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Land positioning and orientation system

1 Overview

The land locating system uses a three-axis fiber optic gyroscope to sense the angular motion of the carrier and output a digital signal proportional to the angular velocity of the carrier. The linear acceleration of the three orthogonally configured quartz flexurometers is proportional to the output. The current signal, the current signal is converted into a frequency signal input to the navigation computer through the I/F conversion circuit. The navigation computer completes the gyroscope, the accelerometer, the external GPS data receiving, the system error compensation calculation, the navigation solution, and transmits the real-time navigation information such as speed, position and posture through the monitoring port at a predetermined period.

1.1 Fiber Optic Gyroscope

The fiber optic gyroscope is a fiber optic interferometer based on the Sagnac effect, that is, two beams of light that are transmitted in opposite directions in the same fiber sensing ring to form a fiber Sagnac interferometer, as shown in FIG. 2 .

Figure 2 Schematic diagram of fiber optic gyro

The light beam from the light source is split into two beams by the splitter/combiner, which are respectively coupled into the fiber sensitive coil from both ends of the fiber loop, and propagate in the forward and counterclockwise directions. The two beams coming out from both ends of the fiber loop are superimposed by the splitter/combiner to generate interference, and the resulting phase difference is proportional to the angular velocity of the ring:

…………………………………………(1)

among them,

L fiber length;

The average diameter of the D fiber optic ring;

The wavelength of light in a vacuum;

The speed of light in a vacuum.

The angular rate information can be obtained by detecting the phase difference (i.e., the interference light intensity), where the term is the scale factor of the gyro.

Figure 3 fiber ring physical map

The fiber optic gyroscope adopts a high-precision three-axis fiber optic gyroscope, which adopts an all-digital closed-loop fiber optic gyroscope scheme, and its optical path portion is composed of a light source, a coupler, an integrated Y-waveguide, an optical fiber sensing ring and a detector. With the scheme of sharing the erbium-doped fiber source, the three fiber sensing loops are sensitive to the angular motion in three directions, and the signals are processed by the corresponding circuit boards and the angular rate information is output.

Figure 4 light source solution block diagram

In the development process, it broke through a number of key technologies such as erbium-doped fiber source technology, zero-start technology, and scale factor error control technology, making the fiber optic gyro within the operating temperature range of -10 ° C to 50 ° C, zero-zero conditions, zero The partial stability is better than 0.02o/h (1σ).

The main technical indicators are as follows:

Preparation time ≤ 15s;

Zero bias stability (average time 100s) ≤ 0.02 / h (1σ);

Zero bias repeatability (stable environment, average time 100s) ≤ 0.02 (1σ) / h;

Random walk coefficient ≤ 0.005/;

Scale factor nonlinearity ≤ 50ppm;

Scale factor repeatability ≤ 50 (1σ) ppm;

The gyro measurement range is not less than ±300/s.


1.1 Accelerometer

The accelerometer uses a quartz flexible accelerometer. The quartz flexible accelerometer is a mechanical pendulum force balance accelerometer, which consists of two parts: the head and the servo circuit. The meter head is composed of a whole quartz flexible detecting mass pendulum assembly, a lower and lower torque device, a connecting piece such as a belly band and an isolating ring, and a casing. The servo circuit is a hybrid integrated circuit, which consists of a reference triangular wave generator, a differential capacitance detector, a current integrator, a transconductance compensation amplifier and a voltage regulator.

The accelerometer is mounted on the carrier. When the carrier has acceleration motion relative to the inertia space in the direction of the input shaft of the accelerometer, the accelerometer detects the mass pendulum and generates an inertia moment, and:

Mg =mLai ..........................................(2)

among them,

Mg ——detects the moment of inertia of the mass pendulum;

M ─ Detect the quality of the quality pendulum;

L ─ Detect the distance from the center of mass of the mass pendulum to the flexible pivot;

Ai —— The input acceleration of the accelerometer input axis direction.

The moment of inertia causes the detected mass to swing around the flexible pivot to produce an angular displacement that causes the differential capacitive sensor to produce a capacitance difference, at small angular displacements:

Δc = KpΔα..........................................(3)

among them,

Δc——the difference in capacitance;

Kp ── the transfer coefficient of the differential capacitance sensor near the zero position;

Δα—Detects the angular displacement of the mass pendulum.

The capacitance difference is converted into a current signal by a servo circuit, and the current output generates an electromagnetic feedback torque to the torque device:

Mt =Kt I ..........................................(4)

among them,

Mt ──the feedback torque of the torque device;

Kt ─ the torque coefficient of the torque device;

I ——The current flowing into the torque coil.

When Mt =Mg:

I=(mL/Kt )ai..........................................(5)

Among them, mL / Kt - current scale factor, that is, the feedback current required when the input acceleration is 1g.

When the torque feedback torque is balanced with the inertia moment of the detected mass pendulum, the current required in the torque coil is proportional to the input acceleration. Therefore, by measuring the current value flowing through the torque coil when the torque balance is measured, the motion acceleration of the carrier along the input shaft of the accelerometer can be measured.

The main technical indicators are as follows:

Measuring range: -20g~+20g;

Threshold: no more than 5×10-6g;

Scale factor monthly repeatability: no more than 3.5×10-5 (1σ);

Scale factor temperature coefficient: no more than 6 × 10 -5 / ° C (-40 ° C ~ +60 ° C);

Second-order nonlinear coefficient: not more than 3×10-5g/g2;

Offset value: no more than 6×10-3g;

Deviation temperature coefficient: not more than 2.5×10-5g/°C (-40°C~+60°C);

Partial monthly repeatability: no more than 2.5×10-5g (1s);

Bandwidth: not less than 800Hz.


2, performance indicators

The Land Positioning Orientation System includes a variety of navigation modes that can be combined with GPS to form a navigation system.

2.1 pure navigation mode

The initial alignment of the land positioning and orientation system is divided into two methods: single-position static alignment and dual-position alignment. The two-position alignment method has higher positioning accuracy than the single-position static alignment method.

Azimuth alignment accuracy: ≤0.01°sec (Φ) (1σ, Φ is the local latitude);

Horizontal attitude alignment accuracy: ≤0.02° (1σ);

Azimuth retention accuracy: 0.05 ° / h;

Horizontal attitude maintaining accuracy: 0.03 ° / h.

Positioning accuracy (50% CEP): ≤ 2nm / h (10min static alignment);

Horizontal speed accuracy (RMS): ≤ 2m / s (10min static alignment);

Positioning accuracy (50% CEP): ≤1nm/h (double position alignment, alignment time less than 30min);

Horizontal speed accuracy (RMS): ≤ 1 m / s (double position alignment, alignment time less than 30 min).

2.2 GPS-assisted navigation mode

Azimuth alignment accuracy: ≤0.01°sec (Φ) (1σ, Φ is the local latitude);

Horizontal attitude alignment accuracy: ≤0.02° (1σ);

Bearing accuracy: ≤0.05°sec (Φ) (1σ, Φ is the local latitude);

Horizontal attitude maintaining accuracy: ≤0.01° (1σ).

Positioning accuracy: ≤ 5m (1σ);

Speed accuracy: ≤0.1m/s (1σ).

2.3 Other

Dimensions: 330mm × 330mm × 315mm;

Quality: less than 20kg;

Data measurement frequency: maximum 100Hz;

Power supply: 23 ~ 31V DC power supply, nominal supply voltage 27V;

Power consumption: power consumption is less than 50W;

Operating temperature: -40 ° C ~ +60 ° C;

Storage temperature: -45 ° C ~ +80 ° C.


3, initial alignment

The alignment process of the land positioning and orientation system is divided into two stages: coarse alignment and fine alignment.

3.1 coarse alignment

The first 130s after power-on of the inertial navigation system is the coarse alignment phase. In order to obtain better alignment effect, it is best to ensure that no acceleration motion is performed at this stage, but the rocking motion (such as the vehicle idle state) is not limited.

3.2 Fine alignment

After 130s, the inertial navigation system is automatically transferred to the fine alignment stage.

Fine alignment uses a two-position alignment algorithm, which means that the product heading needs to be changed twice during the alignment process. In order to ensure that the alignment reference information (GPS/DVL) is valid, the carrier can perform unrestricted motion, but in order to achieve higher alignment accuracy, the following fine alignment route is recommended: the inertial navigation system is energized for about 10 minutes. In one heading maneuver (changing 70° or more), the second maneuver is carried out around the 20th minute (the carrier heading returns to the forward target direction), and the maneuvering process is shown in Figure II-1.

Figure 5 Schematic diagram of the recommended alignment

If the reference information is invalid, the heading can be changed in situ to perform fine alignment.

The precision alignment time is 1400~1600s. If the reference information is invalid, the alignment time is extended accordingly.


4, interface definition

4.1 Coordinate system definition

Carrier coordinate system (b system)──: The origin O of the carrier coordinate system is selected at the inertial center, the axis is the front of the vertical axis, and the axis is the horizontal axis to the right, forming the right-hand coordinate system. The gyroscope and accelerometer are installed in accordance with the carrier coordinate system.

Figure 6 Schematic diagram of the coordinate system definition

Geographical coordinate system (t system)──: The origin O of the geographic coordinate system is selected at the center of gravity of the carrier, pointing to the north, pointing to the sky in the vertical direction, pointing to the east.

Navigation coordinate system (n system)──: The navigation coordinate system coincides with the geographic coordinate system.

When the land positioning and orientation system is mounted on the carrier, the X axis should be consistent with the longitudinal axis of the carrier, and the Y axis should be pointed to the sky.

Figure 8 Installation of the land positioning and orientation system on the carrier

The attitude angles of the land positioning and orientation system are defined as shown in Figure II-5:

Heading

Counterclockwise is positive, clockwise is negative

-180 o ~ +180 o

Pitch angle

Head up is positive, head down is negative

-90 o to 90 o

Rolling angle

Right is positive and left is negative

-180 o to 180 o

Figure 9 attitude angle definition

4.2 Electrical interface

The product uses a J30J series connector manufactured by a 158 factory and an SMA socket as an external connector.

The detailed description of the land positioning and orientation system is shown in Table 1.

Table 1 Land location orientation system definition of external points

SMA
Point number Signal Point number Signal
A GPS signal B Ground
J30J-37ZKP
Point number Signal Point number Signal
1
A communication port 422 receives positive 12
C communication port 422 receives positive
2 A communication port 422 receives negative 13 C communication port 422 receives negative
3 A communication port 422 sends positive 14 C communication port 422 sends positive

4

A communication port 422 sends a negative 15 C communication port 422 sends a negative
5 A communication port 16 C communication port
6 communication port 422 receiving 17 --
7 D communication port 422 sends 18 Odometer pulse signal +
8 D communication port 19 --
9 -- 20 --
10 Navigation data output sync pulse twenty one Odometer pulse signal -
11 Navigation data output synchronization pulse twenty two --
Note: Unmarked point definitions are reserved for disabling.

The communication port D is used as a monitoring port and is used to set the system. The baud rate is fixed at 38400 bps. Communication ports A and C are used for navigation information output, and can be set to RS-422 at the factory according to need. The baud rate of communication port A~C can be set through the monitoring port (communication port D), where RS-422 can be

The communication port D is used as a monitoring port and is used to set the system. The baud rate is fixed at 38400 bps. Communication ports A and C are used for navigation information output, and can be set to RS-422 at the factory according to need. The baud rate of communication ports A~C can be set through the monitoring port (communication port D), where RS-422 can be selected between 9600, 19200, 38400, 57600, 115200, 460800, 614400, 1843200, where RS-422 The baud rate can only be up to 115200bps.

4.3 Thermal Interface

The land positioning and orientation system is powered by a 23V to 31V DC power supply with a nominal supply voltage of 27V. In the 27V power supply normal temperature environment, the steady-state power consumption is less than 17W, the full-temperature steady-state power consumption is less than 20W, the startup transient power consumption is less than 50W, and the startup transient width is less than 1ms.

The six aspects of the land positioning and orientation system are all metal structures, and the heat is mainly transmitted through the bottom surface. The stability of the ambient temperature has a certain influence on the stability of the output accuracy of the land positioning and orientation system. To ensure the output accuracy of the land positioning and orientation system, it is recommended that:

l Require users to use the metal surface with good heat dissipation or large heat capacity as the mounting surface of the land positioning and orientation system. The mounting surface is in good contact, and thermal grease can be used if necessary;

l Try to provide a temperature-stable environment away from heat sources or other objects with fast temperature changes.


5, the scope of use

The product is based on high-precision fiber optic gyroscope and quartz accelerometer as the core components, mainly composed of inertial measurement unit, data acquisition and processing unit, precision indexing mechanism and control display unit. At the same time, according to the use characteristics, GPS/ Components such as GNSS/BD receivers, odometer sensors, altimeters and star sensors provide both the azimuth of the carrier and true north, as well as the motion attitude, velocity and position information of the carrier. The product can be used for missile launch, weapon aiming, and dynamic and static initial alignment and direction control of radar, antenna, vehicle and other objects.



6, software description

Land acquisition system acquisition software

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