Showing papers on "Gyroscope published in 1982"

Source statistics and the Kerr effect in fiber-optic gyroscopes

Abstract: We show theoretically that polarized thermal light as generated by a superluminescent diode has the properties required to compensate for Kerr-effect drift in fiber gyroscopes. Light from some multimode lasers has related properties that can substantially reduce Kerr-effect errors. An experimental gyroscope using a multimode laser diode demonstrates no Kerr-effect error and provides significantly improved long-term stability.

Compensation of the optical Kerr effect in fiber-optic gyroscopes.

Abstract: We describe theoretically and demonstrate experimentally the principle of a simple technique to reduce substantially the Kerr-induced rotation-rate error in fiber-optic gyroscopes. It consists of modulating the source intensity to adjust the nonlinear interaction between the counterpropagating waves.

Birefringence and polarization effects in fiber gyroscopes

Abstract: A formalism is presented for treating birefringence and polarization in fiber optic sensors. This formalism is applied to study theoretical characteristics of fiber gyroscopes which are operated with various states of polarization of the input light including nonpolarized and partially polarized light, which have potentially useful characteristics. Measurements supporting the theoretical predictions are described.

All-fiber gyroscope with inertial-navigation short-term sensitivity.

Abstract: We report new experimental data for an all-fiber gyroscope with a noise density of 0.004(deg/h)2/Hz. This is compatible with the requirements for inertial navigation. Noise contributions from the coherent Rayleigh backscatter when a phase-modulation bias scheme is used and also from acoustic vibrations are discussed.

Sensitivity of a fiber-optic gyroscope to environmental magnetic fields

Abstract: It is shown that environmental magnetic fields may cause a considerable error for the detected rotation rate even though the line integral of the magnetic field along the fiber vanishes. Experimentally, it has been shown that the earth’s magnetic field yields a bias uncertainty of about 10°/h, which can be reduced by at least 1 order of magnitude if the fiber coil is protected against environmental magnetic fields.

Wellbore inertial directional surveying system

Abstract: A wellbore inertial directional surveying system for providing a complete directional survey of an oil or gas well borehole to determine the displacement in all three directions of the borehole path relative to the well head at the surface. The information generated by the present invention is especially useful when numerous wells are drilled to different geographical targets from a single off-shore platform. Accurate knowledge of the path of the borehole allows proper well spacing and provides assurance that target formations are reached. The tool is lowered down into a borehole on the electrical cable. A computer positioned on the surface communicates with the tool via the cable. The tool contains a sensor block which is supported on a single gimbal, the rotation axis of which is aligned with the cylinder axis of the tool and, correspondingly, the borehole. The gyroscope measurement of the sensor block rotation is used in a null-seeking servo loop which essentially prevents rotation of the sensor block aboutthe gimbal axis. Angular rates of the sensor block about axes which are perpendicular to the gimbal axis are measured by gyroscopes in a manner similar to a strapped-down arrangement. Three accelerometers provide acceleration information as the tool is lowered within the borehole. The uphole computer derives position information based upon acceleration information and anular rate information. Kalman estimation techniques are used to compensate for system errors.

Observation of intensity-induced nonreciprocity in a fiber-optic gyroscope.

Abstract: Nonreciprocal phase shift has been predicted and observed in a fiber-optic gyroscope based on a Sagnac interferometer when the intensities of the counterpropagating beams are unequal. The magnitude of this intensity-induced phase shift is 1.4 rad/W power difference. At 1-μW power difference, this is equivalent to a rotation rate of 0.2°/h in our 200-m-long fiber with a core radius of 2.25 μm that is wound around a spool of 19-cm diameter. The data are consistent with theoretical predictions based on four-wave mixing in the quartz fiber.

Relativistic Tidal Forces and the Possibility of Measuring Them.

Abstract: The relativistic corrections to the Newtonian tidal accelerations generated by a rotating system are studied. The possibility of testing the relativistic theory of gravitation by measuring such effects in a laboratory in orbit around the Earth is considered. A recent proposal to measure a rotation-dependent tidal acceleration as an alternative to the Stanford gyroscope experiment is critically examined and it is shown that such an experiment does not circumvent the basic difficulties associated with the gyroscope experiment.

Instruments for monitoring the direction of a borehole

Abstract: An instrument for monitoring the direction of a borehole comprises an elongate casing having its longitudinal axis coincident, in use, with the axis of the borehole, an outer gimbal pivotally mounted within the casing with its pivot axis coincident with the longitudinal axis of the casing, a gyroscope unit mounted in the outer gimbal, a torque motor and a gravity sensor unit At the beginning of a run the instrument is positioned at the mouth of the borehole The rate of rotation about an axis transverse to the outer gimbal axis is then sensed by the gyroscope unit, and the outer gimbal is slewed by the torque motor in dependence on the sensed rate so as to align the transverse axis along an East/West direction The instrument is then moved along the borehole and the rate of rotation about the outer gimbal axis is continually sensed by the gyroscope unit, the outer gimbal being torqued by the motor in dependence on the sensed rate to stabilize the outer gimbal about its axis Simultaneously the components of gravity are sensed by the gravity sensor unit The resulting measurements are used to determine the inclination and azimuth at a plurality of points along the length of the borehole

3 × 2 channel waveguide gyroscope couplers: Theory

Abstract: Gyroscope couplers with three input ports and two output ports which can be implemented in a planar geometry are studied theoretically. Using a local normal mode description in the approximation of coupled mode theory, analytic output power expressions are obtained for the 3 × 2 branching waveguide coupler and the 3 × 2 directional waveguide coupler. When optimized, these devices behave identically to each other and to the three-dimensional 3 × 3 coupler [1] from which they are derived.

Fiber optic rotation-sensing gyroscope with (3×2) coupler

Abstract: A Sagnac gyroscope, for measuring rotation rates, having an optical coupler, adapted for fabrication by integrated optical techniques, which is compact and provides for operation of the gyroscope at quadrature for small rotation rates. The optical coupler is a symmetrical, channel waveguide structure comprising a two-mode central waveguide branching into three one-mode input waveguides at one end and into two one-mode output waveguides at the other end. The output waveguides are optically coupled to the ends of a fiber-optic loop which provides a closed optical path in which the Sagnac phase shift is produced. The middle input waveguide is adapted to transmit an incident beam into the optical coupler while the outer input waveguides are adapted to transmit the output beams of the Sagnac gyroscope to a circuit for measuring and comparing the intensities of the beams in the outer waveguides so that the rotation rate may be determined.

Optical fiber gyroscope

Abstract: PURPOSE:To improve an S/N, by providing optical fiber separately to left rotating light and right rotating light. CONSTITUTION:As left rotating light and right rotating light transfer respectively different optical fibers 2-1, 2-1, even if there is return light at incident terminals T1, T2 by Rayleigh scattering, etc., the return light does not have effects on outputting light of output terminals T3, T4. Therefore, an S/N in output signal of a differential amplifier 5 is improved.

Theoretical Basis of Sagnac Effect in Fiber Gyroscopes

Abstract: Simple kinematics considerations give the first order value of the Sagnac phase shift in a rotating vacuum interferometer [1]. It is more complicated to treat the problem when the waves travel within a dielectric medium, as in the case of a fiber gyroscope. Then both Fizeau and Doppler effects occur and compensate the influence of the index of refraction. The results appear to be independent of the properties of the medium [2]. They depend only on the light frequency, the length of the closed loop and its radius. But for the waveguide configuration of fiber rotation sensors where modal dispersion occurs, an electrodynamic approach is more rigorous.

Multiaxial vibration sensor

Abstract: A single vibration sensor having the capability of sensing vibration along three rotational axes as well as three translational axes and exhibiting consistent dynamics over a wide frequency range. The sensor includes an elongated mass formed of a generally rigid material suspended in a fluid within a housing. The exterior surface of the mass is spaced from the interior surface of the housing to permit limited freedom of motion of the mass within the housing. The mass is provided with multiaxial radial and axial electromagnetic suspensions, and is typically supported by a fluid within the housing. Rotational positioning is provided by a signal generator, torque generator combination. Vibration is sensed by additive or differential measurements of current changes in the coils of different axes of the suspensions or electromagnetic signal and torque generator combinations. The sensor is conveniently implemented as a single degree of freedom inertial gyroscope without the gyroscope wheel and adapted to permit sensing of current changes in coils provided to achieve suspension or suspension and signal and torque generation functions.

Observation of low noise in a passive fibre gyroscope

Abstract: We report short-term noise levels of < 1 deg/h and 10 min drift of < 2 deg/h in a passive fibre gyroscope utilising a fused 3 × 3 fibre coupler and a broadband and partially polarised superluminescent diode. Partially polarised operation of the source is shown to result in less noise than polarised operation.

Nuclear magnetic resonance gyroscope

Abstract: A nuclear magnetic resonance gyroscope which derives angular rotation thef from the phases of precessing nuclear moments utilizes a single-resonance cell situated in the center of a uniform DC magnetic field. The field is generated by current flow through a circular array of coils between parallel plates. It also utilizes a pump and read-out beam and associated electronics for signal processing and control. Encapsulated in the cell for sensing rotation are odd isotopes of Mercury Hg199 and Hg201. Unpolarized intensity modulated light from a pump lamp is directed by lenses to a linear polarizer, quarter wave plate combination producing circularly polarized light. The circularly polarized light is reflected by a mirror to the cell transverse to the field for optical pumping of the isotopes. Unpolarized light from a readout lamp is directed by lenses to another linear polarizer. The linearly polarized light is reflected by another mirror to the cell transverse to the field and orthogonal to the pump lamp light. The linear light after transversing the cell strikes an analyzer where it is converted to an intensity-modulated light. The modulated light is detected by a photodiode processed and utilized as feedback to control the field and pump lamp excitation and readout of angular displacement.

Observation of low noise in a passive fiber gyroscope

Abstract: The concept of a fiber optic gyroscope without active control of noise sources or sensitivity has appeal for applications due to the resulting component simplicity and snail volume requirements. Many applications for such a device require only moderate rotation rate capabilities (1-10 deg/hr). The passive gyroscope with a 3×3 fiber coupler demonstrated by Sheem1 exhibited noise levels in the few deg/sec range. We report improvements to this device which resulted in noise levels of ~ 5 deg/hr and a 10 minute drift of ~ 10 deg/hr.

Induction feedback stabilized suspension gyroscope

Abstract: A suspension gyroscope has a stator and a rotor rotatably mounted with respect to the stator. The rotor has at least one generally hemispherical portion which is, at least in part, electrically conductive. The rotor may also have disc-like portions which project radially outwardly therefrom. Electrical coils serve to generate magnetic fields which induce eddy currents in the hemispherical portions and the disc-like portions. These coils serve to monitor the positions of the rotors with respect to three reference axes. A sensor for measuring departure of the rotor from a desired position is provided and may be optical or magnetic in nature.

Single mirror ring laser gyro readout without combining optics

Abstract: A detector structure for use in a ring laser gyroscope includes a partially reflective surface on an inside face of a carrying substrate for passing a portion of each of the counter rotating gyroscope beams for detection and for reflecting a portion of each of the beams into a light path of the laser gyroscope without passing any optical elements of the detector structure. A detector substrate is spaced with respect to said partially reflective surface to receive the portions of the beams passing the partially reflective surface with patterns formed by the respective beams only partially overlapping. A pair of detectors are provided on the detector substrate, located to receive at least a nonoverlapping portion of each of the beam patterns to provide an intensity indication of the respective beams, and another detector is also located on the substrate, located to receive an overlapping portion of the beams for detecting the rate and sense of motion of interference fringes produced by the respective beams to provide an indication of the frequency difference between said beams. The detector structure also includes yet another detector on the substrate, located to receive an overlapping portion of the beams to provide an indication of the sum of the intensities of the respective beams.

Polarization Problems in Optical Fiber Gyroscopes

Abstract: The importance of polarization control is becoming increasingly recognized in the development of optical fiber gyroscopes [1,2]. Optical gyroscopes depend essentially on the establishment of a single optical path (optical mode), whose length, measured optically in opposite directions, can be taken to indicate rotation rate. However, even a so-called single-mode optical fiber typically provides two optical modes (polarization states) which may couple to each other in a linear but otherwise unpredictable manner. If one of the two polarization states is not suppressed, then it becomes impossible to define (to the accuracy required) which optical path the two counterpropagating beams actually are taking, and therefore the drift stability of the gyro is compromised.

Two-axis gimbal arrangement

Abstract: A gyroscopically stabilized optical seeker for use in a cannon-launched projectile is shown to include a gimbal arrangement wherein a two-axis rate gyroscope and associated torque motors are utilized to attain the requisite stabilization however such seeker is oriented with respect to such projectile, the two-axis rate gyroscope being arranged so that the complete optical system, including the detector unit, may be mounted on the inner gimbal.

Azimuth determining gyroscope

Abstract: In an azimuth determining gyroscope, a mechanically balanced gimbal is suspended from a fixed case by a wire which passes through the generally tubular upper portion of the suspended gimbal. A spin motor and a wheel for rotating about a vertical axis are coupled to the lower portion of the suspended gimbal. The upper portion of the suspended gimbal has pickoff and torquer coils for measuring the position of the suspended gimbal with respect to the fixed case and for providing torque to the suspended gimbal. Leads to the spin motor are configured to act as azimuth restraint means between the suspended gimbal and the fixed case.

Control for gimballed monopulse antenna arrangement

Abstract: An arrangement for determining the rotational position of the rotor of an electrical gyroscope is shown to include: (a) at least one sensor including a Hall effect crystal having a rotating magnetic field applied thereto, such field being synchronous with the field causing rotation of the rotor; (b) a phase-lock loop, responsive to square wave signals corresponding to signals out of the Hall effect crystal and a voltage-controlled oscillator to provide a signal approximating the rotational position of the rotor; and (c) a phase detector, responsive to negative going transitions of the square wave and to reference pulses to synchronize the rotational position of the rotor with the reference pulses.

3 x 2 Channel Waveguide Gyroscope Couplers: Theory

Abstract: Gyroscope couplers with three input ports and two output ports which can be implemented in a planar geometry are studied theoretically. Using a local normal mode description in the approximation of coupled mode theory, analytic output power expressions are obtained for the 3 X 2 branching waveguide coupler and the 3 X 2 directional waveguide coupler. When optimized, these devices behave identically to each other and to the three-dimensional 3 X 3 coupler [1] from which they are derived.

Stabilised optical sighting system with gyroscope - has infrared camera aligned with input in order to generate position signals for aligning motors

Abstract: The stabilised sight includes a first assembly (10) which may be moved about an external axis by a positioning motor (25), and a second assembly mounted on the first in such a way as to be adjusted about a second axis (14), which is perpendicular to the first. A gyroscope is mounted on the second assembly in order to provide movement detection signals, which in turn may be used to control the operation of the positioning motors. A sensor positioned in one of the optical paths of the system includes an extended infra-red camera aligned on the optical axis with a mirror arranged to reflect radiation from the input pupil of the system.

Synchronous electric motor control systems

Abstract: A gyroscope motor control system has a phase-locked loop circuit and an antihunting circuit. The phase-locked loop circuit has a voltage-controlled oscillator which produces the drive signal for the motor. The frequency of the oscillator is controlled by the output of a phase discriminator which is in turn dependent on the difference in phase between a reference frequency and a feedback signal from the motor drive signal. A capacitive pick-off senses the speed of rotation of the gyroscope inertia wheel and a signal in response to this speed is supplied to a directional phase discriminator together with the feedback signal. The output of the discriminator varies with change in phase difference between its two inputs, and is supplied via a switching transistor to the input of the oscillator to effect minor variations in its frequency such as to reduce fluctuations in motor speed. The transistor is held off until there is substantial synchronism with the motor drive signal and the inertia wheel speed.

Operating method for a vehicle navigation device

Abstract: This navigation device contains a displacement sensor which supplies signals corresponding to the vehicle movement, a gyroscope arrangement which continuously supplies signals corresponding to the alignment of the vehicle with respect to the reference direction, and an analysing circuit which determines position signals from these signals So that the drift of the gyroscope arrangement when the vehicle is stopped is at least largely eliminated, the delivery of signals from the gyroscope arrangement to the evaluating circuit is suppressed when the vehicle is stopped However, the signals are supplied to two memories which are in each case cleared after a time T but at an interval of T/2 with respect to one another; T/2 being in each case somewhat greater than the maximum possible period which can occur between the beginning of travel and the occurrence of the first signal of the displacement sensor If the first displacement sensor signal occurs again, the content of the memory which has not been cleared for more than T/2 is used for the sign-correct correction of the value of the alignment of the vehicle with respect to the reference direction and, at the same time, the suppression of the gyroscope signals to the analysing circuit is cancelled