CN112525191B - Airborne distributed POS transfer alignment method based on relative strapdown calculation - Google Patents
Airborne distributed POS transfer alignment method based on relative strapdown calculation Download PDFInfo
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Abstract
The invention discloses an airborne distributed POS (point of sale) transfer alignment method based on relative strapdown calculation, and aims to improve the measurement precision of airborne distributed POS spatial motion information in a dynamic environment. The method comprises the following steps: constructing a pseudo single sample rotation vector by using angular velocities output by the gyroscope at the current and the previous N sampling moments of the main subsystem and a rotation vector error compensation coefficient deduced based on conical motion, and solving a relative attitude quaternion in real time based on the rotation vector to realize updating of the relative attitude; meanwhile, a relative velocity and position updating algorithm is established according to the space position vector relation of the main subsystem and the subsystem, and the relative velocity and position updating is realized by utilizing the specific force and the relative posture output by the accelerometer of the main subsystem and the subsystem; and finally, establishing a transfer alignment state model and a measurement model based on a relative strapdown resolving error differential equation and the three-dimensional relative position and three-dimensional relative attitude measured by the fiber bragg grating, and performing transfer alignment by adopting a linear Kalman filtering estimation method to obtain high-precision motion information.
Description
Technical Field
The invention relates to an airborne distributed POS transfer alignment method based on relative strapdown resolving, belongs to the field of aerial remote sensing, can improve the measurement accuracy of airborne distributed POS motion information and is applied to motion compensation of distributed imaging loads such as a flexible baseline array antenna SAR and the like.
Background
A Distributed Position and attitude measurement System (DPOS) is an important device for acquiring motion parameters such as Position, speed, attitude and the like of multiple nodes in an onboard high-resolution earth observation System. The distributed POS mainly comprises a high-precision main position and attitude Measurement system (main POS), a plurality of low-precision sub-Inertial Measurement Units (IMUs), a navigation computer and a set of post-processing software. The main POS is composed of a high-precision main IMU and a Global Navigation Satellite System (GNSS), the main IMU is generally installed in an engine cabin or an engine belly, the sub IMUs are generally installed on wings on two sides, and the main IMU and the sub IMUs are fixedly connected with imaging loads respectively to provide high-precision position, posture and other motion information for the distributed multi-node imaging loads.
In the flying process of the aircraft, due to the influence of gust, turbulence and engine vibration, the wing generates flexural deformation which changes along with time, so that the precision of transfer alignment can be influenced, and the imaging precision is further influenced. Aiming at the problem, related scholars provide a transfer alignment method based on relative strapdown resolving error differential equations, and flexible deformation measurement can be realized. However, the deformation of the wing will cause relative motion, even cone motion, between the main system and the sub system, and inevitably bring irreplaceable errors in the process of resolving the relative attitude, so that the measurement accuracy of the relative attitude is seriously affected, and further the measurement accuracy of the relative speed and the relative position is affected, and the measurement accuracy of the spatial motion information of the distributed POS is reduced.
Disclosure of Invention
The invention provides a relative strapdown resolving-based airborne distributed POS transfer alignment method aiming at the technical problem of non-commutative errors generated by airborne distributed POS due to flexible deformation.
In order to achieve the above purpose, the invention provides the following technical scheme:
the invention relates to an airborne distributed POS transfer alignment method based on relative strapdown resolving, which comprises the following steps:
(1) establishing a relative attitude updating algorithm based on a pseudo-single-sample rotation vector: and establishing a pseudo-single-sample rotation vector by using angular velocities output by the gyroscope at the current and previous N sampling moments of the main subsystem, deriving a rotation vector error compensation coefficient by adopting typical conical motion, and obtaining a relative attitude quaternion in real time by solving the rotation vector, thereby realizing updating of the relative attitude.
(2) Establishing a relative speed updating algorithm: and a vector equation among the main system, the subsystems and the relative positions of the main subsystem and the subsystems is established according to the vector relation of the spatial positions of the main subsystem and the subsystems, a second derivative is solved relative to an inertial coordinate system to obtain a relative velocity differential equation, and a numerical solution is solved for the relative velocity differential equation based on specific force information and relative attitude information measured by an accelerometer of the main subsystem and the subsystems, so that the relative velocity is updated.
(3) Establishing a relative position updating algorithm: and establishing a relative position differential equation based on a differential relation between the relative position and the relative speed, and solving the numerical solution of the relative position differential equation by utilizing the solved relative speed to realize the update of the relative position.
(4) Establishing a transfer alignment algorithm: establishing a transfer alignment state model and a measurement model based on a relative strapdown resolving error differential equation and three-dimensional relative positions and three-dimensional relative postures measured by the fiber bragg gratings, performing transfer alignment by adopting a linear Kalman filtering estimation method, and performing feedback correction on a relative strapdown resolving result to obtain high-precision motion information.
The principle of the invention is as follows: constructing a pseudo single sample rotation vector by using angular velocities output by the gyroscope at the current and the previous N sampling moments of the main subsystem and a rotation vector error compensation coefficient deduced based on typical conical motion, and solving a relative attitude quaternion in real time based on the rotation vector to realize updating of a relative attitude; meanwhile, a relative velocity and relative position updating algorithm is established according to the vector relation of the spatial positions of the main subsystem and the subsystem, and the relative velocity and the relative position are updated by utilizing the specific force and the posture information output by the accelerometer of the main subsystem and the subsystem; finally, establishing a transfer alignment state model and a measurement model based on a relative strapdown resolving error propagation formula and three-dimensional relative positions and three-dimensional relative postures measured by the fiber bragg gratings, and performing transfer alignment by adopting a linear Kalman filtering estimation method to obtain high-precision motion information; the relative strapdown resolving error propagation formula is obtained by simultaneously obtaining a relative attitude error differential equation, a relative speed error differential equation and a relative position error differential equation.
Compared with the prior art, the invention has the beneficial effects that:
according to the airborne distributed POS transfer alignment method based on relative strapdown calculation, the irreplaceable error under the flexible deformation condition can be reduced, the relative attitude drift is restrained, and the measurement precision of the spatial motion information of the distributed POS is improved. Meanwhile, the relative attitude updating algorithm based on the pseudo-single-subsample rotation vector is adopted, so that the problem of quantization error caused by high-frequency sampling is solved without increasing sampling frequency and reducing the requirement of a hardware system while inhibiting the non-exchangeable error.
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In order to more clearly illustrate the embodiments of the present application or technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and other drawings can be obtained by those skilled in the art according to the drawings.
Fig. 1 is a flowchart of a method provided in an embodiment of the present invention.
Fig. 2 is a diagram illustrating a relationship between an attitude update period and an angular velocity sampling period according to an embodiment of the present invention.
Fig. 3 is a spatial position vector diagram of a main subsystem according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood by those skilled in the art, the present invention will be further described in detail with reference to the accompanying drawings and examples. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the specific method of the present invention is as follows:
1. and establishing a relative attitude updating algorithm based on the pseudo-single-sample rotation vector. And establishing a pseudo-single-sample rotation vector by using angular velocities output by the gyroscope at the current and previous N sampling moments of the main subsystem, deriving a rotation vector error compensation coefficient by adopting typical conical motion, and obtaining a relative attitude quaternion in real time by solving the rotation vector, thereby realizing updating of the relative attitude. The method comprises the following specific steps:
assume that it is currentt k Time subsystem carrier coordinate systems(k) Coordinate system of main system carrierm(k),t k+1 Time subsystem carrier coordinate systems(k+1) Coordinate system of main system carrierm(k+1). Note the books(k) Tos(k+1) Is a rotational quaternion ofq(h),m(k) Tos(k) Is a rotational quaternion ofQ(t k ),m(k+1) Tos(k+1) Is a rotational quaternion ofQ(t k+1),m(k) Tom(k+1) Is a rotational quaternion ofp(h) Wherein, in the step (A),h= t k+1-t k . Then the relationship is expressed as the following quaternion:
in the attitude update periodh= t k+1-t k The coordinate system of the main system carrier changes very slowly due to the position change, and the approximation is thatThe above formula can be rewritten as:
wherein:
in the formula (I), the compound is shown in the specification,is composed ofs(k) Tos(k+1) The equivalent rotation vector of (a) is,. For convenience of description, willQ(t k ) AndQ(t k+1) Are respectively called ast k Andt k+1the relative attitude quaternion at the time of day,q(h) The attitude change quaternion in the period of time.
Because the traditional attitude updating algorithm based on the multi-subsample rotation vector algorithm puts higher requirements on the acquisition frequency of the system, increases the hardware burden and even generates quantization errors, the current and previous attitude updating algorithms are adopted to reduce the data acquisition frequencyNThe pseudo-single-subsample rotation vector relative attitude updating algorithm of the angular velocity at each sampling moment is as follows:
in the formula (I), the compound is shown in the specification,in order to update the rotation vector after the update,for the current sampling instantt k And the next moment of time (t k +h) The relative angular increment of (a) is,G j j is more than or equal to 1 and less than or equal to N for the cone error compensation coefficient to be solved,ω j()is prepared from (a)t k -jh) The relative angular velocity of the moment of time,ωfor the current sampling instantt k Relative angular velocity of (d). Attitude update periodhAnd angular velocity sampling period deltaTEqual as shown in fig. 2.
Generally, for attitude updating of an inertial navigation system, cone motion is the worst working environment condition, which can cause severe drift of a mathematical platform, so that the non-commutative error of the algorithm is generally researched by adopting typical cone motion when the rotating vector algorithm is optimized. Setting the motion of the subsystem relative to the main system as a coordinate system around the subsystem carrierxConical movement of the axis rotation (amplitude ofαAngular frequency is Ω), which can be expressed as:
according to the relation between the quaternion and the rotation vector, the attitude quaternion of the conical motion is as follows:
according to equation (6) and the quaternion differential equation:
the corresponding angular velocity output under the condition of the available conical motion is as follows:
in the attitude update period according to equations (3) and (6)hThe inner attitude change quaternion can be expressed as: (9)
in the attitude update period according to equation (3)hThe equivalent rotation vector of the inner cone motion can be expressed as:
from equation (10), (b) ()t k -jh) Relative angular velocity vector of time:
as can be seen from the above formula, the relative angular velocity vector is obtained onlyxThe component of the axis is a non-periodic term, and the other two axial directions are periodic terms with the same frequency as cone motion, and the influence of the periodic terms can be not considered in error analysis. Due to the fact thatIs constant, therefore, the relative angular velocity increment at the current time can be expressed as:
for simplicity, let the conic error compensation term be as follows:
if only the non-periodic term is considered and the trigonometric function is approximated, the following results are obtained:
order toλ=ΩhThe first two terms of equation (14) are subjected to taylor expansion to obtain:
Similarly, taylor expansion of the last term of equation (14) results in:
in the formula, coefficient Form a matrixACoefficient to be solvedG j (1≤j≤N) Form a column vectorG。
By comparing equations (15) and (16), it can be found that when two equations are usedλ j+21(1≤j≤N) When the coefficients of (a) are the same, i.e. the following formula is satisfied, the error of the algorithm is minimal:
at the same time, the user can select the desired position,Nthe larger, the residual aboutλError of term (2)N+3) The higher the order, the smaller the algorithm error, butNThe actual selection of (a) must also take into account other requirements such as real-time performance of the computer.
Since the direct input quantity of the formula (4) is the relative angular velocity between the main subsystem and the sub-system, the pseudo-single-sample rotation vector relative attitude update algorithm can be rewritten as the final form as follows:
in the formula (I), the compound is shown in the specification,is shown assIs prepared byt-jh) The relative angular velocity of the main subsystem and the subsystem is not more than 1 at any momentj≤N;Is a subsystem gyroscope int k -jh) The original angular velocity output at the time of day,is at presentt k Time of daymIs tied tosA relative attitude matrix of the system is determined,is at at-jh) Time of daymIs tied tosRelative attitude matrix of series, 1 ≦j≤N,Can be prepared byt k -jh) Time of daymIs tied tosQuaternion of relative attitude of systemObtaining:
select the rightNAfter the specific value of (a), the coefficient to be solved can be obtained by the formula (17)G j And is substituted into the formula (18) to obtain an updated rotation vectorAnd substituting into the formula (2) to obtaint k+1Quaternion of relative attitude at timeAnd further realized according to the following formulat k+1Updating the three-dimensional posture at the moment:
in the formula (I), the compound is shown in the specification,are respectively updatedt k+1And (3) relative pitch angle, relative roll angle and relative course angle among the main subsystems at the moment.
2. A relative velocity update algorithm is established. And a vector equation among the main system, the subsystems and the relative positions of the main subsystem and the subsystems is established according to the vector relation of the spatial positions of the main subsystem and the subsystems, a second derivative is solved relative to an inertial coordinate system to obtain a relative velocity differential equation, and a numerical solution is solved for the relative velocity differential equation based on specific force information and relative attitude information measured by an accelerometer of the main subsystem and the subsystems, so that the relative velocity is updated. The method comprises the following specific steps:
influenced by the distributed POS flexible lever armt k At the moment, the relative position of the subsystem with respect to the main systemRAnd relative velocityVIs no longer fixed but is constantly changing with deflection. Defining the position vector of the primary system in the inertial system asR m The position vector of the subsystem in the inertial coordinate system isR s As shown in FIG. 3, the lever arms between the main subsystems have the following vector relationship:
for the relative inertial coordinate system of equation (21)iThe first derivative is calculated, and:
(22) in the formula (I), the compound is shown in the specification,gyroscope at current t for main systemkThe original angular velocity output at any moment;
for formula (22) relative inertial frameiThe first derivative is calculated, and:
specific force equation of main subsystem measurement:
in the formula (I), the compound is shown in the specification,、are respectively the currentt k The specific force measured by the master system at the momentmProjection of the system, specific force measured by the subsystemsProjection of the system;andare respectively the currentt k Time master subsystem universal gravitation acceleration in geographical coordinate systemeDue to the small distance of the main subsystem,(ii) a And bring this formula into the above formula, orderWhereinVIs at presentt k The relative speed of the time main subsystem is shown as follows:
project the above formula tom isThe following can be obtained:
due to the fact thatRelative speed of the main subsystem, not obtained by direct measurementV m May be expressed in another form, such that:
taking equation (26) into formula (22) to obtain the first derivative with respect to the inertial frame, the differential equation of absolute velocity of the subsystem with respect to the main system can be obtained:
solving the speed differential equation in the formula (28) to obtain a numerical solution, and realizing the relative speed between the main system and the sub system according to the formula (27)V m Update to obtaint k+1Three-dimensional relative velocity between time master subsystemsV m (t k+1)。
3. A relative position update algorithm is established. And establishing a relative position differential equation based on a differential relation between the relative position and the relative speed, and solving the numerical solution of the relative position differential equation by utilizing the solved relative speed to realize the update of the relative position. The method comprises the following specific steps:
the relative position can be obtained by integrating the relative velocity, and thus the relative position differential equation can be expressed as:
projecting formula (29) in the coordinate system of the main system carriermThe following can be obtained:
the differential equation of the relative position in the formula (30) is solved to obtain a numerical solution, so that the relative position between the main subsystems can be realizedR m Update to obtaint k+1Three-dimensional relative position between time master subsystemsR m (t k+1)。
4. A transfer alignment algorithm is established. Establishing a transfer alignment state model and a measurement model based on a relative strapdown resolving error propagation formula and three-dimensional relative positions and three-dimensional relative postures measured by the fiber bragg gratings, performing transfer alignment by adopting a linear Kalman filtering estimation method, and performing feedback correction on relative strapdown resolving results to obtain high-precision motion information. The method comprises the following specific steps:
relative attitude matrix due to flexural deformation of lever armsIs a time-varying matrix with the following differential equation:
in the formula (I), the compound is shown in the specification,、the rotation angular rates of the carrier of the main inertial navigation system and the sub inertial navigation system respectively,is composed ofsIs relative tomThe angular rate of rotation of the system ismThe projection in the system is determined by the distance between the projection and the optical system,、、are respectively as、、Is used to generate the inverse symmetric matrix. The relative attitude differential equation can be obtained by the simultaneous equations (31) to (33):
defining an actual relative attitude matrix calculated by a relative strapdown calculation algorithm asWhereinm' for calculating the coordinate system of the main system carrier, anmThe systems differ by a small angle transformation, namely:
in the formula (I), the compound is shown in the specification,µis composed ofmDeviation of systemmDeviation angle of the system.
Taking the inertial device error of the subsystem into consideration, and transposing two sides of the formula (34) to obtain:
in the formula (I), the compound is shown in the specification,is the output value of the main system gyro,is composed ofThe anti-symmetric matrix is a matrix of a plurality of symmetric matrices,is a subsystem gyro output value, which can be expressed as,For subsystem gyro drift atsThe projection of the system is obtained by substituting equation (34) and equation (36) into equation (35) to obtain a relative attitude error differential equation:
definition of,,Because of the error in the subsystem accelerometer output specific force, the relative velocity and position differential equations can be expressed as:
projecting equations (38) and (39) ontomBy subtracting equations (28) and (30) from each other, differential equations for the relative velocity and relative position errors are obtained:
simultaneous equations (37), (40) and (41) can yield the error propagation equation for relative navigation:
and solving an error propagation formula according to the relative strapdown, so as to obtain a state model of transfer alignment. Taking the state vector as:
in the formula (I), the compound is shown in the specification,δФ x ,δФ y ,δФ z is the relative attitude error angle of the main subsystem,δU x ,δU y ,δU z is the absolute value of the relative velocity error of the main subsystem,δR x ,δR y ,δR z in order to account for the relative position error of the main subsystem,ε bx ,ε by ,ε bz is the random constant drift of the subsystem gyro + bx , ▽ by , ▽ bz Is a random constant bias for the subsystem accelerometer.
The state model can be described as:
in the formula (I), the compound is shown in the specification,Ain order to be a matrix of the system,Bthe matrix is driven for the system noise,Wthe system noise includes the random constant drift of the gyroscope and the random constant bias of the accelerometer, namely:
system matrixAComprises the following steps:
system noise driving matrixBComprises the following steps:
the transfer alignment is carried out by adopting a relative position and relative attitude matching mode, and the measurement vector of the transfer alignment is as follows:
in the formula (I), the compound is shown in the specification,Z 1for the relative position to match the measurement vector,Z 2the measurement vectors are matched for relative pose.
To build the transfer alignment measurement model, a transfer alignment coordinate system needs to be specified:mis connected withsAre respectively a main subsystem carrier coordinate system,αis the nominal coordinate system of the subsystem, and in the initial state,αis connected withmThe two layers are overlapped with each other,ηis composed ofαDeviation of systemmAttitude angle of the system, corresponding to the attitude matrix of;ξIs composed ofsDeviation of systemαThe mounting error angle of the system, corresponding to a mounting error matrix of;µIs composed ofmDeviation of systemmThe misalignment angle of the system, the corresponding misalignment angle matrix is;βIs composed ofsDeviation of systemmThe attitude angle of the system, the corresponding relative attitude calculation matrix of the main subsystem is. The following relationship can be obtained from the assumption of small angular deformation:
the following relationship holds according to the coordinate transformation principle:
substituting equations (51) - (54) into equation (55) can result in:
ignoring the second order product fraction yields:
according to the three-dimensional relative attitude obtained by calculationβ c Three-dimensional relative attitude measured by fiber gratingβ M Establishing a measurement vector matched with the relative attitude:
from the calculated three-dimensional relative positionThree-dimensional relative position to fiber grating measurementEstablishing a relative position matching measurement vector:
establishing a transfer alignment measurement model according to a transfer alignment measurement vector expression:
in the formula (I), the compound is shown in the specification,Hin order to measure the matrix, the measurement matrix is,Vin order to measure the noise, the noise is measured,Vthe measurement noise determined by the relative position and attitude of the fiber grating measurements.
The system represented by the established state model and the established measurement model is continuous, and in order to facilitate the linear Kalman filtering recursion calculation in a computer, the continuous model in the transfer alignment needs to be converted into a discrete form.
Discretizing the state model and the measurement model to obtain:
in the formula (I), the compound is shown in the specification,X k is composed ofkOf time of daynThe state of the dimension is changed into a variable,Z k is composed ofkOf time of daymDimension measurementThe amount of the compound (A) is,is composed ofk-1 tokMoment system one-step state transition matrix, Γk-1Driving a noise matrix for the system, characterized byk-1 tokThe system noise at each moment respectively influenceskThe degree of each of the states at a time,W k-1is composed ofk-The system at time 1 excites a noise sequence,V k is composed ofkOf time of daymThe noise sequence is measured in dimension.
in the formula (I), the compound is shown in the specification,Tin order to be the period of the filtering,A k-1is composed ofk-The system matrix at time 1.
Γk-1Can be expressed as:
in the formula, is the filter periodGThe matrix is driven for process noise.
Kalman filtering requirementW k AndV k is a zero-mean white noise sequence which is uncorrelated with each other, and therefore has the following relationship:
in the formula (I), the compound is shown in the specification,R k andQ k the measurement noise variance matrix and the system noise variance matrix, respectively, may be determined based on statistical properties of the process noise and the measurement noise.
According to the distanceScattered state transition matrixSystem noise driving matrix gammak-1Measuring matrixH k =HAnd system noise and measurement noise variance matrixQ k AndR k transfer alignment recursive calculation can be completed by using a discrete Kalman filtering equation, and feedback correction is performed on the relative strapdown resolving result to obtain high-precision motion information.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: it is to be understood that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features thereof, but such modifications or substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (3)
1. An airborne distributed POS transfer alignment method based on relative strapdown calculation is characterized by comprising the following steps:
(1) establishing a relative attitude updating algorithm based on a pseudo-single-sample rotation vector: establishing a pseudo-single sample rotation vector by using angular velocities output by the gyroscope at the current and the previous N sampling moments of the main subsystem, deriving a rotation vector error compensation coefficient by adopting typical conical motion, and obtaining a relative attitude quaternion in real time by solving the rotation vector, thereby realizing updating of a relative attitude;
(2) establishing a relative speed updating algorithm: establishing a vector equation among the main system, the subsystems and the relative positions of the main subsystem and the subsystems according to the vector relation of the spatial positions of the main subsystem and the subsystems, solving a second derivative relative to an inertial coordinate system to obtain a relative velocity differential equation, and solving a numerical solution of the relative velocity differential equation based on specific force information and relative attitude information measured by an accelerometer of the main subsystem and the subsystems so as to realize relative velocity updating;
(3) establishing a relative position updating algorithm: establishing a relative position differential equation based on a differential relation between the relative position and the relative speed, and solving the position differential equation by utilizing the solved relative speed to solve a numerical solution to realize relative position updating;
(4) establishing a transfer alignment algorithm: establishing a transfer alignment state model and a measurement model based on a relative strapdown resolving error propagation formula and three-dimensional relative positions and three-dimensional relative postures measured by the fiber bragg gratings, performing transfer alignment by adopting a linear Kalman filtering estimation method, and performing feedback correction on relative strapdown resolving results to obtain high-precision motion information; the relative strapdown resolving error propagation formula is obtained by simultaneously obtaining a relative attitude error differential equation, a relative speed error differential equation and a relative position error differential equation;
the specific scheme for establishing the relative attitude updating algorithm based on the pseudo-single-sample rotation vector in the step (1) is as follows:
assume that it is currentt k Time subsystem carrier coordinate systems(k) Coordinate system of main system carrierm(k),t k+1 Time subsystem carrier coordinate systems(k+1) Coordinate system of main system carrierm(k+1) Memory for recordings(k) Tos(k+1) Is a rotational quaternion ofq(h),m(k) Tos(k) Is a rotational quaternion ofQ(t k ),m(k+1) Tos(k+1) Is a rotational quaternion ofQ(t k+1),m(k) Tom(k+1) Is a rotational quaternion ofp(h) Wherein, in the step (A),h= t k+1- t k then, the following quaternion expression relationship is given:
in the attitude update periodh= t k+1- t k Approximately consider thatThe above formula can be rewritten as:
wherein the content of the first and second substances,
in the formula (I), the compound is shown in the specification,is composed ofs(k) Tos(k+1) The equivalent rotation vector of (a) is,for convenience of description, willQ(t k ) AndQ(t k+1) Are respectively called ast k Andt k+1the relative attitude quaternion at the time of day,q(h) A quaternion of attitude change in the period of time;
establishing a relative attitude updating algorithm based on a pseudo-simple-sample rotation vector in the step (1), and adopting current and previousNThe pseudo-single-subsample rotation vector relative attitude updating algorithm of the angular velocity at each sampling moment is as follows:
in the formula (I), the compound is shown in the specification,in order to update the rotation vector after the update,is at presentSampling timet k And the next moment of time (t k +h) The relative angular increment of (a) is,G j j is more than or equal to 1 and less than or equal to N for the cone error compensation coefficient to be solved,ω (j)is prepared from (a)t k -jh) The relative angular velocity of the moment in time,ωfor the current sampling instantt k Relative angular velocity of (d), attitude update periodhAnd angular velocity sampling period deltaTEqual;
because the direct input quantity of the above formula is the relative angular velocity between the main subsystem and the sub-system, the pseudo-single-sample rotation vector relative attitude updating algorithm is rewritten into the final form as follows:
in the formula (I), the compound is shown in the specification,is shown assIs prepared byt k -jh) The relative angular velocity of the main subsystem and the subsystem is not more than 1 at any momentj≤N; Is a subsystem gyroscope int k -jh) The original angular velocity output at the time of day,is at presentt k Time of daymIs tied tosA relative attitude matrix of the system is determined,is at at k -jh) Time of daymIs tied tosA relative attitude matrix of the system is determined,by (a)t k -jh) Time of daymIs tied tosQuaternion of relative attitude of systemObtaining:
the relative speed updating algorithm in the step (2) comprises the following contents:
defining a position vector of the host system in the inertial coordinate system asR m The position vector of the subsystem in the inertial coordinate system isR s The relative position of the subsystem with respect to the main system isRThe lever arms between the main subsystems have the following vector relationship:
relative inertial coordinate systemiThe first derivative is calculated, and:
in the formula (I), the compound is shown in the specification,gyroscope for main system is currentlyt k The original angular velocity output at any moment;
relative inertial coordinate systemiThe first derivative is calculated, and:
specific force equation of main subsystem measurement:
in the formula (I), the compound is shown in the specification,、are respectively the currentt k The specific force measured by the master system at the momentmProjection of the system, specific force measured by the subsystemsProjection of the system;andare respectively the currentt k Time master subsystem universal gravitation acceleration in geographical coordinate systemeThe projection of (a) is performed,(ii) a Order toWhereinVIs at presentt k The relative speed of the time main subsystem is shown as follows:
project the above formula tom isThe following can be obtained:
due to the fact thatRelative speed of the main subsystem, not obtained by direct measurementV m Expressed in another form, let:
the differential equation of the absolute velocity of the subsystem relative to the main system can be obtained:
2. The relative strapdown solution based airborne distributed POS delivery alignment method according to claim 1, wherein the relative position update algorithm of step (3) comprises the following:
the relative position is obtained by integrating the relative velocity, and therefore the relative position differential equation is expressed as:
projecting the above formula on a main system carrier coordinate systemmThe following can be obtained:
numerical solution to the differential equation of relative position in the above equationRealizing the relative position between the main subsystem and the sub-systemR m Update to obtaint k+1Three-dimensional relative position between time master subsystemsR m (t k+1)。
3. The relative strapdown solution based onboard distributed POS transfer alignment method of claim 1, wherein the transfer alignment algorithm of step (4) comprises the following: and (3) obtaining a state model of transfer alignment according to a relative strapdown resolving error propagation formula, wherein the state vector is:
in the formula (I), the compound is shown in the specification,δФ x ,δФ y ,δФ z is the relative attitude error angle of the main subsystem,δU x ,δU y ,δU z is the absolute value of the relative velocity error of the main subsystem,δR x ,δR y ,δR z in order to account for the relative position error of the main subsystem,ε bx ,ε by ,ε bz is a random constant drift of the subsystem gyroscope bx , ▽ by , ▽ bz A random constant bias for the subsystem accelerometer;
the state model is described as:
in the formula (I), the compound is shown in the specification,Ain order to be a matrix of the system,Bthe matrix is driven for the system noise,Wthe system noise includes the random constant drift of the gyroscope and the random constant bias of the accelerometer, namely:
system matrixAComprises the following steps:
system noise driving matrixBComprises the following steps:
the transfer alignment is carried out by adopting a relative position and relative attitude matching mode, and the measurement vector of the transfer alignment is as follows:
in the formula (I), the compound is shown in the specification,Z 1for the relative position to match the measurement vector,Z 2matching the measurement vector for the relative pose;
according to the three-dimensional relative attitude obtained by calculationβ c Three-dimensional relative attitude measured by fiber gratingβ M Establishing a measurement vector matched with the relative attitude:
in the formula (I), the compound is shown in the specification,ηis composed ofαDeviation of systemmThe attitude angle of the system is determined,ξis composed ofsDeviation of systemαThe angle of the installation error of the system,mis connected withsAre respectively a main subsystem carrier coordinate system,αis the subsystem nominal coordinate system;
from the calculated three-dimensional relative positionThree-dimensional relative position to fiber grating measurementEstablishing a relative position matching measurement vector:
establishing a transfer alignment measurement model according to a transfer alignment measurement vector expression:
in the formula (I), the compound is shown in the specification,Hin order to measure the matrix, the measurement matrix is,Vin order to measure the noise, the noise is measured,Vthe measurement noise determined by the relative position and attitude of the fiber grating measurements.
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