Inertial navigation systems
Inertial navigation systems

Inertial navigation systems


Inertial systems do not need external sources (ground stations, beacons, radar targets and so on. F.) Systems themselves also do not emit any energy. Furthermore, they do not interfere with no interference. Therefore, they are the most autonomous systems.

The components of inertial systems are such well-known devices as accelerometers, gyroscopes, tracking drives, computing devices. However, in conditions of high temperature differences, shocks, vibrations and significant accelerations, the use of these systems in order to Navigation is made possible only when the machinery was able to ensure the highest accuracy of their manufacture and control, and therefore save their settings.

Operating principle. The mechanical energy of all bodies and parts that make up a plane in flight is constantly changing depending on changes in flight mode, effects of the environment and so on. N. Defining a special device changes mechanical ^ power, transforming them and registering, you can calculate the speed of the plane and passed them way.

Accelerometers are called accelerometers. The simplest accelerometer is a weight with a mass m suspended on springs. If such a gauge is placed on a trolley and a slider of a potentiometer mounted on the same trolley is attached to its weight, then the stationary engine will remain stationary in the middle of the potentiometer and the potential difference will not be observed. If the force F is applied to the trolley, it starts moving and the load t acquires acceleration, as a result of which it begins to shift relative to the platform (potentiometer) until the force is balanced by the compression and extension of the springs.

It is obvious that the shift load (and potentiometer) is proportional to the force F and hence, the acceleration and the potential difference appearing whose sign depends on the direction of acceleration.

If at the time of application of force trolley speed is zero, then knowing the acceleration (accelerometer on), we can calculate the velocity acquired trolley after some time and distance it is time for the path. To use this integration.

The acceleration rate is incrementally per unit of time:

If acceleration is integrated from the start of motion to the moment, we obtain the velocity at this point.

And by integrating the speed, we get the distance traveled by a truck during this time:

Placing the same truck (or plane) of the other accelerometer with a small weight, not moving in the direction of movement and perpendicular to it, it is easy to measure the acceleration acting on the body in the lateral direction.

In this acceleration is calculated similarly and lateral deviation of the body (of the aircraft).

Thus, it is possible to orthodromic coordinate system with the origin at the location of its takeoff point location relative LZP. To do this, electrically coupled pairs of integrators longitudinal and lateral accelerometers indicator traversed path, in which at any time count value from the start of the path and the linear deviation from a predetermined direction.

Accelerometers. In inertial systems are mostly used linear accelerometers for measuring current on the body linear acceleration, r. E. Impacts only those forces which are directed along the axis of the measuring device. The action of the simplest of these accelerometers is based on measuring the movement of the elastically suspended mass.

Difficulties in the development of new accelerometers for navigation purposes are associated with the range of accelerations (the ratio of maximum and minimum accelerations). This ratio must be of the order of 100 000. At an accelerometer with an elastically suspended mass, with such a ratio of maximum and minimum measured accelerations, in the case of small accelerations, the operation of the device will be adversely affected by friction forces, and at large accelerations errors due to the dead zone and hysteresis of the elastic suspension will occur. Even if the dead zone is 0,001 d, an error in the way of reckoning for an hour flight to reach values ​​up to 70 km.

One solution to this issue is the use of an "electric spring". This device is based on the motion in the mass solenoid of the accelerometer rod. When the aircraft moves with acceleration, a current of a certain voltage is applied to the input of the amplifier, which, after amplification, is proportional to the output current of the amplifier fed to the solenoid to counteract the movement of the mass. After the initial acceleration, when the mass moves in the opposite direction, a restoring current also arrives in the opposite direction. Thus, each displacement of the mass can be measured by the voltage at the input to the amplifier or by the force of the restoring current entering the solenoid.

Accelerometers of this type satisfy their sensitivity, which can be increased in almost the entire range of operation.

Many such devices differ from one another only in the form of the kinematic connection with the airframe.

Gyro-stabilized platform. To keep the platform with an accelerometer or accelerometers unit in the horizontal plane is used to keep the property free gyroscope axis position of its rotor constant in inertial space (relative to the stars).

Free called gyroscope with three degrees of freedom, is not subject to any external torques, including friction. The center of gravity of the gyroscope must coincide with the point of intersection of the axes of the gimbal.

The basis of the gyrostabilized platform is the principle of power gyroscopic stabilization. With force stabilization, the gyroscopic moment compensates for the harmful external torque, ie it is unloading only as long as the precession and unloading moment of the engine occurs (it is understood that all three gyro axes have unloading motors installed) has not reached the required value. In the future, the gyro axis is unloaded already at the expense of the moment created by the engine, and not due to the gyroscopic moment. The motor torque can be made large enough.

A stabilized platform thus embodies the idea nonrotating gyro rotor, which, however, retains the same position relative to the rotor axis inertial space. All this makes it possible to use the force to stabilize the gyroscopic platform in the horizontal plane of the inertial navigation instruments, radar antennas and a number of other devices.

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