Hardness sensor based on pressure and strain sensor co-integration and preparation method

Abstract

The invention discloses a hardness sensor based on pressure and strain sensor co-integration and a preparation method, and belongs to the technical field of flexible hardness sensors. The hardness sensor comprises a lower packaging layer, a lower electrode, a lower strain sensor, a lower pressure-sensitive film, an upper pressure-sensitive film, an upper strain sensor, an upper electrode and an upper packaging layer which are sequentially arranged from bottom to top. According to the invention, the pressure-sensitive film is prepared by a template method, the electrode layer is adhered to the pressure-sensitive film through the adhesive, and then the redundant pressure-sensitive film is etched by laser to obtain the pressure sensor; and the strain sensor is obtained through laser etching and chemical plating. As the space utilization rate of the pressure sensor is not high, the strain sensor is embedded into the gap of the pressure sensor, so that the pressure sensor and the strain sensor are positioned on the same plane, the space utilization rate of the device is improved, the sensitivity and the response speed of the sensor are improved, and more accurate and efficient hardness detection is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible hardness sensors, and particularly relates to a hardness sensor based on the co-integration of pressure and strain sensors and a preparation method thereof. Background Art

[0002] A flexible hardness sensor is a multi-modal tactile sensor that can detect the hardness information of an object and transmit environmental information. With the continuous development of robot technology and the continuous expansion of application scenarios, traditional single-tactile perception electronic skins have been difficult to meet the current requirements for intelligent and refined perception. In the field of modern robotics, in addition to basic tactile feedback, it is also necessary to integrate multiple sensing capabilities, such as temperature perception, pressure detection, humidity sensing, hardness capture, and even self-healing and self-adaptive adjustment functions, to more accurately adapt to complex and changing environments. Therefore, the research and development of electronic skins with multi-modal sensing capabilities has become an important direction for promoting the intelligent upgrade of robots.

[0003] At present, there are still many problems in the system design of flexible hardness sensors. First of all, due to the interlayer structure of traditional hardness sensors, the sensitivity of the sensors is low, and signal transmission may be affected by the interlayer interface, resulting in a reduced response speed of the sensors to hardness changes. In addition, in order to enhance the anti-tensile and anti-strain capabilities, current pressure sensor arrays usually design long and winding wires between each pressure unit and leave a certain interval. However, while this design improves performance, it inevitably sacrifices space utilization, limiting the integration of the sensors. How to optimize the spatial layout while maintaining high performance has become an important challenge in the development of current hardness sensor technology.

[0004] Therefore, developing a structural design and preparation method for high-density and high-performance hardness sensors is of great significance for the practical application in the field of flexible hardness sensors. Summary of the Invention

[0005] Aiming at the problems of low space utilization and overall performance in the background art, the present invention proposes a hardness sensor based on the co-integration of pressure and strain sensors and a preparation method thereof. The present invention manufactures pressure sensors through a template method, transfer printing technology, and laser etching, manufactures strain sensors through laser etching and electroless plating, and then embeds the strain sensors into the gaps of the pressure sensor array, so that the pressure and strain sensors are on the same plane, improving the space utilization of the device and the performance of the sensors.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A hardness sensor based on the co-integration of pressure and strain sensors, comprising a lower encapsulation layer, a lower electrode, a lower strain sensor, a lower pressure-sensitive film, an upper pressure-sensitive film, an upper strain sensor, an upper electrode, and an upper encapsulation layer arranged in sequence from bottom to top;

[0008] The pressure-sensitive film includes a plurality of square films arranged in an array. The lower electrode is composed of a serpentine electrode connecting the square films in a row or a column, and the upper electrode is composed of a serpentine electrode connecting the square films in a column or a row. The directions of the square films connected by the upper electrode and the lower electrode are perpendicular to each other;

[0009] The strain sensor is in a strip structure. The lower strain sensor is embedded in the gap of the lower pressure-sensitive film, and the upper strain sensor is embedded in the gap of the upper pressure-sensitive film, and the upper strain sensor and the lower strain sensor are perpendicular to each other;

[0010] The remaining space between each layer is filled with a material having a Young's modulus of 0.157 kPa.

[0011] Further, the materials used for the upper electrode layer and the lower electrode layer are copper, and the thickness is 4-10 micrometers.

[0012] Further, the materials used for the upper pressure-sensitive film and the lower pressure-sensitive film are a composite material of polydimethylsiloxane and carbon nanotubes; the length of each square film is 3.53 mm, the width is 3.53 mm, and the thickness is 0.8-1.2 mm; the interval between each square film is 2.35 mm.

[0013] Further, the materials used for the upper strain sensor and the lower strain sensor are a composite material of polydimethylsiloxane and carbon nanotubes; the length is 56.45 mm, the width is 2 mm, and the thickness is 0.4-0.6 mm.

[0014] A preparation method of a hardness sensor based on the co-integration of pressure and strain sensors, comprising the following steps:

[0015] Step 1. Using a template method, prepare the upper pressure-sensitive film and the lower pressure-sensitive film;

[0016] Step 2. Using an ultraviolet laser etching technique, prepare a patterned electrode;

[0017] Step 3. Stir and mix silicone rubber (Ecoflex) and carbon nanotubes (CNT) evenly according to a mass ratio of 100:(6-8) to obtain an adhesive;

[0018] Step 4. Using a transfer technique, paste the electrode prepared in Step 2 on the upper and lower surfaces of the upper pressure-sensitive film and the upper and lower surfaces of the lower pressure-sensitive film through the adhesive to obtain two pressure sensors; wherein, the electrodes on the upper and lower surfaces of the pressure-sensitive film are perpendicular to each other;

[0019] Step 5. Use an infrared laser to etch away the pressure-sensitive film without electrode coverage to obtain a square film arranged in an array.

[0020] Step 6. Spin-coat silicone rubber (Ecoflex) into a film, place the pressure sensor processed in Step 5 on it, heat and cure it, and then peel it off to obtain two pressure sensors with an array of square films.

[0021] Step 7. Fabricate a strain sensor using laser etching and electroless plating.

[0022] Step 8. Peel off one electrode of the two pressure sensors with an array of square films obtained in Step 6 to expose one side of the pressure-sensitive film.

[0023] Step 9. First, fill a layer of silicone rubber (Ecoflex) in the gap of the pressure sensor processed in Step 8 to fix the strain sensor. Then transfer and embed the strain sensor fabricated in Step 7 into the gap of the pressure sensor. The lower strain sensor is embedded into the lower pressure-sensitive film, and the lower strain sensor is parallel to the electrode on the other side of the lower pressure-sensitive film. The upper strain sensor is embedded into the upper pressure-sensitive film, and the upper strain sensor is parallel to the electrode on the other side of the upper pressure-sensitive film. Finally, place it on a heating table and heat it at a temperature of 120°C to 150°C for 3 to 5 minutes.

[0024] Step 10. Fill the remaining space of the device processed in Step 9 with low-modulus silica gel, place it on a heating table and heat it at a temperature of 120°C to 150°C for 3 to 5 minutes.

[0025] Step 11. Bond the two devices processed in Step 10 using an adhesive. Among them, the upper pressure-sensitive film and the lower pressure-sensitive film are closely attached and the square films in the upper and lower pressure-sensitive films completely overlap. The electrode above the upper pressure-sensitive film is the upper electrode, and the electrode below the lower pressure-sensitive film is the lower electrode, and the upper electrode and the lower electrode are perpendicular to each other. Then place it on a heating table and heat it at a temperature of 120°C to 150°C for 3 to 5 minutes, and then peel it off to obtain the hardness sensor.

[0026] Further, the process of preparing the upper pressure-sensitive film and the lower pressure-sensitive film in Step 1 is specifically as follows: First, dissolve anhydrous NaCl crystals in water, evaporate and crystallize on a heating table at 200°C to 250°C, and then obtain ultrafine NaCl powder through a ball mill and a filter screen. Then, stir and mix polydimethylsiloxane (PDMS), carbon nanotubes (CNT), and the ground ultrafine NaCl powder evenly according to a mass ratio of 100:(3 - 4):(300 - 400), and use the template method to obtain the upper pressure-sensitive film and the lower pressure-sensitive film.

[0027] Further, in Step 2, the laser is an ultraviolet laser, the laser speed is 300 mm / s, and the power is 50%.

[0028] Further, in step 5, the laser is an infrared laser, the laser speed is 1000 mm / s, and the power is 20%.

[0029] Further, the preparation process of the strain sensor in step 7 is as follows: First, according to the mass ratio of polydimethylsiloxane (PDMS): carbon nanotubes (CNT): antimony tin oxide (ATO) = 100: (3 - 4): (5 - 6), weigh polydimethylsiloxane (PDMS), carbon nanotubes (CNT) and antimony tin oxide (ATO), mix and stir evenly, and place them on a spin coater, rotate at a speed of 550 - 600 revolutions per minute for 1 - 2 minutes, then place them on a heating table and heat at 120°C - 150°C for 2 - 5 minutes to obtain a strain film; then, use ultraviolet laser etching to form a patterned strain film and activate antimony tin oxide (ATO); finally, put the activated strain film into a copper plating solution and place it in an incubator at a temperature of 35°C - 40°C, and let it stand for more than 6 - 8 hours to obtain a strain sensor. Among them, the laser is an ultraviolet laser, the laser speed is 2000 mm / s, and the power is 90%.

[0030] Further, in the hardness sensor obtained in step 11, the upper electrode and the lower electrode are perpendicular to each other to form an island - bridge structure; the upper strain sensor and the lower strain sensor are also perpendicular to each other to form a strain network.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] A hardness sensor based on the co - integration of a pressure sensor and a strain sensor and a preparation method provided by the present invention prepare a pressure - sensitive film by a template method, bond an electrode layer on the pressure - sensitive film through an adhesive, and then use laser etching to remove the redundant pressure - sensitive film to obtain a pressure sensor; a strain sensor is obtained through laser etching and electroless plating. Since the space utilization rate of the pressure sensor is not high, therefore, the present invention embeds the strain sensor into the gap of the pressure sensor, so that the pressure sensor and the strain sensor are on the same plane, improving the space utilization rate of the device, enhancing the sensitivity and response speed of the sensor, and thus realizing more accurate and efficient hardness detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic structural diagram of a hardness sensor based on the co - integration of a pressure sensor and a strain sensor provided by the present invention;

[0034] Figure 2 It is a physical diagram of a hardness sensor based on the co - integration of a pressure sensor and a strain sensor provided by the present invention; among them, (a) and (b) are physical diagrams from different perspectives;

[0035] Figure 3The repeatability curve of the resistance change rate of the pressure sensor obtained in Example 1 under different pressures;

[0036] Figure 4 The curve of the pressure sensor obtained in Example 1 when switching between different pressures;

[0037] Figure 5 The curve of the minimum pressure that can be detected by the pressure sensor obtained in Example 1;

[0038] Figure 6 The curve of the response time of the pressure sensor obtained in Example 1;

[0039] Figure 7 The repeatability curve of the resistance change rate when switching between different strains of the strain sensor obtained in Example 1;

[0040] Figure 8 The curve of the resistance change rate of different strains of the strain sensor obtained in Example 1;

[0041] Figure 9 The curve of the change of the GF value of the strain sensor obtained in Example 1;

[0042] Figure 10 The curve of the minimum strain that can be detected by the strain sensor obtained in Example 1;

[0043] Figure 11 The curve of the response time of the strain sensor obtained in Example 1;

[0044] Figure 12 The curve of the cycle life of the strain sensor obtained in Example 1;

[0045] Figure 13 The Young's modulus diagrams of five different hardness silicones;

[0046] Figure 14 The change curve of the indentation depth and pressure of the hardness sensor obtained in Example 1;

[0047] Figure 15 The curve of the hardness sensor obtained in Example 1 for identifying silicones with different Young's moduli;

[0048] Figure 16 The curve of the Young's modulus and pressure / strain change of the hardness sensor obtained in Example 1. Detailed implementation manners

[0049] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the implementation manners and the drawings.

[0050] A hardness sensor based on the co-integration of a pressure sensor and a strain sensor, asFigure 1 As shown, it includes a lower encapsulation layer, a lower electrode, a lower strain sensor, a lower pressure-sensitive film, an upper pressure-sensitive film, an upper strain sensor, an upper electrode, and an upper encapsulation layer which are arranged successively from bottom to top;

[0051] The pressure-sensitive film includes a plurality of square-shaped films arranged in an array. The lower electrode is composed of serpentine electrodes connected to the square-shaped films in the X direction, and the upper electrode is composed of serpentine electrodes connected to the square-shaped films in the Y direction. The directions of the square-shaped films connected by the upper electrode and the lower electrode are perpendicular to each other;

[0052] The strain sensor is in a strip structure. The lower strain sensor is embedded in the gap of the lower pressure-sensitive film, and the upper strain sensor is embedded in the gap of the upper pressure-sensitive film, and the upper strain sensor and the lower strain sensor are perpendicular to each other;

[0053] The remaining space between each layer is filled with a material having a Young's modulus of 0.157 kPa.

[0054] Example 1

[0055] Step 1. Prepare NaCl powder: Dissolve anhydrous NaCl crystals in water at a mass ratio of 1:4 to 1:5, then evaporate and crystallize on a heating table at 200°C to 250°C, then put it into a ball mill and grind at a speed of 600 to 800 r / s for 30 to 40 minutes, and finally pass through a filter sieve with 200 to 300 meshes to obtain ultrafine NaCl powder;

[0056] Step 2. Prepare the pressure-sensitive film: First, mix and stir polydimethylsiloxane (PDMS) and carbon nanotubes (CNT) at a mass ratio of 100:3 to 100:4, then ultrasonicate for 30 to 40 minutes, then add a curing agent and put it into a vacuum mixer and stir for 1 to 2 minutes. The mass ratio of the curing agent to PDMS is 1:10 to 1:15; then add the ground NaCl powder to the above PDMS and mix evenly. The mass ratio of PDMS to NaCl is 1:3 to 1:4; then fill the evenly stirred mixture into a metal groove of 7.5 m×7.5 cm×1 mm, and place it on a heating table at 120°C to 150°C and heat for 3 to 5 minutes to cure and then take it out. Then soak it in deionized water for 12 to 15 hours until the dissolved NaCl is removed, and finally place it in an oven at 50°C to 60°C for 30 to 40 minutes to remove the moisture;

[0057] Step 3. Prepare the electrode: Stick a 7 cm×7 cm two-sided thermal release tape on a glass sheet of the same size, then stick a water-soluble tape of the same size on the other side of the thermal release tape, then stick a 7 cm×7 cm×0.01 mm copper foil on the other side of the water-soluble tape, and finally selectively etch the copper foil with ultraviolet laser according to a certain pattern, and then tear off the excess part and retain the electrode;

[0058] Step 4. Prepare the adhesive: Mix and stir silicone rubber (Ecoflex) and carbon nanotubes (CNT) evenly at a mass ratio of 100:6;

[0059] Step 5. Attach the electrodes to the upper and lower surfaces of the pressure-sensitive film with the adhesive, and the two electrodes on both sides are perpendicular to each other to form an island-bridge structure. Then place it on a heating table at 120 °C and heat for 5 minutes to cure the adhesive and release the thermal release tape at the same time. Then wash off the water-soluble tape with running water and dry it in an oven at 50 °C for 30 minutes;

[0060] Step 6. Infrared laser selective etching: Use infrared laser to etch off the part of the pressure-sensitive piezoresistive film without copper coverage to form a pressure sensor array with an independent island-bridge structure;

[0061] Step 7. Encapsulation: Attach a 7 cm × 7 cm single-sided thermal release tape to a glass sheet of the same size, spray a release agent, then spin-coat Ecoflex at a speed of 600 rpm / s for 2 minutes, place the pressure sensor array on it, remove it after heating at 120 °C for 3 minutes, and separate the Ecoflex and the single-sided thermal release tape film; repeat the above operation to fix two pressure sensor arrays;

[0062] Step 8. Fabricate the strain film: First, mix and stir polydimethylsiloxane (PDMS), carbon nanotubes (CNT), and antimony tin oxide (ATO) at a mass ratio of 100:3:5, then ultrasonicate for 30 minutes, then add a curing agent and place it in a vacuum mixer and stir for 1 minute. The mass ratio of the curing agent to PDMS is 1:10 to 1:15; finally, apply it to a glass sheet and place it on a spin coater and rotate at a speed of 500 to 600 rpm for 1 to 2 minutes, and then place it on a heating table at 120 °C to 150 °C and heat for 3 to 5 minutes;

[0063] Step 9. Ultraviolet laser etching: Use ultraviolet laser to etch the prepared strain film according to a certain pattern to activate antimony tin oxide (ATO);

[0064] Step 10. Put the activated strain film into the copper plating solution and place it in a constant temperature oven at 35 °C to 40 °C, and let it stand for more than 6 to 8 hours to obtain a strain sensor;

[0065] Step 11. Gently peel off the upper electrodes of the two identical pressure sensor arrays in Step 7;

[0066] Step 12. First, fill a thin layer of silicone rubber (Ecoflex) in the gap of the pressure sensor array prepared in Step 11 to fix the strain sensor; then transfer and embed the strain sensor prepared in Step 10 into the gap of the pressure sensor. The strain sensor is parallel to the lower electrode and placed on a heating table at 120 °C to 150 °C and heated for 3 to 5 minutes;

[0067] Step 13. Fill the remaining space with low-modulus silicone, and place it on a heating table at 120°C to 150°C for heating for 3 to 5 minutes;

[0068] Step 14. Uniformly apply the adhesive prepared in Step 4 on the exposed pressure sensor unit, place the upper pressure sensor and the lower pressure sensor perpendicular to each other, and align each pressure unit; and make the upper strain sensor and the lower strain sensor also perpendicular to each other, then stack and join them together, place them on a heating table at 120°C to 150°C for heating for 3 to 5 minutes; finally, peel the device off the thermal release tape to obtain a hardness sensor.

[0069] The resistance changes of the pressure sensor prepared in Step 6 of Example 1 under different pressure conditions are as Figure 3 shown by curves 4, 5, and 6. It can be seen that the prepared pressure sensor has good repeatability under different pressure conditions, can detect small pressures, and has a fast response speed.

[0070] The resistance changes of the strain sensor prepared in Step 10 of Example 1 under different strain conditions are as Figure 7 shown by curves 8, 9, 10, 11, and 12. It can be seen that the prepared strain sensor has a wide sensing range and cyclicity, can detect small strains, has a fast response speed, and has a long working life.

[0071] For the hardness sensor prepared in Example 1, tests were carried out using silicones with different Young's moduli as Figure 13 shown. The Young's moduli of the silicones are 1.27821 MPa (PDMS 10:1), 0.39129 MPa (PDMS 20:1), 0.18257 MPa (PDMS 25:1), 0.10629 MPa (PDMS 30:1), and 0.0725 MPa (Ecoflex 00-30) respectively. The performance test of the prepared hardness sensor is as Figure 14 shown by the curve. It can be seen that as the pressure increases, the depth of depression of the hardness sensor also increases, which means that the resistance changes of the pressure and strain sensors also increase accordingly. Tests were carried out using silicones with different Young's moduli, and there are obvious differences in the depth of depression of the hardness sensor. As Figure 16 shown by the curve, the data of the pressure and strain sensors were fitted to obtain a curve graph of Young's modulus vs. strain / pressure. It can be seen that the prepared hardness sensor can identify silicones with different Young's moduli.

[0072] The above are only specific embodiments of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or all the steps in any method or process, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A hardness sensor based on the co-integration of a pressure sensor and a strain sensor, characterized in that, It includes a lower encapsulation layer, a lower electrode, a lower strain sensor, a lower piezoresistive film, an upper piezoresistive film, an upper strain sensor, an upper electrode and an upper encapsulation layer which are arranged successively from bottom to top; The piezoresistive film includes a plurality of square films arranged in an array. The lower electrode is composed of a serpentine electrode connecting the square films in a row or a column, and the upper electrode is composed of a serpentine electrode connecting the square films in a column or a row. The directions of the square films connected by the upper electrode and the lower electrode are perpendicular to each other; The strain sensor is in a strip structure. The lower strain sensor is embedded in the gap of the lower piezoresistive film, and the upper strain sensor is embedded in the gap of the upper piezoresistive film, and the upper strain sensor and the lower strain sensor are perpendicular to each other.

2. The hardness sensor based on the co-integration of a pressure sensor and a strain sensor according to claim 1, wherein The materials used for the upper electrode layer and the lower electrode layer are copper, and the thickness is 4-10 microns.

3. The hardness sensor based on the co-integration of a pressure sensor and a strain sensor according to claim 1, characterized in that, The materials used for the upper piezoresistive film and the lower piezoresistive film are a composite material of polydimethylsiloxane and carbon nanotubes, and the thickness is 0.8-1.2 mm.

4. The hardness sensor based on the co-integration of a pressure sensor and a strain sensor according to claim 1, characterized in that, The materials used for the upper strain sensor and the lower strain sensor are a composite material of polydimethylsiloxane and carbon nanotubes, and the thickness is 0.4-0.6 mm.

5. A preparation method of a hardness sensor based on the co-integration of a pressure sensor and a strain sensor, characterized in that, It includes the following steps: Step 1. Prepare the upper piezoresistive film and the lower piezoresistive film by the template method; Step 2. Prepare a patterned electrode by the ultraviolet laser etching technology; Step 3. Stir and mix silicone rubber and carbon nanotubes evenly to obtain an adhesive; Step 4. Adopt a transfer technology to paste the electrode prepared in Step 2 on the upper and lower surfaces of the upper piezoresistive film and the upper and lower surfaces of the lower piezoresistive film through the adhesive to obtain two pressure sensors; among them, the electrodes on the upper and lower surfaces of the piezoresistive film are perpendicular to each other; Step 5. Use an infrared laser to etch away the piezoresistive film without electrode coverage to obtain square films arranged in an array; Step 6. Spin-coat the silicone rubber into a film, place the pressure sensor processed in Step 5 on it, heat and cure it, and then peel it off to obtain two pressure sensors with array square films; Step 7. Use laser etching and electroless plating to fabricate the strain sensor; Step 8. Peel off one electrode of the two pressure sensors with array square films obtained in Step 6; Step 9. First, fill a layer of silicone rubber in the gap of the pressure sensor processed in Step 8 to fix the strain sensor; then transfer and embed the strain sensor prepared in Step 7 into the gap of the pressure sensor. The lower strain sensor is embedded in the lower piezoresistive film, and the lower strain sensor is parallel to the electrode on the other side of the lower piezoresistive film. The upper strain sensor is embedded in the upper piezoresistive film, and the upper strain sensor is parallel to the electrode on the other side of the upper piezoresistive film; finally, place it on a heating table and heat it; Step 10. Fill the remaining space of the device processed in Step 9 with a low-modulus silicone rubber, place it on a heating table and heat it; Step 11. Bond the two devices processed in Step 10 with an adhesive. Among them, the upper piezoresistive film and the lower piezoresistive film are closely attached and the square films in the upper and lower piezoresistive films completely overlap; then place it on a heating table and heat it, and peel it off to obtain the hardness sensor.

6. The preparation method of the hardness sensor based on the co-integration of a pressure sensor and a strain sensor according to claim 5, wherein, The process of preparing the upper pressure-sensitive film and the lower pressure-sensitive film in Step 1 is as follows: First, anhydrous NaCl crystals are dissolved in water, evaporated and crystallized on a heating table at 200 °C to 250 °C, and then ultra-fine NaCl powder is obtained through a ball mill and a filter sieve. Then, polydimethylsiloxane, carbon nanotubes, and the ground ultra-fine NaCl powder are stirred and mixed evenly according to the mass ratio of 100:(3 - 4):(300 - 400), and the upper pressure-sensitive film and the lower pressure-sensitive film are obtained by using the template method.

7. The preparation method of the hardness sensor based on the co-integration of a pressure sensor and a strain sensor according to claim 5, characterized in that, In Step 2, the laser is an ultraviolet laser, the laser speed is 300 mm / s, and the power is 50%.

8. The preparation method of the hardness sensor based on the co-integration of a pressure sensor and a strain sensor according to claim 5, characterized in that, In Step 5, the laser is an infrared laser, the laser speed is 1000 mm / s, and the power is 20%.

9. The preparation method of the hardness sensor based on the co-integration of a pressure sensor and a strain sensor according to claim 5, wherein The preparation process of the strain sensor described in Step 7 is as follows: First, according to the mass ratio of polydimethylsiloxane:carbon nanotubes:antimony tin oxide = 100:(3 - 4):(5 - 6), polydimethylsiloxane, carbon nanotubes, and antimony tin oxide are weighed and stirred evenly, placed on a spin coater, rotated at a speed of 550 - 600 revolutions per minute for 1 - 2 minutes, and then placed on a heating table and heated at 120 °C to 150 °C for 2 - 5 minutes to obtain a strain film; Then, ultraviolet laser etching is used to form a patterned strain film and activate the antimony tin oxide; finally, the activated strain film is placed in a copper plating solution and placed in an incubator at a temperature of 35 °C to 40 °C, and left standing for 6 - 8 hours or more to obtain a strain sensor.

10. The preparation method of the hardness sensor based on the co-integration of a pressure sensor and a strain sensor according to claim 9, wherein, The laser is an ultraviolet laser, the laser speed is 2000 mm / s, and the power is 90%.

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