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# What Is An Inertial Measurement Unit?

Jan 06, 2020

The inertial measurement unit is a device that measures the three-axis attitude angle and acceleration of an object. Generally, an IMU contains three single-axis gyroscopes and three single-axis accelerometers. The accelerometer detects the acceleration signals of the object in the carrier coordinate system independently of the three axes, and the gyroscope detects the angular velocity signal of the carrier relative to the navigation coordinate system. , Measure the angular velocity and acceleration of the object in three-dimensional space, and use this solution to calculate the attitude of the object. It has very important application value in navigation.

Inertial measurement unit, theoretical mechanics tells us that all motions can be decomposed into a linear motion and a rotational motion, and this inertial measurement unit is used to measure these two types of motion, linear motion can be measured by an accelerometer, and rotational motion Gyro to measure. The wonderful combination of the two makes the inertial measurement unit come into being.

Adding more sensors to each axis in the inertial measurement unit increases reliability. Generally speaking, the IMU should be installed on the center of gravity of the measured object. IMUs are mostly used in devices that require motion control, such as cars and robots. It is also often used in situations that require precise displacement estimation with attitude, such as inertial navigation equipment for submarines, aircraft, missiles and spacecraft.

We can assume that the measurement of the gyroscope and accelerometer of the inertial measurement unit is without any error, then the attitude of the object can be accurately measured through the gyroscope. The accelerometer can be used to calculate the displacement by the second integration to achieve a complete 6DOF. That is to say, a person who moves this theoretical IMU at any position in the universe can know his current attitude and relative displacement. It will not be limited to any place.

IMU is actually the same. Absolutely accurate sensors do not exist, only relatively accurate. Gyroscopes for inertial measurement units typically use fiber optic gyroscopes or mechanical gyroscopes. The cost of this kind of gyroscope is relatively high, and the accuracy is also high compared to MEMS gyroscope. However, high accuracy does not mean that it is accurate.The attitude accuracy parameter of the IMU is usually how many degrees an hour drifts.

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