WO1986000984A1 - Methode et appareil pour stabiliser la vacillation mecanique d'un capteur angulaire pour laser - Google Patents

Methode et appareil pour stabiliser la vacillation mecanique d'un capteur angulaire pour laser Download PDF

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Publication number
WO1986000984A1
WO1986000984A1 PCT/US1985/001397 US8501397W WO8600984A1 WO 1986000984 A1 WO1986000984 A1 WO 1986000984A1 US 8501397 W US8501397 W US 8501397W WO 8600984 A1 WO8600984 A1 WO 8600984A1
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WO
WIPO (PCT)
Prior art keywords
sensors
dithering
compensating mass
angular
ring laser
Prior art date
Application number
PCT/US1985/001397
Other languages
English (en)
Inventor
Rena S. Fersht
Samuel N. Fersht
Original Assignee
Litton Systems, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Litton Systems, Inc. filed Critical Litton Systems, Inc.
Publication of WO1986000984A1 publication Critical patent/WO1986000984A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/58—Turn-sensitive devices without moving masses
    • G01C19/64—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
    • G01C19/66—Ring laser gyrometers
    • G01C19/68—Lock-in prevention
    • G01C19/70—Lock-in prevention by mechanical means

Definitions

  • the present invention relates generally to a laser angular sensor and, more particularly, to an apparatus and method of stabilizing certain adverse effects of mechanical dither used in such a sensor to prevent laser beam lock-in.
  • a laser angular sensor consists primarily of first and second laser beams which move in opposite directions about a closed loop path enclosing the rotational axis with respect to which the sensor is to detect and determine angular change.
  • Rotation of the apparatus about the axis changes the effective path length that each beam must travel, which, in turn, can be detected as a frequency difference between the two laser beams.
  • the direction and amount of frequency change detected are indicative of the direction of physical rotation being sensed and the rate of this rotation, respectively.
  • the difference in beam frequency detected loses its proportionality to the rotational rate due to a phenomenon frequently referred to as "lock-in" in which the two laser beams exhibit a single frequency.
  • One approach to solving the problem of lock-in that is commonly employed is to effect mechanical oscillation ("dither") of the laser sensor apparatus which, when added to the actual rate of change in rotation experienced by the laser beams, raise the frequency change detected above the critical lock-in limit.
  • dither mechanical oscillation
  • three laser angular sensors are arranged with their sensitive axes orthogonally to each other and mounted on a common platform or instrument block. By sensing the rotational, change and rate of change in each of the three orthogonally related planes, angular movement of the vehicle or change in orientation of the vehicle from an initial direction can be continuously determined.
  • each set of laser angular sensors has its own dithering apparatus.
  • the three sensors are particularly effective when mounted on a common instrument block, however, when this is done, mechanical coupling of dithering motions between the laser sensors is experienced. This coupling of dither motion is frequently referred to as "coning" and can produce serious readout errors. Attempts have been made to solve the coning problem in the past by circuit processing techniques in which pick-off signals from the different laser angular sensors are modified in an attempt to eliminate coning error contributions; however, these attempts have not been completely satisfactory.
  • four dithering bodies are flexibly mounted to a single instrument block to permit oscillatory mechanical motion in each of the bodies.
  • Three of the dithering bodies are ring laser angular rotation sensors which are flexibly mounted with mutually orthogonally sensitive axes and each having a dither motion about its sensitive axis.
  • the fourth dithering body may be either a ring laser angular rotation sensor or a compensating mass.
  • the fourth dithering body has an axis of dither rotation which is oriented, generally yet not necessarily, at equal angles with respect to the sensitive axes of the three angular rotation sensors to satisfy conditions of dynamic equilibrium with the other three angular rotation sensors thus relieving the instrument block from moment actions and the resulting dynamic rotational motion.
  • the masses of the four dithering bodies and the dynamic equilibrium is achieved by designing the four dithering bodies to have substantially the same mass and by mounting these bodies on a dither mechanism so that they may be driven in an oscillatory dither motion which has substantially equal frequency, phases and selected amplitudes.
  • a substantially equal frequency of oscillatory motion is achieved by designing the four dither mechanisms to have substantially the same natural resonant frequency and by driving these dither mechanisms at this frequency.
  • Substantially the same phase in the motion of the dithering bodies is achieved by using a single power source such as a sine wave oscillator and by driving the dither mechanisms-in substantially the same phase.
  • dynamic equilibrium is achieved by selecting the amplitudes of the dither drive signals individually to produce amplitudes of oscillatory motion by their respective dithering bodies so that the vector sum of the angular moments of the four dithering bodies is substantially zero. This dynamic equilibrium is maintained over a period of time by continuing to drive the dither mechanisms with signals having substantially equal frequency, substantially equal phase and the selected amplitudes,
  • Dithered ring laser angular rotation sensors are disclosed in U.S. Patents Numbers 3,373,650 and 3,467,472.
  • One type of known dithering mechanism comprises a flexure and piezo electric member mounted on the flexure. Each sensor or each sensor and compensating mass is mounted on such a dithering mechanism to subject it to a dither motion.
  • the preferred embodiment is but one special case of solutions to the problem of coning of trials of ring laser angular rotation sensors that are within the scope of the invention.
  • a generic teaching is also set forth below.
  • Figure 1 is a side elevational view of an instrument block showing three laser angular sensors being stabilized in accordance with the described method and apparatus.
  • Figure 2 is a top plan view of the instrument block of Figure 1.
  • Figure 3 is a schematic representation depicting pertinent motions and moments acting on the apparatus of Figure 1.
  • Figure 4 is a functional block diagram of the compensating mass dithering control. DESCRIPTION OF A PREFERRED EMBODIMENT
  • a one-piece instrument block 10 is seen to include three planar surfaces 11 - 13 which are flat surfaces precisely arranged to be mutually orthogonal to one another and serve as mounting surfaces for three individual laser angular sensors 14 - 16, respectively, shown in schematic form only.
  • the instrument block 10 has by way of example, three feet, isolators or pedestals 17 - 19 for securing the instrument block, and ring laser angular sensors mounted thereon, to the aircraft or other vehicle whose movement is to be monitored. That is, the three angular sensors are all mounted on a common base or instrument block 10 with each sensing angular movements about an axis which is orthogonal to the plane of the surface to which it is mounted. It is known that by such a combination of three angular sensors, a vehicle carrying the instrument block and sensors mounted thereon will be capable of operating in three dimensions with any movement of the vehicle made in any of the three dimensions being detected by one or more of the sensors.
  • each of the ring laser sensors 14 - 16 includes a pair of laser beams moving in respectively opposite directions along a closed path about the sensing axis and means for determing change in frequency of the laser beams in response to angular motions experienced by the sensor about its sensitive axis.
  • each of the laser sensors incorporates dither means 14a, 15a, 16a, respectively, for producing an oscillatory mechanical movement ("dither") of the laser beam generating means and associated sensing apparatus mounted on the instrument block in a direction along the path of movement of the lasing beams to prevent or minimize lock-in of the light beams at low rates of rotation.
  • Each sensor is dithered to prevent one problem, i.e., lock-in but dithering of three sensors creates another problem, coning by mechanical coupling of each dither motion to the other two sensors. Any such coupled dither which is sensed by another sensors result in an error in the output signal of that sensor.
  • a further dither axis X c is shown on the instrument block which for simplicity is depicted in solid lines.
  • the coning compensation means 21 having an axis of rotation X c includes a compensating mass 21 and means 21a for dithering mass 21 about an axis orthogonal to surface 20 and equiangular with respect to all three sensitive axes of the three sensors.
  • the angular momentum of the compensating means when resolved into components along each of the sensors axes will balance the dithering angular momenta so that the vector sum of all four angular momenta and the vector sum of the moments are both substantially zero.
  • the three dithered laser angular sensors are depicted as cylindrical masses having respective dithering moments M 1 , M 2 and M 3 of nearly equal phase and amplitude; the corresponding dithering rotation angles being ⁇ 1 , ⁇ 2 and ⁇ 3 .
  • the compensating mass moment is M and the corresponding dithering angle of rotation is ⁇ c .
  • ⁇ . rotation angles of instrument blocks about x i where i equals 1, 2, 3.
  • a. rotation angles of three orthogonal angular sensors.
  • M c compensating active moment of compensating dither mass.
  • I i j moment of inertia of the entire assembly including the sensors, the compensating mass, and the instrument block with respect to C. G.
  • I angular sensor moment of inertia about dither axis
  • n. compensating mass axis cosine angles with respect to the orthogonol dithering axes.
  • K i j angular stiffness coefficients of the support systems about the instrument block center of gravity.
  • K stiffness of a single dither mechanism.
  • K c stiffness of the compensating dither mechanism.
  • Inertia is with respect to the center of gravity of each respective item.
  • equations (4) and (5) are c
  • the selectively adjustable means 22 for dithering the compensating mass can be adjusted to a prescribed amplitude, frequency and phase of dither that will compensate for mechanical coupling of the dithering of laser sensors 14 - 16 and, in that way, substantially reduce, if not eliminate, coning errors.
  • FIG. 4 illustrates in function block form a generalized circuit schematic for separately adjusting the frequency, amplitude and phase of the compensating mass dithering means.
  • the instrument block included three mutually perpendicular planar surfaces 11 - 13 on which the laser angular sensors are mounted with the mounting surface 20 for the compensating mass intercepting each of the surfaces 11 - 13 at the same angle.
  • the mounting surface 20 intercepted the surfaces 11 - 13 at different angles.
  • the surfaces 11 - 13 may be angularly arranged other than mutually perpendicular which is depicted in Figure 1 by the dashed line surfaces 11' and 12'.
  • the coning compensation means 21 comprises in its most general aspect a mass of indiscriminate character and means for dithering the mass in the manner described earlier herein.
  • An especially advantageous embodiment of the compensation means 21 is achieved by mounting a redundant fourth laser sensor and dithering means on the flat surface 20. Not only would such a construction operate satisfactorily for purposes of the described invention, but also the redundant laser sensor can be readily and advantageously utilized as an active laser sensor in the event of, say, failure of one of the other three laser sensors 14 - 16.
  • Figure 4 there is shown a functional block diagram of one circuit for generating electrical signals for driving dither mechanisms 14a, 15a, 16a, and 21a into oscillatory motion.
  • AC power source 22 comprises an oscillator circuit which generates a signal having a substantially sine waveform.
  • the frequency of the signal generated by source 22 is approximately equal to each of the natural resonant frequencies of dither mechanisms 14a, 15a, 16a and 21a.
  • Amplifiers 24a, b, c and d each amplify this signal and apply it to dither mechanisms 14a, 15a, 16a, and 21a.
  • amplifiers 24a, b, c and d are identical so that the frequency and phase of the sine wave signal from source 22 is not altered.
  • each amplifier can be separately set to prescribe a particular amplitude in the output signal from each and hence prescribe the amplitude of the dither motion of each dither mechanism and respective mass M 1 , M 2 , M 3 and Mc to achieve cancellation of coning effects as taught above.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Electromagnetism (AREA)
  • Power Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Gyroscopes (AREA)

Abstract

Trois jeux de capteurs angulaires pour laser (14, 15, 16), correspondant à trois plans de captage disposés de manière angulaire (11, 12, 13), sont montés sur un bloc à instruments commun (10), chacun étant muni de dispositifs de vacillation mécanique (14a, 15a, 16a) pour créer un mouvement mécanique oscillatoire afin d'annuler essentiellement le verrouillage. Une masse de compensation (21) est montée sur le même bloc d'instruments (10), et dispose d'un dispositif de vacillation mécanique contrôlable et sélectif (21a). Lorsque la masse de compensation vacille à une amplitude, une fréquence et une phase choisies de manière appropriée, elle permet de compenser automatiquement l'interaction de vacillation entre les trois capteurs (14, 15, 16).
PCT/US1985/001397 1984-07-25 1985-07-23 Methode et appareil pour stabiliser la vacillation mecanique d'un capteur angulaire pour laser WO1986000984A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US63432484A 1984-07-25 1984-07-25
US634,324 1984-07-25

Publications (1)

Publication Number Publication Date
WO1986000984A1 true WO1986000984A1 (fr) 1986-02-13

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Application Number Title Priority Date Filing Date
PCT/US1985/001397 WO1986000984A1 (fr) 1984-07-25 1985-07-23 Methode et appareil pour stabiliser la vacillation mecanique d'un capteur angulaire pour laser

Country Status (4)

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EP (1) EP0190260A4 (fr)
JP (1) JPS61502841A (fr)
NO (1) NO860782L (fr)
WO (1) WO1986000984A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0348087A2 (fr) * 1988-06-20 1989-12-27 Sperry Marine Inc. Procédé et appareil pour éliminer des vibrations
FR2787878A1 (fr) * 1998-12-23 2000-06-30 Sextant Avionique Suspension elastique antivibratoire pour unite de mesure inertielle

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4277173A (en) * 1979-08-31 1981-07-07 The Singer Company Ring laser gyroscope dither drive circuit
US4425040A (en) * 1981-01-29 1984-01-10 The Singer Company Ring laser gyroscope cluster for strapped down navigation

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4277173A (en) * 1979-08-31 1981-07-07 The Singer Company Ring laser gyroscope dither drive circuit
US4425040A (en) * 1981-01-29 1984-01-10 The Singer Company Ring laser gyroscope cluster for strapped down navigation

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0190260A4 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0348087A2 (fr) * 1988-06-20 1989-12-27 Sperry Marine Inc. Procédé et appareil pour éliminer des vibrations
EP0348087A3 (fr) * 1988-06-20 1990-10-03 Sperry Marine Inc. Procédé et appareil pour éliminer des vibrations
FR2787878A1 (fr) * 1998-12-23 2000-06-30 Sextant Avionique Suspension elastique antivibratoire pour unite de mesure inertielle
WO2000039526A1 (fr) * 1998-12-23 2000-07-06 Thomson-Csf Sextant Suspension elastique antivibratoire pour unite de mesure inertielle
US6688174B1 (en) 1998-12-23 2004-02-10 Thomson-Csf Sextant Antivibration elastic suspension for inertial measuring unit

Also Published As

Publication number Publication date
NO860782L (no) 1986-03-03
JPS61502841A (ja) 1986-12-04
EP0190260A1 (fr) 1986-08-13
EP0190260A4 (fr) 1987-01-10

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