Method and device for calibrating sensor of aerial vehicle

Abstract

The present invention relates to an aerial vehicle comprising: a driving device for providing thrust; a first sensor for measuring a first inertial force according to the movement of the aerial vehicle in a state where the driving device does not provide thrust to the aerial vehicle; a second sensor for measuring a second inertial force independent of a first factor; and a processor for calibrating the bias of the first sensor, wherein the processor calibrates the bias of the first sensor by using valid measurement values among the measurement values of the first sensor on the basis of the measurement values of the second sensor.

Description

Method and device for calibrating sensors of an aircraft

[0001] The present invention relates to a method and apparatus for calibrating a sensor of an aircraft.

[0002] Specifically, the present invention relates to a method for correcting the bias of a sensor of an aircraft.

[0003] The use of unmanned aerial vehicles (UAVs) has changed and expanded significantly in recent years. This trend is driven by technological advancements, cost reductions, and increasing applicability across various industries.

[0004] With the increasing application possibilities, pre-flight calibration is necessary to ensure safer flight and mission performance in various environments.

[0005] Therefore, UAVs may typically undergo a pre-takeoff inspection process. This checklist may include assessing the condition of sensors such as the Inertial Measurement Unit (IMU), checking the status of the Global Navigation Satellite System (GNSS) signal, verifying GNSS / Inertial Navigation System (INS) results, assessing battery condition, verifying the gimbal's operating range, confirming signal reception from the remote controller, monitoring CPU resource availability, and measuring equipment temperature.

[0006] Accelerometers, typically used in small multicopters like drones, also suffer from low sensor accuracy. Setting the initial bias is particularly crucial.

[0007] For small multicopters, assuming acceleration remains largely constant, accelerometers can be used to measure gravitational acceleration and estimate the aircraft's angle. However, if the measured values ​​are biased, the angle estimation can be inaccurate, requiring correction.

[0008] Accelerometer bias can be compensated for by taking advantage of the fact that the aircraft is usually stationary and level before takeoff for calibration, but it may be difficult to calibrate the accelerometer when the aircraft must be taken off from a moving vehicle, aircraft, or rocking ship.

[0009] To solve this problem, a leveling landing pad can be used, but this still has the disadvantage of requiring additional equipment and the limitations of the landing pad itself.

[0010] The present invention provides a method and device for calibrating an aircraft's sensor. Furthermore, the present invention provides a computer-readable recording medium containing a program for executing the method on a computer. The technical challenges to be addressed are not limited to the technical challenges described above, and other technical challenges may exist.

[0011] An aircraft for compensating a sensor according to one aspect of the present invention comprises: a driving device for providing thrust; a first sensor for measuring a first inertial force according to the movement of the aircraft when the driving device does not provide thrust to the aircraft; a second sensor for measuring a second inertial force independent of a first element; and a processor for compensating a bias of the first sensor, wherein the processor compensates for a bias of the first sensor by using valid measurement values ​​among measurement values ​​of the first sensor based on measurement values ​​of the second sensor.

[0012] A computer-readable recording medium according to another aspect includes a recording medium having recorded thereon a program for executing the above-described method on a computer.

[0013] According to another aspect, a method for calibrating a sensor of an aircraft comprises: a step of measuring a first inertial force according to a motion of the aircraft while the first sensor does not provide thrust to the aircraft; a step of measuring a second inertial force independent of the first inertial force by the second sensor; and a step of correcting a bias of the first sensor, wherein the step of correcting the bias determines valid measurement values ​​among measurement values ​​of the first sensor based on measurement values ​​of the second sensor, and corrects the bias of the first sensor with the valid measurement values.

[0014] According to the present invention, by measuring acceleration while an aircraft is in motion and compensating the bias of the accelerometer, the accelerometer can be calibrated in various environments.

[0015] In addition, the present invention can determine a valid measurement value by determining whether an external force is applied during upward and / or free-fall motion, and can be used to calibrate the sensor.

[0016] FIG. 1 is a drawing for explaining an example of photographing an object using an aircraft according to one embodiment.

[0017] FIG. 2 is a drawing for explaining the relationship between an aircraft, a controller, a server, and a station according to one embodiment.

[0018] Figure 3 is a schematic diagram illustrating an example of an aircraft according to one embodiment.

[0019] FIG. 4 is a flowchart illustrating a method for calibrating a sensor of an aircraft according to one embodiment.

[0020] FIG. 5 is a drawing for explaining a flight of an aircraft performing correction according to one embodiment.

[0021] FIG. 6 and FIG. 7 are diagrams illustrating measurement values ​​of an accelerometer and a gyro sensor according to one embodiment.

[0022] FIG. 8 is a graph showing changes in measurement values ​​of an accelerometer and a gyro sensor of an aircraft in synchronization according to one embodiment.

[0023] FIG. 9 is a flowchart illustrating a method for calibrating a sensor according to one embodiment.

[0024] FIG. 10 is a diagram for explaining extraction of valid measurement values ​​according to one embodiment.

[0025] FIG. 11 is a drawing illustrating an aircraft calibrating a sensor using a camera according to one embodiment.

[0026] FIG. 12 is a drawing for explaining changes in reference marks within an image according to one embodiment.

[0027] The terms and words used in this specification and claims should not be interpreted based on their general or dictionary meanings. In accordance with the principle that inventors can define the concepts of terms and words to best describe their inventions, they should be interpreted in a way that is consistent with the technical concept of the present invention. Furthermore, the embodiments described in this specification and the configurations depicted in the drawings are merely examples of how the present invention can be realized and do not fully represent the technical concept of the present invention. Therefore, it should be understood that various equivalents, modifications, and applicable examples may exist as of the time of filing.

[0028] The terms first, second, A, B, etc. used in this specification and claims may be used to describe various components, but the components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, a component could be referred to as a second component, and similarly, the second component could also be referred to as a component. The term "and / or" includes any combination of multiple related listed items or any one of multiple related listed items.

[0029] The terminology used in this specification and claims is for the purpose of describing specific embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. It should be understood that terms such as "comprise" or "have" in this application do not preclude the presence or addition of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification.

[0030] The above-described purposes, features and advantages will become clearer through the following detailed description with reference to the attached drawings, so that a person having ordinary skill in the art to which the invention pertains can easily practice the technical idea of ​​the invention.

[0031] Furthermore, when describing the invention, detailed descriptions of known technologies related to the invention will be omitted if they are deemed to unnecessarily obscure the gist of the invention. Below, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0032] FIG. 1 is a drawing for explaining an example of photographing an object using an aircraft according to one embodiment.

[0033] The aircraft (10) may include any aircraft capable of flight, including a drone, an Unmanned Aerial Vehicle (UAV), an Unmanned Aerial Mobility (UAM), an aircraft, a helicopter, etc.

[0034] The aircraft (10) can fly alone or with multiple aircraft capable of collaborating. Furthermore, the aircraft (10) can also collaborate with other types of devices, such as vehicles and robots. Furthermore, the aircraft (10) can automatically fly around the target object (20) along a predetermined flight path, or can manually fly around the target object (20) under user control.

[0035] The aircraft (10) can capture images of the object (20) while flying around the object (20). For example, the captured images of the object (20) can be used to determine whether the object (20) has a defect (e.g., a breakdown, damage, etc.). The user can detect, recognize, and / or identify the object (20) through the aircraft (10).

[0036] As an example, the aircraft (10) can photograph the body or blades of a wind turbine. Specifically, the aircraft (10) can fly around the wind turbine to photograph the body or blades. For example, the aircraft (10) can take off from a station at a starting point and fly to the nose of the wind turbine. Then, the aircraft (10) can start photographing from the nose of the wind turbine and can photograph the blades while flying autonomously (or manually) along the blades. Typically, a wind turbine can include three blades, and the aircraft (10) can photograph the three blades to acquire images. At this time, the images photographed by the aircraft (10) can be utilized for inspection of the blades.

[0037] As another example, the aircraft (10) can photograph the surface of a large building. For example, the aircraft (10) can acquire images by photographing the surface while flying around the perimeter of the large building. In this case, the images captured by the aircraft (10) can be utilized for inspection of the surface of the large building.

[0038] As another example, the aircraft (10) can photograph various structures within a military facility. For example, a military facility may include barbed wire fences, buildings, and exterior walls, and the aircraft (10) can fly over various points within the military facility and photograph the surfaces of the structures. In this case, the images captured by the aircraft (10) can be utilized for inspection of the military facility.

[0039] Although wind turbines, bridges, large buildings, and military facilities are depicted as objects (20) in FIG. 1, the objects are not limited thereto. In other words, any structure having a shape may be applied to the objects (20) without limitation. For example, the objects (20) may be structures in the industrial field. The objects (20) may be structures for power generation (e.g., wind turbines, thermal power plants, hydroelectric power plants, nuclear power plants, solar power plants, etc.), large buildings (e.g., factories, exhibition halls, stadiums, etc.), bridges, dams, power lines, roads, etc., but are not limited thereto. As another example, the objects (20) may be structures that must be detected or information collected in the security and military fields (e.g., barbed wire fences, ammunition depots, exterior walls, etc.). As another example, anything that is difficult for a user to inspect entirely with the naked eye, dangerous, or requires a lot of manpower and cost for inspection may be applied to the objects (20).

[0040] FIG. 2 is a drawing for explaining the relationship between an aircraft, a controller, a server, and a station according to one embodiment.

[0041] Referring to FIG. 2, the server (30), the controller (40), and the station (50) can independently or jointly control the aircraft (10). For example, the server (30), the controller (40), and the station (50) can control the operation (e.g., movement, rotation, etc.) of the aircraft (10) or control the filming of the aircraft (10).

[0042] The aircraft (10) includes at least one camera, and can capture images of an object (20) using the camera. For example, the camera can be installed at a location advantageous for capturing images during flight of the aircraft (10) (e.g., an area not obscured by a propeller, etc., at the front or lower front of the aircraft).

[0043] For example, the aircraft (10) can fly using a global navigation satellite system (GNSS) and / or an inertial navigation system (INS).

[0044] For example, the aircraft (10) can transmit and receive data with a server (30), a controller (40), and / or a station (50). In addition, the controller (40) and the server (30), the server (30) and the station (50), and the station (50) and the controller (40) can transmit and receive data with each other.

[0045] Here, the data may include data required to control the flight of the aircraft (10), data on a flight image of the aircraft (10), data on an image taken of an object (20) by the aircraft (10), etc.

[0046] A flight image represents the field of view of an aircraft (10) when the aircraft (10) is flying. For example, the flight image may be a dynamic image acquired in real time, but is not limited thereto.

[0047] The image captured by the aircraft (10) of the target object (20) refers to an image captured by the aircraft (10) while flying around the target object (20). At this time, the image captured by the aircraft (10) of the target object (20) can be used as an image to check for defects in the target object (20). In this case, the image captured by the aircraft (10) of the target object (20) can be referred to as an inspection image.

[0048] For example, the flight image may be an image with a relatively low resolution (or a low GSD (Ground Sampling Distance)) compared to the inspection image, and the inspection image may be an image with a relatively high resolution (or a high GSD) compared to the flight image. Meanwhile, depending on the type of aircraft (10), the cameras that generate the flight image and the inspection image may be the same or different.

[0049] A user can control the aircraft (10) using the interface of the controller (40). For example, the controller (40) can generate a control signal based on user input received through the interface and transmit the control signal to the aircraft (10). The controller (40) can transmit the control signal to the aircraft (10) via wireless communication. The control signal may be a signal that controls the flight, attitude, navigation, etc. of the aircraft.

[0050] The aircraft (10) can control the motor to rotate the propeller according to the control signal received from the controller (40). The aircraft (10) can move, rotate, etc. by changing the speed and / or attitude, etc. by the rotation of the propeller. Here, the attitude of the aircraft can be expressed as pitch (Y), roll (X), yaw (Z), etc. In addition, the aircraft can perform photographing of the target object (20), etc. according to the control signal received from the controller (40).

[0051] The controller (40) may further include a display device, and the user may check the flight image and / or inspection image of the aircraft (10) through the display device.

[0052] The controller (40) may be a device on which an application for controlling an aircraft (10) is installed. For example, the device on which the application is installed may be a variety of portable devices such as a smartphone, tablet, smart pad, laptop, or wearable device.

[0053] The server (30) or station (50) can control the aircraft (10) by directly transmitting a control signal to the aircraft. In addition, the aircraft (10) can transmit a flight image and / or an inspection image to the server (30), controller (40), or station (50).

[0054] The aircraft (10), server (30), controller (40), and station (50) can each analyze the inspection image. For example, the analysis of the inspection image may be to determine whether there is a defect in the target object (20) in the inspection image through an algorithm such as machine learning or deep learning. The aircraft (10) may directly determine whether there is a defect in the target object (20), or may transmit the inspection image to the server (30), controller (40), or station (50). The server (30), controller (40), or station (50) may analyze the inspection image received from the aircraft (10) to determine whether there is a defect in the target object (20).

[0055] Figure 3 is a schematic diagram illustrating an example of an aircraft according to one embodiment.

[0056] Referring to FIG. 3, the aircraft (10) may include a sensor (110), a camera (120), a memory (130), a driving device (140), a communication device (150), and a processor (160). However, the components of the aircraft (10) are not limited to those illustrated in FIG. 3. In other words, the aircraft (10) may include at least one more component in addition to the components illustrated in FIG. 3, or at least one of the components illustrated in FIG. 3 may be excluded.

[0057] The sensor (110) detects various information necessary for the operation of the aircraft (10) (e.g., flight, photography, etc.), such as the aircraft (10) itself, the surrounding environment of the aircraft (10), identification of the target (20), and confirmation of the distance between the aircraft (10) and the target (20). The sensor (110) may include, but is not limited to, a gyro sensor, a barometer, an ultrasonic sensor, a magnetic sensor, an acceleration sensor, a proximity sensor, a lidar, a radar, and / or a GPS sensor.

[0058] For example, a gyro sensor and / or an acceleration sensor can measure the three-axis angular acceleration of the aircraft (10). A barometer sensor can measure pressure changes and / or air pressure in the atmosphere around the aircraft (10). Since air pressure varies with altitude, the aircraft (10) can also measure the altitude of the aircraft (10) using the barometer sensor. An ultrasonic sensor can measure the distance between the aircraft (10) and the ground or an object (20). A magnetic sensor is a type of terrestrial magnetism sensor (compass sensor) and can detect geomagnetic information.

[0059] For example, a proximity sensor can measure the proximity state of an object (20) to an aircraft (10), the distance between the aircraft (10) and the object (20), and can include an ultrasonic sensor that can measure the distance to the object (20) from a signal reflected from the object (20) by outputting ultrasonic waves. A GPS sensor can calculate the current coordinates (x, y, z) of the aircraft (10) using GPS signals.

[0060] The sensor (110) may include an attitude and heading reference system (AHSR). For example, the attitude and heading reference system may include an inertial sensor or an inertial measurement unit (IMU). For example, the attitude and heading reference system may include a gyro sensor, an acceleration sensor, and a magnetic sensor, and fuse the sensor values ​​to obtain the attitude value of the aircraft (10). ) can be output. Here, the detailed value ( ) can be an angle based on three-dimensional coordinates (x-axis coordinate, y-axis coordinate, z-axis coordinate) according to GPS coordinates.

[0061] The camera (120) can photograph the object (20) according to instructions from the processor (160). For example, the aircraft (10) can include at least one camera, and can include a low-resolution camera and / or a high-resolution camera.

[0062] The camera (120) can be combined with a gimbal whose angle can be adjusted. Accordingly, the shooting angle of the camera (120) can be adjusted by the gimbal.

[0063] The memory (130) may include any non-transitory computer-readable recording medium. As an example, the memory (130) may include a non-permanent mass storage device such as a random access memory (RAM), a read only memory (ROM), a disk drive, a solid state drive (SSD), a flash memory, etc. As another example, the non-permanent mass storage device such as a ROM, an SSD, a flash memory, a disk drive, etc. may be a separate permanent storage device distinct from the memory. In addition, the memory (130) may store an operating system (OS) and at least one program code.

[0064] These software components may be loaded from a computer-readable recording medium separate from the memory (130). This separate computer-readable recording medium may be a recording medium that can be directly connected to a computer, and may include, for example, a computer-readable recording medium such as a floppy drive, a disk, a tape, a DVD / CD-ROM drive, a memory card, etc. Alternatively, the software components may be loaded into the memory (130) via a communication device (150) other than a computer-readable recording medium. For example, at least one program may be loaded into the memory (160) based on a computer program that is installed by files provided by developers or a file distribution system that distributes installation files of applications via the communication device (150).

[0065] The driving device (140) controls the driving of the motor at a speed and direction according to instructions from the processor (160), and accordingly, the rotational speed and direction of the propeller connected to the motor can be controlled. For example, the driving device (140) may include a motor and a propeller.

[0066] The communication device (150) performs data communication between the aircraft (10) and an external device. For example, the communication device (150) may communicate with the controller (40), server (30), and / or station (50) using various communication methods such as infrared communication, RF (Radio Frequency) communication, Wi-Fi communication, ZigBee communication, Bluetooth communication, laser communication, UWB (Ultra-Wideband) communication, LTE, 5G, 6G, and wireless LAN. However, the communication method employed in the communication device (150) is not limited to the above-described method.

[0067] The processor (160) can process instructions of a computer program by performing basic arithmetic, logic, and input / output operations. Here, the instructions can be provided from memory (130) or an external device (e.g., a server (30), a controller (40), a station (50), etc.). In addition, the processor (160) can generally control the operations of other components included in the aircraft (10).

[0068] For example, the functions performed by each module included in the processor (160) may be performed by one processor or by separate processors. The processor (160) may perform calculations or data processing related to control and / or communication of at least one other component of the aircraft (10).

[0069] For example, the processor (160) may be implemented as an array of a plurality of logic gates, or it may be implemented as a combination of a general-purpose microprocessor and a memory storing a program that can be executed on the microprocessor. For example, the processor (160) may include a general-purpose processor, a central processing unit (CPU), a graphics processing unit (GPU), a neural processing unit (NPU), a microprocessor, a digital signal processor (DSP), a controller, a microcontroller, a state machine, and the like. In some environments, the processor (160) may include an application-specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), and the like. For example, the processor (160) may also refer to a combination of processing devices, such as a combination of a digital signal processor (DSP) and a microprocessor, a combination of a plurality of microprocessors, a combination of one or more microprocessors coupled with a digital signal processor (DSP) core, or any other such combination of configurations.

[0070] FIG. 4 is a flowchart illustrating a method for calibrating a sensor of an aircraft according to one embodiment.

[0071] Typically, sensors are composed of tiny machines, and there may be subtle differences between sensors due to the manufacturing process. Furthermore, sensors can be subject to bias due to external factors, such as the environment. For example, sensor measurements can be affected by temperature changes, vibration, and shock.

[0072] The aircraft (10) can recognize its current orientation using sensors. If the measurements of the accelerometer and gyro sensor have errors due to bias, the aircraft's orientation estimation may become inaccurate, which may affect the takeoff and landing of the aircraft (10). Therefore, the aircraft (10) needs to calibrate its sensors before operating the driving device (140).

[0073] At step 410, a first sensor of the aircraft (10) measures a first inertial force according to the movement of the aircraft (10) while not providing thrust to the aircraft (10). In one example, the first sensor may be an accelerometer, and the first inertial force may be acceleration.

[0074] A state in which no thrust is provided to the aircraft (10) indicates a state in which the driving device (140) of the aircraft (10) is not operating. For example, if the aircraft (10) is a drone, the drone's motor may not be operating, and thus the propeller may not rotate due to the motor.

[0075] Even though no thrust is provided to the aircraft (10), the aircraft (10) moves, which may mean that the aircraft (10) descends while freely falling in the air, or that the aircraft (10) is launched into the air by an external force.

[0076] At step 420, the second sensor of the aircraft (10) measures a second inertial force that is independent of the first inertial force. The independence of the first and second inertial forces may mean that the second inertial force is not affected by the first inertial force. In other words, it may mean that even if the first inertial force acts on the aircraft (10), the second inertial force is not measured. Conversely, even if the second inertial force acts on the aircraft (10), the first inertial force is not measured. In one example, the second sensor may be a gyro sensor, and the second inertial force may be angular acceleration.

[0077] The first inertial force and the second inertial force may be measured while the vehicle (10) is in free fall without the drive device (140) providing thrust to the vehicle (10). Alternatively, the first inertial force and the second inertial force may be measured while the vehicle (10) is ascending and / or descending due to an initial external force.

[0078] An accelerometer can measure acceleration, and a gyroscope can measure angular acceleration. An accelerometer or gyro sensor can measure acceleration or angular acceleration in each direction of the X, Y, and Z axes.

[0079] In one embodiment, the accelerometer may be located at the center of gravity of the aircraft (10). By locating the accelerometer at the center of gravity, the influence of external forces may be reduced. Therefore, the aircraft (10) can acquire a large number of valid measurements within a short period of time, allowing the aircraft (10) to calibrate the sensor within a short period of time.

[0080] At step 430, the processor (160) determines valid measurement values ​​among the measurement values ​​of the first sensor based on the measurement values ​​of the second sensor, and corrects the bias of the first sensor with the valid measurement values.

[0081] The bias of the first sensor can be corrected with the measurement values ​​of the first sensor measured while only gravity is acting on the aircraft (10). That is, the processor (160) can determine the measurement values ​​of the first sensor measured while only gravity is acting on the aircraft (10) as valid measurement values. The processor (160) can use the second sensor, the third sensor, etc. to determine whether only gravity is acting on the aircraft (10).

[0082] Valid measurements may be measurements of the second sensor or measurements measured by the first sensor while the change in the measurements of the second sensor does not exceed a threshold value. Valid measurements may be measurements used to calibrate the first sensor. That is, the processor (160) may use the valid measurements to calibrate the bias of the first sensor.

[0083] If the measurement values ​​of the second sensor or the amount of change in the measurement values ​​of the second sensor do not exceed the threshold value, the processor (160) can determine that only gravity is acting on the aircraft (10) (no external force is acting). If the measurement values ​​of the second sensor exceed the threshold value, the processor (160) can determine that an external force is acting on the aircraft (10). However, a value exceeding the threshold value may be measured due to an error in the second sensor. Therefore, the processor (160) can calculate the amount of change in the measurement values ​​of the second sensor to determine whether an external force is acting on the aircraft (10). The processor (160) can also determine the effective measurement values ​​of the first sensor by considering both the measurement values ​​and the amount of change of the second sensor.

[0084] The processor (160) compares the number of valid measurements with a predetermined threshold. The processor (160) may compare the number of valid measurements with the threshold to determine whether a sufficient number of valid measurements have been acquired to calibrate the first sensor. That is, when a sufficient number of valid measurements have been acquired, the processor (160) may compensate for the bias of the first sensor and control the actuator (140) to initiate flight.

[0085] The processor (160) compensates for the bias of the first sensor using a representative value of valid measurement values. When the number of valid measurement values ​​exceeds a threshold value, the processor (160) determines a representative value using the valid measurement values. For example, the representative value may be the average or median of the valid measurement values.

[0086] The processor (160) can determine valid measurements using images. A third sensor can capture images of a reference mark, and the processor (160) can determine valid measurements based on changes in the reference mark within the images. For example, the third sensor can be a camera (120). The reference mark can be an image fixed at a certain point. The reference mark can be installed in a location close to where the aircraft (10) starts flying. The aircraft (10) continuously captures images of the reference mark to acquire images. The processor (160) can calculate changes in the position of the reference mark within the images to determine whether an external force has been applied to the aircraft (10).

[0087] The aircraft (10) may also perform calibration through a server (30) or a controller (40). The aircraft (10) may transmit the measurement values ​​of the sensors to the server (30) or the controller (40) and receive a representative value from the server (30) or the controller (40) to calibrate the first sensor.

[0088] The aircraft (10) can calibrate the first sensor for each direction of the X, Y, and Z axes. In other words, the aircraft (10) can obtain independent measurement values ​​for each direction and calibrate the first sensor for each direction. For example, the aircraft (10) can include an accelerometer for each direction of the X, Y, and Z axes and can calibrate the accelerometer for each direction. When the aircraft (10) flies upward in the Z-axis direction, the accelerometer measures the acceleration of the aircraft (10) ascending against gravity, and the measured measurement value can be expressed as a change in the Z-axis (up and down direction).

[0089] On the other hand, when the aircraft (10) rotates left and right or tilts, the gyro sensor can measure angular acceleration. For example, the rotational motion of the aircraft (10) about each axis can be measured as a change in angular acceleration about each axis.

[0090] FIG. 5 is a drawing for explaining a flight of an aircraft performing correction according to one embodiment.

[0091] The aircraft (10) can calibrate its sensors before flying by the operation of the driving device (140). More specifically, the aircraft (10) can fly through the following stages: 1) a first stage in which an initial external force is applied, 2) a second stage in which an external force due to wind and / or gravity is applied, and 3) a third stage in which the aircraft (10) flies by operating the driving device.

[0092] The first stage, in which an initial external force is applied, is the stage in which force is transmitted to the aircraft (10) by the user or the launcher (500). FIG. 5 illustrates the initial external force applied to the aircraft (10) by the launcher (500). An initial external force of a predetermined magnitude or for a predetermined period of time is applied to the aircraft (10). Accordingly, the aircraft (10) can ascend and / or descend in the air by the initial external force even without operating the drive device (140).

[0093] There may also be instances where the aircraft (10) free-falls in the air. In this case, the aircraft (10) may free-fall in the air without operating the drive device (140). Therefore, there is no first stage, and the aircraft (10) flies through the second and third stages.

[0094] The aircraft (10) and the launcher (500) are connected to each other through communication and can transmit and receive data. The launcher (500) can transmit the start and end times of applying an initial external force to the aircraft (10) to the aircraft (10). After the end time, the aircraft (10) can perform operations to calibrate the sensor.

[0095] The second stage, in which external force due to wind and / or gravity acts, is the stage in which the aircraft (10) in the air moves due to wind and / or gravity. The second stage refers to the period from the moment the aircraft (10) separates from the launcher (500) to before the drive device (140) is operated. In the second stage, the aircraft (10) can ascend, descend after ascending, or descend. In an environment without wind, only gravity can act on the aircraft (10). In the case in which the aircraft (10) is in free fall in the air, the aircraft (10) may only descend.

[0096] The aircraft (10) calibrates its sensors during the second phase. The aircraft (10) can calibrate its sensors using measurements obtained while subjected to external forces such as wind and / or gravity. For example, the aircraft (10) can calibrate its accelerometer using acceleration values ​​obtained while subjected to gravity alone. The aircraft (10) can determine whether gravity alone is acting on the aircraft (10) using other sensors.

[0097] The third step in which the aircraft (10) operates the drive device (140) is a step in which the aircraft (10) operates the drive device (140) to start flight after calibrating the sensor. In FIG. 5, the aircraft (10) is shown to start flight by operating the drive device (140) while descending, but if the sensor calibration is completed while the aircraft (10) is ascending, the aircraft (10) may also start flight by operating the drive device (140).

[0098] In Fig. 5, a case where the aircraft (10) calibrates the sensor using the launcher (500) is described, but a user may also transmit an initial external force to the aircraft (10). In addition, the aircraft (10) may calibrate the sensor while free-falling from a high position without using the launcher (500). In this case, the first step where the initial external force is applied is omitted, and the aircraft (10) free-falls in the second step. The aircraft (10) calibrates the sensor during the free fall, and when the sensor calibration is completed, the aircraft (10) operates the driving device (140) to fly.

[0099] Since the acceleration of the aircraft (10) is measured in a state where the driving device (140) does not provide thrust to the aircraft (10), it can be assumed that the acceleration of the aircraft (10) will be measured as the same within the gravitational field according to the equivalence principle of the theory of relativity.

[0100] At this time, the accelerometer of the aircraft (10) itself also offsets the gravitational acceleration due to gravity by moving with the same acceleration as the aircraft (10), and the relative acceleration of the accelerometer can be measured as 0.

[0101] However, in reality, when an aircraft (10) ascends and then descends due to an initial external force, wind power in the atmosphere, lift generated by the shape of the aircraft, and resistance due to air resistance may occur. In addition, if an external force due to wind acts on the aircraft (10) in a direction perpendicular to the direction in which gravity acts, it may affect the measured values ​​of the accelerometer and gyro sensor of the aircraft (10).

[0102] That is, since the acceleration value measured by the accelerometer includes external influences other than gravity, accurate correction cannot be performed if the acceleration value is used for correction assuming that the acceleration of the aircraft (10) is affected only by gravity.

[0103] Therefore, it is necessary to calculate the bias excluding the acceleration value due to the external force applied during the actual flight of the aircraft (10). In other words, the acceleration value obtained while the external force is applied to the aircraft (10) is not used to calculate the bias.

[0104] FIG. 6 and FIG. 7 are diagrams illustrating measurement values ​​of an accelerometer and a gyro sensor according to one embodiment.

[0105] Referring to Fig. 6, the acceleration of the aircraft (10) may change in the section where an external force is applied during the free fall process.

[0106] Additionally, referring to Fig. 7, the angular acceleration of the aircraft (10) may also change in the section where an external force is applied.

[0107] Therefore, in this embodiment, the aircraft (10) determines the valid section based on the change in angular acceleration, and determines the measured acceleration values ​​obtained in the valid section as valid measured values. This will be described with reference to FIG. 8.

[0108] FIG. 8 is a graph showing changes in measurement values ​​of an accelerometer and a gyro sensor of an aircraft in synchronization according to one embodiment.

[0109] Referring to Fig. 8, changes in measured values ​​are shown after an initial external force is applied to the aircraft (10). An initial external force is applied to the aircraft (10), and after 0 seconds, the initial external force is not applied. The initial external force represents a force applied to the aircraft (10) by a person or device, and is a force that flies the aircraft (10) into the air and creates a state in which only gravity acts on the aircraft (10). The aircraft (10) rises from 0 seconds to 1.4 seconds due to the initial external force, and descends after 1.4 seconds. Between 0 seconds and 2 seconds, only gravity acts on the aircraft (10). Between 2 seconds and 2.5 seconds, an external force such as wind acts on the aircraft (10). Therefore, the measured values ​​of the accelerometer and gyro sensor changed in the section between 2 seconds and 2.5 seconds.

[0110] In Fig. 8, an external force is generated once in the section where the aircraft (10) falls, but an external force due to wind, etc., can also be generated in the section where the aircraft (10) rises, and can be generated more than twice.

[0111] The aircraft (10) can extract acceleration values ​​in section (a) excluding acceleration values ​​in additional exclusion section (b) according to a certain ratio before and after the section as a margin of the external force section as valid measurement values. Since the measurement values ​​of the gyro sensor in section (a) do not exceed the threshold value, the measurement values ​​of the accelerometer measured in section (a) are determined as valid measurement values. The valid measurement values ​​are used for calibration of the accelerometer.

[0112] That is, in this embodiment, by setting an additional margin in areas where the reliability of measured values ​​is low due to external force, the impact of measurement error or uncertainty can be reduced. Furthermore, when measuring bias through multiple measurements, the clarity of interpretation of measured values ​​within the valid range can be improved. The margin ratio can be determined based on the rate of change in the external force range and the magnitude of the measured value within the external force range.

[0113] In this embodiment, the initial external force may be determined as a force of a magnitude that allows the aircraft (10) to ascend to a height at which a sufficient number of measurement values ​​can be acquired for sensor calibration and then descend. Specifically, the aircraft (10) requires time to collect measurement values ​​greater than a threshold value. The threshold value is the minimum number of measurement values ​​required for sensor calibration. The initial external force may be determined based on the measurement period of the accelerometer, the threshold value, and / or the weight of the aircraft (10). Measurement values ​​are acquired from the moment the aircraft (10) is thrown into the air by the initial external force, and the drive device (105) of the aircraft (10) does not operate.

[0114] The required time can be calculated based on the relationship between the collection cycle of the measurement values ​​and the threshold value. However, if multiple repetitive free falls are required depending on the flight conditions of the aircraft (10), the number of flights can also be considered. The required time is the time required to acquire valid measurement values ​​greater than the threshold value. The collection cycle is the measurement cycle of the sensor. For example, the larger the threshold value, the longer the required time can be, and the shorter the measurement cycle, the shorter the required time can be. Depending on the required time, the size of the initial external force or the height of the free fall can be determined.

[0115] FIG. 9 is a flowchart illustrating a method for calibrating a sensor according to one embodiment.

[0116] The aircraft (10) calibrates the sensor by executing the steps of FIG. 9. For example, the aircraft (10) may perform sensor calibration after power is applied and a predetermined period of time has elapsed. Alternatively, the aircraft (10) may perform sensor calibration after power is applied and an initial external force is applied by the launcher (500). Alternatively, the aircraft (10) may perform sensor calibration after power is applied and free fall begins.

[0117] At step 910, the aircraft (10) determines whether the driving device (140) should be operated. For example, the aircraft (10) determines whether a predetermined time has elapsed since the initial external force was applied. If the predetermined time has elapsed, the aircraft (10) calibrates the sensor.

[0118] As another example, the aircraft (10) can measure the height from the ground to determine whether to operate the drive device (140). If the aircraft (10) determines that the distance from the ground is close enough to cause a collision, the aircraft calibrates the sensor and operates the drive device (140). In addition to the ground, the aircraft (10) can calibrate the sensor and operate the drive device (140) if it determines that there is a risk of collision with a person or an object.

[0119] At step 920, the aircraft (10) determines whether the measured values ​​are sufficient. If the measured values ​​are sufficient, the aircraft (10) performs sensor calibration. If the measured values ​​are not sufficient, the aircraft proceeds to step 930. Sufficient measured values ​​mean that the number of measured values ​​is greater than a threshold value and a sufficient number of measured values ​​have been acquired to calibrate the sensor.

[0120] At step 930, the aircraft (10) determines whether an external force has occurred. The external force may be a force other than gravity, such as wind. For example, the aircraft (10) can determine whether an external force has occurred by measuring angular acceleration.

[0121] At step 940, the aircraft (10) stores the measurement values ​​acquired by the sensor to be calibrated. Since no external force has occurred, the aircraft (10) determines the acquired measurement values ​​as valid measurements and stores the measurements. For example, the aircraft (10) may store acceleration values ​​measured by an accelerometer.

[0122] At step 950, the aircraft (10) calibrates the sensors. The aircraft (10) calibrates the sensors if there is a risk of collision or if the measured values ​​are sufficient. For example, the aircraft (10) may calibrate the accelerometer.

[0123] At step 960, the aircraft (10) operates the drive device (140). Since the sensor calibration of the aircraft (10) is completed, the aircraft starts flying by operating the drive device (140).

[0124] FIG. 10 is a diagram for explaining extraction of valid measurement values ​​according to one embodiment.

[0125] Referring to Figure 10, the effective interval (a) where the valid measurement value is measured varies depending on the external force interval (c), so the initial external force can be determined by calculating the required time based on the frequency or duration of the external force action. For example, the required time in an area (or time) with strong and frequent winds may be longer than the required time in an area (or time) with weak and sparse winds.

[0126] If the number of valid measurements (A1 + A2) is less than the threshold, valid measurements can be extracted through a repeated free-fall process. A1 is the measurements obtained between 0 and 1.9 seconds, and A2 is the measurements obtained between 2.6 and 3 seconds.

[0127] If the number of valid measurements is greater than a threshold value, the aircraft (10) estimates a bias using the acquired valid measurements. The aircraft (10) calibrates the sensor with the estimated bias and starts flight by driving the motor.

[0128] As another example, if the number of valid measurements is greater than or equal to a threshold, the aircraft (10) can estimate the bias using the valid measurements. Even if the number of valid measurements is greater than or equal to the threshold, if there is still time remaining for the aircraft (10) to fly without operating the motors, the aircraft (10) can acquire additional valid measurements. Conversely, even if the number of valid measurements is less than the threshold, if the aircraft (10) is to begin flight, the aircraft (10) calibrates the sensors and begins flight.

[0129] Additionally, in the present embodiment, when collecting valid measurements through repeated free falls, the aircraft (10) can calculate a weighted average by dividing it by the number of free fall attempts to derive a representative value. At this time, the weight for each attempt can also be determined by considering the flight time, the magnitude of the external force applied during the flight, and the time.

[0130] Furthermore, in this embodiment, it is also possible to use various sensors other than a gyro sensor to calibrate the accelerometer. That is, a sensor capable of determining an external force applied to the aircraft (10) may be used.

[0131] In another embodiment, the aircraft (10) can calibrate the accelerometer using a GPS sensor or a magnetometer.

[0132] When calibrating an accelerometer using a GPS sensor, the aircraft (10) can calibrate the accelerometer using a change in GPS coordinates or the amount of change in GPS coordinates.

[0133] When an initial external force is applied only in the vertical direction to the aircraft (10), the position of the aircraft (10) changes only in the vertical direction (Z-axis) (after the initial external force is applied to the aircraft (10), only gravity is applied to the aircraft (10)). At this time, when an external force is applied to the aircraft (10), the position of the aircraft (10) also changes in the horizontal direction (X, Y-axis). Therefore, while only the GPS coordinate of the Z-axis of the aircraft (10) changes, the aircraft (10) can acquire an acceleration value and calibrate the accelerometer with the acquired acceleration value. If an external force is applied to the aircraft (10) in the X-axis or Y-axis direction, the GPS coordinate of the X-axis or Y-axis direction changes. If the GPS coordinate of the X-axis or Y-axis direction changes, the aircraft (10) determines that an external force has been applied to the aircraft (10). The aircraft (10) does not use the acceleration values ​​acquired while the GPS coordinates in the X-axis or Y-axis direction are changed for the calibration of the accelerometer.

[0134] An initial external force may be applied to an aircraft (10) in two or more axial directions among the X, Y, and Z axes, and the aircraft (10) may calibrate an accelerometer using the amount of change in GPS coordinates in each axial direction. Before an external force is applied to the aircraft (10), the amount of change in the GPS coordinates of the aircraft (10) may not exceed a threshold value. When an external force is applied to the aircraft (10), the amount of change in the GPS coordinates of the aircraft (10) may exceed the threshold value. Therefore, the aircraft (10) may measure the amount of change in the GPS coordinates and calibrate the accelerometer using the acceleration value measured only in the section where the amount of change does not exceed the threshold value.

[0135] The aircraft (10) can also perform calibration using a magnetometer. When calibrating an accelerometer using a magnetometer, the aircraft (10) can calibrate the accelerometer using a change or amount of change in magnetism.

[0136] During a free fall process (or, the process in which the aircraft ascends and descends due to an initial external force), the aircraft (10) can also calculate a bias using valid measurement values ​​in a section where the change or amount of change in magnetic force is below a threshold value. The method for calibrating an accelerometer using GPS coordinates is equally applicable to the method for calibrating an accelerometer using magnetic force.

[0137] FIG. 11 is a diagram illustrating an example of an aircraft calibrating a sensor using a camera. The aircraft (10) can also calibrate measurements using images.

[0138] The aircraft (10) can use the camera (120) to determine whether an external force has been applied to the aircraft (10) and calibrate the sensor.

[0139] Referring to FIG. 11, the aircraft (10) can determine whether an external force has been applied to the aircraft (10) based on the change or amount of change in the position of the reference mark (1202) within the image. The aircraft (10) starts its initial flight using a camera (120) and continuously captures reference marks (1202) fixed in the vicinity. The aircraft (10) can determine whether an external force has been applied by calculating the change or amount of change in the position of the reference mark (1202) within the captured image.

[0140] In one example, when an aircraft (10) is freely falling in a vertical direction, if no external force is applied, the aircraft (10) does not move in a horizontal direction. When the aircraft (10) is caused to fly to the left by an external force during the free fall process, the position of the reference mark (1202) within the acquired image may change along with the change in acceleration during the application of the external force.

[0141] FIG. 12 is a drawing for explaining changes in reference marks within an image according to one embodiment.

[0142] Specifically, the aircraft (10) can track the change in position of each pixel or specific feature point through the optical flow of pixels in the area where the reference mark (1202) is located within the image, thereby determining the movement of the aircraft (10).

[0143] The movement of pixels or feature points in a sequence of images acquired in time series during a free fall process can be expressed as a motion vector (1302) in a space defined as a feature space. The motion vector (1302) indicates the direction and magnitude (speed) of the movement of each pixel or feature point and can be visualized in a form such as that shown in Fig. 12.

[0144] If the sum of the motion vectors calculated for each pixel or feature point is biased in a specific direction with respect to the origin of the space in which the motion vectors are defined, the movement of the aircraft (10) in the biased direction can be estimated.

[0145] More specifically, the sum of the motion vectors derived from the captured image can be compared with a reference vector determined according to the expected path of the aircraft (10).

[0146] If the sum of the motion vectors as a result of the comparison has a size or direction angle greater than a critical size compared to the reference vector, the point in time at which the image used to calculate the motion vector was acquired can be judged as an external force section in which an external force was applied.

[0147] Therefore, the aircraft (10) can calculate the bias using the effective measurement values ​​sensed within the effective section excluding the external force section.

[0148] Furthermore, the aircraft (10) can extract the features of the reference mark (1202) from the image, determine the section in which the movement of the aircraft (10) due to external force is predicted as the external force section through a recurrent neural network (RNN) or a long short-term memory (LSTM) network, and calculate the bias using the sensed valid measurement values ​​within the valid section excluding the external force section.

[0149] According to the present invention, by correcting the bias through the measurement values ​​obtained in a situation where the aircraft (10) is in motion without stopping, a more flexible correction suitable for the actual environment is performed, and safe flight and faithful mission performance of the aircraft (10) can be expected.

[0150] The various embodiments described herein may be implemented in a recording medium readable by a computer or similar device, for example, using software, hardware, or a combination thereof.

[0151] In terms of hardware implementation, the embodiments described herein can be implemented using at least one of ASICs (application specific integrated circuits), DSPs (digital signal processors), DSPDs (digital signal processing devices), PLDs (programmable logic devices), FPGAs (field programmable gate arrays), processors, controllers, micro-controllers, microprocessors, and other electrical units for performing functions. In some cases, the embodiments described herein can be implemented as a control module itself.

[0152] In a software implementation, the procedures and functions described herein, as well as other embodiments, may be implemented as separate software modules. Each of these software modules may perform one or more of the functions and operations described herein. The software code may be implemented as a software application written in a suitable programming language. The software code may be stored in a memory module and executed by a control module.

[0153] The above description is merely an example of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications, changes, and substitutions can be made without departing from the essential characteristics of the present invention.

[0154] Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are intended to illustrate, rather than limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by these embodiments and the accompanying drawings. The scope of protection of the present invention should be interpreted by the following claims, and all technical concepts within the scope equivalent thereto should be interpreted as being included within the scope of the rights of the present invention.

Claims

1. In an aircraft that calibrates sensors, A drive device that provides thrust; A first sensor for measuring a first inertial force according to the motion of the aircraft while the driving device does not provide thrust to the aircraft; a second sensor measuring a second inertial force independent of the first element; and A processor for correcting the bias of the first sensor is included, An aircraft in which the processor corrects the bias of the first sensor by using valid measurement values ​​among the measurement values ​​of the first sensor based on the measurement values ​​of the second sensor.

2. In paragraph 1, An aircraft in which the first sensor measures acceleration with the first inertial force.

3. In paragraph 1, The above second sensor is an aircraft that measures angular acceleration with the second inertial force.

4. In paragraph 1, Further comprising a third sensor for capturing images by photographing reference marks, The aircraft, wherein the processor determines the valid measurements based on changes in the reference mark within the images, and corrects the bias of the first sensor with the valid measurements.

5. In paragraph 1, An aircraft, characterized in that the valid measurements are measured by the first sensor while the measurements of the second sensor or the amount of change in the measurements of the second sensor does not exceed a threshold value.

6. In paragraph 1, The above processor Compare the number of valid measurements above with a predetermined threshold value, When the number of the above valid measurements exceeds the threshold value, a representative value is determined using the above valid measurements, An aircraft that corrects the bias of the first sensor with the above representative value.

7. In paragraph 1, An aircraft, wherein the first sensor measures the first inertial force and the second sensor measures the second inertial force while the aircraft is in free fall without the driving device providing thrust to the aircraft.

8. In paragraph 1, An aircraft, wherein the first sensor measures the first inertial force and the second sensor measures the second inertial force while the aircraft ascends and / or descends due to an initial external force.

9. In paragraph 1, The aircraft, wherein the first sensor is positioned at the center of gravity of the aircraft.

10. In the method of calibrating the sensor of the aircraft, A step of measuring a first inertial force according to the movement of the aircraft while the first sensor does not provide thrust to the aircraft; A step in which a second sensor measures a second inertial force independent of the first inertial force; and Comprising a step of correcting the bias of the first sensor, The step of correcting the above bias is: A method for determining valid measurement values ​​among the measurement values ​​of the first sensor based on the measurement values ​​of the second sensor, and correcting the bias of the first sensor with the valid measurement values.

11. In paragraph 10, A method in which the step of measuring the first inertial force measures the acceleration of the aircraft.

12. In paragraph 10, A method in which the step of measuring the second inertial force measures the angular acceleration of the aircraft.

13. In paragraph 10, A third sensor comprises a step of capturing images by photographing a reference mark, The step of correcting the bias is a method of determining the valid measurements based on changes in the reference mark within the images and correcting the bias of the first sensor with the valid measurements.

14. In paragraph 10, A method, characterized in that the valid measurement values ​​are measured by the first sensor while the measurement values ​​of the second sensor or the amount of change in the measurement values ​​of the second sensor does not exceed a threshold value.

15. In paragraph 10, The step of correcting the bias comprises the steps of comparing the number of valid measurements with a predetermined threshold value; and When the number of the above valid measurements exceeds the threshold value, a representative value is determined using the above valid measurements, A method for correcting the bias of the first sensor using the representative value.

16. In paragraph 10, The step of measuring the first inertial force and the step of measuring the second inertial force are, A method wherein the driving device is not providing thrust to the aircraft and the aircraft is in free fall.

17. In paragraph 10, The step of measuring the first inertial force and the step of measuring the second inertial force are, A method performed while the aircraft ascends and / or descends by an initial external force.

18. In paragraph 10, The method wherein the first sensor is positioned at the center of gravity of the aircraft.

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