The Universal Joint

Other applications

Universal joints are also used to :

§ prevent shaft’s bending, when the guiding quality of a one-piece component is not good enough ;

§ transmit an angular position when flapping and rotation angles are low ;

§ for joints with two degrees of freedom in various complex assemblies like parallel robots. Long travel capacity and longitudinal load rating are more important than torque transmission, as they are not mounted on a rotational axle.

Assembly

Several rules must be observed to ensure the reliability of a universal joint :

§ the angle shall not exceed 45 , except if the joint is especially designed to work above this value

§ it is recommended to give a minimum angle of a few degrees (1,5 to 2) to “let the transmission work”. The optimal angle is approximately 15 . Above this value, the wear increases, and the universal joint shall be oversized. The maximum working angle is 45° degrees ; above this limit, the universal joint siezes and fails.

§ it is difficult to protect the joint because of the movement amplitude that it allows. A rubber bellow is usually used, but represents a weak point.

§ the efficient torque transmitted is accompanied by a bending torque rotating two times faster than the shafts, which causes vibrations even when homokinetism is respected

History

The invention of this joint in 1545 is attributed to the Italian mathematician Girolamo Cardano (Jérôme Cardan in French) (1501-1576). This famous Italian scientist would have been inspired by a marine compass fastened on two articulated circles.

He described the joint carrying his name in a Treaty of Physics titled De subtilitate rerum

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