Fiber Bragg Grating-based Sensors

Abstract

A sensor based on fiber Bragg gratings comprises a rigid main frame, a rigid sub-frame, a diaphragm and an optical fiber, wherein the rigid main frame has a second chamber, the optical fiber extends to the second chamber, the rigid sub-frame has a third chamber connected to the outside, the second chamber and the third chamber are separated by the diaphragm, the optical fiber smoothly bends and extends in the second chamber and is connected to the diaphragm, and at least the third to fourth fiber Bragg gratings are arranged on the optical fiber, wherein the third fiber Bragg grating is arranged near the edge of the diaphragm, and the fourth fiber Bragg grating is arranged at the center of the diaphragm. The sensor based on fiber Bragg gratings of the present invention is designed by combining inner and outer chambers, diaphragms, optical fibers and their Bragg gratings, and by arranging two Bragg gratings at the center of the diaphragm and near the edge of the diaphragm, so as to compensate for temperature and increase the sensitivity of the sensor in measuring water pressure.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing and robot bionic finger sensing, and in particular to a sensor based on optical fiber Bragg grating. Background Art

[0002] Human fingers have the ability to sense various objects, manipulate them deftly, and interact with the surrounding environment, which has inspired the creation of a large number of tactile sensors. Tactile perception is an irreplaceable source of information for robots to perceive their surroundings and is the basis for promoting robots to achieve dexterous manipulation and precise control. Therefore, the research and development of robot finger tactile sensors has received widespread attention.

[0003] The ocean is an unstructured environment with harsh conditions such as high ambient pressure, salt water corrosion, and low light. Hydrostatic pressure refers to the pressure exerted by a static liquid at any given height in a closed tank. It is very important information for many different industries and applications. In the ocean, seawater pressure needs to be measured to determine the specific depth of the instrument. Traditional hydrostatic pressure sensors generally use strain gauges or piezoresistive sensors as sensing elements. Due to the presence of electromagnetic interference (EMI), electrical noise and electromagnetic interference can cause signal distortion, reduce sensitivity, cause signal drift, lead to signal loss, cause crosstalk, etc.

[0004] It should be noted that the information disclosed in the above background technology section is only used for understanding the background of the present application, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the invention

[0005] The main purpose of the present invention is to solve the problems existing in the above-mentioned background technology and to provide a sensor based on fiber Bragg grating, which can accurately measure the underwater hydrostatic pressure.

[0006] Furthermore, a sensor based on fiber Bragg grating is provided, which can accurately measure underwater hydrostatic pressure and temperature at the same time.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A sensor based on fiber Bragg gratings comprises a rigid main frame, a rigid sub-frame, a diaphragm and an optical fiber, wherein the rigid main frame has a second chamber, the optical fiber extends to the second chamber, the rigid sub-frame has a third chamber connected to the outside, the second chamber and the third chamber are separated by the diaphragm, the optical fiber is smoothly bent and extended in the second chamber and connected to the diaphragm, and at least third to fourth fiber Bragg gratings are arranged on the optical fiber, wherein the third fiber Bragg grating is arranged near the edge of the diaphragm, and the fourth fiber Bragg grating is arranged at the center of the diaphragm.

[0009] Furthermore, it also includes a force isolation tube, the rigid main skeleton also has a first chamber, the force isolation tube is fixed in the first chamber, the force isolation tube is filled with soft material, the optical fiber passes through the force isolation tube and extends to the second chamber; a fifth fiber Bragg grating is also arranged on the optical fiber, and the fifth fiber Bragg grating is arranged in the force isolation tube.

[0010] Furthermore, the force isolation tube is a capillary steel tube.

[0011] Furthermore, the first chamber is filled with soft material outside the force isolation tube.

[0012] Furthermore, the optical fiber is fixed at two ends of the force isolation tube.

[0013] Furthermore, the diaphragm is circular.

[0014] Furthermore, the periphery of the diaphragm is provided with through holes, and a plurality of fixing columns on the rigid sub-skeleton are installed into the assembly holes on the rigid main frame through the through holes, or a plurality of fixing columns on the rigid main frame are installed into the assembly holes on the rigid sub-skeleton through the through holes, so that the rigid main frame, the diaphragm and the rigid sub-skeleton are tightly fitted.

[0015] The outer end of the rigid sub-frame is an arc surface.

[0016] It also includes a connecting piece, a first end face of the connecting piece is connected to the end face of the rigid main frame away from the diaphragm, the optical fiber passes through the optical fiber via hole on the connecting piece into the first chamber, and the second end face of the connecting piece facing outward is provided with a cylindrical protrusion with an external thread, and the cylindrical protrusion is used to integrate the connecting piece onto the underwater actuator.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The fiber Bragg grating-based sensor provided by the present invention, when working, liquid can enter the third chamber of the rigid sub-skeleton. In an underwater environment, the air pressure on the first end face of the diaphragm and the hydrostatic pressure on the second end face of the diaphragm 3 form a pressure difference, resulting in deformation of the diaphragm, causing strains of the third and fourth fiber Bragg gratings located on the first end face of the diaphragm, and obtaining wavelength drifts of optical signals of the two FBGs. Since the two FBGs are arranged near the edge and the center of the diaphragm, respectively, under the action of hydrostatic pressure, from the edge to the center of the diaphragm, the radial strain gradually decreases from a negative value to zero and then to a positive value, resulting in the wavelength drift of the third FBG being the superposition of temperature change and positive radial strain, and the wavelength drift of the fourth FBG being the superposition of temperature change and negative radial strain. After the wavelengths of the third FBG and the fourth FBG are collected by the sensor of the present invention, the wavelength drifts of the two are subtracted, which not only eliminates the influence of temperature on the FBG, but also amplifies the wavelength drift signal generated by the hydrostatic pressure on the diaphragm. Therefore, the fiber Bragg grating-based sensor of the present invention not only compensates for temperature but also increases the sensitivity of the sensor in measuring water pressure by coordinating the design of inner and outer chambers, diaphragms, optical fibers and their Bragg gratings, and arranging two Bragg gratings at the center of the diaphragm and near the edge of the diaphragm.

[0019] Furthermore, the present invention provides a multi-modal sensing sensor based on fiber Bragg grating, which can accurately measure underwater hydrostatic pressure and temperature at the same time.

[0020] Multimodal sensing capability: The present invention integrates the sensing principle based on Fiber Bragg Grating (FBG), which can realize multimodal intelligent perception of underwater hydrostatic pressure and temperature in one sensor. The integration of this single sensing principle avoids the complexity of multi-sensor systems and signal coupling problems.

[0021] Corrosion resistance and anti-electromagnetic interference: By adopting optical fiber sensing technology, the sensor of the present invention has excellent corrosion resistance and anti-electromagnetic interference capabilities, and is suitable for use in harsh environments such as underwater.

[0022] Temperature self-compensation mechanism: Through the ingenious coordination of the inner and outer chambers, diaphragms, optical fibers and their Bragg gratings, and the arrangement of FBGs at the center and near the edge of the diaphragm, not only the underwater hydrostatic pressure measurement is realized, but also the wavelength drift difference of the two FBGs is used to simultaneously realize temperature compensation and enhance the pressure measurement sensitivity, thereby improving the measurement accuracy and stability.

[0023] High sensitivity and fast response: The structural design of the present invention realizes high-sensitivity measurement of hydrostatic pressure, and the optical fiber sensor itself has fast response speed and high sensitivity.

[0024] Packaging technology optimization: By adopting reasonable packaging technology, FBG5 is placed in a force isolation tube and filled with soft materials, which effectively avoids the influence of force on the temperature measurement FBG and ensures the accuracy of temperature measurement.

[0025] Applicable to complex environments: The present invention is particularly suitable for intelligent perception of complex underwater environments, and can achieve accurate tactile feedback and environmental detection in unstructured environments.

[0026] Easy to implement distributed sensing: By utilizing the distributed characteristics of FBG, the present invention can be easily expanded to multi-point measurement, thereby improving the application flexibility and measurement range of the sensor.

[0027] Low transmission loss: Fiber optic sensors have low transmission loss, which facilitates long-distance data transmission and monitoring and is suitable for application scenarios such as deep-sea exploration.

[0028] In the marine environment, the sensing technology based on fiber Bragg grating (FBG) has significant advantages over the traditional electrical sensing technology: (1) corrosion resistance, (2) anti-electromagnetic interference, (3) distributed sensing, (4) small size, and (5) low transmission loss. Due to the temperature cross-sensitivity of FBG, the wavelength shift of FBG sensors is usually affected by the superposition of temperature and strain parameters. Combining the above advantages, the present invention not only improves the intelligence of underwater robots, but also provides effective technical support for deep-sea exploration, safe human-computer interaction, and intelligent perception and control of unstructured environments.

[0029] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the overall structure of a sensor based on a fiber Bragg grating according to an embodiment of the present invention;

[0031] Figure 2 It is a schematic diagram of the explosion structure of a sensor based on a fiber Bragg grating according to an embodiment of the present invention;

[0032] Figure 3 It is a schematic diagram of the sensor optical fiber configuration based on the fiber Bragg grating and the distribution of the FBG according to an embodiment of the present invention;

[0033] Figure 4 It is a schematic diagram of the packaging structure of a temperature sensor FBG in a sensor based on a fiber Bragg grating according to an embodiment of the present invention.

[0034] Reference numerals:

[0035] Flexible finger sleeve 1, rigid sub-skeleton 2, diaphragm 3, rigid main skeleton 4, capillary steel tube 5, soft filler 6, connector 7, bolt 8, optical fiber 9, opening 11, fingertip positive pressure contact area 12, non-contact area 13, third chamber 20, circular hole 21, cylinder 22, circular through hole 31, hollow circular hole 41, second chamber 42, hollow cylinder 61, soft material 62, threaded through hole 71, central cylindrical hole 72, cylindrical protrusion 73, optical cable 91, fifth fiber Bragg grating (FBG5) 92, fourth fiber Bragg grating (FBG4) 93, third fiber Bragg grating (FBG3) 94, second fiber Bragg grating (FBG2) 95, first fiber Bragg grating (FBG1) 96. DETAILED DESCRIPTION

[0036] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.

[0037] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for fixing as well as for coupling or communication.

[0038] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0039] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0040] See also Figures 1 to 4The embodiment of the present invention provides a sensor based on fiber Bragg grating, comprising a rigid main skeleton 4, a rigid sub-skeleton 2, a diaphragm 3 and an optical fiber 9, wherein the rigid main skeleton 4 has a second chamber 42, the optical fiber 9 from the optical cable 91 extends to the second chamber 42, the rigid sub-skeleton 2 has a third chamber 20 connected to the outside (such as through a circular hole 21), the second chamber 42 and the third chamber 20 are separated by the diaphragm 3, the optical fiber smoothly bends and extends in the second chamber 42 and is connected to the diaphragm 3, and at least third to fourth fiber Bragg gratings are arranged on the optical fiber 9, wherein the third fiber Bragg grating (FBG3) 94 is arranged near the edge of the diaphragm 3, and the fourth fiber Bragg grating (FBG4) 93 is arranged at the center of the diaphragm 3.

[0041] During operation, liquid can enter the third chamber 20 of the rigid sub-skeleton 2. In an underwater environment, the air pressure on the first end face of the diaphragm 3 and the hydrostatic pressure on the second end face of the diaphragm 3 form a pressure difference, resulting in deformation of the diaphragm 3, causing strains of FBG3 and FBG4 located on the first end face of the diaphragm 3, and obtaining wavelength drifts of optical signals of FBG3 and FBG4. Since FBG3 and FBG4 are arranged near the edge and the center of the diaphragm, respectively, under the action of hydrostatic pressure, from the edge to the center of the diaphragm, the radial strain gradually decreases from a negative value to zero and then to a positive value, resulting in the wavelength drift of FBG3 being the superposition of temperature change and positive radial strain, and the wavelength drift of FBG4 being the superposition of temperature change and negative radial strain. After the wavelengths of FBG3 and FBG4 are collected by the sensor of the present invention, the wavelength drifts of FBG3 and FBG4 are subtracted, which not only eliminates the influence of temperature on FBG, but also amplifies the wavelength drift signal generated by hydrostatic pressure on the diaphragm. Therefore, the sensor of the present invention not only compensates for temperature but also increases the sensitivity of the sensor in measuring water pressure through the coordinated design of inner and outer chambers, diaphragms, optical fibers and their Bragg gratings, and through the arrangement of two Bragg gratings at the center of the diaphragm and near the edge of the diaphragm.

[0042] See also Figures 1 to 4A further preferred embodiment of the present invention provides a multimodal sensing bionic fingertip sensor based on fiber Bragg grating, comprising a rigid main skeleton 4, a rigid sub-skeleton 2, a flexible finger sleeve 1, a diaphragm 3, an optical fiber 9 and a force isolation tube (such as a capillary steel tube 5), wherein the rigid main skeleton 4 has a first chamber (such as a hollow cylinder 61) and a second chamber 42, the force isolation tube is fixed in the first chamber, the force isolation tube is filled with a soft material 62, the optical fiber 9 from the optical cable 91 passes through the force isolation tube and extends to the second chamber 42, the rigid sub-skeleton 2 has a third chamber 20 connected to the outside (such as through a circular hole 21), the second chamber 42 and the third chamber are separated by the diaphragm 3, the optical fiber 9 smoothly bends and extends in the second chamber 42 and is connected to the diaphragm 3, the flexible finger sleeve 1 is sleeved on the outside of the rigid main skeleton 4 and the rigid sub-skeleton 2, and the flexible finger sleeve 1 is sleeved on the outside of the rigid main skeleton 4 and the rigid sub-skeleton 2, and the flexible The fingertip positive pressure contact area 12 of the flexible finger cuff 1 is provided with a protrusion (preferably in the shape of a finger pad) relative to the non-contact area 13, the optical fiber 9 is led out into the flexible finger cuff 1 through the lead-out hole on the rigid main skeleton 4, and is smoothly bent and arranged in the flexible finger cuff 1, extending from the fingertip positive pressure contact area 12 to the non-contact area 13; the first to fifth fiber Bragg gratings are provided on the optical fiber 9, wherein the first fiber Bragg grating (FBG1) 96 is provided in the non-contact area 13 of the flexible finger cuff 1, the second fiber Bragg grating (FBG2) 95 is provided in the fingertip positive pressure contact area 12 of the flexible finger cuff 1, the third fiber Bragg grating (FBG3) 94 is provided near the edge of the diaphragm 3, the fourth fiber Bragg grating (FBG4) 93 is provided in the center of the diaphragm 3, and the fifth fiber Bragg grating (FBG5) 92 is provided in the force isolation tube.

[0043] like Figure 2 and Figure 3 As shown, in a preferred embodiment, the first chamber is filled with a soft filler 6 outside the force isolation tube.

[0044] In a preferred embodiment, the optical fiber 9 is fixed at both ends of the force isolation tube.

[0045] like Figure 1 and Figure 2 As shown, in a preferred embodiment, the diaphragm 3 is circular.

[0046] like Figure 2As shown, in a preferred embodiment, a circular through hole 31 is provided on the periphery of the diaphragm 3, and a plurality of fixing columns (such as the cylinder 22) on the rigid sub-skeleton 2 are installed into the assembly holes (such as the hollow circular holes 41) on the rigid main skeleton 4 through the circular through holes 31, or a plurality of fixing columns on the rigid main skeleton 4 are installed into the assembly holes on the rigid sub-skeleton 2 through the through holes, so that the rigid main skeleton 4, the diaphragm 3 and the rigid sub-skeleton 2 are tightly fitted.

[0047] like Figures 1 to 3 As shown, in a preferred embodiment, the outer end of the rigid sub-skeleton 2 is an arc surface, such as a spherical surface.

[0048] like Figures 1 to 3 As shown, in a preferred embodiment, the multimodal sensing bionic fingertip sensor also includes a connector 7, a first end face of the connector 7 is connected to the end face of the rigid main skeleton 4 away from the diaphragm 3, and the optical fiber 9 passes through the optical fiber 9 through-hole on the connector 7 into the first chamber.

[0049] like Figures 2 to 3 As shown, in a preferred embodiment, a cylindrical protrusion 73 with an external thread is provided on the second end surface of the connecting member 7 facing outwards, and the cylindrical protrusion 73 is used to integrate the connecting member 7 onto the underwater actuator.

[0050] like Figure 3 As shown, in a preferred embodiment, the optical fiber 9 is connected to the connecting member 7 through the non-contact area of ​​the flexible finger sleeve 1.

[0051] like Figures 1 to 4 As shown, in some embodiments, the multimodal sensing bionic fingertip sensor includes a rigid main frame 4, a rigid sub-frame 2, a flexible finger sleeve 1, a diaphragm 3, a connector 7, an optical fiber 9, a capillary steel tube 5, a soft filling material, and a bolt 8.

[0052] The first end face of the diaphragm 3 is connected to the first end face of the rigid main frame 4 to form a cavity, so that the first end face of the diaphragm 3 is subjected to air pressure. The second end face of the diaphragm 3 is in contact with the rigid sub-frame 2 to introduce liquid into the cavity of the rigid sub-frame 2, so that the second end face of the diaphragm 3 is subjected to hydrostatic pressure.

[0053] The cylinder 22 of the rigid sub-frame 2 is inserted into the cylindrical groove of the rigid main frame 4 (the rigid sub-frame 2 passes through the diaphragm 3 and is connected to the first end surface of the rigid main frame 4 ) to fix the diaphragm 3 .

[0054] The flexible finger sleeve 1 is provided with an opening 11, and the spherical surface of the rigid sub-skeleton 2 is correspondingly provided with a circular hole 21, so that liquid can enter the chamber of the rigid sub-skeleton 2 through the circular hole 21. In an underwater environment, the air pressure on the first end face of the diaphragm 3 and the hydrostatic pressure on the second end face of the diaphragm 3 form a pressure difference, resulting in deformation of the diaphragm 3.

[0055] The capillary steel tube 5 is placed at the center of the hollow cylinder 61 at the second end of the rigid main frame 4, and the remaining hollow area is filled with soft filling material to obtain a capillary steel tube protective shell.

[0056] A threaded through hole is formed on the first end face of the connecting member 7 , and the first end face of the connecting member 7 and the second end face of the rigid main frame 4 are connected by the bolt 8 .

[0057] The flexible finger sleeve 1 is connected to the rigid main frame 4 to obtain the flexible bionic skin of the fingertip sensor. When the pressing area of ​​the flexible finger sleeve 1 is subjected to contact force and friction force, the flexible finger sleeve 1 is deformed.

[0058] The optical fiber 9 is introduced into the rigid main skeleton 4 through the central hole of the connector 7, and then passes through the capillary steel tube 5 and fixes both ends at the two ends of the capillary steel tube 5. After passing through the capillary steel tube 5, the optical fiber 9 is evenly bent in the hollow cylinder at the first end of the rigid main skeleton 4, and the optical fiber 9 is connected to the first end face of the diaphragm 3, and is led out to the flexible finger sleeve 1 through the small hole of the rigid main skeleton 4, and the optical fiber 9 is regularly bent in the flexible finger sleeve 1.

[0059] The specific embodiments of the present invention are further described below.

[0060] As a preferred example, the rigid main skeleton 4 is cylindrical in shape to simulate the exoskeleton of human fingers. The rigid main skeleton 4 has a diameter of 22 mm and a height of 38 mm. Figure 3 In the direction of the middle, the hollow cylindrical parts of the rigid main skeleton 4 are from left to right: a hollow cylinder with a diameter of 6mm and a height of 10mm, a hollow cylinder with a diameter of 4mm and a height of 3mm, a hollow cylinder with a diameter of 0.2mm and a height of 3mm, and a hollow cylinder with a diameter of 16mm and a height of 22mm; the left end face circular array of the rigid main skeleton 4 has 6 M2 threaded holes with a height of 5mm, and the distance between the center of the threaded hole and the center of the left end face of the rigid main skeleton 4 is 8mm. The right end face circular array of the rigid main skeleton 4 has 4 hollow cylinders with a diameter of 1.5mm and a height of 5mm, and the distance between the center of the hollow cylinder and the center of the right end face of the rigid main skeleton 4 is 9.5mm.

[0061] As a preferred example, the diaphragm 3 is cylindrical, with a diameter of 22 mm and a height of 0.3 mm. The diaphragm 3 has four cylindrical through holes with a diameter of 1.5 mm in a circumferential array, and the distance between the center of the cylindrical through hole and the center of the diaphragm 3 is 9.5 mm.

[0062] As a preferred example, one end of the rigid sub-skeleton 2 should be spherical to fit the shape of the skin at the front end of human fingertips. The diameter of the circular hole on the spherical surface of the rigid sub-skeleton 2 is 5 mm, and there are 4 cylinders with a diameter of 5 mm at the other end, which are used to insert the rigid main skeleton 4 and firmly fix the diaphragm 3 between the rigid main skeleton 4 and the rigid sub-skeleton 2.

[0063] As a preferred example, the outer diameter of the capillary steel tube 5 is 2 mm, the wall thickness is 0.2 mm, and the height is 16 mm. The FBG5 is placed in the hollow center of the capillary steel tube 5, and both ends of the optical fiber 9 are sealed with silicone rubber.

[0064] As a preferred example, the first end face of the connector has four M2 threaded through holes, the bolt is a cylindrical hexagon socket bolt made of 304 stainless steel, the size of the bolt is M2×8, and the bolt is screwed into the threaded through hole of the connector and the threaded hole of the second end face of the rigid main frame 4 to connect and fix the connector and the rigid main frame 4. The second end face of the connector has a cylindrical protrusion, and the external thread on the cylinder allows it to be easily integrated and installed at the end of the underwater actuator.

[0065] As a preferred example, the core diameter of the optical fiber 9 is 0.15 mm, and 5 FBGs are engraved on the optical fiber 9, starting from one end of the optical fiber 9, in order of FBG1, FBG2, FBG3, FBG4, and FBG5, and the engraving method is femtosecond laser point-by-point writing. The distance between the center of the FBG1 and the end of the optical fiber 9 is 20 mm, the distance between the center of the FBG1 and the center of the FBG2 is 28 mm, the distance between the center of the FBG2 and the center of the FBG3 is 16 mm, the distance between the center of the FBG3 and the center of the FBG4 is 6 mm, and the distance between the center of the FBG4 and the center of the FBG5 is 40.7 mm. The grating area of ​​each Bragg grating is 2 mm.

[0066] As a preferred example, the contact area of ​​the flexible finger sleeve 1 has a protrusion relative to the non-contact area, which can better conduct the contact force and limit the contact force within the protrusion area to avoid the contact force from affecting the slip sensing area.

[0067] In the process of the fingertip sensor contacting and sliding with the object, based on the stick-slip phenomenon, the friction force will cause the contact area of ​​the flexible fingertip 1 of the fingertip to deform, and the deformation is further transmitted to the slip area of ​​the flexible fingertip 1 through the elastic material, causing the axial strain of the FBG1 located in the slip area of ​​the flexible fingertip 1, resulting in the wavelength drift of the optical signal of the FBG1.

[0068] When the fingertip sensor contacts and presses an object, the positive pressure will cause the contact area of ​​the flexible fingertip 1 of the fingertip to deform, causing strain of the FBG2 located in the contact area of ​​the flexible fingertip 1, resulting in wavelength drift of the optical signal of the FBG2.

[0069] When the fingertip sensor is placed in an underwater environment, the hydrostatic pressure and the air pressure form a pressure difference on both sides of the diaphragm 3. The pressure difference causes the diaphragm 3 to deform, causing strain of the FBG3 and the FBG4 located on the first end face of the diaphragm 3, resulting in wavelength drift of the optical signals of the FBG3 and the FBG4.

[0070] The FBG5 is encapsulated in the capillary steel tube 5 of the fingertip sensor to isolate the influence of force on the signal of the FBG5. The change of temperature will cause the change of the grating pitch of the optical fiber 9, resulting in the wavelength drift of the optical signal of the FBG5.

[0071] Figure 1 A structural schematic diagram of a preferred embodiment of the present invention is shown, as Figure 1 As shown, a fiber Bragg grating bionic fingertip sensor is invented, which includes a flexible finger sleeve 1, a rigid secondary frame 2, a diaphragm 3, a rigid main frame 4, a capillary steel tube 5, a soft filler 6, a connector 7, a bolt 8, and an optical fiber 9.

[0072] The material of the flexible finger sleeve 1 is Ecoflex 00-30, which needs to be cast in two steps during preparation. First, a long strip of soft block is cast to fix the optical fiber 9. Figure 1 The effect is to lay the strip soft and fix it, and then cast the overall shape of the flexible finger sleeve 1.

[0073] The material of the rigid sub-frame 2, diaphragm 3 and rigid main frame 4 is 304 stainless steel. Align the four circular through holes 31 of the diaphragm with the four hollow circular holes 41 of the rigid main frame, then align the four cylinders 22 of the rigid sub-frame with the hollow cylinder and press them into the hollow cylinder to make the rigid main frame, diaphragm and rigid sub-frame fit tightly.

[0074] The material of the capillary steel tube 5 is 304 stainless steel. The optical fiber 9 is passed through the cavity of the capillary steel tube 5, and the optical fiber and the capillary steel tube are concentric. Then the capillary steel tube 5 is placed in the hollow cylinder 61 at the other end of the rigid main frame 4, and the two are concentric. Then the soft material Ecoflex 00-30 is poured into the remaining part of the hollow cylinder, and the soft filler 6 is formed after solidification. In this way, the optical fiber 9 is fixed in the capillary steel tube 5, and the capillary steel tube 5 is fixed in the hollow cylinder of the rigid main frame 4.

[0075] The material of the connector 7 is 304 stainless steel, and the six through holes are M2 threaded through holes 71. The bolt 8 is a hexagon socket head screw, and according to GB / T 70.1-2008, the thread specification is M2×10. The connector 7 is fixed to the rigid main frame 4 by the bolt 8, and the optical fiber 9 is passed through the central cylindrical hole 72 of the connector 7. The external threaded part of the cylindrical protrusion 73 of the connector 7 can be installed on a robot arm for control.

[0076] In this embodiment, the relationship between the fiber Bragg grating wavelength shift and the strain can be described as:

[0077]

[0078] in, is the central wavelength of the reflected signal, is the strain optical coefficient, For strain, is the coefficient of thermal expansion, is the thermo-optical coefficient, is the change in temperature.

[0079] In this embodiment, for a specific fiber type, the strain optical coefficient is is a constant value, which can be obtained by the following formula:

[0080]

[0081] in, and represents the Pockel coefficient of the strain tensor, is Poisson's ratio, is the effective refractive index of the optical fiber.

[0082] When measuring water pressure, since one end of the diaphragm 3 is a sealed cavity, one end is subjected to water pressure. The pressure difference at both ends will cause the diaphragm 3 to deform, and the optical fiber 9 adhered to the diaphragm 3 will also deform, causing the grating pitch of the Bragg grating on the optical fiber 9 to change, thereby causing the reflection wavelength to change. The threshold for measuring the water pressure depends on the thickness of the diaphragm. If the diaphragm is too thin, when the water pressure exceeds the threshold, the diaphragm will undergo plastic deformation, resulting in failure of the overall structure. The sensitivity of measuring the water pressure also depends on the thickness of the diaphragm. If the diaphragm is too thick, the deformation of the diaphragm caused by the unit water pressure is too small, resulting in low measurement sensitivity. The optimal thickness of the diaphragm determined by simulation is 0.4mm, and the elastic range of the water pressure resistance of this thickness diaphragm in the simulation is 0-2Mpa. The water pressure of 0-100m can be measured relatively safely.

[0083] Under the action of water pressure, the diaphragm 3 will produce radial strain and tangential strain. According to the small deformation theory, the radial strain and tangential strain of the diaphragm can be expressed as follows:

[0084]

[0085]

[0086] in, is the radial strain, is the tangential strain, is Poisson's ratio, is the radius of the diaphragm pressure surface, is the distance between the measuring point and the center of the diaphragm, is Young's modulus, is the thickness of the film, is the magnitude of the water pressure. For radial strain , exist between, is a negative value; exist between, is a positive value. , from hour, All are positive values.

[0087]

[0088]

[0089] In the arrangement of the Bragg grating (FBG), the first FBG is arranged at the center of the diaphragm circle, so that , . Place the second FBG at at that place Since the reflection center wavelengths of the two FBGs and are very close, their difference can be ignored, and it can be considered . Based on this, the following formula can be obtained after simplification:

[0090]

[0091]

[0092]

[0093] By means of the above Bragg grating arrangement, it is possible to achieve The Bragg grating arrangement at the center and edge of the diaphragm not only compensates for the temperature but also increases the sensitivity of the sensor.

[0094] Specifically, in this embodiment, , , Substituting into the above formula we get:

[0095]

[0096]

[0097]

[0098] The supporting system can have the following basic components: light source, optical fiber, FBG interrogator (for signal processing, including photodetector and analog-to-digital converter), control unit. Laser diode or superluminescent diode is used to generate broadband optical signal, and when light passes through the Bragg grating surface, reflected light is generated at the Bragg wavelength. When pressure or temperature changes the grating pitch, the Bragg wavelength will change, and the wavelength shift is output through the signal demodulation of the FBG interrogator. By calibrating the wavelength shift with the applied force and temperature, accurate measurement of force, temperature, etc. can be achieved.

[0099] Compared with traditional sensors, the main advantages of the embodiments of the present invention are:

[0100] (1) The present invention is a sensor integrating the FBG (Bragg grating) sensing principle. Fiber optic sensing has the characteristics of corrosion resistance, anti-electromagnetic interference, distributed sensing, low transmission loss, fast response speed and high sensitivity. It has important significance in the fields of underwater intelligent perception, deep sea exploration, safe human-computer interaction, and intelligent perception and control of unstructured environments. The present invention integrates FBG into a soft actuator, which can realize multi-modal tactile perception in an unstructured environment.

[0101] (2) The present invention uses a sensing principle to achieve multi-modal intelligent perception of hydrostatic pressure and temperature. The perception and measurement accuracy of each mode is high, the signal crosstalk is small, and the decoupling method is simple.

[0102] (3) The present invention achieves high sensitivity and temperature self-compensation in hydrostatic pressure measurement through structural design. The diaphragm is designed as a simply supported beam with both ends fixed on the section through the center of the circle, and FBG3 and FBG4 are arranged near the edge of the diaphragm and the center of the diaphragm respectively. Under the action of hydrostatic pressure, the radial strain gradually decreases from positive to zero and then becomes positive from the edge to the center of the diaphragm. The wavelength drift of FBG3 is the superposition of temperature change and positive radial strain, and the wavelength drift of FBG4 is the superposition of temperature change and negative radial strain. Subtracting the wavelength drift of FBG3 and FBG4 not only eliminates the influence of temperature on FBG, but also amplifies the wavelength drift signal generated by hydrostatic pressure on the diaphragm.

[0103] (4) The present invention avoids the influence of other interferences on the temperature measurement FBG5 through reasonable packaging technology. By placing the FBG5 in the hollow of the capillary steel tube, filling the remaining hollow part of the capillary steel tube with soft material, and then placing the capillary steel tube in the hollow cylinder on the first end face of the rigid main skeleton in the same way, and filling the remaining part of the hollow cylinder with soft material. This packaging technology reduces the influence of the deformation of the steel structure on the optical fiber through the elasticity of the soft material, so that the packaged FBG5 will not produce signal drift due to the action of force, but only due to temperature changes.

[0104] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of the reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A multi-modal sensing bionic fingertip sensor based on fiber Bragg grating for an underwater robot, characterized in that: The invention comprises a rigid main frame, a rigid sub-frame, a membrane and an optical fiber, wherein the rigid main frame has a second chamber, the optical fiber extends into the second chamber, the rigid sub-frame has a third chamber connected to the outside, the second chamber and the third chamber are separated by the membrane, the optical fiber smoothly bends and extends in the second chamber and is connected to the membrane, and at least a third to a fourth fiber Bragg grating are arranged on the optical fiber, wherein the third fiber Bragg grating is arranged near the edge of the membrane, and the fourth fiber Bragg grating is arranged at the center of the membrane; and further comprises a flexible finger sleeve, the flexible finger sleeve The flexible finger cuff is sleeved on the outside of the rigid main frame and the rigid sub-frame, the fingertip positive pressure contact area of ​​the flexible finger cuff is provided with a fingertip-shaped protrusion relative to the non-contact area, the optical fiber is led out into the flexible finger cuff through the lead-out hole on the rigid main frame, and is smoothly bent and arranged in the flexible finger cuff, extending from the fingertip positive pressure contact area to the non-contact area; the first and second fiber Bragg gratings are also provided on the optical fiber, wherein the first fiber Bragg grating is provided in the non-contact area of ​​the flexible finger cuff, and the second fiber Bragg grating is provided in the fingertip positive pressure contact area of ​​the flexible finger cuff.

2. The multi-modal sensing bionic fingertip sensor based on fiber Bragg grating of the underwater robot as claimed in claim 1, characterized in that: It also includes a force isolation tube, the rigid main skeleton also has a first chamber, the force isolation tube is fixed in the first chamber, the force isolation tube is filled with soft material, the optical fiber passes through the force isolation tube and extends to the second chamber; a fifth fiber Bragg grating is also arranged on the optical fiber, and the fifth fiber Bragg grating is arranged in the force isolation tube.

3. The multi-modal sensing bionic fingertip sensor based on fiber Bragg grating of the underwater robot as claimed in claim 2, characterized in that: The force isolation tube is a capillary steel tube.

4. The multi-modal sensing bionic fingertip sensor based on fiber Bragg grating of the underwater robot as claimed in claim 2 or 3, characterized in that: The first chamber is filled with soft material outside the force isolation tube.

5. The multi-modal sensing bionic fingertip sensor based on fiber Bragg grating of the underwater robot as claimed in claim 2 or 3, characterized in that: The optical fiber is fixed at both ends of the force isolation tube.

6. The multi-modal sensing bionic fingertip sensor based on fiber Bragg grating of the underwater robot as claimed in claim 1 or 2, characterized in that: The diaphragm is circular.

7. The multi-modal sensing bionic fingertip sensor based on fiber Bragg grating of the underwater robot as claimed in claim 1 or 2, characterized in that: The periphery of the diaphragm is provided with through holes, and the multiple fixing columns on the rigid sub-frame are installed into the assembly holes on the rigid main frame through the through holes, or the multiple fixing columns on the rigid main frame are installed into the assembly holes on the rigid sub-frame through the through holes, so that the rigid main frame, the diaphragm and the rigid sub-frame are tightly fitted.

8. The multi-modal sensing bionic fingertip sensor based on fiber Bragg grating of an underwater robot as claimed in claim 1 or 2, characterized in that: The outer end of the rigid sub-frame is an arc surface.

9. The multi-modal sensing bionic fingertip sensor based on fiber Bragg grating of the underwater robot as claimed in claim 2, characterized in that: It also includes a connecting piece, a first end face of the connecting piece is connected to the end face of the rigid main frame away from the diaphragm, the optical fiber passes through the optical fiber via hole on the connecting piece into the first chamber, and the second end face of the connecting piece facing outward is provided with a cylindrical protrusion with an external thread, and the cylindrical protrusion is used to integrate the connecting piece onto the underwater actuator.

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