I. Project design background and overview
In many engineering applications, it is necessary to measure the angle of inclination of the carrier to the horizontal plane. For navigation and positioning systems, attitude information is an important parameter. The main goal of the system is to obtain accurate pitch and roll angles through attitude fusion under dynamic conditions. Firstly, the acceleration sensor is used to measure the tilt angle, and the measurement angle is preprocessed to reduce the error. Secondly, the gyroscope is added for attitude fusion. The main method is Kalman filter, and the roll angle and pitch angle of the system are obtained. The method is widely used in engineering, the technology is mature, and the attitude fusion effect is good.
The inertial measurement unit can be seen in the field of aircraft manufacturing and sensor technology, and has a wide application prospect. In general, an IMU includes three single-axis accelerometers and three single-axis gyros. The accelerometer detects an acceleration signal of an independent three-axis of the object in the carrier coordinate system, and the angular velocity signal of the gyro detection carrier relative to the navigation coordinate system. The angular velocity and acceleration of the object in three-dimensional space are measured, and the posture of the object is calculated. It has important application value in navigation.
To increase reliability, you can also equip each axis with more sensors. In general, the IMU is to be mounted on the center of gravity of the object being measured. IMUs are mostly used in devices that require motion control, such as cars and robots. It is also used in situations where precise displacement calculations are required, such as inertial navigation devices for submarines, airplanes, missiles, and spacecraft. With the three-axis accelerometer, the acceleration of the external force is greatly affected, and in the environment of motion/vibration, the output direction angle error is large. Acceleration measures the direction of gravity. In the absence of external force acceleration, the ROLL/PITCH two-axis attitude angle can be accurately output, and this angle has no cumulative error and is accurate over a longer time scale. However, the disadvantage of the accelerometer's angle measurement is that the accelerometer actually uses the MEMS technology to detect the micro-deformation caused by the inertial force, and the inertial force is the same as the gravity. Therefore, the accelerometer does not distinguish between the gravity acceleration and the external force acceleration. When the three-dimensional space is doing the shifting motion, its output is not correct.
Second, the project design principle
1, an overview of the principle
The output angular velocity of the gyroscope is instantaneous. The angular velocity cannot be directly used in the attitude balance. The angular velocity and the time integral are needed to calculate the angle. The obtained angular variation is added to the initial angle to obtain the target angle. The smaller the integration time Dt is, The more accurate the output angle, but the principle of the gyroscope determines that its measurement reference is itself, there is no absolute reference outside the system, and Dt is impossible to be infinitely small, so the cumulative error of the integral will increase rapidly with the passage of time. Eventually the output angle does not match the actual, so the gyroscope can only work on a relatively short time scale.
Therefore, on the basis of no other reference objects, to obtain a more realistic attitude angle, it is necessary to use weighting algorithms to promote strengths and avoid weaknesses, combine the advantages of both, and abandon their respective shortcomings. The design algorithm increases the weight of the gyroscope in a short time scale. Increase the acceleration weight over a longer time scale so that the system output angle is close to the true value.
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