A flapping and folding motion mechanism for a flapping-wing aircraft

Abstract

The present invention discloses a flapping and folding motion mechanism for a flapping-wing aircraft, belonging to the technical field of flapping-wing aircraft. It includes a flapping and folding wing and a flapping and folding drive mechanism; the flapping and folding wing is mainly composed of a flapping wing and a folding wing located at the outer end of the flapping wing; the flapping and folding drive mechanism includes a flapping and folding drive mechanism mounting frame and a guide shaft arranged on the flapping and folding drive mechanism mounting frame, a flapping drive mechanism and a folding drive mechanism; the flapping drive mechanism includes an eccentric drive structure and a flapping drive arm; the folding drive mechanism includes a synchronous drive gear, a slider reciprocating drive structure and a folding drive slider; the synchronous drive gear is meshed and connected with the eccentric drive gear so that the flapping motion and the folding and stretching motion of the flapping and folding wing are carried out synchronously. The inner end of the flapping arm is fixedly connected with the other end of the flapping drive arm, and the folding arm is hinged with the other end of the folding drive arm. It has the characteristics of light weight, good maneuverability, high flight efficiency, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of flapping-wing aircraft. Background Art

[0002] Flapping-wing aircraft have great application prospects in the fields of national defense and military, and have become the research focus of various countries. In nature, birds change the motion state of their wings through folding, twisting, and sweeping, and achieve the deformation of the wings through these actions, so as to improve flight efficiency, reduce energy consumption, and achieve the purpose of long-term flight.

[0003] The folding motion of a bird's wing refers to the stretching and bending along the wingspan. Research shows that flapping-wing aircraft adopt the bionic principle, and the flapping wing realizes the deformation of the wing by adding a folding motion (folding the wing) on the basis of the flapping motion. When the flapping wing moves upward, the area of the flapping wing decreases, which can effectively reduce the negative lift generated during the upward stroke. When the flapping wing moves downward, the area of the flapping wing increases, which can effectively increase the lift of the flapping wing, thereby greatly improving its aerodynamic efficiency and achieving the purpose of improving flight efficiency by actively changing the wing shape like a bird.

[0004] Current flapping-wing aircraft generally only have a simple flapping motion. A few flapping wings have added a folding motion on the basis of the flapping motion. However, at present, the way of changing the wing shape by folding the flapping wing is generally passive. For example, the Chinese invention patent "A mechanism capable of realizing passive folding and twisting of a wing" with the application number CN201910117942.0 and the authorization announcement number CN109823532A.

[0005] Compared with active deformation, there are large errors in changing the shape of the flapping wing through passive folding, so that the improvement of aerodynamic efficiency is not very ideal. Even if some flapping aircraft achieve the folding motion of the flapping wing through active control, it is generally realized through a link structure, which will make the overall structure heavier. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a flapping and folding motion mechanism for a flapping-wing aircraft, which has the characteristics of light weight, good mobility, high flight efficiency, etc.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A flapping and folding motion mechanism for a flapping-wing aircraft, which includes a flapping and folding wing and a flapping and folding drive mechanism;

[0009] The flapping and folding wing is mainly composed of a flapping wing and a folding wing located at the outer end of the flapping wing;

[0010] The flapping folding wing comprises a flapping arm, a folding arm, a flapping wing frame and a wing membrane, the outer end of the flapping arm is hinged to the inner end of the folding arm so that the folding arm can perform a forward and backward reciprocating folding and stretching movement relative to the flapping arm, the flapping wing frame is fixed above the flapping arm, the wing membrane is bonded to the flapping wing frame and the folding arm, the flapping wing frame and the wing membrane supported by it form a flapping wing, the folding arm and the wing membrane supported by it form a folding wing, and the wing membrane portion supported by the folding arm forms the leading edge of the folding wing;

[0011] The flapping and folding driving mechanism comprises a flapping and folding driving mechanism mounting frame and a guide shaft arranged on the flapping and folding driving mechanism mounting frame, a flapping driving mechanism and a folding driving mechanism;

[0012] The flapping drive mechanism includes an eccentric drive structure and a flapping drive arm;

[0013] The eccentric driving structure includes an eccentric driving gear, an eccentric shaft connecting rod, a swing arm and a driving connecting rod, and the middle part of the flapping driving arm is rotatably connected to the guide shaft; the eccentric driving gear is eccentrically provided with an eccentric shaft, and one end of the eccentric shaft connecting rod 14 is rotatably connected to the eccentric shaft; the other end of the eccentric shaft connecting rod is hinged to one end of the swing arm, the other end of the swing arm is hinged to one end of the driving connecting rod, and the other end of the driving connecting rod is hinged to one end of the flapping driving arm;

[0014] When the eccentric driving gear rotates, the eccentric shaft generates a circular motion, so that the eccentric shaft connecting rod drives the swing arm to reciprocate, and the swing arm drives the flapping driving arm to generate a reciprocating flapping motion around the guide shaft through the driving connecting rod;

[0015] The folding drive mechanism includes a synchronous drive gear, a slider reciprocating drive structure and a folding drive slider;

[0016] The slider reciprocating drive structure includes a pair of rope drive gears with the same structure, a rope and at least one rope guide pulley, the rope drive gear is eccentrically provided with a rope connection structure, one end of the rope is fixed to the rope connection structure of one of the rope drive gears, and the other end of the rope is fixed to the rope connection structure of another rope drive gear after being folded through the rope guide pulley, the two rope drive gears are meshed and connected so that they rotate synchronously in opposite directions, the rope connection structures of the two rope drive gears are 180° out of phase, so that when the two rope drive gears rotate synchronously in opposite directions, the ropes are driven to move synchronously in opposite directions, so that the ropes produce reciprocating motion, and one of the rope drive gears is transmission-connected to the synchronous drive gear; the folding drive slider includes a slider and a folding drive arm, one end of the folding drive arm is hinged to the slider, the slider is slidably connected to the guide shaft and is fixed on the rope, and when the rope produces reciprocating motion, it drives the folding drive slider to slide reciprocatingly along the guide shaft;

[0017] The synchronous drive gear is meshed and connected with the eccentric drive gear so that the flapping motion of the flapping folding wing is synchronized with the folding and stretching motion. The inner end of the flapping arm is fixedly connected to the other end of the flapping drive arm, and the folding arm is hinged to the other end of the folding drive arm;

[0018] The drive motor drives the eccentric drive gear to rotate, causing the flapping drive arm to drive the flapping arm to generate a flapping motion. The eccentric drive gear drives the synchronous drive gear to rotate, so that the folding drive arm drives the folding arm to perform a reciprocating folding and stretching motion synchronous with the flapping arm. When the flapping wing moves upward, the folding wing performs a folding motion to reduce the area of the flapping folding wing, thereby reducing the negative lift generated during the upward flapping process. When the flapping wing moves downward, the folding wing performs a stretching motion to increase the area of the flapping folding wing, thereby increasing the lift generated during the downward flapping process.

[0019] The further improvement of the present invention lies in:

[0020] A pull rope drive gear transmission shaft 26 is provided between one of the pull rope drive gears and the synchronous drive gear. The pull rope drive gear transmission shaft coaxially fixes and connects them together to form a transmission connection.

[0021] There are two pull rope guiding pulleys.

[0022] The folding arm is hinged to the folding drive arm through a triangular hinge frame. The angular connecting frame includes two hinge rods. One end of the two hinge rods is hinged to form the folding drive arm hinge end. One of the hinge rods is coaxially hinged to the folding arm and the flapping arm, and the other hinge rod is hinged to the folding arm, so that the two hinge rods and part of the folding arm form a triangular hinge frame. The folding drive arm is hinged to the folding drive arm hinge end of the triangular hinge frame, so that the folding drive arm can more smoothly drive the folding arm to perform a reciprocating folding and stretching motion.

[0023] The beneficial effects produced by adopting the above technical solutions are as follows:

[0024] The flapping folding wing is mainly composed of a flapping wing and a folding wing located at the outer end of the flapping wing; the flapping folding motion mechanism enables the flapping drive arm to drive the flapping arm to generate a flapping motion, and at the same time enables the folding drive arm to drive the folding arm to perform a reciprocating folding and stretching motion synchronous with the flapping arm. Thus, when the flapping wing moves upward, the folding wing performs a folding motion to reduce the area of the flapping folding wing, thereby reducing the negative lift generated during the upward flapping process. When the flapping wing moves downward, the folding wing performs a stretching motion to increase the area of the flapping folding wing, thereby increasing the lift generated during the downward flapping process, so as to improve its aerodynamic efficiency. It adopts the bionic principle that birds improve flight efficiency by actively changing the shape of their wings; using a pull rope to replace the traditional connecting rod to realize the folding and stretching motion of the flapping arm has the advantages of simple and reasonable structure, light weight, good mobility, etc. compared with the connecting rod structure method. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of a flapping-wing aircraft;

[0026] Figure 2 is Figure 1 a schematic structural diagram of the flapping and folding flapping-wing device in

[0027] Figure 3 is Figure 1 a schematic structural diagram of the flapping and folding motion mechanism when the folding wing is in the extended state in

[0028] Figure 4 is Figure 3 a schematic structural diagram after removing the wing membrane;

[0029] Figure 5 is Figure 1 a schematic structural diagram of the flapping and folding motion mechanism when the folding wing is in the folded state in

[0030] Figure 6 is Figure 5 a schematic structural diagram after removing the wing membrane.

[0031] In the attached drawings: 1. fuselage; 2. drive motor; 3. flapping wing; 4. folding wing; 5. flapping arm; 6. folding arm; 7. first longitudinal beam; 8. second longitudinal beam; 9. longitudinal beam rear connection beam; 10. diagonal beam; 11. moving folding drive mechanism mounting bracket; 12. guide shaft; 13. flapping drive arm; 14. eccentric shaft connecting rod; 15. swing arm; 16. drive connecting rod; 17. eccentric drive gear; 18. eccentric shaft; 19. synchronous drive gear; 20. cable drive gear; 21. cable; 22. cable guide pulley; 23. cable drive gear; 24. slider; 25. folding drive arm; 26. cable drive gear transmission shaft; 27. articulated rod; 28. tail rudder.

[0032] In this application, the orientation description is based on the orientation of the flapping-wing aircraft. The direction of flight of the flapping-wing aircraft is the front, and the upper side is the upper side of the flight state of the flapping-wing aircraft. Detailed implementation manners

[0033] The present invention will be further described in detail below with reference to the attached drawings and specific embodiments.

[0034] For ease of description, the flapping-wing aircraft is taken as an example for detailed introduction

[0035] The standard parts used in the present invention can all be purchased from the market. The special-shaped parts can be customized according to the description in the specification and the attached drawings. The specific connection methods of each part all adopt conventional means such as bolts, rivets, welding, and pasting, which are mature in the prior art, and will not be elaborated here.

[0036] As can be seen from the embodiments shown Figures 1 to 6 in this embodiment, it includes a fuselage 1, a flight control system and a flapping wing device. The flapping wing device is a flapping and folding flapping wing device, which includes a driving motor 2 [micro DC planetary reduction motor, model: PG28-385] and a pair of flapping and folding motion mechanisms with the same structure. The flapping and folding motion mechanism includes a flapping and folding wing and a flapping and folding driving mechanism;

[0037] The flapping and folding wing is mainly composed of a flapping wing 3 and a folding wing 4 located at the outer end of the flapping wing 3;

[0038] The flapping and folding wing includes a flapping arm 5, a folding arm 6, a flapping wing skeleton and a wing membrane. The outer end of the flapping arm 5 is hinged to the inner end of the folding arm 6 so that the folding arm 6 can perform reciprocating folding and stretching motion back and forth relative to the flapping arm 5. The flapping wing skeleton is fixed above the flapping arm 5. The flapping wing skeleton includes a first longitudinal beam 7, a second longitudinal beam 8, a longitudinal beam rear connecting beam 9 and an inclined beam 10. The front end of the second longitudinal beam 8 is fixed on the hinge shaft where the flapping arm 5 and the folding arm 6 extend upward. The front end of the first longitudinal beam 7 is fixed on the flapping arm 5 through a vertical beam (not shown in the figure). Both ends of the longitudinal beam rear connecting beam 9 fixedly connect the rear ends of the first longitudinal beam 7 and the second longitudinal beam 8 together. The front end of the inclined beam 10 is fixedly connected to the front end of the second longitudinal beam 8. The inclined beam 10 is inclined outward from front to back. The wing membrane is bonded to the flapping wing skeleton and the folding arm 6. The flapping wing skeleton and the wing membrane it supports form the flapping wing 3. The folding arm 6 and the wing membrane it supports form the folding wing 4. The wing membrane part supported by the folding arm 6 forms the leading edge of the folding wing 4; The flapping wing skeleton is fixed above the flapping arm 5, so as to form a folding space at the connection part between the folding wing 4 and the flapping wing 3, so that when the folding wing 4 performs front-back folding motion, it can produce relative folding and stretching states with the flapping wing 3;

[0039] The flapping and folding driving mechanism includes a flapping and folding driving mechanism mounting frame 11 and a guide shaft 12, a flapping driving mechanism and a folding driving mechanism arranged on the flapping and folding driving mechanism mounting frame 11;

[0040] The flapping driving mechanism includes an eccentric driving structure and a flapping driving arm 13;

[0041] The eccentric driving structure includes an eccentric driving gear 17, an eccentric shaft connecting rod 14, a swing arm 15 and a driving connecting rod 16. The middle part of the flapping driving arm 13 is rotatably connected to the guide shaft 12; The eccentric driving gear 17 is eccentrically provided with an eccentric shaft 18, and one end of the eccentric shaft connecting rod 14 is rotatably connected to the eccentric shaft 18; The other end of the eccentric shaft connecting rod 14 is hinged to one end of the swing arm 15. The other end of the swing arm 15 is hinged to one end of the driving connecting rod 16. The other end of the driving connecting rod 16 is hinged to one end of the flapping driving arm 13;

[0042] When the eccentric driving gear 17 rotates, the eccentric shaft 18 generates a circular motion, so that the eccentric shaft connecting rod 14 drives the swing arm 15 to reciprocate, and the swing arm 15 drives the flapping driving arm 13 to generate a reciprocating flapping motion around the guide shaft 12 through the driving connecting rod 16; by changing the length of the eccentric shaft connecting rod 14 or the driving connecting rod 16, the flapping amplitude of the flapping folding wing can be changed, so that the flapping amplitude can be effectively changed as needed;

[0043] The folding drive mechanism includes a synchronous drive gear 19, a slider reciprocating drive structure and a folding drive slider;

[0044] The slider reciprocating drive structure includes a pair of pull rope drive gears 20 with the same structure, a pull rope 21 and at least one pull rope guide pulley 22. The pull rope drive gear 20 is eccentrically provided with a pull rope connection structure 23. One end of the pull rope 21 is fixed to the pull rope connection structure 23 of one of the pull rope drive gears 20. The other end of the pull rope 21 is folded through the pull rope guide pulley 22 and fixed to the pull rope connection structure 23 of another pull rope drive gear 20. The two pull rope drive gears 20 are meshed and connected so that they rotate synchronously in opposite directions. The connection structure 23 is 180° out of phase, so that when the two rope drive gears 20 rotate synchronously in opposite directions, the rope 21 is driven to move synchronously in opposite directions, so that the rope 21 reciprocates, and one rope drive gear 20 is transmission-connected with the synchronous drive gear 19; the folding drive slider includes a slider 24 and a folding drive arm 25, one end of the folding drive arm 25 is hinged to the slider 24, the slider 24 is slidably connected to the guide shaft 12, and is fixed on the rope 21, and when the rope 21 reciprocates, it drives the folding drive slider 24 to slide reciprocatingly along the guide shaft 12;

[0045] The synchronous drive gear 19 is meshedly connected with the eccentric drive gear 17 so that the flapping motion of the flapping folding wing is synchronized with the folding and stretching motion, the inner end of the flapping arm 5 is fixedly connected with the other end of the flapping drive arm 13, and the folding arm 6 is hinged with the other end of the folding drive arm 25;

[0046] The drive motor 2 drives the eccentric drive gear 17 to rotate, causing the flapping drive arm 13 to drive the flapping arm 5 to produce a flapping motion. The eccentric drive gear 17 drives the synchronous drive gear 19 to rotate, so that the folding drive arm 25 drives the folding arm 6 to perform a reciprocating folding and unfolding motion synchronous with the flapping arm 5. When the flapping wing 3 flaps upward, the folding wing 4 performs a folding motion to reduce the area of the flapping and folding wing, thereby reducing the negative lift generated during the upward flap. When the flapping wing 3 flaps downward, the folding wing 4 performs an unfolding motion to increase the area of the flapping and folding wing, thereby increasing the lift generated during the downward flap; thus greatly improving its aerodynamic efficiency and achieving the purpose of actively changing the wing shape like a bird to improve flight efficiency; by changing the distance that the slider 24 reciprocally slides along the guide shaft 12, its folding angle can be changed, and the adjustment of this reciprocating sliding distance is achieved by changing the speed ratio between the cable drive gear 20 and the eccentric drive gear 17;

[0047] A pair of flapping and folding motion mechanisms with the same structure are symmetrically arranged left and right, so that the two flapping and folding wings are symmetrically arranged on the left and right sides of the fuselage 1; the flapping and folding motion mechanism arranged on the left is the left flapping and folding motion mechanism, and the flapping and folding motion mechanism arranged on the right is the right flapping and folding motion mechanism. The drive motor 2 drives the left flapping and folding motion mechanism and the right flapping and folding motion mechanism to operate synchronously, so that the two flapping and folding wings respectively produce synchronous flapping motions and folding and unfolding motions.

[0048] A cable drive gear transmission shaft 26 is provided between one of the cable drive gears 20 and the synchronous drive gear 19, and the cable drive gear transmission shaft 26 coaxially fixes and connects them together to form a transmission connection.

[0049] An eccentric drive gear transmission shaft (not shown in the figure) is provided between the eccentric drive gear 17 of the left flapping and folding motion mechanism and the eccentric drive gear 17 of the right flapping and folding motion mechanism. The eccentric drive gear transmission shaft coaxially fixes and connects them together to form a transmission connection. The rotating shaft of the drive motor 2 is in transmission connection with one of the eccentric drive gears 17 through a gear transmission structure, thereby driving the two flapping and folding motion mechanisms to operate synchronously, so that the two flapping and folding wings respectively produce synchronous flapping motions and folding and unfolding motions.

[0050] There are two cable guide pulleys 22.

[0051] The folding arm 6 is articulated to the folding drive arm 25 through a triangular articulated frame. The angular connecting frame includes two articulated rods 27. One ends of the two articulated rods 27 are articulated to form a folding drive arm articulated end. One of the articulated rods 27 is coaxially articulated to the folding arm 6 and the flapping arm 5, and the other articulated rod 27 is articulated to the folding arm 6. Thus, the two articulated rods 27 and a part of the folding arm 6 form a triangular articulated frame. The folding drive arm 25 is articulated to the folding drive arm articulated end of the triangular articulated frame, so that the folding drive arm 25 can drive the folding arm 6 to perform reciprocating folding and extending movements more smoothly.

Claims

1. A flapping and folding motion mechanism for a flapping-wing aircraft, which comprises a flapping and folding wing and a flapping and folding drive mechanism; The flapping and folding wing mainly consists of a flapping wing (3) and a folding wing (4) located at the outer end of the flapping wing (3); The flapping and folding wing includes a flapping arm (5), a folding arm (6), a flapping wing skeleton and a wing membrane. The outer end of the flapping arm (5) is hinged to the inner end of the folding arm (6) so that the folding arm (6) can perform reciprocating folding and stretching motions back and forth relative to the flapping arm (5). The flapping wing skeleton is fixed above the flapping arm (5), and the wing membrane is bonded to the flapping wing skeleton and the folding arm (6). The flapping wing skeleton and the wing membrane it supports form the flapping wing (3), and the folding arm (6) and the wing membrane it supports form the folding wing (4). The part of the wing membrane supported by the folding arm (6) forms the leading edge of the folding wing (4); The flapping and folding drive mechanism includes a flapping and folding drive mechanism mounting bracket (11), a guide shaft (12) provided on the flapping and folding drive mechanism mounting bracket (11), a flapping drive mechanism and a folding drive mechanism; The flapping drive mechanism includes an eccentric drive structure and a flapping drive arm (13); The eccentric drive structure includes an eccentric drive gear (17), an eccentric shaft connecting rod (14), a swing arm (15) and a drive connecting rod (16). The middle of the flapping drive arm (13) is rotatably connected to the guide shaft (12); the eccentric drive gear (17) is eccentrically provided with an eccentric shaft (18), and one end of the eccentric shaft connecting rod (14) is rotatably connected to the eccentric shaft (18); the other end of the eccentric shaft connecting rod (14) is hinged to one end of the swing arm (15), the other end of the swing arm (15) is hinged to one end of the drive connecting rod (16), and the other end of the drive connecting rod (16) is hinged to one end of the flapping drive arm (13); When the eccentric drive gear (17) rotates, the eccentric shaft (18) generates a circular motion, so that the eccentric shaft connecting rod (14) drives the swing arm (15) to reciprocate, and the swing arm (15) drives the flapping drive arm (13) to generate a reciprocating flapping motion around the guide shaft (12) through the drive connecting rod (16); The folding drive mechanism includes a synchronous drive gear (19), a slider reciprocating drive structure and a folding drive slider; The reciprocating driving structure of the slider includes a pair of rope driving gears (20) with the same structure, a rope (21) and at least one rope guiding pulley (22). The rope driving gear (20) is eccentrically provided with a rope connecting structure (23). One end of the rope (21) is fixed to the rope connecting structure (23) of one of the rope driving gears (20), and the other end of the rope (21) is fixed to the rope connecting structure (23) of the other rope driving gear (20) after being turned around by the rope guiding pulley (22). The two rope driving gears (20) are meshed and connected to rotate synchronously and in opposite directions. The rope connecting structures (23) of the two rope driving gears (20) have a phase difference of 180°, so that when the two rope driving gears (20) rotate synchronously and in opposite directions, they drive the rope (21) to move in the opposite direction synchronously, thereby making the rope (21) produce a reciprocating motion. One of the rope driving gears (20) is in transmission connection with the synchronous driving gear (19). The folding driving slider includes a slider (24) and a folding driving arm (25). One end of the folding driving arm (25) is hinged to the slider (24). The slider (24) is slidably connected to the guiding shaft (12) and fixed to the rope (21). When the rope (21) produces a reciprocating motion, it drives the folding driving slider (24) to slide reciprocally along the guiding shaft (12). The synchronous driving gear (19) is meshed and connected to the eccentric driving gear (17) so that the flapping motion of the flapping folding wing and the folding and stretching motion are synchronized. The inner end of the flapping arm (5) is fixedly connected to the other end of the flapping driving arm (13). The folding arm (6) is hinged to the other end of the folding driving arm (25). The driving motor (2) drives the eccentric driving gear (17) to rotate, so that the flapping driving arm (13) drives the flapping arm (5) to produce a flapping motion. The eccentric driving gear (17) drives the synchronous driving gear (19) to rotate, so that the folding driving arm (25) drives the folding arm (6) to perform a reciprocating folding and stretching motion synchronous with the flapping arm (5). When the flapping wing (3) flaps upward, the folding wing (4) performs a folding motion to reduce the area of the flapping folding wing, thereby reducing the negative lift generated during the upward flapping process. When the flapping wing (3) flaps downward, the folding wing (4) performs a stretching motion to increase the area of the flapping folding wing, thereby increasing the lift generated during the downward flapping process.

2. The flapping and folding motion mechanism for a flapping-wing aircraft according to claim 1, wherein: A pull cord drive gear transmission shaft (26) is provided between one of the pull cord drive gears (20) and the synchronous drive gear (19), and the pull cord drive gear transmission shaft (26) coaxially and fixedly connects them together to form a transmission connection.

3. The flapping and folding motion mechanism for a flapping-wing aircraft according to claim 1, wherein: There are two of the pull cord guide pulleys (22).

4. The flapping folding motion mechanism for a flapping wing aircraft according to claim 1, characterized in that: The folding arm (6) is hinged to the folding drive arm (25) through a triangular hinge bracket. The angular connecting bracket includes two hinge rods (27). One ends of the two hinge rods (27) are hinged to form a folding drive arm hinge end. One of the hinge rods (27) is coaxially hinged to the folding arm (6) and the flapping arm (5). The other hinge rod (27) is hinged to the folding arm (6), so that the two hinge rods (27) and a part of the folding arm (6) form a triangular hinge bracket. The folding drive arm (25) is hinged to the folding drive arm hinge end of the triangular hinge bracket, so that the folding drive arm (25) can drive the folding arm (6) to perform reciprocating folding and stretching movements more smoothly.

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