Unmanned aerial vehicle and stop system

Abstract

This unmanned aerial vehicle comprises a plurality of electric motors for rotating a plurality of rotors, respectively, a plurality of motor drive circuits for driving the plurality of electric motors, respectively, and a controller for controlling the operation of each of the plurality of motor drive circuits. The controller changes the operations of the plurality of motor drive circuits from a state in which the unmanned aerial vehicle is in flight to a state in which flight is disabled in response to a stop signal.

Description

Unmanned Aerial Vehicles and Termination Systems

[0001] The present disclosure relates to unmanned aerial vehicles and arresting systems.

[0002] An unmanned aerial vehicle (UAV) is an aircraft that cannot carry a person due to its structure and can fly by remote control or automatic pilot. Rotary-wing unmanned aerial vehicles are unmanned aerial vehicles that obtain lift using propellers, i.e., rotors, that rotate around an axis. Small unmanned aerial vehicles equipped with multiple rotors (multi-rotor UAVs) are also called "drones," "multirotors," or "multicopters," and are widely used for applications such as aerial photography, surveying, logistics, and pesticide spraying.

[0003] Patent Document 1 describes a fault diagnosis circuit for diagnosing whether a relay used in a PLC (Programmable Logic Controller) is stuck open or stuck closed.

[0004] Japanese Patent Application Laid-Open No. 2020-134157

[0005] The unmanned aerial vehicle may be equipped with a relay circuit for emergency stopping of rotor rotation. Improved technology for diagnosing faults in the relay circuit is desirable.

[0006] The present disclosure provides a stopping system capable of stopping the flight of an unmanned aerial vehicle, and an unmanned aerial vehicle equipped with the stopping system.

[0007] In an exemplary and non-limiting embodiment, the unmanned aerial vehicle of the present disclosure is an unmanned aerial vehicle having multiple rotors, and includes multiple electric motors that rotate the multiple rotors, respectively, multiple motor drive circuits that drive the multiple electric motors, respectively, and a controller that controls the operation of the multiple motor drive circuits, and the controller changes the operation of the multiple motor drive circuits from the flight state of the unmanned aerial vehicle to the flight-incapable state in response to a stop signal.

[0008] In an exemplary and non-limiting embodiment, the stopping system of the present disclosure is used in an unmanned aerial vehicle having multiple rotors, multiple electric motors that rotate the multiple rotors, multiple motor drive circuits that drive the multiple electric motors, and a controller that controls the operation of the multiple motor drive circuits, and is a stopping system for stopping the operation of the multiple motor drive circuits, configured to output a stop signal to the controller and change the operation of the multiple motor drive circuits from a flight state of the unmanned aerial vehicle to a state in which flight is impossible.

[0009] According to an embodiment of the present disclosure, there is provided a stopping system capable of stopping the flight of an unmanned aerial vehicle, and an unmanned aerial vehicle equipped with the stopping system.

[0010] 1 is a block diagram schematically showing several examples of a rotary drive device that rotates rotors in an unmanned aerial vehicle having multiple rotors. FIG. 2 is a plan view schematically showing one basic configuration example of an unmanned aerial vehicle having multiple rotors. FIG. 3 is a side view schematically showing one basic configuration example of an unmanned aerial vehicle having multiple rotors. FIG. 4 is a plan view schematically showing another basic configuration example of an unmanned aerial vehicle having multiple rotors. FIG. 5 is a block diagram showing an example basic configuration of a battery-powered multicopter. FIG. 6 is a block diagram showing an example basic configuration of a series hybrid drive multicopter. FIG. 7 is a block diagram showing an example basic configuration of a parallel hybrid drive multicopter. FIG. 8 is a block diagram showing detailed configuration examples of a relay circuit and a diagnostic device. FIG. 9 is a flowchart showing example 1 of a procedure for fault diagnosis by a diagnostic device. FIG. 10 is a flowchart showing example 2 of a procedure for fault diagnosis by a diagnostic device. FIG. 11 is a flowchart showing example 3 of a procedure for fault diagnosis by a diagnostic device. FIG. 12 is a schematic diagram showing an example in which a multicopter, an agricultural machine, a server, and a terminal device are connected via a communication network.

[0011] An unmanned aerial vehicle with multiple rotors includes a rotary drive unit that rotates the rotors (hereinafter sometimes referred to as "propellers"). Hereinafter, such an unmanned aerial vehicle will be referred to as a "multicopters."

[0012] There are various configurations of the rotary drive device provided in a multicopter. Fig. 1A is a block diagram schematically illustrating four examples of the rotary drive device 3 in the present disclosure.

[0013] The first rotation drive device 3A shown in FIG. 1A has a plurality of electric motors (hereinafter referred to as "motors") 14 that rotate a plurality of rotors, and a battery 52 that stores power to be supplied to each motor 14. The battery 52 is, for example, a secondary battery such as a polymer lithium-ion battery. Each rotor 2 is connected to the output shaft of the corresponding motor 14 and is rotated by the motor 14. In order to increase the payload and / or flight time, it is necessary to increase the power storage capacity of the battery 52. ​​The power storage capacity of the battery 52 can be increased by increasing the size of the battery 52, but increasing the size of the battery 52 results in an increase in weight.

[0014] The second rotation drive device 3B shown in FIG. 1A includes a power transmission system 23 mechanically connected to the rotor 2 and an internal combustion engine 7a that provides driving force (torque) to the power transmission system 23. The power transmission system 23 includes mechanical components such as gears or belts, and transmits torque from the output shaft of the internal combustion engine 7a to the rotor 2. The internal combustion engine 7a can efficiently generate mechanical energy by burning fuel. Examples of the internal combustion engine 7a include a gasoline engine, a diesel engine, and a hydrogen engine. The number of internal combustion engines 7a included in the rotation drive device 3B is not limited to one.

[0015] The third rotary drive device 3C shown in FIG. 1A includes multiple motors 14, a power buffer 9 that stores power to be supplied to each motor 14, a power generator 8 such as an alternator that generates power, and an internal combustion engine 7a that provides mechanical energy for the power generator 8 to generate electricity. A typical example of the power buffer 9 is a battery such as a secondary battery, but it may also be a capacitor. In the third rotary drive device 3C, even if the power buffer 9 does not have a large storage capacity, the power generator 8 generates power using the driving force (mechanical energy) of the internal combustion engine 7a, thereby enabling an increase in payload and / or flight time. This type of drive is called a "series hybrid drive." The power generator 8 and internal combustion engine 7a in the series hybrid drive are called a "range extender" because they extend the flight distance of the multicopter.

[0016] 1A includes a plurality of motors 14, a power buffer 9 that stores power to be supplied to each motor 14, a power generator 8 such as an alternator that generates power, an internal combustion engine 7a that provides driving force for generating power to the power generator 8, and a power transmission system 23 that transmits the driving force generated by the internal combustion engine 7a to a rotor 2 to rotate the rotor 2. At least one rotor 2 of the plurality of rotors 2 is rotated by the internal combustion engine 7a, and the other rotors 2 are rotated by the motor 14. In the fourth rotary drive device 3D, the mechanical energy generated by the internal combustion engine 7a can also be used to rotate the rotor 2 without being converted into electric power, thereby improving energy utilization efficiency. This type of drive is called a "parallel hybrid drive."

[0017] Fig. 1B is a plan view schematically illustrating one basic configuration example of multicopter 10. The configuration example of Fig. 1B includes the first rotational drive device 3A shown in Fig. 1A as the rotational drive device 3. That is, the rotational drive device 3 (3A) in this example includes a motor 14 and a battery 52. ​​Fig. 1C is a side view schematically illustrating the multicopter.

[0018] 1B and 1C includes a plurality of rotors 2, an airframe 4, and an airframe frame 5 that supports the rotors 2 and the airframe 4. The airframe frame 5 supports the airframe 4 at its center and rotatably supports the plurality of rotors 2 with a plurality of arms 5A extending outward from the center. A motor 14 that rotates the rotor 2 is provided near the tip of each arm 5A.

[0019] 1B, the multicopter 10 is a quad-type multicopter (quadcopter) having four rotors 2. The rotors 2 located on one diagonal line rotate in the same direction (clockwise or counterclockwise), while the rotors 2 located on different diagonal lines rotate in opposite directions.

[0020] The main body 4 includes a control device 4a that controls the operation of devices and components mounted on the multicopter 10, a group of sensors 4b connected to the control device 4a, a communication device 4c connected to the control device 4a, and a battery 52.

[0021] The control device 4 a may include, for example, a flight control device such as a flight controller and a host computer (companion computer). The companion computer can perform advanced arithmetic processing such as image processing, obstacle detection, and obstacle avoidance based on the sensor data acquired by the sensor group 4 b.

[0022] The sensor group 4b may include an acceleration sensor, an angular velocity sensor, a geomagnetic sensor, a barometric pressure sensor, an altitude sensor, a temperature sensor, a flow rate sensor, an imaging device, a laser sensor, an ultrasonic sensor, an obstacle contact sensor, and a Global Navigation Satellite System (GNSS) receiver. The acceleration sensor and the angular velocity sensor may be mounted on the airframe main body 4 as components of an IMU (Inertial Measurement Unit). Examples of the laser sensor may include, for example, a laser range finder used to measure the distance to the ground, and a two-dimensional or three-dimensional LiDAR.

[0023] The communication device 4c may include a wireless communication module for transmitting and receiving signals via an antenna to a transmitter or ground station (Ground Control Station (GCS)) on the ground, a mobile communication module using a cellular communication network, etc. The communication device 4c may receive signals such as control commands transmitted from the ground and transmit sensor data such as image data acquired by the sensor group 4b as telemetry information. The communication device 4c may have a function for communicating between multicopters and a satellite communication function. The control device 4a can be connected to a computer on the cloud via the communication device 4c. Some or all of the functions of the companion computer may be performed by the computer on the cloud.

[0024] The battery 52 is a secondary battery that stores power by charging and supplies power to the motors 14 by discharging. The battery 52 and the multiple motors 14 operate to rotate the multiple rotors 2, making it possible to generate a desired thrust.

[0025] Each of the multiple rotors 2 generally has multiple blades with a fixed pitch angle and generates thrust by rotation. The pitch angle may be variable. The multiple rotors 2 do not all need to have the same diameter (propeller diameter); one or more rotors 2 may have a larger diameter than the other rotors 2. The thrust (static thrust) generated by a rotating rotor 2 is generally proportional to the cube of the rotor 2 diameter. Therefore, when rotors 2 with different diameters are included, the rotor 2 with a relatively larger diameter may be referred to as the "main rotor," and the rotor 2 with a relatively smaller diameter may be referred to as the "sub-rotor." Note that, regardless of the diameter, the configuration of the rotary drive device 3 may include a rotor 2 capable of generating a relatively larger thrust and a rotor 2 with a relatively smaller thrust. In this case, the rotor 2 capable of generating a relatively larger thrust may be referred to as the "main rotor," and the rotor 2 with a relatively smaller thrust may be referred to as the "sub-rotor." For example, the rotor 2 that generates a relatively large thrust per rotation may be referred to as the "main rotor," and the rotor 2 that generates a relatively small thrust per rotation may be referred to as the "sub-rotor." In one example, the main rotor may be positioned more inward than the sub-rotors. In other words, each rotor 2 may be positioned so that the distance from the center of the airframe to the rotation axis of each main rotor is shorter than the distance from the center of the airframe to the rotation axis of each sub-rotor.

[0026] In this example, the rotary drive device 3 includes a plurality of motors 14. As mentioned above, the rotary drive device 3 may include an internal combustion engine 7a.

[0027] 1D is a plan view schematically illustrating an example of the basic configuration of a multicopter 10 including a second rotational drive device 3B as the rotational drive device 3. In the example shown in FIG. 1D, an internal combustion engine 7a is supported by the airframe main body 4. In this example, the driving force generated by the internal combustion engine 7a is transmitted to multiple rotors 2 via multiple power transmission systems 23, causing each rotor 2 to rotate. The control device 4a can change the rotational speed of each rotor 2 by controlling each power transmission system 23.

[0028] In a "parallel hybrid drive" in which some of the multiple rotors 2 are rotated by the internal combustion engine 7a and the other rotors 2 are rotated by the motor 14, the internal combustion engine 7a and the battery 52 are supported on the aircraft body 4. At least one rotor 2 of the multiple rotors 2 is connected to the internal combustion engine 7a via the power transmission system 23, and the other rotors 2 are connected to the motor 14.

[0029] In such a parallel hybrid drive, the diameter of one or more rotors 2 rotated by the internal combustion engine 7a may be larger than the diameter of the other rotors 2 rotated by the motor 14. In other words, the internal combustion engine 7a may be used to rotate the main rotor, and the motor 14 may be used to rotate the sub-rotor. In such a case, the main rotor is mainly used to generate thrust, and the sub-rotor is used to generate thrust and for attitude control. The main rotor may also be called a "booster rotor," and the sub-rotor may also be called an "attitude control rotor."

[0030] In the case of parallel hybrid drive, the internal combustion engine 7a is used for both thrust generation and power generation. By selectively transmitting the driving force (torque) generated by the internal combustion engine to one or both of the rotor and the power generator, it is possible to achieve a good balance between thrust generation and power generation.

[0031] Equipping a multicopter with an internal combustion engine 7a and using the internal combustion engine 7a to generate thrust and / or electricity contributes to an increase in payload and flight time. It is desirable to control the attitude of a multicopter by rotating the propellers with a motor, which has better response characteristics than an internal combustion engine. Therefore, in applications where precise control of the attitude of a multicopter is required, it is desirable to employ a parallel hybrid drive or a series hybrid drive to increase the payload and flight time.

[0032] Increased payload and flight time may further expand the applications of multicopters. For example, in the agricultural field, multicopters are currently being used for spraying pesticides or monitoring crop growth conditions. However, by connecting various ground implements (hereinafter, sometimes simply referred to as "implements") to a multicopter, various agricultural tasks can be performed from the air. Agricultural implements are sometimes called "implements." Examples of implements include sprayers that spray pesticides on crops, mowers, seeders, spreaders, rakes, balers, harvesters, plows, harrows, or rotary tillers. Work vehicles such as tractors are not included in the "implements" of this disclosure.

[0033] In the example shown in FIG. 1C , a work implement 200 is coupled to the multicopter 10. The work implement 200 can spray, for example, pesticides or fertilizers on a field or crops within the field. Increasing the payload and flight time allows for a larger and / or more versatile work implement 200. For example, by changing the work implement 200 coupled to the multicopter 10, a variety of ground tasks (agricultural operations) can be performed, including liquid and granular application of pesticides, fertilization, thinning, weeding, transplanting, direct seeding, and harvesting. The work implement 200 may be equipped with a mechanism such as a robotic hand. In this case, a single work implement 200 can perform a variety of ground tasks. Furthermore, if the work implement 200 has a sufficient space to accommodate the materials, the work implement 200 can also transport agricultural materials or harvested products over a wide area.

[0034] 1C , the multicopter 10 includes a power supply device 76. The power supply device 76 is a device that supplies power to the work machine 200 from a drive energy source, such as the battery 52 or the power generation device 8, included in the multicopter 10. Various functions of the work machine 200 can be performed using this power. The work machine 200 includes actuators such as motors that operate using power obtained from the power supply device 76 of the multicopter 10. The work machine 200 preferably includes a battery that stores power.

[0035] 2A is a block diagram showing an example of the basic configuration of a battery-powered multicopter 10. The battery-powered multicopter 10 includes a plurality of rotors 12, a plurality of motors 14 that rotate the rotors 12, a plurality of ESCs (electric speed controllers) 16 each having a motor drive circuit that drives the motors 14, a battery 52 that supplies power to the corresponding motor 14 via each ESC 16, a control device 4a that controls the plurality of ESCs 16 to control attitude while flying, a sensor group 4b, a communication device 4c, and a power supply device 76 electrically connected to the battery 52. ​​The rotor 12 is an example of a rotor 2. The control device 4a, the sensor group 4b, the communication device 4c, and other devices are connected to each other so that they can communicate with each other, for example, via a controller area network (CAN) bus. 2A, for simplicity, the rotor 12, the motor 14, and the ESC 16 are each shown as a single block, but there are actually multiple rotors 12, motors 14, and ESCs 16. This also applies to FIGS. 2B and 2C.

[0036] The control device 4a can receive control commands wirelessly from, for example, a ground station 6 located on the ground via the communication device 4c. The number of ground stations 6 is not limited to one, and they may be distributed across multiple locations. The communication device 4c can also receive control commands wirelessly from an operation terminal of a pilot located on the ground. The control device 4a may have a function to automatically or autonomously perform each of the operations of takeoff, flight, obstacle avoidance, and landing based on sensor data obtained from the sensor group 4b.

[0037] The control device 4a may be configured to communicate with the work machine 200 connected to the power supply device 76 and to acquire a signal indicating the state of the work machine 200 from the work machine 200. The control device 4a may also provide a signal to the work machine 200 that controls the operation of the work machine 200. Furthermore, the work machine 200 may generate a signal instructing the operation of the multicopter 10 and transmit the signal to the control device 4a. Such communication between the control device 4a and the work machine 200 may be performed wired or wirelessly.

[0038] The multicopter 10 according to the embodiment of the present disclosure further includes a relay circuit 80 configured to interrupt a control signal transmitted from the control device 4a to each ESC 16 in response to a stop signal for stopping the rotation of the multiple rotors 12, and a diagnostic device 82 configured to perform fault diagnosis of the relay circuit 80 based on the output from the relay circuit 80. In this specification, the relay circuit 80 and the diagnostic device 82 are collectively referred to as a "stop system." The stop system may be used to emergency stop the rotation of the multiple rotors 12. For this reason, the stop system may also be referred to as a "safety device."

[0039] The relay circuit 80 is electrically connected between the multiple ESCs 16 (or multiple motor drive circuits) and the control device 4a. The relay circuit 80 has multiple relays corresponding to the multiple ESCs 16. The configuration and operation of the stop system including the relay circuit 80 and the diagnostic device 82 will be described in detail later.

[0040] FIG. 2B is a block diagram showing an example of the basic configuration of a series hybrid drive multicopter 10. Similar to the battery-powered multicopter 10, the series hybrid drive multicopter 10 includes multiple rotors 12, multiple motors 14, multiple ESCs 16, a control device 4a, a sensor group 4b, a communication device 4c, a relay circuit 80, and a diagnostic device 82. The illustrated series hybrid drive multicopter 10 further includes an internal combustion engine 7a, a fuel tank 7b for storing fuel for the internal combustion engine 7a, a power generation device 8 driven by the internal combustion engine 7a to generate electric power, a power buffer 9 for temporarily storing the electric power generated by the power generation device 8, and a power supply device 76 electrically connected to the power buffer 9. The power buffer 9 is, for example, a battery such as a secondary battery. The electric power generated by the power generation device 8 is supplied to the motor 14 via the power buffer 9 and the ESC 16. The electric power generated by the power generation device 8 may also be supplied to the work machine 200 via the power supply device 76.

[0041] 2C is a block diagram showing an example of the basic configuration of a parallel hybrid drive multicopter 10. Similar to the series hybrid drive multicopter 10, the parallel hybrid drive multicopter 10 includes multiple rotors 12, multiple motors 14, multiple ESCs 16, a control device 4a, a sensor group 4b, a communication device 4c, a relay circuit 80, a diagnostic device 82, an internal combustion engine 7a, a fuel tank 7b, a power generator 8, a power buffer 9, and a power supply device 76. The parallel hybrid drive multicopter 10 further includes a drive train 27 that transmits the driving force of the internal combustion engine 7a, and a rotor 22 that rotates by receiving the driving force of the internal combustion engine 7a from the drive train 27. The rotor 22 is an example of a rotor 2. The number of rotors 22 connected to the drive train 27 and rotating may be one or more.

[0042] In the parallel hybrid drive multicopter 10, the internal combustion engine 7a not only drives the power generation device 8 to generate electricity, but also mechanically transmits energy to the rotor 22 to rotate the rotor 22. On the other hand, in the series hybrid drive multicopter 10, all of the rotors 12 are rotated by the electric power generated by the power generation device 8. For this reason, in the series hybrid drive multicopter 10, if the power generation device 8 is, for example, a fuel cell, the internal combustion engine 7a is not an essential component.

[0043] Fig. 3 is a block diagram showing a detailed configuration example of the relay circuit 80 and the diagnostic device 82. Fig. 3 shows a configuration example of the relay circuit 80 and the diagnostic device 82 (i.e., the stop system) mounted on a quad-type multicopter. However, the multicopter is not limited to a quad-type multicopter, and may be, for example, a hexa-type multicopter (hexacopter) having six rotors, or an octo-type multicopter (octocopter) having eight rotors.

[0044] In the example shown in FIG. 3, the quad-type multicopter includes four rotors 12a to 12d, four motors 14a to 14d that rotate the four rotors 12a to 12d, respectively, four ESCs 16a to 16d that drive the four motors 14a to 14d, respectively, a controller (Micro Controller Unit: MCU) 70, a relay circuit 80 electrically connected between the four ESCs 16a to 16d and the controller 70, and a diagnostic device 82 connected between the relay circuit 80 and the four ESCs 16a to 16d. The rotor 12a, motor 14a, and ESC 16a may be collectively referred to as the "first system," the rotor 12b, motor 14b, and ESC 16b may be collectively referred to as the "second system," the rotor 12c, motor 14c, and ESC 16c may be collectively referred to as the "third system," and the rotor 12d, motor 14d, and ESC 16d may be collectively referred to as the "fourth system."

[0045] The controller 70 controls the operation of each of the multiple motor drive circuits (ESCs 16) and transmits control signals to each of the multiple motor drive circuits for controlling the rotational speed of the rotor 12. In other words, the controller 70 transmits control commands to each of the first to fourth systems for controlling the rotational speed of each rotor 12. The rotational speed is also referred to as the rotation speed. The rotation speed is the number of rotations per unit time and is expressed, for example, in revolutions per minute (rpm). In the example shown in FIG. 3 , the controller 70 controls the operation of each of the four ESCs 16a to 16d and transmits control signals to each of the four ESCs 16a to 16d for controlling the rotational speed of each rotor 12. An example of the controller 70 is the flight controller described above. In the following description, the controller 70 will be referred to as the "first controller 70" to distinguish it from the second controller described below.

[0046] In the embodiment of the present disclosure, an example of the control signal for controlling the rotational speed of each rotor 12 is a pulse signal, a PMW (Pulse Width Modulation) signal. The first controller 70 outputs a PWM signal having a duty ratio that defines a command value for the rotational speed of each motor 14. The duty ratio has a magnitude proportional to the rotational speed (command value). The duty ratio during fault diagnosis, which will be described later, is set to a range of 40% to 80%, for example.

[0047] The controller 70 is further configured to change the operation of the multiple motor drive circuits from a flight state of the multicopter to a flight-disabled state in response to a stop signal (STOP shown in FIG. 3 ). The stop signal is a signal transmitted to stop the rotation of the multiple rotors 12. In other words, the stop signal is a signal transmitted to stop the operation of the multiple motor drive circuits.

[0048] The relay circuit 80 is configured to interrupt, in response to the stop signal, the control signal transmitted from the first controller 70 to each ESC 16. The relay circuit 80 has a plurality of relays 81, each of which interrupts the control signal in response to the stop signal.

[0049] The stopping system in this embodiment is configured to output a stop signal to the controller 70 and change the operation of the multiple motor drive circuits from the multicopter's flight state to a state in which flight is disabled. The stopping system may include an operation terminal 99 for outputting the stop signal to the controller 70. The operation terminal 99 can notify the multicopter of a flight stop command, for example, when the multicopter is positioned above a farm field. This causes the stop signal to be sent to the controller 70. Examples of the operation terminal 99 include a mobile terminal such as a terminal device, smartphone, or tablet computer. The stop signal may be sent from the companion computer in response to a flight stop command sent from the operation terminal 99 used by the pilot. Alternatively, the companion computer may determine whether an emergency exists based on sensor data obtained from the sensor group 4b, for example, and send a stop signal to the relay circuit 80 based on the determination result. The pilot can intentionally stop the rotation of the multiple rotors of the multicopter by sending a flight stop command to the multicopter from the operation terminal 99. For example, when flying in an area with few buildings, such as a field (agricultural work area), if for some reason the flight cannot be continued or the flight becomes unstable, emergency measures such as forcing the multicopter to land or crash can be taken.

[0050] In the example shown in FIG. 3 , the relay circuit 80 is configured to interrupt the PWM signals transmitted from the first controller 70 to each ESC 16 in response to a stop signal for stopping the rotation of the four rotors 12a to 12d. Specifically, the relay circuit 80 includes four relays 81a to 81d, each of which interrupts the PWM signal in response to the stop signal. The relay circuit 80 may further include a transistor for turning each relay on and off. One end of the relay 81a is connected to the ESC 16a, and the other end of the relay 81a is connected to the first controller 70. One end of the relay 81b is connected to the ESC 16b, and the other end of the relay 81b is connected to the first controller 70. One end of the relay 81c is connected to the ESC 16c, and the other end of the relay 81c is connected to the first controller 70. One end of the relay 81d is connected to the ESC 16d, and the other end of the relay 81d is connected to the first controller 70.

[0051] The PWM signals PWM1 to PWM4 transmitted from the first controller 70 are input to the first to fourth systems via four relays 81a to 81d, respectively. During operations such as takeoff, flight, and landing, all four relays 81a to 81d are always in the ON state. In an emergency, all four relays 81a to 81d are turned OFF in response to a stop signal.

[0052] Each of the multiple relays in relay circuit 80 may experience an on-failure or an off-failure. An on-failure is a failure in which the relay is always in the on state and does not transition to the off state, and an off-failure is a failure in which the relay is always in the off state and does not transition to the on state. An on-failure may be called a "stuck on" and an off-failure may be called a "stuck off."

[0053] In order for the relay circuit 80 to function as a safety device, it is important to ensure the operation of the relay circuit 80 before the flight of the multicopter. The diagnostic device 82 is configured to diagnose on / off failures of the multiple relays. The diagnostic device 82 preferably performs a fault diagnosis of the relay circuit 80 before the takeoff of the multicopter. In other words, the diagnostic device 82 preferably performs a diagnosis of on / off failures of the multiple relays before the takeoff of the multicopter. However, the timing of the diagnosis of on / off failures is not limited to before takeoff and may be, for example, after landing.

[0054] As illustrated in FIG. 3 , the multicopter according to an embodiment of the present disclosure may include a warning device 90. The warning device 90 issues a warning indicating an on-off failure of at least one of the relays. Examples of the warning device 90 include a buzzer that emits a warning sound to notify of a relay failure, or an optical device such as an LED (Light Emitting Diode) lamp. For example, the diagnostic device 82 may diagnose an on-off failure of the relays when the multicopter is powered on. If the diagnostic device 82 detects an on-off failure of at least one of the relays, it causes the warning device 90 to issue a warning. This allows the operation of the relay circuit 80 to be guaranteed before the multicopter flies, ensuring the safety of the multicopter. If a failure of the relay circuit 80 is detected, a warning sound, for example, from a buzzer, can be used to prompt the pilot to abort the multicopter flight.

[0055] The diagnostic device 82 includes multiple averaging circuits 83, an integrating circuit 84, an analog-to-digital (AD) conversion circuit 85, and a second controller (MCU) 86. However, if the second controller 86 has an AD conversion function, the AD conversion circuit 85 is not necessary. The multiple averaging circuits 83 are connected to the multiple ESCs 16 sides of the multiple relays, respectively. Each of the multiple averaging circuits 83 outputs an analog voltage corresponding to the duty ratio of the PWM signal. The integrating circuit 84 includes one or more adders 87 and integrates the output values ​​from the multiple averaging circuits 83 to output an integrated value. The AD conversion circuit 85 converts the integrated value output as an analog signal from the integrating circuit 84 into a digital signal. The second controller 86 detects an on / off fault in at least one of the multiple relays 81 based on the integrated value output from the integrating circuit 84. More specifically, the second controller 86 detects an on / off failure of at least one of the plurality of relays based on the output value of the digital signal output from the AD conversion circuit 85 .

[0056] In the example shown in FIG. 3 , the four averaging circuits 83a to 83d are connected to the ESC 16 sides of the four relays 81a to 81d, respectively. Specifically, the averaging circuit 83a is connected to one end of the relay 81a and the integrating circuit 84. The averaging circuit 83b is connected to one end of the relay 81b and the integrating circuit 84. The averaging circuit 83c is connected to one end of the relay 81c and the integrating circuit 84. The averaging circuit 83d is connected to one end of the relay 81d and the integrating circuit 84. With these electrical connections, the PWM signal output from the first controller 70 is input to each ESC 16 and each averaging circuit 83 via each relay 81.

[0057] Each averaging circuit 83 converts the input PWM signal into an analog voltage signal according to its duty ratio. For example, in the case of a 40% duty ratio, each averaging circuit 83 converts the input PWM signal into an analog voltage signal of 0.25 V. In the case of an 80% duty ratio, each averaging circuit 83 converts the input PWM signal into an analog voltage signal of 0.5 V.

[0058] The integrating circuit 84 includes an adder 87a that adds the output from the averaging circuit 83a and the output from the averaging circuit 83b, an adder 87b that adds the output from the averaging circuit 83c and the output from the adder 87a, and an adder 87c that adds the output from the averaging circuit 83d and the output from the adder 87b. For example, in the case of a 40% duty ratio, when all four relays 81a to 81d are in the ON state, the integrated value output from the integrating circuit 84 is 1V. In the case of an 80% duty ratio, when all four relays 81a to 81d are in the ON state, the integrated value output from the integrating circuit 84 is 2V. Thus, in the case of a duty ratio of 40 to 80% in the four systems, the integrated value output from the integrating circuit 84 is, for example, 1 to 2V. In other words, a digital signal corresponding to an analog signal of 1 to 2V is input to the second controller 86. In the case of eight systems, the integrated value output from the integrating circuit 84 is, for example, 2 to 4V.

[0059] 4 is a flowchart showing a first example of a procedure for fault diagnosis by the diagnostic device 82. Example 1 shows a procedure for diagnosing whether any of a plurality of relays has an on-failure. In an embodiment of the present disclosure, the diagnostic device 82 performs fault diagnosis when the multicopter is powered on. A method for diagnosing an on-failure of a relay will be described in detail with reference to FIG. 4.

[0060] First, the first controller 70 outputs a PWM signal to each of the first to fourth systems (step S11). In Example 1, the duty ratio of the PWM signal is 40%. However, the duty ratio is not limited to this value.

[0061] Next, the second controller 86 of the diagnostic device 82 outputs a relay open / close control signal to the relay circuit 80, thereby turning all four relays 81a to 81d off (step S12). The second controller 86 controls the on / off operation of each of the four relays 81a to 81d. For example, with a PWM signal input from the first controller 70 to the relay circuit 80, the second controller 86 controls the four relays 81a to 81d so that all four relays 81a to 81d are turned off. However, the order of the processes in steps S11 and S12 may be reversed. That is, the PWM signal may be input from the first controller 70 to the relay circuit 80 after all four relays 81a to 81d are turned off.

[0062] The second controller 86 compares the integrated value output from the integrating circuit 84 with a first threshold value to determine (or diagnose) whether at least one of the four relays 81a to 81d has an on-failure (step S13). Here, the first threshold value is determined based on the duty ratio of the PWM signal. In Example 1, the duty ratio is 40%, and in this case, an analog voltage signal of 0.25 V is output from the averaging circuit connected to the on-state relay. If at least one of the four relays 81a to 81d is in the on-state, an integrated value of 0.25 V or greater is output from the integrating circuit 84. Therefore, 0.25 V is set as the first threshold value.

[0063] If all four relays 81a to 81d are in the off state, the output value of the output signal output from the integrator circuit 84 (or the AD converter circuit 85) is zero. In contrast, if at least one of the four relays 81a to 81d has an on-failure, the integrator circuit 84 outputs an output signal with an output value proportional to the number of relays with an on-failure. In Example 1, for example, if one of the four relays 81a to 81d has an on-failure, the integrated value output from the integrator circuit 84 is 0.25 V, and if two of the four relays 81a to 81d have an on-failure, the integrated value output from the integrator circuit 84 is 0.5 V.

[0064] If the integrated value output from the integrating circuit 84 is equal to or greater than the first threshold value (Yes in step S13), the second controller 86 determines that at least one of the four relays 81 a to 81 d has an ON fault (step S14). On the other hand, if the integrated value output from the integrating circuit 84 is less than the first threshold value (No in step S13), the second controller 86 determines that all of the four relays 81 a to 81 d are normal with respect to the ON fault (step S15).

[0065] When the second controller 86 detects an ON failure in at least one of the four relays 81 a to 81 d in step S14, it can send a warning command to the warning device 90. In response to the warning command, the warning device 90 emits, for example, a warning sound. When the second controller 86 determines in step S15 that all of the relays are normal with respect to the ON failure, it proceeds to processing for diagnosing an OFF failure.

[0066] 5 is a flowchart showing Example 2 of the procedure for fault diagnosis by the diagnostic device 82. Example 2 shows the procedure for identifying a relay having an OFF fault from among a plurality of relays. The duty ratio of the PWM signal in Example 2 is 40%, the same as in Example 1. The diagnostic device 82 sequentially diagnoses relays 81a, 81b, 81c, and 81d for OFF faults in this order.

[0067] First, the first controller 70 selects the relay 81a, which is first in the diagnosis order, as the relay to be diagnosed for an OFF failure (step S21). Next, the second controller 86 outputs a control signal to the relay circuit 80 to turn off all four relays 81a to 81d, thereby turning all four relays 81a to 81d off (step S22). Next, the second controller 86 controls the relay circuit 80 to turn on relay 81a while keeping three relays 81b to 81d off (step S23). In other words, with the PWM signal input from the first controller 70 to the relay circuit 80, the second controller 86 controls the four relays 81a to 81d so that all four relays 81a to 81d are turned off, and then controls the four relays 81a to 81d so that only relay 81a among the four relays 81a to 81d is turned on.

[0068] The second controller 86 identifies the relay that has an OFF fault among the four relays 81a to 81d by comparing the integrated value output from the integrating circuit 84 with the second threshold value. Here, the second threshold value, like the first threshold value, is determined based on the duty ratio of the PWM signal. In Example 2, the duty ratio is 40%, and in this case, an analog voltage signal of 0.25 V is output from the averaging circuit connected to the relay that is in the ON state. Therefore, 0.25 V is set as the second threshold value. If all four relays 81a to 81d are normal with respect to OFF faults, and the relay selected to be diagnosed for faults among the four relays 81a to 81d is in the ON state, the integrated value output from the integrating circuit 84 (or the AD conversion circuit 85) is 0.25 V. In contrast, if the relay selected to be diagnosed for faults among the four relays 81a to 81d has an OFF fault, that relay will not be in the ON state, and the integrated value output from the integrating circuit 84 is 0 V.

[0069] If the integrated value output from the integrating circuit 84 is equal to or greater than the second threshold value (Yes in step S24), the second controller 86 determines that the relay selected as the diagnosis target among the four relays 81 a to 81 d is normal with respect to an OFF fault (step S25). On the other hand, if the integrated value output from the integrating circuit 84 is less than the second threshold value (No in step S24), the second controller 86 determines that the relay selected as the diagnosis target among the four relays 81 a to 81 d is suffering from an OFF fault (step S27).

[0070] When the second controller 86 detects an OFF failure of one of the four relays 81a to 81d in step S27, it can transmit a warning command to the warning device 90. In response to the warning command, the warning device 90 emits, for example, a warning sound.

[0071] In this way, the second controller 86 completes the diagnosis of an off fault of the relay 81a, which is first to be diagnosed. Subsequently, the second controller 86 diagnoses an off fault of the relay 81b, which is second to be diagnosed, using the same procedure as the procedure for diagnosing an off fault of the relay 81a (step S28). Thereafter, the second controller 86 repeatedly executes the processes of steps S22 to S24, diagnosing for an off fault of the relay 81c, which is third to be diagnosed, and the relay 81d, which is fourth to be diagnosed, until the diagnosis of all relays is completed (step S26).

[0072] 6 is a flowchart showing Example 3 of the procedure for fault diagnosis by the diagnostic device 82. Example 3 shows a procedure for identifying a relay that has an on-fault from among a plurality of relays. The procedure shown in Example 3 differs from the procedure shown in Example 2 in that the threshold value is different. The following mainly describes the differences from the procedure in Example 2.

[0073] If the diagnostic device 82 determines that one of the four relays 81a to 81d has an on-failure as a result of performing a fault diagnosis according to the procedure of Example 1, it can further perform a fault diagnosis according to the procedure of Example 3 to identify the relay that has an on-failure from among the four relays 81a to 81d.

[0074] The third threshold value used when determining an ON failure of one of the four relays 81a to 81d is greater than the second threshold value used when determining an OFF failure of one of the four relays 81a to 81d. The third threshold value, like the first and second threshold values, is determined based on the duty ratio of the PWM signal. In Example 3, the duty ratio of the PWM signal is 40%, and the third threshold value is set to 0.5 V.

[0075] If none of the four relays 81a to 81d has an on-failure, and the four relays 81a to 81d are turned on one by one in turn, the integrated value output from the integrator circuit 84 each time is 0.25 V. In contrast, if any of the four relays 81a to 81d has an on-failure, and a relay other than the relay with the on-failure is turned on, the integrated value output from the integrator circuit 84 becomes 0.5 V, and if the relay with the on-failure is turned on, the integrated value output from the integrator circuit 84 becomes 0.25 V.

[0076] If the integrated value output from the integrating circuit 84 is equal to or greater than the third threshold value (Yes in step S34), the second controller 86 determines that the relay selected as the target of diagnosis among the four relays 81a to 81d is normal with respect to an ON-fault (step S35). On the other hand, if the integrated value output from the integrating circuit 84 is less than the third threshold value (No in step S34), the second controller 86 determines that the relay selected as the target of diagnosis among the four relays 81a to 81d has an ON-fault (step S37). In this way, the second controller 86 can identify the relay with an ON-fault from among the multiple relays.

[0077] While it is possible to verify whether a typical relay drive circuit outputs a correct output signal, it is difficult to verify whether the circuit is operating normally—that is, whether the relay is operating on or off. As mentioned above, relay circuits are susceptible to on / off failures, so verifying the actual output state is more important than the reliability of the control signal provided to the relay circuit. In particular, relay circuits that function as safety devices mounted on multicopters require operational assurance before flight. When using a general-purpose electronic control unit (ECU), as the number of relays to be controlled on and off increases, port count limitations or connector optimization make it difficult to monitor the status of the output signals from all relays. Similar challenges remain even when using a custom (dedicated) ECU.

[0078] The shutdown system according to the embodiment of the present disclosure, and a multicopter equipped with the shutdown system, enable fault diagnosis of relay circuits with a relatively simple circuit configuration. This reduces not only the number of MCU ports but also the number of AD conversion circuits. Even if the number of rotors, i.e., the number of relays, increases, it becomes possible to appropriately diagnose faults in relay circuits using, for example, a general-purpose ECU without increasing the number of input circuits. This is also advantageous in terms of cost.

[0079] As described above, the control device 4a may include, for example, a flight control device such as a flight controller and a host computer (companion computer). The companion computer may perform various processes required for fault diagnosis and issue a command to halt flight based on the results of those processes to the relay circuit 80. Furthermore, some or all of the functions of the electrical components mounted on the multicopter 10, such as the control device 4a and diagnostic device 82, may be implemented by one or more servers (computers) 500 or terminal devices (including portable and fixed types) 600 connected to the communication device 4c of the multicopter 10 via a communication network N, as shown in FIG. 7 . An agricultural machine 700, such as a tractor, may be connected to such communication network N, and communication may be performed between the multicopter 10 and the agricultural machine 700. Some of the data used in processing by the control device 4a or diagnostic device 82, as well as control signals for the multicopter 10, may be transmitted from the agricultural machine 700 to the multicopter 10 via the communication network N.

[0080] A system providing various functions in the embodiments can also be retrofitted to a multicopter that does not have those functions. Such a system can be manufactured and sold independently of the multicopter. A computer program used in such a system can also be manufactured and sold independently of the multicopter. The computer program can be provided, for example, by being stored in a computer-readable non-transitory storage medium. The computer program can also be provided by downloading via a telecommunications line (e.g., the Internet).

[0081] This specification discloses the solutions described in the following items.

[0082] [Item 1] An unmanned aerial vehicle having multiple rotors, comprising: multiple electric motors that rotate the multiple rotors, respectively; multiple motor drive circuits that drive the multiple electric motors, respectively; and a controller that controls the operation of the multiple motor drive circuits, respectively, wherein the controller changes the operation of the multiple motor drive circuits from the flight state of the unmanned aerial vehicle to the flight-disabled state in response to a stop signal.

[0083] [Item 2] The unmanned aerial vehicle described in Item 1, further comprising: a relay circuit electrically connected between the plurality of motor drive circuits and the controller, the relay circuit configured to interrupt a control signal for controlling the rotational speed of the rotor, which is transmitted from the controller in response to the stop signal for stopping operation of the plurality of motor drive circuits.

[0084] [Item 3] The unmanned aerial vehicle according to Item 2, further comprising a diagnostic device that performs fault diagnosis of the relay circuit based on an output from the relay circuit.

[0085] [Item 4] The unmanned aerial vehicle according to Item 3, wherein the diagnostic device performs a fault diagnosis of the relay circuit before takeoff of the unmanned aerial vehicle.

[0086] [Item 5] The unmanned aerial vehicle according to Item 4, wherein the relay circuit has a plurality of relays, each of which interrupts the control signal in response to the stop signal.

[0087] [Item 6] The unmanned aerial vehicle according to Item 5, wherein the diagnostic device performs a diagnosis of an on / off failure of the plurality of relays.

[0088] [Item 7] An unmanned aerial vehicle as described in Item 6, further comprising a warning device that issues a warning to notify of an on / off failure of at least one of the plurality of relays, wherein the diagnostic device diagnoses on / off failures of the plurality of relays when the unmanned aerial vehicle is powered on, and when an on / off failure of at least one of the plurality of relays is detected, causes the warning device to issue the warning.

[0089] [Item 8] An unmanned aerial vehicle as described in Item 6 or 7, wherein the controller is a first controller, and the diagnostic device has: a plurality of averaging circuits respectively connected to the plurality of motor drive circuit sides of the plurality of relays; an integrating circuit which integrates output values ​​output from each of the plurality of averaging circuits and outputs an integrated value; and a second controller which detects an on / off failure of at least one of the plurality of relays based on the integrated value output from the integrating circuit.

[0090] [Item 9] The unmanned aerial vehicle described in Item 8, wherein the control signal is a PWM signal, and each of the plurality of averaging circuits outputs an analog voltage according to a duty ratio of the PWM signal.

[0091] [Item 10] The second controller controls the on / off operation of each of the plurality of relays, and when the control signal is input from the first controller to the relay circuit and the plurality of relays are controlled so that all of the plurality of relays are in the off state, if the integrated value output from the integrator circuit is greater than or equal to a threshold value, determines that at least one of the plurality of relays has an on-failure.

[0092] [Item 11] The second controller controls the on / off operation of each of the plurality of relays, and when the control signal is input from the first controller to the relay circuit, the second controller controls the plurality of relays so that all of the plurality of relays are in the off state, and then controls the plurality of relays so that one of the plurality of relays is in the on state, and if the integrated value output from the integrating circuit is less than a threshold value, the unmanned aerial vehicle described in item 8 or 9 is determined to have an on-failure or an off-failure in the one of the plurality of relays.

[0093] [Item 12] The unmanned aerial vehicle described in Item 11, wherein the threshold value used when determining an on-failure of the one of the plurality of relays is greater than the threshold value used when determining an off-failure of the one of the plurality of relays.

[0094] [Item 13] A stopping system for use in an unmanned aerial vehicle having a plurality of rotors, a plurality of electric motors that respectively rotate the plurality of rotors, a plurality of motor drive circuits that respectively drive the plurality of electric motors, and a controller that respectively controls the operation of the plurality of motor drive circuits, the stopping system being configured to output a stop signal to the controller and change the operation of the plurality of motor drive circuits from a flight state of the unmanned aerial vehicle to a state in which flight is impossible.

[0095] [Item 14] The stopping system according to Item 13, further comprising an operation terminal for outputting the stop signal to the controller when the unmanned aerial vehicle is located above a farm field.

[0096] [Item 15] The stopping system according to item 13 or 14, further comprising a relay circuit electrically connected between the plurality of motor drive circuits and the controller, the relay circuit being configured to interrupt a control signal for controlling the rotational speed of a rotor, which is transmitted from the controller in response to the stop signal for stopping operation of the plurality of motor drive circuits.

[0097] [Item 16] The shutdown system according to item 15, further comprising a diagnostic device that performs fault diagnosis of the relay circuit based on an output from the relay circuit.

[0098] The unmanned aerial vehicle disclosed herein can be widely used not only for aerial photography, surveying, logistics, and pesticide spraying, but also for ground work related to agricultural work, transporting harvested products and agricultural materials, and the like.

[0099] 2: Rotor (propeller), 3: Rotation drive device, 4: Airframe body, 4a: Control device, 4b: Sensor group, 4c: Communication device, 5: Airframe frame, 6: Ground station, 7a: Internal combustion engine, 7b: Fuel tank, 8: Power generation device, 9: Power buffer, 10: Multicopter, 12: Rotor, 14: Motor, 16: ESC, 70: First controller, 76: Power supply device, 80: Relay circuit, 81, 81a to 81d: Relays, 82: Diagnostic device, 83, 83a to 83d: Averaging circuit, 84: Integration circuit, 85: AD conversion circuit, 86: Second controller, 87, 87a to 87c: Adders, 90: Warning device, 200: Work machine

Claims

1. 1. An unmanned aerial vehicle having multiple rotors, a plurality of electric motors that rotate the plurality of rotors, respectively; a plurality of motor drive circuits for driving the plurality of electric motors, respectively; a controller that controls the operation of each of the plurality of motor drive circuits; Equipped with The controller changes the operation of the plurality of motor drive circuits from the flight state of the unmanned aerial vehicle to the flight-disabled state in response to a stop signal.

2. 2. The unmanned aerial vehicle according to claim 1, further comprising: a relay circuit electrically connected between the plurality of motor drive circuits and the controller, the relay circuit configured to interrupt a control signal for controlling the rotational speed of a rotor, which is transmitted from the controller in response to the stop signal for stopping operation of the plurality of motor drive circuits.

3. The unmanned aerial vehicle according to claim 2 , further comprising a diagnostic device that performs fault diagnosis of the relay circuit based on an output from the relay circuit.

4. The unmanned aerial vehicle according to claim 3 , wherein the diagnostic device performs a fault diagnosis of the relay circuit before takeoff of the unmanned aerial vehicle.

5. The unmanned aerial vehicle according to claim 4 , wherein the relay circuit includes a plurality of relays, each of which interrupts the control signal in response to the stop signal.

6. The unmanned aerial vehicle according to claim 5 , wherein the diagnostic device performs a diagnosis of an on / off failure of the plurality of relays.

7. a warning device that issues a warning to notify of an on / off failure of at least one of the plurality of relays; The diagnostic device comprises: performing a diagnosis of an on / off failure of the plurality of relays when power is turned on for the unmanned aerial vehicle; The unmanned aerial vehicle according to claim 6 , wherein the warning device generates the warning when an on / off failure of at least one of the plurality of relays is detected.

8. the controller is a first controller; The diagnostic device comprises: a plurality of averaging circuits connected to the plurality of relays on the sides of the plurality of motor drive circuits, respectively; an integrating circuit that integrates the output values output from the plurality of averaging circuits and outputs the integrated value; a second controller that detects an on-off failure of at least one of the plurality of relays based on the integrated value output from the integrating circuit; The unmanned aerial vehicle according to claim 6 or 7, comprising:

9. the control signal is a PWM signal, The unmanned aerial vehicle according to claim 8 , wherein each of the plurality of averaging circuits outputs an analog voltage corresponding to a duty ratio of the PWM signal.

10. The second controller Controlling the on / off operation of each of the plurality of relays; An unmanned aerial vehicle as described in claim 8, wherein when the control signal is input from the first controller to the relay circuit and the plurality of relays are controlled so that all of the plurality of relays are in an off state, if the integrated value output from the integrating circuit is greater than or equal to a threshold value, it is determined that at least one of the plurality of relays has an on-failure.

11. The second controller Controlling the on / off operation of each of the plurality of relays; 9. An unmanned aerial vehicle as described in claim 8, wherein, when the control signal is input from the first controller to the relay circuit, the plurality of relays are controlled so that all of the plurality of relays are in an off state, and then the plurality of relays are controlled so that one of the plurality of relays is in an on state, if the integrated value output from the integrator circuit is less than a threshold value, it is determined that the one of the plurality of relays has an on-failure or an off-failure.

12. The unmanned aerial vehicle described in claim 11, wherein the threshold value used when determining an on-failure of the one of the plurality of relays is greater than the threshold value used when determining an off-failure of the one of the plurality of relays.

13. A stopping system for stopping operation of a plurality of motor drive circuits used in an unmanned aerial vehicle having a plurality of rotors, a plurality of electric motors that respectively rotate the plurality of rotors, a plurality of motor drive circuits that respectively drive the plurality of electric motors, and a controller that respectively controls operation of the plurality of motor drive circuits, comprising: A stop system configured to output a stop signal to the controller and change operation of the plurality of motor drive circuits from a flight state of the unmanned aerial vehicle to a flight-disabled state.

14. The stopping system according to claim 13 , further comprising an operation terminal for outputting the stopping signal to the controller when the unmanned aerial vehicle is located above a farm field.

15. 15. The stopping system according to claim 13 or 14, further comprising a relay circuit electrically connected between the plurality of motor drive circuits and the controller, the relay circuit configured to interrupt a control signal for controlling the rotational speed of a rotor, which is transmitted from the controller in response to the stop signal for stopping operation of the plurality of motor drive circuits.

16. The shutdown system of claim 15 , further comprising a diagnostic device that performs a fault diagnosis of the relay circuit based on an output from the relay circuit.