This brief deals with attitude-independent threeaxis magnetometer calibration in real time. The first part of this note presents a new model used for real-time estimation without any knowledge of the attitude of the projectile. The second part describes the other main contribution, which consists of a new simple and useful filter used for parameters estimation. The latter is formulated within the framework of an extended Kalman filter (EKF), which includes previous measurements in order to increase the performance and stability of the estimator. Finally, numerical simulations support the contribution of the presented algorithm. A good performance is shown through a smart projectile example in a noisy context, without requiring much more computation time than the classical EKF.
The location of objects is a growing research topic due, for instance, to the expansion of civil drones or intelligent vehicles. This expansion was made possible through the development of microelectromechanical systems (MEMS), inexpensive and miniaturized inertial sensors. In this context, this article describes the development of a new simulator which generates sensor measurements, giving a specific input trajectory. This will allow the comparison of pose estimation algorithms. To develop this simulator, the measurement equations of every type of sensor have to be analytically determined. To achieve this objective, classical kinematic equations are used for the more common sensors, i.e., accelerometers and rate gyroscopes. As nowadays, the MEMS inertial measurement units (IMUs) are generally magnetometer-augmented, an absolute world magnetic model is implemented. After the determination of the perfect measurement (through the error-free sensor models), realistic error models are developed to simulate real IMU behavior. Finally, the developed simulator is subjected to different validation tests.
The knowledge of the roll angle of a projectile is decisive to apply guidance and control law. For example, the goal of ISL's project GSP (Guided Supersonic Projectile) is to change the flight path of an air-defence projectile in order to correct the aim error due to the target manoeuvres. The originality of the concept is based on pyrotechnical actuators and onboard sensors which control the angular motion of the projectile. First of all, the control of the actuators requires the precise control of the roll angle of the projectile. To estimate the roll angle of the projectile, two magnetometers are embedded in the projectile to measure the projection of the earth magnetic field along radials axes of the projectiles. Then, an extended Kalman nIter is used to compute the roll angle estimation. As the rolling frequency of the GSP is about 22 Hz, it is easy to test the navigation algorithm in laboratory. So in previous papers ([1),[5)) the in-lab demonstration of this concept shows that the roll angle estimation was possible with an accuracy of about 1° at 22 Hz. In this paper, the demonstration is extended to in-flight test, with a roll rate about 35 Hz. Thus, two magnetometers, a DSP and a LED (to simulate a thruster) are embedded inside the projectile; the DSP runs an extended Kalman nIter and a guidance algorithm to compute the trigger times of the LED. By using a high speed camera (a trajectory tracker), we can observe that the LED is switch on at the target angle.
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