KR100447243B1 - Aircraft Attitude Measurement using the Difference of Atmospheric Pressures - Google Patents

Abstract

The present invention relates to a system for measuring the attitude of the aircraft by measuring the pressure difference between the atmospheric pressure measurement holes installed on both sides of the wing or the front and rear of the aircraft, using an inexpensive pressure sensor without the attitude error at a wide altitude of the aircraft It is to be able to measure posture.

Basically, as the altitude rises, the pressure difference per unit altitude decreases, but when the air pressure is over 6,000m, the pressure difference is 6.35 Pa / m. There is a number.

Although the accuracy of the general altitude sensor is a few m, it is not suitable for measuring the attitude of the aircraft, but if a precise differential pressure sensor is used, it can be used in a narrow range of about 500 m. The error can be used without diverging.

The present invention has a strong characteristic against interference by predicting the attitude angle only by the sensor information inside without diverging accumulated attitude errors in principle of the sensor system.

Description

Aircraft Attitude Measurement using the Difference of Atmospheric Pressures}

The present invention relates to a system for measuring the attitude of the aircraft by measuring the pressure difference between the atmospheric pressure measurement holes installed on both sides of the wing or the front and rear of the aircraft, using an inexpensive pressure sensor without the attitude error at a wide altitude of the aircraft It is to be able to measure posture.

For aircraft to fly automatically, the attitude of the aircraft is required. For conventional aircraft, the vertical gyro, attitude attitude and heading reference system (AHRS), and the Inertial Navigation System (INS) provide attitude information. , GPS / INS and other systems are used.

In general, a gyro used in an aircraft uses a high-precision gyro, which is a high precision gimbal mechanical gyro, and a navigation system composed of a ring laser gyro (RLG) and a fiber optic gyro (FOG) provides attitude information.

Such systems are very expensive and have limitations in their application to low cost drones.

In addition, every angle prediction system that calculates angles using a strap gyro using a rate gyroscope has to continuously perform error correction as the angle errors are accumulated.

As the drone market expands, low-cost attitude information providing systems have begun to develop.

Examples include a strap-down vertical gyro combined with a gravitational field using a rate gyro that causes hundreds to tens of degrees of error per hour, a low-cost rate gyro, an accelerometer, and a GPS / INS system with GPS.

The strap-down vertical gyro, which combines a coarse rate gyro and an accelerometer, uses the earth's gravity to correct the attitude.

Therefore, it cannot be applied to low-cost, low-cost and small drones that measure weather data under strong turbulence.

In general, it is known that the rate gyro and GPS can be used to maintain the attitude of the aircraft inaccurately, but automatic flight is very difficult under strong turbulence.

As such, the coarse rate gyro has very low accuracy and must perform posture correction within a few tens of seconds.

When the airplane performs the non-accelerated flight movement, the gravity sensor is used to measure the direction of gravity and the attitude information of the plane is acquired. Therefore, in order to acquire the attitude information for the posture correction operation, the flight movement must be restricted.

In the case of drones, it is difficult to expect non-accelerated gravitational movement in general because they are constantly changing their attitude. Especially, when a small drone is flying in turbulent conditions, it is known that the aircraft receives about 4g of acceleration. There is a difficulty.

In addition, the combination of the rate gyro and the accelerometer requires a calibration process using a high-precision rate table, and thus, the unit price of the product is very expensive (10 KUS $).

A low-cost GPS / INS system that combines a coarse rate gyro, accelerometer, and GPS receiver, like a strapdown vertical gyro that combines a coarse rate gyro and an accelerometer, uses a coarse rate gyro, resulting in very high posture error and within a few seconds Posture correction must be performed.

In general, GPS signals can be disconnected, and after they are disconnected, they must receive a good GPS signal for at least 15 seconds to obtain reliable position and speed information.Therefore, there is a limit to using a coarse rate gyro. There is a need for a system that installs and integrates GPS antennas in multiple locations so that they can be used or disconnected from the GPS signal.

In addition, the combination of the rate gyro and the accelerometer requires a calibration process using a high-precision rate table.

In particular, the use of multiple GPS antennas may facilitate GPS jamming from the outside, requiring effective GPS antenna switching depending on the attitude of the aircraft.

The present invention has been devised to solve this problem, by measuring the atmospheric pressure difference on the left and right sides of the wing and by measuring the attitude of the wing, the phenomenon of error divergence of the wing attitude does not occur in principle.

In addition, by using a cheap pressure sensor can be applied to low-cost unmanned aerial vehicles.

The present invention comprises at least two or more pressure measuring means mounted on the left and right of the wing of the aircraft to measure the static pressure through the atmospheric pressure connection pipe and a mounting computer for calculating the attitude angle with the static pressure measured by the pressure measuring means.

1 is a conceptual diagram of altitude measurement and attitude determination of the left and right of an aircraft wing of the present invention

Figure 2 is a conceptual diagram of altitude measurement and attitude determination of the left and right of the aircraft wing using a high precision absolute barometer in the present invention

Figure 3 is a conceptual diagram of measuring the pressure difference between the left and right of the aircraft wing and attitude determination using two high-precision differential pressure gauge in the present invention

4 is an operation state diagram showing the opening and closing of the valve according to the altitude when using two high-precision differential pressure gauge of FIG.

5 is a conceptual diagram of the pressure difference measurement and attitude determination of the left and right of the aircraft wing using four high-precision differential pressure gauge in the present invention

6 is an operating state diagram showing the opening and closing of the valve according to the altitude when using two high-precision differential pressure gauge of FIG.

7 is a conceptual diagram showing the pressure difference between the left and right of the aircraft wing and attitude angle in the present invention

{Description of symbols for main parts of the drawing}

1: upper surface of the wing of an aircraft

2, 3: atmospheric pressure connecting pipe

4: onboard computer

5, 6: wire connecting the output of the pressure measuring means to the onboard computer

10: pressure measuring means

10a: high precision absolute barometer

10b: high precision differential pressure gauge

11, 12, 13, 14: valve

15, 16: valve drive wire

The present invention relates to a system for measuring the attitude of the aircraft by measuring the pressure difference between the atmospheric pressure measurement holes installed on both sides of the wing or the front and rear of the aircraft, using an inexpensive pressure sensor without the attitude error at a wide altitude of the aircraft It is to be able to measure posture.

The present invention is mounted on the left and right wing of the aircraft as shown in Figure 1 at least two or more pressure measuring means 10 for measuring the static pressure through the atmospheric pressure connection pipe (2) (3), and in the pressure measuring means 10 It consists of an onboard computer 4 which calculates the attitude angle with the measured pressure.

Figure 2 is a system for measuring the attitude of the aircraft using a high-precision absolute barometer (10a) pressure measuring means attached to both sides of the wing as a current technology, it is impossible to precisely measure a wide range of altitude, but the non-consumable unmanned aerial vehicle It is possible to enter the deep roll position of the player and prevent it from falling out of automatic control.

If only the low altitude signal is amplified and used in the absolute barometer 10a, the automatic drone can be prevented from falling into the deep roll attitude of the drone.

3 and 5 show a system using the high-precision differential pressure gauge 10b for the pressure measuring means 10. When the valves 11, 12, 13 and 14 are open, the differential pressure gauge 10b is absolute as shown in FIG. It operates in the same way as the barometer 10a, but when the valve is closed, the inner pressure of the differential pressure sensor is fixed and the outer side connected to the atmosphere changes according to the atmospheric pressure, so that a relative pressure difference can be obtained if necessary. If a port of 10b) is closed with a valve, the differential pressure gauge 10b operates in the same manner as the gauge pressure gauge, so that even the 1 cm altitude difference, which is difficult to measure with the absolute barometer 10a, can be measured using the advantages of the precision differential pressure gauge 10b. .

In FIG. 3, a 1 cm altitude difference can be measured using a ± 3,000 Pa differential pressure sensor in the case of a 200 m altitude displacement. In FIG. 5, two systems (differential pressure sensors) are simultaneously mounted at both ends of a wing, and two systems are used as shown in FIG. 6. If outside the operating range of the first system, the second system is activated before leaving the first system operating range, and the second system is operated out of the first system operating range. If you use the system of 200m altitude alternately, you can measure 1cm altitude difference for all altitudes.If you use the system several times, the accuracy may be reduced, but if the aircraft is equipped with low-cost Yaw Rate sensor, you can easily prevent the attitude divergence. The principle of attitude divergence is that when the aircraft is flying horizontally, the yaw rate is '0'. do.

In FIG. 3, when using one differential pressure sensor on both sides of a wing, a low-cost low cost drone has no problem with horizontal flight, but there is a risk of entering into a deep roll angle during a turning flight. In a turning flight, the valve is locked and a differential pressure is measured to predict a roll angle. When used as an autopilot system, it can turn stably.

5 shows the use of two differential pressure sensors on both sides of the vane, when one differential pressure sensor is used, the valve of the other differential pressure sensor is opened, and the valve of the other differential pressure sensor is locked when the differential pressure sensor exceeds the maximum input range. Measure

Thus, alternating measurements can be used extensively over a wide range of altitudes.

As such, the roll angle can be measured by mounting the pressure sensor at the tip of the wing, and can also measure the pitch angle when installed in front and rear of the aircraft, and when used in combination with a posture measuring system, accelerometer, and GPS receiver using a pressure sensor. Errors in the measurement system can also be corrected while flying.

Looking at the measurement of the atmospheric pressure difference of the wing tip of the small unmanned aerial vehicle and predicting the tilt of the wing in the present invention, when the wing of the small unmanned aerial vehicle, which is a rigid body, is tilted, the relation is as follows.

Where b is the wing span, The wing tip height difference, Indicates the tilt of the wing.

At this time, the height difference of the wing tip is calculated as follows.

here Pressure difference at the tip of the wing, Is the air density at flight altitude, g is the acceleration of gravity (9.8 m / sec ² ).

At flight altitude, atmospheric density is obtained from the gas state equation.

Where P is atmospheric pressure (Pa), T is atmospheric temperature (° K), and R is air gas constant (287).

As such, when the atmospheric pressure, the atmospheric temperature, and the pressure difference between the blade tip at the flight altitude are measured, the slope of the blade may be calculated using Equations 1, 2, and 3.

For example, if the drone with a wingspan of 3m flying at an altitude of 1,200m turns at a constant posture angle, and the difference between the pressure gauges installed at both ends is 0.105 Kg / m ^{2, the} roll angle θ is calculated as follows.

First, the air density in the standard atmospheric equation of Equation 3 at an altitude of 1,200 m can be obtained as follows.

Therefore, wing length b = 3m, gravitational acceleration g = 9.8m / sec ² , pressure difference If you find the roll angle

That is, the attitude angle of the aircraft can be obtained by measuring the differential pressure of the pressure gauge installed at both ends of the wing because the knowing the density, wing length, and gravity acceleration values according to the altitude.

Looking at the resolution according to the altitude change required by the present invention, the precision of the attitude angle of the aircraft is enough to fall within ± 0.3 degrees.

If the wing length of a small drone is assumed to be 300cm, the resolution is 1.57cm.However, if the wing attitude is used to enhance the automatic turning stability of the small consumable drone, a resolution of about 5 degrees can be used. The case requires a resolution of around 26cm.

First, if you look at the resolution of the absolute barometer to measure the atmospheric pressure at the tip of the aircraft wing, the atmospheric pressure according to the altitude in the standard atmosphere is as follows.

Table 1. Atmospheric pressure values with altitude in standard atmosphere

Altitude (m) Atmospheric pressure (Pa) Pressure change per meter (Pa) (density x gravity acceleration) 0 101,325 11.84 1,200 87,718 10.53 2,400 75,634 9.33 3,600 64,939 8.24 4,800 55,506 7.25 6,000 47,217 6.35 9,900 26,906 4.10 15,000 12,112 1.91 18,900 6,570 1.04

To measure with 1cm accuracy up to 9,900m, the pressure measurement accuracy can be obtained as follows.

Required pressure precision = pressure change per meter (4.10 Pa) at 9,900m altitude / 100cm = 0.041Pa

Required pressure sensor resolution = (atmospheric pressure (101,325Pa) at 0m-atmospheric pressure (26,906Pa) at 9,900m) / required pressure precision (0.041 Pa) = 1,815,097 resolution

As such, a precision altimeter with a million-fold resolution has not been developed in reality.

To measure up to 1,200 m with an accuracy of 1 cm, the pressure measurement accuracy can be obtained as follows.

Required pressure accuracy = pressure change per meter (10.53Pa) at 1,200m altitude / 100cm = 0.105Pa

Required pressure sensor resolution = (atmospheric pressure (101,325Pa) at 0m-atmospheric pressure (87,718Pa) at 1,200m) / required pressure precision (0.105 Pa) = 13,607 resolution

The circuit can be configured to generate 0 to 5 volt electrical signals when the output of the barometric pressure sensor changes from 0m to 1200m, so that a 14-bit analog-to-digital converter can have sufficient resolution, so it can be applied to low altitude and small unmanned aerial vehicles.

In the attitude measurement system using a differential pressure gauge in FIGS. 3 and 5, a sensor capable of detecting a change of 1 cm in altitude by an aircraft flying at an altitude of ± 200 m at an altitude should be a sensor having a resolution of 20,000 times.

When using a 16-bit analog-to-digital signal converter, resolution can be 65,535 times, so a resolution of 20,000 times is sufficient. The signal resolution of the differential pressure sensor may satisfy the required resolution.

Air is denser at low altitudes, so maximum pressure changes occur from 0m to 200m.

The maximum pressure change is 11.84 Pa / m x 200 m = 2,368 Pa. Differential pressure gauges with a maximum pressure range of ± 3,000 Pa allow for accurate detection of pressure changes at the tip of the vane.

Looking at the dynamic response characteristics (Bandwidth) in the present invention, when the distance from the pressure hole to the pressure sensor is long, the dynamic response characteristics are lowered, but within 5m, it is possible to maintain the several Hz response characteristics required for a normal aircraft automatic flight system. The response characteristic of the differential pressure sensor is more than a few hundred Hz, and the most problematic part is the problem of pipe diameter and length connecting the differential pressure sensor and atmospheric pressure.

Large pipe diameters and short lengths provide fast response characteristics. Therefore, pipes typically used in aircrafts can achieve response characteristics of 10 Hz or more. Short cycle movements on small aircraft should also be fast, so there is no problem with the automatic steering system at 1-2Hz.

In case of requiring very fast response, high-speed response can be obtained by using rate gyro fusion.

The present invention can obtain attitude information by utilizing a pressure sensor which is a very low-cost sensor without using advanced sensors such as a GPS receiver, a rate gyroscope and an accelerometer.

The present invention has a strong characteristic against external disturbances by predicting the attitude angle only by internal sensor information without the emission of accumulated attitude errors due to the principle of the sensor system.

This invention will be applied to the automatic steering system of low-cost consumable drone will contribute to the increase in the civilian drone market.

Claims (4)

At least two pressure measuring means (10) mounted on the left and right sides of the aircraft and measuring the static pressure through the atmospheric pressure connecting pipes (2) and (3), and the attitude angle is calculated by the static pressure measured by the pressure measuring means (10) Attitude measurement system of the aircraft using the atmospheric pressure difference, characterized in that consisting of a mounted computer (4). The system of claim 1, wherein the pressure measuring means (10) comprises an absolute barometer (10a) for measuring atmospheric pressure. The pressure measuring means (10) according to claim 1, wherein the pressure measuring means (10) is a valve (11) for controlling the pressure difference between the differential pressure gauge (10b) for measuring the static pressure difference and the differential pressure gauge (10b) by a control signal of the onboard computer (4). 12) (13) (14) characterized in that the aircraft attitude measurement system. 4. The system of claim 3, wherein the valve (11) (12) (13) (14) is configured to control the pressure difference between the differential pressure gauges (10b) by opening and closing alternately according to the altitude.