JP2012185046A - Fiber optic gyroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber optic gyroscope which eliminates an influence of thermal stress generated by a difference in thermal expansion coefficient between a bobbin and an optical fiber, has excellent temperature characteristics, and has high performance.SOLUTION: In the fiber optic gyroscope which propagates light to a sensing coil 30 formed of an optical fiber 31 both clockwise and counterclockwise, and detects an input angular velocity from a phase difference between the counterclockwise light and the clockwise light generated by an angular velocity input, a buffer layer 40 is constituted so that an optical fiber 41 different from the optical fiber 31 constituting the sensing coil 30 is wound around a bobbin 32, and the sensing coil 30 is wound on the buffer layer 40.

Description

  The present invention relates to an optical fiber gyro which detects a rotational motion of a moving body with respect to an inertial space.

  FIG. 7 shows a configuration of a phase modulation type optical fiber gyro described in Patent Document 1 as a configuration of a conventionally used optical fiber gyro.

  In FIG. 7, what is indicated by reference numeral 1 is an optical system having a sensing coil 2 formed of an optical fiber. The sensing coil 2 is connected to a light source module via a first coupler 3, a polarizer 4 and a second coupler 5. 6 and the detector module 7 are connected by an optical fiber 8. A phase modulator 9 is provided between the sensing coil 2 and the first coupler 3 so as to be in contact with the optical fiber 8 and located in the vicinity of the sensing coil 2.

  In such an optical system 1, the laser light entering the optical fiber 8 from the light source module 6 is modulated by the phase modulator 9 via the first coupler 3, the polarizer 4, and the second coupler 5, and then the sensing coil. 2 is incident. The laser beam incident on the sensing coil 2 is again photoelectrically converted by the detector module 7 through the second coupler 5, the polarizer 4 and the first coupler 3, and the optical system output S is taken out.

  An electrical system 10 is connected to the optical system 1, and an optical system output S is input to an input amplifier 11 of the electrical system 10 and is output as a detected optical system output S 1. This detected optical system output S1 includes a phase difference Δθ due to the well-known Sagnac effect. A light source drive circuit 12, a modulation control circuit 14, and a lock-in amplifier 17 are connected to the output side of the input amplifier 11.

  The light source driving circuit 12 is connected to the light source module 6 via the laser driver 13, the modulation control circuit 14 is an oscillation circuit 15 that supplies a detection clock C to the lock-in amplifier 17, and a driver 16 that is connected to the phase modulator 9. The lock-in amplifier 17 is connected to the output amplifier 18.

  In the conventional phase modulation type optical fiber gyro, the detected optical system output S1 is synchronously detected by the lock-in amplifier 17 with the configuration as described above, and the phase difference of the light generated by the angular velocity input is interfered and output by the Sagnac effect. The gyro output S2 is obtained via the amplifier 18. In such an optical fiber gyro, the optical fiber 8 is wound around a bobbin 20 for a sensing coil.

  FIG. 8 shows a cross-sectional structure of the bobbin 20 described in Patent Document 1, and a polymer gel 21 is coated on a surface 20a around which the optical fiber 8 is wound. The optical fiber 8 is wound around the coating of the polymer gel 21.

  In Patent Document 1, by coating the bobbin 20 with the polymer gel 21 in this way, the thermal stress applied to the optical fiber 8 due to thermal expansion / contraction of the bobbin 20 is absorbed by the polymer gel 21. Thereby, the thermal stress applied to the optical fiber 8 is suppressed.

JP 2002-228455 A

  By the way, in winding an optical fiber around a bobbin, a quadrupole winding having a winding start point as an intermediate point of the entire length of the optical fiber is generally employed in order to reduce drift during temperature change.

  FIG. 9 schematically shows a winding method of this quadrupole winding. In the figure, an optical fiber 31 indicated by a black circle is an optical fiber in the + direction (one end direction) from the middle point of the entire length. An optical fiber 31 shown by a white circle indicates an optical fiber in the − direction (the other end direction) from the midpoint of the entire length. In FIG. 9, the bobbin 32 shows only one side with respect to the central axis.

  The quadrupole winding as shown in FIG. 9 is arranged such that a symmetrical position from the middle point of the entire length of the optical fiber is arranged close to the inside of the coil, thereby changing the refractive index of the optical fiber due to temperature change. This cancels out the phase difference between the left and right light beams caused by the above.

  On the other hand, even if such a quadrupole winding is adopted, the problem that the optical fiber is subjected to thermal stress caused by a temperature change due to the difference in thermal expansion coefficient between the bobbin and the optical fiber is another problem and cannot be excluded. Conventionally, as described above, it has been proposed to coat a bobbin with a polymer gel in order to absorb thermal stress.

  However, in the method of winding an optical fiber on such a flexible polymer gel coating, it becomes difficult to align the optical fiber with high accuracy, and an optical fiber that requires a highly accurate alignment winding of the sensing coil is required. It was difficult to adopt in the gyro.

  In view of such circumstances, the object of the present invention is to eliminate the influence of the thermal stress generated by the difference in thermal expansion coefficient between the bobbin and the optical fiber on the sensing coil, and to provide a highly accurate aligned winding of the sensing coil. An object of the present invention is to provide a high-performance optical fiber gyro which can be easily realized and thus has excellent temperature characteristics.

  According to the first aspect of the present invention, in the optical fiber gyro for propagating light left and right around the sensing coil made of an optical fiber and detecting the input angular velocity from the phase difference between the counterclockwise light and the clockwise light generated by the angular velocity input, An optical fiber different from the optical fiber constituting the sensing coil is wound around the bobbin to form a buffer layer, and the sensing coil is wound on the buffer layer.

  In the invention of claim 2, in the invention of claim 1, the optical fiber constituting the buffer layer is the same as the optical fiber constituting the sensing coil.

  In the invention of claim 3, in the invention of claim 1 or 2, the optical fiber constituting the buffer layer is used for detection of strain generated in the optical fiber.

  In the invention of claim 4, in the invention of claim 1 or 2, the optical fiber constituting the buffer layer is used as a redundant system of the sensing coil.

  According to the present invention, the sensing coil is not affected by the thermal stress generated by the difference between the thermal expansion coefficients of the bobbin and the optical fiber, so that the generation of strain inside the sensing coil due to the thermal stress can be eliminated, Can also solve the problem of drift caused by the influence of strain during temperature changes.

  In addition, unlike conventional methods in which a bobbin is coated with a polymer gel to form a buffer layer, the buffer layer is formed by wrapping an optical fiber. It can be easily realized without being done.

  Therefore, according to the present invention, a high-performance optical fiber gyro having excellent temperature characteristics can be obtained.

The graph which shows the result of having measured the distortion inside a sensing coil. The graph which expanded and showed the midpoint vicinity of the optical fiber full length in FIG. A graph showing how the strain near the midpoint (coil inner layer portion) of the entire length of the optical fiber constituting the sensing coil changes with temperature, A is the measurement result at 25 ° C., B is the measurement result at 40 ° C., and C is Measurement results at 60 ° C. Sectional drawing which shows an example of the coil | winding structure of the sensing coil used in the optical fiber gyro by this invention. The figure which shows the example which uses the optical fiber which comprises a buffer layer for distortion detection. The figure which shows the example which uses the optical fiber which comprises a buffer layer as a redundant system of a sensing coil. The block diagram which shows the structural example of an optical fiber gyro. Sectional drawing which shows the prior art example of the bobbin which winds a sensing coil. The figure for demonstrating the winding method of a quadrupole winding.

  First, the result of examining the strain state inside the sensing coil wound around the bobbin by the BOTDR method will be described.

  The BOTDR method uses a phenomenon in which the frequency of the stimulated Brillouin scattered light generated when an optical pulse is incident from one end of an optical fiber shifts in proportion to the distortion. The shifted frequency is measured by optical heterodyne detection, This is to calculate the strain of the fiber. An optical fiber strain analyzer AQ8603 (Yokogawa Electric Corp.) was used as a measuring device.

  The bobbin is made of aluminum, and a single mode optical fiber having a total length of 3400 m is wound around this bobbin by a quadrupole winding to form a sensing coil.

  FIG. 1 shows measurement results, where the horizontal axis indicates the length of the optical fiber and the vertical axis indicates the strain.

  In an optical fiber, strain due to tension at the time of winding and strain due to coil bending occur as initial strains, but it can be seen from FIG. 1 that the strain near the midpoint of the entire length of the optical fiber is specifically large. This part is a part located in the inner layer of the coil in the quadrupole winding.

  FIG. 2 is an enlarged view of a portion surrounded by a broken-line circle in FIG. 1, and FIG. 2 shows the position of the intermediate point of the optical fiber and the number of layers of the coil. It can be seen that the strain in the first layer is the largest.

  The reason why the strain of the inner layer is large is that after the optical fiber is wound around the bobbin, the coil is bonded and fixed so that the aligned winding state does not break, but at this time, the adhesive is cured at a high temperature. It is considered that thermal stress is generated due to the difference in the thermal expansion coefficient of the optical fiber, and it remains as residual stress even when the thermal stress returns to room temperature. The first layer is an interface with the bobbin, and is greatly affected by thermal stress, resulting in large distortion. In the second and subsequent layers, the effect of thermal stress is mitigated by the buffering effect of the optical fiber in the lower layer, and the strain gradually decreases. From FIG. 2, it can be seen that the strain due to the thermal stress is not evident in the eighth and subsequent layers.

  Next, the result of examining the relationship between the strain inside the sensing coil and the temperature will be described.

  FIG. 3A shows the strain at normal temperature (25 ° C.) of the coil inner layer portion as in FIG. 2, and the strain measurement results when the temperature is raised to 40 ° C. and 60 ° C. from this state are shown in FIG. 3B and FIG. Shown in C. From FIGS. 3A, B, and C, it has been found that the strain varies greatly with temperature and increases with increasing temperature.

  From the above investigation results, a large strain has occurred in the inner layer of the sensing coil, and this strain changes with temperature, and the temperature change caused by the change in the refractive index of the optical fiber due to the temperature change known so far In addition to the drift inside, it was revealed that drift occurs during temperature change due to the effect of strain in optical fiber gyros.

  The present invention is based on the facts clarified by the investigation results described above, and examples of the present invention will be described below.

  FIG. 4 shows a winding structure of a sensing coil used in the optical fiber gyro according to the present invention. In this example, an optical fiber 41 different from the optical fiber constituting the sensing coil is wound around the bobbin 32 to constitute the buffer layer 40, and the optical fiber 31 is wound on the buffer layer 40 to constitute the sensing coil 30. Has been.

  The buffer layer 40 is configured by winding seven layers of optical fibers 41 in this example, based on the measurement results shown in FIG. The optical fiber 41 constituting the buffer layer 40 is the same as the optical fiber 31 constituting the sensing coil 30 (the same specification). In this example, the sensing coil 30 uses a quadrupole winding, and the sensing coil 30 and the buffer layer 40 are bonded and fixed to each other.

  As described above, the buffer layer 40 is provided on the bobbin 32 by the separate optical fiber 41 independent of the optical fiber 31 of the sensing coil 30, and the sensing coil 30 is wound on the buffer layer 40, so The sensing coil 30 is not affected by the thermal stress generated by the difference in the thermal expansion coefficients of the fibers. Therefore, a large strain does not occur in the inner layer portion of the sensing coil 30, and a problem that has been clarified in the process leading to the present invention, such as a drift occurring during temperature change due to the strain, can be solved.

  Also, unlike the conventional case where the buffer layer is formed by coating the bobbin with a flexible polymer gel, in this example, the optical fiber 41 itself is wound as a buffer material to form the buffer layer 40. As shown in FIG. 4, the optical fiber 41 is aligned and wound to form the buffer layer 40, thereby enabling highly accurate aligned winding of each layer of the sensing coil 30 wound thereon. This is an important factor in placing a symmetric position from the middle point of the entire length of the optical fiber in the quadrupole winding that reduces drift during temperature changes due to refractive index changes. If the winding structure of the sensing coil 30 as described above is employed, a high-performance optical fiber gyro excellent in temperature characteristics can be realized.

  In order to realize such a high-performance optical fiber gyro, the optical fiber 41 constituting the buffer layer 40 is preferably the same as the optical fiber 31 of the sensing coil 30, but is not necessarily limited thereto. Is not to be done. Further, the winding method of the sensing coil 30 is not necessarily limited to the quadrupole winding.

  In the example described above, the optical fiber 41 wound around the bobbin 32 simply functions as the buffer layer 40. However, the optical fiber 41 can also be positively used to enhance the function of the optical fiber gyro. FIG. 5 shows an example thereof. In this example, one end of the optical fiber 41 is connected to a BOTDR type optical fiber strain measuring device 51, and the optical fiber 41 is used for strain detection.

  By adopting such a configuration, it is possible to detect the state of distortion in the coil inner layer portion, and for example, to increase the functionality of an optical fiber gyro such as issuing a warning when the amount of strain exceeds a preset value. Is possible.

  On the other hand, in FIG. 6, both ends of the optical fiber 41 constituting the buffer layer 40 are connected to another Sagnac interferometer 52 so that rotational motion (input angular velocity) can be detected, and the coil made of the optical fiber 41 is connected to the sensing coil 30. The optical fiber gyro can be made highly reliable by using the optical fiber 41 as a backup as described above.

DESCRIPTION OF SYMBOLS 1 Optical system 2 Sensing coil 3 1st coupler 4 Polarizer 5 2nd coupler 6 Light source module 7 Detector module 8 Optical fiber 9 Phase modulator 10 Electrical system 11 Input amplifier 12 Light source drive circuit 13 Laser driver 14 Modulation control circuit 15 Oscillation circuit 16 Driver 17 Lock-in amplifier 18 Output amplifier 20 Bobbin 20a Surface 21 Polymer gel 30 Sensing coil 31 Optical fiber 32 Bobbin 40 Buffer layer 41 Optical fiber 51 Optical fiber strain measuring device 52 Sagnac interferometer

Claims (4)

An optical fiber gyro that propagates light left and right in a sensing coil made of an optical fiber and detects an input angular velocity from a phase difference between counterclockwise and clockwise light generated by angular velocity input,
An optical fiber gyro, wherein an optical fiber different from the optical fiber constituting the sensing coil is wound around a bobbin to form a buffer layer, and the sensing coil is wound on the buffer layer. The optical fiber gyro according to claim 1, wherein
An optical fiber gyro, wherein the optical fiber constituting the buffer layer is the same optical fiber as the optical fiber constituting the sensing coil. The optical fiber gyro according to claim 1 or 2,
An optical fiber gyro, wherein an optical fiber constituting the buffer layer is used for detecting strain generated in the optical fiber. The optical fiber gyro according to claim 1 or 2,
An optical fiber gyro using an optical fiber constituting the buffer layer as a redundant system of the sensing coil.

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