10/21/2015sme 3252: mechatronics lecture 5 1 pneumatic and hydraulic actuation system (cont.)...

04/20/23 SME 3252: Mechatronics Lecture 5

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Pneumatic and hydraulic actuation system (cont.)

Lecture 5


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Hydraulic actuation system



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Hydraulic schematic



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Schematics and Symbols

Valve – Shows blocks to denote the different paths the air can take through the valve

Cylinder – Shows simplified shape, piston, rod and two air ports

Pressure regulator – Reduces the pressure. This allows you to adjust the force of actuators



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Schematics – Symbols

Flow Control Valve – Regulates the amount of air through the line. Used to regulate the speed of actuators

Check valve – Allows flow only in one direction. The symbol shows a physical representation of the valve operation




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Schematics – Symbols

Reservoir –

Air service unit –


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7.3 : Directional control valves

• Pneumatic and hydraulic system use directional control valve

• Direct flow of fluid/air • Not to vary rate, either completely

open or completely closed• On/off device to develop sequenced

control system• Types – spool valve, poppet valve,

rotary valve


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Spool valve• Spool moves horizontally within

valve to control flow


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Figure 7.5 Spool valve


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Poppet valve

• Normally in closed condition• Ball, disk or cone are used to control

flow


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Figure 7.6 Poppet valve


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7.3.1: Valve Symbols• Symbols for valve consists of square

for each switching position• E.g. two-position valve has 2

squares, three-position valve has 3 squares

• Arrow head lines – indicate directions of flow in each position

• Blocked off line – closed flow lines• Initial position - connection to ports


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Valves symbol:

position

2 switching position valve – two squares

Flow path

Flow shut off position

Initial connection (inlet/outlet ports) shown outside the box (i.e. 4 ports)


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Figure 7.7 (a) Flow path, (b) flow shut-off, (c) initial connections


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Valve actuation symbolThere are various ways the valves can be actuated:

General /manual

“push-button”

“pull” “lever”

“pedal “spring”

“roller” “solenoid”

pneumatic


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Figure 7.8 Valve actuation symbols


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3/2 Valve• 3 indicates no. of ports, 2 indicates

no. of positions• Valve is actuated by current passing

through solenoid, return to its original position by a spring

1 – pressure supply2 – connection to cylinder3 – exhaust port

Lift system

• Refer to figure 7.11 page 157 – application of valves in a pneumatic lift

• Two push button 2/2 valves are used

• Button on the up valve is pressed – load is lifted

• Button on the down valve is pressed, load is lowered


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3/2 valve (cont.)

• 3/2-valve usually for controlling single-acting cylinder

• Usually use poppet valve


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5/2 Valve• 5 - no. of ports, 2 - no. of positions

1 – pressure supply2 & 4 – connection to cylinder3 & 5 – exhaust port


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5/2 valve (cont.)

• 5/2-valve usually for controlling double-acting cylinder

• Usually use slide valve

Actuator


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5.5: Cylinders• Hydraulic or pneumatic cylinder – is

an example of linear actuator• Two types:1. Linear – using cylinder single acting cylinder double acting cylinder

2. Rotary


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Single-acting cylinder

• Control pressure is applied to just one side of cylinder

• This cylinder uses a spring force to move the piston in one direction

• When pressurized, the air pressure overcomes the force of the spring and compresses it


27Single-acting cylinder

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Control of a single-acting cylinder

• Current passes through solenoid – valve switches position – pressure applied to move piston

• Current ceases – valve reverts to initial position – air is vented

• Refer to Figure 7.17 of Textbook


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Double-acting cylinder

• Control pressures are applied to each side of piston

• A difference in pressure between two sides results in motion of piston

• Piston is able to move either direction along cylinder due to high pressure signals


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Double-acting cylinder

http://www.dtonline.org/apps/infopage/app?1&5&1&7&1&0


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Control of a double-acting cylinder

• Refer to Figure 5.19 of textbook

Solenoid activated, piston extends


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Cylinders (cont.)

• Choice of cylinder – determined by force required to move load and speed required

• Hydraulic cylinder – capable of much large forces than pneumatic

• Pneumatic cylinder – capable of greater speed

• Force produced by cylinder


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Force = (Pressure)*(Area). • The pressurized air pushes against the piston

inside the cylinder• This force is dependent on two things: the

pressure of the air and the area of the piston

• If air pressure = 60 psi, dpiston = 10mm, effective surface area A = 78mm2 = 0.1217in2, Force = 7.3 lbf or 32.5 N.

• Because the piston rod reduces the effective area on one side of the piston, the pull force is not as great as the push force


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• For the pull force, the effective area = (Piston area) - (rod area)

• drod = 4mm, the rod area = 12.5mm2

• The effective area = 65.5mm2 • The pull force = 27.1 N or 6.09 lbf.


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5.6.3: Example of fluid control system

• Control level of liquid in container by controlling rate of liquid enters

• Output from sensor and signal conditioning transmitted to current to pressure converter into a pressure gauge ( 4 to 20 mA – 20 to 100 kPa)

• Actuates a pneumatic control valve to control rate of liquid allowed to flow to container


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Fluid control system

Flow control valve

Current to pressure converter – Fig 7.6 (b)

Signal conditioner

Sensor

- - - - - - - - - -- - - - - - - - - -

- - - - - - - -

- - - - - - - - - -- - - - - - - - - -

- - - - - - - - -

- - - - - - - - - -- - - - - - - - - -

- - -


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Exercises

• Differentiate between hydraulic and pneumatic cylinders

• Differentiate between single-acting and double acting cylinders

• Identify 3/2-valve, 5/2-valve, and others like 5/3-valve, 4/2-valve and etc.

• Explain the application of valve in pneumatic system

• Explain the flow control valve in application of fluid control system


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End of Lecture 5

10/21/2015sme 3252: mechatronics lecture 5 1 pneumatic and hydraulic actuation system (cont.)...

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