A capacitive flexible tactile sensor based on suction cup structure

Abstract

The present invention discloses a capacitive flexible tactile sensor based on a suction cup structure. The dielectric layer is located between an upper electrode layer and a lower electrode layer. The dielectric layer includes a plurality of micro-pillars extending from the upper electrode layer toward the lower electrode layer. The plurality of micro-pillars are spaced between the upper and lower electrode layers, and each micro-pillar has a cavity extending from one end to the middle. The capacitive flexible tactile sensor based on the suction cup structure, which is optimized and designed as described above, forms a suction cup microstructure in the dielectric layer. Compared to traditional tactile sensors, under the same force conditions, it has advantages such as lower hysteresis and better repeatability. Furthermore, based on the suction cup microstructure, the sensor can be easily expanded into arrays of different sizes. The dielectric layer is easily deformed by bending, resulting in a shorter response time, better stability, and greater flexibility.

Description

Technical Field

[0001] The present invention relates to the technical field of tactile sensors, and in particular to a capacitive flexible tactile sensor based on a suction cup structure. Background Art

[0002] With the widespread application of flexible tactile sensors in intelligent robots, electronic skin, and other fields, tactile perception, as a crucial means of human interaction with the external world, has been actively researched. The widespread industrial application of intelligent robots, coupled with the high-precision requirements of specialized industries, has led to even higher demands on their manufacturing. As a key component of intelligent robots, tactile sensors have garnered significant attention from researchers both domestically and internationally, aiming to improve their sensing performance, achieving, for example, shorter response / recovery times, higher sensitivity, and lower hysteresis.

[0003] Many different types of tactile sensors have been reported recently, such as capacitive, resistive, and piezoelectric. Since capacitive sensors rely on their geometric changes to detect pressure, and capacitive tactile sensors have the advantages of good dynamic response, simple structure, low cost, and temperature insensitivity, they have become the subject of active research, resulting in great application potential in wearable electronic devices, soft robots, human physiological signal detection, auxiliary medical diagnosis, prostheses, etc. However, it is difficult to design a sensor with a unique microstructure and good performance.

[0004] At present, there are several aspects of capacitive tactile sensors at home and abroad that need to be improved:

[0005] 1) Existing capacitive tactile sensors are difficult to have fast response time and low hysteresis. For example, a flexible capacitive pressure sensor based on a microarray polydimethylsiloxane dielectric layer is known. The sensor consists of a typical sandwich structure consisting of a polydimethylsiloxane base sheet and a microarray polydimethylsiloxane dielectric layer. A polydimethylsiloxane flexible substrate with silver-plated nanowires is used as the upper and lower electrode materials, and the response time is as low as 100ms. In addition, a bionic design of a flexible tactile sensor is known. The sensor is based on a bionic hierarchical array structure of silver-plated nanowires. It consists of micro-domes and micro-cones. The former is adsorbed from the through-hole array by vacuum adsorption, and the latter is adsorbed by replicating zebrafish leaves. The response time is as low as 78ms.

[0006] 2) While pursuing high sensitivity, capacitive touch weakens the adhesion between the sensor medium layer and the electrode layer, resulting in the risk of falling off under high force conditions, which prevents tactile sensors from being widely used. For example, a known ionization-type flexible tactile sensor adopts a multi-level fillable structure, which is composed of unstable raised microstructures (represented as protrusions) of different heights. These microstructures are easy to bend and fill grooves when compressed. The grooves achieve additional compressibility by accommodating the compressed protrusions, but there is still the disadvantage of weak adhesion between the medium layer and the electrode layer. In addition, a known bio-inspired cilia array is used as the medium layer of a flexible capacitive tactile sensor. Although it has high sensitivity and a wide detection range, and the tapered cilia can improve the compressibility of the medium layer, the medium layer and the electrode layer are prone to slipping under high force conditions, thereby destroying the sensor structure. Summary of the Invention

[0007] In order to solve the technical problems existing in the background technology, the present invention proposes a capacitive flexible tactile sensor based on a suction cup structure.

[0008] The present invention proposes a capacitive flexible tactile sensor based on a suction cup structure, comprising: an upper electrode layer, a dielectric layer and a lower electrode layer;

[0009] The dielectric layer is located between the upper electrode layer and the lower electrode layer. The dielectric layer includes a plurality of microcolumns extending from the upper electrode layer toward the lower electrode layer. The plurality of microcolumns are arranged at intervals between the upper electrode layer and the lower electrode layer. Each microcolumn has a cavity extending from one end to the middle.

[0010] Preferably, the microcolumn adopts a cylindrical structure, and the inner diameter of the cavity gradually decreases from the upper electrode layer to the lower electrode layer or from the lower electrode layer to the upper electrode layer.

[0011] Preferably, the plurality of microcolumns are evenly distributed between the upper electrode layer and the lower electrode layer.

[0012] Preferably, the diameter of the microcolumns is D, the distance between two adjacent microcolumns is L, and D=L.

[0013] Preferably, the radius of the small end of the cavity is r and the radius of the large end is R, and r:R=3:4.

[0014] Preferably, the dielectric layer further includes a dielectric upper base layer and a dielectric lower base layer, the dielectric upper base layer is located at the bottom of the upper electrode layer and connected to the upper electrode layer, and the dielectric lower base layer is located at the top of the lower electrode layer and connected to the lower electrode layer, and a plurality of microcolumns are located between the dielectric upper base layer and the dielectric lower base layer and their two ends are respectively connected to the dielectric upper base layer and the dielectric lower base layer.

[0015] Preferably, the upper electrode layer includes an upper substrate and an upper electrode, the upper electrode is located above the dielectric layer, and the upper substrate is located above the upper electrode layer.

[0016] Preferably, the lower electrode layer includes a lower substrate and a lower electrode, the lower electrode is located below the dielectric layer, and the lower substrate is located below the lower electrode layer.

[0017] Preferably, the upper substrate and / or the lower substrate is made of silicone rubber or polydimethylsiloxane.

[0018] Preferably, the upper electrode and the lower electrode are made of commercial conductive silver paste or flexible conductive cloth.

[0019] Preferably, the dielectric layer is made of polydimethylsiloxane or hydrogel.

[0020] In the present invention, the proposed capacitive flexible tactile sensor based on a suction cup structure has a dielectric layer located between an upper electrode layer and a lower electrode layer. The dielectric layer includes a plurality of micro-pillars extending from the upper electrode layer toward the lower electrode layer. The plurality of micro-pillars are spaced apart between the upper electrode layer and the lower electrode layer, and each micro-pillar has a cavity extending from one end toward the middle. The capacitive flexible tactile sensor based on a suction cup structure, which is optimized and designed as described above, forms a suction cup microstructure in the dielectric layer. Compared to traditional tactile sensors, under the same force conditions, it has advantages such as lower hysteresis and better repeatability. Furthermore, based on the suction cup microstructure, the sensor can be easily expanded into arrays of different sizes. The dielectric layer is easily bent and deformed, resulting in a shorter response time, better stability, and greater flexibility.

[0021] The present invention also provides a method for preparing a capacitive flexible tactile sensor based on a suction cup structure, comprising the following steps:

[0022] A mold for the micro-pillar array of the dielectric layer is made using 3D printing technology. PDMS is spin-coated on the mold using a spin coating process and allowed to stand. The mold is then dried and cured before being peeled off to form the dielectric layer.

[0023] Conductive silver paste is evenly spin-coated on both sides of the dielectric layer, and then dried to pre-solidify the conductive silver paste to form a flexible electrode. Then, a layer of PDMS is spin-coated on the surface of the flexible electrode, followed by drying and solidification to form a flexible substrate. Finally, the tactile sensor is constructed using a layer-by-layer self-assembly process.

[0024] In the present invention, the method for preparing a capacitive flexible tactile sensor based on a suction cup structure proposed has a technical effect similar to that of the above-mentioned capacitive flexible tactile sensor based on a suction cup structure, so it will not be described in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a structural schematic diagram of a capacitive flexible tactile sensor based on a suction cup structure according to an embodiment of the present invention.

[0026] Figure 2A three-dimensional schematic diagram of an embodiment of the present invention.

[0027] Figure 3 A schematic diagram of the flexibility of an array according to an embodiment of the present invention.

[0028] Figure 4 Schematic diagram of two-dimensional stress distribution according to an embodiment of the present invention.

[0029] Figure 5 FIG2 shows the relationship between the signal output and the loading force of different microstructure tactile sensors in some embodiments of the present invention.

[0030] Figure 6 FIG4 is the relationship between the tactile sensor signal output and the loading force for different ratios of the upper diameter of the micro-pillars to the spacing in some embodiments of the present invention.

[0031] Figure 7 FIG4 is the relationship between the tactile sensor signal output and the loading force for different ratios of the small end radius to the large end radius of the micro-column cavity in some embodiments of the present invention.

[0032] Figure 8 1 is a test curve diagram of the response / recovery time of the tactile sensor in some embodiments of the present invention.

[0033] Figure 9 Graph showing sensitivity of tactile sensors in some embodiments of the present invention.

[0034] Figure 10 is the hysteresis of the tactile sensor in some embodiments of the present invention.

[0035] Figure 11 Graph showing a repeatability test response curve of a tactile sensor in some embodiments of the present invention.

[0036] Figure 12 Schematic diagram of the preparation process of a tactile sensor in some embodiments of the present invention. DETAILED DESCRIPTION

[0037] like Figures 1 to 12 As shown, Figure 1 FIG1 is a structural diagram of a capacitive flexible tactile sensor based on a suction cup structure according to an embodiment of the present invention. Figure 2 is a three-dimensional schematic diagram of an embodiment of the present invention, Figure 3 This is a flexible schematic diagram of an array according to an embodiment of the present invention. Figure 4 This is a schematic diagram of two-dimensional stress distribution according to an embodiment of the present invention. Figure 5 The relationship between the signal output and the loading force of different microstructure tactile sensors in some embodiments of the present invention is shown in FIG. Figure 6The relationship between the tactile sensor signal output and the loading force for different ratios of the upper diameter of the micro-pillars to the spacing in some embodiments of the present invention is shown in FIG. Figure 7 The relationship between the tactile sensor signal output and the loading force for different ratios of the micro-column cavity small end radius to the large end radius in some embodiments of the present invention is shown in FIG. Figure 8 1 is a test curve diagram of the response / recovery time of the tactile sensor in some embodiments of the present invention. Figure 9 is a sensitivity curve diagram of a tactile sensor in some embodiments of the present invention, Figure 10 is the hysteresis of the tactile sensor in some embodiments of the present invention, Figure 11 is a repeatability test response curve diagram of a tactile sensor in some embodiments of the present invention, Figure 12 Schematic diagram of the preparation process of a tactile sensor in some embodiments of the present invention.

[0038] Reference Figure 1-3 The present invention proposes a capacitive flexible tactile sensor based on a suction cup structure, comprising: an upper electrode layer 1, a dielectric layer 3 and a lower electrode layer 2;

[0039] The dielectric layer 3 is located between the upper electrode layer 1 and the lower electrode layer 2. The dielectric layer 3 includes a plurality of microcolumns 31 extending from the upper electrode layer 1 toward the lower electrode layer 2. The plurality of microcolumns 31 are arranged at intervals between the upper electrode layer 1 and the lower electrode layer 2. Each microcolumn 31 has a cavity 311 extending from one end to the middle.

[0040] In this embodiment, the proposed capacitive flexible tactile sensor based on a suction cup structure has a dielectric layer located between an upper electrode layer and a lower electrode layer. The dielectric layer includes a plurality of micro-pillars extending from the upper electrode layer toward the lower electrode layer. The plurality of micro-pillars are spaced apart between the upper and lower electrode layers, and each micro-pillar has a cavity extending from one end toward the middle. The capacitive flexible tactile sensor based on a suction cup structure, which is optimized and designed as described above, forms a suction cup microstructure in the dielectric layer. Compared to traditional tactile sensors, under the same force conditions, it has advantages such as lower hysteresis and better repeatability. Furthermore, based on the suction cup microstructure, the sensor can be easily expanded into arrays of different sizes. The dielectric layer is easily bent and deformed, resulting in a shorter response time, better stability, and greater flexibility.

[0041] In a specific embodiment, the micropillar 31 has a cylindrical structure, and the inner diameter of the cavity 311 gradually decreases from the upper electrode layer 1 to the lower electrode layer 2, or from the lower electrode layer 2 to the upper electrode layer 1. The micropillar is designed as a cylindrical structure, and the cavity inside is designed as a truncated cone structure. The sidewall thickness of the cavity gradually decreases along the axis, resulting in an axial gradient distribution of the deformation capacity of the cavity sidewall. Under different stress conditions, the deformation area of ​​the dielectric layer changes, thereby ensuring detection sensitivity and resilience under different stress conditions.

[0042] In the specific design of the dielectric layer, dielectric layer 3 also includes a dielectric upper base layer 32 and a dielectric lower base layer 33. Upper base layer 32 is located at the bottom of and connected to upper electrode layer 1, while lower base layer 33 is located at the top of and connected to lower electrode layer 2. Multiple micropillars 31 are located between upper base layer 32 and lower base layer 33, with their ends connected to upper base layer 32 and lower base layer 33, respectively. In actual use, the ends of the micropillars are connected to the upper and lower base layers, respectively, to prevent poor contact with the upper and lower base layers caused by long-term deformation of the micropillars.

[0043] In the selection of the material of the dielectric layer, the dielectric layer 3 is made of polydimethylsiloxane or hydrogel.

[0044] In a specific design of the electrode layer, the upper electrode layer 1 includes an upper substrate 11 and an upper electrode 12 . The upper electrode 12 is located above the dielectric layer 3 , and the upper substrate 11 is located above the upper electrode layer 1 .

[0045] Correspondingly, the lower electrode layer 2 includes a lower substrate 21 and a lower electrode 22 . The lower electrode 22 is located below the dielectric layer 3 , and the lower substrate 21 is located below the lower electrode layer 2 .

[0046] In the material selection of the electrode layer, the upper substrate 11 and the lower substrate 21 are made of silicone rubber or polydimethylsiloxane, and the upper electrode 12 and the lower electrode 22 are made of commercial conductive silver paste or flexible conductive cloth.

[0047] In order to make the capacitive flexible tactile sensor based on the suction cup structure of this embodiment exhibit better sensing performance, this embodiment also optimizes the specific arrangement and design parameters of the dielectric layer.

[0048] In the specific arrangement of the dielectric layer, multiple micropillars 31 are evenly distributed between the upper electrode layer 1 and the lower electrode layer 2. The diameter of each micropillar 31 is D, and the spacing between two adjacent micropillars 31 is L, where D = L. The radius of the small end of the cavity 311 is r, and the radius of the large end is R, where r:R = 3:4.

[0049] The results of a two-dimensional finite element simulation of a tactile sensor according to one embodiment of the present invention based on COMSOL are as follows: Figure 4 The two-dimensional stress distribution diagrams of an embodiment of the present invention are respectively shown. The simulation images verify the deformation of the sensor dielectric layer in three different stages after pressure application. The sensor dielectric layer is prone to rapid deformation under low pressure and drastically deforms under high pressure. This is mainly attributed to the use of a bionic octopus suction cup structure in the dielectric layer.

[0050] Reference Figure 5-12,The tactile sensor with a 3×3 micro-hollow cylindrical unit structure is taken as an example below to explain in detail the specific detection structure of the sensor designed with corresponding parameters.

[0051] First, in this embodiment, a tactile sensor is prepared by the following method. Figure 12 This figure shows the fabrication process for the tactile sensor. Using 3D printing technology, PLA (polylactic acid) was used to create the dielectric layer and other components of the mold for the suction cup octopus structure. PDMS (polydimethylsiloxane) was spin-coated onto the recessed mold and allowed to stand for 30 minutes. The PDMS was cured in a 50°C drying oven for 4 hours before being peeled off to form a complete dielectric layer. Commercially available conductive silver paste was evenly spin-coated on the dielectric layer to form the flexible electrodes. After pre-curing the conductive silver paste in a 50°C drying oven for 1 hour, a layer of PDMS was spin-coated on the electrode surface to form the flexible substrate, which was then cured in a 50°C drying oven for 3 hours. A layer of PDMS was spin-coated on the other side of the electrode layer to form the dielectric base layer, which was then cured in a drying oven for 3 hours. Finally, the components were assembled using a layer-by-layer self-assembly process to create the capacitive tactile sensor with the suction cup structure.

[0052] The specific structural design of the tactile sensor fabricated using the above-described fabrication method is as follows: The dielectric layer micro-hollow cylinders 31 are 5 mm tall; the upper and lower substrates 11 and 21 are 0.4 mm thick, with lengths and widths of 24 mm each; the upper and lower substrates 32 and 33 are both 0.2 mm thick; the upper and lower electrodes 12 and 22 are both 0.1 mm thick, with lengths and widths of 24 mm each; and the diameter (R) of the dielectric layer micro-hollow cylinders remains unchanged at 5 mm. By designing and optimizing the ratio of the dielectric layer micro-cylinder upper diameter (D) to the spacing (D:L) and the ratio of the micro-cylinder cavity's small end radius r to its large end radius R (r:R), the optimal structural parameters of the capacitive flexible tactile sensor are obtained, thereby improving sensor performance.

[0053] Figure 5 The relationship between the signal output and the loading force of different microstructured tactile sensors is shown. While keeping other structural parameters of the tactile sensor unchanged, only the structure of the dielectric layer was adjusted. Experimental results show that the micro-cylindrical sensor with an octopus suction cup structure has better performance than the block and cylindrical structures.

[0054] Figure 6The relationship between the tactile sensor's signal output and the applied force for different ratios of the upper diameter to spacing of the micro-cylinders in the dielectric layer. While keeping other structural parameters of the tactile sensor unchanged, only the ratio of the upper diameter to spacing of the micro-hollow cylinders in the dielectric layer was adjusted. Experimental results show that the ratio of the upper diameter to spacing of the micro-hollow cylinders in the dielectric layer significantly affects the sensor's output performance, and the tactile sensor achieves optimal sensing performance when the ratio is 1:1.

[0055] Figure 7 The relationship between the tactile sensor's signal output and the applied force for different ratios of the micro-pillar's small-end radius to its large-end radius is shown in Figure 2. While keeping other structural parameters of the tactile sensor unchanged, only the ratio of the cone's upper to lower diameter is varied. Experimental results show that varying the cone's upper to lower diameter ratio significantly affects sensor output performance. Furthermore, when the ratio of the micro-pillar's small-end radius r to its large-end radius R is 3:4, the relative capacitance of the tactile sensor changes the most, resulting in optimal sensor performance.

[0056] Through multiple groups of comparative tests, combined with the sensitivity and detection limit of the sensor, the structural parameters of the capacitive flexible tactile sensor with a bionic octopus suction cup structure were determined: the ratio of the upper end diameter D of the micro-pillar to the spacing L is 1:1, and the ratio of the small end radius r and the large end radius R of the micro-pillar cavity is 3:4. The tactile sensor exhibits better sensing performance.

[0057] Figure 8 The following curves show the response / recovery time of the tactile sensor. When subjected to a force of 28 kPa, the sensor's response time is 40 ms, demonstrating a fast response, meaning the sensor's relative capacitance changes from a minimum to a maximum. When the tactile sensor is unloaded at a pressure of 28 kPa, the relative capacitance changes from a maximum to a minimum. This experimental data demonstrates that the tactile sensor, thanks to its bionic octopus suction cup structure, exhibits excellent response / recovery time.

[0058] Figure 9 This is the sensitivity curve of the tactile sensor. In the low pressure range (<5kPa), the sensor sensitivity reaches 0.6kPa -1 In the medium pressure range (5-60kPa), the sensor sensitivity reaches 0.1kPa -1 In the high pressure range (60-500kPa), the sensor sensitivity reaches 0.027kPa -1 .

[0059] Figure 10 The hysteresis of the tactile sensor was tested in the range of 0-500 kPa. The loading / unloading curves show that the sensor has a small hysteresis error.

[0060] Figure 11 The following is a response curve for the tactile sensor's repeatability test. The test involved 6000 dynamic cycles of loading and unloading at a pressure of 16 kPa. The experimental results show that the relative capacitance change remains stable under long-term cyclic pressure. The three insets show magnified waveforms of six cycles at different numbers of cycles. The waveform amplitude and shape remain similar across the different numbers of cycles, demonstrating the tactile sensor's excellent stability and durability.

[0061] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A capacitive flexible tactile sensor based on a suction cup structure, characterized in that: include: An upper electrode layer (1), a dielectric layer (3) and a lower electrode layer (2); The dielectric layer (3) is located between the upper electrode layer (1) and the lower electrode layer (2), and the dielectric layer (3) includes a plurality of microcolumns (31) extending from the upper electrode layer (1) toward the lower electrode layer (2). The plurality of microcolumns (31) are arranged at intervals between the upper electrode layer (1) and the lower electrode layer (2), and each microcolumn (31) has a cavity (311) extending from one end toward the middle. The microcolumn (31) adopts a cylindrical structure, and the inner diameter of the cavity (311) gradually decreases from the upper electrode layer (1) to the lower electrode layer (2) or from the lower electrode layer (2) to the upper electrode layer (1); The small end radius of the cavity (311) is r and the large end radius is R, and r:R=3:

4.

2. The capacitive flexible tactile sensor based on the suction cup structure according to claim 1, characterized in that: A plurality of microcolumns (31) are evenly distributed between the upper electrode layer (1) and the lower electrode layer (2).

3. The capacitive flexible tactile sensor based on the suction cup structure according to claim 2, characterized in that: The diameter of the microcolumns (31) is D, and the distance between two adjacent microcolumns (31) is L, where D=L.

4. The capacitive flexible tactile sensor based on the suction cup structure according to claim 1, characterized in that: The dielectric layer (3) further includes a dielectric upper base layer (32) and a dielectric lower base layer (33), wherein the dielectric upper base layer (32) is located at the bottom of the upper electrode layer (1) and is connected to the upper electrode layer (1), and the dielectric lower base layer (33) is located at the top of the lower electrode layer (2) and is connected to the lower electrode layer (2), and the plurality of microcolumns (31) are located between the dielectric upper base layer (32) and the dielectric lower base layer (33), and are connected at both ends to the dielectric upper base layer (32) and the dielectric lower base layer (33), respectively.

5. The capacitive flexible tactile sensor based on the suction cup structure according to claim 1, characterized in that: The upper electrode layer (1) comprises an upper substrate (11) and an upper electrode (12), wherein the upper electrode (12) is located above the dielectric layer (3), and the upper substrate (11) is located above the upper electrode layer (1); The lower electrode layer (2) comprises a lower substrate (21) and a lower electrode (22), the lower electrode (22) is located below the dielectric layer (3), and the lower substrate (21) is located below the lower electrode layer (2).

6. The capacitive flexible tactile sensor based on the suction cup structure according to claim 5, characterized in that: The upper substrate (11) and / or the lower substrate (21) are made of silicone rubber or polydimethylsiloxane; The upper electrode (12) and the lower electrode (22) are made of commercial conductive silver glue or flexible conductive cloth.

7. The capacitive flexible tactile sensor based on a suction cup structure according to claim 1, characterized in that: The dielectric layer (3) is made of polydimethylsiloxane or hydrogel.

8. A method for preparing a capacitive flexible tactile sensor based on a suction cup structure according to any one of claims 1 to 7, characterized in that: The following steps are involved: A mold for the micro-pillar array of the dielectric layer is made using 3D printing technology. PDMS is spin-coated on the mold using a spin coating process and allowed to stand. The mold is then dried and cured before being peeled off to form a dielectric layer. Conductive silver paste is evenly spin-coated on both sides of the dielectric layer, and then dried to pre-solidify the conductive silver paste to form a flexible electrode. Then, a layer of PDMS is spin-coated on the surface of the flexible electrode, followed by drying and solidification to form a flexible substrate. Finally, the tactile sensor is constructed using a layer-by-layer self-assembly process.

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