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In the study of mechanisms, a four-bar linkage, also called a four-bar, is the simplest closed-chain movable 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. Spherical and ...
Link 1 (horizontal distance between ground joints): 4a Illustration of the limits. In kinematics, Chebyshev's linkage is a four-bar linkage that converts rotational motion to approximate linear motion. It was invented by the 19th-century mathematician Pafnuty Chebyshev, who studied theoretical problems in kinematic mechanisms.
Watt's linkage consists of three bars bolted together in a chain. The chain of bars consists of two end bars and a middle bar. The middle bar is bolted at each of its ends to one of the ends of each outer bar. The two outer bars are of equal length, and are longer than the middle bar. The three bars can pivot around the two bolts.
Linkage mobility Locking pliers exemplify a four-bar, one degree of freedom mechanical linkage. The adjustable base pivot makes this a two degree-of-freedom five-bar linkage . It is common practice to design the linkage system so that the movement of all of the bodies are constrained to lie on parallel planes, to form what is known as a planar ...
The coupler (link 3) point stays within 1% positional tolerance while intersecting the ideal straight line 6 times. The linkage was first shown in Paris on the Exposition Universelle (1878) as "The Plantigrade Machine". [5] [3] The Chebyshev Lambda Linkage is a cognate linkage of the Chebyshev linkage.
Two cranks designed in this way form the desired four-bar linkage. This formulation of the mathematical synthesis of a four-bar linkage and the solution to the resulting equations is known as Burmester Theory. [3] [4] [5] The approach has been generalized to the synthesis of spherical and spatial mechanisms. [6]
An example of a simple closed chain is the RSSR spatial four-bar linkage. The sum of the freedom of these joints is eight, so the mobility of the linkage is two, where one of the degrees of freedom is the rotation of the coupler around the line joining the two S joints.
The former ground link of the fusing 4-bar linkage becomes a rectilinear link that travels follows the same coupler curve. Each of these paired six-bar cognate linkages can also be converted into another cognate linkage by flipping the linkage over, and switching the roles of the rectilinear link and the ground link.