Mechanism

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Mechanism
Machines are mechanical devices used to
accomplish work. A mechanism is a heart of a
machine. It is the mechanical portion of the
machine that has the function of transferring
motion and forces from a power source to an
output. Mechanism is a system of rigid elements
(linkages) arranged and connected to transmit
motion in a predetermined fashion. Mechanism
consists of linkages and joints.
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Example of Mechanism
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Example of Mechanisms
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Example of Mechanisms
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Example of Mechanisms
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Example of Mechanisms
Extension position
Flexed position
Six-bar linkage prosthetic knee mechanism
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Four-Bar Linkage
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Four-Bar Linkage Categories
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Four-Bar Linkage Categories
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4-Bar mechanisms
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4-Bar mechanisms
S l gt p q
4 double rocker mechanisms
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The Slider-Crank Mechanism
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The Slider-Crank Mechanism
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Slider-Crank Mechanism - Inversion
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Mechanism Categories
Function Generation Mechanisms A function
generator is a linkage in which the relative
motion between links connected to the ground is
of interest.
A four-bar hand actuated wheelchair brake
mechanism
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Mechanism Categories
Function Generation Mechanisms
A four-bar drive linkage for a lawn sprinkler
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Mechanism Categories
Motion Generation Mechanisms In motion
generation, the entire motion of the coupler link
is of interest (rigid body guidance).
New Rollerblade brake system
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Mechanism Categories
Motion Generation Mechanisms
Four-bar automobile hood linkage design
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Mechanism Categories
Path Generation Mechanisms In path generation, we
are concerned only with the path of a tracer
point and not with the motion (rotation) of the
coupler link.
Crane straight line motion
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Primary Joints
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Higher Order Joints
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Motion Generation Mechanisms
Moving a storage bin from an accessible position
to a stored position
Rotating a monitor into a storage position
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Motion Generation Mechanisms
Moving a trash pan from the floor up over a trash
bin and into a dump position
Lifting a boat out of water
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Function Generation MechanismsGraphical Solution
Two position synthesis Design a four-bar crank
and rocker mechanism to give 45o of rocker
rotation with equal time forward and back, from a
constant speed motor input.
1 Draw the rocker O4B in both extreme
positions, B1and B2 in any convenient location
with angle ?4 45o. 2 select a convenient
point O2 on line B1B2 extended. 3 Bisect line
B1B2 , and draw a circle with that radius about
O2. 4 Label the two intersection of the circle
with B1B2 extended, A1 and A2. 5 Measure O2A
(crank, link2) and AB (coupler, link3).
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Function Generation MechanismsGraphical Solution
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Crank-Rocker Mechanism

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Motion Generation MechanismsGraphical Solution
Two position synthesis C1D1 and C2D2

1. Draw the link CD in its two desired positions,
   C1D1 and C2D2
2. Connect C1 to C2 and D1 to D2.
3. Draw two lines perpendicular to C1 C2 and D1D2
   at the midpoint (midnormals)
4. Select two fixed pivot points, O2 and O4,
   anywhere on the two midnormals.

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Motion Generation MechanismsGraphical Solution
Two position synthesis (coupler output) C1D1
and C2D2
The rigid body to be moved from position 1 to 2
is secured to link 3.
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Motion Generation MechanismsGraphical Solution
Two position synthesis (coupler output) with Dyad
added.
1 Select any point B1 on link O2C1. Locate
B2. 2 Choose O6 anywhere on B1B2 extension. 3
Draw a circle from O6 with radius B1B2/ 2. Mark
the intersection with B1B2 extension as A1 and A2.
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Motion Generation MechanismsGraphical Solution
Two position synthesis (coupler output) with Dyad
added.
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Motion Generation MechanismsGraphical Solution
Two position synthesis (rocker output) C1D1 and
C2D2
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2 Position Motion rocker output


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Motion Generation MechanismsGraphical Solution
Three position synthesis C1D1, C2D2 and C3D3

1. Draw the link CD in its three desired positions.
2. Follow the same procedure,draw construction
   lines, C1C2, C1C3 and C2C3. Same for point D.
3. Draw three midnormals for each point.
4. Locate the intersection of the three midnormal,
   O2 and O4 are the two fixed pivot points.

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Motion Generation MechanismsGraphical Solution
Three position synthesis C1D1, C2D2 and C3D3
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3 Position Motion
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3 Position Motion
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3 Position Motion
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Slider-Crank Mechanism
The mechanism has a stroke B1B2 equal twice the
crank length r2. Locations B1 and B2 are called
the extreme positions (limiting) of the slider
In-line slider crank mechanism
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Slider-Crank Mechanism
Offset slider-crank mechanism
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Straight line Mechanisms
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Straight Line Mechanism
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Scotch Yoke Mechanism
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Geneva Mechanism
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Linear Geneva Mechanism
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Ratchet Mechanism
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Straight Beam Walking Mechanism
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(No Transcript)
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Roller and Flat Follower Cams
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Cylindrical Cam Mechanism
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Gears Rack and Pinion
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Gears
Worm Gear Sets
Bevel gears
Planetary Gear set
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V-8 Engine
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Type of Motion and Mechanisms
Most power sources that are readily available
today are either of the pure rotational motion
type, such as electric motor or hand crank, or of
the pure translational type, such as pneumatic or
hydraulic cylinder.
Translation to Translation
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Type of Motion and Mechanisms
Rotational to Rotational
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Type of Motion and Mechanisms
Rotation to Translation
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References

• Mechanism Design, Analysis and Synthesis by
  Erdman and sander, fourth edition, Prentice-Hall,
  2001,
• Machines and Mechanisms by Uicker, Pennock and
  Shigley, third edition, Oxford, 2002.
• Machines and Mechanisms by Myszka, Prentice-Hall,
  1999