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Pneumatics

How do they work; why do we use them?

Robotics 101

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Pneumatic Terminology

  • Cylinder (Bore /Stroke)
  • Extend / Retract

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Pneumatics on Robots

  • Simplified model

Compressed

Air

Tank

Geek

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Safety

Glasses

60 lbs./in2

Pneumatic Cylinder

Whoa! That’s a lot of force.

Plunger

Diaphragm

FORCE= Area of diaphragm X Pressure (lbs./in) in tank

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Force = 1.76 in2 X 60 lbs./in2

= 105.6 lbs. of Force

 

(PSI)

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Force calculations by cylinder

At 60 PSI pressure

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Cylinder Bore Diameter (in)

Force (lbs) to extend at 60 psi

0.750

26.5

0.875

36.1

1.000

47.1

1.125

59.6

1.250

73.6

1.375

89.1

1.500

106.0

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Pneumatic Parts

  • Compressor- 125 PSI, 20 Amps Max, Weight 2.4 lbs.
    • Provides source of pneumatic power

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  • Pressure Switch & gages- 115 PSI high pressure circuit
    • Pressure switch turns compressor on and off
      • On at approx. 100 PSI, Off at 115 PSI

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  • Air Tanks- Reservoir so robot functions are not diminished due to loss of pressure; stores pneumatic power, like a battery
    • Compressor output will not always keep up with usage
      • How many on last year’s robot?

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Pneumatic Parts

  • Regulator to regulate pressure to components:

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  • Single & Double Solenoid Valves: electrical control from roboRio

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  • Flow Control Valves Change speed of extending and retracting:

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Single=> On=Extend, Off=Retract

Double=> Side 1 On Pulse Extend

Side 1 Off Same Position

Side 2 On Pulse Retract

Side 2 Off Same Position

Usually it is 60 PSI or Less; 2 Regulators are provided for regulating High Pressure System 115 PSI and Low pressure system 60 PSI simultaneously.

Too Fast, Slow it down with Flow control.

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Pneumatic Parts

  • Valve to Release or Fill with Air

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  • Fittings

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  • Cylinder (Various Sizes)
    • Diameter Range: ½” to 2”
    • Stroke Range: ½” to 24”

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Teflon tape helps prevent leaks at connections- don’t use too much

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Pneumatic diagram

High pressure 115 PSI

Low pressure 60 PSI

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Pros and Cons of Pneumatics

  • Reasons for using Pneumatics
    • Weight: May be less total weight than using Gears and Pulleys & multiple electrical motors while keeping the same Force
    • Simple to Design/Easy to Build: A closed loop pneumatic system is easier to design than gears and pulleys.
    • Reliable: Pneumatics perform the same over and over again
    • Force is adjustable and the Force cylinders produce can be significant.
    • A variety of pneumatic cylinders are offered
    • We will probably have cylinders already for shifting 2 speed gearbox
  • Potential Issues with Pneumatics
    • Pneumatic support system weight – compressor, tanks, regulator, gages
      • Need all of these components whether we use 1 or 10 cylinders
    • Stroke Length is limited to 2 ft. max (There are limits).
    • Fixed increments of travel – full stroke in or out limited variable positions
    • Need to make sure system is charged before every match
    • Leaks are possible and can be annoying to find – always plan on putting compressor on robot to avoid complete robot system shut-down

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Questions?

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Rotary Actuator

  • Rotary Actuator

Rotational Force =Torque

(0.075/2)2 * PI X 60 PSI = 0.26 ft.-lbs.

(0.875/2)2 * PI X 60 PSI = 36 ft.-lbs.

(1.06/2)2 * PI X 60 PSI= 52 ft.-lbs.

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Application Information

  • Force Range @ 100 PSI

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  • Rod diameter – ¼” to ½”
    • ¼” may bend when robots crash into each other

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  • Mounting options

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