Transcript DRIVE SYSTEM ENT 271

HYDRAULICS & PNEUMATICS
Actuators
Presented by: Dr. Abootorabi
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Hydraulic Cylinders
 Actuators are the components used in a hydraulic system to provide
power to a required work location.
 Cylinders are the hydraulic system components that convert fluid
pressure and flow into linear mechanical force and movement.
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Hydraulic Cylinders
 A basic cylinder consists of:

Piston

Piston rod

Barrel
 The piston forms sealed, variable-volume chambers in the
cylinder.
 System fluid forced into the chambers, drives the piston and
rod assembly.
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Hydraulic Cylinders
 Seals prevent leakage between:

Piston and cylinder barrel

Piston rod and head

Barrel and its end pieces
 Wiper seal, or scraper, prevents dirt and water from entering the
cylinder during rod retraction.
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Hydraulic Cylinders
 Various seals are used in a cylinder
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Hydraulic Cylinders
 Various seals are used in a cylinder
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Hydraulic Cylinders
 Various seals are used in a cylinder
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Hydraulic Cylinders
 Cylinders are typically classified by operating principle:

Single-acting

Double-acting
Single-acting
Double-acting
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Hydraulic Cylinders
 Single-acting
cylinder exert force either on extension or
retraction:

They require an outside force to complete the second
motion (either by a spring or by the weight load).
 Double-acting cylinder generate force during both extension and
retraction:

Directional control valve alternately directs fluid to opposite
sides of the piston

Force output varies between extension and retraction
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Hydraulic Cylinders
 Single-acting cylinder
 hydraulic ram (or plunger cylinder): piston and rod form one unit
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Hydraulic Cylinders
 Single-acting cylinder
Scissor lifting table:
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Hydraulic Cylinders
 Double-acting cylinder
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Hydraulic Cylinders
 Double-acting cylinder types:
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Hydraulic Cylinders
 Double-acting cylinder types:
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Hydraulic Cylinders
 Effective piston area is reduced on retraction due to the rod
cross section.
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Hydraulic Cylinders
 Telescoping cylinders are available for applications requiring long
extension distances:

Rod is made up of several tubes of varying size nested inside
of the barrel

Each tube extends, producing a rod longer than the cylinder
barrel

Typical example is the actuator that raises the box on a dump
truck
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Hydraulic Cylinders
 Telescoping cylinders:

The maximum force
is at the collapsed
position

The
increase
speed
will
at
each
stage, but will not
allow much force
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Hydraulic Cylinders
 Cylinders often use hydraulic
cushions (to brake high stroke
speeds):

Provide
a
controlled
approach to the end of the
stroke

Reduces the shock of the
impact
as
the
piston
contacts the cylinder head
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Hydraulic Cylinders
 Cylinders with end position cushioning:

Cushioning is not required
for speeds of v<6 m/min.

This type of end position
cushioning is used for
stroke speed between 6
m/min and 20 m/min. At
higher speed, additional
cushioning
or
braking
devices must be used.
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Hydraulic Cylinders
 A variety of mounting configurations are used to attach the cylinder
body and rod end to machinery:


Fixed centerline

Fixed noncenterline

Pivoting centerline
Expected cylinder loading is the major factor in the selection of the
mounting style.
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Hydraulic Cylinders
 Head-end (Fixed centerline) flange mount
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Hydraulic Cylinders
 Fixed-noncenterline mount
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Hydraulic Cylinders
 Pivoting-centerline, clevis mount
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Hydraulic Cylinders
 Pivoting-centerline, trunnion mount
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Hydraulic Cylinders
 Types of mounting:
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Hydraulic Cylinders
 The force generated by a cylinder is calculated by multiplying
the effective area of the piston by the system pressure.
F=p.A
 By
consideration
of
mechanical efficiency:
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Hydraulic Cylinders
 Cylinder characteristics
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 Cylinder characteristics
Hydraulic Cylinders
dp: cylinder dia.
Ap: cylinder area
dST: piston rod dia.
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Hydraulic Cylinders
 Speed at which the cylinder extends or retracts is determined
by:

Flow Rate (Q)

Effective Area (A)
Q [m3/s] = A [m2] X  [m/s]
Effective area
Piston velocity
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Hydraulic Cylinders
 Buckling resistance
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Hydraulic Cylinders
 Selecting a cylinder (Example)
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Hydraulic Cylinders
 Selecting a cylinder (Example)
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Hydraulic Cylinders
 Selecting a cylinder (Example)
Buckling resistance diagram:
Reference: Festo Didactic Hydraulic
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Hydraulic Cylinders
 Selecting a cylinder (Example)
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Hydraulic Cylinders
 Selecting a cylinder (Example)
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Hydraulic Cylinders
 Selecting a cylinder (Example)
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Hydraulic Cylinders
 Hydraulic cylinder manufacturers provide detailed specifications and
basic factors such as:

Bore

Stroke

Pressure rating

Other details, such as service rating, rod end configurations,
and dimensions
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Hydraulic Cylinders
 Typical manufacturer’s catalog page
Bailey International Corporation
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Limited-Rotation Hydraulic Actuators
 Limited-rotation devices (swivel drive) are actuators with an output
shaft that typically applies torque through approximately 360° of
rotation.
 Models are available that are limited to less than one revolution,
while others may produce several revolutions.
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Limited-Rotation Hydraulic Actuators
 Most common designs of limited-rotation actuators are:

Rack-and-pinion

Vane

Helical piston and rod
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Limited-Rotation Hydraulic Actuators
 Rack-and-pinion limited rotation actuator
Here maximum
angle
may
be
larger than 360°.
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Limited-Rotation Hydraulic Actuators
 Vane limited-rotation actuator
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Limited-Rotation Hydraulic Actuators
 Helical piston and rod limited-rotation actuator
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Limited-Rotation Hydraulic Actuators
 Limited-rotation actuators are used to perform a number of
functions in a variety of industrial situations:

Indexing devices on machine tools

Clamping of workpieces

Operation of large valves
 Limited-rotation
actuators
are used in this robotic arm:
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Hydraulic Motors
 Hydraulic motors are called rotary actuators.
 They convert fluid pressure and flow into torque and rotational
movement.
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Hydraulic Motors
 System fluid enters the housing and applies pressure to the
rotating internal parts.
 This, in turn, moves the power output shaft and applies torque
to rotate a load.
 Primary parts that produce the rotating motion in most
hydraulic motors are either:

Gears

Vanes

Pistons
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Hydraulic Motors
 The external gear hydraulic motor is the most common and simplest
of the basic motor types:

Unbalanced load on the bearings
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Hydraulic Motors
 The most common internal gear motor has a gerotor design
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Hydraulic Motors
 Basic vane motor (unbalanced)
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Hydraulic Motors
 A basic, balanced vane motor
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Hydraulic Motors
 Axial piston motors are
available
in
two
configurations:

Inline

Bent axis
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Hydraulic Motors
 Inline piston motor
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Hydraulic Motors
 Inline piston motor
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Hydraulic Motors
 Bent-axis piston motor
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Hydraulic Motors
 Radial piston motor
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Hydraulic Motors
 Hydraulic motors may be incorporated into circuits using series or
parallel connections:

Series circuits: total system pressure is determined by adding
the loads placed on each unit

Parallel circuits: each motor receives full system pressure;
loads must be matched or equal flow supplied to each motor if
constant speed is desired from each unit
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Hydraulic Motors
 Motors in series
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Hydraulic Motors
 Motors in parallel
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Hydraulic Motors
 Motors in parallel with flow control
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Hydraulic Motors
 Hydraulic motor formulas:
Power:
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The end.
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