Planar flexible three-dimensional force sensing system

Abstract

The invention provides a planar flexible three-dimensional force sensing system, which comprises a three-dimensional force sensor and an upper computer, and is characterized in that the three-dimensional force sensor is of a five-layer structure and comprises a surface layer with micro bulges, 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; the array type three-dimensional force sensor is subjected to information acquisition through a designed acquisition circuit, the resistance value of each unit can be acquired through an ADC (Analog to Digital Converter), and then the magnitude and change of three-dimensional force are predicted by utilizing a model trained by a simple neural network containing three hidden layers according to the resistance change of each piezoresistive sensing unit. The three-dimensional force touch sensor is easy to manufacture, high in sensitivity and easy to decouple, and normal force and tangential force can be measured at the same time; according to the three-dimensional force prediction system, the data processing precision and response speed of the force sensor can be remarkably improved, and the requirements of complex engineering scenes are met.

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 in health detection, intelligent robots and wearable devices is becoming more and more extensive. The core of this technology is to capture the multi-directional force and tactile information exerted by objects in real time, and flexible sensors are the key tools to realize this technology. Flexible sensors can not only provide accurate force information, but also have excellent flexibility and adaptability, so that intelligent systems can better understand and respond to changes in the external environment.

[0003] Among various types of flexible sensors, resistive three-dimensional force sensors are highly valued due to their simple structure, mature manufacturing process and relatively low cost. Its working principle is to measure force by monitoring the resistance change caused by the external force applied to the sensor surface. Compared with traditional uniaxial pressure sensors, resistive three-dimensional force sensors can detect multi-directional forces, which makes their application in flexible three-dimensional force monitoring show significant advantages and can comprehensively and accurately detect mechanical information in three-dimensional space. Therefore, resistive three-dimensional force sensors can be widely used in the detection of object texture and sliding.

[0004] Flexible piezoresistive three-dimensional interface stress sensors have good stability and a large measurement range, but their sensitivity is relatively low due to the limitations of sensing materials. Capacitive three-dimensional interface stress sensors have the advantages of high sensitivity, strong temperature independence, mature manufacturing technology, and high spatial resolution, and have been widely used in three-dimensional interface stress measurement. However, the capacitor is prone to parasitic capacitance and stray capacitance, and has poor stability. Piezoelectric three-dimensional interface stress sensors have high dynamic characteristics, but poor static characteristics.

[0005] At present, the sensors have the disadvantages of complex decoupling, poor stability, and relatively low sensitivity, which makes it difficult to make flexible and highly sensitive three-dimensional force sensors. There are also disadvantages such as the three-dimensional force feedback display is not intuitive and the three-dimensional force information cannot be displayed in real time. Summary of the invention

[0006] In view of this, the present invention aims to overcome the shortcomings of the above-mentioned problems in the prior art and proposes a planar flexible three-dimensional force sensing system, which has the advantages of simple decoupling, high sensitivity, and can simultaneously measure normal force and tangential force. The three-dimensional flexible sensor can also realize the complete functions from data acquisition, filtering to prediction and three-dimensional force visualization. By combining the sliding average filter with the deep learning model, the system effectively reduces the noise of the collected data, improves the accuracy and stability of force prediction, and can display 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 comprises 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 presents an axisymmetric structure, and includes a protrusion, an upper electrode layer, a conductive layer, a positioning layer, and a lower electrode layer from top to bottom;

[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 has 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, is laid flat in the cavity of the positioning layer, and forms a 2×2 array sensor of a sandwich structure with the upper electrode layer and the lower electrode layer, 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 have 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. Each electrode unit has a size of a 4mm×4mm square structure, and the interval between each electrode is 2mm.

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

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

[0019] Furthermore, the material of the protrusions 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 by glue, place the conductive layer in the cavity of the positioning layer, and fix the positioning layer to the upper and lower electrodes by glue.

[0026] Furthermore, the step 1 specifically includes:

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

[0028] S2, adding deionized water to the obtained mixed solution, centrifuging at 10000r / min for 5 minutes, pouring out the upper solution containing impurities after the centrifugation, and adding deionized water again to the remaining precipitate. Repeat this step 7 times to obtain a mixed slurry;

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

[0030] S4. Add deionized water 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 the base gel and the 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 squeezed out and the surface is made flat. 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 processing on the predicted values.

[0034] Furthermore, the host computer also draws the prediction results through a 3D drawing tool to achieve a three-dimensional visual display of the force.

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

[0036] The piezoresistive three-dimensional force sensor of the present invention forms a conductive circuit through the upper and lower electrodes and the conductive layer. When the conductive layer is pressurized, the conductive paths become more numerous, thereby reducing the resistance; at the same time, the contact area between the electrode and the conductive layer increases, thereby reducing the resistance, thereby utilizing the change in resistance to achieve the measurement of the size and direction of the three-dimensional force and significantly improve the sensitivity of the sensor.

[0037] The conductive layer of the present invention is made by soaking and drying dust-free paper in a MXene solution, and the production process is simple and the cost is low.

[0038] The system of the present invention has the advantages of real-time performance, high precision, strong intuitiveness and strong flexibility, and at the same time has good compatibility, can be applied to a variety of three-dimensional force sensor devices, and supports application requirements in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

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

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

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

[0043] Figure 4 A flow chart for preparing a conductive layer for a three-dimensional force sensor;

[0044] Figure 5 The figure is a flow chart of the preparation of the three-dimensional force sensor;

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

[0046] Figure 7 It is an experimental platform for three-dimensional force sensors;

[0047] Figure 8 Collect the schematic diagram of the circuit for the three-dimensional force sensor;

[0048] Fig. 9 It is the logic diagram of the acquisition circuit of the three-dimensional force sensor;

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

[0050] Fig.11 This is a graph of the neural network training results for the three-dimensional force sensor;

[0051] Fig.12 A comparison chart of the actual value and predicted value of the force applied by the three-dimensional force sensor;

[0052] Fig.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] Fig.14 The conductive layer of the three-dimensional force sensor is shown in the real object and electron microscope image;

[0054] Fig.15 The relative resistance change rate curve of the three-dimensional force sensor when 20,000 normal repeated compression-release cycles are applied;

[0055] Fig.16 A curve diagram of the relative resistance change rate of the three-dimensional force sensor when different pressures are continuously applied;

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

[0057] Fig.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 invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0062] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

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

[0064] like Figure 1 and Figure 2 As shown, the three-dimensional force sensor of the present invention comprises, 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 2×2 array of electrodes and a square structure in which each electrode unit has a size of 4mm×4mm, 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] Wherein, the material of the protrusion 1 is a flexible high molecular polymer; preferably, the flexible high molecular polymer is silicone rubber or PDMS;

[0066] Wherein, the conductive layer 3 used for conducting electricity is a fiber substrate soaked in a 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, which fits the outer periphery of the upper and lower electrodes of the sensor, and an inner diameter of 10mm, which fits the copper electrode and the middle armor conductive layer;

[0068] Among them, the material of the positive electrode and the negative electrode is copper with a thickness of 36 μm (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 that the electrode still has good conductivity and stability when subjected to large deformation).

[0069] like Figure 2 The square conductive copper foil of the upper electrode 2 and the conductive copper foil of the lower electrode 5 form a conductive loop; the force is measured by the resistance change caused by the deformation of the conductive layer 3 under pressure; in the unloaded state, the MXene nanosheets are randomly distributed in the fiber network, and the high porosity of the fiber film causes the contact between the MXene nanosheets to be loose, resulting in fewer conductive paths. When the sensor is subjected to external pressure, the fiber film deforms, the contact between the MXene nanosheets becomes closer, and more conductive channels are formed.

[0070] like Figure 3 As shown, the protrusion 1 can protect the sensor body from damage while achieving the accuracy of force conduction. Compared with other shapes, the prismatic protrusion structure can distribute 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 membrane, 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 force. As the upper edge length increases, the maximum deformation area of ​​the protrusion expands from the center to the edge. In these four cases, the force transmitted to the conductive layer 3 is also different. Figure 3 (b) shows that the maximum equivalent stress transmitted to the piezoresistive film by the protrusions 1 with edge lengths of 6mm, 7mm, 8mm and 9mm are 0.021MPa, 0.018MPa, 0.015MPa and 0.017MPa respectively. Although the 6mm and 9mm protrusions transmit larger equivalent stresses in the center and edge areas of the film, this leads to the limitation of the contact area between the conductive layer 3 and the upper electrode 2 and the lower electrode 5, which in turn affects the sensor performance. In contrast, the 7mm and 8mm protrusions 1 can transmit the force to the pressure-sensitive material layer more evenly, which helps 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 3(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. On the whole, 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 comprises the following steps:

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

[0075] S2, adding deionized water to the obtained mixed solution, centrifuging at 10000r / min for 5 minutes, pouring out the upper solution containing impurities after the centrifugation, and adding deionized water again to the remaining precipitate. Repeat this step 7 times to obtain a mixed slurry;

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

[0077] S4. Add deionized water 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:

[0079] S1. First, an aluminum mold is used to make a surface protrusion 1. The PDMS solution is mixed with a base gel and a curing agent (Sylgard184, Dow Chemical Co., Milander, MI, USA) in a weight ratio of 10:1. This ratio gives the surface a higher Young's modulus. After pouring the mixed solution into the mold, degas it in a vacuum dryer for 25 minutes to ensure that all residual bubbles are removed. Then select a flat acrylic plate, laminate it on the surface of the mold, gently press and squeeze out the excess PDMS, and make the surface flat. Put the mold into a vacuum dryer at 85°C and heat it for 3 hours. After completion, demold it 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 needs to be pre-applied around the lower electrode layer 5 before the electrode is adhered to the film, wherein the lower electrode layer 5 is bonded to the positioning layer 4 by silica gel;

[0081] S3, sandwich the prepared MXene sensitive layer 3 between the upper and lower electrodes, and use silicone adhesive to bond the four sides of the sensor. Finally, bond the silicone between the surface of the protrusion 1 and the sensor, and place a 200g weight on the top of the protrusion and let it stand for 24 hours to ensure that the silicone is fully cured. After this process is completed, the production of the flexible three-dimensional tactile sensor is completed.

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

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

[0084] The sensor consists of four piezoresistive sensing units (R 1 , R 2 , R 3 , R 4 ), these units are formed by an upper electrode and a lower electrode symmetrically distributed around the center, forming a single sensor unit as a whole. Figure 6 As shown in (b), when the normal force is applied, the bump on the sensor surface is compressed, and the four piezoresistive sensing units are subjected to equal compressive stress. Due to the piezoresistive effect, the resistance of the four units decreases synchronously, and the resistance change is equal (ΔR 1 =ΔR 2 =ΔR 3 =ΔR 4 ).like Figure 6 (c) and Figure 6 As shown in (d), under the action of shear force, the bump deforms and generates torque at the fixed end. The two units on one side of the sensor are subjected to compressive stress, while the two units on the other side are subjected to tensile stress, resulting in opposite changes in the resistance of the sensing units on both sides. Therefore, by calculating the change in the resistance value of the four sensing units, the magnitude and direction of the real force can be predicted through a neural network.

[0085] like Figure 7As shown in the figure, this device is an experimental device for testing the performance of sensors. The device consists of a three-axis mobile platform (Huike, LD40-RM) and a commercial three-axis force sensor (Sparto, SBT301-40A). The commercial three-axis sensor is used to provide accurate force measurement parameters. In order to ensure accuracy during loading, the loading rod is 3D printed with a certain material and mounted 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 is subjected to normal force and shear force respectively, simulating the multi-dimensional force in the actual working environment.

[0086] like Figure 8 As shown in the figure, this schematic diagram is the circuit acquisition principle diagram of the three-dimensional force sensor. The sensors connected to the circuit are controlled by using different switches in the control rows and columns. ref is the voltage divider resistor, a 1K resistor is used here.

[0087] like Fig. 9 As shown in the figure, the data acquisition uses the STM32F103C8T6 microcontroller, which has 10 built-in 12-bit ADC converters. In order to improve the measurement efficiency, a multi-way switch is used to sequentially scan the pins, and the position of the collected unit sensor is determined by the connected rows and columns. The sampling frequency is set to 50Hz. The information obtained by the commercial three-axis force sensor and the three-dimensional force sensor acquisition board will be transmitted to the host computer system developed using Python through different serial ports through different communication protocols. Here, the lower computer will pass the information to the upper computer through the frame header 0xAABBCCDD+8-bit information+frame tail 0xDDCCBBAA. The upper computer will parse the information and receive the three-axis force information measured by the sensor transmitted by the commercial sensor transmitter. The two types of information are stored and corresponded one by one. The system can receive information from both parties in real time, and preliminarily organize and save the information to prepare for subsequent decoupling analysis.

[0088] like Fig.10 As shown in the figure, since the decoupling of the forces in three directions of this type of three-dimensional force sensor is not a relatively complex problem, a simple neural network model is used here to decouple the three-dimensional forces. The neural network model is set to have four input layers (respectively, the resistance (R 1 , R 2 , R 3 , R 4 ), three output layers (respectively the forces Fz, Fx, Fy), and three hidden layers (respectively 64, 128, and 64 neurons).

[0089] like Fig.11As shown in the figure, after 5000 cycles of training on 5000 training sets, the Loss value tends to be stable.

[0090] like Fig.12 As shown in Figure 2, in order to verify the effectiveness of the model, 4000 test sets were predicted, and the R 2 The coefficients reached 0.9985, 0.9986, and 0.9958, respectively, demonstrating excellent prediction performance.

[0091] like Fig.13 As shown, the sensitivity of the piezoresistive sensor can be expressed as Where ΔR is the resistance change, R 0 is the resistance when there is no external force, and ΔF is the change in force. The figure shows the relative resistance change rate of the four sensor units under the normal force of 0 to 15N and their sensitivity in different pressure ranges. When the pressure is lower than 2N, the sensitivity of the sensor can be as high as 0.789N -1 In the pressure ranges of 2-5N and 5-15N, the sensitivity drops to 0.460N respectively. -1 and 0.115N -1 This result indicates that the sensitivity of the sensor decreases as the applied external force increases.

[0092] Among them, under low pressure, 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 a new conductive network, resulting in a decrease in the sensitivity of the sensor. Usually, the shear force acting on the sensor is smaller than the normal force, and the two forces often exist at the same time. Therefore, we measured the sensitivity of the sensor to shear force when the normal pressure is 5N. Figure 6 As shown in Fig. 6b and Fig. 6c, as the shear force increases, the resistance change of the compression sensing unit is smaller than that of the tension sensing unit. In the range of 0-6N, the average sensitivity of the sensor on the x-axis and y-axis is 0.025N respectively. -1 and 0.019N -1 .

[0093] like Fig.14 As shown in Figure 2, the MXene surface is rich in functional groups, and the large specific surface area enhances its bonding with the substrate, thus giving it excellent mechanical properties. Its metallic 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 it to be firmly bonded to substrates such as cotton fabrics.

[0094] like Fig.15As shown, after 10,000 repeated compression-release cycle tests under a normal force of 5N, it can be found that the dynamic change of the relative resistivity of the sensor remains stable, and the sensor exhibits good repeatability, stability and consistency.

[0095] like Fig.16 As shown, when different normal pressures are continuously applied to the sensor, it exhibits a good stable output signal.

[0096] like Fig.17 As shown, when the sensor is quickly loaded and unloaded with a normal pressure of 0.5N, the sensor exhibits a fast response time and short hysteresis time, and its response and recovery times are 63ms and 86ms respectively.

[0097] like Fig.18 As shown in the figure, it is a graphical interface display module, which establishes communication with the three-dimensional force sensor through the serial communication module to read the real-time acquisition data; then the data is preprocessed, including the sliding average filter and data normalization processing module; the independent models of the X, Y, and Z direction forces are loaded for prediction, and the predicted values ​​are denormalized; the prediction results are drawn through the 3D drawing tool to realize the three-dimensional visualization display of the force.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A planar flexible three-dimensional force sensing system, characterized in that: 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 presents an axisymmetric structure, and includes a protrusion, an upper electrode layer, a conductive layer, a positioning layer, and a lower electrode layer from top to bottom; 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 has 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, is laid flat in the cavity of the positioning layer, and forms a 2×2 array sensor of a sandwich structure with the upper electrode layer and the lower electrode layer, forming four piezoresistive sensing units; The thickness of the conductive layer is the same as that of the positioning layer; 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.

2. A 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 of the same size and have 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. Each electrode unit has a size of a 4mm×4mm square structure, and the interval between each electrode is 2mm.

3. A 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 by means of silica gel.

5. The planar flexible three-dimensional force sensing system according to claim 1, characterized in that: The material of the protrusions 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 comprises: 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 by glue, place the conductive layer in the cavity of the positioning layer, and fix the positioning layer to the upper and lower electrodes by glue.

7. A 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 certain proportion of deionized water and concentrated hydrochloric acid, and magnetically stirred for 24 hours for full fusion; S2, adding deionized water to the obtained mixed solution, centrifuging at 10000r / min for 5 minutes, pouring out the upper solution containing impurities after the centrifugation, and adding deionized water again to the remaining precipitate. Repeat this step 7 times to obtain a mixed slurry; S3, adding deionized water to the obtained mixed slurry, and centrifuging at 3000 r / min for 20 minutes to obtain a MXene stock solution; S4. Add deionized water 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 the base gel and the 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 squeezed out and the surface is made flat. 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 processing on the predicted values.

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

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