Method for rotating around multiple axes by alternating rotation based on a triaxial hybrid fiber-optic inertial navigation system

Abstract

The application discloses a method for rotating around multiple axes alternately based on a three-axis hybrid optical fiber inertial navigation system, and comprises the following steps: 1, powering on the inertial navigation system, returning the three-frame grating to zero, setting the initial position and completing initialization; 2, completing static coarse alignment and rotating around the inner frame in positive and negative directions to modulate fine alignment; 3, after entering navigation, the inertial navigation system is controlled to rotate around the inner frame, the middle frame and the outer frame in positive and negative directions in sequence, and the rotation is repeated until the system needs to end the navigation and is powered off. The method for rotating around multiple axes alternately is designed by using the structural advantages of the rotating mechanism of the three-axis hybrid optical fiber inertial navigation system, is simple in principle and easy to implement, effectively reduces the polar axis drift of the three-axis hybrid inertial navigation system, compensates for system errors and improves navigation precision, and has important significance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inertial technology, and is suitable for a multi-axis rotation type or a hybrid type inertial navigation system, and particularly relates to a multi-axis alternate rotation method based on a three-axis hybrid type optical fiber inertial navigation system. BACKGROUND

[0002] The rotation modulation technology is a method for effectively suppressing the influence of the constant drift of a device on navigation accuracy. Taking a continuous rotation type rotation modulation inertial navigation system as an example, the rotation modulation technology can modulate the constant drift of two gyros in the vertical direction of the rotation axis into a cosine variation quantity with a mean value of zero under the projection of the carrier body, so as to greatly reduce the divergence of navigation error and improve the navigation accuracy. The rotation modulation technology is widely used in new generation inertial navigation systems, mainly including a rotation type inertial navigation system and a hybrid type inertial navigation system.

[0003] According to the error principle of the inertial navigation system, 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] wherein, δλ 积 is the longitude error, L is the geographic latitude, and t is the navigation time. In the present patent, ε p =-(ε N cosL+ε U sinL) is collectively referred to as the polar axis drift of the inertial navigation system. For the inertial navigation system, the cumulative error increases linearly with time t, which is the main factor causing the divergence of navigation error and needs to be reduced as much as possible or even eliminated. The rotation modulation technology can offset the constant and slowly varying drift of the inertial measurement unit (IMU) by rotation, and can improve the accuracy of the inertial navigation system by at least one order of magnitude. The IMU is generally composed of three-axis gyros and three-axis accelerometers. For the rotation type or hybrid type inertial navigation system, the north gyro drift ε N and the azimuth gyro drift ε UThe residual drift of three gyroscopes after rotation modulation in the inertial navigation system is not the performance parameter of the gyro itself, and researchers can inhibit the polar axis drift by designing different rotation methods to maximize the navigation accuracy of the inertial navigation system under the condition of using the same inertial device. The commonly used rotation methods are mainly based on single-axis and double-axis inertial navigation systems, and there are few related literature reports on three-axis rotation methods. The single-axis rotation method can inhibit fewer error types and has lower navigation accuracy, and the multi-axis rotation method needs to complete detailed error analysis and complex strategy design. The multi-axis alternating rotation method proposed in the application has simple and easy-to-implement principle, and each frame is rotated by 360° and returns to the original position. The error related to the rotation angle does not accumulate, the inhibition effect of the polar axis drift is remarkable, and the navigation accuracy of the inertial navigation system can be effectively improved. SUMMARY

[0006] The technical problem to be solved by the application is to overcome the shortcomings of the prior art and provide a multi-axis alternating rotation method based on a three-axis hybrid optical fiber inertial navigation system, which can effectively inhibit the navigation error caused by the polar axis drift of the inertial navigation system and improve the navigation accuracy of the inertial navigation system.

[0007] The technical solution adopted by the application to solve the above technical problem is a multi-axis alternating rotation method based on a three-axis hybrid optical fiber inertial navigation system, and the steps are as follows:

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

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

[0010] Step (3), after the inertial navigation system enters the navigation state, the multi-axis alternating rotation method is used for navigation, the driving rotation mechanism is driven to rotate forward and reverse around the inner, middle and outer frames by 360° in turn, and the cycle is repeated. When the navigation needs to be ended, power off.

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

[0012] Further, the control of the inertial navigation system in step (2) completes stationary coarse alignment and continuous positive and negative rotation modulation fine alignment around the inner frame, and the specific steps are as follows: after entering the coarse alignment process, the inertial navigation system is controlled to lock three frames for 1 min, gyro, accelerometer, temperature and grating outputs are sampled, processed and compensated, coarse alignment results are obtained according to a preset coarse alignment program, and the inertial navigation system is switched to a fine alignment state.

[0013] After the inertial navigation system enters the fine alignment process, the inertial navigation system is controlled to continuously rotate around the inner frame in positive and negative directions for 8 min, a fine alignment program using the least square method is used to complete fine alignment, platform angle correction and compensation are completed at the end time, and a 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 rotate around the inner, middle and outer frames in positive and negative directions for 360° in turn, and the system is powered off when the system needs to end navigation, and the specific steps are as follows: after the inertial navigation system enters the navigation state, the rotating mechanism is driven to rotate around the inner frame in positive and negative directions for 360° in turn, then around the middle frame in positive and negative directions for 360° in turn, and then around the outer frame in positive and negative directions for 360° in turn, and the system is powered off when the system completes navigation.

[0015] In order to reflect the advantages of the multi-axis alternate rotation method, the polar drift of the continuous positive and negative rotation around the inner frame and the multi-axis alternate rotation method is compared below, assuming that the drifts of the three-axis gyros are all 0.01° / h, the geographic latitude L is 40°, the initial attitude and heading of the inertial navigation system are local geographic coordinates, the system heading angle ψ is 0°, and the polar drifts of the two methods are as follows:

[0016]

[0017] Wherein, ε p1 and ε p2 are the polar drifts of the continuous positive and negative rotation around the inner frame and the multi-axis alternate rotation method respectively, △ε x , △ε y and △ε z are the residual gyro drifts of the x, y and z gyros after calibration and compensation respectively, ψ is the system heading angle, and L is the geographic latitude.

[0018] As can be seen from (2), the multi-axis alternate rotation method can effectively reduce the polar drift of the inertial navigation system, and the rotation method flow chart is shown in the accompanying Figure 1 , and the overall flow chart is shown in Figure 2 .

[0019] Compared with the prior art, the present application has the following advantages:

[0020] (1) The present application makes full use of the structural advantages of the multi-axis rotation type or hybrid inertial navigation system, and effectively improves the navigation accuracy of the inertial navigation system without changing the inertial devices.

[0021] (2), the application does not need additional experimental equipment, only by the rotation structure of the inertial navigation system itself can be realized;

[0022] (3), the application does not need complex navigation calculation, only need to change the control program, navigation solution still uses strapdown algorithm;

[0023] (4), the application is widely used, suitable for various inertial navigation systems with rotating mechanism, good extensibility, after modifying the experimental scheme, it can be applied to various multi-axis rotating or hybrid inertial navigation systems. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a schematic diagram of the multi-axis alternating rotation method based on the three-axis hybrid optical fiber inertial navigation system.

[0025] Figure 2 It is a general flowchart of the application.

[0026] Figure 3 It is a schematic diagram of the three-axis hybrid optical fiber inertial navigation system, wherein 1 is a rotating structure, 2 is an electrical equipment, 3 is a three-axis optical fiber gyroscope and a three-axis accelerometer, and 4 is a whole machine shell.

[0027] Figure 4 It is a schematic diagram of the rotating mechanism of the three-axis hybrid optical fiber inertial navigation system, wherein 5 is an outer frame, 6 is a middle frame, and 7 is an inner frame.

[0028] Figure 5 It is a navigation position error comparison diagram of the multi-axis alternating rotation method and the continuous forward and reverse rotation method around the inner frame proposed by the application. DETAILED DESCRIPTION

[0029] The method of the application will be described in detail below in combination with specific embodiments.

[0030] The application proposes a multi-axis alternating rotation method based on a three-axis hybrid optical fiber inertial navigation system. The inertial navigation system in this embodiment is a three-axis hybrid optical fiber inertial navigation system, and the principle diagram of the whole system is shown in Figure 3 , which includes a three-axis optical fiber gyroscope, a three-axis accelerometer 3, a rotating mechanism 1, an electrical equipment 2 and a whole machine shell 4.

[0031] As shown in Figure 4 , the rotating mechanism is divided into an inner frame 7, a middle frame 6 and an outer frame 5, and the three frames have different degrees of freedom, so that the whole system can rotate around the three axes. Outside the three-axis frame, the system is configured with a whole machine shell, which is shown in detail in Figure 3 , during the fixing of the inertial navigation system, the system assembly is mainly realized by adjusting the position of the shell.

[0032] A schematic diagram of the entire rotation method is shown below. Figure 1 As shown in Figure 1. After the inertial navigation system (INS) enters navigation mode, it first rotates 360° clockwise and then counterclockwise around the inner frame, as shown in Figure 2; then, it rotates 360° clockwise and then counterclockwise around the middle frame, as shown in Figure 3; finally, it rotates 360° clockwise and then counterclockwise around the outer frame, as shown in Figure 4. This process is repeated until the INS completes navigation and powers off. s Y s Z s The inertial reference coordinate system of the inertial navigation system (referred to as the S-frame) is defined by the x and y accelerator sensitive axes. s OY s Plane, OX s The x-axis of the gyroscope points towards the X-axis. s OY s Projection on a plane, OY s In X s OY s In-plane edge and OX s The direction perpendicular to and forming an acute angle with the y-axis of the accelerator, OZ s With OX s OY s Together they form a right-handed rectangular coordinate system. OX b Y b Z b Let b be the inertial reference coordinate system of the inertial navigation system. When the rotation angle of the outer frame grating is 0, the outer frame axis is Y. b The axis, the middle frame axis is in relation to the Y b The projection of the axis into the plane perpendicular to the axis is X. b Axis, Z b The axis is determined according to the right-hand rule. OX s Y s Z s exist Figure 1 The term "OX" is used to refer to the spatial pointer of the IMU. b Y b Z b exist Figure 1 The term "inertial navigation system" is used to refer to the spatial orientation of an inertial navigation system.

[0033] like Figure 2 As shown, the specific experimental steps of this embodiment of the invention are as follows:

[0034] (1) The system is powered on, the three-frame grating returns to zero, the initial position is set and the system initialization is completed.

[0035] (2) Complete the static coarse alignment and the fine alignment by continuous forward and reverse modulation around the inner frame.

[0036] (3) After entering the navigation state, control the inertial navigation system to navigate by two methods: continuous forward and reverse rotation around the inner frame and alternating rotation around multiple axes. When the inertial navigation system needs to end the navigation, power off the system.

[0037] Table 1 summarizes the navigation results of two methods: continuous forward and reverse rotation around the inner frame and alternating rotation around multiple axes. Circular Error Probability (CEP) is a method for representing the navigation accuracy of an inertial navigation system, and its unit is nautical miles per hour (n mile / h, 1 n mile = 1852 m).

[0038] Table 1. Navigation results of the two rotation methods

[0039]

[0040] like Figure 5 As shown, the multi-axis alternating rotation method proposed in this invention can effectively improve the navigation accuracy of the inertial navigation system without changing the performance of the inertial devices in the system. The principle is simple and easy to implement. Figure 5 The results of a set of experiments on static navigation using continuous forward and reverse rotation around the inner frame and alternating rotation around multiple axes are presented. The upper figure shows the position error in the east direction, and the lower figure shows the position error in the north direction. The vertical axis is in meters (m), and the horizontal axis is in hours (h). The solid line represents the navigation error of continuous forward and reverse rotation around the inner frame, and the dashed line represents the navigation error of the alternating rotation around multiple axes method. (See Table 1 and...) Figure 5 It is evident that the navigation CEP and position error are smaller and the navigation accuracy is higher when the method of alternating rotation around multiple axes is adopted.

[0041] Experimental results show that the multi-axis alternating rotation method of the present invention can effectively suppress polar axis drift and improve the navigation accuracy of the inertial navigation system.

[0042] The parts of this invention not disclosed in detail are well-known technologies in the field.

[0043] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes will be obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A method of rotating around multiple axes alternately based on a triad hybrid fiber-optic inertial navigation system, said system comprising at least three orthogonal continuously rotatable rotation mechanisms, characterized in that, The method comprises the following steps: Step (1), power on the system, the three orthogonal rotating mechanisms return to their respective zero positions according to the preset control instructions, the binding initial position, and the system initialization is completed; Step (2), the system is used to complete the static coarse alignment and the continuous positive and negative rotation modulation fine alignment around the inner frame; the continuous positive and negative rotation around the inner frame is 8 min; Step (3), after the system enters the navigation state, the multi-axis alternate rotation method is used for navigation, the rotating mechanisms are driven to rotate 360° in sequence around the inner, middle and outer frames in positive and negative directions, and the cycle is repeated, and the system is powered off when the navigation is completed; The multi-axis alternate rotation method in step (3) comprises the following steps: (1) the rotating mechanisms of the system are driven to continuously rotate 360° in positive and negative directions around the inner frame; (2) the rotating mechanisms of the system are driven to continuously rotate 360° in positive and negative directions around the middle frame; (3) the rotating mechanisms of the system are driven to continuously rotate 360° in positive and negative directions around the outer frame; (4) return to (1) and repeat the cycle, and the system is powered off when the navigation is completed.

2. The method of rotating about multiple axes alternately based on a triad hybrid fiber optic inertial navigation system as claimed in claim 1, wherein, The static coarse alignment and the continuous positive and negative rotation modulation fine alignment around the inner frame in step (2) comprise the following steps: (1) control the three-frame rotating mechanisms of the system to be locked for 1 min, obtain the coarse alignment result according to the preset analysis coarse alignment program, and convert the system into the fine alignment state; (2) control the system to continuously rotate in positive and negative directions around the inner frame for 8 min, and complete the least square method fine alignment process according to the preset scheme; (3) the platform deflection correction and compensation are completed at the end of the alignment, and the system is converted into the navigation state.

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