Tactile sensor with multi-stage dome structure, preparation method and braille recognition equipment

Abstract

The invention belongs to the technical field of sensing, and particularly relates to a touch sensor with a multi-stage dome structure, a preparation method of the touch sensor and braille recognition equipment. The tactile pressure sensor comprises a substrate and at least three dome structure units which are arranged on the substrate and are of different-size hemispherical structures, all the dome structure units are arranged in a gradient size mode to form a multi-stage dome structure, and the multi-stage dome structure is arranged in a central symmetry mode, a diagonal symmetry mode or an axial symmetry mode with the central dome structure unit as the center. And the radius of each dome structure unit is 200 [mu] m to 500 [mu] m. According to the gradient design of the multi-stage dome structure, stress distribution is more uniform, local stress concentration is avoided, the anti-fatigue performance of the structure is improved, the service life of the structure is prolonged, high sensitivity and smooth response transition are achieved through a degree size arrangement mode, the linear working range of the sensor is widened from 1N-5N to 0.1 N-20N, and the linear working range of the sensor is widened from 1N-5N to 0.1 N-20N. And dual optimization of the measuring range and the sensitivity is realized.

Description

Technical Field

[0001] This invention belongs to the field of sensing technology, specifically relating to a tactile sensor with a multi-level dome structure and its preparation method, as well as a Braille recognition device. Background Technology

[0002] Traditional Braille learning primarily relies on paper Braille books and periodicals. However, these media are not only expensive to produce but also have long update cycles, making it difficult to meet the thirst for new knowledge among visually impaired individuals. For example, the production cost of a typical Braille textbook is about 10 times that of a regular printed book, and its content often lags behind the times. Mechanical dot displays, another commonly used Braille learning tool, also have many drawbacks: they are bulky and inconvenient to carry, severely limiting the ability of visually impaired individuals to learn anytime, anywhere; furthermore, limited by technological capabilities, mechanical dot displays have limited sensitivity and response speed, failing to accurately represent the subtle features of Braille, significantly impacting learning efficiency.

[0003] In recent years, groundbreaking advancements have been made in cutting-edge technologies such as biomimetic synaptic devices and pressure sensors. These technological achievements provide solid technical support for designing Braille tactile sensors that can simulate human sensory functions and overcome existing limitations. They also point to new directions for improving learning conditions for visually impaired individuals and promoting the development of Braille education. Braille is a core tool for visually impaired individuals to obtain information. Traditional Braille recognition relies on manual feature extraction, which suffers from low efficiency and poor accuracy. With the development of flexible electronics technology, intelligent Braille recognition systems based on flexible pressure sensors have become a research hotspot.

[0004] Existing sensors have low sensitivity and struggle to capture subtle deformation differences in Braille dots, requiring users to apply significant pressure to perceive the characters. This not only increases hand fatigue but also easily leads to recognition errors due to uneven force. The pressure range is mostly concentrated in a narrow range of 1N to 5N, which cannot accommodate the varying pressure levels of different users, nor can it handle the occasional large pressures encountered in daily use, such as the impact of rapid touches. This often results in "overload failure" or "no response to light touches." Summary of the Invention

[0005] The purpose of this invention is to provide a tactile sensor with a multi-level dome structure and its fabrication method, as well as a Braille recognition device. The multi-level dome structure is formed by arranging at least three hemispherical dome structural units in a gradient size arrangement. This gradient design allows for more uniform stress distribution, avoiding localized stress concentration and thus improving the structure's fatigue resistance and service life. The gradient size arrangement also achieves high sensitivity and a smooth response transition, with a sensitivity of 0.4V / N to 1.5V / N, accurately capturing pressure changes corresponding to a Braille dot height difference of 0.1mm to 0.5mm. The multi-level structural design formed by the gradient size arrangement expands the sensor's linear operating range from 1N to 5N to 0.1N to 20N, achieving dual optimization of measurement range and sensitivity, covering all scenarios from light touch to forceful pressing.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0007] The first objective of this invention is to provide a tactile sensor with a multi-level dome structure. The tactile pressure sensor includes a substrate and at least three dome structure units of different sizes arranged on the substrate. All dome structure units are arranged in a gradient size manner to form a multi-level dome structure. The central dome structure unit in the multi-level dome structure has the largest radius, and the dome structure units surrounding it gradually decrease in size in a gradient manner, forming a size gradient characteristic, so that the stress is evenly distributed and the response is smoothly transitioned, and the tactile signal is converted into a pressure signal. The multi-level dome structure is arranged in a centrally symmetrical, diagonally symmetrical, or axially symmetrical manner with respect to the central dome structure unit. The radius of each dome structure unit is 200um to 500um.

[0008] Furthermore, the dome structure unit includes a first dome structure unit, a second dome structure unit, and a third dome structure unit. The radius of the first dome structure unit is 400um to 500um, the radius of the second dome structure unit is 300um to 400um, and the radius of the third dome structure unit is 200um to 300um.

[0009] Furthermore, the distance between the center points of adjacent dome structural units is 1mm to 1.5mm.

[0010] Furthermore, each dome structure unit includes an upper electrode layer and a lower electrode layer arranged opposite to each other, with a piezoelectric thin film disposed between the upper electrode layer and the lower electrode layer. The piezoelectric thin film and the electrode are integrated to form a micro / nano structure.

[0011] Furthermore, both the upper and lower electrode layers are made of conductive metals, and the piezoelectric film is made of vinylidene fluoride-trifluoroethylene copolymer.

[0012] Furthermore, the thickness of the upper electrode layer is 50 nm to 100 nm, the thickness of the lower electrode layer is 50 nm to 100 nm, and the thickness of the piezoelectric film is 28 μm to 50 μm.

[0013] Furthermore, the thickness of the substrate is 100um to 150um.

[0014] A second objective of this invention is to provide a method for fabricating a tactile sensor with a multi-level dome structure, comprising the following steps: S1. Using polydimethylsiloxane solution as raw material, spin coating is applied to a mold and cured to obtain the substrate.

[0015] S2. Under a protective gas atmosphere, a conductive metal is sputtered onto the substrate by magnetron sputtering to obtain the lower electrode layer.

[0016] S3. Spin-coat a solution of vinylidene fluoride-trifluoroethylene copolymer onto the lower electrode layer and cure it to obtain a piezoelectric film.

[0017] S4. After spin-coating a buffer layer onto the piezoelectric thin film, a conductive metal is vacuum-deposited, and after annealing, an upper electrode layer is obtained; after connecting the electrode wires, it is packaged to obtain a tactile pressure sensor.

[0018] Furthermore, the buffer layer is a polydimethylsiloxane film with a thickness of 30µm to 50µm.

[0019] A third objective of this invention is to provide a Braille recognition device, including the aforementioned tactile sensor with a multi-level dome structure.

[0020] Compared with the prior art, the present invention has the following advantages: The tactile pressure sensor provided by this invention comprises at least three dome-shaped structural units of different hemispherical sizes on a substrate. All dome-shaped structural units are arranged in a gradient size manner to form a multi-level dome structure. The central dome-shaped structural unit in the multi-level dome structure has the largest radius, and the sizes of the surrounding dome-shaped structural units gradually decrease in a gradient manner, forming a size gradient characteristic. This ensures uniform stress distribution and smooth response transition, converting tactile signals into pressure signals. Since the at least three dome-shaped structural units of different hemispherical sizes have different sensitivities and linear ranges, the gradient design can make the stress distribution more uniform, avoid local stress concentration, and thus improve the fatigue resistance and service life of the structure. Also, through the gradient size arrangement, the response curve under 10kPa to 100kPa pressure exhibits a "smooth transition characteristic," achieving high sensitivity and smooth response transition. This solves the pain points of stress concentration and narrow range in single-level structures. Its sensitivity can reach 0.4V / N to 1.5V / N, and it can accurately capture the pressure change corresponding to the height difference of 0.1mm to 0.5mm Braille bumps. By using a multi-level structural design with gradient dimensions, the linear operating range of the sensor is expanded from 1N to 5N to 0.1N to 20N, achieving dual optimization of measurement range and sensitivity, covering all scenarios from light touch to forceful pressing.

[0021] This invention uses dome structural units with radii of 400um to 500um to enhance the "pressure concentration effect" by utilizing larger deformation, resulting in higher sensitivity. Dome structural units with radii of 200um to 300um can withstand greater pressure through high structural stiffness, avoiding "overload failure" and thus widening the linear range.

[0022] The tactile sensor provided by this invention utilizes the piezoelectric effect. The sensor collects the pressure distribution signal when a fingertip presses on the raised dots of Braille. This signal can be directly mapped to multi-dimensional features such as "dot position (unit corresponding to peak voltage), pressure intensity (voltage amplitude), and sliding speed (voltage change rate)." The signal is converted into multi-dimensional feature data (including pressure values, peak pressure, and pressure change rate of each sensing unit). By rationally adjusting the gradient parameters, the dynamic response characteristics of the sensor can be optimized, ensuring good linearity across different pressure ranges and avoiding signal saturation or distortion problems caused by excessive pressure in traditional structures. Combined with a random forest classifier, the accuracy of Braille recognition can be improved. The sensor exhibits good stability and can accommodate the pressing habits of different users. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a tactile sensor with a multi-level dome structure according to Embodiment 1 of the present invention.

[0024] Figure 2This is a flowchart illustrating the composition of dome structure units of different sizes of hemispherical structures in Embodiment 1 of the present invention.

[0025] Figure 3 This is a flowchart of the fabrication of a tactile sensor according to Embodiment 1 of the present invention.

[0026] Figure 4 This is a graph showing the changes of dome structure units of different sizes under pressures ranging from 10 kPa to 100 kPa in Embodiment 1 of the present invention.

[0027] Figure 5 This is a voltage waveform diagram of the output of the tactile sensor of the present invention under a pressure of 8N.

[0028] Figure 6 This is a flowchart of the random forest classifier algorithm of the present invention.

[0029] Figure 7 This is a diagram showing the prediction results of the Braille characters in this invention.

[0030] Figure 8 This invention relates to four types of Braille based on tactile sensors.

[0031] Figure 9 for Figure 7 This invention presents voltage waveforms corresponding to four types of Braille patterns generated based on a tactile sensor. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0034] Existing Braille tactile sensors employ a relatively simple planar thin-film structure. However, these structures lack effective stress concentration and deformation amplification mechanisms when pressed, resulting in low overall deformation. The difficulty in capturing subtle deformation differences in Braille dots necessitates users applying significant pressure to perceive characters. However, excessive pressure can damage the sensor due to overcompression of the planar structure. The pressure range is largely confined to a narrow range of 1N to 5N, failing to accommodate varying user pressure levels and struggling to handle occasional large pressures from rapid touches, often resulting in "overload failure" or "no response to light touches." Researchers have attempted to improve performance through material substitution, such as using materials with higher intrinsic piezoresistive coefficients, but the limitations of the planar structure have yielded unsatisfactory results and significantly increased costs.

[0035] Based on this, the present invention improves the sensitivity and measurement range of the sensor through the design of a dome structure. However, although a single-stage dome structure can effectively enhance the sensor sensitivity, during the stress process, the stress distribution often concentrates at the top or edge of the structure, which can easily cause local overload. This not only reduces the structural stability but may also induce nonlinear response, affecting measurement accuracy. Therefore, a multi-stage dome structure is formed by arranging multiple hemispherical dome structural units in a gradient size manner. The gradient design can make the stress distribution more uniform, avoid local stress concentration, thereby improving the fatigue resistance and service life of the structure. The gradient size arrangement also achieves a smooth transition between high sensitivity and response. Specifically:

[0036] On one hand, the present invention provides a tactile sensor with a multi-level dome structure. The tactile pressure sensor includes a substrate and at least three dome structure units of different sizes of hemispherical structures disposed on the substrate. All dome structure units are arranged in a gradient size manner to form a multi-level dome structure. The radius of the central dome structure unit in the multi-level dome structure is the largest, and the size of the surrounding dome structure units gradually decreases in a gradient manner, forming a size gradient characteristic, so that the stress is evenly distributed and the response is smoothly transitioned, and the tactile signal is converted into a pressure signal. The multi-level dome structure is arranged in a centrally symmetrical, diagonally symmetrical, or axially symmetrical manner with the central dome structure unit. The radius of each dome structure unit is 200um to 500um.

[0037] In this invention, since at least three dome structure units with different hemispherical structures have different sensitivities and linear ranges, the dome structure unit with a radius of 400um to 500um uses a larger deformation to enhance the "pressure concentration effect" and has higher sensitivity, while the dome structure unit with a radius of 200um to 300um can withstand greater pressure through high structural stiffness, avoid "overload failure", and can broaden the linear range. A multi-level dome structure is formed by arranging multiple hemispherical dome units in a gradient size pattern. The central dome unit has the largest radius, while the surrounding units gradually decrease in size. This gradient design ensures more uniform stress distribution, avoids localized stress concentration, and improves the structure's fatigue resistance and lifespan. The gradient size arrangement also results in a smooth transition in the response curve under pressures ranging from 10kPa to 100kPa, achieving high sensitivity and a smooth response transition. This addresses the pain points of stress concentration and narrow measurement range in single-level structures, achieving a sensitivity of 0.4V / N to 1.5V / N, accurately capturing pressure changes corresponding to height differences of 0.1mm to 0.5mm Braille bumps. This multi-level structural design, formed by the gradient size pattern, expands the sensor's linear operating range from 1N to 5N to 0.1N to 20N, achieving dual optimization of measurement range and sensitivity, covering all scenarios from light touches to forceful presses.

[0038] In this invention, the tactile sensor is a sensor fabricated using the piezoelectric effect. The sensor collects the pressure distribution signal when the fingertip presses on the Braille dots. This signal can be directly mapped to multi-dimensional features such as "dot position (unit corresponding to peak voltage), pressure intensity (voltage amplitude), and sliding speed (voltage change rate)". The signal is converted into multi-dimensional feature data (including pressure value, peak pressure, and pressure change rate of each sensing unit). By reasonably adjusting the gradient parameters, the dynamic response characteristics of the sensor can be optimized, ensuring that the sensor maintains good linearity across different pressure ranges and avoiding signal saturation or distortion problems caused by excessive pressure in traditional structures. Combined with a random forest classifier, the accuracy of Braille recognition can be improved; the sensor has good stability and can accommodate the pressing habits of different users.

[0039] In this invention, through finite element analysis and testing of dome structure units with radii of 200µm to 500µm and multi-level dome structures, a targeted optimization strategy is proposed: if it is necessary to expand the linear measurement range of the sensor, the number of small-sized dome structure units can be increased and the multi-level structure can be designed with gradients to achieve uniform stress distribution and smooth response transition by utilizing the size gradient characteristics; if higher sensitivity is desired, more large-sized dome units can be introduced into the structure to enhance the pressure concentration effect and improve the electrical signal conversion efficiency of the sensor.

[0040] In some embodiments, the dome structure unit includes a first dome structure unit, a second dome structure unit, and a third dome structure unit, wherein the radius of the first dome structure unit is 400um to 500um, the radius of the second dome structure unit is 300um to 400um, and the radius of the third dome structure unit is 200um to 300um.

[0041] In some embodiments, the distance between the center points of adjacent dome structural units is 1 mm to 1.5 mm.

[0042] In some embodiments, each dome structure unit includes an upper electrode layer and a lower electrode layer disposed opposite to each other, a piezoelectric thin film is disposed between the upper electrode layer and the lower electrode layer, and the piezoelectric thin film and the electrode are integrated to form a micro / nano structure.

[0043] In some embodiments, both the upper and lower electrode layers are made of conductive metals, and the piezoelectric film is made of vinylidene fluoride-trifluoroethylene copolymer. As a preferred embodiment of the invention, the upper electrode layer is gold, and the lower electrode layer is copper.

[0044] On the other hand, the present invention provides a method for fabricating a tactile sensor with a multi-level dome structure, comprising the following steps: S1. Using polydimethylsiloxane solution as raw material, spin coating is applied to a mold and cured to obtain the substrate.

[0045] The mold is a dome-shaped structure unit, fabricated using acrylic. Polydimethylsiloxane (PDMS) and a curing agent are mixed at a mass ratio of 10:1 and stirred until a PDMS solution is formed. This solution is then poured into the mold and spin-coated at 300-800 rpm for 30-60 seconds. The mold is then placed in a vacuum dryer and evacuated for 20-40 minutes to eliminate air bubbles. After the PDMS is fully cured, it is peeled off to obtain a dome-shaped substrate. The substrate thickness is 100-150 μm, and the thickness of the dome within the substrate includes the dome radius.

[0046] S2. Under a protective gas atmosphere, a conductive metal is sputtered onto the substrate by magnetron sputtering to obtain the lower electrode layer.

[0047] Before magnetron sputtering, the substrate is cleaned for 15 minutes. A high-purity copper target (commonly 99.99% purity) is selected to avoid impurities (such as oxygen and iron) affecting the conductivity or structure of the copper film. High-purity argon gas is introduced at a flow rate of 30 sccm, the sputtering power is 50W to 500W, and the sputtering time is 10 minutes. The thickness of the lower electrode layer is 50nm to 100nm.

[0048] S3. Spin-coat a solution of vinylidene fluoride-trifluoroethylene copolymer onto the lower electrode layer and dry it to obtain a piezoelectric film.

[0049] In this process, 1 g of vinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE) was dissolved in 9.5 mL of dimethylformamide (DMF) solution (10 wt%). The mixture was magnetically stirred at 60 °C for 2 h to obtain a PVDF-TrFE solution. The prepared PVDF-TrFE solution was spin-coated onto the lower electrode layer. After each spin-coating, the layer was dried at 80 °C for 15 min. A total of 5 spin-coatings were performed to obtain a piezoelectric film. The thickness of the piezoelectric film ranged from 28 μm to 50 μm.

[0050] S4. After spin-coating a buffer layer onto the piezoelectric thin film, a conductive metal is vacuum-deposited, and after annealing, an upper electrode layer is obtained with a thickness of 40-60 nm. After connecting the electrode wires, the film is packaged to obtain a tactile pressure sensor.

[0051] In this process, a polydimethylsiloxane film with a thickness of 30µm to 50µm is spin-coated onto the upper surface of the piezoelectric film as a buffer layer. Gold electrodes are deposited by vacuum evaporation and annealed at 130°C for 1 hour to obtain the upper electrode layer. Copper foil is selected as the material, cut to a suitable size, and then firmly attached to the upper and lower surfaces of the copper-plated piezoelectric film with PI tape. The upper and lower electrodes are led out, and shielding wires are welded. The prepared sensor is then encapsulated with medical tape to obtain a tactile pressure sensor.

[0052] The following specific examples will provide further explanation.

[0053] Example 1 A tactile sensor with a multi-level dome structure, such as Figure 1 As shown, the tactile pressure sensor includes a base 1 and multiple dome structure units of different sizes of hemispherical structures disposed on the base 1. The dome structure units include a first dome structure unit 2, a second dome structure unit 3, and a third dome structure unit 4. The radius of the first dome structure unit 2 is 450 μm, the radius of the second dome structure unit 3 is 350 μm, the radius of the third dome structure unit 4 is 250 μm, and the distance between the center points of adjacent dome structure units is 1 mm.

[0054] like Figure 2As shown, the multi-level dome structure is arranged in a gradient of three rows and three columns on the base, with the first dome structure unit 2, the second dome structure unit 3, and the third dome structure unit 4. The radius of the most central dome structure unit is the largest, which is the first dome structure unit 2. The second dome structure unit 3 and the third dome structure unit gradually decrease in size around the first dome structure unit 2. Specifically, the first and third rows are arranged in a gradient of the second dome structure unit 3, the first dome structure unit 2, and the second dome structure unit 3, while the second row is arranged in a gradient of the first dome structure unit 2, the third dome structure unit 4, and the first dome structure unit 2. The multi-level dome structure is centrally symmetrical with respect to the central dome structure unit.

[0055] The above-mentioned method for fabricating a tactile sensor with a multi-level dome structure, such as... Figure 3 As shown, it includes the following steps: S1. A dome-shaped mold was fabricated using acrylic processing. Polydimethylsiloxane and a curing agent were mixed at a mass ratio of 10:1 and stirred until a homogeneous polydimethylsiloxane solution was formed. This solution was then poured into the mold and spin-coated at 500 rpm for 30 seconds. Subsequently, the mold was placed in a vacuum dryer and evacuated for 30 minutes to eliminate air bubbles in the mixture. After the PDMS was completely cured, it was peeled off to obtain a dome-shaped substrate with a thickness of 100 μm.

[0056] S2. After ultrasonically cleaning the substrate for 15 minutes, magnetron sputtering is performed. A high-purity copper target (usually 99.99% purity) is selected as the target material. High-purity argon gas is introduced at a flow rate of 30 sccm, the sputtering power is 200W, and the sputtering time is 10 minutes to obtain the lower electrode layer with a thickness of 50 nm.

[0057] S3. Dissolve 1g of vinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE) in 9.5mL of dimethylformamide (DMF) solution at a mass ratio of 10wt%. Stir the mixture magnetically at 60℃ for 2h to obtain a PVDF-TrFE solution. Spin-coat the prepared PVDF-TrFE solution onto the lower electrode layer. After each spin-coating, dry at 80℃ for 15min. Spin-coat a total of 5 times to obtain a piezoelectric film with a thickness of 25µm.

[0058] S4. Spin-coat a polydimethylsiloxane film with a thickness of 30 μm onto the upper surface of the piezoelectric film as a buffer layer. Vacuum evaporation is used to deposit gold electrodes to obtain the upper electrode layer with a thickness of 50 nm. This forms the precursor of the tactile pressure sensor. The precursor is annealed at 130°C for 1 hour. Copper foil is then selected as the material, cut to a suitable size, and firmly attached to the surfaces of the upper and lower electrodes with PI tape. The upper and lower electrodes are led out, and shielding wires are welded. The prepared sensor is encapsulated with medical tape to obtain the tactile pressure sensor.

[0059] Figure 4 This is a graph showing the changes in different sized dome structure units of Embodiment 1 of the present invention under pressures ranging from 10 kPa to 100 kPa. Figure 4 The figures shown are the changes under pressures of 10 kPa to 100 kPa for the first, second, and third dome structure units, respectively. This illustrates that the tactile sensor of the large-size dome structure unit can produce a greater degree of thin-film deformation when subjected to the same contact force, that is, it can output a higher amplitude voltage signal under the same force conditions. Under the same pressure, the deformation of the small-size dome structure is smaller than that of the large-size dome structure, so its sensitivity is lower.

[0060] To investigate the piezoelectric response characteristics of the sensor, a precision piezoelectric testing system was built, including a charge amplifier, a DC power supply, an oscilloscope, a pressure gauge, and a computer. During testing, a press applied different external forces to the sensor, and the pressure detection module simultaneously displayed the applied forces. The dynamic charge generated by the sensor was converted into a voltage signal by the charge amplifier, which was then transmitted to the computer via the oscilloscope. The signal acquisition software collected and recorded the voltage waveform in real time. Figure 5 This is a voltage waveform diagram of the output of the tactile sensor of the present invention under a pressure of 8N. (See diagram for example.) Figure 5 As shown, after five consecutive measurements, the output voltage waveform and peak value were basically consistent, indicating that the sensor has good stability.

[0061] The algorithm uses sensors to collect pressure distribution signals when fingertips press Braille dots, converting the voltage changes of different Braille characters into multi-dimensional feature data (including pressure values, peak pressure, and pressure change rates of each sensing unit). The raw data is then preprocessed to remove noise and standardize feature scales. Key features strongly correlated with the Braille dot matrix structure (such as pressure peaks corresponding to dot positions and pressure differences between adjacent sensing units) are extracted through feature selection. The preprocessed feature dataset is then divided into training and testing sets. A random forest classifier is trained on the training set—multiple different subsets are generated from the original training set using sampling with replacement. A decision tree is built for each subset, and each tree selects the optimal split point from randomly selected features when splitting nodes. After training, the test set is input into the model, allowing all decision trees to predict Braille character features and output category results. The classification result is determined by majority voting. Simultaneously, the model accuracy is evaluated and parameters (such as the number of decision trees and the feature selection ratio) are optimized using the test set until the model can stably distinguish different Braille characters. The flowchart of the random forest classifier algorithm is shown below. Figure 6As shown, this algorithm, as a classic ensemble learning algorithm, effectively improves the prediction accuracy and generalization performance of the model by constructing multiple decision tree models and integrating their prediction results. Voltage waveform data of different characters are input into the algorithm and divided into training and test sets. Each waveform has 30 training and 30 test sets.

[0062] Figure 7 This is a diagram showing the predicted Braille characters of this invention. (Example) Figure 7 As shown, the accuracy rates for characters b, m, and p are 29 / 30, and the accuracy rate for character f is 29 / 30. The overall accuracy rate reaches 98.33%, indicating that the model can distinguish different Braille characters.

[0063] Figure 8 This invention relates to four types of Braille based on tactile sensors. Figure 9 for Figure 7 This invention presents voltage waveforms corresponding to four types of Braille patterns generated based on a tactile sensor. For example... Figure 8 and Figure 9 As shown, when the sensor is fixed on the index finger and slid across the Braille character with the same force, a voltage waveform will be output. Different waveforms indicate that the sensor can recognize different Braille characters.

[0064] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0065] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A tactile sensor with a multi-level dome structure, characterized in that, The tactile pressure sensor includes a substrate and at least three dome structure units of different sizes arranged on the substrate. All dome structure units are arranged in a gradient size manner to form a multi-level dome structure. The central dome structure unit in the multi-level dome structure has the largest radius, and the dome structure units around it gradually decrease in size in a gradient manner, forming a size gradient characteristic, so that the stress is evenly distributed and the response is smoothly transitioned, converting the tactile signal into a pressure signal. The multi-level dome structure is arranged in a centrally symmetrical, diagonally symmetrical, or axially symmetrical manner with the central dome structure unit. The radius of each dome structure unit is 200um to 500um.

2. The tactile sensor with a multi-level dome structure according to claim 1, characterized in that, The dome structure unit includes a first dome structure unit, a second dome structure unit, and a third dome structure unit. The radius of the first dome structure unit is 400um to 500um, the radius of the second dome structure unit is 300um to 400um, and the radius of the third dome structure unit is 200um to 300um.

3. The tactile sensor with a multi-level dome structure according to claim 1, characterized in that, The distance between the center points of adjacent dome structural units is 1mm to 1.5mm.

4. The tactile sensor with a multi-level dome structure according to claim 1, characterized in that, Each dome structure unit includes an upper electrode layer and a lower electrode layer arranged opposite each other, with a piezoelectric thin film disposed between the upper and lower electrode layers. The piezoelectric thin film and the electrode are integrated to form a micro-nano structure.

5. The tactile sensor with a multi-level dome structure according to claim 4, characterized in that, Both the upper and lower electrode layers are made of conductive metals, while the piezoelectric film is made of vinylidene fluoride-trifluoroethylene copolymer.

6. The tactile sensor with a multi-level dome structure according to claim 4, characterized in that, The thickness of the upper electrode layer is 50 nm to 100 nm, the thickness of the lower electrode layer is 50 nm to 100 nm, and the thickness of the piezoelectric film is 28 μm to 50 μm.

7. The tactile sensor with a multi-level dome structure according to claim 1, characterized in that, The thickness of the substrate is 100um to 150um.

8. A method for fabricating a tactile sensor with a multi-level dome structure as described in any one of claims 1 to 7, characterized in that, Includes the following steps: A substrate is obtained by spin-coating a polydimethylsiloxane solution onto a mold and then curing it. Under a protective gas atmosphere, a conductive metal is sputtered onto a substrate by magnetron sputtering to obtain a lower electrode layer; A solution of vinylidene fluoride-trifluoroethylene copolymer is spin-coated onto the lower electrode layer and cured to obtain a piezoelectric film. After spin-coating a buffer layer onto a piezoelectric thin film, a conductive metal is vacuum-deposited, and then annealed to obtain an upper electrode layer. After connecting electrode wires, the film is packaged to obtain a tactile pressure sensor.

9. The method for fabricating a tactile sensor with a multi-level dome structure according to claim 8, characterized in that, The buffer layer is a polydimethylsiloxane film with a thickness of 30um to 50um.

10. A Braille recognition device, characterized in that, Including the tactile sensor with a multi-level dome structure as described in any one of claims 1 to 7.

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