1. MECHANICAL TECHNOLOGY MECHANISMS – 4 BAR LINKAGE
The software program that created the simulations shown above is available for FREE at the following website:
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2. A 4-bar linkage mechanism has a crank that rotates at a constant angular speed. The crank is connected to the coupler which is connected to the follower. The frame does not move.
coupler
crank
follower
frame
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3. 4-06 Notice that the crank rotates at a constant angular speed.
In other words, it moves around in a complete circle in a fixed constant amount of time. The animation below shows the position of the crank every 5 degrees of rotation.
The coupler provides a constant distance between the movable ends of the crank and the follower.
In this example design, the follower does not move at a constant rate.
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4. There are many possible variations in the design of a 4-bar linkage mechanism. Four examples are given in the diagrams below.
coupler
crank
follower
frame
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5. 4-06 A Grashof linkage is a planar four-bar linkage with
S + L < P + Q
where S = length of the shortest link
L = length of longest link
P and Q are the lengths of the two remaining links.
1. Crank-Rocker : a Grashof linkage where the shortest link is the input link (crank).
2. Double-Rocker: a Grashof linkage where the shortest link is the floating link (coupler).
3. Rocker-Crank : a Grashof linkage where the shortest link is the output link (follower).
4. Crank-Crank : a Grashof linkage where the shortest link is the ground link (frame).
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6. 4-06 The mechanism below is a crank-rocker. crank 90 S coupler 180 P
follower Q
frame L
S + L < P + Q
<
275 < 310
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7. This mechanism is a crank-rocker
This mechanism is a crank-rocker. Notice that the crank is the shortest link.
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8. 4-06 The mechanism below is a crank-crank. crank 140 P coupler 180 L
follower Q
frame S
S + L < P + Q
<
260 < 270
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9. 4-06 This mechanism is a crank-crank.
Notice that the frame is the shortest link.
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10. 4-06 This mechanism is a double rocker.
Notice that the coupler is the shortest link.
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11. HOMEWORK: Design AND DRAW one example of each of the following 4 types of Grashof linkages. The drawings must be NEAT and PRECISE.
A Grashof linkage is a planar four-bar linkage with
S + L < P + Q where S = length of the shortest link
L = length of longest link
P and Q are the lengths of the two remaining links.
1. Crank-Rocker : a Grashof linkage where the shortest link is the input link (crank).
2. Double-Rocker: a Grashof linkage where the shortest link is the floating link (coupler).
3. Rocker-Crank : a Grashof linkage where the shortest link is the output link (follower).
4. Crank-Crank : a Grashof linkage where the shortest link is the ground link (frame).
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4-06