Wednesday, December 27, 2023

How the MEMS Inertial Measurement Unit works?

 The inertial measurement unit is a device that measures the three-axis attitude angle (or angular rate) and acceleration of an object. Generally, an inertial measurement unit contains three single-axis accelerometers and three single-axis gyroscopes. The accelerometer detects the acceleration signals of the object in three independent axes of the carrier coordinate system, while 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 to calculate the attitude of the object. It has very important application value in navigation. IMUs are mostly used in equipment that require motion control, such as cars and robots. It is also used in situations where precise displacement calculations using attitude are required, such as inertial navigation equipment for submarines, aircraft, missiles and spacecraft.

The principle of an inertial measurement unit is very similar to taking small steps in the dark. In the dark, due to the error between your estimate of the step length and the actual distance traveled, as you take more and more steps, the difference between your estimated position and the actual position will become farther and farther. When taking the first step, the estimated position is relatively close to the actual position; but as the number of steps increases, the difference between the estimated position and the actual position becomes larger and larger. This method is extended to three dimensions, which is the principle of the inertial measurement unit.

The academic expression is: Based on Newton’s laws of mechanics, by measuring the acceleration of the carrier in the inertial reference system, integrating it over time, and transforming it into the navigation coordinate system, the velocity in the navigation coordinate system can be obtained. , yaw angle and position information.

Therefore, in layman’s terms, the inertial measurement unit is a strapdown inertial navigation system. The system consists of three acceleration sensors and three angular velocity sensors (gyros). The accelerometer is used to feel the acceleration component relative to the vertical line of the ground. The speed sensor is used to get a feel for the angle information.

It is worth noting that the inertial measurement unit provides relative positioning information. Its function is to measure the movement route of the object relative to the starting point, so it cannot provide information about your specific location. Therefore, it is often combined with GPS. Used together, when the GPS signal is weak in certain places, the IMU can play its role, allowing the car to continue to obtain absolute position information and not get “lost.”

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