Weight-reduced and reinforced industrial robot rotating big arm

Abstract

The invention relates to a weight-reduced and reinforced industrial robot rotating big arm which comprises a machine body connecting part, a small arm connecting part and a connecting piece. The connecting piece comprises main supporting beams which are symmetrically arranged at intervals; first auxiliary supporting beams are respectively connected between the fuselage connecting part and the two main supporting beams; second auxiliary supporting beams located between the main supporting beams are connected between the small arm connecting part and the two main supporting beams. The extension direction of the main supporting beam is the main stress direction of the big arm of the robot; the extension direction of the first auxiliary supporting beam is the maximum stress direction of the large arm of the robot; therefore, the area except the main supporting beam and the first auxiliary supporting beam is a non-bearing or low-efficiency material area, the performance of the big arm cannot be reduced by removing the area, the weight of the big arm is greatly reduced, the material cost and the load of the robot are reduced, the requirement for a driving system is reduced, and therefore the energy consumption of the whole machine is effectively reduced, and the cost of the whole machine is reduced. And the movement speed and the dynamic response performance of the robot are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial robots, in particular to a weight-reducing and strength-enhancing rotating large arm of an industrial robot. BACKGROUND

[0002] The large arm of an industrial robot is a key load-bearing component connecting the robot body and the small arm, and its structural performance directly affects the load capacity, motion accuracy and overall stability of the robot. The traditional large arm adopts a long circular plate structure (refer to Figure 4 ), which is relatively mature in manufacturing process, but has several inherent defects in actual application for a long time: Firstly, the traditional long circular plate structure of the large arm is heavy and has low material utilization efficiency. This not only leads to unnecessary material waste, increases the manufacturing cost, but also increases the motion load of the robot itself, puts higher requirements on the driving system, and further increases the overall energy consumption, limiting the further improvement of the dynamic performance of the robot.

[0003] Secondly, the stress distribution of this structure is uneven when bearing complex multi-directional load. Finite element analysis and actual working condition test show that the maximum Mises equivalent stress value is high, and stress concentration phenomenon is significant, especially in the hole shaft connection and cross section mutation area. High stress level directly leads to low minimum safety factor of the component, which has potential fatigue failure risk and affects the working reliability and service life of the robot.

[0004] Thirdly, the structural stiffness of the traditional large arm is insufficient. Under heavy load or high-speed motion working condition, the large arm is easy to produce large elastic deformation, which not only reduces the absolute positioning accuracy of the robot, but also may cause vibration of the end effector, which is difficult to meet the demand of high-precision and high-stability operation.

[0005] Therefore, it is urgent to optimize the structure of the existing large arm of the industrial robot to significantly reduce the weight, improve the stress distribution, increase the safety factor and enhance the overall stiffness under the premise of ensuring the strength, so as to improve the comprehensive performance of the industrial robot. SUMMARY

[0006] To solve the technical problems in the background art, the present application discloses a weight-reducing and strength-enhancing rotating large arm of an industrial robot.

[0007] The present application provides a weight-reducing and strength-enhancing rotating large arm of an industrial robot, which comprises a body connecting part connected with the robot body and a small arm connecting part connected with the small arm of the robot, and the body connecting part and the small arm connecting part are connected by a connecting piece integrally formed. The two ends of the main support beam in the width direction are flush with the axial ends of the body connecting part and the small arm connecting part. The distance between the outer sides of the main support beams is equal to the diameter of the fuselage connecting part and the small arm connecting part; The common tangent line of the fuselage connecting part and the small arm connecting part is line a; the outer sides of the main support beams coincide with line a; The fuselage connecting part is connected with two first auxiliary support beams between the main support beams respectively; the two first auxiliary support beams are symmetrically arranged; the fuselage connecting part, the main support beams and the first auxiliary support beams form a triangle; The connecting point of the first auxiliary support beam and the fuselage connecting part coincides with point b, and the center line of the main support beam is line c, which coincides with point b; The extension direction of the first auxiliary support beam is consistent with the maximum stress direction of the rotating large arm; The small arm connecting part is connected with two second auxiliary support beams between the main support beams respectively; the two second auxiliary support beams are symmetrically arranged; the small arm connecting part, the main support beams and the second auxiliary support beams form a triangle; The first auxiliary support beam and the second auxiliary support beam are both the same width as the main support beam.

[0008] Further, the main support beam is composed of a first connecting part and a second connecting part connected in sequence; The thickness of the first connecting part is greater than that of the second connecting part.

[0009] Further, the inner sides of the first connecting part and the second connecting part are coplanar.

[0010] Further, the length of the first connecting part is greater than that of the second connecting part.

[0011] Further, the length of the first connecting part is 1.5 times that of the second connecting part.

[0012] Further, the width of the first auxiliary support beam increases from the middle position to both ends.

[0013] Further, the minimum width of the first auxiliary support beam is located near the main support beam.

[0014] Further, the thickness of point b is twice the thickness of the end of the first auxiliary support beam near the fuselage connecting part.

[0015] Further, the thickness of the first auxiliary support beam increases from one end adjacent to the fuselage connecting part to the other end.

[0016] Further, a distance is provided between the connecting points of the first auxiliary support beam, the second auxiliary support beam and the main support beam; The connecting point of the first connecting part and the second connecting part is point d; The first auxiliary support beam is connected with the first connecting part, and the connecting point is located near point d. The second auxiliary support beam is connected with the second connecting part, and the connecting point is located close to point d; The part between the main support beam and the connecting points of the first and second auxiliary support beams has a honeycomb hollow structure.

[0017] The present application has the following advantages: 1. The extension direction of the main support beam is the main stress direction of the robot arm, and the extension direction of the first auxiliary support beam is the maximum stress direction of the robot arm. Therefore, the area outside the main support beam and the first auxiliary support beam is a non-load-bearing or low-efficiency material area. The removal of these areas not only does not reduce the performance of the arm, but also greatly reduces the weight of the arm, reduces the material cost and the load of the robot, reduces the demand for the driving system, thereby effectively reducing the overall energy consumption, improving the motion speed and dynamic response performance of the robot.

[0018] 2. The extension direction of the first auxiliary support beam is consistent with the maximum stress direction, so that the maximum stress does not generate a component perpendicular to the direction of the first auxiliary support beam, thereby enabling the cross section of the first auxiliary support beam to be designed to be minimized, further reducing the weight of the arm. 3. The main support beam, the first auxiliary support beam, and the fuselage connecting part form a triangle, and the main support beam, the second auxiliary support beam, and the small arm connecting part form a triangle. The triangular structure is cleverly used to stabilize the characteristics, forming a high-stiffness truss system that can more effectively resist bending and torsional deformation.

[0019] 4. The extension direction of the first auxiliary support beam, together with the triangular structure, improves the stress distribution of the arm under complex multi-directional loads, effectively reduces the maximum Mises equivalent stress value, alleviates the stress concentration phenomenon in key areas such as hole shaft connection and cross section mutation, realizes the uniformization of stress distribution, directly improves the minimum safety factor of the component, reduces the risk of fatigue failure, and enhances the reliability and service life of the robot under long-term and repeated operation.

[0020] 5. The small arm connecting part is a stress point, and the load is more concentrated, and the force flow path is single. Therefore, the interval arrangement of the second auxiliary support beam can make the main support beam uniformly stressed, and the two main support beams will not be unevenly stressed.

[0021] 6. The connecting point of the first auxiliary support beam and the fuselage connecting part is coincident, which has the following advantages: (1) The load from the small arm connection part is transmitted through the main support beam, then is received by two symmetrical first auxiliary support beams at the same point b, and is smoothly guided to the fuselage connection part. If the two first auxiliary support beams are connected at different points of the fuselage connection part, the force flow path will have a turn or branch, and stress concentration will easily occur at the connection root. The "coincidence of the connection points" ensures that the force flow flows into the fuselage connection part, the final load bearing body, in the most direct and smooth way, avoiding unnecessary bending moments and stress peaks on the key force transmission path, which significantly reduces the maximum Mises equivalent stress value at the root of the fuselage connection part when the large arm bears complex load, and the stress distribution is more uniform, thereby directly improving the fatigue life and reliability of the component.

[0022] (2) The support points of the two first auxiliary support beams are converged at one point, establishing a highly concentrated rigid support core. This structure can most effectively resist the force from the small arm that attempts to cause bending or torsional deformation of the large arm. When the robot is carrying heavy load or moving at high speed, this design can minimize the elastic deformation of the large arm, so that the robot end effector has higher absolute positioning accuracy, and effectively suppresses the vibration caused by structural deformation, meeting the needs of high-precision and high-stability operation.

[0023] (3) The load is transmitted through the triangular truss structure, and point b is the key hub of this efficient force flow path, which ensures the maximization of structural efficiency. Under the premise of meeting or even exceeding the original strength and stiffness requirements, all unnecessary materials can be safely removed. This directly leads to a significant reduction in the overall weight of the rotating large arm. BRIEF DESCRIPTION OF DRAWINGS

[0024] The application will be further described below in conjunction with the drawings and examples.

[0025] Figure 1 is a structural schematic diagram of the application; Figure 2 is a front view of the application; Figure 3 is Figure 2 is a sectional view of A-A in Figure 4 is a structural schematic diagram of a conventional robot large arm; In the figure: 1, fuselage connection part; 2, small arm connection part; 3, main support beam; 4, first auxiliary support beam; 5, second auxiliary support beam; 31, first connection part; 32, second connection part. DETAILED DESCRIPTION

[0026] The application will now be further described in conjunction with the drawings. These drawings are all simplified schematic diagrams, and only illustrate the basic structure of the application in a schematic manner, and therefore only show the components related to the application.

[0027] Example 1: like Figure 1 and Figure 2 As shown, the present invention discloses a weight-reducing and enhanced industrial robot rotating arm, including a body connecting part 1 connected to the robot body and a forearm connecting part 2 connected to the robot forearm. The body connecting part 1 and the forearm connecting part 2 are connected by an integrally formed connector, so that the front view of the robot arm forms an elongated oval shape.

[0028] by Figure 2 From a reference perspective, the connector includes two symmetrically arranged, spaced-apart main support beams 3. The two ends of the main support beams 3 are connected to the outer walls of the fuselage connecting part 1 and the forearm connecting part 2, respectively. The two ends of the main support beams 3 in the width direction are flush with the axial ends of the fuselage connecting part 1 and the forearm connecting part 2. The common tangent line of the fuselage connecting part 1 and the forearm connecting part 2 is defined as line a; the upper side of the upper main support beam 3 coincides with line a, and the lower side of the lower main support beam 3 coincides with line a.

[0029] The connection between the main support beam 3 and the fuselage connection 1 is inclined inward, so that the extension direction of this connection forms an obtuse angle with the main support beam 3. In this embodiment, the obtuse angle is 165°. The obtuse angle allows the load transmitted by the main support beam 3 to transition to the fuselage connection 1 at a gentler angle, effectively dispersing bending moment and shear force, thereby significantly reducing the peak value of the Mises equivalent stress at the connection. Furthermore, the connection is flared to increase the connection area between the main support beam 3 and the fuselage connection 1, improving its connection strength. The line connecting the axis of the fuselage connection 1 and the center of this connection is designated as line e. The connection surface between the main support beam 3 and the fuselage connection 1 is perpendicular to line e. Line e, representing the main force direction at this connection point, is the line connecting the axis of the fuselage connection 1 and the center of the connection. Designing the connection surface perpendicular to this line means that the connection interface is exactly perpendicular to the direction of the main reaction force from the fuselage connection part 1. This vertical layout makes the connection interface mainly bear compressive stress, which makes the connection deform less and more stable under the same load, further enhancing the stiffness and strength of the connection.

[0030] The connection between the main support beam 3 and the forearm connection 2 also slopes inward, and the extension direction of this connection forms a 165° obtuse angle with the main support beam 3. This obtuse angle allows the load transmitted by the forearm connection 2 to transition to the main support beam 3 at a gentler angle, effectively dispersing bending moment and shear force, thereby significantly reducing the peak Mises equivalent stress at the connection. Furthermore, the connection is flared to increase the connection area between the main support beam 3 and the forearm connection 2, improving its connection strength. The line connecting the axis of the forearm connection 2 and the center of this connection is designated as line f. The connection surface between the main support beam 3 and the forearm connection 2 is perpendicular to line f. Line f, representing the main force direction at this connection point, is the line connecting the axis of the forearm connection 2 and the center of the connection. Designing the connection surface perpendicular to this line means that the connection interface is exactly perpendicular to the direction of the main reaction force from the forearm connection 2. This vertical layout makes the connection interface mainly bear compressive stress, which makes the connection deform less and more stable under the same load, further enhancing the stiffness and strength of the connection.

[0031] The fuselage connecting part 1 is connected to the two main support beams 3 by first auxiliary support beams 4 located between the main support beams 3; the two first auxiliary support beams 4 are symmetrically arranged and have the same width as the main support beams 3; the fuselage connecting part 1, the main support beams 3 and the first auxiliary support beams 4 form a triangle. This triangular structure constitutes the main stress point of the connecting part. The extension direction of the main support beam 3 corresponds to the main stress direction of the robot arm; the extension direction of the first auxiliary support beam 4 corresponds to the maximum stress direction of the robot arm. The advantages of this design are: 1. The areas outside the main support beam 3 and the first auxiliary support beam 4 are non-load-bearing or inefficient material areas. Removing these areas not only does not reduce the performance of the arm but also significantly reduces its weight, lowers material costs and the robot's load, and reduces the demand on the drive system, thereby effectively reducing overall energy consumption and improving the robot's movement speed and dynamic response performance. 2. The alignment of the extension direction of the first auxiliary support beam 4 with the maximum stress direction ensures that the maximum stress does not generate a component force perpendicular to the direction of the first auxiliary support beam 4, allowing for a smaller cross-section design of the first auxiliary support beam 4 and further reducing the weight of the arm. 3. The clever use of the stable characteristics of a triangular structure creates a high-rigidity truss system that can more effectively resist bending and torsional deformation. 4. The extension direction of the first auxiliary support beam 4, together with the triangular structure, improves the stress distribution of the boom under complex multi-directional loads, effectively reduces the maximum Mises equivalent stress value, alleviates stress concentration in key areas such as hole-shaft connections and abrupt changes in cross-section, achieves uniform stress distribution, directly improves the minimum safety factor of the component, reduces the risk of fatigue failure, and enhances the reliability and service life of the robot under long-term, repetitive operation.

[0032] The connection point of the first auxiliary support beam 4 with the fuselage connection 1 is designated as point b, and the symmetrical center line of the main support beam 3 is designated as line c, which coincides with point b. The thickness at point b is more than twice the thickness of the left end of the first auxiliary support beam 4. The advantages of this arrangement are: (1) The load from the forearm connection 2 is transmitted through the main support beam 3 and then borne by the two symmetrical first auxiliary support beams 4 at the same point b, and smoothly guided to the fuselage connection 1. If the two first auxiliary support beams 4 are connected at different points in the fuselage connection 1, the force flow path will have a turn or branch, which is easy to generate stress concentration at the connection root. The "connection point coincidence" ensures that the force flow enters the fuselage connection 1, the final load-bearing body, in the most direct and smooth way, avoiding unnecessary bending moments and stress peaks on the key force transmission path. This makes the maximum Mises equivalent stress value at the root of the fuselage connection 1 significantly reduced when the boom is subjected to complex loads, and the stress distribution is more uniform, thereby directly improving the fatigue life and reliability of the component. (2) The support points of the two first auxiliary support beams 4 are converged at one point to establish a highly concentrated rigid support core. This structure can most effectively resist the force from the forearm that attempts to cause the upper arm to bend or twist. When the robot is carrying heavy loads or moving at high speed, this design can minimize the elastic deformation of the upper arm, resulting in higher absolute positioning accuracy for the robot's end effector and effectively suppressing vibrations caused by structural deformation, thus meeting the requirements of high-precision and high-stability operation. (3) The load is transferred through the triangular truss structure, and point b is the key hub of this efficient force flow path, which ensures the maximization of structural efficiency. Under the premise of meeting or even exceeding the original strength and stiffness requirements, all unnecessary materials can be safely removed. This directly leads to a significant reduction in the overall weight of the rotating upper arm.

[0033] The forearm connection 2 is connected to each of the two main support beams 3 by a second auxiliary support beam 5 located between the main support beams 3; the two second auxiliary support beams 5 are arranged symmetrically at intervals; the forearm connection 2, the main support beams 3, and the second auxiliary support beams 5 form a triangle; the second auxiliary support beams 5 are also the same width as the main support beams 3. The reason for this arrangement is that the forearm connection 2 is the stress point, where the load is more concentrated and the force flow path is singular. Therefore, the interval arrangement of the second auxiliary support beams 5 ensures that the main support beams 3 are evenly stressed, preventing uneven stress on the two main support beams 3.

[0034] The main support beam 3 is composed of a first connecting part 31 and a second connecting part 32 connected in sequence; the thickness of the first connecting part 31 is greater than the thickness of the second connecting part 32. In this embodiment, the thickness of the first connecting part 31 is twice the thickness of the second connecting part 32. The length of the first connecting part 31 is greater than the length of the second connecting part 32. In this embodiment, the length of the first connecting part 31 is 1.5 times that of the second connecting part 32. The above arrangement follows the principle of "allocating materials as needed," that is, using more material (increasing the thickness) in key parts with high stress and high strength and stiffness requirements (the first connecting part 31), and reducing the material in secondary parts with relatively low stress (the second connecting part 32). This makes the material distribution more reasonable and improves the material utilization efficiency.

[0035] The inner surfaces of the first connecting part 31 and the second connecting part 32 are coplanar. The rationale for this design is as follows: 1. With the inner surfaces in the same plane, when force is transmitted from the second connecting part 32 to the thicker first connecting part 31, no steps or abrupt changes in cross-section occur on the inner surface. This avoids stress concentration caused by sudden changes in geometry, allowing for a smooth and continuous transition of stress flow. This is crucial for boom structures subjected to dynamic and complex loads, effectively reducing the risk of fatigue failure and increasing the service life of components. 2. The coplanar inner surfaces, combined with the greater thickness of the first connecting part 31, form a wide and continuous load-bearing plane in the critical connection area between the main support beam 3 and the first and second connecting parts 31 and 32. This significantly enhances the resistance to buckling and deformation in this area, thereby improving the local stability and overall stiffness of the main support beam 3 and even the entire boom structure. Under heavy loads or high-speed movements, it can more effectively suppress elastic deformation, ensuring the robot's motion accuracy.

[0036] like Figure 3 As shown, the width of the first auxiliary support beam 4 increases from the middle to both ends. The minimum width of the first auxiliary support beam 4 is located near the main support beam 3. Since the stress on the first auxiliary support beam 4 is mainly concentrated at the connection point to the fuselage 1, the stress at the connection point to the main support beam 3 is low, resulting in a non-load-bearing or inefficient material area. Therefore, removing this area can further reduce the weight of the boom.

[0037] like Figure 3 As shown, the section between the main support beam 3 and the first auxiliary support beam 4 and the second auxiliary support beam 5 has a honeycomb-shaped perforated structure in its cross-section. This part is a non-load-bearing area, and the honeycomb perforated structure (honeycomb aperture 10mm, wall thickness 2mm) is used to disperse local stress and avoid stress concentration by utilizing the multi-directional stress characteristics of the honeycomb structure.

[0038] In this embodiment, the upper arm is made of 316L stainless steel. The outer diameter of both the body connection 1 and the forearm connection 2 is 185mm, and their thickness is 100mm. The center distance between the body connection 1 and the forearm connection 2 is 375mm. The thickness of the first connection is 20mm, and the thickness of the second connection is 10mm. The thickness of the first auxiliary support beam 4 near the body connection 1 is 16.5mm, and its outer side of the triangular structure is arc-shaped, causing the thickness of the first auxiliary support beam 4 to increase to 20mm to the right. The thickness of the second auxiliary support beam 5 near the forearm connection 2 is 13mm, and its outer side of the triangular structure is arc-shaped, causing the thickness of the second auxiliary support beam 5 to increase to 14.2mm to the left. With these settings, the weight of the robot upper arm is 34.878kg.

[0039] When a force of 10000N is applied to the forearm connection 2 in three directions (axial, radial parallel to line c, and radial perpendicular to line c), the maximum deformation displacement is 16.77mm, the maximum safety factor is 5.1, and the maximum Mises equivalent stress is 40.47MPa.

[0040] Comparative Example 1: like Figure 4 As shown, the traditional robot arm is also made of 316L elongated oval material. The outer diameter of both the body connection part 1 and the forearm connection part 2 is 185mm, and the thickness is 100mm. The center distance between the body connection part 1 and the forearm connection part 2 is 375mm, and the connector is a rectangular plate with a thickness of 100mm. The robot arm weighs 50kg. When a force of 10000N is applied to the forearm connection part 2 in three directions (axial, radial parallel to line c, and radial perpendicular to line c), the maximum deformation displacement is 20.59mm, the maximum safety factor is 4.8, and the maximum Mises equivalent stress is 42.74MPa.

[0041] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A weight-reducing and enhanced industrial robot rotary arm, comprising a body connecting part (1) connected to the robot body and a forearm connecting part (2) connected to the robot forearm, wherein the body connecting part (1) and the forearm connecting part (2) are connected by an integrally formed connector, characterized in that: The connector includes symmetrically and spaced main support beams (3); The two ends of the main support beam (3) in the width direction are flush with the two ends of the fuselage connection part (1) and the forearm connection part (2) in the axial direction; The spacing between the outer sides of the main support beam (3) is equal to the diameter of the fuselage connection part (1) and the forearm connection part (2); The common tangent of the fuselage connecting part (1) and the forearm connecting part (2) is set as line a; the outer surface of the main support beam (3) coincides with line a; The fuselage connecting part (1) is connected to the two main support beams (3) by a first auxiliary support beam (4) located between the main support beams (3); the two first auxiliary support beams (4) are arranged symmetrically; the fuselage connecting part (1), the main support beams (3) and the first auxiliary support beams (4) form a triangle; The connection point of the first auxiliary support beam (4) and the fuselage connection part (1) coincides and is set as point b. The symmetrical center line of the main support beam (3) is set as line c, and line c coincides with point b. The extension direction of the first auxiliary support beam (4) is consistent with the direction of the maximum stress of the rotating arm; The forearm connecting part (2) is connected to the two main support beams (3) by a second auxiliary support beam (5) located between the main support beams (3); the two second auxiliary support beams (5) are arranged symmetrically at intervals; the forearm connecting part (2), the main support beams (3) and the second auxiliary support beams (5) form a triangle; The first auxiliary support beam (4) and the second auxiliary support beam (5) are both the same width as the main support beam (3).

2. The weight-reducing and enhanced industrial robot rotary arm according to claim 1, characterized in that: The main support beam (3) is composed of a first connecting part (31) and a second connecting part (32) connected in sequence; The first connecting part (31) is connected to the fuselage connecting part (1); The second connecting part (32) is connected to the forearm connecting part (2); The thickness of the first connecting part (31) is greater than the thickness of the second connecting part (32).

3. The weight-reducing and enhanced industrial robot rotary arm according to claim 2, characterized in that: The inner surfaces of the first connecting part (31) and the second connecting part (32) are coplanar.

4. The weight-reducing and enhanced industrial robot rotary arm according to claim 2, characterized in that: The length of the first connecting part (31) is greater than the length of the second connecting part (32).

5. The weight-reducing and enhanced industrial robot rotary arm according to claim 4, characterized in that: The length of the first connecting part (31) is 1.5 times that of the second connecting part (32).

6. The weight-reducing and enhanced industrial robot rotary arm according to claim 1, characterized in that: The width of the first auxiliary support beam (4) increases from the middle position to both ends.

7. The weight-reducing and enhanced industrial robot rotary arm according to claim 6, characterized in that: The first auxiliary support beam (4) is located at its minimum width near the main support beam (3).

8. The weight-reducing and enhanced industrial robot rotary arm according to claim 1, characterized in that: The thickness at point b is more than twice the thickness of the end of the first auxiliary support beam (4) near the fuselage connection (1).

9. The weight-reducing and enhanced industrial robot rotary arm according to claim 1, characterized in that: The thickness of the first auxiliary support beam (4) increases from one end adjacent to the fuselage connection (1) to the other end.

10. A weight-reduced and enhanced industrial robot rotary arm according to claim 2, characterized in that: A gap is provided between the connection points of the first auxiliary support beam (4), the second auxiliary support beam (5) and the main support beam (3); The connection point between the first connecting part (31) and the second connecting part (32) is set as point d; The first auxiliary support beam (4) is connected to the first connecting part (31), and the connection point is located near point d; The second auxiliary support beam (5) is connected to the second connecting part (32), and the connection point is located near point d; The portion between the connection points of the main support beam (3) and the first auxiliary support beam (4) and the second auxiliary support beam (5) has a honeycomb-shaped hollow structure in its cross section.

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