JP2001349733A - Orientation sensor - Google Patents

Abstract

(57) [Problem] To provide an azimuth sensor which enables accurate azimuth measurement by eliminating the influence of precession movement. SOLUTION: An optical fiber gyro for detecting an angular velocity due to the rotation of the earth and an optical fiber gyro for detecting a rotational angular velocity in the horizontal direction are combined, and a direction is periodically calculated from the angular velocity due to the rotation of the earth. During this period, the rotational angle is obtained by integrating the horizontal rotational angular velocity, and the azimuth is interpolated with this rotational angle to continuously output the azimuth of the sensor main axis. Inclinometers 5 and 6 for measuring the inclination of two horizontal orthogonal axes on the sensor with respect to the true horizontal
Then, the occurrence of precession of the gravity axis on the sensor is detected based on the measured inclinations of the two axes, and when the precession occurs, the direction of the sensor main axis is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an azimuth sensor using an optical fiber gyro, and more particularly, to an azimuth sensor capable of accurately measuring an azimuth by eliminating the influence of precession movement.

[0002]

2. Description of the Related Art Generally, a geomagnetic sensor or a mechanical gyro is used for azimuth measurement. The geomagnetic sensor detects the direction using the magnetic field of the earth, and the mechanical gyro detects the direction using the rotation of the earth. When precise azimuth measurement is required, a method of observing celestial bodies such as the polar star and the sun is used. However, since the geomagnetic sensor indicates magnetic north, it is necessary to correct the latitude in order to obtain true north. Also, the mechanical gyro needs to maintain gyro rotation. The method of observing astronomical objects is problematic in terms of practicality because the weather and time are restricted in surveying.

On the other hand, an optical fiber gyro (Fiber Optic)
A direction sensor using Gyroscope (FOG) is known. An optical fiber gyro is a device that propagates right and left bidirectional light through an optical fiber loop, multiplexes the propagated right and left bidirectional light, detects the phase difference between the two, and detects the angular velocity in the loop plane from the phase difference. It is. For example, Japanese Patent Application No. 9-975
The azimuth sensor shown in No. 05 combines an optical fiber gyro that detects the angular velocity due to the rotation of the earth and an optical fiber gyro that detects the rotational angular velocity in the horizontal direction, and periodically calculates the azimuth from the angular velocity due to the rotation of the earth. During the calculation, the rotation angle is obtained by integrating the horizontal rotation angular velocity, and the azimuth can be continuously output by interpolating the azimuth with the rotation angle.

[0004]

However, the above-mentioned 2
The azimuth sensor using the optical fiber gyro of the axis has two axes orthogonal to the input axis (horizontal orthogonal two axes) with respect to the input axis (gravity axis on the sensor) of the optical fiber gyro for detecting the horizontal rotation. When an angular vibration with the same frequency and a different phase acts on the input shaft (this is called precession), the input shaft is displaced while drawing a conical trajectory, and an angular velocity is generated around the input shaft. An error occurs (the angular velocity error at this time is called a coning error).

The precession motion and the coning error will be described in detail. As shown in FIG. 3, when angular vibrations having the same frequency and different phases act on two axes y and z orthogonal to the input axis x of the gyro, The input axis x is displaced while drawing a conical trajectory, and an angular velocity occurs around the input axis x. Figure in illustrates the state when it entered the input of vibration theta _x and theta _y.
The Corning error omega _x of the time is expressed by the following equation.

[0006]

(Equation 1)

As shown in the equation, the coning error ω
_x is a function of the input angular frequency (angular frequency) and amplitude. A specific calculation example is shown below.

[0008]

[Table 1]

[0009]

(Equation 2)

As described above, when the precession movement occurs on the gravity axis on the sensor, the rotational angular velocity and the rotational angle in the horizontal direction cannot be accurately detected due to the coning error, and an error occurs in the output direction. For this reason, it is difficult to use the conventional direction sensor in an environment where the gravity axis on the sensor is difficult to stop.

An object of the present invention is to provide an azimuth sensor that solves the above-mentioned problems and eliminates the influence of precession movement to enable accurate azimuth measurement.

[0012]

In order to achieve the above object, the present invention provides a first optical fiber loop having a loop surface arranged along a gravity axis on a sensor; Rotating means for rotating around, a second optical fiber loop arranged so that the loop surface is horizontal on the sensor, and detection was performed using the first optical fiber loop at a plurality of rotation angles by the rotating means. Calculating means for calculating the azimuth of the sensor main axis from the angular velocity due to the rotation of the earth; andinterpolating means for interpolating the azimuth of the sensor main axis based on the rotation angle of the sensor main axis based on the angular velocity detected using the second optical fiber loop. An inclinometer for measuring the inclination of two axes perpendicular to the horizontal with respect to the true horizontal in the direction sensor provided, and a difference of the gravity axis based on the measured inclinations of the two axes. Detecting the occurrence of dynamic, when the nutation occurs is provided with a and precession correction means for correcting the orientation of the sensor main shaft.

The precession correcting means calculates an angular velocity component or a rotation angle component due to precession motion from the vibration frequency and amplitude of the tilt of the two axes, and calculates the angular velocity or the angular velocity detected using the second optical fiber loop. The component may be removed from the rotation angle of the sensor main shaft.

The precession correcting means may add the rotation angle of the sensor main shaft to the azimuth of the sensor main shaft obtained before the occurrence of the precession movement to obtain the current azimuth of the sensor main shaft.

[0015]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

As shown in FIG. 1, an azimuth sensor according to the present invention includes an optical fiber loop (first optical fiber loop) 1 constituting an optical fiber gyro for detecting rotation, and the optical fiber loop 1 is connected to a rotary table. 2, a rotation mechanism (rotation means) 3 for rotating the optical fiber gyro, an optical fiber loop (second optical fiber loop) 4 constituting an optical fiber gyro for horizontal rotation detection, and a gravity axis on the sensor as an X axis. Assuming that two horizontal orthogonal axes on the sensor that are orthogonal to the X axis and orthogonal to each other are the Y axis and the Z axis, a Y axis inclinometer 5 that measures the tilt angle around the Y axis and a tilt angle around the Z axis are measured. It comprises a Z-axis inclinometer 6, a computer (calculating means, interpolating means, precession correcting means) 7 for executing various operations to be described later and a sensor base 8 for supporting the above-mentioned components. .
The Y-axis and the Z-axis may be any one axis orthogonal to the X-axis, the Y-axis, and the horizontal axis orthogonal to the Y-axis may be the Z-axis, regardless of the north-south direction and the east-west direction. It is.

The optical fiber loop 1 is erected on a rotary table 2 parallel to the sensor base 8 so that the loop surface is along the axis of gravity on the sensor. The optical fiber loop 4 has a loop surface. It is arranged parallel to the sensor base 8 so as to be horizontal on the sensor. Preferably, when the sensor base 8 is in the horizontal position, the gravity axis on the sensor is equal to the true gravity axis, and the horizontal on the sensor is the true horizontal. An arbitrary direction of the sensor base 8 is defined as a sensor main axis.

FIG. 2 shows the operation procedure of the direction sensor according to the present invention.
This will be described below.

The procedure of FIG. 2 is performed by repeatedly executing a processing loop from the beginning to the end of the loop.
This is for continuously measuring the direction.

Step 1: An angular velocity in the loop plane of the optical fiber loop 1 due to the rotation of the earth is detected by the rotation detecting optical fiber gyro.

Step 2: The optical fiber loop 1 is rotated by 90 ° around the axis of gravity by the rotation mechanism 3, and the angular velocity due to the rotation of the earth is detected again.

Step 3: Step 2 after Step 1
Is repeated three times, a total of four angular velocity detection processes are executed. When the four angular velocity detection processes are performed, the obtained four angular velocities are ω0 to ω3, and the azimuth θa of the sensor main axis is calculated from these values by least square approximation. When the four executions have not been completed, the azimuth θa is not calculated.

In the azimuth detection in steps 1 to 3, first, while rotating the optical fiber loop 1 about the axis of gravity, the angular velocity in the plane of the loop due to the rotation of the earth is determined based on the phase difference between the left and right surrounding lights. By detecting, the north-south direction at which this angular velocity becomes almost zero is detected, and then the optical fiber loop 1 is rotated 90 ° from the north-south direction to the east-west direction,
Angular velocity in the loop plane due to the rotation of the earth in the east-west orientation (= rotational angular velocity of the earth) is detected, and the azimuth θa of the sensor main axis is determined based on the angular velocity detected in the north-south azimuth and the angular velocity detected in the east-west azimuth. The calculation may be performed.

Step 4: Since it takes time to rotate the turntable 2 for the azimuth detection in steps 1 to 3, the azimuth in steps 1 to 3 is determined at a certain time interval, for example,
It will be output at intervals of several minutes. Therefore, in parallel with the operations in steps 1 to 3, the horizontal rotation detecting optical fiber gyro is used at a fixed time interval Δt shorter than the above-mentioned time interval, and the angular velocity in the horizontal direction (angular velocity of the sensor main shaft).
While measuring ωx, the inclination θy and θz of the sensor base are measured by the Y-axis inclinometer 5 and the Z-axis inclinometer 6. The instantaneous value of the inclination angle at time Δt × 0, 1, 2,..., N is θy0, θy1, θy2,.
θz1, θz2,..., θzn. The number of measurements n is at least three. Therefore, the number of measurements n is a specified number (≦
If 3) has not been reached, return to step 1. However,
Steps 1-3 and 4 are simultaneous and parallel processing,
Even during steps 1 to 3, the measurement at the fixed time interval Δt in step 4 is executed. Step 5 is executed when the number of measurements n reaches the specified number.

Step 5: Instantaneous values θy0, θy1, θy2 at time intervals Δt of the measured inclinations θy and θz.
, Θyn and θz0, θz1, θz2,..., Θzn, the vibration frequencies fy, fz and the amplitudes Ay, Az are calculated by least squares approximation or Fourier analysis.

Step 6: The vibration frequency fy is compared with the vibration frequency fz. If the frequency difference between the two is within a preset threshold range, that is, if the vibration frequency fy is substantially equal to the vibration frequency fz, it is determined that precession movement has occurred, and the angular velocity due to precession movement is determined. ωc is obtained, for example, from the following equation.

Ωc = (１ ／) · Ay · Az · 2πfz As shown in FIG. 2, ωc can also be obtained by the least square method.

Step 7: Correction is made by removing the angular velocity ωc determined in Step 6 from the horizontal angular velocity ωx determined in Step 4 (removing the angular velocity component due to precession movement). This angular velocity ωx−angular velocity ωc is integrated (summed) over a time interval Δt × the number of measurements n, for example, 3Δt, to obtain an angle θ _YAW . This angle θ _YAW is the angle at which the sensor base 8 is actually rotated in the horizontal direction.

The angle component due to the precession movement is calculated,
Correction is also possible by the procedure of removing the angular component due to precession from the horizontal rotation angle based on the measurement of the horizontal rotation detecting optical fiber gyro.

Step 8: If precession occurs,
Since the rotation detecting optical fiber gyro cannot accurately detect the angular velocity due to the rotation of the earth, the azimuth θa of the sensor main axis obtained in step 3 is not reliable. Therefore, the orientation θout latest sensor spindle by adding angle theta _YAW the azimuth θout' sensor main shaft obtained before the precession occurs.

Step 9: When precession does not occur, the horizontal angular velocity ωx obtained in Step 4 is added to the azimuth θa of the sensor main axis obtained in Step 3 at the time interval Δt.
× Angle θ _YAW integrated (summed) in the time range of the number of measurements n
Is added to the latest azimuth θout of the sensor main axis.

Step 10: Latest orientation of sensor main axis θ
out is output, and the process returns to step 1 which is the beginning of the processing loop.

With the above operation, it is possible to detect the occurrence of the X-axis precession based on the two-axis inclination measured by the Y-axis inclinometer 5 and the Z-axis inclinometer 6. When the precession movement occurs, the direction of the sensor main axis is corrected. The correction removes the component due to the precession movement from the measured rotation angle (angular velocity) of the sensor spindle,
This is realized by adding the rotation angle of the sensor main shaft to the azimuth of the sensor main shaft obtained before the occurrence of the precession movement. Thereby, accurate azimuth measurement can be performed without the influence of the precession movement.

In the process of obtaining the azimuth of the sensor main axis from the angular velocity obtained by the rotation-detecting optical fiber gyro, the degree of variation of the measured angular velocity is measured when measuring the angular velocity. By setting a threshold value and determining whether or not to use the calculated azimuth based on whether or not the degree of variation exceeds the threshold value, the azimuth measurement accuracy can be improved.

The azimuth sensor of the present invention is preferably mounted on, for example, a continuous wall excavator. This makes it possible to measure the displacement of the torsion angle (yaw angle) of the continuous wall excavator without being affected by the precession movement, and to reduce the deviation from the planned excavation route.

[0036]

The present invention exhibits the following excellent effects.

(1) Even if a precession movement is applied during the direction measurement, an accurate direction measurement can be performed by eliminating the influence of the precession movement.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an orientation sensor according to an embodiment of the present invention.

FIG. 2 is an operation procedure diagram of the direction sensor of FIG. 1;

FIG. 3 is a three-dimensional view for explaining precession movement.

[Explanation of symbols]

 Reference Signs List 1 optical fiber loop (first optical fiber loop) 2 rotary table 3 rotating mechanism (rotating means) 4 optical fiber loop (second optical fiber loop) 5 Y-axis inclinometer 6 Z-axis inclinometer 7 computer (calculation means, Interpolation means, talent correction means) 8 Sensor base

Claims (3)

[Claims] 1. A first optical fiber loop having a loop surface arranged along a gravity axis on a sensor, a rotating means for rotating the optical fiber loop around the gravity axis, and a loop surface being horizontal on the sensor. A second optical fiber loop disposed so as to provide: and a calculating means for calculating the azimuth of the sensor main axis from the angular velocity due to the rotation of the earth detected using the first optical fiber loop at a plurality of rotation angles by the rotating means. And an interpolating means for interpolating the azimuth of the sensor main axis based on the rotation angle of the sensor main axis based on the angular velocity detected using the second optical fiber loop. An inclinometer for measuring the inclination of the two axes, and detecting the occurrence of the precession movement of the gravity axis based on the measured inclinations of the two axes; An azimuth sensor provided with a precession correcting means for correcting the azimuth of the sensor main axis. 2. The precession correction means calculates an angular velocity component or a rotation angle component due to precession movement from the vibration frequency and amplitude of the tilt of the two axes, and detects the angular velocity detected using the second optical fiber loop. The azimuth sensor according to claim 1, wherein the component is removed from a rotation angle of the sensor main shaft. 3. The precession correction means adds the rotation angle of the main sensor axis to the azimuth of the main sensor axis obtained before the precession movement occurs to obtain the current azimuth of the main sensor axis. The azimuth sensor according to 1 or 2.