A variable stiffness unit, variable stiffness metamaterial and mechanical metamaterial

Abstract

A variable stiffness unit, a variable stiffness metamaterial and a mechanical metamaterial belong to the fields of mechanical engineering, mechanics, vibration and noise control, and aerospace. The variable stiffness unit includes a residual cantilever, a central axis, a cantilever and a crossbeam. The crossbeam is symmetrically arranged on the side wall of the central axis. The cantilever and the residual cantilever are arranged around the periphery of the central axis by embracing, and the cantilever and the residual cantilever are arranged in a central symmetrical manner. Gear teeth are processed on the outer side walls of the cantilever and the residual cantilever. The variable stiffness metamaterial includes a plurality of the variable stiffness units, and each of the variable stiffness units is distributed in a periodic array, adjacent variable stiffness units are arranged chirally, and each column of two longitudinally adjacent variable stiffness units is closely matched. The mechanical metamaterial includes a compression module and a tension module both of which apply the variable stiffness metamaterial. The present invention proposes a mechanical metamaterial with a large range of continuously adjustable stiffness under tensile and compressive loads, which has the characteristics of continuous and large range adjustment of stiffness under tensile loads or compressive loads, simple structural drive, and is conducive to integrated manufacturing.

Description

Technical Field

[0001] The invention relates to the fields of mechanical engineering, mechanics, vibration and noise control, and aerospace, and in particular to a mechanical metamaterial with continuously adjustable stiffness over a wide range under tensile and compressive loads. Background Art

[0002] Mechanical metamaterials with variable stiffness are of great significance in the fields of collaborative robots, aerospace, and vibration and noise control. For example, in the field of collaborative robots, mechanical metamaterials with variable stiffness can meet the contradiction between performance and safety. In the field of aerospace, the engine mount system made of mechanical metamaterials with variable stiffness can enable the aircraft to maintain optimal performance and efficiency at different flight stages. In the field of vibration and noise control, semi-active vibration isolators / absorbers made of mechanical metamaterials with variable stiffness can avoid / maintain the resonant frequency and improve vibration isolation and vibration absorption capabilities. However, traditional magnetorheological materials, shape memory materials, etc. have many disadvantages such as slow response speed and small adjustment range, and are difficult to be effectively applied.

[0003] The existing patent publication number CN114519236A, "A gear mechanical metamaterial with continuously adjustable elastic parameters over a wide range", discloses a mechanical metamaterial that uses a gear array to achieve smooth and continuous adjustment of elastic parameters. It has the advantages of continuous stiffness adjustment, a large adjustment range, and strong robustness, but is restricted by the frame connection and can only achieve stiffness adjustment under compressive loads.

[0004] Therefore, it is urgent to propose a mechanical metamaterial with continuously adjustable stiffness over a wide range under tensile and compressive loads to solve the above technical problems. Summary of the invention

[0005] The present invention aims to propose a mechanical metamaterial with a large range of continuously adjustable stiffness under tensile or compressive loads, which has the characteristics of continuous and large range adjustment of stiffness under tensile or compressive loads, simple structure drive, and is conducive to integrated manufacturing. A brief overview of the present invention is given below to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to determine the key or important parts of the present invention, nor is it intended to limit the scope of the present invention.

[0006] The technical solution of the present invention:

[0007] Solution 1: A variable stiffness unit includes a residual cantilever, a central axis, a cantilever and a cross beam. A central hole is processed on the central axis, and cross beams are symmetrically arranged on the side walls of the central axis. The cantilever and the residual cantilever are arranged on the periphery of the central axis by embracing, and the cantilever and the residual cantilever are arranged in a centrally symmetrical manner. Gear teeth are processed on the outer side walls of the cantilever and the residual cantilever.

[0008] Preferably: the cantilever extends from the beam at an angle greater than 90 degrees;

[0009] The excess cantilever extends from the crossbeam at an angle of less than 90 degrees;

[0010] A spare gap is left between the cantilever and the excess cantilever.

[0011] Preferably, the number of the gear teeth is set to an odd number, and it is ensured that the intersection of the center line of the crossbeam and the gear teeth is the tooth top and tooth root of the gear teeth respectively.

[0012] Solution 2: A variable stiffness metamaterial comprises a plurality of variable stiffness units as described in Solution 1, wherein the variable stiffness units are distributed in a periodic array, adjacent variable stiffness units are chirally arranged, and two longitudinally adjacent variable stiffness units in each column are tightly matched, and motion is transmitted through the gear teeth of the variable stiffness units.

[0013] Preferably, in the variable stiffness units in the bottom row, each variable stiffness unit is coaxially mounted with a transmission gear, and two adjacent transmission gears are tightly meshed.

[0014] Solution 3, a mechanical metamaterial, characterized in that it includes a compression module, the compression module includes a compression cover, a first limit screw, a first screw shaft, a motor bracket, a first worm gear reduction motor, a first U-shaped frame, a first long screw shaft, a first motor connecting screw, a first hexagonal thin nut, a first hexagonal nut, a first coupling and the variable stiffness metamaterial described in Solution 2, the variable stiffness metamaterial is arranged in the first U-shaped frame, a plurality of first sliding grooves penetrating the first U-shaped frame are opened, a first screw shaft is slidably arranged in the first sliding groove, and the front and rear sides of the middle part of the variable stiffness metamaterial are fixedly installed on the first screw shaft through the first hexagonal thin nut, the compression cover is buckled on the top of the first U-shaped frame, and the variable stiffness metamaterial The front and rear sides of the top are fixedly installed on the first long screw shaft through the first hexagonal thin nut, and the bottom surface of the compression cover is in contact with the first long screw shaft. A through stretching limit groove is processed on the compression cover. The first limit screw passes through the first stretching limit screw hole on the first U-shaped frame and cooperates with the first hexagonal nut. The end of the first limit screw and the first hexagonal nut cooperating therewith are both slidably installed in the stretching limit groove. The first worm gear reduction motor is installed on the outside of the first U-shaped frame through the motor bracket. One side of the first motor connecting screw is connected to the output end of the first worm gear reduction motor through the first coupling, and the other side of the first motor connecting screw establishes a coaxial transmission connection with any one of the transmission gears of the lowest row of variable stiffness units.

[0015] Preferably: it also includes a stretching module, which includes a stretching cover, a second limit screw, a second screw shaft, a high motor bracket, a second worm gear reduction motor, a second U-shaped frame, a second long screw shaft, a second motor connecting screw, a second hexagonal thin nut, a second hexagonal nut, a second coupling and the variable stiffness metamaterial described in Scheme 2, the variable stiffness metamaterial is arranged in the second U-shaped frame, a plurality of penetrating second sliding grooves are opened on the second U-shaped frame, a second screw shaft is slidably arranged in the second sliding groove, and the front and rear sides of the middle part of the variable stiffness metamaterial are fixedly installed on the second screw shaft through the second hexagonal thin nut, the stretching cover is buckled on the outside of the second U-shaped frame from the bottom, a penetrating screw shaft sliding groove is processed on the stretching cover, the screw shaft sliding groove is aligned with the second sliding groove, and the front and rear sides of the top of the variable stiffness metamaterial are fixedly installed through the second hexagonal thin nut Installed on the second long screw shaft, the stretching cover contacts the second long screw shaft through the screw shaft slide groove, and the load on the stretching cover is transmitted to the variable stiffness metamaterial connected to the second long screw shaft. A through compression limit groove is processed on the stretching cover. The second limit screw passes through the first compression limit screw hole on the second U-shaped frame and cooperates with the second hexagonal nut. The end of the second limit screw and the second hexagonal nut matched with it are both slidably installed in the compression limit groove in the stretching limit groove. A motor bracket slide groove is processed on the stretching cover. The high motor bracket foot of the high motor bracket passes through the motor bracket slide groove and is fixedly connected to the outside of the second U-shaped frame. One side of the second motor connecting screw is connected to the output end of the second worm gear reduction motor through the second coupling, and the other side of the second motor connecting screw establishes a coaxial transmission connection with any one of the transmission gears of the bottom row of variable stiffness units.

[0016] Preferably, the compression module and the tension module are fixedly connected.

[0017] The present invention has the following beneficial effects:

[0018] 1. The variable stiffness unit of the present invention is cleverly designed, and different variants thereof have different angle-stiffness variation curves, thereby adapting to the stiffness requirements in complex environments;

[0019] 2. The rotation of any variable stiffness unit in a variable stiffness metamaterial of the present invention can cause all variable stiffness units to rotate, thereby realizing the change of the overall stiffness of the mechanical metamaterial, and ensuring that any variable stiffness unit can reach the maximum stiffness state, which is conducive to integrated manufacturing;

[0020] 3. A mechanical metamaterial of the present invention utilizes a worm gear reduction motor to drive all variable stiffness units to rotate synchronously to produce stiffness changes. Compared with traditional variable stiffness units, it has the advantages of a wide range of stiffness and continuous changes, a simple structure drive, and is conducive to integrated manufacturing;

[0021] 4. A mechanical metamaterial of the present invention provides a compression module and a tension module, which can be assembled and used in a modular manner to adapt to the stiffness requirements in different environments, and has the ability to change stiffness under tensile loads and compressive loads when used in connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a variable stiffness unit of the present invention;

[0023] Figure 2 1 is an axonometric diagram of different variants of the variable stiffness unit described in the first embodiment, wherein (a), (b), (c), and (d) are dimensional forms of four different variants of the variable stiffness unit as examples;

[0024] Figure 3 It is a schematic structural diagram of a variable stiffness metamaterial of the present invention;

[0025] Figure 4 It is a front view of a compression module in a mechanical metamaterial of the present invention;

[0026] Figure 5 yes Figure 4 II section view;

[0027] Figure 6 yes Figure 4 GG profile diagram;

[0028] Figure 7 is a stereogram of a stretching module in a mechanical metamaterial of the present invention;

[0029] Figure 8 It is a front view of a stretching module in a mechanical metamaterial of the present invention;

[0030] Fig. 9 yes Figure 8 EE profile of

[0031] Fig.10 yes Figure 8 FF cross-section diagram;

[0032] Fig.11 This is a diagram of the coordinated installation of a compression module and a tension module in a mechanical metamaterial of the present invention.

[0033] In the figure, 1-variable stiffness unit, 101-residual cantilever, 102-center hole, 103-cantilever, 104-crossbeam, 105-center axis, 2-transmission gear;

[0034] 3-compression cover, 301-stretching limit groove, 4-first limit screw, 5-first screw shaft, 6-motor bracket, 7-first worm gear reduction motor, 8-first U-shaped frame, 801-first sliding groove, 802-first stretching limit screw hole, 803-first compression limit screw hole, 9-first long screw shaft, 901-first motor connecting screw shaft, 10-first hexagonal thin nut, 1001-first hexagonal nut, 11-first coupling;

[0035] 12-high motor bracket, 1201-high motor bracket foot, 13-stretching cover, 1301-motor bracket slide, 1302-compression limit groove, 1303-screw shaft slide, 14-compression module, 15-stretching module, 16-second limit screw, 17-second screw shaft, 18-second worm gear reduction motor, 19-second U-shaped frame, 1901-second sliding groove, 20-second long screw shaft, 2001-second motor connecting screw, 21-second hexagonal thin nut, 2101-second hexagonal nut, 22-second coupling. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described below by the specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0037] The connection mentioned in the present invention is divided into fixed connection and detachable connection. The fixed connection is a non-detachable connection including but not limited to conventional fixed connection methods such as folding connection, rivet connection, bonding connection and welding connection. The detachable connection includes but not limited to conventional detachable methods such as threaded connection, snap connection, pin connection and hinge connection. When the specific connection method is not clearly defined, it is assumed that at least one connection method can always be found in the existing connection methods to achieve the function. Those skilled in the art can choose according to their needs. For example: a fixed connection is selected as a welding connection, and a detachable connection is selected as a hinge connection.

[0038] Specific implementation method 1: Combination Figure 1-Figure 2 To illustrate the present embodiment, a variable stiffness unit of the present embodiment includes a residual cantilever 101, a central axis 105, a cantilever 103 and a cross beam 104, a central axis 105 is processed with a central hole 102, a side wall of the central axis 105 is symmetrically provided with cross beams 104, the cantilever 103 and the residual cantilever 101 are arranged on the periphery of the central axis 105 by means of 104, and the cantilever 103 and the residual cantilever 101 are centrally symmetrically provided, and gear teeth are processed on the outer side walls of the cantilever 103 and the residual cantilever 101.

[0039] The cantilever 103 cantilevers out from the beam 104 at an angle greater than 90 degrees;

[0040] The excess cantilever 101 is cantilevered from the crossbeam 104 at an angle less than 90 degrees; a gap is left between the cantilever 103 and the excess cantilever 101 .

[0041] The surplus cantilever 101, the central axis 105, the cantilever 103 and the cross beam 104 are similar to an "S shape" as a whole. A variable stiffness unit 1 of this embodiment can also be referred to as an S gear.

[0042] When the cantilever 103 rotates with the center hole 102 as the rotation center, that is, by rotating the S gear, the force acting on the cantilever 103 and the angle between the beam 104 change continuously. According to the Cartesian theorem, the cantilever curved beam stiffness is:

[0043]

[0044] Since a variable stiffness unit 1 includes two cantilevers 103 and two residual cantilevers 101, the stiffness of the variable stiffness unit 1 is:

[0045] k=k arm / 2

[0046] Wherein, E is the Young's modulus of the material, I is the equivalent section inertia moment of the cantilever 103, R is the equivalent radius of the cantilever 103, and θ is a continuous angle change from 0 to 90°, so the stiffness of the variable stiffness unit 1 will continuously change with the continuous change of the angle.

[0047] Furthermore, when the gear module and pitch circle diameter of the gear teeth are determined, the influence of the gear teeth on the stiffness of the variable stiffness unit 1 can be reduced by increasing the number of gear teeth.

[0048] When the central hole 102 is used as the rotation center, the rotation angle is 90°, that is, Figure 1 , Figure 3 In the angle state shown, the variable stiffness unit 1 is infinitely stiff according to the Cartesian theorem. In practice, the cross beam 104 is compressed and deformed less than the cantilever 103 is bent, and the stiffness of the cross beam 104 under compression is related to the length l of the cross beam 104, the cross-sectional area A of the cross beam 104 and the Young's modulus E of the material. Therefore, when rotating from 0° to 90°, the stiffness will change over a wide range.

[0049] The number of the gear teeth is set to an odd number, and ensures that the intersection of the center line of the beam 104 and the gear teeth is the tooth top and tooth root of the gear teeth respectively. The purpose of such design is that when a variable stiffness unit 1 of this embodiment is used in groups, the variable stiffness units 1 are coupled through the gear teeth, so that the variable stiffness unit 1 can rotate to 90° to achieve the maximum stiffness state.

[0050] The angle area with a spare gap between the cantilever 103 and the surplus cantilever 101 is set as a dead zone D. The size of the dead zone D is related to the angle range of the cantilever 103 and the surplus cantilever 101. Within the angle range of the dead zone D, the variable stiffness unit 1 cannot be coupled through the gear teeth, which is prone to hazards such as incorrect meshing and gear tooth disengagement. The angle range of the cantilever 103 extending from the beam 104 greater than 90 degrees and the angle range of the surplus cantilever 101 extending from the beam 104 are set as the surplus of the variable stiffness unit 1. The effective working range of the variable stiffness unit 1 is 0~90°, thereby preventing the variable stiffness unit 1 from rotating to the dead zone D range.

[0051] A variable stiffness unit 1 of this embodiment can have different variations by changing the width b, thickness h, width b and thickness h, etc. Since the section inertia moment is related to the width b and thickness h, changing the width b or thickness h can change the equivalent section inertia moment of the cantilever 103, so that the variable stiffness unit 1 has different angle-stiffness change curves, thereby adapting to the stiffness requirements in complex environments, such as Figure 2 As shown, it is an axonometric view of variable stiffness units 1 of different shapes, among which (a), (b) (c) and (d) are 4 different dimensional forms of variable stiffness units 1 as examples.

[0052] The excess cantilever 101, the central axis 105, the cantilever 103 and the crossbeam 104 can be integrally formed, that is, they can be manufactured by laser cutting, wire cutting and other methods; they can be manufactured by machining after casting; they can also be manufactured by powder metallurgy, additive manufacturing and other methods. They are highly feasible and easy to manufacture.

[0053] Specific implementation method 2: Combination Figure 1-Figure 3 This embodiment is described. Based on a variable stiffness unit described in specific embodiment 1, a variable stiffness metamaterial of this embodiment comprises a plurality of variable stiffness units 1 as described in any one of claims 1 to 4, and each of the variable stiffness units 1 is distributed in a periodic array, adjacent variable stiffness units 1 are chirally arranged, the installation angle and front and back sides of every other variable stiffness unit 1 are the same, the up and down directions of all variable stiffness units 1 are the same, and the two longitudinally adjacent variable stiffness units 1 in each column are tightly matched, that is, the variable stiffness units 1 are meshed through gear teeth, and the motion is transmitted through the gear teeth.

[0054] Figure 3 The state shown is the maximum stiffness state. Each variable stiffness unit 1 has two sides, front and back, and two directions, up and down. The sides with dead zone D at the upper left and lower right corners of the variable stiffness unit 1 are defined as the front side, and the direction where the center line of the crossbeam 104 intersects with the gear teeth as the tooth root is defined as the upper side. According to Embodiment 1, in order to ensure that the variable stiffness unit 1 can reach the maximum stiffness state, the up and down directions of all variable stiffness units 1 must be the same.

[0055] The variable stiffness units 1 in the upper and lower adjacent rows are coupled through the gear teeth of the S gear itself to transmit the load power. Since the variable stiffness units 1 in the left and right adjacent columns cannot be transmitted through the S gear due to the dead zone D, they are transmitted through the transmission gear 2 coaxially connected to the S gear. Therefore, the adjacent variable stiffness units 1 are arranged in a chiral manner, that is, the front and back sides of every other variable stiffness unit 1 in the horizontal direction (or vertical direction) in the variable stiffness unit 1 array are the same, and the up and down directions of all variable stiffness units 1 are the same, so that any variable stiffness unit 1 in the rotating mechanical metamaterial can cause all variable stiffness units 1 to rotate, thereby realizing the overall stiffness change of the mechanical metamaterial.

[0056] In the variable stiffness units 1 in the bottom row, each variable stiffness unit 1 is coaxially mounted with a transmission gear 2, and two adjacent transmission gears 2 are tightly meshed.

[0057] Specific implementation method three: Combination Figure 1-Figure 11 This embodiment is described, based on a variable stiffness metamaterial described in Specific Embodiment 2, a mechanical metamaterial of this embodiment: includes a compression module 14, the compression module 14 includes a compression cover 3, a first limit screw 4, a first screw shaft 5, a motor bracket 6, a first worm gear reduction motor 7, a first U-shaped frame 8, a first long screw shaft 9, a first motor connecting screw 901, a first hexagonal thin nut 10, a first coupling 11, a first hexagonal nut 1001, and the variable stiffness metamaterial described in claim 6;

[0058] A variable stiffness metamaterial is arranged in the first U-shaped frame 8, and a plurality of first sliding grooves 801 are provided on the first U-shaped frame 8. A first screw shaft 5 is slidably arranged in the first sliding groove 801, and the front and rear sides of the middle part of the variable stiffness metamaterial are fixedly mounted on the first screw shaft 5 through a first hexagonal thin nut 10. The compression cover 3 is buckled on the top of the first U-shaped frame 8, and the front and rear sides of the top of the variable stiffness metamaterial are fixedly mounted on the first long screw shaft 9 through the first hexagonal thin nut 10, and the bottom surface of the compression cover 3 is in contact with the first long screw shaft 9. A through stretching limit groove 301 is processed on the compression cover 3, and the first limit screw 4 passes through the first stretching limit screw hole 802 on the first U-shaped frame 8 and then cooperates with the first hexagonal nut 1001, and the end of the first limit screw 4 and the first hexagonal nut 1001 cooperating therewith are both slidably mounted In the stretching limit groove 301, the first worm gear reduction motor 7 is fixedly installed on the outside of the first U-shaped frame 8 through the motor bracket 6 and screws. One side of the first motor connecting screw 901 is connected to the output end of the first worm gear reduction motor 7 through the first coupling 11, and the other side of the first motor connecting screw 901 establishes a coaxial transmission connection with any one of the transmission gears 2 of the bottom row of variable stiffness units 1. The bottom row of variable stiffness units 1 and the coaxially connected transmission gear 2 are axially separated by a first hexagonal thin nut 10 to prevent the transmission gear 2 from interfering with the movement of the variable stiffness metamaterial. The first long screw shaft 9 in contact with the compression cover 3 and the first motor connecting screw shaft 901 connected to the first worm gear reduction motor 7 are slightly longer than the first screw shaft 5, and transmit load and power through the part extending out of the first U-shaped frame 8.

[0059] The variable stiffness unit 1 of the variable stiffness metamaterial and the first screw shaft 5, the first long screw shaft 9, and the first motor connection screw shaft 901 are all interference fit through the center hole 102, and the axial positioning and locking of the variable stiffness metamaterial are achieved through the first hexagonal thin nuts 10 on both sides of the screw shaft. There is an appropriate spacing between the first hexagonal thin nut 10 and the inner wall of the first U-shaped frame 8, so as to prevent the axial positioning of the variable stiffness metamaterial from being inaccurate due to the large spacing, and to prevent the rotation damping of the variable stiffness metamaterial from being too large due to the small spacing, resulting in jamming.

[0060] like Figure 4 As shown, the compression cover 3 is located above the first U-shaped frame 8 and partially overlaps with the first U-shaped frame 8 in the height direction, and the bottom of the compression cover 3 contacts the first long screw shaft 9. In the width direction, the compression cover 3 and the first U-shaped frame 8 are clearance-matched. It is worth noting that the upper inner wall of the compression cover 3 and the upper wall of the first U-shaped frame 8 should have a distance that satisfies the maximum compression deformation of all variable stiffness units 1, so as to prevent the upper inner wall of the compression cover 3 from contacting the upper wall of the first U-shaped frame 8.

[0061] The compression cover 3 is provided with a plurality of stretching limit grooves 301, which are located on the symmetry line of two adjacent columns of variable stiffness units 1. The upper part of the first U-shaped frame 8 is provided with a plurality of first stretching limit screw holes 802, which are located on the upper part of the first U-shaped frame 8 and on the symmetry line of two adjacent columns of variable stiffness units 1, so as to avoid interference between the variable stiffness units 1 and the first limit screws 4. The width of the stretching limit groove 301 is the same as the diameter of the screw head, and the length of the stretching limit groove 301 is greater than the distance that satisfies the maximum compression deformation of all variable stiffness units 1. The first limit screw 4 is preferably a cylindrical head hexagon socket screw, which passes through the stretching limit groove 301 and the first stretching limit screw hole 802 and is connected to the first U-shaped frame 8 with the first hexagonal nut 1001 on the other side. The screw head of the first limit screw 4 and the first hexagonal nut 1001 are located in the tensile limit groove 301 to hinder the compression cover 3 from moving along the positive direction of the y-axis, so that it can only move along the negative direction of the y-axis. Therefore, the stiffness of the compression module 14 under the tensile load is theoretically infinite, and under the compressive load, only the compression module 14 plays a role of variable stiffness.

[0062] It is worth noting that the first limit screws 4 and the first hexagonal nuts 1001 are arranged in an alternating and opposite manner. Figure 4 As shown, the screw head and the first hexagonal nut 1001 are alternately located on the front. The width dimension of the stretching limit groove 301 is the same as the diameter of the screw head. The first hexagonal nut 1001 is subject to the size limitation of the stretching limit groove 301, and the two diagonals are always located at the upper and lower sides. The hexagonal side length of the first hexagonal nut 1001 is larger than the radius of the cylindrical head of the screw, which will generate a downward pre-tightening force on the compression cover 3, thereby generating a certain degree of pre-tightening on all the variable stiffness units 1, preventing the variable stiffness units 1 from moving along the first sliding groove 801 and causing incorrect engagement between the variable stiffness units 1.

[0063] A mechanical metamaterial of this embodiment further includes a stretching module 15, the stretching module 15 includes a stretching cover 13, a second limit screw 16, a second screw shaft 17, a high motor bracket 12, a second worm gear reduction motor 18, a second U-shaped frame 19, a second long screw shaft 20, a second motor connecting screw 2001, a second hexagonal thin nut 21, a second coupling 22, a second hexagonal nut 2101, and the variable stiffness metamaterial according to claim 6;

[0064] The second U-shaped frame 19 is provided with a variable stiffness metamaterial, and a plurality of second sliding grooves 1901 are provided on the second U-shaped frame 19, and a second screw shaft 17 is slidably provided in the second sliding groove 1901, and the front and rear sides of the middle part of the variable stiffness metamaterial are fixedly mounted on the second screw shaft 17 through a second hexagonal thin nut 21, and the front and rear sides of the top of the variable stiffness metamaterial are fixedly mounted on the second long screw shaft 20 through a second hexagonal thin nut 21, and a through compression limit groove 1302 is processed on the stretching cover 13, and the second limit screw 16 passes through the first compression limit screw hole 803 on the second U-shaped frame 19 and is fixed with the second hexagonal nut 2101 In cooperation, the end of the second limit screw 16 and the second hexagonal nut 2101 matched therewith are both slidably installed in the compression limit groove 1302 in the stretching limit groove, and a motor bracket slide groove 1301 is processed on the stretching cover 13. The high motor bracket foot 1201 of the high motor bracket 12 passes through the motor bracket slide groove 1301 and is fixedly connected to the outer side of the second U-shaped frame 19 by screws. One side of the second motor connecting screw 2001 is connected to the output end of the second worm gear reduction motor 18 through the second coupling 22, and the other side of the second motor connecting screw 2001 establishes a coaxial transmission connection with any one of the transmission gears 2 of the bottom row of variable stiffness units 1.

[0065] like Fig. 9 As shown, the stretching cover 13 is buckled on the outside of the second U-shaped frame 19 from the bottom, and is gap-matched with the second U-shaped frame 19 in the width direction. The stretching cover 13 is provided with a plurality of screw shaft sliding grooves 1303 that overlap with the second sliding grooves 1901 but have a width greater than the diameter of the screw head. The stretching cover 13 contacts the second long screw shaft 20 through the screw shaft sliding grooves 1303, and the load on the stretching cover 13 is transmitted to the variable stiffness unit 1 connected to the second long screw shaft 20.

[0066] The stretching cover 13 is provided with a plurality of compression limit grooves 1302, which have the same shape and size as the screw shaft slide grooves 1303 and are located on the symmetry line of two adjacent rows of variable stiffness units 1. The middle part of the second U-shaped frame 19 is provided with a plurality of compression limit screw holes 803, which are located in the middle of the four adjacent variable stiffness units 1 to avoid the second limit screw 16 from interfering with the variable stiffness unit 1. The second limit screw 16 passes through the compression limit groove 1302 and the compression limit screw hole 803 and is connected to the second U-shaped frame 19 with the second hexagonal nut 2101 on the other side, wherein the compression limit groove 1302 has the same function as the stretching limit groove 301, that is, the screw head of the second limit screw 16 and the second hexagonal nut 2101 are in the compression limit groove 1302, hindering the stretching cover 13 from moving along the positive direction of the y-axis, so that it can only move along the negative direction of the y-axis, so that the stiffness of the stretching module 15 under the compression load is theoretically infinite, and under the tensile load, only the stretching module 15 plays a role of variable stiffness.

[0067] It is worth noting that, similar to the compression module 14, the second limit screw 16 and the second hexagonal nut 2101 matched therewith are arranged in an alternating opposite manner. The second hexagonal nut 2101 also pre-tightens all the variable stiffness units 1 to prevent incorrect engagement between the variable stiffness units 1. The first worm gear reduction motor 7 and the second worm gear reduction motor 18 have a large reduction ratio and self-locking characteristics, and can output a large torque to rotate the variable stiffness unit 1, and after the stiffness change is completed, no additional driving force is required to maintain the current stiffness.

[0068] The compression module 14 and the tension module 15 are fixedly connected, and the fixed connection form can be bonding, welding, bolt connection, etc. A wide range and continuous adjustment of the stiffness under tension and compression loads can be achieved to meet the stiffness requirements under different working conditions. The compression module 14 and the tension module 15 can also be used separately according to different environments.

[0069] A mechanical metamaterial in this embodiment has the following working principle:

[0070] Under the compressive load, the load is applied to the bottom of the compression cover 3 and the stretching cover 13, and the compression cover 3 applies a negative force along the y-axis to the first long screw shaft 9, so that each column of variable stiffness units 1 moves along the first sliding groove 801 and squeezes each other. Since the stiffness of the stretching module 15 is close to infinity when compressed, the stiffness of the mechanical metamaterial depends only on the angle of the variable stiffness unit 1 in the compression module 14. The first worm gear reduction motor 7 drives the variable stiffness unit 1 in the compression module 14 to rotate the same angle, so that the continuous large-range adjustment of the stiffness under the compressive load can be achieved.

[0071] Similar to the compressive load, the tensile load is applied to the bottom of the compression cover 3 and the tensile cover 13. The tensile cover 13 applies a negative force along the y-axis to the second long screw shaft 20, so that each column of variable stiffness units 1 moves along the second sliding groove 1901 and squeezes each other. Since the stiffness of the compression module 14 is close to infinity when stretched, the stiffness of the mechanical metamaterial depends only on the angle of the variable stiffness unit 1 in the tensile module 15. The second worm gear motor 18 drives the variable stiffness unit 1 in the tensile module 15 to rotate the same angle, which can achieve continuous large-range adjustment of stiffness under tensile load.

[0072] It is worth noting that when the compression module 14 and the tension module 15 are bonded together, the stiffness can be adjusted independently under the compression load and the tension load. There are three different states: the compression stiffness is greater than the tension stiffness, the compression stiffness is equal to the tension stiffness, and the compression stiffness is less than the tension stiffness. In addition, in the case where only the stiffness under the compression / tension load is required, the compression module 14 / tension module 15 can be used separately.

[0073] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be arranged and combined, and those skilled in the art can exhaust all possibilities based on the mathematical knowledge of arrangement and combination. Therefore, the present invention will no longer describe the technical solutions after arrangement and combination one by one, but it should be understood that the technical solutions after arrangement and combination have been disclosed by the present invention.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A variable stiffness unit, characterized in that: The invention comprises a surplus cantilever (101), a central axis (105), a cantilever (103) and a crossbeam (104); a central hole (102) is processed on the central axis (105); a crossbeam (104) is symmetrically arranged on the side wall of the central axis (105); the cantilever (103) and the surplus cantilever (101) are arranged around the periphery of the central axis (105) through the crossbeam (104); the cantilever (103) and the surplus cantilever (101) are arranged in a centrally symmetrical manner; gear teeth are processed on the outer side walls of the cantilever (103) and the surplus cantilever (101); and the cantilever (103) and the surplus cantilever (101) are overhung at an angle greater than 90 degrees from the crossbeam (104); The excess cantilever (101) is cantilevered from the crossbeam (104) at an angle of less than 90 degrees; A spare gap is left between the cantilever (103) and the remaining cantilever (101).

2. A variable stiffness unit according to claim 1, characterized in that: The number of the gear teeth is set to an odd number, and it is ensured that the intersection point between the center line of the crossbeam (104) and the gear teeth is the tooth top and tooth root of the gear teeth respectively.

3. A variable stiffness metamaterial, characterized in that: It comprises a plurality of variable stiffness units (1) as claimed in claim 1 or 2, and each of the variable stiffness units (1) is distributed in a periodic array, adjacent variable stiffness units (1) are arranged chirally, and two longitudinally adjacent variable stiffness units (1) in each column are tightly matched, and motion is transmitted through the gear teeth of the variable stiffness unit (1).

4. The variable stiffness metamaterial according to claim 3, characterized in that: In the variable stiffness units (1) in the bottom row, each variable stiffness unit (1) is coaxially mounted with a transmission gear (2), and two adjacent transmission gears (2) are tightly meshed.

5. A mechanical metamaterial, characterized in that: The invention comprises a compression module (14), wherein the compression module (14) comprises a compression cover (3), a first limit screw (4), a first screw shaft (5), a motor bracket (6), a first worm gear reduction motor (7), a first U-shaped frame (8), a first long screw shaft (9), a first motor connecting screw (901), a first hexagonal thin nut (10), a first hexagonal nut (1001), a first coupling (11), and the variable stiffness metamaterial according to claim 4, wherein the variable stiffness metamaterial is arranged in the first U-shaped frame (8), a plurality of first sliding grooves (801) penetrating the first U-shaped frame (8), a first screw shaft (5) is slidably arranged in the first sliding groove (801), and the front and rear sides of the middle part of the variable stiffness metamaterial are fixedly mounted on the first screw shaft (5) by means of the first hexagonal thin nut (10), the compression cover (3) is buckled on the top of the first U-shaped frame (8), and the front and rear sides of the top of the variable stiffness metamaterial are connected by means of the first A hexagonal thin nut (10) is fixedly mounted on the first long screw shaft (9), and the bottom surface of the compression cover (3) contacts the first long screw shaft (9). A through stretching limit groove (301) is machined on the compression cover (3). The first limit screw (4) passes through the first stretching limit screw hole (802) on the first U-shaped frame (8) and then matches with the first hexagonal nut (1001). The end of the first limit screw (4) and the first hexagonal nut (1001) matched therewith are both slidably mounted in the stretching limit groove (301). The first worm gear reduction motor (7) is mounted on the outside of the first U-shaped frame (8) through the motor bracket (6). One side of the first motor connecting screw (901) is connected to the output end of the first worm gear reduction motor (7) through the first coupling (11), and the other side of the first motor connecting screw (901) establishes a coaxial transmission connection with any one of the transmission gears (2) of the lowest row of variable stiffness units (1).

6. A mechanical metamaterial according to claim 5, characterized in that: The invention also comprises a stretching module (15), wherein the stretching module (15) comprises a stretching cover (13), a second limit screw (16), a second screw shaft (17), a high motor bracket (12), a second worm gear reduction motor (18), a second U-shaped frame (19), a second long screw shaft (20), a second motor connecting screw (2001), a second hexagonal thin nut (21), a second hexagonal nut (2101), a second coupling (22), and the variable stiffness metamaterial according to claim 4, wherein the variable stiffness metamaterial is arranged in the second U-shaped frame (19), and a second U-shaped frame (19) is provided with a A plurality of penetrating second sliding grooves (1901) are provided, a second screw shaft (17) is slidably arranged in the second sliding grooves (1901), and the front and rear sides of the middle part of the variable stiffness metamaterial are fixedly mounted on the second screw shaft (17) through second hexagonal thin nuts (21), the stretching cover (13) is buckled on the outside of the second U-shaped frame (19) from the bottom, a penetrating screw shaft sliding groove (1303) is processed on the stretching cover (13), the screw shaft sliding groove (1303) is aligned with the second sliding groove (1901), and the front and rear sides of the top of the variable stiffness metamaterial are fixedly mounted on the second U-shaped frame (19) through second hexagonal thin nuts (21). On the long screw shaft (20), the stretching cover (13) contacts the second long screw shaft (20) through the screw shaft sliding groove (1303), and the load on the stretching cover (13) is transmitted to the variable stiffness metamaterial connected to the second long screw shaft (20). The stretching cover (13) is processed with a through compression limit groove (1302). The second limit screw (16) passes through the first compression limit screw hole (803) on the second U-shaped frame (19) and then cooperates with the second hexagonal nut (2101). The end of the second limit screw (16) and the second hexagonal nut (2101) that cooperates with it are both slidably installed. A compression limit groove (1302) is formed in the stretch limit groove, a motor bracket slide groove (1301) is processed on the stretch cover (13), a high motor bracket foot (1201) of the high motor bracket (12) passes through the motor bracket slide groove (1301) and is fixedly connected to the outer side of the second U-shaped frame (19), one side of the second motor connecting screw (2001) is connected to the output end of the second worm gear reduction motor (18) through a second coupling (22), and the other side of the second motor connecting screw (2001) is connected to any one of the transmission gears (2) of the lowest row of variable stiffness units (1) to establish a coaxial transmission connection.

7. A mechanical metamaterial according to claim 6, characterized in that: The compression module (14) and the stretching module (15) are fixedly connected.

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