An on-track torsion spring driven unfolding truss structure

Abstract

The present invention belongs to the field of aerospace technology, and specifically relates to an on-track torsion spring-driven unfolding truss structure, which includes a plurality of folding trusses, wherein the folding rods between adjacent trusses are connected by a rotating pair, and the rotation of the rotating pair is driven by a torsion spring to control the unfolding of the folding rods; a timing mechanism is arranged between each truss to control the orderly unfolding of the trusses; after the trusses are orderly unfolded, a locking mechanism is used to restrict them; the structure is composed of a plurality of trusses, and a docking mechanism is designed for the unfolding truss structure to implement docking; a guide rail is arranged on the unfolding truss structure to realize the load-bearing function after unfolding; the structure can provide guarantee for the long-term steady-state operation and very long baseline observation of the platform, meet the requirements of lightweight, high rigidity and high storage rate, and realize the functions of unfolding, docking, timing unfolding and guide rail bearing.

Description

Technical Field

[0001] The invention belongs to the field of aviation technology, and in particular relates to an unfolding truss structure driven by an on-track torsion spring. Background Art

[0002] Aiming at the needs of long baseline observation, with satellites as nodes and large-scale light and small folding rods as baselines, a kilometer-class very long baseline spacecraft is constructed to provide guarantee for the long-term steady-state operation of the platform and very long baseline observation. As a flexible component, the structural parameters of the large-scale light and small folding rod have a significant impact on the dynamic characteristics of the entire spacecraft system. Therefore, in order to achieve the observation conditions of kilometer-class phased array payloads, the folding rod is required to have the characteristics of large scale, light weight, high stiffness, high storage rate and low thermal deformation. It is urgent to solve the problems of large-scale light and small folding rod stiffness design, model parameter uncertainty, structure-thermal coupling and vibration, and develop high-precision, high-stability and multifunctional large-scale light and small folding rods to ensure the stable operation of kilometer-class very long baseline spacecraft. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide an on-track torsion spring driven unfolding truss structure.

[0004] In order to achieve the purpose of the present invention, the present invention will be implemented by adopting the technical solution described below.

[0005] An on-track torsion spring driven unfolding truss structure comprises at least two trusses, a folding rod, a torsion spring and a locking mechanism, wherein:

[0006] A truss is a polygonal frame consisting of three or more truss rods connected end to end via truss joints;

[0007] The folding rod is formed by connecting two short folding rods through a folding rod joint, and is used to connect two adjacent trusses; wherein the two ends of the short folding rod are respectively set as a truss joint rotation pair and a folding rod joint rotation pair;

[0008] The torsion spring is arranged on a pin shaft fixedly connected to the truss joint rotation pair and the folding rod joint rotation pair, and is used to drive the truss joint rotation pair and the folding rod joint rotation pair to rotate;

[0009] The locking mechanism is arranged at the hinge of the truss joint rotation pair and the step of the truss joint and at the hinge of the folding rod joint rotation pair and the step of the folding rod joint, which can limit the angular displacement of the folding rod joint and the truss joint after the truss structure is unfolded into place; it is characterized in that it also includes a timing mechanism, which is arranged on the same side of the truss joint set at the same vertex position of each polygonal frame, so that the folded folding rod can be unfolded in an orderly manner.

[0010] As a preferred solution of the present invention, the locking mechanism includes a locking slide groove, a locking rod, a spring and a locking groove, wherein:

[0011] The locking slots include two corresponding locking slots arranged on the truss joint rotating pair, and the length directions of the two locking slots are perpendicular to the central axes of the two pin holes on the truss joint rotating pair, and two corresponding locking slots arranged on the folding rod joint rotating pair, and the length directions of the two locking slots are perpendicular to the central axes of the two pin holes on the folding rod joint rotating pair;

[0012] A spring is disposed in the rotating pair of the truss joint, and applies elastic force to the central axis of the two pin shaft holes through the locking rod that slides with the two locking slots; and a spring is disposed in the rotating pair of the folding rod joint, and applies elastic force to the central axis of the two pin shaft holes through the locking rod that slides with the two locking slots;

[0013] The locking groove includes corresponding positions respectively arranged on the steps at both ends of the folding rod joint and one side step respectively arranged on the steps at both ends of the truss joint, so that the locking rod can automatically slide into the groove under the action of elastic force.

[0014] As a preferred embodiment of the present invention, the timing mechanism includes a truss joint timing lock A, a truss joint frame timing lock and a truss joint timing lock B, wherein:

[0015] A truss joint timing lock A is fixedly connected to a truss joint rotation pair hinged at one end of the truss joint, and can rotate with the rotation of the truss joint rotation pair;

[0016] The truss joint timing lock B is fixedly connected to the truss joint rotation pair hinged to the step at the other end of the truss joint, and can rotate with the rotation of the truss joint rotation pair;

[0017] The truss joint frame timing lock is fixedly connected to the truss joint frame, so that the truss joint timing lock A can remove the restriction on the truss joint timing lock B during the rotation process and release the truss joint timing lock B.

[0018] As a preferred embodiment of the present invention, the specific structure of the truss joint timing lock A limiting the release of the truss joint timing lock B is as follows: the specific structure is composed of the truss joint timing lock A, the truss joint frame timing lock and the truss joint timing lock B, wherein the truss joint timing lock A is a locking rod of an arc-shaped structure; the locking hole of the truss joint frame timing lock and the locking hole of the truss joint timing lock B are slidably matched with the locking rod of the arc-shaped structure of the truss joint timing lock A;

[0019] When the truss joint timing lock A is deployed into place along with the truss joint rotating pair fixedly connected to it, the truss joint timing lock A loses its restriction on the truss joint timing lock B and releases the truss joint timing lock B. The truss joint timing lock B is deployed along with the truss joint rotating pair fixedly connected to it under the action of the torsion spring, wherein the truss joint frame timing lock is used to guide the movement trajectory of the truss joint timing lock A.

[0020] As a preferred solution of the present invention, two edges on any surface of the unfolded truss structure are processed into guide rails, and the guide rails are grooved rails, wherein the beginning and end ends of the grooved rails are load interfaces that allow the load seat to slide in.

[0021] As a preferred solution of the present invention, the load seat can envelop the grooved track, and the load seat can slide on the grooved track.

[0022] As a preferred solution of the present invention, the load seat clamps the bottom of the groove of the groove track through fixed pulleys arranged up and down, so that the load seat can slide on the groove track.

[0023] As a preferred solution of the present invention, the unfolded truss structure is provided with a docking mechanism, which can install panels and dock with other unfolded truss structures and satellite bodies.

[0024] As a preferred solution of the present invention, the docking mechanism is composed of a male and a female joint; the female joint is composed of a female butt joint, a tightening ring, a spring and a mounting seat, wherein:

[0025] The female butt joint is used to butt with the male joint, and a tightening opening is provided on the top of the female butt joint to facilitate the insertion of the male joint;

[0026] A spring, used for driving the tightening ring provided on the top thereof to tighten the tightening opening to lock the male connector;

[0027] A mounting seat is used to fix the spring.

[0028] As a preferred solution of the present invention, the pin shaft is fixedly connected to the truss joint rotation pair and the folding rod joint rotation pair at both ends of the short folding rod, and is hinged to the steps of the truss joint and the steps of the folding rod joint through bearings.

[0029] Beneficial Effects

[0030] (1) Compared with a fixed truss, the truss structure of the present invention can reduce the space occupation and increase the space utilization rate, and its theoretical minimum folding and spreading ratio is 3.221%;

[0031] (2) Compared with the pneumatic deployment structure, the present invention has a higher strength level through rope control;

[0032] (3) The current special material shape memory alloy unfolded structure has fatigue characteristics and high requirements for environmental conditions. With the current level of science and technology, there is a lack of sufficient experimental data, which makes it difficult to ensure reliability and has high research costs. The structure of the present invention is simple, stable and reliable, and requires fewer iterative experiments. Moreover, most of the experimental data can be obtained in a laboratory environment and simulation iterations, which reduces costs while increasing the reliability of practical applications.

[0033] (4) The timing mechanism of the present invention makes the deployment more controllable;

[0034] (5) The modular design of the present invention makes the truss more widely used;

[0035] (6) The present invention provides a guide rail design concept that saves space and makes load-carrying more convenient and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a diagram of the folded state of a ten-meter truss structure;

[0037] Figure 2 This is a semi-expanded state diagram of a ten-meter truss structure;

[0038] Figure 3 It is the folding state diagram of two adjacent trusses;

[0039] Figure 4 It is the semi-expanded state diagram of two adjacent trusses;

[0040] Figure 5 It is the unfolded state diagram of two adjacent trusses;

[0041] Figure 6 It is a schematic diagram of the structure of a short folding rod;

[0042] Figure 7 It is the structural schematic diagram of the truss joint revolute pair;

[0043] Figure 8 It is a schematic diagram of the truss joint frame structure;

[0044] Fig. 9 Assemble exploded views for truss joints;

[0045] Fig.10 It is a schematic diagram of the assembly structure of the truss joint and the truss joint revolute pair;

[0046] Fig.11 It is a schematic diagram of the revolute structure of the folding rod joint;

[0047] Fig.12 Schematic diagram of the folding rod joint frame structure;

[0048] Fig.13It is a schematic diagram of the assembly structure of the folding rod joint frame and the folding rod joint revolute pair;

[0049] Fig.14 It is the cross-section of the revolute pair of the folding rod joint;

[0050] Fig.15 It is the state diagram of the locking process of the locking mechanism;

[0051] Fig.16 is a locking state diagram of the locking mechanism;

[0052] Fig.17 , 18 , 19 are diagrams of the folded, semi-expanded, and expanded states of the timing mechanism, respectively;

[0053] Fig. 20 is a schematic diagram of the structure of the guide rail;

[0054] Fig.21 It is a schematic diagram of the structure of the guide rail at the truss joint;

[0055] Fig. 22 It is a structural schematic diagram of the guide rail at the folding rod joint;

[0056] Fig.23 It is a structural schematic diagram of the load seat;

[0057] Fig.24 A schematic diagram of the load base being connected to the guide rail;

[0058] Fig.25 It is a schematic diagram of the load seat enveloping on the guide rail;

[0059] Fig.26 It is a structural schematic diagram of the truss structure of the present invention being connected with other truss structures and solar panels;

[0060] Fig. 27 It is a structural schematic diagram of the docking mechanism. DETAILED DESCRIPTION

[0061] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments:

[0063] As a specific embodiment of the present invention, Figures 1 to 27As shown, an on-track torsion spring driven unfolding truss structure comprises a truss 1, a folding rod 2, a torsion spring 3, a locking mechanism 4 and a timing mechanism 5, wherein:

[0064] The truss 1 is a square frame composed of four truss rods 11 connected end to end in sequence through truss joints 12;

[0065] The folding rod 2 is formed by two short folding rods 21 connected by a folding rod joint 22, and is used to connect two adjacent trusses 1; wherein the two ends of the short folding rod 21 are respectively provided with a truss joint rotation pair 23 and a folding rod joint rotation pair 24 to cooperate with each other;

[0066] The torsion spring 3 is arranged on the pin 25 fixedly connected to the truss joint rotating pair 23 and the folding rod joint rotating pair 24, and is used to drive the truss joint rotating pair 23 and the folding rod joint rotating pair 24 to rotate;

[0067] The locking mechanism 4 is provided at the hinged joint between the truss joint rotation pair 23 and the step 121 of the truss joint 12 and the hinged joint between the folding rod joint rotation pair 24 and the step 221 of the folding rod joint 22, and can limit the angular displacement of the folding rod joint 22 and the truss joint 12 after the truss structure is unfolded in place;

[0068] The timing mechanism 5 is arranged on the same side of the truss joint 12 at the same vertex position of each truss 1, so that the folded folding rods 2 can be unfolded in an orderly manner.

[0069] like Figure 1 and Figure 2 As shown, the deployable truss structure is composed of 8 trusses 1, the folded theoretical length is 0.352 meters (the folded theoretical length of a single module is 0.044 meters), and the unfolded theoretical length is 10.928 meters; the basic parameters are shown in Table 1;

[0070] Table 1 Design parameters of ten-meter folding pole

[0071]

[0072] like Figures 3 to 5 As shown, the folded length of two adjacent trusses 1 in the deployable truss structure is 0.044 meters, and the unfolded length is 1.366 meters; the basic parameters are shown in Table 2;

[0073] Table 2 Structural parameters of a single module

[0074]

[0075]

[0076] As an embodiment of the present invention, Figure 1-6As shown, the truss rod and the short folding rod are both made of carbon fiber rods to ensure light weight, with a density of 1800kg / m 3 , elastic modulus 395GPa, Poisson's ratio 0.307, cross section is 22mm×22mm square, hollow in the middle, size is subject to actual specifications, truss rod length is 0.909m;

[0077] As an embodiment of the present invention, Figures 7 to 10 As shown, the pin 25 is fixedly connected to the pin hole 231 on the truss joint rotating pair 23 at both ends of the folding rod 2, and is fixedly connected to the pin hole 124 at the step 122 of the truss joint frame 121 of the truss joint 12 through the inner ring of the bearing 26, and the outer ring of the bearing 26 is fixedly connected to the bearing hole 123.

[0078] As an embodiment of the present invention, Figures 11 to 14 As shown, the pin 25 is fixedly connected to the pin hole 241 on the folding rod joint rotating pair 24 at the inner end of the short folding rod 21, and is fixedly connected to the pin hole 222 at the step of the folding rod joint frame 221 of the folding rod joint 22 through the inner ring of the bearing 26, and the outer ring of the bearing 26 is fixedly connected to the bearing hole 223.

[0079] As an embodiment of the present invention, Figures 15 to 16 As shown, the locking mechanism 4 includes a locking slot 41, a locking rod 42, a spring 43 and a locking slot 44, wherein:

[0080] The locking slots 41 include two corresponding locking slots 41 provided on the truss joint rotating pair 23, and the length directions of the two locking slots 41 are perpendicular to the central axes of the two pin holes 231 on the truss joint rotating pair 23, and two corresponding locking slots 41 provided on the folding rod joint rotating pair 24, and the length directions of the two locking slots 41 are perpendicular to the central axes of the two pin holes 241 on the folding rod joint rotating pair 24;

[0081] The spring 43 is arranged in the truss joint rotation pair 23, and applies elastic force to the central axis of the two pin shaft holes 231 through the locking rod 42 that slides with the two locking slots 41, and is arranged in the folding rod joint rotation pair 24, and applies elastic force to the central axis of the two pin shaft holes 241 through the locking rod 42 that slides with the two locking slots 41;

[0082] The locking groove 44 includes corresponding positions on the steps 222 at both ends of the folding rod joint 22 and on one side step 122 of the steps 122 at both ends of the truss joint 12, so that the locking rod 42 can automatically slide into the groove 44 under the action of elastic force.

[0083] As an embodiment of the present invention, Fig.17 , 18 As shown in , 19, the timing mechanism 5 includes a truss joint timing lock A51, a truss joint frame timing lock 52 and a truss joint timing lock B53, wherein,

[0084] The truss joint timing lock A51 is fixedly connected to the truss joint rotation pair 23 hinged to the step 122 on one side of the truss joint 12, and can rotate with the rotation of the truss joint rotation pair 23;

[0085] The truss joint timing lock B53 is fixedly connected to the truss joint rotation pair 23 hinged to the step 122 on the other side of the truss joint 12, and can rotate with the rotation of the truss joint rotation pair 23;

[0086] The truss joint frame timing lock 52 is fixedly connected to the truss joint frame 121, can guide the movement trajectory of the truss joint timing lock A51, and can make the truss joint timing lock A51 lose the restriction on the truss joint timing lock B53 during the rotation process, and release the truss joint timing lock B53.

[0087] The restriction and release mechanism of the truss joint timing lock A51 on the truss joint timing lock B53 is composed of the truss joint timing lock A51, the truss joint frame timing lock 52 and the truss joint timing lock B53, wherein the truss joint timing lock A51 is a locking rod with an arc structure; the locking hole of the truss joint frame timing lock 52 and the locking hole of the truss joint timing lock B53 are slidably matched with the locking rod of the arc structure of the truss joint timing lock A51;

[0088] When the truss joint timing lock A51 is deployed into place along with the truss joint rotation pair 23 fixedly connected to it, the truss joint timing lock A51 loses its restriction on the truss joint timing lock B53 and releases the truss joint timing lock B53, and the truss joint timing lock B53 is deployed along with the truss joint rotation pair 23 fixedly connected to it under the action of the torsion spring 3; wherein, the truss joint frame timing lock 52 is used to guide the movement trajectory of the truss joint timing lock A51.

[0089] As an embodiment of the present invention, Figures 20 to 22 As shown, two edges on any surface of the unfolded truss structure are processed into guide rails 6, and the guide rails 6 are grooved rails, wherein the beginning and end of the grooved rails are load interfaces 61, which can slide the load seat 7. The guide rail connection structure at the truss joint is as shown in FIG. Fig.21 As shown; the guide rail connection structure at the folding rod joint is as shown Fig. 22 shown.

[0090] As an embodiment of the present invention, Figures 23 to 25 As shown, the load seat 7 can envelop the grooved track 6, and the load seat 7 can slide on the grooved track 6; the load seat 7 is connected to the guide rail 6 from the beginning and end of the guide rail 6, and the groove bottom plate of the grooved track 6 is clamped by the fixed pulleys 71 arranged up and down to realize the function of the load seat 7 sliding on the grooved track 6.

[0091] As an embodiment of the present invention, Figures 26 to 27 As shown, the unfolded truss structure is provided with a docking mechanism 8, which can install panels and dock with other unfolded truss structures and satellite bodies.

[0092] The docking mechanism 8 is composed of male and female joints 81 and 82; the female joint 82 is composed of a female butt joint 821, a tightening ring 822, a spring 823 and a mounting seat 824, wherein:

[0093] The female butt joint 821 is used to butt with the male joint 81, and a tightening opening is provided on the top thereof to facilitate the insertion of the male joint;

[0094] The spring 823 is used to drive the tightening ring 822 disposed on the top thereof to tighten the tightening opening to lock the male connector 81;

[0095] The mounting seat 824 is used to fix the spring 823 .

[0096] As an embodiment of the present invention, Figures 7 to 10 As shown, the truss joint rotational pair 23 is connected to the bearing 26 by the pin 25, and the bearing 26 is fixed to the boss 123 of the step 122 of the truss joint frame 121. The pin 25 is fixed to the truss joint rotational pair 23 and driven by the built-in torsion spring 3;

[0097] As an embodiment of the present invention, Figures 12 to 14 As shown, the folding rod joint rotating pair 24 is connected to the bearing 26 by a pin 25, and the bearing 26 is fixed in the bearing hole 223 of the folding rod joint frame 221 of the folding rod joint 22. The pin 25 passes through the pin hole 222 of the folding rod joint 22 and is fixed to the inner ring of the bearing 26, and is driven by the built-in torsion spring 3.

[0098] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but the scope of the rights of the present invention is not limited thereto. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present invention should be within the scope of the rights of the present invention.

Claims

1. An on-track torsion spring driven unfolding truss structure, comprising at least two trusses, a folding rod, a torsion spring and a locking mechanism, wherein: A truss is a polygonal frame consisting of three or more truss rods connected end to end via truss joints; The folding rod is formed by connecting two short folding rods through a folding rod joint, and is used to connect two adjacent trusses; wherein the two ends of the short folding rod are respectively set as a truss joint rotation pair and a folding rod joint rotation pair; The torsion spring is arranged on a pin shaft fixedly connected to the truss joint rotation pair and the folding rod joint rotation pair, and is used to drive the truss joint rotation pair and the folding rod joint rotation pair to rotate; The locking mechanism is arranged at the hinge of the truss joint rotation pair and the step of the truss joint and at the hinge of the folding rod joint rotation pair and the step of the folding rod joint, which can limit the angular displacement of the folding rod joint and the truss joint after the truss structure is unfolded into place; it is characterized in that it also includes a timing mechanism, which is arranged on the same side of the truss joint set at the same vertex position of each polygonal frame, so that the folded folding rod can be unfolded in an orderly manner.

2. The on-track torsion spring driven unfolding truss structure according to claim 1, characterized in that: The locking mechanism includes a locking slot, a locking rod, a spring and a locking slot, wherein: The locking slots include two corresponding locking slots arranged on the truss joint rotating pair, and the length directions of the two locking slots are perpendicular to the central axes of the two pin holes on the truss joint rotating pair, and two corresponding locking slots arranged on the folding rod joint rotating pair, and the length directions of the two locking slots are perpendicular to the central axes of the two pin holes on the folding rod joint rotating pair; A spring is disposed in the rotating pair of the truss joint, and applies elastic force to the central axis of the two pin shaft holes through the locking rod that slides with the two locking slots; and a spring is disposed in the rotating pair of the folding rod joint, and applies elastic force to the central axis of the two pin shaft holes through the locking rod that slides with the two locking slots; The locking groove includes corresponding positions respectively arranged on the steps at both ends of the folding rod joint and one side step respectively arranged on the steps at both ends of the truss joint, so that the locking rod can automatically slide into the groove under the action of elastic force.

3. The on-track torsion spring driven unfolding truss structure according to claim 1, characterized in that: The timing mechanism includes a truss joint timing lock A, a truss joint frame timing lock and a truss joint timing lock B, wherein: A truss joint timing lock A is fixedly connected to a truss joint rotation pair hinged at one end of the truss joint, and can rotate with the rotation of the truss joint rotation pair; The truss joint timing lock B is fixedly connected to the truss joint rotation pair hinged to the step at the other end of the truss joint, and can rotate with the rotation of the truss joint rotation pair; The truss joint frame timing lock is fixedly connected to the truss joint frame, so that the truss joint timing lock A can remove the restriction on the truss joint timing lock B during the rotation process and release the truss joint timing lock B.

4. The on-track torsion spring driven unfolding truss structure according to claim 3, characterized in that: The specific structure of the truss joint timing lock A restricting the release of the truss joint timing lock B: the specific structure is composed of the truss joint timing lock A, the truss joint frame timing lock and the truss joint timing lock B, wherein the truss joint timing lock A is a locking rod of an arc-shaped structure; the locking hole of the truss joint frame timing lock and the locking hole of the truss joint timing lock B are slidably matched with the locking rod of the arc-shaped structure of the truss joint timing lock A; When the truss joint timing lock A is deployed into place along with the truss joint rotating pair fixedly connected to it, the truss joint timing lock A loses its restriction on the truss joint timing lock B and releases the truss joint timing lock B. The truss joint timing lock B is deployed along with the truss joint rotating pair fixedly connected to it under the action of the torsion spring; wherein, the truss joint frame timing lock is used to guide the movement trajectory of the truss joint timing lock A.

5. The on-track torsion spring driven unfolding truss structure according to claim 1, characterized in that: Two edges on any surface of the unfolded truss structure are processed into guide rails, and the guide rails are grooved rails, wherein the beginning and end ends of the grooved rails are load interfaces, which can allow the load seat to slide in.

6. The on-track torsion spring driven unfolding truss structure according to claim 5, characterized in that: The load seat can envelop the grooved track, and the load seat can slide on the grooved track.

7. The on-track torsion spring driven unfolding truss structure according to claim 6, characterized in that: The load seat clamps the bottom of the groove of the groove track through fixed pulleys arranged up and down, so that the load seat can slide on the groove track.

8. The on-track torsion spring driven unfolding truss structure according to claim 1, characterized in that: The unfolded truss structure is provided with a docking mechanism, which can install panels and dock with other unfolded truss structures and satellite bodies.

9. The on-track torsion spring driven unfolding truss structure according to claim 8, characterized in that: The docking mechanism is composed of a male and a female joint; the female joint is composed of a female butt joint, a tightening ring, a spring and a mounting seat, wherein: The female butt joint is used to butt with the male joint, and a tightening opening is provided on the top of the female butt joint to facilitate the insertion of the male joint; A spring, used for driving the tightening ring provided on the top thereof to tighten the tightening opening to lock the male connector; A mounting seat is used to fix the spring.

10. The on-track torsion spring driven unfolding truss structure according to claim 1, characterized in that: The pins are respectively fixedly connected to the truss joint rotating pair and the folding rod joint rotating pair at both ends of the short folding rod, and are respectively hinged to the steps of the truss joint and the steps of the folding rod joint through bearings.

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