Flexible touch sensor capable of resolving power direction and preparation method thereof

Abstract

The invention discloses a flexible touch sensor capable of distinguishing a force direction and a preparation method thereof. The sensor comprises a force loading layer, a force amplification block, a test electrode, a piezoresistive layer, a reference electrode and a substrate, the piezoresistive layer is of a micro-pyramid structure; the bottom surface of the force loading layer is fixedly connected with the force amplification block and the substrate respectively; the piezoresistive layer is cross-shaped and is arranged between the reference electrode and the test electrode; the test electrode is of a cross-shaped structure, and the tail part of each channel forms an electrode of the sensor; the piezoresistive layer is tightly attached to the reference electrode and the test electrode respectively; the force amplification blocks are distributed corresponding to the four channels of the test electrode; a wire hole is formed in the substrate, and a wire of the reference electrode penetrates out of the wire hole. According to the invention, high-sensitivity detection of shear forces and normal pressures in different directions is realized, and simultaneous detection of directions and magnitudes of forces is realized.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a flexible tactile sensor capable of distinguishing force direction and a preparation method thereof. Background Art

[0002] A tactile sensor is a device that can sense external physical properties through contact and convert them into electrical signals. Early tactile sensors were mainly used for simple force or pressure detection. With the continuous advancement of microelectronics and nanotechnology, the sensitivity and diversity of tactile sensors have been significantly improved. Modern tactile sensors can not only detect basic physical parameters such as pressure, temperature and sliding, but also achieve higher accuracy and a wider range of applications with the support of materials science. Today, tactile sensors play an indispensable role in many fields such as robotics, medical equipment, and the automotive industry.

[0003] With the development of science and technology in recent years, hot fields such as flexible robots, intelligent prostheses, wearable devices, and human-computer interaction have put forward higher requirements for the flexibility of sensors. Traditional tactile sensors are usually made of rigid structures, such as metal or hard plastic. These sensors are relatively mature in design and manufacturing, but they have many disadvantages: the rigid structure makes it unable to adapt to irregular or curved surfaces, limiting its use in applications such as robot skin that require highly flexible sensing technology, and cannot meet the flexibility requirements of sensors in some fields; and rigid materials are often heavy and bulky, which are not suitable for equipment that needs to be lightweight and miniaturized; in an environment of repeated bending or stretching, rigid materials are prone to fatigue and damage, and their service life is limited. Therefore, the research on flexible tactile sensors is currently a hot spot in the field of new sensors.

[0004] Flexible tactile sensors have extremely high adaptability and sensitivity in sensing external physical properties. According to their sensing principles and application scenarios, flexible tactile sensors can be divided into the following categories: resistive type senses pressure or contact by measuring changes in resistance, with simple structure, low cost and easy integration; capacitive type uses capacitance changes to detect tactile information. When the sensor is under pressure, the distance or dielectric constant between the flexible electrodes changes, resulting in a change in capacitance value, which is then converted into a readable electrical signal. It has a fast response speed and high sensitivity, and is suitable for dynamic and static pressure detection; piezoelectric type uses the characteristics of piezoelectric materials, that is, it generates charges or voltages under the action of external forces, and senses touch by measuring the changes in these charges or voltages. It has high sensitivity and fast response, and is suitable for applications that require precise and real-time feedback. The excellent sensing performance of flexible tactile sensors is usually reflected in high sensitivity, wide detection range, long life, good repeatability and other aspects. These flexible tactile sensors have shown great application potential in many fields such as robots, wearable devices, bionic skin, medical diagnosis, etc., and have promoted the development of intelligent interaction and personalized technology.

[0005] Most dense tactile sensing films are made of dispersed conductive polymer composite materials. They obtain good softness and piezoresistive properties by doping conductive fillers in an elastic rubber matrix. The initial resistance value decreases with the increase of the concentration of conductive particles in the rubber. In addition, the resistance of the composite film is also related to the contact area of ​​the electrodes. The larger the contact area, the smaller the contact resistance. Therefore, when subjected to pressure, the resistance of the sensor decreases as the pressure increases. However, due to the inherent viscoelasticity of elastic polymer materials, such sensors have problems such as low sensitivity, high detection limit, large deformation hysteresis, and long relaxation time.

[0006] In order to solve the above problems, many microstructures have been introduced into flexible pressure sensors to replace planar structures, thereby improving the key performance parameters of the sensor, such as sensitivity, detection limit, and response speed. This type of tactile sensor is called a microstructured tactile sensor. The existing microstructures mainly include pyramid structures, hemispherical structures, microcolumn structures, pyramid porous structures, and some natural micro-nanostructures prepared by bionic template methods. However, these microstructures still have their own shortcomings. For example, pyramid-structured pressure sensors show high sensitivity and linearity in the low pressure range, but their linearity range is limited; thanks to the uniform structure, microcolumn-structured pressure sensors have good linearity, but the pressure sensitivity is relatively low. In addition, although bionic microstructured pressure sensors have been developed, their geometric features and material properties have not been studied in depth, and natural microstructures are too complex for current preparation technologies to achieve low-cost production on a large scale.

[0007] Micro-electromechanical system (MEMS) tactile sensors have the advantages of low power consumption, light weight, small size, accurate measurement in a limited space, low cost, and little impact on the detected object. However, the preparation process of MEMS sensors is usually complicated and delicate, requiring expensive photolithography machines, etching (DRIE deep silicon etching, wet etching, etc.) equipment, and thin film deposition (chemical vapor deposition, magnetron sputtering, etc.) equipment.

[0008] In summary, in addition to their own defects, the existing types of tactile sensors also have a common shortcoming, that is, they are unable to simultaneously detect the magnitude and direction of the external force.

[0009] In summary, the existing research on flexible tactile sensors has achieved certain results, but there are still many shortcomings that need to be overcome. For example, the dense tactile sensor film has low sensitivity, high detection limit, large deformation hysteresis, and long relaxation time; the microstructure tactile sensor based on different microstructure characteristics will also have a certain impact on the sensing performance, and some microstructures are difficult to prepare; MEMS tactile sensors have complex preparation processes and high costs. And these types of tactile sensors have a common shortcoming, that is, they are generally unable to detect the magnitude and direction of external forces at the same time. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a flexible tactile sensor that can distinguish force direction and a preparation method thereof. The sensor has a cross-shaped conductive structure. By screen-printing a conductive layer on a cross-shaped flexible substrate, the micro-pyramid structure produces different deformations under different force magnitudes, thereby using the principle that the contact area with the conductive layer is different, resulting in a change in the resistance value of the path, thereby achieving highly sensitive detection of shear forces and normal pressures in different directions.

[0011] The present invention provides a flexible tactile sensor capable of distinguishing force direction, and the specific technical solution is as follows:

[0012] It includes a force loading layer, a force amplification block, a test electrode, a piezoresistive layer, a reference electrode and a substrate;

[0013] The piezoresistive layer is a micro-pyramid structure, wherein the micro-pyramid structure is only sensitive to strain perpendicular to its direction, and the different signals of the four channels can show the direction of the shear force, thereby ensuring that the sensor has good detection capabilities for both pressure and shear force;

[0014] The bottom surface of the force loading layer is fixedly connected to the force amplification block and the substrate respectively;

[0015] The piezoresistive layer is cross-shaped and is disposed between the reference electrode and the test electrode; the test electrode is cross-shaped, and the tail of each channel constitutes the electrode of the sensor; the piezoresistive layer is closely attached to the reference electrode and the test electrode respectively;

[0016] The force amplification block is distributed and arranged corresponding to the four channels of the test electrode; the base is provided with a wire hole, and the wire of the reference electrode passes through the wire hole.

[0017] The sensor adopts a cross-shaped structure inside, and the piezoresistive layers are distributed in the channels in the four directions of the cross. The four channels of the cross-shaped structure are perpendicular to each other, and each channel corresponds to a changing resistance. The cross-shaped structure can ensure that the response trend of the shear force generated in each channel is balanced and similar, which makes it easy to analyze the size and direction of the shear force and the size of the normal pressure through the change of resistance.

[0018] On the other hand, the test electrode of the sensor is located at the end of each channel, but the reference electrode is the same and is located in the middle of the sensor. Through the wire hole designed on the substrate, the wire of the reference electrode can pass through the wire hole on the substrate. Based on this, the reference electrode is located in the middle, which is conducive to reducing the number of wires, making the entire structure more concise, and also bringing more convenience to the resistance change measurement of the sensor.

[0019] Furthermore, the substrate, the force amplification block and the force loading layer are all made of a PDMS mixed liquid; the piezoresistive layer of the micro-pyramid structure is composed of a multi-walled carbon nanotube and a PDMS mixed liquid; the test electrode and the reference electrode are made by screen printing using conductive carbon paste as a printing material.

[0020] Furthermore, a prism is provided above the force loading layer, a hole is provided on the bottom surface of the force loading layer, and the force amplification block is arranged in the hole on the bottom surface of the force loading layer.

[0021] By applying force on the top surface of the prism, the force is evenly dispersed to the bottom surface of the force loading layer through the prism; the force amplification block set on the bottom surface of the force loading layer can make the force more accurately distributed on the four channels of the cross structure, thereby improving the sensitivity and accuracy of the sensor.

[0022] Furthermore, the substrate includes a bottom and a supporting portion, and a supporting hole is provided on the bottom surface of the force loading layer, and the supporting portion of the substrate is inserted into the supporting hole.

[0023] The support portion facilitates the coordination between the substrate and the force loading layer.

[0024] Furthermore, the substrate and the force loading layer are bonded and fixedly connected via a PDMS mixed liquid.

[0025] The present invention also provides a method for preparing a flexible tactile sensor capable of distinguishing force direction, and the specific process is as follows:

[0026] S1: Based on the sensor structure and corresponding parameters described above, a mold model is constructed and 3D printed to obtain molds of various parts of the sensor;

[0027] S2: preparing a PDMS mixed liquid and pouring it into the molds of the force loading layer, the force amplification block and the substrate, and performing drying and curing treatment after the pouring is completed to obtain the force loading layer, the force amplification block and the substrate;

[0028] S3: preparing a piezoresistive layer casting liquid, and casting it into a piezoresistive layer mold, and performing drying and curing after casting to obtain a piezoresistive layer with a micro-pyramid structure;

[0029] S4: Screen printing is performed using a conductive carbon paste, and the printed conductive layer is dried and then cut into a preset cross-shaped structure to obtain a test electrode and a reference electrode;

[0030] S5: bonding the test electrode, the reference electrode, the piezoresistive layer, the force loading layer, the force amplification block and the substrate by means of a PDMS mixture;

[0031] S6: Bond the wires at the ends of the four channel test electrodes and the center of the reference electrode using conductive carbon paste.

[0032] Furthermore, the overall size of the sensor is 16×16×8.9 mm, the thickness of the substrate is 1.5 mm, the wire hole on the substrate is a through hole with a diameter of 2 mm, and the thickness of the force loading layer is 4.5 mm.

[0033] A thinner substrate can improve the flexibility of the sensor.

[0034] Furthermore, the PDMS mixed solution preparation process is as follows:

[0035] The basic components of PDMS and the curing agent were weighed and prepared in a ratio of 10:1, 5 g of the basic component of polydimethylsiloxane was weighed, 0.5 g of the cross-linking agent was added, and the mixture was evenly mixed, and bubbles in the mixed reagents were removed.

[0036] Furthermore, the piezoresistive layer casting liquid preparation process is as follows:

[0037] The multi-walled carbon nanotube ethanol dispersion was added to 3 g of the PDMS basic component, and 0.3 g of a cross-linking agent was added, and the mixture was evenly mixed, and bubbles in the mixed reagents were removed.

[0038] Furthermore, the printing preparation process of the conductive layer is as follows:

[0039] Get a piece of flexible material that is similar in size to the screen printing plate, pour about 1.5g of conductive carbon paste on one end of the screen printing plate, and press the template tightly;

[0040] Use a scraper to apply pressure to the carbon paste part on the screen printing plate, and move it at a constant speed toward the other end of the screen printing plate to print. After printing is completed, lift the scraper and remove the flexible material.

[0041] The beneficial effects of the present invention are as follows:

[0042] 1. The piezoresistive layer of the present invention is cross-shaped and is arranged between the test electrode and the reference electrode. Based on the cross-shaped sensing structure, it has the ability to measure three-dimensional force. When the force loading layer is under pressure, the contact area between the microstructure of the four channels of the sensor and the electrode increases, the conductive path increases, and the resistance value decreases; and when the force loading layer is subjected to shear force, different directions of the shear force will cause different changes in the four channels, thereby realizing the detection of the direction and magnitude of the force.

[0043] 2. The present invention uses a force loading layer and a force amplification block to more accurately distribute the force on the four channels of the cross-shaped structure, thereby improving the sensitivity and accuracy of the sensor. At the same time, the piezoresistive layer of the micro-pyramid structure is only sensitive to strains perpendicular to its direction. The different signals of the four channels can show the direction of the shear force, thereby ensuring that the sensor has good detection capabilities for both pressure and shear force.

[0044] 3. The present invention uses PDMS as a substrate, which has good flexibility compared to traditional rigid tactile sensors, and the sensor has a simple structure and is easy to prepare and assemble. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the explosion structure of the sensor of the present invention.

[0046] Figure 2 It is a schematic diagram of the overall structure of the sensor of the present invention.

[0047] Figure 3 It is a schematic front view of the sensor structure of the present invention.

[0048] Figure 4 It is a schematic diagram of the cross-sectional structure of the sensor of the present invention.

[0049] Figure 5 It is a schematic diagram of the sensor preparation process of the present invention.

[0050] Explanation of the reference numerals: 1 - force loading layer, 2 - force amplification block, 3 - test electrode, 4 - piezoresistive layer, 5 - reference electrode, 6 - substrate. DETAILED DESCRIPTION

[0051] The following description clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] In the description of the embodiments of the present invention, it should be noted that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the invention product is usually placed when in use, or the orientation or positional relationship commonly understood by those skilled in the art, or the orientation or positional relationship in which the invention product is usually placed when in use, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply 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 a limitation on the present invention. In addition, the terms "first" and "second" are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0053] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set" and "connection" 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 direct connection, or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0054] Example 1

[0055] Embodiment 1 of the present invention discloses a flexible tactile sensor capable of distinguishing force direction, such as Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the specific structure is as follows:

[0056] It includes a force loading layer 1, a force amplification block 2, a test electrode 3, a piezoresistive layer 4, a reference electrode 5 and a substrate 6;

[0057] Specifically, the substrate 6, the force amplification block 2 and the force loading layer 1 are all made of a polydimethylsiloxane (PDMS) mixed liquid. During preparation, the substrate 6, the force amplification block 2 and the force loading layer 1 of the sensor are all made by filling the PDMS mixed liquid in a 3D printed mold.

[0058] As a preferred embodiment, a prism is provided above the force loading layer 1, a hole is provided on the bottom surface of the force loading layer 1, and the force amplification block 2 is provided in the hole on the bottom surface of the force loading layer 1;

[0059] Specifically, the force amplification block 2 is provided with four, corresponding to four channel test electrodes 3 respectively;

[0060] As a preferred embodiment, the base 6 includes a bottom and a supporting portion, and the bottom surface of the force loading layer 1 is also provided with a supporting hole, and the supporting portion of the base 6 is inserted into the supporting hole;

[0061] Specifically, the support portion is a support cylinder arranged around the base 6 .

[0062] The substrate 6 and the force loading layer 1 are bonded and fixedly connected via a PDMS mixed liquid.

[0063] The piezoresistive layer 4 is a micro-pyramid structure. Specifically, the piezoresistive layer 4 of the micro-pyramid structure is composed of a mixed solution of multi-walled carbon nanotubes and PDMS;

[0064] Under the action of positive pressure, the force is transmitted to the force amplification block 2 through the force loading layer 1, and is evenly distributed and acts on the micro-pyramid structure piezoresistive layer 4 of the four channels, causing the micro-pyramid structure to be squeezed, resulting in a change in the contact area between it and the test electrode 3, and the resistance on the four channels changes synchronously. When shear force is applied, because the angles between the four channels and the shear force are different, the directions of the torques acting on the four channels are different, and the contact states between the force amplification block 2 and the piezoresistive layer 4 below are different, resulting in differences in the contact areas between the piezoresistive layer 4 and the test electrode 3 on each channel. Therefore, the different signals of the four channels can detect the direction of the force.

[0065] The bottom surface of the force application layer 1 is fixedly connected to the force amplification block 2 and the base 6 respectively.

[0066] The piezoresistive layer 4 is cross-shaped and is disposed between the reference electrode 5 and the test electrode 3; the test electrode 3 is cross-shaped, and the tail of each channel constitutes the electrode of the sensor; the piezoresistive layer 4 is closely attached to the reference electrode 5 and the test electrode 3 respectively;

[0067] Specifically, the test electrode 3 and the reference electrode 5 are made by screen printing using conductive carbon paste as printing material.

[0068] The substrate 6 is provided with a wire hole, and the wire of the reference electrode 5 passes through the wire hole;

[0069] Specifically, the wire hole is a through hole with a diameter of 2 mm.

[0070] By applying external mechanical stimulation to the force loading layer 1, the force is transmitted to the force amplification block 2, and then the four force amplification blocks 2 evenly transmit the forces in four directions to the micro-pyramid structure piezoresistive layer 4 at four positions of the "cross", causing a slight deformation of the micro-pyramid structure of the piezoresistive layer 4, thereby changing the contact area with the test electrode 3, thereby causing the resistance change of the piezoresistive layer 4. The high sensitivity of the micro-pyramid structure and the role of the force amplification block 2 in transmitting and amplifying external stimulation can improve the sensitivity of detection.

[0071] Due to the action of force and torque, the channel that is at an acute angle to the direction of the force applied by the force-loading layer 1 squeezes the piezoresistive layer 4, compresses the micro-pyramid structure, increases the contact area with the electrode, increases the number of conductive channels, and reduces the resistance. On the contrary, due to the action of force and torque, although the force squeezes the piezoresistive layer 4 in the channel that is at an obtuse angle to the direction of the force applied by the force-loading layer 1, the torque offsets this effect in the opposite direction, so that the contact area does not change much or even detaches from the electrode surface, resulting in a decrease in conductive channels and an increase in resistance.

[0072] Example 2

[0073] Embodiment 2 of the present invention discloses a method for preparing a flexible tactile sensor capable of distinguishing force direction, such as Figure 5 As shown,

[0074] S1: Based on the sensor structure and corresponding parameters described above, a mold model is constructed and 3D printed to obtain molds of various parts of the sensor;

[0075] The overall size of the sensor is 16×16×8.9 mm, the thickness of the substrate 6 is 1.5 mm, the wire hole on the substrate 6 is a through hole with a diameter of 2 mm, and the thickness of the force loading layer 1 is 4.5 mm.

[0076] Specifically, a mold model can be established on SolidWorks 3D modeling software, size parameters can be set, and the mold can be printed using a 3D printer. The mold used for production can be obtained by performing a reverse molding operation on the models of various parts of the sensor.

[0077] S2: Prepare a PDMS mixed liquid, and pour it into the mold of the force loading layer 1, the force amplification block 2 and the substrate 6, and use a stirring rod to scrape off the PDMS mixed liquid above the mold. After pouring, put it into a forced air dryer and dry it at 60°C for 3h for drying and curing. After the PDMS mixed liquid is cured, remove it from the 3D printed mold to obtain the force loading layer 1, the force amplification block 2 and the substrate 6;

[0078] As a preferred embodiment, the PDMS mixed solution preparation process is as follows:

[0079] The basic components of PDMS and the curing agent were weighed and prepared in a ratio of 10:1. 5 g of the polydimethylsiloxane basic component was weighed, and 0.5 g of the cross-linking agent was added. The mixture was stirred with a stirring rod for about 10 minutes to fully mix them. The mixed reagents were vacuum treated for 1 hour to remove bubbles in the reagents.

[0080] S3: preparing a casting liquid for the piezoresistive layer 4, and casting it into the mold for the piezoresistive layer 4, and scraping off the PDMS mixed liquid above the mold with a stirring rod, and placing it in a forced air dryer after casting, and drying it at 60° C. for 3 h for drying and curing treatment, and after the PDMS mixed liquid is cured, removing it from the 3D printed mold to obtain a piezoresistive layer 4 with a micro-pyramid structure;

[0081] As a preferred embodiment, the process of preparing the casting liquid for the piezoresistive layer 4 is as follows:

[0082] Add the multi-walled carbon nanotube ethanol dispersion to 3g of the PDMS basic component, add 0.3g of the cross-linking agent, stir with a stirring rod for about 10 minutes to fully mix them, and vacuum treat the mixed reagents for 1 hour to remove bubbles in the reagents.

[0083] S4: Screen printing is performed using a conductive carbon paste, and the printed conductive layer is placed in a dryer and dried at 60° C. for 30 minutes. After the conductive layer is completely dried, it is cut into a preset cross-shaped structure to obtain a test electrode 3 and a reference electrode 5;

[0084] As a preferred embodiment, the printing preparation process of the conductive layer is as follows:

[0085] Get a piece of flexible material that is similar in size to the screen printing plate, pour about 1.5g of conductive carbon paste on one end of the screen printing plate, and press the template tightly;

[0086] Use a scraper to apply a certain pressure on the carbon paste part of the screen printing plate, and move it at a constant speed toward the other end of the screen printing plate to print. After printing is completed, lift the scraper and remove the flexible material.

[0087] S5: bonding the test electrode 3, the reference electrode 5, the piezoresistive layer 4, the force loading layer 1, the force amplification block 2 and the substrate 6 by means of a PDMS mixed liquid;

[0088] S6: Cut five silver wires with a length of 10 cm, and bond the silver wires to the ends of the four channel test electrodes 3 and the center of the reference electrode 5 using conductive carbon paste.

[0089] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A flexible tactile sensor capable of distinguishing force direction, characterized in that: It includes a force loading layer, a force amplification block, a test electrode, a piezoresistive layer, a reference electrode and a substrate; the piezoresistive layer is a micro-pyramid structure; The bottom surface of the force loading layer is fixedly connected to the force amplification block and the substrate respectively; The piezoresistive layer is cross-shaped and is disposed between the reference electrode and the test electrode; the test electrode is cross-shaped, and the tail of each channel constitutes the electrode of the sensor; the piezoresistive layer is closely attached to the reference electrode and the test electrode respectively; The force amplification block is distributed and arranged corresponding to the four channels of the test electrode; the base is provided with a wire hole, and the wire of the reference electrode passes through the wire hole.

2. The flexible tactile sensor capable of distinguishing force direction according to claim 1, characterized in that: The substrate, the force amplification block and the force loading layer are all made of a PDMS mixed liquid; the piezoresistive layer of the micro-pyramid structure is composed of a multi-walled carbon nanotube and a PDMS mixed liquid; the test electrode and the reference electrode are made by screen printing using conductive carbon paste as a printing material.

3. The flexible tactile sensor capable of distinguishing force direction according to claim 1, characterized in that: A prism is arranged above the force loading layer, a hole is arranged on the bottom surface of the force loading layer, and the force amplification block is arranged in the hole on the bottom surface of the force loading layer.

4. The flexible tactile sensor capable of distinguishing force direction according to claim 3, characterized in that: The substrate comprises a bottom and a supporting portion. The bottom surface of the force loading layer is further provided with a supporting hole, and the supporting portion of the substrate is inserted into the supporting hole.

5. The flexible tactile sensor capable of distinguishing force direction according to claim 1, characterized in that: The substrate and the force loading layer are bonded and fixedly connected via a PDMS mixed liquid.

6. A method for preparing a flexible tactile sensor capable of distinguishing force direction, characterized in that: include: S1: Based on the sensor structure and corresponding parameters described in any one of claims 1 to 5, a mold model is constructed, and 3D printing is performed to obtain molds of various parts of the sensor; S2: preparing a PDMS mixed liquid and pouring it into the molds of the force loading layer, the force amplification block and the substrate, and performing drying and curing treatment after the pouring is completed to obtain the force loading layer, the force amplification block and the substrate; S3: preparing a piezoresistive layer casting liquid, and casting it into a piezoresistive layer mold, and performing drying and curing after casting to obtain a piezoresistive layer with a micro-pyramid structure; S4: Screen printing is performed using a conductive carbon paste, and the printed conductive layer is dried and then cut into a preset cross-shaped structure to obtain a test electrode and a reference electrode; S5: bonding the test electrode, the reference electrode, the piezoresistive layer, the force loading layer, the force amplification block and the substrate by means of a PDMS mixture; S6: Bond the wires at the ends of the four channel test electrodes and the center of the reference electrode using conductive carbon paste.

7. The method for preparing a flexible tactile sensor capable of distinguishing force directions according to claim 6, characterized in that: The overall size of the sensor is 16×16×8.9 mm, the thickness of the substrate is 1.5 mm, and the thickness of the force loading layer is 4.5 mm.

8. The method for preparing a flexible tactile sensor capable of distinguishing force directions according to claim 6, characterized in that: The PDMS mixed solution preparation process is as follows: The basic components of PDMS and the curing agent were weighed and prepared in a ratio of 10:1, 5 g of the basic component of polydimethylsiloxane was weighed, 0.5 g of the cross-linking agent was added, and the mixture was evenly mixed, and bubbles in the mixed reagents were removed.

9. The method for preparing a flexible tactile sensor capable of distinguishing force directions according to claim 6, characterized in that: The preparation process of the piezoresistive layer casting liquid is as follows: The multi-walled carbon nanotube ethanol dispersion was added to 3 g of the PDMS basic component, and 0.3 g of a cross-linking agent was added, and the mixture was evenly mixed, and bubbles in the mixed reagents were removed.

10. The method for preparing a flexible tactile sensor capable of distinguishing force directions according to claim 6, characterized in that: The printing preparation process of the conductive layer is as follows: Get a piece of flexible material that is similar in size to the screen printing plate, pour 1.5g of conductive carbon paste on one end of the screen printing plate, and press the template tightly; Use a scraper to apply pressure to the carbon paste part on the screen printing plate, and move it at a constant speed toward the other end of the screen printing plate to print. After printing is completed, lift the scraper and remove the flexible material.

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