Tutorial 6: Mechanism Fundermentals
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Transcript of Tutorial 6: Mechanism Fundermentals
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Tutorial 6:Mechanism FundermentalsZhengjian, XUOct 15, 2008
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Fundermentals:Design of Mechinary Mobility: Degree of Freedom (DOF), In 2D mechanism every rigid body has 3 DOF. Link: A Rigid body in the mechinary system Joint (Kinematic Pair) Connect between different Links, the joints can restrain some DOF
of the links.
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Analysis of the mobility (DOF) 2D mechanism
3D mechanism
Where: M is the DOF of the mechanism N is number of links including the ground J1 is number of 1 DOF joints J2 is number of 2 DOF joints
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Examples
(b) N=3 J1=2 J2=1 M= 1
(a) N=6 J1=7 J2=1 M=0
(d) N=7 J1=7 J2= 1 M=3
(c) N=4 J1=4 J2=0 M=1
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Classification of four-bar linkage Grashof condition
PQSL Where: L: length of shortest link S: length of longest link P: length of one remaining link Q: the length of another remaining link
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Classification of four-bar linkage
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Position analysis of 4-bar linkage: graphical method
O2O4
A
2=45°
B1
B2
3
4
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Position analysis of 4-bar linkage: graphical method
O2
A
2=45°
B1
B2
3
4
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Position analysis for Crank-Rocker mechanism The calculation of out-put angle
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Transmission angle
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Example Given L1=12 ,L2=4, L3=8, L4=9; (1) Calculate range of output angle (2) Calculate range of the transmission angle
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(1) , S=4, L=11, Q=9, P=8; therefore S+L<Q+P
(2) a=4, b=9, c=8, d=11
A
O1
B
O2
A
B
O1 O2
(2.1)
(2.2)
cdabdc
2)(cos222
4
cdabdc
2)(cos222
4
4
4
d
c
a
b
a
bc
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Transmission angle
bcabbc
trans 2)(cos222
A
O1
B
O2
AO1
B
O2
(3.1)
(3.2)
bcadcb
trans 2)(cos222
Two limited status:
trans
trans
a
b
b
a
c
d
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Four-Bar slider-crank mechanismThe output range:
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Inverted slider-crank mechanism