Four-bar linkage

What is it?

4 Bar Linkages



The four bar linkage is a mechanism that lies in a plane and consists of four bars connected by joints that allow rotation only in the plane of the mechanism.
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If you take four links and connect them with four joints, you get a simple four bar mechanism. To get it working, you just need to fix one link. This fixed link is usually called link 1. You then number the rest of the links 2-4. Link 2 is usually the input link, which is the link that you move to power your device. Either links 3 and 4 can be the output link. Depending on the lengths of the links, and what you consider the input and output, you get different types of motion from the same 4 bar mechanism.

http://beam.berkeley.edu/sites/default/files/Kinetic_Sculptures_Lesson.pdf

You can use paper and paper fasteners or this simulation to investigate the possibilities of motion for the other three links. Play with your model by changing the length of links h and b and experiencing the motions that are possible.

The link OA is the input crank and link CB the output crank. Angle θ is the input angle.



Here's a great animation of a Theo Jansen's four-bar mechanism from www.mekanizmalar.com..

And another demonstration by Sándor Kabai at Wolfram.

And here is a Jansen Klann Linkage comparison from www.mechanicalspider.com.