JP2013200162A - Compact attitude sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact attitude sensor capable of estimating attitude and orientation of a mobile object under acceleration with high precision using an algorithm that takes the gyro bias error into account.SOLUTION: A compact attitude sensor includes an angular velocity sensor 101 for measuring angular velocity of a mobile object on three independent axes, an acceleration sensor 102, a magnetic sensor 103, and an arithmetic processing unit 104 which computes a quaternion estimate based on the values measured by the angular velocity sensor 101, the acceleration sensor 102, and the magnetic sensor 103. The arithmetic processing unit 104 computes a bias error, a scale factor error, a misalignment error, an angular velocity sensor error including a noise factor, and a quaternion level error for angular velocity data, and obtains a quaternion estimate representing the current attitude of the mobile object by using an extended Kalman filter obtained by using the error values. The compact attitude sensor outputs the quaternion estimate.

Description

  The present invention relates to a small posture sensor that is mounted on a moving object that requires posture control and realizes high-precision posture / orientation estimation under an acceleration environment using an algorithm that introduces a gyro bias error.

  A moving object that requires posture control, such as a small unmanned helicopter, is equipped with a posture sensor to measure its three-dimensional posture angle. In general, the posture sensor acquires the three-dimensional posture angle of a moving object by temporally integrating the angular velocity sensor that measures the angular velocity on three independent axes of the moving object and the angular velocity measurement value obtained by the angular velocity sensor. An arithmetic processing unit for performing the processing is provided. Some three-dimensional posture angles are expressed by Euler angles using roll, pitch, yaw angle, etc., and the posture control of the moving object is performed based on the three-dimensional posture angle measured by the posture sensor. As a conventional example of such a moving object posture control technique, for example, there is one described in Patent Document 1. Moreover, there exists invention described in patent document 2 as a technique used as the foundation of this invention.

Japanese Patent Laid-Open No. 9-5104 JP 2007-183138 A

Hereinafter, a conventional attitude control technique for a moving object will be described. A sensor disclosed in Patent Document 2 is manufactured as a sensor that is a premise of the present invention, and this is referred to as a MARG sensor. Table 1 shows the specifications of the MARG sensor.

  Although the accuracy is relatively low as shown in Table 1, the proposed algorithm is implemented and verified for hardware that is very lightweight and can be fully installed in a small unmanned helicopter. If such a small and lightweight sensor is realized, it can be expected to be applied not only to a small unmanned helicopter but also to a general aircraft or a mobile robot in terms of weight. Hereinafter, the coordinate system and quaternion used in this description will be described.

1) Coordinate system and quaternion First, the coordinate system used in this description and the notation method of vectors represented on each coordinate system are defined. The coordinate system used here is shown in FIG. Here, the r-frame in the figure is referred to as a reference frame, with an arbitrary point on the ground as the origin, magnetic north as the Xr axis, gravity direction as the Zr axis, and XrZr plane vertical direction as the Yr axis. Coordinate system. The b-frame is called a body frame, and is a coordinate system in which the center of gravity of the aircraft is the origin, the Xb axis is the front of the aircraft, the Zb axis is below the aircraft, and the Yb axis is the vertical direction of the XbZb plane. Here, assuming that an arbitrary geometric vector in the three-dimensional space is r, those expressing r as an algebraic vector on each coordinate system are defined as r _r and r _b , respectively. Also, the attitude of the b-frame relative to the r-frame is defined as the body attitude.

Next, an outline of a quaternion used as a method for expressing the body posture used in this description will be described. A quaternion is a number obtained by expanding a complex number (usually the imaginary part is represented in one dimension as in a + bi) to three dimensions, and the quaternion q has one real part and three imaginary parts as shown in the following equation. It is composed of
q = q _o + q ₁ i + q ₂ j + q ₃ k (1)
However, here, i, j, and k in the formula are imaginary units, and satisfy the relationship as shown in the following formula.
i ² = j ² = k ² = −1 (2)
ij = k, jk = i, ki = j (3)

Quaternions are sometimes referred to as quaternions or Euler parameters (see, for example, Hiroshi Tajima, Multibody Dynamics-3D Equations of Motion, Tokyo Denki University Press, 2006). It is often used as a method for expressing the rotational posture of The quaternion that expresses the rotation posture can be defined using Simple Rotation in the above document. Now, according to Euler's theorem, the unit vector representing the rotation axis and the rotation angle around that axis are used regardless of the rotation posture of the b-frame in FIG. 10 relative to the r-frame. It is possible to express the rotation posture. A method of expressing a rotation posture using a set of the vector and the rotation angle is called Simple Rotation. However, the vector can be expressed by a component as shown in Equation 4, and its norm is 1 as shown in Equation (5).
V = [l m n] ^T
... (4)
Where V: vector (l ² + m ² + n ² ) ^1/2 = 1
... (5)

The quaternion that expresses the rotation orientation of the b-frame with respect to the r-frame using Simple Rotation as described above is defined as follows.
Here, the norm of the quaternion is always 1 from the equation (5).

Quaternions are often expressed in vector notation such that q = [qo q ₁ q ₂ q ₃ ] ^T , and the sum, difference, and product of quaternions p and q are expressed as Is defined as
q + p = [qo + po q ₁ + p ₁ q ₂ + p ₂ q ₃ + p ₃ ] ^T
... (7)
q-p = [qo-po q 1 -p 1 q 2 -p 2 q 3 -p 3] T
... (8)
... (9)

A quaternion q ^* conjugated to q is defined as follows.
q ^* = [qo−q ₁ −q ₂ −q ₃ ] ^T
... (10)
Now, the coordinate transformation from the algebraic vector r _r on r-frame to the algebraic vector r _b on b-frame can be expressed by the following equation.
(11)
However, here, (r _b ) _q and (r _r ) _q in the equation are quaternion notation of a three-dimensional vector, and are respectively defined as the following equations.
(12)

[MARG sensor]
Here, the hardware specifications of the MARG sensor developed in the prior art, the outline of the conventional aircraft attitude estimation algorithm, and its problems will be described. Table 2 shows the specifications of the MARG sensor.

  This sensor is a kind of attitude sensor that implements an algorithm for estimating a quaternion that represents the current attitude by using outputs of a three-axis acceleration sensor, a gyro sensor, and a magnetic sensor.

The outline of the posture estimation algorithm implemented in the conventional MARG sensor will be described. First, the gravity vector on the r-frame is g _r = [0 0 g] ^T , and the geomagnetic vector is m _r = [m _n 0 m _d ] ^T. However, g is the gravitational acceleration, m _n denotes the horizontal geomagnetic, m _d is the vertical geomagnetic respectively. Here, when the gravity vector and the geomagnetic vector estimation value on the b-frame are obtained from the quaternion estimation value representing the current posture, the following equations are obtained.

Subsequently, assuming that the outputs of the acceleration sensor and the magnetic sensor mounted on the body are a _measure = [a _x a _y a _z ] ^T and m _measure = [m _x m _y m _z ] ^T , respectively, and b described above The error vector between the gravity vector and the geomagnetic vector estimate on the -frame is as follows.

Assuming that there is no error in each sensor, the most probable quaternion estimate is
It can be seen that it can be obtained by solving the simultaneous equations. However, since equation (15) is an over-condition simultaneous equation with six equations for four unknowns, it cannot generally be solved. Therefore, an approximate solution that minimizes the sum of squared errors is obtained using the least square method. If the Gauss-Newton iteration method is used, a correction vector that brings the sum of squares of errors close to the minimum in a certain step is represented by the following equation.
Where X is a Jacobian as shown below.

On the other hand, it is known that the true quaternion time derivative indicating the current posture and the airframe angular velocity ω _b are the following relational expressions.
Accordingly, it can be understood that the following relationship is similarly established for the time differentiation of the estimated value of the quaternion.

The conventional algorithm is to obtain the quaternion estimated value by combining the equations (16) and (20) as follows. Here, k is a scalar gain.

  The above algorithm is represented by signal lines as shown in FIG. This algorithm is a simple filter algorithm, which corrects the quaternion time derivative calculated from the angular velocity using acceleration and geomagnetic data, integrates it, and normalizes it to obtain an estimated value of unit quaternion. . Basically, low-frequency posture fluctuations are estimated from acceleration and geomagnetism data, while high-frequency posture fluctuations are estimated using a gyro. However, this algorithm has the following problems.

  In Expression (15), am includes not only a component obtained by coordinate conversion of gravity on b-frame but also a component of dynamic acceleration generated by the movement of the sensor. For this reason, the posture data has a large error by applying the dynamic acceleration. FIG. 21 shows posture data when a large acceleration is applied while the sensor is actually kept horizontal. However, what is shown in FIG. 21 is the Euler angle obtained by converting the estimated quaternion. From FIG. 21, it can be seen that a posture error of about 20 [deg] at maximum is generated by applying acceleration. Such an error due to dynamic acceleration is fatal for a sensor to be mounted on a moving body, and it is necessary to reduce the error.

  The present invention has been made in view of the above-described problems of the prior art. The purpose of the present invention is to perform highly accurate posture / orientation estimation under an acceleration environment, particularly under a low-frequency acceleration disturbance, using an extended Kalman filter algorithm. It is to provide a small attitude sensor to be realized.

In order to achieve the above object, the present invention provides an angular velocity sensor, an acceleration sensor, and a magnetic sensor that measure angular velocities on three independent axes of a moving object, and measured values of the angular velocity sensor, the acceleration sensor, and the magnetic sensor. An arithmetic processing unit that calculates a quaternion estimated value based on the quaternion estimated value, the coordinate processing matrix is calculated using the estimated quaternion estimated value, and the ground fixed coordinates are calculated using the coordinate transformation matrix. A coordinate conversion unit for converting a geomagnetic vector and a gravitational acceleration vector of a system component to estimate a geomagnetic vector and a gravitational acceleration vector of a sensor coordinate system component of the current step; and a sensor coordinate system component of the current step from the magnetic sensor and the acceleration sensor A magnetic / acceleration sensor data acquisition unit that acquires a geomagnetic vector and a gravitational acceleration vector of A vector for calculating an error between the geomagnetic vector and gravitational acceleration vector of the sensor coordinate system component of the determined current step and the geomagnetic vector and gravitational acceleration vector of the sensor coordinate system component of the current step acquired by the magnetic / acceleration sensor data acquisition unit. An error calculation unit, an angular velocity sensor data acquisition unit that acquires an angular velocity vector of a sensor coordinate system component of the current step from the angular velocity sensor, and elements of bias error, scale factor error, misalignment error, and noise for the acquired angular velocity data An angular velocity data error calculating unit that calculates an angular velocity sensor error including calculation, a quaternion calculating unit that calculates a time change between the quaternion of the previous step and the quaternion of the current step, the coordinate conversion unit, the magnetic / acceleration sensor data acquisition unit, and the vector Error calculation A quaternion representing the current posture and an extended Kalman filter for estimating the angular velocity error based on the angular velocity data error calculating unit and the quaternion calculating unit, and outputting a quaternion estimated value by the extended Kalman filter as the current posture An attitude sensor is provided.

  According to the present invention, with respect to angular velocity data, a bias error, a scale factor error, a misalignment error, and an angular velocity sensor error including a noise element are obtained by calculation, and this error is corrected, whereby a highly accurate posture in an acceleration environment is obtained.・ A small-size attitude sensor that realizes direction estimation can be realized.

  In the present invention, even when a constant low frequency acceleration disturbance is applied to the moving body, the disturbance due to the low frequency acceleration is normally estimated, and the posture / orientation estimation with high accuracy in the low frequency acceleration environment is performed. A small attitude sensor can be realized.

The figure which showed each structure with which the small attitude | position sensor used in the 1st Embodiment of this invention was equipped with the block The figure which showed the process performed by the arithmetic processing part of the small attitude | position sensor used in the said 1st Embodiment with the block The figure which showed the process performed by the arithmetic processing part of the small posture sensor used in the said 1st Embodiment with the flow The figure which shows the simulation result when the value of the covariance matrix of observation noise is determined so that the small posture sensor may be mounted on a moving object and the error due to dynamic acceleration may be reduced in the first embodiment. The figure which shows the simulation result when the value of the covariance matrix of observation noise is determined so that a small posture sensor may be mounted on a moving object and the posture tracking may be made sufficiently fast in the first embodiment. In the first embodiment, when a small attitude sensor is mounted on a moving object, the value of the covariance matrix of the observation noise is determined so that the error due to dynamic acceleration is small and the attitude can be tracked sufficiently quickly Of simulation results In the first embodiment, a simulation result of the roll angle when the linear error estimation Kalman filter (KF) is used for the small attitude sensor mounted on the moving object and when the extended Kalman filter (EKF) of the present invention is used. Figure comparing and showing In the first embodiment, the simulation results for the pitch angle when using the linear error estimation Kalman filter (KF) and the extended Kalman filter (EKF) of the present invention for the small attitude sensor mounted on the moving object. Figure comparing and showing In the first embodiment, the simulation result of the yaw angle when the linear error estimation Kalman filter (KF) is used for the small posture sensor mounted on the moving object and when the extended Kalman filter (EKF) of the present invention is used. Figure comparing and showing In the first embodiment, the roll angle is obtained in an angular velocity environment in which the conventional algorithm and the extended Kalman filter algorithm of the present invention are mounted on a microcomputer and greatly exceed the angular velocity generated when a small unmanned helicopter moves. Showing the result of posture / orientation estimation in real time In the first embodiment, the pitch angle is obtained in an angular velocity environment in which the conventional algorithm and the extended Kalman filter algorithm of the present invention are mounted on a microcomputer and greatly exceed the angular velocity generated when a small unmanned helicopter moves. Showing the result of posture / orientation estimation in real time In the first embodiment, the conventional algorithm and the extended Kalman filter algorithm of the present invention are mounted on a microcomputer, and the yaw angle is under an angular velocity environment that greatly exceeds the angular velocity generated during the movement of a small unmanned helicopter. Showing the result of posture / orientation estimation in real time In the first embodiment, the conventional algorithm and the extended Kalman filter algorithm of the present invention are mounted on a microcomputer, and a sufficiently large acceleration is applied as compared with the acceleration applied during the flight of a small unmanned helicopter. Figure showing the results of posture / orientation estimation in real time The figure which shows the acceleration data of each axis | shaft used for the attitude | position estimation simulation when applying the low-frequency acceleration disturbance of a fixed value to a moving body in the 2nd Embodiment of this invention. The figure which shows the attitude | position estimation result of each algorithm in the attitude | position estimation simulation of the said 2nd Embodiment The figure which shows the comparison with the acceleration disturbance estimated value in the attitude | position estimation simulation of the said 2nd Embodiment, and the true value of an acceleration disturbance The figure which shows the attitude | position measurement result of each algorithm in the experiment which mounted the sensor in the said 2nd Embodiment and added the acceleration disturbance of the low frequency of a fixed value in the said 2nd Embodiment. The figure which shows the comparison of the acceleration disturbance estimated value and the true value of an acceleration disturbance in the algorithm of this invention in the experiment of the said 2nd Embodiment. The figure which showed the three-dimensional coordinate for demonstrating the outline | summary of the quaternion used as the premise of this invention A diagram showing the flow of mathematical formulas and data used when processing is performed by the arithmetic processing unit of the small attitude sensor used in the prior art Figure showing experimental data obtained by measuring a three-dimensional attitude angle expressed by a quaternion with a conventional attitude sensor mounted on a moving object

  Hereinafter, modes for carrying out the present invention will be described. Also in the present invention, a sensor device circuit having the same configuration as the device disclosed in Patent Document 2 is used. However, the content of arithmetic processing differs between the sensor device circuit of the present invention and the conventional sensor device circuit.

(First embodiment)
FIG. 1 is a block diagram showing each hardware configuration provided in the small posture sensor according to the first embodiment of the present invention. The small posture sensor 100 includes an angular velocity sensor 101 that measures angular velocities on three independent axes of a moving object, an acceleration sensor 102 that measures acceleration on three independent axes of the moving object, and a geomagnetism on three independent axes of the moving object. And an arithmetic processing unit 104 that calculates a quaternion based on measurement values of the angular velocity sensor 101, the acceleration sensor 102, and the magnetic sensor 103. The small posture sensor 100 according to the first embodiment is applied to a linear system with one input and one output, constitutes a stationary Kalman filter, and introduces an error of a gyro sensor (angular velocity sensor) into a calculation item. Calculation of “Kalman gain” and “quaternion” can be made more precise, enabling realistic implementation, and further enabling miniaturization and real-time processing.

  FIG. 2 shows processing performed by the arithmetic processing unit 104 as functional blocks. The arithmetic processing unit 104 includes an extended Kalman filter 200, a magnetic / acceleration sensor data acquisition unit 202, an angular velocity sensor data acquisition unit 205, and an angular velocity data error calculation unit 208. The extended Kalman filter 200 includes a coordinate conversion unit 201, an observation update calculation unit 203, and a time update calculation unit 207. FIG. 3 is a flowchart showing processing performed by the arithmetic processing unit 104.

  Focusing on the fact that the dynamic acceleration corresponds to the observation noise of the attitude sensor system as a basic idea of the present invention, a Kalman filter suitable for estimating the true state of the system from the observation signal including noise is provided. It is considered that the error can be reduced by using the attitude estimation algorithm.

[Attitude and orientation estimation algorithm]
Construction of a process model To construct a Kalman filter, a process model of the system is required. In the following, a discrete time process model of the system targeted by the present invention is derived. First, the equation of state is obtained. On the right side of Equation (19), the airframe angular velocity ω _b can be obtained from a gyro sensor, but it is known that inertial sensors such as a gyro sensor and an acceleration sensor have errors due to various factors. Since it is desirable to estimate such an error in order to perform more accurate estimation, a gyro sensor error is introduced as a state quantity. Assuming that the angular velocity obtained from the gyro sensor is ω _measure = [ω _x ω _y ω _z ] ^T and the error of the gyro sensor is Δω _b = [δω _x δω _y δω _z ] ^T , these and ω _b are as follows: It becomes a relationship like this.
ω _measure = ω _b + Δω _b
(22)
By substituting this equation into equation (19), the following equation is obtained.

In general, as a cause of a gyro sensor error, a bias error, a scale factor error, a misalignment error, noise, and the like can be considered, and this is expressed by the following equation.

In the above equation, the first item on the right side represents a bias error, the second item represents a scale factor error, the third item represents a misalignment error, and the fourth item represents noise. Among them, the scale factor error and the misalignment error can be corrected based on data that has been subjected to a measurement test in advance, so that only the bias error and noise need to be estimated in real time. Also, since it is impossible to estimate noise in real time, here
Only the bias error is estimated.
The bias error of the gyro sensor is empirically known to have the following dynamics.

Here, w = [w _x w _y w _z ] ^T is white noise. Also, β _x , β _y , β _z are parameters, and these values and the variance of the white noise w are such that the static test data and the Allan variance [13] of the output data of Equation (25) match. Adjusted and decided. Table 3 shows the values of each parameter.

From the above,
The state equation when is a state quantity is as follows.
However, here, each matrix is as follows.

When equation (26) is discretized, equation (30) is obtained. However, x _t is the state quantity at the t step, and Δt is the sampling time. Here, since the sampling frequency is 50 [Hz], Δt = 0.02 [s].
Here again
Then, the state equation in discrete time is as follows.

Subsequently, the observation equation is obtained. Acceleration error Δa including dynamic acceleration applied to the body _{= [δa x δa y δa z} ] Given the ^T and geomagnetic error _{Δm = [δm x δm y δm} z] T, the acceleration sensor output and the magnetic sensor output is expressed by the following equation It can be expressed as
here,
When, observation equation to output a y _t is expressed by the following equation.
Here, h _t (x _t ) is expressed by the following equation.

[Extended Kalman filter algorithm]
It was possible to obtain a discrete-time process model such as Equation (31) and Equation (34) shown above. However, since both equations are nonlinear equations, the linear Kalman filter algorithm cannot be applied as it is. In such a case, a method of linearizing Equations (31) and (34) with respect to an estimation error with respect to a true value, selecting an estimation error as a state quantity, and applying a linear Kalman filter to configure an error estimation Kalman filter, and a nonlinear system There are two methods of constructing an extended Kalman filter which is an approximation method for applying a linear Kalman filter to the above, but the latter was selected here. Hereinafter, the extended Kalman filter algorithm will be described. Now, regarding the systems of Equation (31) and Equation (34), when the filtered estimated value and preliminary estimated value of x _{t at} the t-th step are expressed as follows,
The matrices F _t and H _t are defined as follows:

The extended Kalman filter algorithm using the matrix defined as above is given by the following equation.

Where K _t is Kalman gain, P _{t / t} and P _{t / t-1} are covariance matrices of estimation errors, Q _t is a covariance matrix of system noise, and R _t is a covariance of observation noise. Each matrix is represented. The algorithms of the above equations (37) to (41) are composed of two parts, a part for filtering the estimated value using the obtained observation value and a part for predicting the estimated value of the next step. (37) to (39) correspond to the former, and expressions (40) to (41) correspond to the latter. In addition, the former may be called observation update and the latter may be called time update. By calculating the given formulas in order as described above, the most probable filtered estimated value of x _t at the t-th step.
Can be obtained.

  Hereinafter, processing performed by the arithmetic processing unit 104 will be described with reference to FIGS. 2 and 3. In step 301, the coordinate conversion unit 201 performs coordinate conversion from r-frame to b-frame described above using the equation (11) expressed in quaternions for the magnetism and acceleration in the initial posture. Each element of the quaternion is defined by Expression (6) using a posture expression method called “Simple Rotation”. Expression (6) is expressed using Expression (1) and Expression (10), which are preset quaternion initial values using a fourth-order vector expression composed of three imaginary numbers and one real number. The magnetism in the initial posture is the ground fixed coordinate system (r-frame) component of the geomagnetic vector, while the acceleration in the initial posture is the ground fixed coordinate system (r-frame) component of the gravitational acceleration vector.

  Next, in step 302, the magnetism and acceleration of the sensor coordinate system in the current step can be estimated based on the preset initial value of the quaternion, and these are input to the observation update calculation unit 203.

In Step 303, the magnetic / acceleration sensor data acquisition unit 202 outputs the current sensor's magnetic sensor output (vector) a _measure = [a _x a _y a _z ] ^T , acceleration sensor output (vector) from the magnetic sensor 103 and the acceleration sensor 102. m _measure = [m _x m _y m _z ] ^T is acquired. The acquired magnetic sensor output and acceleration sensor output at the current step are sensor coordinate system component data, which are input to the observation update calculation unit 203.

  In step 304, the observation update calculation unit 203 calculates the estimated geomagnetic vector estimated value and gravitational acceleration vector estimated value of the current step calculated by the coordinate conversion unit 201 in step 302, and in step 303 the magnetic / acceleration sensor data acquisition unit 202. An error between the geomagnetic vector and the gravitational acceleration vector of the current step acquired from the above is obtained, and further, the estimated values are filtered by performing the calculations of Expressions (37) to (39) using Expression (34).

  The angular velocity is detected and its error is calculated separately or in parallel with the processing in steps 301 to 304 described above. In step 305, the angular velocity sensor data acquisition unit 205 acquires the angular velocity of the current step from the angular velocity sensor 101. The angular velocity of the current step to be acquired is sensor coordinate system component data, which is input to the angular velocity data error calculation unit 208 to calculate the angular velocity data error.

  In step 306, the angular velocity data error calculation unit 208 calculates an angular velocity data error in consideration of a bias error, a scale factor error, and a misalignment error that are errors of the angular velocity sensor 101. In calculating the error of the angular velocity data, the above-described equations (22) to (31) are calculated, and the state equation of equation (26) and the state equation of discrete time of equation (31) obtained by further modifying the equation (26). Ask for.

The calculation result in the previous step 304 and the error calculation result of the angular velocity data in step 306 are added and input to the time update calculation unit 207. The time update calculation unit 207 performs calculations of Expression (40) and Expression (41) using Expression (26), and filters the estimated value. As a result of the above arithmetic processing, quaternion correction is also performed, and the most probable filtered estimated value of x _t in the next step can be obtained.

  Finally, in step 308, the calculated filtered estimated value of the next step obtained as described above is input to the coordinate conversion unit 201. That is, the coordinate conversion unit 201 calculates the next step coordinate conversion matrix using the calculated next-step filtered estimated value, and the result is input to the observation update calculation unit 203 as a quaternion estimated value. While it is the final output, it is used for observation update calculation processing in the next step, and further for time update calculation processing. The processing from step 301 to step 308 is one-step processing performed by the arithmetic processing unit 104 of the small posture sensor, which is repeated.

[Simulation 1]
In order to realize the reduction of the attitude error under the dynamic acceleration environment, which is the main object of the present invention, it is important to determine the covariance matrix R _t of the observation noise. Here, determined by simulation the value of R _t. First, the value of R _t was determined so that the error due to dynamic acceleration was reduced. The value at this time is R ₁ . FIG. 4 shows a simulation result by R ₁ . When FIG. 4A changes the posture, FIG. 4B keeps the sensor horizontal, and the Xb axis direction on the b-frame in FIG. 19, that is, the direction in which a large error is likely to occur in the pitch angle. It is a simulation result when sinusoidal dynamic acceleration is applied to. Also, the broken lines are the results of the conventional algorithm, the solid lines are the results of the extended Kalman filter, and the dotted lines are the true posture values at that time. From FIG. 4, it can be seen that when R ₁ is used, errors due to dynamic acceleration are reduced, but posture tracking becomes extremely slow. On the other hand, the value of such R _t is sufficiently fast tracking attitude as R _2, shows the results of R ₂ in FIG. From FIG. 5, it can be seen that using R ₂ improves the tracking of the posture, but the dynamic acceleration error cannot be reduced. So, the R _t and function as the following equation using the R _1, R ₂ described above. However, K _R is an appropriate gain. For T, an appropriate value was determined by repeating the simulation. In this example, the value of T is 11 [s].

The simulation result at this time is shown in FIG. By using the _Rt as described above, it was possible to obtain a result that the posture can be followed quickly and errors due to dynamic acceleration can be reduced. 7 to 9 show a comparison between the linear error estimation Kalman filter (KF) and the extended Kalman filter (EKF) used in the present invention. Among these, FIG. 7 shows the simulation results of the roll angle when the linear error estimation Kalman filter (KF) is used for the small posture sensor mounted on the moving object and when the extended Kalman filter (EKF) of the present invention is used. It is a figure shown in comparison. In FIG. 7, a line indicated by a dotted line is a simulation result by KF, and a line indicated by a solid line is a simulation result by EKF. Comparing both, it can be seen that the result of KF has become more vibrant than that of EKF. This is presumably because the nonlinearity of the coordinate transformation included in the observation equation of Equation (34) cannot be sufficiently considered by KF.

  FIG. 8 shows a comparison of simulation results for pitch angles when a linear error estimation Kalman filter (KF) is used for a small attitude sensor mounted on a moving object and when an extended Kalman filter (EKF) of the present invention is used. FIG. In FIG. 8, the line indicated by the dotted line is the simulation result by KF, and the line indicated by the solid line is the simulation result by EKF. Comparing the two, it can be seen that the result of KF is more oscillating than that of EKF, as in FIG.

  FIG. 9 shows a comparison of simulation results for yaw angles when a linear error estimation Kalman filter (KF) is used for a small posture sensor mounted on a moving object and when an extended Kalman filter (EKF) of the present invention is used. FIG. In FIG. 9, the line indicated by a dotted line is a simulation result by KF, and the line indicated by a solid line is a simulation result by EKF. When both are compared, it can be seen that the result of KF is more oscillating than that of EKF, as in FIGS.

[Experiment 1]
The conventional algorithm and the extended Kalman filter algorithm of the present invention are mounted on a microcomputer and the results of posture / orientation estimation in real time are shown in FIGS. As a comparison target, a high-precision posture sensor AHRS400 manufactured by Crossbow was selected. The AHRS 400 is a posture sensor intended to be mounted on a moving body, and has a feature that a posture error hardly occurs even when dynamic acceleration is applied. However, the weight is 700 (g), which is more than 10 times that of the MARG sensor. Originally, it would be desirable to have both AHRS400 and MARG sensors mounted on a small unmanned helicopter mount and compare attitude data while flying, but because of the weight of AHRS400, it is difficult to do so. The test method of moving the mount on the ground while mounted on the same mount was used. Incidentally, in order to facilitate comparison, the obtained quaternion estimated value is plotted after being converted to Euler angle. FIG. 10 shows a conventional algorithm and the extended Kalman filter algorithm of the present invention mounted on a microcomputer, and in real-time posture and roll angle in an angular velocity environment that greatly exceeds the angular velocity generated when a small unmanned helicopter moves. It is a figure which shows the result of having performed azimuth | direction estimation. In this figure, the solid line shows the direction estimation result by the extended Kalman filter algorithm, and the fine dotted line shows the direction estimation result by the conventional algorithm. A coarse chain line indicates a direction estimation result obtained by the high-accuracy posture sensor AHRS400. From these graphs, it can be seen that the extended Kalman filter algorithm of the present invention can obtain a highly accurate posture / orientation estimation result.

  FIG. 11 shows the pitch angle in real time in an angular velocity environment in which the conventional algorithm and the extended Kalman filter algorithm of the present invention are mounted on a microcomputer, and greatly exceed the angular velocity generated when a small unmanned helicopter moves. It is a figure which shows the result of having performed azimuth | direction estimation. The breakdown of the lines in the graph is the same as in FIG. FIG. 11 also shows that the extended Kalman filter algorithm of the present invention can obtain a highly accurate posture / orientation estimation result. FIG. 12 shows the yaw angle in real time in an angular velocity environment in which the conventional algorithm and the extended Kalman filter algorithm of the present invention are mounted on a microcomputer and greatly exceed the angular velocity generated when a small unmanned helicopter moves. It is a figure which shows the result of having performed azimuth | direction estimation. The breakdown of the lines in the graph is the same as in FIGS. Also from FIG. 12, it can be seen that the extended Kalman filter algorithm of the present invention can obtain a highly accurate posture / orientation estimation result. FIG. 13 shows that the conventional algorithm and the extended Kalman filter algorithm of the present invention are mounted on a microcomputer and the sensor is kept horizontal, as in the simulation, compared with the acceleration applied during the flight of a small unmanned helicopter. FIG. 20 is a diagram showing a result of performing posture / orientation estimation in real time for a pitch angle by applying a sinusoidal dynamic acceleration in the Xb axis direction on the b-frame in FIG. The breakdown of the lines in the graph is the same as in FIGS. Also from FIG. 13, it can be seen that the extended Kalman filter algorithm of the present invention can obtain a highly accurate posture / orientation estimation result.

In the experiment at this time, with respect to FIGS. 10 to 12, tests were performed in an angular velocity environment of a maximum of 250 [deg / s] so as to greatly exceed the angular velocity generated during the movement of the small unmanned helicopter. Applies a sufficiently large acceleration compared to the acceleration applied during the flight of the small unmanned helicopter, because it is assumed that the small attitude sensor is mounted on the small unmanned helicopter. Table 4 shows each flight state of the small unmanned helicopter and the acceleration RMS value in this test.

  “Experiment” is a value during the test shown in FIG. 13, while “Hover” is during hovering flight, “Circular flight” is during a turning flight to which a relatively large acceleration is applied. 10 to 12, it can be seen that the data of the AHRS 400 and the MARG sensor are almost the same, and accurate estimation is performed. However, it can be seen that the data of the proposed method and the conventional method have an error in comparison with the AHRS 400 in the vicinity of 6 to 16 seconds in FIG. This is considered to be the effect of magnetic disturbance, and is not a major problem outdoors where small unmanned helicopters fly, but it is thought that it will be necessary to improve in the future to reduce the influence of such magnetic disturbance. . In addition, there are some places where the data of AHRS 400 has a constant value. This is because AHRS 400 can estimate the posture only when the angular velocity is 200 [deg / s] or less, and is 200 [deg / s] or more. This is because posture estimation stops when angular velocity is given. On the other hand, the MARG sensor can estimate the posture even when an angular velocity of 200 [deg / s] or more is given. On the other hand, it can be seen that the posture error can be sufficiently reduced even when dynamic acceleration is applied, and the specification is sufficiently satisfied.

  As described above, according to the present invention, the extended Kalman filter including the bias estimation of the inertial sensor is used to reduce the posture error under the dynamic acceleration environment, which is a problem of the MARG sensor developed in the prior art. Was applied as a posture estimation algorithm, and the posture and orientation estimation with high accuracy under the dynamic acceleration environment was realized.

(Embodiment 2)
The second embodiment of the present invention is intended to reduce posture estimation errors under a low-frequency acceleration environment in order to realize highly accurate posture / orientation estimation under an acceleration environment.

[Modeling of acceleration signal and incorporation into extended Kalman filter]
In the method of the first embodiment, high-precision posture / orientation estimation under an acceleration environment is realized to some extent. However, when a low-frequency acceleration disturbance close to a certain value is applied, the estimated posture value drifts. Therefore, a method for reducing the attitude error by estimating low-frequency acceleration disturbance as a part of the system state is proposed below. As another method for estimating acceleration disturbance, we propose a method to estimate posture and acceleration disturbance at the same time by including acceleration disturbance in the state quantity of Kalman filter. Since the acceleration disturbance generated due to the movement and rotation motion is sufficiently low in frequency compared to the sampling period of the acceleration sensor, the dynamics of the acceleration disturbance during sampling is expressed by the following equation.

First, the low-frequency acceleration disturbance is expressed as a _dr = [a _bx a _by a _bz ] ^T
And the disturbance dynamics is expressed as
From equation (44)
The state equation where is a state quantity is replaced as the following equation (45).

However, here, each matrix is as follows.

When the expression (45) is discretized, the following expression (49) is obtained. Here, x _t is the state quantity at the t step, and Δt is the sampling time.
Here again
Then, the state equation in discrete time is as follows.

Subsequently, the observation equation is obtained. When the low-frequency acceleration disturbance estimated by the equation (45) is included in the observation equation, it can be written as the following equation.
here,
When, observation equation to output a y _t is expressed by the following equation.
Here, h _t (x _t ) is expressed by the following equation.

Similar to the method of the first embodiment, the matrices F _t and H _t are defined as follows:
The extended Kalman filter algorithm using the matrix defined above and the equations (50) and (53) is given by the following equation.

[Simulation 2]
In the following, in order to confirm that the low-frequency acceleration disturbance is normally estimated by the extended filter algorithm of the present invention, a constant low-frequency acceleration disturbance is applied to the moving object, and the low-frequency acceleration disturbance is correctly estimated. Confirm by simulation. In this simulation, it is assumed that the aircraft accelerates at a maximum acceleration from a stationary state, moves for a certain period of time, and then, as a rule, uses the maximum acceleration, and the magnitude of the applied disturbance is 0.2G. Further, in order to clarify the performance of each algorithm, the application time of acceleration disturbance due to acceleration / deceleration was set to 20 seconds, which is sufficiently longer than the actual flight. FIG. 14 shows acceleration data of each axis used in this simulation. In FIG. 14, the solid line indicates acceleration data in the X-axis direction, the alternate long and short dash line indicates acceleration data in the Y-axis direction, and the dotted line indicates acceleration data in the Z-axis direction. FIG. 14 shows that a constant disturbance is applied to the x-axis acceleration once in the negative direction and the positive direction about 15 seconds after the start. There is no acceleration on the y-axis, and gravitational acceleration is applied on the z-axis. FIG. 15 shows the posture estimation result of each algorithm, FIG. 15A shows the posture estimation result in the roll direction, FIG. 15B shows the posture estimation result in the pitch direction, and FIG. 15C shows the yaw direction. The posture estimation result in is shown. In FIG. 15, True indicates the true value of the posture estimation result with a solid line, Prev indicates the posture estimation result according to the conventional algorithm with a dotted line (thin line), and New displays the state quantity in the present invention. The posture estimation result by the extended Kalman filter algorithm including disturbance is shown by a dotted line (thick line). FIG. 16 is a diagram showing a comparison between the acceleration disturbance estimated value and the true value of the acceleration disturbance in the algorithm of the present invention. FIG. 16A shows a comparison result of the acceleration disturbance in the X direction, and FIG. The comparison result of the acceleration disturbance in the Y direction is shown, and FIG. 16C shows the comparison result of the acceleration disturbance in the Z direction. In FIG. 16, True displays the true value of the acceleration disturbance with a solid line, and New displays the acceleration disturbance estimation result according to the algorithm of the present invention with a dotted line (thick line).

In the above simulation, the measured acceleration is an acceleration disturbance due to gravity and movement, and it can be seen from the true values in FIG. Since each axis component of acceleration and gravity in FIG. 14 is (g _x g _y g _z ) = [0, 0, 1] [G], the X axis extends from time 15 [sec] to 35 [sec]. A disturbance of -0.2 [G] due to acceleration is applied to the X axis, and a disturbance of 0.2 [G] due to deceleration is applied to the X axis from time 50 [sec] to 70 [sec]. The acceleration disturbance estimated value according to the algorithm of the present invention in FIG. 16 agrees well with the true value. Comparing the estimated pose values of the algorithms shown in FIG. 15, the pose estimation using the conventional algorithm has a maximum error of 12 [deg] in the pitch angle, whereas the two proposed algorithms have an error of 0. It is within 1 [deg], and its effectiveness can be confirmed. The posture estimation error in the conventional algorithm is considered to be caused by treating the applied acceleration disturbance as a gravity component applied to the X axis when the pitch angle is tilted.

[Experiment 2]
Based on the measurement results in an actual acceleration disturbance environment, the performance comparison between the conventional posture estimation algorithm and the posture estimation algorithm of the present invention is performed. The small attitude sensor of the present invention is used as hardware for implementing the algorithm. However, since the microprocessor (MPU) mounted on the small attitude sensor is small, a plurality of types of algorithms cannot be calculated simultaneously in real time. Therefore, we implemented an algorithm for estimating the acceleration disturbance using the Kalman filter, and performed an off-line estimation calculation based on the acceleration, angular velocity, and magnetic data obtained by the measurement. Since it is clear that the calculation amount of the acceleration disturbance estimation algorithm using the Kalman filter is large from the order of the matrix used for the calculation, if this method can be implemented in the MPU, it can be sufficiently realized by other methods. A true value for performing comparison verification of the posture estimation algorithm is acquired from a high-precision posture sensor AHRS440 manufactured by Crossbow.

  In this experiment, an on-vehicle attitude measurement experiment is performed, and the results of a running experiment in which each sensor, a data collection notebook personal computer, and a power source are mounted on a general vehicle are shown in FIGS. 17 and 18. Originally, it is desirable that the above-described sensor or the like is mounted on a small unmanned helicopter for measurement, but the attitude sensor AHRS 440 is not of an appropriate weight for mounting on a small unmanned helicopter. Therefore, as a means of confirming the effectiveness when applied to a moving body, it was selected to be mounted on a vehicle. The test runs linearly on a flat road and stops due to sudden deceleration when it reaches 40 km / h. At this time, there is almost no change in the attitude of the sensor, and a large acceleration disturbance is applied in the front-rear direction.

  FIGS. 17 and 18 are diagrams showing the result of posture measurement by the sensor in the above experiment. FIG. 17 shows the attitude measurement results of each algorithm, FIG. 17A shows the attitude measurement results in the roll direction, FIG. 17B shows the attitude measurement results in the pitch direction, and FIG. 17C shows the yaw direction. The attitude measurement result in is shown. In FIG. 17, the Ref display indicates the posture measurement result (true value) by the high accuracy posture sensor AHRS440 manufactured by Crossbow, and the Prev display indicates the posture measurement result by the conventional algorithm by a dotted line (thin line). , New indicates the posture measurement result by the extended Kalman filter algorithm of the present invention with a dotted line (thick line). FIG. 18 is a diagram showing a comparison between the acceleration disturbance estimated value and the true value of the acceleration disturbance in the algorithm of the present invention. FIG. 18A shows a comparison result of the acceleration disturbance in the X direction, and FIG. The comparison result of the acceleration disturbance in the Y direction is shown, and FIG. 18C shows the comparison result of the acceleration disturbance in the Z direction. In FIG. 18, True indicates the true value of the acceleration disturbance with a solid line, and New indicates the acceleration disturbance estimation result according to the algorithm of the present invention with a dotted line (thick line).

  From FIG. 17, in the conventional algorithm, an error of a maximum of 18 [deg] is generated in the pitch angle in accordance with the application of the acceleration disturbance, and the yaw angle fluctuates from around 8 seconds. On the other hand, in the acceleration disturbance estimation by the extended Kalman filter algorithm of the present invention, as is apparent from FIG. 18, the disturbance suppression effect equivalent to the high accuracy attitude sensor AHRS440 manufactured by Crossbow is obtained. In any of the roll angle (FIG. 17A), pitch angle (FIG. 17B), and yaw angle (FIG. 17C), the error is within 0.1 [deg]. Thus, according to the extended Kalman filter algorithm of the present invention, it can be seen that the posture estimation is correctly performed, and the effectiveness thereof can be confirmed.

Claims (4)

An angular velocity sensor that measures angular velocities on three independent axes of the moving object;
An acceleration sensor that measures acceleration on three independent axes of the moving object;
A magnetic sensor for measuring geomagnetism on three independent axes of a moving object;
An arithmetic processing unit that calculates an estimated value of a quaternion based on measurement values of the angular velocity sensor, the acceleration sensor, and the magnetic sensor;
The arithmetic processing unit calculates a coordinate transformation matrix using a pre-estimated quaternion estimated value, converts a geomagnetic vector and a gravitational acceleration vector of a ground fixed coordinate system component using the coordinate transformation matrix, A coordinate conversion unit for estimating the geomagnetic vector and the gravitational acceleration vector of the coordinate system component;
A magnetic / acceleration sensor data acquisition unit for acquiring a geomagnetic vector and a gravitational acceleration vector of a sensor coordinate system component of the current step from the magnetic sensor and the acceleration sensor;
The geomagnetic vector and gravitational acceleration vector of the current step sensor coordinate system component estimated by the coordinate conversion unit, and the geomagnetic vector and gravitational acceleration vector of the current step sensor coordinate system component acquired by the magnetic / acceleration sensor data acquisition unit. A vector error calculation unit for calculating an error;
An angular velocity sensor data acquisition unit that acquires an angular velocity vector of a sensor coordinate system component of the current step from the angular velocity sensor;
About the acquired angular velocity data, an angular velocity data error calculating unit for calculating an angular velocity sensor error including a bias error, a scale factor error, a misalignment error, and a noise element;
A quaternion calculation unit and a coordinate conversion unit, a magnetic / acceleration sensor data acquisition unit, a vector error calculation unit, an angular velocity data error calculation unit, and a quaternion calculation unit that obtain time changes between the quaternion of the previous step and the quaternion of the current step Construct a quaternion representing the current posture based on, and an extended Kalman filter that estimates angular velocity error,
A small attitude sensor that outputs a quaternion estimated value by the extended Kalman filter as a current attitude. The extended Kalman filter is
And the formula
Low-frequency acceleration disturbance a _dr = [a _bx a _by a _bz ] ^T
Against
Define the dynamics of Eq. (61) and for this dynamics:
Equation of state where is a state quantity
However, each matrix in the state equation is as follows:
The small posture sensor according to claim 1, wherein: In addition to the operation of claim 2, the extended Kalman filter discretizes the state equation of equation (62),
However, x _t is the state quantity at the t step, Δt is the sampling time,
Where, again,
Where the discrete-time equation of state is
Next, the low-frequency acceleration disturbance estimated by the state equation of Equation (62) is included in the observation equation,
Find the observation equation
here,
As
Where h _t (x _t ) is
The small attitude sensor according to claim 1, wherein an observation equation having _yt as an output is obtained and an estimated value is calculated by the observation equation. The extended Kalman filter is added to the operation of claim 3,
The matrices F _t and H _t are
Defined as
The extended Kalman filter algorithm using the matrix defined above and Equations (64) and (67) is given by the following equation:
The small-sized attitude sensor according to claim 1, wherein arithmetic processing is performed by these algorithms.