Post on 08-Apr-2015
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
PneumaticsPneumatics–– on the SparX 2003 Roboton the SparX 2003 Robot
Elevation Cylinder
PneumaticsPneumatics–– on the SparX 2003 Roboton the SparX 2003 Robot
AcquisitionCylinders
PneumaticsPneumatics–– on the SparX 2003 Roboton the SparX 2003 Robot
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
Com
pres
sor r
e-pr
essu
rizes
the
syst
em
SystemPressure dropsdue to air leaks
Com
pres
sor r
e-pr
essu
rizes
the
syst
em
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
Accumulator Volume = 37.7 cubic inches
Compressor
Over PressureRelief Valve
PressureSwitch
PrimaryRegulator
Primary Air Circuit Secondary Air Circuit60 Psi max
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
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
Com
pres
sor r
e-pr
essu
rizes
the
syst
em
SystemPressure dropsdue to air leaks
Com
pres
sor r
e-pr
essu
rizes
the
syst
em
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
CompressorPumps system
till Pressureswitch turns it
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
n C
law
Clo
se K
icke
r Bar
101.4Psi
89.8Psi
Com
pres
sor r
e-pr
essu
rizes
the
syst
em
Open ClawOpen KickerOpen Elevation
50.2Psi
42.7Psi
Ope
n C
law
Clo
se C
law
Clo
se C
law
Com
pres
sor r
e-pr
essu
rizes
the
syst
em
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 Ken.Buck@usa.xerox.com
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