Application

Strapdown inertial navigation system

Definition:

Strapdown Inertial Navigation System (SINS) is developed on the basis of platform inertial navigation system. It is a frameless system composed of three rate gyros, three linear accelerometers and a microcomputer. The gyroscope and accelerometer are directly attached to the carrier. Gyroscope and accelerometer are used to measure the angular motion information and linear motion information of the carrier respectively, and the on-board computer can calculate the heading, attitude, speed and position of the carrier according to the measurement information. The strapdown inertial navigation system is simple in structure, small in size, light in weight, low in cost, easy in maintenance, high in reliability, and can improve its fault tolerance through redundancy technology.

System features:

Strapdown inertial navigation system does not rely on external information, nor radiates energy to the outside world, and is not easy to be disturbed and damaged. It is an autonomous navigation system. There are two main differences between the strapdown inertial navigation system and the platform inertial navigation system:

(1) The inertial platform is omitted, and the gyroscope and accelerometer are directly installed on the aircraft, which makes the system small in size, light in weight, low in cost and easy to maintain. However, the gyroscope and accelerometer directly bear the vibration, shock and angular motion of the aircraft, so additional dynamic errors will be generated. This puts higher demands on gyroscopes and accelerometers.

(2) It is necessary to use the computer to coordinate the acceleration signal of the aircraft measured by the accelerometer, and then conduct navigation calculation to obtain the required navigation parameters (heading, ground speed, sailing distance and geographical position, etc.). This kind of system needs to carry out coordinate transformation, and must carry out real-time calculation, so it requires the computer to have high computing speed and large capacity.

Depending on the gyro’s different, strapdown inertial navigation system (SINS) is divided into two classes: one use the rate gyroscope, such as single degree freedom flexible gyroscope, laser gyroscope etc. They are measuring aircraft angular velocity. This system is called rate of strapdown inertial navigation system; Another kind of double freedom gyro, such as electrostatic gyroscope, it measures the angular displacement of aircraft. This system is called position type strapdown inertial navigation system. Refers to the rate of strapdown inertial navigation system, it is also called strapdown inertial navigation system.

The essence of the strapdown inertial navigation system and the platform inertial navigation system are the same, but there are obvious differences in the implementation of the system.

Differences:

(1) The dynamic range requirements of gyro are different. The platform inertial navigation system gyro is installed on the platform body, the gyro sensing platform body deviation from the navigation coordinate system, the platform through the stability loop to eliminate this deviation, its role is to isolate the angular movement of the carrier, so that the working environment of the gyro is not affected by the angular movement of the carrier. However, the strapdown inertial navigation gyroscope is directly installed on the carrier, the gyroscope must follow the angular movement of the carrier, and the torque current is much larger than that only tracking the navigation coordinate system, that is, the dynamic range of the gyroscope used in strapdown inertial navigation is much larger than that used in platform inertial navigation.

(2) The operating environment of inertial navigation devices is different, and the compensation requirements for dynamic error and static error of inertial navigation devices are also different. In the platform inertial navigation system, the platform plays an isolated role in the angular motion of the carrier, and the inertial navigation device installed on the platform only needs to compensate the static error caused by linear acceleration. In addition to compensating static errors, the inertial components in the strapdown inertial navigation system also need to compensate the dynamic errors caused by diagonal velocity and angular acceleration. Therefore, the dynamic and static error coefficients of strapdown gyro and accelerometer must be strictly tested and calibrated under laboratory conditions.

(3) Different amount of calculation. In platform inertial navigation, the platform exists in the form of physical entity, the platform simulates the navigation coordinate system, and the attitude Angle and heading Angle of the carrier can be picked up directly from the platform frame or obtained only through a small amount of calculation. However, in the strapdown inertial navigation system, the platform does not exist physically, but exists in the form of a mathematical platform, and the attitude Angle and heading Angle must be calculated, which requires a huge amount of calculation.

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