A planar flexible three-dimensional force sensing system

Abstract

The application provides a planar flexible three-dimensional force sensing system, comprising a three-dimensional force sensor and an upper computer, the three-dimensional force sensor is composed of a five-layer structure, comprising a surface layer with micro-protrusions, an upper electrode layer, a conductive layer, a positioning layer and a lower electrode layer; the system shows fast response and recovery time and good stability; through the information collection of the designed acquisition circuit to the array type three-dimensional force sensor, the resistance value of each unit can be collected through ADC, and then through the resistance change of each piezoresistive sensing unit, the model trained by the simple neural network containing three hidden layers is used to predict the size and change of three-dimensional force. The three-dimensional force tactile sensor of the application is simple to manufacture, high in sensitivity, simple in decoupling and can measure normal force and tangential force at the same time; the three-dimensional force prediction system of the application can significantly improve the accuracy and response speed of force sensor data processing, and meet the needs of complex engineering scenes.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible three-dimensional force tactile sensors, and in particular relates to a planar flexible three-dimensional force sensing system. Background Art

[0002] With the continuous advancement of science and technology, the application of three-dimensional sensing technology is becoming increasingly widespread in fields such as health monitoring, intelligent robotics, and wearable devices. The core of this technology lies in the real-time capture of multi-directional force and tactile information exerted by objects, and flexible sensors are a key tool for realizing this technology. Flexible sensors not only provide accurate force information but also possess excellent flexibility and adaptability, enabling intelligent systems to better understand and respond to changes in the external environment.

[0003] Among various types of flexible sensors, resistive three-dimensional force sensors have attracted considerable attention due to their simple structure, mature manufacturing process, and relatively low cost. Their operating principle is to measure force by monitoring the change in resistance caused by external force applied to the sensor surface. Compared to traditional uniaxial pressure sensors, resistive three-dimensional force sensors can detect multi-directional forces, which gives them significant advantages in flexible three-dimensional force monitoring and enables comprehensive and accurate detection of mechanical information in three-dimensional space. Therefore, resistive three-dimensional force sensors can be widely used to detect object texture and slippage.

[0004] Flexible piezoresistive 3D interface stress sensors offer excellent stability and a wide measurement range, but their sensitivity is relatively low due to limitations in the sensing material. Capacitive 3D interface stress sensors, with their advantages of high sensitivity, strong temperature independence, mature manufacturing processes, and high spatial resolution, have been widely used in 3D interface stress measurement. However, these capacitors are prone to parasitic and stray capacitance, resulting in poor stability. Piezoelectric 3D interface stress sensors have excellent dynamic characteristics but poor static characteristics.

[0005] Current sensors suffer from complex decoupling, poor stability, and relatively low sensitivity, making it difficult to create flexible and highly sensitive 3D force sensors. They also suffer from unintuitive 3D force feedback and the inability to display 3D force information in real time. Summary of the Invention

[0006] In light of this, the present invention aims to overcome the shortcomings of the prior art by proposing a planar, flexible, three-dimensional force sensing system. This system features simple decoupling, high sensitivity, and the ability to simultaneously measure normal and tangential forces. It also offers comprehensive functionality, from data acquisition and filtering to prediction and three-dimensional force visualization. By combining a sliding average filter with a deep learning model, the system effectively reduces noise in the collected data, improves the accuracy and stability of force prediction, and displays the direction and magnitude of the three-dimensional force vector in real time.

[0007] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A planar flexible three-dimensional force sensing system includes a three-dimensional force sensor and a host computer, wherein the three-dimensional force sensor is connected to the host computer;

[0009] The three-dimensional force sensor has an axisymmetric structure, and includes, from top to bottom, a protrusion, an upper electrode layer, a conductive layer, a positioning layer, and a lower electrode layer;

[0010] The upper electrode layer and the lower electrode layer each include four electrodes in a 2×2 array;

[0011] The conductive layer is a dust-free paper conductive fiber structure soaked in MXene solution;

[0012] The positioning layer is a square ring structure and fits the surface of the upper electrode layer and the lower electrode layer. The outer edge of the positioning layer is the same length as the outer edge of the sensor.

[0013] The conductive layer has the same side length as the inner side of the positioning layer and is laid flat in the cavity of the positioning layer to form a 2×2 array sensor with the upper electrode layer and the lower electrode layer in a sandwich structure, forming four piezoresistive sensing units;

[0014] The thickness of the conductive layer is the same as that of the positioning layer;

[0015] The protrusion is located directly above the upper electrode layer, and the bottom area is the same as the area formed by the electrodes of the upper electrode layer, the area of ​​the conductive layer, and the area formed by the electrodes of the lower electrode layer 5.

[0016] Furthermore, the four electrodes of the upper electrode layer are located above the conductive layer, and the four electrodes of the lower electrode layer are located below the conductive layer. The electrodes of the upper electrode layer and the lower electrode layer are the same size and the same periphery. The upper electrode layer forms two passages to form rows, and the lower electrode layer forms two passages to form columns, forming a 2×2 sensor array. The size of each electrode unit is a 4mm×4mm square structure, and the interval between each electrode is 2mm.

[0017] Furthermore, the upper electrode layer and the lower electrode layer are made of conductive materials such as gold, silver or copper.

[0018] Furthermore, the protrusion is fixedly bonded to the upper electrode layer by silicone.

[0019] Furthermore, the material of the protrusion is a flexible high molecular polymer.

[0020] Furthermore, the manufacturing method of the three-dimensional force sensor includes:

[0021] Step 1: Prepare a conductive fiber substrate: soak the dust-free paper in the prepared MXene solution, dry it, and cut it to obtain a conductive layer;

[0022] Step 2: Prepare the mold: Make the mold of the top boss by additive manufacturing process;

[0023] Step 3: Prepare the top boss: Mix PDMS and curing agent and pour them into the corresponding mold for preparation;

[0024] Step 4: Prepare the middle positioning layer: Use a laser cutting machine to make a hollow square positioning layer;

[0025] Step 5: Prepare a flexible three-dimensional force sensor: fix the top boss to the upper electrode with glue, place the conductive layer in the cavity of the positioning layer, and fix the positioning layer to the upper and lower electrodes with glue.

[0026] Furthermore, the step 1 specifically includes:

[0027] S1. First, lithium fluoride and carbon aluminum titanium are added to a mixture of deionized water and concentrated hydrochloric acid in a certain proportion, and magnetically stirred for 24 hours to fully fuse;

[0028] S2. Add deionized water to the resulting mixed solution and centrifuge at 10,000 rpm for 5 minutes. After centrifugation, discard the upper layer of solution containing impurities and the remaining precipitate, then add deionized water again. Repeat this step 7 times to obtain a mixed slurry.

[0029] S3. Add deionized water to the obtained mixed slurry and centrifuge at 3000 r / min for 20 minutes to obtain a MXene stock solution;

[0030] S4. Deionized water is added to the obtained MXene stock solution to obtain a well-proportioned MXene solution.

[0031] Furthermore, the step three specifically includes:

[0032] The PDMS solution is mixed with base gel and curing agent in a weight ratio of 10:1. After the mixed solution is poured into the mold, it is degassed in a vacuum dryer for 25 minutes to remove all residual bubbles. A flat acrylic plate is selected and laminated on the surface of the mold. The excess PDMS is gently pressed out and the surface is smoothed. The mold is placed in a vacuum dryer at 85°C and heated for 3 hours. After completion, it is demolded to obtain a protrusion.

[0033] Furthermore, a data processing unit is provided in the host computer, and the data processing unit includes a sliding average filter and a data normalization processing module; the data processing unit loads independent models of X, Y, and Z direction forces for prediction, and performs denormalization on the predicted values.

[0034] Further, the host computer also draws the prediction result through a 3D drawing tool, and realizes three-dimensional visual display of force.

[0035] Compared with the prior art, the planar flexible three-dimensional force sensing system has the following advantages:

[0036] The piezoresistive three-dimensional force sensor forms a conductive loop through the upper and lower electrodes and the conductive layer, the conductive path of the conductive layer becomes more after being pressed, so that the resistance becomes smaller; at the same time, the contact area of the electrode and the conductive layer increases, so that the resistance decreases, thereby utilizing the resistance change to realize the measurement of the size and direction of three-dimensional force, and significantly improving the sensitivity of the sensor.

[0037] The conductive layer of the application is made by soaking and drying the dust-free paper in the MXene solution, which has simple manufacturing process and low cost.

[0038] The system has the advantages of real-time, high precision, strong intuitiveness and flexibility, and has good compatibility, and can be applied to various three-dimensional force sensor devices and support application requirements in complex environments. BRIEF DESCRIPTION OF DRAWINGS

[0039] The accompanying drawings, which form a part of the present application, are included to provide a further understanding of the application, and are incorporated herein for purposes of illustrating the illustrative embodiments of the present application and the explanations provided herein and are not intended as a limitation. In the drawings:

[0040] Figure 1 It is a schematic diagram of the overall structure of the three-dimensional force sensor;

[0041] Figure 2 It is a structure diagram of the upper electrode layer and the lower electrode layer of the three-dimensional force sensor;

[0042] Figure 3 It is a simulation diagram of the convex force of the three-dimensional force sensor;

[0043] Figure 4 It is a preparation flowchart of the conductive layer of the three-dimensional force sensor;

[0044] Figure 5 It is a preparation flowchart of the three-dimensional force sensor;

[0045] Figure 6 It is a three-dimensional force detection principle diagram of the three-dimensional force sensor;

[0046] Figure 7 It is an experimental platform of the three-dimensional force sensor;

[0047] Figure 8 It is a circuit acquisition principle diagram of the three-dimensional force sensor;

[0048] Figure 9 This is the logic diagram of the acquisition circuit of the three-dimensional force sensor;

[0049] Figure 10 Schematic diagram of the neural network decoupling model of the three-dimensional force sensor;

[0050] Figure 11 This is the neural network training result diagram of the three-dimensional force sensor;

[0051] Figure 12 A comparison chart of the actual and predicted values ​​of the force applied by the three-dimensional force sensor;

[0052] Figure 13 The relative resistance change curve of each sensing unit output when Fz, Fx and Fy are applied to the three-dimensional force sensor, as well as the sensitivity in different directions;

[0053] Figure 14 The conductive layer of the three-dimensional force sensor is shown in the real object and electron microscope image;

[0054] Figure 15 The relative resistance change rate curve of the three-dimensional force sensor after 20,000 normal repeated compression-release cycles;

[0055] Figure 16 A graph showing the relative resistance change rate of a three-dimensional force sensor when different pressures are continuously applied;

[0056] Figure 17 The resistance change rate curve of the normal direction pressure applied to the three-dimensional force sensor under rapid loading and unloading, as well as the response and hysteresis time of the sensor;

[0057] Figure 18 It is a 3D graphical interface display module;

[0058] Description of reference numerals:

[0059] 1- raised layer; 2- upper electrode layer; 3- conductive layer; 4- positioning layer; 5- lower electrode layer. DETAILED DESCRIPTION

[0060] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0061] In the description of the present application, it needs to be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" and the like can be explicitly or implicitly included one or more. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0062] In the description of the present application, it needs to be understood that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0063] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0064] As shown in Figure 1 and Figure 2 The three-dimensional force sensor of the present application is sequentially arranged from top to bottom: a protrusion 1 for protecting the sensor and transmitting external force to the pressure sensitive layer, an upper electrode 2 with a square structure of 2x2 array of electrode units, each electrode unit size is 4mmx4mm, a conductive layer 3 for conducting electricity, a positioning layer 4 for fixing the conductive layer, and a lower electrode layer 5 for forming a sandwich sensor structure with the upper electrode 2 and the conductive layer 3.

[0065] Among them, the material of the protrusion 1 is a flexible high polymer; preferably, the flexible high polymer is silicone rubber or PDMS;

[0066] Among them, the conductive layer 3 for conducting electricity is a fiber substrate soaked in MXene solution; preferably, the fiber substrate is dust-free paper;

[0067] Among them, the positioning layer 4 is a square ring cut from PET, with an outer diameter of 12mm, fitting the periphery of the upper and lower electrodes of the sensor, and an inner diameter of 10mm, fitting the copper electrode and the middle conductive layer;

[0068] Among them, the material of the positive electrode and the negative electrode is copper, with a thickness of 36μm (the thickness of the electrode material will affect the transmission stability of the signal and thus affect the sensitivity and stability of the sensor; the selection of this thickness can ensure good conductivity and stability when the electrode is subjected to large deformation).

[0069] like Figure 2 The square conductive copper foil of upper electrode 2 forms a conductive loop with the conductive copper foil of lower electrode 5. Force is measured by the change in resistance caused by the deformation of conductive layer 3 under pressure. In the unloaded state, MXene nanosheets are randomly distributed within the fiber network. The high porosity of the fiber film results in loose contact between the MXene nanosheets, resulting in fewer conductive paths. When the sensor is subjected to external pressure, the fiber film deforms, tightening the contact between the MXene nanosheets and forming more conductive paths.

[0070] like Figure 3 As shown, the protrusion 1 can protect the sensor body from being damaged while achieving the accuracy of force conduction. Compared with other shapes, the prismatic protrusion structure can distribute the external force more evenly, thereby improving the sensitivity of the sensor. The size of the top surface of the protrusion has an important influence on the force transmission effect. To this end, the present invention uses Ansys Workbench 2022R1 to perform finite element analysis on prismatic protrusions 1 of different sizes. The bottom edge length of the protrusion 1 is set to 10 mm, the top edge length is 6 to 9 mm, and the height is 2 mm. A fixed support constraint is applied to the bottom of the piezoresistive film, and a normal force of 1 N is applied to the top of the protrusion 1.

[0071] in Figure 3 (a) shows the deformation behavior of protrusions 1 with four different edge lengths under load. As the upper edge length increases, the area of ​​maximum deformation of the protrusion expands from the center toward the edge. The forces transmitted to the conductive layer 3 also differ in these four cases. Figure 3 (b) shows that the maximum equivalent stresses transmitted to the piezoresistive film by protrusions 1 with edge lengths of 6 mm, 7 mm, 8 mm, and 9 mm are 0.021 MPa, 0.018 MPa, 0.015 MPa, and 0.017 MPa, respectively. Although the 6 mm and 9 mm protrusions transmit larger equivalent stresses in the center and edge areas of the film, this leads to limitations in the contact area between the conductive layer 3 and the upper electrode 2 and lower electrode 5, which in turn affects the sensor performance. In contrast, the 7 mm and 8 mm protrusions 1 can transmit force to the pressure-sensitive material layer more uniformly, which helps to ensure the consistency of the response of the sensing unit, thereby improving the measurement accuracy.

[0072] In addition, the performance of the sensor was further analyzed by applying a normal force and a shear force of 1 N, as shown in Figure 2. Figure 3As shown in (c). Since the resistance change of the sensor is mainly determined by the contact area between the conductive layer 3 and the upper electrode 2 and the lower electrode 5, when the edge length of the protrusion is 8mm and 9mm, the larger equivalent stress is concentrated on the smaller contact area, which is not conducive to the reduction of resistance. Similarly, although the 6mm protrusion produces a larger equivalent stress and area, under unidirectional force, the equivalent stress is concentrated in the central area, limiting the expansion of the contact area. Overall, the protrusion 1 with an edge length of 7mm exhibits better force transmission characteristics under the combined action of normal force and shear force, which gives it greater advantages in measurement accuracy and sensor performance.

[0073] like Figure 4 As shown, the method for preparing the conductive layer 3 includes the following steps:

[0074] S1. First, lithium fluoride and carbon aluminum titanium are added to a mixture of deionized water and concentrated hydrochloric acid in a certain proportion, and magnetically stirred for 24 hours to fully fuse;

[0075] S2. Add deionized water to the resulting mixed solution and centrifuge at 10,000 rpm for 5 minutes. After centrifugation, discard the upper layer of solution containing impurities and the remaining precipitate, then add deionized water again. Repeat this step 7 times to obtain a mixed slurry.

[0076] S3. Add deionized water to the obtained mixed slurry and centrifuge at 3000 r / min for 20 minutes to obtain a MXene stock solution;

[0077] S4. Deionized water is added to the obtained MXene stock solution to obtain a well-proportioned MXene solution.

[0078] like Figure 5 As shown, the preparation method of the three-dimensional force sensor is as follows:

[0079] S1. First, an aluminum mold was used to create a surface protrusion 1. The PDMS solution was mixed with a base gel and a curing agent (Sylgard 184, Dow Chemical Co., Milander, MI, USA) in a weight ratio of 10:1. This ratio imparts a high Young's modulus to the surface. After pouring the mixed solution into the mold, it was degassed in a vacuum desiccator for 25 minutes to ensure that all remaining bubbles were removed. A flat acrylic sheet was then selected and laminated onto the mold surface. Excess PDMS was gently squeezed out and the surface was smoothed. The mold was then placed in a vacuum desiccator and heated for 3 hours at 85°C. After completion, the mold was demolded to obtain a protrusion 1.

[0080] S2, in order to ensure good adhesion between the flexible printed circuit (FPC) electrode and the piezoresistive film 3, a positioning layer 4 is applied around the lower electrode layer 5 before the electrode is adhered to the film, wherein the lower electrode layer 5 is adhered to the positioning layer 4 by silicone;

[0081] S3, the prepared MXene sensitive layer 3 is clamped between the upper and lower electrodes, and the four sides of the sensor are bonded using a silicone adhesive. Finally, the silicone is adhered between the surface of the protrusion 1 and the sensor, and a 200g weight is placed on the top of the protrusion, and left to stand for 24 hours to ensure that the silicone is fully cured. After this process is completed, the flexible three-dimensional tactile sensor is completed.

[0082] The detection principle of the present application is as follows:

[0083] As shown in Figure 6 (a), any external force can be decomposed into three force components, i.e. normal force Fz and shear force components Fx and Fy. Ft represents the resultant force of the two shear components, and angle θ represents the direction of the applied force on the horizontal plane, and angle α represents the angle between the external force F and the horizontal plane.

[0084] The sensor is composed of four piezoresistive sensing units (R1, R2, R3, R4), which are formed by an upper electrode and a lower electrode symmetrically distributed in the center, and constitute a single sensor unit as a whole. As shown in Figure 6 (b), when a normal force is applied, the protrusions on the surface of the sensor are compressed, and the four piezoresistive sensing units bear equal compressive stress. Due to the piezoresistive effect, the resistance of the four units decreases synchronously, and the resistance change is equal (ΔR1=ΔR2=ΔR3=ΔR4). As shown in Figure 6 (c) and Figure 6 (d), under the action of shear force, the protrusions deform and generate torque at the fixed end. Two units on one side of the sensor bear compressive stress, while two units on the other side bear tensile stress, resulting in opposite changes in the resistance of the sensing units on both sides. Therefore, by calculating the change in resistance value of the four sensing units, the size and direction of the real force can be predicted by means of a neural network.

[0085] As shown in Figure 7 , the device is an experimental device for testing the performance of the sensor. The device is composed of a three-axis mobile platform (Huike, LD40-RM) and a commercial three-axis force sensor (Spindt, SBT301-40A). The commercial three-axis sensor is used to provide accurate force measurement parameters. In order to ensure the accuracy during loading, the loading rod is 3D printed using a certain material and installed on the three-axis mobile platform, so that the center of the rod is perfectly aligned with the sensor. When the loading rod moves in the x, y and z directions, the sensor bears normal force and shear force respectively, simulating the multi-dimensional force action in the actual working environment.

[0086] As Figure 8 shown, this schematic diagram is the circuit acquisition principle diagram of three-dimensional force sensor. By using different switches to control the access circuit of the sensor. Where R ref is the voltage divider resistance, here the resistance size is 1K.

[0087] As Figure 9 shown, the data acquisition uses STM32F103C8T6 single-chip microcomputer, which has 10 built-in 12-bit ADC converters. In order to improve the measurement efficiency, multi-channel switch sequential scanning pins are used, and the position of the unit sensor collected is determined by the access row and column. The sampling frequency is set to 50Hz. The information obtained by the commercial three-axis force sensor and three-dimensional force sensor acquisition board will be transmitted to the host computer system developed by Python through different serial ports through different communication protocols. Here the lower computer will pass the frame header 0xAABBCCDD+8-bit information+frame trailer 0xDDCCBBAA to the host computer, and the host computer will analyze the information while receiving the three-axis force information measured by the sensor transmitted by the commercial sensor transmitter. Store and correspond one by one. The system can receive information from both sides in real time, and can preliminarily arrange and save the information, and prepare for subsequent decoupling analysis.

[0088] As Figure 10 shown, since the decoupling of the three-dimensional force sensor in three directions is not a relatively complex problem, a simple neural network model is used here to decouple the three-dimensional force. The neural network model is set to four input layers (respectively, the resistance formed by the collected three-dimensional force sensor (R1, R2, R3, R4)), three output layers (respectively, the force Fz, Fx, Fy), and three hidden layers (respectively, 64, 128, 64 neurons).

[0089] As Figure 11 shown, through 5000 times of cyclic training of 5000 training sets, the Loss value tends to be stable.

[0090] As Figure 12 shown, in order to verify the effectiveness of the model, 4000 test sets are predicted, and the R 2 coefficient respectively reached 0.9985, 0.9986, 0.9958, showing excellent prediction performance.

[0091] As Figure 13 shown, the sensitivity of the piezoresistive sensor can be expressed as where ΔR is the resistance change, R0 is the resistance without external force, and ΔF is the force change. As shown in the figure, the relative resistance change rate of four sensor units under 0-15 N normal force and their sensitivity in different pressure ranges are shown. When the pressure is less than 2 N, the sensitivity of the sensor can be as high as 0.789 N -1 ; while in the pressure intervals of 2-5 N and 5-15 N, the sensitivity decreases to 0.460 N -1 and 0.115 N -1 , respectively. This result shows that the sensitivity of the sensor decreases with the increase of the applied external force.

[0092] where, in the low pressure state, a large number of conductive paths are formed between the electrode and the piezoresistive material, resulting in a rapid decrease in the interface contact resistance. As the pressure gradually increases, the resistance gradually decreases and reaches a saturation state, making it difficult to form new conductive networks, thus leading to a decrease in the sensitivity of the sensor. Under normal circumstances, the shear force acting on the sensor is smaller than the normal force, and the two forces often exist simultaneously. Therefore, we measured the sensitivity of the sensor to shear force when the normal pressure was 5 N. As shown in Figure 6 b and 6c, with the increase of the shear force, the resistance change of the compression sensing unit is smaller than that of the stretching sensing unit. In the range of 0-6 N, the average sensitivity of the sensor on the x-axis and y-axis is 0.025 N -1 and 0.019 N -1 , respectively.

[0093] As shown in Figure 14 , MXene is rich in functional groups on the surface, and the large specific surface area enhances the bonding force with the substrate, thus giving it excellent mechanical properties. Its metal conductivity and interlayer spacing give MXene a wide range of resistance adjustment, making it very sensitive to pressure changes. The rich functional groups on the surface of MXene nanosheets enable them to be firmly bonded to substrates such as cotton fabric.

[0094] As shown in Figure 15 , under 5 N normal force, the pressure-release cycle test was repeated 10,000 times, and it was found that the dynamic change of the relative resistivity of the sensor remained stable, and the sensor showed good repeatability, stability and consistency.

[0095] As shown in Figure 16 , when different normal pressures were continuously applied to the sensor, it showed a good stable output signal.

[0096] As shown in Figure 17 , under the condition of rapid loading and unloading of 0.5 N normal pressure on the sensor, the sensor showed a short response time block and hysteresis time, with a response and recovery time of 63 ms and 86 ms, respectively.

[0097] As Figure 18 shown, it is a graphical interface display module, which establishes communication with three-dimensional force sensor through serial communication module to read real-time data collection; then the data is preprocessed, including sliding average filter and data normalization processing module; the independent model of X, Y, Z direction force is loaded respectively to predict, and the predicted value is normalized; the prediction result is drawn through 3D drawing tool to realize three-dimensional visualization display of force.

[0098] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A planar flexible three-dimensional force sensing system, characterized by: It includes a three-dimensional force sensor and a host computer, wherein the three-dimensional force sensor is connected to the host computer; The three-dimensional force sensor has an axisymmetric structure, and includes, from top to bottom, a protrusion, an upper electrode layer, a conductive layer, a positioning layer, and a lower electrode layer; The upper electrode layer and the lower electrode layer each include four electrodes in a 2×2 array; The conductive layer is a dust-free paper conductive fiber structure soaked in MXene solution; The positioning layer is a square ring structure and fits the surface of the upper electrode layer and the lower electrode layer. The outer edge of the positioning layer is the same length as the outer edge of the sensor. The conductive layer has the same side length as the inner side of the positioning layer and is laid flat in the cavity of the positioning layer to form a 2×2 array sensor with the upper electrode layer and the lower electrode layer in a sandwich structure, forming four piezoresistive sensing units; The thickness of the conductive layer is the same as that of the positioning layer; The protrusion is directly above the upper electrode layer, and the bottom area is the same as the area formed by the electrodes of the upper electrode layer, the area of ​​the conductive layer, and the area formed by the electrodes of the lower electrode layer 5; The protrusion is prism-shaped, with a bottom edge length of 10 mm, a top edge length of 7 mm, and a height of 2 mm.

2. The planar flexible three-dimensional force sensing system according to claim 1, characterized in that: The four electrodes of the upper electrode layer are located above the conductive layer, and the four electrodes of the lower electrode layer are located below the conductive layer. The electrodes of the upper electrode layer and the lower electrode layer are the same size and the same periphery. The upper electrode layer forms two passages to form rows, and the lower electrode layer forms two passages to form columns, forming a 2×2 sensor array. The size of each electrode unit is a 4mm×4mm square structure, and the interval between each electrode is 2mm.

3. The planar flexible three-dimensional force sensing system according to claim 1, characterized in that: The materials of the upper electrode layer and the lower electrode layer are conductive materials such as gold, silver or copper.

4. The planar flexible three-dimensional force sensing system according to claim 1, characterized in that: The protrusion is fixedly bonded to the upper electrode layer through silica gel.

5. The planar flexible three-dimensional force sensing system according to claim 1, characterized in that: The material of the protrusion is a flexible high molecular polymer.

6. The planar flexible three-dimensional force sensing system according to claim 1, characterized in that: The manufacturing method of the three-dimensional force sensor includes: Step 1: Prepare a conductive fiber substrate: soak the dust-free paper in the prepared MXene solution, dry it, and cut it to obtain a conductive layer; Step 2: Prepare the mold: Make the mold of the top boss by additive manufacturing process; Step 3: Prepare the top boss: Mix PDMS and curing agent and pour them into the corresponding mold for preparation; Step 4: Prepare the middle positioning layer: Use a laser cutting machine to make a hollow square positioning layer; Step 5: Prepare a flexible three-dimensional force sensor: fix the top boss to the upper electrode with glue, place the conductive layer in the cavity of the positioning layer, and fix the positioning layer to the upper and lower electrodes with glue.

7. The planar flexible three-dimensional force sensing system according to claim 6, characterized in that: The step 1 specifically includes: S1. First, lithium fluoride and carbon aluminum titanium are added to a mixture of deionized water and concentrated hydrochloric acid in a certain proportion, and magnetically stirred for 24 hours to fully fuse; S2. Add deionized water to the obtained mixed solution and centrifuge at 10,000 rpm for 5 minutes. After centrifugation, discard the upper layer of the solution containing impurities and the remaining precipitate, add deionized water again, and repeat this step 7 times to obtain a mixed slurry; S3. Add deionized water to the obtained mixed slurry and centrifuge at 3000 r / min for 20 minutes to obtain a MXene stock solution; S4. Deionized water is added to the obtained MXene stock solution to obtain a well-proportioned MXene solution.

8. The planar flexible three-dimensional force sensing system according to claim 6, characterized in that: The step three specifically includes: The PDMS solution is mixed with a base gel and a curing agent in a weight ratio of 10:

1. After the mixed solution is poured into the mold, it is degassed in a vacuum dryer for 25 minutes to remove all residual bubbles. A flat acrylic plate is selected and laminated on the surface of the mold. The excess PDMS is gently pressed out and the surface is leveled. The mold is placed in a vacuum dryer at 85°C and heated for 3 hours. After completion, it is demolded to obtain a protrusion.

9. The planar flexible three-dimensional force sensing system according to claim 1, characterized in that: The host computer is provided with a data processing unit, which includes a sliding average filter and a data normalization processing module; the data processing unit loads independent models of X, Y, and Z direction forces for prediction, and performs denormalization on the predicted values.

10. The planar flexible three-dimensional force sensing system according to claim 9, characterized in that: The host computer also draws the prediction results using a 3D drawing tool to achieve three-dimensional visualization of the force.

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