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The software program that created the simulations shown above is available for FREE at the following website:http://www.edu-ctr.pref.kanagawa.jp/LinkWeb/index_e.htm

MECHANICAL TECHNOLOGYMECHANISMS – 4 BAR LINKAGE

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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.

crank

coupler

follower

frame

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. IOT

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There are many possible variations in the design of a 4-bar linkage mechanism. Four examples are given in the diagrams below.

crank

coupler

follo

wer

frame

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A Grashof linkage is a planar four-bar linkage withS + L < P + Qwhere 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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The mechanism below is a crank-rocker. crank 90 S coupler 180 P follower 130 Q frame 185 L

S + L < P + Q 90 + 185 < 180 + 130 275 < 310

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This mechanism is a crank-rocker. Notice that the crank is the shortest link.

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The mechanism below is a crank-crank. crank 140 P coupler 180 L follower 130 Q frame 80 S

S + L < P + Q 80 + 180 < 140 + 130 260 < 270

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This mechanism is a crank-crank.Notice that the frame is the shortest link.

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This mechanism is a double rocker.Notice that the coupler is the shortest link.

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A Grashof linkage is a planar four-bar linkage withS + 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).

HOMEWORK: Design AND DRAW one example of each of the following 4 types of Grashof linkages. The drawings must be NEAT and PRECISE.