FR2558951A1 - METHOD FOR STABILIZING THE MECHANICAL VIBRATION OF AN ANGULAR LASER SENSOR AND APPARATUS USING THE SAME - Google Patents

Abstract

THE INVENTION CONCERNS A PROCESS FOR NEUTRALIZING THE INTERACTION WHICH OCCURS BETWEEN THE MECHANICAL VIBRATIONS OF ANGULAR SENSORS11, 12, 13 A LASER MOUNTED ON A COMMON MOUNTING BLOCK10 AND EACH EQUIPPED WITH A MECHANICAL VIBRATION DEVICE TO BE AVOIDED LOCKING. THE PROCESS CONSISTS OF PLACING A COMPENSATING MASS21 ON THE MOUNTING BLOCK AND OSCILLATING THE MASS AT A PREDETERMINED FREQUENCY AND AMPLITUDE IN ORDER TO COMPENSATE AUTOMATICALLY IN THE MOUNTING BLOCK FOR THE INTERACTION OF THE MECHANICAL VIBRATIONS OF THE THREE SENSORS. APPLICATION TO INERTIAL GUIDANCE SYSTEMS.

Description

The present invention relates generally to

  laser angular sensor and, more particularly, an apparatus and method of stabilizing with respect to

  certain adverse effects of mechanical vibration

  in such a sensor to prevent the locking or

attachment of the laser beams.

  An angular laser sensor consists essentially of

  first and second laser beams which travel in opposite directions around a closed loop path surrounding the axis of rotation with respect to which the sensor is to detect and measure the angular variation. The rotation of the apparatus about the axis changes the effective length of the path that each beam must travel, which in turn can be detected as a difference in frequency between the two laser beams. The direction and the importance of the detected frequency change are representative of both the direction of the physical rotation to be detected and the speed of this rotation. At low rotational speeds, the difference

  detection of beam frequencies loses its proportiona-

  with the speed of rotation due to a phenomenon

  often referred to as "locking" whereby the two

  those lasers have a unique frequency.

  A commonly used way of solving the problem

  locking problem consists of having an oscillating

  mechanical release (or vibration) to the laser sensor device,

  which, when added to the actual speed of variation,

  resulting from the rotation of the laser beams, increases the frequency variation detected above

the critical threshold of locking.

  In a practical application for the purposes, for example

  In the navigation of an aircraft, three laser angular sensor units are arranged orthogonally to each other and are mounted on a common device carrier or mounting block. The movement of the vehicle or the change of its orientation from a deposit, a site and a

  initial positions can be determined continuously in de-

  sensing the rotational variation and rate of change in each of the three orthogonal two-to-two planes. In order to avoid locking, each laser angular sensor unit has its own vibrator device. The three sensor units operate particularly efficiently

  when mounted on a common mounting block: always

  sometimes, when this is done, a coupling occurs

  vibratory motion between the laser sensors. This cou-

  range of vibratory movements is also called

  action "and may result in serious misreading.

  Attempts to solve the problem of interaction

  have been carried out in the past by treatment techniques

  in circuit according to which the output signals

  different angular laser sensors are modified.

  in order to eliminate what results from the errors of inter-

  action; these attempts, however, have not proved

totally satisfactory.

  In the practice of the present invention,

  several laser angular sensor units corresponding to

  laying on orthogonal detection planes (eg X, Y, Z) are mounted on a device carrier or block of

  common mounting and are each provided with vibrating devices

  mechanical motors inducing mechanical oscillatory

  in each of the laser angle sensors to

  avoid or delay locking. This vibratory movement

  may be random or periodic, both in terms of

  Circle the amplitude as the oscillation frequency.

  A compensating mass (for example a fourth angular laser sensor, redundancy) is mounted on the same mounting block or device support and has a

  selectively adjustable mechanical vibrator device.

  When the compensating mass is mounted so that its vibratory plane of rotation makes determined angles (for example equal angles) with the planes of the three angular laser sensors, the vibration of the

  compensating mass at a suitable amplitude and frequency

  selected choice will automatically compensate the interaction

between the three sensors.

  In the accompanying drawings: Fig. 1 is a side elevational view of a mounting block showing the three laser angular sensors stabilized in accordance with the described method and apparatus; Figure 2 is a top plan view of the mounting block of Figure 1; FIG. 3 is a schematic representation

  illustrating interesting movements and moments that

  on the apparatus of Figure 1; and FIG. 4 is a functional block diagram

  of the vibration control of the compensating mass.

  Referring now to the drawings, and in

  Particularly in FIGS. 1 and 2, an integral mounting block 10 has three planar surfaces 11-13 which are accurately arranged to be orthogonal to each other and serve as mounting surfaces for, respectively,

  three individual laser angle sensors 14-16,

  only in a schematic way. The mounting block has three legs or bases 17-19 for attaching the mounting block, and the laser angle sensors mounted thereon, to the aircraft or to another vehicle whose

  movement must be controlled. In other words, the three cap-

  angular motors are fully mounted on a seat

  common unit, namely the mounting block 10, each of them detects

  both rotational movements about an axis orthogonal to the plane of the surface on which it is mounted. We know

  that thanks to such a combination of three angular sensors

  a vehicle carrying the storage unit and the sensors therein can move in three

  dimensions, any movement that the vehicle makes in any

  which one of the three dimensions is detected by one or

several of the sensors.

  Each of the 14-16 laser sensors includes conventional

  a pair of laser beams traveling in respectively opposite directions following a closed path around the detection axis, and means for measuring the frequency variation of the laser beams. In addition, a necessity

  prior to the implementation of the apparatus and the

  According to the invention, each of the laser sensors comprises a device generating an oscillatory (or vibratory) mechanical movement of the means for producing the laser beams and the associated detection apparatus which are mounted on the mounting block, in a direction that follows. the path

routing laser beams.

  Angular sensors provided with mechanical vibrator means which are in question here are of a construction and operation and therefore will not be

not described in detail.

  The mounting block is provided with an additional flat surface 20 which, for the sake of simplification, is shown in solid lines in an o

  it makes precisely equal angles with the three sur-

  mounting faces 11-13 of the sensors. 21 means of communication

  the interaction of the interaction, mounted on the surface 20, comprise a mass and selectively adjustable means for vibrating the mass in a parallel plane

  20. As will be developed in the descrip-

  following, the angular momentum of the compensating

  when projected on each of the detection axes, balanced

  will break the angular moments of vibration.

  For the following analysis, reference is made to

  schematic diagram of Figure 3. The three angular vibration laser sensors are shown as

  cylindrical masses having vibration moments

  Since M1, M2 and M3 are almost equal in phase and amplitude, the corresponding vibration angles of rotation are "i 'a2 and a3. Similarly, the moment of the compensating mass is Mc and the corresponding vibration angle is equal to admitting that only small angles of rotation are involved, the dynamic equations of motion in Cartesian tensor notation for the rotation of the

  mounting block, the angle sensors and the compensating mass

  in the vibratory mode, are the following: (Iij I- ij Icnin.j) j + K (ei - i) + K (Ojnj -c) n + K Ki j = Mi + Mc i (1) I 'i + K (Yi - ii) -Mi (2) Ic 'c + Kc (% - Ojnj) = -Mc (3)

  o, 8i = rotation angles of the mounting block around xi.

  ai = rotation angles of the three orthogonal angular sensors.

  ac = angle of rotation of the compensating mass.

  Iij = moment of inertia of the complete set.

  I = moment of inertia of an angular sensor around

of the vibration axis.

  Ic = moment of inertia of the compensating mass.

  ni = cosine of the angles of the axis of the compensating mass

trice with respect to xi.

  Kij = coefficients of angular stiffness of the support system around the center of gravity of the mounting block.

K = vibration rigidity alone.

  Kc = compensation vibration rigidity.

1 if i = j

&. =

  iJ 0 if iLj Admitting more than the center of elasticity

  supports coincide with the center of gravity, and in

  thus reducing the separation between rotation and trans-

  By placing equation (1) equal to zero, we obtain: (I iij ij Icnin) 8j + K (8i - ai) + Kc (6.n-c) ni + K. ej = 0 ( 4)

  Multiplying equation (3) by ni and adding

  at (2), we have: I -i + Icac ni + K (E-8i) + Kcc-8n) ni c 0 (5) In the case where Kc = K- equations (4) and (5) Ic I constitute a system of six homogeneous equations whose

  six unknowns are Ei and (I. + n) The static solution

of these equations is:

O = 0 (6)

  i = 0; I ai + Icac ni = (6) either, s. = (7) I ai = -Icc neither

  This result demonstrates the elimination of interac-

  and resulting errors.

  In the particular case where n1 = n2 = n3 = 3/3, then 1 = 3 () On the basis of the previous analysis, it appears

  clearly that the selectively adjustable means 22

  designed to vibrate the compensating mass can be adjusted to a vibration amplitude and frequency

  which will compensate for the mechanical coupling of

  laser 14-16 vibrators and, in this way, reduce

  strongly, if not eliminate, errors due to

  action. Although admitted, as an initial condition

  simplification in the development of dynamic equations

  the mounting plane 20 of the compensating mass intersects the mounting planes 11-13 of the sensors under

  equal angles, it must be emphasized that this is not indis-

  thinkable and that the angles of intersection with the different

  plans may be different. This eventuality is

  shown in Figure 1 o is shown in lines with inter-

  broken the compensation plane which is inclined with respect to the original plane 20 and, therefore, clearly intersects the respective planes 11-13 at substantially different angles. In addition, although it is thought that the compensating mass, the vibration amplitude of the compensating mass and its frequency can be modified, the simplest and most direct construction is to ensure that

  that the compensating mass is identical to that of a cap-

  tor, and adjust either the amplitude of vibration of the compensating mass or its frequency, while keeping the other magnitude at a value substantially identical to the corresponding value of the sensors. Figure 4 illustrates in form

  functional synoptic a general diagram of a circuit des-

  to adjust separately the frequency and the amplitude of the means for vibrating the compensating mass. These MVC means being controlled by a control unit CF of the vibration frequency and by a control unit CA

the amplitude of vibration.

  In the first embodiment described, the mounting block comprises three flat surfaces 11-13 two

  two orthogonal ones on which three

  angular laser planes, the plane of the mounting surface of the compensating mass intersecting each of the planes of surfaces 11-13 at the same angle. In the second embodiment described, the plane of the intersecting surface 20

  the planes of surfaces 11-13 from different angles.

  It is further contemplated that the surfaces 11-13 may have an angular arrangement other than that where they are two to two perpendicular, as shown in FIG. 1 by the dash line surfaces 11 'and 12'. We now present the

  analytical bases of this other embodiment.

  We now consider the case where the three gyros

  Laser copes are in planes 11 ', 12' and 13 which are not two to two perpendicular. This case is best described in an affine coordinate system whose axes are normal to vibratory planes. In an affine coordinate system, indices and exponents will designate

  respectively the covariant and contravariant components.

  Using the same notation as the modes of reali-

  sation previously described, we can write: (I. _ - Icn nj) ii + K (8i _ a) + K (<Jnj - c) n + K 8i = Mi + Mcn jc jc I i + K (i _ 8i ) = -Mi cIc + Kc (oc-8 nj) = -Mc where the mixed tensors of inertia and rigidity are defined as follows: Ii = f (r2 ji - yjy) dm; KJ nj - nj Yn) yi is measured along affine axes yi comes from the relation: Yi = gijy

  o gij are the covariant components of the basic tensors

mentally.

  The equations of motion in the case of oblicity (that is to say in the case in which the planes 11-13 are not two to two perpendicular), are, when used

  the affine coordinates and writes them in covariate

  laughing, algebraically identical to those of the ortho-

  gonality [equations (1), (2) and (3)]. It can then be inferred that the dynamic compensation of the interaction applies to the case of oblicity as well as it has been demonstrated in the case

  of two to two perpendicular ring laser gyroscopes.

  The means 21 for compensation of the interaction consist, from the most general point of view, in a mass of indeterminate nature, and in means for vibrating the mass in the manner described above. A particularly advantageous embodiment of the compensation means 21 is obtained by mounting on the flat surface 20 a fourth redundancy laser sensor and means of

  set in vibration. Not only does such a structure

  would be satisfactory in the views of the pre-

  invention, but the redundancy laser sensor can

  be easily and conveniently used as a

  active laser in the event, for example, of a

  failure of one of the other three laser sensors 14-16.

Claims (10)

  A method of neutralizing the interaction that occurs between the mechanical vibrations of two or more laser angle sensors mounted on a common mounting block, characterized in that it comprises the steps of: disposing a mass compensator on the mounting block; and swing the mass to   a predetermined frequency and amplitude in order to counter   to substantially complete the interactions resulting from the vibration of the angular laser sensors, in the mounting block.   2. Method according to claim 1, characterized in that the oscillation is carried out around an axis having a   angular relationship fixed with respect to the mounting block.   3. Apparatus comprising a plurality of laser angle sensor units (14, 15, 16) mounted on the same mounting block (10), each laser angular sensor unit   comprising individual means for mechanically vibrating   characterized in that it comprises: an object (21) of predetermined mass mounted on the mounting block; and   means for mechanical oscillation of the object.   jet at a frequency and amplitude suitable for neutralizing   the interaction of vibrations that occurs between   individual means of vibrating the angular sensors lar.   4. Apparatus according to claim 3, characterized in that it comprises three units (14, 15, 16) of laser angular sensors respectively mounted on plans (11, 12, 13) arranged orthogonally and intended to detect the applied movements. around axes normal to these planes, and in that the object (21) is mounted on a plane intersecting the planes arranged orthogonally under at least two different angles. 5. Apparatus according to claim 4, characterized in that the means of mechanical vibration of each angular sensor (14, 15 and 16) to laser cause 2558951,   he oscillates in a plane parallel to the assembly plan   (11, 12 and 13) of the sensor device, and that the oscillator   tion of the object (21) takes place in a plane parallel to the plan of assembly of the object.   Apparatus according to claim 3, characterized   in that the means for vibrating the angular sensors   (14, 15, 16) oscillate at approximately the same frequency   quences, amplitude and phase, and in that the oscillation of the object (21) is effected at substantially the same frequency as that of the vibration of the angular sensors while   the amplitude of the oscillation of the object is set to   nance. Angle laser sensor apparatus, characterized in that it comprises: a unitary mounting block (10); three laser angle sensors (14, 15, 16) mounted on respective surfaces (11 or 11 ', 12 or 12', 13) of the mounting block; individual vibration means associated with each of the laser angle sensors for mechanically oscillating the sensors in parallel with   their mounting surface; a compensating mass (21)   movable head on an additional surface (20) of the mounting block; and selectively adjustable means for oscillating the compensating mass at an amplitude and a frequency data.   8. Angle laser sensor apparatus according to the   Claim 7, characterized in that the amplitudes, fre-   quences and phases of the vibrating means are   respectively substantially identical.   Angle laser sensor apparatus according to claim 7, characterized in that the three mounting surfaces (11, 12, 13) of the angle sensors (14, 15, 16)   to laser are two to two perpendicular.   Angle laser sensor apparatus according to claim 9, characterized in that the mounting plane (20)   the compensating mass (21) intersects each plan of   sensor stage (11, 12, 13) at the same angle.