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Actuators -

Feb 19, 2018

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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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