A four-bar linkage, also called a four-bar, is the simplest movable closed chain linkage. It consists of four bodies, called bars or links, connected in a loop by four joints. Generally, the joints are configured so the links move in parallel planes, and the assembly is called a planar four-bar linkage. If the linkage has four hinged joints with axes angled to intersect in a single point, then the links move on concentric spheres and the assembly is called a spherical four-bar linkage. Bennett's linkage is a spatial four-bar linkage with hinged joints that have their axes angled in a particular way that makes the system movable.[
| Introduction to Mechanisms Yi Zhang
Stephannie Behrens Table of Contents 1. Linkage mechanisms 1.1 Four bar linkages Linkage are composed of links and lower pairs. The simplest closed-loop linkage is the four-bar linkage, which has three moving links, one fixed link and four pin joints. A linkage with one link fixed is a mechanism. You can load the following four-bar linkage into SimDesign from the file mechanisms/fourbar.sim. This mechanism has three moving links. Two of them are pinned to the frame, which is not shown in this picture. In SimDesign, you can nail these two links to the background. How many degrees of freedom (DOF) does this mechanism have? If it has one, you can impose one constraint on the mechanism for it to have definite motion. For example, you can pull the nailed link on the left (making it the input link) and it will turn around the nail. The right link (now the output link) will make an oscillating motion. Suppose you put a pen on the top of the triangle-shaped link. (The triangle is also called a link. A link is not necessarily a simple line-shaped body). The pen will trace its path. The triangle-shaped link connects the two moving pivots and couples the input and the output motion; hence, it is called coupler. Linkages have different functions. The functions are classified depending...
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