Mécanismes à barres trajectoires et conception.pdf


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Problem 6.2:
Design a double rocker, four-bar linkage so that the base link is 4-in and the output rocker is 2-in
long. The input link turns counterclockwise 40˚ when the output link turns counterclockwise
through 80˚. The initial angle for the input link is 20˚ counterclockwise from the horizontal, and the
initial angle for the output link is 25˚. The geometry is indicated in the figure.
B2

A2
60˚
O2

B1

80˚

A1
O4

20˚

25˚

Solution
Invert the motion and solve the problem graphically. Draw a line from O2 to B2 and rotate it
clockwise 60˚ to locate the position of B'2 . Draw the perpendicular bisector of B'2 B1 and locate the
intersection of that line with the line O2 A1 . This will locate A1 . The solution is given in the first
figure. Measure the lengths os 02 A1 and A1 B1 . This gives the linkage shown in the second figure.
The link lengths are:
r1 = 4"
r2 = 2.77"
r3 = 3.21"
r4 = 2"

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