Pneumatics Tutorial

PNEUMATICSApplied to the FIRST Competition

With Examples from the 2003 Xerox & Webster School’s SparX Robot

Ken Buck

What Does Pneumatics Offer?What Does Pneumatics Offer?

Linear MotionTo provide a push or pulling force in a straight line

Create VacuumDouble Acting cylinder – pressure on one side creates vacuum on the other as the piston moves in the cylinder

Controlled ForceBased on the piston size (area) and pressure, a wide range of constant force is available. Can be used to hold things in place

Combined with other cylinders & mechanismsCan provide complex motion like the claw on a back hoe

How was Pneumatics Used on SparX How was Pneumatics Used on SparX 2003 Robot?2003 Robot?

Kicker BarSimple linear motion to extend the bar into position to engage the lip of the totesAcquisition SystemTwo cylinders acting in parallel combined with the claw arms, pulled them together to clamp the tote so it could be grasped then liftedElevationCombined with a 4 bar link to both lift the kicker and acquisition system, and to move it forward. Provided the kicking motion to topple the first row of totes.

PneumaticsPneumatics–– on the SparX 2003 Roboton the SparX 2003 Robot

Kicker Bar

Kicker Bar Cylinder


Elevation Cylinder


AcquisitionCylinders


Compressor

Accumulator

Accumulator

RegulatorPressure Gage

Plug Valve

Accumulator

Plug Valve

Flow Restrictor

First Pneumatic RulesFirst Pneumatic RulesOnly items listed under the PNEUMATICS section of the Kit list may be used to store, generate or transmit compressed air or vacuumOnly the allowed air cylinders may be used to generate vacuum.

You may only use pneumatic components from the pneumatics kit, no extras are allowed.Custom-made pneumatic components (fittings, air cylinders, pumps, valves, etc) are not allowed. Additional off-the-shelf pneumatic components are not allowed.Primary Regulator set to maximum of 60 psi.You can only use the 1 cylinder from the kit of parts plus the 3 free cylinders = 4 total on your robot. (with 3 valves max)Compressor must be powered through a Spike relay driven by the system controller. Pressure switch cannot be wired in series with the pump.

Pneumatics Parts Included in FIRST Robotics Competition

Kit

These are the basic building blocks of the system

The 2003 FIRST Demonstration BoardThe 2003 FIRST Demonstration Board

Preliminary Preliminary Pneumatics mounted Pneumatics mounted

to prototype test to prototype test boardboard

Enabled us to Enabled us to experiment with the experiment with the pneumatic system pneumatic system

without the need for without the need for functional controls functional controls

electronics and electronics and software.software.

SparX Experimentation BoardSparX Experimentation Board

Pneumatic System PartitionPneumatic System PartitionThere are two independent sections of the

pneumatic system.Primary System (High pressure side)Contains the compressor and a tank for storing compressed air. Also includes components to turn the compressor on and off whichmaintains pressure within a control band. First sets this band between 95 and 115 Psi.Secondary System (Low pressure side)Starts with the regulator which controls the lower pressure, to a maximum of 60Psi. Also includes cylinders, the valves that control them and all interconnecting tubing. Note that there can be morethan one Secondary System, and that they can run at a different pressure. Note that cylinders and valves are Never connected tothe Primary System.

System Operation – Primary Side

Accumulator Volume = 37.7 cubic inches

Compressor

Over PressureRelief Valve

PressureSwitch

PrimaryRegulator

Primary Air Circuit Secondary Air Circuit60 Psi max

To PneumaticSwitches

CompressorPumps system

till Pressureswitch turns it

off

SystemPressure dropsdue to air leaks

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Primary System Pressure Vs TimeWith no loads applied

115Psi

95Psi

Time

Pressure

1) At power up, the compressor is energized throughthe pressure switch.

2) When the accumulator and Primary Circuit reach115Psi, the switch opens, turning the compressor off.

3) If there are air leaks in the system, pressure willbleed down to 95 Psi, at which point the switch willclose and the compressor will come on again.

This on and off cycle will continue as long as power isavailable.

Pneumatics ComponentsPneumatics Components

Compressor (& add’l components)

ConnectorsValvesActuators (cylinders)

Pneumatic ComponentsPneumatic ComponentsRelief Valveon Compressor

Accumulator(2pcs.)Plug Valve

Pressure Gauge

Pressure Switch

Compressor

Compressor OperationCompressor Operation

Check Valves in the Inlet and ExhaustAllow Air Flow in one direction

Air In Air Out

Cylinder

Piston

Co

nnec

ting

Rod

When Pistonmoves down,air is drawn

past the inletcheck valve

into thecylinder

CheckValve

CheckValve

When Pistonmoves up, air

is forced out ofthe cylinder,

past theexhaust checkvalve into the

primary system

Pneumatic ComponentsPneumatic ComponentsRegulator Made by Norgren Regulator Made by Monnier


Compressor


PressureSwitch

PrimaryRegulator


SecondaryRegulator

Secondary Air Circuitwith Different Pressure

Norgren istypically used

Here

Monnier istypically used

Here

To Solenoids Running Cylinders @Secondary Pressure

Primary System ComponentsPrimary System Components

•Compressor and Relief Valve•Tanks and Pressure Switch•Gauge and Plug Valve•Regulators with gauges

ConnectorsConnectorsMany Variations Available

Size, Type of Connection, Number of Ports

Tapered Pipe ThreadGenerally Brass – Require Teflon TapeNote – do not use Teflon tape on plastic threaded parts – it can strip the threads off

FittingsFittingsConnection and DisconnectionConnection and Disconnection

44--way Valves in the FIRST way Valves in the FIRST Robotics KitRobotics Kit

Double Solenoid (detented)

Single Solenoid (spring offset)(Festo)

Pneumatics Pneumatics –– CylindersCylindersMany variations

of Bore and Stroke

Available.

Pneumatics

How it works and how it applies to your robot

Pneumatics Pneumatics –– How it Works.How it Works.

ValvesDirectional control – controls the flow to the actuator - analogous to relays or controllersFlow control – controls the rate or the direction of flow – analogous to resistors or diodesPressure control – controls the level of potential energy – analogous to transformers

Pneumatics Pneumatics –– How it Works.How it Works.

ActuatorsTransform potential energy to work

Linear – often called cylinders – straight line but can be configured to perform complex motion

Pneumatics Pneumatics –– How it Works.How it Works.Compressor - converts energy – electrical to pneumaticConnectors - wires & terminalsValves - relays, controllers

Directional controlFlow controlPressure control

Actuators - Force to Motion: Motors, Solenoids, etc.Linear – often called cylindersRotary – limited rotation – air motorsClamps

PneumaticsPneumatics–– Why?Why?The AdvantagesThe Advantages

Weightequal or lighter than comparable alternativesSimplereview the manual and you’re ready to goAdjustable forceby adjusting the regulator pressure you can instantly adjust theforce developed by the cylinder.Reliable & DurableCompressor is shock mounted, fan cooled, and protected from over pressure and over temperature. A very robust component.

PneumaticsPneumatics–– Why?Why?The AdvantagesThe Advantages

Powerfulfrom 9 lbs to 180 lbs based on cylinder size and regulator pressure – easily adjustableCompleteall necessary parts included in the kit – 3 free cylinders available if desiredEasy Mountingall parts come ready to mount or tie wrap in placeFlexible & easy for last minute additionsadd a valve or a cylinder, change routing quickly

Air SupplyAir SupplyAmbient Air is compressed - In industrial applications the air is ‘prepared’

Air Preparation – FRL – Filter - Regulator – Lubricator

Here’s Why ….

Air SupplyAir SupplyAmbient air is compressed

Air preparation – FRL – filter - regulator - lubricator

But dust, dirt and water are included

In industrial applications, contaminants are removed

through the use of filters

Air Supply - FiltersMesh screens or sintered metal baffles remove dirtSpinning action forces water and contaminants out of the air streamSpecial filter materials can remove other entrained contaminants like oil vaporsFabric air filter is permanently mounted on the side of the Thomas Compressor that comes in the First kit

Example Industrial Air Example Industrial Air Filter / DryerFilter / Dryer

Air Supply Air Supply -- RegulatorRegulatorRegulators Control Pressure

Relieving type in the FIRST kitNon-Relieving type can trap pressure

The use of Regulators enables maximum efficiency. Using the lowest pressure needed draws the least power from the system.

For Cylinders used to provide simple motion, Set Regulators to about twice minimum pressure necessary to operate the cylinder under load.

For Cylinders used to generate Force, set regulator pressure as determined by dividing Force required by Piston cross sectional area.

About PressureAbout PressureSafetyMUST Always be considered.

Compressed Air is like a coiled spring that can be routed to where it is needed

About PressureThe bore, stroke and motor horsepower control the pressure from the compressor

The ratio of the uncompressed volume to the compressedvolume is the compression ratio

Relief valve and regulator control the working pressure

Compressed air is stored in the tanks as a reserve.The higher the storage pressure and the greater the volume, the more usable energy will be available

Facts About Pneumatics

Facts about PneumaticsFacts about Pneumatics

Pressure – Potential Energy – Like VoltageLbs per in2 or Force per unit areaAbsolute Pressure – 14.7 psia at sea levelGauge Pressure – measured relative to ambient

Flow – Like electrical currentcfm or Volume per unit timeScfm

Facts about PneumaticsFacts about PneumaticsUniversal Gas Laws – Boyle’s Law

P1 x V1 = P2 x V2 ifif Temperature remains constantTemperature remains constantThat means if you cut the volume in half the absoluteabsolutepressurepressure doubles – That’s how the Compressor works

73.558.844.129.414.7PSIAAbsolute

58.843.529.414.70PSIGGauge

Relationship between Gauge and Absolute Pressure

Facts about PneumaticsFacts about PneumaticsUniversal Gas Laws – Boyle’s Law

P1 x V1 = P2 x V2 ifif Temperature remains constantTemperature remains constantThat means if you cut the volume in half the absoluteabsolutepressurepressure doubles – That’s how the Compressor works

~164.1 psig at sea level P1*V1 = P2*V2 Where all pressures are absoluteP1 = 30+14.7 = 44.7PsiaV1 = 4 cu ftV2 = 1 cu ftThen solving for P2 = (P1*V1) V2

P2 = 44.7PsiA * 4 cu ft 1 cu ft

P2 = 178.8Psia - 14.7Psi = 164.1 Psi Gage

System Operation – Primary Side


Compressor


PressureSwitch

PrimaryRegulator


To PneumaticSwitches



off


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Primary System Pressure Vs TimeWith no loads applied

115Psi

95Psi

Time

Pressure

1) At power up, the compressor is energized throughthe pressure switch.

2) When the accumulator and Primary Circuit reach115Psi, the switch opens, turning the compressor off.

3) If there are air leaks in the system, pressure willbleed down to 95 Psi, at which point the switch willclose and the compressor will come on again.

This on and off cycle will continue as long as power isavailable.

M+

M-

Spike Relay

B

A

+12V

Ground

M+

M-

Spike Relay

B

A

+12V

Ground

M+

M-

Spike Relay

B

A

+12V

Ground

M+

M-

Spike Relay

B

A

+12V

Ground

+12V Ground

Pressure Switch

Battery

Control Zone95 - 115Psi

SystemController

Compressor

Festo Solenoid

B

A

Dual Solenoid

B

A

B

A

Dual Solenoid

B

A

B

A

Extender

Kicker

Claw

Fuse

Electrical Schematic for Pneumatics on SparX 2003 Robot

Force Principles

Force Principles

Gauge pressure works against each square inch of piston surface

The greater the square inch surface of the fluid, the less internal pressure will be developed.

Force PrinciplesForce PrinciplesUniversal gas laws - Pascal’s law

Pressure acts at right angles to the confining vessel –that’s how a cylinder works

Transmission PrinciplesTransmission Principles

Valves Are In Control

Valves Valves Are in ControlAre in ControlControl Pressure

Relief Valves & RegulatorsControl Flow

Check Valves (used on compressor)

Flow ControlsNeedle Valves

44--way Valves way Valves -- Control FlowControl Flow

Passage A Passage B

Spool

Valve Body

PressurePassage

ExhaustPassage

SolenoidSpring

44--way Valves in the FIRST way Valves in the FIRST Robotics KitRobotics Kit

Double Solenoid (detented)

Single Solenoid (spring offset)

Valve SymbolsThe 4-way valves included in the kit are actually pilot-operated valves.Pilot-operators are actually 3-waynnp (normally not passing or normally closed) valves.This allows low-power solenoids to use the air pressure to switch the main spool. Solenoids that would actually move the main spool would be large, heavy and consume a lot of power.

Actuators – Make Things Move

Actuators Actuators -- Makes things moveMakes things moveMost common types of linear actuators

Double acting – single ended

Double acting - double ended

All containCylinder BarrelPistonRodSealsSpring if used

Actuators Actuators -- Makes Things MoveMakes Things MoveMost Common types of Linear Actuators

Single Acting - Single Ended

Single Ended - Spring Return

All containCylinder BarrelPistonRodSealsSpring if used

Actuators Actuators -- Construction & OperationConstruction & Operation

Basic Construction

Operation

Actuators Actuators -- Operation with Flow Operation with Flow ControlsControls

Operation

Typically Flow Controls are mounted between the 4-way valve and the cylinder as close to the cylinder as practical.

The internal check valve permits free flow to the cylinder from the valve and metered flow from the cylinder to exhaust

Actuators Actuators -- Differential AreasDifferential Areas

Force Consideration

• Consider the effective area on which the pressure acts

• On single ended cylinders there is a differential

• Don’t forget friction, and volume of air needed relative to stored volume in the accumulator tanks

Applying Your Components

You’ll get the best results by applying the components carefully, following good

design practice and the following information.

Actuators Actuators -- AnglesAngles

.96675

.86760

1.090

.76650

.70745

.34220

.17410FactorAngle A•

Power Factor

Force T = Cylinder Force x sin A

Actuators Actuators -- AnglesAnglesBe sure to check all cylinder for freedom of movement.

With pressure off, manually move the cylinder and mechanical components through the full stroke of the cylinders.

Potential Interference Points

Actuators Actuators -- AnglesAnglesExample: How much force must the cylinder develop?• Load 15 lbs - Boom Angle 50•

• Solution• Step 1 – Force at right angles to support weight = 15 x .643 (cos 50•) = 9.65 lbs = F2

• Step 2 – Effective Cylinder Force at right angles to support weight = 9.65 x arm ratio (17/5) = 32.79 lbs = F1

• Step 3 – Actual Cylinder Force acting at 30• = F1 / sin 30• = 65.59 lbs = F

Actuator (cylinder) Do’s and Don’tsYou do not have to fully extend a cylinder but you’ll need an external stop.Avoid side-loading – increases friction and wear

Avoid getting grit or metal shavings on the rod or in the cylinder – causes abrasion and seal damageUse flow controls for safety

Weight or force applied at 90° angle to the rod

Wear, friction and leakage can occurat the rod seal and at the piston seal

Actuator (cylinder) Do’s and Don’tsCylinder Force to just balance the load

Push Force = π x cylinder radius2 x Pressure (psig)Pull Force = Push Force - π x rod radius2 x Pressure (psig)Use roughly twice the balance force for good control.

Teams may order additional cylinders (including spares) for rapid delivery using the FAX form on the back of the manual. ¾”, 1-1/2” or 2” bore are available – see form in the manual for available strokes

Avoid leaks – reduces available energy

Actuators Actuators –– Mounting ThoughtsMounting ThoughtsExample: Arm to be raised by Cylinder

• Determine overall length of retracted cylinder

• Draw an arc from the mounting point on arm

• Determine overall length of extended cylinder

• Draw an arc from the mounting point on arm

• Where arcs intersect is the mounting point

• Check for intermediate interference

Calculating Cylinder Dimensions

Based on the drawings in the pneumatic manualRetracted length from pivot pin to clevis hole =

Base dimension +Stroke length +Locking nut +Clevis dimension

Extended length from pivot pin to clevis hole =Retracted length plus stroke

1.5” Bore Cylinder

Retracted Length = 4.38 + Stroke + .25 + 1.31 = 5.94 + Stroke

Base Dimension = 4.38 +Stroke Length = ? +Locking Nut = .25 +Clevis Dimension = 1.31

Extended Length = 5.94 + (2 x Stroke Length)

System Example From SparX 2003 Robot

PrimaryRegulator

Secondary Air Circuit60 Psi max



off

Ope

n K

icke

r Bar

Open ElevationThen Compressorre-pressurizes the system

Primary & Regulated System Pressure Vs TimeWith different loads applied

115Psi

95Psi

Time

Pressure

Elevation Cylinder2in dia x 12 in long

Volume = 37.7 cubic inches

Valve ExhaustExhaust

Valve ExhaustExhaust

Kicker Cylinder3/4 in dia x 10 in long

Volume = 4.4 cubic inches

Val

veE

xhau

stE

xhau

st

Claw Cylinders (2)3/4 in dia x 6 in longVolume = 2.65 each5.3 total cubic inches

80Psi

50Psi

70Psi

60Psi

90Psi

30Psi

0Psi

20Psi

10Psi

40Psi

Primary Pressure

Regulated Secondary Pressure

Ope

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law

Clo

se K

icke

r Bar

101.4Psi

89.8Psi

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Open ClawOpen KickerOpen Elevation

50.2Psi

42.7Psi

Ope

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Clo

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law

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The graph below shows how the secondary sees relatively consistent air pressure, while the primary side has wide swings in pressure.

Always connect your cylinders to the regulated side to avoid these wide swings in pressure

Tips & TricksTips & TricksMinimize leaks (better yet, remove them completely) by careful use of teflon® tape and careful assembly of tubing and fittings. Teflon tape should start two threads back and wrap in the direction of the threads.

With no movement taking place the compressor should charge the tanks and then shut off. It should not restart until a valve and cylinder is operated.

Use the compressor vibration isolators. The compressor is a reciprocating device and will cause sympathetic vibrations throughout your assembly unless they are used.

When ordering custom cylinders, use extreme care in completing the form,both on the address and models ordered.

Tips & TricksTips & TricksThe Pressure Switch contacts must be used as inputs to the controller. They cannot handle the amperage of the compressor.

The Norgren Regulator should be first with the Monnier unit used after that if needed.

Make sure you have adequate pilot pressure for the valves.

When using the double solenoid valve, energize only one at time.

The fittings for the FESTO valve are different, use them in that valve only. Fittings are not required in the exhaust ports unless the circuit requires them.

Always stay clear of cylinders in motion. Until compressed air is being metered, flow controls do little to control speed.

Review QuestionsWhich statement is true ?

1. There is no benefit in using a regulator to reduce pressure.2. You’re “stuck” with the cylinders that come in the kit. 3. A pressurized cylinder at rest cannot apply force.4. You can save some inputs on the controller by forgetting

about the pressure switch and running the compressor continuously.

5. There is no such thing as a pneumatic “diode” or one-way valve.

6. A 2” bore cylinder at 100 psig yields 200 lbs of force.7. None of the above.

Review QuestionsWhich statements are true ?

1. There is no benefit in using a regulator to reduce pressure.2. You’re “stuck” with the cylinders that come in the kit.3. A pressurized cylinder at rest cannot apply force.4. You can save some inputs on the controller by forgetting

about the pressure switch and running the compressor continuously.

5. There is no such thing as a pneumatic “diode” or one-way valve.

6. A 2” bore cylinder at 100 psig yields 200 lbs of force.7. None of the above. Correct answer – None of the above.

Review Question - Statements1. Using the lowest pressure that will run your system, uses the

least volume of air saving running time on the compressor and time on the battery.

2. You can order custom cylinders with the form that comes with the kit.

3. A pressurized cylinder applies force based on pressure and piston area.

4. You would drain your battery too quickly. If there is no movement, the compressor doesn’t run, even though force is being exerted. Use the pressure switch.

5. A pneumatic diode is called a check valve. 6. The force is equal to π x cylinder radius2 x Pressure (psig) – or

3.14 x 12 x 100 psig or 314 lbs

Review Questions

Which statement is correct ? 1. Your pneumatic kit is complete, although custom

cylinders can be received quickly. 2. You need to supply an extension cord to power the

compressor from a wall outlet.3. Because air is weightless, it will reduce the weight of

your robot when pressurized.4. The pressure switch is only included to sound an alarm

if ambient pressure falls.

Review Questions

Which statement is correct ? 1. Your pneumatic kit is complete, although custom cylinders can

be received quickly. 2. You need to supply an extension cord to power the compressor

from a wall outlet.3. Because air is weightless, it will reduce the weight of your robot

when pressurized.4. The pressure switch is only included to sound an alarm if ambient

pressure falls.Correct answer – 1. The pneumatic kit is complete.

ReferencesSlides based on "Pneumatics and the FIRST Competition" by John R. Groot of the Fluid Power Educational Foundation, taken from the First web siteSparX content added by Ken Buck [email protected]

Interesting Links

Fluid Power Journalwww.FluidPowerJournal.com

Parker www.parker.com

Festowww.festo.com

Nat’l Fluid Power Ass’n www.nfpa.com

Norgrenwww.norgren.com

Wikawww.Wika.com

Fluid Power Society www.ifps.org

Monnier, Inc. www.monnier.com

Clippard Instrument Lab.www.clippard.com

Fluid Power Dist. Ass’n www.fpda.org

Lord Corp www.lordmpd.com

Bimba Manufacturingwww.bimba.com

SMC Pneumatics www.smcusa.com

Nason Corpwww.nasonptc.com

Fluid Power Educational Foundation

www.fpef.org

Documents

Pneumatics Tutorial