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Suril V. Shah

ME 222: Kinematics of Machines and Mechanisms

[L11] Synthesis Part 1

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Suril V. Shah

Overview

SynthesisFunction, path and motion generationLimiting conditionDimensional synthesis

• Two position synthesis

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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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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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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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Dimensional Synthesis

Determination of the proportions (lengths) of the links necessary to accomplish the desired motions

Path GenerationMotion GenerationFunction Generation

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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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Motion Generation

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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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The toggle positions are determined by the colinearity of two of the moving links.

Toggle position

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Toggle position

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Application

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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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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

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