Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
25-Jan-19
1
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
2
25-Jan-19
2
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.
3
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.
4
25-Jan-19
3
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.
5
Suril V. Shah
Dimensional Synthesis
Determination of the proportions (lengths) of the links necessary to accomplish the desired motions
Path GenerationMotion GenerationFunction Generation
6
25-Jan-19
4
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
7
Suril V. Shah
Motion Generation
8
25-Jan-19
5
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
9
Suril V. Shah
The toggle positions are determined by the colinearity of two of the moving links.
Toggle position
10
25-Jan-19
6
Suril V. Shah
Toggle position
11
Suril V. Shah
Application
12
25-Jan-19
7
Suril V. Shah
The angle between the output link and the coupler
Transmission angle
13
• 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).
14
25-Jan-19
8
15
Rocker output (pure rotation)
Suril V. Shah
Motion of a rocker
16
Design a fourbar Grashof crank-rocker to give θ of rocker rotationwith equal time forward and back,from a constant speed motor input
25-Jan-19
9
Suril V. Shah
Motion of a rocker
17
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
25-Jan-19
10
Suril V. Shah
Control of line CD through rocker
19
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
20
Design a fourbar Grashof to move link CD from position C1D1 to C2D2
25-Jan-19
11
Suril V. Shah25-Jan-19 21IIT Jodhpur
22
Coupler output (complex motion)
25-Jan-19
12
Suril V. Shah
Control of line CD through Coupler
23
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
24
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
25-Jan-19
13
Suril V. Shah25-Jan-19 25IIT Jodhpur
Suril V. Shah
Control of line CD through Coupler
26
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
25-Jan-19
14
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.
25-Jan-19
15
Thank youNext Class: 3 Position Dimensional Synthesis
25-Jan-19 IIT Jodhpur 29