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[¦fȯr ¦bär ′liŋk·ij]
(mechanical engineering)
A plane linkage consisting of four links pinned tail to head in a closed loop with lower, or closed, joints.

a plane mechanism consisting of four links that form rotating kinematic pairs. A four-bar linkage (Figure 1) consists of a fixed link (0, the base), two rotating links (1 and 3), and a connecting link (2), which is also called a connecting rod or coupler. A rotating link is called a crank if it can undergo a complete rotation with respect to the axis of rotation; it is called a rocker if it can undergo only part of a rotation.

Figure 1

Depending on the type of rotating links present, four-bar linkages are subdivided into crank-and-rocker, draglink, and double-rocker types. A crank-and-rocker mechanism is used to convert the constant rotation of the crank into the reciprocal motion of the rocker. In manufacturing machinery, the crank is set in motion by a main shaft, and a working member that performs a given production operation is connected to the rocker. A drag-link mechanism converts uniform rotation into nonuniform rotation in a single direction; it is used in machines where the working member, while moving in a single direction, must have a velocity that significantly exceeds the average velocity on some segment. Double-rocker linkages are used chiefly in instruments to provide a mechanical reproduction of a given function, such as y = log x. Four-bar linkages are also used to reproduce the motion of a point along a given curve; for example, the Chebyshev parallel motion can be used to approximate a segment of a straight line.

N. I. LEVITSKII

References in periodicals archive ?
Then, the robot radius HI can swing quickly through the parallel four-bar linkage GHIJ.
A planar four-bar linkage with coupler extension was selected as the basic design.
The hinges may include hinges based on a three-bar linkage, hinges based on a four-bar linkage, hinges with slotted members, hinges formed from flexible support structures, and hinges based on flexible housing structures.
What you can see here is this four-bar linkage mechanism.
The app is based entirety around the four-bar linkage, which is something that every mechanical engineer learns about in college," says Kevin Loewke, co-founder and CEO of Cellogy and creator of the game.
Four-bar linkage prosthetic knee mechanism: Kinematics, alignment and prescription criteria.
In our prototype, we used a crossed four-bar linkage system as a rigid adaptive interface.
The L48 offers maximum lift height of 9 feet 7 inches and utilizes a four-bar linkage system to facilitate its 45-degree bucket rollback and dump angle.
To correct this problem we stayed with our four-bar linkage design," said Isaac Kaminer.
A careful ATM might produce the double curvature entirely by hand, but I decided to use a double four-bar linkage like that described by Sasian in an earlier article (S&T: August 1988, page 198).

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