Three-dimensional force flexible touch sensor and preparation method thereof

Abstract

The invention discloses a three-dimensional force flexible tactile sensor and a preparation method thereof, the three-dimensional force flexible tactile sensor comprises a layered structure, a top electrode layer and a bottom electrode layer, the top electrode layer comprises a second PET substrate and a top copper electrode, the top copper electrode is installed below the second PET substrate, the top copper electrode is a square common electrode, a copper film with the thickness of 0.006 mm is adopted, the side length is 20 mm, and the thickness of the top copper electrode is 20 mm; the top copper electrode is connected with an external lead through a conductive adhesive; the elastic dielectric layer is located below the top electrode layer and is made of an Ecoflex00-30 material, the elastic dielectric layer comprises micro circular truncated cone structures arranged in an array mode, the height of each micro circular truncated cone is 0.9 mm, and the interval between every two micro circular truncated cones is 1 mm; and the bottom electrode layer comprises a first PET substrate and a bottom copper electrode. The sensor has the advantages of high sensitivity, wide temperature range stability, lightness, thinness, easiness in integration and three-dimensional force synchronous decoupling, and is simple in preparation process and low in cost.

Description

Technical Field

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

[0002] Tactile sensors are widely used in robotic perception. Existing capacitive three-dimensional force tactile sensors primarily achieve force detection through electrode structure design, dielectric layer optimization, and packaging processes. Electrode structures include asymmetric arrangements (such as an L-shaped arrangement of a square top electrode and three small square bottom electrodes), coplanar designs (hemispherical contacts + a central common electrode + four peripheral curved excitation electrodes), petal-shaped multi-electrode arrangements (eight independent petal electrodes at the top + a circular common electrode at the bottom), and cross-stacked electrodes (a 2×2 rectangular array of upper and lower electrodes stacked in a cross). The dielectric layer utilizes porous / microstructured dielectrics (such as PDMS micropillar arrays, graphene / PDMS foam, and Ecoflex-carbon nanotube composites) or air-cavity dielectrics (where the dielectric constant is changed by compression of the air layer). The packaging structure utilizes a flexible substrate of PDMS, silicone rubber, or polyimide, with surface designs such as hemispherical contacts, rectangular protrusions, or semicircular grooves. Some utilize a hybrid piezoresistive-capacitive sensing mechanism to enhance performance.

[0003] However, the existing technology has significant defects: First, there is a prominent contradiction between sensitivity and range. The air cavity structure has high sensitivity but the range is usually <15mN. The pore uniformity of porous media is poor and the micro-pillars are prone to deformation and fracture. The consistency of gradient material process is difficult to control; second, the three-dimensional force decoupling capability is insufficient. Most of them require time-sharing measurement of normal and tangential forces. The triangular electrodes have blind spots in the 45° and 135° directions. The coupling interference between the tangential force and the normal spacing changes leads to a decoupling error of >10%; third, the preparation process is complicated. The deviation of multi-layer manual bonding reaches 200-500μm. The planar process is difficult to adapt to curved surfaces (coverage <60%). Traditional photolithography technology limits the electrode size to ≥3mm; fourth, the environmental adaptability is poor. Contact with conductive objects can easily cause 20% signal drift. Temperature and humidity fluctuations lead to sensitivity attenuation (15% attenuation at humidity 25-85%). The strain transmission crosstalk between adjacent units reaches 12% of the true value.

[0004] Therefore, it is necessary to design a three-dimensional force flexible tactile sensor and a preparation method thereof to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and propose a three-dimensional force flexible tactile sensor and its preparation method. The sensor has the advantages of high sensitivity, wide temperature range stability, light weight and easy integration, and three-dimensional force synchronous decoupling, and the preparation process is simple and the cost is low.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A three-dimensional force flexible tactile sensor, comprising a layered structure: Top electrode layer: includes a second PET substrate and a top copper electrode. The top copper electrode is installed below the second PET substrate. The top copper electrode is a square common electrode made of a copper film with a thickness of 0.006 mm and a side length of 20 mm. The top copper electrode is connected to an external lead through a conductive adhesive. Elastic dielectric layer: The elastic dielectric layer is located below the top electrode layer and is made of Ecoflex00-30 material. The elastic dielectric layer comprises an array of micro-cone structures, each of which has a height of 0.9 mm and a spacing of 1 mm. Bottom electrode layer: includes a first PET substrate 1 and a bottom copper electrode. The bottom copper electrode is installed above the first PET substrate. The bottom copper electrode is four independent square electrodes distributed in a cross shape. The bottom copper electrode adopts a copper film with a thickness of 0.006mm. The side length of each electrode is 4.5mm. Each electrode forms an independent capacitor unit with the top electrode. Ecoflex adhesive layer: the top electrode layer, the elastic medium layer and the bottom electrode layer are tightly adhered to each other through the Ecoflex adhesive layer, and the thickness of the Ecoflex adhesive layer is controlled to be 50-100 μm.

[0007] Preferably, the four independent electrodes of the cross-shaped bottom electrode are connected to an external circuit via copper wires with a width of 0.5 mm and a length of 10-20 mm.

[0008] Preferably, the Ecoflex adhesive layer is spin-coated underneath the second PET substrate.

[0009] A method for preparing the three-dimensional force flexible tactile sensor as described above comprises the following steps: S1 electrode layer preparation: The top and bottom electrodes were prepared on an 80μm PET substrate by vacuum evaporation, with the thickness controlled to be 0.006mm±0.0005mm. S2 elastic medium layer molding: A custom mold was created by 3D printing. The mold had a frustum-shaped hole array with a hole diameter consistent with the bottom diameter of the micro-frustum and a 1mm hole spacing. A 50nm-thick PMMA sacrificial layer was spin-coated on the mold surface. Ecoflex components A and B were mixed in a 1:1 ratio and spin-coated at 2000 rpm for 30 seconds to fill the mold holes. After vacuum degassing for 15 minutes and curing at 80°C for 1 hour, the mold was demolded by dissolving the PMMA with acetone, forming an elastic dielectric layer with a micro-frustum height of 0.9mm. S3 overall assembly: The top electrode layer, copper side facing downward, was aligned with the elastic dielectric layer and laminated using the Ecoflex adhesive layer. Curing was then performed at 80°C for 1 hour. After curing, the top electrode layer was aligned and encapsulated with the upper and lower PET substrates. The sensor was cured again at 80°C for 30 minutes to complete the fabrication.

[0010] Preferably, a performance calibration step is further included: within a temperature range of 30-90° C., by applying standard normal force and tangential force, recording the capacitance drift and establishing a temperature compensation model.

[0011] Preferably, the normal force is calculated by detecting the synchronous capacitance increments of the four capacitor units, and the tangential force is calculated by calculating the magnitude and direction of the tangential force through the differential capacitance change.

[0012] The present invention has the following beneficial effects: Compared with existing technologies, the cross-shaped four-electrode layout is combined with a micro-cone structured dielectric layer to accurately map the tangential force direction through the change of electrode area and detect the normal force through the compression deformation of the dielectric layer, thus achieving synchronous decoupling of three-dimensional forces. Compared with existing technologies, the micro-cone array elastic dielectric layer concentrates the pressure on the top of the cone, significantly enhancing the deformation response. The sensitivity reaches 3.47kPa-1 in the ultra-low pressure range of 0-50Pa, and maintains a step-by-step stable response in the wide range of 0-80kPa. Compared with existing technologies, by setting up a PET substrate + Ecoflex dielectric layer and optimizing the material system, the capacitance drift is less than 1% in a wide temperature range of 30-90°C, and only a single temperature calibration is required.

[0013] Compared with existing technologies, 3D printed molds replace traditional photolithography, eliminating the multi-layer alignment process, and reducing manufacturing costs to 1 / 5 of traditional processes, making them suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic structural diagram of a three-dimensional force flexible tactile sensor proposed by the present invention; Figure 2 Schematic diagram of the structure of the second PET substrate; Figure 3 Schematic diagram of the structure of the first PET substrate; Figure 4 This is the principle diagram of capacitance change; Figure 5 Schematic diagram of the lower structure of the second PET substrate.

[0015] In the figure: 1 first PET substrate, 2 elastic medium layer, 3 Ecoflex adhesive layer, 4 second PET substrate, 5 bottom copper electrode, 6 top copper electrode. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0017] Reference Figure 1-Figure 5 , a three-dimensional force flexible tactile sensor, including a layered structure: Top electrode layer: includes a second PET substrate 4 and a top copper electrode 6. The top copper electrode 6 is installed below the second PET substrate 4. The top copper electrode 6 is a square common electrode made of a copper film with a thickness of 0.006 mm and a side length of 20 mm. The top copper electrode 6 is connected to an external lead through a conductive adhesive. Elastic dielectric layer 2: Elastic dielectric layer 2 is located below the top electrode layer and is made of Ecoflex00-30 material. Elastic dielectric layer 2 contains an array of micro-cone structures, each micro-cone is 0.9 mm high and spaced 1 mm apart. Bottom electrode layer: includes the first PET substrate 1 and the bottom copper electrode 5. The bottom copper electrode 5 is installed above the first PET substrate 1. The bottom copper electrode 5 is four independent square electrodes distributed in a cross shape. It uses a copper film with a thickness of 0.006mm. The side length of a single electrode is 4.5mm. They form independent capacitor units with the top electrode ( ); Ecoflex adhesive layer 3: The top electrode layer, elastic medium layer and bottom electrode layer are tightly bonded together by the Ecoflex adhesive layer. The thickness of the Ecoflex adhesive layer 3 is controlled at 50-100 μm. The Ecoflex adhesive layer is spin-coated on the bottom of the second PET substrate 4, and the overall thickness is ≤0.5 mm.

[0018] Among them, the four independent electrodes of the cross-shaped bottom electrode are connected to the external circuit through copper leads with a width of 0.5mm. The lead length is 10-20mm and is arranged in a radial pattern to avoid signal crosstalk.

[0019] Among them, the roughness of the bonding interface between the top electrode layer and the elastic medium layer is ≤1μm, and the adhesive layer is formed by spin coating Ecoflex prepolymer (4000rpm, 20s) to ensure that the force transmission efficiency is greater than 95%.

[0020] A method for preparing the above-mentioned three-dimensional force flexible tactile sensor is characterized by comprising the following steps: S1 electrode layer preparation: On an 80μm PET substrate, a top electrode (20mm×20mm copper film) and a bottom electrode (four 4.5mm×4.5mm copper electrodes arranged in a cross shape) were deposited by vacuum evaporation. The evaporation thickness was controlled to 0.006mm±0.0005mm. Before vacuum evaporation, the PET electromechanical device was ultrasonically cleaned for 15 minutes and then dried. S2 elastic medium layer molding: A custom mold was created by 3D printing. The mold had a frustum-shaped hole array with a hole diameter consistent with the bottom diameter of the micro-frustum and a 1mm hole spacing. A 50nm-thick PMMA sacrificial layer was spin-coated on the mold surface. Ecoflex components A and B were mixed in a 1:1 ratio and spin-coated at 2000 rpm for 30 seconds to fill the mold holes. After vacuum degassing for 15 minutes and curing at 80°C for 1 hour, the mold was demolded by dissolving the PMMA with acetone, forming an elastic dielectric layer with a micro-frustum height of 0.9mm. S3 overall assembly: The copper surface of the top electrode layer was aligned with the elastic medium layer facing down, pressed with the Ecoflex adhesive layer, and cured at 80°C for 1 hour. After curing, it was aligned with the bottom electrode layer, encapsulated with the upper and lower PET substrates, and cured again at 80°C for 30 minutes to complete the sensor preparation.

[0021] It also includes a performance calibration step: within the temperature range of 30-90°C, by applying standard normal force (10Pa) and tangential force (2N), recording the capacitance drift and establishing a temperature compensation model to ensure that the initial capacitance calibration error is less than 1%.

[0022] The normal force is calculated by detecting the synchronous capacitance increment of the four capacitor units. The capacitance increment is ΔC1=ΔC2=ΔC3=ΔC4. The normal force calculation formula is: ,in The tangential force is calculated by calculating the magnitude and direction of the tangential force through the differential capacitance change. The capacitance change is ΔC2+ΔC4-ΔC1-ΔC3. The tangential force calculation formula is ,in .

[0023] Normal force sensitivity: In the range of 0-50Pa, the capacitance change is measured by TH2810B LCR bridge (1kHz, 1V), with a sensitivity of , linearity error <2%.

[0024] Tangential force sensitivity: Under the action of 0-5N tangential force, the difference of the four capacitor units changes significantly, and the sensitivity , direction recognition error is less than 3°.

[0025] Temperature stability: In an environment of 30-90°C, with a normal force of 10Pa applied, the capacitance drift is less than 1% and the sensitivity fluctuation is less than 5%, meeting the temperature requirements of industrial scenarios.

[0026] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A three-dimensional force flexible tactile sensor, characterized in that: Includes a hierarchical structure: Top electrode layer: comprising a second PET substrate (4) and a top copper electrode (6), wherein the top copper electrode (6) is mounted below the second PET substrate (4), the top copper electrode (6) is a square common electrode, made of a copper film with a thickness of 0.006 mm and a side length of 20 mm, and the top copper electrode (6) is connected to an external lead through a conductive adhesive; Elastic medium layer (2): the elastic medium layer (2) is located below the top electrode layer and is made of Ecoflex00-30 material. The elastic medium layer (2) comprises an array of micro-cone structures, each of which has a height of 0.9 mm and a spacing of 1 mm. Bottom electrode layer: comprising a first PET substrate (1) and a bottom copper electrode (5), wherein the bottom copper electrode (5) is mounted above the first PET substrate (1), and the bottom copper electrode (5) is four independent square electrodes distributed in a cross shape, using a copper film with a thickness of 0.006 mm, and a single electrode with a side length of 4.5 mm, and each electrode forms an independent capacitor unit with the top electrode; Ecoflex adhesive layer (3): the top electrode layer, the elastic medium layer and the bottom electrode layer are tightly adhered to each other through the Ecoflex adhesive layer (3), and the thickness of the Ecoflex adhesive layer (3) is controlled to be 50-100 μm.

2. The three-dimensional force flexible tactile sensor according to claim 1, characterized in that: The four independent electrodes of the cross-shaped bottom electrode are connected to an external circuit via copper leads with a width of 0.5 mm and a length of 10-20 mm.

3. The three-dimensional force flexible tactile sensor according to claim 1, characterized in that: The Ecoflex adhesive layer (3) is spin-coated underneath the second PET substrate (4).

4. A method for preparing a three-dimensional force flexible tactile sensor according to claims 1-3, characterized in that: The following steps are involved: S1 electrode layer preparation: The top and bottom electrodes were prepared on an 80μm PET substrate by vacuum evaporation, with the thickness controlled to be 0.006mm±0.0005mm. S2 elastic medium layer molding: A custom mold was created by 3D printing. The mold had a frustum-shaped hole array with a hole diameter consistent with the bottom diameter of the micro-frustum and a 1mm hole spacing. A 50nm-thick PMMA sacrificial layer was spin-coated on the mold surface. Ecoflex components A and B were mixed in a 1:1 ratio and spin-coated at 2000 rpm for 30 seconds to fill the mold holes. After vacuum degassing for 15 minutes and curing at 80°C for 1 hour, the mold was demolded by dissolving the PMMA with acetone, forming an elastic dielectric layer with a micro-frustum height of 0.9mm. S3 overall assembly: The copper surface of the top electrode layer was aligned with the elastic medium layer facing down, pressed with the Ecoflex adhesive layer, and cured at 80°C for 1 hour. After curing, it was aligned with the bottom electrode layer, encapsulated with the upper and lower PET substrates, and cured again at 80°C for 30 minutes to complete the sensor preparation.

5. The method for preparing a three-dimensional force flexible tactile sensor according to claim 4, characterized in that: It also includes a performance calibration step: by applying standard normal and tangential forces within the temperature range of 30-90°C, the capacitance drift is recorded and a temperature compensation model is established.

6. The method for preparing a three-dimensional force flexible tactile sensor according to claim 5, characterized in that: The normal force is calculated by detecting the synchronous capacitance increments of the four capacitor units, and the tangential force is calculated by calculating the magnitude and direction of the tangential force through the differential capacitance change.

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