Tactile sensor and preparation method and application thereof

Abstract

The invention relates to a touch sensor and a preparation method and application thereof, and relates to the technical field of flexible sensing equipment. The touch sensor sequentially comprises a first packaging layer, a first electrode layer, a first conductive sensitive layer, a protruding layer, a second conductive sensitive layer, a second electrode layer and a second packaging layer from top to bottom. A plurality of conical bulges are arranged on one surface, close to the first conductive sensitive layer, of the bulge layer; and a plurality of fish scale-like bulges are arranged on one surface close to the second conductive sensitive layer. The invention also provides a preparation method of the tactile sensor, the whole process is simple in preparation, the tactile sensor has environmental protection property and high repeatability, and the prepared tactile sensor has wide detection range, high sensitivity, good cycle stability, low response time and fast recovery time. The touch sensor can work in a large temperature range and underwater, can detect the slippage of an object, and has a good application prospect in the fields of health monitoring, intelligent agriculture and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensors, and in particular to a tactile sensor and a preparation method and application thereof. Background Art

[0002] Fruit is an indispensable part of human daily diet. At present, fruit picking mainly relies on a large number of manual labor, which is time-consuming, labor-intensive and costly. Although the emergence of fruit picking robots has effectively alleviated the problem of labor shortage, the hard material and difficult-to-control gripping force of the end effector of the picking robot make the fruit very easy to be damaged during picking. Accurately controlling the gripping force and sliding action of the end effector during fruit picking can effectively reduce the damage to the fruit.

[0003] Flexible sensors can accurately identify various contact forces, such as normal pressure, slip and shear force, and have the characteristics of high integration, softness, lightness, and bendability. They can fit tightly to curved surfaces such as human skin and bionic robot hands. They have been widely used in many research fields such as wearable devices, smart textiles, health monitoring, soft robots, and electronic skin. Flexible sensors are particularly important as the sensing end of wearable devices. Therefore, as an important branch of wearable flexible sensors, tactile sensors have attracted domestic and foreign scholars to pursue faster response speeds, higher sensitivity, wider detection ranges, and better durability.

[0004] Flexible tactile sensors used to obtain external information can directly detect tactile information such as deformation and contact force of external objects. The patent (application number: 202411148262.2) discloses a highly sensitive flexible pressure sensor and its preparation method. The graphene / polyimide composite film is prepared using photolithography, etching, water transfer and other technologies to ensure the sensitivity and production yield of the sensor. It can accurately detect pressure changes at the wellhead of a natural gas extraction well or in a natural gas transmission pipeline; however, it can only detect pressure as an indicator data, and the cumbersome preparation process still has room for improvement.

[0005] In summary, in the field of flexible tactile sensor research, there is still a need to propose a solution that is easy to integrate, has a wide detection range, high sensitivity, and can detect two indicator data at the same time. However, existing flexible tactile sensors can usually only detect the pressure of an object alone, and cannot simultaneously identify the sliding of the object. The development of a new generation of intelligent fruit automatic picking robot equipment urgently needs a flexible tactile sensor that can simultaneously identify contact force and sliding action. To this end, the present invention proposes a tactile sensor and a preparation method thereof for identifying object pressure and sliding perception. Summary of the invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a tactile sensor and its preparation method and application. The tactile sensor of the present invention can simultaneously identify contact force and sliding action, and has a wide detection range, high sensitivity, low response time and fast recovery time, and good cycle stability. The tactile sensor can work in a large temperature range and underwater, and can detect the sliding of objects, and has good application prospects in the fields of health monitoring, smart agriculture, etc.

[0007] The technical solution of the present invention to solve the above technical problems is as follows:

[0008] The first object of the present invention is to provide a tactile sensor, which comprises, from top to bottom, a first packaging layer, a first electrode layer, a first conductive sensitive layer, a protrusion layer, a second conductive sensitive layer, a second electrode layer, and a second packaging layer; a side of the protrusion layer close to the first conductive sensitive layer is a plurality of conical protrusions; a side close to the second conductive sensitive layer is a plurality of fish-scale-shaped protrusions.

[0009] The beneficial effects of the present invention are as follows: the present application provides a tactile sensor having a wide detection range (0.01 kPa to 450 kPa), a high sensitivity (0.10 kPa -1 ~5.57kPa -1 ), low response time (0.10s), fast recovery time (0.07s), and good cycle stability (>8000 times). The tactile sensor can work in a wide temperature range and underwater, and can detect the slip of objects. It has good application prospects in health monitoring, smart agriculture and other fields.

[0010] Based on the above technical solution, the present invention can also be improved as follows.

[0011] Furthermore, the raised layer includes the following raw materials: polydimethylsiloxane (PDMS), conductive particles A, and a curing agent; the mass ratio of the polydimethylsiloxane, the curing agent, and the conductive particles A is 10-15: 1-2: 0.067-0.816.

[0012] Furthermore, the mass ratio of the polydimethylsiloxane, the curing agent, and the conductive particles A is 10:1:0.102.

[0013] The beneficial effect of adopting the above further scheme is that polydimethylsiloxane has good flexibility and biocompatibility and is non-toxic and has almost no side effects on the skin surface of the human body or other organisms.

[0014] Furthermore, the cone height of the multiple conical protrusions is 810μm~850μm, the bottom diameter is 800μm~850μm, and the distance between two adjacent conical protrusions is 900μm~1000μm; the height of the multiple fish-scale-shaped protrusions is 30μm~70μm; the bottom width is 180μm~230μm; the distance between two adjacent fish-scale-shaped protrusions is 120μm~140μm.

[0015] Furthermore, the material of the first conductive sensitive layer is carbon nanotubes, the diameter of the carbon nanotubes is 50nm~150nm, and the length of the carbon nanotubes is 15μm~30μm; the material of the second conductive sensitive layer is carbon nanotubes, the diameter of the carbon nanotubes is 50nm~150nm, and the length of the carbon nanotubes is 15μm~30μm.

[0016] The beneficial effect of adopting the above further scheme is that the carbon nanotubes have high strength, high conductivity, good mechanical properties and thermal conductivity. The carbon nanotubes with the structure defined by the present invention are used in tactile sensors to make the mechanical, electrical and chemical properties of the sensors better.

[0017] Furthermore, the conductive particles A include at least one of carbon nanotubes (CNTs), polypyrrole, and graphene; the material of the first electrode layer includes at least one of copper foil, gold foil, and silver foil; the material of the second electrode layer includes at least one of copper foil, gold foil, and silver foil.

[0018] Furthermore, the material of the first encapsulation layer includes at least one of PET, polydimethylsiloxane, and polyimide; the material of the second encapsulation layer includes at least one of PET, polydimethylsiloxane, and polyimide.

[0019] A second object of the present invention is to provide a method for preparing a tactile sensor, comprising the following steps:

[0020] (1) mixing polydimethylsiloxane and conductive particles A and adding a curing agent to obtain a conductive modified polydimethylsiloxane mixture; uniformly coating the conductive modified polydimethylsiloxane mixture on the surface of the 3D printed cone template, placing it in a vacuum box and evacuating it to obtain a polydimethylsiloxane conductive mixture that fills the inner cavity of the 3D printed cone; laying a screen template flat on the surface of the polydimethylsiloxane conductive mixture that fills the inner cavity of the 3D printed cone, and curing it; taking it out after it is completely cured, and peeling off the 3D printed cone template and the screen template to obtain a protrusion layer;

[0021] (2) Conductive particles B are sprayed on the upper and lower surfaces of the raised layer to obtain a first conductive sensitive layer and a second conductive sensitive layer respectively; copper foil is pasted on a side of the first conductive sensitive layer away from the raised layer to obtain a first electrode layer; PET film is pasted on a side of the first electrode layer away from the raised layer to obtain a first packaging layer; copper foil is pasted on a side of the second conductive sensitive layer away from the raised layer to obtain a second electrode layer; PET film is pasted on a side of the second electrode layer away from the raised layer to obtain a second packaging layer, thereby obtaining a tactile sensor.

[0022] The beneficial effects of the present invention are as follows: the preparation method of the present invention is simple, environmentally friendly and highly repeatable, and can simultaneously identify contact force and sliding action.

[0023] Furthermore, the curing temperature in step (1) is 60° C. to 100° C., and the curing time is 1 h to 3 h.

[0024] Furthermore, during spraying in step (2), the distance between the spray gun and the raised layer is 1 cm to 10 cm, the pressure is 0.15 MPa to 0.3 MPa, the speed is 10 cm / s to 20 cm / s, and the number of spraying cycles is 1 to 3; the thickness of the first conductive sensitive layer is 0.938 μm to 1.875 μm; the thickness of the second conductive sensitive layer coating is 0.938 μm to 1.875 μm.

[0025] Furthermore, the conductive particles B in step (2) include at least one of carbon nanotubes, polypyrrole, and graphene; the drying temperature is 60° C. to 100° C., and the drying time is 0.2 h to 1 h.

[0026] A third object of the present invention is to provide an application of a tactile sensor, wherein the tactile sensor is used for identifying pressure and / or sliding sensing of an object.

[0027] Furthermore, the sensor is used to detect the gripping force and slip data of the end effector of the fruit picking robot during the fruit picking process.

[0028] The beneficial effect of adopting the above further scheme is that the tactile sensor of the present invention can accurately identify the grasping force and sliding action applied by the end effector during the fruit picking process, thereby greatly reducing the damage to the fruit by the end effector during the fruit picking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a process flow chart of preparing a tactile sensor according to Example 1 of the present invention;

[0030] Figure 2The scanning electron microscope images and energy spectrum analysis images of Example 1 of the present invention; (a) is a scanning electron microscope image of the P sample; (b) is a scanning electron microscope magnified image of the P sample; (c) is a surface energy spectrum image of the P sample; (d) is a surface energy spectrum image of the P / C / C / S sample; (e) to (l) are scanning electron microscope images of P / C / S / S; (m) to (t) are scanning electron microscope images of P / C / C / S;

[0031] Figure 3 1 is a diagram of the sensing performance of the tactile sensor of Example 1 of the present invention; wherein (a) is a schematic diagram of the response under different pressures; (b) is a schematic diagram of the sensitivity curve; (c) is a schematic diagram of the sensitivity and detection range comparison of the tactile sensor of Example 1 and other reported sensors; (d) is a schematic diagram of the response time and recovery time of the tactile sensor; (e) is a schematic diagram of the cyclic stability; (f) is a schematic diagram of the response time and recovery time after experiencing cyclic stability; (g) is a schematic diagram of the current change at different temperatures; (h) is a schematic diagram of the current change under different humidity environments; (i) is a schematic diagram of the contact angle and rolling angle of different material surfaces;

[0032] Figure 4 The diagram is a diagram of the slip signal monitoring and conductive mechanism of the tactile sensor of Example 1 of the present invention; wherein (a) is a schematic diagram of the slip test structure; (b) is a schematic diagram of the normal conduction circuit; (c) is a schematic diagram of the conduction circuit when only subjected to positive pressure; (d) is a three-dimensional morphology of the surface after the conical structure layer is sprayed with conductive particles; (e) is a current response curve diagram of the slip process; (f) is a schematic diagram of the structure after slip behavior occurs; (g) is a schematic diagram of the conduction circuit when only subjected to tangential force; (h) is a schematic diagram of the conduction circuit when slip behavior occurs.

[0033] Figure 5 Schematic diagram of the application of the tactile sensor of Example 1 of the present invention in the process of fruit picking; wherein (a) is a diagram of the node stress detection device of citrus in different compression stages; (b) is a diagram of the slight deformation of citrus under pressure; (c) is a diagram of the serious deformation of citrus under pressure; (d) is a diagram of the damage and deformation of citrus under pressure; (e) to (f) are detection and application diagrams of the tactile sensor collaborative robot end effector in the process of citrus picking; (g) is a current response curve diagram of the tactile sensor at position 1 marked in (f) under a pressure of 70 kPa; (h) is a current response curve diagram of the tactile sensor at position 2 marked in (f) under a pressure of 70 kPa; (i) is a current response curve diagram of the tactile sensor at position 3 marked in (f) under a pressure of 70 kPa. DETAILED DESCRIPTION

[0034] The principles and features of the present invention are described below, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased through regular channels.

[0035] Example 1: Preparation of tactile sensor

[0036] (1) Mold cleaning: First, cut the 800-mesh stainless steel screen with a hollow grid structure composed of intersecting wires into a shape of 10mm x 10mm. The horizontal distance of the mesh is 9.23μm, the vertical distance is 109.25μm, the depth of each hollow grid is 47.36μm, and the average diameter of each wire of the mesh is 50.24μm. Then, the stainless steel screen and the 3D printed cone template with a spacing of 1mm between each adjacent cone and a cone height of 1mm were placed in anhydrous ethanol and ultrasonicated in a CNC ultrasonic cleaner (KQ-250DE, Kunshan Ultrasonic Instrument Co., Ltd.) for 10 minutes;

[0037] (2) 3 g of PDMS (Dow Corning DC184, USA), 0.3 g of PDMS curing agent (Dow Corning DC 184, USA) and 102 mg of CNTs with a tube diameter of 102 nm and a tube length of 18 μm were weighed by an electronic analytical balance (FA3104N, Shanghai Jinghai Instrument Co., Ltd.), and the PDMS and CNTs were manually stirred and evenly mixed using a glass rod, and then the PDMS curing agent was added to form a PDMS / CNTs conductive mixed solution; the conductive mixed solution was evenly coated on the surface of the 3D printed cone template, and then vacuumed in a vacuum drying oven (DZF-6050; Shanghai Shanzhi Instrument Equipment Co., Ltd.) for 20 minutes to allow the conductive mixed solution to fill the inner cavity of the cone template and discharge the gas inside the substrate, and then an 800-mesh stainless steel screen template was flatly laid on the conductive mixed solution, dried at 80°C in a vacuum drying oven for two hours, and taken out after complete curing, and the 3D printed cone template and the screen template were peeled off to obtain a PDMS / CNTs layer, i.e., a protrusion layer;

[0038] (3) Prepare a 2.5% CNTs anhydrous ethanol solution, the dispersion method is magnetic stirring, the rotation speed is 3000rpm, the stirring environment is room temperature, and the stirring time is 6h. Use a spray gun (HD130, Ningbo Yinzhou Wuxiang Junyou Trading Company) to spray a layer of 2.5% CNTs anhydrous ethanol solution on both surfaces of the cured PDMS / CNTs layer. During spraying, the distance between the spray gun and the PDMS / CNTs layer material is 3cm, the spraying pressure is 0.25MPa, the spraying speed is 15cm / s, and the number of spraying cycles is 2. Then dry it in a vacuum drying oven at 80℃ for 20 minutes to obtain the first conductive sensitive layer and the second conductive sensitive layer. A copper foil with a thickness of 0.17 mm is pasted on the side of the first conductive sensitive layer away from the PDMS / CNTs layer to obtain a first electrode layer; a PET film with a thickness of 0.1 mm is pasted on the side of the first electrode layer away from the PDMS / CNTs layer to obtain a first packaging layer; a copper foil with a thickness of 0.17 mm is pasted on the side of the second conductive sensitive layer away from the PDMS / CNTs layer to obtain a second electrode layer, and a PET film with a thickness of 0.1 mm is pasted on the side of the second electrode layer away from the PDMS / CNTs layer using tape to obtain a second packaging layer, so as to obtain a tactile sensor, such as Figure 1 shown.

[0039] Example 2: Preparation of tactile sensor II

[0040] (1) Mold cleaning: First, cut the 800-mesh stainless steel screen with a hollow grid structure composed of intersecting wires into a shape of 10mm x 10mm. The horizontal distance of the mesh is 9.23μm, the vertical distance is 109.25μm, the depth of each hollow grid is 47.36μm, and the average diameter of each wire of the screen is 50.24μm. Then, the stainless steel screen and the 3D printed conical template with a spacing of 1mm between each adjacent cone and a cone height of 0.5mm were placed in anhydrous ethanol and ultrasonicated in a CNC ultrasonic cleaner (KQ-250DE, Kunshan Ultrasonic Instrument Co., Ltd.) for 10 minutes;

[0041] (2) 3 g of PDMS (Dow Corning DC184, USA), 0.3 g of PDMS curing agent (Dow Corning DC 184, USA) and 102 mg of CNTs with a tube diameter of 50 nm and a tube length of 15 μm were weighed by an electronic analytical balance (FA3104N, Shanghai Jinghai Instrument Co., Ltd.), PDMS and CNTs were mixed and then the PDMS curing agent was added to form a PDMS / CNTs conductive mixed solution; the conductive mixed solution was evenly coated on the surface of the 3D printed cone template, and then vacuumed in a vacuum drying oven (DZF-6050; Shanghai Shanzhi Instrument Equipment Co., Ltd.) for 20 minutes to allow the conductive mixed solution to fill the inner cavity of the cone template and discharge the gas inside the substrate, and then an 800-mesh stainless steel screen template was flatly laid on the conductive mixed solution, dried at 80°C in a vacuum drying oven for two hours, and taken out after complete curing, and the 3D printed cone template and the screen template were peeled off to obtain a PDMS / CNTs layer, i.e., a protrusion layer;

[0042] (3) Prepare an anhydrous ethanol solution of CNTs with a mass fraction of 2.5%, the dispersion method is magnetic stirring, the rotation speed is 500 rpm, the stirring environment is room temperature, and the stirring time is 8 hours. Use a spray gun (HD130, Ningbo Yinzhou Wuxiang Junyou Trading Company) to spray a layer of anhydrous ethanol solution of CNTs with a mass fraction of 2.5% on both surfaces of the cured PDMS / CNTs layer. During spraying, the distance between the spray gun and the PDMS / CNTs layer material is 5 cm, the spraying pressure is 0.2 MPa, the spraying speed is 10 cm / s, and the number of spraying cycles is 3. Then dry in a vacuum drying oven at 60°C for 30 minutes to obtain the first conductive sensitive layer and the second conductive sensitive layer. A copper foil with a thickness of 0.05 mm was pasted on the side of the first conductive sensitive layer away from the PDMS / CNTs layer to obtain a first electrode layer; a PET film with a thickness of 0.1 mm was pasted on the side of the first electrode layer away from the PDMS / CNTs layer to obtain a first packaging layer; a copper foil with a thickness of 0.05 mm was pasted on the side of the second conductive sensitive layer away from the PDMS / CNTs layer to obtain a second electrode layer, and a PET film with a thickness of 0.1 mm was pasted on the side of the second electrode layer away from the PDMS / CNTs layer using tape to obtain a second packaging layer, thereby obtaining a tactile sensor.

[0043] Example 3: Preparation of tactile sensor

[0044] (1) Mold cleaning: First, cut the 800-mesh stainless steel screen with a hollow grid structure composed of intersecting wires into a shape of 10mm x 10mm. The horizontal distance between the mesh grids of the screen is 9.23μm, the vertical distance is 109.25μm, the depth of each hollow grid is 47.36μm, and the average diameter of each wire of the screen is 50.24μm. Subsequently, the stainless steel screen and the 3D printed conical template with a spacing of 1.2mm between each adjacent cone and a cone height of 0.5mm were placed in anhydrous ethanol and ultrasonicated in a CNC ultrasonic cleaner (KQ-250DE, Kunshan Ultrasonic Instrument Co., Ltd.) for 10 minutes;

[0045] (2) 3 g of PDMS (Dow Corning DC184, USA), 0.3 g of PDMS curing agent (Dow Corning DC 184, USA) and 102 mg of CNTs with a tube diameter of 100 nm and a tube length of 20 μm were weighed by an electronic analytical balance (FA3104N, Shanghai Jinghai Instrument Co., Ltd.), PDMS and CNTs were mixed and then the PDMS curing agent was added to form a PDMS / CNTs conductive mixed solution; the conductive mixed solution was evenly coated on the surface of the 3D printed cone template, and then vacuumed in a vacuum drying oven (DZF-6050; Shanghai Shanzhi Instrument Equipment Co., Ltd.) for 20 minutes to allow the conductive mixed solution to fill the inner cavity of the cone template and discharge the gas inside the substrate to obtain a PDMS / CNTs layer, and then an 800-mesh stainless steel screen template was flatly laid on the conductive mixed solution, dried at 80°C in a vacuum drying oven for two hours, and taken out after complete curing, and the 3D printed cone template and the screen template were peeled off to obtain a PDMS / CNTs layer, i.e., a protrusion layer;

[0046] (3) Prepare a 2.5% CNTs anhydrous ethanol solution, the dispersion method is magnetic stirring, the rotation speed is 4500rpm, the stirring environment is room temperature, and the stirring time is 4h. Use a spray gun (HD130, Ningbo Yinzhou Wuxiang Junyou Trading Company) to spray a layer of 2.5% CNTs anhydrous ethanol solution on both surfaces of the cured PDMS / CNTs layer. During spraying, the distance between the spray gun and the PDMS / CNTs layer material is 2cm, the spraying pressure is 0.3MPa, the spraying speed is 30cm / s, and the number of spraying is 1 cycle. Then dry it in a vacuum drying oven at 80℃ for 20 minutes to obtain the first conductive sensitive layer and the second conductive sensitive layer. A copper foil with a thickness of 0.3 mm was pasted on the side of the first conductive sensitive layer away from the PDMS / CNTs layer to obtain a first electrode layer; a PET film with a thickness of 0.1 mm was pasted on the side of the first electrode layer away from the PDMS / CNTs layer to obtain a first packaging layer; a copper foil with a thickness of 0.3 mm was pasted on the side of the second conductive sensitive layer away from the PDMS / CNTs layer to obtain a second electrode layer, and a PET film with a thickness of 0.1 mm was pasted on the side of the second electrode layer away from the PDMS / CNTs layer using tape to obtain a second packaging layer, thereby obtaining a tactile sensor.

[0047] Comparative Example 1: Preparation of PDMS Sample

[0048] 3 g of PDMS (Dow Corning DC184, USA) and 0.3 g of PDMS curing agent (Dow Corning DC 184, USA) were weighed by an electronic analytical balance (FA3104N, Shanghai Jinghai Instrument Co., Ltd.), and the PDMS and PDMS curing agent were mixed to form a mixed solution; the mixed solution was evenly coated on the surface of the polytetrafluoroethylene template, naturally leveled, and then evacuated in a vacuum drying oven (DZF-6050; Shanghai Shanzhi Instrument Equipment Co., Ltd.) for 20 minutes to exhaust the internal gas of the mixed solution, and dried at 80°C in a vacuum drying oven for two hours. After complete curing, it was taken out and the template was peeled off to obtain a PDMS sample, which was defined as P.

[0049] Comparative Example 2: Preparation of PDMS / CNTs Samples

[0050] 3 g PDMS (Dow Corning DC184, USA), 0.3 g PDMS curing agent (Dow Corning DC 184, USA) and 102 mg CNTs with a tube diameter of 102 nm and a tube length of 18 μm were weighed by an electronic analytical balance (FA3104N, Shanghai Jinghai Instrument Co., Ltd.), PDMS and CNTs were mixed and then the PDMS curing agent was added to form a PDMS / CNTs conductive mixed liquid; the conductive mixed liquid was evenly coated on the surface of the polytetrafluoroethylene template, naturally leveled, and then vacuumed in a vacuum drying oven (DZF-6050; Shanghai Shanzhi Instrument Equipment Co., Ltd.) for 20 minutes to exhaust the gas inside the conductive mixed liquid, and then dried at 80°C in a vacuum drying oven for two hours. After complete curing, it was taken out and the template was peeled off to obtain a PDMS / CNTs sample, which was defined as P / C.

[0051] Comparative Example 3: Preparation of PDMS / CNTs / Screen mesh sample

[0052] (1) Mold cleaning: First, cut the 800-mesh stainless steel screen with a hollow grid structure composed of intersecting wires into a shape of 10 mm x 10 mm. The horizontal distance of the mesh is 9.23 μm, the vertical distance is 109.25 μm, the depth of each hollow grid is 47.36 μm, and the average diameter of each wire of the mesh is 50.24 μm. Then, put the stainless steel mesh into anhydrous ethanol and ultrasonicate it in a CNC ultrasonic cleaner (KQ-250DE, Kunshan Ultrasonic Instrument Co., Ltd.) for 10 minutes;

[0053] (2) 3 g of PDMS (Dow Corning DC184, USA), 0.3 g of PDMS curing agent (Dow Corning DC 184, USA) and 102 mg of CNTs with a tube diameter of 102 nm and a tube length of 18 μm were weighed by an electronic analytical balance (FA3104N, Shanghai Jinghai Instrument Co., Ltd.), PDMS and CNTs were mixed and then PDMS curing agent was added to form a PDMS / CNTs conductive mixed solution; the conductive mixed solution was evenly coated on the surface of the 3D printed cone template, and then vacuumed in a vacuum drying oven (DZF-6050; Shanghai Shanzhi Instrument Equipment Co., Ltd.) for 20 minutes to allow the conductive mixed solution to fill the inner cavity of the 3D printed cone template and exhaust the internal gas, then an 800-mesh stainless steel screen template was flatly laid on the conductive mixed solution, dried at 80°C in a vacuum drying oven for two hours, taken out after complete curing, and the stainless steel screen template was peeled off to obtain a PDMS / CNTs / Screen mesh sample, which was defined as P / C / S.

[0054] Comparative Example 4: Preparation of PDMS / CNTs / Screen mesh / Spray sample

[0055] The difference between this comparative example and comparative example 3 is that spraying is performed after the PDMS / CNTs / Screen mesh sample is prepared. The specific spraying steps are as follows:

[0056] Prepare a 2.5% CNTs anhydrous ethanol solution, the dispersion method is magnetic stirring, the rotation speed is 3000rpm, the stirring environment is room temperature, and the stirring time is 6h. Use a spray gun (HD130, Ningbo Yinzhou Wuxiang Junyou Trading Company) to spray a layer of 2.5% CNTs anhydrous ethanol solution on the surface of the cured PDMS / CNTs / Screenmesh sample. During spraying, the distance between the spray gun and the PDMS / CNTs / Screen mesh sample is 3cm, the spraying pressure is 0.25MPa, the spraying speed is 15cm / s, and the number of spraying is 2 cycles. Then dry it in a vacuum drying oven at 80℃ for 20 minutes to obtain a PDMS / CNTs / Screen mesh / Spray sample, which is defined as P / C / S / S.

[0057] Comparative Example 5: Preparation of PDMS / CNTs / Conical template sample

[0058] (1) Mold cleaning: A 3D printed cone template with a spacing of 1 mm between adjacent cones and a cone height of 1 mm was placed in anhydrous ethanol and ultrasonicated in a CNC ultrasonic cleaner (KQ-250DE, Kunshan Ultrasonic Instrument Co., Ltd.) for 10 minutes;

[0059] (2) 3 g of PDMS (Dow Corning DC184, USA), 0.3 g of PDMS curing agent (Dow Corning DC 184, USA) and 102 mg of CNTs with a tube diameter of 102 nm and a tube length of 18 μm were weighed by an electronic analytical balance (FA3104N, Shanghai Jinghai Instrument Co., Ltd.), PDMS and CNTs were mixed and then the PDMS curing agent was added to form a PDMS / CNTs conductive mixed liquid; the conductive mixed liquid was evenly coated on the surface of the 3D printed conical template, and then vacuumed in a vacuum drying oven (DZF-6050; Shanghai Shanzhi Instrument Equipment Co., Ltd.) for 20 minutes to allow the conductive mixed liquid to fill the inner cavity of the conical template and discharge the gas inside the matrix, and then dried in a vacuum drying oven at 80°C for two hours. After complete curing, it was taken out and the 3D printed conical template was peeled off to obtain a PDMS / CNTs / Conical template sample, which was defined as P / C / C.

[0060] Comparative Example 6: Preparation of PDMS / CNTs / Conical template / Spray sample

[0061] The difference between this comparative example and comparative example 5 is that spraying is performed after the PDMS / CNTs / Conical template sample is prepared. The specific spraying steps are as follows:

[0062] Prepare a 2.5% CNTs anhydrous ethanol solution, the dispersion method is magnetic stirring, the rotation speed is 3000rpm, the stirring environment is room temperature, and the stirring time is 6h. Use a spray gun (HD130, Ningbo Yinzhou Wuxiang Junyou Trading Company) to spray a layer of 2.5% CNTs anhydrous ethanol solution on the surface of the cured PDMS / CNTs / Conical template sample. During spraying, the distance between the spray gun and the PDMS / CNTs / Conical template sample is 3cm, the spraying pressure is 0.25MPa, the spraying speed is 15cm / s, and the number of spraying is 2 cycles. Subsequently, the PDMS / CNTs / Conical template / Spray sample is obtained by drying at 80°C in a vacuum drying oven for 20 minutes, and the definition name is P / C / C / S.

[0063] Test example

[0064] 1. Structural characterization and energy spectrum analysis

[0065] The structures of the samples prepared in Comparative Examples 1, 4, and 6 were characterized and analyzed by scanning electron microscopy (SEM, SU8010, HITACHI Co., Ltd.; Japan). Figure 2 shown.

[0066] Depend on Figure 2 We can get:

[0067] like Figure 2 (a)~ Figure 2 As shown in (c), the surface of the P sample is smooth and uniform, and its surface C content is 33.72%, O content is 36.37%, and Si content is 29.91%. Figure 2 (e)~ Figure 2 As shown in (l), the P / C / S / S surface presents a regularly arranged fish-scale structure. The diameter of the carbon nanotube particles coated on its surface by spraying technology is 102nm, and the height of its protruding structure is 68μm as measured by the cross-sectional image. Figure 2 (m)~ Figure 2 (t) and Figure 2 As shown in (d), the surface of P / C / C / S presents a regularly arranged conical structure. After being molded and sprayed through a conical mold, the cone height is 844μm, the bottom diameter is 837μm, and the distance between adjacent cones is 951μm. Its surface energy spectrum shows that the C element content is 58.98%, the O element content is 28.12%, and the Si element content is 12.9%.

[0068] 2. Sensing performance test

[0069] (1) First, the tactile sensor prepared in Example 1 was tested for sensing response at 0.01 kPa, 0.1 kPa, 1 kPa, 10 kPa, 50 kPa, 100 kPa, 150 kPa, 200 kPa, 250 kPa, 300 kPa, 350 kPa, 400 kPa, and 450 kPa, respectively. The results are as follows: Figure 3 (a) and (b) show that the detection range of the tactile sensor is 0.01 to 450 kPa, and the response sensitivity is 0.10 kPa within the pressure range of 0.01 to 50 kPa. -1 , the response sensitivity in the pressure range of 50~250kPa is 2.63kPa -1 , the response sensitivity in the pressure range of 250~350kPa is 1.82kPa -1 , the response sensitivity in the pressure range of 350~400kPa is 5.57kPa -1 .

[0070] (2) The sensitivity and detection range of the sensor prepared in Example 1 were compared with those of other reported sensors. Figure 3 (c) as shown, Figure 3 [1] in (c) is the sensor proposed by Cao Kunli et al., with a sensitivity of 3.1 kPa -1 , the detection range is 400 kPa (DOI:10.1002 / adf m.202202360); Figure 3 [2] in (c) is the sensor proposed by Wang Shuai et al., with a sensitivity of 3.74 kPa -1 , with a detection range of 800 kPa (DOI: 10.1016 / j.cej.2022.136446); [3] is the sensor proposed by Zhou Bin et al., with a sensitivity of 1.77 kPa -1 , with a detection range of 30 kPa (DOI:10.1021 / acssensors.3c00818); [4] is the sensor proposed by Shi Jidong et al., with a sensitivity of 3.74 kPa -1 , with a detection range of 800 kPa (DOI: 10.1002 / smll.201800819); [5] is a sensor proposed by Wang Xin et al., with a sensitivity of 3.997 kPa -1 , with a detection range of 100 kPa (DOI: 10.1002 / adma.202410312); the sensitivity of the sensor proposed by Liu Chong et al. is 0.24 kPa -1, the detection range is 10kPa (DOI:10.1039 / D2TC02326A), such as Figure 3 (c) is shown in [6]; [7] is the sensor proposed by Zheng Shaodi et al., with a sensitivity of 0.641 kPa -1 , with a detection range of 60 kPa (DOI: 10.1016 / j.compscitech.2020.108546); [8] is the sensor proposed by Guan Hao et al., with a sensitivity of 1.85 kPa -1 , with a detection range of 120 kPa (DOI: 10.1021 / acsami.0c12561); [9] is the sensor proposed by Xu Li et al., with a sensitivity of 1.104 kPa -1 , with a detection range of 20 kPa (DOI:10.1016 / j.cej.2022.138820);

[10] is the sensor proposed by Du Qifeng et al., with a sensitivity of 4.48 kPa -1 , with a detection range of 65 kPa (DOI:10.1002 / admt.202100122);

[11] is the sensor proposed by Ge Gang et al., with a sensitivity of 0.152 kPa -1 , the detection range is 27.39 kPa (DOI: 10.1039 / C8NR02813C). The results show that the comprehensive performance of the tactile sensor of the present invention is substantially higher than the average level.

[0071] (3) Under a pressure of 30 kPa, the response time and recovery time of the tactile sensor of Example 1 were measured. Here, the response time and recovery time are defined as the time taken from 10% of the initial value to 90% of the final value. The results are shown in Figure 3 As shown in (d): when the tactile sensor is subjected to a pressure of 30 kPa, its response time is 0.1 s and its recovery time is 0.07 s.

[0072] (4) The cyclic stability of the tactile sensor of Example 1 was tested using a universal tensile testing machine (Shimadzu AGS-X, Japan) and a digital source meter (Keithley 2450, Keithley, USA). Figure 3 As shown in (e), the tactile sensor in the embodiment of the present invention is tested for cycle stability more than 8000 times at a pressure of 0.8 kPa and a voltage of 0.5 V, indicating that the tactile sensor has good cycle stability.

[0073] (5) After 8000 cycles of stability testing, the response time and recovery time of the tactile sensor of Example 1 were tested again under a pressure of 30 kPa. Figure 3As shown in (f), when the tactile sensor is subjected to a pressure of 30 kPa after undergoing 8000 cycles of stability testing, its response time is 0.13 s and its recovery time is 0.09 s.

[0074] (6) Keeping the experimental environment humidity at a constant 30% RH, test the change of the current of the tactile sensor under a pressure of 50 kPa with temperature. Figure 3 As shown in (g): When the test environment temperature varies in the range of 15 to 60°C, the current response of the tactile sensor under a pressure of 50 kPa remains stable.

[0075] (7) While keeping the experimental environment temperature constant at 25°C, change the experimental environment humidity and test the current response of the tactile sensor under a pressure of 50 kPa. Figure 3 As shown in (h), when the sensor is in a humidity condition of 20%-80% RH or even in an underwater test environment, its current response to an applied pressure of 50 kPa remains stable.

[0076] (8) A contact angle meter (JC2000D1, Shanghai Zhongchen Digital Technology Equipment Co., Ltd.) and distilled water with a volume content of 4 μl and 15 μl, respectively, were used to measure the contact angle and rolling angle of the sample surfaces at each stage of preparation of Comparative Examples 1 to 6.

[0077] like Figure 3 As shown in (i), the contact angle of the P sample surface is 109.58±1.02°, and the rolling angle is greater than 90°, indicating that the initial substrate surface is hydrophobic. The contact angle of the P / C sample surface is 109.89±0.63°, and the rolling angle is greater than 90°. The contact angle of the P / C / S sample surface is 131.30±1.10°, and the rolling angle is greater than 90°. The contact angle of the P / C / S / S sample surface is 156.80±0.41°, and the rolling angle is 2°. The contact angle of the P / C / C sample surface is 145.46±0.95°, and the rolling angle is greater than 90°. The contact angle of the P / C / C / S sample surface is 164.63±1.16°, and the rolling angle is 1°. The above changes in the wettability of the sample surface indicate that the template remolding or spraying changes the surface microstructure of the P sample, increases the roughness of the P surface, and further improves the hydrophobicity of the P surface. It is the good hydrophobic properties of the internal structure of the tactile sensor that enable it to operate stably in an underwater environment.

[0078] 3. Slip signal test

[0079] Detection method: A 5 g weight was pulled on the surface of the tactile sensor to simulate the sliding process, and the current signal generated during the sliding process was read by a digital source meter (Keithley 2450, Keithley, USA).

[0080] Depend on Figure 4 We can get:

[0081] like Figure 4 (a)~ Figure 4 (c) and Figure 4 (f)~ Figure 4 As shown in (h), when the tactile sensor in the embodiment of the present invention is subjected to positive pressure and tangential force, the internal structure of the tactile sensor undergoes longitudinal and transverse deformation, its conductive path increases, and the current in the conductive circuit increases with the increase of pressure.

[0082] like Figure 4 As shown in (d), the three-dimensional morphology further proves that the surface of the conical structure layer presents a regularly arranged conical structure, with an arithmetic average height of 130.2 μm and a maximum height of 834.2 μm.

[0083] The slip process can be roughly divided into four stages: in the first stage, such as Figure 4 (b) and Figure 4 As shown in (e), in the presence of only vertical normal force, the tangential deformation and electrical output signal of the sensor remain unchanged. Figure 4 (c) and Figure 4 As shown in (e), the mutual tension and tangential deformation gradually increase. Before the object starts to slide, the tension (tangential deformation) applied to the tactile sensor increases with the increase of static friction, resulting in a decrease in resistance and an increase in current. In the third stage, as shown in Figure 4 (e) and Figure 4 As shown in (g), the pulling force continues to increase until it equals the maximum static friction force. At the moment of slipping, the tangential deformation of the sensor increases rapidly, resulting in a sharp increase in the conduction path. In the fourth stage, as Figure 4 (e) and Figure 4 (h) shows that the object is in a sliding state. The pulling force is balanced by the dynamic friction force, and the number of conductive paths is greater than that in the first stage.

[0084] 4. Application of tactile sensors in fruit picking

[0085] The force gauge (HPB-500, Yueqing Aidebao Instrument Co., Ltd., China) was used to measure the surface area of ​​the sample with a diameter of D = 16 mm and a surface area of ​​S = 2.01 cm 2 The pressure plate test shows the pressure range of each stage in the process of "initial state - slight deformation - severe deformation - damage" of citrus.

[0086] The three tactile sensors prepared in Example 1 are respectively adhered to the end effector of the picking robot, and are marked as No. 1, No. 2, and No. 3. Figure 5As shown in (f), the range and size of the grasping force are fed back through real-time current response. A digital source meter (Keithley 2450, Keithley, USA) was used to read the current signal of the tactile sensor and the end effector of the picking robot during the fruit picking process. The experiment was repeated three times, and the results are shown in Figure 5 And as shown in Table 1.

[0087] Table 1 Node stress of citrus at different compression stages

[0088] Original state Slight deformation Severe deformation damage Tangerine 0kPa 40±5kPa 90±2kPa 125±3kPa

[0089] From Table 1 and Figure 5 We can get:

[0090] (1) Figure 5 (a)~ Figure 5 (d) and Table 1 show that the average value of the data of three citrus fruits was obtained, and the pressure range of the nodes in each stage of the citrus fruits was finally obtained. When the pressure on the citrus fruits was 40±5kPa, the citrus fruits were slightly deformed; when the pressure on the citrus fruits was 90±2kPa, the citrus fruits were seriously deformed; when the pressure on the citrus fruits was 125±3kPa, the citrus fruits were damaged.

[0091] (2) Figure 5 (e)~ Figure 5 As shown in (f), when the end effector is in the picking process, the real-time current response feedback of the three tactile sensors attached to the end effector indicates the range and size of the gripping force. In order to ensure that the citrus is not damaged, the preset gripping force of the end effector should not exceed the pressure range when the citrus is severely deformed. At this time, the maximum current response value of each tactile sensor corresponds to the current response of the sensor unit under a pressure of 90kPa, and the end effector should not continue to increase the clamping force.

[0092] (3) Figure 5 (g)~ Figure 5 As shown in (i), they correspond to the three tactile sensors attached to the end effector, and the pressure applied to the end effector is 70 kPa. Due to the different positions of the three tactile sensors, there is a small difference in the current response output by the tactile sensors No. 1 and No. 2 on both sides of the actuator, indicating that the pressure difference between the tactile sensors No. 1 and No. 2 is very small, and the tactile sensor No. 3 at the bottom is under the greatest pressure and has the most obvious current response. Due to the real-time current response of the tactile sensor, the end effector will not exceed the pressure range where the fruit will be damaged while holding it firmly.

[0093] In summary, the tactile sensor prepared by the present invention is used for the detection of the gripping force and sliding data of the end effector of the fruit picking robot during the fruit picking process, and cooperates with the end effector to complete the adaptive gripping operation. The tactile sensor of the present invention can accurately identify the gripping force and sliding action applied by the end effector during the fruit picking process, thereby greatly reducing the damage to the fruit by the end effector during the fruit picking process. It can be seen that the tactile sensor prepared by the present invention can cooperate with the end effector of the fruit picking robot to perform non-destructive fruit picking, and has a good application prospect.

[0094] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A tactile sensor, characterized in that: The tactile sensor includes, from top to bottom, a first packaging layer, a first electrode layer, a first conductive sensitive layer, a protrusion layer, a second conductive sensitive layer, a second electrode layer, and a second packaging layer; a side of the protrusion layer close to the first conductive sensitive layer is a plurality of conical protrusions; a side close to the second conductive sensitive layer is a plurality of fish scale-shaped protrusions.

2. A tactile sensor according to claim 1, characterized in that: The raised layer includes the following raw materials: polydimethylsiloxane, conductive particles A, and a curing agent; the mass ratio of the polydimethylsiloxane, the curing agent, and the conductive particles A is 10-15: 1-2: 0.067-0.

816.

3. A tactile sensor according to claim 1, characterized in that: The cone height of the multiple conical protrusions is 810μm~850μm, the bottom diameter is 800μm~850μm, and the distance between two adjacent conical protrusions is 900μm~1000μm; the height of the multiple fish scale-like protrusions is 30μm~70μm; the bottom width is 180μm~230μm; the distance between two adjacent fish scale-like protrusions is 120μm~140μm.

4. A tactile sensor according to claim 1, characterized in that: The material of the first conductive sensitive layer is carbon nanotubes, the diameter of the carbon nanotubes is 50nm-150nm, and the length of the carbon nanotubes is 15μm-30μm; the material of the second conductive sensitive layer is carbon nanotubes, the diameter of the carbon nanotubes is 50nm-150nm, and the length of the carbon nanotubes is 15μm-30μm.

5. The tactile sensor according to claim 1, characterized in that: The conductive particles A include at least one of carbon nanotubes, polypyrrole, and graphene; the material of the first electrode layer includes at least one of copper foil, gold foil, and silver foil; the material of the second electrode layer includes at least one of copper foil, gold foil, and silver foil.

6. The tactile sensor according to claim 1, characterized in that: The material of the first encapsulation layer includes at least one of PET, polydimethylsiloxane, and polyimide; the material of the second encapsulation layer includes at least one of PET, polydimethylsiloxane, and polyimide.

7. A method for preparing a tactile sensor according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: (1) mixing polydimethylsiloxane and conductive particles A and adding a curing agent to obtain a conductive modified polydimethylsiloxane mixture; coating the conductive modified polydimethylsiloxane mixture on the surface of a 3D printed cone template, placing the mixture in a vacuum box and evacuating the vacuum box to obtain a polydimethylsiloxane conductive mixture that fills the inner cavity of the 3D printed cone; laying a screen template on the surface of the polydimethylsiloxane conductive mixture that fills the inner cavity of the 3D printed cone, curing the mixture, and then peeling off the 3D printed cone template and the screen template to obtain a protrusion layer; (2) Spraying conductive particles B on the upper and lower surfaces of the raised layer and drying them to obtain a first conductive sensitive layer and a second conductive sensitive layer on the upper and lower surfaces of the raised layer respectively; pasting copper foil on a side of the first conductive sensitive layer away from the raised layer to obtain a first electrode layer; pasting PET film on a side of the first electrode layer away from the raised layer to obtain a first packaging layer; pasting copper foil on a side of the second conductive sensitive layer away from the raised layer to obtain a second electrode layer; pasting PET film on a side of the second electrode layer away from the raised layer to obtain a second packaging layer, thereby obtaining a tactile sensor.

8. The method for preparing a tactile sensor according to claim 7, characterized in that: During spraying in step (2), the distance between the spray gun and the raised layer is 1 cm to 10 cm, the pressure is 0.15 MPa to 0.3 MPa, the speed is 10 cm / s to 20 cm / s, and the number of spraying cycles is 1 to 3; the thickness of the first conductive sensitive layer is 0.938 μm to 1.875 μm; the thickness of the second conductive sensitive layer coating is 0.938 μm to 1.875 μm.

9. The method for preparing a tactile sensor according to claim 7, characterized in that: The conductive particles B in step (2) include at least one of carbon nanotubes, polypyrrole, and graphene; the drying temperature is 60° C. to 100° C., and the drying time is 0.2 h to 1 h.

10. An application of a tactile sensor, characterized in that: The tactile sensor according to any one of claims 1 to 6 is used for identifying object pressure and / or slippage sensing.

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