CN102490187B - Parallel manipulator with five freedom degrees - Google Patents

Abstract

The invention discloses a novel five-degree-of-freedom parallel manipulator, which includes a fixed frame, a first main kinematic chain, a second main kinematic chain, a third main kinematic chain, and a driven branch chain, and the first main kinematic chain includes a first active branch chain , the second main kinematic chain includes the second and third active branch chains, the third main kinematic chain includes the fourth and fifth active branch chains, and the driven branch chain is located in the driven branch chain seat arranged in the central opening of the fixed frame Inside, each active branch chain seat is connected to the inner wall of the corresponding fixed frame opening through the first rotating shaft, and each active branch chain is connected to the corresponding active branch chain seat through the second rotating shaft. The main kinematic chain transmits the motion to the first transmission system, and then to the positioning head from the first transmission system, and the third main kinematic chain transmits the motion to the second transmission system, and then to the rotating shaft from the second transmission system. In this structure, the double active branch chain can increase the stiffness/mass ratio, so that the dynamic performance of the mechanism is good, and the positioning accuracy and repeat positioning accuracy are high.

Description

New five-degree-of-freedom parallel manipulator

technical field

The invention relates to a robot, in particular to a parallel manipulator capable of realizing five-degree-of-freedom operations.

Background technique

According to patents US4732525 and ZL200510015095.5, it is known that the existing multi-coordinate manipulator with a positioning head is generally realized in the form of a parallel mechanism with few degrees of freedom and a hybrid structure with A/C double swing heads. Among them, the parallel mechanism with few degrees of freedom realizes the positioning of the moving platform of the mechanism by adjusting the servo motor installed on the active branch chain, and the A/C double swing head realizes the attitude positioning of the end effector by adjusting the servo motor installed on the double swing head , so as to realize the multi-coordinate machining capability of the mechanism.

This kind of manipulator, because the servo motor and reducer are installed in the A/C double swing head, its disadvantages are: the weight of the end effector is too large, which affects the fast forwarding ability and dynamic performance of the mechanism; because the carrying capacity of the mechanism is completely determined by The branch chain bearing of the parallel mechanism with few degrees of freedom is not conducive to the pursuit of high stiffness/mass ratio of the mechanism.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a novel five-degree-of-freedom parallel manipulator with advantageous feed direction, good dynamic performance, high stiffness/mass ratio, high positioning accuracy and repeat positioning accuracy.

The novel five-degree-of-freedom parallel manipulator of the present invention comprises a fixed frame, a first main kinematic chain, a second main kinematic chain, a third main kinematic chain and a driven branch chain, and the first main kinematic chain includes a first active branch chain, the second main kinematic chain includes the second active branch chain and the third active branch chain, the third main kinematic chain includes the fourth active branch chain and the fifth active branch chain, and the driven The branch chain is located in the driven branch chain seat set in the central opening of the fixed frame. The first main kinematic chain, the second main kinematic chain and the third main kinematic chain are placed symmetrically with respect to the driven branch chain and the phases between them are is 120°, the first active branch chain is located in the first active branch seat set in the first opening of the fixing frame, the second active branch chain and the third active branch chain are respectively located in the second opening hole of the fixing frame In the second active branch chain seat and the third active branch chain seat, the fourth active branch chain and the fifth active branch chain are respectively located in the fourth active branch chain seat and the fifth active branch chain seat arranged in the third opening of the fixed frame. In the chain seat, each of the active branch chain seats is connected to the inner wall of the corresponding fixing frame opening through the first rotating shaft, and each of the active branch chains and the active branch chain seat corresponding to it are respectively passed through The second rotating shaft is connected in rotation, the first rotating shaft and the second rotating shaft are not collinear with each other, the driven branch chain is a tubular structure, and the driven branch chain seat includes an outer ring and an inner ring, the outer ring The outer ring is rotationally connected to the inner wall of the central opening of the fixed frame through the outer ring rotating shaft, the inner ring is connected to the outer ring through the inner ring rotating shaft, and the outer wall and inner ring of the driven branch chain pass through the first slider guide rail The structure is connected, the shaft axis of the inner ring and the shaft axis of the outer ring are not collinear, a transmission system housing is arranged under the fixed frame, and the lower end of the driven branch chain is connected to the transmission system housing Fixedly connected, the lower end of the first active branch chain is connected to the first hinge seat through the rotating shaft, the lower ends of the second active branch chain and the third active branch chain are connected with a rotating shaft of the first cross hinge, and the fourth active branch chain The lower ends of the branch chain and the fifth active branch chain are connected with a rotating shaft of the second cross hinge, and the first cross hinge and the second cross hinge are respectively connected with the second hinge seat and the third hinge seat through bearings, and the first The hinge seat, the second hinge seat and the bottom of the third hinge seat are respectively fixedly connected with a third shaft, a fourth shaft and a fifth shaft, and the third shaft, the fourth shaft and the fifth shaft are rotated with the transmission system housing through bearings The bottom of the transmission system casing is connected with a positioning head through bearing rotation, and the other rotating shaft of each cross hinge is connected with a driving bevel gear arranged in the transmission system casing, each of the driving bevel gears The gears are meshed with a driven bevel gear set in the transmission system housing, wherein the fifth shaft connected to the first driven bevel gear is connected to the sixth shaft arranged in the middle of the transmission system housing through the first synchronous pulley structure. The third driving bevel gear is connected to the sixth rotating shaft, and the third driving bevel gear is meshed with the third driven bevel gear mounted on the rotating shaft of the positioning head through the bearing. , the driving pulley is installed on the fourth rotating shaft connected to the second driven bevel gear, in The positioning head is provided with a driven pulley shaft through a bearing frame, and the driving pulley is connected with the driven pulley installed on the driven pulley shaft through the rotation of the pulley, and the positioning head is connected to the driven pulley , the gear shafts of the first driven bevel gear and the second driven bevel gear and the axis of the sixth rotating shaft are parallel to each other and perpendicular to the rotating shaft.

The beneficial effect of the new five-degree-of-freedom parallel manipulator of the present invention is that the main kinematic chain adopts the form of double active branch chains, which can not only drive the mechanism to realize the motion of one translation and two rotations, but also drive it to realize the rotation around the A/C axis, effectively Reduce the mass of the positioning head, realize the modular structure design, and have an advantageous feed direction. The double active branch chain can increase the stiffness/mass ratio, so that the dynamic performance of the mechanism is good, and the positioning accuracy and repeat positioning accuracy are high.

Description of drawings

Fig. 1 is the structural representation of novel five-degree-of-freedom parallel manipulator of the present invention;

Fig. 2 is the top view of the manipulator shown in Fig. 1;

Fig. 3 is a schematic structural view of the first active branch chain of the manipulator shown in Fig. 1;

Fig. 4 is the structural representation of the second, third, fourth and fifth active branch chains of the manipulator shown in Fig. 1;

Fig. 5 is a partial sectional view of the transmission system and the positioning head of the manipulator shown in Fig. 1;

Fig. 6 is a schematic structural diagram of the application example of the manipulator shown in Fig. 1 .

Detailed ways

Below in conjunction with specific embodiment, and with reference to accompanying drawing, the present invention will be further described:

As shown in the accompanying drawings, the novel five-degree-of-freedom parallel manipulator of the present invention includes a fixed frame 2, a first main kinematic chain, a second main kinematic chain, a third main kinematic chain and a driven branch chain 8, the first described A main kinematic chain includes a first active branch chain 1, the second main kinematic chain includes a second active branch chain 3 and a third active branch chain 4, and the third main kinematic chain includes a fourth active branch chain 9 And the 5th driving branch chain 10, described driven branch chain is positioned at the driven branch chain seat that is arranged on the central opening of fixed mount, and first main kinematic chain, second main kinematic chain and the 3rd main kinematic chain are relative to The driven branch chains are symmetrically placed and the phases between them are 120°. The first driving branch chain 1 is located in the first driving branch chain seat arranged in the first opening of the fixed frame. The second driving branch chain 3 and the third driving branch chain The active branch chain 4 is respectively located in the second active branch chain seat and the third active branch chain seat arranged in the second opening of the fixing frame, and the fourth active branch chain 9 and the fifth active branch chain 10 are respectively located in the second opening of the fixing frame. In the fourth active branch seat and the fifth active branch seat in the third opening, each of the active branch seats is connected to the inner wall of the corresponding fixed frame opening through the first rotating shaft, and each of the The active branch chain and the corresponding active branch chain seat are respectively connected in rotation through the second rotating shaft, and the axis of the first rotating shaft and the axis of the second rotating shaft are not collinear. The driven branch chain is a tubular structure. The driven branch chain seat includes an outer ring and an inner ring. The rotation shaft of the ring is connected with the outer ring, the outer wall of the driven branch chain is connected with the inner ring through the first slider guide rail structure, and the axis of the rotation shaft of the inner ring and the axis of the rotation shaft of the outer ring are not collinear. A transmission system casing 5 is arranged below the fixed frame, the lower end of the driven branch chain is fixedly connected with the transmission system casing, and the lower end of the first active branch chain 1 is connected with a first hinge seat through a rotating shaft , the lower ends of the second active branch chain 3 and the third active branch chain are connected with a rotating shaft of the first cross hinge, and the lower ends of the fourth active branch chain and the fifth active branch chain are connected with a rotating shaft of the second cross hinge , the first cross hinge 27 and the second cross hinge 45 are respectively connected to the second hinge seat and the third hinge seat through bearings, and the bottoms of the first hinge seat, the second hinge seat and the third hinge seat are respectively fixedly connected The third rotating shaft, the fourth rotating shaft 31 and the fifth rotating shaft 41 are respectively rotationally connected with the transmission system housing 5 through bearings. The bottom of the transmission system housing 5 is rotatably connected with the positioning head 6 through bearings, and the other rotating shafts of the first cross hinge 27 and the second cross hinge 45 are respectively connected with the first cross hinges arranged in the transmission system housing 5 . The driving bevel gear 43 is connected with the second driving bevel gear 29, and the first driving bevel gear 43 and the second driving bevel gear 29 are respectively connected with the first driven bevel gear 42 and the second driven bevel gear arranged in the transmission system housing. The bevel gears 30 are engaged with each other, wherein the fifth shaft 41 connected to the first driven bevel gear 42 rotates with the sixth shaft 38 arranged in the middle of the transmission system housing through the first synchronous pulley structure. The third driving bevel gear 37 is connected to the six rotating shafts 38, and the third driving bevel gear 37 is meshed with the third driven bevel gear 36 mounted on the rotating shaft 35 on the positioning head through bearings. Drive pulley 32 is housed on the 4th rotating shaft 31 of two driven bevel gears 30, is provided with driven pulley shaft by bearing frame on positioning head 6, described driving pulley and driven belt that are installed on the driven pulley shaft The pulley 33 is connected by the rotation of the pulley, and the positioning head 6 is connected on the driven pulley, the gear shaft of the first driven bevel gear, the gear shaft of the second driven bevel gear and the sixth rotating shaft 38 The axes are parallel to each other and perpendicular to the said axis of rotation 35 .

The present invention is further described below in conjunction with each figure:

As shown in Figures 1 and 2, the first active branch chain 1 is the first main kinematic chain, the second active branch chain 3 and the third active branch chain 4 are combined into the second main kinematic chain, and the fourth active branch chain 9 It is combined with the fifth active branch chain 10 to form the third main kinematic chain. The driven branch chain 8 is located in the center of the fixed frame, and the first main kinematic chain, the second main kinematic chain and the third main kinematic chain are placed symmetrically about the circumference of the driven branch chain 8, and the phase angle between them is 120°. The fixed frame 2 and the first active branch chain 1, the second active branch chain 3, the third active branch chain 4, the fourth active branch chain 9 and the fifth active branch chain 10 pass through the first hinge 11 and the second hinge respectively. 12. The third hinge 13, the fourth hinge 14 and the fifth hinge 15 are connected; the first hinge 11, the second hinge 12, the third hinge 13, the fourth hinge 14 and the fifth hinge 15 respectively pass through the first rotating shaft An active branch chain seat that is rotatably connected to the opening of the fixed frame. The driven branch chain 8 is a tubular structure, connected to the fixed frame 2 through the sixth hinge 16, the sixth hinge 16 is a driven branch chain seat, and the driven branch chain seat includes an outer ring and an inner ring structure , the outer ring is rotatably connected with the fixed frame through the outer ring shaft, the inner ring is connected with the outer ring through the inner ring shaft, and the outer wall of the driven branch chain 8 and the inner ring of the sixth hinge 16 pass through the first Slider rail structures 17 are connected. Here, the axis of the inner ring shaft and the outer ring shaft are not collinear, and the lower end of the driven branch chain 8 is fixedly connected to the transmission system housing 5 .

As shown in Figures 3 and 4, the first active branch chain 1 includes a first outer tube 23-1 that is rotatably connected to the corresponding active branch chain seat through a rotating shaft 21-1, and the first outer tube 23-1 The top is equipped with a servo motor 18-1, the output shaft of the servo motor 18-1 is fixedly connected with one end of the first lead screw 20-1 through the reducer 19-1, and the first lead screw 20-1 A nut threaded with it is mounted on the top, and the nut is fixedly connected with a first inner tube 22-1 inserted in the first outer tube. The first outer tube 23-1 and the first inner tube 22-1 The second active branch chain 3, the third active branch chain 4, the fourth active branch chain 9 and the fifth active branch chain 10 all include the corresponding active branch chain through the rotating shaft 21-2. The second outer tube 23-2 that is connected to the chain seat is rotatable, and a servo motor 18-2 is installed on the top of the second outer tube 23-2, and the output shaft of the servo motor 18-2 passes through the second reducer 19-2 is fixedly connected with one end of the second lead screw 20-2, and the second lead screw 20-2 is provided with a nut threaded with it, and the nut is connected with a first screw inserted in the second outer tube. The two inner tubes 22-2 are fixedly connected, and the lower end of the first inner tube 22-1 of the first active branch chain is connected to the first hinge seat 24 through a rotating shaft, and the bottom of the first hinge seat 24 is fixedly connected to the third rotating shaft. The rotating shaft is connected to the transmission system housing through bearings. The lower ends of the second inner tubes 22-2 of the second active branch chain 3 and the third active branch chain 4 are connected with a rotating shaft of the first cross hinge 27. The lower ends of the second inner tubes 22 - 2 of the four active branch chains 9 and the fifth active branch chain 10 are connected with the second cross hinge 45 by a rotating shaft. In this embodiment, the inner tubes all adopt the driving mode of servo motor-reducer-ball screw, but hydraulic, pneumatic and other structures can also be used as the driving mode.

The second main kinematic chain is connected with the first transmission system, that is, the lower ends of the inner tubes 22-2 of the second active branch chain 3 and the third active branch chain 4 are connected with a rotating shaft of 27 of the first cross hinge, and the first cross hinge The other rotating shaft of 27 is connected with the second hinge base 28 and the second driving bevel gear 29 arranged in the transmission system housing, the bottom of the second hinge base 28 is fixedly connected with the fourth rotating shaft 31, and the fourth rotating shaft 31 is connected with the transmission system housing The body 5 is rotationally connected through a bearing, and the fourth rotating shaft 31 is connected to the second driven bevel gear 30 and the driving pulley 32 through a key.

The third main kinematic chain is connected with the second transmission system, that is, the lower end of the inner tube 22-2 of the fourth active branch chain 9 and the fifth active branch chain 10 is connected with a rotating shaft of 45 of the second cross hinge, and the second cross hinge The other rotating shaft of 45 is connected with the third hinge seat 44 and the first driving bevel gear 43 arranged in the transmission system housing, the bottom of the third hinge seat 44 is fixedly connected with the fifth rotating shaft 41, and the fifth rotating shaft 41 is connected with the transmission system housing The bodies 5 are rotationally connected through bearings, and the fifth rotating shaft 41 is connected with a first driven bevel gear 42 and a driving pulley 40 through a key.

The second main kinematic chain transmits the motion to the first transmission system, and then to the positioning head 6 by the first transmission system. The third main kinematic chain transmits the motion to the second transmission system, and then to the rotating shaft 35 by the second transmission system.

The first transmission system is realized through bevel gear transmission and synchronous belt transmission. The different input values of the second active branch chain 3 and the fourth active branch chain 4 servo motors cause the first cross hinge 27 to rotate, driving the second driving bevel gear 29 to rotate; the second driving bevel gear 29 and the second driven bevel gear 30 meshing, so that the rotation is transmitted to the fourth rotating shaft 31; the fourth rotating shaft 31 drives the driving pulley 32 to rotate, and the motion is transmitted to the driven pulley 33 through the synchronous belt; the driven pulley 33 is connected with the positioning head 6 through a key, and then The rotation of the driving pulley 33 is the rotation of the positioning head 6 .

The second transmission system is realized through bevel gear transmission, synchronous belt transmission and bevel gear transmission. The different input values of the servo motors of the fourth active branch chain 9 and the fifth active branch chain 10 cause the second cross hinge 45 to rotate, driving the first driving bevel gear 43 to rotate; the first driving bevel gear 43 and the first driven bevel gear 42 meshing, so that the rotation is transmitted to the fifth rotating shaft 41; the fifth rotating shaft 41 drives the driving pulley 40 to rotate, and the motion is transmitted to the driven pulley 39 through the synchronous belt; the driven pulley 39 is connected to the sixth rotating shaft 38 through a key connection, Then the rotation of pulley can be passed to the sixth rotating shaft 38; The sixth rotating shaft 38 links to each other with the 3rd driving bevel gear 37 by key, then the rotation of the 6th rotating shaft 38 passes to the 3rd driving bevel gear 37; The 3rd driving bevel gear 37 Mesh with the third driven bevel gear 36 , and the third driven bevel gear 36 is keyed to the rotating shaft 35 , the rotation of the bevel gear 37 is finally transmitted to the rotating shaft 35 .

The novel five-degree-of-freedom parallel manipulator of the present invention can realize five-degree-of-freedom movements. When the servo motors of the second active branch chain 3 and the third active branch chain 4 in the second main kinematic chain have the same input value, and the servo motors of the fourth active branch chain 9 and the fifth active branch chain 10 in the third main kinematic chain When the motor has the same input value, since the first hinge, the second hinge, the third hinge, the fourth hinge and the fifth hinge have two rotational degrees of freedom, each of the active branch chains can drive the terminal to move under the drive of the servo motor. The platform realizes two degrees of freedom of rotation. The inner tube of the active branch chain is connected to the outer tube through the screw nut and the first guide rail slider mechanism. The inner tube can move axially relative to the outer tube, so the moving platform can realize a flat The movement of moving and turning, that is, the mechanism can reach any position in a given working space to realize the positioning function. When the servo motors of the second active branch chain 3 and the third active branch chain 4 in the second main kinematic chain have different input values, the rotation generated at the ends of the two branch chains can be transmitted to the positioning head 6 through the first transmission system to realize The rotation of the positioning head 6 around the C axis. When the servo motors of the fourth active branch chain 9 and the fifth active branch chain 10 in the third main kinematic chain have different input values, the rotation generated at the ends of the two branch chains can be transmitted to the rotating shaft 35 through the second transmission system to realize The rotating shaft 35 rotates around the A-axis, so the mechanism can realize five-degree-of-freedom motion.

In the novel five-degree-of-freedom parallel manipulator of the present invention, the second main kinematic chain and the third main kinematic chain adopt the structural form of double active branch chains. The dual active branch chains have the same input and can drive the mechanism to achieve a translational movement and two rotations; the dual active branch chains have different inputs and can drive the mechanism to realize the rotation around the A/C axis, thereby effectively reducing the mass of the positioning head and increasing the mechanism. The overall rigidity improves the positioning accuracy and repeat positioning accuracy of the positioning head, and realizes the fast-forwarding ability and dynamic performance of the mechanism.

An overview of the use of the new five-degree-of-freedom parallel manipulator of the present invention: as shown in Figure 6 Embodiment 1, the five-degree-of-freedom parallel manipulator of the present invention is used as a module and integrated with long-stroke guide rail units in three directions to achieve greater work processing capacity in the space.

The above description of the present invention is only illustrative rather than restrictive, so the embodiments of the present invention are not limited to the above-mentioned specific embodiments. If a person of ordinary skill in the art is inspired by it, without departing from the gist of the present invention and the protection scope of the claims, other changes or modifications are made, all of which belong to the protection scope of the present invention.

Claims (2)

1. The new five-degree-of-freedom parallel manipulator is characterized in that: it includes a fixed frame, a first main kinematic chain, a second main kinematic chain, a third main kinematic chain and a driven branch chain, and the first main kinematic chain includes The first active branch chain, the second main kinematic chain includes the second active branch chain and the third active branch chain, the third main kinematic chain includes the fourth active branch chain and the fifth active branch chain, the The driven branch chain is located in the driven branch chain seat set in the central opening of the fixed frame, the first main kinematic chain, the second main kinematic chain and the third main kinematic chain are placed symmetrically with respect to the driven branch chain and mutually The phase between them is 120°, the first active branch chain is located in the first active branch seat set in the first opening of the fixed frame, the second active branch chain and the third active branch chain are respectively located in the second active branch chain set in the fixed frame In the second active branch chain seat and the third active branch chain seat in the opening, the fourth active branch chain and the fifth active branch chain are respectively located in the fourth active branch chain seat and the first active branch chain seat arranged in the third opening of the fixing frame. In the five active branch chain seats, each of the active branch chain seats is connected to the inner wall of the corresponding fixed frame opening through the rotation of the first rotating shaft, and each of the active branch chain seats and the corresponding active chain branch seat They are respectively connected by rotation of the second rotating shaft, the first rotating shaft and the second rotating shaft are not collinear with each other, the driven branch chain is a tubular structure, and the driven branch chain seat includes an outer ring and an inner ring, The outer ring is rotatably connected to the inner wall of the central opening of the fixing frame through the outer ring rotating shaft, the inner ring is connected to the outer ring through the inner ring rotating shaft, and the outer wall of the driven branch chain is connected to the inner ring through the first The sliding block guide rail structure is connected, the shaft axis of the inner ring and the shaft axis of the outer ring are not collinear, a transmission system housing is arranged under the fixed frame, and the lower end of the driven branch chain is connected with the transmission The system housing is fixedly connected, the lower end of the first active branch chain is connected to the first hinge base through a rotating shaft, the lower ends of the second active branch chain and the third active branch chain are connected with a rotating shaft of the first cross hinge, and the The lower ends of the fourth active branch chain and the fifth active branch chain are connected to a rotating shaft of the second cross hinge, and the first cross hinge and the second cross hinge are respectively connected to the second hinge seat and the third hinge seat through bearings, so The bottoms of the first hinge seat, the second hinge seat and the third hinge seat are respectively fixedly connected with the third rotating shaft, the fourth rotating shaft and the fifth rotating shaft, and the third rotating shaft, the fourth rotating shaft and the fifth rotating shaft are connected with the transmission system housing Connected by bearing rotation, the positioning head is connected by bearing rotation at the bottom of the transmission system housing, and the other rotating shaft of each cross hinge is respectively connected with a driving bevel gear arranged in the transmission system housing, each of the The driving bevel gears are engaged with a driven bevel gear set in the transmission system casing respectively, wherein the fifth rotating shaft connected to the first driven bevel gear is connected to the middle of the transmission system casing through the first synchronous pulley structure. The sixth rotating shaft rotates and cooperates, and the third driving bevel gear is connected to the sixth rotating shaft, and the third driving bevel gear and the third driven bevel gear mounted on the rotating shaft on the positioning head through bearings Mesh and cooperate, the fourth shaft connected to the second driven bevel gear is equipped with a driving The pulley is provided with a driven pulley shaft through a bearing frame on the positioning head, and the driving pulley is connected with the driven pulley installed on the driven pulley shaft through the pulley rotation, and connected on the driven pulley The positioning head, the gear shafts of the first driven bevel gear and the second driven bevel gear, and the sixth rotating shaft are arranged parallel to each other and perpendicular to the rotating shaft. 2. The new five-degree-of-freedom parallel manipulator according to claim 1, characterized in that: the first active branch chain includes a first outer tube that is rotationally connected to the first active branch chain base through a rotating shaft, and the first outer tube The top of the pipe is equipped with a servo motor, the output shaft of the servo motor is fixedly connected with one end of the first lead screw through a reducer, and a nut threaded with the first lead screw is installed on the first lead screw, and the nut and the A first inner tube inserted in the first outer tube is fixedly connected, and the first outer tube and the first inner tube are connected through the second guide rail slider structure; the second active branch chain and the third active branch chain 1. Both the fourth active branch chain and the fifth active branch chain include a second outer tube connected to the corresponding active branch chain seat through a rotating shaft in rotation, and a servo motor is installed on the top of the second outer tube, and the servo motor The output shaft of the motor is fixedly connected with one end of the second lead screw through the reducer, and a nut threaded with the second lead screw is installed on the second lead screw, and the nut is connected with a second inner tube inserted in the second outer tube. The tubes are fixedly connected, the lower end of the first inner tube is connected to a hinge seat through a rotating shaft, the lower ends of the second inner tubes of the second active branch chain and the third active branch chain are connected with a rotating shaft of the first cross hinge, and the fourth The lower end of the second inner tube of the active branch chain and the fifth active branch chain is connected with a rotating shaft of the second cross hinge.

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