Sole stress sensor based on conductive polymer, sensing element preparation method and sensor calibration test device and method

Abstract

The invention relates to a sole stress sensor based on a conductive polymer, a preparation method of a sensing element and a sensor calibration test device and method, and aims to solve the problems of poor practicability, complex structure and high cost of a sensor when the sensor is used for detecting normal force and shear force of feet of a diabetic patient. The sensor assembly and the supporting columns are installed between the upper clamping plate and the base plate, the bottom end of the sensor assembly is fixedly connected with the end face of the base plate, and pressure borne by the upper clamping plate and the base plate is monitored through the sensor assembly. The normal force loading mechanism and the tangential force loading mechanism are fixed on the shockproof workbench through the fixing frame, the stress sensor is arranged on the shockproof workbench, the linear brake is fixed above the sole stress sensor based on the conductive polymer, the loading end of the normal force loading mechanism abuts against the upper end face of the linear brake, and the loading end of the tangential force loading mechanism abuts against the lower end face of the linear brake. The four tangential force loading mechanisms abut against the side faces of the linear brake respectively. The invention belongs to the field of sensors and preparation thereof.

Description

Technical Field

[0001] The present invention relates to a stress sensor, a method for preparing a sensing element, and a sensor calibration and testing device and method, and in particular to a conductive polymer-based foot stress sensor, a method for preparing a sensing element, and a sensor calibration and testing device and method. The present invention belongs to the field of sensors and their preparation. Background Art

[0002] Diabetes is a chronic disease characterized by hyperglycemia, which is caused by absolute or relative insulin deficiency and utilization disorder. Most diabetic patients will experience nerve damage or neuropathy in their limbs (such as feet) due to disease complications, resulting in loss of tactile perception. This loss of tactile perception may cause ulcers or open wounds to form on the skin of the patient's feet. Recent studies have shown that this type of foot ulcer is related to the normal force and shear force exerted on the plantar part or the bottom surface of the foot. Therefore, people have developed a variety of measurement systems that try to use load sensors and pressure sensors to detect the force applied to the feet of diabetic patients in real time. For example, System and The system uses an array of pressure sensors to measure the pressure distribution on the foot. However, a disadvantage of these force measurement systems is that although they are sensitive to normal forces, they are less sensitive to shear forces.

[0003] In addition, some sensor array devices have been developed that can detect normal force and shear force at the same time. However, such sensor array devices are large in size and difficult to attach directly to the patient's foot, making them less practical. Some compact sensors have also been developed to overcome the above shortcomings, combining two shear sensors and one Pressure sensors are integrated into shoe insoles. However, due to their complex design, these devices are extremely expensive, making them unaffordable for many diabetic patients who could benefit from wearable force monitoring devices. Therefore, there is an urgent need for a small, highly accurate, and large-deformation foot stress sensor that can dynamically and synchronously measure the normal and shear forces applied to the feet of diabetic patients at a low cost. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of poor practicality, complex sensor structure and high cost when using sensors to detect normal force and shear force on the feet of diabetic patients, and to provide a foot stress sensor based on conductive polymer, a preparation method of the sensing element, and a sensor calibration test device and method.

[0005] The technical solution of the present invention is:

[0006] A conductive polymer-based plantar stress sensor comprising an upper splint, a base plate, a sensing component, and a plurality of support columns;

[0007] The upper splint and the base plate are arranged opposite to each other, the sensor assembly and multiple support columns are installed between the upper splint and the base plate, the bottom end of the sensor assembly is fixedly connected to the end surface of the base plate, and the top of the sensor assembly is arranged in contact with the upper splint, and the pressure exerted on the upper splint and the base plate is monitored by the sensor assembly.

[0008] Furthermore, a plurality of support columns are evenly distributed around the sensor component.

[0009] Furthermore, the sensing assembly includes a column, a resistance tester and five sensing elements. The column is a rectangular structure. The five sensing elements are respectively arranged on the bottom end face and four side faces of the rectangular structure. The five sensing elements are all connected to a resistance tester, and the five sensing elements are arranged in parallel.

[0010] Furthermore, the sensing element includes a PDMS elastic layer, a PEDOT:PSS conductive layer, a base layer, and two copper electrodes;

[0011] The PDMS elastic layer, PEDOT:PSS conductive layer, two copper electrodes and the base layer are fixedly pasted together in sequence. The PDMS elastic layer of each sensing element is in contact with the column. The two parallel copper electrodes are relatively arranged between the PEDOT:PSS conductive layer and the base layer, and a gap is provided between the two copper electrodes.

[0012] Furthermore, the support column is a support column made of rubber material, and the upright column is a cubic column made of polymethyl methacrylate material.

[0013] The preparation method of the sensor element is achieved by following the steps:

[0014] Step 1: The silicon substrate is cleaned and a mixture of PDMS prepolymer and curing agent is spin-coated on the silicon substrate and cured to form a PDMS elastic layer with a thickness of about 2 mm;

[0015] Step 2: Add about 5% by volume of dimethyl sulfoxide to the PEDOT:PSS dispersion and mix them. Then, apply the PEDOT:PSS dispersion and dimethyl sulfoxide mixture on the PDMS elastic layer formed by solidification in step 1, and dry to form a PEDOT:PSS conductive layer with a thickness of about 10 μm.

[0016] Step 3: Attach a copper electrode to the same end surface of the PEDOT:PSS conductive layer dried in step 2 using conductive epoxy adhesive. The copper electrode and the PDMS elastic layer are respectively located at both ends of the conductive layer. Cut and separate the PDMS elastic layer dried in step 1 on the silicon substrate.

[0017] Step 4: Glue the two copper electrodes onto PMMA using UV-curable adhesive to complete the fabrication of the sensing element.

[0018] Furthermore, in step 1, the elastic layer is prepared as follows: a silicon wafer substrate with a diameter of 100 mm is placed in a cleaning container, and ultrasonically cleaned with acetone and isopropyl alcohol for 10 minutes to remove surface impurities, and then blown dry with high-purity nitrogen. PDMS prepolymer and curing agent are mixed in a mass ratio of 10:1, mechanically stirred for 5 minutes until the mixture is uniform, and the mixture is degassed under vacuum for 30 minutes to eliminate bubbles. 25 ml of the evenly mixed PDMS prepolymer and curing agent mixture is poured onto the surface of the silicon wafer substrate.

[0019] A two-step spin coating process was used to form a uniform film: the first step was to spin-coat at 500 rpm for 10 seconds to evenly spread the PDMS prepolymer and curing agent mixture on the substrate; the second step was to spin-coat at 1000 rpm for 30 seconds to obtain an elastic layer film with a thickness of approximately 2 mm. The PDMS-coated substrate was then placed in a vacuum oven and cured at 80°C for 5 hours to ensure that the PDMS prepolymer and curing agent mixture were fully cross-linked and cured.

[0020] Preparation of the conductive layer in step 2: Prepare a PEDOT:PSS aqueous dispersion and 5% by volume of dimethyl sulfoxide, add dimethyl sulfoxide to the PEDOT:PSS aqueous dispersion, and magnetically stir for 2 hours. Place the PDMS elastic layer cured in step 1 on a spin coating apparatus and spin-coat the mixture of the PEDOT:PSS aqueous dispersion and dimethyl sulfoxide solution at 1000 rpm for 30 seconds to form a conductive layer film with a thickness of approximately 10 μm. Then, place the conductive layer film in a drying oven and dry it in a nitrogen inert environment at approximately 50°C for 1 hour to allow the mixture of the PEDOT:PSS aqueous dispersion and dimethyl sulfoxide solution to fully form a film and improve the uniformity of the conductive layer.

[0021] Paste the copper electrodes in step three: Use a diamond dicing machine to precisely cut the PDMS elastic layer in step one and the PEDOT:PSS conductive layer in step two according to the size of 1.5mm×1.5mm, and paste two copper sheets on the same end face of the PEDOT:PSS conductive layer through conductive epoxy glue. The size of the copper sheet is 1.5mm×0.5mm×1.5mm. After pasting, the pasted PDMS elastic layer, PEDOT:PSS conductive layer and copper electrode are heated and cured at 120°C for 30 minutes. After curing, the silicon wafer substrate in step one is separated on the elastic layer, and then a UV curing glue is used to paste and fix the base layer of PMMA with a size of 1.5mm×1.5mm×1mm to the two copper electrodes, and the glue is cured by irradiating 365nm wavelength ultraviolet light for 60 seconds to complete the production of a single sensor element.

[0022] A calibration and testing device for a foot stress sensor based on conductive polymer, which includes a vibration-proof workbench, a fixing frame, a linear actuator, a normal force loading mechanism, and four tangential force loading mechanisms;

[0023] The normal force loading mechanism and the tangential force loading mechanism are fixed to the anti-vibration workbench through a fixing frame. A foot stress sensor based on a conductive polymer is set on the anti-vibration workbench. The linear brake is fixed above the foot stress sensor based on a conductive polymer. The loading end of the normal force loading mechanism is pressed against the upper end surface of the linear brake, and the four tangential force loading mechanisms are respectively pressed against the side surfaces of the linear brake.

[0024] Furthermore, the normal force loading mechanism includes a normal loading cylinder, a normal air supply tank and a normal solenoid valve; the tangential force loading mechanism includes a tangential loading cylinder, a tangential air supply tank and a tangential solenoid valve;

[0025] The shell of the normal loading cylinder is fixedly installed on the fixed frame, the normal air supply tank is connected to the normal loading cylinder and supplies air, the normal solenoid valve is installed on the normal air supply tank and controls the operation of the normal air supply tank, the piston end of the normal loading cylinder is at the center position of the upper end surface of the linear brake, the shell of the tangential loading cylinder is fixedly installed on the fixed frame, the tangential air supply tank is connected to the tangential loading cylinder and supplies air, the tangential solenoid valve is installed on the tangential air supply tank and controls the operation of the tangential air supply tank, and the piston end of the tangential loading cylinder is at the side end surface of the linear brake.

[0026] A conductive polymer-based foot stress sensor calibration and testing method is implemented as follows: normal pressure is applied to align the piston end of the normal loading cylinder with the center of the linear brake, the output pressure is adjusted by the normal loading cylinder, tangential pressure is applied to align the piston end of the tangential loading cylinder with the side of the linear brake, a resistance tester is connected in parallel to the copper electrodes of five sensing elements, a 1kHz measurement signal is introduced, and the resistance change of each sensing element is recorded in real time.

[0027] First, the initial resistance of each sensor element was measured in a stress-free state to confirm that its baseline was approximately 50 kΩ. Normal stress calibration was then performed: the normal load cylinder pressure was gradually increased to 530 kPa and held for 10 seconds. The resistance of the sensor element located at the bottom end face of sensor assembly 3 was recorded as a function of stress. The loading and unloading cycles were repeated multiple times to evaluate the hysteresis error of the sensor output.

[0028] Then, perform shear pressure calibration: calibrate in four directions separately, gradually increasing the tangential loading cylinder to 530kPa for 10 seconds in each direction, and record the curve of the resistance of the sensor element on the side of the sensor assembly as a function of stress. Repeat the loading and unloading cycles in this direction multiple times to evaluate the hysteresis error of the sensor output.

[0029] When the sensor element is subjected to external force and its resistance changes, the voltage across it will change accordingly. By utilizing the corresponding relationship between resistance and stress obtained from the aforementioned calibration test, the measured voltage signal can be converted into the corresponding stress value, realizing real-time measurement of plantar stress.

[0030] Compared with the prior art, the present invention has the following effects:

[0031] This application uses a basalt fiber three-dimensional grid as a reinforcement material for the concrete matrix. The warp and weft yarns of the basalt fiber three-dimensional grid are crisscrossed to form an upper and lower surface layer, and the core column connects the two surface layers to form a whole.

[0032] 1. This application realizes stress-resistance signal conversion by stretching the PEDOT:PSS conductive layer through deformation of the PDMS layer, causing the resistance to change from about 50kΩ to about 250kΩ. The sensor uses PEDOT:PSS conductive polymer to replace traditional conductive elastomers or metal strain gauges, and has high precision (error <5%), multi-axis synchronous detection and large deformation adaptability, which solves the limitations of large errors, high brittleness and only single-axis detection in the existing technology. The total size of the sensor is about 14mm×14mm×8.5mm, which is suitable for fields such as foot pressure distribution analysis, medical rehabilitation and sports biomechanics monitoring. The preparation method includes PDMS spin coating, PEDOT:PSS film processing, precision cutting and component assembly. The process is highly controllable and suitable for mass production.

[0033] 2. This application uses PEDOT:PSS conductive polymer as the sensing layer, which has higher flexibility and sensitivity than traditional metal or carbon-based materials; by adjusting the elastic modulus of the PDMS elastic layer (about 400kPa) and the chloroprene rubber support layer (about 50kPa), the detection sensitivity to normal stress and shear stress are optimized respectively; a double-layer composite structure (PDMS+PEDOT:PSS) is designed to improve the durability and signal repeatability of the sensor; through geometric structure design, the sensor can obtain a larger resistance change amplitude under lower stress, thereby improving sensitivity; a copper spacer is used as the electrode support to form a fixed clamping end, thereby enhancing the stability of the sensor structure; the thickness of the conductive polymer PEDOT:PSS layer is optimized (about 10μm) to ensure that the sensor still has good recovery performance after multiple cyclic loading.

[0034] 3. This application utilizes a five-axis decoupled force measurement structure, enabling independent measurement of normal and shear stresses with minimal mutual interference. Through structural design, normal pressure is centrally transmitted from the central PMMA cube to the central sensing element, while shear force causes horizontal displacement of the cube, which is sensed by the surrounding edge sensing elements. Combined with the elastic isolation design of the rubber support layer, each sensing element independently responds to stress changes in different axial directions, effectively reducing inter-axis coupling errors. This provides a simpler and more accurate solution compared to traditional multi-strain gauge rosette solutions.

[0035] 4. The sensor of this application has excellent repeatability and anti-fatigue performance.

[0036] By optimizing the thickness of the PDMS elastic layer and the PEDOT:PSS conductive film, the sensor maintains a stable resistance response over multiple load-unload cycles, with a hysteresis error of less than 3% and a resistance drift of less than 5%. Compared to traditional conductive rubber or carbon-based composites, the PEDOT:PSS film conduction path is more stable and less susceptible to drift due to particle migration, making it suitable for long-term repeated use.

[0037] 5. The sensor material of this application has good biocompatibility and safety.

[0038] The materials used, such as PDMS, PMMA, PEDOT:PSS, and chloroprene rubber, are all polymers widely used in the biomedical field. They are low-toxic, non-irritating to the skin, and soft and conformable, making them suitable for use with sensitive skin, such as those with diabetic foot disease, the elderly, and children. This device eliminates the risk of metal peeling and damage to rigid structures, making it safer than lead-containing ceramic piezoelectric materials or optical fiber structures.

[0039] 6. The preparation process of this application is simple and suitable for low-cost mass production.

[0040] The sensor fabrication process includes standardized processes such as PDMS spin coating, PEDOT:PSS film formation, laser / blade dicing, copper electrode bonding, and component assembly. It eliminates the need for high-temperature sintering, vacuum deposition, or photolithography, and all steps can be completed at room temperature, facilitating assembly line and mass production. Compared to solutions requiring MEMS processing or expensive fiber optic components, this significantly reduces costs and is suitable for widespread deployment.

[0041] 7. The sensor of this application is highly compatible with conventional embedded electronic systems and the signal readout is simple.

[0042] The sensor element has a resistive output, and the voltage division reading scheme is simple and reliable, making it suitable for low-power, low-cost wireless modules. The sensor resistance range is tens of kilo-ohms, and can be directly sampled by the microcontroller ADC without the need for complex external conditioning circuits or shielding modules, making it particularly suitable for wearable device system integration. Compared to capacitive, piezoelectric, and fiber optic sensors that rely on dedicated circuits, this invention is more easily disseminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic diagram of a foot stress sensor based on conductive polymer;

[0044] Figure 2 This is a schematic diagram of the installation of the upper clamping plate 1, the base plate 2 and the sensor component 3;

[0045] Figure 3 This is a schematic diagram of the connection between the five sensor elements and the resistance tester;

[0046] Figure 4Schematic diagram of a foot stress sensor based on conductive polymer under normal loading;

[0047] Figure 5 Schematic diagram of a foot stress sensor based on conductive polymer subjected to tangential loading;

[0048] Figure 6 is a schematic diagram of the sensing element;

[0049] Figure 7 Schematic diagram of a conductive polymer-based foot stress sensor installed in a calibration test setup;

[0050] Figure 8 This is a diagram of a foot stress sensor based on conductive polymer subjected to normal loading;

[0051] Figure 9 This is a diagram of a foot stress sensor based on conductive polymer subjected to tangential loading;

[0052] Figure 10 Figure 2 shows a conductive polymer-based foot stress sensor mounted in a calibration test setup. DETAILED DESCRIPTION

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0054] Specific implementation method 1: Combination Figure 1-Figure 3 To illustrate this embodiment, the conductive polymer-based foot stress sensor of this embodiment includes an upper splint 1, a base plate 2, a sensing component 3 and a plurality of support columns 4;

[0055] The upper splint 1 and the base plate 2 are arranged opposite to each other, and the sensor component 3 and multiple support columns 4 are installed between the upper splint 1 and the base plate 2. The bottom end of the sensor component 3 is fixedly connected to the end face of the base plate 2, and the top of the sensor component 3 is arranged in contact with the upper splint 1. The pressure exerted on the upper splint 1 and the base plate 2 is monitored by the sensor component 3.

[0056] In this embodiment, substrate 2 is subjected to a plasma surface treatment, such as a 50W oxygen plasma cleaning system for 2 minutes, to improve its surface adhesion. A high-strength epoxy adhesive, such as 3M DP460, is applied to the four corners of substrate 2. Four support posts 4, measuring approximately 2mm x 2mm x 3mm, are then secured. A pressure of approximately 1N is applied for 5 minutes to ensure that support posts 4 are firmly adhered to substrate 2.

[0057] In this embodiment, the sensor component 3 is adhered and fixed on the substrate 2 .

[0058] Specific implementation method 2: Combination Figure 1-Figure 3 To illustrate this embodiment, the conductive polymer-based foot stress sensor of this embodiment has multiple support columns 4 evenly distributed around the sensing component 3. Other components and connection relationships are the same as those of the first embodiment.

[0059] Specific implementation method three: Combination Figure 1-Figure 3 This embodiment describes a conductive polymer-based foot stress sensor. The sensor assembly 3 includes a column, a resistance meter, and five sensor elements. The column is a rectangular parallelepiped structure, and the five sensor elements are located on the bottom end and four side surfaces of the column. Each of the five sensor elements is connected to a resistance meter, and the five sensor elements are arranged in parallel. Other components and connections are the same as those in the second embodiment.

[0060] This embodiment comprises a polymethyl methacrylate (PMMA) substrate 2 and a parallel PMMA upper plywood 1, with a PMMA column fixed to the center of the top plate. Four support columns 4 are fixed to the four corners of the substrate 2 to provide support and deformation space. Five sensing elements are included, of which the first sensing element is perpendicularly positioned at the center of the substrate 2 and directly below the PMMA cube, detecting normal stress in the z-direction of the sole. The second to fifth sensing elements are distributed around the columns of the PMMA cube, detecting shear stress in the x- and y-directions of the sole, respectively. The resistance meter is an LCR meter, such as the Keysight model E4980A.

[0061] Specific implementation method four: Combination Figure 1-Figure 3 This embodiment describes a conductive polymer-based foot stress sensor, wherein the sensing element includes a PDMS elastic layer, a PEDOT:PSS conductive layer, a base layer, and two copper electrodes.

[0062] The PDMS elastic layer, PEDOT:PSS conductive layer, two copper electrodes, and base layer are sequentially bonded together. The PDMS elastic layer of each sensor element is in contact with the pillar. Two parallel copper electrodes are positioned opposite each other between the PEDOT:PSS conductive layer and the base layer, with a gap between them. Other components and connections are the same as those in Specific Embodiment 3.

[0063] In this embodiment, when normal pressure is applied, the PDMS elastic layer is compressed, causing the length of the PEDOT:PSS conductive layer to increase and the thickness of the PEDOT:PSS conductive layer to decrease, thereby causing the resistance to increase; when a tangential force is applied, the columns of the PMMA cube are offset, causing the PDMS elastic layer of the edge sensing element to undergo extrusion deformation, resulting in a change in the thickness of the PEDOT:PSS conductive layer, thereby causing a change in resistance and realizing stress-resistance conversion.

[0064] The conductivity of the PEDOT:PSS conductive layer can be controlled by adjusting the conductivity, and the resistance change under deformation follows the formula:

[0065] R = ρ·L / A, where L is the length of the conductive layer, A is the cross-sectional area, and ρ represents the resistivity.

[0066] The upper layer of each sensor element is a polydimethylsiloxane (PDMS) elastic layer with a size of approximately 1.5mm×1.5mm×2mm, which is used to transmit stress and produce deformation; the middle layer is a PEDOT:PSS conductive layer of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate, with a thickness of approximately 10μm, whose resistance changes with the deformation it is subjected to; the base layer is made of PMMA material, and two copper electrodes are used to lead out the resistance signal of the conductive layer.

[0067] The base layer of the first sensing element is bonded and fixed to the upper surface of substrate 2. The second to fifth sensing elements are bonded to substrate 2 at the locations where the side surfaces of the base layers contact the upper surface of substrate 2. The first sensing element is vertically positioned at the center of the substrate and directly below the PMMA cube to detect normal stress (σz). The second to fifth sensing elements are vertically distributed around the PMMA cube to detect shear stress in the x- and y-directions (σx, σy), respectively.

[0068] Specific implementation method five: Combination Figure 1-Figure 3 In this embodiment, the conductive polymer-based foot stress sensor has a support column 4 made of rubber material and a vertical column made of polymethyl methacrylate. Other components and connections are the same as those in the fourth embodiment.

[0069] Specific implementation method six: combination Figure 1-Figure 3 The present embodiment describes a method for preparing a sensor element according to the present embodiment. The method is implemented according to the following steps:

[0070] Step 1: The silicon substrate is cleaned and a mixture of PDMS prepolymer and curing agent is spin-coated on the silicon substrate and cured to form a PDMS elastic layer with a thickness of about 2 mm;

[0071] Step 2: Add about 5% by volume of dimethyl sulfoxide to the PEDOT:PSS dispersion and mix them. Then, apply the PEDOT:PSS dispersion and dimethyl sulfoxide mixture on the PDMS elastic layer formed by solidification in step 1, and dry to form a PEDOT:PSS conductive layer with a thickness of about 10 μm.

[0072] Step 3: Attach a copper electrode to the same end surface of the PEDOT:PSS conductive layer dried in step 2 using conductive epoxy adhesive. The copper electrode and the PDMS elastic layer are respectively located at both ends of the conductive layer. Cut and separate the PDMS elastic layer dried in step 1 on the silicon substrate.

[0073] Step 4: Glue the two copper electrodes onto PMMA using UV-curable adhesive to complete the fabrication of the sensing element.

[0074] Specific implementation method seven: combination Figure 1-Figure 3 This embodiment and the method for preparing the sensor element of this embodiment are described.

[0075] Preparation of the elastic layer in step 1: Place a silicon wafer substrate with a diameter of 100 mm in a cleaning container and ultrasonically clean it with acetone and isopropyl alcohol for 10 minutes to remove surface impurities. Then blow it dry with high-purity nitrogen. Take PDMS prepolymer and curing agent, mix them in a mass ratio of 10:1, and use Dow Corning Sylgard184 as the curing agent. Mechanically stir for 5 minutes until the mixture is uniform. Degas the mixture under vacuum for 30 minutes to eliminate bubbles. Pour 25 ml of the evenly mixed PDMS prepolymer and curing agent mixture on the surface of the silicon wafer substrate.

[0076] A two-step spin coating process was used to form a uniform film: the first step was to spin-coat at 500 rpm for 10 seconds to evenly spread the PDMS prepolymer and curing agent mixture on the substrate; the second step was to spin-coat at 1000 rpm for 30 seconds to obtain an elastic layer film with a thickness of approximately 2 mm. The PDMS-coated substrate was then placed in a vacuum oven and cured at 80°C for 5 hours to ensure that the PDMS prepolymer and curing agent mixture were fully cross-linked and cured.

[0077] Preparation of the conductive layer in step 2: Prepare a PEDOT:PSS aqueous dispersion and 5% dimethyl sulfoxide (DMSO) by volume, using Clevios PH1000 as the PEDOT:PSS aqueous dispersion. Add DMSO to the PEDOT:PSS aqueous dispersion and magnetically stir for 2 hours. Place the PDMS elastic layer cured in step 1 on a spin coater and spin-coat the mixture of the PEDOT:PSS aqueous dispersion and DMSO solution at 1000 rpm for 30 seconds to form a conductive layer film having a thickness of approximately 10 μm. The conductive layer film is then dried in a drying oven at approximately 50° C. in an inert nitrogen atmosphere for 1 hour to allow the mixture of the PEDOT:PSS aqueous dispersion and DMSO solution to fully form a film and improve the uniformity of the conductive layer.

[0078] Paste the copper electrodes in step three: Use a diamond dicing machine to precisely cut the PDMS elastic layer in step one and the PEDOT:PSS conductive layer in step two according to the size of 1.5mm×1.5mm. During cutting, the blade speed is about 30000rpm, the feed speed is 1mm / s, the dimensional tolerance is controlled within ±0.05mm, and two copper sheets are pasted on the same end face of the PEDOT:PSS conductive layer through conductive epoxy glue. The size of the copper sheet is 1.5mm×0.5mm×1.5mm. After pasting, the pasted PDMS elastic layer, PEDOT:PSS conductive layer and copper electrode are heated and cured at 120℃ for 30 minutes. After curing, the silicon wafer substrate in step one is separated on the elastic layer, and then the PMMA base layer with a size of 1.5mm×1.5mm×1mm is pasted and fixed to the two copper electrodes using UV curing glue, and the glue is cured by 365nm wavelength ultraviolet light for 60 seconds to complete the production of a single sensor element.

[0079] Specific implementation method eight: combination Figure 1-Figure 4 This embodiment describes a calibration and testing device for a foot stress sensor based on a conductive polymer, which includes a vibration-proof workbench 10, a fixing frame 20, a linear brake 50, a normal force loading mechanism 30, and four tangential force loading mechanisms 40.

[0080] The normal force loading mechanism 30 and the tangential force loading mechanism 40 are fixed to the anti-vibration workbench 10 through the fixing frame 20. The anti-vibration workbench 10 is a TMC 63-500 damping vibration isolation table. A conductive polymer-based sole stress sensor is set on the anti-vibration workbench 10. The linear brake 50 is fixed above the conductive polymer-based sole stress sensor. The loading end of the normal force loading mechanism 30 is pressed against the upper end surface of the linear brake 50, and the four tangential force loading mechanisms 40 are respectively pressed against the side surfaces of the linear brake 50.

[0081] In this embodiment, the linear actuator 50 is a Thorlabs MLS203 model, which can apply tangential stress up to about 38 kPa in the x and y directions, and has a displacement control accuracy of ±1 μm.

[0082] Specific implementation method nine: Combination Figure 1-Figure 4 This embodiment describes a calibration and testing device for a foot stress sensor based on a conductive polymer. The normal force loading mechanism 30 includes a normal loading cylinder, a normal air supply tank, and a normal solenoid valve. The tangential force loading mechanism 40 includes a tangential loading cylinder, a tangential air supply tank, and a tangential solenoid valve.

[0083] The housing of the normal loading cylinder is fixedly mounted on the fixed frame 20. The normal air supply tank is connected to the normal loading cylinder and supplies air. The normal solenoid valve is installed on the normal air supply tank and controls its operation. The piston end of the normal loading cylinder abuts the center of the upper end surface of the linear brake 50. The housing of the tangential loading cylinder is fixedly mounted on the fixed frame 20. The tangential air supply tank is connected to the tangential loading cylinder and supplies air. The tangential solenoid valve is installed on the tangential air supply tank and controls its operation. The piston end of the tangential loading cylinder abuts the side end surface of the linear brake 50. The other components and connection relationships are the same as those of the first embodiment.

[0084] In this embodiment, the pressure range of the normal loading cylinder and the tangential loading cylinder is 0-600 kPa, with a resolution of 0.1 kPa.

[0085] Specific implementation method ten: Combination Figure 1-Figure 3 This embodiment describes a calibration and testing method for a conductive polymer-based foot stress sensor. The method is implemented as follows: normal pressure is applied to align the piston end of the normal loading cylinder with the center of the linear actuator 50. The output pressure is adjusted by the normal loading cylinder. Tangential pressure is applied to align the piston end of the tangential loading cylinder with the side of the linear actuator 50. A resistance meter is connected in parallel to the copper electrodes of five sensing elements. The sensing elements are 1.5 mm × 1.5 mm × 1 mm in size, and the copper electrodes are 1.5 mm × 0.5 mm × 1.5 mm in size. A 1 kHz measurement signal is introduced, and the resistance change of each sensing element is recorded in real time.

[0086] First, the initial resistance of each sensor element was measured in a stress-free state to confirm that its baseline was approximately 50 kΩ. Normal stress calibration was then performed: the normal load cylinder pressure was gradually increased to 530 kPa and held for 10 seconds. The resistance of the sensor element located at the bottom end face of sensor assembly 3 was recorded as a function of stress. The loading and unloading cycles were repeated multiple times to evaluate the hysteresis error of the sensor output.

[0087] Then, perform shear pressure calibration: calibrate in four directions separately, gradually increasing the tangential loading cylinder to 530kPa for 10 seconds in each direction, and record the curve of the resistance of the sensor element on the side of the sensor assembly 3 as a function of stress. Repeat the loading and unloading cycle in this direction multiple times to evaluate the hysteresis error of the sensor output;

[0088] The resistance of the PEDOT:PSS conductive layer in the unstressed state is about 50 kΩ. When a normal stress of about 530 kPa or a shear stress of about 38 kPa is applied, the resistance increases to about 250 kΩ.

[0089] When the sensor element is subjected to external force and its resistance changes, the voltage across it will change accordingly. By utilizing the corresponding relationship between resistance and stress obtained from the aforementioned calibration test, the measured voltage signal can be converted into the corresponding stress value, realizing real-time measurement of plantar stress.

[0090] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A foot stress sensor based on conductive polymer, characterized by: It includes an upper clamping plate (1), a base plate (2), a sensing component (3) and a plurality of supporting columns (4); The upper clamping plate (1) and the base plate (2) are arranged relative to each other, and the sensor component (3) and a plurality of support columns (4) are installed between the upper clamping plate (1) and the base plate (2). The bottom end of the sensor component (3) is fixedly connected to the end face of the base plate (2), and the top end of the sensor component (3) is arranged in contact with the upper clamping plate (1). The pressure exerted on the upper clamping plate (1) and the base plate (2) is monitored by the sensor component (3).

2. The conductive polymer-based foot stress sensor according to claim 1, characterized in that: A plurality of support columns (4) are evenly distributed around the sensor component (3).

3. The conductive polymer-based foot stress sensor according to claim 1, characterized in that: The sensing assembly (3) comprises a column, a resistance tester and five sensing elements. The column is a rectangular parallelepiped structure. The five sensing elements are respectively arranged on the bottom end face and four side faces of the rectangular parallelepiped. The five sensing elements are all connected to a resistance tester, and the five sensing elements are arranged in parallel.

4. The conductive polymer-based foot stress sensor according to claim 3, characterized in that: The sensing element includes a PDMS elastic layer, a PEDOT:PSS conductive layer, a base layer, and two copper electrodes; The PDMS elastic layer, PEDOT:PSS conductive layer, two copper electrodes and the base layer are fixedly pasted together in sequence. The PDMS elastic layer of each sensing element is in contact with the column. The two parallel copper electrodes are relatively arranged between the PEDOT:PSS conductive layer and the base layer, and a gap is provided between the two copper electrodes.

5. The conductive polymer-based foot stress sensor according to claim 3, characterized in that: The support column (4) is a support column made of rubber material, and the upright column is a cubic column made of polymethyl methacrylate material.

6. A method for preparing a sensor element according to any one of claims 1 to 4, characterized in that: The method is implemented according to the following steps: Step 1: The silicon substrate is cleaned and a mixture of PDMS prepolymer and curing agent is spin-coated on the silicon substrate and cured to form a PDMS elastic layer with a thickness of about 2 mm; Step 2: Add about 5% by volume of dimethyl sulfoxide to the PEDOT:PSS dispersion and mix them. Then, apply the PEDOT:PSS dispersion and dimethyl sulfoxide mixture on the PDMS elastic layer formed by solidification in step 1, and dry to form a PEDOT:PSS conductive layer with a thickness of about 10 μm. Step 3: Attach a copper electrode to the same end surface of the PEDOT:PSS conductive layer dried in step 2 using conductive epoxy adhesive. The copper electrode and the PDMS elastic layer are respectively located at both ends of the conductive layer. Cut and separate the PDMS elastic layer dried in step 1 on the silicon substrate. Step 4: Glue the two copper electrodes onto PMMA using UV-curable adhesive to complete the fabrication of the sensing element.

7. The method for preparing the sensor element according to claim 6, characterized in that: Preparation of the elastic layer in step 1: Place a silicon wafer substrate with a diameter of 100 mm in a cleaning container and ultrasonically clean it with acetone and isopropyl alcohol for 10 minutes to remove surface impurities. Then blow it dry with high-purity nitrogen. Take PDMS prepolymer and curing agent, mix them in a mass ratio of 10:1, and mechanically stir for 5 minutes until the mixture is uniform. Degas the mixture under vacuum for 30 minutes to eliminate bubbles. Pour 25 ml of the evenly mixed PDMS prepolymer and curing agent mixture onto the surface of the silicon wafer substrate. A two-step spin coating process was used to form a uniform film: the first step was to spin-coat at 500 rpm for 10 seconds to evenly spread the PDMS prepolymer and curing agent mixture on the substrate; the second step was to spin-coat at 1000 rpm for 30 seconds to obtain an elastic layer film with a thickness of approximately 2 mm. The PDMS-coated substrate was then placed in a vacuum oven and cured at 80°C for 5 hours to ensure that the PDMS prepolymer and curing agent mixture were fully cross-linked and cured. Preparation of the conductive layer in step 2: Prepare a PEDOT:PSS aqueous dispersion and 5% by volume of dimethyl sulfoxide, add dimethyl sulfoxide to the PEDOT:PSS aqueous dispersion, and magnetically stir for 2 hours. Place the PDMS elastic layer cured in step 1 on a spin coating apparatus and spin-coat the mixture of the PEDOT:PSS aqueous dispersion and dimethyl sulfoxide solution at 1000 rpm for 30 seconds to form a conductive layer film with a thickness of approximately 10 μm. Then, place the conductive layer film in a drying oven and dry it in a nitrogen inert environment at approximately 50°C for 1 hour to allow the mixture of the PEDOT:PSS aqueous dispersion and dimethyl sulfoxide solution to fully form a film and improve the uniformity of the conductive layer. Paste the copper electrodes in step three: Use a diamond dicing machine to precisely cut the PDMS elastic layer in step one and the PEDOT:PSS conductive layer in step two according to the size of 1.5mm×1.5mm, and paste two copper sheets on the same end face of the PEDOT:PSS conductive layer with conductive epoxy glue. The size of the copper sheet is 1.5mm×0.5mm×1.5mm. After pasting, the pasted PDMS elastic layer, PEDOT:PSS conductive layer and copper electrode are heated and cured at 120°C for 30 minutes. After curing, the silicon wafer substrate in step one is separated on the elastic layer, and then a PMMA base layer with a size of 1.5mm×1.5mm×1mm is pasted and fixed to the two copper electrodes using UV curing glue, and the glue is cured by irradiating with 365nm wavelength ultraviolet light for 60 seconds to complete the production of a single sensor element.

8. A calibration and testing device for a foot stress sensor based on a conductive polymer, characterized in that: It includes a shockproof workbench (10), a fixing frame (20), a linear brake (50), a normal force loading mechanism (30) and four tangential force loading mechanisms (40); A normal force loading mechanism (30) and a tangential force loading mechanism (40) are fixed to a shockproof workbench (10) via a fixing frame (20); a foot stress sensor based on a conductive polymer is arranged on the shockproof workbench (10); a linear brake (50) is fixed above the foot stress sensor based on a conductive polymer; a loading end of the normal force loading mechanism (30) is pressed against an upper end surface of the linear brake (50); and four tangential force loading mechanisms (40) are respectively pressed against side surfaces of the linear brake (50).

9. The conductive polymer-based foot stress sensor calibration and testing device according to claim 8, characterized in that: The normal force loading mechanism (30) includes a normal loading cylinder, a normal air supply tank, and a normal electromagnetic valve; the tangential force loading mechanism (40) includes a tangential loading cylinder, a tangential air supply tank, and a tangential electromagnetic valve; The shell of the normal loading cylinder is fixedly mounted on the fixing frame (20), the normal air supply tank is connected to the normal loading cylinder and supplies air, the normal solenoid valve is mounted on the normal air supply tank and controls the normal air supply tank to operate, the piston end of the normal loading cylinder is pressed against the center position of the upper end surface of the linear brake (50), the shell of the tangential loading cylinder is fixedly mounted on the fixing frame (20), the tangential air supply tank is connected to the tangential loading cylinder and supplies air, the tangential solenoid valve is mounted on the tangential air supply tank and controls the tangential air supply tank to operate, and the piston end of the tangential loading cylinder is pressed against the side end surface of the linear brake (50).

10. A calibration and testing method for a foot stress sensor based on a conductive polymer, characterized in that: The method is implemented in the following manner: applying normal pressure to align the piston end of the normal loading cylinder with the center of the linear brake (50), adjusting the output pressure through the normal loading cylinder, applying tangential pressure to align the piston end of the tangential loading cylinder with the side of the linear brake (50), connecting a resistance tester in parallel with the copper electrodes of five sensing elements, introducing a 1kHz measurement signal, and recording the resistance change of each sensing element in real time. First, the initial resistance of each sensor element is measured in a stress-free state to confirm that its baseline is approximately 50 kΩ. Normal stress calibration is then performed: the normal loading cylinder is gradually increased to 530 kPa and maintained for 10 seconds. The curve of the resistance of the sensor element at the bottom end face of the sensor assembly (3) is recorded as a function of stress. The loading and unloading cycles are repeated several times to evaluate the hysteresis error of the sensor output. Then, shear pressure calibration is performed: calibration is performed in four directions respectively. When calibrating in each direction, the tangential loading cylinder is gradually increased to 530 kPa and maintained for 10 seconds. The curve of the resistance of the sensor element located on the side of the sensor component (3) is recorded as a function of stress. The loading and unloading cycles in this direction are repeated many times to evaluate the hysteresis error of the sensor output. When the sensor element is subjected to external force and its resistance changes, the voltage across it will change accordingly. By utilizing the corresponding relationship between resistance and stress obtained from the aforementioned calibration test, the measured voltage signal can be converted into the corresponding stress value, realizing real-time measurement of plantar stress.

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