Hydraulic actuators: cylinders Cylinder...
Transcript of Hydraulic actuators: cylinders Cylinder...
2005/2006 I. Hydraulic and Pneumatic Systems 1
Hydraulic actuators: cylindersCylinder types:
Single acting:
work can be done only in one direction
Piston
Double acting piston:
Piston rod on both sides
Plunger
Work is done in both
directions
Telescopic Telescopic Fast moving
Tandem
Fast moving
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Hydraulic cylinders
Hydraulic cylinderHidraulikus munkahengerek
Rögzítőpálcás kivitel 1.
Rögzítőpálcás hidraulika henger, a hengerfejen található karimás rögzítéssel
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Hydraulic cylinders
Hydraulic cylinder Hidraulikus munkahengerek
Hengeres kivitel 1.
Hengeres építési móddal készült hidraulika henger
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Hydraulic cylinders
Properties:
The cylinders have to be good quality steel with close tolerances.
There have to be good sealing both at the piston rod and at the
cylinder.
With time dirt may come in and damage the surfaces. This has to be
possibly reduced.
In this case, the leakage will increase all the time.
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Hydraulic cylinders
Calculation of cylinders
1maxmaxFFFF FLc ++= FLC FFF +≈
maxmax
22110 pApAFC −=
1122 pApAFCB −=
1
0A
Qv =
2A
Qv
B=
friction forces inertial forcesmaximum loadslow motion, can
be often neglected
Backward:
Outward:
Q
A2A1
p1
p2vB
v0
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Hydraulic cylinders
Calculation of cylinders
Hydraulic cylinders should be possibly
operated in the 3rd region for smooth
operation.
If the cylinder is new, the leakage losses are
negligibly small so that:
ηc = ηmech
Ff1
v
2 3
1. Stick-slip
2. Transition
3. Normal behaviour
22112211ApAp
F
QpQp
Fv LLc −
=−⋅
=η
92,085,0max
−=cη
ηc
∆p
outwardsinwards
at higher pressures
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Hydraulic cylinders
Checking for buckling
n: safety factor: 1-3,5
lk: buckling length
I1: moment of inertia of the piston rod
E: elasticity modulus of the rod material
1
2
max
1IE
lnF
k
L ⋅⋅
=
π
64
4πd
Maximum permissible force:
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Hydraulic cylinders
Cushioning of cylinders:
A hard impact of the piston at the end surfaces has to be inhibited
– kinetic energy has to be absorbed.
This is done by increasing the hydraulic resistance at the end of
the stroke.
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Rotary hydraulic actuators
Swivel vane rotary actuator:
Limited angle in both directions
Maximum angle always smaller than 360°
The same torque in both directions
Piston rotary actuator:
With rack and gear coupling
Here maximum angle may be larger than 360°Mindkét irányban azonosan
működő hengerrel és fogasléces
meghajtással működtetett
tolódugattyús lengőhajtás
Párhuzamdugattyús
lengőhajtás
Forgódugattyús
lengőhajtás menettel
működtetett meghajtócsappal
Limited angle rotary
actuatorLimited angle rotary
actuator
Parallel
piston rotary
actuator
??? ???
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Big pictures
End of normal presentation
Beginning of big pictures
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Hydraulic cylinders
Cylinder types: plunger
smaller force, better efficiency, axial support is necessary
but cylinder does not have to be so good quality
Without inner buffer With inner buffer (pilot piston)
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Hydraulic cylinders
Cylinder types: piston, single acting, pressing-cylinder
Spring
inside outside
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Hydraulic cylinders
Cylinder types: piston, single acting, puller
Spring
inside outside
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Hydraulic cylinders
Cylinder types: piston, double acting
Velocity is different
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Hydraulic cylinders
Cylinder types: piston, double acting
Piston rod on both side
Velocity is the same in both directions
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Hydraulic cylinders
Cylinder types: piston, double acting
Piston rod on both side
Velocity is different in the two directions depending on
cross section ratio of the rods
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Hydraulic cylinders
Cylinder types: double acting piston, tandem
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Hydraulic cylinders
Cylinder types: single acting, fast moving
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Hydraulic cylinders
Cylinder types: double acting, fast moving
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Hydraulic cylinders
Cylinder types: telescopic, single acting
Large working paths
or limited space
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Hydraulic cylinders
Cylinder types: telescopic, double acting
Large working paths
or limited space
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Hydraulic cylinders
Checking for buckling:
Euler’s
cases
Picture
Free buckling length
Manner of end fixing
Note
1. Case
One end freeOne end fixed
Or trunnion at end
mounting style mounting style mounting style
2. Case
Two ends pivoted and guided
3. Case
One end guided and pivoted, other end
fixed
4. Case
Two ends fixed and guided
mounting style
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Hydraulic cylinders
Cushioning of cylinders:
1. Piston
2. Cushion nose
3. Cylinder cap
4. Stroke volume
5. Cushion orifice
6. Throttle
7. Cushion adjustment screw
8. Mother
9. Non-return valve
10. Gas valve
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Rotary hydraulic actuators
Parallel piston rotary
actuator
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Rotary hydraulic actuators
???
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Rotary hydraulic actuators
Rack-and-pinion piston-type rotary actuator:
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Rotary hydraulic actuatorsLimited angle rotary actuator:
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Rotary hydraulic actuators
Limited angle rotary actuator:
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Rotary hydraulic actuators
Helix actuator: