four-bar linkage

[¦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.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Four-Bar Linkage

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

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References in periodicals archive

The equation of closure for the four-bar linkage in its first position will be

Dimensional synthesis of a planar five-bar mechanism for motion between two extreme positions

where: [chi](s) is output angle or transmission function; P = [+ or -][r.sub.3]/[r.sub.5] is gear ratio; [phi](s),[psi](s) is transmission functions of the base four-bar linkage.

Type Synthesis and Analysis of Geared Linkages with Linear Actuation

Four-bar linkage mechanism has been used for compression springs and varying arch angle.

Adaptive Foot in Lower-Limb Prostheses

What you can see here is this four-bar linkage mechanism.

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Four-bar linkage prosthetic knee mechanism: Kinematics, alignment and prescription criteria.

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In our prototype, we used a crossed four-bar linkage system as a rigid adaptive interface.

Crossed four-bar mechanism for improved prosthetic grasp

The four-bar linkage moves it both up and back, providing low-angle access.

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