TW202201159A - Method for determining airspeed and flying control system - Google Patents

Abstract

A method for determining airspeed and a flying control system using the method are disclosed. The method contains the steps of: a) continuously recording acceleration values in three mutually perpendicular directions of a flying vehicle in a time interval using a three-axis accelerometer; b) obtaining a first airspeed value along the flight direction of the flying vehicle with an airspeed meter; c) calculating a second airspeed value along the flight direction of the flight vehicle with the three acceleration values obtained at the moment; d) subtracting the first airspeed value from the second airspeed value to obtain an absolute difference; e) determining whether a ratio of the absolute difference to the second airspeed value falls within an allowable range; and f) when the ratio falls within the allowable range, the airspeed of the flying vehicle is set to be the first airspeed value, or when the ratio falls out of the allowable range, the airspeed of the flying vehicle is set to the second airspeed value. The invention utilizes the calculation results of the three-axis accelerometer to determine if the airspeed meter is still in correct function. If not, replace it with the result from the three-axis accelerometer. It can also be calibrated by the GPS signals. This arrangement provides a steady air speed data to flight computer to ensure flight safety.

Description

Method and flight control system for determining airspeed

The present invention relates to a method for determining airspeed and a flight control system using the method, in particular to a method for determining airspeed by comparing and calculating the data of a three-axis accelerometer and a traditional airspeed meter, and a flight control system using the method .

Since the Wright brothers created the prototype of the first aircraft in history, flying in the sky is no longer an unreachable dream. After more than 100 years of research and improvement, whether it is payload weight, sailing distance, maximum flight altitude or even flight safety, the flight capability of the aircraft has been greatly increased. Traditionally, these flight capabilities have been achieved by mechanical operation and pilot experience. However, as the aircraft has entered the era of unmanned aircraft, the flight of drones does not need to rely on human experience, but requires the use of more automated electronic equipment.

In terms of airspeed calculation related to flight speed, general drones will use physical airspeed meters, such as pitot tubes, to complete, and the corresponding automated electronic device is a three-axis accelerometer. The three-axis accelerometer is a micro-electromechanical product. After calibration, it can maintain the detection of the three-axis acceleration of the aircraft for a period of time. Therefore, the current speed of the drone can be obtained by integrating the acceleration. However, due to usage habits, triaxial accelerometers are not widely used in airspeed calculations. Of course, the airspeed can also be calculated directly using the GPS signal obtained by the global positioning system (Global Positioning System, GPS) signal receiver. Although the results are the closest to reality (within 0.2 km/h), the GPS signal update rate is about once per second, which is much lower than the sampling rate of triaxial accelerometers and airspeed meters, and is easily affected by weather. It cannot be detected and cannot be directly applied to the flight control computer of the drone. However, historically, there are records of crashes due to physical factors (such as freezing or altitude difference) causing the airspeed meter to malfunction, which in turn caused the flight computer to misjudge the current state of the aircraft many times. In the case of drones, this potential danger also exists, so the assistance of other equipment is required.

Although the three-axis accelerometer has accuracy problems, other auxiliary methods can be used to reduce the problem of accuracy degradation (such as correction with the speed value obtained by GPS). The speed of the drone is determined by the meter, so the result will be quite close to the real and stable, which can ensure the flight safety. The present invention proposes related methods and applications to increase the safety of the flight control system.

This text extracts and compiles certain features of the invention. Other features will be disclosed in subsequent paragraphs. It is intended to cover various modifications and similar permutations and combinations within the spirit and scope of the appended claims.

In order to meet the aforementioned requirements, the present invention proposes a method for determining airspeed, comprising the steps of: a) using a three-axis accelerometer to continuously record the acceleration values in three mutually perpendicular directions of the flying vehicle at a time interval; b ) obtain a first airspeed value along the flight direction of the aircraft with an airspeed meter; c) calculate a second airspeed along the flight direction of the aircraft by integrating the three currently obtained acceleration values and the time interval d) subtract the first airspeed value from the second airspeed value to obtain an absolute difference value; e) determine whether a ratio of the absolute difference value to the second airspeed value falls within an allowable range and f) set the airspeed of the aircraft to the first airspeed value when the aforementioned ratio falls within the allowable range, or set the airspeed of the aircraft to the first airspeed value when the aforementioned ratio falls outside the allowable range is set to the second airspeed value.

The method for determining airspeed may further include steps after step f): g) calculating a third airspeed value using GPS signals obtained by a global positioning system (Global Positioning System, GPS) signal receiver, and using the third airspeed value The airspeed value corrects the result of the triaxial accelerometer integration and replaces the second airspeed value; and h) repeats steps a) through f).

The method for determining airspeed may further include steps after step f): i) repeating step a) to step f), if the first airspeed value of the airspeed meter and the second airspeed value of the airspeed meter are within a preset failure time If the absolute difference between the airspeed values falls outside the allowable range, it is determined that the airspeed meter is invalid, and the airspeed is set as the second airspeed value.

According to the present invention, the allowable range may be between 0.5% and 5%.

The invention also discloses a flight control system. The flight control system is installed in an air vehicle, and includes: a three-axis accelerometer, which continuously records acceleration values in three mutually perpendicular directions of the air vehicle at a time interval; an airspeed The airspeed meter can obtain a first airspeed value along the flight direction of the aircraft; and a calculation module is connected with the three-axis accelerometer and the airspeed meter signal to obtain the acceleration values , the first airspeed value, calculate a second airspeed value along the flight direction of the aircraft by integrating the three acceleration values obtained at the moment and the time interval, and determine the difference between the absolute difference value and the second airspeed value Whether a ratio falls within an allowable range, and when the aforementioned ratio falls within the allowable range, the airspeed of the aircraft is set to the first airspeed value, or when the aforementioned ratio falls outside the allowable range , the airspeed of the aircraft is set to the second airspeed value.

The flight control system may further include a global positioning system signal receiver, which is connected with the signal of the computing module to obtain the GPS signal and transmit it to the computing module, so that the computing module uses the GPS signal to calculate a third space The third airspeed value is used to correct the result of the triaxial accelerometer integration and replace the second airspeed value. If the absolute difference between the first airspeed value and the second airspeed value of the airspeed meter falls outside the allowable range within a failure time, the calculation module determines that the airspeed meter is invalid and sets the airspeed as the second airspeed value.

According to the present invention, the allowable range may be between 0.5% and 5%.

The invention uses the integral calculation result of the three-axis accelerometer to determine the correctness of the airspeed meter, and uses the GPS signal calculation result to correct the three-axis accelerometer, so that the final determined airspeed is the closest to the real and stable.

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

Please refer to FIG. 1 , which is a schematic diagram of a flight control system according to an embodiment of the present invention. The flight control system is installed in a flying vehicle 1 (such as an unmanned aerial vehicle), and is independent of the power system (not shown), and basically includes a three-axis accelerometer 10 , an airspeed meter 20 , a computing module 30 and A GPS signal receiver 40 . The functions and combined operation of these components are described below.

The three-axis accelerometer 10, as mentioned above, is an electronic (micro-electromechanical) product, which records the time in three mutually perpendicular directions by the change of the electromagnetic field generated by the relative displacement of the internal components under the action of gravity and other accelerations. the acceleration value. The triaxial accelerometer 10 is not limited in its accuracy. In practice, the triaxial accelerometer 10 continuously provides its own acceleration values in three mutually perpendicular directions at a fixed sampling rate. As far as the existing three-axis accelerometer products are concerned, the sampling rate is between 100-200Hz. At the aforementioned sampling rate, the time interval is about 5-10 milliseconds. Since the triaxial accelerometer 10 is installed on the flying vehicle 1 , it can continuously present the acceleration values of the flying vehicle 1 in three mutually perpendicular directions at the aforementioned time interval.

The function of the airspeed meter 20 is to obtain a first airspeed value along the flight direction of the aircraft 1 . In this embodiment, the airspeed meter 20 is formed by combining a pitot tube and a signal transmission device. In accordance with the spirit of the present invention, the airspeed meter 20 may also be other types of non-pure electronic physical airspeed measurement devices. In practice, the sampling rate of the airspeed meter 20 is around 100 Hz.

The calculation module 30 is connected with the signals of the three-axis accelerometer 10 and the airspeed meter 20 , and can obtain the acceleration values and the first airspeed value, and calculate the time interval along the flight vehicle 1 based on the three acceleration values obtained at the moment and the time interval. A second airspeed value for the direction of flight. Here, the second airspeed value is completely a value obtained by calculation, and there are two ways. Assuming that the acceleration values of the three-axis accelerometer 10 in three mutually perpendicular directions are respectively a _x , a _y and _az , the time interval is Δt, and the current speed during integration is V, the second airspeed value can be ( a _x ² + a _y ² + a _z ² ) ^1/2 x Δt + V, or ((a _x x Δt) ² + (a _y x Δt) ² + ( _az x Δt) ² ) ^1/2 +V. Because Δt is small, the two are basically the same.

In addition, the calculation module 30 can determine whether a ratio between the absolute difference value and the second airspeed value falls within an allowable range. According to the present invention, the data of the three-axis accelerometer 10 is used to judge whether the data of the airspeed meter 20 is available. Although the airspeed meter 20 is mainly used to obtain the current airspeed along the flight direction of the flight vehicle 1 , it may output wrong or large error data due to factors such as freezing ice and damage to the internal transmission line. The determination of whether the data of the airspeed meter 20 is available is achieved by the ratio of the absolute difference to the second airspeed value. Regardless of the combination of the three-axis accelerometer 10 and the airspeed meter 20 (difference in accuracy), the calculated ratio will develop toward a larger direction. If the second airspeed value can be corrected, the ratio can fall within the aforementioned tolerance range, thereby maintaining the ability to determine whether airspeed gauge 20 data is available. In principle, if the airspeed meter 20 is OK, the first airspeed value can be used as the airspeed of the vehicle 1; if there is a problem with the airspeed meter 20, the second airspeed value can be used to temporarily replace the airspeed airspeed until the cause of the transient error in the airspeed meter 20 is eliminated. Therefore, the calculation module 30 can set the airspeed of the flight vehicle 1 to the first airspeed value when the aforementioned ratio falls within the allowable range, or set the airspeed of the flight vehicle 1 to the first airspeed value when the aforementioned ratio falls outside the allowable range. An airspeed of 1 is set to this second airspeed value. After experiments, according to different combinations of triaxial accelerometers and airspeed meters, the allowable range can be set between 0.5% and 5%, such as 2%. That is, if the ratio of the absolute difference obtained by subtracting the first airspeed value from the second airspeed value to the second airspeed value is less than or equal to the allowable range (2%), the airspeed is the first airspeed value; the absolute difference value If the ratio to the second airspeed value is greater than the allowable range (2%), the airspeed is the second airspeed value.

The GPS signal receiver 40 is connected with the signal of the computing module 30 to obtain the GPS signal and transmit it to the computing module 30 . Therefore, the calculation module 30 can use the GPS signal to calculate a third airspeed value. The technique of calculating velocity from GPS signals is common and is not limited by the present invention. Generally speaking, the use of GPS signals to calculate airspeed is the most accurate, but the update speed of GPS signals is much lower than the sampling rate of triaxial accelerometers and airspeed meters, and it is easily affected by weather and cannot be detected, so it cannot replace triaxial accelerometers10 To judge the correctness of the airspeed meter 20. Therefore, if the GPS signal receiver 40 can obtain the GPS signal, if a more accurate third airspeed value is calculated in real time, the third airspeed value can be corrected and replaced with the second airspeed value.

Consider a situation: if the erroneous state of the airspeed meter 20 persists and cannot be restored to normal, the airspeed meter 20 is not necessary to be used during the flight of the aircraft 1 . Based on this, when the calculation module 30 continues to correct the second airspeed value, it also monitors the state of the airspeed meter 20 at the same time. If the absolute difference between the first airspeed value and the second airspeed value of the airspeed meter 20 falls outside the allowable range within a failure time, the calculation module 30 determines that the airspeed meter 20 is invalid, and will Airspeed is set to the second airspeed value (of course, the second airspeed value may also be replaced by the third airspeed value and thus corrected). For example, if all calculated absolute differences within 10 seconds (failure time) fall outside the allowable range, the airspeed meter 20 is judged to fail. The length of the failure time can be set according to the flight speed or airspace characteristics of the air vehicle 1 .

According to the above flight control system, the present invention also provides a method for determining the airspeed. Please refer to Figure 2, which is a flow chart of the aforementioned method of determining airspeed. The method includes the following steps. First, the first step is to use a three-axis accelerometer to continuously record acceleration values in three mutually perpendicular directions of the flying vehicle at a time interval ( S01 ). Next, the second step is to obtain a first airspeed value along the flight direction of the aircraft with an airspeed meter ( S02 ). The third step is to integrate a second airspeed value along the flight direction of the aircraft based on the three currently obtained acceleration values and the time interval ( S03 ). The fourth step is to subtract the first airspeed value from the second airspeed value to obtain an absolute difference ( S04 ). Next, the fifth step is to determine whether a ratio between the absolute difference value and the second airspeed value falls within an allowable range ( S05 ). The allowable range can be between 0.5% and 5% as previously mentioned. Finally, the sixth step is to set the airspeed of the flying vehicle to the first airspeed value when the aforementioned ratio falls within the allowable range, or set the airspeed of the flying vehicle to the first airspeed value when the aforementioned ratio falls outside the allowable range The airspeed of the vehicle is set to the second airspeed value (S06).

In order to correct the airspeed comparison or the second airspeed value, the method for determining the airspeed may further include the step after step ( S06 ): calculating a third airspeed using GPS signals obtained by a global positioning system signal receiver The third airspeed value is used to correct the integrated result of the three-axis accelerometer, and replace the second airspeed value ( S07 ); and steps ( S01 ) to ( S06 ) ( S08 ) are repeated. The purpose of step S08 is to replace the second airspeed value with the third airspeed value calculated by the GPS signal, and continue to determine whether the data of the airspeed meter is available and whether the airspeed meter is in a normal state. Of course, after step S08, steps S07 and S08 may be executed again, and at this time, the updated third airspeed value is brought in to replace the previous third airspeed value.

In order to determine whether the airspeed meter is really unusable, the method for determining the airspeed may further include steps after step ( S06 ): repeating steps ( S01 ) to ( S06 ), if the airspeed meter’s If the absolute difference between the first airspeed value and the second airspeed value falls outside the allowable range, it is determined that the airspeed meter is invalid and the airspeed is set to the second airspeed value ( S09 ).

Although the embodiments of the present invention have been shown and described above, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principle and spirit of the invention Variations, the scope of the invention is defined by the appended claims and their equivalents.

1: Flying vehicle 10: Three-axis accelerometer 20: Airspeed meter 30: Computing Module 40: GPS signal receiver

FIG. 1 is a schematic diagram of a flight control system according to an embodiment of the present invention, and FIG. 2 is a flowchart of a method for determining airspeed.

1: Flying vehicle

10: Three-axis accelerometer

20: Airspeed meter

30: Computing Module

40: GPS signal receiver

Claims (8)

A method of determining airspeed, consisting of the steps: a) Use a three-axis accelerometer to continuously record the acceleration values in three mutually perpendicular directions of the flying vehicle at a time interval; b) obtaining a first airspeed value along the flight direction of the aircraft with an airspeed meter; c) Calculate a second airspeed value along the flight direction of the aircraft by integrating the three acceleration values obtained at the moment and the time interval; d) subtracting the first airspeed value from the second airspeed value to obtain an absolute difference; e) determine whether a ratio of the absolute difference to the second airspeed value falls within an allowable range; and f) When the aforementioned ratio falls within the allowable range, set the airspeed of the aircraft to the first airspeed value, or when the aforementioned ratio falls outside the allowable range, set the airspeed of the aircraft to the first airspeed value Set to this second airspeed value. The method for determining airspeed as described in item 1 of the claimed scope further comprises steps after step f): g) Calculate a third airspeed value using the GPS signal obtained by a Global Positioning System (GPS) signal receiver, and use the third airspeed value to correct the result of the three-axis accelerometer integration, and replace the third airspeed value 2 airspeed values; and h) Repeat step a) to step f). The method for determining airspeed as described in item 1 of the claimed scope further comprises steps after step f): i) Repeat step a) to step f), if the absolute difference between the first airspeed value and the second airspeed value of the airspeed meter falls outside the allowable range within a failure time, the airspeed is judged deactivate the gauge and set the airspeed to this second airspeed value. The method for determining airspeed as described in claim 1, wherein the allowable range is between 0.5% and 5%. A flight control system installed in a flight vehicle, comprising: a three-axis accelerometer, the three-axis accelerometer continuously records the acceleration values of the flying vehicle in three mutually perpendicular directions at a time interval; an airspeed meter capable of obtaining a first airspeed value along the flight direction of the aircraft; and a calculation module, connected with the three-axis accelerometer and the airspeed signal, to obtain the acceleration values, the first airspeed value, the three acceleration values obtained at the moment and the time interval integral calculation along the flight load A second airspeed value with the flight direction, determine whether a ratio between the absolute difference and the second airspeed value falls within an allowable range, and when the aforementioned ratio falls within the allowable range, determine whether the flight load is within the allowable range. The airspeed of the vehicle is set to the first airspeed value, or when the aforementioned ratio falls outside the allowable range, the airspeed of the aircraft is set to the second airspeed value. The flight control system as described in item 5 of the patent application scope further comprises a global positioning system signal receiver, which is connected with the signal of the computing module, obtains the GPS signal and transmits it to the computing module, so that the computing module uses the GPS The signal calculates a third airspeed value and corrects the result of the triaxial accelerometer integration with the third airspeed value in place of the second airspeed value. The flight control system as described in claim 5, wherein if the absolute difference between the first airspeed value and the second airspeed value of the airspeed meter within a failure time falls outside the allowable range, the The calculation module determines that the airspeed meter is invalid and sets the airspeed to the second airspeed value. The flight control system as described in claim 5, wherein the allowable range is between 0.5% and 5%.

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