Unmanned aircraft control method

Abstract

Provided is an unmanned aircraft control method capable of causing an airframe loaded with a heavy load to rapidly ascend, and performing stable attitude control.　This unmanned aircraft control method controls a vertical takeoff and landing unmanned aircraft that is provided with a plurality of propellers driven by an engine and in which the pitch angle (θ) of each propeller can be individually set. During airframe throttle control, the opening degree of a throttle valve of the engine is increased or decreased, and the rotational speed of the engine is increased or decreased, thereby increasing or decreasing the rotational speed of each propeller. During airframe attitude control, the pitch angle (θ) of each propeller for obtaining lift is set to be large when the rotational speed of the engine is low, and is set to be small when the rotational speed of the engine is high.

Description

Control Method for Unmanned Aerial Vehicle

[0001] The present invention relates to a control method for an unmanned aerial vehicle and an unmanned aerial vehicle. More specifically, by controlling the throttle valve of the engine to perform the ascent of an unmanned aerial vehicle equipped with an engine, the engine speed is kept constant and the pitch angle of the propeller is adjusted to perform the ascent. Compared with the control method of obtaining a large thrust, the present invention relates to a control method for an unmanned aerial vehicle and an unmanned aerial vehicle that can obtain a large thrust.

[0002] In order to carry a load on a rotary-wing aircraft and make it ascend, it is necessary to increase the thrust compared to when hovering without load. In conventional variable pitch electric quadcopters and unmanned helicopters, since the engine speed is kept constant, in order to increase the thrust, it is common to increase the pitch angle of the propeller.

[0003] When the pitch angle of the propeller is increased, the drag increases. Therefore, if it is an electric motor, it is necessary to increase the current, and if it is an engine, it is necessary to increase the opening degree of the throttle valve to increase the horsepower. If it is an engine, two systems of control, namely the pitch angle control of the propeller and the opening degree control of the throttle valve of the engine, must be operated. Since this operation is troublesome, the flight control is performed only by controlling the pitch angle (elevation angle) of the propeller while keeping the engine speed constant. This makes it easier to control the attitude of the aircraft body. The engine speed is, for example, about 5000 rpm, but is decelerated by a gear so that the propeller speed is about 1250 rpm.

[0004] As an example, when returning an inclined airframe to horizontal, assume that the pitch angle of the propeller is operated by 1° at low speed rotation and the lift is increased to make the airframe horizontal. Similarly, even if the pitch angle of the propeller is operated by 1° at high speed rotation, there is a problem that the airframe cannot be made horizontal because the lift is greater than in the case of low speed rotation. In order to avoid such difficulty in control, in the conventional aircraft, the engine speed is kept constant. That is, the propeller speed is kept constant.

[0005] Conventional control methods that maintain a constant propeller speed limit operation to a certain horsepower range, even when the load increases due to ascent or cargo loading. As shown in Figure 8, electric motors with high output at low rotational speeds are suitable for this type of use. However, if a high-speed, high-output engine is used as the propeller drive and a control method that maintains a constant engine speed is employed, the following problems arise.

[0006] When prioritizing low-speed, low-load operation, especially during no-load conditions or when fuel efficiency is a priority, setting the engine speed low results in low engine output. As shown in Figure 9, even with the throttle valve open, significant power cannot be obtained, making it impossible to lift heavy loads. Conversely, setting the engine speed high results in significant power output, as shown in Figure 8, allowing the machine to lift heavy loads. However, when the load is light or unloaded in the low-load range, the unnecessarily high engine speed leads to problems such as decreased fuel efficiency and increased noise.

[0007] Patent Document 1 discloses a quadcopter in which a propeller is driven by a two-stroke single-cylinder engine. Each propeller consists of two blades, and the pitch angle of the blades can be changed by a pitch angle changing mechanism.

[0008] Japanese Patent Publication No. 2020-100387

[0009] The object of the present invention is to provide a control method for an unmanned aerial vehicle that can rapidly ascend an aircraft carrying a heavy load and maintain stable attitude control.

[0010] The control method for an unmanned aerial vehicle according to the present invention is a control method for a vertical take-off and landing type unmanned aerial vehicle equipped with a plurality of propellers driven by an engine, wherein the pitch angle of each propeller can be set individually, characterized in that when controlling the throttle of the aircraft, the rotational speed of each propeller is increased or decreased by increasing or decreasing the opening degree of the throttle valve of the engine and increasing or decreasing the rotational speed of the engine, and when controlling the attitude of the aircraft, the pitch angle of each propeller for obtaining lift is set to be large when the engine rotational speed is low and small when the engine rotational speed is high.

[0011] The system is characterized by increasing the opening of the throttle valve and operating the engine at high speed when a heavy load is loaded, and decreasing the opening of the throttle valve and operating the engine at low speed when a light load is loaded.

[0012] According to the control method and unmanned aircraft of the present invention: (1) When controlling the throttle of the aircraft, instead of increasing the pitch angle of the propeller, the opening of the engine's throttle valve is increased or decreased to increase or decrease the engine speed, thereby obtaining a large or small thrust. This allows the aircraft to ascend even when carrying heavy loads. Emergency ascents to avoid obstacles are also possible. Furthermore, since the propeller pitch angle is set to be small when the engine is rotating at high speed and larger when the engine is rotating at low speed, stable control of the aircraft is possible. (2) The aircraft receives lift from the propeller. Here, the lift is proportional to the wind speed on which the propeller is acting, so when the engine is rotating at high speed, the lift is large, and when it is rotating at low speed, the lift is small. On the other hand, the lift is proportional to the pitch angle, so when the engine is rotating at high speed, the lift is small, and when it is rotating at low speed, the lift is small. Therefore, in terms of aircraft attitude control, the tilt of the aircraft when operating at high rotation speed and moving forward can be made approximately the same as the tilt when operating at low rotation speed and moving forward. When correcting the aircraft's attitude, the same method can be used regardless of the operating speed.

[0013] When carrying a light load, the engine operates at a low speed, saving energy. When carrying a heavy load, the engine operates at a high speed, allowing for rapid ascent even with a heavy aircraft, and maximizing engine performance. Beyond this type of operation, high-speed rotation may also be used for emergency ascents or descents to avoid obstacles.

[0014] This flowchart shows the throttle control of the aircraft in the control method for an unmanned aerial vehicle according to the present invention. This flowchart shows the attitude control of the aircraft in the control method for an unmanned aerial vehicle according to the present invention. This is an explanatory diagram of the aircraft and propellers of the unmanned aerial vehicle. This is a diagram showing the pitch angle of each propeller when the aircraft is moving forward. This is a left side view of the aircraft in Figure 4 when it is moving forward. This is an explanatory diagram of the pitch angle. This is a graph showing the relationship between the throttle opening and pitch angle of the valve according to the present invention. This is a graph showing the relationship between the engine speed and pitch angle during attitude control according to the present invention. This is a graph showing the relationship between the engine speed and torque of a typical engine.

[0015] The control method for unmanned aerial vehicles and the unmanned aerial vehicle according to the present invention will be described in detail below with reference to the drawings.

[0016] Figure 1 is a flowchart of the control method for an unmanned aerial vehicle according to the present invention, showing the flowchart for throttle control of the aircraft. The unmanned aerial vehicle 100 in this embodiment is a quadcopter, and the aircraft body 1 is equipped with four propellers 5, which are driven by engines 4 (see Figure 3). The aircraft body 1 also has a built-in program that receives commands via wireless communication from the ground and controls each part.

[0017] As shown in Figure 1, S1 is a determination of whether or not the aircraft's throttle is being controlled. If the answer to S1 is YES, then it is throttle control, and in S10, it is determined whether or not the throttle is being used to raise the aircraft. Examples of such operations include pushing the handle forward to raise the aircraft or pushing the handle backward to lower the aircraft. If the answer to S10 is YES, then it is a control to increase the throttle valve opening, and the processes of S11 and S12 are performed. S11 instructs the engine to increase the opening of the throttle valve. S12 operates the engine according to the opening of the throttle valve. As the throttle valve opens, the engine rotates at high speed. When the engine rotates at high speed, the propeller also rotates at a higher speed than before, allowing the aircraft to climb. When a heavy load is loaded onto the aircraft, compared to the conventional control where the engine speed is constant and the propeller pitch angle is increased, the engine torque allows for a powerful climb.

[0018] If the answer to S10 is NO, then S13 and S14 are performed. S13 instructs the engine to reduce the opening of the throttle valve. S14 operates the engine according to the opening of the throttle valve. As the throttle valve is closed, the engine rotates at a low speed. When the engine rotates at a low speed, the propeller also rotates at a lower speed than before, allowing the aircraft to descend. In addition, when the aircraft is loaded with a light load, low-speed operation can be applied. In that case, energy-saving operation is possible compared to the conventional control that keeps the engine speed constant at a medium speed.

[0019] Figure 2 is a flowchart of the control method for an unmanned aerial vehicle, showing the flowchart for aircraft attitude control. S2 is a determination of whether or not attitude control is being performed. If S2 is YES, then attitude control is performed, and the determinations and processes in S21 to S26 are carried out. Attitude control consists of three parts: rudder, aileron, and elevator. In attitude control, the process in S20 is performed first. The current engine speed is determined, and a specific value α is calculated as the pitch angle θ (see Figure 6, which has an explanation of pitch angle) corresponding to the engine speed. The pitch angle α is applied to the propeller that increases lift. A pitch angle β with a value smaller than the pitch angle α is calculated and applied to the propeller that does not increase lift. β is the value obtained by subtracting a predetermined value from α.

[0020] As shown in Figure 2, if the command is for the rudder (YES in S21), the program branches to S24 and the aircraft turns. There are two types of turns: right turns and left turns. For a right turn, if the propellers are P1 to P4 in a plan view (see Figure 3), the pitch angle θ of P1 and P3 is set to be large, and the pitch angle θ of P2 and P4 is set to be small. This increases the lift of P1 and P3, which are rotating clockwise, causing the aircraft to turn to the right. For a left turn, the pitch angle θ of P2 and P4 is set to be large, and the pitch angle θ of P1 and P3 is set to be small. This increases the lift of P2 and P4, which are rotating counterclockwise, causing the aircraft to turn to the left.

[0021] If the pitch angles of P1 to P4 are all set to the same value, the aircraft will neither turn right nor left. Depending on the engine speed at that time, if the propeller lift is greater than the load, the aircraft will ascend. If the propeller lift balances the load, the aircraft will hover. If the propeller lift is less than the load, the aircraft will descend.

[0022] If the aileron command is given (YES in S22), the program branches to S25 and the aircraft slides. To slide the aircraft to the left, the pitch angles of P1 and P2 are set large, and the pitch angles of P3 and P4 are set small. This increases the lift of P1 and P2, causing the left side of the aircraft to drop and the aircraft to slide to the left. To slide the aircraft to the right, the pitch angles of P1 and P2 are set small, and the pitch angles of P3 and P4 are set large. This increases the lift of the left side of the aircraft, causing it to rise, causing the right side of the aircraft to drop and the aircraft to slide to the right.

[0023] If the command is for the elevator (YES in S23), the process branches to S26, where the aircraft moves in the forward and backward directions. For forward movement, the pitch angles of P2 and P3 are set to be large, and the pitch angles of P1 and P4 are set to be small. This increases the lift at the rear of the aircraft, causing it to rise, while the front of the aircraft lowers, and the aircraft moves forward. For backward movement, the pitch angles of P2 and P3 are set to be small, and the pitch angles of P1 and P4 are set to be large. This increases the lift at the front of the aircraft, causing it to rise, while the rear of the aircraft lowers, and the aircraft moves backward. The processes in S24, S25, and S26 are continued.

[0024] Figure 3 is an explanatory diagram of the airframe 1 and propeller 5 of the unmanned aerial vehicle 100. The unmanned aerial vehicle 100 in this embodiment is a vertical take-off and landing quadcopter equipped with propellers P1 (clockwise), P2 (counterclockwise), P3 (clockwise), and P4 (counterclockwise). The propeller 5 has two blades. The engine 4 is an in-line four-cylinder reciprocating engine, with a throttle valve 2 for each cylinder. The propeller 5's pitch angle can be individually set by driving a linkage mechanism (not shown) with a servo motor (not shown) provided on the airframe.

[0025] Figure 4 shows the pitch angles of each propeller when the aircraft 1 is moved forward by elevator attitude control. To move the aircraft forward, the pitch angles of P2 and P3 are set large, and the pitch angles of P1 and P4 are set small. This increases the lift at the rear of the aircraft, causing it to rise and the front of the aircraft to drop, moving the aircraft forward. Since the propeller 5 is at an angle, thrust is obtained to move forward. Specifically, the pitch angles θ are set so that θ = β for P1 and P4, and θ = α for P2 and P3, such that α > β.

[0026] Figure 5 is a left side view of the aircraft shown in Figure 4 when it is moving forward. The front of the aircraft 1 sinks down due to the small amount of lift, and the rear of the aircraft 1 rises due to the large amount of lift, causing the aircraft 1 to tilt downwards overall.

[0027] Figure 6 is an explanatory diagram of the pitch angle. As shown in the right-hand lead circle, the pitch angle 3 is the angle indicated by θ. A larger pitch angle 3 results in a larger lift. A smaller pitch angle 3 results in a smaller lift. In other words, the lift is proportional to the pitch angle. Here, since the lift is also proportional to the wind speed, the lift is larger when the propeller rotates at high speed and smaller when the propeller rotates at low speed. As shown in the left-hand lead circle, the pitch angle 3 of the propeller 5 can be set individually. The pitch angle 3 of the propeller blades is set by a servo motor and linkage mechanism installed on the aircraft body 1.

[0028] Figure 7 is a graph showing the relationship between the throttle opening and pitch angle of the valve according to the present invention. The throttle valve opening (circled A) is controlled to rise to the right with respect to the load. When a heavy load is loaded, the throttle valve opening is increased, and when a light load is loaded, the throttle valve opening is decreased. When the aircraft is ascending and descending, if the pitch angles of propellers P1 to P4 (circled B) are all the same and fixed, increasing the engine speed will increase the propeller speed and the aircraft will ascend rapidly vertically. Decreasing the engine speed will decrease the propeller speed and the aircraft will descend vertically. When the aircraft is moving forward, the propeller pitch angles of P1 and P4 at the front of the aircraft and P2 and P3 at the rear of the aircraft are set differently, so for example, if the engine speed is increased, the aircraft will ascend from horizontal to diagonally upward. In that case, since forward attitude control is maintained, the pitch angle adjustment, which matches the engine speed indicated in S20, is performed as needed.

[0029] Figure 8 is a graph showing the relationship between engine speed and pitch angle during attitude control according to the present invention. When the engine speed is high and the engine is operating at high speed, the pitch angle is set to be smaller than when it is rotating at low speed. Specifically, for propellers that increase lift, a pitch angle α is applied, and for propellers that decrease lift, a pitch angle β is applied. When the engine speed is low and the engine is operating at low speed, the pitch angle is set to be larger than when it is rotating at high speed. For propellers that increase lift, a pitch angle α' is applied, and for propellers that decrease lift, a pitch angle β' is applied.

[0030] The present invention is suitable as a control method for unmanned aerial vehicles that allows for rapid ascent by increasing engine speed when carrying a heavy load, and for energy-efficient operation by lowering engine speed when carrying a light load.

[0031] 1. Aircraft 2. Throttle valve 3. Pitch angle 4. Engine 5. Propeller 100 Unmanned aerial vehicle

Claims

1. A control method for a vertical take-off and landing unmanned aircraft equipped with multiple propellers driven by a multi-cylinder reciprocating engine, wherein the pitch angle of each propeller can be individually set, comprising: throttle control which increases or decreases the rotational speed of each propeller by increasing or decreasing the opening of the throttle valve of the reciprocating engine, thereby increasing or decreasing the rotational speed of the reciprocating engine, to cause the aircraft to ascend or descend; and attitude control which controls the pitch angle of each propeller to perform the following actions: rudder for turning the aircraft, aileron for sliding the aircraft from side to side, and elevator for moving the aircraft in the forward and backward directions. A control method for an unmanned aerial vehicle, characterized in that, during attitude control, when the engine speed is low, the propeller pitch angle (α') that generates high lift is set to be greater than the propeller pitch angle (β') that generates low lift, and when the engine speed is high, the propeller pitch angle (α) that generates high lift is set to be greater than the propeller pitch angle (β) that generates low lift, and both the pitch angle (α) and the pitch angle (β) are set to be smaller than the pitch angle (α') and the pitch angle (β').

2. The control method for an unmanned aircraft according to claim 1, characterized in that when a heavy load is loaded, the engine is operated at high speed, and when a light load is loaded, the engine is operated at low speed.

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