Bionic thigh joint action mechanism

Abstract

The present application belongs to the technical field of bionic robot, and particularly relates to a bionic thigh joint action mechanism. The technical scheme is as follows: a bionic thigh joint action mechanism, comprising a thigh torsion power device, the output end of the thigh torsion power device is fixed with a support fixed fork; further comprising a differential rotation power device, the differential rotation power device comprises a cross ring, the cross ring is rotationally connected with the support fixed fork, both sides of the cross ring are rotationally connected with thigh swing reduction motors, the shell of the thigh swing reduction motor is rotationally connected with the cross ring, the shell of the thigh swing reduction motor is fixed with a large gear, a small gear is rotationally connected on the cross ring, and the large gear is engaged with the small gear. The present application provides a bionic thigh joint action mechanism which can swing forward and backward, swing left and right and twist.

Description

Technical Field

[0001] This invention belongs to the field of biomimetic robot technology, and specifically relates to a biomimetic thigh joint motion mechanism. Background Technology

[0002] Compared to wheeled and tracked mobile robots, bionic robots only require discrete points of contact with the ground during movement, allowing them to traverse larger obstacles and adapt more effectively to complex terrain. Furthermore, the legs of bionic robots can possess multiple degrees of freedom, greatly enhancing their mobility and performance capabilities. They can maintain balance by adjusting the angle of their supporting legs and the position of their feet, making them less prone to tipping over and exhibiting high stability. In the future, bionic robots will have broader application prospects in areas such as daily life services, pipeline maintenance, flood relief, film and television performances, security, and the military.

[0003] Patent application CN201821113655.X discloses a three-joint bionic mechanical leg with autonomous hydraulic power distribution, including a thigh, lower leg, and foot. It also includes a connecting frame, a hydraulic power system, and a control device. The connecting frame, thigh, lower leg, and foot are sequentially connected by joints. The connecting frame secures or detaches the bionic mechanical leg from the bionic robot. The hydraulic power system is located in the thigh and / or lower leg and / or foot. The control device is located in the thigh and / or lower leg and / or connecting frame and / or foot. This patented three-joint bionic mechanical leg with autonomous hydraulic power distribution allows for rapid connection and disconnection from the bionic robot, offers greater torque, and simplifies operation and control.

[0004] However, the thigh of the aforementioned bionic mechanical leg can only swing back and forth, and cannot twist or swing left and right. Its bionicity is poor and it cannot simulate the movements of a real human thigh. Summary of the Invention

[0005] In order to solve the above-mentioned problems in the prior art, the purpose of this invention is to provide a bionic thigh joint movement mechanism that can swing back and forth, swing left and right, and twist.

[0006] The technical solution adopted in this invention is as follows:

[0007] A biomimetic thigh joint motion mechanism includes a thigh torsion power device, the output end of which is fixed with a support fork; it also includes a differential rotation power device, which includes a cross ring, the cross ring being rotatably connected to the support fork, and thigh swing reduction motors being rotatably connected to both sides of the cross ring. The housing of the thigh swing reduction motor is rotatably connected to the cross ring, and a large gear is fixed to the housing of the thigh swing reduction motor. A small gear is rotatably connected to the cross ring, and the large gear and the small gear mesh.

[0008] The thigh torsion power unit drives the support fork to rotate around its vertical center, simulating thigh torsion. When the two thigh swing reduction motors rotate in the same direction and at the same speed, their outputs rotate synchronously, simulating forward and backward thigh lifting. When the two thigh swing reduction motors rotate in opposite directions and at the same speed, they rotate around the shaft of a small gear, simulating left and right thigh lifting. In other motion states, the thigh performs a composite motion in these three directions.

[0009] The biomimetic thigh joint movement structure of this invention can simulate the complex movements of human thigh twisting, swinging forward and backward, and swinging left and right, exhibiting a high degree of biomimicry. Two thigh swing reduction motors are located on both sides of the cross ring, and are driven by a large gear and a small gear on the cross ring to achieve a differential speed effect. This allows for a more compact structure of the differential rotation power device, saving layout space and simplifying the device's structure.

[0010] As a preferred embodiment of the present invention, both the thigh torsion power device and the thigh swing reduction motor include a single harmonic reduction motor. The single harmonic reduction motor includes a central shaft, a motor stator connected to the central shaft, a motor rotor sleeved on the motor stator, and a harmonic reduction unit connected to the motor rotor. The output end of the harmonic reduction unit of the thigh swing reduction motor is fixed to the central shaft, and the output end of the harmonic reduction unit of the thigh torsion power device is rotatably connected to the central shaft. The output end of the harmonic reduction unit is engaged with a harmonic rigid wheel, and the harmonic rigid wheel of the thigh swing reduction motor is rotatably connected to a cross ring. A rear cover is fixed to one end of the central shaft of the thigh torsion power device, and the rear cover is fixed to the harmonic rigid wheel of the thigh torsion power device.

[0011] The output speed of the harmonic reduction unit of this invention is significantly reduced relative to the cam speed, resulting in stable and low-speed output of the single harmonic reduction motor. The harmonic reduction unit meshes with the harmonic gear, thus providing high transmission accuracy at the output of the single harmonic reduction motor relative to the cam.

[0012] As a preferred embodiment of the present invention, the harmonic reduction unit includes a cam, which is fixed on the motor rotor. A flexible bearing is mounted on the cam, and a flexible wheel is sleeved on the outer ring of the flexible bearing. The flexible wheel meshes with the harmonic rigid wheel, and the number of teeth on the flexible wheel is less than the number of teeth on the harmonic rigid wheel. An output flange is fixed on the flexible wheel. The flexible wheel of the thigh swing reduction motor is fixed to the central shaft. The flexible wheel of the thigh torsion power device is rotatably connected to the central shaft. The output flange of the thigh torsion power device is fixed to the support fixing fork. The output flange of the thigh swing reduction motor is connected to the thigh structure.

[0013] When the motor is powered on, the motor rotor rotates relative to the motor stator. The motor rotor drives the cam to rotate, and the cam drives the flex wheel to mesh with the harmonic rigid wheel through a flexible bearing. If the number of teeth on the flex wheel is N less than the number of teeth on the harmonic rigid wheel, then when the cam rotates one revolution, the flex wheel rotates N teeth relative to the harmonic rigid wheel. This results in a greater speed reduction for the output flange connected to the flex wheel, ensuring a stable output force, and ensuring transmission accuracy through gear transmission.

[0014] In a preferred embodiment of the present invention, the inner side of the cam is connected to the central shaft via a rolling bearing. The central shaft reliably supports the cam, and the central shaft and the cam can rotate relative to each other.

[0015] In a preferred embodiment of the present invention, both the cam and the flexible bearing are elliptical in shape, and the flexible wheel meshes with the harmonic rigid wheel at two positions. The flexible bearing pushes the flexible wheel to engage with the harmonic rigid wheel from two points, ensuring stable transmission between the flexible wheel and the harmonic rigid wheel.

[0016] As a preferred embodiment of the present invention, the single harmonic geared motor further includes a crossed roller bearing, the inner ring of which is integrally formed or fixedly connected to the output flange, the outer ring of which is integrally formed or fixedly connected to the harmonic rigid wheel of the thigh torsion power device, and the outer ring of which is integrally formed or fixedly connected to the large gear of the thigh swing geared motor.

[0017] In a preferred embodiment of the present invention, a wiring hole is provided on the central shaft, through which the wiring of the motor stator passes. Passing the wiring through the wiring hole facilitates wiring. In another preferred embodiment, two rotating connectors are provided at 180° intervals on the cross ring. The pinion is connected to the cross ring through one of the rotating connectors, and the support fixing fork is connected to both rotating connectors respectively. The support fixing fork can be connected to both rotating connectors respectively, ensuring the stability of the differential rotation power device after it is installed on the support fixing fork.

[0018] In a preferred embodiment of the present invention, an end cap for limiting positioning is fixed to the rotating connector. The end cap is used to limit the support and fixing fork, preventing the differential rotation power device from disengaging from the support and fixing fork.

[0019] In a preferred embodiment of the present invention, the rotating connector includes a protruding connecting post disposed on the cross ring, and a ball or bearing is mounted on the connecting post. The pinion is connected to one of the connecting posts via a ball or bearing, one of the connectors supporting the fixing fork is connected to the pinion via a bolt, and the other connector supporting the fixing fork is connected to the connecting post on the opposite side via a ball or bearing.

[0020] The beneficial effects of this invention are as follows:

[0021] The biomimetic thigh joint movement structure of this invention can simulate the complex movements of human thigh twisting, swinging forward and backward, and swinging left and right, exhibiting a high degree of biomimicry. Two thigh swing reduction motors are located on both sides of the cross ring, and are driven by a large gear and a small gear on the cross ring to achieve a differential speed effect. This allows for a more compact structure of the differential rotation power device, saving layout space and simplifying the device's structure. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention;

[0023] Figure 2 This is a schematic diagram of the differential rotation power device;

[0024] Figure 3 This is a cross-sectional view of a differential rotational power unit;

[0025] Figure 4 yes Figure 3 A magnified view of a section at point A in the middle;

[0026] Figure 5 This is a cross-sectional view of the thigh torsional power unit;

[0027] Figure 6 This is a partial structural diagram of a single harmonic geared motor.

[0028] In the diagram: 1- Thigh torsion power unit; 2- Support and fixing fork; 3- Cross ring; 4- Thigh swing reduction motor; 5- Large gear; 6- Small gear; 31- Rotating connector; 32- End cover; a1- Central shaft; a2- Motor stator; a3- Motor rotor; a4- Harmonic reduction unit; a5- Harmonic rigid wheel; a6- Crossed roller bearing; a7- Rear cover; a11- Rolling bearing; a41- Cam; a42- Flexible bearing; a43- Flexible wheel; a44- Output flange. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the invention can be combined with each other.

[0031] like Figure 1 As shown, the bionic thigh joint motion mechanism of this embodiment includes a thigh torsion power device 1, the output end of which is fixed with a support fork 2; it also includes a differential rotation power device, which includes a cross ring 3, the cross ring 3 is rotatably connected to the support fork 2, and thigh swing reduction motors 4 are rotatably connected to both sides of the cross ring 3. The housing of the thigh swing reduction motor 4 is rotatably connected to the cross ring 3. A large gear 5 is fixed to the housing of the thigh swing reduction motor 4, and a small gear 6 is rotatably connected to the cross ring 3. The large gear 5 and the small gear 6 mesh.

[0032] The thigh torsion power device 1 drives the support fixed fork 2 to rotate around the vertical center of the thigh torsion power device 1, simulating thigh torsion. When the two thigh swing reduction motors 4 rotate in the same direction and at the same speed, the output ends of the two thigh swing reduction motors 4 rotate synchronously, simulating the forward and backward lifting motion of the thigh. When the two thigh swing reduction motors 4 rotate in opposite directions and at the same speed, the two thigh swing reduction motors 4 rotate around the shaft of the pinion 6, simulating the left and right lifting motion of the thigh. In other motion states, the thigh performs a composite motion of rotation in the above three directions.

[0033] The biomimetic thigh joint movement structure of this invention can simulate the complex movements of human thigh twisting, swinging back and forth, and swinging left and right, exhibiting a high degree of biomimicry. Two thigh swing reduction motors 4 are located on both sides of the cross ring 3, and are driven by a large gear 5 and a small gear 6 on the cross ring 3 to achieve a differential speed effect. This allows for a more compact structure of the differential rotation power device, saving layout space and simplifying the device's structure.

[0034] Specifically, such as Figures 2-5As shown, both the thigh torsion power device 1 and the thigh swing reduction motor 4 include a single harmonic reduction motor. The single harmonic reduction motor includes a central shaft a1, a motor stator a2 connected to the central shaft a1, a motor rotor a3 sleeved on the motor stator a2, and a harmonic reduction unit a4 connected to the motor rotor a3. The output end of the harmonic reduction unit a4 of the thigh swing reduction motor 4 is fixed to the central shaft a1, and the output end of the harmonic reduction unit a4 of the thigh torsion power device 1 is rotatably connected to the central shaft a1. The output end of the harmonic reduction unit a4 is meshed with a harmonic rigid wheel a5, and the harmonic rigid wheel a5 of the thigh swing reduction motor 4 is rotatably connected to the cross ring 3. A rear cover a7 is fixed to one end of the central shaft of the thigh torsion power device 1, and the rear cover a7 is fixed to the harmonic rigid wheel a5 of the thigh torsion power device 1.

[0035] The output speed of the harmonic reduction unit a4 of this invention is significantly reduced relative to the speed of the cam a41, resulting in a stable and low-speed output from the single harmonic reduction motor. The harmonic reduction unit a4 meshes with the harmonic rigid wheel a5, thereby providing high transmission accuracy at the output of the single harmonic reduction motor relative to the cam a41.

[0036] like Figure 6 As shown, the harmonic deceleration unit a4 includes a cam a41, which is fixed on the motor rotor a3. A flexible bearing a42 is mounted on the cam a41. A flexible wheel a43 is sleeved on the outer ring of the flexible bearing a42. The flexible wheel a43 meshes with the harmonic rigid wheel a5. The number of teeth on the flexible wheel a43 is less than the number of teeth on the harmonic rigid wheel a5. An output flange a44 is fixed on the flexible wheel a43. The flexible wheel a43 of the thigh swing deceleration motor 4 is fixed to the central shaft a1. The flexible wheel a43 of the thigh torsion power device 1 is rotatably connected to the central shaft a1.

[0037] The motor stator a2 and electronic rotor a3 are built into the flexible wheel a43, which can effectively utilize space, reduce the volume of the single harmonic geared motor, and simplify the structure.

[0038] The output flange a44 of the thigh torsion power device 1 is fixed to the support fixing fork 2, and the harmonic rigid wheel a5 of the thigh torsion power device 1 is fixedly connected to the hip joint. The output flange a44 of the thigh swing reduction motor 4 is connected to the thigh structure, and the harmonic rigid wheel a5 of the thigh swing reduction motor 4 is rotatably connected to the cross ring 3.

[0039] The reduction principle of a single harmonic geared motor utilizes the relative motion of the flexure a43, the harmonic rigid wheel a5, and the cam a41, primarily through the controllable elastic deformation of the flexure a43 to achieve motion and power transmission. The elliptical cam a41 rotates within the flexure a43, causing the flexure a43 to deform. When the teeth of the flexure a43 at both ends of the major axis of the elliptical cam a41 engage with the teeth of the harmonic rigid wheel a5, the teeth of the flexure a43 at both ends of the minor axis disengage from the teeth of the harmonic rigid wheel a5. For the teeth between the major and minor axes of the cam a41, the gradual engagement (partial engagement) along different sections of the circumference of the flexure a43 and the harmonic rigid wheel a5 is called engagement. The gradual disengagement (partial engagement) is called disengagement. As cam a41 rotates continuously, flexure a43 undergoes continuous deformation, causing the teeth of the two gears to constantly change their original working states in four motions: engagement, disengagement, and retraction, resulting in a tooth-shifting motion. This achieves motion transmission between cam a41 and flexure a43. The single-unit harmonic geared motor offers smooth transmission, low noise, high motion accuracy, and a backlash of less than 10 arcseconds.

[0040] When the motor is powered on, the motor rotor a3 rotates relative to the motor stator a2. The motor rotor a3 drives the cam a41 to rotate, and the cam a41 drives the flexure a43 to mesh with the harmonic rigid wheel a5 through the flexible bearing a42. The flexible bearing a42 is also elliptical and rotates synchronously with the cam a41. The flexure a43 is made of flexible material and is sleeved on the cam a42. When the flexible bearing a42 rotates, the teeth of the harmonic rigid wheel a5 block the teeth of the flexure a43, causing the flexure a43 to slide on the flexible bearing a42. Due to the pressing action of the flexible bearing a42, the meshing position of the flexure a43 and the harmonic rigid wheel a5 changes continuously. Since the number of teeth on the flexure a43 is less than the number of teeth on the harmonic rigid wheel a5, the meshing position of the flexure a43 and the harmonic rigid wheel a5 does not change by one revolution when the cam a41 rotates one revolution. If the number of teeth on the flexible wheel a43 is N less than the number of teeth on the harmonic rigid wheel a5, then when the cam a41 rotates one revolution, the flexible wheel a43 rotates N teeth relative to the harmonic rigid wheel a5, thereby the output flange a44 connected to the flexible wheel a43 is significantly decelerated, ensuring a stable output force, and the transmission accuracy is ensured through gear transmission. Figure 6 In the process, the number of teeth of the flexible wheel a43 is two fewer than the number of teeth of the harmonic rigid wheel a5. When the cam a41 rotates one revolution, the flexible wheel a43 rotates two teeth, and the output flange a44 rotates by the corresponding angle with the cam a41.

[0041] To provide support for the cam a41, the inner side of the cam a41 is connected to the central shaft a1 via a rolling bearing a11. The central shaft a1 reliably supports the cam a41, and the central shaft a1 and the cam a41 can rotate relative to each other.

[0042] To provide support for the large gear 5, the single harmonic geared motor also includes a crossed roller bearing a6. The inner ring of the crossed roller bearing a6 is integrally formed or fixedly connected to the output flange a44. The outer ring of the crossed roller bearing a6 of the thigh torsion power device 1 is integrally formed or fixedly connected to the harmonic rigid wheel a5. The outer ring of the crossed roller bearing a6 of the thigh swing geared motor 4 is integrally formed or fixedly connected to the large gear 5.

[0043] To facilitate wiring connections, a wiring hole is provided on the central shaft a1, through which the wiring of the motor stator a2 passes. This allows for easy wiring of the wires.

[0044] To further reduce the space occupied, both the pinion 6 and the gear 5 are bevel gears, so that the outer contour of the reducer of the present invention is closer to a sphere, making it easier to install it at the joint of a humanoid robot.

[0045] The flexible wheel a43 and the output flange a44 have bolt holes at the same location. The connecting bolts pass through the flexible wheel a43 and the output flange a44 respectively and are then connected to the operating end, further improving the connection stability of the output end. The flexible wheel a43 is fixedly connected to the central shaft a1, ensuring that the central shaft a1 provides stable support for the motor stator a2 and ensuring that the motor rotor a3 can rotate reliably relative to the motor stator a2.

[0046] Rotary connectors 31 are provided at two positions 180° apart on the cross ring 3. The pinion 6 is connected to the cross ring 3 through one of the rotary connectors 31, and the support fork 2 is connected to both rotary connectors 31 respectively. The support fork 2 can be connected to both rotary connectors 31 respectively to ensure the stability of the differential rotation power device of the present invention after it is installed on the support fork 2.

[0047] like Figure 4 As shown, an end cap 32 for limiting positioning is fixed to the rotating connector 31. The end cap 32 is used to limit the support fork 2 to prevent the differential rotation power device from disengaging from the support fork 2. The rotating connector 31 includes a protruding connecting post disposed on the cross ring 3, and a ball bearing or bearing is installed on the connecting post. The pinion 6 is connected to one of the connecting posts through a ball bearing or bearing, one of the connectors of the support fork 2 is connected to the pinion 6 by a bolt, and the other connector of the support fork 2 is connected to the connecting post on the opposite side through a ball bearing or bearing.

[0048] This invention is not limited to the above-described optional embodiments. Anyone can derive other various forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that falls within the scope of the claims of this invention shall be protected by this invention.

Claims

1. A bionic thigh joint action mechanism, characterized in that: The thigh torsion power device (1) is fixed with the support fixed fork (2) at the output end; the differential rotation power device includes the cross ring (3), the cross ring (3) is rotatably connected with the support fixed fork (2), both sides of the cross ring (3) are rotatably connected with the thigh swing reduction motor (4), the shell of the thigh swing reduction motor (4) is rotatably connected with the cross ring (3), the large gear (5) is fixed on the shell of the thigh swing reduction motor (4), the small gear (6) is rotatably connected on the cross ring (3), and the two large gears (5) are engaged with the small gear (6); The thigh torsion power device (1) drives the support fixed fork (2) to rotate with the vertical center of the thigh torsion power device (1) as the rotation shaft, so as to simulate the thigh torsion; when the two thigh swing reduction motors (4) rotate in the same direction and at the same speed, the output ends of the two thigh swing reduction motors (4) rotate synchronously, so as to simulate the thigh lifting action forward and backward; when the two thigh swing reduction motors (4) rotate in opposite directions and at the same speed, the two thigh swing reduction motors (4) rotate around the shaft of the small gear (6), so as to simulate the thigh lifting action left and right; The output flange (a44) of the thigh torsion power device (1) is fixed with the support fixed fork (2), and the harmonic gear (a5) of the thigh torsion power device (1) is fixedly connected with the hip joint; the output flange (a44) of the thigh swing reduction motor (4) is connected with the thigh structure, and the harmonic gear (a5) of the thigh swing reduction motor (4) is rotatably connected with the cross ring (3).

2. The bionic thigh joint action mechanism according to claim 1, characterized in that: The thigh torsion power device (1) and the thigh swing reduction motor (4) both include a single harmonic reduction motor, the single harmonic reduction motor includes a central shaft (a1), the central shaft (a1) is connected with a motor stator (a2), the motor stator (a2) is sleeved with a motor rotor (a3), the motor rotor (a3) is connected with a harmonic reduction unit (a4), the output end of the harmonic reduction unit (a4) of the thigh swing reduction motor (4) is fixed with the central shaft (a1), the output end of the harmonic reduction unit (a4) is engaged with the harmonic gear (a5), the harmonic gear (a5) of the thigh swing reduction motor (4) is rotatably connected with the cross ring (3), and one end of the central shaft (a1) of the thigh torsion power device (1) is fixed with a rear cover (a7).

3. The bionic thigh joint action mechanism according to claim 2, characterized in that: The harmonic reduction unit (a4) comprises a cam (a41) fixed on the motor rotor (a3), a flexible bearing (a42) is installed on the cam (a41), an outer ring of the flexible bearing (a42) is sleeved with a flexible gear (a43), the flexible gear (a43) is in gear engagement with the harmonic gear (a5), the number of teeth of the flexible gear (a43) is less than that of the harmonic gear (a5), an output flange (a44) is fixed on the flexible gear (a43), the flexible gear (a43) of the thigh swing reduction motor (4) is fixed with the central shaft (a1), the output flange (a44) of the thigh torsion power device (1) is fixed with the support fixed fork (2), and the output flange (a44) of the thigh swing reduction motor (4) is connected with the thigh structure.

4. The bionic thigh joint action mechanism according to claim 3, characterized in that: The inner side of the cam (a41) is connected with the central shaft (a1) through a rolling bearing (a11).

5. The bionic thigh joint action mechanism according to claim 3, characterized in that: The cam (a41) and the flexible bearing (a42) are both in the shape of an ellipse, and the flexible gear (a43) is engaged with the harmonic gear (a5) at two positions.

6. The bionic thigh joint action mechanism according to claim 3, characterized in that: The single harmonic reduction motor further comprises a cross roller bearing (a6), an inner ring of the cross roller bearing (a6) is integrally formed or fixedly connected with the output flange (a44), an outer ring of the cross roller bearing (a6) of the thigh torsion power device (1) is integrally formed or fixedly connected with the harmonic gear (a5), and an outer ring of the cross roller bearing (a6) of the thigh swing reduction motor (4) is integrally formed or fixedly connected with the large gear (5).

7. The bionic thigh joint action mechanism according to claim 2, characterized in that: The central shaft (a1) is provided with a wiring hole, and the wiring of the motor stator (a2) is led out from the wiring hole.

8. The bionic thigh joint action mechanism according to any one of claims 1-7, characterized in that: Two positions of the cross ring (3) separated by 180° are both provided with a rotating connecting head (31), the pinion (6) is connected with the cross ring (3) through one of the rotating connecting heads (31), and the support fixed fork (2) is connected with the two rotating connecting heads (31) respectively.

9. The bionic thigh joint action mechanism according to claim 8, characterized in that: The rotating connecting head (31) is fixed with an end cover (32) for limiting.

10. The bionic thigh joint action mechanism according to claim 8, characterized in that: The rotating connecting head (31) comprises a protruding connecting column provided on the cross ring (3), and a ball or a bearing is installed on the connecting column.

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