Flexible tactile sensor based on high-sensitivity crack resistance principle and manufacturing method thereof

Abstract

The application discloses a flexible slip sensor based on a high-sensitivity crack resistance variable resistance principle and a manufacturing method thereof, and the synchronous preparation of a grid-shaped micro-channel on the upper surface of a PDMS film and a pyramid-shaped structure array on the lower surface of the PDMS film is completed through a stamping process, then surface hydrophilic treatment is carried out, then a mixture of carbon nanotubes and silver paste is scraped and coated in the grid-shaped micro-channel on the upper surface to form a conductive network, the conductive network is pre-stretched to generate micro-cracks, and finally a high-sensitivity flexible slip sensor is obtained; the sensing structure and the conductive material of the application are integrated on a film, and thus assembly is not needed, process steps are simplified, and production efficiency is improved; the grid-shaped embedded distribution of the conductive material filling form avoids abrasion of the conductive material, the sensor performance is more stable, meanwhile, the flexible slip sensor is transparentized, and it is beneficial to integration into a flexible electronic system.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of micro-nano manufacturing technology, and particularly relates to a flexible tactile sensor based on a high-sensitivity crack resistance principle and a manufacturing method thereof. BACKGROUND

[0002] It is of great significance to study a tactile sensor for sensing the texture information of an object surface for improving the robot sensing technology and promoting the intelligent development of robots. The texture of an object surface is usually a concave-convex microstructure which is difficult to sense. First, a sensing structure similar to a fingerprint needs to be in effective contact and sliding with the object surface to sense the microstructure of the object surface. Meanwhile, a very sensitive signal conversion mechanism is needed to convert and amplify the weak strain or vibration signal caused during the sliding into an electric signal which can be read.

[0003] At present, the flexible tactile sensor mainly based on two principles, one is piezoelectric type, and the other is contact resistance type. From the structural form, both are used for sensing on the outer surface, and the inner layer is coated with piezoelectric material or conductive material on the microstructure surface of the two films. Then, the two films are assembled to form an interlocking structure of the microstructure of the two layers of films. When the sensor slides over the surface of the object, the surface texture information is detected through the dynamic contact action of the two layers of material coating. From the above structural form, the repeated dynamic friction of the two layers of material coating will cause the wear of the contact point material, which will reduce the performance and reliability of the sensor. In addition, the material coating covering the entire surface affects the transparency of the sensor, and this structural form has the unavoidable disadvantage for some application occasions which require transparency, so the application range has limitations. Finally, the assembly effect of the two films will also affect the stability and consistency of the sensor performance, so the assembly process increases the uncertainty of the process quality, which will have a certain impact on the yield rate in actual production. Therefore, how to solve the problems of difficult sensing and weak signal in the detection of the texture of the surface of an object, and how to prepare a flexible tactile sensor with stable and reliable performance, wide application occasions and simple production process have become a technical bottleneck to be solved.

[0004] In nature, spiders have the ability to sense extremely small deformations, which is due to the crack-like receptors at the joints of the spider legs, which have high sensitivity and response frequency. Inspired by this structure, by introducing this bionic micro-crack structure into the flexible tactile sensor, high sensitivity sensing of micro-surface texture is expected to be achieved. SUMMARY

[0005] In order to overcome the above-mentioned prior art defects, the purpose of the present application is to provide a high-sensitivity crack resistance principle flexible tactile sensor and its manufacturing method, the sensing structure and the conductive material are integrated on a thin film, without assembly, simplifying the process steps, improving the production efficiency; the grid-embedded distribution of the conductive material filling form avoids the wear of the conductive material, the sensor performance is more stable, and the transparency of the sensor is realized.

[0006] In order to achieve the above-mentioned purpose, the technical route adopted by the present application is:

[0007] A high-sensitivity crack resistance principle flexible tactile sensor, comprising a PDMS thin film, the upper surface of the PDMS thin film is a grid-shaped microchannel, and the lower surface is a pyramid structure array; the grid-shaped microchannel on the upper surface is filled with conductive material to form a conductive network, and the conductive network is distributed with microcracks.

[0008] A manufacturing method of a high-sensitivity crack resistance principle flexible tactile sensor, comprising the following steps:

[0009] First step, preparation of embossing mold and surface treatment: the mold comprises an upper mold and a lower mold, both of which are prepared on the surface of a silicon wafer by photolithography and etching process; the upper mold is a square grid-shaped convex structure, and the lower mold is an inverted pyramid conical structure array; the upper mold and the lower mold are surface treated to facilitate demolding after embossing;

[0010] Second step, embossing and demolding: pouring PDMS on the lower mold, pressing the upper mold on the PDMS, degassing in a vacuum box for 10 minutes, then pressing the PDMS into a thin film with a certain thickness, the thickness control is realized by padding PET films with different thicknesses between the upper mold and the lower mold; baking in an oven at 85℃ for 30 minutes to solidify the PDMS, cooling to room temperature, demolding, forming a grid-shaped microchannel on the upper surface of the PDMS thin film and a pyramid conical structure array on the lower surface;

[0011] Third step, PDMS surface treatment: treating the demolded PDMS thin film in a 300W oxygen plasma environment for 90s to make its surface hydrophilic, which is beneficial for conductive material filling;

[0012] Fourth step, filling conductive material: dropping the mixture of carbon nanotubes and silver paste on the upper surface of the PDMS thin film, reciprocating with a scraper, the liquid fills the microchannel under the driving of capillary force, then baking on a hot plate at 60℃ for 5 minutes to wipe off the surface dry film; repeating the above steps of scraping, drying 1-3 times until the conductive material in the grid-shaped microchannel is uniformly and continuously distributed;

[0013] The fifth step is to obtain the tactile sensor after pre-stretching: the PDMS film is pre-stretched for 10-20 times at 5%, micro-cracks are generated in the conductive network formed by the carbon nanotubes and silver, and the two ends are connected to form a tactile sensor;

[0014] The sixth step is to detect the surface texture of the object by the tactile sensor: a constant voltage value is applied to the tactile sensor, when the lower surface is rubbed on the surface of the object with different texture structures, the pyramid structure is deformed to different degrees, the grid-shaped micro-channels are deformed, the conductive network embedded in the grid-shaped micro-channels is opened and closed correspondingly, and the resistance changes accordingly, the current signal in the test process is collected, and then the texture structure and roughness information of the surface of different objects can be distinguished through signal analysis and processing.

[0015] The PDMS is mixed by mixing the PDMS body and the curing agent at a mass ratio of 10:1, stirring for 5 minutes, and removing bubbles in a vacuum box for 5 minutes.

[0016] The carbon nanotube and silver paste mixture is mixed by mixing 10%wt of the multi-walled carbon nanotube water dispersion and silver paste at a mass ratio of 2:1, and magnetically stirring at room temperature for 1 hour.

[0017] The present application has the following advantages:

[0018] The flexible tactile sensor of the present application is based on the micro-crack principle, which greatly improves the sensitivity of the sensor and can effectively detect the surface texture of the object. Meanwhile, the conductive material is embedded in the grid-shaped micro-channels in the structure of the tactile sensor, which avoids the wear of the conductive material, makes the sensor performance more stable, realizes the transparency of the sensor, and widens the application range. The manufacturing method of the present application simplifies the process steps, improves the processing efficiency, and can be produced in large area, cut and attached flexibly. The technical scheme has good application prospect in robot touch, electronic skin and surface nondestructive testing. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a structure diagram of the upper mold of the present application.

[0020] Figure 2 It is a structure diagram of the lower mold of the present application.

[0021] Figure 3 It is a schematic diagram of extruding PDMS by the upper and lower molds of the present application.

[0022] Figure 4 It is a schematic diagram of the PDMS film after demolding, which has a grid-shaped micro-channel on the upper surface and a pyramid structure array on the lower surface.

[0023] Figure 5This is a schematic diagram of the mixture of carbon nanotubes and silver paste coated by the present invention.

[0024] Figure 6 This is a schematic diagram of the conductive network film formed after the dried film of the carbon nanotube and silver paste mixture is wiped off according to the present invention.

[0025] Figure 7 This is a top view schematic diagram of the conductive network film formed after the dried film of the carbon nanotube and silver paste mixture is wiped off according to the present invention.

[0026] Figure 8 This is a top view schematic diagram of the slip sensor formed after pre-stretching to generate microcracks according to the present invention.

[0027] Figure 9 This is a schematic diagram illustrating the detection of the surface texture structure of an object when it slides across the surface. Detailed Implementation

[0028] The manufacturing method of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] A method for manufacturing a flexible slip sensor based on the principle of highly sensitive crack resistivity includes the following steps:

[0030] The first step is the fabrication and surface treatment of the imprinting mold: The mold includes an upper mold 1 and a lower mold 2, both of which are fabricated on the silicon wafer surface using photolithography and etching processes; the upper mold 1 has a square grid-like raised structure, such as... Figure 1 As shown, the lower mold 2 is an array of inverted pyramidal cone structures, as... Figure 2 As shown; after the upper mold 1 and the lower mold 2 are prepared, they are soaked in fluorosilane solution for 6 hours and baked at 170°C for 12 hours to perform low surface energy treatment to prevent damage to the microstructure during demolding;

[0031] The second step, imprinting and demolding: PDMS 3 is poured onto the lower mold 2, and the upper mold 1 presses onto the PDMS 3. The mixture is then degassed in a vacuum chamber for 10 minutes. Pressure is applied to press the PDMS 3 to a certain thickness. Thickness control is achieved by placing PET films 4 of varying thicknesses between the upper mold 1 and the lower mold 2. Figure 3 As shown; PDMS3 was cured in an oven at 85°C for 30 minutes, cooled to room temperature, and demolded to obtain a PDMS film 5 with a mesh-like microchannel upper surface and a pyramidal structure array on the lower surface, as shown. Figure 4 As shown;

[0032] Step 3, PDMS surface treatment: The PDMS film 5 after demolding is treated in a 300W oxygen plasma environment for 50 seconds to make its surface hydrophilic, which is conducive to the filling of conductive materials.

[0033] Fourth step, filling conductive material: drop the mixture of carbon nanotubes and silver paste 6 on the upper surface of the PDMS film 5, and use a scraper 7 to coat the mixture 6, the mixture 6 fills the microchannels of the PDMS film 5 under the action of capillary force, as shown in Figure 5 ; then bake on a hot plate at 60 DEG C for 5 minutes, and wipe off the surface dried film; repeat the above coating and drying steps 1-3 times until the conductive material in the grid-shaped microchannels is uniformly and continuously distributed to form a conductive network 8, as shown in Figure 6 and Figure 7 ; and

[0034] Fifth step, pre-stretching to obtain a tactile sensor: pre-stretch the PDMS film 5 for 10-20 times at 5%, so that the carbon nanotube and silver conductive network 8 embedded in the microchannels produces micro-cracks 9, and wires are connected at both ends of the conductive network 8 to form a tactile sensor 10, as shown in Figure 8 ; and

[0035] Sixth step, the tactile sensor detects the surface texture of an object: a digital source table 11 is used to apply a constant voltage to the tactile sensor 10, when the lower surface of the tactile sensor 10 rubs on the surface of an object 12 with different texture structures, the pyramid-shaped structure deforms to different degrees, causing the deformation of the grid-shaped microchannels, the embedded conductive network 8 in the grid-shaped microchannels will change the opening and closing of the micro-cracks 9, and the resistance will change accordingly, the current signal during the test process is collected by the digital source table 11, and then signal analysis and processing are performed, so that the texture structure and roughness information of the surface of different objects can be distinguished, as shown in Figure 9 .

[0036] The structure size in the above method is: the size W1 of the recessed part of the upper mold 1 is 50-150 microns, the size W2 of the raised part is 2-10 microns, and the recessed depth h1 is 5-20 microns; the size W4 of the pyramid structure opening and the pitch W3 of the lower mold 2 are both 20-50 microns, and the etching depth h2 of the pyramid structure is determined by the size W4 of the opening and is related to the angle formed by the anisotropic wet etching of silicon; the thickness h3 of the imprinted film is 150-400 microns.

[0037] The present application adopts an imprinting process and a coating filling process, the lower sensing microstructure and the upper microchannel are formed at one time, the sensing structure and the conductive material are integrated in a film, and assembly is not required, so that the process steps are simplified and the production efficiency is improved. Meanwhile, the grid-embedded distribution of the conductive material filling form avoids the wear of the conductive material and realizes the transparency of the sensor, so that the sensor performance is more stable and the application range is wider. The present application can be made in a large area and at a low cost, can be cut flexibly, can be attached according to the shape, and can be widely applied in the fields of robot touch, electronic skin, surface nondestructive testing, etc.

Claims

1. A method for manufacturing a flexible tactile sensor of high sensitive crack resistance variable resistance principle, characterized in that, The application discloses a flexible tactile sensor based on a high-sensitivity crack resistance variable resistance principle. The manufacturing method comprises the following steps: In a first step, a stamping mold is prepared and surface treated: the mold comprises an upper mold and a lower mold, both of which are prepared on a silicon wafer surface through a photoetching and etching process; the upper mold is a square grid-shaped convex structure, and the lower mold is an inverted-pyramid-shaped array structure; the upper mold and the lower mold are surface treated to facilitate demolding after stamping; In a second step, stamping and demolding are performed: the PDMS is poured on the lower mold, and the upper mold is pressed on the PDMS; after degassing in a vacuum box for 10 minutes, the PDMS is stamped into a thin film with a certain thickness; the thickness is controlled by placing PET films with different thicknesses between the upper mold and the lower mold; the PDMS is solidified in an oven at 85 DEG C for 30 minutes, and then cooled to room temperature and demolded; a grid-shaped microchannel is formed on the upper surface of the PDMS thin film, and an inverted-pyramid-shaped array structure is formed on the lower surface; In a third step, the PDMS surface is treated: the demolded PDMS thin film is treated in a 300W oxygen plasma environment for 90s to make the surface hydrophilic, which facilitates filling of the conductive material; In a fourth step, the conductive material is filled: a mixture of carbon nanotubes and silver paste is dropped on the upper surface of the PDMS thin film, and a scraper is reciprocally scraped to fill the microchannels under the capillary force driving; then the mixture is dried on a hot plate at 60 DEG C for 5 minutes, and the surface dried film is wiped off; the above steps of scraping and drying are repeated 1-3 times until the conductive material in the grid-shaped microchannels is uniformly and continuously distributed; In a fifth step, a tactile sensor is obtained after pre-stretching: the PDMS thin film is pre-stretched 10-20 times at 5%, so that microcracks are generated in the conductive network formed by the carbon nanotubes and silver, and the tactile sensor is formed by connecting the two ends; In a sixth step, the tactile sensor detects the surface texture of an object: a constant voltage value is applied to the tactile sensor, and when the lower surface is rubbed on the surface of an object with different texture structures, the pyramid-shaped structure is deformed to different degrees, which causes the deformation of the grid-shaped microchannels, the opening and closing changes of the conductive network embedded in the grid-shaped microchannels, and the change of the resistance; the current signal in the test process is collected, and then the texture structure and roughness information of the surface of different objects can be distinguished through signal analysis and processing.

2. The manufacturing method of a flexible slip sensor based on the highly sensitive crack resistive switching principle according to claim 1, characterized in that: In the second step, the PDMS is prepared by mixing a PDMS body and a curing agent at a mass ratio of 10:1, stirring for 5 minutes and degassing in a vacuum box for 5 minutes to remove bubbles.

3. The manufacturing method of a flexible slip sensor based on the highly sensitive crack resistive switching principle according to claim 1, characterized in that: In the fourth step, the carbon nanotube and silver paste mixture is prepared by mixing 10%wt of a multi-walled carbon nanotube water dispersion and silver paste at a mass ratio of 2:1, and magnetically stirring at room temperature for 1 hour.

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