Introduction to Pneumatics

Report
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Slides by Raul Olivera from FRC 111 –
WildStang
› Presentation from the FIRST Championships in
2008
› http://first.wpi.edu/Images/CMS/First/2008C
ON_Pneumatic_Power_Olivera.ppt
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FRC 358
› Lots of great resources!
› http://team358.org/files/pneumatic/
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FIRST Pneumatics Manual
› http://www.usfirst.org/roboticsprograms/frc/
2012-kit-of-parts-pneumatics
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Pneumatics:
› “The study of the mechanical properties of air and other
gases”
› The system on an FRC robot which uses pressurized air to
transfer force
Pressure = matter pushing against matter
› Object pushing against another object
Absolute (psia): true matter-based pressure
› 0 psia - no matter present to press against objects
› Not too important in our designs
Gauge (psig): Relative to Atmosphere
› 0 psig - pressure in equilibrium with atmosphere
› All regulators and gauges based on this
› At sea level: 0 psig = ~14.7 psia
Pressure = Force / Area
 Force = Pressure X Area
 Example: 30 psig in 2” diameter cylinder
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30 psig
Area = pr2 = p(1”)2 = 3.14 in2
94.2 lbs
Force = 30 psi X 3.14 in2 = 94.2 lbs
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Low to high force applications
› Up to 188 lbs (plus any mechanical advantage in
design)
› Can vary force by changing pressure
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Linear and rotational motion
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Two positions
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Flexible design options
› Linear is much more common
› Great for applications where a motor would stall
› Open/close or on/off applications
 Claws, lifters, pushers, pokers, levers
 Shifters and clutches
› Excess cylinder length can be accommodated in
design
 Move mounting point
 Push against rigid object
› Can start match with force applied, and keep it
applied at end of match
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Relatively straightforward rules and
implementation
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Mounting hardware included
Easy interface to robot
Can test manually without code
FIRST provides instructions!
Economy of scale – easy to add more later
Easy to transfer energy from robot “base” to
manipulator
› Flexible tubes
› Don’t need chain, belt, or perfectly aligned shafts
› All components except for cylinder can be mounted
anywhere
High Pressure
(120 psi)
Working Pressure
(60 psi)
Optional
Lower Working
Pressure (30 psi)

Compressor
› Mount with rubber vibration
isolation mounts
› Must power with Spike relay with
20 amp breaker (not fuse)
› Gets hot!
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Pressure Relief Valve (Norgren)
› Must be installed on output of
compressor
› Vents at 120 psi for safety (in case
your code to shut off compressor
doesn’t work right …)
› Must check that this is calibrated
properly
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Pressure switch (Nason)
› Normally closed (compressor runs)
› Opens at ~115 psi (code to turn
compressor off when switch is open)
› Wire to digital input and ground on
digital sidecar

Accumulator (Air Tank)
› Check rules regarding # allowed
› Make sure to mount on high pressure
side to take advantage of higher
pressure storage!
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Primary Regulator (Norgren)
› Restricts working pressure to 60 psi
max on output side of regulator
› Can adjust to less than 60 psi if
desired
› Make sure arrow points in direction of
air flow!
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Secondary Regulator (Monnier)
› Yellow ring
› Allows additional lower pressure
circuit if desired
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Gauges
› Provide readout of pressure in line
› Place one on high pressure side and
one on working pressure side (can
attach directly to regulator)
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Plug Valve (manual release valve)
› Install on high pressure side
› Must be able to release all pressure in
system
› Must be easily accessed and labeled
on your robot
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Cylinders (aka “Pistons”)
› Donated by Bimba
› Order to team specifications from FIRST-
specific options
› Single or double acting
 Single = spring-based return when vented
 Double = air pressure drives both directions
› Magnetic position sensing option
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Solenoid valves (Festo/SMC)
› Switches direction of air flow to drive
cylinder motion
› Connect to solenoid breakout on CRIO
› Need a double solenoid to drive double
acting cylinder
› Can activate manually with blue buttons
Safety
› Pressurized air has a lot of potential
energy
› Follow rules EXACTLY and be careful
 Rotation
› Difficult to control orientation of the end
of a round shaft
 Leaks
› Can be hard to find – so prevent them
with good assembly technique!
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 Cut tubing straight and clean
 Tighten fittings with proper tools
› Use methodical approach to narrow in
on one area
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Pipe thread wrap
› Too much is not a good thing
› Leave last 2 threads clear
› Avoid getting into valves and hoses
Extra components
› Bring spec sheets for non-KOP items to
inspection
Cylinders are sensitive to side loads
“Pulling” force is slightly reduced due to area
of rod
Large cylinders use a lot of air – make sure your
compressor and storage can keep up with
expected use
Plug valve must be closed before you start the
match!
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MYTH: Using pneumatics is complicated
FACT:
› Simple system with detailed instructions, and it’s the same
every time!
› Robust system with fewer parts to fail
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MYTH: Pneumatics is heavy
FACT:
› 2013 compressor is only 2.5 lbs
 Could be left off robot to save weight (check rules in 2014!)
› Cylinders have high force/weight ratio (compare to
CIM+gearbox+chain+speed controller…)
› Adding a second, third, etc. cylinder is trivial
› Plastic air tanks are available
› Solenoid and tubing weights are negligible
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MYTH: Pneumatic cylinders are uncontrollable
FACT:
› Flow control valves can slow down motion
› Can choose piston length based on geometry
› Magnetic reed switches can be used to sense
piston position
MYTH: Pneumatics is difficult to program
FACT:
› Program compressor to run when pressure switch
is closed – connected directly to digital sidecar
› Double solenoid consists of two on/off switches –
when one is on, other is off!
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Use all 24v or 12v solenoids – don’t mix!
Even if you aren’t using pneumatics on your
robot, take advantage of the Bimba donation
– play with them in the off-season or have on
hand for next year!
Solenoids need a minimum pressure (~30 psi) to
work. Test your code with pressure in the
system!
Clevis pins can be replaced with bolts for more
mounting options

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