Three-dimensional shape reconstruction system combined with grating inversion technology and sensor preparation method

Abstract

The invention discloses a three-dimensional shape reconstruction system combined with a grating inversion technology and a sensor preparation method, and belongs to the technical field of optical fiber sensing. The system comprises a shape sensor, a grating demodulation device and a shape reconstruction device, an optical fiber bundle formed by a plurality of optical fiber grating strings or a multi-core optical fiber is attached to the outer side of the base material, but is not completely bonded, and is only subjected to point constraint to form a shape sensor; the demodulation device acquires spectral information in real time; the reconstruction device is combined with a spectrum inversion technology to restore and display a three-dimensional shape with high precision. The invention also comprises a manufacturing method of the shape sensor. The method comprises the following steps of: 1, manufacturing the optical fiber bundle or the multi-core optical fiber; secondly, the optical fiber bundle is arranged in a hollow hose bonded to the side edge of the base material, and only one end of the optical fiber bundle is fixed; the problem of low spatial resolution in the fiber bragg grating shape sensing technology is solved, meanwhile, the shape sensor structure can eliminate strain on the outer side of the base material when the base material is bent, and the optical fiber is protected.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber sensing technology, and in particular relates to a high-precision three-dimensional shape sensing reconstruction system combined with optical fiber grating inversion technology and a preparation method of a sensor used therein. Background Art

[0002] In recent years, medical surgical robots in minimally invasive surgery have attracted much attention. They provide doctors with more precise and safer means of operation and have achieved remarkable results. In order to achieve precise operation of surgical robots, shape sensing reconstruction technology is particularly critical. Shape sensing reconstruction technology can monitor and track the shape and position of surgical tools or robots in real time, providing accurate navigation and control for surgery. Among many shape sensors, fiber optic shape sensors have attracted much attention due to their unique working principles and technical advantages. Fiber optic shape sensors use optical principles to transmit light signals to the optical fiber on the object being measured, and monitor the reflection or transmission of the light signal to capture the morphological changes of the object in real time. Compared with other shape sensors, fiber optic shape sensors have the advantages of high precision, real-time monitoring and anti-interference.

[0003] In fiber shape sensing technology, FBG sensing is widely used in three-dimensional shape sensing reconstruction technology with high precision requirements due to its high sensitivity to strain and strong anti-interference performance. However, due to its quasi-distributed sensing characteristics, only a limited number of strain points can be obtained over a certain length. Therefore, FBG shape sensors using central wavelength demodulation usually require densely distributed gratings to obtain sufficient information points. However, in the case of long-distance shape sensing, when the bending conditions of some sections are complex, this method is prone to lose important strain information, resulting in large errors in the reconstruction results.

[0004] Therefore, there is an urgent need for a high-precision three-dimensional shape sensing reconstruction system that can obtain more information points without increasing the number of gratings to solve the above measurement problems.

[0005] During the bending process, the strain on the FBG is usually not uniform, but continuous and smooth non-uniform strain, and its reflection spectrum can contain information about the non-uniform strain in the grating area. The FBG spectral inversion technology can use the reflection spectrum signal of the FBG when it is subjected to non-uniform strain, and obtain the non-uniform strain field applied to a single grating through inversion. Inversion methods include particle swarm optimization algorithm, simulated annealing algorithm, deep learning, etc. Then, the smooth non-uniform strain information on the entire shape sensor is obtained through data processing methods such as interpolation. Interpolation methods include spline interpolation, Hermite interpolation, etc. The reconstruction algorithm is used to achieve high-precision three-dimensional shape reconstruction from continuous non-uniform strain.

[0006] Secondly, the core sensing element in the shape sensor is a fiber bundle or multi-core optical fiber composed of multiple optical fibers bonded together, which is generally tightly bonded to the substrate in the sensor or the core sensing element is the reconstruction object. In surgical robots, the central space needs to be reserved to integrate surgical equipment, so the shape sensor is suitable for being placed on the outside of the instrument. When the optical fiber is located on the outside of a thick diameter substrate and the substrate is bent more violently, the outside of the substrate itself will produce strain relative to the neutral axis of the substrate, and the larger the diameter, the greater the strain. For substrates with larger diameters and complex curved shapes, the sensing structure in which the optical fiber is tightly bonded to the substrate will cause the optical fiber to be subjected to extreme strain, thereby reducing the service life of the device and even failing to accurately measure the bending. Summary of the invention

[0007] In order to solve the above technical problems, the present invention uses a hollow hose tightly bonded to the substrate to control the position of the optical fiber, but there is room for relative movement between the optical fiber and the hollow hose. This structure can offset the external additional strain caused by the bending of the thick diameter substrate, so that the optical fiber only needs to bear the strain generated when its optical fiber bundle is bent, thereby significantly improving its service life and expanding the measurement range.

[0008] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0009] A high-precision three-dimensional shape sensing and reconstruction system combined with fiber grating inversion technology, comprising a shape sensor 1, a real-time fiber optic spectrum demodulation device 2 and a three-dimensional shape reconstruction device 3 combined with spectrum inversion technology, characterized in that: the shape sensor comprises a hollow substrate 1, a hollow hose 7 and an optical fiber bundle 8, the hollow hose 7 is fixed to the outer wall of the hollow substrate 1, the optical fiber bundle 8 is located inside the hollow hose 7, the front end of the optical fiber bundle 8 is fixed to the front end of the hollow hose 7, and the rear end of the optical fiber bundle 8 is a free end and connected to the real-time fiber optic spectrum demodulation device 2.

[0010] The optical fiber bundle 8 is made by bonding a plurality of optical fiber grating strings 6 in parallel.

[0011] Each fiber grating string 6 has a plurality of fiber gratings 10 , the fiber gratings 10 near the front end have smaller spacing, and the fiber gratings 10 in the remaining parts have larger spacing.

[0012] The three fiber grating strings 6 are bonded together with acrylic glue 9. From the cross section, the three fiber grating strings 6 are at an angle of 60° to each other. There are ten fiber gratings 10 in each fiber grating string 6. The four fiber gratings 10 near the front end have a spacing of 1-3mm, and the remaining fiber gratings 10 have a spacing of 8-12mm.

[0013] Another design: the optical fiber bundle 8 is a multi-core optical fiber that is evenly and stably arranged, and a plurality of gratings are engraved inside the optical fiber.

[0014] The reconstruction algorithm used in the reconstruction device is combined with spectral inversion technology. The spectrum generated after the grating is bent contains the non-uniform strain information of all grating regions. The non-uniform strain on each grating can be obtained from the spectral information by spectral inversion. The spectral inversion method is a particle swarm optimization algorithm, a simulated annealing algorithm or a deep learning method.

[0015] A method for preparing a shape sensor comprises the following steps:

[0016] (1) preparing a plurality of fiber grating strings or evenly and stably arranged multi-core optical fibers as an optical fiber bundle, preparing a hollow hose with an inner diameter slightly larger than the cross-sectional diameter of the expected optical fiber bundle, and a bendable substrate of any diameter;

[0017] (2) using an adhesive to make a fiber grating string into a fiber bundle with a central rotational symmetry in cross section, or writing a fiber grating inside a multi-core optical fiber with a uniform and stable arrangement;

[0018] (3) Insert the prepared optical fiber bundle or multi-core optical fiber into the hollow hose, and fix the optical fiber bundle or multi-core optical fiber to one end of the hollow hose with an adhesive, while leaving the other end unfixed. The fixed end is usually used as the front end of the sensor, and the pigtail at the unfixed end is used to connect to the demodulation device;

[0019] (4) Bond the hollow hose to the outer wall of the substrate.

[0020] The optical fiber bundle is made of an adhesive having certain flexibility after curing. The adhesive can tightly bond the optical fiber grating string to form an optical fiber bundle. Multiple optical fiber gratings are distributed in the optical fiber grating string. The optical fiber gratings near the front end have a smaller spacing, while the optical fiber gratings at other positions have a larger spacing.

[0021] The three fiber grating strings are bonded into a fiber bundle. From the cross section, the three fiber grating strings have an angle of 60° with each other. The grating positions in the three fiber grating strings are aligned and then bonded.

[0022] The beneficial effects of the present invention are:

[0023] (1) The shape sensing reconstruction system provided by the present invention uses a spectral inversion method to infer the reflection spectrum containing multiple micro-element strain information on the FBG. Compared with the central wavelength demodulation method that only obtains one strain information, this method obtains more strain points without increasing the number of gratings used, improves the spatial resolution, and reconstructs the three-dimensional shape with higher accuracy.

[0024] (2) In the shape sensing reconstruction system provided by the present invention, the structure of the hollow shape sensor can effectively offset the external strain of the large diameter and strong curved substrate. This prolongs the service life of the sensor and expands the sensor's measurement range, enabling it to cope with more measurement tasks in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of the high-precision three-dimensional shape sensing and reconstruction system of the present invention;

[0026] Figure 2 It is a structural schematic diagram of the shape sensor of the present invention;

[0027] Figure 3 It is a schematic diagram of the structure of the optical fiber bundle and the hose in the shape sensor of the present invention;

[0028] In the accompanying drawings: 1 is a shape sensor, 2 is a demodulation device, 3 is a reconstruction device, 4 is a shape display, 5 is a hollow substrate, 6 is a fiber grating string, 7 is a hollow hose, 8 is a fiber bundle made of three fiber gratings, 9 is acrylic glue, and 10 is a fiber grating. DETAILED DESCRIPTION

[0029] The specific embodiments of the present invention are further described in detail below, but the present invention is not limited to these embodiments, and any improvement or substitution based on the basic spirit of the present embodiment still falls within the scope of protection required by the claims of the present invention.

[0030] A high-precision three-dimensional shape sensing and reconstruction system combined with fiber Bragg grating inversion technology comprises: a shape sensor 1 of arbitrary diameter, a real-time fiber optic spectrum demodulation device 2, and a three-dimensional shape reconstruction device 3 combined with spectrum inversion technology, which can realize real-time sensing reconstruction and display of three-dimensional shape.

[0031] Preferably, the three-dimensional shape sensor 1 is composed of a substrate of any diameter (the neutral axis of the substrate is the reconstruction object), a core sensing element placed outside the hollow substrate, and other components for fixing the sensor structure. This structure places the sensing element outside the substrate and can be applied to shape sensing of a solid substrate or a substrate with a space in the center of the substrate reserved for other components.

[0032] Preferably, the core sensing element in the three-dimensional shape sensor is a fiber bundle 8 consisting of three or more fiber grating strings 6 or a multi-core optical fiber with three or more cores. The fiber bundle or multi-core optical fiber as a sensing element should have good flexibility, be able to bend freely, and have no length limit.

[0033] Preferably, the core sensing element is fitted to the outside of the substrate, but is not tightly bonded, and is only constrained at a point. Except for the constraint point, the sensing element is movable relative to the substrate, and the friction force received during the movement is small, and it will not be subject to large additional stress. The structure can be realized using a hollow hose 7: the sensing element is placed in the hollow hose 7, and only one or several constraint points are fixed, and the constraint point can be an arbitrary position. When the substrate is bent, the sensing element can move freely except for the constraint point. The hollow hose 7 is tightly bonded to the outside of the substrate to control the movable range of the sensing element. The range can be any shape, but it is best to make it relatively parallel to the neutral axis of the substrate. The sensor structure can offset the additional strain outside caused by the bending of the substrate, reduce the strain that the optical fiber bears when the substrate is bent, can expand the curvature measurement range of the sensor, and can prevent the damage caused by breaking, and increase the life of the sensing element.

[0034] Preferably, the reconstruction algorithm used in the reconstruction device is combined with spectral inversion technology. The spectrum generated after the grating is bent contains the non-uniform strain information of all grating regions, and the non-uniform strain on each grating can be obtained through spectral information through spectral inversion. The method includes but is not limited to: particle swarm optimization algorithm, simulated annealing algorithm, deep learning method, etc. Compared with using the grating center wavelength to demodulate the strain information and reconstruct it, this method has higher accuracy and solves the problem that the center wavelength of the spectrum is difficult to identify under strong bending.

[0035] The method for preparing the shape sensor 1 comprises the following steps:

[0036] (1) Prepare a plurality of fiber grating strings 6 (the number and position of gratings are the same: the number of gratings is greater than or equal to 3, and the gratings are unevenly distributed, depending on the shape complexity of the actual shape. The grating interval is smaller when the shape complexity is high, and the interval is larger when the complexity is low), adhesive, a hollow hose 7 with an inner diameter slightly larger than the expected cross-sectional diameter of the fiber bundle, and a flexible substrate of any diameter; (or use a multi-core optical fiber with a uniform and stable arrangement, and write a fiber grating inside).

[0037] (2) The fiber grating string 6 is made into a fiber bundle 8 with a cross section showing central rotational symmetry by using an adhesive.

[0038] (3) Insert the prepared optical fiber bundle 8 or multi-core optical fiber into the hollow hose 7, and fix the optical fiber bundle 8 to one end of the hollow hose 7 with an adhesive, while leaving the other end unfixed. The fixed end is usually used as the front end of the sensor, and the pigtail at the unfixed end will be connected to the demodulation device.

[0039] The optical fiber bundle 8 is made of an adhesive having a certain flexibility after curing, and the adhesive can tightly bond the fiber grating string 6 to form an optical fiber bundle 7. When the optical fiber bundle 8 is bent, the optical fiber inside the bend is compressed, and the optical fiber outside the bend is stretched. The strain of the corresponding grating can be obtained through the real-time spectrum of the fiber grating string 6, and the three-dimensional bending information can be obtained through the strain, so as to reconstruct the shape.

[0040] The sensor diameter can be selected arbitrarily, and a sensor with a large diameter shape can be made. The core sensing element optical fiber bundle is located outside the sensor, and the reconstructed shape is the neutral axis of the substrate. Other devices can be integrated inside the substrate or it can be in a solid state. The optical fiber bundle 8 is not directly bonded to the substrate as a whole, but is placed in a hollow hose 7 bonded to the substrate. And only one end of the optical fiber bundle 8 and the hollow hose 7 is fixed, and the other end can move with the bending of the substrate. When the substrate is bent, the optical fiber bundle 8 is located on the outside of the bend, and the hollow hose 7 is stretched, and the optical fiber bundle 8 will not bear the redundant strain outside the substrate, showing a phenomenon of contraction to the inside of the hollow hose 7. Conversely, when the substrate is bent, the optical fiber bundle 8 is located on the inside of the bend, and the hollow hose 7 is compressed, and the optical fiber bundle 8 shows a phenomenon of extending out of the hollow hose 7. This structure can offset the outer strain caused by the bending of the large diameter substrate, and the optical fiber bundle 8 only needs to sense the strain corresponding to its own shape, which can expand the sensing range and increase the life of the sensor. In addition, the optical fiber bundles mentioned here can be replaced with multi-core optical fibers with corresponding characteristics.

[0041] The present invention provides the application of the high-precision three-dimensional shape sensing and reconstruction system combined with fiber Bragg grating inversion technology in a medical surgical robot, which can realize the real-time sensing and reconstruction of the shape of a surgical robot with an internal integrated surgical device. Applying it to a surgical robot can not only directly perform shape sensing and reconstruction on a surgical robot with an integrated surgical device, but also greatly improve the accuracy.

[0042] Example 1: Shape Sensor

[0043] like Figure 1 , Figure 2 and Figure 3 As shown, the three-dimensional shape sensing and reconstruction system includes: 1 is a shape sensor, 2 is a demodulation device, 3 is a reconstruction device, 4 is a shape display, 5 is a hollow substrate, 6 is a fiber grating string, 7 is a hollow hose, 8 is a fiber bundle made of three fiber gratings, 9 is acrylic glue, and 10 is a fiber grating.

[0044] The demodulation device 2 obtains spectral information, the reconstruction device 3 has a built-in reconstruction algorithm combined with deep learning spectral inversion, the hollow substrate 5 is a plastic metal hollow substrate with a diameter greater than or equal to 4 mm, the fiber grating string 6 is an optical fiber engraved with 125μm quartz single-mode optical fiber with a coating layer and contains 10 FBGs (6 FBGs are spaced 10mm apart in pairs, and the 4 FBGs near the front end are spaced 2mm apart in pairs), the hollow hose 7 is a polyfluoro tube with an inner diameter of 6mm, and the fiber grating 10 is a 15mm FBG.

[0045] The preparation method of the shape sensor 1 is as follows: prepare three fiber grating strings 6 with the same number and position of gratings (one end has densely distributed gratings, which is the front end of the sensor), acrylate glue 9, a hollow hose 7 with an inner diameter of 0.6 mm, and a hollow substrate 5; use acrylate glue 9 to make the three fiber grating strings 6 into a fiber bundle 8 with a cross section showing central rotational symmetry; insert the prepared fiber bundle 8 into the hollow hose 7, and use glue to fix the grating-dense end of the fiber bundle 8 to the front end of the hollow hose 7, while the other end is not fixed. The fixed end will serve as the strong bending part at the end of the sensor, and the pigtail at the unfixed end will be connected to the demodulation device.

[0046] Example 2: Application of high-precision three-dimensional shape sensing reconstruction system for large diameter hollow substrate

[0047] The shape sensor 1 prepared in Example 1 is applied to the entire large diameter hollow substrate high-precision three-dimensional shape sensing reconstruction system: Figure 1 As shown, the three-dimensional shape sensing and reconstruction system includes the shape sensor 1 prepared in Example 1, the light beam enters the fiber grating string 6 from the demodulation system 2, the light beam reflected by the internal fiber grating 10 returns to the demodulation system 2 to obtain spectral information, the spectral information is input into the reconstruction system 3, and the shape is reconstructed by the reconstruction system 3 and displayed on the display 4.

[0048] like Figure 1 As shown, the experimental steps of a high-precision three-dimensional shape sensing reconstruction system for a large-diameter hollow substrate are as follows:

[0049] (1) The shape sensor 1 prepared in Example 1 is mounted on a large-diameter hollow substrate to ensure a stable connection;

[0050] (2) Light is introduced from the demodulation system 2 into the fiber Bragg grating string 6, and the optical signal reflected by the fiber Bragg grating 10 returns to the demodulation system 2 and then enters the reconstruction system 3;

[0051] (3) processing the collected optical signal by the reconstruction system 3, including two processes of inversion and reconstruction, to obtain the three-dimensional shape information sensed by the shape sensor 1;

[0052] (4) Finally, the shape information is displayed on the display 4, so that the operator can intuitively observe the shape change of the large-diameter hollow base material.

[0053] It is necessary to point out here that the above embodiments are limited to further elaboration and understanding of the technical solution of the present invention and cannot be understood as further limitation of the technical solution of the present invention. Inventions and creations with non-outstanding essential features and significant progress made by those skilled in the art still fall within the protection scope of the present invention.

Claims

1. A high-precision three-dimensional shape sensing and reconstruction system combined with fiber Bragg grating inversion technology, comprising a shape sensor (1), a real-time fiber spectral demodulation device (2) and a three-dimensional shape reconstruction device (3) combined with spectral inversion technology, characterized in that: The shape sensor comprises a substrate (1), a hollow hose (7) and an optical fiber bundle (8), wherein the hollow hose (7) is fixed to the outer wall of the substrate (1), the optical fiber bundle (8) is located inside the hollow hose (7), the front end of the optical fiber bundle (8) is fixed to the front end of the hollow hose (7), and the rear end of the optical fiber bundle (8) is a free end and connected to a real-time optical fiber spectrum demodulation device (2).

2. The high-precision three-dimensional shape sensing reconstruction system combined with fiber Bragg grating inversion technology according to claim 1, characterized in that: The optical fiber bundle (8) is made by bonding a plurality of optical fiber grating strings (6) in parallel.

3. The high-precision three-dimensional shape sensing reconstruction system combined with fiber Bragg grating inversion technology according to claim 2, characterized in that: Each fiber grating string (6) contains a plurality of fiber gratings (10), which are pre-designed according to the shape that may appear on the substrate during application. The fiber gratings (10) in the portion with a more complex shape have a smaller spacing, while the fiber gratings (10) in the remaining portion have a larger spacing.

4. The high-precision three-dimensional shape sensing reconstruction system combined with fiber Bragg grating inversion technology according to claim 3, characterized in that: The three fiber grating strings (6) are bonded together using a glue that becomes flexible and bendable after curing, and the three fiber grating strings (6) are mutually angled at 60° when viewed from a cross section, or more than three fiber grating strings are bonded together, with one optical fiber as the center and the remaining optical fibers distributed around the center optical fiber.

5. The high-precision three-dimensional shape sensing and reconstruction system combined with fiber Bragg grating inversion technology according to claim 4, characterized in that: The glue is acrylic glue (9), and each fiber grating string (6) has ten fiber gratings (10), the four fiber gratings (10) near the front end have a spacing of 1-3 mm, and the remaining fiber gratings (10) have a spacing of 8-12 mm.

6. The high-precision three-dimensional shape sensing and reconstruction system combined with fiber Bragg grating inversion technology according to claim 1, characterized in that: The optical fiber bundle (8) is a multi-core optical fiber that is evenly and stably arranged, and a plurality of gratings are engraved inside the optical fiber.

7. The high-precision three-dimensional shape sensing and reconstruction system combined with fiber Bragg grating inversion technology according to any one of claims 1 to 6, characterized in that: The reconstruction algorithm used in the reconstruction device is combined with spectral inversion technology. The spectrum generated after the grating is bent contains the non-uniform strain information of all grating areas. Spectral inversion can be used to obtain the non-uniform strain on each grating from the spectral information. The spectral inversion method is a particle swarm optimization algorithm, a simulated annealing algorithm or a deep learning method.

8. A method for preparing a shape sensor, characterized in that The following steps are involved: (i) preparing a plurality of fiber grating strings (6) or evenly and stably arranged multi-core optical fibers as an optical fiber bundle (8), preparing a hollow hose (7) with an inner diameter slightly larger than the expected cross-sectional diameter of the optical fiber bundle, and a bendable substrate of any diameter; (ii) using an adhesive to form a fiber grating string (6) into a fiber bundle (8) whose cross section presents central rotational symmetry, or writing gratings inside a multi-core optical fiber that is evenly and stably arranged; (iii) inserting the prepared optical fiber bundle (8) or multi-core optical fiber into the hollow hose (7), fixing the optical fiber bundle (8) or multi-core optical fiber to one end of the hollow hose (7) with an adhesive, and leaving the other end unfixed, the fixed end usually serving as the front end of the sensor, and the pigtail at the unfixed end serving to connect to a demodulation device; (iv) bonding the hollow hose (7) to the outer side wall of the substrate.

9. The method for preparing the shape sensor according to claim 6, characterized in that: The optical fiber bundle 8 is made of an adhesive having a certain flexibility after curing. The adhesive can tightly bond the optical fiber grating string 6 to form an optical fiber bundle 8. A plurality of optical fiber gratings 10 are distributed in the optical fiber grating string 6. The optical fiber gratings 10 near the front end have a smaller spacing, while the optical fiber gratings 10 at other positions have a larger spacing.

10. The method for preparing the shape sensor according to claim 7, characterized in that: The three fiber grating strings 6 are bonded into a fiber bundle 8. The three fiber grating strings 6 have an angle of 60° with each other as seen from the cross section. The gratings in the three fiber grating strings 6 are aligned before bonding.

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