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7/23/2019 Actuators - Introduction.ppt
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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.
– 0he ports are 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.
• A p / Area of -iston
• Ar / Area of Rod
– *xtension stroke
• 2ext 4 - 5 A p
• vext 4 6in7A p
– Retraction stroke• 2ret 4 - 5 'A p – Ar (
• vret 4 6in7'A p – 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 <Ans, =;>psi?
– 0he piston velocity during the extending stroke <Ans, 9.:@ft7s?
– 0he cylinder horsepower during the extending stroke <Ans, =.9 !-?
– 0he hydraulic pressure during the retraction stroke <Ans, B9@ psi?
– 0he piston velocity during the retraction stroke <Ans, 9.= ft7s?
– 0he cylinder horsepower during the retraction stroke <Ans, B.D !-?
Eote,
-ower 'FG( 4 v p 'm7s( 5 2 'FE( 4 6 in 'm=7s( 5 p 'k-a(
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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.
<Ans,>B:l)?
• 2ind the cylinder force 2 reHuired to lift the D:::/l) weight GJ along a
direction which is =:o from the hori1ontal. 0he weight is moved at constant
velocity. <Ans, =:::l)?
• 0he D:::/l) weight is to )e lifted upward in a vertical direction. 2ind the
cylinder force reHuired to
– Move the weight at constant velocity of > ft7s. <Ans, >>: l)?
–
Accelerate the weight from 1ero velocity to a velocity of > ft7s in :.@:s.<Ans, ;Dft7s9 & 2accel 4 9>: 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 L9 4 ;:in.&
K 4 :o& 2load 4 ;::: l) . <Ans, ;::: l)& @:: l)& 9::: l)?
• A pump delivers oil at a rate of ;>.9gpm into the )lank end of the =/inch
diameter hydraulic cylinder shown in fig. 0he piston contains a ;/inch
diameter cushion plunger that is :.@ inch long& and therefore the piston
decelerates over a distance of :.@ 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
cushion.<Ans, >@Dpsi?
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Linear !ydraulic Actuators
+ou)le Rod Cylinder •Cylinder 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 Cylinders•0hese 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
– R R 4 outer radius of rotor 'in& m(
– R 3 4 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 - 'R 3 / R R ( L
– 0 4 - 'R 3 / R R ( L ''R 3 R R ( 79( 4 '-L79( 'R 93 / R 9R (
– 3+ 4 'R 93 / R 9R ( 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 :.@ inch& outer radius of vane 4 ;.@ inch& width of vane 4 ; inch.
If the torHue load is ;::: in.l)& what pressure must )e developed to
overcome the loadO <Ans, ;:::psi?
• A hydraulic motor has a @in= volumetric displacement. If it has a pressure
rating of ;::: psi and it receives oil from a ;:/gpm theoretical flow rate
pump& find the motor 'a( speed& ')( 0heoretical torHue and 'c( 0heoretical
horsepower. <Ans , BD9rpm& @ in.l)& @.>=!-?
• A hydraulic motor has a displacement of ;:in= and operates with a pressure
of ;::: psi and a speed of 9::: rpm. If the actual flow rate consumed )y
the motor is @ gpm and the actual torHue delivered )y the motor is
;@::in.l)& find , 'a( Nv ')( Nm 'c( No 'd( the actual horsepower delivered )y
the motor. <Ans, ;.;P& B.9P& >@.>P& B.D !-?
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*xercises
• A hydrostatic transmission& operating at ;:::psi pressure& has the
following characteristics,
2ind the 'a( +isplacement of the motor & ')( Motor output torHue
<Ans , B.; in= & DB in.l) ?
Pump Motor
3+ 4 @in= 3+ 4O
Nv 4 >9P Nv 4 9P
Nm 4>>P Nm 4 :P
E4@::rpm E4B::rpm