Rigidity-adjustable multi-tooth mechanical metamaterial and preparation method and application thereof

Abstract

The invention discloses a rigidity-adjustable multi-tooth mechanical metamaterial and a preparation method and application thereof. The invention belongs to the field of mechanical metamaterials. The defects of an existing fixed-rigidity structure are overcome. The metamaterial unit cell is formed by assembling an inner barrel and an outer barrel. The variable-stiffness shell is a main bearing structure of the inner barrel and the outer barrel, in order to facilitate assembly of the unit cells, a first limiting ring, a second limiting ring and a limiting block are designed on the inner barrel and the outer barrel correspondingly, and the first limiting ring and the second limiting ring play a role in clamping when the adjacent unit cells are connected, so that the different unit cells are prevented from being disengaged. The limiting blocks play a role in transmitting loads between the adjacent unit cells. The inner barrel and the outer barrel of the unit cell rotate relatively, so that the fan-shaped teeth with different sizes and specifications are in contact with each other, and the rigidity adjustment of the metamaterial is realized. The multi-tooth mechanical metamaterial provided by the invention can be used for joint transmission of flexible robots, self-adaptive adjustment of mechanical arms and manufacturing of undercarriages of airplanes.

Description

Technical Field

[0001] The present invention belongs to the field of mechanical metamaterials, and in particular relates to a multi-tooth mechanical metamaterial with adjustable stiffness, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of modern engineering technology, traditional fixed stiffness structures are difficult to meet the requirements of high performance, multi-function and dynamic adaptation. As an innovative structural design concept, variable stiffness structure is gradually becoming a research hotspot, showing unique advantages and huge application potential in many fields. In actual engineering applications, the loads borne by the structure are often not single and constant. For example, in the field of aerospace, the magnitude and direction of the loads such as aerodynamic force, gravity, and inertial force borne by the aircraft will change significantly during different stages such as take-off, flight, and landing. Variable stiffness structure can adjust its stiffness characteristics in real time according to different load conditions, increase stiffness when bearing large loads to ensure the strength and stability of the structure, and appropriately reduce stiffness when bearing small loads to avoid stress concentration or other adverse effects caused by excessive rigidity of the structure, thereby improving the reliability and durability of the structure throughout its service life. In addition, in some energy transmission and conversion systems, such as the joint transmission of flexible robots, variable stiffness structure can play a key role. By adjusting the stiffness, the force transmission path and method can be optimized, and the loss and waste of energy during the transmission process can be reduced. For example, a variable stiffness structure is used at the joints of a flexible robot. When performing different action tasks, the joint stiffness is adjusted according to the required force and motion characteristics. This can not only ensure the accuracy and flexibility of the action, but also reduce the consumption of driving energy and improve the overall energy utilization efficiency of the robot. Summary of the invention

[0003] In order to overcome the shortcomings of existing fixed stiffness structures, the present invention provides a multi-tooth mechanical metamaterial with adjustable stiffness, a preparation method and application thereof.

[0004] One of the purposes of the present invention is to provide a multi-tooth mechanical metamaterial with adjustable stiffness, wherein the metamaterial comprises a plurality of unit cells, wherein the unit cells are formed by sleeves of two inner and outer barrel-shaped parts, wherein the inner barrel and the outer barrel are both integral structures;

[0005] The inner barrel comprises a first barrel body, a first variable rigidity shell, a plurality of limiting columns and a first limiting ring, wherein the first variable rigidity shell is located at the bottom of the inner barrel, the limiting columns are evenly distributed on the outer wall of the first barrel body, and the limiting columns are arranged around the outer wall of the barrel top of the first barrel body;

[0006] The outer barrel comprises a second barrel body, a second variable stiffness shell, a plurality of limiting grooves, a second limiting ring and a limiting block, the second variable stiffness shell is arranged at the lower part of the outer barrel, the limiting grooves are evenly distributed on the inner wall of the second barrel body and are adapted to the limiting column, the second limiting is arranged around the inner wall of the second barrel body and is arranged between the second variable stiffness shell and the bottom end of the second barrel body, and the limiting block is arranged around the inner wall of the second barrel body and is arranged between the second limiting ring and the second variable stiffness shell;

[0007] The first variable stiffness shell is composed of an outer circular ring, a circular hole in the center, and an even number of sector teeth between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. The sector teeth and the horizontal plane where the outer circumference of the first variable stiffness shell is located are preset at an angle α, so that the sector teeth are warped toward the outside of the inner barrel. At least one group of adjacent sector teeth has different size specifications. The different size refers to at least one of the central angle θ and the tooth thickness t of the sector teeth.

[0008] The second variable stiffness shell in the unit cell has the same structure as the first variable stiffness shell, and the sector teeth are warped in opposite directions. Specifically: the second variable stiffness shell is composed of an outer circular ring, a circular hole in the center, and an even number of sector teeth between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. The sector teeth and the horizontal plane where the outer circumference of the second variable stiffness shell is located are preset at an angle α, so that the sector teeth are warped inward of the barrel of the outer barrel. At least one group of adjacent sector teeth has different size specifications, and the different sizes refer to at least one of the central angle θ and the tooth thickness t of the sector teeth.

[0009] Further definition, the number of pairs of sector teeth N p ≥2 pairs.

[0010] It is further defined that α=10-30°.

[0011] Further definition: the tooth thickness t of the sector tooth ≤ the ring thickness t B .

[0012] It is further defined that the central angle θ of the sector tooth satisfies 0<θ≤120° / N p .

[0013] Further restricting, when N p When the number of pairs is greater than 2, at least one set of sector teeth thickness t of the first variable stiffness shell and the second variable stiffness shell is the same, and the difference in thickness between the inner and outer sector teeth is between 0.1-0.5 mm.

[0014] It is further defined that a plurality of unit cells are connected in series and are stacked axially, wherein a first limiting ring of one unit cell is matched with a gap formed between a second limiting ring and a limiting block of another unit cell, and an end face of the barrel wall of the first barrel body abuts against a side wall of the limiting block.

[0015] It is further defined that a plurality of unit cells are connected in parallel, the unit cells are tiled, and are limited and fixed by an external mechanism.

[0016] It is further defined that the metamaterial is made of photosensitive resin.

[0017] Further defined, the photosensitive resin includes tough resin materials, biocompatible resins and flexible resins.

[0018] A second object of the present invention is to provide a method for preparing a multi-tooth mechanical metamaterial with adjustable stiffness, wherein:

[0019] The stereolithography method is used to first perform three-dimensional modeling, then slice processing, and finally 3D printing. After printing is completed, secondary curing is performed.

[0020] The third object of the present invention is to provide a method for adjusting the stiffness of the above-mentioned multi-tooth mechanical metamaterial with adjustable stiffness, wherein the method adjusts the stiffness of the metamaterial by causing the inner and outer barrels of the unit cell to rotate relative to each other so that the fan-shaped teeth of different sizes contact each other.

[0021] Further definition, each rotation angle φ is 180° / N p An integer multiple of .

[0022] A fourth object of the present invention is to provide a multi-tooth mechanical metamaterial with adjustable stiffness for use in aerospace vehicles.

[0023] A fifth object of the present invention is to provide a multi-tooth mechanical metamaterial with adjustable stiffness for use in joint transmission and adaptive adjustment of a flexible robot's mechanical arm.

[0024] Compared with the prior art, the present invention has the following significant effects:

[0025] The present invention provides a multi-tooth mechanical metamaterial based on rotation drive, which realizes a wide range of adjustment of structural stiffness. The multi-tooth structural unit cell is assembled by inner and outer barrels. Since the contact between different teeth is small during compression, in order to limit the displacement of the structure, limit columns 1-3 are set on the inner barrel, and limit grooves 2-3 are designed to match the outer barrel. In particular, the limit columns 1-3 and the limit grooves 2-3 can also play a role in precise positioning when the structural stiffness is adjusted by rotation. Among them, the variable stiffness shell is the main bearing structure of the inner barrel and the outer barrel. In order to facilitate the assembly between the unit cells, the first limit ring, the second limit ring and the limit block are respectively designed on the inner barrel and the outer barrel. The function of the first limit ring and the second limit ring is to play a "clamping" role when the adjacent unit cells are connected to prevent the different unit cells from being separated. The limit block plays the role of transmitting the load between adjacent unit cells. By making the inner and outer barrels of the unit cell rotate relative to each other, the fan-shaped teeth of different sizes are brought into contact with each other, so as to realize the stiffness adjustment of the metamaterial. For the number of tooth pairs N p For the variable stiffness shell, the rotation angle φ is 180 / N each time. pAn integer multiple of .

[0026] The present invention realizes the stiffness decoupling of the truncated cone shell structure through structural design, breaking the problem that the performance of the traditional structure is difficult to change after manufacturing, improving the application potential, and providing a possible way to realize the stiffness adaptive structure. The multi-tooth configuration of the present invention has a simple structure and is easy to process, and can be mass-produced through stereolithography molding technology. At the same time, it has excellent adjustable stiffness capabilities, and through reasonable design of geometric dimensions, it can customize the production of structures with specific stiffness changes. In addition, the mechanical metamaterial of the present invention has the advantages of small size, simple structure, light weight, easy assembly, adjustable stiffness, etc., and can well match different working conditions. The multi-tooth mechanical metamaterial proposed in the present invention can be used for joint transmission of flexible robots, adaptive adjustment of mechanical arms, and landing gear of aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of a multi-tooth mechanical metamaterial unit cell with adjustable stiffness according to the present invention;

[0028] Figure 2 for Figure 1 Schematic diagram of the inverted structure of the barrel in a single cell;

[0029] Figure 3 It is an internal schematic diagram of the assembly of the inner and outer barrels of a unit cell of a multi-tooth mechanical metamaterial with adjustable stiffness according to the present invention;

[0030] Figure 4 A top view of the first variable stiffness shell in the multi-tooth mechanical metamaterial unit cell with adjustable stiffness of the present invention;

[0031] Figure 5 It is a front view of the first variable stiffness shell in the multi-tooth mechanical metamaterial unit cell with adjustable stiffness of the present invention;

[0032] Figure 6 A schematic diagram of the structure of two unit cells of the multi-tooth mechanical metamaterial with adjustable stiffness in series according to the present invention;

[0033] Figure 7 for Figure 6 A partial enlarged view of the marked area;

[0034] Figure 8 N in Example 1 p = 2 when the inner and outer barrels of a single unit cell have different relative rotation angles;

[0035] Fig. 9 The two N in series in Example 1 p =2 when the inner and outer barrels of the unit cell have different relative rotation angles;

[0036] Fig.10 The two N in parallel in Example 1 p =2 when the inner and outer barrels of the unit cell have different relative rotation angles;

[0037] Fig.11 In Example 1, N p = 3 for the quasi-static compression response curves of the inner and outer barrels of a single unit cell at different relative rotation angles;

[0038] In the figure, 1-1 is the first barrel body, 1-2 is the first variable stiffness shell, 1-3 is the limiting column, 1-4 is the first limiting ring, 2-1 is the second barrel body, 2-2 is the second variable stiffness shell, 2-3 is the limiting groove, 2-4 is the second limiting ring, 2-5 is the limiting block, 1-2-1 is the outer peripheral ring of the first variable stiffness shell, and 1-2-2 is the fan-shaped tooth of the first variable stiffness shell;

[0039] Figure 8 and Fig.11 The midpoint line is the simulation calculation result, and the area is the experimental test result;

[0040] Fig. 9 and Fig.10 Here, K0L0 means that the relative rotation angle φ of the inner and outer barrels of the two unit cells is 0°, K0L90 means that the relative rotation angle φ of the inner and outer barrels of one unit cell is 0°, and the relative rotation angle φ of the inner and outer barrels of the other unit cell is 90°, and K90L90 means that the relative rotation angle φ of the inner and outer barrels of the two unit cells is 90°. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the 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.

[0042] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0043] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0045] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0046] The terms "comprising," "including," "having," "containing," or any other variations thereof, as used in the following examples, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus comprising the listed elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0047] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0048] The "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0049] The endpoints and any values ​​of the ranges disclosed in the invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0050] Embodiment 1: The multi-tooth mechanical metamaterial with adjustable stiffness in this embodiment includes two unit cells, the unit cell (see Figure 1-3 ) It is composed of two barrel-shaped parts, the inner barrel and the outer barrel, which are both integrated structures;

[0051] Inner barrel (see Figure 1-3 ) includes a first barrel body 1-1, a first variable stiffness shell 1-2, four limiting columns 1-3 and a first limiting ring 1-4, the first variable stiffness shell 1-2 is located at the bottom of the inner barrel, the limiting columns 1-3 are evenly distributed on the outer wall of the first barrel body 1-1, and the limiting ring 1-4 is arranged around the outer wall of the barrel top of the first barrel body 1-1; wherein the inner diameter of the first barrel body 1-1 is 40mm, the outer diameter is 43mm, the height is 47mm, and the length of the limiting column 1-3 is L R1 =25mm;

[0052] The outer barrel includes a second barrel body 2-1, a second variable stiffness shell 2-2, four limiting grooves 2-3, a second limiting ring 2-4 and a limiting block 2-5. The second variable stiffness shell 2-2 is arranged at the lower part of the outer barrel. The limiting grooves 2-3 are evenly distributed on the inner wall of the second barrel body 2-1 and are adapted to the limiting columns 1-3. The second limiting ring 2-4 is arranged around the inner wall of the second barrel body 2-1 and is arranged between the second variable stiffness shell 2-2 and the bottom end of the second barrel body 2-1. The limiting block 2-5 is arranged around the inner wall of the second barrel body 2-1 and is arranged between the second limiting ring 2-4 and the second variable stiffness shell 2-2. Among them, the inner diameter of the second barrel body 2-1 is 44mm, the outer diameter is 47mm, the height is 60mm, the second variable stiffness shell 2-2 is 25mm away from the bottom end of the second barrel body 2-1, and the limiting groove 2-3 is Length L R2 =25mm;

[0053] The first variable stiffness shell 1-2 (see Figure 4-5 ) is composed of an outer circular ring 1-2-1, a circular hole in the center, and four (two pairs) sector teeth 1-2-2 between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. The sector teeth 1-2-2 and the horizontal plane where the outer circumference of the first variable stiffness shell 1-2 are located are preset at an angle α, so that the sector teeth are warped toward the outside of the barrel of the inner barrel. Adjacent sector teeth have different size specifications. The different size refers to at least one of the central angle θ and the tooth thickness t of the sector teeth; wherein the radius R of the first variable stiffness shell 1-2 B1 =40mm, width L of ring 1-2-1 B1 =10mm, thickness t of ring 1-2-1 B1 =3mm, α1 = 20°, number of pairs of sector teeth N p =2 pairs, the dimensions of the two pairs of sector teeth are θ1=30°, t1=1mm, θ2=45°, t2=3mm;

[0054] The second variable stiffness shell 2-2 in the unit cell is symmetrical with the first variable stiffness shell 1-2 along the horizontal plane. Specifically, the second variable stiffness shell 2-2 is composed of an outer circular ring 2-2-1, a circular hole in the center, and four (two pairs) sector teeth 2-2-2 between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. The sector teeth 2-2-2 and the horizontal plane where the outer circumference of the second variable stiffness shell 2-2 is located are preset at an angle α, so that the sector teeth are warped into the barrel of the outer barrel. Adjacent sector teeth have different size specifications, and the different sizes refer to at least one of the central angle θ and the tooth thickness t of the sector teeth; wherein, the radius R of the second variable stiffness shell 2-2 B2 =44mm, width L of ring 2-2-1 B2 =14.2mm, thickness t of ring 2-2-1 B2 =3mm, α2 = 20°, number of sector teeth N p =2 pairs, the dimensions of the two pairs of sector teeth are θ1=30°, t1=1mm, θ2=45°, t2=3mm;

[0055] Combination Figure 6-7 The two unit cells are connected in series and stacked axially, wherein the first limiting ring 1-4 of one unit cell is matched with the gap formed between the second limiting ring 2-4 and the limiting block 2-5 of the other unit cell, and the end face of the barrel wall of the first barrel body 1-1 abuts against the side wall of the limiting block 2-5.

[0056] In the structure of this embodiment, since the contact between different teeth during compression is small, in order to limit the displacement of the structure, the limiting columns 1-3 are set on the inner barrel, and the limiting grooves 2-3 are matched and designed on the outer barrel. In particular, the limiting columns 1-3 and the limiting grooves 2-3 can also play a role in precise positioning when rotating to adjust the rigidity of the structure.

[0057] The variable stiffness shell is the main bearing structure of the inner barrel and the outer barrel. In order to facilitate the assembly between the unit cells, the first limiting ring 1-4, the second limiting ring 2-4 and the limiting block 2-5 are designed on the inner barrel and the outer barrel respectively. The first limiting ring 1-4 and the second limiting ring 2-4 play a "clamping" role when the adjacent unit cells are connected to prevent the separation of different unit cells. The limiting block 2-5 plays the role of transferring the load between the adjacent unit cells.

[0058] By making the inner and outer barrels of the unit cell rotate relative to each other, the sector teeth of different sizes come into contact with each other, thus achieving the stiffness adjustment of the metamaterial. p For the variable stiffness shell, the rotation angle φ is 180 / N each time. p An integer multiple of .

[0059] Preparation method: This embodiment selects green anti-bending photosensitive resin as the substrate, and its elastic modulus is 2136MPa (provided by Beijing EasyPure Technology Co., Ltd.), uses SolidWorks software for accurate three-dimensional modeling, converts the model into an STL format file, and slices it, the slice thickness is 0.2mm, and uses a G6 light-curing printer (purchased from Shenzhen Aurora Elvo Technology Co., Ltd.) for printing and curing. After the curing is completed, the taken out structure is placed in alcohol for cleaning, and the uncured resin remaining on the surface is removed with an ultrasonic cleaning device. In order to further improve the performance and stability of the variable stiffness structure, the printed structure is placed in an oven and secondary cured at 50°C for 30 minutes to make the resin more fully cross-linked and cured, thereby improving the strength and stiffness of the structure.

[0060] In Example 1, N p =2, the quasi-static compression response curves when the inner and outer barrels of a single unit cell are rotated at relative angles of φ = 0° and φ = 90° are as follows: Figure 8 shown.

[0061] In Example 1, two N p = 2 unit cells are connected in series, the inner and outer barrels of the two unit cells rotate relative to each other at an angle of φ = 0° (K0L0); the inner and outer barrels of one unit cell rotate relative to each other at an angle of φ = 0°, and the inner and outer barrels of the other unit cell rotate relative to each other at an angle of φ = 90° (K0L90); the quasi-static compression response curve when the inner and outer barrels of the two unit cells rotate relative to each other at an angle of φ = 90° (K90L90) is as follows Fig. 9 shown.

[0062] Embodiment 2:

[0063] The difference between this embodiment and embodiment 1 is that two unit cells are connected in parallel. Other steps and parameters are the same as those in embodiment 1.

[0064] When two unit cells are tiled in parallel in Example 2, the inner and outer barrels of the two unit cells are rotated at a relative angle of φ = 0° (K0L0); the inner and outer barrels of one unit cell are rotated at a relative angle of φ = 0°, and the inner and outer barrels of the other unit cell are rotated at a relative angle of φ = 90° (K0L90); the quasi-static compression response curve when the inner and outer barrels of the two unit cells are rotated at a relative angle of φ = 90° (K90L90) is as follows: Fig.10 As shown, from Fig. 9 and Fig.10 It can be seen that the series connection will cause the overall stiffness of the system to show a downward trend, while when arranged in parallel, the system stiffness is equal to the sum of the stiffness of each unit cell, which increases with the increase of the number of units. This change law is consistent with the series principle of springs. The multi-tooth mechanical metamaterial with adjustable stiffness proposed in the present invention has broad application potential in the fields of vibration control, industrial manufacturing, and intelligent robots.

[0065] Embodiment 3:

[0066] The difference between this embodiment and embodiment 1 is that: the number of pairs of sector teeth N p =3 pairs, at this time, the sector tooth thickness t of the first variable stiffness shell and the second variable stiffness shell must meet the requirement of at most one set of the same thickness, and the difference in thickness between the inner and outer sector teeth is between 0.1-0.5mm. Specifically: the sector tooth parameters of the inner barrel are: θ1=30°, t1=1mm, θ2=35°, t2=2mm, θ3=35°, t3=3mm. The sector tooth parameters of the outer barrel are: θ1=30°, t1=1mm, θ2=35°, t2=1.5mm, θ3=35°, t3=2.5mm. The other steps and parameters are the same as those in Example 1.

[0067] In Example 3, N p =3, the quasi-static compression response curves of the inner and outer barrels of a single unit cell when the relative rotation angles are φ = 0°, φ = 60° and φ = 120° are as follows: Fig.11 As shown, from Figure 8 and Fig.11 It can be seen from the figure that for different rotation angles φ, as the compression displacement increases, the structure can show different load responses, showing the excellent characteristic of adjustable stiffness. At the same time, the number of stiffness changes that the variable stiffness shell structure with different tooth pairs can show is exactly the same as N p equal.

[0068] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A multi-tooth mechanical metamaterial with adjustable stiffness, characterized in that: The metamaterial comprises a plurality of unit cells, each unit cell being formed by a sleeve of two inner and outer barrel-shaped parts, wherein the inner barrel and the outer barrel are both integral structures; The inner barrel comprises a first barrel body (1-1), a first variable rigidity shell (1-2), a plurality of limiting columns (1-3) and a first limiting ring (1-4); the first variable rigidity shell (1-2) is located at the bottom of the inner barrel, the limiting columns (1-3) are evenly distributed on the outer wall of the first barrel body (1-1), and the limiting ring (1-4) is arranged around the outer wall of the barrel top of the first barrel body (1-1); The outer barrel comprises a second barrel body (2-1), a second variable stiffness shell (2-2), a plurality of limiting grooves (2-3), a second limiting ring (2-4) and a limiting block (2-5); the second variable stiffness shell (2-2) is arranged at the lower part of the outer barrel; the limiting grooves (2-3) are evenly distributed on the inner wall of the second barrel body (2-1) and are matched with the limiting pillars (1-3); the second limiting ring (2-4) is arranged around the inner wall of the second barrel body (2-1) and is arranged between the second variable stiffness shell (2-2) and the bottom end of the second barrel body (2-1); and the limiting block (2-5) is arranged around the inner wall of the second barrel body (2-1) and is arranged between the second limiting ring (2-4) and the second variable stiffness shell (2-2); The first variable stiffness shell (1-2) is composed of an outer circular ring (1-2-1), a circular hole in the center, and an even number of sector teeth (1-2-2) between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. A preset angle α is formed between the sector teeth (1-2-2) and a horizontal plane where the outer circumference of the first variable stiffness shell (1-2) is located, so that the sector teeth are warped toward the outside of the inner barrel. At least one group of adjacent sector teeth has different size specifications, and the different size refers to at least one of the central angle θ and the tooth thickness t of the sector teeth. In a unit cell, the second variable stiffness shell (2-2) has the same structure as the first variable stiffness shell (1-2), and the sector teeth are warped in opposite directions.

2. The metamaterial according to claim 1, characterized in that Number of sector teeth N p ≥2 pairs, α=10-30°, the thickness of the sector tooth (1-2-2) t≤ the thickness of the ring (1-2-1) t B , the central angle θ of the sector tooth satisfies 0<θ≤120° / N p .

3. The metamaterial according to claim 1, characterized in that A plurality of unit cells are connected in series and stacked in an axial direction, wherein a first limiting ring (1-4) of one unit cell is matched with a gap formed between a second limiting ring (2-4) and a limiting block (2-5) of another unit cell, and a barrel wall end face of the first barrel body (1-1) abuts against a side wall of the limiting block (2-5).

4. The metamaterial according to claim 1, characterized in that Several unit cells are connected in parallel, the unit cells are laid flat, and are fixed by an external mechanism.

5. The metamaterial according to claim 1, characterized in that: The metamaterial is made of photosensitive resin.

6. The method for preparing the metamaterial according to any one of claims 1 to 5, characterized in that: The method: The stereolithography method is used to first perform three-dimensional modeling, then slice processing, and finally 3D printing. After printing is completed, secondary curing is performed.

7. The method for adjusting the stiffness of a metamaterial according to any one of claims 1 to 5, characterized in that: The method achieves stiffness adjustment of the metamaterial by making the inner and outer barrels of the unit cell rotate relative to each other so that sector teeth of different sizes come into contact with each other.

8. The method according to claim 7, characterized in that The rotation angle φ of each rotation is 180° / N p An integer multiple of .

9. Use of the metamaterial according to any one of claims 1 to 5 in aerospace vehicles.

10. Application of the metamaterial according to any one of claims 1 to 5 in joint transmission and adaptive adjustment of a flexible robot's mechanical arm.

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