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Gimbal

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For the former settlement in California, see Gimbal, California.
Illustration of a simple two-axis gimbal set.

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 immobile (i.e., vertical in the animation) regardless of the motion of its support. For example: on a ship, the 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),[1] who described the device in detail, but did not claim its invention.

History

Cardan suspension in Villard de Honnecourt's sketchbook (ca. 1230)
Early modern dry compass suspended by gimbals (1570)

The gimbal was first invented by the Greek inventor Philo of Byzantium (280–220 BC).[2][3][4][5] Philo described an eight-sided ink pot with an opening on each side, which can be turned so that while any face is on top, a pen can be dipped and inked - yet the ink never runs out through the holes of the other sides. 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 is turned.[2]

The authenticity of Philo's description of a cardan suspension has been doubted by some authors on the ground that the part of Philo's Pneumatica which describes the use of the gimbal survived only in an Arabic translation of the early 9th century AD.[2] Thus, the sinologist Joseph Needham suspected Arab interpolation as late as 1965.[6] However, Carra de Vaux, author of the French translation which still provides the basis for modern scholars,[7] regards the Pneumatics as essentially genuine.[8] The historian of technology George Sarton (1959), too, 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.[9] So does his colleague Michael Lewis (2001).[10] In fact, research by the latter scholar (1997) demonstrates that the Arab copy contains sequences of Greek letters which fell out of use after the time of Christ, thereby strengthening the case that it is a faithful copy of the Hellenistic original,[11] a view recently also shared by the classicist Andrew Wilson (2002).[12]

The ancient author Athenaeus Mechanicus, who flourished during the reign of Augustus (30 BC–AD 14), described the military use of a gimbal-like 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".[13]

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 (Template:Lang-la).[14] The French inventor Villard de Honnecourt depicts a set of gimbals in his famous sketchbook (see right). In the early modern period, dry compasses were suspended in gimbals.

In China, the Han Dynasty (202 BC – AD 220) inventor Ding Huan created a gimbal incense burner around AD 180.[2][15] 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.[16] 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.[17] 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.[18]

Applications

Inertial navigation

In inertial navigation, as applied to ships and submarines, a minimum of three gimbals is needed to allow an inertial navigation system (stable table) to remain fixed in inertial space, compensating for changes in the ship's yaw, 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.

Similar sensing platforms are used on aircraft.

In 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.

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.

The word "gimbal" began as a noun. Most modern dictionaries continue to list it as such. Lacking a convenient term to describe the swinging movement of a rocket engine, engineers began also using the word "gimbal" as a verb. When a thrust chamber is swung by an attached actuator, the movement is referred to as "gimballed" or "gimballing". Official rocket documentation reflects this usage.

Photography and imaging

A Baker-Nunn satellite-tracking camera on an altitude-altitude-azimuth mount.

Gimbals are also used to mount every thing from small camera lenses to large photographic telescopes.

In portable photography equipment single-axis gimbal heads are used in order to allow a balanced movement for camera and lenses. This proves useful in wildlife photography as well as in any other case where very long and heavy telephoto lenses are adopted: a gimbal head rotates a lens around its center of gravity, thus allowing for easy and smooth manipulation while tracking moving subjects.

Very large gimbal mounts in the form 2 or 3 axis altitude-altitude mounts[19] are used in satellite photography for tracking purposes.

See also

References

  1. ^ Needham, Joseph. (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering. Taipei: Caves Books Ltd. Page 229.
  2. ^ a b c d 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.
  3. ^ Ernest Frank Carter: “Dictionary of Inventions and Discoveries”, 1967, p.74
  4. ^ Hans-Christoph Seherr-Thoss, Friedrich Schmelz, Erich Aucktor: “Universal Joints and Driveshafts: Analysis, Design, Applications”, 2006, ISBN 9783540301691, p.1
  5. ^ Robert E. Krebs, Carolyn A. Krebs: “Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Ancient World”, 2003, ISBN 9780313313424, p.216
  6. ^ Needham, Joseph. (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering. Taipei: Caves Books Ltd. Page 236.
  7. ^ D.R. Hill: "History of Technology", Part 2 (1977), p.75
  8. ^ 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
  9. ^ 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.
  10. ^ M.J.T. Lewis: "Surveying Instruments of Greece and Rome", Cambridge University Press, 2001, ISBN 9780521792974, p.76, Fn.45
  11. ^ M.J.T. Lewis: "Millstone and Hammer: the Origins of Water Power" (1997), p.26-36
  12. ^ Andrew Wilson: "Machines, Power and the Ancient Economy", The Journal of Roman Studies, Vol 92. (2002), pp. 1-32 (7)
  13. ^ Athenaeus Mechanicus, "On Machines" ("Peri Mēchanēmatōn"), 32.1-33.3
  14. ^ 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.
  15. ^ Needham, Joseph. (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering. Taipei: Caves Books Ltd. Page 233.
  16. ^ 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.
  17. ^ Needham, Joseph. (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology; Part 2, Mechanical Engineering. Taipei: Caves Books Ltd. Page 234.
  18. ^ 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.
  19. ^ Soviet journal of optical technology: Volume 43, Optical Society of America, American Institute of Physics , page 119
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