The attitude reference system is also AHRS. The AHRS is composed of accelerometer, magnetic field meter and gyroscope. The real reference of AHRS comes from the earth's gravity field and the earth's magnetic field. In other words, if AHRS leaves the earth, there is gravity and When the magnetic field environment is not working properly, the more orthogonal the general magnetic field and the gravity field, the better the attitude measurement effect, that is, if the magnetic field and the gravity field are parallel, such as in the geomagnetic north and south poles. The magnetic field here is downward, that is, the same direction as the weight field. At this time, the route can not be measured, which is the defect of the attitude system. At high latitudes, the error of the route angle will become larger and larger.
The IMU is also an inertial measurement unit. All motions can be decomposed into a linear motion and a rotary motion. Therefore, the inertial measurement unit measures the two motions. The linear motion can be measured by an accelerometer, and the rotary motion is passed through the gyro.
AHRS has one more magnetic field sensor than IMU. Why is AHRS lower than IMU and depends on gravity field and magnetic field? ~ This is determined by the sensor device architecture. AHRS sensor is usually a low cost MEMS sensor. The noise of the gyroscope and accelerometer of the sensor is relatively large. Taking the planar gyro as an example, the integration of the gyro gyroscope will drift about 2 degrees for one minute. If there is no magnetic field and gravity field to correct the three axes. In the case of the gyro, then the actual attitude and the measured output attitude of the object are completely changed after 3 minutes, so the field vector must be used for correction under the framework of such a low-cost gyroscope and accelerometer.
The IMU is actually the same. Only the relatively accurate sensor, the IMU's gyroscope uses fiber optic gyro or mechanical gyro. The cost of this gyro is very high, and the accuracy is relatively high precision compared with the mems gyro.
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