICS

ADVANTAGES & CHARACTERISTICS OF COMPRESSED AIR

DISADVANTAGES OF PNEUMATICS

GENERAL FACTORS FOR COMPARING OTHER FORMS OF ENERGY

CRITERIA FOR WORKING MEDIA

• Power requirements

• Temperature variations

CRITERIA FOR CONTROL MEDIA

PNEUMATICS & CONTROL SYSTEM DEVELOPMENT

STRUCTURE & SIGNAL FLOW OF PNEUMATIC SYSTEMS

PNEUMATIC CONTROL SYSTEM

BREAKDOWN OF CONTROL CHAIN

CIRCUIT DIAGRAM & PNEUMATIC ELE.

1. Compressor plant

2. Pipeline

3. Control valves

4. Air actuator

5. Auxiliary appliances

BASIC REQUIREMENTS FOR INTRODUCING PNEUMATICS IN A PLANT

COMPONENTS – PNEUMATIC SYSTEM

COMPARISION

PNEUMATICACTUATORS

• Similar to Hydraulic actuators• Converts air pressure into linear or rotary motion • Used for variety of applications such as Gripping, Pulling or pushing

of objectsCLSSIFICATION• Linear actuators ( air cylinders)

- Single acting- Double acting (Normal, Double rod, Turn cylinder, Tandem

cylinder, Multi-position cylinder)- Ram cylinders - Single rod- Rod-less cylinders - Diaphragm cylinders- Rolling diaphragm cylinder

• Rotary actuators ( air motors)- Vane type Semi-rotary actuator- Rack & pinion type actuator- Rotary cylinder type actuator

PNEUMATIC ACTUATORS

SINGLE ACTING CYLINDER

PNEUMATIC ACTUATORS

PNEUMATIC ACTUATORS

DOUBLR ROD NON-ROTATING CYLINDER

PNEUMATIC ACTUATORS

ROTARY CYLINDER

• Three different operational principles used for construction of rodless cylinders are

- Sealing band cylinder- Band or cable cylinder- Cylinder with magnetic coupling

ROD-LESS CYLINDERS

SEALING BAND CYLINDER

ROD-LESS CYLINDERS

BAND or CABLE CYLINDER

ROD-LESS CYLINDERS

CYLINDER WITH MAGNETIC COUPLING

ROTARY CYLINDER TYPE ACTUATOR

1. Size

2. Speed

3. Environmental protection

4. Maintenance

5. Direction reversal

DESIGN PARAMETER - SELECTION

Previously Discussed Bits…..

• End position cushioning

• Seals

• Mounting arrangements

DIRECTIONALCONTROLVALVES

PURPOSE OF VALVE• For controlling the to and fro motion of a pneumatic cylinder, the air

energy has to be regulated, controlled and reversed with a predetermined sequence in a pneumatic system

• Control of pressure and flowVALVE DEFINATION• Fluid power elements used for controlling and regulating the

working mediumVALVE USAGE• To start & stop pneumatic energy• Control the direction of flow of compressed air• Control the flow rate of the compressed air• Control the pressure rating of the compressed airVALVE TYPES1. DCV 2. Non-return valves 3. FCV 4. PCV

PNEUMATIC CONTROLS

• Used mainly to direct the flow of the pressure fluid in the desired direction

• Main function – To start, stop and regulate the direction of air flow and help distribution of air in the desired line

• DCV’s has generally 2, 3, 4, or 5 ports / openings / ways• Ways are designated by letters or alphabets such as :

P = Compressor line portR = Exhaust portA & B = working ports to cylinders or motors

• DCV’s are basically classified as- Seat or poppet valves- Spool or sliding valves

DIRECTION CONTROL VALVES

SEAT Vs SPOOL VALVES

SEAT / POPPET TYPE VALVES

3/2 SEAT TYPE VALVE

4/2 SEAT TYPE

SPOOL / SLIDING TYPE VALVES

2/2 SPOOL VALVE

3/2 SPOOL VALVE

4/2 SPOOL VALVE

5/2 DCV

5/2 PILOT OPERATED DCV

5/3 WAY VALVE

SUSPENDED SEAT TYPE VALVE

CONTROL

ACTUATION OF VALVES

SPEED REGULATORS

FIXED TYPE FCV

NON-RETURN TYPE FCV

CHECK VALVE

TWIN PRESSURE VALVE

TWIN PRESSURE VALVE - USAGE

SOLENOID OPERATED VALVE (3 WAY)

SIMPLEPNEUMATIC

CONTROL

ISO SYMBOLS FOR FLUID CIRCUITS

ELECTRICAL SYMBOLS USED IN

PNEUMATIC CIRCUITS

PNEUMATIC CIRCUITS

DIRECT CONTROL

DIRECT ACTUATION

INDIRECT ACTUATION

PILOT CONTROL OF A SINGLE ACTING CYL.

PILOT CONTROL OF A DOUBLE ACTING CYL.

SPEED CONTROL – SINGLE ACTING CYL.

SPEED CONTROL – DOUBLE ACTING CYL.

AIR PILOT CONTROL – DOUBLE ACTING CYL.

SEMI AUTOMATIC CONTROL – DOUBLE ACTING

TWO STEP SPEED CONTROL OF A CYLINDER

ACTUATION OF A PNEUMATIC MOTOR

AUTOMATIC TO & FRO MOTION OF A DOUBLE ACTING CYLINDER

SEQUENCING CIRCUIT

MEMORY VALVE

FLOW CONTROL VALVE

SUPPLY AIR THROTLLING

EXHAUST AIR THROTLLING

QUICK EXHAUST VALVE

SIGNALPROCESSINGELEMENTS

• Non-moving logic elements find a prominent place in Finer Control Engineering

• Characteristics offered by fluidic elements proves them to be at par with electronic controls

• Development of various fluidic elements conforms the need of logic functions in Industrial Automation

• Tesla’s fluid-diode & Theory of “Wall-attachment” – Canada forms the basic principle

• Better control & feedback to the Pneumatic systems – Use Logic Gates along with power pneumatic circuits

• Major area of application – Field of Sensors

SYNOPSIS

• Susceptibility to wear & tear of mechanical parts – Major problem in Hydraulics and Pneumatics

• Challenge – Development of reliable control system without turning towards Electronics

• Specific need of control engineering forced engineers for a solution within the fluid power system – Development of new types of fluid power elements in early 60’s – FLUIDIC ELEMENTS or FLUID LOGIC ELEMENTS

• Biggest advantage – Minimum number of mechanical moving parts (no wear & tear) – NON-MOVING LOGIC CONTROLLERS

• Much more reliable under adverse environmental conditions (vibration, shock, heat, radiation, electromagnetic interference etc.)

• Simpler in construction, Smaller in size, Mode of energy feeding is very simple, Very little space to mount

• Mostly employ working medium as AIR• Easily adoptable to Logic Functions

FLUIDICS

It is the study of the performance and response characteristics of control

systems, computing devices and logical switchgears based on fluidic elements

OR

The subject which deals with the area of fluid logics is called fluidics

FLUIDICS

• Tesla invented a conduit in 1916 for fluids• Easy & Difficult floe direction owing to the interference caused by the

divided branch flow opposing the intended flow direction• Strong influence of electronics in this era accounts for the terminology

“fluid-diode” used to describe Tesla’s valved conduit• Real Development – CONANDA EFFECT – Named after Henri

Conanda – Observed and reported WALL-ATTACHMENTphenomenon

HISTORICAL BACKGROUND

• WALL-ATTACHMENTWhen a jet of fluid is pushed into an inclined wall, it will stay there, even after the pushing control jet is removed (1933)He noted that entrainment of the trapped air next to the surface of the body over which it is moving creates a partial vacuum and the atmospheric air forces the fluid stream to cling to the surface of the solid over which the fluid is to travel

• Existence of fluidic devices – 60’s - termed as fluid amplifier

• Working pressure used for pneumatic fluidic devices is very less –within 0 to 0.05 to 0.1 bar

HISTORICAL BACKGROUND

WHAT MAKES IT WORK?

BI-STABLE FLIP-FLOP

• Involves use of Pneumatic Logic Elements• Uses of air valves & other devices for control actions• Application of control actions to power systems to obtain the required

actuation• Conversion of minimum force to signals to operate high pressure

control valves

PNEUMATIC SIGNAL PROCESSING

• Logic Controls – Design of control system based on reasoning arising out of deductive principle

• Famous Greek philosopher ARISTOTLE (384 – 322 BC) – Father of deductive logic

LOGICS IN PNEUMATIC CIRCUIT DESIGN

LOGIC FUNCTIONS

• Pneumatic Shuttle valve and Dual pressure valve have logic functions

• Both have two inputs and two outputs each

• Shuttle valve characteristic – OR function

• Dual pressure valve characteristic – AND function

COMMON LOGIC FUNCTIONS

Memory


Time Dependent Limited Memory


AND Function

LOGIC FUNCTIONS & BOOLEAN ALGEBRA

LOGIC AND FUNCTION

Logic Symbol

Logic Equation

Truth Table

LOGIC AND FUNCTION

PROBLEM - 1

Pneumatic Symbol

LOGIC AND

FUNCTION

SOLUTION

ALTERNATIVE SOLUTION

PROBLEM - 2

POSITIONAL SKETCH

LOGIC OR FUNCTION

Logic Symbol Truth Table

Logic Equation

LOGIC OR FUNCTION

Pneumatic Symbol

LOGIC OR FUNCTIONPROBLEM - 3

SOLUTION

PROBLEM - 4

SOLUTION

LOGIC OR FUNCTION

PROBLEM - 5

POSITIONAL SKETCH

PRESSURE DEPENDENT CONTROLPROBLEM - 6

SOLUTION

POSITIONAL SKETCH

PRESSURE DEPENDENT CONTROL

PRESSURE DEPENDENT CONTROL –EMBOSSING OF PLASTIC COMPONENTS

PROBLEM - 7

POSITIONAL SKETCH

• In certain applications, the cylinder may have to be retained in its extended position for a particular time

• Automated Adhesive bonding operation

• Usage of TIME DELAY VALVE

TIME DEPENDENT CONTROL

TIME DELAY VALVE

TIME DELAY VALVE - Symbol

TIME DELAY VALVEPROBLEM - 8

SOLUTION

POSITIONAL SKETCH

PROBLEM - 9

POSITIONAL SKETCH

MULTI-CYLINDER

APPLICATIONS

INTRODUCTION

MOVEMENT DIAGRAM

TRAVEL TIME DIAGRAM

POSITION STEP DIAGRAM / MOTION CONTROL DIAGRAM

POSITION STEP DIAGRAM OF A PNEUMATIC CIRCUIT WITH TWO CYLINDERS

PNEUMATIC CIRCUIT AS PER POSITION STEP DIAGRAM

POSITIONAL SKETCH

DISPLACEMENT - STEP DIAGRAM

CIRCUIT DIAGRAM – INITIAL POSITION

SOLUTION Continued…..

REPRESENTATION OF STEP - 1

CASCADE SYSTEM OF PNEUMATIC CIRCUIT DESIGN

PRINCIPLE & PROCEDURE

PRINCIPLE & PROCEDURE Continued…..

FLOW LINES IN CASCADE SYSTEM

FIG. 10.6

POSITION STEP DIAGRAM FOR A 3CYLINDER PNEUMATIC SYSTEM

FIG. 10.7

FIG. 10.8

CO-ORDINATED MOTIONPROBLEM - 1

SOLUTION

SEQUENTIAL MOTION CONTROL

INEFFECTIVE WAY

LIMIT SWITCHES

EFFECTIVE WAY

SIGNAL ELIMINATION BY REVERSING VALVES

PROBLEM - 2

SOLUTION

SOLUTION Continued…..

PROBLEM - 3

POSITIONAL SKETCH

DISPLACEMENT -STEP DIAGRAM

pneumatics

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