JP2001141507A - Inertial navigation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the precision of positional information calculated based on a detected value of an inertia measuring unit. SOLUTION: A bias error of an acceleration sensor for detecting an acceleration along a detection-axis direction is detected by comparing the acceleration along the detection-axis direction detected when one detection shaft of the inertia measuring unit 1 is attitude-set in a vertical condition by an attitude setting part 2 with a gravitational acceleration data stored preliminarily, bias error of respective gyroscopes for detecting respective angular velocities around other two axes is detected by comparing the angular velocities around the two axes orthogonal to the detection shaft detected when the one detection shaft is set in the vertical condition with angular velocities around the two shafts calculated by respective data of an angular velocity S stored preliminarily, rotation velocity Ω of the glove and a latitude λ of a navigator, and the positional information is corrected by the bias error of the acceleration sensor and the bias errors of the respective gyroscopes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inertial navigation system using a strapdown type inertial measurement unit.

[0002]

2. Description of the Related Art In a traveling vehicle such as a ship (for example, a ship), position information (GPS data) such as a navigation position (latitude and longitude) is based on an inertial navigation system (INS) based on a GPS (Global Positioning System). System)
Provided to the operator or each device. On the other hand, azimuth system information such as the azimuth angle, pitch angle, and roll angle of a ship is provided by an inertial measurement unit (IMU: Inertial Measuring).
Unit) is provided to operators and the like by a gyro compass that operates based on measurement data.
The inertial measurement unit is composed of inertial sensors (a plurality of gyroscopes and accelerometers arranged orthogonally) and an arithmetic unit, and the arithmetic unit calculates the azimuth angle, pitch angle or pitch angle of the ship based on the detection values of each inertial sensor. The roll angle is calculated and output to the outside as azimuth information.

As is well known, such inertial measurement units include a strap-down system and a platform system (gimbal servo system). Strap-down type inertial measurement units have recently been put into practical use with the development of optical gyros and high-performance computers (computing devices) with a wide dynamic range. The azimuth, pitch, and roll angles of the ship with respect to the reference coordinates, that is, the hull coordinate axes, are calculated by sequentially converting the coordinate axes of the reference coordinates in the arithmetic unit based on the detected values. On the other hand, the platform type inertial measurement unit has an inertial sensor provided on the platform (a type of face plate), and constantly moves the platform horizontally and northward using a gimbal servo mechanism that operates based on the detection value of the inertial sensor. By controlling the attitude, the azimuth based on the platform,
The pitch angle and the roll angle are calculated.

[0004]

The above-mentioned inertial navigation system obtains position system information of a ship by using radio waves received from a GPS, that is, a GPS satellite. Cannot provide positional information to an external device. To solve such a problem, it is conceivable to obtain position system information by integrating azimuth system information constantly calculated by the inertial measurement unit during a period in which radio waves cannot be received.

However, the gyroscope and the accelerometer in the inertial measurement unit have an error corresponding to the structure, and this error is not constant every time the inertial measurement unit is started. The position information with the required accuracy cannot be calculated. For example, even when a unit having a relatively high-precision ring laser gyro (RLG: Ring Laser Gyro) is used as the inertial measurement unit, the accuracy of the position system information that can be achieved is one digit of the required accuracy. It will be bad.

The present invention has been made in view of the above-described problems, and has as its object to improve the accuracy of position-based information calculated based on a detection value of an inertial measurement unit.

[0007]

In order to achieve the above object, as a first means, orthogonal detection axes (X axis, Y axis)
Axis, Z axis), an inertial measurement unit that detects each angular velocity around each axis and each acceleration in the direction of each of the detected axes, and outputs the inertial information as inertia information. And an arithmetic unit for calculating position system information indicating
A rotating means for rotating at a constant angular velocity S around one axis of a three-dimensional rectangular coordinate system (U axis, V axis, W axis); and an inertial measurement unit provided on the rotating means, wherein the three-dimensional rectangular coordinate system (U
An axis, a V-axis, and a W-axis) to rotate around the other two axes to set a desired attitude. The bias in the acceleration sensor for detecting the acceleration in the detection axis direction is detected by comparing the acceleration in the detection axis direction detected when the posture is set to the state with the gravitational acceleration data stored in advance. The angular velocities S, the earth's rotation speed Ω, and the latitude λ of the vehicle are stored in advance, where the angular velocities around the other two axes orthogonal to the detection axes detected when one of the detection axes is set in the vertical state are stored in advance. By comparing with the angular velocities around the other two axes calculated from the respective data, the bias errors of the gyros for detecting the angular velocities around the two axes are detected, and the bias error of the acceleration sensor and each of the gyros are detected. A means for correcting the position information based on the gyro bias error is employed.

As a second means, each of the orthogonal detection axes (X
A gyro for detecting angular velocities around the axes (Y, Z, and Z axes) and an accelerometer for detecting accelerations in the respective detection axis directions, and an inertial measurement unit that outputs the angular velocities and the accelerations as inertial information. The inertial measurement unit is connected to a three-dimensional rectangular coordinate system (U axis,
Rotating means for rotating the axis about one axis (V axis, W axis) constantly;
Means for calculating a position system information indicating a current position of the vehicle by applying a predetermined operation to the inertia information.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an inertial navigation system according to the present invention will be described below with reference to the drawings. Note that the present embodiment relates to a case where the inertial navigation device is attached to a ship which is one of the navigation bodies.

[First Embodiment] FIG. 1 is a conceptual diagram showing a configuration of a first embodiment. In this figure, reference numeral 1 denotes an inertial measurement unit, 2 denotes an attitude setting unit, 3 denotes a rotary table (rotating means), 4 denotes a rotation drive unit, 5 denotes a calculation unit, and 6 denotes a GPS (Global Positioning System). The inertial measurement unit 1 includes three RLGs (ring laser gyros) for detecting angular velocities around a three-dimensional orthogonal axis including an X axis, a Y axis, and a Z axis, and detecting acceleration in a hull coordinate axis direction.
It consists of two accelerometers. Inertial measurement unit 1
Outputs the respective angular velocities and the respective accelerations to the arithmetic unit 5 as inertia information. The three-dimensional orthogonal coordinate system including the X axis, the Y axis, and the Z axis is a coordinate system (unit coordinate system) unique to the inertial measurement unit 1.

The attitude setting unit 2 supports the inertial measurement unit 1 on a rotary table 3 so as to be rotatable about two rotation axes (X axis and Y axis) as shown in the figure. The attitude setting unit 2 includes an axis driving means (not shown), and sets the attitude of the inertial measurement unit 1 around the X axis and the Y axis by the driving force of the axis driving means.

The rotary table 3 is a coordinate system (hull coordinate system composed of U, V, and W axes) unique to a ship (hull).
It is supported by the hull so that it can rotate around the W axis. That is, although the rotary table 3 rotates in a plane including the U axis and the V axis, the upper surface 3a on which the inertial measurement unit 1 is supported via the attitude setting unit 2 is fixed to the hull coordinate axes. ing. The rotation drive unit 4 rotates such a rotary table 3 at a constant angular velocity S in the UV plane.

The arithmetic unit 5 is a kind of computer that operates at a high speed, and calculates predetermined position information such as latitude and longitude of the ship by performing predetermined arithmetic processing on the inertia information output from the inertial measurement unit 1. Things. Arithmetic unit 5
Outputs the position system information calculated for each predetermined calculation cycle to the outside in order to provide the ship with navigation. In addition to the position-system information calculation processing function, the calculation unit 5 of the present embodiment includes an error correction processing function that cooperates with the attitude setting unit 2, the rotary table 3, and the rotation drive unit 4, that is, the inertial measurement unit 1
Is provided with a function of correcting an error of each accelerometer constituting the above. The GPS 6 obtains position system information of a ship using radio waves received from GPS satellites.

The strap-down system is characterized in that the inertial measurement unit 1 is fixedly arranged on the hull. The inertial measurement unit 1 of the present embodiment has the attitude setting unit 2 and the rotary table 3 as described above. By fixing to the hull through the hull, it is possible to take a free attitude with respect to the hull coordinate system.

Next, the operation of the inertial navigation device thus configured will be described. The calculation processing of the position system information in the inertial navigation system is the same as that of the well-known one, so that the description thereof is omitted, and the details of the error correction processing which is a feature of the present invention will be described below.

The arithmetic unit 5 internally forms a reference coordinate axis by arithmetic processing based on inertia information in an initial startup state (a state in which the ship is stationary), similarly to a known strap-down type inertial navigation apparatus. The ship starts navigation and sequentially calculates the latitude and longitude of the ship on the reference coordinate axes based on inertia information sequentially input from the inertial measurement unit 1. Normally, in the process of forming the reference coordinate axes, a leveling process using each acceleration included in the inertial information and a northing process using each angular velocity are performed. In addition, generally, the leveling process and the northing process are collectively referred to as a static determination (alignment) process.

The leveling process is a process of calculating a horizontal plane (local horizontal plane) at the current position (local area) of the ship based on an acceleration G detected by an arbitrary accelerometer K among the three accelerometers. . For example, accelerometer K
Is inclined by a certain angle A (inclination angle) with respect to the horizontal plane, the following equation (1) is established when the gravitational acceleration is g. G = g · sin A (1) When the gravitational acceleration g is stored in the arithmetic unit 5 as basic data in advance, the arithmetic unit 5 easily calculates the inclination angle A of the accelerometer K based on the equation (1). Can be calculated. Then, the horizontal plane of the reference coordinate axis, that is, the vertical axis of the reference coordinate axis can be calculated based on the inclination angle A thus calculated.

In the northern search processing, RLG is performed while the ship is stationary.
This is a process of detecting the direction of true north based on the rotational angular velocity of the earth detected by the computer and the rotational angular velocity Ω of the earth stored in the arithmetic unit 5. Since this northing process is a process well known to those skilled in the art, detailed description thereof will be omitted, but the directions of the two axes constituting the local horizontal plane are calculated by the northing process. That is, the direction of the vertical axis of the reference coordinate axis is determined by the leveling processing, and the directions of the other two axes of the reference coordinate axis are determined by the subsequent north search processing.

The above-described static determination processing by the arithmetic unit 5 is performed based on inertia information acquired from the inertial measurement unit 1, that is, detection values of each RLG and each accelerometer in the inertial measurement unit 1. If the error of the detected value is included, the accuracy of the position system information finally calculated is reduced. In the present embodiment, the following processing is performed to detect such an error. That is,
The following error detection processing is added to the static determination processing to detect erroneous calculation of each RLG and each accelerometer, and the position error is corrected by correcting each processing result of the leveling processing and the northing processing using the detection error. To improve the accuracy of system information.

First, as shown in FIG. 1, the outputs of the accelerometer (X) and the accelerometer (Y) for detecting the acceleration around two axes of the X axis and the Y axis are both set to "zero". The X axis and the Y axis of the inertial measurement unit 1 are set in a horizontal state. Then, in this state, the inertial measurement unit 1 is rotated around the Z axis by slowly rotating the turntable 3 at a constant angular speed S of several minutes to several tens of hours.

Here, as described above, the earth rotation angular velocity Ω
Is stored in advance in the arithmetic unit 5, and the initial latitude λ of the ship at the stationary position can be obtained from the GPS 6, so that the arithmetic unit 5 calculates the north-directional earth rotation angular velocity based on the following equation (2). Ωn can be calculated. In addition, the earth rotation angular velocity Ωe in the east direction is always “zero”. Ωn = Ω · cosλ (2)

As described above, it is possible to easily calculate the earth rotation angular velocity Ωn in the north direction and the earth rotation angular velocity Ωe in the east direction based on the earth rotation angular velocity Ω and the latitude λ of the ship. S is also known. Therefore, X on the rotary table 3 that rotates at a constant angular velocity S
Detected value of RLG (X) for detecting angular velocity around axis and Y
By comparing the detected value of RLG (Y), which detects the angular velocity around the axis, with the angular velocity of the earth, RLG (X) and RLG (Y) calculated from the earth rotation angular velocity Ω, the latitude λ of the vessel, and the angular velocity S, The bias errors of RLG (X) and RLG (Y) can be detected.

The rotation speed S of the turntable 3 is R
By integrating the detection values of LG (X) and RLG (Y) over a longer time, RLG (X) and RLG (X)
(Y) Since each bias error can be detected more accurately, the speed is set to a relatively slow speed of several minutes to several tens of hours.

In the state shown in FIG. 1, the detection value of the accelerometer (Z) for detecting the acceleration in the Z-axis direction is monitored for a certain period of time and compared with the local gravitational acceleration data.
The bias error of the accelerometer (Z) can be detected. That is, in this state, the Z-axis is in the vertical state, so that if there is no bias error, the detected value of the accelerometer (Z) becomes equal to the local gravitational acceleration, and if not, the difference is the accelerometer. This is the bias error of (Z). Since the latitude and longitude of the local area are known by the GPS 6 and the gravitational acceleration of each location according to the latitude and longitude can be easily obtained as data, by storing this gravitational acceleration data in the arithmetic unit 5 in advance. ,
As described above, the bias error of the accelerometer (Z) can be detected.

Next, as shown in FIG. 2, the outputs of the accelerometer (X) and the accelerometer (Z) for detecting acceleration around two axes of the X axis and the Z axis are both set to "zero". The X axis and the Z axis of the inertial measurement unit 1 are set in a horizontal state. Then, in this state, the rotary table 3 is slowly rotated at a constant rotation speed S of several minutes to several tens of hours, thereby rotating the inertial measurement unit 1 around the Y axis, thereby obtaining the same as the case of FIG. 1 described above. RLG (X)
And RLG (Z) bias errors and accelerometer (Y)
Can be detected.

Further, as shown in FIG. 3, the inertia is set so that the outputs of the accelerometer (Y) and the accelerometer (Z) for detecting the acceleration around two axes of the X axis and the Z axis are both "zero". The Y axis and the Z axis of the measurement unit 1 are set in a horizontal state, and in this state, the turntable 3 is slowly rotated at a constant rotation speed S of several minutes to several tens of hours. By rotating the inertial measurement unit 1 about the X axis, RLG (Y) and RLG (Y) are
Each bias error of (Z) and the bias error of the accelerometer (X) can be detected.

In the above description, the case where the error detection processing is performed at the time of static settling, that is, the state in which the hull is stationary, has been described. However, the bias error of each RLG and each accelerometer changes after the vessel starts sailing. There are cases. With respect to such a change in the bias error, the change in the bias error can be detected by performing the above-described error detection processing periodically even after the stabilization treatment.

[Second Embodiment] In this second embodiment, as shown in FIG. 4, the inertial measurement unit 1 is provided with a rotary table 3 '.
It is directly fixed on the top and constantly rotated at a rotation speed Sa of several rotations to several tens of rotations per second. Such relatively high-speed rotation averages and reduces errors in the detection values of the accelerometer (X), the accelerometer (Y), and RLG (X) and RLG (Y), and also reduces these bias errors. Can be prevented from varying depending on the attitude of the hull. Therefore, it is possible to stably detect each bias error even during the navigation of the ship.

It is known that the error fluctuation period of the inertial navigation device depends on the Schuler period of 84.4 minutes. By setting the rotation speed Sa faster than the Schuler period, the errors cancel each other out with positive or negative and average. Is done. In the present embodiment, since the posture setting unit 2 is not provided, X
Since the axis and the Y axis are not set in a horizontal state, it is necessary to set the rotation speed Sa to a speed faster than the oscillation cycle of the hull. Under such circumstances, the rotation speed Sa is set to several rotations to several tens rotations per second.

[0030]

As described above, the inertial navigation system according to the present invention has the following effects.

(1) According to the first aspect of the present invention, the arithmetic unit detects the acceleration in the direction of the detected axis detected when one of the detection axes of the inertial measurement unit is set in the vertical state by the posture setting unit. Is compared with gravitational acceleration data stored in advance to detect a bias error of an acceleration sensor for detecting acceleration in the detection axis direction,
Each of the angular velocities, the rotation speed of the earth, and the latitude of the sailing body are stored in advance in which the angular velocities around two other axes orthogonal to the detection axes detected when one of the detection axes is set in the vertical state are stored in advance. By detecting the bias error of each gyro for detecting each angular velocity around the two axes by comparing the angular velocity around the other two axes calculated from the above, each acceleration for detecting the acceleration in the direction of each detected axis By sequentially setting the attitudes of the meters in the vertical state, the bias error of each accelerometer and the bias error of each gyro can be individually detected. Therefore, it is possible to improve the accuracy of the position system information finally calculated by the calculation unit.

(2) According to the second aspect of the present invention, the inertia measuring unit is rotated at the angular velocity Sa at which the bias error of each accelerometer and gyro is averaged by the rotating means. The value error is reduced. Therefore, it is possible to improve the accuracy of the position system information finally calculated by the calculation unit. Further, it is possible to prevent a situation in which the error amount of the bias error varies depending on the attitude of the navigation body due to the rotation.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a first conceptual diagram for explaining the operation of the first embodiment of the present invention.

FIG. 3 is a second conceptual diagram for explaining the operation of the first embodiment of the present invention.

FIG. 4 is a conceptual diagram showing a configuration of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inertial measurement unit 2 ... Attitude setting part 3, 3 '... Rotary table (rotation means) 3a ... Top surface 4 ... Rotation drive part 5 ... Calculation part 6 ... GPS

Claims (2)

[Claims] 1. Each orthogonal detection axis (X axis, Y axis, Z axis)
An inertial measurement unit (1) for detecting each angular velocity around and each acceleration in each of the detection axis directions and outputting the detected inertial information as inertia information; and performing a predetermined arithmetic processing on the inertial information to indicate a current position of the vehicle. An inertial navigation device comprising a calculation unit (5) for calculating position system information, comprising: a three-dimensional orthogonal coordinate system (U axis, V axis, W axis) fixed to a vehicle.
A rotating means (3) rotating at a constant angular velocity (S) about one axis of the axis (A), and an inertial measurement unit (1) provided on the rotating means (3), and connecting the inertial measurement unit (1) to the three-dimensional orthogonal coordinate system (U-axis). , V-axis, W-axis), and a posture setting unit (2) for setting the desired posture by rotating around two other axes. The arithmetic unit comprises: an inertia measurement unit (1) by the posture setting unit (2). ) 1
The bias error of the acceleration sensor that detects the acceleration in the detection axis direction is detected by comparing the acceleration in the detection axis direction detected when the two detection axes are set in the vertical posture with the gravitational acceleration data stored in advance. At the same time, the angular velocities (S) stored in advance and the angular velocities (S) of the earth, the angular velocities around the other two axes orthogonal to the detection axis detected when the one detection axis is set in the vertical state, are stored. Ω) and the angular velocities around the other two axes calculated from the data on the latitude (λ) of the sailing body and the bias error of each gyro for detecting each angular velocity around the two axes. An inertial navigation device, wherein position information is corrected by a bias error of the acceleration sensor and a bias error of each gyro. 2. Detection axes orthogonal to each other (X axis, Y axis, Z axis)
An inertial measurement unit (1), comprising: a gyro for detecting each angular velocity around the accelerometer; and an accelerometer for detecting each acceleration in each of the detection axis directions, the inertial measurement unit (1) outputting the angular velocity and each acceleration as inertia information; (1) A three-dimensional rectangular coordinate system (U-axis, V-axis, W-axis) fixed to a cruising body at an angular velocity (Sa) at which the bias error of each of the accelerometer and gyro is averaged
A rotating means (3 ') for making a constant rotation about one axis of: a calculating section (5) for calculating position system information indicating a current position of the navigation body by performing predetermined arithmetic processing on the inertial information;
An inertial navigation device, comprising: