Method and application of non-prestressed artificial muscle fiber, sheath layer sacrifice continuous preparation

Abstract

The application provides a method and application of prestress-free artificial muscle fiber, sheath layer sacrifice continuous preparation. The method comprises the following steps: preparing an original artificial muscle fiber containing a sheath layer and a fiber core; performing twisting or winding to form a spiral structure fiber with a tight spiral; performing annealing setting treatment; removing the sheath layer to obtain a spiral pitch opening prestress-free artificial muscle fiber. The application obtains the prestress-free artificial muscle fiber with natural spiral pitch gap by tightly twisting when the sheath layer is present and sacrificing the sheath layer later. The artificial muscle fiber prepared by the method has high shrinkage and strong work function, is simple and efficient, has continuous preparation capacity, and is more suitable for industrial production. Furthermore, the thickness of the sheath layer can be controlled to flexibly regulate the fiber spiral pitch, so that the preparation of artificial muscle fiber with any spiral pitch can be realized.

Description

Technical Field

[0001] This invention belongs to the field of artificial muscle technology, specifically relating to a method and application for the continuous preparation of artificial muscle fibers and sheath sacrificial membranes without prestress. Background Technology

[0002] Artificial muscle fibers, with their advantages of high power density, large contraction stroke, flexibility, and quiet operation, have shown application potential in humanoid robots, medical rehabilitation, and smart wearables, serving as a core support for the development of flexible intelligent equipment and embodied intelligence. Achieving continuous fabrication of artificial muscle fibers with large stroke and no pre-stress drive is a prerequisite for their application development. While some solutions have achieved continuous fabrication, several technical challenges remain. The invention patent CN114481381A, which proposes a method for continuously fabricating polymer artificial muscle fibers using a torque motor, produces fibers with closely spaced pitches. A load is needed to separate the fiber pitches to achieve a driving effect. Furthermore, the fabricated fibers become uneven in spiral structure as the winding coil thickens, limiting application scenarios. The invention patent CN120519990A achieves the fabrication of helical artificial muscle fibers through a tension control system and a motor. It uses two differential motors and an annealing device to separate the fiber pitches, achieving a large-pitch, pre-stress-free driving structure. However, the uneven pitch structure formed during differential motor operation and annealing poses a risk of breakage. The invention patent with publication number US20240263361A1 prepared artificial muscle fibers with large pitch and no prestressed drive structure by simultaneously twisting, annealing and disassembling two or more fibers. However, the method is complicated and does not meet the conditions for continuous preparation. Summary of the Invention

[0003] The main objective of this invention is to provide a method and application for the continuous preparation of artificial muscle fibers and sheath sacrificial membranes without prestress, so as to overcome the shortcomings of the prior art.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for continuous preparation of stress-free artificial muscle fibers by sheath sacrifice, comprising: Prepare primitive artificial muscle fibers containing a sheath and a fibrous core; The original artificial muscle fibers are twisted or wound to form a helical structure fiber with a tight spiral. The spiral structure fiber is annealed and shaped to obtain shaped fiber; The sheath layer of the shaped fiber is removed to obtain unstressed artificial muscle fibers.

[0005] Secondly, the present invention also provides continuous, stress-free artificial muscle fibers prepared by the above method.

[0006] Thirdly, the present invention also provides the application of the above-mentioned stress-free artificial muscle fibers in the fields of humanoid robots, medical rehabilitation, and smart wearables.

[0007] Compared with the prior art, the beneficial effects of the present invention include at least the following: The method provided by this invention obtains artificial muscle fibers with natural pitch gaps by tightly twisting them while they have a sheath layer and then sacrificing the sheath layer. Compared with artificial muscle fibers prepared by traditional mandrel winding technology, the artificial muscle fibers prepared by this method have both high contractility and strong working ability. Compared with artificial muscle fibers with large pitch (spread pitch) and no prestress driving structure prepared by simultaneously twisting, annealing and disassembling two or more fibers, this scheme is simple and efficient, has continuous preparation capability, and is more suitable for industrial production. Furthermore, by controlling the thickness of the sheath layer, the fiber pitch can be flexibly adjusted, thereby realizing the preparation of artificial muscle fibers with arbitrary pitch.

[0008] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of a method for preparing stress-free driven artificial muscle fibers by sheath dissolution, provided in a typical embodiment of the present invention. Figure 2 This is a comparison diagram of the driving process of artificial muscle fibers with no pitch prepared by the traditional twisting method and artificial muscle fibers with large pitch prepared by the sheath sacrificial method, provided in a typical embodiment of the present invention. Figure 3 This is an optical image of the process of preparing stress-free artificial muscle fibers by sheath dissolution, provided in a typical embodiment of the present invention. Figure 4 This is a typical embodiment of the present invention, showing the contraction amount and functional capacity test diagram of artificial muscle fibers under different applied stresses. Figure 5This is a test diagram of the driving force generated by artificial muscle fibers under different energizing times, provided in a typical embodiment of the present invention. Figure 6 This is a test diagram of the contraction amount of artificial muscle fibers under different duty cycles and different response frequencies provided in a typical embodiment of the present invention. Figure 7 This is a typical embodiment of the present invention, showing the test diagram of the equidistant contractile force of artificial muscle fibers under different currents. Figure 8 This is a test diagram of the cyclic stability of artificial muscle fibers provided in a typical embodiment of the present invention. Figure 9 This is a schematic diagram of the process of preparing mandrel-wound large-pitch artificial muscle fibers by the sacrificial layer removal method provided in another typical embodiment of the present invention. Detailed Implementation

[0011] The existing technology has the following main drawbacks: 1) Artificial muscle fibers prepared by mandrel winding technology (such as the article Twisted-and-Coiled Actuators with Free Strokes Enable Soft Robots with Programmable Motions, Soft Robotics, 2021, 8, 2, 213-225; and the invention patent with publication number CN120023796A) have a large contraction amount, but very low work capacity, require metal mandrel assistance, and cannot achieve continuous preparation.

[0012] 2) The invention patent with publication number US20240263361A1 prepared artificial muscle fibers with large pitch and no prestress driving structure by simultaneously twisting, annealing and disassembling two or more fibers. However, the scheme is complicated and does not have the conditions for continuous preparation.

[0013] 3) The invention patent with publication number CN114481381A proposes a method for continuously preparing polymer artificial muscle fibers using a torque motor. The fiber pitches are closely packed together, requiring a load to pull the fiber pitches apart before a driving effect can be achieved. Moreover, as the winding coil thickens, the spiral structure of the prepared fibers becomes uneven, limiting its application scenarios.

[0014] 4) The invention patent with publication number CN120519990A realizes the preparation of spiral artificial muscle fibers through a tension control system and a motor. It also realizes a large pitch, stress-free drive structure by pulling the fiber pitch apart through two differential motors and an annealing device. However, the pitch structure formed during the operation of the differential motor and the annealing process is uneven, which poses a risk of breakage.

[0015] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0016] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0017] The purpose of this invention is to design a method for removing the sheath material in the later stage, so that the sheath thickness is used as the pitch of the original helical fiber. After annealing, the sheath is removed, while the helical fiber core retains the open pitch structure. Therefore, the prepared artificial muscle fiber has the characteristics of natural large stroke and no pre-stress drive, and can have high work capacity. At the same time, this method can realize the low-cost continuous preparation of the above-mentioned artificial muscle fiber.

[0018] Based on the above objectives, embodiments of the present invention first provide a method for continuous preparation of stress-free artificial muscle fibers by sacrificial sheath preparation, which includes the following steps: Prepare primitive artificial muscle fibers containing a sheath and a fibrous core; The original artificial muscle fibers are twisted or wound to form a helical structure fiber with a tight spiral. The spiral structure fiber is annealed and shaped to obtain shaped fiber; The sheath layer of the shaped fiber is removed to obtain unstressed artificial muscle fibers.

[0019] The above-described technical solution is a method for continuously preparing large-pitch, stress-free driven artificial muscle fibers through sacrificial removal of the surface sheath. This method can not only realize the preparation of large-pitch self-twisting artificial muscle fibers, but also the preparation of large-pitch mandrel-wound helical artificial muscle fibers; at the same time, this method is a universal, applicable, and environmentally friendly method for preparing large-pitch, stress-free driven artificial muscle fibers of different material systems.

[0020] In some embodiments, the fiber core is made of an electrothermal fiber material.

[0021] In some embodiments, the electrothermal material comprises metal-plated polymer fibers.

[0022] The above technical solution takes the electrothermal drive form as an example, but it does not mean that the feasible methods of the present invention are limited to this.

[0023] Regarding the sheath layer and its removal method, the preferred embodiment of the present invention is to achieve the preparation and removal of the sheath layer using a solvent-based method with soluble materials, namely: In some embodiments, the sheath is made of a soluble polymer material.

[0024] In some implementations, the method specifically includes the following steps: Prepare solutions of soluble polymer materials; The fiber core surface is dried after adsorbing the solution to form the sheath layer.

[0025] In some implementations, the sheath is removed in the following ways: The sheath layer was dissolved using a solvent bath.

[0026] In some embodiments, the solvent bath comprises any one or a combination of two or more of water, ethanol, dichloromethane, dimethyl sulfoxide, and N,N-dimethylformamide.

[0027] However, the choice of materials and removal methods for the sheath are not limited to this. Possible directions include, but are not limited to, various materials and removal methods such as evaporation removal, reaction removal (e.g., chemical corrosion), and physical removal.

[0028] For the material system described above, in some embodiments, the annealing and shaping treatment temperature does not exceed 210°C. This is to prevent adverse reactions such as carbonization, oxidation, or charring of the soluble polymer materials, which would make them difficult to remove.

[0029] As a typical application example of the above technical solution, see [link to relevant documentation]. Figure 1 As shown, the method provided by this invention can be implemented through the following steps: Step 1: Pass the silver-plated nylon fiber and other polymer fibers through a composite solution of polyvinyl alcohol: starch = 2:1 (total weight fraction of 10wt%-90wt%), and then through a drying device. This process can be repeated until the sheath thickness is 100-500μm. The concentration of the composite solution is not specifically required. The number of repetitions can be combined to offset the change in solution concentration, with the final sheath thickness as the fundamental control target.

[0030] Step 2: Then, the above fibers are continuously twisted and inserted through a twisting machine at a twist rate of 600-900 turn / m to form a spiral fiber structure. The specific twist rate may not be limited to this and needs to be adjusted according to the material and diameter of the fiber core to form a tight spiral structure (the turns are tightly stacked with no obvious gaps).

[0031] Step 3: Anneal and set the spiral fibers in a tube furnace or oven at 150-210℃. The specific temperature and processing time usually depend on the material and diameter of the fiber core used. You can refer to the processing conditions of traditional artificial muscles with the same material and diameter, but you need to pay attention to controlling the maximum temperature to prevent adverse reactions in the sheath layer. Step 4: After annealing, the fiber is subjected to a water bath at 25-80℃ to remove the polyvinyl alcohol / starch composite coating on the sheath layer, resulting in artificial muscle fibers with a large pitch structure. The specific processing temperature and time can be adjusted adaptively to ensure that the sheath layer is fully removed.

[0032] The above method is environmentally friendly, and the dissolved polyvinyl alcohol / starch mixture can be concentrated and reused. Meanwhile, in step 1, the nylon thread can be replaced with other polymer fibers (spandex, aramid, polyimide, polyethylene, polyethylene terephthalate, polypropylene, liquid crystal elastomer, polyvinylidene fluoride and copolymers, polyetheretherketone, polyoxymethylene, thermoplastic polyurethane, etc.), and the polyvinyl alcohol / starch can be replaced with chitosan, sodium alginate, cellulose, flour, gelatin, or any one or more combinations thereof. In step 4, the water bath can be changed to an organic solvent bath, such as ethanol, dichloromethane, dimethyl sulfoxide, or N,N-dimethylformamide, depending on the water-insoluble nature of other sheath materials.

[0033] This invention also provides continuous, stress-free artificial muscle fibers prepared by the method provided in any of the above embodiments.

[0034] The embodiments of the present invention also provide the application of the above-mentioned stress-free artificial muscle fibers in the fields of humanoid robots, medical rehabilitation, and smart wearables.

[0035] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0036] Example 1 This embodiment illustrates the preparation and testing of a spontaneously spiraling, stress-free artificial muscle fiber, as detailed below.

[0037] Step 1: Pass the silver-plated nylon fiber through a composite solution of polyvinyl alcohol and starch in a mass ratio of 2:1 (total weight fraction of 50 wt%), and then pass it through a drying device. This process can be repeated until the sheath thickness is 300 μm.

[0038] Step 2: Then, the above fibers are continuously twisted and inserted through a twisting machine to form a tightly stacked spiral structure fiber.

[0039] Step 3: Anneal and set the spiral fibers in a tube furnace or oven at 180°C. Step 4: After annealing, the sheath layer of polyvinyl alcohol / starch composite coating is removed by water bath to obtain artificial muscle fibers with a large pitch structure.

[0040] Figure 2 This comparison examines the driving processes of helical artificial muscle fibers prepared using the traditional twisting method (without pitch) and those prepared using the sacrificial sheath method (with large pitch). Helical artificial muscle fibers prepared using the traditional twisting method lack an initial pitch to provide contraction space and thus have almost no driving force. They require a suspension load to open the fiber pitch and create contraction space; the fiber performs zero useful work during this contraction / recovery process. In contrast, large-pitch artificial muscle fibers prepared using the sacrificial sheath method possess an initial large-pitch structure and can maintain this structure without preload tension. Therefore, these fibers can perform reversible cyclic contraction under no-load and / or load conditions, and can also perform useful work during the driving process. The useful work performed during the entire driving process can be understood as follows: the fiber contracts under a large load, and the recovery process can be completed under a small load; the work done during contraction exceeds the work done during recovery, thus offsetting the work done during recovery.

[0041] Figure 3 These are structural optical images of the fibers during the fabrication process. Polyvinyl alcohol / starch@nylon coaxial fibers are twisted to form a uniform helical structure. The nylon fibers have a diameter of approximately 200 μm, and the sheath thickness is ~100 μm. In warm water, the polyvinyl alcohol / starch sheath gradually dissolves to form artificial muscle fibers with a stable, large-pitch structure.

[0042] Figure 4 The contractile amount and working capacity of the artificial muscle fibers prepared by the above method under different applied stresses are shown. The maximum driving force of the fiber is 52%, and the driving force gradually decreases as the stress on the fiber increases. It can generate a working capacity of 0.1 J / g under a stress of 750 kPa.

[0043] Figure 5 This is a graph showing the relationship between the driving force generated by artificial muscle fibers under different energizing times. Under a 0.4A current and a 2g load, the times required for the fibers to generate 10%, 20%, 30%, and 40% driving force are 1.5s, 3s, 4s, and 5s, respectively. As the energizing time increases, the driving force generated by the fibers increases, and the driving force of the fibers is directly proportional to the energizing time.

[0044] Figure 6This represents the contraction amount of artificial muscle fibers at different duty cycles and response frequencies. All tests were conducted with a current of 0.4A and a load of 2g. At the same duty cycle, the driving force of the fiber gradually increases as the frequency decreases. At the same frequency, the higher the duty cycle, the greater the driving force generated by the fiber. This is because a higher duty cycle results in a longer energizing time for the fiber, leading to more heat accumulation and greater pitch contraction, thus resulting in a larger driving force. The driving force reaches its maximum when the pitch is reduced to zero. At a 15% duty cycle, the fiber contraction amount at 0.75Hz is ~2%.

[0045] Figure 7 These are the isometric contractile forces of artificial muscle fibers under different currents. When the current increases from 0.25 A to 0.40 A, the isometric force generated during fiber contraction increases from 40 mN to nearly 90 mN.

[0046] Figure 8 This is a test of the cyclic performance of artificial muscle fibers. The cyclic performance was measured under the conditions of a 0.4A current, a 2g load, a 4s on-time, and a 36s off-time. The graph shows that the fiber retains good actuation performance even after prolonged cycling, remaining capable of actuation after 400 cycles. The actuation performance of the fiber in the first three cycles, the middle three cycles, and the last three cycles were 30%, 32%, and 35%, respectively. Unlike traditional artificial muscle fibers, which show an increase in performance initially due to actuation training followed by a slow decline, this artificial muscle fiber gradually achieves maximum actuation efficiency throughout the long cycling process.

[0047] Example 2 This embodiment is largely the same as Embodiment 1, with the main difference being: The fiber helical pattern is changed to, for example Figure 9 The mandrel winding method shown involves initially twisting the fibers (but not yet forming a spiral) and then tightly winding them without gaps onto a rod-shaped mandrel, followed by heat treatment under the same conditions for shaping and sheath removal.

[0048] Compared with the existing mandrel winding method, the above method can stably control the helical gap, avoid uneven helical gap, and is more conducive to product consistency control and wide application.

[0049] Example 3 This embodiment is largely the same as Embodiment 1, with the main difference being: The fiber core was replaced with spandex silver-plated fiber, and the sheath material was replaced with chitosan.

[0050] Example 4 This embodiment is largely the same as Embodiment 1, with the main difference being: Replace the fiber core with spandex silver-plated fiber and the sheath material with gelatin.

[0051] The above embodiments involve uniformly coating the fiber surface with a soluble polymer, then using a continuous twisting machine to insert twists or tightly wind the resulting coaxial fibers to obtain helical fibers with closely spaced pitches. After high-temperature annealing, setting, and dissolution, the process is continuously refined to obtain polymer artificial muscle fibers with large stroke and no pre-stress drive, prepared using a mandrel-less method. This method can not only achieve the preparation of large-pitch self-twisting artificial muscle fibers but also the preparation of large-pitch mandrel-wound helical artificial muscle fibers. It is environmentally friendly and represents a key method and technology for the continuous preparation of artificial muscle fibers with large stroke and high work output.

[0052] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for continuous preparation of stress-free artificial muscle fibers by sacrificial sheath preparation, characterized in that, include: Prepare primitive artificial muscle fibers containing a sheath and a fibrous core; The original artificial muscle fibers are twisted or wound to form a helical structure fiber with a tight spiral. The spiral structure fiber is annealed and shaped to obtain shaped fiber; The sheath layer of the shaped fiber is removed to obtain unstressed artificial muscle fibers.

2. The method according to claim 1, characterized in that, The fiber core is made of electrothermal fiber material.

3. The method according to claim 2, characterized in that, The electrothermal material includes metal-plated polymer fibers.

4. The method according to claim 1, characterized in that, The sheath is made of soluble polymer materials.

5. The method according to claim 4, characterized in that, Specifically, it includes: Prepare solutions of soluble polymer materials; The fiber core surface is dried after adsorbing the solution to form the sheath layer.

6. The method according to claim 4, characterized in that, The methods for removing the sheath include: The sheath layer was dissolved using a solvent bath.

7. The method according to claim 6, characterized in that, The solvent bath includes any one or a combination of two or more of water, ethanol, dichloromethane, dimethyl sulfoxide, and N,N-dimethylformamide.

8. The method according to claim 1, characterized in that, The annealing and shaping temperature shall not exceed 210℃.

9. Continuous, stress-free artificial muscle fibers prepared by the method of any one of claims 1-8.

10. The application of the prestress-free artificial muscle fiber as described in claim 9 in the fields of humanoid robots, medical rehabilitation, and smart wearables.

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