Universal joint (universal coupling,
U-joint, Cardan joint, Spicer or Hardy Spicer joint, or Hooke's joint) is a
joint or coupling in a rigid rod that allows the rod to "bend" in any
direction, and is commonly used in shafts that transmit rotary motion. It
consists of a pair of hinges located close together, oriented at 90° to each
other, connected by a cross shaft.
The main concept of the china universal joint is based on the design of
gimbals, which have been in use since antiquity. One anticipation of the
universal joint was its use by the ancient Greeks on ballistae.[citation
needed] In Europe the universal joint is often called the Cardano joint or
Cardan shaft, after the Italian mathematician Gerolamo Cardano; however, in his
writings, he mentioned only gimbal mountings, not universal joints.
The mechanism was later described in
Technica curiosa sive mirabilia artis (1664) by Gaspar Schott, who mistakenly
claimed that it was a constant-velocity joint. Shortly afterwards, between 1667
and 1675, Robert Hooke analysed the joint and found that its speed of rotation
was nonuniform, but that this property could be used to track the motion of the
shadow on the face of a sundial. In fact, the component of the equation of time
which accounts for the tilt of the equatorial plane relative to the ecliptic is
entirely analogous to the mathematical description of the china universal joint. The first recorded use of the
term universal joint for this device was by Hooke in 1676, in his book
Helioscopes. He published a description in 1678, resulting in the use of the term
Hooke's joint in the English-speaking world. In 1683, Hooke proposed a solution
to the nonuniform rotary speed of the universal joint: a pair of Hooke's joints
90° out of phase at either end of an intermediate shaft, an arrangement that is
now known as a type of constant-velocity joint. Christopher Polhem of Sweden later
re-invented the universal joint, giving rise to the name Polhemsknut in
Swedish.
In 1841, the English scientist Robert
Willis analyzed the motion of the universal joint.By 1845, the French engineer
and mathematician Jean-Victor Poncelet had analyzed the movement of the china universal joint using spherical trigonometry.
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