JPH0668445B2 - True north surveying device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a surveying apparatus using a fiber optic gyro that measures the direction of the rotation axis of the earth from true north, that is, from an arbitrary point on the earth.

(Background of the Invention) When surveying, especially topographical survey, it is necessary to survey true north.

In the conventional true north survey, the true north direction was obtained by checking the time when the sun was southing and measuring the direction of the sun at that time. However, this method is very inconvenient because the measurement can be performed only at noon on a sunny day.

A method of obtaining the true north direction by measuring the direction of a star (for example, North Pole star) was also used. But according to this method,
It was very inconvenient because the measurement was possible only on a clear night and when the star was visible from the measurement point.

Although surveying with a magnet is simple, it cannot be used when precision is required because magnetic north is constantly moving.

Accurate measurement is possible by using a mechanical gyroscope, but it takes a long time from the rotation start of the gyroscope to stable rotation, the weight of the device is heavy, and it takes time to measure the amplitude of the gyro precession movement. There were drawbacks such as hanging.

(Object of the Invention) The present invention solves the above-described drawbacks, and an object of the present invention is to obtain a true north surveying device that is easy to operate, is small in size, and has high accuracy without being affected by conditions such as weather.

(Summary of the Invention) The present invention has an optical fiber gyro (1) which has a fiber surface formed by winding an optical fiber (10) and outputs a signal according to a rotational angular velocity of the fiber surface, and the fiber surface. Is held substantially in the vertical plane, and a holding and rotating device (2, 3) for rotating the fiber surface around a vertical axis, and a true north in response to an output signal of the optical fiber gyro (1). Output circuit (18
The technical point is a true north surveying device characterized by having 7) and an indicating device (4, 188, 189) for indicating true north when the detection signal is generated.

(Example) FIG. 1 is an external view of a true north surveying apparatus according to the present invention. 1
The optical fiber gyro 1'is a bobbin whose cross section has an optical fiber 10 wound around a groove provided on the outer peripheral surface of the bobbin 1'as shown in FIG. ing. Reference numeral 2 is a level, 3 is a tripod with a platform, and 4 is a collimating telescope installed so that an optical axis lies in a plane formed by winding an optical fiber. FIG. 3 shows the structure of the optical fiber gyro shown in FIG. 1, 10 is a polarization maintaining optical fiber wound around a bobbin 1 ', 11 is a circuit section including a power supply and a signal processing system, and 12 is a supermarket. A light source unit including a luminescence diode, a coupler, a light guiding fiber, and a lens, and 13 is a half prism that efficiently divides light from the light source 12 into two equal parts. Therefore, the transmittance and the reflectance are respectively about 50%. Reference numerals 14a and 14b are polarizing plates, and 15a and 15b are condenser lenses provided at both ends of the optical fiber 10.
The optical fiber 10 is wound around the bobbin 1'to form a loop that produces the Sagnac effect, and the light from the light source 12 received by the lenses 15a and 15b is configured to enter from both ends of the loop. 16 is a piezo element for phase modulation provided at one end of the loop, the optical fiber 10 is tightly wound,
When a constant AC signal is applied to the piezo element 16, the optical fiber
10 expands and contracts. As a result, the interference output between the clockwise rotation and the counterclockwise rotation of the optical fiber loop is modulated, and the measurement sensitivity for minute rotational angular velocity is increased. The light emitted to the end opposite to the incident end through the loop is again polarized plates 14a and 14a, respectively.
It passes through b and is reflected by the half prisms 17a and 17b, and detected by the photodetectors 18a and 18b. The amount of light before the Sagnac interference can be known by the photodetectors 18a and 18b. The transmittance of the half prisms 17a and 17b is high, and is set to about 90%, for example. The light transmitted through the half prisms 17a and 17b undergoes Sagnac interference at the half prism 13, and the interference light is detected by the photodetector 18c. The optical signals before and after the Sagnac interference are photoelectrically converted by the optical detectors 18a, 18b, 18c and sent to the circuit unit 11. In the circuit unit 11, the light amount after the interference and the light amount before the interference are differentiated to obtain a light source.
Eliminate 12 drifts. The polarizing plates 14a and 14b are provided to remove noise generated when light passes through the loop of the optical fiber 10. The outer shape of the bobbin 1'may be rectangular as shown in FIG. 1 or circular as shown in FIG. The light incident on the half prism 13 travels halfway to 17a and 17b. Light that has almost passed through 17 rotates around the fiber loop 10 counterclockwise and enters the half prism 17b. Part of the light entering the half prism 17b goes to the photodetector 18b for intensity detection, and most of the rest goes to the half prism 13.
On the other hand, the light that has almost passed through the half prism 17b turns clockwise around the fiber loop 10 and enters the half prism 17a.
Part of the light entering the half prism 17a goes to the photodetector 18a for intensity detection, and most of the rest goes to the half prism 13. The interference light of the two lights, which return to the half prism 13 and are clockwise and counterclockwise, are detected by the photodetector 18c. Here, there is return light to the light source 12, but if a super luminescence diode is used for the light source, coherence noise is not generated because the coherence length is about several tens of microns. FIG. 4 is a block diagram showing a part of the circuit system of the surveying instrument according to the present invention. 181, 182, 183 are amplifiers for amplifying the signals from the photodetectors 18a, 18b, 18c. 184
Is a multiplication circuit, which is the product of the signals of the amplifiers 181 and 182, and the product of the clockwise and counterclockwise light intensity of the optical fiber loop 10, which is the Sagnac loop, which is the light intensity before the Sagnac interference. is there. Reference numeral 183 is an amplifier that amplifies the intensity of light after Sagnac interference. 185 is an amplifier 183 and a multiplication circuit 184
And a differential circuit for removing the drift included in the output light of the light source 12. By removing this drift, the accuracy of the surveying instrument can be improved. Reference numeral 186 is a lock-in amplifier that receives the modulation frequency of the phase modulation by the piezo element 16 from the drive circuit 161, and performs lock-in detection of the signal by the differential circuit 185.

Reference numeral 187 is a 0-point detection circuit for detecting 0 points in the signal obtained by the lock-in amplifier 186.

A display 188 displays the output of the 0-point detection circuit 187.

It is convenient to use a display 188 whose range is automatically switched and a signal is displayed accurately.

Reference numeral 189 is a sounding device which produces a sound when it approaches the zero point by the output of the zero point detection circuit 187.

The sounding device 189 is arranged so that a current flows through a buzzer or the like when the 0-point detection circuit 187 outputs a 0-point signal.

Next, the procedure of surveying by the true north surveying apparatus shown in FIGS. 1 to 4 is shown below.

When performing true north survey from a certain base point Install this device on the base point so that the fiber surface is almost in the vertical plane.

Of course, if you want to be accurate, use plumb bob.

Adjust the tripod 3 with the platform using the level 2 to bring the level.

The circuit system is turned on and the tripod with a platform is operated to rotate in a horizontal plane, and the direction in which sound is emitted by the sounding device 189, that is, the fiber surface is in the north-south direction (direction parallel to the meridian of the earth). In accord with, the direction in which the rotational angular velocity of the optical fiber gyro becomes zero and the output of the lock-in amplifier 186 becomes zero is searched.

An index is set at a point separated by an appropriate distance by a collimating telescope so as to match the collimation (crosshair) in the field of view of the telescope. The extension of one end of the line connecting this index and the base point indicates true north.

The true north is measured by the above procedure.

FIG. 5 is an external view showing another embodiment, in which the optical axis of the collimating telescope is mounted so as to be in a relationship perpendicular to the plane formed by the loop of the optical fiber gyro. Therefore, this embodiment is the same as the embodiment shown in FIG. 1 except that the maximum output of the lock-in amplifier 186 indicates true north.

FIG. 6 is an external view showing still another embodiment, in which another optical fiber gyro 5 is combined with the first embodiment shown in FIG. 1, and after the true north is measured by the above-mentioned procedure. After resetting the output of the optical fiber gyro 5 to 0, or after resetting the output of the optical fiber gyro 5 by obtaining a signal that detects true north, that is, a signal when the output of the lock-in amplifier 186 becomes 0 If the index set at the point to be surveyed is aligned with the collimation within the field of view of the collimating telescope 4, the output of the optical fiber gyro 5 at that time is displayed on the display 188 as to how many angles from the true north the point is. You can know it directly. Of course, not only the display but also the angle may be memorized or printed.

(Effect of the Invention) As described above, according to the present invention, since a true north side surveying device using an optical fiber gyro can be obtained, it is easy to operate without being affected by conditions such as weather, and is relatively small in size and accurate. It is possible to obtain a high true north surveying device.

In particular, by using an optical fiber gyro, true north surveying can be easily performed in a place where a magnet (compass) cannot be used, which is useful for tunnel construction and the like.

[Brief description of drawings]

 FIG. 1 is an external view of an embodiment of the present invention. FIG. 2 is a sectional view of an optical fiber gyro. FIG. 3 is a view showing the structure of an optical fiber gyro. FIG. 4 is a block diagram showing a circuit system of the present invention. 6 and 6 are external views of another embodiment of the present invention. (Explanation of main symbols) 1,5 ...... Optical fiber gyro 1 '... Bobbin 2 ...... Level 3 ...... Tripod with pan head 4 ...... Telescope with collimation 10 ...... Optical fiber

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-46-1714 (JP, A) JP-A-53-64175 (JP, A)

Claims (1)

[Claims] 1. An optical fiber gyro having a fiber surface formed by winding an optical fiber and outputting a signal according to a rotation angular velocity of the fiber surface, and holding the fiber surface so that the fiber surface is substantially in a vertical plane. In addition, a holding and rotating device that rotates the fiber surface around a vertical axis, and an output circuit that outputs a true north detection signal in response to an output signal of the optical fiber gyro obtained by rotation around the vertical axis. A true north surveying device comprising: an indicating device that indicates true north when the detection signal is generated.