Preparation method of thermoplastic composite torsion spring and its application in exoskeleton power assist device

Abstract

This invention discloses a method for preparing thermoplastic composite torsion springs and their application in exoskeleton assistive devices. The preparation method comprises the following steps: Step 1: Selecting polyamide resin as the matrix material and nano-silica powder, the matrix material and nano-silica powder are thoroughly mixed at a mass ratio of 9:1 using a high-speed mixer to form a uniform preform; Step 2: Selecting aramid fiber as the reinforcing material, the preform and reinforcing material from Step 1 are dried to ensure their moisture content is below 0.5%; Mass production of composite torsion springs is achieved by employing efficient screw extrusion and metal-like torsion spring forming blades, realizing a fully automated production process from material mixing to the final product. This process not only improves production efficiency and ensures the consistency and stability of product quality, but also significantly reduces production costs.

Description

Technical Field

[0001] This invention belongs to the technical field of thermoplastic composite torsion springs, specifically relating to a high-stiffness, lightweight thermoplastic composite torsion spring prepared by extrusion molding process, and the application of the torsion spring in a lower limb exoskeleton assistive device. Background Technology

[0002] With the increasing aging population and the development of medical technology, lower limb exoskeleton assistive devices are being used more and more widely in rehabilitation medicine, assisted walking, and enhancing human motor abilities. These devices can help the elderly, disabled people, and those requiring rehabilitation training to better perform daily activities and improve their quality of life. However, while traditional metal springs have good mechanical properties, they have the following problems:

[0003] Heavy weight: Traditional metal torsion springs (such as steel springs) have a high density, resulting in a relatively heavy overall weight for the exoskeleton device. This not only increases the burden on the wearer but may also affect their user experience and comfort.

[0004] Susceptible to corrosion: Metal torsion springs are prone to rust in humid or corrosive environments, affecting their service life and reliability. The durability of metal springs is particularly poor in outdoor or humid environments.

[0005] Poor fatigue resistance: When subjected to repeated alternating loads, metal torsion springs will deform, causing them to be unable to fully return to their initial position.

[0006] Composite materials are renowned for their lightweight, high modulus, and excellent specific strength, with superior corrosion resistance far exceeding that of traditional metals. Even in harsh environments such as high temperature, high humidity, or salt spray, these materials maintain their performance, thereby enhancing product reliability and reducing maintenance costs. In recent years, researchers have been searching for lighter, stronger, more corrosion-resistant, and more cost-effective alternative materials. Among them, thermoplastic composites have found widespread application in numerous industries due to their excellent mechanical properties, lightweight effect, and recyclability. Nevertheless, how to effectively apply these thermoplastic composites in the manufacture of torsion springs and ensure their efficient operation in lower limb exoskeleton assistive devices remains a key problem that needs to be solved. Summary of the Invention

[0007] During their research, the inventors discovered several challenges in applying thermoplastic composite materials to the manufacture of torsion springs:

[0008] Interfacial bonding: The interfacial bonding between the thermoplastic matrix and the reinforcing fibers is a key factor affecting the properties of composite materials. Poor interfacial bonding can lead to a decline in the mechanical properties of the material, especially under high stress and fatigue conditions.

[0009] Molding process: Extrusion molding is a common method for molding thermoplastic composite materials, but it requires precise control of parameters such as temperature, pressure and speed to ensure that the material is mixed uniformly and forms the desired shape.

[0010] This invention aims to establish a complete manufacturing process for thermoplastic composite torsion springs. It utilizes the lightweight and high-strength properties of composite materials and employs recyclable thermoplastic materials for processing and production. Furthermore, based on the traditional manufacturing process for metal torsion springs, a complete manufacturing process suitable for thermoplastic composite torsion springs has been established. In addition, the thermoplastic composite torsion springs produced by this invention can be applied to human exoskeleton knee joint assistive devices, effectively reducing the weight of the assistive device and significantly improving its fatigue life, thus having a wide range of applications.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing a thermoplastic composite torsion spring, characterized in that: the preparation method steps are as follows.

[0012] Step 1: Select polyamide resin as the matrix material and nano-silica powder. Mix the matrix material and nano-silica powder at a mass ratio of 9:1 using a high-speed mixer to form a uniform preform.

[0013] Step 2: Select aramid fiber as the reinforcing material, and dry the preform and reinforcing material from Step 1 to ensure that their moisture content is below 0.5%.

[0014] Step 3: The reinforcing material and preform from Step 2 are melt-mixed and extruded through an extruder to form a uniform, slender cylinder;

[0015] Step 4: The slender cylinder from Step 3 is shaped into a thermoplastic composite torsion spring using a torsion spring forming device.

[0016] Furthermore, in step one, the polyamide resin is preferably nylon 66; the average particle size of the nano-silica powder is 20-50 nanometers.

[0017] Furthermore, in step two, the aramid fiber is preferably Kevlar fiber.

[0018] Furthermore, in step three, the extruder includes a heating device located at the front end of the screw, and the temperature provided by the heating device is 270-290 degrees Celsius.

[0019] The extruder includes a cooling device located at the front end of the heating device, and the cooling device provides a temperature of 10-20 degrees Celsius.

[0020] The extrusion speed of the extruder is 10-30 mm / s.

[0021] Furthermore, in step three, the screw of the extruder is hollow along its axis, and one end of the aramid fiber enters the extruder along the hollow part of the screw, and passes through the heating device and cooling device in sequence, and is pre-installed at the discharge port of the extruder through the end cap.

[0022] Furthermore, in step four, the torsion spring forming device includes a driving part, a metal-like torsion spring forming blade fixing part, and a metal-like torsion spring forming blade moving part; both the metal-like torsion spring forming blade fixing part and the metal-like torsion spring forming blade moving part are provided with mutually cooperating forming grooves, and the forming grooves are adapted to the shape of the thermoplastic composite torsion spring.

[0023] The thermoplastic composite torsion spring described herein is used in the exoskeleton assist device.

[0024] Furthermore, the exoskeleton assistive device includes a thigh fixation mechanism, a lower leg fixation mechanism, a thigh connecting frame, a lower leg connecting frame, and an adjustable pretension mechanism disposed between the thigh connecting frame and the lower leg connecting frame; the thermoplastic composite torsion spring is disposed within the adjustable pretension mechanism.

[0025] Furthermore, an adjustment cavity is provided longitudinally between the thigh connecting frame and the calf connecting frame, and the adjustable preload mechanism includes:

[0026] A positioning pin is installed on the thigh connecting frame, one end of which extends into the adjustment cavity of the calf connecting frame and can move along the adjustment cavity.

[0027] An adjustment block is mounted on the thigh connector frame and is installed within an adjustment cavity of the thigh connector frame, and is movable along the adjustment cavity.

[0028] An adjusting bolt is mounted on the adjusting block and is movable within the adjusting cavity of the thigh connecting frame;

[0029] A fastening nut is provided, and the fastening bolt is screwed onto the adjusting bolt.

[0030] A thermoplastic composite torsion spring, wherein the thermoplastic composite torsion spring is sleeved on a positioning pin, with one end abutting against the lower leg connecting frame and the other end abutting against the adjusting block.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) Mass production of composite torsion springs has been achieved. By employing efficient screw extrusion and metal-like torsion spring forming blades, a fully automated production process from material mixing to the final product has been realized. This process not only improves production efficiency and ensures the consistency and stability of product quality, but also significantly reduces production costs. Compared to traditional metal torsion spring manufacturing, the production process of thermoplastic composite torsion springs simplifies steps, reduces mold change frequency, and boasts high material utilization and low waste. Furthermore, the production line can quickly adjust output to meet the needs of different customers, especially demonstrating strong adaptability to large-scale production and customized orders. Each batch of products undergoes rigorous mechanical performance and environmental adaptability testing to ensure that all products leaving the factory meet high-quality standards.

[0033] (2) The innovative extrusion molding technology combines a high-speed mixer and a screw compounder to ensure that the thermoplastic resin and nano-silica are fully and uniformly mixed to form a homogeneous composite material, avoiding local defects and enhancing overall performance. A special metal-like torsion spring forming blade design, combined with a preheated metal mandrel as an intermediate support, allows the molten material to be extruded uniformly and formed into the desired torsion spring shape. During the rapid cooling and shaping process, temperature control is achieved through a water-cooling tank to ensure product dimensional stability and prevent stress concentration and deformation.

[0034] (3) The application of thermoplastic composite torsion springs in exoskeleton assistive devices significantly improves device performance and user experience. Compared to traditional metal torsion springs, this new material is lighter, reducing the overall burden on the exoskeleton and improving the wearer's comfort and flexibility, making it particularly suitable for long-term wear or high-intensity use scenarios. Composite materials have higher elasticity and fatigue resistance, extending service life and maintaining stable performance even in complex working environments. In addition, their excellent wear resistance and corrosion resistance allow the device to be used for a long time in harsh environments without easily being damaged. Through the adjustable preload device, users can easily adjust the initial torque and working range according to their needs, better adapting to different movement patterns and load changes, thereby enhancing the device's flexibility and personalized experience. Attached Figure Description

[0035] Figure 1 This is a structural schematic diagram of the extruder in this application document;

[0036] Figure 2 This is a schematic diagram of the extrusion molding structure (with thermoplastic composite torsion spring) in this application document;

[0037] Figure 3 This is a schematic diagram of the extrusion molding structure in this application document;

[0038] Figure 4 This is a structural schematic diagram of the exoskeleton assistive device in this application document;

[0039] Figure 5 This is a structural schematic diagram of the adjustable preload mechanism in this application document.

[0040] In the diagram: 1. Feed inlet; 2. Extruder; 3. Kevlar fiber; 4. Heating device; 5. Cooling device; 6. End cap; 7. Moving part of metal-like torsion spring forming knife; 8. Fixing part of metal-like torsion spring forming knife; 9. Ring-shaped thrust device; 10. Positioning body; 11. Thermoplastic composite torsion spring; 12. Thigh connecting frame; 13. Thigh fixing mechanism; 14. Adjusting block; 15. Fastening nut; 16. Lower leg connecting frame; 17. Lower leg fixing mechanism. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] like Figure 1-Figure 5 As shown, the technical solution adopted by the present invention is as follows: This embodiment provides a method for preparing a thermoplastic composite torsion spring, and the preparation method steps are as follows:

[0043] Step 1: Select polyamide resin as the matrix material and nano-silica powder. Mix the matrix material and nano-silica powder at a mass ratio of 9:1 using a high-speed mixer to form a uniform preform.

[0044] Step 2: Select aramid fiber as the reinforcing material, and dry the preform and reinforcing material from Step 1 to ensure that their moisture content is below 0.5%.

[0045] Step 3: The reinforcing material and preform from Step 2 are melt-mixed and extruded through extruder 2 to form a uniform, slender cylinder;

[0046] Step 4: The slender cylinder from Step 3 is shaped into a thermoplastic composite torsion spring 11 using a torsion spring forming device.

[0047] In step one, a suitable thermoplastic matrix material needs to be selected. When choosing a thermoplastic matrix material, the performance of the matrix, molding conditions, and material price must be considered to select the material with the best cost-performance ratio. Common thermoplastic materials include polyethylene, polyetheretherketone (PEEK), polyimide, and polyamide. Polyethylene is a lightweight, chemically resistant, impact-resistant, and well-insulated thermoplastic, but it is relatively expensive. PEEK is a high-performance thermoplastic polymer with excellent mechanical properties, heat resistance, and chemical resistance. It exhibits good fatigue performance under cyclic loading and is suitable for components subjected to repeated loads over long periods. However, due to its high price, it is typically used in high-strength and high-durability applications. Polyphenylene sulfide (PPS) has excellent heat and chemical resistance, and its fatigue performance is also good, especially at high temperatures. However, it usually has a high viscosity, which can lead to surface irregularities during extrusion molding. Polyamide has high tensile strength and impact toughness, especially relative to its density. Under repeated stress, polyamide exhibits good fatigue life and is relatively inexpensive. Therefore, polyamide is chosen as the matrix material. Nylon 66 (PA66) is a thermoplastic polyamide material with high strength and high modulus, providing excellent mechanical properties suitable for applications subjected to high loads. It also exhibits excellent abrasion and fatigue resistance, maintaining stable performance even during long-term use, making it particularly suitable for high-wear and high-stress environments. PA66 has good chemical resistance to most chemicals (such as oils, solvents, acids, and alkalis) and excellent processing properties, including good melt flow and suitability for various manufacturing processes such as injection molding and extrusion molding, facilitating the production of parts with complex shapes. Furthermore, it has a high melting point (approximately 260°C) and good thermal stability, making it suitable for applications in high-temperature environments, while its low density contributes to lightweight design and reduced overall weight.

[0048] In step one, polyamide (PA) resin was used as the matrix material. This is because it not only has good flowability and strong heat resistance, but also maintains stable physical properties even at high temperatures. The selected resin particles were uniform and free of impurities to ensure excellent mixing and guarantee the quality of the final product. For the selection of nano-silica, high-purity powder with an average particle size in the range of 20-50 nanometers was chosen. This powder can effectively enhance the mechanical properties, wear resistance, and fatigue resistance of the composite material.

[0049] In step two, a suitable material needs to be selected as the reinforcing material. Aramid fibers (such as Kevlar) are chosen as the reinforcing material. Kevlar fiber 3 is known for its extremely high tensile strength (approximately 3.5 GPa) and high elastic modulus (100-150 GPa), providing excellent stiffness and mechanical properties. It exhibits excellent wear resistance and fatigue resistance, maintaining performance for extended periods in high-wear environments and performing well under repeated loading conditions, making it suitable for applications subjected to long-term high stress. Kevlar fiber 3 has good chemical resistance to most acids and alkalis, making it suitable for a variety of chemical environments. Kevlar fiber 3 has good chemical compatibility with nylon 66 because they are both members of the polyamide family. This allows Kevlar fiber 3 to bond well with the nylon 66 matrix, resulting in uniform dispersion in the composite material.

[0050] In step two, for the selection of nano-silica, high-purity powder with an average particle size in the range of 20-50 nanometers was chosen. This powder can effectively enhance the mechanical properties, wear resistance, and fatigue resistance of the composite material. In addition, to improve the dispersibility of nano-silica in the resin matrix and its bonding force with the interface, it was specially surface-treated with a silane coupling agent.

[0051] Pretreatment: The matrix material and aramid fiber are dried to ensure that the moisture content is below 0.5%.

[0052] In step three, the matrix material and aramid fibers need to be extruded and melt-molded. The dried matrix material and nano-silica are uniformly mixed in a predetermined ratio (mass ratio of 9:1). The mixing process ensures that the nano-silica is uniformly distributed in the matrix to enhance the material's performance. To ensure uniform mixing, high-speed stirring or ball milling techniques are used to fully disperse the nano-silica in the matrix material and avoid agglomeration. After mixing, it is fed into extruder 2.

[0053] In step three, a single-screw extruder 2 is selected from the extruders 2. The single-screw extruder 2 includes a heating device 4 located at the front end of the screw, a cooling device 5 located at the front end of the heating device 4, and the screw of the single-screw extruder 2 is hollow along its axis.

[0054] The extruder 2 is equipped with a screw, which generates shear force through rotation, aiding in further mixing and homogenization of the mixture. To ensure the material reaches an optimal molten state during extrusion, a heating device 4 is installed at the outer end of the screw in the extruder 2. The temperature can be adjusted according to the material characteristics to ensure that the mixed material transforms from a solid state to a uniform molten state during screw rotation. This process ensures that the molten mixture has sufficient fluidity, facilitating extrusion molding through a die.

[0055] The molten mixture is then uniformly extruded through a carefully designed die, which ensures the mixture forms an elongated cylinder of a predetermined diameter. The size and shape of the die, and its fit with the single-screw extruder 2, are crucial to the quality of the final product. To provide additional support during extrusion, the screw center is connected to the end of a Kevlar fiber 3 via an opening design. The Kevlar fiber 3 is connected to the center of the single-screw die via a specific device, ensuring the fiber remains on the central axis of the cylindrical resin during extrusion, thus enhancing the material's mechanical properties and providing intermediate support.

[0056] After the molten mixture is extruded through the screw die, the material quickly enters the cooling device 5. The cooling medium (such as water or air) in the cooling device 5 can quickly cool and solidify the material, ensuring that it maintains its cylindrical shape and causing the molecular structure of the material to solidify. After cooling, the shape of the slender cylinder is stabilized, ensuring that subsequent molding operations are not affected.

[0057] In this embodiment, a single-screw extruder 2 is used for extrusion molding, and the temperature of the heating device 4 is set at approximately 280°C to ensure that the material can be fully melted and maintain good fluidity. Before feeding, the mixed material is thoroughly dried to remove moisture and prevent the formation of bubbles and voids during extrusion. The dried material is fed into the extruder feed inlet 1 through an automatic feeding system. The screw rotation not only ensures a constant feed rate but also promotes uniform mixing of the two materials. The screw rotation speed and thrust are optimized according to the material characteristics to ensure uniform mixing and consistent distribution.

[0058] During extrusion, a single-screw mixer is responsible for mixing and advancing the preform from step one, which then enters the heating zone for melting. The molten preform continues to advance via the screw mechanism. At the central shaft of the screw mixer, a disc of Kevlar filaments 3 is introduced into the center of the mixer through an opening in the central shaft. The ends of the Kevlar filaments are bound to the center of the end cap 6, which provides preload force, keeping the filaments taut on the central shaft. Simultaneously, the material at the cooling device 5 is pushed out after reaching a certain pressure. When the molten resin mixture enters the cooling device 5, it impregnates the Kevlar filaments, forming a central shaft reinforcement of the resin, thereby significantly improving the fatigue resistance and durability of the torsion spring and playing a key role in enhancing the mechanical properties of the torsion spring.

[0059] During the extrusion process, the extrusion speed and pressure are strictly controlled to ensure that the molten material is extruded uniformly and forms a consistent cross-sectional shape. The extrusion speed is 10-30 mm / s. The temperature of the water-cooling tank is controlled at 10-20℃, with cold water injected through the lower inlet, and the water circulation system is used to maintain a stable water temperature inside the tank.

[0060] In step four, the slender cylinder from step three needs to be shaped into a torsion spring state using a torsion spring forming device. The torsion spring forming device includes a drive unit, a metal-like torsion spring forming blade fixing unit 8, and a metal-like torsion spring forming blade moving unit 7. Both the metal-like torsion spring forming blade fixing unit 8 and the metal-like torsion spring forming blade moving unit 7 are provided with mutually matching forming grooves, which are adapted to the shape of the thermoplastic composite torsion spring 11. This torsion spring forming device needs to have precise dimensional control and a smooth surface to reduce friction and improve forming accuracy. After passing through the cooling device 5, the extruded slender cylindrical material will be shaped into a torsion spring by the torsion spring forming device. The specific steps are as follows:

[0061] First, the extruded slender cylinder is pulled out a certain distance, and then the cylinder forming groove of the metal-like torsion spring forming cutter 7 is controlled to move to the lower end of the cylinder.

[0062] Furthermore, the metal-like torsion spring forming blade moving part 7 is pressed upward from below by the driving part, pressing the horizontal slender cylindrical material into a ring structure.

[0063] Furthermore, while pressing the slender cylinder upwards, the control system moves back and forth at a certain speed, allowing the slender cylindrical material to be smoothly fixed within the forming grooves of the moving part 7 and the fixing part 8. Precise control is required during this process. Movement stops when the forming grooves of the moving part 7 and the fixing part 8 are closed. At this point, the slender cylinder will move along the forming grooves formed by the moving part 7 and the fixing part 8, gradually shaping it into a ring.

[0064] Furthermore, the single-screw extruder 2 continues to extrude an elongated cylinder. The outer cylindrical portion of the positioning body 10 winds the annular body shaped by the torsion spring forming device into a thermoplastic composite torsion spring 11 and fixes it. When the required number of turns is reached, the elongated cylindrical material at the extruder 2 port is cut off using a cutter. The metal-like torsion spring forming cutter 7 moves away, and the cylindrical surface of the positioning body 10 carries the formed thermoplastic composite torsion spring 11.

[0065] After the first positioning body 10 completes winding a thermoplastic composite torsion spring 11, the control system moves it away to allow for air cooling. Simultaneously, the second positioning body 10 begins repeating the process of the first, continuing to wind the ring formed by the torsion spring molding device to create a new thermoplastic composite torsion spring 11. This process is repeated continuously, with a total of six positioning bodies 10 participating to ensure continuous operation of the production line.

[0066] While the sixth positioning body 10 is in operation, the thermoplastic composite torsion spring 11 on the first positioning body 10 has essentially cooled and solidified. At this point, the annular thrust device 9 on the positioning body 10 pushes out the already wound thermoplastic composite torsion spring 11. This cyclical production method enables automated production line manufacturing of the thermoplastic composite torsion spring 11, providing an effective solution for mechanisms requiring large quantities of such springs. Furthermore, this process is not only suitable for producing composite torsion springs but can also be used to produce similar components, greatly improving the production efficiency of composite materials. Compared to the traditional mold-forming method for composite torsion springs, this method is more convenient and conducive to continuous production.

[0067] In another embodiment, an exoskeleton assistive device is designed for middle-aged and elderly people with mobility issues. It uses a lightweight engineering plastic structure to bind to the user's legs, with a composite torsion spring at the knee joint for walking assistance. Traditional exoskeleton assistive devices are often made of carbon steel, which has a shear modulus of approximately 77 GPa, while nylon 66 has a shear modulus of approximately 4 GPa, and Kevlar fiber 3 has a shear modulus of approximately 19 GPa. Adding nano-silica can improve the mechanical properties of the composite material. For the same specifications, the torque of a metal torsion spring is approximately three times that of a composite torsion spring. This can be achieved by increasing the wire diameter of the composite material to 1.5 times that of the metal torsion spring. Furthermore, the density ratio of the metal to composite torsion spring is 7:1, thus significantly reducing the weight of the torsion spring. In terms of price, although carbon steel is slightly cheaper than composite material, the raw material costs for both are very low. The production process of carbon steel torsion springs is more complex, and thermoplastic polyamide has the advantage of being recyclable. Therefore, overall, using composite torsion springs is more advantageous than metal springs.

[0068] In another embodiment, the exoskeleton assistive device includes a thigh fixation mechanism 13, a lower leg fixation mechanism 17, a thigh connecting frame 12, a lower leg connecting frame 16, and an adjustable pretension mechanism disposed between the thigh connecting frame 12 and the lower leg connecting frame 16; the thermoplastic composite torsion spring 11 is disposed within the adjustable pretension mechanism.

[0069] The thigh connecting frame 12 and the calf connecting frame 16 are each provided with an adjustment cavity along their longitudinal direction. The adjustable preload mechanism includes:

[0070] A positioning pin is installed on the thigh connecting frame 12, one end of which extends into the adjustment cavity of the calf connecting frame 16 and can move along the adjustment cavity.

[0071] Adjustment block 14, the adjustment block 14 is mounted on thigh connecting frame 12, the adjustment block 14 is installed in the adjustment cavity of thigh connecting frame 12, and can move along the adjustment cavity;

[0072] An adjusting bolt is mounted on the adjusting block 14 and is movable within the adjusting cavity of the thigh connecting frame 12;

[0073] Fastening nut 15, the fastening bolt is screwed onto the adjusting bolt;

[0074] A thermoplastic composite torsion spring 11 is sleeved on a positioning pin, with one end abutting against the lower leg connecting frame 16 and the other end abutting against the adjusting block 14.

[0075] To better suit different types of people, this exoskeleton device is equipped with an adjustable pretension mechanism. By adjusting the position of the adjusting block 14 within the adjusting cavity of the thigh connecting frame 12, the rotation of the end of the thermoplastic composite torsion spring 11 is controlled to achieve different pretension forces.

[0076] The thigh fixation mechanism 13 and the calf fixation mechanism 17 are designed according to the average height of adults to ensure that they can meet the needs of most users. The rigid fixation device is placed on the back of the thigh and calf. The purpose is to ensure that when the user bends the knee joint, the force is mainly borne by the back of the thigh and calf. Through the connection of the rigid components, the force transmission effect is faster and more accurate. The front strap connects to the strap hole on the fixation device, and the user can adjust the comfort of the binding. At the same time, two straps are provided for both the thigh and calf, which makes the user more stable when wearing the device, simplifies the user's wearing and adjustment, and provides a more comfortable experience for the user while meeting the assistance requirements.

[0077] This device not only uses lightweight, high-performance composite material torsion springs for assistance, but also greatly improves its applicability to various users through an adjustable preload device. Its ergonomic design ensures excellent force distribution and provides users with exceptional comfort. The calf support 16 is placed on the inside, while the thigh support 12 is placed on the outside, making its structure more conform to the human leg's shape.

[0078] In lower limb exoskeletons, properly fitted torsion springs are carefully installed in key areas, such as the knee and ankle joints, to provide necessary power support. This design aims to reduce the user's physical burden, thereby improving walking efficiency and comfort.

[0079] The principle behind exoskeleton assistive devices is that when a user performs actions such as walking, running, or squatting, the exoskeleton's knee joint begins to move. As the movement continues, the exoskeleton's elastic elements (torsion springs) begin to deform. For example, during walking, when the user bends their knee, the spring is compressed, and the deformation of the elastic element increases its internal stress, thus storing energy. This energy exists in the form of elastic potential energy, the magnitude of which is proportional to the amount of deformation of the elastic element. Energy release is the reverse process of energy storage; when the user completes the preparatory movement and begins the reverse movement (such as from bending the knee to straightening it), the elastic element begins to return to its original shape. During this recovery process, the elastic element converts the stored elastic potential energy into kinetic energy, propelling the exoskeleton's joint movement and thus assisting the user's movement. The assistive effect of the exoskeleton is most pronounced during energy release, reducing the muscle strength required for the user to extend the joint.

[0080] For the fixation system, the main frame is made of high-strength engineering plastics (such as polycarbonate), maintaining lightweight while possessing good strength and toughness. Both the thigh and calf support straps use highly elastic fabric straps (such as nylon or elastic fibers) and are combined with quick-release buckles to improve wearing comfort and convenience. The thigh support strap wraps around the middle of the thigh, equipped with a multi-point fixation system and soft cushioning to reduce pressure on the skin, and allows for precise adjustment via a micro-adjustment knob. The strap surface has ventilation holes to enhance airflow and prevent skin discomfort from prolonged wear. The calf support strap also uses a multi-point fixation system, working in conjunction with the thigh support strap to provide all-around support, and is equipped with a micro-adjustment knob to accommodate different calf sizes.

[0081] In terms of joint protection, a flexible protective layer is designed near the knee joint, allowing natural flexion while providing additional support and reducing impact during exercise. The hinge mechanism simulates the natural range of motion of the knee joint, allowing flexion and extension. Symmetrical hinge mechanisms are set on both the internal and external sides to provide additional support and stability. One end of the connecting rod connects to the thigh or calf fixation device, and the other end connects via a hinge mechanism. A torsion spring is placed at the hinge to provide the assistive function. The overall design aims to provide users with a comfortable and reliable lower limb exoskeleton assistive experience through the synergy of the adjustable preload device and the fixation device.

[0082] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a thermoplastic composite torsion spring, characterized in that: The preparation method steps are as follows: Step 1: Select polyamide resin as the matrix material and nano-silica powder. Mix the matrix material and nano-silica powder at a mass ratio of 9:1 using a high-speed mixer to form a uniform preform. Step 2: Select aramid fiber as the reinforcing material, and dry the preform and reinforcing material from Step 1 to ensure that their moisture content is below 0.5%; Step 3: The reinforcing material and preform from Step 2 are melted and mixed and extruded through an extruder (2) to form a uniform, slender cylinder; the extruder (2) includes a heating device (4) located at the front end of the screw, the temperature provided by the heating device (4) is 270-290 degrees; the extruder (2) includes a cooling device (5) located at the front end of the heating device (4), the temperature provided by the cooling device (5) is 10-20 degrees; the extrusion speed of the extruder (2) is 10-30 mm / s; the screw of the extruder (2) is hollow along its axis, one end of the aramid fiber enters the extruder (2) along the hollow part of the screw, and passes through the heating device (4) and the cooling device (5) in sequence, and is pre-installed at the discharge port of the extruder (2) through the end cap (6); Step 4: The slender cylinder from Step 3 is shaped into a thermoplastic composite torsion spring (11) using a torsion spring forming device. The torsion spring forming device includes a drive unit, a metal-like torsion spring forming blade fixing unit (8), and a metal-like torsion spring forming blade moving unit (7). Both the metal-like torsion spring forming blade fixing unit (8) and the metal-like torsion spring forming blade moving unit (7) are provided with mutually cooperating forming grooves, which are adapted to the shape of the thermoplastic composite torsion spring (11). The extruder (2) continues to extrude a slender cylinder. The outer cylindrical part of the positioning body (10) winds the annular body shaped by the torsion spring forming device into a thermoplastic composite torsion spring (11) and fixes it. When the required number of turns is reached, the slender cylindrical material at the port of the extruder (2) is cut off with a cutter. The metal-like torsion spring forming cutter moving part (7) moves away, and the cylindrical surface of the positioning body (10) carries the formed thermoplastic composite torsion spring (11). After the first positioning body (10) finishes winding a thermoplastic composite torsion spring (11), the control system will move it away to allow for air cooling; at the same time, the second positioning body (10) begins to repeat the process of the first positioning body (10), continuing to wind the annular body shaped by the torsion spring forming device to form a new thermoplastic composite torsion spring (11). After the thermoplastic composite torsion spring (11) on the first positioning body (10) is cooled and formed, the wound thermoplastic composite torsion spring (11) is pushed out by the annular thrust device (9) on the positioning body (10).

2. The method for preparing the thermoplastic composite torsion spring according to claim 1, characterized in that: In step one, the polyamide resin is nylon 66; the average particle size of the nano-silica powder is 20-50 nanometers.

3. The method for preparing the thermoplastic composite torsion spring according to claim 1, characterized in that: In step two, the aramid fiber is Kevlar fiber (3).

4. The application of the thermoplastic composite torsion spring in the preparation method of the thermoplastic composite torsion spring according to any one of claims 1-3 in an exoskeleton assistive device.

5. The application of the thermoplastic composite torsion spring according to claim 4 in an exoskeleton assistive device, characterized in that: The exoskeleton assist device includes a thigh fixation mechanism (13), a lower leg fixation mechanism (17), a thigh connecting frame (12), a lower leg connecting frame (16), and an adjustable pretension mechanism disposed between the thigh connecting frame (12) and the lower leg connecting frame (16); the thermoplastic composite torsion spring (11) is disposed within the adjustable pretension mechanism.

6. The application of the thermoplastic composite torsion spring according to claim 5 in an exoskeleton assistive device, characterized in that: An adjustment cavity is provided longitudinally between the thigh connecting frame (12) and the lower leg connecting frame (16), and the adjustable preload mechanism includes: Positioning pin, which is installed on the thigh connecting frame (12), one end of which extends into the adjustment cavity of the calf connecting frame (16) and can move along the adjustment cavity; Adjustment block (14), the adjustment block (14) is mounted on the thigh connecting frame (12), the adjustment block (14) is mounted in the adjustment cavity of the thigh connecting frame (12) and can move along the adjustment cavity; An adjusting bolt is mounted on the adjusting block (14) and is movable within the adjusting cavity of the thigh connecting frame (12); A fastening nut (15) is screwed onto an adjusting bolt; Thermoplastic composite torsion spring (11) is sleeved on the positioning pin, with one end abutting against the lower leg connecting frame (16) and the other end abutting against the adjusting block (14).

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