CN-121995568-A - Double-spiral-structure multi-core fiber grating array and torsion measurement method

CN121995568ACN 121995568 ACN121995568 ACN 121995568ACN-121995568-A

Abstract

The invention discloses a double-helix-structure multi-core fiber grating array and a torsion measurement method. The array comprises 1+N+M independent optical fibers, wherein gratings are engraved on the independent optical fibers, and the independent optical fibers are wrapped by a coating layer to form a double-layer spiral structure. The inner layer is composed of 1 central straight optical fiber and N inner spiral optical fibers coiled along a first direction. The outer layer is composed of M outer spiral optical fibers coiled in opposite directions. The present invention provides both raster interleaving and alignment configurations. The invention utilizes the same-layer phase difference to accurately decouple the bending interference, breaks the limited bottleneck of single-helix measurement by the complementary characteristics of double-layer reverse helices, realizes omnidirectional large-scale torsion measurement, and can improve the space sampling rate or the micro torsion measurement precision according to configuration.

Inventors

GAO HAORAN
YU DONGYOU
ZHAO CHUNLIU

Assignees

峰澜科技(绍兴)有限公司

Dates

Publication Date: 20260508
Application Date: 20260324

Claims (9)

1. The utility model provides a double helix structure multicore fiber bragg grating array which characterized in that: comprises 1+N+M independent optical fibers, and is jointly wrapped by an external coating layer; The 1+N+M optical fibers are spatially arranged into a double-layer spiral structure; The double-layer spiral structure comprises an inner layer structure, an outer layer structure and a plurality of outer layers, wherein the inner layer structure is formed by 1+N optical fibers and comprises a central straight optical fiber which is positioned at the geometric center of the cross section of the optical fiber and has the extending direction parallel to the axis of the optical fiber, and N inner spiral optical fibers which are coiled around the central straight optical fiber in a first spiral direction; wherein N is more than or equal to 3, and M is more than or equal to 3.
2. The dual spiral structure multicore fiber grating array of claim 1, wherein: Comprises 1+N+M independent optical fibers, wherein all the optical fibers comprise a series of inscribed fiber Bragg gratings; A series of gratings are carved in all the internal spiral optical fibers along the axial direction of the optical fibers to form a first group of periodic measuring points; All the outer spiral optical fibers are inscribed with a series of gratings along the axial direction of the optical fibers to form a second group of periodic measuring points; And a series of gratings are inscribed in the central straight optical fiber along the axial direction, and the axial positions of the gratings in the central straight optical fiber are aligned with the axial positions of the first group of periodic measurement points or the second group of periodic measurement points in a one-to-one correspondence manner respectively, so as to provide tensile strain and environmental temperature compensation.
3. The dual spiral structure multicore fiber grating array of claim 2, wherein: a series of gratings inscribed in all the internal spiral optical fibers, the centers of which are aligned with each other in the axial direction of the optical fibers; A series of gratings inscribed in all the external spiral optical fibers, the centers of which are aligned with each other in the axial direction of the optical fibers; the first set of periodic measurement points and the second set of periodic measurement points are distributed in an axially staggered manner.
4. A dual spiral structure multicore fiber grating array according to claim 3, wherein: setting the axial distribution period of the gratings as L, wherein a series of gratings in the internal spiral optical fiber are positioned at positions 0, L, 2L and 3L; A series of gratings in the outer spiral fiber are located at positions L/2, 3L/2, 5L/2, 7L/2. A series of gratings in the central straight fiber are located at positions 0, L/2, L, 3L/2. The position offset of each grating is (+ -) DeltaL, and DeltaL is not more than L/5.
5. The dual spiral structure multicore fiber grating array of claim 2, wherein: a series of gratings inscribed in all the internal spiral optical fibers, the centers of which are aligned with each other in the axial direction of the optical fibers; A series of gratings inscribed in all the external spiral optical fibers, the centers of which are aligned with each other in the axial direction of the optical fibers; the periodic positions in the optical fiber axis of the series of gratings written in all the inner spiral optical fibers and the series of gratings written in all the outer spiral optical fibers are all aligned with each other.
6. The dual spiral structure multi-core fiber grating array of claim 5, wherein: setting the axial distribution period of the gratings as L, wherein a series of gratings of the inner spiral optical fiber, the outer spiral optical fiber and the central straight optical fiber are all positioned at positions 0, L, 2L and 3L; The position offset of each grating is (+ -) DeltaL, and DeltaL is not more than L/5.
7. A torsion measurement method based on the double helix-structured multicore fiber grating array according to any one of claims 1 to 6, comprising the steps of: step one, decoupling bending strain and initial calculation of torsion Collecting grating wavelength offset of a plurality of internal spiral optical fibers or external spiral optical fibers with specific spatial phase difference in the same spiral layer, carrying out joint calculation by utilizing spatial distribution characteristics of different fiber cores in the same layer, eliminating additional strain interference caused by bending, and preliminarily calculating torsional strain of the spiral layer; step two, double-layer torsion rate independent calculation Based on the physical configuration of the inner spiral optical fiber and the outer spiral optical fiber with opposite spiral directions, respectively processing sensing signals of the inner spiral layer and the outer spiral layer, and independently calculating to obtain the torsion rate of the inner spiral layer and the torsion rate of the outer spiral layer; step three, omnidirectional torsion synthesis and range expansion And when the unidirectional torsion is detected to cause the single-layer optical fiber to enter a measurement nonlinear region or a dead zone, the measurement data of the other reverse spiral layer is used for compensation or replacement, thereby realizing the reconstruction and accurate measurement of the omnidirectional and large-scale torsion morphology.
8. The torsion measurement method according to claim 7, wherein: By adopting the staggered distribution of the grating axial positions in the inner spiral optical fiber and the outer spiral optical fiber according to the claim 3 and the claim 4, the effective space sampling rate of the whole array is improved by utilizing the complementation of the interlayer grating positions under the condition that the writing density of the single fiber grating is unchanged.
9. The torsion measurement method according to claim 7, wherein: When the double-helix multi-core fiber grating array adopts a distribution mode that the axial positions of gratings in an inner helical fiber and an outer helical fiber are aligned, the first torsion rate data calculated by an inner helical fiber layer and the second torsion rate data calculated by an outer helical fiber layer are synchronously acquired at the same axial position, differential processing is carried out on the first torsion rate data and the second torsion rate data, the measuring variation amplitude is increased, random measuring noise is reduced, and high-precision measurement of small torsion in a small range is realized.

Description

Double-spiral-structure multi-core fiber grating array and torsion measurement method Technical Field The invention belongs to the technical field of fiber bragg grating arrays, and particularly relates to a double-helix-structure multi-core fiber bragg grating array and a torsion measurement method. Background With the continuous development of high-end equipment and intelligent systems to the flexible, precise and large-scale directions, unprecedented high requirements are put forward on real-time, online and distributed sensing of complex three-dimensional space shapes and multidimensional mechanical parameters. Under the background, the optical fiber shape sensing technology has the outstanding advantages of electromagnetic interference resistance, severe environment resistance, small volume, light weight, absolute measurement and the like, and becomes a key enabling technology in the front fields of robot smart hand and continuum mechanical arm gesture feedback, aerospace aircraft wing deformation monitoring, large-scale wind driven generator blade load analysis, cardiovascular and nerve intervention surgical instrument navigation and the like. The Fiber Bragg Grating (FBG) is a device for linearly modulating physical quantities such as environmental strain, temperature and the like into reflected wavelength changes, and is a core sensing unit for realizing discrete or quasi-distributed measurement. The multi-core optical fiber provides a physical carrier for acquiring information of a plurality of space points in parallel by integrating a plurality of independent fiber cores which are separated in space in a single cladding. The fiber grating array is inscribed in each fiber core of the multi-core fiber, so that the advantages of multi-point measurement and space diversity multiplexing are effectively combined, the information dimension and reliability of shape reconstruction are remarkably improved, and the fiber grating array becomes one of the most active research directions in the current fiber sensing field. The current mainstream multi-core fiber grating array technical route still faces fundamental challenges when dealing with complex deformations, especially deformation sensing accompanied by torsion. First, the most common array of parallel-arranged cores, in which the cores are symmetrically distributed in the fiber cross-section, is sensitive to bending strain, but has almost the same response to torsional deformation about the fiber axis, and it is difficult to effectively decouple pure torsional components. This results in a sensor that, when monitoring scenes that contain significant torsional deformations, such as robot arm joint rotation, cable twisting, helicopter rotor torsional vibrations, etc., has a perceived "dead zone" or produces serious resolving errors that do not allow complete and accurate restoration of the three-dimensional space curve. Secondly, to enhance torsional sensitivity, recent studies have proposed the introduction of a helically arranged structure in the core. Such single-layer helical-structured multicore fibers successfully convert torsional strain into axial strain of the core by deflecting the core from the neutral axis and extending helically, and are thus perceived by the FBG. However, the scheme has obvious limitations that firstly, all fiber cores are of a spiral structure in a single direction, so that the measurement of the forward torsion of the spiral is more sensitive, the measurement range of the reverse torsion of the spiral is limited, and secondly, in order to obtain enough spatial resolution to accurately describe the shape (especially curvature) change, a dense grating array (the grating area spacing is often in the centimeter level) is usually required to be written on each spiral fiber core, and the preparation complexity and the system cost are greatly increased. In order to prepare the technological level, the existing manufacturing process of the high-performance multi-core fiber grating array forms another main bottleneck of large-scale application. The main stream method is to firstly prepare or purchase multi-core optical fibers with specific fiber core arrangement (parallel or spiral) and then write gratings point by point in the fiber cores through complex post-processing flow. This process typically involves the steps of precision stripping of the coating, point-by-point scanning writing based on a phase mask and an ultraviolet laser, and recoating protection. The mode has the inherent defects of multiple process steps, low production efficiency, possibility of damaging the mechanical strength of the optical fiber in the stripping and recoating process, difficulty in overcoming the defects of difficulty in ensuring high consistency of grating forming quality (such as center wavelength, reflectivity and bandwidth) in a plurality of fiber cores, huge positioning precision and repeatability challenges in long-distance writing, discret