FR2548357A1 - ROUND LASER GYROSCOPE FOR SURVEY BASE - Google Patents

Abstract

THE INVENTION RELATES TO A RING LASER GYROSCOPE ASSEMBLY INTENDED FOR MEASURING ROTATION AROUND AN AXIS. IT INCLUDES A BODY 10 IN A CAVITY WHICH TURN TWO LASER BEAMS, IN REVERSE DIRECTION. THE BODY, OF POLYGONAL SHAPE, HAS TWO RELATIVELY LONG SIDES 30, 32 AND SHORT SIDES ON WHICH THE MIRRORS 20, 22, 26 ARE PROVIDED. TWO OF THESE MIRRORS ARE ANIMATED BY PHASE OPPOSITION VIBRATIONS TO PREVENT THE LOCKING OF THE BEAMS. FIELD OF APPLICATION: ROTATION MEASUREMENTS IN THE BOTTOM OF OIL, GAS, ETC.

Description

The invention relates to a ring laser gyroscope, and more

  particularly an extremely precise and compact ring laser gyroscope, intended to be used in a sounding, for example in an oil well. Due to the small diameter of the oil well soundings, the size of the instruments used in these soundings is critical. The known ring laser gyroscope assemblies are generally unsuitable for use in a borehole, alone or in a group. because these gyroscope sets are too large, or the gyroscope is not

sufficiently precise.

  Conventional ring laser gyroscopes 15 comprise a cavity forming a closed circuit loop in which two oppositely rotating laser beams move. In known attempts to reduce the overall size of the gyroscope, it has been reduced to 6 cm. However, it has been found that the accuracy of the gyroscope is directly proportional to the size of the area delimited by the cavity and therefore to the length of the path. By reducing the length of the path to reduce the overall dimension of gyroscope, one obtains a gyroscope, for example 6 cm, which is not precise enough for most applications, including

  the applications in the background.

  One of the problems affecting the accuracy of a ring laser gyroscope is the locking or latching phenomenon of the two reverse-rotating laser beams. To prevent locking, various dithering techniques have been used using a device. Although a known polarization device increases the accuracy of the gyroscope, such a device generally substantially increases the overall dimensions of the gyroscope assembly Gyroscope assemblies having such a device are therefore generally too

  bulky to be used in the background.

  The invention eliminates the disadvantages of prior art ring laser gyroscopes as described above. The ring laser gyroscope assembly according to the invention is both extremely precise and very small in size. to be used in a survey sample, for example in a poll

oil wells.

  The scanning ring laser gyroscope comprises a body having a polygonal cavity forming a closed circuit path traversed by two beams rotating in opposite directions, a mirror being disposed at each corner of the cavity 15 in order to reflect the beams. The body of the gyroscope is of polygonal shape, two opposite sides of which are substantially longer than the other sides which are short so as to form a long, narrow body, which can be used in the bottom of the tube. Each of the mirrors is disposed on one, different, short sides of the body of the gyroscope, the number of short sides of the body being equal to the number of mirrors to minimize the width of the body The cavity is located inside the body of the gyroscope in such a position relative to the mirrors, that the length of the path of the closed circuit formed by the cavity is maximum for the body

narrow gyroscope.

  One technique used to prevent the locking of two opposing laser beams is mirror shake, a technique in which two of the gyro mirrors are subjected to anti-phase vibrations. The two shaking mirrors can be arranged on short sides. adjacent to the body of the gyroscope, the cavity being formed inside the body relative to the mirrors, so that the long sides of the cavity are parallel to the long sides of the body The two mirrors in shake can also be arranged on sides opposite sides of the body of the gyroscope, the cavity being offset from the body so that the path length of the cavity is maximum and the width of the body of the gyroscope is minimal. The ring laser gyroscope set for the sounding floor further comprises a polarization device for imparting a tremor to the body of the gyroscope to prevent the locking or catching of the two laser beams rotating in opposite directions. The polarization device comprises first and second flexible assemblies arranged in close proximity to opposite sides of the body of the gyroscope, each assembly being mounted between the body 15 and a support; means are provided for driving

  the two flexible assemblies in phase opposition relative to each other in order to shake the body of the gyroscope around an axis of entry of this body.

  Each of the flexible assemblies is extremely narrow so as to increase the overall width only to a minimum

  of the ring laser gyroscope assembly.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting examples and in which: FIG. 1 is an exploded perspective view of the ring laser gyroscope assembly for a sampling base according to FIG. invention; Fig. 2 is a sectional view of the laser ring gyroscope body taken along the line 2-2 of Fig. 1; Figure 3 is a section, similar to that of Figure 2, of a second embodiment of the body of the ring laser gyroscope according to the invention; Fig. 4 is a top view, partially broken away, of the ring laser gyroscope assembly of Fig. 1 showing the polarization device for imparting tremor to the body of the gyroscope; Figure 5 is a perspective view of a flexible blade of the biasing device shown in Figure 4; Fig. 6 is a cross-section of the ring laser gyroscope assembly housed in a housing; and FIG. 7 is a partial view in

  end, with partial section, of the laser ring gyroscope assembly 10 in its housing.

  The ring probing laser gyro, as shown in FIGS. 1 and 2, comprises a body 10 which may be made of quartz, delimiting an interior cavity 12 of polygonal shape which forms a closed circuit path. The cavity contains one or more gases suitable for laser operation, for example 90% helium and 10% Neon, at a pressure of 400 Pa. A gas discharge is established between a cathode 14 and two anodes 16 and 18 each communicating with the cavity 12, in order to produce two laser beams rotating in opposite directions The beams go through

  the closed circuit path by reflection on mirrors 20, 22, 24 and 26 placed in the corners of the cavity.

  When the gyro rotates about any axis of input parallel to the Z axis, the effective length of the path of one beam is increased while that of the other beam is decreased as a result of Doppler shift. beat, proportional to the speed of rotation, is produced in response to the application of a heterodyne effect to the two beams, for example under the action of a prism associated with the mirror 24 The beat frequency produces a configuration of fringes which is detected by a double photodiode

  28 producing the output signal of the gyroscope.

  The body of the ring laser gyroscope is made to be very narrow and very compact for use in an oil well bore, alone or in a group of instruments.

  body, measured along the X axis, is about 2.5 cm.

  However, the body is substantially longer than wide. The length, viewed along the Y axis, is about 12.5 cm so that the body encloses a cavity having a path length of about 25 cm. Since cavities with shorter length paths are known, it appears that the larger the cavity, and hence the longer the path, the more accurate the gyroscope

is tall.

  To give the body of the gyroscope a minimum width, but a maximum length to the closed circuit path formed by the cavity, the body 10 of the gyroscope is made to have a polygonal shape of which two non-adjacent or opposite sides 30 and 32 are substantially longer than the other two sides 34-40 on which the mirrors are mounted, the remaining sides being shorter to form a long and narrow body. In addition, the short sides 34-40 of the body 10 are equal in number to that of the necessary mirrors, so

  to give the gyroscope a minimum overall width.

  The cavity 12 is made to have a long and narrow polygonal shape, with two channels or amplifying tubes 42 and 44 being longer than the remaining amplifier tubes 46 and 48. The long amplifying tubes are arranged adjacent to the long sides 30 and 32 of the short tubes 46 and 48 intersecting the long tubes 42 and 44 at the mirrors The cavity 12 is positioned inside the body of the gyroscope with respect to the mirrors so that the length of the closed circuit path formed by Although the cavity as shown is rectangular and located within an irregular hexagonal body, it could have various other polygonal shapes. For example, a cavity forming a long narrow triangle could

  be disposed within an irregular pentagonal body, according to the invention.

  To prevent the locking of the two counter-rotating laser beams, the probing ring laser gyro uses both a body tremor, as described in detail below, and a mirror arrangement by which each of the mirrors 20 and 22 is subjected to periodic vibration in a direction perpendicular to its face. The mirrors 20 and 22 are oppositely controlled diaphragm mirrors to maintain a constant path length of the cavity. 45 or 47 controlling the length of the cavity and responsive to the output signal of a single photodiode 49 associated with the mirror 26 The photodiode 49 detects the intensity of the laser beams and applies to the mirrors in shake a current output signal continuous so that the beams are kept in the center of the mode Details of two shaking mirrors and a control circuit intended for hand hold their phase shift of 180 are given in the United States patent application

N 462 548.

  In one embodiment of the ring-bottom laser gyroscope 25, as shown in FIG. 2, the diaphragm mirrors 20 and 22 are positioned on adjacent short sides 34 and 36 of the gyroscope body 10. Cavity 12 is positioned within the body of the gyroscope so that the long amplifier tubes 42 and 44 are parallel to the long sides 30 and 32 of the body. This configuration results in a sufficiently gyroscope assembly.

  narrow for most applications.

  However, to further reduce the width of the gyroscope while allowing the use of diaphgram mirrors 20 and 22 which are larger than other mirrors, the ring laser gyroscope can be modified as shown in Fig. 3 In this configuration , the diaphragm mirrors 20 'and 22' are positioned on opposite short sides 34 'and 38' of the body 10 'and the cavity 12' is shifted inside the body so that the beams intersect the central portion of the mirrors The sides 34 'and 38' are made to be long enough to accommodate the large diaphragm mirrors 20 'and 22', the sides 36 'and 40' being shorter than the sides 34 'and 38' to minimize the width of the gyroscope The small mirrors 24 'and 26' are positioned on the sides 36 'and 40, closer to respective adjacent long sides 32' and 30 'of the body to maximize the path length of the cavity 12'. Another feature that minimizes the overall width of the ring laser gyroscope assembly while providing a maximum length to the length of the closed circuit path is also a relative feature of the mirrors and the offset cavity.

by the cavity.

  In addition to the shaking of the mirrors, the

  body 10 of the ring laser gyroscope is subjected to tremor by a polarization device.

  The latter causes the body of the gyroscope to vibrate in a rotational fashion, around an input axis of the gyroscope, to prevent the laser beams from being locked, the polarization device being shown in detail in FIGS. 1 and 4 to FIG. This biasing device is extremely narrow, increasing only slightly the overall width of the gyroscope assembly. The biasing device 30 comprises two flexible assemblies 50 and 52 adjacent to the long sides 30 and 32, respectively, of the body of the gyroscope. The flexible assemblies 50 and 52 are connected to the body of the gyroscope by means of two mounting blocks 62 and 64. The mounting blocks 62 and 64 are made of quartz and fixed by an epoxy glue to the body 10 on the opposite sides of the body. a central input axis 65 of the gyroscope The arrangement of the cathode 14, the anodes 16 and 18, a getter 19 and the blocks 62 and 64 for mounting on the same surface 67 of the gyroscope makes it possible to minimize the overall height of the the The laser ring gyroscope assembly and its width, the resulting structure is extremely compact. The flexible assembly 50 comprises two flexible blades 54 and 56 which may be in "INVAR" or beryllium-copper alloy, these materials having a high strength and being sufficiently rigid so that the only IG movement communicated to the gyroscope is the trembling movement The flexible blades 54 and 56 are attached, at their respective outer ends 58 and 60, to a support 61, shown in FIGS. 6 and 7, of the gyroscope and their inner ends 15 are connected to the body of the gyroscope via the respective mounting blocks 62 and 64 Similarly, the flexible assembly 52 comprises two flexible blades 66 and 68 made of "INVAR" or other. The blades 66 and 68 are attached by their respective outer ends 70 and 72 to the support 61 and their inner ends are connected to the respective blocks 62

and 64 mounting.

  As described in detail below, the blades 54 and 56 are controlled in phase opposition with respect to each other, as are the blades 66 and 68. In addition, the blades 54 and 66 are controlled in opposition to each other. This control results in the application of a push-pull force 30 to the mounting block 62, which is in opposition to the phase with respect to each other, as well as the blades 56 and 68.

  to the resulting force of push-pull applied to the mounting block 64 The push-pull forces applied to the mounting blocks 62 and 64, in phase shift of 180, vibrate the body of the gyroscope in a rotational mode about the axis. central entrance 65.

  The flexible blades 54, 56, 66 and 68 are of the same embodiment, so that only the flexible blade 56 will be described in detail with reference to the figure. The flexible blade 56 has, at its outer end 60, a flange 74 extending outwardly and which has two holes 75 in which screws, such as a screw 76 shown in Fig. 7, pass to fix this flexible blade to the support 61 A portion 78 of the flexible blade, located at its outer end ,

  extends inward towards the body of the gyroscope and limits the distance that the body of the gyroscope 10 can travel when subjected to a tremor.

  A rubber pad 80 is attached to the portion 78 to absorb any shock or stress between the body of the gyro and the outer end of the flexible blade,

  such a constraint or shock that may result from the trembling of the body 10.

  The inner end 84 of the flexible blade 56 has a flange 90 which extends inward towards the body of the gyro and bears against the mounting block 64. The inner end of the flexible blade 56 is attached to three-screw mounting block 64 passing through respective holes 98 of the flange 90 and penetrating into corresponding threaded holes 102 of the mounting block 64. The flexible blade 68 also has, at its inner end, a flange 104 of the same construction as the flange 90 of the flexible blade 56 The flange 104 is attached to the mounting block 64 by three screws 106 passing through respective holes 108 of the flange 104 and penetrating into tapped holes 102 of the mounting block 64, the screws 106 penetrating the the holes 102 from the end

  opposite to that by which the screws 96 penetrate.

  It should be noted that three screws, inserted into respective holes of a flange and mounting block 64 and into respective threaded holes of the other flange, may be used in place of the six screws 96 and 106. simple ones would compress the mounting blocks to maintain

the stability of the input shaft.

  The blocks 62 and 64 of assembly are realized

  in quartz and each have a hexagonal section.

  Each of the flanges of the flexible blades, e.g. flange 90, has a V-shaped cut to correspond to the respective outwardly extending V-shaped side of the mounting blocks Due to the V configuration With the sides of the mounting blocks bearing against the flanges of the flexible assemblies, the blocks 62 and 64 minimize any forces due to the mounting of the flexible assemblies that can be transmitted to the body of the gyro. The quartz blocks 62 and 64 therefore allow the assemblies flexible to be mounted on the body of the gyroscope without deforming the gyroscope

  or create constraints in the latter.

  The inner ends 84 of the flexible blades are notched so as to have a generally U-shaped portion 114, as shown for the blade 56 in FIG. 5 The U-shaped portions 114 of the flexible blades 54 and 56 extend between two 20 washers 116 and 118 of rubber in notches

  formed in opposite sides of a damper 120.

  The damper 120 is centered in close proximity to the gyro body side 10 Similarly, the U-shaped portions 114 of the flexible blades 66 and 68 extend between two washers 122 and 124 of

  rubber to penetrate respective notches on opposite sides of a damper 126.

  The latter is centered in the immediate vicinity of the side 32 of the body of the gyroscope, directly opposite the amor30 weaver 120.

  A rubber pad 128 is disposed between the damper 120 and the quartz body 10 of the gyroscope to eliminate any stress appearing between them. A rubber pad 130 is similarly disposed between the damper 126 and the body of the gyroscope. Preload is applied to the rubber 128, 130 and to the body 10 of the gyroscope by screws 134 and 135 passing through central threaded holes formed in the dampers 120 and 126, respectively. These dampers 120 and 126 virtually eliminate any translation in the X direction due to shocks which may correspond to an acceleration of the order of 10000 m / s 2. The dampers 120 and 126 are fixed to the support 61 of the ring laser gyroscope as shown in Figure 6 These dampers 120 and 126 comprise flanges 140 and 142 extending respectively outwardly and traversed by two threaded holes

  136 and 148 in which screws 147 and 149 pass.

  The screws also penetrate threaded holes formed in the support 61 Although the dampers are fixedly mounted on the support 61, when the flexible blades are actuated, their inner ends 84 are urged to penetrate the notches of the dampers in order to to get closer

  and to move away from the body of the gyroscope and communicate to it the movement of trembling.

  To control the flexible blades, a piezoelectric transducer element is mounted on opposite sides of each of the blades. The elements react to a control voltage which may take the form of a sine wave or the like in order to impart the desired tremor When the piezoelectric transducer elements are all controlled under a voltage of the same polarity, they are mounted on the blades in different crystallographic orientations. For example, the transducer element 150 mounted on the outer surface of the flexible blade 54 may have a first orientation such that, under the application of a positive voltage, the element expands. The transducer element 152 mounted on the inner surface of the flexible blade 54 has a second orientation such that, under the application of a positive voltage, this transducer element 152 also expands. as a result of a thrust of the flexible blade 54 to the block 62 mounting under the application of a positive polarity voltage, the blade away from the block under the application

  a negative polarity voltage.

  Given the above orientation of the piezoelectric transducer elements associated with the flexible blade 54, the other transducer elements have the following orientations. The outer transducer elements 154 and 156 associated with the respective flexible blades 54 and 66 have the second orientation while the elements Transducers 158 and 160 mounted on the inner surface of the respective flexible blades 56 and 66 have the first orientation. The outer transducer element 162 of the flexible blade 68 has the first orientation while the transducer element 164 mounted on the inner surface of the Flexible blade 68 has the second orientation. In general, the inner and outer piezoelectric transducer elements associated with a flexible blade have the same orientation as the respective inner and outer transducer elements associated with the flexible blade diagonally opposed to the first flexible blade. and have the opposite orientation to that of the inner and outer elements associated with the flexible blade being directly opposite, through the gyroscope, of the first flexible blade. It should be noted that instead of alternating the orientation of the transducer elements of each of the flexible blades, one can use transducer elements of the same orientation, but controlled by voltages of opposite polarity to communicate

  the desired trembling movement.

  The ring laser gyroscope assembly is housed in a housing including a cover 170 and the support 61 which forms the base. The cover 170 of the housing is secured to the support by bolts 172 or screws. The support 61 has a flat bottom. 174, which facilitates assembly of the gyroscope assembly

  in a group of instruments or whatever.

  It goes without saying that many modifications can be made to the gyroscope described and shown without departing from the scope of the invention.

Claims (12)

  A ring laser gyroscope assembly for measuring a rotation about an input axis, the gyroscope having a body (10) having a polygonal cavity (12) constituting a closed circuit path traversed by two beams rotating in the opposite direction, a mirror (20, 22, 24, 26) being disposed at each corner of the cavity for reflecting the beams in the path, the gyroscope assembly being characterized in that the body of the gyroscope presents a polygonal shape of which two opposite sides (30, 32) are substantially longer than the other sides (34-40) which are short so as to form a long and narrow body, each of the mirrors being arranged on one, different short sides of the body and the cavity being formed inside the body with respect to the mirrors so that the length of the closed circuit path constituted by the cavity is maximum for the narrow body of the gyroscope.   2 gyroscope assembly according to claim 1, characterized in that the number of short sides   body is equal to the number of mirrors.   3 gyroscope assembly according to claim 1, characterized in that the width of the gyroscope 25 is less than 5 cm and the length of the circuit path closed is at least 25 cm.   4 gyroscope assembly according to claim 1, characterized in that it further comprises means (50, 52) for vibrating two of the mirrors 30 in phase opposition with respect to each other.   A gyroscope assembly according to claim 1, characterized in that it further comprises means disposed in close proximity to each of the long sides of the body of the gyroscope to impart tremor to the body of the gyroscope around of an input axis of this gyroscope.   A ring laser gyroscope assembly for measuring a rotation about an input axis, the gyroscope having a body (10) having a cavity (12) of rectangular shape forming a closed circuit path traveled by two beams rotating in the opposite direction, four mirrors (20, 22, 24, 26) being each arranged at an angle of the cavity to reflect the beams in the path, the gyroscope assembly being characterized in that the body of the gyroscope is 10 of hexagonal shape whose two opposite sides (30, 32) are longer than the other sides (34-40) which are short so as to form a long and narrow body, each of the mirrors being arranged on one, different, short sides of the body and the cavity being disposed within the body, with respect to the mirrors, so that the length of the closed circuit path formed by   the cavity is maximum for the narrow body of the gyroscope.   7 gyroscope assembly according to claim 6, characterized in that it further comprises means for vibrating two (20, 22) said mirrors in phase opposition with respect to each other, the two mirrors in vibration being disposed on adjacent short sides of the body of the gyroscope and the cavity being disposed within the body so that two sides of this cavity are parallel to the two long sides of the body.   8 gyroscope assembly according to claim 6, characterized in that it further comprises means for vibrating two of the mirrors in phase opposition with respect to each other, the vibration mirrors being arranged on opposite short sides of the body of the gyroscope and the cavity being shifted   inside the body of the gyroscope.   9 gyroscope assembly according to revendica35 tion 6, characterized in that it further comprises means for vibrating two mirrors in phase opposition relative to each other and movens arranged in the immediate vicinity of two long sides of the body of the gyroscope to impart a tremor movement to the body, about an axis of entry of the gyroscope. A ring laser gyroscope assembly for measuring a rotational speed about an input axis, the gyroscope having a body (10) having a polygonal cavity (12) forming a closed circuit path traversed by two beams rotating in the opposite direction, mirrors (20, 22, 24, 26) being each arranged at an angle of the cavity to reflect the beams in the path, the assembly comprising means for supporting the body of the gyroscope and being characterized in that the body of the gyroscope is of polygonal shape, two opposite sides (30, 32) of which are longer than the other sides (34-40) which are short so as to form a long and narrow body, each of the mirrors being disposed on one, different, short sides of the body, a device   polarizer being disposed in close proximity to each of the long sides of the body of the gyroscope to impart tremor to the body about an input axis to prevent the beams from locking.   11 gyroscope assembly according to claim 10, characterized in that the biasing device comprises a first flexible assembly (50) mounted between the body of the gyroscope and the support means 30 and disposed in close proximity to one of the long sides of the gyro. gyroscope body, a second flexible assembly (52) mounted between the body of the gyroscope and the support means and disposed in close proximity to the other of the long sides of the body of the gyroscope, and means (150, 152) for to control each of the flexible sets in opposition of phase to make tremble   the body of the gyroscope around the axis of entry.   A gyroscope assembly according to claim 11, characterized in that it further comprises two mounting blocks (62, 64) attached to a surface of the gyroscope body on opposite sides of the input axis so as to to connect each of the flexible sets to the body of the gyroscope.   A gyroscope assembly according to claim 12, characterized in that each of the mounting blocks has outwardly extending V-shaped sides toward each of the flexible assemblies, and each flexible assembly comprises an element ( 90) which has a V-shaped notch for mating with the shaped sides in   V, extending outward, mounting blocks.   14 gyroscope assembly according to claim 12, characterized in that the body of the gyroscope and each of the mounting blocks are made of quartz, an adhesive   Epoxy bonding the mounting blocks to the body of the gyroscope.   A gyroscope assembly according to claim 12, characterized in that the gyroscope further comprises a cathode (14) and two anodes (16, 18) each communicating with the cavity, the cathode, the anodes and the mounting blocks being mounted on the   same body surface of the gyroscope to minimize the height and width of the gyro assembly.