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Linkages are designed to convert input motion into a different output motion. A linkage typically consists of a series of rigid links. Each link has one or more joints which rotate freely, connecting the links together. Typically, one link is fixed and cannot move and one link is driven in some input motion. Linkages are a fundamental part of machine design because of their ability to create such a wide variety of output motions and their ability to alter the path, velocity, and acceleration of the input. Very precise and somewhat complicated motions can be designed using a simple linkage design. Linkage motions are extremely repeatable.  
 
Linkages are all around us in the world. A simple linkage found on a pair of vice grips is shown here. 

[[Image:Linkage1.JPG|center]]

The second picture shows the linkage at the other end of its motion. This is a linkage with four links; each link has two joints and they are connected in a closed system. This is one of the most common types of linkage system. 

[[Image:Linkage2.JPG|center]] 

The simplest and one of the most common linkage types is the four-bar linkage. This is a closed-loop linkage system that can provide a wide variety of motion types. The most basic type of four-bar linkage is one in which the links are equal length and parallel to each other. 
 
By modifying the lengths of the links in the linkage, it is possible to create very different motions. This is extremely useful for robot design. Imagine needing a robot that can pick up a cup of water, lift it up without spilling, and then pour it out once it reaches over the height of a bucket. This motion is possible by using a modified linkage. 
Try playing with linkage lengths and experiment to find the optimal motion for your application.
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== See Also ==
*[[Term - Four-Bar Linkage|Four-Bar Linkage]]
*[[Term - Joint|Joint]]
*[[Term - Mechanism|Mechanism]]