History of the double cardan joint
In mechanical engineering the universal joint, Cardano joint or simply cardan joint is a spatial articulated quadrilateral.
It allows to transmit motion between two rotating axes whose extensions are incident in one point and is therefore classifiable as a transmission organ.
The invention of this type of joint dates back to at least the third century BC, by Greek scientists such as Philo of Byzantium,
that in his work Belopoiika describes him clearly. Furthermore, as early as the 4th century BC, with
the invention of the catapult, it was used to aim the weapon. It was rediscovered in 1545, from the work of the Italian mathematician Gerolamo Cardano (1501-1576),
which initially reported its paternity to Joanello Torriani. The famous Italian scientist would have been inspired by a compass for maritime navigation,
fixed on two articulated circles. He described the articulation that bears his name in a treatise entitled De subtilitate rerum.
It consists (in addition to the axes between which the motion is transmitted, which are not properly part of the joint) of two rotational pairs arranged on the same member bent at 90 °,
each on one side, connected to an axis. This central element, often in the shape of a cross, is called a cross.
The cardan joint is widely used in mechanics for its properties, but also for its relative simplicity and cost-effectiveness compared to other types of
connection between trees of the above type.
In mechanics it is generally used in steering shafts and in transmission.
Agricultural machinery also uses a telescopic shaft with two universal joints to transmit the rotary motion from the tractor PTO to the connected implements
(for example milling machine).
It is important to underline that the use of the cardan joint is necessary where the axis that transmits the motion is not perfectly coincident with the driven axis,
or when the latter is susceptible to even minimal misalignments. For example, the axle shaft of cars and the wheel axis are almost never perfectly coincident,
due to the damping effect, for which it is necessary to use the cardan. And in any case, even millimetric constant or alternating movements between 2 axes make it necessary to use the
cardan joint, under penalty of breaking the organs.