Triaxial force flexible sensor and preparation method and application thereof

Abstract

The invention discloses a triaxial force flexible sensor and a preparation method and application thereof, and relates to the technical field of flexible sensor design, and the sensor comprises an interdigital electrode, a porous piezoresistive layer, at least four second electrodes and a first electrode which are sequentially arranged from bottom to top; the interdigital electrode is electrically connected with the first conductive circuit, and the first electrode and the second electrode are electrically connected with the second conductive circuit; the porous piezoresistive layer is attached to the interdigital electrode and is close to the second electrode; the porous piezoresistive layer is of a porous conductive structure and is electrically connected with the interdigital electrode; the first electrode is arranged at the central position of the first flexible substrate layer, and the second electrode is arranged on the second flexible substrate layer and is arranged around the first electrode; the first flexible substrate layer is of a flexible stretchable structure, and the second flexible substrate layer is of a flexible non-stretchable structure; compared with a traditional flexible sensor, the three-axis force flexible sensor has the advantages that the problem of mutual interference during detection of tangential force and normal force is avoided, and the measurement accuracy of the tangential force and the normal force is improved.

Description

Technical Field

[0001] This application generally relates to the technical field of flexible sensor design, and particularly to a triaxial force flexible sensor, a preparation method thereof, and an application thereof. Background Art

[0002] Tactile perception plays a crucial role in robots, especially triaxial force tactile perception, which enables robots to more accurately perceive and manipulate objects. By detecting the applied forces and pressures in three dimensions, robots can not only judge the shape and hardness of objects, but also sense the contact state with objects and the intensity of interaction. This information helps to optimize the grasping strategy and avoid damaging objects or holding them insecurely due to excessive force application. At the same time, triaxial force tactile perception can enhance the dynamic adaptability of robots, enabling them to better interact in complex and changing environments.

[0003] Currently, the implementation principles of flexible tactile sensors mainly include resistive, capacitive, magnetic, optical waveguide, triboelectric, etc. Among them, resistive sensors have a simple structure, low cost, high sensitivity to small pressure changes, are applicable to a wide pressure range, and have a relatively simple readout circuit. Capacitive sensors, on the other hand, have great scalability, relatively simple structural design, sensitive capacitance changes, and can provide high resolution. However, the structures of traditional triaxial force flexible sensors are relatively complex, and their detections all adopt the same sensing principle, which inevitably causes the coupling of tangential force and normal force, signal interference with each other, and it is impossible to accurately detect tangential force and normal force simultaneously. Therefore, we propose a triaxial force flexible sensor, a preparation method thereof, and an application thereof to solve the above problems. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desired to provide a triaxial force flexible sensor, a preparation method thereof, and an application thereof that solve the problem of force coupling of traditional flexible sensors.

[0005] In a first aspect, this application provides a triaxial force flexible sensor, including: interdigital electrodes, a porous piezoresistive layer, at least four second electrodes, and a first electrode arranged in sequence from bottom to top; the interdigital electrodes are electrically connected to a first conductive circuit, and the first electrode and the second electrodes are electrically connected to a second conductive circuit; The porous piezoresistive layer is attached to the interdigital electrodes and is arranged close to the second electrodes; the porous piezoresistive layer is a porous conductive structure and is electrically connected to the interdigital electrodes; The first electrode is arranged at the central position of a first flexible substrate layer, and the second electrodes are arranged on a second flexible substrate layer and are arranged around the first electrode; the first flexible substrate layer is a flexible and stretchable structure, and the second flexible substrate layer is a flexible and non-stretchable structure; When a normal force acts on the triaxial force flexible sensor, the pores inside the porous piezoresistive layer are compressed, enabling the first conductive circuit to conduct. The resistance of the interdigital electrodes changes, while the gap between the first electrode and the second electrode remains unchanged and the capacitance does not change. When a tangential force acts on the triaxial force flexible sensor, the first electrode undergoes a displacement change, causing the gap between it and the second electrode to change, thereby inducing a capacitance change, while the porous piezoresistive layer remains unchanged.

[0006] According to the technical solution provided by the embodiment of the present application, the first electrode is connected to the first flexible base layer through a packaging layer, and the second electrode is connected to the second flexible base layer through a packaging layer.

[0007] According to the technical solution provided by the embodiment of the present application, the first flexible base layer is polydimethylsiloxane, and the second flexible base layer and the packaging layer are polyethylene terephthalate.

[0008] According to the technical solution provided by the embodiment of the present application, the first flexible base layer, the second flexible base layer, and the porous piezoresistive layer are adhesively connected.

[0009] According to the technical solution provided by the embodiment of the present application, the second conductive circuit includes: A first sub-conductive circuit that is electrically connected to the first electrode; A second sub-conductive circuit that is electrically connected to the second electrode; A bridge circuit that is electrically connected to the first electrode and the second electrode and is used to detect the capacitance between the first electrode and the second electrode.

[0010] According to the technical solution provided by the embodiment of the present application, the bridge circuit is also electrically connected to the interdigital electrodes and is used to detect the resistance of the interdigital electrodes.

[0011] According to the technical solution provided by the embodiment of the present application, the thickness of the first electrode and the second electrode is 0.5 mm; when the triaxial force flexible sensor is not stressed, the gap between the first electrode and the second electrode is 1 mm.

[0012] In a second aspect, the present application provides a preparation method for a triaxial force flexible sensor for preparing the above-mentioned triaxial force flexible sensor, and the preparation method includes the following steps: Using laser cutting and polishing equipment to process copper with a copper content of more than 99.95% to obtain a first electrode and at least four second electrodes; Prepare a first flexible base layer by mixing polydimethylsiloxane resin and a curing agent in a preset mass ratio, and cut a second flexible base layer on a polyethylene terephthalate film using a cutting machine; and mount the first electrode on the first flexible base layer through a packaging layer, and mount the second electrode on the second flexible base layer through a packaging layer; Incorporate flexible conductive fillers into water-soluble paper. After the flexible conductive fillers are cured, soak the water-soluble paper in water for 30 minutes, and then put it into a drying oven for drying at 40 °C for 30 minutes to obtain a porous piezoresistive layer; and attach the porous piezoresistive layer to the interdigital electrodes; Connect the first flexible base layer, the second flexible base layer and the porous piezoresistive layer through a silicone adhesive to obtain a triaxial force flexible sensor.

[0013] According to the technical solution provided by the embodiment of the present application, prepare the flexible conductive filler according to the following steps: Add 6 steel balls, 0.4 g of multi-walled carbon nanotubes with a purity of 95% and 6 g of isopropanol into a 150 ml container bottle, and then put the container bottle into a blender for material mixing for 4 minutes. And, within the 4-minute period of material mixing, take out the container bottle and let it stand for 30 seconds every 1.5 minutes; After 4 minutes of material mixing, add 8 g of polydimethylsiloxane resin and 0.8 g of silicone diluent, and perform 3 times of mixing at a mixing interval of 1.5 minutes, then add 0.8 g of curing agent, mix for 1 minute and defoam for 1.5 minutes to obtain the flexible conductive filler.

[0014] In a third aspect, the present application provides an application of a triaxial force flexible sensor, including: using the above triaxial force flexible sensor for a manipulator to identify the slip problem that occurs when the manipulator grasps an object.

[0015] It can be seen from the above technical solutions that the present application has at least the following beneficial effects: The present application provides a triaxial force flexible sensor, which includes: interdigital electrodes, a porous piezoresistive layer, at least four second electrodes, and a first electrode arranged in sequence from bottom to top; the interdigital electrodes are electrically connected to a first conductive circuit, and the first electrode and the second electrodes are electrically connected to a second conductive circuit; the porous piezoresistive layer is attached to the interdigital electrodes and is arranged close to the second electrodes; the porous piezoresistive layer is a porous conductive structure and is electrically connected to the interdigital electrodes; the first electrode is arranged at the central position of a first flexible base layer, and the second electrodes are arranged on a second flexible base layer and are arranged around the first electrode in a ring shape; the first flexible base layer is a flexible and stretchable structure, and the second flexible base layer is a flexible non-stretchable structure; when a normal force acts on the triaxial force flexible sensor, the pores inside the porous piezoresistive layer are compressed, so that the first conductive circuit is turned on, the resistance of the interdigital electrodes changes, and the gap between the first electrode and the second electrodes remains unchanged, and the capacitance does not change; when a tangential force acts on the triaxial force flexible sensor, the first electrode generates a displacement change, so that the gap between it and the second electrodes changes, thereby causing a change in capacitance, and the porous piezoresistive layer does not change.

[0016] The present application forms a triaxial force flexible sensor by adopting a sensing method combining capacitance and resistance. When a normal force acts on the triaxial force flexible sensor of the present application, only the porous piezoresistive layer is compressed, so that the resistance of the interdigital electrodes changes. When a tangential force acts on the triaxial force flexible sensor of the present application, only the gap between the first electrode and the second electrodes changes, so that the capacitance changes. Compared with traditional flexible sensors, the triaxial force flexible sensor of the present application can avoid the problem of mutual interference during the detection of tangential force and normal force, and improve the measurement accuracy of tangential force and normal force. Description of the Drawings

[0017] By reading the detailed description of the non-restrictive embodiments with reference to the following drawings, other features, objectives, and advantages of the present application will become more obvious.

[0018] Figure 1 It is a schematic structural diagram of a triaxial force flexible sensor.

[0019] Figure 2 It is a sensing principle diagram of a triaxial force flexible sensor.

[0020] Figure 3 It is a principle diagram of a normal force acting on a triaxial force flexible sensor.

[0021] Figure 4 It is a principle diagram of a tangential force acting on a triaxial force flexible sensor.

[0022] Figure 5 It is a principle diagram for optimizing the structural parameters of a triaxial force flexible sensor.

[0023] Figure 6 It is a flowchart of the preparation method of a triaxial force flexible sensor.

[0024] Figure 7 It is a characterization result diagram for the normal force performance test of a triaxial force flexible sensor.

[0025] Figure 8 It is a characterization result diagram for the tangential force performance test of a triaxial force flexible sensor.

[0026] Figure 9 It is a verification diagram for the decoupling of tangential force and normal force of a triaxial force flexible sensor.

[0027] Figure 10 It is a demonstration diagram for the first robotic arm test experiment.

[0028] Figure 11 It is a demonstration diagram for the second robotic arm test experiment.

[0029] Reference numerals in the figure: 1. interdigital electrode; 2. porous piezoresistive layer; 3. first electrode; 4. second electrode; 5. first flexible base layer; 6. second flexible base layer; 7. encapsulation layer. Specific implementation manners

[0030] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention, rather than limiting the invention. Additionally, it should be noted that for the convenience of description, only the parts related to the invention are shown in the drawings.

[0031] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the drawings and embodiments.

[0032] For the clear and concise description of the following embodiments, a brief introduction to the related technologies is given first: The triaxial force flexible sensor can significantly improve the operation accuracy, flexibility and human-robot interaction safety of the robot by real-time sensing the force conditions of the robot in three directions. Its dynamic measurement and real-time feedback capabilities enable the robot to better adapt to complex tasks and dynamic environments, promoting the wide application of robot technology in the fields of automation, medical treatment, cooperation, etc. For decades, researchers have been committed to the design of multi-axis force sensors.

[0033] For example, a hybrid sensor, that is, a hybrid capacitive sensor and a resistive sensor, with the two sensors stacked. The upper-layer capacitive sensor is responsible for detecting the tangential force, and the lower-layer resistive sensor is responsible for detecting the normal force. However, the upper-layer capacitive sensor adopts a parallel-plate capacitor structure, and the detection of the tangential force will be affected by the normal force. Therefore, for the design of multi-dimensional force sensors, the problem of decoupling shear force and normal force needs to be solved.

[0034] In view of this, the present application adopts a sensing method combining a capacitor and a resistor to form a triaxial force flexible sensor. When a normal force acts on the triaxial force flexible sensor, only the porous piezoresistive layer is compressed, causing a change in the resistance of the interdigital electrodes. When a tangential force acts on the triaxial force flexible sensor, only the gap between the first electrode and the second electrode changes, causing a change in the capacitance. Compared with traditional flexible sensors, the triaxial force flexible sensor of the present application can avoid the problem of mutual interference during the detection of tangential force and normal force, and improve the measurement accuracy of tangential force and normal force.

[0035] In order to make the triaxial force flexible sensor provided by the embodiments of the present application clearer and easier to understand, the sensor will be introduced below with reference to the accompanying drawings. As Figure 1 shown, this figure is a schematic structural diagram of the triaxial force flexible sensor provided by the embodiments of the present application. The sensor includes: The interdigital electrodes 1, the porous piezoresistive layer 2, at least four second electrodes 4 and a first electrode 3 arranged in sequence from bottom to top; the interdigital electrodes 1 are electrically connected to the first conductive circuit, and the first electrode 3 and the second electrodes 4 are electrically connected to the second conductive circuit; The porous piezoresistive layer 2 is attached to the interdigital electrodes 1 and is disposed close to the second electrodes 4; the porous piezoresistive layer 2 is a porous conductive structure and is electrically connected to the interdigital electrodes 1; The first electrode 3 is disposed at the central position of the first flexible base layer 5, and the second electrodes 4 are disposed on the second flexible base layer 6 and are arranged around the first electrode 3; the first flexible base layer 5 is a flexible and stretchable structure, and the second flexible base layer 6 is a flexible non-stretchable structure; When a normal force acts on the triaxial force flexible sensor, the pores inside the porous piezoresistive layer 2 are compressed, causing the first conductive circuit to conduct, and the resistance of the interdigital electrodes 1 changes. The gap between the first electrode 3 and the second electrodes 4 remains unchanged, and the capacitance does not change. When a tangential force acts on the triaxial force flexible sensor, the first electrode 3 generates a displacement change, causing the gap between it and the second electrodes 4 to change, thereby causing a change in the capacitance. The porous piezoresistive layer 2 does not change.

[0036] It should be noted that as Figure 1 and Figure 2As shown in the figure, this three-axis force flexible sensor adopts a layered structure design. The bottom layer is the interdigital electrode 1. The interdigital electrode 1 is not only the basic support part of the entire sensor, but also electrically connected to the first conductive circuit. Moreover, a porous piezoresistive layer 2 is attached to the interdigital electrode 1, and the two are closely connected and electrically connected. The porous piezoresistive layer 2 is arranged close to the second electrode 4 above. The porous piezoresistive layer 2 is a porous conductive structure. When the porous piezoresistive layer 2 is subjected to an external force, since it is electrically connected to the interdigital electrode 1, the current in the circuit will change. Above the porous piezoresistive layer 2, there is a first electrode 3 and at least four second electrodes 4. The first electrode 3 is arranged at the center position of the first flexible base layer 5, and the second electrodes 4 are arranged on the second flexible base layer 6 and surround the first electrode 3. The first electrode 3 and the second electrodes 4 are electrically connected to the second conductive circuit and are used to detect the tangential force. Here, in Figure 2 PDMS represents the first flexible base layer 5, Cu represents the copper electrode, mainly referring to the first electrode 3 or the second electrode 4, PET represents the second flexible base layer 6; Capctitive represents the capacitive type, mainly referring to the structure formed by the first electrode 3 and the second electrodes 4, Resistive represents the resistive type, mainly referring to the structure formed by the porous piezoresistive layer 2 and the interdigital electrode 1, and C3 and C4 respectively represent the capacitance between the first electrode 3 and a certain second electrode 4.

[0037] The first flexible base layer 5 is a flexible and stretchable structure, enabling the first electrode 3 to displace under the action of the tangential force. When the tangential force is applied to this three-axis force flexible sensor, the first flexible base layer 5 will undergo corresponding tensile or compressive deformation, thereby driving the first electrode 3 to move. The second flexible base layer 6 is a flexible non-stretchable structure, which can fix the position of the second electrode 4 and ensure that the second electrode 4 will not move randomly due to external forces during the force application process, guaranteeing the accuracy and stability of the tangential force detection.

[0038] It should be noted that the flexible and stretchable structure is a flexible structure that can undergo tensile deformation when subjected to an external force and can return to its original shape or close to its original shape after the external force is removed. The flexible non-stretchable structure refers to a structure with a certain degree of flexibility but with strict restrictions on stretching, usually only able to stretch to a small extent or basically not stretchable.

[0039] As Figure 3 shown, Normal Force represents the normal force, and C3 and C4 respectively represent the capacitance between the first electrode 3 and a certain second electrode 4. Indicates the gap between the first electrode 3 and the second electrode 4. When a normal force acts on the triaxial force flexible sensor, the force is applied vertically to the surface of the triaxial force flexible sensor. At this time, the porous piezoresistive layer 2 is subjected to pressure. Since the porous piezoresistive layer 2 is a porous conductive structure, the compression of the pores will change the conductive path, thereby enabling the first conductive circuit to conduct, and the resistance of the interdigital electrode 1 changes. Due to the characteristics of the flexible substrate layer where the first electrode 3 and the second electrode 4 are located, under the action of the normal force, the entire first flexible substrate layer 5 and the second flexible substrate layer 6 only displace vertically downward, and the gap between the first electrode 3 and the second electrode 4 remains unchanged, so the capacitance does not change. That is, by detecting the change in the resistance of the interdigital electrode 1, the magnitude information of the normal force can be obtained.

[0040] As Figure 4 shown, Shear Force represents the tangential force. When the tangential force acts on the triaxial force flexible sensor, the direction of the force is parallel to the surface of the triaxial force sensor. The flexible and stretchable structure of the first flexible substrate layer 5 enables the first electrode 3 to displace along with the direction of the tangential force, thereby changing the gap between the first electrode 3 and the second electrode 4. Since the first electrode 3 and the second electrode 4 form the two poles of the capacitor, the change in the gap will then cause a change in capacitance. As Figure 4 shown, the tangential force is to the left, causing the first electrode 3 to move closer to the left, resulting in a decrease in the gap between the first electrode 3 and the second electrode 4 on the left and an increase in the gap between the first electrode 3 and the second electrode 4 on the right. The corresponding capacitance will decrease or increase. And since the porous piezoresistive layer 2 is not directly affected by the tangential force, the internal pore structure does not change, so the resistance does not change either. That is, by detecting the change in the capacitance between the first electrode 3 and the second electrode 4, the magnitude and direction of the tangential force can be determined.

[0041] Through the above structural design, the decoupling of the tangential force and the normal force at the mechanical level is achieved, avoiding the mutual interference in the detection of the tangential force and the normal force in traditional sensors.

[0042] Furthermore, the first electrode 3 is connected to the first flexible substrate layer 5 through the encapsulation layer 7, and the second electrode 4 is connected to the second flexible substrate layer 6 through the encapsulation layer 7.

[0043] The encapsulation layer 7 plays a fixing role for the first electrode 3 and the second electrode 4. Here, the encapsulation layer 7 is, for example, polyethylene terephthalate (PET). PET has good flexibility, chemical stability and insulation properties. Among them, the flexibility enables it to adapt to the deformation of the first flexible base layer 5 and the second flexible base layer 6. When the triaxial force flexible sensor is subjected to an external force, it will not hinder the normal deformation of the base layer due to the excessive hardness of the material itself; the chemical stability ensures that the encapsulation layer can stably exist in various environments and is not easily chemically reacted with surrounding materials, thereby ensuring the long-term reliability of the triaxial force flexible sensor; the insulation property effectively prevents the leakage between the corresponding electrodes and the base layer and between different electrodes, ensuring the accuracy of the electrical signal transmission. And, the first flexible base layer 5 and the second flexible base layer 6 are, for example, polydimethylsiloxane (PDMS).

[0044] Furthermore, the first flexible base layer 5, the second flexible base layer 6 and the porous piezoresistive layer 2 are adhesively connected. For example, a silicone adhesive is used for the adhesive connection, Furthermore, the second conductive circuit includes: The first sub-conductive circuit, and the first sub-conductive circuit is electrically connected to the first electrode 3; The second sub-conductive circuit, and the second sub-conductive circuit is electrically connected to the second electrode 4; The bridge circuit, and the bridge circuit is electrically connected to the first electrode 3 and the second electrode 4 for detecting the capacitance between the first electrode 3 and the second electrode 4.

[0045] It should be noted that the first sub-conductive circuit is used to transmit the electrical signal generated by the first electrode 3 under the action of the tangential force. The second sub-conductive circuit is used to receive the electrical signal from the second electrode 4 and, together with the signal transmitted by the first sub-conductive circuit, provides comprehensive capacitance change information for the bridge circuit. Among them, the bridge circuit is also electrically connected to the interdigital electrode 1 for detecting the resistance of the interdigital electrode 1.

[0046] The inside of the bridge circuit is, for example, a Wheatstone bridge structure. When the capacitance between the first electrode 3 and the second electrode 4 changes (the tangential force acts on this sensor), it will break the original balance state of the bridge circuit, causing the output end of the bridge circuit to generate a voltage or current signal related to the capacitance change. By analyzing and processing these signals, the change amount of the capacitance can be accurately calculated, thereby determining the magnitude and direction of the tangential force. When the normal force acts on this sensor, the pores of the porous piezoresistive layer 2 are compressed, resulting in a change in the resistance of the interdigital electrode 1. The bridge circuit measures the change in the resistance of the interdigital electrode 1. Similarly, based on its internal structure, the resistance change is converted into a detectable voltage or current signal. By analyzing these signals, the magnitude information of the normal force can be accurately obtained.

[0047] Further, the thicknesses of the first electrode 3 and the second electrode 4 are, for example, 0.5 mm; when the triaxial force flexible sensor is not stressed, the gap between the first electrode 3 and the second electrode 4 is, for example, 1 mm.

[0048] In addition, the present application also performs simulation optimization on the structural parameters of the above triaxial force flexible sensor. Specifically as follows: The structural parameters of the first electrode 3 and the second electrode 4 are compared through simulation optimization by using a multi-physics simulation software (COMSOL Multiphysics, COMSOL), and the test of the influence of the inability of the first electrode 3 and the second electrode 4 to be strictly coplanar on the capacitance is carried out through simulation, as Figure 5 shown. The dimensional parameters of the electrodes include the length dimensions a and b of the electrodes, the gap dimension d of the electrodes, the thickness dimension t, and the height difference dimension e between the first electrode 3 and the four second electrodes 4. Here, the height difference dimension e mainly considers the small displacements ( Figure 5 a) of the first electrode 3 in the cross-section and the second electrode 4 in the plane when the sensor is being fabricated or when the force on the sensor is uneven. Considering the overall size of this sensor, it is necessary to make the overall length and width of the sensor conform to the size of a human finger as much as possible. Therefore, the length and width dimensions a and b of the electrodes are selected to be 3 mm and 5 mm.

[0049] First, under the variation of the height difference dimension e parameter, the variation relationship of the capacitance between the first electrode 3 and the four second electrodes 4, that is, the variation of the capacitance value between the first electrode 3 and the four second electrodes 4 under the up and down displacements of ±0.5 mm of the first electrode 3, can be seen that the variation of the capacitance between the first electrode 3 and the second electrode 4 within the height difference of ±0.2 mm is only about 0.001 PF. The corresponding results are shown in Figure 5 b, indicating that the small displacement of the first electrode 3 will not cause too much influence on the capacitance variation when the first electrode 3 cannot be strictly coplanar with the second electrode 4 during manufacturing and when it is subjected to uneven normal pressure. As Figure 5 shown in c-d, it mainly shows the influence of the thickness of the electrode on the capacitance response. The capacitance data is simulated and calculated in sequence at intervals of 0.1 mm for the electrode thickness from 0.2 mm to 0.8 mm. When the first electrode 3 moves upward, four change diagrams of capacitances C1, C2, C3, and C4 are plotted (C1, C2, C3, and C4 respectively represent the capacitances between the first electrode 3 and the four second electrodes 4). Here, as Figure 5 shown in c-d, they are the change diagrams of C1 and C3. It can be seen that as the first electrode 3 approaches the second electrode 4 above, the capacitance C1 increases, the capacitance C2 decreases, while the capacitances C3 and C4 remain basically unchanged. At the same time, it also verifies the feasibility of the sensor designed in the present application for detecting the tangential force. As the thickness increases, the sensitivity also increases, but if the electrode thickness is too large, it will cause the overall size of this sensor to be too large. From Figure 5It can be observed that when the thickness exceeds 0.5 mm, the sensitivity begins to change insignificantly. Considering the overall thickness dimension of this sensor, the thickness t of the sensor is finally selected as 0.5 mm. As Figure 5 shown in e-f, it mainly shows the influence of the electrode gap on the capacitance response. The electrode gap ranges from 0.6 mm to 1.2 mm, and the capacitance data is simulated and calculated at intervals of 0.1 mm. When the first electrode 3 moves upward, the change diagrams of four capacitances C1, C2, C3, and C4 are plotted. It can be seen that the smaller the gap, the higher the sensitivity, but the displacement limit will be reached faster. The larger the gap, the lower the sensitivity and the larger the overall area of the sensor. The smaller the gap, not only the displacement of the central electrode is limited, but also the manufacturing becomes complicated. Therefore, a suitable intermediate value of 1 mm is selected, so that there is good sensitivity and it is more convenient for the displacement of the central electrode.

[0050] As Figure 6 shown, this application provides a preparation method for a three-axis force flexible sensor for preparing the above-mentioned three-axis force flexible sensor. The preparation method includes the following steps: S100. Use laser cutting and polishing equipment to process copper with a copper content of more than 99.95% to obtain a first electrode 3 and at least four second electrodes 4.

[0051] S200. Make the first flexible base layer 5 by mixing polydimethylsiloxane resin and curing agent in a preset mass ratio and cut out the second flexible base layer 6 on a polyethylene terephthalate film through a cutting machine; and install the first electrode 3 on the first flexible base layer 5 through the encapsulation layer 7, and install the second electrode 4 on the second flexible base layer 6 through the encapsulation layer 7.

[0052] S300. Incorporate flexible conductive filler into water-soluble paper. After the flexible conductive filler is cured, soak the water-soluble paper in water for 30 minutes, and then put it into a drying oven to dry at 40 °C for 30 minutes to obtain the porous piezoresistive layer 2; and attach the porous piezoresistive layer 2 to the interdigital electrode 1.

[0053] S400. Connect the first flexible base layer 5, the second flexible base layer 6, and the porous piezoresistive layer 2 through a silicone adhesive to obtain a three-axis force flexible sensor.

[0054] It should be noted that copper with a copper content of more than 99.95% is selected as the electrode material. High-purity copper has good electrical conductivity, which can ensure the efficient transmission of electrical signals by the electrode during the operation of the sensor, reduce resistance loss, and thus improve the detection accuracy and sensitivity of the sensor. The copper is processed using laser cutting and polishing equipment. Laser cutting features high precision and high speed, and can accurately cut the copper into the shapes and sizes of a first electrode 3 and at least four second electrodes 4 as required, ensuring the geometric accuracy of the electrodes. The polishing equipment is used to treat the surface of the cut electrodes, removing impurities such as burrs and oxide layers on the surface, making the electrode surface smooth and flat, which is beneficial for subsequent connection with other components and the stable transmission of electrical signals.

[0055] The polydimethylsiloxane-based resin and the curing agent are mixed in a preset mass ratio to make a first flexible base layer 5, and a second flexible base layer 6 is cut out on a polyethylene terephthalate film by a cutting machine. Here, the preset mass ratio is, for example, 10:1. Polydimethylsiloxane has good flexibility, chemical stability, and biocompatibility. By adjusting the ratio of the resin and the curing agent, the physical properties such as the hardness and elasticity of the flexible base layer can be controlled to meet the different working requirements of the sensor. For example, the first flexible base layer 5 needs to have stretchability to sense the tangential force, and this property can be imparted by appropriate proportioning; while the second flexible base layer 6 is a flexible non-stretchable structure, and the PET film is a conventional structure. The second flexible base layer 6 can be formed by cutting the required shape on the PET film using a cutting machine, and then a conductive material is dispensed on the surface using a 3D printer for circuit connection. The first electrode 3 is installed at the center position of the first flexible base layer 5 using a packaging layer 7, and the second electrodes 4 are installed on the second flexible base layer 6 and arranged around the first electrode 3 in a ring shape. The packaging layer 7 plays a role in fixing and protecting the electrodes, and at the same time can ensure good electrical insulation and mechanical connection between the electrodes and the flexible base layer.

[0056] Flexible conductive fillers are incorporated into the water-soluble paper, and the water-soluble paper acts as a template to provide certain structural support for the flexible conductive fillers. Flexible conductive fillers usually have good conductivity and deformability. When subjected to external forces, the internal conductive pathways change, resulting in a change in resistance, thereby achieving the detection of force. After the flexible conductive fillers are cured, the water-soluble paper is soaked in water and dissolved for 30 minutes. After the water-soluble paper dissolves, many pores are left in the flexible conductive fillers, forming a porous structure. This porous structure makes the porous piezoresistive layer 2 more sensitive to force changes. When subjected to a normal force, the internal pores are compressed, the conductive pathways change, and the resistance changes significantly, which is beneficial to improving the detection sensitivity of the sensor to the normal force. The dissolved sample is placed in an oven and dried at 40°C for 30 minutes to remove moisture and make the structure of the porous piezoresistive layer 2 more stable. Appropriate drying temperature and time can prevent the flexible conductive fillers from being damaged due to excessive temperature, while ensuring that the moisture is fully removed and the performance of the porous piezoresistive layer 2 is stable. The prepared porous piezoresistive layer 2 is attached to the interdigital electrode 1. The interdigital electrode 1 is electrically connected to the porous piezoresistive layer 2. When the resistance of the porous piezoresistive layer 2 changes, the interdigital electrode 1 can convert this change into an electrical signal output, thereby achieving the detection of the normal force.

[0057] The first flexible base layer 5, the second flexible base layer 6 and the porous piezoresistive layer 2 are connected by a silicone adhesive. The silicone adhesive has good flexibility and adhesiveness, and can firmly connect each component together to form a complete three-axis force flexible sensor. At the same time, the silicone adhesive can also adapt to the deformation of the sensor during operation, ensure the stable connection between components, and will not loosen or separate due to external forces, thereby ensuring that the sensor can work stably for a long time. Through the above four steps, the three-axis force flexible sensor of the present application can be prepared.

[0058] Further, the flexible conductive filler is prepared according to the following steps: Six steel balls, 0.4 g of multi-walled carbon nanotubes with a purity of 95%, and 6 g of isopropanol are added to a 150 ml container bottle, and then the container bottle is placed in a blender for material mixing for 4 minutes. And, within the 4-minute period of material mixing, the container bottle is taken out and left stationary for 30 seconds every 1.5 minutes; After 4 minutes of material mixing, 8 g of polydimethylsiloxane resin and 0.8 g of silicone diluent are added, and mixing is carried out 3 times at a mixing interval of 1.5 minutes. Then 0.8 g of curing agent is added, mixed for 1 minute and degassed for 1.5 minutes to obtain the flexible conductive filler.

[0059] It should be noted that 6 steel balls, 0.4 g of multi-walled carbon nanotubes with a purity of 95%, and 6 g of isopropanol are added to a 150 ml volumetric flask. The steel balls play a role in grinding and dispersing during the stirring process. Through rolling and collision, they help the multi-walled carbon nanotubes disperse more evenly in isopropanol, avoiding agglomeration phenomena and ensuring that the multi-walled carbon nanotubes can fully exert their conductive properties. Multi-walled carbon nanotubes have excellent electrical conductivity and good flexibility, and are the key components for flexible conductive fillers to achieve conductive functions, capable of constructing conductive pathways inside the material. Isopropanol, as a solvent, helps the dispersion of multi-walled carbon nanotubes, enabling them to be evenly distributed in the solution. At the same time, it can also reduce the viscosity during the mixing process, facilitating the stirring operation.

[0060] The volumetric flask is placed in a blender for material mixing for 4 minutes. During this period, the volumetric flask is taken out every 1.5 minutes and left stationary for 30 seconds. Continuous stirring can promote the full mixing of multi-walled carbon nanotubes and isopropanol. However, long-term stirring will generate heat, which may cause the destruction of the multi-walled carbon nanotube structure or the volatilization of isopropanol. Taking it out and leaving it stationary for 30 seconds every 1.5 minutes can effectively dissipate heat, ensure the stability of material properties, and at the same time give the multi-walled carbon nanotubes time to further disperse evenly in the solution, improving the mixing effect.

[0061] After 4 minutes of material mixing, 8 g of polydimethylsiloxane-based resin and 0.8 g of silica gel diluent are added. The polydimethylsiloxane-based resin provides flexibility and elasticity for the flexible conductive filler, enabling it to adapt to the deformation of the porous piezoresistive layer during the operation of the sensor. The silica gel diluent can adjust the viscosity of the material, making it easier to process and form. At the same time, it also helps the uniform mixing of other components. Mixing is carried out 3 times at an interval of 1.5 minutes to ensure the full fusion of these materials and form a uniform system.

[0062] Then 0.8 g of curing agent is added and mixed for 1 minute. The role of the curing agent is to cause the polydimethylsiloxane-based resin to undergo a cross-linking reaction, forming a stable three-dimensional network structure, enhancing the mechanical properties and stability of the flexible conductive filler. Mixing for 1 minute can evenly distribute the curing agent in the material, ensuring the uniform progress of the cross-linking reaction. Subsequently, a 1.5-minute degassing treatment is carried out to remove the bubbles introduced during the mixing process. The presence of bubbles will affect the performance of the flexible conductive filler, such as reducing its electrical conductivity and mechanical strength. The degassing treatment can improve the quality and performance consistency of the material. Through these steps, a flexible conductive filler with good performance is finally obtained, laying a foundation for the preparation of a high-performance porous piezoresistive layer of a three-axis force flexible sensor.

[0063] This application also tests the above-prepared three-axis force flexible sensor as follows: Install the high-precision six-axis force sensor ATI Nano17 on the Z-axis. The prepared sensor is attached to an acrylic board. A 13*13 mm square acrylic board is installed on the probe of the high-precision six-axis force sensor ATI Nano17 as a contact head, and glue is applied to the contact head and bonded to the upper surface of this sensor to facilitate the application of a pure tangential force to the sensor surface. At the same time, there is also an LCR digital bridge (such as Victory Instruments, model VC4092B), whose detection frequency can support up to 200 KHz, for detecting capacitance and resistance data. The experimental device can adjust the parallelism of the sensor and the contact head through bolts.

[0064] Test the normal force performance of this sensor, and the characterization result diagram is as Figure 7 shown. The sensitivity curve of the pressure sensor is as Figure 7 shown in a. The shaded area represents the variance, a statistic for measuring the degree of data dispersion, showing the linear relationship between the normalized resistance change and the applied pressure. The sensitivity curve is mainly divided into the first half and the second half, showing a linear change. The sensitivity corresponding to 0 - 45 kPa in the first half is S1 = 0.0127 kPa -1 , and the sensitivity corresponding to 90 - 185 kPa in the second half is S2 = 0.0009 kPa -1 . Then, conduct the dynamic response experiment of the normal pressure of the sensor. Suddenly place a 500 g weight on the sensor surface and then remove it. At the same time, the digital bridge records the change in resistance response. The digital bridge transmits a data to the host computer every 25 ms. Plot the recorded data in a graph and calculate that the response time of the designed porous piezoresistive layer is about 200 ms, and the recovery time is about 175 ms, with a very fast response and recovery speed. Finally, to prove the repeatability of the normal force of the sensor, use a three-dimensional workbench to control the movement of the Z-axis, so that the contact head applies a certain normal load to the sensor every 2 s, and cycle the test 1000 times ( Figure 7 c), and at the same time select a small section in the front, middle, and back for enlarged display. The results show that the peak value and the original value of the measured resistance remain unchanged, indicating that the normal force sensing has good repeatability. The porous piezoresistive layer prepared according to the preparation method provided in this application has a fast speed and can be easily prepared in a large area. Only need to scrape the prepared conductive sensitive material on the purchased water-soluble paper, air-dry it, soak it in water, leave it standing for 10 min and then take it out, and it is completed after drying. The total time used before and after does not exceed 1 h, and the cost is extremely low.

[0065] Characterize the sensing performance of the tangential force through the test platform, and the characterization result diagram is as Figure 8As shown, due to the influence of external noise, all the original capacitance data has a certain amount of noise. The capacitance data was filtered using the mean filtering method in MATLAB, and an appropriate window size was selected according to different data densities to make the data look smoother. Before calibrating the XY axes of the tangential force, a certain amount of silicone adhesive Sil-Poxy was pre-coated on the contact tip, and the upper surface of the sensor was strictly controlled to be parallel to the contact tip by adjusting the bolts, so that it is convenient to apply pure tangential force after the contact tip is bonded to the upper surface of the sensor, without the need to apply a certain initial normal load on the surface of the sensor in advance. First, control the three-dimensional workbench to strictly align and parallelize the sensor and the contact tip, observe the force data feedback by ATI Nano17, and then control the Z-axis to move the contact tip downward. Apply a certain pressure between the contact tip and the sensor in advance to facilitate the bonding of the contact tip and the upper surface of the sensor, and then control the Z-axis to slowly move upward. When the force data returns to zero, that is, the contact tip and the upper surface of the sensor are in a critical state without pressure. Then, control the platform to conduct tangential force calibration experiments on the X-axis and Y-axis respectively. The tangential force calibration experiments on the X-axis and Y-axis are each done three times to record the data, and the images and variances of the normalized capacitance changing with the tangential forces Fx and Fy are plotted. The results are shown in Figure 8 Figures 8a and 8b, and the capacitance relationship diagram and force diagram between the first electrode 3 and the four second electrodes 4 of the sensor are marked. The results show a good linear change, and it is observed that the variances are approximately the same. Here, it is analyzed that this may be related to the accuracy of the digital bridge in detecting small capacitance values and has nothing to do with the sensor itself. And it is obvious that there are slight differences in the sensitivities of the X-axis and Y-axis, which is caused by the manufacturing of the sensor and the inability to completely accurately align and parallelize the contact tip and the surface of the sensor.

[0066] Then, in order to prove the stability of the tangential force, different magnitudes of cyclic loads were applied to the sensor, and the measurement results are as Figure 8 shown in Figure 8b. Control the movement of the X-axis of the three-dimensional workbench, and the contact tip applies a predetermined displacement to the sensor. Apply it cyclically 5 times, and increase the displacement by 0.02 mm every five times and then apply it 5 times again, for a total of four times. It can be observed that when the tangential force increases, the capacitance C1 increases, and the initial capacitance and the peak capacitance under each force are approximately the same. This indicates that the tangential force sensing has good amplitude stability. And, during the load holding and unloading stages, there are slight errors in the measured capacitance, which may be due to the problem of the accuracy of the digital bridge itself in detecting capacitance, the same as the variance of the XY-axis tangential force calibration before. In addition, a fixed tangential load was applied to the sensor, and multiple cyclic load experiments were carried out. The results are shown in Figure 8 Figure 8d. The above results all prove that the tangential force sensing of this sensor has good stability.

[0067] Finally, in order to verify the capacitance change relationship between the first electrode 3 and the four second electrodes 4 of the sensor, the X and Y axes of the three-dimensional workbench were controlled to apply tangential loads to the upper surface of the sensor back and forth in the up, down, left, and right directions, which were divided into four parts, and the changes of the four capacitance values C1, C2, C3, and C4 were recorded, and the result graph was plotted as shown in Figure 8 Figure e. The results show that the capacitance values between the central electrode and the four surrounding electrodes of the sensor can well display the magnitude and direction of the tangential force.

[0068] Furthermore, since the above-mentioned structural design of the sensor can achieve the mutual decoupling of tangential force and normal force at the mechanical level, corresponding experiments were designed to verify this, as shown in Figure 9 Figure. Similar to the previous tangential force calibration experiment, the contact head was bonded to the upper surface of the sensor, so that the contact head and the sensor were in the critical state of normal force (that is, the normal force was 0, but a small displacement of the contact head would apply a normal force), and then the Y axis of the three-dimensional workbench was controlled to apply a fixed Y-direction displacement of ±0.6 mm to the upper surface of the sensor (that is, a certain tangential force was applied), and then the Z axis was controlled to move, and the contact head was displaced downward by 0.02 mm (that is, a certain normal force was applied), and then a fixed Y-direction displacement of ±0.6 mm was applied to the upper surface of the sensor again, and this was cycled five times. Each time after a fixed Y-direction displacement of ±0.6 mm was applied to the upper surface of the sensor, the Z axis was controlled to move downward by 0.02 mm, and at the same time, the changes of resistance and capacitance were recorded. The final result graph is shown in Figure 9 Figure b. It can be observed that since the sensor uses two different sensing principles, the change of capacitance mainly depends on the displacement of the central electrode, and the change of resistance mainly depends on the porous piezoresistive layer. The capacitance data under the five steps have no obvious change, and the resistance also shows a stepped change, indicating that the two can separately detect normal force and tangential force, the sensor has the ability to detect tangential force and normal force simultaneously, and the response of normal pressure to capacitance will not cause an impact, proving that tangential force and normal force can achieve mechanical-level coupling.

[0069] This application also provides an application of a triaxial force flexible sensor, including: using the above-mentioned triaxial force flexible sensor for a manipulator to identify the slipping problem that occurs when the manipulator grasps an object.

[0070] The specific test process is as follows: The above-designed triaxial force sensor was assembled on the mechanical finger, and two different application demonstration experiments were carried out, as shown in Figure 10 and Figure 11 Figure. The sensor assembled on the manipulator can be used for the detection of grasping force and the detection of the weight of the lifted object, and has a good triaxial force response. The device of the first application demonstration experiment is shown in Figure 10As shown in Fig. a, the 3D-printed mechanical finger is assembled on a pneumatic slide rail. The grasping and releasing of the mechanical finger are achieved by inflating and deflating. The magnitude of the grasping force can be controlled by controlling the air pressure for inflation. The pneumatic guide rail is assembled on the Z-axis of a high-precision three-dimensional workbench. Three-axis force sensors are installed at both ends of the finger. During the experiment, only the sensing data of one end sensor is detected. A weight with a certain mass is placed on the 3D-printed part. The mechanical finger grasps the 3D-printed part bearing weights of different masses, and lifting and lowering operations are performed. The weight is increased by 100 g in sequence. At the same time, the resistance data and the capacitance C2 data are detected. As Figure 10 shown in Fig. b, the results show that when the pneumatic guide rail is inflated, the mechanical finger closes, the sensor is compressed, the resistance drops instantaneously and then stabilizes, indicating that the mechanical hand grasps the 3D-printed part. After placing a heavy object on the 3D-printed part, the capacitance detection channel is opened before the mechanical hand starts to lift, and the change of capacitance C2 is detected. Then, the weight is increased by 100 g again and the lifting and lowering are repeated. As the weight increases, the capacitance C2 also gradually increases, indicating that the sensor can detect the change of the object weight through the change of capacitance C2. It should be noted here that whenever the mechanical finger lifts and lowers the object, the resistance will have a small fluctuation and then tend to be stable, and the greater the weight of the lifted and lowered object, the greater the fluctuation. Here, the analysis is that when the mechanical finger lifts and lowers the heavy object, the sensor does not bear a pure tangential force in the downward direction, but will have a certain torsional force. Therefore, the resistance fluctuation phenomenon occurs during the lifting and lowering process.

[0071] The experimental device for the second application demonstration is as Figure 11 shown in Fig. a. Similar to the first application demonstration device, the mechanical finger is horizontally installed on the Z-axis, and the Z-axis is fixed. The 3D-printed part is replaced with a sphere. The center of the spherical 3D-printed part is aligned with the centers of the two sensors on both sides. After the mechanical finger grasps the spherical 3D-printed part, external forces in the -Z and +Y directions are applied to the spherical object under the intervention of a human hand, and the changes of the resistance and four capacitance values are recorded simultaneously. The results are plotted in Figure 11In Figure b, the results show that when the robotic finger grasps an object, the resistance decreases significantly. When a -Z direction force is applied to the spherical object, the spherical object transfers the force to the -Z direction tangential force of the sensor, and the capacitance C3 increases while C4 decreases. The capacitances C1 and C2 decrease slightly. The possible reason for the analysis is that there is no shielding layer on the outer layer of the sensor, and the capacitance is more susceptible to the influence of the external magnetic field. When an external force is applied to the sphere by hand, the change in the external magnetic field causes a slight decrease in C1 and C2. When a +Y direction force is applied to the spherical object, the sensor receives a +Y direction tangential force, the capacitance C1 increases, C2 decreases, and the capacitances C3 and C4 decrease slightly. Here, it should be noted that when -Z and +Y direction forces are applied to the sensor, the resistance value also changes to a certain extent. The reason is that the applied external force cannot be a pure tangential force but has a certain torsional force. This experiment proves that the sensor has a good three-axis force response and can detect the magnitude and direction of the tangential force within the sensor plane.

[0072] Through the sensor decoupling experiment designed above, the results show that the tangential force and the normal force of the sensor designed in this application can achieve a result of not affecting each other, which proves that the sensor can achieve force decoupling at the mechanical level. Finally, when the sensor is fixed on the surface of the fingertips of two robotic fingers, it can not only detect the grasping force but also detect the weight of the grasped object, and has a good three-axis force response.

[0073] Here, the normal force sensitivity of the three-axis force flexible sensor designed in this application can be 1.27*10 -2 N -1 , the maximum detection range of the normal force is about 0 - 185 kPa, and the effective detection range of the tangential force is about 0.5 - 4 N.

[0074] The above description is only a preferred embodiment of this application and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solution formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the technical solutions formed by mutually replacing the above features with the (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A three-axis force flexible sensor, characterized in that: include: An interdigitated electrode (1), a porous piezoresistive layer (2), at least four second electrodes (4) and a first electrode (3) are arranged in sequence from bottom to top; the interdigitated electrode (1) is electrically connected to a first conductive circuit, and the first electrode (3) and the second electrode (4) are electrically connected to the second conductive circuit; The porous piezoresistive layer (2) is applied on the interdigital electrode (1) and is arranged close to the second electrode (4); the porous piezoresistive layer (2) is a porous conductive structure and is electrically connected to the interdigital electrode (1); The first electrode (3) is arranged at the center of the first flexible base layer (5), and the second electrode (4) is arranged on the second flexible base layer (6) and is arranged around the first electrode (3); the first flexible base layer (5) is a flexible stretchable structure, and the second flexible base layer (6) is a flexible non-stretchable structure; When a normal force acts on the three-axis force flexible sensor, the internal pores of the porous piezoresistive layer (2) are compressed, so that the first conductive circuit is turned on, the resistance of the interdigitated electrode (1) changes, the gap between the first electrode (3) and the second electrode (4) does not change, and the capacitance does not change; when a tangential force acts on the three-axis force flexible sensor, the first electrode (3) produces a displacement change, so that the gap between it and the second electrode (4) changes, thereby causing the capacitance to change, and the porous piezoresistive layer (2) does not change.

2. A three-axis force flexible sensor according to claim 1, characterized in that: The first electrode (3) is connected to the first flexible base layer (5) through a packaging layer (7), and the second electrode (4) is connected to the second flexible base layer (6) through a packaging layer (7).

3. A three-axis force flexible sensor according to claim 2, characterized in that: The first flexible substrate layer (5) is polydimethylsiloxane, and the second flexible substrate layer (6) and the packaging layer (7) are polyethylene terephthalate.

4. The three-axis force flexible sensor according to claim 1, characterized in that: The first flexible base layer (5), the second flexible base layer (6) and the porous piezoresistive layer (2) are adhesively connected.

5. The three-axis force flexible sensor according to claim 1, characterized in that: The second conductive circuit comprises: a first sub-conductive circuit, the first sub-conductive circuit being electrically connected to the first electrode (3); a second sub-conductive circuit, the second sub-conductive circuit being electrically connected to the second electrode (4); A bridge circuit, the bridge circuit being electrically connected to the first electrode (3) and the second electrode (4), and being used to detect the capacitance between the first electrode (3) and the second electrode (4).

6. A three-axis force flexible sensor according to claim 5, characterized in that: The bridge circuit is also electrically connected to the interdigital electrodes (1) and is used to detect the resistance of the interdigital electrodes (1).

7. The three-axis force flexible sensor according to claim 1, characterized in that: The thickness of the first electrode (3) and the second electrode (4) is 0.5 mm; when the three-axis force flexible sensor is not subjected to force, the gap between the first electrode (3) and the second electrode (4) is 1 mm.

8. A method for preparing a three-axis force flexible sensor, used for preparing a three-axis force flexible sensor according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: Using laser cutting and grinding equipment to process red copper with a copper content of more than 99.95% to obtain a first electrode (3) and at least four second electrodes (4); A first flexible base layer (5) is prepared by using a polydimethylsiloxane resin and a curing agent in a preset mass ratio, and a second flexible base layer (6) is cut on a polyethylene terephthalate film by using a cutting machine; and the first electrode (3) is mounted on the first flexible base layer (5) via a packaging layer (7), and the second electrode (4) is mounted on the second flexible base layer (6) via a packaging layer (7); A flexible conductive filler is added to a water-soluble paper. After the flexible conductive filler is solidified, the water-soluble paper is soaked in water to dissolve for 30 minutes, and then placed in a drying oven for drying at 40° C. for 30 minutes to obtain a porous piezoresistive layer (2); and the porous piezoresistive layer (2) is attached to the interdigital electrode (1); The first flexible base layer (5), the second flexible base layer (6) and the porous piezoresistive layer (2) are connected via a silicone adhesive to obtain a three-axis force flexible sensor.

9. The method for preparing a three-axis force flexible sensor according to claim 8, characterized in that: The flexible conductive filler is prepared according to the following steps: Six steel balls, 0.4 g of multi-walled carbon nanotubes with a purity of 95%, and 6 g of isopropyl alcohol were added to a 150 ml container bottle, and the container bottle was placed in a blender to mix the materials for 4 minutes. During the 4-minute mixing period, the container bottle was taken out every 1.5 minutes and left to stand for 30 seconds. After the materials were mixed for 4 minutes, 8 g of polydimethylsiloxane resin and 0.8 g of silicone diluent were added and mixed three times at a mixing interval of 1.5 minutes, and then 0.8 g of curing agent was added, mixed for 1 minute and degassed for 1.5 minutes to obtain the flexible conductive filler.

10. An application of a three-axis force flexible sensor, characterized in that: include: The three-axis force flexible sensor according to any one of claims 1 to 7 is used in a manipulator to identify slippage problems that occur when the manipulator grasps an object.

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