Double-layer structure sensor for robotic skin and preparation method and application thereof

Abstract

The application provides a double-layer structure sensor for a robot skin and a preparation method and application thereof, and belongs to the fields of bionics and high polymers. The double-layer structure sensor for the robot skin comprises a conductive foam layer and an ionic gel layer. The material of the conductive foam layer comprises polyurethane porous foam and a first conductive material loaded in the polyurethane porous foam. The material of the ionic gel layer comprises a polyacrylic acid-based semi-interpenetrating network gel and a second conductive material. The conductive foam layer and the ionic gel layer are adhered and attached through an interface. The double-layer structure sensor has a wide detection range, stable electrical signal output, intrinsic repair capacity, structural integrity and signal acquisition reliability under long-term dynamic load.

Description

Technical Field

[0001] This application relates to the fields of bionics and polymer science, and in particular to a bilayer structure sensor for robotic skin, its preparation method, and its application. Background Technology

[0002] With the development of humanoid robot technology, endowing them with human-like tactile perception capabilities is the core of achieving safe and intelligent interaction. Robot skin, as a key carrier, needs to integrate flexible sensors capable of stably detecting multidimensional physical signals. Among these, ionogels, due to their high ionic conductivity and excellent elasticity, are considered important candidate materials for constructing high-sensitivity tactile sensors. However, applying ionogels to actual robot skin faces significant challenges. Conventional ionogel materials have limited mechanical strength and resilience, making it difficult to match the frequent and large-scale dynamic deformations of robot joints, leading to fatigue damage and signal drift during long-term use. Furthermore, the interfacial adhesion between ionogels and the robot body or electrodes is generally weak, easily peeling off during dynamic movement, resulting in signal acquisition failure. Although self-healing performance is generally considered crucial for extending device lifespan, existing technologies often struggle to achieve a balance between material repair efficiency, environmental stability, and core sensing performance.

[0003] Therefore, there is an urgent need to develop a robotic skin solution that combines higher ionic conductivity, active interfacial adhesion, and efficient intrinsic self-healing capabilities. Summary of the Invention

[0004] In view of this, in order to at least partially solve at least one of the aforementioned technical problems, this application provides a double-layer structure sensor for robot skin, a method for its fabrication, and its application.

[0005] According to one embodiment of this application, a dual-layer sensor for robotic skin is provided, comprising a conductive foam layer and an ionogel layer; the conductive foam layer is made of polyurethane porous foam and a first conductive material loaded in the polyurethane porous foam; the ionogel layer is made of polyacrylic acid-based semi-interpenetrating network gel and a second conductive material; wherein the conductive foam layer and the ionogel layer are bonded together by interfacial adhesion.

[0006] According to another embodiment of this application, a method for preparing a dual-layer sensor for robotic skin is provided, comprising: foaming, shaping, and drying a wet-process polyurethane resin to obtain a porous polyurethane foam, wherein the wet-process polyurethane resin is obtained by mixing and stirring polyvinyl alcohol powder and polyamide wax; impregnating the porous polyurethane foam in a solution containing a first conductive material and drying it to obtain a conductive foam layer; mixing acrylic acid, a photoinitiator, and a solvent, and performing a polymerization reaction under light irradiation to obtain a polyacrylic acid solution; mixing the polyacrylic acid solution, a polymeric monomer, a crosslinking agent, a thermal initiator, and a second conductive material, and reacting them by heating to obtain an ionogel layer, wherein the polymeric monomer includes at least one of hydroxyethyl acrylate and hydroxyethyl methacrylate; and attaching the conductive foam layer and the ionogel layer to the interface via interfacial adhesion to obtain a dual-layer sensor for robotic skin.

[0007] According to another embodiment of this application, an application of a dual-layer structure sensor that provides robotic skin is provided, including at least one of the following: (1) application in humanoid robot tactile sensing skin and bionic systems; (2) application in medical rehabilitation equipment for monitoring human movement and physiological signals.

[0008] According to embodiments of this application, a conductive foam layer composed of a first conductive material supported by polyurethane porous foam provides a highly elastic, compressible porous framework, endowing the sensor with excellent flexibility and mechanical resilience, enabling it to adapt to large-amplitude, high-frequency dynamic deformations of robot skin. Its porous structure also effectively enhances pressure sensitivity and response range. An ionogel layer composed of a polyacrylic acid-based semi-interpenetrating network gel and a second conductive material, dominated by the macroscopic deformation and ion migration of its semi-interpenetrating network, maintains continuous electrical response under high pressure, thereby broadening the detection upper limit and providing high ionic conductivity. This ensures stable electrical signal output from the sensor over a wide strain range. Simultaneously, this semi-interpenetrating network gel material possesses highly efficient intrinsic self-healing capabilities, rapidly restoring its structure and conductivity after damage, extending the sensor's lifespan. Through interfacial adhesion bonding, a strong molecular-level bond is formed between the two layers, generating active and durable interfacial adhesion forces. This effectively prevents interlayer delamination under complex mechanical stress, ensuring the structural integrity and signal acquisition reliability of the sensing unit under long-term dynamic loads. Attached Figure Description

[0009] Figure 1 This is a 150x scanning electron microscope image of the polyurethane porous foam of Example 1 of this application;

[0010] Figure 2 This is a graph showing the test results of the piezoresistive performance of the double-layer structure sensor in Embodiment 3 of this application;

[0011] Figure 3 This is a graph showing the test results of the piezoresistive performance of a single-layer polyurethane porous material sensor, which is a comparative example of this application.

[0012] Figure 4 The figure shows the piezoresistive performance test results of the monolayer structure ion gel sensor of Comparative Example 2 of this application. Detailed Implementation

[0013] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0014] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0015] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0016] In realizing the concept of this application, it was discovered that the technical routes for flexible pressure sensors mainly revolve around the principles of piezoresistive, capacitive, and piezoelectric sensors. Sensitivity is enhanced by employing composites of elastomer substrates (such as silicone rubber and thermoplastic polyurethane TPU) and nano-conductive materials (such as carbon nanotubes, graphene, and metal nanowires), or by designing microstructures (such as micro pyramids and porous sponges). However, a common and critical performance contradiction exists: the difficulty of simultaneously achieving high sensitivity, large range, and excellent flexibility.

[0017] To achieve a softness mimicking human skin, with moduli as low as kPa-MPa, ultrasoft materials (such as hydrogels and low-modulus silicone) are often used in related fields. These materials exhibit significant deformation under minute pressures, resulting in extremely high sensitivity. However, the ultrasoft nature of these materials also means low mechanical strength, making them prone to structural collapse or irreversible deformation under high pressures, leading to narrow measurement ranges, poor linearity, and easy saturation. Conversely, materials that can withstand greater pressure often have higher moduli, but lack sufficient softness and conformability. Furthermore, when combining materials with different properties to compensate for each other's shortcomings, additional adhesive layers or complex interface treatment processes are usually required. This not only increases manufacturing costs and steps, but also poses a potential threat to the long-term reliability of devices due to adhesion failure at the interface of heterogeneous materials under dynamic deformation.

[0018] Specifically, according to one aspect of this application, a dual-layer sensor for robotic skin is provided, comprising a conductive foam layer and an ionogel layer; the conductive foam layer is made of polyurethane porous foam and a first conductive material loaded in the polyurethane porous foam, and the ionogel layer is made of polyacrylic acid-based semi-interpenetrating network gel and a second conductive material; wherein the conductive foam layer and the ionogel layer are bonded together by interfacial adhesion.

[0019] According to embodiments of this application, a conductive foam layer composed of a first conductive material supported by polyurethane porous foam provides a highly elastic, compressible porous framework, endowing the sensor with excellent flexibility and mechanical resilience, enabling it to adapt to large-amplitude, high-frequency dynamic deformations of robot skin. Its porous structure also effectively enhances pressure sensitivity and response range. An ionogel layer composed of a polyacrylic acid-based semi-interpenetrating network gel and a second conductive material, dominated by the macroscopic deformation and ion migration of its semi-interpenetrating network, maintains continuous electrical response under high pressure, thereby broadening the detection upper limit and providing high ionic conductivity. This ensures stable electrical signal output from the sensor over a wide strain range. Simultaneously, this semi-interpenetrating network gel material possesses highly efficient intrinsic self-healing capabilities, rapidly restoring its structure and conductivity after damage, extending the sensor's lifespan. Through interfacial adhesion bonding, a strong molecular-level bond is formed between the two layers, generating active and durable interfacial adhesion forces. This effectively prevents interlayer delamination under complex mechanical stress, ensuring the structural integrity and signal acquisition reliability of the sensing unit under long-term dynamic loads.

[0020] Furthermore, the dual-layer collaborative response mechanism ensures that the sensor can simultaneously and accurately capture continuous mechanical stimuli ranging from slight contact to severe compression (wide detection range) and output high signal-to-noise ratio, distinguishable electrical signals. The integrated sensor design can overcome the shortcomings of insufficient mechanical properties of ion gel skin, easy interface failure, and difficulty in balancing self-healing efficiency and sensing performance, thereby improving the sensitivity, durability, and environmental adaptability of the robotic skin.

[0021] According to embodiments of this application, the polyacrylic acid-based semi-interpenetrating network gel is a cross-linked network gel formed by the interpenetration of linear polyacrylic acid and poly(hydroxyethyl acrylate-co-hydroxyethyl methacrylate); the mass ratio of linear polyacrylic acid to poly(hydroxyethyl acrylate-co-hydroxyethyl methacrylate) is (0.01~0.5):1.

[0022] According to embodiments of this application, the mass ratio of linear polyacrylic acid to poly(hydroxyethyl acrylate-co-hydroxyethyl methacrylate) can be 0.01:1, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.3:1, 0.4:1, or 0.5:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as (0.01~0.25):1, (0.1~0.5):1, etc.

[0023] According to embodiments of this application, the semi-interpenetrating network structure of linear polyacrylic acid and poly(hydroxyethyl acrylate-co-hydroxyethyl methacrylate) enables a better balance between the entanglement and interaction of the two polymer chains, thereby regulating the mechanical toughness, swelling rate, interfacial compatibility with conductive foam, and self-healing efficiency of the gel at the molecular level. This ensures the stability of the gel layer structure and the functional recoverability under dynamic deformation, providing material-level protection for reliable sensing of robotic skin under actual complex working conditions.

[0024] According to an embodiment of this application, the mass ratio of the first conductive material to the polyurethane porous foam in the conductive foam layer is (0.001~0.1):1.

[0025] According to embodiments of this application, the mass ratio of the first conductive material to the polyurethane porous foam in the conductive foam layer can be 0.001:1, 0.005:1, 0.01:1, 0.03:1, 0.05:1, 0.08:1, or 0.1:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range of any two values, such as (0.001~0.005):1, (0.05~0.1):1, etc. According to embodiments of this application, an appropriate mass ratio between the first conductive material and the polyurethane porous foam in the conductive foam layer ensures that the load of the conductive material in the foam skeleton can both construct a continuous and efficient conductive network to guarantee excellent electronic conductivity and pressure sensitivity, and avoid excessive filling that blocks the foam pores or impairs its inherent high elasticity and compressibility, thereby achieving an ideal balance between conductivity and mechanical flexibility.

[0026] According to the embodiments of this application, the solvent of the ionogel layer is at least one of polyethylene glycol, ethylene glycol, and polypropylene glycol, wherein the molecular weight of polyethylene glycol is 200~600 Da.

[0027] In one or more specific embodiments of the application, the solvent for the ionogel layer is polyethylene glycol, and the molecular weight of polyethylene glycol can be 200 Da, 300 Da, 400 Da, 500 Da, or 600 Da, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as 200~400 Da, 300~500 Da, etc.

[0028] According to embodiments of this application, polyethylene glycol with a relatively low molecular weight provides an ion-conducting medium with suitable viscosity and a high dielectric constant that is not easily volatile, providing a stable environment for the ion migration of the second conductive material dissolved therein, thereby improving the ionic conductivity, response speed and electrical stability of the sensor over a wide temperature range.

[0029] According to embodiments of this application, the porous polyurethane foam is formed by foaming and shaping a wet-process polyurethane resin, wherein the wet-process polyurethane resin includes polyurethane resin, polyvinyl alcohol, and polyamide wax. Thus, by foaming and molding the wet-process polyurethane resin using a phase transfer method, a porous foam with a three-dimensional interconnected microporous structure is formed.

[0030] According to embodiments of this application, polyurethane resin can be polymerized from polyols, polysiloxanes, and diisocyanates. The types of polyols, polysiloxanes, and diisocyanates are not particularly limited.

[0031] According to an embodiment of this application, the first conductive material includes a carbon-based conductive material.

[0032] According to the embodiments of this application, carbon-based conductive materials are loaded into a polyurethane foam skeleton, which can construct a stable three-dimensional conductive network inside the foam, giving the conductive foam layer excellent electronic conductivity to assist in rapid signal transmission. Moreover, the high mechanical strength and chemical stability of the carbon-based conductive materials themselves can enhance the structural durability of the polyurethane foam skeleton.

[0033] According to embodiments of this application, the first conductive material includes one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, conductive carbon black, silver nanowires, silver powder, and copper powder.

[0034] In one or more embodiments of this application, the first conductive material is a multi-walled carbon nanotube. The carbon nanotube network produces a relatively significant change in contact resistance under minute pressure, providing the sensor with high initial sensitivity.

[0035] According to an embodiment of this application, the mass content of the first conductive material is 0.1% to 10% based on the total mass of the wet-process polyurethane resin.

[0036] According to embodiments of this application, based on the total mass of the wet-process polyurethane resin, the mass content of the first conductive material can be 0.1%, 1%, 3%, 5%, 7%, 9%, or 10%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as 0.1% to 5%, 2% to 8%, etc.

[0037] According to the embodiments of this application, when the mass content of the first conductive material is too low, the filler concentration is insufficient to construct a continuous and complete conductive permeation network in the three-dimensional porous skeleton of the foam, which will result in a low overall conductivity of the foam and a weak or insignificant response to changes in resistance to external pressure stimulation, thus failing to achieve an effective pressure sensing function. When the mass content of the first conductive material is too high, the excessive conductive filler will occupy too much volume, which may not only hinder the formation of an ideal interconnected open-cell structure in the polyurethane resin during the foaming process, but also increase the stiffness of the composite material, causing the final conductive polyurethane foam to become hard and brittle, losing its high elasticity and compressibility, and failing to meet the dynamic deformation and compliant fit requirements of robot skin.

[0038] According to embodiments of this application, the second conductive material comprises a metal salt.

[0039] According to embodiments of this application, the second conductive material includes one or more of lithium salt, sodium salt, potassium salt, calcium salt, magnesium salt, iron salt, and aluminum salt.

[0040] In one or more embodiments of this application, the second conductive material is a lithium salt, such as lithium chloride.

[0041] According to embodiments of this application, metal salts, as the second conductive material in the ionogel layer, provide abundant mobile ions for the ionogel. These mobile ions have high mobility in the stable medium composed of polyethylene glycol solvent and a semi-interpenetrating polymer network, thereby ensuring that the ionogel layer has superior and stable ionic conductivity at the molecular level, providing a physical basis for high-sensitivity sensing.

[0042] According to embodiments of this application, the thickness of the conductive foam layer is 2~10mm, and the compression modulus is 1~20kPa.

[0043] According to embodiments of this application, the thickness of the conductive foam layer can be 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, or 10mm, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as 4~6mm, 2~8mm, etc.

[0044] According to embodiments of this application, the compressive modulus of the conductive foam layer can be 1 kPa, 3 kPa, 5 kPa, 8 kPa, 10 kPa, 13 kPa, 15 kPa, 18 kPa, or 20 kPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as 5~15 kPa, 1~10 kPa, etc.

[0045] According to the embodiments of this application, the thickness of the ionogel layer is 2~10mm, and the compressive modulus is 20~200kPa.

[0046] According to embodiments of this application, the thickness of the ionogel layer can be 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as 4~6 mm, 2~8 mm, etc.

[0047] According to embodiments of this application, the compressive modulus of the ionogel layer can be 20 kPa, 50 kPa, 80 kPa, 100 kPa, 120 kPa, 150 kPa, 180 kPa, or 200 kPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as 50–150 kPa, 100–200 kPa, etc.

[0048] According to embodiments of this application, the thickness and compressive modulus of the conductive foam layer enable it to possess a sufficient three-dimensional porous structure to maintain high elasticity and compressibility. Its low compressive modulus allows the conductive foam layer to undergo significant deformation under minor pressure, thereby sensitively responding to external stress through changes in the internal conductive network, thus improving the sensor's detection sensitivity and response range. The thickness and compressive modulus of the ionogel layer enable it to possess both high-efficiency ion conductivity and self-healing capabilities, while also exhibiting moderate mechanical stiffness. This allows it to form good interfacial adhesion and stress transfer with the softer conductive foam layer, while also providing necessary structural support for the entire sensor, preventing excessive creep or fatigue damage under dynamic loads or repeated deformation.

[0049] Furthermore, the matching thickness of the conductive foam layer and the gradient design of the compressive modulus of the ionogel layer together ensure that the sensor maintains structural integrity, stable interlayer bonding, and reliable electrical signal output under complex working conditions. This ensures both the smooth and conforming properties required for robot skin and the durability and sensing consistency of its long-term use.

[0050] According to embodiments of this application, the mass content of the second conductive material is 1% to 10% based on the total mass of the ionogel layer; and the mass content of polyethylene glycol is 30% to 70% based on the total mass of the ionogel layer.

[0051] According to embodiments of this application, the mass content of the second conductive material can be 1%, 3%, 5%, 7%, 9%, or 10%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as 5% to 9%, 1% to 8%, etc.

[0052] According to embodiments of this application, the mass content of polyethylene glycol can be 30%, 40%, 50%, 60%, or 70% based on the total mass of the ionogel layer, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as 50%~65%, 40%~50%, etc.

[0053] According to the embodiments of this application, the mass content of the second conductive material ensures the concentration of mobile ions in the gel, thereby ensuring ionic conductivity. When the content is too high, the excessive salt concentration will cause the gel network to harden and become brittle due to excessive salting-out effect, damaging its flexibility and interfacial adhesion performance with the foam layer. Therefore, an appropriate content of the second conductive material can ensure the balance between the ion conduction mechanism and the mechanical properties of the material.

[0054] According to the embodiments of this application, the mass content of polyethylene glycol ensures that the gel has a suitable network structure and physical state, avoiding the situation where the mass content of polyethylene glycol is too low, causing the cross-linked network of the gel to be too dense and lose the elasticity and adhesion required for it to be a flexible sensitive layer; while if the content is too high, the viscosity of the prepolymer system will be too low, making it difficult to form a stable gel, affecting the feasibility of the process and the structural integrity of the device.

[0055] According to an embodiment of this application, the sensor further includes a first electrode and a second electrode; the first electrode is attached to the side of the conductive foam layer away from the ionogel layer; the second electrode is attached to the side of the ionogel layer away from the conductive foam layer.

[0056] Specifically, the first electrode and the second electrode are each independently connected to a wire.

[0057] According to embodiments of this application, the materials of the first electrode and the second electrode can be selected from metallic conductive materials, such as copper foil, gold foil, aluminum foil, silver foil, etc. They can also be formed by printing or coating with conductive ink or coating, such as silver paste, carbon paste, etc. They can also be used as the first electrode or the second electrode by conductive polymer, nanomaterial-based electrode, etc. This application does not limit them.

[0058] According to another embodiment of this application, a method for fabricating a double-layer structure sensor for robot skin is also provided, comprising the following steps S1 to S5.

[0059] Step S1: The wet polyurethane resin is foamed, shaped and dried to obtain porous polyurethane foam. The wet polyurethane resin is obtained by mixing and stirring polyurethane resin, polyvinyl alcohol powder and polyamide wax.

[0060] Step S2: Impregnate the polyurethane porous foam in a solution containing the first conductive material and dry it to obtain a conductive foam layer.

[0061] Step S3: Mix acrylic acid, photoinitiator and solvent, and carry out polymerization reaction under light to obtain polyacrylic acid solution.

[0062] Step S4: Mix the polyacrylic acid solution, polymeric monomer, crosslinking agent, thermal initiator, and second conductive material, and react them by heating to obtain an ion gel layer, wherein the polymeric monomer includes at least one of hydroxyethyl acrylate and hydroxyethyl methacrylate.

[0063] Step S5: The conductive foam layer and the ionogel layer are attached by interfacial adhesion to obtain a dual-layer sensor for robotic skin.

[0064] According to the embodiments of this application, steps S1 and S2 of the above preparation method involve mixing and stirring polyvinyl alcohol powder and polyamide wax to obtain wet-process polyurethane resin. This ensures the specific rheological and pore-forming characteristics of the resin matrix from the source, laying the foundation for the subsequent preparation of polyurethane porous foam with ideal open-cell structure and mechanical properties. By preparing the ion gel layer in steps S3 and S4, its microstructure and material properties can be precisely controlled through preparation parameters to adapt to conductive foam layers with different properties. In step S5, the strong bond between the two layers can be achieved by relying on the adhesiveness of the ion gel itself, without the need for additional adhesives. This avoids the stress or instability that may be introduced by complex interface processing processes, and avoids the problems of easy damage to the sensing layer, easy peeling of the interface, and poor dynamic stability of the overall device. This ensures the structural integrity of the double-layer device when it is fabricated over a large area.

[0065] According to an embodiment of this application, the mass ratio of polymeric monomer to crosslinking agent is (15~100):1.

[0066] According to embodiments of this application, the mass ratio of polymeric monomer to crosslinking agent can be 15:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 100:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Alternatively, it can be within a range consisting of any two values, such as (30~50):1, (40~60):1, etc.

[0067] According to embodiments of this application, the ratio of crosslinking agent to polymeric monomer affects the flexibility and brittleness of the ionogel layer. If the crosslinking agent ratio is too high, the gel network will be overly crosslinked, making the gel brittle and reducing its flexibility. Furthermore, functional groups (such as hydroxyl and carboxyl groups) on its surface that can form adhesive hydrogen bonds will be excessively consumed or shielded, leading to a decrease in interfacial adhesion strength between the ionogel layer and the conductive foam layer. Simultaneously, an overly dense network will hinder ion migration, resulting in a decrease in ionic conductivity. If the ratio is too high, it will be difficult to form a sufficiently complete and stable three-dimensional crosslinked network, resulting in poor mechanical strength, shape retention, and durability of the gel. Therefore, a suitable mass ratio of crosslinking agent to polymeric monomer can form an ionogel layer with a semi-interpenetrating network structure of moderate crosslinking degree. This allows the ionogel layer to maintain excellent flexibility and high ionic conductivity while generating high-density hydrogen bonds with the polyurethane foam surface through the abundant hydroxyl and carboxyl groups in its network. This achieves strong interfacial adhesion between the two without the need for external adhesives, ensuring the integrity and operational reliability of the bilayer sensor's bilayer structure.

[0068] According to an embodiment of another aspect of this application, the application of a dual-layer structure sensor for robotic skin is provided, including at least one of the following: (1) application in humanoid robot tactile sensing skin and bionic systems; (2) application in medical rehabilitation equipment for monitoring human movement and physiological signals.

[0069] In one or more embodiments of this application, multiple sensing units can be arranged in an array to distinguish and plot the distribution of pressure on a two-dimensional plane.

[0070] According to embodiments of this application, the dual-layer structure of this application can densely and flexibly integrate thousands of micro-sensing units in an array, mimicking the ability of human skin to sense changes in contact position, shape, and force. It stably conforms to the complex curved surface of the robot, and under long-term friction, compression, and other working conditions, it can achieve continuous and reliable monitoring of contact force, sliding, and other signals, thereby improving the environmental robustness and operational durability of the robot's tactile skin.

[0071] The following will further explain the solution of this application through specific embodiments. Unless otherwise specified, all reagents used are commercially available reagents, and all test methods or experimental methods used are conventional experimental methods in the art.

[0072] Example 1

[0073] Preparation of wet polyurethane:

[0074] (1) Prepolymerization reaction and raw material processing: The polymer polyol and the double-hydroxyl-terminated polysiloxane were put into the reactor and stirred under vacuum at 120°C for 2 hours; then the temperature was lowered to 70°C and a portion of diphenylmethane-4,4'-diisocyanate (MDI) was added. The molar ratio of hydroxyl to isocyanate groups in the system was controlled to be 1:2 for the reaction to proceed until the viscosity of the reaction liquid reached 150 Pa·s (at 50°C), thus completing the first step of the prepolymerization reaction.

[0075] (2) Chain extension and end-capping reaction: Add the remaining diphenylmethane-4,4′-diisocyanate (MDI) and chain extender to the reaction vessel, control the total isocyanate index of the system to be 1 (i.e., the equivalent ratio of isocyanate group (NCO) to hydroxyl group (-OH) is 1:1), and carry out the chain extension reaction; during this period, add N,N-dimethylformamide (DMF) in 4-5 batches to adjust the solution concentration, and continue the reaction until the viscosity of the system drops to 30 Pa·s (under 50℃ conditions), and add methanol to end-cap the remaining isocyanate groups.

[0076] (3) Blending reaction and resin preparation: Polyvinyl alcohol powder and polyamide wax are added to the reaction system and stirred and blended at a certain temperature (90 °C) until the system is evenly dispersed to obtain wet polyurethane resin.

[0077] 20g of wet-process polyurethane resin was weighed and vacuum stirred to remove bubbles. It was then placed in hot water at 50℃ for static setting, followed by dynamic stirring for 12 hours. Finally, it was dried in an oven at 70℃ to obtain open-cell polyurethane foam. Next, 5g of multi-walled carbon nanotubes and 95g of ethanol were weighed and added to a 250mL beaker for stirring and ultrasonic dispersion for 30 minutes. The pre-prepared open-cell polyurethane foam was then placed in the beaker and ultrasonicated for 30 minutes. After removing the foam, the ethanol solvent was dried in an oven at 60℃ to obtain conductive porous polyurethane foam, i.e., the conductive foam layer. This was characterized by scanning electron microscopy at 150x magnification. The results are as follows: Figure 1 As shown.

[0078] Figure 1 This is a 150x scanning electron microscope image of the polyurethane porous foam of Example 1 of this application.

[0079] according to Figure 1It can be seen that the prepared conductive polyurethane porous foam has a uniform porous foam structure.

[0080] Thickness testing revealed that the prepared conductive foam layer was 5 mm thick. According to GB / T 1041 "Determination of Compression Properties of Plastics", the compression modulus was measured to be 5 kPa.

[0081] Example 2

[0082] Using 50g of 200 molecular weight polyethylene glycol (PEG200) as a solvent, 5g of acrylic acid (AA) and 0.05g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone (I1173) were added. The mixture was irradiated under a 365nm UV lamp for 1 hour to obtain a polyacrylic acid solution. To the obtained polyacrylic acid solution, 20g of hydroxyethyl acrylate (HEA), 20g of hydroxyethyl methacrylate (HEMA), 0.8g of crosslinking agent poly(ethylene glycol) diacrylate (CL), 0.4g of initiator azobisisobutyrazoline hydrochloride (VA044), and 5g of lithium chloride (LiCl) were added. The mixture was stirred and heated at 50℃ under sealed conditions for 8 hours to obtain a conductive ionomer gel.

[0083] Thickness testing revealed that the prepared conductive ionogel layer was 5 mm thick. According to GB / T 1041 "Determination of Compression Properties of Plastics", the compression modulus was measured to be 160 kPa.

[0084] Example 3

[0085] The conductive foam layer prepared in Example 1 is attached to the ion gel layer prepared in Example 2 to form a sensing material with a double-layer structure. Then, a copper foil is attached to the upper and lower surfaces of the sensing material with the double-layer structure as an electrode for encapsulation. Each copper foil layer is connected by a wire to obtain a double-layer sensor.

[0086] The piezoresistive performance of the double-layer structure sensor was tested. The test procedure was as follows: The double-layer structure sensor was fixed on the test platform of an E44.104 electronic universal testing machine and connected to a Keithley 2400 device. Then, pressure was applied to the sensor surface at a set compression rate, and the real-time pressure signal (converted to pressure ΔP based on the effective contact area of ​​the sensor) and resistance signal were recorded simultaneously. The sensitivity was calculated based on the recorded signals using the formula: S = (ΔR / R0) / ΔP, where S is the sensitivity (kPa). -1 ); ΔR is the relative change in resistance; R0 is the initial resistance value (Ω); ΔP is the applied pressure (kPa). The results are as follows: Figure 2 As shown.

[0087] Figure 2This is a graph showing the test results of the piezoresistive performance of the double-layer structure sensor in Embodiment 3 of this application.

[0088] according to Figure 2 It can be seen that in the low-pressure range of 0~12 kPa, the sensor exhibits a reading as high as 5.12 kPa. -1 The sensitivity is primarily due to the dramatic resistance change induced by the microporous structure of the underlying conductive polyurethane foam under initial pressure, which is the dominant factor. When the pressure rises to the medium pressure range of 12-45 kPa, the sensitivity transitions to 0.82 kPa. -1 At this point, the foam structure is gradually compacted, and its resistance change tends to level off. Meanwhile, the network deformation and ion channel modulation of the upper ion gel begin to play an increasingly important role. When the pressure further increases to the high-pressure range of 45-62 kPa, the foam layer is almost completely compressed, and the sensing mechanism is completely dominated by the ion gel layer. The stable deformation of its dense network under high pressure keeps the sensitivity at 0.03 kPa. -1 .

[0089] Example 4

[0090] The same preparation method as in Example 3 was used, except that lithium chloride in the ionogel layer was replaced with potassium chloride.

[0091] Comparative Example 1

[0092] The conductive polyurethane foam prepared in Example 1 was encapsulated by attaching a layer of copper foil to each of its upper and lower surfaces as the first and second electrodes, resulting in a single-layer polyurethane porous material sensor.

[0093] The piezoresistive properties of the polyurethane porous metamaterial sensor were tested, and the results are as follows: Figure 3 As shown.

[0094] Figure 3 The figure shows the test results of the piezoresistive performance of the polyurethane porous material monolayer sensor, which is Comparative Example 1 of this application.

[0095] according to Figure 3 It can be seen that the single-layer polyurethane porous material sensor, based on the electronic conduction mechanism, exhibits segmented high sensitivity within the 0-28 kPa pressure range thanks to its unique three-dimensional open-pore structure and loaded multi-walled carbon nanotube network. Especially in the extremely low pressure range of 0-2 kPa, the sensitivity reaches as high as 24.51 kPa. -1 This demonstrates its excellent ability to capture micro-force signals. However, as the pressure increases to 2–8 kPa and 8–28 kPa, its sensitivity decreases to 1.91 kPa, respectively. -1 and 0.81 kPa -1 The nonlinear decay indicates poor response consistency across a wide pressure range.

[0096] Comparative Example 2

[0097] The conductive ion gel prepared in Example 2 was encapsulated by attaching a layer of copper foil to each of its upper and lower surfaces as electrodes, resulting in a single-layer ion gel sensor.

[0098] The piezoresistive properties of the monolayer ionogel sensor were tested, and the results are as follows: Figure 4 As shown.

[0099] Figure 4 The figure shows the piezoresistive performance test results of the monolayer structure ion gel sensor of Comparative Example 2 of this application.

[0100] according to Figure 4 It can be seen that the single-layer ion gel sensor has a sensitivity of 2.82 kPa in the low-pressure range of 0–22 kPa. -1 That is, although it has a wider detection range, its initial sensitivity is poor.

[0101] Comparative Example 3

[0102] The same preparation method as in Example 3 was used, except that the solvent added to the ionogel layer was replaced with 50g of deionized water instead of polyethylene glycol.

[0103] Comparative Example 4

[0104] The same preparation method as in Example 3 was used, except that the preparation method of the ionogel layer is as follows:

[0105] Using 50 g of 200 molecular weight polyethylene glycol (PEG200) as a solvent, add 25 g of acrylic acid (AA), 25 g of hydroxyethyl methacrylate (HEMA), and 0.05 g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone (I1173), stir and mix, and irradiate under a 365 nm UV lamp for 1 h under sealed conditions to obtain an adhesive ionogel layer.

[0106] Comparative Example 5

[0107] The same preparation method as in Example 3 was used, except that the amount of crosslinking agent used in the ionogel layer was different, that is, 4 g of crosslinking agent poly(ethylene glycol) diacrylate (CL) was used.

[0108] Comparative Example 6

[0109] The same preparation method as in Example 3 was used, except that polyvinyl alcohol was not added during the preparation of wet polyurethane.

[0110] Test case

[0111] The sensors prepared in Examples 3, 4, and Comparative Examples 1 to 6 were tested using the following methods:

[0112] The compression modulus was tested according to GB / T 1041 "Determination of compressibility of plastics".

[0113] Adhesion strength test method: Partially bond the two layers of materials together, use the clamps of a universal testing machine to clamp the upper polyurethane layer and the lower gel layer respectively, stretch at a speed of 50 mm / min, and test the tensile strength, which is the adhesion strength.

[0114] Ionic conductivity test method: Cut a 1*1*0.5cm block of gel, cover the top and bottom surfaces of the gel with two copper foils respectively, connect the positive and negative terminals of a multimeter, measure the resistance R of the gel, and calculate the ionic conductivity according to the following formula: =l / (R*S).

[0115] Natural environment static stability test method: Place the double-layer structure sensor in an indoor environment with a temperature of 25℃ and a humidity of 50%RH. After 3 days, observe and weigh the mass. If the mass becomes lighter, it is considered that the properties have changed.

[0116] The test results are shown in Table 1 below.

[0117] Table 1

[0118]

[0119] As shown in Table 1, the bilayer sensor (Examples 3 and 4) has a moderate compressive modulus, and its bilayer structure still has considerable flexibility, making it suitable for use in robotic skin. Using water as a solvent to prepare the ionogel layer (Comparative Example 3) leads to instability in the sensor's physical properties. Using different gel preparation methods (Comparative Example 4) fails to obtain a semi-interpenetrating network structure, resulting in a random network through monomer random copolymerization, which reduces the adhesive strength of the gel. Increasing the proportion of crosslinking agent in the ionogel layer (Comparative Example 5) reduces the adhesion of the ionogel layer, making it brittle, and also reduces its ionic conductivity. Changing the wet polyurethane resin preparation method (Comparative Example 6) causes changes in the hardness and adhesion of the wet polyurethane, which in turn changes the overall compressive modulus of the sensor.

[0120] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A dual-layer sensor for robotic skin, characterized in that, Includes a conductive foam layer and an ion gel layer; The conductive foam layer is made of polyurethane porous foam and a first conductive material loaded in the polyurethane porous foam. The material of the ionogel layer includes a polyacrylic acid-based semi-interpenetrating network gel and a second conductive material. The conductive foam layer and the ionogel layer are bonded together by interfacial adhesion; The polyacrylic acid-based semi-interpenetrating network gel is a cross-linked network gel formed by the interpenetration of linear polyacrylic acid and poly(hydroxyethyl acrylate-co-hydroxyethyl methacrylate); The mass ratio of the linear polyacrylic acid to the poly(hydroxyethyl acrylate-co-hydroxyethyl methacrylate) is 0.01:1 to 0.5:

1.

2. The sensor according to claim 1, characterized in that, The mass ratio of the first conductive material to the polyurethane porous foam in the conductive foam layer is 0.001:1 to 0.1:

1. The solvent of the ionogel layer is at least one of polyethylene glycol, ethylene glycol, and polypropylene glycol, wherein the molecular weight of the polyethylene glycol is 200-600 Da.

3. The sensor according to claim 1, characterized in that, The first conductive material includes carbon-based conductive materials and / or metallic conductive materials; The second conductive material includes a metal salt.

4. The sensor according to claim 1 or 3, characterized in that, The first conductive material includes one or more of the following: multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, conductive carbon black, silver nanowires, silver powder, and copper powder. The second conductive material includes one or more of lithium salt, sodium salt, potassium salt, calcium salt, magnesium salt, iron salt, and aluminum salt.

5. The sensor according to claim 1, characterized in that, The thickness of the conductive foam layer is 2~10mm, and the compression modulus is 1~20kPa; The thickness of the ionogel layer is 2~10mm, and the compressive modulus is 20~200kPa.

6. The sensor according to claim 2, characterized in that, Based on the total mass of the ionogel layer, the mass content of the second conductive material is 1% to 10%; Based on the total mass of the ionogel layer, the mass content of the polyethylene glycol is 30% to 70%.

7. The sensor according to claim 1, characterized in that, Also includes: First electrode and second electrode; The first electrode is attached to the side of the conductive foam layer away from the ionogel layer; The second electrode is attached to the side of the ionogel layer away from the conductive foam layer.

8. A method for fabricating a double-layer structure sensor for robotic skin according to any one of claims 1 to 7, characterized in that, include: The wet polyurethane resin is foamed, shaped and dried to obtain porous polyurethane foam, wherein the wet polyurethane resin is obtained by mixing and stirring polyurethane resin, polyvinyl alcohol powder and polyamide wax. The polyurethane porous foam is impregnated in a solution containing a first conductive material and then dried to obtain a conductive foam layer. Acrylic acid, photoinitiator and solvent are mixed and polymerized under light to obtain polyacrylic acid solution; The polyacrylic acid solution, polymeric monomer, crosslinking agent, thermal initiator, and second conductive material are mixed and heated to obtain the ionogel layer, wherein the polymeric monomer includes at least one of hydroxyethyl acrylate and hydroxyethyl methacrylate; A dual-layer sensor for robotic skin is obtained by attaching the conductive foam layer and the ionogel layer through interfacial adhesion.

9. The preparation method according to claim 8, characterized in that, The mass ratio of polymeric monomer to crosslinking agent is 15:1 to 100:

1.

10. An application of the dual-layer structure sensor for robotic skin as described in any one of claims 1 to 7, characterized in that, Includes at least one of the following: (1) Application in humanoid robot tactile sensory skin and bionic systems; (2) Application of medical rehabilitation equipment in monitoring human movement and physiological signals.

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