Gyroscope

7 Key excerpts on "Gyroscope"

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  eBook - PDF

  Inertial Navigation Systems with Geodetic Applications

  • Christopher Jekeli(Author)
  • 2012(Publication Date)
  • De Gruyter

    (Publisher)

  We begin with a discussion of the Gyroscope, in particular the mechanical gyro, since its dynamics and that of today's pendulous accelerometer are related. 3.2 Gyroscopes The term Gyroscope originates with J.B.L. Foucault, who in 1850, using a spin-ning disc, demonstrated that the Earth rotates. His demonstration was based on the fact that since the rotation axis of the disc must remain fixed in inertial space in the absence of applied torques (constant angular momentum, see below), its direction with respect to the Earth changes as the Earth rotates underneath it. Gyroscopes provide a means to determine relative attitude, or orientation, as well as absolute direction in a number of applications, including, of course, inertial navigation, where traditionally the primary application of gyros is to isolate the vehicle motion from the platform holding the accelerometers. Viewed generally as measuring angles or angular rates, the gyro has also found utility as an auxiliary device in such science and engineering endeavors as remote sensing, photogrammetry (Schwarz et al., 1993), terrestrial surveying (see Chapter 10), and terrain profiling using syn-thetic aperture radar (SAR) (Madsen and Zebker, 1993). Gyros of one or another kind play an important part where rotational stability or accurate angular registra-tion is required, not only for navigation and positioning, but for any platform of instruments or devices on any vehicle (ground vehicles, aircraft, ships, or satellites) 54 3 Inertial Measurement Units or portable system for military, civil, commercial, consumer, science, and engineer-ing purposes. We will be concerned with inertial navigation systems and their use in geodesy, but the analyses can easily be carried to the many other applications.

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  eBook - ePub

  Modern Sensors Handbook

  • Pavel Ripka, Alois Tipek, Pavel Ripka, Alois Tipek(Authors)
  • 2013(Publication Date)
  • Wiley-ISTE

    (Publisher)

  The Gyroscope is a fast rotating body suspended by a Cardan suspension allowing movements in all directions. The Gyroscope generally describes a circular cone (movement of precession around an axis). The direction of this axis remains fixed in space (in a Galilean reference frame).

  The gyroscopic effect is concerned with the fact that the Gyroscope moves in a direction perpendicular to a force which is exerted on it. This effect is used to detect forces, angular movement, particularly in inertial navigation systems or in inertial platforms (which make it possible to define the position of a mobile unit per integration of its acceleration). In inertial navigation the Gyroscope is a sensor commonly used to measure a rotary angle. The output of a Gyroscope is an angle.

  The gyrometer is a sensor commonly used to measure an angular rate. The traditional gyrometer with an axis is primarily made up of: – a spinning top turning around an axis Δ carried by a ring itself connected to the case of the gyrometer by the axis of exit S perpendicular to the axis Δ; – a torque motor; – a detector of variation acting on the moving element around S.

  Because of the gyroscopic phenomena, an angular movement of housing with an angular velocity ω according to the axis of entry will cause the appearance of a couple being exerted around the axis of exit and proportional to ω. The ring is brought under control to remain in its position of balance by means of a torque motor, so that the driving current it being proportional to the couple applied. The output is a voltage across the sensing resistor, which is proportional to that current and thus a function of the measured angular velocity. The general diagram of the traditional gyrometer with one axis is shown in Figure 9.4 .

  Figure 9.4.  Diagram of the traditional gyrometer

  9.2.2. Use of rate sensors

  The gyrometers constitute the basic elements of the inertial frames of reference used to provide the functions of guidance, piloting, navigation and stabilization of various vehicles or particular platforms. In the systems with bound components, called “strapdown”, only the gyrometers are used.

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  Mechatronics

  A Foundation Course

  • Clarence W. de Silva(Author)
  • 2010(Publication Date)
  • CRC Press

    (Publisher)

  These sensors are commonly used in control systems for stabilizing vehicle systems. Since a spinning body (a Gyroscope) requires an external torque to turn (precess) its axis of spin, it is clear that if this gyro is mounted on a rigid vehicle so that there are a sufficient number of degrees of freedom (at most three) between the gyro and the vehicle, the spin axis will remain unchanged in Sensors and Transducers 399 space, regardless of the motion of the vehicle. Hence, the axis of spin of the gyro will pro-vide a reference with respect to which the vehicle orientation (e.g., azimuth or yaw, pitch, and roll angles) and angular speed can be measured. The orientation can be measured by using angular sensors at the pivots of the structure, which mounts the gyro on the vehicle. The angular speed about an orthogonal axis can be determined; for example, by measur-ing the precession torque (which is proportional to the angular speed) using a strain-gage sensor; or by measuring using a resolver, the deflection of a torsional spring that restrains the precession. The angular deflection in the latter case is proportional to the precession torque and hence to the angular speed. 6.9.1 Rate Gyro A rate gyro is used to measure angular speeds. The arrangement shown in Figure 6.35a may be used to explain its principle of operation. A rigid disk (gyroscopic disk) of a polar moment of inertia J is spun at angular speed ω about frictionless bearings using a constant-speed motor spinning about an axis. The angular momentum H about the same axis is given by = ω H J (6.39) This vector is shown by the solid line in Figure 6.35b. Due to the angular speed (rate) Ω , which is the quantity to be measured (measurand or sensor input), the vector H will turn through angle Ω ∙ Δ t in an infinitesimal time Δ t , as shown.

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  Sensors for Mobile Robots

  • H.R. Everett(Author)
  • 1995(Publication Date)
  • A K Peters/CRC Press

    (Publisher)

  13 Gyroscopes Gyroscopes are for the most part insensitive to the electromagnetic and ferromagnetic anomalies that affect the accuracy of compasses and are particularly useful in applications where there is no geomagnetic field present at all (i.e., deep space), or in situations where the local field is disturbed. Two broad categories of Gyroscopes will be discussed: 1) mechanical Gyroscopes and 2) optical Gyroscopes. Mechanical Gyroscopes operate by sensing the change in direction of some actively sustained angular or linear momentum, which in either case can be continuous or oscillatory in nature (Cochin, 1963). Probably the most well-known mechanical configuration is the flywheel Gyroscope, a reliable orientation sensor based on the inertial properties of a rapidly spinning rotor, first demonstrated in 1810 by G.C. Bohnenberger of Germany. In 1852, the French physicist Leon Foucault showed that such a Gyroscope could detect the rotation of the earth (Carter, 1966). More recently there has been considerable interest shown in a number of new products classified as vibrating structure Gyroscopes earmarked for applications in stabilized camera optics, robotics, and intelligent-vehicle highway systems. Optical Gyroscopes have been under development now as replacements for their mechanical counterparts for over three decades. With little or no moving parts, such rotation sensors are virtually maintenance free and display no gravitational sensitivities, eliminating the need for gimbaled mounting. Fueled by a large anticipated market in the automotive industry, highly linear fiber-optic versions are now evolving that have wide dynamic range and very low projected costs. There are two basic classes of rotation-sensing gyros, whether optical or mechanical in nature: 1) rate gyros , which provide a voltage or frequency output signal proportional to the turning rate and 2) rate integrating gyros, which indicate the actual turn angle or heading (Udd, 1991).

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  eBook - ePub

  Position, Navigation, and Timing Technologies in the 21st Century

  Integrated Satellite Navigation, Sensor Systems, and Civil Applications, Volume 2

  • Y. Jade Morton, Frank van Diggelen, James J. Spilker, Bradford W. Parkinson, Y. Jade Morton, Frank van Diggelen, James J. Spilker, Jr., Bradford W. Parkinson(Authors)
  • 2020(Publication Date)
  • Wiley-IEEE Press

    (Publisher)

  12 ]. The scale factor depends on the angular momentum of the wheel and the pendulosity of the proof mass. This type of accelerometer has demonstrated excellent performance in many high‐performance applications.

  The mechanical complexity of this class of accelerometer limits their application to high‐value missions requiring very high performance. For example, they were used in the Apollo guidance systems and also in strategic missile guidance systems [13 ]. These systems typically have a very precisely controlled operating environment for the instruments including careful temperature control and an inertially stabilized platform.

  44.5 Gyroscopes

  Accelerometers determine how far we have traveled; Gyroscopes keep track of what direction we are going. For our nominal navigation‐grade system, the required angle uncertainty after an hour is about 30 arc seconds, or 145 micro‐radians. To try to put this in perspective, that is the angle that the hour hand on an analog clock moves in 1 s.

  44.5.1 Taxonomy

  Similar to the discussion of accelerometers, Gyroscopes can be sorted by the mechanisms used to measure angular rotation or rate. As shown in Figure 44.15 , three major mechanisms are used to measure rotation: first, Gyroscopes that use the angular momentum of either a macroscopic spinning mass or the internal spin states of atoms or molecules; second, those that use the Coriolis effect on objects moving in a rotating frame; third, gyros that use the Sagnac effect on photons or particles with mass in a rotating frame.

  Figure 44.15

  A family tree for rotation sensing mechanizations commonly used for inertial navigation instruments. The discussion of the mechanism can be found in the section number shown in parenthesis in the figure.

  44.5.2 Angular Momentum – Rotating Mass

  Gyroscopes using the angular momentum of a spinning mass dominated early inertial systems in almost every application including short‐range weapon systems, aircraft, ships, and spacecraft. This type of Gyroscope was used for the Gravity‐B probe and they hold the record as most accurate Gyroscopes ever built [14

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  eBook - ePub

  Marine Electronic Navigation

  • Stephen F. Appleyard(Author)
  • 2006(Publication Date)
  • Routledge

    (Publisher)

  The Gyro-Compass

  G. A. A. Grant J. Klinkert 17.1 Theory 17.1.1 The Free Gyroscope

  The basis of marine gyro-compasses lies in the free Gyroscope. It is a spinning wheel or rotor so mounted in a frame that the axis upon which the wheel spins may be pointed initially in any preferred direction. A study of Figure 17.1 shows that apart from the fairly obvious spinning axis the mounting framework contains two further axes mutually perpendicular. In practice one of these is invariably vertical because the gyro will eventually be used as a compass which must afford direction-indication about a vertical axis, or that axis around which a ship turns from one course to another. It therefore follows that if one axis is to be substantially vertical the other will be horizontal, and this permits the gyro assembly to turn in azimuth about the former and tilt about the latter. If the Gyroscope were needed for purposes other than as a gyro compass the problem of mounting would be satisfied with any two axes mutually perpendicular as might be required in space equipment where the terms vertical and horizontal have, of course, no meaning. Freedom for the rotor to spin and for the spin axis to turn and tilt are referred to as the ‘three degrees of freedom’.

  Figure 17.1

  17.1.2 Gyroscopic Inertia

  When the rotor is stopped no effort is required to topple and turn it within the frame described and illustrated above. The situation is quite different if the rotor is set spinning. It exhibits a property which is popularly termed ‘rigidity in space’, or more correctly gyroscopic inertia. This property is assessed quantitatively from the angular momentum of the rotor which in turn is the product of its angular velocity and moment of inertia. Whenever possible gyro wheels are made to rotate very quickly, and the size, shape and distribution of weight is a matter of careful design to ensure adequate angular momentum without excessive frictional losses or wear at the supporting bearings.

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  Mechanics

  The Science of Machinery

  • A. Russell (Alexander Russell) Bond(Author)
  • 2015(Publication Date)
  • Perlego

    (Publisher)

  In 1907 a sensation was created by the exhibition of a car which ran on a single rail. The inventor of this monorail car was Mr. Louis Brennan. The public was astonished at the ease with which this car maintained its balance on the rail, leaning in as it rounded a curve to keep its equilibrium. Passengers could move about at will without the slightest danger of upsetting the car; in fact, if a heavy weight was placed on one side of the car that side would rise rather than fall. The car could run with equal ease upon a cable of a crooked pipe line. The Gyroscope that maintained the balance of the car consisted of a couple of small wheels which revolved in a vacuum chamber at the rate of 7,000 revolutions per minute. Once started, little power was required to keep them going. Interesting as this car was, it did not offer sufficient advantages over the present-day double rail cars and locomotives to justify its development on a commercial scale. Although witnesses of the exhibition marveled at the strange spectacle of this mechanical tight-rope walker, they did not realize that they themselves had had gyroscopic cars in their midst for years. The gyroscopic action of the wheels of a motorcycle is very marked. It is this action which is mainly responsible for holding the machine upright. The same is true of a bicycle, although the gyroscopic effect is not quite so marked, because of the lower velocity of the wheels. However, we all know that any tendency for the machine to fall to one side or the other may be corrected by a slight turn of the front wheel in that direction which at once has the effect of bringing the bicycle back to vertical position.

  THE AUTOMATIC AEROPLANE PILOT

  Still another recent development of the Gyroscope is its use as an “automatic pilot” on aeroplanes. Two sensitive Gyroscopes are used to stabilize the aeroplane. If a gust of wind tends to tilt the machine, the Gyroscopes immediately sense the deviation and by closing electrical circuits operate the ailerons to bring the machine back to a horizontal plane.

  An aviator possesses a certain sense of balance which is highly developed by experience and long practice, but at its best it does not begin to compare with sense of balance possessed by the Gyroscope. Not only will it keep the machine from tipping laterally, but it will also hold it on a level keel and can be used to steer the aeroplane in any desired direction, so that the human pilot may surrender the helm to the faithful mechanical pilot with perfect confidence in the ability of this animated machine to hold the aeroplane on a true course despite the vagaries of the wind. While this is theoretically possible, in practice certain difficulties are encountered which up to the present have prevented gyroscopic control of aeroplanes from being entirely successful.

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