Light-driven and sensing integrated flexible joint based on photothermal effect and its optical path system

Abstract

The present invention discloses a flexible joint with integrated optical drive and sensing based on the photothermal effect and its optical path system. The flexible joint comprises a multimode optical fiber and a photothermal conversion elastomer. The photothermal conversion elastomer is in the shape of an arc joint and contains a material for photothermal conversion. The multimode optical fiber is eccentrically embedded in the photothermal conversion elastomer. The core of the multimode optical fiber is engraved with a fiber Bragg grating, and the midpoint of the fiber Bragg grating is aligned with the midpoint of the flexible joint. When the incident light power of the multimode optical fiber increases, the photothermal conversion elastomer bends in a direction with decreasing curvature, and the reflection spectrum signal of the fiber Bragg grating reflects the changing angle of the photothermal conversion elastomer. The present invention utilizes a fiber Bragg grating to integrate sensing and driving functions. It has the advantages of high integration, low energy consumption, small size, light weight, and anti-interference, and is convenient for application in soft robotics, in vivo surgery, high-radiation, flammable and explosive environments, and the like.

Description

Technical Field

[0001] The present invention relates to the field of flexible robots, and in particular to a light-driven, sensing-integrated flexible joint and an optical path system thereof. Background Art

[0002] In the field of flexible robots, most flexible actuators only have actuation functions, lack real-time perception feedback, and have single functions. The additional installation of perception equipment will make the structure complicated, increase the volume, and reduce reliability.

[0003] Existing flexible robots are mostly driven by pneumatic or hydraulic methods, requiring large and bulky power sources. This leads to high energy consumption and poor flexibility. The lifespan of the flexible cylinder is severely limited due to frequent expansion and contraction, and hydraulic oil leaks can easily cause environmental pollution. Pneumatic equipment is also prone to malfunctions such as air leaks due to overuse.

[0004] For some flexible joints that use reduced graphene oxide as a deformable material to generate thermal drive and utilize its conductivity to integrate a sensing network, their sensing network adopts electrical principles and is exposed on the outer layer of the body. They are susceptible to adverse effects of the working environment, have poor anti-interference capabilities, suffer from large power loss caused by resistance, and have electric heat affecting control accuracy, making them susceptible to damage.

[0005] Currently available flexible robots include components for sensing, actuation, computing, power storage, and communication embedded within soft materials. These components are complex, and most achieve continuous flexible motion by embedding rigid joints within the soft material. Others use tensile fibers or fluid elastomers as artificial tendons. These limitations stem from the limited functionality of each component, resulting in complex structures, low reliability, and high costs. Summary of the Invention

[0006] The main purpose of the present invention is to provide a light-driven and sensing integrated flexible joint based on photothermal effect and its optical path system, which can realize the design of a highly integrated drive-sensing integrated light-driven flexible joint and complete the drive-sensing integrated joint movement with a streamlined structure.

[0007] The technical solution adopted in the present invention is:

[0008] Provided is a light-driven, sensing-integrated flexible joint based on the photothermal effect, comprising a multimode optical fiber and a photothermal conversion elastomer, wherein the photothermal conversion elastomer is in the shape of an arc joint and contains a material for photothermal conversion. The multimode optical fiber is eccentrically embedded in the photothermal conversion elastomer.

[0009] A fiber Bragg grating is engraved on the core of the multimode optical fiber, and the midpoint of the fiber Bragg grating is flush with the midpoint of the flexible joint;

[0010] When the incident light power of the multimode optical fiber increases, the photothermal conversion elastomer will bend in the direction of decreasing curvature, and the reflection spectrum signal of the fiber Bragg grating reflects the changing angle of the photothermal conversion elastomer.

[0011] Following the above technical solution, the multimode optical fiber is embedded in a position close to the large radius side of the arc-shaped joint of the photothermal conversion elastomer.

[0012] Following the above technical solution, the material used for photothermal conversion is gold nanoparticles, carbon nanotubes or graphene oxide powder with photothermal effect.

[0013] According to the above technical solution, the reflection peak wavelength range of the fiber Bragg grating is 1550-1630 nm, the length is 1-15 mm, and the reflectivity is at least 90%.

[0014] Following the above technical solution, the multimode optical fiber is in an eccentric state inside the photothermal conversion elastomer, and the eccentricity ranges from 0 to 375 μm. The actuation effect of the flexible joint becomes better as the eccentricity increases.

[0015] Following the above technical solution, the material of the photothermal conversion elastomer is a material with a large thermal expansion coefficient and a small specific heat capacity.

[0016] Following the above technical solution, the material of the photothermal conversion elastomer includes but is not limited to epoxy resin or polyimide plastic.

[0017] According to the above technical solution, the multimode optical fiber and the photothermal conversion elastomer have different thermal expansion coefficients. When the temperature changes, the photothermal conversion elastomer bends due to the unbalanced thermal stress generated inside.

[0018] Following the above technical solution, a cladding and a coating layer are further provided outside the core of the multimode optical fiber, wherein the core diameter is 105 μm, the cladding diameter is 125 μm, and the coating diameter is 250 μm.

[0019] The present invention also provides an optical path system of an optically driven and sensed integrated flexible joint, comprising a flexible joint, a 1*3 optical splitter, a high-power laser and a sensing component, wherein the sensing component comprises a tunable laser, an optical power meter and an optical isolator, the high-power laser is connected to the first branch port of the 1*3 optical splitter; the input end of the optical isolator is connected to the tunable laser, and the output end of the optical isolator is connected to the second branch port of the 1*3 optical splitter; the optical power meter is connected to the third branch port of the 1*3 optical splitter, and the flexible joint is connected to the combining port of the 1*3 optical splitter, wherein the flexible joint is the optically driven and sensed integrated flexible joint based on the photothermal effect as described in the above technical solution.

[0020] The beneficial effects of the present invention are as follows: the present invention utilizes fiber Bragg gratings to realize bending curvature sensing of flexible joints, eccentrically embeds multimode optical fibers into a photothermal conversion elastomer, and the photothermal conversion elastomer contains materials capable of photothermal conversion. Under the irradiation of laser, the flexible joint produces temperature changes, and the eccentric structure composed of the photothermal conversion elastomer and the multimode optical fiber will produce bending deformation due to the temperature change. The fiber Bragg grating has good linearity and high sensitivity to changes in strain and temperature, and can fully meet the requirements of real-time monitoring of joint status. The present invention utilizes fiber Bragg gratings to integrate sensing and driving functions, and has the advantages of high integration, low energy consumption, simple structure, small size, light weight, and anti-interference, and is convenient for application in soft robots, in vivo surgery, high radiation, flammable and explosive environments, and the like.

[0021] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Schematic diagram of the flexible joint structure of an embodiment of the present invention.

[0024] Figure 2 Schematic diagram of an optical path system according to an embodiment of the present invention.

[0025] Figure 3 Schematic diagram of a 1*3 optical splitter according to an embodiment of the present invention.

[0026] Figure 4 Schematic diagram of an optical isolator according to an embodiment of the present invention.

[0027] Figure 5 Schematic diagram of the working of the flexible joint according to an embodiment of the present invention.

[0028] The components in the figure are numbered as follows:

[0029] 1. Flexible joint; 2. Multimode optical fiber; 3. Photothermal conversion elastomer; 4. Coating; 5. Cladding; 6. Fiber core; 7. Fiber Bragg grating; 8. High-power laser; 9. Tunable laser; 10. Optical power meter; 11. Optical isolator; 12. 1*3 optical splitter; 13. Sensor component. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention 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 invention and are not intended to limit the present invention.

[0031] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic illustrations of the basic concept of the present invention. Therefore, the drawings only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0032] In the present invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like are used to indicate positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate the description of the present application and to simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present application. Furthermore, the terms "first" and "second" are used solely for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0033] This light-driven flexible joint integrates sensing and driving functions using multimode optical fibers, adopts a new light energy driving method to achieve bending movement of the flexible joint, and uses fiber Bragg gratings to achieve bending curvature sensing of the flexible joint. The multimode optical fiber is eccentrically embedded in a photothermal conversion elastomer, which contains a photothermal conversion material. Under the irradiation of the laser, the flexible joint produces temperature changes, and the eccentric structure composed of the photothermal conversion elastomer and the multimode optical fiber will produce bending deformation due to the temperature change. The present invention integrates sensing and driving functions using fiber Bragg gratings, and has the advantages of high integration, low energy consumption, streamlined structure, small size, light weight, and anti-interference, making it easy to apply to soft robots, in vivo surgery, high radiation, flammable and explosive occasions, etc.

[0034] Fiber Bragg gratings (FBGs) are compact and, as part of a deformable structure, integrate sensing functions while still meeting the requirements for joint motion. This enables the design of a highly integrated optically driven flexible joint with integrated drive and sensing, achieving joint motion with a streamlined structure. FBGs also exhibit excellent linearity and high sensitivity to changes in strain and temperature, fully capable of real-time monitoring of joint status.

[0035] like Figure 1As shown, this embodiment of the optically driven, photothermal-sensing integrated flexible joint 1 comprises a multimode optical fiber 2 and a photothermal converter elastomer 3. The photothermal converter elastomer 3 is arc-shaped and contains a material for photothermal conversion. The multimode optical fiber 2 is eccentrically embedded within the elastomer 3. A fiber Bragg grating 7 is inscribed on the core of the multimode optical fiber 2, with the midpoint of the fiber Bragg grating 7 aligned with the midpoint of the flexible joint 1. When the incident light power of the multimode optical fiber 2 increases, the photothermal converter elastomer 3 bends in a direction of decreasing curvature, and the reflection spectrum signal of the fiber Bragg grating 7 reflects the changing angle of the photothermal converter 3. There is an eccentricity e between the axis of the multimode optical fiber 2 and the axis of the flexible joint 1. The eccentricity e ranges from 0 to 375 μm, with larger values ​​of the eccentricity e resulting in better actuation of the flexible joint 1. In its initial state, the flexible joint 1 has a certain degree of curvature, with a bending radius of R. In the working state, as the incident light power to the flexible joint 1 increases, the flexible joint 1 will bend in the direction of decreasing curvature. During the movement, the reflection spectrum signal of the fiber Bragg grating 7 reflects the change in angle of the flexible joint 1.

[0036] A multimode optical fiber 2, typically a quartz optical fiber, is selected as the medium for energy transmission. From the outside in, the multimode optical fiber 2 comprises a coating 4, a cladding 5, and a core 6. A fiber Bragg grating 7 is inscribed within the core 6 of the multimode optical fiber 1. In one embodiment of the present invention, the core diameter is 105 μm, the cladding diameter is 125 μm, the coating diameter is 250 μm, and the numerical aperture is 0.15 ± 0.02. During the preparation of the flexible joint 1, the mold and the multimode optical fiber 2 are positioned so that the midpoint of the fiber Bragg grating 7 is aligned with the midpoint of the flexible joint 1.

[0037] Specifically, femtosecond laser technology can be used to write the fiber Bragg grating 7 on the multimode optical fiber 2, with a reflection peak wavelength range of 1550-1630 nm, a length of 1-15 mm, and a reflectivity of not less than 90%.

[0038] Materials used for the photothermal elastomer include, but are not limited to, epoxy resins, polyimide plastics, and other materials with high thermal expansion coefficients and low specific heat capacities. When the material has a low specific heat capacity, the flexible joint 1 reacts more quickly to movement. A material with a high thermal expansion coefficient exhibits more significant volume changes when the temperature fluctuates, resulting in greater driving force. In a preferred embodiment of the present invention, the multimode optical fiber 2 and the photothermal elastomer 3 within the flexible joint 1 have different thermal expansion coefficients. When the temperature fluctuates, uneven thermal stress is generated within the flexible joint 1, causing the flexible joint 1 to flex.

[0039] The materials used for the photothermal conversion particles embedded in the photothermal conversion elastomer 3 include, but are not limited to, gold nanoparticles, carbon nanotubes, graphene oxide powder and other materials with photothermal effects.

[0040] In one embodiment of the present invention, the matrix material of the photothermal converter elastomer 3 is epoxy resin, and the photothermal converter material is graphene powder. To prepare the flexible joint 1, it is first necessary to prepare a photothermal converter elastomer 3 material solution: in a preferred embodiment, 5g of epoxy resin B component curing agent can be added to a 100mL beaker, followed by adding 1g of graphene powder, and initially stirred with a glass rod, and then 15g of epoxy resin A component resin is added and stirred. After the reagent is poured into a centrifuge tube, it is placed in a centrifuge for centrifugation, the centrifuge speed is adjusted to 5000rpm / min, and the components are evenly mixed by centrifugation for 5 minutes. Then, the graphene powder is ultrasonically dispersed using an ultrasonic instrument so that the graphene powder is evenly mixed in the epoxy resin solution, and then the solution is placed in a vacuum machine to remove bubbles in the reagent using negative pressure.

[0041] A capillary silicone tube with an inner diameter of 0.3 to 1 mm and a length of 4 to 6 cm that is easy to peel off can be used as a filling mold for the photothermal conversion elastomer (3); a metal octagonal prism with a side length of 0.5 to 1.2 cm is used as a fixed mold during the thermal curing process of the flexible joint 1 to ensure that the eccentricity of the multimode optical fiber 2 in the flexible joint 1 reaches the maximum value. Before filling the photothermal conversion elastomer 3 material solution, vacuum defoaming or centrifugal defoaming technology is used to significantly reduce product defects after thermal curing molding.

[0042] In a preferred embodiment of the present invention, a syringe with a pinhole diameter of 0.45 mm is used to inject the above-mentioned photothermal conversion elastomer 3 material solution into a silicone tube through which a multimode optical fiber 2 is inserted (the silicone tube specification is 60 mm in length, 1.6 mm in outer diameter, and 0.6 mm in inner diameter. The inner wall needs to be cleaned in advance, and the multimode optical fiber 2 also needs to be cleaned of surface dust with alcohol in advance to improve the bonding ability between the multimode optical fiber 2 and the epoxy resin, until the reagent fills the entire silicone tube, and the fiber Bragg grating 7 is adjusted to be located in the middle of the silicone tube. It should be noted that the multimode optical fiber 2 must have a length of at least 40 mm after passing through the silicone tube. The silicone tubing is then wrapped and secured around an octagonal prism mold (5mm side length, 100mm length). This ensures that the multimode fiber 2 is eccentrically confined to the larger radius end of the flexible joint 1. The pre-set bend diameter of the flexible joint 1 can reach 20mm. The entire flexible joint 1, along with the mold, is then placed in a hot air oven for curing at 80°C for 2 hours. After curing, the silicone tubing is removed section by section using wire strippers to obtain the prepared flexible joint 1. The eccentricity of the multimode fiber 2 within the photothermal conversion elastomer 3 must be checked to ensure that the flexible joint 1 has good actuation properties.

[0043] See Figures 2 to 5The optical path system of the light-driven sensing integrated flexible joint includes a flexible joint 1, a 1*3 optical splitter 12, a high-power laser 8 and a sensing component 13, wherein the sensing component includes a tunable laser 9, an optical power meter 10 and an optical isolator 11.

[0044] like Figure 3 As shown, the flexible joint 1 is connected to port D of the 1*3 optical splitter 12; the high-power laser 8 is connected to port A of the 1*3 optical splitter 12; the tunable laser 9 is connected to the input end of the optical isolator 11, and the output end of the optical isolator 11 is connected to port B of the 1*3 optical splitter 12; and the optical power meter 10 is connected to port C of the 1*3 optical splitter 12. The driving method of this optically driven and sensing integrated flexible joint is photothermal drive. The high-power laser 8 is connected to the flexible joint 1 through a 1*3 optical splitter 12. When the driving light enters the flexible joint 1, the transmission characteristics of the optical path will change due to the initial bending of the flexible joint 1. Part of the constrained light becomes a leakage mode and leaks out from the multimode optical fiber 2. Additional energy loss will occur along the bending radius, and this part of the leaked light energy will be absorbed by the photothermal conversion elastomer 3 to generate heat. The heat generation of the photothermal conversion elastomer 3 can be controlled by adjusting the output power of the high-power laser 8, thereby controlling the temperature of the photothermal conversion elastomer 3 and generating a thermal deformation response. The large difference in thermal expansion coefficient between the photothermal conversion elastomer 3 and the multimode optical fiber 2 causes them to generate an interaction force when experiencing temperature changes. This force generates a bending moment on the eccentric structure and completes the drive of the flexible joint movement. The flexible joint 1 is sensed using fiber Bragg grating sensing: the optical power meter 10 is connected to the multimode optical fiber 2 through a 1*3 optical splitter 12. The light waves within a specific wavelength range will be modulated by the fiber Bragg grating 7 to form a central wavelength. The central wavelength drifts under the combined action of temperature and strain. The central wavelength drift detected by the optical power meter 10 can reflect the bending condition of the flexible joint 1.

[0045] A high-power laser 8 is selected as the driving light source, with an output power of 0 to 9 W, a wavelength range of 915 to 980 nm, a pigtail of 110 / 125 μm multimode fiber, and a numerical aperture of <0.15.

[0046] A tunable laser 9 is selected as the sensing light source, with a wavelength tuning range of 1500-1630 nm, a peak output power ≥13 dBm, and a single-mode optical fiber as the pigtail.

[0047] The optical power meter 10 is selected to analyze the reflection spectrum data of the fiber Bragg grating 7, with a power range of -75 to 1.5 dBm, a wavelength range of 800 to 1600 nm, and a sampling rate of 50 ms.

[0048] The optical isolator 11 is used to protect the tunable laser 9, with an operating wavelength of 1550±20 nm and a minimum isolation of 44 dB.

[0049] In this embodiment, the IPG PLD-9-962 laser is selected as the high-power laser 8, the SanteC TSL-550 laser is selected as the tunable laser 9, the FPM-8200 fiber power meter is selected as the optical power meter 10, the optical isolator 11 with a working wavelength of 1550±20nm is selected to protect the tunable laser 9, and the 1*3 optical splitter 12 is selected to realize the connection of the optical path system.

[0050] The 1*3 optical splitter 12 has an equal split ratio, and a 105 / 125 μm multimode optical fiber (core diameter of 105 μm, cladding diameter of 125 μm) can be used.

[0051] The driving light output by high-power laser 8 passes through a 1*3 optical splitter 12 to flexible joint 1. Controlling the driving light power of high-power laser 8 changes the amplitude and speed of the bending motion of flexible joint 1. Tunable laser 9 outputs sensing light through an optical isolator 11 and a 1*3 optical splitter 12 to the fiber Bragg grating 7 inside flexible joint 1. The reflected spectrum light signal passes through the 1*3 optical splitter 12 to an optical power meter 10, which analyzes and determines the bending curvature of flexible joint 1.

[0052] In its initial state, the flexible joint 1 has a certain amount of bending. In the operating state, the high-power laser 8, tunable laser 9, and optical power meter 10 are activated, and the driving light and sensing light are coupled into the flexible joint 1 with the help of the 1*3 optical splitter 12. Due to the bending loss in the multimode optical fiber 2, part of the driving light leaks from the multimode optical fiber 2 into the photothermal conversion elastomer 3, causing the temperature to rise. Due to the different thermal expansion coefficients of the multimode optical fiber 2 and the photothermal conversion elastomer 3, when the temperature changes, unbalanced thermal stress is generated inside the flexible joint 1, causing the flexible joint 1 to bend. At the same time, the change angle of the flexible joint 1 is obtained by analyzing the reflection spectrum signal of the fiber Bragg grating 7 measured by the optical power meter 10.

[0053] It can be seen that the light-driven and sensing integrated flexible joint and its optical path system described in the present invention use multi-mode optical fiber as the energy transmission medium, and engrave fiber Bragg gratings on the multi-mode optical fiber, integrating the sensing and driving functions of the flexible joint into one. It has low manufacturing cost and strong applicability. It can be used in corrosive, radiation, flammable and explosive environments, and is expected to be used in medical, fuel pipeline, military and other fields.

[0054] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0055] The size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0056] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A light-driven sensing integrated flexible joint based on photothermal effect, characterized in that: It includes a multimode optical fiber and a photothermal conversion elastomer, wherein the photothermal conversion elastomer is in an arc-shaped joint shape, contains a material for photothermal conversion, and the multimode optical fiber is eccentrically embedded in the photothermal conversion elastomer; A fiber Bragg grating is engraved on the core of the multimode optical fiber, and the midpoint of the fiber Bragg grating is flush with the midpoint of the flexible joint; When the incident light power of the multimode optical fiber increases, the photothermal conversion elastomer will bend in the direction of decreasing curvature, and the reflection spectrum signal of the fiber Bragg grating reflects the changing angle of the photothermal conversion elastomer.

2. The light-driven sensing integrated flexible joint based on photothermal effect according to claim 1 is characterized in that: The multimode optical fiber is embedded in a position close to the large radius side of the arc-shaped joint of the photothermal conversion elastomer.

3. The light-driven sensing integrated flexible joint based on photothermal effect according to claim 1 is characterized in that: The materials used for photothermal conversion are gold nanoparticles, carbon nanotubes or graphene oxide powder with photothermal effect.

4. The light-driven sensing integrated flexible joint based on photothermal effect according to claim 1 is characterized in that: The fiber Bragg grating has a reflection peak wavelength range of 1550 to 1630 nm, a length of 1 to 15 mm, and a reflectivity of at least 90%.

5. The light-driven sensing integrated flexible joint based on photothermal effect according to claim 1 is characterized in that: The multimode optical fiber is in an eccentric state inside the photothermal conversion elastomer, and the eccentricity ranges from 0 to 375 μm. The actuation effect of the flexible joint becomes better as the eccentricity increases.

6. The light-driven sensing integrated flexible joint based on photothermal effect according to claim 1 is characterized in that: The material of the photothermal conversion elastomer is a material with a large thermal expansion coefficient and a small specific heat capacity.

7. The light-driven sensing integrated flexible joint based on photothermal effect according to claim 1 is characterized in that: The material of the photothermal conversion elastomer is epoxy resin or polyimide plastic.

8. The light-driven sensing integrated flexible joint based on photothermal effect according to claim 1 is characterized in that: Multimode optical fiber and photothermal conversion elastomer have different thermal expansion coefficients. When temperature changes occur, the flexible joint bends due to the uneven thermal stress generated inside.

9. The light-driven sensing integrated flexible joint based on photothermal effect according to any one of claims 1 to 8, characterized in that: The core of the multimode optical fiber is also provided with a cladding and a coating layer, wherein the core diameter is 105μm, the cladding diameter is 125μm, and the coating diameter is 250μm.

10. An optical path system for a light-driven, sensing-integrated flexible joint, characterized in that: The invention comprises a flexible joint, a 1*3 optical splitter, a high-power laser and a sensor component, wherein the sensor component comprises a tunable laser, an optical power meter and an optical isolator, the high-power laser is connected to the first branch port of the 1*3 optical splitter; the input end of the optical isolator is connected to the tunable laser, and the output end of the optical isolator is connected to the second branch port of the 1*3 optical splitter; the optical power meter is connected to the third branch port of the 1*3 optical splitter, and the flexible joint is connected to the combining port of the 1*3 optical splitter, wherein the flexible joint is an optically driven and sensed integrated flexible joint based on the photothermal effect according to any one of claims 1 to 9.

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