Gimbal

A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of two gimbals, one mounted on the other with pivot axes orthogonal, may be used to allow an object mounted on the innermost gimbal to remain vertical regardless of the motion of its support. For example, gyroscopes, shipboard compasses, stoves and even drink holders typically use gimbals to keep them upright with respect to the horizon despite the ship's pitching and rolling.

The 'Cardan' suspension of a gimbal is named after the Italian inventor Gerolamo Cardano (1501–1576), [Needham, Joseph. (1986). "Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering". Taipei: Caves Books Ltd. Page 229.] who described the device in detail, but did not claim its invention.

History

The gimbal was first invented by the Greek inventor Philo of Byzantium (280–220 BC). [Ernest Frank Carter: “Dictionary of Inventions and Discoveries”, 1967, p.74] [Hans-Christoph Seherr-Thoss, Friedrich Schmelz, Erich Aucktor: “Universal Joints and Driveshafts: Analysis, Design, Applications”, 2006, ISBN 9783540301691, p.1] [Robert E. Krebs, Carolyn A. Krebs: “Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Ancient World”, 2003, ISBN 9780313313424, p.216] Philo described an eight-sided ink pot with an opening on each side, which can be turned so that any face is on top, dip in a pen and ink it - yet the ink never runs out through the holes of the side. This was done by the suspension of the inkwell at the center, which was mounted on a series of concentric metal rings which remained stationary no matter which way the pot turns itself.Sarton, George. (1959). A History of Science: Hellenistic Science and Culture in the Last Three Centuries B.C. New York: The Norton Library, Norton & Company Inc. SBN 393005267. Page 349–350.]

Philo's original text of the "Pneumatica" describing this use of the gimbal exists in a later Arabic translation made roughly the time of Caliph Al-Ma'mun (r. 813–833). Carra de Vaux, author of the French translation which still provides the basis for modern scholars, [D.R. Hill: "History of Technology", Part 2 (1977), p.75] regards the Pneumatics as essentially genuine. [Carra de Vaux: "Le livre des appareils pneumatiques et des machines hydrauliques de Philon de Byzance d'après les versions d'Oxford et de Constantinople", Académie des Inscriptions et des Belles Artes: notice et extraits des mss. de la Bibliothèque nationale, Paris 38 (1903), pp.27-235] George Sarton (1959) asserts that it is safe to assume the Arabic version is a faithful copying of Philo's original, and credits Philon explicitly with the invention. [Sarton, George. (1959). A History of Science: Hellenistic Science and Culture in the Last Three Centuries B.C. New York: The Norton Library, Norton & Company Inc. SBN 393005267. Page 343–350.] So does Michael Lewis (2001). [M.J.T. Lewis: "Surveying Instruments of Greece and Rome", Cambridge University Press, 2001, ISBN 9780521792974, p.76, Fn.45] The sinologist Joseph Needham (1965) suspects Arab interpolation. [Needham, Joseph. (1986). "Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering". Taipei: Caves Books Ltd. Page 236.] Lucio Russo and Silvio Levy (2004) write that the transmitted text of Philo was likely corrupted in the Arab version which may have mixed in materials from other sources, since it is "highly uneven in terms of technical sophistication and subject matter" [Russo, Lucio and Silvio Levy (2004). "The Forgotten Revolution: How Science Was Born in 300 BC and Why It Had to Be Reborn". Berlin: Springer. ISBN 3540200681.] , but do not specify whether this attributes to the relevant passage containing the gimbal.

Recent research by Michael Lewis (1997), however, has shown that the letter sequences of the Arab copy contain Greek letters which fell out of use after the time of Christ, thereby asserting that the Arabic version is faithful to Philo's original, [M.J.T. Lewis: "Millstone and Hammer: the Origins of Water Power" (1997), p.26-36] a view also shared by Andrew Wilson (2002). [Andrew Wilson: "Machines, Power and the Ancient Economy", "The Journal of Roman Studies", Vol 92. (2002), pp. 1-32 (7)]

The ancient author Athenaeus Mechanicus, who flourished during the reign of Augustus (30 BC–14 AD), described the military use of a gimbal mechanism, calling it "little ape" ("pithêkion"): When preparing to attack coastal towns from the sea-side, military engineers used to yoke merchant-ships together to take the siege machines up to the walls. But to prevent the shipborne machinery from rolling around the deck in heavy seas, Athenaeus advises that "you must fix the "pithêkion" on the platform attached to the merchant-ships in the middle, so that the machine stays upright in any angle". [Athenaeus Mechanicus, "On Machines" ("Peri Mēchanēmatōn"), 32.1-33.3]

After antiquity, gimbals remained widely known in the Near East. In the Latin West, reference to the device appeared again in the 9th century recipe book called the "Little Key of Painting" (Latin: "Mappae Clavicula"). [Needham, Joseph. (1986). "Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering". Taipei: Caves Books Ltd. Page 229 & 231.] The French inventor Villard de Honnecourt depicts a gimbal in his famous sketchbook (see right). In the early modern period, dry compasses were suspended in gimbals.

In China, the Han Dynasty (202 BC – 220 AD) inventor Ding Huan (丁緩) created an gimbal incense burner around 180 AD. [Needham, Joseph. (1986). "Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering". Taipei: Caves Books Ltd. Page 233.] There is a hint in the writing of the earlier Sima Xiangru (179–117 BC) that the gimbal existed in China since the 2nd century BC. [Needham, Joseph. (1986). "Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering". Taipei: Caves Books Ltd. Page 233–234.] There is mention during the Liang Dynasty (502–557) that gimbals were used for hinges of doors and windows, while an artisan once presented a portable warming stove to Empress Wu Zetian (r. 690–705) which employed gimbals. [Needham, Joseph. (1986). "Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering". Taipei: Caves Books Ltd. Page 234.] Extant specimens of Chinese gimbals used for incense burners date to the early Tang Dynasty (618–907), and were part of the silver-smithing tradition in China. [Needham, Joseph. (1986). "Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering". Taipei: Caves Books Ltd. Page 234–235.]

Inertial navigation

Marine

In inertial navigation, as applied to ships and submarines, a minimum of three gimbals is needed to allow an Inertial Navigation System platform (stable table) to remain fixed in inertial space, compensating for the ship's Yaw (direction) as well as its Pitch and Roll. In this application, the Inertial Measurement Unit (IMU) is equipped with three orthogonally mounted gyros to sense rotation about all axes in three dimensional space. The gyro outputs drive motors controlling the orientation of the three gimbals as required to maintain the orientation of the IMU. In turn, angular measurement devices, called "resolvers" mounted on the three gimbals provide the nine cosine values for the direction cosine matrix needed to orient the ship.

Aerospace

In aerospace inertial navigation systems, gimbal lock may occur when vehicle rotation causes two of the three gimbal rings to align with their pivot axes in a single plane. When this occurs, it is no longer possible to maintain the sensing platform's orientation. To avoid this problem, a fourth gimbal must be employed, driven so as to keep the other three at substantial angles to each other. Modern practice is to avoid the use of gimbals entirely by mounting the inertial sensors directly to the body of the vehicle strapdown system and integrating sensed rotation and acceleration digitally using quaternion methods to derive vehicle orientation and velocity.

Rocket engines

In spacecraft propulsion, rocket engines are generally mounted on a pair of gimbals to allow a single engine to vector thrust about both the pitch and yaw axes; or sometimes just one axis is provided per engine. To control roll, twin engines with differential pitch or yaw control signals are used to provide torque about the vehicle's roll axis.

Fishing

In big-game fishing, a two axis gimbal may be used as a fixed pivot for the butt of the rod, with the gimbals mounted in a "fighting belt" or a "fighting chair". In either case, this is a considerable advantage to the angler. Inside the gimbal there is usually a horizontal pin that the fishing rod locks into, preventing rotation about the long axis of the rod, making it easier to reel.This is demonstrated in the 1975 film "Jaws", where the character Quint uses a "fighting chair" & "fighting belt/harness" to attempt to catch the shark they were pursuing.

ee also

*Gimbal lock
*Canfield joint
*Heligimbal
*Cardan shaft
*Gyroscope
*Euler angles

References