Four-bar linkage

The rocker arm (also crank gear ) is one of the coupling gear - gear that convert rotary motion into rectilinear or oscillating movements and vice versa. Like all linkage, it is characterized by the coupling of at least two of the movable elements with a paddock. Usually a crank as a drive and a rocker arm is used as an output, but also the reverse is possible (see Dutch ).

Crank - rocker - types are used inter alia in the automation and semi-automation, for example, in producing a discontinuous excavation of material. Commonly (and occasionally seen ) in sawmills for advancing the logs or boards, the tool drive of slotting machines for cutting material processing or when windshield wipers of a motor vehicle (see diagram drawings ).

Rocker -crank models are often used in hand-operated equipment, such as pumps or track cars.

See also linkage

Functional requirements

The crank is only full rotation ( for circulation ) when the lengths of the parts of the rocker arm in a certain relationship to each other.

The German engineer Franz Grashof has to formulate a theorem: " The crank as the smallest member of a crank-rocker mechanism ( four-bar chain ) is fully capable of rotation when the crank along with the longest term of the rocker arm is smaller than the other two terms. "

Basically, there are two scenarios to distinguish two inequalities must be satisfied by the crank-rocker:

From these two inequalities also follows that a must be less than c in any case, by exactly twice the difference between b and d

A b = c d, and / or A D = b c, the rocker unit at least one of the two extreme positions of the crank in the dead center position. There is the risk that the rocker is transformed into the opposite direction. Should the rocker arm new start up again in this position, problems would also occur.

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