tutorial 6: mechanism...
TRANSCRIPT
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
� 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
Classification of four-bar linkage
� Grashof condition
PQSL +≤+
Where: L: length of shortest linkS: length of longest link
P: length of one remaining linkQ: the length of another remaining link
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
A
O1
B
O2
A
B
O1 O2
(2.1)
(2.2)
cd
abdc
2
)(cos
222
4
+−+=θ
cd
abdc
2
)(cos
222
4
−−+=θ
4θ
4θ
d
c
a
b
a
b
c
Transmission angle
bc
abbc
trans
2
)(cos
222+−+
=θ
AO1
B
O2
AO1
B
O2
(3.1)
(3.2)
bc
adcbtrans
2
)(cos
222−−+
=θ
Two limited status:
transθ
transθ
a
b
b
a
c
d