Actuators -

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ACTUATORS

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Introduction

Actuators extract energy from a fluid and

convert it to mechanical energy to perform

useful work.

Linear actuators Cylinders

Rotary actuators Motors

Limited rotation motors scillation fluidmotors

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Linear !ydraulic Actuators

"ingle acting cylinder Consists of a piston inside a cylindrical housing called a

#$arrel%.

Attached to one end of the piston is a rod& which extendsoutside one end of the cylinder 'rod end(.

At the other end ')lank end( is a port for the entrance and

exit of oil.

*xerts a force in only one direction.

Retraction can )e accomplished )y gravity or )y the

inclusion of a compression spring in the rod end.

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Linear !ydraulic Actuators

"ingle acting cylinder

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Linear !ydraulic Actuators

+ou)le acting cylinder Capa)le of delivering forces in )oth the directions.

$arrel,"eamless steel tu)ing& honed to a fine finish on inside surface

-iston,+uctile iron& contains /cup packings to seal leakage )etween

piston and )arrel.

0heportsare located in the end caps which are secured to )arrel )y tie

rods.

0he load of the piston rod at the neck is taken )y a rod )earing& which

is made of )rass or )ron1e. Rod wiper is provided at the end of the neck to prevent foreign

particles and dust from entering into the cylinder along with the piston

rod.

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Linear !ydraulic Actuators

+ou)le acting cylinder

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Linear !ydraulic Actuators

+ou)le acting cylinder

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Linear !ydraulic Actuators

Cylinder mountings and mechanical linkages

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Linear !ydraulic Actuators

Cylinder mountings and mechanical linkages

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Linear !ydraulic Actuators

Cylinder mountings and mechanical linkages

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Linear !ydraulic Actuators

Cylinder 2orce& 3elocity and -ower

2orce '2( and 3elocity 'v( of a dou)le acting cylinders are not same for

extension and retraction strokes.

Ap / Area of -iston

Ar / Area of Rod

*xtension stroke

2ext4 - 5 Ap

vext 4 6in7Ap

Retraction stroke 2ret4 - 5 'Ap Ar(

vret 4 6in7'Ap Ar(

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Linear !ydraulic Actuators

Cylinder cushions 0o slow down the piston near the ends of the stroke. 0his prevents

excessive impact when the piston is stopped )y the end caps.

+eceleration starts when the tapered plunger enters the opening in the

cap.

0his restricts the exhaust flow from the )arrel to the port.

+uring the last small portion of the stroke& the oil must exhaust through

an ad8usta)le opening.

0he check valve allow the free flow to the piston during directionreversal.

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Linear !ydraulic Actuators

Cylinder cushions

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*xercises A pump supplies oil at 9: gpm to a 9/in diameter dou)le/acting hydraulic

cylinder. If the load is ;:::l).'extending and retracting( and the roddiameter is ;in& find

0he hydraulic pressure during the extending stroke psi?

0he piston velocity during the extending stroke

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*xercises

2ind the cylinder force 2 reHuired to move a D:::/l) weight GJ along a

hori1ontal surface at a constant velocity. 0he coefficient of friction 'C2(

)etween the weight and hori1ontal support surface eHuals :.;B.

B:l)?

2ind the cylinder force 2 reHuired to lift the D:::/l) weight GJ along a

direction which is =:ofrom the hori1ontal. 0he weight is moved at constant

velocity. ft7s. >: l)?

Accelerate the weight from 1ero velocity to a velocity of > ft7s in :[email protected]:s.: l)?

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Cylinder loadings through Mechanical linkages

2irst/class lever system

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Cylinder loadings through Mechanical linkages

"econd / class lever system

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Cylinder loadings through Mechanical linkages

0hird/class lever system

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*xercises

Calculate the cylinder force reHuired to overcome the load force for first&

second and third class lever using the following data, L;4 L94 ;:in.&

K 4 :o& 2load 4 ;::: l) . .9gpm into the )lank end of the =/inch

diameter hydraulic cylinder shown in fig. 0he piston contains a ;/inch

diameter cushion plunger that is :[email protected] inch long& and therefore the piston

decelerates over a distance of :[email protected] inch at the end of its extension stroke.

0he cylinder drives a ;@::/l) weight& which slides on a flat hori1ontal

surface having a coefficient of friction 'C2( eHual to :.;9. 0he pressure

relief valve setting eHuals @:psi. 0herefore& the maximum pressure 'p ;( at

the )lank end of the cylinder eHuals @:psi while the cushion is

decelerating the piston. 2ind the maximum pressure 'p9( developed )y the

[email protected]?

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Linear !ydraulic Actuators

+ou)le Rod CylinderCylinder with single piston with piston rod extending from each end.

Cylinder allows work to )e performed at either or )oth ends.

It may )e desira)le when operating speed and return speed are eHual.

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Linear !ydraulic Actuators

0andem Cylinder!as two cylinders mounted in line with pistons connected )y a common

piston rod.

0hese cylinders provide increased output force when the )ore si1e of a

cylinder is limited.

$ut the length of the cylinder is more than a standard cylinder and also

reHuires a larger flow rate to achieve a speed )ecause flow must go to

)oth pistons.

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Linear !ydraulic Actuators

0elescopic Cylinders0hese cylinders are where long work/strokes are needed.

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Rotary !ydraulic Actuators

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Rotary !ydraulic Actuators

Limited angle rotary actuator:

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Rotary !ydraulic Actuators

Analysis of 0orHue Capacity

RR4 outer radius of rotor 'in& m(

R34 outer radius of vane 'in& m(

L 4 width of vane 'in& m( - 4 hydraulic pressure 'psi& -a(

2 4 hydraulic force acting on vane 'l)& E(

A 4 surface area of vane in contact with oil 'in9& m9(

0 4 torHue capacity 'in. l)& E .m(

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Rotary !ydraulic Actuators

Analysis of 0orHue Capacity

2 4 - A 4 - 'R3 / RR( L

0 4 - 'R3 / RR( L ''R3 RR( 79( 4 '-L79( 'R93 / R9R(

3+4 'R93 / R9R( L

0 4 '- 3+79 (

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Rotary !ydraulic Actuators

Rack/and/pinion piston/type rotary actuator,

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Rotary !ydraulic Actuators

!elix actuator,

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Rotary !ydraulic Actuators

-arallel piston rotary actuator,

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Rotary !ydraulic Actuators

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Rotary !ydraulic Actuators

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Rotary !ydraulic Actuators

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Rotary !ydraulic Actuators

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Rotary !ydraulic Actuators

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Rotary !ydraulic Actuators

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!ydraulic Motor theoretical torHue& -ower and

2low rate

English Units Metric Units

0heoretical -ower 'G( 4

!ydraulic -ower 4 !ydraulic -ower 4

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Motor *fficiencies

3olumetric efficiency 'Nv(

Mechanical efficiency 'Nm

(

verall efficiency 'No(

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*xercises

A single/vane rotary actuator has the following physical data, outer radius

of rotor 4 :[email protected] inch& outer radius of vane 4 ;[email protected] inch& width of vane 4 ; inch.

If the torHue load is ;::: in.l)& what pressure must )e developed to

overcome the loadO

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