Truss unfolding mechanism and control method

Abstract

The invention discloses a truss unfolding mechanism and a control method. The truss unfolding mechanism is formed by connecting twelve unit cell mechanisms together. The unit cell mechanism comprises a unit cell fixing seat I, a unit cell fixing seat II, a unit cell fixing seat III, a unit cell fixing seat IV and an adjacent cell connecting seat; the unit cell mechanism is of a symmetrical structure; a first telescopic sleeve is arranged between the first unit cell fixing base and the adjacent cell connecting base, a second telescopic sleeve is arranged between the second unit cell fixing base and the adjacent cell connecting base, a third telescopic sleeve is arranged between the fourth unit cell fixing base and the adjacent cell connecting base, and a fourth telescopic sleeve is arranged between the third unit cell fixing base and the adjacent cell connecting base. Based on a novel double-ring truss structure unfolding principle obtained by improving a traditional single-ring structure, the structure has the advantages that the storage rate is high, the precision is high, the rigidity is large, the stability is high, and the quality is not multiplied along with the increase of the aperture of the antenna.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite-borne antennas, and in particular to an unfolding truss mechanism and a control method. Background Art

[0002] With the development and application of aerospace technology, large-scale deployable truss structures in space have been widely used in satellite antennas, solar panels, etc. For example, large-scale deployable antennas on board have been widely used in navigation satellites, communication satellites, relay satellites, meteorological satellites and reconnaissance satellites. However, due to the transportation characteristics of the aerospace field, such as the size and carrying capacity of the launch vehicle, the satellite antenna needs to be foldable. It is required to be folded and fixed in the payload compartment of the launch vehicle during the launch phase. After the spacecraft enters the orbit, the ground control center will instruct it to gradually complete the deployment action in the space orbit according to the design requirements, and then lock and maintain it in a working state.

[0003] Traditional satellite antenna trusses are mostly single-ring structures. When the antenna is expanded and retracted, it does not have a high storage ratio and high rigidity, which seriously affects the terminal positioning and operation accuracy. In addition, traditional satellite antenna trusses make the satellite antenna bulky.

[0004] As a type of satellite-borne antenna, the space scissor-fork truss satellite antenna has the advantages of high storage rate (ratio of folded size to unfolded size), high precision, high rigidity, strong stability, and mass that does not increase exponentially with the increase of antenna diameter. It has become an important topic in the research of large-aperture space deployable antennas, and is even expected to develop in the direction of the development of space ultra-large-aperture satellite-borne antennas. Therefore, it is urgent to design an unfolding truss mechanism and control method to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide an unfolding truss mechanism and a control method to solve the above-mentioned deficiencies in the prior art.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The unfolding truss mechanism and control method include twelve unit cell mechanisms connected to each other;

[0008] The unit cell mechanism comprises a unit cell fixing seat 1, a unit cell fixing seat 2, a unit cell fixing seat 3, a unit cell fixing seat 4 and a neighboring cell connecting seat;

[0009] The unit cell mechanism is a symmetrical structure;

[0010] A telescopic sleeve 1 is provided between the single cell fixing seat 1 and the adjacent cell connecting seat, a telescopic sleeve 2 is provided between the single cell fixing seat 2 and the adjacent cell connecting seat, a telescopic sleeve 3 is provided between the single cell fixing seat 4 and the adjacent cell connecting seat, and a telescopic sleeve 4 is provided between the single cell fixing seat 3 and the adjacent cell connecting seat;

[0011] A pair of folding rods 1 are rotatably connected between the unit cell fixing seat 1 and the unit cell fixing seat 4, and a pair of folding rods 2 are rotatably connected between the unit cell fixing seat 2 and the unit cell fixing seat 3;

[0012] The first pair of folding rods and the second pair of folding rods are rotatably connected with a connecting rod.

[0013] Preferably, the structures of the single-cell fixing seat 1, the single-cell fixing seat 2, the single-cell fixing seat 3 and the single-cell fixing seat 4 are the same, and the structures and lengths of the telescopic sleeve 1, the telescopic sleeve 2, the telescopic sleeve 3 and the telescopic sleeve 4 are the same.

[0014] Preferably, a symmetrically distributed connecting claw 1 and a connecting claw 2 are fixedly provided on the outer wall of the unit cell fixing seat 1.

[0015] Preferably, the twelve unit cell mechanisms are distributed on the same circular trajectory, the unit cell fixing seat 1 and the unit cell fixing seat 2 are distributed on the inner circular trajectory, and the unit cell fixing seat 3 and the unit cell fixing seat 4 are distributed on the outer circular trajectory.

[0016] Preferably,

[0017] The radii of the inner circle trajectory and the outer circle trajectory are defined as r and R respectively; the length of the telescopic sleeve 1 is S; the distance between two unit cell fixing seats 1 in adjacent unit cell mechanisms is L; the distance between two unit cell fixing seats 3 in the unit cell mechanism is l, the telescopic sleeve is an outer ring chord, the folding rod is an inner ring chord, the number of inner ring chords is half of the number of outer ring chords, and the number of inner ring chords is recorded as n;

[0018]

[0019] Preferably, when the chord between N1 and N9 rotates around N1 by an angle θ on the vertical plane, the other chords and connecting rods rotate by the same angle θ, and the height of the expandable unit is recorded as h, that is, the length of the vertical component between N3 and N4. When the unit is folded to angle θ, its height remains unchanged, and the Z coordinate of N4 is equal to the height h of the truss. Because N1 is located at the origin of the coordinates, using the first path N4-N12-N8, the Z coordinate of N12 can be calculated as h+Ssinθ, the Z coordinate of N8 is h+Ssinθ, and N8=N12=N2. In each folded state of the spatial scissors-type truss satellite antenna structure, when the three nodes are folded at the same frequency and at the same height, no interference occurs.

[0020] Preferably, it is composed of front and rear parabolic cable nets, and the front and rear parabolic cable nets are composed of parabolas rotating around their axes. On the XOY plane, the parabola with point O as the vertex and F as the focus is expressed as: 2 =4fz;

[0021] The ratio f / D between the focal length f and the major diameter D is an important feature of the parabola. When the f / D value is large, it is relatively simple to manufacture the parabola. However, as the distance between the feed source and the main reflector increases, the antenna's resistance decreases. In this paper, the f / D value is 1.2 for the front surface and 5 for the rear surface. The aperture D is 5m according to engineering requirements.

[0022] Points A and B are not only on the parabola, but also on the edge of the deployable support truss. By substituting into the formula χ 2 =4fz; the Z coordinate from point A to point B can be obtained. To ensure the normal performance of the antenna, the height h of the entire antenna must be greater than the total height Z of the front and rear parabolic cable network. A +Z B ;

[0023] h min =Z A +Z B =0.194+0.062=0.256;

[0024] h max =Hl=H-2Rsin(π / 2n).

[0025] Preferably, the height of the space scissor-fork truss satellite antenna structure increases during the folding process, and the folded height and the original truss height h in the fully deployed state are determined by the inner and outer ring connecting rods S, which can be written as: H 1 =H 2 =H 3 =h+Ssinθ;

[0026] The relationship between S and small l, S = 2lsin(π / n);

[0027] The folding ratio of the deployable and foldable antenna should be greater than 4, hmax ≥ hmin, which can be expressed as: H-2Rsin(π / 2n) ≥ 0.256;

[0028] The lower bound of n can be calculated as: 0.95-5sin(π / 2n)≥0.256;

[0029] It can be obtained that n ≥ 11.28, therefore, the number of inner ring edges n of the closed-loop expandable truss must be greater than or equal to 12;

[0030] The natural frequency changes with the value of n; for components with different cross sections, the percentage increase of the natural frequency f1 is always less than 5%. Since increasing the number of sides of the outer ring crossbar of the space scissor-type truss satellite antenna structure will lead to a more complex truss, and the increase of the natural frequency f1 is rarely less than 5%, the number of sides of the inner ring crossbar n is selected as 12; once again proving the rationality of n taking 12.

[0031] The control method of the unfolding truss mechanism comprises the movement steps obtained by using the unfolding truss mechanism to realize the unfolding and contraction of the truss.

[0032] In the above technical scheme, the unfolding truss mechanism and control method provided by the present invention are based on the unfolding principle of a novel double-ring truss structure obtained by improving the traditional single-ring structure. The structure has the advantages of high storage rate (ratio of folded size to unfolded size), high precision, high rigidity, strong stability, and mass that does not increase exponentially with the increase of antenna aperture.

[0033] The double-ring deployable truss structure has the highest stability. In the future, when used in ring antennas, it will have the ability to resist elastic deformation caused by large-scale movement and thermal deformation caused by experiencing high-temperature sunshine areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0035] Figure 1 A schematic diagram of the fully deployed state structure provided by an embodiment of an deployment truss mechanism and a control method of the present invention.

[0036] Figure 2 A schematic diagram of the unit cell structure provided for an embodiment of an unfolding truss mechanism and a control method of the present invention.

[0037] Figure 3 A schematic diagram of the semi-retracted state structure provided for an embodiment of an unfolding truss mechanism and a control method of the present invention.

[0038] Figure 4 A schematic diagram of the fully retracted state structure provided for an embodiment of an unfolding truss mechanism and a control method of the present invention.

[0039] Figure 5 A schematic diagram of the arrangement of a single-cell fixing seat, an adjacent-cell connecting seat, a telescopic sleeve, and a folding rod member provided in an embodiment of the unfolding truss mechanism and control method of the present invention.

[0040] Figure 6A schematic diagram of the unfolding / folding principle of a unit cell mechanism provided in an embodiment of an unfolding truss mechanism and a control method of the present invention.

[0041] Figure 7 The geometric figure of the parabola provided for the embodiment of the unfolding truss mechanism and control method of the present invention.

[0042] Figure 8 A displacement diagram of a single cell fixing seat, an adjacent cell connecting seat, a telescopic sleeve, a folding rod and a connecting rod provided in an embodiment of the unfolding truss mechanism and the control method of the present invention.

[0043] Fig. 9 A speed diagram of a single cell fixing seat, an adjacent cell connecting seat, a telescopic sleeve, a folding rod and a connecting rod provided in an embodiment of the unfolding truss mechanism and the control method of the present invention.

[0044] Fig.10 Acceleration diagram of a single cell fixing seat, a neighboring cell connecting seat, a telescopic sleeve, a folding rod and a connecting rod provided in an embodiment of the unfolding truss mechanism and the control method of the present invention.

[0045] Fig.11 A diagram showing the changes in crossbar displacement, velocity and acceleration provided for an embodiment of an unfolding truss mechanism and a control method of the present invention.

[0046] Fig.12 A diagram showing the change in vertical rod displacement and velocity acceleration provided for an embodiment of an unfolding truss mechanism and a control method of the present invention.

[0047] Fig.13 A diagram showing the changes in radial rod displacement and velocity acceleration provided for an embodiment of an unfolding truss mechanism and a control method of the present invention.

[0048] Fig.14 A schematic diagram of the motor installation position structure provided for an embodiment of an unfolding truss mechanism and a control method of the present invention.

[0049] Description of reference numerals:

[0050] 1. Single-cell mechanism; 2. Single-cell fixing seat 1; 3. Connecting claw 1; 4. Connecting claw 2; 5. Single-cell fixing seat 2; 6. Single-cell fixing seat 3; 7. Single-cell fixing seat 4; 8. Adjacent-cell connecting seat; 9. Telescopic sleeve 1; 10. Telescopic sleeve 2; 11. Telescopic sleeve 3; 12. Telescopic sleeve 4; 13. Folding rod 1; 14. Folding rod 2; 15. Connecting rod; 16. Driving motor. DETAILED DESCRIPTION

[0051] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0052] like Figure 1-5As shown, the unfolding truss mechanism and control method provided by the embodiment of the present invention include twelve unit cell mechanisms 1 connected to each other; the unit cell mechanism 1 includes a unit cell fixing seat 1 2, a unit cell fixing seat 2 5, a unit cell fixing seat 3 6, a unit cell fixing seat 4 7 and a neighboring cell connecting seat 8; the unit cell mechanism 1 is a symmetrical structure; a telescopic sleeve 1 9 is arranged between the unit cell fixing seat 1 2 and the neighboring cell connecting seat 8, a telescopic sleeve 2 10 is arranged between the unit cell fixing seat 2 5 and the neighboring cell connecting seat 8, a telescopic sleeve 3 11 is arranged between the unit cell fixing seat 4 7 and the neighboring cell connecting seat 8, and a telescopic sleeve 4 12 is arranged between the unit cell fixing seat 3 6 and the neighboring cell connecting seat 8; a pair of folding rods 13 are rotatably connected between the unit cell fixing seat 1 2 and the unit cell fixing seat 4 7, and a pair of folding rods 14 are rotatably connected between the unit cell fixing seat 2 5 and the unit cell fixing seat 3 6; a connecting rod 15 is rotatably connected between the pair of folding rods 13 and the pair of folding rods 14.

[0053] In this embodiment, twelve unit cell mechanisms 1 are connected to each other to form a whole;

[0054] Specifically, the unit cell mechanism 1 includes a unit cell fixing seat 1 2, a unit cell fixing seat 2 5, a unit cell fixing seat 3 6, a unit cell fixing seat 4 7 and a neighboring cell connecting seat 8;

[0055] Specifically, the structures of the single cell fixing seat 1 2, the single cell fixing seat 2 5, the single cell fixing seat 3 6, and the single cell fixing seat 4 7 are the same;

[0056] Specifically, a symmetrically distributed connecting claw 1 3 and a connecting claw 2 4 are fixedly arranged on the outer wall of the unit cell fixing seat 1 2 .

[0057] Specifically, the unit cell mechanism 1 is a symmetrical structure;

[0058] Specifically, a telescopic sleeve 1 9 is provided between the single cell fixing seat 1 2 and the adjacent cell connecting seat 8, and the adjacent single cell mechanisms are connected through the adjacent cell connecting seat 8, so that the truss of the antenna is composed of 12 single cell mechanisms 1, a telescopic sleeve 2 10 is provided between the single cell fixing seat 2 5 and the adjacent cell connecting seat 8, a telescopic sleeve 3 11 is provided between the single cell fixing seat 4 7 and the adjacent cell connecting seat 8, and a telescopic sleeve 4 12 is provided between the single cell fixing seat 3 6 and the adjacent cell connecting seat 8;

[0059] Specifically, the structures and lengths of telescopic sleeve 1 9 , telescopic sleeve 2 10 , telescopic sleeve 3 11 and telescopic sleeve 4 12 are the same.

[0060] Specifically, a pair of folding rods 13 are rotatably connected between the single cell fixing seat 1 2 and the single cell fixing seat 4 7, and a pair of folding rods 14 are rotatably connected between the single cell fixing seat 2 5 and the single cell fixing seat 3 6;

[0061] Specifically, the first folding rod 13 and the second folding rod 14 are rotatably connected with a connecting rod 15 .

[0062] like Figure 4 As shown, this is the state of the deployable antenna mechanism when it is fully folded. At this time, the two adjacent outer ring nodes in the deployable antenna mechanism are completely close to each other, and the volume of the deployable antenna structure is the smallest. As the deployable antenna structure gradually unfolds, the distance between adjacent inner ring nodes and outer ring nodes continues to increase.

[0063] like Figure 3 As shown, the deployable antenna mechanism is in a semi-deployed state, at which time the distance between two adjacent inner ring nodes and between two adjacent outer ring nodes in the mechanism gradually increases.

[0064] like Figure 1 As shown, the deployable antenna mechanism is in a fully deployed state, the volume reaches the maximum, the angle between the two outer connecting rods connected by the rotating pair in the deployable antenna mechanism is 180°, and the deployable antenna mechanism is in a singular position state.

[0065] like Figure 5 As shown, in this embodiment, the twelve unit cell mechanisms 1 are distributed on the same circular trajectory, the unit cell fixing seat 1 2 and the unit cell fixing seat 2 5 are distributed on the inner circular trajectory, and the unit cell fixing seat 3 6 and the unit cell fixing seat 4 7 are distributed on the outer circular trajectory.

[0066] In this embodiment, Figure 5 As shown,

[0067] The radii of the inner circle trajectory and the outer circle trajectory are defined as r and R respectively; the length of the telescopic sleeve 9 is S; the distance between two unit cell fixing seats 2 in adjacent unit cell mechanisms 1 is L; the distance between two unit cell fixing seats 36 in the unit cell mechanism 1 is l, the telescopic sleeve is an outer ring chord rod, the folding rod is an inner ring chord rod, the number of inner ring chord rods is half of the number of outer ring chord rods, and the number of inner ring chord rods is recorded as n;

[0068]

[0069] In this embodiment, Figure 6 As shown, when the chord between N1 and N9 rotates an angle θ around N1 on the vertical plane, the other chords and connecting rods rotate the same angle θ, and the height of the expandable unit is recorded as h, that is, the length of the vertical member between N3 and N4. When the unit is folded to angle θ, its height remains unchanged. The Z coordinate of N4 is equal to the height h of the truss. Because N1 is located at the origin of the coordinates, using the first path N4-N12-N8, the Z coordinate of N12 can be calculated as h+Ssinθ, the Z coordinate of N8 is h+Ssinθ, and N8=N12=N2. In each folded state, the spatial scissor-fork truss satellite antenna structure does not interfere with the three nodes when they are folded at the same frequency and at the same height.

[0070] In this embodiment, Figure 7 As shown in Figure 1, the front and rear parabolic cable nets are composed of parabolas rotating around their axes. On the XOY plane, the parabola with point O as the vertex and F as the focus is expressed as: 2 =4fz;

[0071] The ratio f / D between the focal length f and the major diameter D is an important feature of the parabola. When the f / D value is large, it is relatively simple to manufacture the parabola. However, as the distance between the feed source and the main reflector increases, the antenna's resistance decreases. In this paper, the f / D value is 1.2 for the front surface and 5 for the rear surface. The aperture D is 5m according to engineering requirements.

[0072] Points A and B are not only on the parabola, but also on the edge of the deployable support truss. By substituting into the formula χ 2 =4fz; the Z coordinate from point A to point B can be obtained. To ensure the normal performance of the antenna, the height h of the entire antenna must be greater than the total height Z of the front and rear parabolic cable network. A +Z B ;

[0073] h min =Z A +Z B =0.194+0.062=0.256;

[0074] h max =Hl=H-2Rsin(π / 2n).

[0075] In this embodiment, the height of the space scissor-type truss satellite antenna structure increases during the folding process. The folded height and the original truss height h in the fully deployed state are determined by the inner and outer ring connecting rods S, which can be written as: H 1 =H 2 =H 3 =h+Ssinθ;

[0076] The relationship between S and small l, S = 2lsin(π / n);

[0077] The folding ratio of the deployable and foldable antenna should be greater than 4, hmax ≥ hmin, which can be expressed as: H-2Rsin(π / 2n) ≥ 0.256;

[0078] The lower bound of n can be calculated as: 0.95-5sin(π / 2n)≥0.256;

[0079] It can be obtained that n ≥ 11.28, therefore, the number of inner ring edges n of the closed-loop expandable truss must be greater than or equal to 12;

[0080] The natural frequency changes with the value of n; for components with different cross sections, the increase percentage of the natural frequency f1 is always less than 5%. Since increasing the number of sides of the outer ring crossbar of the space scissor-type truss satellite antenna structure will lead to a more complex truss, and the increase of the natural frequency f1 is rarely less than 5%, the number of sides of the inner ring crossbar n is selected as 12; once again proving the rationality of n taking 12.

[0081] The invention discloses a control method for an unfolding truss mechanism, comprising a motion step obtained by using the unfolding truss mechanism to realize the unfolding and contraction of the truss.

[0082] The rigid simulation process of the ring truss from folding to unfolding is completed in the dynamic simulation software. The satellite truss components are connected through kinematic pairs in ADAMS. According to the motion relationship of the flexible body simulation, the folding rods, connecting rods and telescopic sleeves are connected through rotation pairs (single cell fixed seat, adjacent cell connecting seat), and moving pairs are added between the telescopic sleeves. After the kinematic pairs are added, the satellite truss is as follows: Figure 1-4 As shown, add a drive to the revolute joint between the horizontal bar and the vertical bar (such as Fig.14 As shown, add a drive motor 16), the drive function is the Step function, and the annular truss expansion function is step(time, 0, 0, 5.55, 180d). After setting the drive parameters, turn on gravity, set the simulation time to 5.55s, the number of steps to 2500, and then perform dynamic simulation.

[0083] The horizontal bar, vertical bar, radial bar and three telescopic bars in the unit mechanism whose unit coordinate system coincides with the global coordinate system are selected as the target components. The simulation results of the kinematic characteristic curves of the six components along the X-axis direction are shown in Figure 8 , Fig. 9 and Fig.10 The displacement, velocity and acceleration result curves of each component (folding rod, telescopic sleeve and connecting rod) are smooth, indicating that the space scissor-type truss satellite antenna is unfolded smoothly without impact and vibration during the unfolding process.

[0084] The folding rod is a horizontal rod, the telescopic sleeve is a radial rod, and the connecting rod is a vertical rod.

[0085] like Fig.11 , Fig.12 and Fig.13 As shown, the displacement, velocity and acceleration changes of the horizontal rod, vertical rod and radial rod after being made flexible. It is not difficult to see that the vibration deviation is negligible, with only a small fluctuation during the retraction process, and the vibration slope difference is basically negligible. This also shows from the side the rationality of the space scissors-type truss satellite antenna structure, which is wirelessly close to the idealized model. It can also be seen from the side that the double-ring structure is very stable.

[0086] In the crossbar velocity change diagram, the flexible crossbar only fluctuates in the early stage, but the overall velocity change is consistent with the velocity change trend of the crossbar rigid body. In the crossbar acceleration change diagram, the flexible crossbar fluctuates more obviously in the first 2 seconds of simulation. This is because instantaneous acceleration will be generated due to inertia at the beginning and end of the movement. In the flexible coupling simulation curve of the vertical rod and radial rod, the curve in the extension stage is basically consistent with the rigid trend. At the end of the unfolding process, the acceleration curve oscillates up and down at the same time. This is because the inertia at the end of the movement causes the flexible body to change, which is reflected in the acceleration curve of the marked point.

[0087] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An unfolded truss mechanism, characterized in that: It comprises twelve unit cell mechanisms (1) connected to each other; The unit cell mechanism (1) comprises a unit cell fixing seat 1 (2), a unit cell fixing seat 2 (5), a unit cell fixing seat 3 (6), a unit cell fixing seat 4 (7) and an adjacent cell connecting seat (8); The unit cell mechanism (1) is a symmetrical structure; A telescopic sleeve 1 (9) is provided between the single cell fixing seat 1 (2) and the adjacent cell connecting seat (8), a telescopic sleeve 2 (10) is provided between the single cell fixing seat 2 (5) and the adjacent cell connecting seat (8), a telescopic sleeve 3 (11) is provided between the single cell fixing seat 4 (7) and the adjacent cell connecting seat (8), and a telescopic sleeve 4 (12) is provided between the single cell fixing seat 3 (6) and the adjacent cell connecting seat (8); A pair of folding rods (13) are rotatably connected between the single cell fixing seat (2) and the single cell fixing seat (7), and a pair of folding rods (14) are rotatably connected between the single cell fixing seat (5) and the single cell fixing seat (6); The first pair of folding rods (13) and the second pair of folding rods (14) are rotatably connected by a connecting rod (15).

2. The unfolding truss mechanism according to claim 1, characterized in that: The structures of the single-cell fixing seat 1 (2), the single-cell fixing seat 2 (5), the single-cell fixing seat 3 (6), and the single-cell fixing seat 4 (7) are the same, and the structures and lengths of the telescopic sleeve 1 (9), the telescopic sleeve 2 (10), the telescopic sleeve 3 (11), and the telescopic sleeve 4 (12) are the same.

3. The unfolding truss mechanism according to claim 2, characterized in that: A symmetrically distributed connecting claw 1 (3) and a connecting claw 2 (4) are fixedly arranged on the outer wall of the unit cell fixing seat 1 (2).

4. The unfolding truss mechanism according to claim 1, characterized in that: The twelve unit cell mechanisms (1) are distributed on the same circular track, the unit cell fixing seat 1 (2) and the unit cell fixing seat 2 (5) are distributed on the inner circular track, and the unit cell fixing seat 3 (6) and the unit cell fixing seat 4 (7) are distributed on the outer circular track.

5. The unfolding truss mechanism according to claim 4, characterized in that: The radii of the inner circle trajectory and the outer circle trajectory are defined as r and R respectively; the length of the telescopic sleeve 1 (9) is S; the distance between two unit cell fixing seats 1 (2) in adjacent unit cell mechanisms (1) is L; the distance between two unit cell fixing seats 3 (6) in the unit cell mechanism (1) is l, the telescopic sleeve is an outer ring chord, the folding rod is an inner ring chord, the number of inner ring chords is half of the number of outer ring chords, and the number of inner ring chords is recorded as n; 6. The unfolding truss mechanism according to claim 5, characterized in that: When the chord between N1 and N9 rotates an angle θ around N1 on the vertical plane, the other chords and connecting rods rotate the same angle θ. The height of the expandable unit is recorded as h, that is, the length of the vertical member between N3 and N4. When the unit is folded to angle θ, its height remains unchanged. The Z coordinate of N4 is equal to the height h of the truss. Because N1 is located at the origin of the coordinates, using the first path N4-N12-N8, the Z coordinate of N12 can be calculated as h+Ssinθ, the Z coordinate of N8 is h+Ssinθ, and N8=N12=N2. In each folded state, the spatial scissor-fork truss satellite antenna structure does not interfere when the three nodes are folded at the same frequency and at the same height.

7. The unfolding truss mechanism according to claim 6, characterized in that: It is composed of front and rear parabolic cable nets, both of which are composed of parabolas rotating around their axes. On the XOY plane, the parabola with point O as the vertex and F as the focus is expressed as: 2 =4fz; The ratio f / D between the focal length f and the major diameter D is an important feature of the parabola. When the f / D value is large, it is relatively simple to manufacture the parabola. However, as the distance between the feed source and the main reflector increases, the antenna's resistance decreases. In this paper, the f / D value is 1.2 for the front surface and 5 for the rear surface. The aperture D is 5m according to engineering requirements. Points A and B are not only on the parabola, but also on the edge of the deployable support truss. By substituting into the formula χ 2 =4fz; the Z coordinate from point A to point B can be obtained. To ensure the normal performance of the antenna, the height h of the entire antenna must be greater than the total height Z of the front and rear parabolic cable network. A +Z B ; h min =Z A +Z B =0.194+0.062=0.256; h max =Hl=H-2Rsin(π / 2n).

8. The unfolding truss mechanism according to claim 7, characterized in that: The height of the space scissor-type truss satellite antenna structure increases during the folding process. The folded height and the original truss height h in the fully deployed state are determined by the inner and outer ring connecting rods S, which can be written as: H1 = H2 = H3 = h + Ssinθ; The relationship between S and small l, S = 2lsin(π / n); The folding ratio of the deployable and foldable antenna should be greater than 4, hmax ≥ hmin, which can be expressed as: H-2Rsin(π / 2n) ≥ 0.256; The lower bound of n can be calculated as: 0.95-5sin(π / 2n)≥0.256; It can be obtained that n≥11.28, therefore, the number of inner ring edges n of the closed-loop expandable truss must be greater than or equal to 12; The natural frequency changes with the value of n; for components with different cross sections, the percentage increase of the natural frequency f1 is always less than 5%; since increasing the number of sides of the outer ring cross bar of the spatial scissors-type truss satellite antenna structure will lead to a more complex truss, and the increase in the natural frequency f1 is very small (less than 5%), the number of sides of the inner ring cross bar n is selected to be 12; once again proving the rationality of n taking 12.

9. A control method for unfolding a truss mechanism, characterized in that: The method comprises the movement steps obtained by using the unfolding truss mechanism described in any one of claims 1 to 8 to realize the unfolding and contraction of the truss.

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