A stretchable soft body variable stiffness structure and its preparation method

Abstract

The present invention discloses a stretchable soft variable stiffness structure, which includes a square sealed soft cavity and two square soft film layers laid inside the sealed soft cavity; an air path joint is provided on the top of the sealed soft cavity; the soft film layer is cast from a castable flexible material and rough lines, the rough lines are evenly spaced in the middle of the flexible material, the rough lines are parallel to one side of the soft film layer, and the upper ends of the rough lines are against the upper edge of the soft film layer, while the lower ends of the rough lines are shorter and do not reach the lower edge of the soft film layer; the soft film layer is divided into an upper rough line-containing area and a lower rough line-free area according to the distribution of the rough lines in the soft film layer; the two soft film layers in the sealed soft cavity are placed in an overlapping manner, and the rough line-containing area of one soft film layer and the rough line-free area of the other soft film layer are arranged on the same side of the sealed soft cavity. The tensile stiffness variation range of the present invention is determined by the tensile stiffness difference between the lines and the flexible material, and can be designed according to the specific application scenario.

Description

Technical Field

[0001] The present invention relates to the technical field of soft body variable stiffness, in particular to a stretchable soft body variable stiffness structure and a preparation method thereof. Background Art

[0002] Variable stiffness technology is a key technology in robotics, medical devices, wearable devices, smart structures, and other fields. Compared to rigid variable stiffness technology, soft variable stiffness technology is applicable to all rigid, flexible, and soft systems. It is particularly significant for flexible and soft systems, enabling the adjustment of stiffness while maintaining compliance. This offers unique advantages for flexible wearables, flexible medical devices, and soft robots. Currently, fiber / wire jamming soft variable stiffness technology has emerged. This type of structure consists of a soft cavity and a wire bundle or fiber bundle. The soft cavity encloses the wire bundle or fiber bundle, and then negative pressure is applied to the cavity. The cavity contracts radially, squeezing the wire bundle or fiber bundle. This generates friction between the wires and between the wires and the inner surface of the cavity, as well as between the fibers and the inner surface of the cavity. This friction hinders the relative motion of the wires or fibers, further hindering the deformation of the entire soft structure. Compared to the initial, no-negative-pressure state, the stiffness of the entire structure changes. Line-blocking soft variable stiffness technology has the advantages of light weight, compact structure, safety and environmental protection, low cost, and easy integration, and has good application prospects.

[0003] An existing design scheme for a wire-blocking soft variable stiffness structure consists of wires (including kraft paper wire, hemp wire, nylon wire) and a sealed soft cavity. Under negative pressure, the soft cavity contracts and squeezes the wires, causing friction between the wires. When there is no friction between the wires and the structure is in a free state, the wires will slide relative to each other under bending or torsional deformation. Under negative pressure, friction will hinder this deformation, thereby changing the stiffness of the entire structure. The disadvantages of this structural design are: (1) This type of structure itself cannot achieve tensile deformation, which will limit the deformation of the soft object itself; (2) This type of structure relies on friction between the wires, and multiple wires must be used to form the wire bundle, which increases the volume of the overall structure and does not take advantage of miniaturization; (3) This type of structure uses friction between the wires to hinder the relative sliding of the wires, which requires the wires used to have a certain axial stiffness to ensure that the wires themselves do not buckle or wrinkle, which limits the material and thickness of the wires.

[0004] Another design for a thread-blocking, variable-stiffness soft structure utilizes polyester fiber (terylene) threads cured into silicone rubber to form the basic blocking unit. Multiple such composite threads are then sealed into a soft cavity, creating a soft, variable-stiffness structure controlled by negative air pressure. When negative pressure is applied, the blocking units squeeze each other, generating friction. The polyester fibers hinder the elongation and deformation of the silicone rubber. When negative pressure is not applied, the silicone rubber areas without the polyester fibers experience stretching and deformation. The resulting stiffness changes between the two states, thus achieving a stretchable, variable-stiffness soft structure. This structural design also has some disadvantages: (1) This type of structure directly solidifies the polyester fiber thread into the silicone rubber flexible material, which is due to the fact that the polyester fiber thread and silicone rubber can be firmly bonded, but there are certain limitations on general material threads; (2) This type of structure still uses a bundle structure composed of multiple blocking units, which makes the overall structure larger and does not take advantage of miniaturization applications; (3) This type of structure uses a multi-bundle blocking structure, and the arrangement between the blocking units is somewhat random, which makes it difficult to model the tensile deformation and stiffness adjustment process, and it is not easy to predict its behavior theoretically. Summary of the Invention

[0005] In view of the above-mentioned problems existing in the existing line-blocking soft variable stiffness structure design, the present invention provides a method for stretching a soft variable stiffness structure and a preparation method thereof.

[0006] The stretchable soft body variable stiffness structure provided by the present invention comprises: a square sealed soft body cavity, two square soft film layers laid inside the sealed soft body cavity; and an air path joint is arranged on the top of the sealed soft body cavity.

[0007] The soft film layer is cast from a flexible material that can be cast and rough lines. The rough lines are evenly spaced in the middle of the flexible material. The rough lines are parallel to one side of the soft film layer, and the upper ends of the rough lines abut the upper edge of the soft film layer, while the lower ends of the rough lines are shorter and do not reach the lower edge of the soft film layer. Based on the distribution of the rough lines within the soft film layer, the soft film layer is divided into an upper region containing rough lines and a lower region without rough lines. The two soft film layers are placed overlapping in the sealed soft body cavity, and the region containing rough lines of one soft film layer is arranged opposite the region without rough lines of the other soft film layer; the upper and lower ends of the two soft film layers are respectively connected to the upper and lower ends of the soft body cavity.

[0008] The rough wire is pre-roughened on the surface, and microparticles are bonded to the surface of the wire to increase the roughness of the surface of the wire.

[0009] Preferably, the rough thread is selected from the group consisting of cotton, nylon, and hemp. The rough thread has a diameter in the micrometer or millimeter range. The microparticles on the surface of the rough thread are metal particles or resin particles with a diameter in the micrometer or millimeter range. For example, the metal particles may be iron particles, copper particles, aluminum particles, or the like.

[0010] Preferably, the sealed soft cavity is made of a flexible material that can be cast.

[0011] Preferably, the castable flexible material is selected from silicone rubber, Ecoflex, and hydrogel.

[0012] A method for preparing the above-mentioned stretchable soft variable stiffness structure comprises the following steps:

[0013] Step 1: Prepare a rough line: soak the line in flexible glue, then place the line containing glue into a container containing microparticles, and rotate the line so that its surface is fully bonded with the microparticles to obtain a rough line.

[0014] Step 2: Prepare a soft film layer: pour a castable flexible material into a mold, lay a layer of flexible material on the bottom of the mold, and then arrange rough lines on the surface of the flexible material in the mold one by one; finally, pour the flexible material again, wait for it to dry and solidify into shape, and then obtain a soft film layer.

[0015] Step 3: Prepare a sealed soft cavity: Use a castable flexible material combined with a specific mold to prepare the soft cavity body and the sealing plate respectively. One side of the soft cavity body is open for placing the soft film layer, and then the opening is sealed with a sealing plate. An air path connector is set on the top of the sealed soft cavity.

[0016] Compared with the prior art, the present invention is beneficial in that:

[0017] While maintaining stretchability, this soft variable stiffness structure improves upon existing wire-blocking soft variable stiffness technology by: ① Roughening the wire surface: Microparticles are bonded to the wire surface to increase the roughness of the wire surface, thereby enhancing the connection strength between the wire and the flexible material and expanding the material range of the wire. ② Transforming the "bundle-like" blocking into a "thin-layer" blocking: The entire blocking structure consists of two thin-layer blocking units, reducing the volume of this type of variable stiffness structure. ③ The thin-layer blocking units are formed by uniformly distributing multiple rough wires and curing them in one go, ensuring the consistency and controllability of the composite material and facilitating theoretical analysis of the deformation and variable stiffness characteristics of this type of structure.

[0018] Other advantages, objectives and features of the present invention will be reflected in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 , schematic structural diagram of the soft film layer.

[0020] Figure 2 , schematic diagram of the internal structure of the sealed soft cavity.

[0021] Numbers in the figure: 1-soft film layer, 2-rough line, 3-soft film layer, 4-soft body cavity, 5-air path connector, 6-area containing rough lines, 7-area without rough lines. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0023] like Figure 1 and 2 As shown, the stretchable soft body variable stiffness structure provided by the present invention includes: a square sealed soft body cavity 4, two square soft film layers (soft film layer 1 and soft film layer 3) with the same structure laid inside the sealed soft body cavity. An air path connector 5 is set on the top of the sealed soft body cavity 4.

[0024] The soft film layer is cast from a flexible material that can be cast and rough lines 2. The rough lines are evenly spaced in the middle of the flexible material. The rough lines are parallel to one side of the soft film layer, and the upper end of the rough lines is against the upper edge of the soft film layer, while the lower end of the rough lines is shorter and does not reach the lower edge of the soft film layer. According to the distribution of the rough lines in the soft film layer, the soft film layer is divided into an upper rough line area 6 and a lower rough line free area 7. The tensile deformation of the rough line area is restricted, while the tensile deformation of the rough line free area is not restricted. The two soft film layers in the sealed soft body cavity are overlapped, and the rough line area 6 of one soft film layer is arranged opposite to the rough line free area 7 of the other soft film layer. For example Figure 2 In the embodiment, the roughened area 6 of the soft film layer 1 and the roughened area 7 of the soft film layer 3 are arranged on the same side of the sealed soft cavity 4 and face each other. The upper and lower ends of the two soft film layers are connected to the upper and lower ends of the soft cavity respectively, and the stretching deformation of the three is synchronized.

[0025] The sealed soft cavity 4, soft film layer 1, and soft film layer 3 are all produced by casting, using castable flexible materials such as silicone rubber, Ecoflex, and hydrogel. During the casting process of soft film layers 1 and 3, roughened threads 2 are solidified into the soft film layers. The roughened threads 2 are made of microparticles bonded to the surface of the threads. The threads can be made of cotton, nylon, or hemp, with diameters ranging from microns to millimeters depending on the structural dimensions. The diameters of the microparticles can also be determined from microns to millimeters depending on the structural dimensions. The bonding process is achieved by impregnating the threads with a flexible glue.

[0026] When the air pressure inside the sealed soft cavity 4 is equal to the external atmospheric pressure, there is no interaction between the soft film layers 1 and 3, allowing them to deform with the tensile deformation of the soft cavity 4. Here, the deformed portion is the roughness-free region of the film layers. When negative air pressure is applied to the soft cavity 4, the two larger surfaces of the soft cavity, under the action of the external atmospheric pressure, squeeze the two soft film layers, generating friction between the soft film layers. Friction occurs between the roughness-containing region of soft film layer 1 and the roughness-free region of soft film layer 3, and between the roughness-free region of soft film layer 1 and the roughness-containing region of soft film layer 3. This hinders the tensile deformation of both soft film layers, thereby changing the tensile stiffness of the overall structure, thereby achieving a change in the stiffness of the entire soft structure. When no negative air pressure is applied, the tensile stiffness of this type of soft structure is primarily provided by the roughness-free regions of soft film layers 1 and 3. When negative air pressure is applied, the tensile stiffness is primarily provided by the roughness-free regions of soft film layers 1 and 3. This difference in tensile stiffness represents the stiffness variation range of this type of soft structure.

[0027] Compared to existing stretchable soft-body variable-stiffness structures, the present invention's tensile stiffness variation range is determined by the difference in tensile stiffness between the wire and the flexible material, allowing for tailored design based on specific application scenarios. Furthermore, by roughening the wire surface, special requirements for the wire material are eliminated, expanding the range of material options available. Furthermore, the present invention's variable-stiffness structure is thin and compact, facilitating integrated applications. Furthermore, the composite design and preparation of the wire and flexible material ensures consistency and controllability of the overall structure, facilitating theoretical prediction of its variable-stiffness properties.

[0028] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A stretchable soft body variable stiffness structure, characterized in that: It includes a square sealed soft cavity and two square soft film layers laid inside the sealed soft cavity; an air path connector is provided on the top of the sealed soft cavity; The soft film layer is cast from a castable flexible material and rough lines, with the rough lines evenly spaced in the middle of the flexible material. The rough lines are parallel to one side of the soft film layer, and the upper ends of the rough lines abut against the upper edge of the soft film layer, while the lower ends of the rough lines are shorter and do not reach the lower edge of the soft film layer. The soft film layer is divided into an upper rough line-containing area and a lower rough line-free area according to the distribution of the rough lines in the soft film layer. The two soft film layers are overlapped in the sealed soft body cavity, and the rough line-containing area of one soft film layer and the rough line-free area of the other soft film layer are arranged on the same side of the sealed soft body cavity. The rough thread is one of cotton thread, nylon thread and hemp thread; the rough thread is pre-roughened on the surface, and micro particles are bonded on the surface of the thread to increase the roughness of the thread surface.

2. The stretchable soft body variable stiffness structure according to claim 1, characterized in that: The diameter of the rough lines is in the micrometer or millimeter order.

3. The stretchable soft body variable stiffness structure according to claim 2, characterized in that: The microparticles on the surface of the rough lines are metal particles or resin particles with a diameter of micrometer or millimeter.

4. The stretchable soft body variable stiffness structure according to claim 1, wherein: The sealed soft cavity is made of a flexible material that can be cast.

5. The stretchable soft body variable stiffness structure according to claim 4, characterized in that: The flexible material is one of silicone rubber, Ecoflex and hydrogel.

6. The stretchable soft body variable stiffness structure according to claim 1, characterized in that: The upper and lower ends of the two soft film layers are respectively connected to the upper and lower ends of the soft body cavity.

7. A method for preparing a stretchable soft variable stiffness structure according to any one of claims 1 to 6, characterized in that: Here are the steps: Step 1: Prepare a rough line: soak the line in flexible glue, then place the line containing glue into a container containing microparticles, and rotate the line so that the microparticles are fully bonded to its surface to obtain a rough line; Step 2: Preparing a soft film layer: Pour a castable flexible material into a mold, lay a layer of the flexible material on the bottom of the mold, and then arrange rough lines on the surface of the flexible material in the mold one by one; finally, pour the flexible material again, wait for it to dry and solidify, and thus obtain a soft film layer; Step 3: Prepare a sealed soft cavity: Use a castable flexible material combined with a specific mold to prepare the soft cavity body and the sealing plate respectively. One side of the soft cavity body is open for placing the soft film layer, and then the opening is sealed with a sealing plate. An air path connector is set on the top of the sealed soft cavity.

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