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Tutorial 6: Mechanism Fundermentals. Zhengjian, XU Oct 15, 2008. 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)
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Tutorial 6:Mechanism Fundermentals Zhengjian, XU Oct 15, 2008
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.
Analysis of the mobility (DOF) • 2D 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 • 3D mechanism
Examples • N=6 • J1=7 • J2=1 • M=0 (b) N=3 J1=2 J2=1 M= 1 (c) N=4 J1=4 J2=0 M=1 (d) N=7 J1=7 J2= 1 M=3
Classification of four-bar linkage • Grashof condition Where: L: length of shortest link S: length of longest link P: length of one remaining link Q: the length of another remaining link
A 3 4 2=45° O4 O2 Position analysis of 4-bar linkage: graphical method B1 B2
A 2=45° O2 4 3 Position analysis of 4-bar linkage: graphical method B1 B2
Position analysis for Crank-Rocker mechanism • The calculation of out-put angle
Example • Given L1=12 ,L2=4, L3=8, L4=9; • (1) Calculate range of output angle • (2) Calculate range of the transmission angle
(1) , S=4, L=11, Q=9, P=8; therefore S+L<Q+P (2) a=4, b=9, c=8, d=11 B b c O1 (2.1) a O2 A B (2.2) b A c a d O1 O2
Transmission angle Two limited status: B b (3.1) A O1 a O2 B (3.2) b c a O1 A d O2
Four-Bar slider-crank mechanism The output range: