The inertial system is an autonomous dead reckoning navigation system that uses inertial sensors, reference directions, and initial position information to determine the orientation, position, and velocity of the carrier. It should at least consist of an inertial measurement device, a digital computer, a control display device and a dedicated precision power supply. The motion of the carrier is carried out in three-dimensional space, and its motion forms are linear motion and angular motion. Both linear motion and angular motion are in three-dimensional space. To establish a three-dimensional space coordinate system, it is necessary to establish a three-axis inertial platform. A three-axis inertial platform can provide a benchmark for measuring three-degree-of-freedom linear acceleration. The three linear acceleration components of the known orientation are measured, and the moving speed and position of the carrier are calculated by the computer. Therefore, the first type of inertial navigation system solution is the platform inertial navigation system. There is no "electromechanical" platform, the inertial component gyroscope and accelerometer are directly installed on the carrier, a "mathematical" platform is established in the computer, and the speed and position of the carrier are obtained through complex calculations and transformations. This kind of non-mechanical platform Strapdown inertial navigation system is the second largest type of inertial navigation system scheme, called strapdown inertial navigation system.
Broadly speaking, the process of guiding a navigation carrier from a starting point to a destination is collectively called navigation. In a narrow sense, navigation refers to the technology and method of providing real-time attitude, speed and position information to the navigation carrier. In the early days, people relied on astronomical and geographical methods such as geomagnetic field, starlight, and sun altitude to obtain positioning and orientation information. With the development of science and technology, technologies such as radio navigation, inertial navigation, and satellite navigation came out one after another, and were widely used in military and civilian fields. Among them, inertial navigation is a technical method that uses gyroscopes and accelerometers mounted on the carrier to measure the attitude, speed, position and other information of the carrier. The software and hardware devices that realize inertial navigation are called inertial navigation systems, or inertial navigation systems for short.
Strap-down Inertial Navigation System (SINS for short) installs the accelerometer and gyroscope directly on the carrier, and calculates the attitude matrix in the computer in real time, that is, calculates the distance between the carrier coordinate system and the navigation coordinate system. relationship, so that the accelerometer information in the carrier coordinate system is converted into information in the navigation coordinate system, and then the navigation calculation is performed. Because of its high reliability, strong function, light weight, low cost, high precision and flexible use, SINS has become the mainstream of inertial navigation system development. The strapdown inertial measurement unit (IMU for short) is the core component of the inertial navigation system, and the accuracy of the output information of the IMU determines the accuracy of the system to a large extent.
Gyroscopes and accelerometers are indispensable core measurement devices in inertial navigation systems. Modern high-precision inertial navigation systems place high demands on the gyroscopes and accelerometers used, because the drift error of the gyroscope and the zero offset of the accelerometer are the most direct and important factors that affect the accuracy of the inertial navigation system. Therefore, how to improve the performance of inertial devices and improve the measurement accuracy of inertial components, especially the measurement accuracy of gyroscopes, has always been the focus of research in the field of inertial navigation. The development of gyroscopes has gone through several stages. The initial ball-bearing gyroscope has a drift rate of (l-2)°/h, and the air-floating, liquid-floating and magnetic-floating gyroscopes developed by overcoming the inertial instrument support technology can achieve an accuracy of 0.001°/h, while The accuracy of electrostatically supported gyroscopes can be better than 0.0001°/h. Since the 1960s, the development of flexible gyroscopes has started, and its drift accuracy is better than 0.05°/h, and the best level can reach 0.001°/h.
In 1960, the laser gyroscope was successfully developed for the first time, marking the beginning of the optical gyroscope to dominate the gyroscope market. At present, the zero bias stability of the laser gyro can reach up to 0.0005°/h. The biggest problem facing the laser gyro is that its manufacturing process is relatively complicated, resulting in high cost, and its volume and weight are also relatively large. This aspect is to a certain extent On the one hand, it limits its development and application in some fields, and on the other hand, it also promotes the development of laser gyroscopes in the direction of low cost, miniaturization, and three-axis integration. Another optical gyroscope, the fiber optic gyroscope, not only has many advantages of the laser gyroscope, but also has the characteristics of simple manufacturing process, low cost and light weight, and is currently becoming the fastest growing optical gyroscope.
