Altitude estimation system and altitude estimation program

Abstract

Provided is an altitude estimation system 1 for estimating the altitude of an aircraft 2 which generates lift via rotation of rotor blades 5, said altitude estimation system 1 comprising: an encoder 6 that rotates together with the rotor blades; a sensor 7 that detects the rotation of the encoder and that outputs an electric signal on the basis thereof; an angular velocity calculation unit 10 that calculates the angular velocity of the rotor blades from the electric signal; and an altitude estimation unit 11 that estimates the altitude of the aircraft from the angular velocity of the rotor blades.

Description

Altitude estimation system and altitude estimation program

[0001] The present invention relates to an altitude estimation system and an altitude estimation program for estimating the altitude of an aircraft that generates lift through the rotation of its rotor blades.

[0002] Conventionally, aircraft such as helicopters and drones with rotor blades have been known to measure or estimate their altitude using distance sensors mounted on the aircraft. For example, Patent Document 1 below discloses an aircraft-mounted radio altimeter that measures altitude by measuring the propagation time width of transmitted and received radio waves from the time radio waves are emitted toward the ground until the radio waves reflected by the ground are received.

[0003] Patent No. 3755225

[0004] Incidentally, the radio altimeter described in Patent Document 1 above measures the distance (altitude) from the ground based on the propagation time width of the transmitted and received radio waves. Therefore, even if an aircraft continues to fly at a constant altitude, there is a concern that variations in the propagation time width will occur in areas with large irregularities on the ground surface, such as undulating terrain or areas with scattered buildings, causing discrepancies in the measured altitude.

[0005] This invention has been made in view of the above circumstances, and aims to provide an altitude estimation system and an altitude estimation program using an encoder.

[0006] To achieve the above objective, the present invention provides an altitude estimation system for estimating the altitude of an aircraft that generates lift by the rotation of a rotor blade, characterized by comprising: an encoder that rotates together with the rotor blade; a sensor that detects the rotation of the encoder and outputs an electrical signal based thereon; an angular velocity calculation unit that calculates the angular velocity of the rotor blade from the electrical signal; and an altitude estimation unit that estimates the altitude of the aircraft from the angular velocity of the rotor blade.

[0007] In the above configuration, the altitude estimation unit may estimate the altitude z [m] of the aircraft having N rotors at time t [s] using the following formula 1. (m: represents the mass of the flying object [kg]. C Ｌ: The proportionality constant [N·rad] for converting the angular velocity of a rotor blade into lift. －２ ・s ２ ] represents ω ｉ : Represents the angular velocity of the rotor blade [rad / s]. g: Gravitational acceleration [m / s] ２ This represents the air resistance coefficient [N・m]. k: Air resistance coefficient [N・m] －１ ・Represents [s].

[0008] Furthermore, in the above configuration, the altitude estimation unit may estimate the current altitude of the aircraft using the altitude from the ground surface at the start of altitude estimation as a reference value.

[0009] Furthermore, in order to achieve the above objective, the altitude estimation program of the present invention is an altitude estimation program for estimating the altitude of an aircraft that generates lift by the rotation of a rotor blade, and is characterized by performing the steps of: obtaining the angular velocity of the rotor blade from an electrical signal output by a sensor that detects the rotation of an encoder provided to rotate together with the rotation of the rotor blade; and estimating the altitude of the aircraft from the obtained angular velocity of the rotor blade.

[0010] Since the altitude estimation system and altitude estimation program of the present invention have the above-described configuration, altitude estimation can be achieved using an encoder.

[0011] This is a schematic system configuration diagram showing an example of an altitude estimation system in one embodiment of the present invention. (a) is a schematic diagram showing an example of a block diagram of an aircraft constituting the altitude estimation system, and (b) is a schematic diagram showing an example of a block diagram of a terminal device constituting the altitude estimation system. (a) and (b) are diagrams showing examples of altitude estimation by the altitude estimation system, respectively. This is a flowchart schematically showing an example of processing by the altitude estimation system (altitude estimation program). This is a diagram showing the results of a comparative test between the embodiment and the comparative example.

[0012] Hereinafter, an example of the altitude estimation system and altitude estimation program according to this embodiment will be described with reference to the drawings. The altitude estimation system 1 according to this embodiment is a system for estimating the altitude of an aircraft 2 that generates lift by the rotation of its rotor blades 5. The altitude estimation system 1 includes an encoder 6 that rotates together with the rotor blades 5, a sensor 7 that detects the rotation of the encoder 6 and outputs an electrical signal based on it, an angular velocity calculation unit 10 that calculates the angular velocity of the rotor blades 5 from the electrical signal, and an altitude estimation unit 11 that estimates the altitude of the aircraft 2 from the angular velocity of the rotor blades 5.

[0013] Furthermore, the altitude estimation program according to this embodiment is a program that estimates the altitude of an aircraft 2 that generates lift by the rotation of its rotor blades 5. The altitude estimation program performs the following steps: (S103) acquires the angular velocity of the rotor blades 5 from an electrical signal output by a sensor 7 that detects the rotation of an encoder 6, which is provided to rotate together with the rotation of the rotor blades 5; and (S104) estimates the altitude of the aircraft 2 from the acquired angular velocity of the rotor blades 5. A detailed explanation follows below.

[0014] As shown in Figure 1, the altitude estimation system 1 connects the aircraft 2 and the terminal device 4 to each other via a communication network 3 so that they can communicate with one another. The communication standard for the communication network 3 is not particularly limited, as long as the aircraft 2 and the terminal device 4 can communicate with each other and transmit and receive altitude information estimated by the altitude estimation unit 11, and transmit and receive operation signals for the aircraft 2. For example, the communication network 3 includes any network that provides data communication via wireless signals, and may be a wireless local area network (WLAN) using Wi-Fi / WiMax communication, LPWA (Low Power Wide Area), etc.

[0015] The aircraft 2 is not particularly limited as long as it generates lift through the rotation of its rotor blades 5, allowing it to ascend (take off) and become capable of flight. Figure 1 schematically shows a drone (unmanned aerial vehicle) as an example of the aircraft 2, which has multiple rotor blades 5 (four in the example), an arm section 21 that supports the rotor blades 5, and a frame section 20 that houses a circuit board incorporating a battery, lights, camera, and the control unit 8 described later. However, it may also be a helicopter, eVTOL, etc. The number of rotor blades 5 on the aircraft 2 may be one or multiple. The aircraft 2 may be a manned aircraft or an unmanned aerial vehicle, but here we will describe an example in which the takeoff, landing, and turning of the aircraft 2 are controlled from a terminal device 4.

[0016] As shown in Figure 2(a), the aircraft 2 comprises a rotor 5, an encoder 6, a sensor 7, a control unit 8, a communication unit 9, an angular velocity calculation unit 10, and an altitude estimation unit 11. The rotor 5 is composed of a propeller, and its rotation generates lift. The encoder 6 rotates together with the rotor 5, and the sensor 7 can detect the rotation speed of the rotor 5 (the number of rotations per unit time). The encoder 6 functions as a rotation detection mechanism that works in cooperation with the sensor 7 to detect the rotation of the rotor 5. The encoder 6 is composed of a ring shape, a disc shape, or the like, and is installed on the rotor 5 or a rotating shaft connected to the rotor 5.

[0017] The type of sensor 7 is not particularly limited, as long as it detects the rotation of the encoder 6, which rotates in conjunction with the rotation of the rotor blade 5, and outputs an electrical signal based on this. For example, if the encoder 6 is magnetized with alternating north and south poles, the sensor 7 is a magnetic sensor, and it detects the rotation of the rotor blade 5 by detecting the change in magnetic flux density accompanying the rotation of the encoder 6. Also, if the encoder 6 has multiple slits that penetrate it at intervals in the circumferential direction, the sensor 7 is an optical sensor, and it detects the rotation of the rotor blade 5 by detecting the light that passes through the slits of the rotating encoder 6 or the light reflected from the encoder 6. Note that if the sensor 7 is an optical sensor, it may be configured to detect infrared light other than visible light, and the aircraft 2 may be equipped with an illumination unit that irradiates infrared light toward the encoder 6.

[0018] The control unit 8 is composed of various processors such as a CPU and MPU that perform various controls on the aircraft 2. Various processes are executed when the control unit 8 executes various calculation programs such as the angular velocity calculation unit 10 and the altitude estimation unit 11 stored in the memory unit (not shown). The communication unit 9 performs the transmission and reception of data commands, etc. between the aircraft 2 and the terminal device 4. The angular velocity calculation unit 10 calculates the angular velocity of the rotor blade 5 from the electrical signal output by the sensor 7. The altitude estimation unit 11 estimates the altitude of the aircraft 2 from the angular velocity of the rotor blade 5 calculated by the angular velocity calculation unit 10.

[0019] The terminal device 4 may be a personal computer or a mobile terminal such as a smartphone or tablet, and is not particularly limited, but here we will describe an example in which a notebook computer is used as the terminal device 4. The terminal device 4 is capable of communicating various data with the aircraft 2 via the communication network 3. The terminal device 4 is also configured as an operating terminal for the aircraft 2, which can be remotely controlled. As shown in Figure 2(b), the terminal device 4 comprises a control unit 12, a storage unit 13, a communication unit 14, and a display unit 15. The control unit 12 is composed of various processors such as a CPU or MPU that perform various controls of the terminal device 4. The storage unit 13 is equipped with an HDD (hard disk drive), an SSD (solid state drive), flash memory, etc. The communication unit 14 is connected to the communication network 3 and is configured to send and receive data with the outside world, and may be connected to the communication network 3 by a wired connection or by a wireless connection. The display unit 15 is a user interface that displays various information based on the control of the control unit 12, and is composed of an LCD panel or the like. In addition, terminal device 4 includes a user interface that accepts user operations, and is equipped with an operation unit (not shown) consisting of a keyboard and mouse.

[0020] The flying object 2 generates lift (lifting force) by the rotation of the rotary wings 5, and the higher the angular velocity, the greater the lift, enabling it to ascend in altitude. Utilizing this characteristic, the altitude estimation system 1 according to the present embodiment models the vertical movement of the flying object 2 based on the equation of motion, calculates the angular velocity of the rotary wings 5 by the encoder 6, the sensor 7, and the angular velocity calculation unit 10, and estimates the altitude of the flying object 2 by the altitude estimation unit 11 from the calculated angular velocity. At this time, the altitude estimation unit 11 calculates the altitude z [m] of the flying object 2 having N rotary wings 5 at time t [s] using the following mathematical formula 1 which is a differential equation of motion.

[0021] (m represents the mass [kg] of the flying object 2. C Ｌ : proportional coefficient for converting the angular velocity of the rotary wings 5 into lift [N·rad －２ ·s ２ . ω ｉ : represents the angular velocity [rad / s] of the rotary wings 5. g: gravitational acceleration [m / s ２ . k: air resistance coefficient [N·m －１ ·s].)

[0022] The proportional coefficient of C Ｌ is a unique value based on the configuration of the rotary wings 5 of the flying object 2. N is the number of rotary wings 5 (propellers), and the air resistance coefficient of k is a value estimated from the flying object 2 used. When the flying object 2 is hovering (stationary in the air), since the speed and acceleration of the flying object 2 are "0", the formula (1) shown in the following mathematical formula 2 becomes the formula (2), and C Ｌ can be derived from the formula (3).

[0023]

[0024] A program is executed to estimate the altitude of the aircraft 2 using the angular velocity of the rotor blades 5 and the above formula 1. The estimated altitude of the aircraft 2 is transmitted to the terminal device 4 via the communication network 3 by the communication unit 9, and the terminal device 4 displays the received estimated altitude of the aircraft 2 on the display unit 15. If the estimated altitude of the aircraft 2 differs from the target altitude, the control unit 8 of the aircraft 2 may automatically execute a control to correct the altitude of the aircraft 2, or the terminal device 4 may instruct the correction of the altitude of the aircraft 2 via the communication network 3.

[0025] The altitude estimation unit 11 may estimate the altitude of the aircraft 2 using the altitude from the ground surface at the start of altitude estimation as a reference value, or it may estimate the current altitude of the aircraft 2 using the altitude at the start of altitude estimation as a reference value. Figure 3(a) shows an example in which the current altitude of the aircraft 2 is estimated using the altitude from the "ground surface" at the start of altitude estimation as a reference value. In this case, the altitude H from the ground surface at the start of estimation is used as the reference, so this method is applied when the altitude H is known or when used in conjunction with a device that can measure altitude, such as a distance sensor. For example, when the aircraft 2 is launched from a building that is 100m above the ground surface, the reference altitude H = 100m is added to the altitude estimated by the altitude estimation unit 11. Therefore, if, at time t1 in Figure 3(a), the altitude is derived from equation 1 to be "+α1" above point z(0), the altitude estimation unit 11 estimates "altitude H + α1". Furthermore, at time t2 in Figure 3(a), if the altitude is derived from equation 1 as "-α2" compared to point z(0), the altitude estimation unit 11 estimates the altitude as "altitude H-α2". With this configuration, the estimated altitude of the aircraft 2 after the start of estimation becomes less susceptible to the influence of the ground surface conditions. Also, if the altitude from the ground surface at the start of estimation is known, then highly accurate altitude estimation can be performed thereafter.

[0026] Figure 3(b) shows an example of estimating the altitude of the aircraft 2 using the altitude at the start of the altitude estimation as the reference value. In this case, the point at the start of the estimation is set to an altitude of 0m, and this is used as the reference. For example, this is effective when the aircraft 2 is placed directly on the ground and flown, or when you want to understand the vertical movement, sway, and altitude difference of the aircraft 2 after it has reached a stable flight state. Therefore, for example, if at time t1 in Figure 3(b) the altitude is derived from equation 1 to be "+α3" from point z(0), the altitude estimation unit 11 estimates "altitude α3". Also, if at time t2 in Figure 3(b) the altitude is derived from equation 1 to be "-α4" from point z(0), the altitude estimation unit 11 estimates "altitude -α4".

[0027] Next, an example of altitude estimation of the aircraft 2 by the altitude estimation system 1 (altitude estimation program) will be explained with reference to the flowchart in Figure 4. When the rotor blades 5 of the aircraft 2 rotate, the aircraft 2 begins to fly (S100). As the encoder 6 rotates along with the rotation of the rotor blades 5, the sensor 7 detects the rotation of the encoder 6 and outputs an electrical signal based on this (S101, 102). Upon receiving the electrical signal output by the sensor 7, the angular velocity calculation unit 10 calculates the angular velocity of the rotor blades 5 based on the received electrical signal (S103). Once the angular velocity of the rotor blades 5 is calculated, the altitude estimation unit 11 calculates the estimated altitude of the aircraft 2 based on this angular velocity (S104). The estimated altitude of the aircraft 2 estimated by the altitude estimation unit 11 is transmitted to the terminal device 4 (S105), and the aircraft 2 continues to fly under flight control until it stops flying (S107) (S106).

[0028] According to the altitude estimation system 1 with the above configuration, the altitude estimation unit 11 can estimate the altitude of the aircraft 2 based on the angular velocity of the rotor blade 5 calculated by the angular velocity calculation unit 10, so the altitude estimation is not affected by the condition of the ground directly below the aircraft 2. Therefore, even if there are uneven terrain or buildings scattered along the flight path of the aircraft 2, the altitude estimation of the aircraft 2 does not fluctuate due to obstacles scattered on the ground, such as those that would cause the system to react to each obstacle, unlike, for example, a distance sensor.

[0029] The altitude estimation system 1 is not limited to the flowchart shown in Figure 4. For example, the angular velocity calculation unit 10 and the altitude estimation unit 11 may be provided in the terminal device 4, and the terminal device 4 may perform the steps of calculating the angular velocity in step S103 and estimating the altitude in step S104 based on the data transmitted from the aircraft 2. Alternatively, the angular velocity calculation unit 10 may be provided in the aircraft 2 and the altitude estimation unit 11 in the terminal device 4, with the aircraft 2 performing the angular velocity calculation in step S103 and the terminal device performing the altitude estimation in step S104. Furthermore, although the above description explains the flow when the altitude estimation system 1 is ON while the aircraft 2 is in flight, even when the aircraft 2 is in flight, the system may be turned ON only when altitude estimation is necessary and turned OFF when it is not necessary.

[0030] Next, referring to Figure 5, we will describe a comparative verification test comparing an example in which the aircraft 2 was flown while its altitude was actually measured by a distance sensor (comparative example) with an example in which the aircraft was flown while altitude estimation was performed using the altitude estimation system 1 according to this embodiment (example).

[0031] The conditions for the comparative verification test were as follows: Test location: Outdoors Drone used (flight 2): Quadcopter Number of rotor blades (5): 4 in total Distance sensor mounted on the drone: Ultrasonic sensor Encoder mounted on the drone (6): Magnetic encoder Sensor mounted on the drone (7): Hall sensor

[0032] In this comparative verification test, a distance sensor was mounted on a drone capable of running the altitude estimation system 1 according to this embodiment, and the test was conducted. Using the measurement start point as a reference, the comparative test was started approximately 40 seconds after the flight of the aircraft 2 stabilized, and the drone was flown for 140 seconds.

[0033] <Results> Figure 5 shows the results of the comparative verification test in a graph. The solid line represents the altitude estimation result by the altitude estimation system 1, and the dotted line represents the measured value by the distance sensor. The solid and dotted lines generally coincide in terms of their contours, and no significant errors were observed. <Verification> It was found that the altitude of the aircraft can be sufficiently determined using the altitude estimation system 1 according to this embodiment. Furthermore, if the altitude estimation system 1 is adopted while the aircraft is equipped with a distance sensor, as in this comparative verification test, it is possible to measure the altitude with the distance sensor while estimating the altitude based on the rotation speed of the rotor blades 5, thereby improving the reliability of the altitude information. Therefore, even if the distance sensor malfunctions, for example, the altitude estimation system 1 can cover the problem. Alternatively, for example, the average value of the altitude measured by the distance sensor and the altitude estimated by the altitude estimation system 1 may be calculated and adopted as the estimated altitude of the aircraft 2. Furthermore, in the case of an aircraft 2 whose flight altitude is controlled to a constant altitude, even if the onboard distance sensor reacts to every small obstacle due to its performance limitations, the flight altitude of the aircraft 2 can be stabilized by also referring to the altitude estimation result from the altitude estimation system 1 when controlling the flight altitude of the aircraft 2.

[0034] The configuration and form of the altitude estimation system 1 and altitude estimation program according to this embodiment are not limited to the above embodiment. For example, the configuration and structure of the aircraft 2 and terminal device 4, and the shape and number of rotor blades 5 are not limited to the illustrated example. Also, the sensor 7 may be a sensor other than a magnetic sensor or optical sensor. Furthermore, the aircraft 2 may have both a configuration for measuring altitude using distance sensors such as ultrasonic waves or light, as well as a barometric pressure sensor, imaging unit, etc., and a configuration for estimating altitude using the altitude estimation system 1. In addition, the aircraft 2 may be operated using a dedicated transmitter (remote control).

[0035] 1 Altitude estimation system 2 Aircraft 5 Rotor wing 10 Angular velocity calculation unit 11 Altitude estimation unit

Claims

1. An altitude estimation system for estimating the altitude of an aircraft that generates lift by the rotation of a rotor blade, comprising: an encoder that rotates together with the rotor blade; a sensor that detects the rotation of the encoder and outputs an electrical signal based thereon; an angular velocity calculation unit that calculates the angular velocity of the rotor blade from the electrical signal; and an altitude estimation unit that estimates the altitude of the aircraft from the angular velocity of the rotor blade.

2. In claim 1, the altitude estimation unit estimates the altitude z [m] of the aircraft having N of the rotor blades at time t [s] using the following formula 1. A altitude estimation system characterized by this. (m represents the mass [kg] of the aircraft. C ２ , －１ : Proportional coefficient [N·rad －２ ·s ２ representing the conversion of the angular velocity of the rotor blade into lift. ω ｉ : Represents the angular velocity [rad / s] of the rotor blade. g: Gravitational acceleration [m / s ２ is represented. k: Air resistance coefficient [N·m －１ ·s] is represented.) 3. The altitude estimation system according to claim 1 or claim 2, characterized in that the altitude estimation unit estimates the current altitude of the aircraft using the altitude from the ground surface at the start of altitude estimation of the aircraft as a reference value.

4. The altitude estimation system according to claim 1 or claim 2, characterized in that the altitude estimation unit estimates the current altitude of the aircraft using the altitude at the start of altitude estimation of the aircraft as a reference value.

5. An altitude estimation program for estimating the altitude of an aircraft that generates lift by the rotation of a rotor blade, characterized by performing the steps of: obtaining the angular velocity of the rotor blade from an electrical signal output by a sensor that detects the rotation of an encoder provided to rotate together with the rotation of the rotor blade; and estimating the altitude of the aircraft from the obtained angular velocity of the rotor blade.

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