A Composite Rotation Method Based on a Triaxial Hybrid Fiber Optic Inertial Navigation System

Abstract

The present invention discloses a composite rotation method based on a three-axis hybrid fiber optic inertial navigation system. Step 1: Power on the inertial navigation system, return the three-frame grating to zero, bind the initial position and complete initialization; Step 2: Complete static coarse alignment and fine alignment by rotating forward and backward modulation around the inner frame; Step 3: After entering navigation, control the inertial navigation system to lock the inner frame at two positions of 0° and 180° respectively, and rotate 360° forward, backward, backward and forward in sequence around the middle and outer frames, and repeat in cycles. When the system needs to end navigation, power off. The present invention utilizes the structural advantages of the self-rotating mechanism of the three-axis hybrid fiber optic inertial navigation system, fully combines the advantages of the continuous rotation and the multi-position rotation and stop rotation methods, effectively reduces the polar axis drift of the three-axis hybrid inertial navigation system and suppresses the navigation error oscillation caused by the characteristics of the fiber optic gyroscope itself in the initial stage of navigation through the design of the composite rotation method, significantly improves the navigation accuracy, and has important significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of inertial technology and is applicable to multi-axis rotary or hybrid inertial navigation systems. Specifically, it relates to a composite rotation method based on a three-axis hybrid fiber optic inertial navigation system. Background Art

[0002] The rotation modulation technology is a method to effectively suppress the influence of the constant drift of devices on the navigation accuracy. Taking the continuous rotation type rotation modulation inertial navigation system as an example, it can modulate the projections of the constant drifts of two gyroscopes in the direction perpendicular to the rotation axis into sinusoidal and cosinusoidal variations with a mean value of zero in the body frame, thereby greatly reducing the divergence of navigation errors and improving the navigation accuracy. The rotation modulation technology is widely used in the new generation of inertial navigation systems, mainly including rotary inertial navigation systems and hybrid inertial navigation systems.

[0003] According to the error principle of the inertial navigation system, it is known that the north gyro drift ε N and the azimuth gyro drift ε U will cause the cumulative error of longitude, and this error will diverge with time:

[0004] δλ 积 = -(ε N cosL + ε U sinL)t (1)

[0005] where, δλ 积 is the longitude error, L is the geographical latitude, and t is the navigation time. In the present invention, ε p = -(ε N cosL + ε U sinL) is collectively referred to as the polar axis drift of the inertial navigation system. For an inertial navigation system, there are three types of navigation errors, namely, oscillatory type, constant type, and cumulative type. Among them, the cumulative error increases linearly with time t and has a greater impact on the system accuracy. It is the main factor causing the divergence of navigation errors and needs to be reduced or even eliminated as much as possible. The rotation modulation technology cancels the constant and slow-changing drifts of the inertial measurement unit (abbreviated as IMU) through rotation, and improves the accuracy of the inertial navigation system by at least one order of magnitude. The IMU is generally composed of a three-axis gyroscope and a three-axis accelerometer. For a rotary or hybrid inertial navigation system, the north gyro drift ε N and the azimuth gyro drift ε UIt is the residual drift after the rotation modulation of the three gyros in the inertial navigation system, rather than the performance parameter of the gyro itself. Researchers can suppress the polar axis drift by designing different rotation methods, and maximize the navigation accuracy of the inertial navigation system under the condition of using the same inertial devices. The classification basis of the rotation methods is diverse. According to the number of rotation axes, it can be divided into single-axis and multi-axis rotation methods. According to the rotation mode, it can be divided into continuous rotation and multi-position rotation and stop. The modulation effect of the continuous rotation mode is better, but it can only suppress the errors perpendicular to the rotation axis direction, and the errors along the rotation axis cannot be cancelled by rotation. The multi-position rotation and stop mode can fully suppress various errors in the three axes. However, during the flipping process of the IMU, due to the characteristics of the fiber optic gyro, the navigation error does not diverge but oscillates greatly, especially in the initial stage of navigation. Therefore, there are many literature on the design of rotation methods based on the laser inertial navigation system, and few relevant literature on the fiber optic inertial navigation system. There is no relevant literature report on the composite rotation method that combines the continuous rotation and multi-position rotation and stop methods. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, in order to achieve the simultaneous suppression effect of navigation error oscillation and divergence, a composite rotation method based on a three-axis hybrid fiber optic inertial navigation system is provided, which effectively suppresses the navigation error caused by the polar axis drift of the inertial navigation system and improves the navigation accuracy of the inertial navigation system.

[0007] The technical solution adopted by the present invention to solve the above technical problem is: a composite rotation method based on a three-axis hybrid fiber optic inertial navigation system, the steps are as follows:

[0008] Step (1), power on the inertial navigation system, return the three-frame grating to zero, bind the initial position and complete the system initialization;

[0009] Step (2), control the inertial navigation system to complete the static coarse alignment and the fine alignment of continuous positive and negative rotation modulation around the inner frame;

[0010] Step (3), after the inertial navigation system enters the navigation state, use the composite rotation method for navigation, drive the rotation mechanism to lock the inner frame at two positions of 0° and 180° respectively, and rotate 360° in turn forward, backward, backward and forward around the middle and outer frames, and repeat in a cycle. Power off when the navigation needs to end.

[0011] Further, in step (1), the power on of the inertial navigation system, the return of the three-frame grating to zero, the binding of the initial position and the completion of the system initialization, the specific steps are to power on the inertial navigation system, drive the rotation mechanism to return to the grating zero position at an angular velocity of 6° / s according to the absolute grating rotation angle information of the inner, middle and outer frames, then lock to the zero position, and issue a "zero return good" flag, bind the initial position according to the upper computer or differential GPS, and after the system initialization is completed, transfer to the coarse alignment process.

[0012] Further, in step (2), the controlled inertial navigation system completes static coarse alignment and fine alignment with continuous forward and reverse modulation around the inner frame. The specific steps are as follows: After entering the coarse alignment process, the three frames of the inertial navigation system are locked for 1 minute, the outputs of the gyroscope, accelerometer, temperature, and grating are sampled, processed and compensated, and the coarse alignment result is obtained according to the preset analytical coarse alignment program, and the inertial navigation system is transferred to the fine alignment state.

[0013] After the inertial navigation system enters the fine alignment process, the inertial navigation system is controlled to continuously rotate forward and reverse around the inner frame for 8 minutes, and the fine alignment is completed using the fine alignment program of the least squares method. At the end moment, the platform deflection angle is corrected and compensated, and the navigation process is entered.

[0014] Further, after the inertial navigation system enters the navigation state in step (3), the inertial navigation system is controlled to lock the inner frame at two positions of 0° and 180° respectively, and rotate forward, reverse, reverse, and forward 360° in sequence around the middle and outer frames, and repeat in a cycle. When the system needs to end the navigation, power off the system. The specific steps are as follows: After the inertial navigation system enters the navigation state, drive the rotating mechanism to lock the inner frame at 0°, and rotate forward, reverse, reverse, and forward 360° in sequence around the middle and outer frames respectively; then, after rotating the inner frame forward to 180° and locking it, rotate forward, reverse, reverse, and forward 360° in sequence around the middle and outer frames respectively; then, after rotating the inner frame backward to 0° and locking it, rotate forward, reverse, reverse, and forward 360° in sequence around the middle and outer frames respectively; finally, after rotating the inner frame backward to 180° and locking it, rotate forward, reverse, reverse, and forward 360° in sequence around the middle and outer frames respectively; after rotating the inner frame forward to 0° and locking it, repeat the above process until the system completes navigation and powers off.

[0015] In the compound rotation method, the middle and outer frames rotate in a full circle, and only the inner frame is locked at two positions of 0° and 180°. Therefore, there are fewer error excitations related to the rotation angle, and the excitation of the self-error of the fiber optic gyroscope is not as significant as that of the multi-position rotation and stop method. The oscillation of the navigation error can be effectively reduced in the initial stage of navigation. In addition, the constant and slow-changing drifts of the x and y gyros have been completely cancelled out by the symmetric positions of 0° and 180° of the inner frame. If the three-frame rotating mechanism rotates at an angular velocity of 6° / s, then the constant and slow-changing drifts of the z gyro can only not be cancelled out during the rotation around the inner frame, accounting for 1 / 17 of the entire rotation process. In order to reflect the advantages of the compound rotation method, the following compares the polar axis drift of continuous forward and reverse rotation around the inner frame axis and the compound rotation method. Assume that the drifts of the three-axis gyros are all Geographical latitude L = 40°, then the polar axis drifts of the two rotation methods are:

[0016]

[0017] Among them, ε p1 and ε p3They are the polar axis drift of the continuous forward and reverse rotation around the inner frame and the multi-axis alternating rotation method, △ε z is the residual gyro drift of the z gyro after calibration compensation, and L is the geographic latitude.

[0018] From (2), it can be seen that the composite rotation method can greatly reduce the polar axis drift of the inertial navigation system. The rotation method flow chart is shown in the attached Figure 1 , the overall flow chart is shown in Figure 2 .

[0019] The advantages of the present invention compared with the prior art are:

[0020] (1) The present invention fully utilizes the structural advantages of multi-axis rotary or hybrid inertial navigation systems, combines the advantages of continuous rotation and multi-position stop, and effectively improves the navigation accuracy of the inertial navigation system without changing the inertial components and suppresses the navigation error oscillation caused by the inherent characteristics of the fiber optic gyroscope in the early stage of navigation;

[0021] (2) The present invention does not require additional experimental equipment and can be realized only by the rotation structure of the inertial navigation system itself;

[0022] (3) The present invention does not require complex navigation calculations, only requires changing the control program, and the navigation solution still uses the strapdown algorithm;

[0023] (4) The present invention has a wide range of applications and is applicable to various inertial navigation systems with rotating mechanisms. It has good scalability and can be applied to various multi-axis rotary or hybrid inertial navigation systems after modifying the experimental scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the composite rotation method based on the three-axis hybrid fiber-optic inertial navigation system;

[0025] Figure 2 This is the overall flow chart;

[0026] Figure 3 This is the schematic diagram of the three-axis hybrid fiber-optic inertial navigation system, where 1 is the rotating structure, 2 is the electrical equipment, 3 is the three-axis fiber-optic gyroscope and three-axis accelerometer, and 4 is the entire machine casing;

[0027] Figure 4 The schematic diagram of the rotation mechanism of the three-axis hybrid fiber-optic inertial navigation system, where 5 is the outer frame, 6 is the middle frame, and 7 is the inner frame;

[0028] Figure 5 This is a comparison chart of the navigation position errors of the composite rotation method proposed in the present invention and the continuous forward and reverse rotation method around the inner frame. DETAILED DESCRIPTION

[0029] The method of the present invention is described in detail below with reference to specific embodiments.

[0030] The present invention proposes a composite rotation method based on a three-axis hybrid fiber optic inertial navigation system. The schematic diagram of the entire rotation method is as shown in Figure 1 . After the inertial navigation system enters the navigation state, first, control the inertial navigation system to rotate 360° forward, reverse, reverse, and forward in sequence around the middle and outer frames, as shown in (1-1) and (1-2); then, after controlling the inertial navigation system to rotate 180° forward around the inner frame, rotate 360° forward, reverse, reverse, and forward in sequence around the middle and outer frames, as shown in (2-1) and (2-2); next, after controlling the inertial navigation system to rotate 180° backward around the inner frame, rotate 360° forward, reverse, reverse, and forward in sequence around the middle and outer frames, as shown in (3-1) and (3-2); finally, after controlling the inertial navigation system to rotate 180° backward around the inner frame again, rotate 360° forward, reverse, reverse, and forward in sequence around the middle and outer frames, as shown in (4-1) and (4-2); finally, rotate 180° forward around the inner frame and return to the original position. Repeat the above steps until the inertial navigation system completes navigation and powers off.

[0031] In Figure 1 , O-X s Y s Z s is the inertial reference coordinate system of the inertial navigation system (abbreviated as the s system). The x and y accelerometer sensitive axes are defined in the X s OY s plane. OX s points along the projection of the x gyroscope sensitive axis on the X s OY s plane. OY s is in the X s OY s plane and is perpendicular to OX s and forms an acute angle with the direction of the y accelerometer sensitive axis. OZ s and OX s , OY s together form a right-handed rectangular coordinate system. O-X b Y b Z b is the inertial reference coordinate system of the inertial navigation system (abbreviated as the b system). The outer frame axis when the outer frame grating rotation angle is 0 is the Y b axis. The projection of the middle frame axis in the plane perpendicular to the Y b axis is the X b axis. The Z b axis is determined according to the right-hand rule. O-X s Y s Z s is used in Figure 1 to represent the spatial orientation of the IMU. O-X b Y b Z bIn Figure 1 it is used to represent the spatial orientation of the inertial navigation system.

[0032] The principle diagram of the entire system is as shown in Figure 3 . In this embodiment, the inertial navigation system is a three-axis hybrid fiber optic inertial navigation system, including a three-axis fiber optic gyroscope, a three-axis accelerometer 3, a rotating mechanism 1, electrical equipment 2, and an overall machine housing 4.

[0033] As shown in Figure 4 , the rotating mechanism is divided into an inner frame 7, a middle frame 6, and an outer frame 5. The three frames have different degrees of freedom respectively, enabling the entire system to rotate around three axes. Outside the three-axis frame, an overall machine housing is configured, as specifically shown in Figure 3 . During the fixing process of the inertial navigation system, the system assembly is mainly achieved by adjusting the position of the housing.

[0034] As shown in Figure 2 , the specific experimental steps of this embodiment of the present invention are as follows:

[0035] (1). Power on the system, return the gratings of the three frames to zero, bind the initial position, and complete the system initialization.

[0036] (2). Complete the static coarse alignment and the fine alignment by continuous forward and reverse rotation modulation around the inner frame.

[0037] (3). After entering the navigation state, perform navigation using two methods, namely continuous forward and reverse rotation around the inner frame and the compound rotation method respectively. When the inertial navigation system needs to end navigation, power off the system.

[0038] The summary of the navigation results of the two methods of continuous forward and reverse rotation around the inner frame and the compound rotation method is shown in Table 1. Among them, the Circular Error Probability (abbreviated as CEP) is a representation method of the navigation accuracy of the inertial navigation system, and the unit is nautical miles per hour (n mile / h, 1 n mile = 1852 m).

[0039] Table 1 Navigation results of two rotation methods

[0040]

[0041] As shown in Figure 5 , the compound rotation method proposed by the present invention fully combines the advantages of the two rotation methods of continuous rotation and multi-position rotation and stop. Without changing the performance of the inertial devices inside the system, it can effectively improve the navigation accuracy of the inertial navigation system. Figure 5Shows the test results of a group of static navigation using the continuous forward and reverse rotation around the inner frame and the compound rotation method respectively. The upper figure is the eastward position error, and the lower figure is the northward position error. The unit of the vertical coordinate is meter (m), and the unit of the horizontal coordinate is hour (h). The solid line is the navigation error of the continuous forward and reverse rotation around the inner frame, and the dashed line is the navigation error of the compound rotation method. From Table 1 and Figure 5 It can be clearly seen that the navigation CEP and position error of the compound rotation method are smaller, and the navigation accuracy is higher.

[0042] The experimental results show that the compound rotation method of the present invention can effectively suppress the polar axis drift and improve the navigation accuracy of the inertial navigation system.

[0043] The parts not detailedly disclosed in the present invention belong to the well-known technologies in the art.

[0044] Although the illustrative specific embodiments of the present invention are described above for the convenience of those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those ordinary skilled in the art in the technical field, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the concept of the present invention are within the scope of protection.

Claims

1. A composite rotation method based on a three-axis hybrid fiber-optic inertial navigation system, wherein the system comprises three orthogonal continuously rotatable rotating mechanisms, characterized in that: The method utilizes the structural advantages of a multi-axis rotary or hybrid inertial navigation system and combines the advantages of continuous rotation and multi-position stop rotation methods. Without changing the inertial components, it effectively improves the navigation accuracy of the inertial navigation system and suppresses navigation error oscillations caused by the inherent characteristics of the fiber optic gyroscope in the early stages of navigation. The method comprises the following steps: Step (1), power on the system, and the three orthogonal rotation mechanisms return to their respective zero positions according to the preset control instructions, bind to the initial positions, and complete the system initialization; Step (2), using the system to complete static coarse alignment and continuous forward and reverse modulation fine alignment around the inner frame; Step (3), after the system enters the navigation state, a composite rotation method is used for navigation, the rotation mechanism is driven to lock the inner frame at two positions of 0° and 180° respectively, and the inner frame and the outer frame are rotated forward, reverse, reverse and forward 360° in sequence, and the system is powered off when it needs to end navigation; The composite rotation method in step (3) specifically includes the following steps: (1) driving the rotation mechanism of the system to lock the inner frame at 0°, and then continuously rotating forward, reverse, reverse, and forward 360° around the middle and outer frames respectively; (2) driving the rotating mechanism of the system to rotate forward 180° around the inner frame and then lock it, and then rotate forward, reverse, reverse, and forward 360° around the middle and outer frames respectively; (3) driving the rotating mechanism of the system to rotate around the inner frame to 0° and then lock it, and then rotate forward, reverse, reverse, and forward 360° around the middle and outer frames respectively; (4) driving the rotating mechanism of the system to rotate 180° around the inner frame and then lock it, and then rotate forward, reverse, reverse, and forward 360° around the middle and outer frames respectively; (5) After the rotating mechanism of the system is driven to rotate forward around the inner frame to 0°, it jumps back to (1) and repeats the cycle until the system is powered off when it needs to end navigation.

2. The composite rotation method based on the three-axis hybrid fiber-optic inertial navigation system according to claim 1, characterized in that: The static coarse alignment and the continuous forward and reverse modulation fine alignment around the inner frame in step (2) include the following steps: (1) driving the three-frame rotation mechanism of the system to lock for 1 minute, obtaining the coarse alignment result according to the preset analytical coarse alignment procedure, and switching the system to the fine alignment state; (2) Control the system to rotate continuously forward and reverse around the inner frame for 8 minutes, and complete the least squares method precision alignment process according to the preset plan; (3) At the end of the alignment, the platform deflection correction and compensation are completed, and the system is switched to the navigation state.

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