CN204452936U - A kind of flapping-wing modal can auto-folder and launch flapping wing - Google Patents

Abstract

The utility model discloses a kind of flapping-wing modal can auto-folder and launch flapping wing, be made up of an engine installation, two hydraulic pipes, some folding lines, some strut bars, ala and two folding devices; It adopts hydraulic principle realize the folding of flapping wing and launch.This flapping wing forms the vein of bionic flapping-wing by two hydraulic pipes and some strut bars, bionical vein bonds ala and forms aerofoil.This flapping wing produces pressure by miniflow pump to pumping liquid in different sap cavity, to drive the folding of flapping wing and to launch.The utility model not only contributes to reducing the lateral dimension of micro flapping wing air vehicle when not flying; space required when reducing to carry, transport and deposit; reduce transportation request; be convenient to protect flapping wing for ornithopter; make it from damage; but also contribute to changing the flapping wing after damaging, improve the service life of minute vehicle.

Description

Automatic folding and unfolding flapping wings of a flapping-wing micro-aircraft

technical field

The utility model relates to a foldable and unfoldable flapping wing of a flapping-wing aircraft, in particular to an automatically foldable and unfoldable flapping wing of a bionic flapping-wing micro-aircraft.

Background technique

Since American scientists proposed the concept of micro-aircraft in 1992, in view of its huge application value in military and civilian fields, many researchers at home and abroad have launched research on related fields of micro-aircraft. After more than 20 years of development, MAVs have formed three main types: fixed-wing, rotary-wing and flapping-wing. Because flapping-wing MAVs can still generate sufficient lift and thrust under smaller scales and weights, they have become one of the research hotspots in the field of MAVs.

In order to make the flapping-wing MAV have good aerodynamic performance under smaller size and weight, most of its flapping wings adopt membrane structure. In order to provide sufficient lift and thrust, the flapping wings of the flapping-wing aircraft must reach a certain aspect ratio. Therefore, the area of these flapping wings is often relatively large, the strength is low, easy to damage, the requirements for carrying conditions are very high, and it is inconvenient to carry. Currently, research on flapping wings for bionic flapping-wing MAVs is mainly focused on the distribution of insect rear wing veins, while there are few studies on the specific structure of flapping wings, and there are relatively few related patents related to the foldable flapping wings of flapping-wing MAVs. few.

The wings of scarabs are divided into hind wings and elytra. The hind wings are thin and easily damaged, while the elytra are thick and strong, and the hind wings are much larger than the elytra. When the scarab flies, the hind wings spread and flutter to generate lift and thrust. When not flying, the hind wings are folded and placed under the elytra, protected by the elytra.

The utility model proposes a foldable/deployable wing of a fluttering-wing micro-aircraft based on the hydraulic principle by observing the unfolding and folding process of the rear wing of the scarab. The flapping wing can be folded and unfolded under the condition of meeting the flight requirements, which effectively reduces the difficulty of carrying and transportation.

Contents of the invention

The purpose of the utility model is to reduce the lateral size of the flapping-wing micro-aircraft when it is not flying, reduce the area of the flapping-wing micro-aircraft, protect the flapping wings of the aircraft, and reduce the carrying capacity of the flapping-wing micro-aircraft without reducing the wingspan of the flapping-wing micro-aircraft Difficulty, and provide a flapping-wing micro air vehicle that can automatically fold and unfold the flapping wings.

The utility model is composed of a power device, a first hydraulic pipe, a second hydraulic pipe, several creases, a first support rod, a second support rod, a third support rod, a fourth support rod, a fifth support rod, a sixth It consists of a support rod, a membrane and two folding devices; the first hydraulic pipe, the second hydraulic pipe and the sixth support rod are radially distributed around the power device; the first support rod, the second support rod, the third support rod, the Four support rods, the fifth support rod and the sixth support rod end suspension;

The power device includes two liquid chambers, a two-way micro-flow pump, several inelastic hoses, wing handles, two elastic parts, hollow links, common hinges, two micro sensors, a microcontroller and a The interface of energy transmission and information transmission. The wing handle is the main structure of the power device. Two-way micro-flow pumps, ordinary hinges and hollow link parts are installed on the wing handle. One end of the elastic part is fixedly connected to the wing handle. There are two Liquid cavity, built-in micro sensor in the liquid cavity, a non-elastic hose is installed on the wing handle to form a hydraulic pipeline, and the hydraulic pipeline is connected with the micro flow pump, the liquid cavity, the first hydraulic tube, the second hydraulic tube and the support rod, the wing handle A microcontroller and an interface for energy transmission and information exchange are also installed on the board.

The folding device is composed of the fan-shaped cavity at the end of the first hydraulic pipe and the second hydraulic pipe, the front ends of the first support rod and the third support rod, a film, a pin shaft, a torsion spring, a rigid plate and an elastic cable. The first hydraulic pipe The front end of the first hydraulic pipe is connected to the power unit, the front end pipe wall of the first hydraulic pipe is connected to the wing handle of the power unit through a hollow link, and the liquid cavity inside the first hydraulic pipe communicates with the hydraulic pipeline in the power unit through an inelastic hose; There is an arc-shaped protrusion on the outside of the first hydraulic pipe, which is used for bonding with the end of the arc-shaped inelastic hose protruding from the power device; an elastic member is also connected to the outer wall of the first hydraulic pipe, and the elastic The other end of the piece is fixed on the wing handle of the power unit.

The end of the first hydraulic pipe is connected with the folding device, and the end of the first hydraulic pipe expands to form a fan-shaped cavity, and small holes are opened on the wall of the cavity. There are rigid plates and films in the fan-shaped cavity. The film is bag-shaped, and its shape is consistent with the fan-shaped cavity. The pocket part of the film is glued to the entrance of the fan-shaped cavity to form a closed liquid cavity, and the other parts of the film are separated from the fan-shaped cavity; Rigid The plate is glued on the film, and the end of the first hydraulic pipe is hinged with the front end of the first support rod through a pin shaft. A torsion spring is installed on the pin shaft. One torsion arm of the torsion spring is fixedly connected with the first hydraulic pipe. The other torsion arm is fixedly connected with the first support rod, the non-elastic cable passes through the small hole on the wall of the first hydraulic lumen, one end of the non-elastic cable is fastened to the rigid plate, and the other end of the non-elastic cable is connected to the first hydraulic tube. The front end of a support rod is fastened and connected.

The pipe wall of the second hydraulic pipe is fixedly connected with the wing handle of the power unit, and the inside of the second hydraulic pipe communicates with the hydraulic pipeline in the power unit through an inelastic hose; the end of the second hydraulic pipe is the same as that of the first hydraulic pipe , the second hydraulic pipe is connected to the front end of the third support rod through the folding device.

The front end of the second support rod is fixedly connected to the first support rod, and the front ends of the fourth support rod and the fifth support rod are fixedly connected to the second hydraulic pipe.

The front end of the sixth support rod is linked to the wing handle of the power unit through a common hinge; the outer side of the sixth support rod has an arc-shaped protrusion, which is glued together with the arc-shaped end of the inelastic hose protruding from the power unit ; The outer wall of the sixth support rod is also connected with an elastic piece, and the other end of the elastic piece is fixed on the wing handle of the power device.

The patellar membrane is bonded on the first hydraulic pipe, the second hydraulic pipe, the first support rod, the second support rod, the third support rod, the fourth support rod, the fifth support rod and the sixth support rod to form the airfoil. The mask has creases.

The creases formed on the airfoil during the unfolding and folding process are as follows: the straight line formed by the power unit and the end of the fifth support rod; the straight line formed between the two folding units; the connection line between the power unit and the two folding units The straight line formed by the midpoint of the ; the straight line formed by the folding device and the end of the fourth support bar; the straight line formed by the folding device and the end of the second support bar.

The beneficial effects of the utility model:

1. The folding and unfolding of the flapping wing is completed by its own mechanism, which realizes the separation of the folding/deploying movement of the flapping wing and the normal flight movement of the MAV. Compared with other folding wings, it can greatly simplify the complexity of the motion mechanism of the MAV.

2. The flapping wing keeps unfolded during flight to obtain the best aerodynamic performance; when not flying, the flapping wing remains fully folded, with a small lateral size and wing surface, which is convenient for protecting the wing surface of the micro aircraft and making the flapping wing Not easily damaged. At the same time, the folded flapping wings are conducive to saving space and are convenient for carrying and storage.

3. The flapping wing adopts a packaged structure, which integrates the drive system and the actuator, and is connected to the aircraft fuselage through an interface. It only needs to transmit energy and information, which is convenient for disassembly and assembly, and can realize rapid assembly and maintenance. replace. It helps to improve the versatility and interchangeability of parts, facilitates timely replacement of damaged parts, maximizes the value of parts, and improves the service life of the micro air vehicle.

4. Information exchange is carried out between the flapping wing and the aircraft fuselage through the data interface, which is convenient for the micro aircraft fuselage to grasp the state of the flapping wing at any time, and make corresponding adjustments, which helps to maintain the flight performance of the aircraft.

5. Adopting hydraulic drive, it is convenient to package the drive system and actuator inside the flapping wing, and the aerodynamic performance of the flapping wing will not be affected by the drive system and actuator.

Description of drawings

Fig. 1 is a schematic diagram of the fully expanded state of the utility model.

Fig. 2 is a schematic diagram of the state after the first folding/unfolding of the utility model.

Fig. 3 is a schematic diagram of the fully folded state of the utility model.

Fig. 4 is the enlarged schematic view of parts A of the present utility model;

FIG. 5 is an enlarged schematic diagram of point C in FIG. 4 .

FIG. 6 is an enlarged schematic diagram of point D in FIG. 4 .

Fig. 7 is an enlarged schematic view of the hollow link of the present invention.

Fig. 8 is an enlarged schematic view of the folding device of the present invention.

Detailed ways

Please refer to Fig. 1, Fig. 2 and Fig. 3, the utility model is composed of a power unit A, a first hydraulic pipe 1, a second hydraulic pipe 2, several creases 3, a first support rod 4, and a second support rod 6. The third support rod 7, the fourth support rod 8, the fifth support rod 9, the sixth support rod 10, the membrane 5 and two folding devices B; the first hydraulic pipe 1, the second hydraulic pipe 2 and the first hydraulic pipe Six support rods 10 are radially distributed around the power unit A, the ends of the first support rod 4, the second support rod 6, the third support rod 7, the fourth support rod 8, the fifth support rod 9 and the sixth support rod 10 are suspended set;

Referring to Fig. 4, Fig. 5 and Fig. 6, the power device A includes two liquid chambers 11, a two-way micro-flow pump 12, several inelastic hoses 13, a wing handle 14, and two elastic parts 15 , a hollow link 16, a common hinge 17, two microsensors 23, a microcontroller 25 and an interface 24 for energy transmission and information transmission. Flow pump 12, ordinary hinge 17 and hollow link 16, one end of elastic member 15 is fixedly connected with wing handle 14, and two liquid chambers 11 are opened on wing handle 14, and micro sensor 23 is built in liquid chamber 11, and wing handle 14 is equipped with There is no elastic hose 13 to form a hydraulic pipeline, and the hydraulic pipeline is connected with the micro-flow pump 12, the liquid chamber 11, the first hydraulic pipe 1, the second hydraulic pipe 2 and the support rod 10, and the micro-controller is also installed on the wing handle 14. Device 25 and interface 24 for energy transmission and information exchange.

Please refer to Fig. 7 and Fig. 8, the folding device B is composed of the fan-shaped cavity at the end of the first hydraulic pipe 1 and the second hydraulic pipe 2, the front ends of the first support rod 4 and the third support rod 7, a film 18, a pin 19. A torsion spring 20, a rigid plate 22 and an inelastic cable 21 are formed. The front end of the first hydraulic pipe 1 is connected to the power unit A, and the front end of the first hydraulic pipe 1 is connected to the wing of the power unit A through the hollow link 16. The handle 14 is connected, and the internal liquid chamber of the first hydraulic pipe 1 communicates with the hydraulic pipeline in the power unit A through an inelastic hose 13; The end of the arc-shaped non-elastic hose 13 protruding from the center is bonded; the outer wall of the first hydraulic pipe 1 is also connected with an elastic piece 15, and the other end of the elastic piece 15 is fixed on the wing handle 14 of the power unit A.

The end of the first hydraulic pipe 1 is connected to the folding device B, and the end of the first hydraulic pipe 1 expands to form a fan-shaped cavity, and small holes are opened on the wall of the cavity. Rigid plate 22 and film 18 are arranged in fan-shaped cavity, and film 18 is bag-shaped, and its shape is consistent with fan-shaped cavity, and the bag mouth part of film 18 is bonded at the entrance of fan-shaped cavity to form airtight liquid cavity, and other parts of film and fan-shaped cavity The cavity is separated; the rigid plate 22 is glued on the film 18, the end of the first hydraulic pipe 1 is hinged with the front end of the first support rod 4 through the pin 19, and the torsion spring 20 is installed on the pin 19, and a torsion spring 20 The arm is fixedly connected with the first hydraulic pipe 1, and the other torsion arm of the torsion spring 20 is fixedly connected with the first support rod 4, and the non-elastic cord 21 passes through the small hole on the wall of the first hydraulic pipe 1, and the non-elastic cord 21 One end of the cable 21 is fastened together with the rigid plate 22, and the other end of the non-elastic cable 21 is fastened to the front end of the first support rod 4.

The pipe wall of the second hydraulic pipe 2 is fixedly connected with the wing handle 14 of the power unit A, and the inside of the second hydraulic pipe 2 communicates with the hydraulic pipeline in the power unit A through an inelastic hose 13; The end is the same as the first hydraulic pipe 1, and the second hydraulic pipe 2 is connected to the front end of the third support rod 7 through the folding device B.

The front end of the second support rod 6 is fixedly connected to the first support rod 4 , and the front ends of the fourth support rod 8 and the fifth support rod 9 are fixedly connected to the second hydraulic pipe 2 .

The front end of the sixth support rod 10 is connected to the wing handle 14 of the power unit A through a common hinge; The outer wall of the sixth support rod 10 is also connected with an elastic piece 15, and the other end of the elastic piece 15 is fixed on the wing handle 14 of the power unit A.

The membrane 5 is bonded to the first hydraulic pipe 1, the second hydraulic pipe 2, the first support rod 4, the second support rod 6, the third support rod 7, the fourth support rod 8, the fifth support rod 9 and the sixth support rod. Airfoils are formed on the struts 10 and the airfoils have creases 3 .

The creases 3 formed on the airfoil during the unfolding and folding process have the following places: the straight line formed between the power unit A and the end of the fifth support rod 9; the straight line formed between the two folding units B; the line between the power unit A and the two The straight line formed by the midpoint of the connecting line of two folding devices B; the straight line formed by the folding device B and the end of the fourth support rod 8; the straight line formed by the folding device B and the end of the second support rod 6.

The folding and unfolding of the utility model are carried out in two steps. The fully unfolded state is shown in FIG. 1 , the half-folded/unfolded state is shown in FIG. 2 , and the fully folded state is shown in FIG. 3 .

Folding principle:

The flapping wings are in an unfolded state before folding, as shown in Figure 1. At this time, hydraulic pressure pushes the first hydraulic pipe 1 and the sixth support rod 10 to keep unfolding, and the elastic member 15 is stretched under force. In the folding device B, the torsion spring 20 is in a free state without generating elastic force, and the film 18 is relaxed and deformed.

When the flapping wing needs to be folded, the hydraulic pressure in the part of the hydraulic line connected with the sixth support rod 10 and the outer wall of the first hydraulic pipe 1 is reduced, and the sixth support rod 10 and the first hydraulic pipe 1 are gradually wound around under the action of the elastic member 15. The hinges are folded into a half-folded state, as shown in Figure 2.

As the flapping wings continue to fold, the hydraulic pressure in the lumens inside the first hydraulic pipe 1 and the second hydraulic pipe 2 gradually increases, and the liquid gradually fills the fan-shaped cavity in FIG. 8 , pushing the rigid plate 22 to pull the inelastic cable 21. Under the action of tension, the first support rod 4 and the third support rod 7 overcome the elastic force of the torsion spring 20 and rotate around the pin shaft 19, and the flapping wings are folded to the state shown in FIG. 3 .

Expansion principle:

Before unfolding, the flapping wings are in a folded state, as shown in Figure 3. At this time, the elastic member 15 is free to elongate without elastic force, and the torsion spring 20 is twisted under the pressure of the elastic cable 21 .

When the flapping wing needs to be unfolded, the hydraulic pressure in the fan-shaped cavity gradually decreases, and the torsion spring 20 gradually recovers under the action of elasticity, and the wing surface unfolds into a half-expanded state, as shown in FIG. 2 .

As the flapping wings continue to expand, the internal pressure of the hydraulic pipeline connected to the sixth support rod 10 and the outer wall of the first hydraulic pipe 1 increases, pushing the first hydraulic pipe 1 and the sixth support rod 10 to rotate counterclockwise and clockwise around their joint points respectively. , the airfoil is deployed to the extent shown in FIG. 1 , and the elastic member 15 is stretched under force.

Folding process:

Before the flapping wings need to be folded, the micro-aircraft judges the current state of the flapping wings through the pressure inside each liquid chamber measured by the micro sensors in the liquid chambers. Take the fully expanded state as an example. At this time, the pressure in the left liquid chamber 11 in Fig. 5 is high, and the micro-flow valve at the communication end between the two-way micro-flow pump 12 and the left liquid chamber remains closed, and the liquid is filled with the left liquid chamber 11. In the entire pipeline, the first hydraulic pipe 1 and the sixth support rod 10 are in the unfolded state, the inelastic hose 13 is of normal length, and the elastic member 15 is stretched under force. In the folding device B, the torsion spring 20 is in a free state without generating elastic force, the film 18 is loosely deformed, and a cavity is formed in the fan-shaped cavity.

After the micro-aircraft sends a folding command to the flapping wing, the microcontroller on the flapping wing controls the left micro-flow valve of the two-way micro-flow pump 12 to open, and pumps the liquid in the left liquid chamber 11 to the right liquid chamber 11. The hydraulic pressure in the left liquid chamber 11 and its communication pipeline gradually decreases, the sixth support rod 10 and the first hydraulic pipe 1 are respectively folded under the elastic action of the elastic member 15, and the inelastic hose 13 deforms and shortens under force. Finally, the flapping wing is folded to a half-folded state as shown in Figure 2. At this time, the sixth support rod 10 drives the part of the wing membrane 5 connected to it to fold to the rear of the wing surface, and forms a folding line; the first hydraulic tube 1 is folded close to The position of the second hydraulic pipe 2 forms two folding lines. The position of the folding line is shown by the dotted line in Fig. 1 .

The two-way micro-flow pump 12 continues to pump the liquid from the left liquid chamber 11 into the right liquid chamber 11, and the hydraulic pressure in the right fan-shaped chamber continues to rise to push the rigid plate 22 to rotate clockwise; the non-elastic cable 21 pulls the first support rod 4 and The third support rod 7 rotates clockwise around the pin shaft 19, and the torsion spring 20 is stressed to generate elastic force. Eventually the fluid fills the scalloped cavity and the wing membrane folds into a fully folded state as shown in Figure 3. At this time, the first support rod 4 and the second support rod 6 and the membrane 5 connected thereto are located in the innermost layer, and the sixth support rod 10 and the membrane 5 are located in the middle layer. Refer to Figure 1 for the corresponding folding lines.

After the folding is completed, the microfluidic valve connected between the two-way microfluidic pump 12 and the right side liquid chamber 11 is closed to keep the flapping wings in a completely folded state.

Unfolding process:

The flapping wing unfolding process is roughly the reverse process of folding, and will not be described in detail.

Claims (2)

1. A flapping wing micro-aircraft that can automatically fold and unfold the flapping wing is characterized in that: it is composed of a power unit (A), the first hydraulic pipe (1), the second hydraulic pipe (2), some creases ( 3), the first support rod (4), the second support rod (6), the third support rod (7), the fourth support rod (8), the fifth support rod (9), the sixth support rod (10) , membrane (5) and two folding devices (B); the first hydraulic pipe (1), the second hydraulic pipe (2) and the sixth support rod (10) are radially distributed around the power device (A), The ends of the first support rod (4), the second support rod (6), the third support rod (7), the fourth support rod (8), the fifth support rod (9) and the sixth support rod (10) are suspended ; The power device (A) includes two liquid chambers (11), a two-way micro-flow pump (12), several inelastic hoses (13), wing handles (14), two elastic parts (15), Hollow link (16), ordinary hinge (17), two micro sensors (23), a microcontroller (25) and an interface (24) for energy transmission and information transmission, and the wing handle (14) is the power device ( The main structure of A) is equipped with a two-way micro-flow pump (12), a common hinge (17) and a hollow link (16) on the wing handle (14), and one end of the elastic member (15) is fixedly connected with the wing handle (14), There are two liquid chambers (11) on the wing handle (14), the liquid chamber (11) is equipped with a micro sensor (23), and the non-elastic hose (13) is installed on the wing handle (14) to form a hydraulic pipeline. The micro-flow pump (12), the liquid chamber (11), the first hydraulic pipe (1), the second hydraulic pipe (2) and the support rod (10) are connected with each other, and a microcontroller is also installed on the wing handle (14) (25) and an interface for energy transmission and information exchange (24); The folding device (B) is composed of the fan-shaped cavity at the end of the first hydraulic pipe (1) and the second hydraulic pipe (2), the front ends of the first support rod (4) and the third support rod (7), the film (18), Pin shaft (19), torsion spring (20), rigid plate (22) and no elastic cable (21), the front end of the first hydraulic pipe (1) is connected with the power unit (A), the first hydraulic pipe (1) The front end pipe wall of the first hydraulic pipe (1) is connected to the wing handle (14) of the power unit (A) through a hollow link (16), and the internal liquid cavity of the first hydraulic pipe (1) is connected to the power unit (A) through an inelastic hose (13). The hydraulic pipeline in the first hydraulic pipe (1) has an arc-shaped protrusion on the outside, which is used to bond with the end of the arc-shaped inelastic hose (13) protruding from the power unit (A) ;The outer wall of the first hydraulic pipe (1) is also connected with an elastic piece (15), and the other end of the elastic piece (15) is fixed on the wing handle (14) of the power unit (A); The end of the first hydraulic pipe (1) is connected to the folding device (B), and the end of the first hydraulic pipe (1) expands to form a fan-shaped cavity with small holes on the cavity wall; there are rigid plates (22) and films ( 18), the film (18) is bag-shaped, and its shape is consistent with the fan-shaped cavity, and the pocket part of the film (18) is glued to the entrance of the fan-shaped cavity to form a closed liquid cavity, and the other parts of the film are separated from the fan-shaped cavity; the rigid plate (22) Stick on the film (18), the end of the first hydraulic pipe (1) is hinged with the front end of the first support rod (4) through the pin shaft (19), and the torsion spring (20) is installed on the pin shaft (19) ), one torsion arm of the torsion spring (20) is fixedly connected with the first hydraulic pipe (1), the other torsion arm of the torsion spring (20) is fixedly connected with the first support rod (4), and there is no elastic cable (21 ) through the small hole on the cavity wall of the first hydraulic pipe (1), one end of the non-elastic cable (21) is fastened to the rigid plate (22), and the other end of the non-elastic cable (21) is connected to the first support rod (4) The front end is fastened and connected; The pipe wall of the second hydraulic pipe (2) is fixedly connected with the wing handle (14) of the power unit (A), and the inside of the second hydraulic pipe (2) is connected to the center of the power unit (A) through an inelastic hose (13). The hydraulic pipeline is connected; the end of the second hydraulic pipe (2) is the same as the first hydraulic pipe (1), and the second hydraulic pipe (2) is connected to the front end of the third support rod (7) through the folding device (B); The front end of the second support rod (6) is fixedly connected to the first support rod (4), and the front ends of the fourth support rod (8) and the fifth support rod (9) are fixedly connected to the second hydraulic pipe (2); The front end of the sixth support rod (10) is connected to the wing handle (14) of the power unit (A) through an ordinary hinge; The arc-shaped ends of the non-elastic hose (13) are glued together; an elastic piece (15) is also connected to the outer wall of the sixth support rod (10), and the other end of the elastic piece (15) is fixed on the power unit (A) on the wing handle (14); The patellar membrane (5) is bonded to the first hydraulic pipe (1), the second hydraulic pipe (2), the first support rod (4), the second support rod (6), the third support rod (7), the fourth Airfoils are formed on the support rods (8), fifth support rods (9) and sixth support rods (10), and the airfoils have creases (3). 2. The automatic folding and unfolding flapping wing of a flapping-wing micro-aircraft according to claim 1, characterized in that: the crease (3) has the following several places: the power unit (A) and the fifth support The line formed by the ends of the rod (9); the line formed between the two folding devices (B); the line formed by the midpoint of the line connecting the power unit (A) to the two folding devices (B); the folding device (B) The line formed with the end of the fourth support bar (8); the line formed by the folding device (B) with the end of the second support bar (6).