Collapsible arms for multi-copter drones and control methods

Abstract

This invention relates to a retractable arm and control method for a multi-rotor unmanned aerial vehicle (UAV), belonging to the field of UAV technology. It includes a fixed arm, a movable arm, a telescopic drive mechanism, a length monitoring device, a vibration sensor, and a piezoelectric actuator. The fixed arm has an external guide groove; the movable arm is fitted over the fixed arm, with an inner wall slider engaging the guide groove, allowing non-axial loads to be transmitted to the fuselage via the slider and guide groove, achieving separation of drive and load-bearing. The telescopic drive mechanism uses a self-locking screw-nut transmission mechanism, allowing for stepless continuous adjustment and self-locking upon power failure. A length monitoring device provides feedback on the arm length to the flight controller, forming a closed-loop control of the arm length configuration. The vibration sensor monitors fuselage vibration, and the flight controller controls fuselage vibration through primary vibration suppression of the rotor and piezoelectric actuator, and secondary vibration suppression through fine-tuning of the movable arm length. This invention solves the problems of easy wear, inability to achieve stepless continuous adjustment, and lack of active vibration damping in existing telescopic arm drive mechanisms, improving flight stability and reliability.

Description

Technical Field

[0001] This invention belongs to the field of unmanned aerial vehicle (UAV) technology, and relates to a retractable arm for a multi-rotor UAV and a control method thereof. Background Technology

[0002] Variable arm length drones can retract during storage and transportation to reduce overall size and simplify packaging and transport. They can also flexibly adjust their configuration to avoid collisions when taking off and landing in confined spaces, and extend during flight to increase rotor spacing and improve aerodynamic stability. This combination takes into account the size and flight performance requirements of drones in different mission scenarios and has strong adaptability to various scenarios.

[0003] Existing variable-length UAVs employ various types of telescopic devices. Some telescopic devices use springs to achieve automatic extension and retraction of the arm. While their structure is simple, they are prone to rebound due to the spring force and arm inertia, leading to increased swaying during flight, affecting arm stability, and making it difficult to achieve continuous variable arm length adjustment.

[0004] Some telescopic devices are driven by motors, using gear and rack transmission mechanisms to extend and retract the boom. However, in these systems, the drive mechanism often directly bears the non-axial loads during flight. Prolonged use can lead to wear, increased clearances, and even breakage of transmission components, causing the telescopic function to fail. Furthermore, most of these devices use open-loop control, making it impossible to sense and accurately maintain the boom's position in real time. In terms of vibration resistance, they rely solely on mechanical locking or passive damping, lacking the ability to actively suppress vibrations and making it difficult to meet the stable flight requirements under complex wind conditions.

[0005] Furthermore, while conventional square sleeve telescopic arms can limit the radial displacement of the movable arm, they cannot effectively constrain its circumferential rotation. Reducing the sleeve clearance to suppress rotation would increase sliding friction resistance and even cause jamming, creating a design contradiction between limiting effect and smooth sliding. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a retractable arm and control method for a multi-rotor unmanned aerial vehicle, which solves the problems of easy wear of the drive mechanism under non-axial load, inability to be continuously adjusted steplessly, and lack of active vibration resistance in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A retractable arm for a multi-rotor unmanned aerial vehicle (UAV) includes a fixed arm and a movable arm nested together. The fixed arm and the movable arm are coaxially connected and their retractable connection is achieved through a telescopic drive device. A rotor is connected to the end of the movable arm away from the fixed arm. A vibration sensor is provided on the outer surface of the movable arm. A length monitoring device is provided on the telescopic drive device. A piezoelectric actuator is also provided on the surface of the fixed arm or the movable arm. The rotor, telescopic drive device, vibration sensor, length monitoring device, and piezoelectric actuator are electrically connected to a flight control system. The flight control system drives the rotor, piezoelectric actuator, and telescopic drive device to make adjustments based on feedback arm length signals and vibration signals.

[0008] Optionally, the telescopic drive device is a motor push rod consisting of a rotary motor and a lead screw and nut transmission mechanism; the rotary motor is mounted on the fixed arm, and the end of the lead screw and nut transmission mechanism away from the rotary motor is fixedly connected to the movable arm; the length monitoring device is any one of a rotary encoder, Hall sensor, or grating ruler installed in the rotary motor.

[0009] Optionally, the rotary motor is located at the end of the lead screw and nut transmission mechanism. The rotary motor includes a motor drive gear, a transmission gear set, a lead screw driven gear, and an encoder driven gear. The motor drive gear is fixed to the motor output shaft. The lead screw driven gear is fixedly connected to the lead screw. The encoder driven gear is coaxially connected to the rotary encoder. The transmission gear set is meshed with the motor drive gear, the lead screw driven gear, and the encoder driven gear, respectively. The nut is threadedly connected to the lead screw. When the lead screw rotates, the nut moves linearly. A telescopic rod is connected to the nut, and the end of the telescopic rod away from the nut is fixedly connected to the movable arm.

[0010] Optionally, the lead screw and nut transmission mechanism has a self-locking characteristic.

[0011] Optionally, the telescopic drive device is any one of a linear motor, an electric push rod, a hydraulic cylinder, or a pneumatic cylinder; the length monitoring device is any one of a potentiometer, a Hall sensor, or a grating ruler.

[0012] Optionally, both the fixed arm and the movable arm are hollow tubular structures, with the fixed arm having a hollow receiving cavity inside; the outer surface of the fixed arm has several guide grooves along the axial direction of the fixed arm, and the inner surface of the movable arm has a slider that cooperates with the guide grooves to form a sliding guide structure.

[0013] Optionally, both the fixed arm and the movable arm are hollow tubular structures, with the fixed arm having a hollow receiving cavity inside; the inner surface of the movable arm has several guide grooves along the axial direction of the movable arm, and the outer surface of the fixed arm has a slider that cooperates with the guide grooves, forming a sliding guide structure.

[0014] Optionally, the telescopic drive device is installed inside the hollow receiving cavity of the fixed arm.

[0015] Optionally, the piezoelectric actuator is any one of a piezoelectric ceramic sheet, a piezoelectric fiber composite material, or a piezoelectric stack actuator.

[0016] A control method employing any of the above-mentioned retractable arms for multi-rotor UAVs; including dual closed-loop control of outer loop length control and inner loop vibration suppression; In outer loop length control, the flight control system sets the target arm length according to user instructions or flight mission, reads the length signal fed back by the length monitoring device in real time, calculates the deviation between the actual and target arm length through the length feedback algorithm, and drives the telescopic drive device to compensate for the deviation to accurately reach the target arm length. In the inner-loop vibration suppression, the flight control system receives the airframe amplitude signal monitored by the vibration sensor in real time; when abnormal vibration of the arm is detected, the flight control system takes two-stage suppression measures: First-level suppression: The flight control system dynamically adjusts the rotational speed of each rotor based on the vibration signal, changing the rotor lift distribution; at the same time, it drives the piezoelectric actuator to generate a control force opposite to the vibration phase, actively counteracting the vibration energy of the arm. Second-level suppression: If the vibration is still not eliminated after the first-level suppression, the flight control system actively and finely adjusts the extension length of the movable arm within a small range near the target arm length, changes the equivalent stiffness and modal frequency of the arm, thereby avoiding the resonance zone or increasing structural damping to further suppress the vibration. After the second level of suppression is applied and the arm length is dynamically adjusted, once the vibration is completely eliminated, the flight control system controls the movable arm to slowly extend and retract to return to the set target arm length.

[0017] The beneficial effects of this invention are as follows: This invention provides a retractable arm and control method for a multi-rotor UAV. A guide groove is provided on the outer wall of the fixed arm; the movable arm is fitted over the fixed arm, and a slider on the inner wall cooperates with the guide groove, allowing non-axial loads to be transmitted to the fuselage via the slider and guide groove. The lead screw is only subjected to axial thrust, thus achieving separation of drive and load-bearing, avoiding the risk of wear and breakage of transmission components, and significantly improving the reliability and service life of the arm. The "rotary motor + lead screw + nut" structure, due to the constraints of the thread helix angle and friction, has little influence from axial forces; it is only affected by the rotational force of its own cross-section (which may be generated by flight loads). The sliding guide structure composed of the slider and guide groove transmits this rotational force to the fuselage, thereby preventing it from acting on the lead screw and ensuring that the lead screw is only subjected to axial thrust. This rotational force is eliminated by two-stage dynamic suppression in the flight control system, thus ensuring the overall stability of the arm whether it is working or stationary.

[0018] The telescopic drive unit uses a self-locking screw and nut transmission mechanism in conjunction with a length monitoring device, enabling stepless continuous adjustment, precise stopping at any telescopic length, and power-off self-locking, eliminating the need for an external locking mechanism. The telescopic drive unit is equipped with a rotary encoder that provides real-time feedback on the actual arm length to the flight controller, forming a closed-loop control system for the telescopic arm length.

[0019] Vibration sensors monitor airframe vibration. Based on the vibration signals, the flight control system performs parallel adjustments to rotor speed and active vibration suppression via piezoelectric actuators as the first level of suppression. If the vibration persists, it actively fine-tunes the extension length of the movable arm to change the arm stiffness as the second level of suppression. This effectively copes with complex wind fields and has strong active vibration resistance.

[0020] This invention solves the problems of easy wear, inability to achieve stepless continuous adjustment, and lack of active vibration resistance in existing telescopic boom drive mechanisms, thereby improving flight stability and reliability. Furthermore, it features a compact structure that facilitates cable routing. Guide grooves, sliders, lead screws, and push rods are integrated within a nested space, forming an embedded configuration. Both the fixed and movable arms are hollow structures, with interconnected internal cavities forming a continuous cable channel, avoiding the risk of external wiring entanglement.

[0021] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the fully retracted telescopic arm of the multi-rotor UAV of the present invention; Figure 2 This is an enlarged schematic diagram of the telescopic boom; Figure 3 This is an enlarged schematic diagram of the interior of the telescopic motor; Figure 4 This is an enlarged schematic diagram of the telescopic boom when it is extended. Figure 5 This is an enlarged schematic diagram of the connection between the arm and the fuselage. Figure 6 This is a schematic diagram of the fully extended retractable arm of the multi-rotor UAV of the present invention. Figure 7 This is a logic block diagram of the control method of the present invention.

[0023] Figure label: 1. Body, 11. Screws, 12. Arm mounting interface, 2. Fixed arm, 21. Motor push rod, 22. Guide groove, 23. Motor drive gear, 24. Transmission gear set, 25. Screw driven gear, 26. Telescopic rod, 27. Encoder driven gear, 28. Rotary encoder, 29. Data return line, 3. Movable arm, 31. Rotor seat, 32. Rotor, 33. Slider, 34. Vibration sensor, 4. Piezoelectric actuator. Detailed Implementation

[0024] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0026] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0027] Please see Figures 1 to 7 This is a retractable arm for a multi-rotor unmanned aerial vehicle (UAV), comprising a fixed arm 2 and a movable arm 3 nested together. The fixed arm 2 and the movable arm 3 are coaxially connected and their telescopic connection is achieved through a telescopic drive device. A rotor 32 is connected to the end of the movable arm 3 away from the fixed arm 2. The rotor 32 is mounted on the end of the movable arm 3 via a rotor mount 31, and the rotor 32 is mounted on the rotor mount 31 via a quick-release interface.

[0028] A vibration sensor 34 is installed in the middle section of the outer surface of the movable arm 3 to monitor the vibration amplitude and frequency of the arm. A length monitoring device is installed on the telescopic drive device to monitor the extension length of the movable arm 3 in real time and feed it back to the flight control system, forming a closed loop for telescopic arm length control. A piezoelectric actuator 4 is also installed on the surface of the fixed arm 2 or the movable arm 3 to generate a reverse force to actively suppress vibration according to flight control commands. Through the positive and inverse piezoelectric effects, it autonomously generates a control force opposite to the phase of the vibration to actively cancel the vibration energy. Optionally, in actual operation, the piezoelectric actuator 4 can feed back a portion of the vibration signal as an auxiliary signal as needed, while the majority of the vibration signal is still transmitted by the vibration sensor. The rotor 32, telescopic drive device, vibration sensor 34, length monitoring device, and piezoelectric actuator 4 are electrically connected to the flight control system. The flight control system drives the rotor 32, piezoelectric actuator 4, and telescopic drive device to make adjustments based on the feedback arm length signal and vibration signal.

[0029] Both the fixed arm 2 and the movable arm 3 are hollow tubular structures, with their internal cavities interconnected to form a continuous cable channel. The head end of the fixed arm 2 is used to fix it to the UAV fuselage 1 via the arm mounting interface 12. The fixing connection method can be either threaded fastener connection (screw 11) or one-piece molding. The fixed arm 2 has a hollow receiving cavity, and the telescopic drive device is installed in the hollow receiving cavity of the fixed arm 2. The head end of the movable arm 3 is open and slidably fitted onto the outside of the fixed arm 2.

[0030] In some embodiments of the present invention, the piezoelectric actuator 4 is any one of a piezoelectric ceramic sheet, a piezoelectric fiber composite material, or a piezoelectric stack actuator.

[0031] Example 1 The telescopic drive device is a motor push rod 21 consisting of a rotary motor and a lead screw and nut transmission mechanism; the rotary motor is mounted on the fixed arm 2, and the end of the lead screw and nut transmission mechanism away from the rotary motor is fixedly connected to the movable arm 3; the length monitoring device is either a rotary encoder 28 installed in the rotary motor, a Hall sensor, or a grating ruler.

[0032] A rotary motor is located at the end of the lead screw and nut transmission mechanism. The rotary motor includes a motor drive gear 23, a transmission gear set 24, a lead screw driven gear 25, and an encoder driven gear 27. The motor drive gear 23 is fixed to the motor output shaft, the lead screw driven gear 25 is fixedly connected to the lead screw, and the encoder driven gear 27 is coaxially connected to the rotary encoder 28. The transmission gear set 24 is meshed with the motor drive gear 23, the lead screw driven gear 25, and the encoder driven gear 27, respectively. The nut is threadedly connected to the lead screw; when the lead screw rotates, the nut moves linearly. A telescopic rod 26 is connected to the nut, and the end of the telescopic rod 26 away from the nut is fixedly connected to the movable arm 3.

[0033] The transmission gear set 24 drives the lead screw driven gear 25 to rotate. The lead screw driven gear 25 is fixedly connected to the lead screw, thereby driving the lead screw to rotate. The rotational motion of the lead screw is converted into the linear motion of the telescopic rod 26. At the same time, the lead screw driven gear 25 also drives the encoder driven gear 27 to rotate through the transmission gear set 24. The encoder driven gear 27 is coaxially connected to the incremental rotary encoder 28. The incremental rotary encoder 28 monitors the rotation angle of the lead screw in real time and sends the length signal to the flight controller through the data return line 29, which is then converted into the extension length of the movable arm 3, forming a length closed loop.

[0034] Because of the use of a screw and nut transmission mechanism, the extension length of the telescopic rod 26 can be precisely adjusted by controlling the rotation angle and direction of the motor, so that the movable arm 3 can stay and be fixed at any desired length within the stroke range defined by the guide groove 22, thereby realizing the ability to continuously adjust the arm length and adapt to different space environments and aerodynamic requirements.

[0035] When the motor of the telescopic drive device is working, its internal rotary motor drives the lead screw to rotate, causing the telescopic rod 26 to extend or retract axially. The lead screw is rigidly connected to the head end of the movable arm 3. When the telescopic rod 26 extends, it pushes the movable arm 3 to slide outward along the fixed arm 2. When the telescopic rod 26 retracts, it pulls the movable arm 3 to slide inward.

[0036] The lead screw and nut transmission mechanism has a self-locking characteristic. The rotary motor body is fixed to the fixed arm 2, the lead screw extends from the tail end of the fixed arm 2, and the end of the telescopic rod 26 is rigidly connected to the inside of the head end of the movable arm 3 through a flange, which is used to realize the stepless continuous telescopic adjustment of the movable arm 3 and the self-locking when the power is off.

[0037] The rotary encoder 28 is electrically connected to the flight control system via the data feedback line 29 to transmit signals. It is used to monitor the rotation angle of the lead screw in real time and convert it into the extension length of the movable arm 3, and then feed the length signal back to the flight control system.

[0038] Example 2 The telescopic drive device is any one of a linear motor, an electric actuator, a hydraulic cylinder, or a pneumatic cylinder; the length monitoring device is any one of a potentiometer, a Hall sensor, or a grating ruler.

[0039] Example 3 The outer surface of the fixed arm 2 is provided with several guide grooves 22 along the axial direction of the fixed arm 2, and the inner surface of the movable arm 3 is provided with a slider 33 that cooperates with the guide grooves 22 to form a sliding guide structure.

[0040] When the movable arm 3 slides, the slider 33 on its inner wall moves synchronously within the guide groove 22 on the outer wall of the fixed arm 2. The side wall of the guide groove 22 abuts against the outer wall of the slider 33, confining the slider 33 within the groove. This ensures that the slider 33 can only move axially along the guide groove 22, preventing lateral oscillation or circumferential rotation. After the slider 33 is confined, the movable arm 3 can only slide axially along the fixed arm 2, preventing radial offset or rotation. This protects the push rod from lateral pulling, and the telescopic movement is entirely controlled by the lead screw, smoothly driving the movable arm 3 along the direction of the guide groove 22, ensuring that the telescopic process is free from jamming and error.

[0041] When the telescopic rod 26 extends or retracts into place, the movable arm 3 stops sliding, and the slider 33 remains embedded in the guide groove 22 to form a fixed position. The rotor seat 31 and rotor 32 remain stable, and the rotors 32 of multiple arms always rotate in the same horizontal plane, eliminating the attitude deviation caused by the swaying of the arms.

[0042] Example 4 Unlike embodiment 3 described above, the engagement relationship between the fixed arm 2 and the movable arm 3 is reversed in this embodiment. The inner surface of the movable arm 3 has several guide grooves 22 running along its axial direction, and the outer surface of the fixed arm 2 has sliders 33 that cooperate with the guide grooves 22, forming a sliding guide structure.

[0043] There are multiple guide grooves 22, evenly distributed along the circumference of the fixed arm 2. In some embodiments of the present invention, there are three guide grooves 22, evenly distributed along the circumference of the fixed arm 2. The number of sliders 33 is equal to the number of guide grooves 22 and their positions correspond one-to-one. The cross-sectional shape of the guide groove 22 is any one of T-shaped, dovetail-shaped, rectangular, or V-shaped.

[0044] This invention disperses the contact surface to multiple independent guide points through multi-point distributed guide grooves 22, ensuring that the slider 33 only forms point or line contact with a local area of ​​the guide groove 22. This avoids sliding resistance caused by large-area contact and ensures smooth telescopic movement. The multi-point distributed guide grooves 22 and slider 33 structure precisely constrain the movable arm 3, making the movement path of each movable arm 3 independent and definite, avoiding the body resonance phenomenon induced by the coupling of the swing frequencies of multiple movable arms 3. When external disturbances are applied to the arms, the guide structure directly transmits the disturbance to the fuselage 1, blocking the dynamic coupling path between the movable arm 3 and the fuselage, thereby effectively suppressing the amplification of the overall vibration mode caused by the arm swaying and improving the dynamic stability of the flight platform.

[0045] This invention provides a variable-length arm for multi-rotor UAVs, employing a lead screw and nut transmission mechanism in conjunction with a rotary encoder 28 for length feedback. This allows the movable arm 3 to be continuously adjusted between retracted and extended states and to remain at any length, thus forming a variable arm length configuration adaptable to different flight scenarios. Furthermore, addressing the problem in existing telescopic drive devices where the non-axial load generated by the rotor 32 causes motor torsion and sway, affecting telescopic accuracy and reliability, this invention separates the guiding and load-bearing function from the telescopic drive function. By setting an independent guiding structure to constrain the movement path of the movable arm 3, the non-axial load is transmitted to the fixed arm 2 via the guiding structure, thereby blocking the influence of external interference on the motor of the telescopic drive device.

[0046] A control method for a retractable arm of a multi-rotor UAV 32 includes dual closed-loop control of outer loop length control and inner loop vibration suppression; the outer loop achieves precise compensation of the retractable length based on length feedback from a rotary encoder 28; the inner loop, based on feedback from a main sensor (barometer, accelerometer, etc.) and a vibration sensor 34, first adjusts the rotor speed 32 and then fine-tunes the arm length to suppress vibration.

[0047] In the outer loop length control, the flight controller sets the target arm length according to user instructions or flight mission. During the extension and retraction movement, it reads the angle feedback data from the rotary encoder 28 and converts it into the actual movement length of the extension rod 26. The deviation between the actual and target lengths is calculated by the length feedback algorithm of the PID flight control system, and the extension motor is driven to compensate, so that the movable arm 3 accurately reaches the target length. Due to the self-locking characteristic of the lead screw and nut transmission mechanism, the movable arm 3 can maintain any extension and retraction length after power failure, realizing stepless continuous adjustment.

[0048] In the inner-loop vibration suppression, the flight controller collects vibration feedback signals sensed by the piezoelectric actuator 4 in real time. First, based on data from main sensors such as barometers and accelerometers, the flight controller dynamically adjusts the rotational speed distribution of each rotor 32, changing the lift distribution of the rotor 32 to maintain the basic flight stability of the UAV. If the vibration is still not effectively suppressed, the flight controller analyzes the vibration feedback signal and actively fine-tunes the extension length of the movable arm 3 within a small range near the basic configuration, changing the equivalent stiffness and modal frequency of the arm system to avoid the resonance zone or increase structural damping, further suppressing the vibration. These two levels of measures work together: the rotor 32 speed adjustment responds quickly, and the arm length fine-tuning fundamentally changes the system characteristics. After the vibration is eliminated, the flight controller slowly returns the movable arm 3 to the basic configuration. User manual commands have the highest priority and can interrupt the active suppression mode at any time.

[0049] The control logic of the control method of this invention prioritizes outer loop length control. In the absence of user instructions, the arm is first brought to the target length before inner loop vibration suppression is activated. During vibration fine-tuning, the length is not immediately reset; it automatically resets after the vibration ends.

[0050] like Figure 6 As shown, when the arms are fully extended, the movable arm 3 extends to the position where the slider 33 abuts against the tail end of the guide groove 22, increasing the distance between the rotors 32 and improving flight stability; when the arms are fully retracted (as shown in the image), the movable arm 3 extends to the position where the slider 33 abuts against the tail end of the guide groove 22, increasing the distance between the rotors 32 and improving flight stability; Figure 1 The movable arm 3 retracts to the position where the slider 33 abuts against the head end of the guide groove 22, reducing the overall size of the machine and making it easier to store and transport.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A retractable arm for a multi-rotor unmanned aerial vehicle, comprising a fixed arm (2) and a movable arm (3) nested together, characterized in that: The fixed arm (2) and the movable arm (3) are coaxially connected and are telescopically connected through a telescopic drive device. A rotor (32) is connected to the end of the movable arm (3) away from the fixed arm (2). A vibration sensor (34) is provided on the outer surface of the movable arm (3). A length monitoring device is provided on the telescopic drive device. A piezoelectric actuator (4) is also provided on the surface of the fixed arm (2) or the movable arm (3). The rotor (32), the telescopic drive device, the vibration sensor (34), the length monitoring device, and the piezoelectric actuator (4) are electrically connected to the flight control system. The flight control system drives the rotor (32), the piezoelectric actuator (4), and the telescopic drive device to make adjustments based on the feedback arm length signal and vibration signal.

2. The retractable arm for a multi-rotor UAV according to claim 1, characterized in that: The telescopic drive device is a motor push rod (21) consisting of a rotary motor and a lead screw and nut transmission mechanism; the rotary motor is mounted on the fixed arm (2), and the end of the lead screw and nut transmission mechanism away from the rotary motor is fixedly connected to the movable arm (3); the length monitoring device is any one of a rotary encoder (28), a Hall sensor, or a grating ruler installed in the rotary motor.

3. The retractable arm for a multi-rotor UAV according to claim 2, characterized in that: The rotary motor is located at the end of the lead screw and nut transmission mechanism. The rotary motor includes a motor drive gear (23), a transmission gear set (24), a lead screw driven gear (25), and an encoder driven gear (27). The motor drive gear (23) is fixed on the motor output shaft. The lead screw driven gear (25) is coaxially connected to the lead screw. The encoder driven gear (27) is coaxially connected to the rotary encoder (28). The transmission gear set (24) is meshed with the motor drive gear (23), the lead screw driven gear (25), and the encoder driven gear (27) respectively. The nut is threadedly connected to the lead screw. When the lead screw rotates, the nut moves linearly. A telescopic rod (26) is connected to the nut. The end of the telescopic rod (26) away from the nut is fixedly connected to the movable arm (3).

4. The retractable arm for a multi-rotor UAV according to claim 2, characterized in that: The lead screw and nut transmission mechanism has a self-locking characteristic.

5. The retractable arm for a multi-rotor UAV according to claim 1, characterized in that: The telescopic drive device is any one of a linear motor, an electric push rod, a hydraulic cylinder, or a pneumatic cylinder; the length monitoring device is any one of a potentiometer, a Hall sensor, or a grating ruler.

6. The retractable arm for a multi-rotor UAV according to claim 1, characterized in that: Both the fixed arm (2) and the movable arm (3) are hollow tubular structures. The fixed arm (2) has a hollow cavity inside. The outer surface of the fixed arm (2) is provided with several guide grooves (22) along the axial direction of the fixed arm (2). The inner surface of the movable arm (3) is provided with a slider (33) that cooperates with the guide grooves (22), forming a sliding guide structure.

7. The retractable arm for a multi-rotor UAV according to claim 1, characterized in that: Both the fixed arm (2) and the movable arm (3) are hollow tubular structures. The fixed arm (2) has a hollow cavity inside. The inner surface of the movable arm (3) has several guide grooves (22) along the axial direction of the movable arm (3). The outer surface of the fixed arm (2) has a slider (33) that cooperates with the guide grooves (22) to form a sliding guide structure.

8. The retractable arm for a multi-rotor unmanned aerial vehicle according to any one of claims 6 or 7, characterized in that: The telescopic drive device is installed in the hollow cavity of the fixed arm (2).

9. The retractable arm for a multi-rotor unmanned aerial vehicle according to claim 1, characterized in that: The piezoelectric actuator (4) is any one of piezoelectric ceramic sheet, piezoelectric fiber composite material or piezoelectric stack actuator.

10. A control method, characterized in that: The retractable arm for a multi-rotor UAV as described in any one of claims 1 to 9 is employed, including dual closed-loop control of outer ring length control and inner ring vibration suppression; In outer loop length control, the flight control system sets the target arm length according to user instructions or flight mission, reads the length signal fed back by the length monitoring device in real time, calculates the deviation between the actual and target arm length through the length feedback algorithm, and drives the telescopic drive device to compensate for the deviation to accurately reach the target arm length. In the inner-loop vibration suppression, the flight control system receives the airframe amplitude signal monitored by the vibration sensor (34) in real time; when abnormal vibration of the arm is detected, the flight control system takes two-stage suppression measures: First-level suppression: The flight control dynamically adjusts the rotational speed of each rotor (32) according to the vibration signal, and changes the lift distribution of the rotor (32); at the same time, it drives the piezoelectric actuator (4) to generate a control force opposite to the vibration phase, actively canceling the vibration energy of the arm; Second-level suppression: If the vibration is still not eliminated after the first-level suppression, the flight control system actively fine-tunes the extension length of the movable arm (3) in a small range near the target arm length, changes the equivalent stiffness and modal frequency of the arm, thereby avoiding the resonance zone or increasing structural damping, and further suppressing the vibration. After the second level of suppression is applied to dynamically adjust the arm length, and after the vibration is completely eliminated, the flight control system controls the movable arm (3) to slowly extend and retract back to the set target arm length.

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