1. Velocities by Instantaneous Axis
Lecture Notes
Reference: Elements of
Mechanism by V.L. Doughtie
and W.H. James
2. Floating Link
A floating link is simply a link that does not
limited to pure rotation or pure translation.
The cranks of a machine rotate or oscillate about
their respective fixed axes, Q, and the floating link
(i.e., connecting rod) rotates with an absolute
angular velocity about an instantaneous axis of
velocity.
Reference: Elements of
Mechanism by V.L. Doughtie
and W.H. James
3. Instantaneous Angular Velocity of a
Floating Link
The instantaneous axis of velocity, Q, may be
found by locating the intersection of the lines
perpendicular to the point interest in the
floating link.
Reference: Elements of
Mechanism by V.L. Doughtie
and W.H. James
4. Illustration:
The method for obtaining the
instantaneous angular velocity
is shown below.
In the figure, the
instantaneous linear velocity
of crank is 15 ft/sec. AB = 15
in, BC = 55 in, CD = 50 in.
Calculate velocity C and the
angular velocity of the floating
link AC, using instantaneous
axis velocity method.
Reference: Elements of
Mechanism by V.L. Doughtie
and W.H. James
6. Example 1:
In the link shown below, the instantaneous angular velocity of the crank
AB is 100 rpm counter clockwise. AB = 25 in, 60 deg with respect to the
horizontal, BC = 40 in, CD = 20 in, CE is 70 deg with respect to the
horizontal. Calculate the velocity B, C, D in the floating link using
instantaneous axis velocity method.
Reference: Elements of
Mechanism by V.L. Doughtie
and W.H. James
8. Example 2:
In the figure, the instantaneous angular velocity of the crank is 100 rpm.
Find the linear velocity of E using instantaneous axis velocity method. AB =
20 in, BCD = 60 in, DE = 60 in.
Reference: Elements of
Mechanism by V.L. Doughtie
and W.H. James
