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Suril V. Shah
ME 222: Kinematics of Machines and Mechanisms
[L11] Synthesis Part 1
25-Jan-19 1IIT Jodhpur
Suril V. Shah
Overview
SynthesisFunction, path and motion generationLimiting conditionDimensional synthesis
• Two position synthesis
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Suril V. Shah
Design of mechanisms
Two fold objectivesSynthesis of mechanisms in order to accomplish desired motions or tasks
Analysis of mechanisms in order to determine their rigid-body dynamic behavior.
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Suril V. Shah
Number Synthesis
Determination of the number and order of links and joints necessary to produce motion of a particular DOF
4-link,6-link,8-link, etc.
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Suril V. Shah
Type Synthesis
Refers to the definition of the proper type of mechanism best suited to the problem, e.g.,
Fourbar linkage,Slider crank,Cam-follower, etc.
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Suril V. Shah
Dimensional Synthesis
Determination of the proportions (lengths) of the links necessary to accomplish the desired motions
Path GenerationMotion GenerationFunction Generation
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Suril V. Shah
MOTION GENERATION The control of a line in the plane such that it assumes some prescribed set of sequential positions.
PATH GENERATION The control of a point in the plane such that it follows some prescribed path.
FUNCTION GENERATION The correlation of an input motion with an output motion in a mechanism.
Dimensional Synthesis
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Suril V. Shah
Motion Generation
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Suril V. Shah
Limiting Conditions
Once a potential solution is found, it must be evaluated for its quality.
Some simple and quick evaluations.Toggle/ Stationary positionTransmission angle
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Suril V. Shah
The toggle positions are determined by the colinearity of two of the moving links.
Toggle position
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Suril V. Shah
Toggle position
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Application
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Suril V. Shah
The angle between the output link and the coupler
Transmission angle
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• Optimum value: for the transmission angle is 90°. • Minimum value: above 40° to promote smooth running and good force transmission
Suril V. Shah
Two-Position Dimensional Synthesis
Rocker output (pure rotation)
Coupler output (complex motion).
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Rocker output (pure rotation)
Suril V. Shah
Motion of a rocker
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Design a fourbar Grashof crank-rocker to give θ of rocker rotationwith equal time forward and back,from a constant speed motor input
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Suril V. Shah
Motion of a rocker
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Design a fourbar Grashof crank-rocker to give θ of rocker rotationwith equal time forward and back,from a constant speed motor input
B2
O4
B1
O2A1
Suril V. Shah25-Jan-19 18IIT Jodhpur
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Suril V. Shah
Control of line CD through rocker
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Design a fourbar Grashof to move link CD from position C1D1 to C2D2
D1
C1
D2
C2
O4
O2 A2 B1 B2
Suril V. Shah
Control of line CD through rocker
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Design a fourbar Grashof to move link CD from position C1D1 to C2D2
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Suril V. Shah25-Jan-19 21IIT Jodhpur
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Coupler output (complex motion)
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Suril V. Shah
Control of line CD through Coupler
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Design a fourbar linkage to move the link CD shown from position C1D1 to C2D2 (with moving pivots at C and D).
Suril V. Shah
Control of line CD through Coupler
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Design a fourbar linkage to move the link CD shown from position C1D1 to C2D2 (with moving pivots at C and D).
D1
C1
D2
C2
O4
O2
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Suril V. Shah25-Jan-19 25IIT Jodhpur
Suril V. Shah
Control of line CD through Coupler
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Design a fourbar linkage to move the link CD shown from position C1D1 to C2D2 (with moving pivots at C and D).
D1
C1
D2
C2
O4
O2
O2A1B1 B2
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Suril V. Shah25-Jan-19 27IIT Jodhpur
Suril V. Shah
Design of A Bicycle Storage
A student wishes to design a four-bar linkage that will store a bicycle above his bed. Two positions of the storage rack are shown in Fig. 1. Find acceptable ground and moving pivots for this design objective.
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Thank youNext Class: 3 Position Dimensional Synthesis
25-Jan-19 IIT Jodhpur 29