A mirror-symmetry chiral multicore optical fiber
By using the reverse spiral distribution of the outer and inner rings of a mirror-chiral multi-core fiber and the conversion of the absolute azimuth angle of the reference fiber core, the problem of inaccurate identification of the absolute orientation angle in a spiral structure of a multi-core fiber is solved, and stable recovery of the absolute bending direction is achieved. This method is suitable for shape sensing and health monitoring of complex structures.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN ENG UNIV
- Filing Date
- 2026-03-11
- Publication Date
- 2026-06-09
Smart Images
Figure CN122170796A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of fiber optic sensing and shape reconstruction technology, and in particular to a mirror-chiral multi-core fiber. Specifically, it relates to a bending direction sensing device and demodulation method based on a mirror-chiral multi-core fiber. Implementation scenarios include, but are not limited to, discrete measurement forms such as FBG arrays, multi-core fibers, or distributed fiber shape sensing, as well as systems and devices for fiber optic design, parameter calculation, shape reconstruction, and sensor fabrication / installation based on this demodulation method. Background Technology
[0002] In recent years, fiber optic shape sensing technology has seen rapid development in applications such as flexible robots, minimally invasive interventional instruments, endoscopic guidance, and health monitoring of complex pipelines / structures due to its advantages including flexibility, resistance to electromagnetic interference, and integration into slender structures. These applications generally require high accuracy in shape reconstruction, with the bending direction determining the extension direction of the reconstructed curve and significantly impacting the quality of the curve reconstruction.
[0003] Multi-core optical fibers, capable of simultaneously acquiring strain information at multiple spatial locations, have wide applications in curvature measurement, shape reconstruction, and bending-torsional decoupling. Existing multi-core optical fiber shape sensing methods typically invert bending curvature and bending direction by the relative positional relationship of multiple cores within a cross-section. However, in helical arrangements or structures rotating axially, the orientation of the core cross-section continuously changes with the axial position. The orientation angle directly obtained from strain inversion usually only represents a local orientation angle relative to a reference core, rather than an absolute orientation angle relative to a fixed spatial coordinate system.
[0004] In this case, if the judgment is made based solely on the local orientation angle or solely on the undirected geometric information of the bending axis, an orientation angle deviation problem will occur, resulting in the inability to accurately identify the absolute bending direction.
[0005] In addition, existing methods are mostly designed for single-layer fiber core distribution or fixed cross-section arrangement, and lack a unified directional demodulation framework for double-layer, reverse spiral, and multi-reference coordinate system conditions, making it difficult to simultaneously take into account local demodulation accuracy and global directional recovery capability.
[0006] Therefore, it is necessary to propose a bending direction sensing device and demodulation method suitable for mirror-chiral multi-core optical fibers. By constructing a mapping relationship between the instantaneous azimuth angle of the reference core and the local direction angle, the direction conversion from the relative coordinate system to the absolute coordinate system is realized, thereby obtaining unique and continuous absolute bending direction information. Summary of the Invention
[0007] The purpose of this invention is to solve the problems in the prior art where local orientation angles are difficult to convert into absolute orientation angles and where double-layer reverse spiral structures are difficult to demodulate uniformly. This invention proposes a bending direction sensing device and demodulation method based on mirror-chiral multi-core optical fiber.
[0008] This invention is achieved through the following technical solution: This invention proposes a bending direction sensing device based on a mirrored chiral multi-core optical fiber. The sensing device includes an optical fiber carrier, a mirrored chiral multi-core optical fiber unit disposed within the optical fiber carrier or in its circumferential direction, a data acquisition module, and a demodulation processing module; the mirrored chiral multi-core optical fiber unit includes an outer core group and an inner core group. The data acquisition module is used to obtain the strain distribution information of each fiber core along the axial direction; The demodulation processing module is used to obtain the local curvature vector and local orientation angle in the corresponding relative coordinate system based on the strain data of the outer and inner fiber core groups, and to convert the local curvature vector into the absolute bending orientation angle in the absolute coordinate system based on the absolute azimuth angle of the reference fiber core in the absolute coordinate system, or to obtain the absolute bending orientation angle by adding the local orientation angles.
[0009] Furthermore, the outer ring fiber core assembly includes a first, third, and fifth fiber core, which are distributed at 120-degree intervals along the circumferential direction within the cross-section and extend spirally along the axial direction in a first direction of rotation; the inner ring fiber core assembly includes a second, fourth, and sixth fiber core, which are distributed at 120-degree intervals along the circumferential direction within the cross-section and extend spirally along the axial direction in a second direction of rotation opposite to the first direction of rotation; the first and second fiber cores serve as reference fiber cores for the outer ring and inner ring, respectively.
[0010] This invention also proposes a bending direction demodulation method based on mirror-chiral multi-core optical fiber, the demodulation method being implemented based on the aforementioned sensing device; the demodulation method specifically includes: Obtain strain data for the outer and inner fiber core assemblies; Based on the 120-degree distribution relationship between the three fiber cores in each group, the local curvature components of the outer and inner rings relative to the reference fiber core coordinate system are calculated respectively. Calculate the absolute azimuth angles of the outer and inner reference fiber cores at their respective axial positions; Based on the absolute azimuth angle, the local curvature vector is transformed to the absolute coordinate system using a rotation matrix; The absolute curvature direction angle is obtained from the absolute curvature vector in the absolute coordinate system.
[0011] Furthermore, the local curvature components are determined by the following equation:
[0012] in, These are the strain values of the three fiber cores in the same group, and r is the distribution radius of the three fiber cores relative to the center of the group.
[0013] Furthermore, the local curvature vector is represented as: .
[0014] Furthermore, the absolute azimuth angle of the reference fiber core is expressed as:
[0015] in, As a reference to the initial phase of the fiber core, It represents the helical angular velocity, with positive and negative signs corresponding to opposite helical directions of the two fiber core layers, respectively.
[0016] Furthermore, the absolute curvature vector is represented as:
[0017] in, .
[0018] Furthermore, the absolute bending direction angle is expressed as: .
[0019] Furthermore, the local orientation angle is: .
[0020] Furthermore, the absolute bending direction angle is obtained directly by adding the local direction angles, i.e.: .
[0021] The beneficial effects of this invention are: 1. This invention divides a mirrored chiral multi-core optical fiber into two three-core demodulation units, an outer ring and an inner ring, and establishes a local direction demodulation model in a relative coordinate system. Furthermore, it introduces the absolute azimuth angle of the reference fiber core to realize the conversion of the local direction angle to the absolute direction angle, and can stably recover the absolute bending direction under the condition that the spiral reference direction continues to change.
[0022] 2. This invention retains the directional information of the bending direction by constructing the local curvature vector and transforming the rotation matrix, thereby overcoming the problem of core position calibration caused by judging only based on the undirected bending axis. It can effectively distinguish the angles in the absolute coordinate system and the different physical bending states corresponding to the same straight line.
[0023] 3. This invention utilizes two sets of fiber cores with opposite rotation directions, outer and inner rings, to sense bending direction, enabling mutual verification and redundancy compensation, thereby improving the stability and reliability of direction recovery. It is applicable to applications such as continuum robots, flexible conduits, structural health monitoring, and three-dimensional shape perception. Attached Figure Description
[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0025] Figure 1 This is a schematic diagram of the cross-sectional structure of the mirrored chiral multi-core optical fiber of the present invention; Figure 2 This is a schematic diagram showing the outer and inner fiber core groups of the present invention distributed in opposite directions along the axial direction in a spiral pattern. Figure 3 This is a schematic diagram illustrating the principle of the present invention in recovering the local curvature vector and local orientation angle from three-core strain data in a relative coordinate system; Figure 4 This is a schematic diagram illustrating how the absolute bending direction angle is recovered from the relative direction angle and the absolute azimuth angle of the reference fiber core according to the present invention; Figure 5 This is a schematic diagram showing the results of the outer and inner fiber core groups of the present invention restoring their absolute bending directions. Detailed Implementation
[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0027] This invention proposes a bending direction sensing device and demodulation method based on a mirror-chiral multi-core optical fiber. The main innovation of this invention is that it abandons the traditional single-layer helical structure for measuring torsion, and instead uses a mirror-chiral multi-core optical fiber with the outer and inner rings arranged in opposite helical patterns to measure strain information. Compared to the problem of the absolute bending direction relying on the fiber's own coordinate system for calibration in conventional single-helical structures, this invention combines the transformation relationship between the relative and absolute coordinate systems of the reference core to achieve a demodulation method and device for bending direction identification and absolute direction recovery.
[0028] Specifically, in combination Figures 1-5 This invention proposes a bending direction sensing device based on a mirrored chiral multi-core optical fiber. The sensing device includes an optical fiber carrier, a mirrored chiral multi-core optical fiber unit disposed within the optical fiber carrier or in its circumferential direction, a data acquisition module, and a demodulation processing module. The mirrored chiral multi-core optical fiber unit includes an outer core group and an inner core group. The data acquisition module is used to obtain the strain distribution information of each fiber core along the axial direction; The demodulation processing module is used to obtain the local curvature vector and local orientation angle in the corresponding relative coordinate system based on the strain data of the outer and inner fiber core groups, and to convert the local curvature vector into the absolute bending orientation angle in the absolute coordinate system based on the absolute azimuth angle of the reference fiber core in the absolute coordinate system, or to obtain the absolute bending orientation angle by adding the local orientation angles.
[0029] Furthermore, the outer ring fiber core assembly includes a first, third, and fifth fiber core, which are distributed at 120-degree intervals along the circumferential direction within the cross-section and extend spirally along the axial direction in a first direction of rotation; the inner ring fiber core assembly includes a second, fourth, and sixth fiber core, which are distributed at 120-degree intervals along the circumferential direction within the cross-section and extend spirally along the axial direction in a second direction of rotation opposite to the first direction of rotation; the first and second fiber cores serve as reference fiber cores for the outer ring and inner ring, respectively.
[0030] This invention also proposes a bending direction demodulation method based on mirror-chiral multi-core optical fiber, the demodulation method being implemented based on the aforementioned sensing device; the demodulation method specifically includes: Obtain strain data for the outer and inner fiber core assemblies; Based on the 120-degree distribution relationship between the three fiber cores in each group, the local curvature components of the outer and inner rings relative to the reference fiber core coordinate system are calculated respectively. Calculate the absolute azimuth angles of the outer and inner reference fiber cores at their respective axial positions; Based on the absolute azimuth angle, the local curvature vector is transformed to the absolute coordinate system using a rotation matrix; The absolute curvature direction angle is obtained from the absolute curvature vector in the absolute coordinate system.
[0031] Furthermore, the local curvature components are determined by the following equation:
[0032] in, These are the strain values of the three fiber cores in the same group, and r is the distribution radius of the three fiber cores relative to the center of the group.
[0033] Furthermore, the local curvature vector is represented as: .
[0034] Furthermore, the absolute azimuth angle of the reference fiber core is expressed as:
[0035] in, As a reference to the initial phase of the fiber core, It represents the helical angular velocity, with positive and negative signs corresponding to opposite helical directions of the two fiber core layers, respectively.
[0036] Furthermore, the absolute curvature vector is represented as:
[0037] in, .
[0038] Furthermore, the absolute bending direction angle is expressed as: .
[0039] Furthermore, the local orientation angle is: .
[0040] Furthermore, the absolute bending direction angle is obtained directly by adding the local direction angles, i.e.: .
[0041] in, This is a local orientation angle defined relative to the reference fiber core direction.
[0042] Example The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0043] This embodiment provides a bending direction sensing device based on a mirror-chiral multi-core optical fiber. The device includes a multi-core optical fiber with a double-layer core. The double-layer core includes a first, third, and fifth core located in the outer ring, and a second, fourth, and sixth core located in the inner ring. The three outer cores are arranged at 120-degree intervals within the cross-section and extend helically in a clockwise direction along the axial direction; the three inner cores are also arranged at 120-degree intervals within the cross-section and extend helically in a counter-clockwise direction along the axial direction. The first and second cores are defined as the zero-degree reference direction cores of each layer.
[0044] In one embodiment, the pitch of the double-layer fiber cores is the same, both being five millimeters; the distribution radii of the outer and inner fiber cores are different; at the zero axial coordinate, the first and second fiber cores are located in the positive x-axis direction of the global coordinate system of the cross-section. For a certain axial position z, the absolute azimuth angles of the outer and inner reference fiber cores are respectively expressed as:
[0045] in, For the initial phase, p is the pitch.
[0046] Under bending, the strain of each fiber core satisfies:
[0047] in, The curvature is denoted by r, and r is the radius of the corresponding fiber core assembly. This is the absolute azimuth angle of the fiber core in the cross-section. This is the absolute curvature direction angle relative to the global coordinate system.
[0048] For any three-core group, based on the strain values of the three fiber cores... structure:
[0049]
[0050] Therefore, the local curvature vector is defined as:
[0051] Its corresponding local orientation angle is:
[0052] Since this local orientation angle is defined relative to the reference fiber core direction, it cannot be directly used as the global bending direction. Therefore, this invention further utilizes the absolute azimuth angle of the reference fiber core to transform the local curvature vector to an absolute coordinate system:
[0053] And further, we obtained:
[0054] In another embodiment, the absolute bending direction angle can also be obtained directly by adding the angles together, that is:
[0055] The summation of the above angles can be further normalized to limit the angles to a preset range.
[0056] In one example, when a bend of 37 degrees relative to the global x-axis and a radius of curvature of 1m is applied within an axial range of 100 mm to 150 mm, the orientation angles recovered by the outer and inner fiber core groups in the relative coordinate system will show different trends with the axial change. However, after the coordinate transformation described in this invention, both sets of data can be restored to a consistent absolute bending direction, thereby verifying the effectiveness of the method of this invention.
[0057] This invention can also be further combined with curvature modulus and orientation angle continuity constraints to achieve more robust orientation recovery; it can also be combined with torsional load demodulation module to extend to three-dimensional shape perception applications.
[0058] The foregoing has provided a detailed description of the bending direction sensing device and demodulation method based on mirrored chiral multi-core optical fiber proposed in this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.
Claims
1. A bending direction sensing device based on mirror-chiral multi-core optical fiber, characterized in that, The sensing device includes an optical fiber carrier, a mirrored chiral multi-core optical fiber unit disposed within or circumferentially on the optical fiber carrier, a data acquisition module, and a demodulation processing module; the mirrored chiral multi-core optical fiber unit includes an outer core group and an inner core group. The data acquisition module is used to obtain the strain distribution information of each fiber core along the axial direction; The demodulation processing module is used to obtain the local curvature vector and local orientation angle in the corresponding relative coordinate system based on the strain data of the outer and inner fiber core groups, and to convert the local curvature vector into the absolute bending orientation angle in the absolute coordinate system based on the absolute azimuth angle of the reference fiber core in the absolute coordinate system, or to obtain the absolute bending orientation angle by adding the local orientation angles.
2. The sensing device according to claim 1, characterized in that, The outer ring fiber core group includes a first, third, and fifth fiber core, which are distributed at 120-degree intervals along the circumferential direction within the cross-section and extend along the axial direction in a first spiral direction; the inner ring fiber core group includes a second, fourth, and sixth fiber core, which are distributed at 120-degree intervals along the circumferential direction within the cross-section and extend along the axial direction in a second spiral direction opposite to the first spiral direction; the first and second fiber cores serve as reference fiber cores for the outer ring and inner ring, respectively.
3. A bending direction demodulation method based on mirror-chiral multi-core optical fiber, characterized in that, The demodulation method is implemented based on the sensing device according to any one of claims 1-2; the demodulation method specifically includes: Obtain strain data for the outer and inner fiber core assemblies; Based on the 120-degree distribution relationship between the three fiber cores in each group, the local curvature components of the outer and inner rings relative to the reference fiber core coordinate system are calculated respectively. Calculate the absolute azimuth angles of the outer and inner reference fiber cores at their respective axial positions; Based on the absolute azimuth angle, the local curvature vector is transformed to the absolute coordinate system using a rotation matrix; The absolute curvature direction angle is obtained from the absolute curvature vector in the absolute coordinate system.
4. The demodulation method according to claim 3, characterized in that, The local curvature component is determined by the following formula: in, These are the strain values of the three fiber cores in the same group, and r is the distribution radius of the three fiber cores relative to the center of the group.
5. The demodulation method according to claim 4, characterized in that, The local curvature vector is represented as: 。 6. The demodulation method according to claim 3, characterized in that, The absolute azimuth angle of the reference fiber core is expressed as: in, As a reference to the initial phase of the fiber core, It represents the helical angular velocity, with positive and negative signs corresponding to opposite helical directions of the two fiber core layers, respectively.
7. The demodulation method according to claim 6, characterized in that, The absolute curvature vector is represented as: in, 。 8. The demodulation method according to claim 7, characterized in that, The absolute bending direction angle is expressed as: 。 9. The demodulation method according to claim 4, characterized in that, The local orientation angle is: 。 10. The demodulation method according to claim 9, characterized in that, The absolute bending direction angle can be obtained by directly adding the local direction angles, that is: 。