Flexible tactile sensor and method of manufacturing the same

Abstract

The application provides a flexible tactile sensor and a preparation method thereof. The flexible tactile sensor comprises a flexible optical fiber sensing element and a PDMS packaging element. The flexible optical fiber sensing element is packaged in the PDMS packaging element. The flexible optical fiber sensing element is formed with a draw taper part. The draw taper part is provided with a left stress sensing grating, a normal stress sensing grating and a right stress sensing grating. The left stress sensing grating and the right stress sensing grating are respectively arranged on the two sides of the normal stress sensing grating. The draw taper part of the flexible optical fiber sensing element has a small cross-sectional area, and is therefore more sensitive to changes in the local environment when the grating is prepared. This makes the left stress sensing grating, the normal stress sensing grating and the right stress sensing grating have higher sensitivity when monitoring local bending, stress size and other physical quantities, and is suitable for some application scenarios that require high spatial resolution.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sensors, and particularly relates to a flexible tactile sensor and a preparation method thereof. BACKGROUND

[0002] Bionic flexible tactile sensors have the ability to better simulate human tactile perception, and can perceive and quantify various tactile stimuli, including but not limited to stress, hardness and surface texture. This technology enables robots to accurately, quickly and flexibly perceive touch, providing a significant improvement in the perception and response capabilities of robots, and has rapidly developed in recent years.

[0003] In the past decade, flexible tactile sensors based on electrical sensing schemes, such as capacitive, resistive, piezoelectric and triboelectric mechanisms, have been widely studied. These electronic tactile sensors usually simulate the fine tactile biological characteristics of human skin, including the epidermis-dermis interface, sensory receptors, fingerprint patterns and ion stimuli in afferent neurons. Although multi-modal sensing capabilities and other special features, such as self-healing, self-powering, energy harvesting, stimulus visualization and environmental adaptation, have been tried in electronic tactile sensors, they still have some drawbacks, including high manufacturing cost, parasitic effects, circuit complexity and signal crosstalk, which may limit their practical application in robots.

[0004] On the other hand, with the development of femtosecond laser technology, flexible tactile sensors based on optical sensing schemes show great prospects. Flexible optical fibers, as one of the important technologies, have the advantages of small size, strong flexibility, high sensitivity, resistance to electromagnetic interference and easy fabrication. In recent years, domestic laboratories have carried out research on various types of optical fiber tactile sensors, achieving single-parameter detection in stress, strain, sliding, object hardness, and dual-mode detection in stress-temperature, stress-humidity. In addition, for human-computer interaction and physiological parameter detection applications, including gesture recognition and pulse wave detection, have also been thoroughly explored.

[0005] Currently, optical fiber tactile sensors need to balance between sensing range and touch sensitivity. Some designs may perform well in terms of sensitivity, but have a narrow sensing range, while others may have a wider sensing range but lower sensitivity. SUMMARY

[0006] The purpose of the present application is to provide a flexible tactile sensor and a preparation method thereof, to widen the sensing range and improve the sensitivity.

[0007] The first aspect of the present application discloses a flexible tactile sensor, comprising a flexible optical fiber sensing piece and a PDMS encapsulating piece, the flexible optical fiber sensing piece is encapsulated in the PDMS encapsulating piece, the flexible optical fiber sensing piece is formed with a draw taper part, the draw taper part is provided with a left stress-induced grating, a normal stress-induced grating and a right stress-induced grating, and the left stress-induced grating and the right stress-induced grating are respectively arranged on the two sides of the normal stress-induced grating.

[0008] Further, the wavelength of the left stress-induced grating, the normal stress-induced grating and the right stress-induced grating is 1530nm-1550nm.

[0009] Further, the draw taper part is bent and encapsulated in the PDMS encapsulating piece, so as to adapt to the finger curvature.

[0010] Further, the interval between the left stress-induced grating and the normal stress-induced grating is 5mm, and the interval between the right stress-induced grating and the normal stress-induced grating is 5mm.

[0011] Further, the flexible tactile sensor further comprises a finger sleeve wearable on a finger, the PDMS encapsulating piece is fixed to the inner surface of the finger sleeve, so that the normal stress-induced grating can be attached to the finger center, the left stress-induced grating can be attached to the left side of the finger center, and the right stress-induced grating can be attached to the right side of the finger center.

[0012] The second aspect of the present application discloses a preparation method of a flexible tactile sensor, comprising:

[0013] The fiber sensing head is engraved, the left stress-induced grating, the normal stress-induced grating and the right stress-induced grating are engraved on the draw taper part of the fiber sensing head through a femtosecond laser system, wherein the left stress-induced grating and the right stress-induced grating are respectively arranged on the two sides of the normal stress-induced grating.

[0014] The sensor is encapsulated, the fiber sensing head is placed in a PDMS high polymer material, and the edge is cured and trimmed to obtain a flexible tactile sensor with a PDMS encapsulating piece.

[0015] Further, before the fiber sensing head is engraved, the method further comprises:

[0016] The fiber is drawn, the end of the fiber is fixed on a stretching device, the fiber is started to be drawn, the diameter of the fiber is reduced through the process of gradually lengthening, the size change of the draw tapered fiber is ensured to be smooth and uniform, the fiber is heated at the same time of being drawn, the fiber is ensured to maintain a certain temperature at the same time of being drawn, the material is caused to flow and form the draw taper part of the tapered structure, and the middle core diameter of the double taper is 50um.

[0017] Further, the inscription fiber sensing head comprises:

[0018] The fiber is fixed on a high-precision motion platform of the inscription system, and a femtosecond laser system is used to inscribe FBG gratings with a wavelength of 1530nm-1550nm on the taper part at intervals of 5mm to form the left stress-induced grating, the normal stress-induced grating and the right stress-induced grating respectively.

[0019] Further, the sensor package comprises:

[0020] The PDMS base solution and the crosslinking agent are stirred and mixed at a ratio of 10:1;

[0021] The fiber sensing head is positioned in the packaging container, the mixed PDMS solution is poured, and the taper part is fixed in the PDSM packaging member to adapt to the finger curvature after curing.

[0022] After curing, the edges of the PDMS packaging member are trimmed to obtain the flexible tactile sensor.

[0023] Further, after the sensor package, further comprising:

[0024] The finger sleeve is installed, and the packaged flexible tactile sensor is fixed to the inner surface of the finger sleeve, so that the normal stress-induced grating can be attached to the finger center, the left stress-induced grating can be attached to the left side of the finger center, and the right stress-induced grating can be attached to the right side of the finger center.

[0025] The present application has the following advantages:

[0026] The taper part of the flexible fiber sensing member has a small cross-sectional area, so it is more sensitive to changes in the local environment when preparing the grating. This makes the left stress-induced grating, the normal stress-induced grating and the right stress-induced grating have higher sensitivity when monitoring local bending, stress size and other physical quantities, and are suitable for some application scenarios that require high spatial resolution. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a flexible tactile sensor;

[0028] Figure 2 It is a principle schematic diagram of a tactile-deformation measurement system;

[0029] Figure 3 It is a principle schematic diagram of a tactile-force measurement system;

[0030] Figure 4 It is a grating spectrum change graph of 1536nm wavelength-displacement;

[0031] Figure 5Linear fitting curve of grating intensity vs. displacement for 1536 nm wavelength;

[0032] Figure 6 Grating spectrum variation graph for 1542 nm wavelength vs. displacement;

[0033] Figure 7 Linear fitting curve of grating intensity vs. displacement for 1542 nm wavelength;

[0034] Figure 8 Grating spectrum variation graph for 1548 nm wavelength vs. displacement;

[0035] Figure 9 Linear fitting curve of grating intensity vs. displacement for 1548 nm wavelength;

[0036] Figure 10 Grating spectrum variation graph for 1536 nm wavelength vs. force;

[0037] Figure 11 Linear fitting curve of grating intensity vs. force for 1536 nm wavelength;

[0038] Figure 12 Grating spectrum variation graph for 1542 nm wavelength vs. force;

[0039] Figure 13 Linear fitting curve of grating intensity vs. force for 1542 nm wavelength;

[0040] Figure 14 Grating spectrum variation graph for 1548 nm wavelength vs. force;

[0041] Figure 15 Linear fitting curve of grating intensity vs. force for 1548 nm wavelength.

[0042] BRIEF DESCRIPTION OF DRAWINGS

[0043] 10, PDMS package; 20, finger cot; 30, flexible optical fiber sensing member; FBG1, left stress sensing grating; FBG2, normal stress sensing grating; FBG3, right stress sensing grating. DETAILED DESCRIPTION

[0044] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0045] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application; the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance; in addition, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium, or the communication between two components. For those skilled in the art, the specific meaning of the terms in the present application can be understood according to the specific circumstances.

[0046] Referring to Figure 1 The present application discloses a kind of flexible tactile sensor, including flexible optical fiber sensing piece 30 and PDMS package 10, flexible optical fiber sensing piece 30 is encapsulated in PDMS package 10, and flexible optical fiber sensing piece 30 is formed with draw taper part, and left stress sensing grating FBG1, normal stress sensing grating FBG2 and right stress sensing grating FBG3 are equipped on draw taper part, left stress sensing grating FBG1 and right stress sensing grating FBG3 are respectively equipped at both sides of normal stress sensing grating FBG2.

[0047] The draw taper part of flexible optical fiber sensing piece 30 has smaller cross-sectional area, so it is more sensitive to local environmental changes when preparing grating.This makes left stress sensing grating FBG1, normal stress sensing grating FBG2 and right stress sensing grating FBG3 have higher sensitivity when monitoring local bending, stress size and other physical quantities, and are suitable for some application scenarios that require high spatial resolution.

[0048] It should be noted that the left stress sensing grating FBG1, normal stress sensing grating FBG2 and right stress sensing grating FBG3 of the present scheme are all FBG gratings.FBG stands for Fiber Bragg Grating, which is a fiber Bragg grating, i.e.a spatial phase periodic distribution grating formed in the core, and its essence is to form a narrow-band (transmission or reflection) filter or mirror in the core.

[0049] Compared with the traditional fiber grating preparation method, the preparation process of the tapered fiber FBG is relatively simple and can be completed more quickly. The process of writing FBG only needs to be performed locally at the tapering part of the optical fiber. Compared with the preparation of full fiber grating, it has lower optical loss. This is beneficial to reduce the optical loss in signal transmission for application scenarios that require long optical fibers, such as communication systems.

[0050] Specifically, the present scheme adopts a single-mode flexible optical fiber, the middle diameter of the double taper of the tapering part is 50um, and a femtosecond laser system with a wavelength of 1030nm and a power of 0.60mW is used to write FBG with wavelengths of 1536nm, 1542nm and 1548nm respectively at intervals of 5mm. The flexible tactile sensor also includes a finger sleeve 20 that can be worn on the finger, and the PDMS packaging 10 is fixed to the inner surface of the finger sleeve 20, and the tapering part is bent and packaged in the PDMS packaging 10, which is used to adapt to the curvature of the finger, so that the normal stress sensing grating FBG2 can be attached to the finger center, the left stress sensing grating FBG1 can be attached to the left side of the finger center, and the right stress sensing grating FBG3 can be attached to the right side of the finger center, as shown in the structure of Figure 1 The wearable design can meet the application of such sensors in intelligent robot hands and wearable fields.

[0051] The flexible tactile sensor can be worn on the robot finger to measure the relationship between tactile and deformation and the relationship between tactile and force, as shown in Figure 2 Figure 3 The tactile-deformation measurement system includes a computer, a high-precision optical displacement platform, a wideband light source, and the flexible tactile sensor of the present scheme. A flexible contact is installed on the micro-displacement platform to press the sensor without causing damage to the sensor. In this experiment, the three grating strings were bent and tested at room temperature. This part of the experiment is at intervals of 60um, from no contact (0um) to 300um, and each group of data collects 6 data points. The tactile-force measurement system includes a computer, a high-precision optical displacement platform, a wideband light source, and the flexible tactile sensor of the present scheme, a digital pressure gauge, and the flexible tactile sensor is worn on the robot finger. The optical displacement platform is moved to make the digital pressure gauge act on the flexible tactile sensor. In the experiment, the three grating strings were tested under stress at room temperature. In this experiment, the force applied to the sensor is at intervals of 0.01N, from 0.05N to 0.1N, and a total of 6 data points are collected. Figures 4-5 is a graph of the intensity change of the spectrum of the 1536nm wavelength grating with increasing deformation, Figures 6-7 is a graph of the intensity change of the spectrum of the 1542nm wavelength grating with increasing deformation, Figures 8-9 ​Figure 6 is a graph of the intensity variation of the spectrum of the 1548nm grating as the deformation increases. From the experimental results, it can be seen that when the contact is pressed on the grating, the intensity of the reflected spectrum increases as the bending radius increases.

[0052] Figures 10-11 Figure 7 is a graph of the intensity variation of the spectrum of the 1536nm grating as the force increases, Figures 12-13 Figure 8 is a graph of the intensity variation of the spectrum of the 1542nm grating as the force increases, Figures 14-15 Figure 9 is a graph of the intensity variation of the spectrum of the 1548nm grating as the force increases. From the experimental results, it can be seen that, similar to the results in the bending experiment, the intensity of the reflected spectrum gradually increases as the force gradually increases.

[0053] The working principle of the flexible tactile sensor is as follows: when the tapered part of the optical fiber is deformed by a contact object, the periodic structure in the FBG grating changes, causing a shift in the center wavelength. This shift causes modulation of the intensity in the reflected spectrum. By monitoring the intensity variation in the spectrum, the degree of contact force on the tapered part of the optical fiber can be accurately measured.

[0054] The preparation method of the flexible tactile sensor of the present scheme comprises:

[0055] S10, tapering the optical fiber, fixing the end of the optical fiber on a stretching device, starting to stretch the optical fiber, gradually lengthening the process to reduce the diameter, ensuring that the size change of the tapered optical fiber is smooth and uniform, and heating the optical fiber while stretching to ensure that the optical fiber maintains a certain temperature while stretching, prompting the material to flow and form a tapered structure of the tapering part, and the middle core diameter of the double taper is 50um;

[0056] S20, writing the optical fiber sensing head, fixing the optical fiber on a high-precision motion platform of a writing system, using a femtosecond laser system to write FBG gratings with wavelengths of 1530nm-1550nm on the tapering part at intervals of 5mm to form left stress sensing gratings, normal stress sensing gratings and right stress sensing gratings, respectively;

[0057] S30, sensor packaging, stirring and mixing the PDMS base solution and the crosslinking agent according to a ratio of 10:1; positioning the optical fiber sensing head in a packaging container, pouring the mixed PDMS solution, and curing to fix the tapering part in the PDSM packaging piece to adapt to the finger curvature; trimming the edges of the PDMS packaging piece after curing to obtain a flexible tactile sensor;

[0058] S40, installing a finger sleeve, fixing the packaged flexible tactile sensor on the inner surface of the finger sleeve, so that the normal stress sensing gratings can be attached to the finger center, the left stress sensing gratings can be attached to the left side of the finger center, and the right stress sensing gratings can be attached to the right side of the finger center.

[0059] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement, and improvement made in the spirit and principle of the present application shall fall in the protection scope of the present application.

Claims

1. A flexible tactile sensor, characterized by, The flexible tactile sensor comprises a flexible optical fiber sensing member and a PDMS encapsulating member, the flexible optical fiber sensing member is encapsulated in the PDMS encapsulating member, the flexible optical fiber sensing member is formed with a tapering portion, the tapering portion is provided with a left stress-induced grating, a normal stress-induced grating and a right stress-induced grating, and the left stress-induced grating and the right stress-induced grating are respectively arranged on the two sides of the normal stress-induced grating. The tapering portion is bent and encapsulated in the PDMS encapsulating member, so as to be adapted to the finger curvature. The flexible tactile sensor further comprises a finger sleeve which can be worn on the finger, and the PDMS encapsulating member is fixed to the inner surface of the finger sleeve, so that the normal stress-induced grating can be attached to the finger center, the left stress-induced grating can be attached to the left side of the finger center, and the right stress-induced grating can be attached to the right side of the finger center.

2. The flexible tactile sensor of claim 1, wherein, The wavelengths of the left stress-induced grating, the normal stress-induced grating and the right stress-induced grating are 1530nm-1550nm.

3. The flexible tactile sensor of claim 1, wherein, The distance between the left stress-induced grating and the normal stress-induced grating is 5mm, and the distance between the right stress-induced grating and the normal stress-induced grating is 5mm.

4. A method of producing a flexible tactile sensor based on any one of claims 1 to 3, characterized in that, The method comprises the following steps: The fiber sensing head is engraved by a femtosecond laser system, and the left stress-induced grating, the normal stress-induced grating and the right stress-induced grating are engraved on the tapering portion of the fiber sensing head, wherein the left stress-induced grating and the right stress-induced grating are respectively arranged on the two sides of the normal stress-induced grating. The sensor encapsulation is placed in a PDMS high polymer material, and the edge is trimmed after curing to obtain a flexible tactile sensor with a PDMS encapsulating member.

5. The method of claim 4, wherein the flexible tactile sensor is prepared by the steps of: Before the fiber sensing head is engraved, the method further comprises the following steps: The fiber sensing head is fixed on the stretching device, and the fiber is stretched, and the diameter is reduced through the process of gradually lengthening, so as to ensure that the size change of the tapering fiber is smooth and uniform. At the same time of stretching, the fiber is heated to ensure that the fiber maintains a certain temperature while stretching, so as to promote the material flow and form the tapering portion. The middle core diameter of the double taper is 50um.

6. The method of claim 4, wherein the flexible tactile sensor is prepared by the steps of: The fiber sensing head comprises the following steps: The fiber is fixed on the high-precision motion platform of the engraving system, and the FBG grating with a wavelength of 1530nm-1550nm is engraved on the tapering portion in sequence with an interval of 5mm by using the femtosecond laser system, so as to form the left stress-induced grating, the normal stress-induced grating and the right stress-induced grating.

7. The method of claim 4, wherein the flexible tactile sensor is prepared by a process comprising: The sensor encapsulation comprises the following steps: The PDMS base solution and the crosslinking agent are stirred and mixed according to the ratio of 10:

1. The fiber sensing head is positioned in the encapsulation container, the mixed PDMS solution is poured, and the tapering portion is bent and fixed in the PDSM encapsulating member for adapting to the finger curvature after curing. After curing, the edge of the PDMS encapsulating member is trimmed to obtain the flexible tactile sensor.

8. The method of claim 4, wherein the flexible tactile sensor is prepared by a process comprising: After the sensor encapsulation, the method further comprises the following steps: Install the finger sleeve, and fix the encapsulated flexible tactile sensor on the inner surface of the finger sleeve, so that the normal stress sensing grating can be attached to the finger core, the left stress sensing grating can be attached to the left side of the finger core, and the right stress sensing grating can be attached to the right side of the finger core.

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