Five-axis force sensor based on fiber bragg grating and manufacturing method

Abstract

The invention provides a fiber grating-based five-axis force sensor and a manufacturing method, the fiber grating-based five-axis force sensor comprises a base ring, spiral beams and a stress ring, the spiral beams are connected with the base ring and the stress ring, three spiral beams are arranged between the base ring and the stress ring at equal intervals, and at least two cavities for accommodating optical fibers are arranged in any spiral beam; any optical fiber in the spiral beam is provided with at least two Bragg fiber gratings. A spiral beam structure and a fiber grating sensing technology are adopted, so that the sensor has five-axis external force sensing capacity under the condition of small size, and meanwhile, the sensor is provided with a large inner cavity reserved for an external instrument, for example, the external instrument intervenes into a human body through a continuous cavity and a sensor cavity. And through the design of the cavity channel, the optical fiber is arranged in the cavity channel, so that the optical fiber can be protected, and the service life of the sensor is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a five-axis force sensor based on fiber grating and a manufacturing method thereof. Background Art

[0002] Force sensors are devices that convert force values ​​into related electrical signals. Force is the direct cause of changes in material movement. Force sensors can detect mechanical quantities such as tension, pulling force, pressure, weight, torque, internal stress and strain. Specific devices include metal strain gauges, pressure sensors, etc., which have become indispensable core components in power equipment, engineering machinery, various machine tools and industrial automation systems.

[0003] The existing Chinese patent application document with publication number CN115839792A discloses a three-dimensional force sensor for minimally invasive abdominal surgical instruments and a method of using the same, including a strain elastomer and a fiber grating sensor; the strain elastomer is an integrated structure and is made of elastic material, the strain elastomer includes an upper disc, a lower disc and three spiral beams, the top of the spiral beam is connected to the bottom of the upper disc, the bottom of the spiral beam is connected to the top of the lower disc, and the three spiral beams are distributed on the circumference of the upper disc and the lower disc at intervals of 120 degrees; the fiber grating sensor includes a first fiber grating, a second fiber grating, a third fiber grating and a fourth fiber grating connected in sequence; the first fiber grating, the second fiber grating and the third fiber grating are respectively arranged on the inclined surface of the spiral beam, and the fourth fiber grating is arranged on the surface of the lower disc.

[0004] The force sensor in the prior art is a three-dimensional force sensor, which is unable to sense five-axis external force. Currently, the market is in urgent need of a five-axis force sensor that has five-axis external force sensing capability in a small size and has a large inner cavity reserved for external instruments. Summary of the invention

[0005] In view of the defects in the prior art, an object of the present invention is to provide a five-axis force sensor based on fiber grating and a manufacturing method thereof.

[0006] According to the present invention, a five-axis force sensor based on fiber grating includes a base ring, a spiral beam and a force ring, wherein the spiral beam connects the base ring and the force ring, and three spiral beams are arranged at equal intervals between the base ring and the force ring, and at least two cavities for accommodating optical fibers are arranged in any of the spiral beams; and at least two Bragg fiber gratings are arranged on any optical fiber in the spiral beam.

[0007] Preferably, the spiral beam is provided with two cavities for accommodating optical fibers, and the two cavities on the spiral beam are symmetrically distributed along the center line of the spiral beam.

[0008] Preferably, the fiber Bragg gratings on the two optical fibers on any one of the spiral beams are symmetrically distributed along the center line of the spiral beam.

[0009] Preferably, the fiber Bragg gratings located in the same cross section on the three spiral beams are distributed along the circumference of the sensor.

[0010] Preferably, the middle parts of the base ring and the stress ring are both provided with through holes, and the three spiral beams are all arranged on the circumference of the base ring and the stress ring.

[0011] Preferably, the wavelength change of the fiber Bragg grating caused by temperature change can be calculated from the wavelength changes of the 12 gratings as follows:

[0012]

[0013] Where: Δλ in the formula i The wavelength changed for each grating.

[0014] Preferably, the five-axis force is predicted by a machine learning method, the input of the prediction network is the wavelength of 12 gratings after temperature compensation, and the output is three-axis forces Fx, Fy and Fz, and two radial moments Mx and My.

[0015] According to a method for manufacturing a five-axis force sensor based on fiber grating provided by the present invention, the manufacturing method comprises the following steps:

[0016] Step S1, manufacturing a preform according to the size and cavity distribution of a target product;

[0017] Step S2, stretching the preform rod by heating and drawing;

[0018] Step S3, cutting out a sensor body having three straight beam structures from the stretched preform rod;

[0019] Step S4, twisting the sensor body;

[0020] Step S5, heating and shaping the twisted sensor body.

[0021] Preferably, for step S3, three straight beam structures are distributed along the circumference of the sensor body, and any two adjacent straight beam structures are spaced 120 degrees apart from each other.

[0022] Preferably, for step S4, the spiral fixing body and at least three spiral fixing blocks are assembled onto a sensor body having three straight beam structures, and the three straight beam structures are rotated to form a spiral state;

[0023] For step five, during heating and shaping, the assembly having the spiral fixing body and at least three spiral fixing blocks is placed in an oven for heating and shaping. After the preset time is reached, the assembly is taken out of the oven and the spiral fixing body and all the spiral fixing blocks are taken out to obtain the sensor spiral beam body.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention adopts a spiral beam structure and fiber grating sensing technology, so that the sensor has five-axis external force sensing capability in a small size, and also has a large inner cavity reserved for external instruments, such as external instruments inserted into the human body through the continuous body cavity and the sensor cavity.

[0026] 2. The present invention realizes temperature compensation of the sensor by arranging the FBGs in a circumferential distribution on the spiral beam, overcomes the influence of temperature change on the sensor measurement, and improves the measurement accuracy of the sensor.

[0027] 3. The present invention takes into account that when the outer diameter of the sensor is as small as the millimeter level, the spiral structure and the cavity within the spiral structure are difficult to manufacture through conventional 3D printing, machining and the like, and adopts hot drawing and hot twisting to solve the manufacturing problem.

[0028] 4. The present invention arranges the optical fiber in the cavity through the design of the cavity, which can protect the optical fiber and increase the service life of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of 1. non-limiting embodiment with reference to the following drawings:

[0030] Figure 1 This is a schematic diagram of the overall structure of the sensor body mainly embodied in the present invention;

[0031] Figure 2 This is a schematic diagram of the overall cross-sectional structure of the sensor body that mainly embodies the present invention;

[0032] Figure 3 This is a schematic diagram of preform stretching mainly embodied in the present invention;

[0033] Figure 4 This is a schematic diagram of the overall structure of the sensor body before torsion, which is mainly embodied in the present invention;

[0034] Figure 5 This is a schematic diagram of the torsion of the sensor body mainly embodied in the present invention.

[0035] As shown in the figure:

[0036] Sensor body 1 Force ring 103

[0037] Base ring 101 Fiber Bragg grating 2

[0038] Spiral beam 102 Spiral fixing block 8 DETAILED DESCRIPTION

[0039] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0040] like Figure 1 and Figure 2 As shown, a five-axis force sensor based on a fiber Bragg grating 2 provided according to the present invention includes a base ring 101, a spiral beam 102 and a force ring 103, wherein the spiral beam 102 connects the base ring 101 and the force ring 103, and three spiral beams 102 are arranged at equal intervals between the base ring 101 and the force ring 103, and at least two cavities for accommodating optical fibers are arranged in any spiral beam 102. At least two Bragg fiber Bragg gratings 2 are arranged on any optical fiber in the spiral beam 102.

[0041] In a preferred embodiment: two cavities for accommodating optical fibers are provided on the spiral beam 102, and the two cavities on the spiral beam 102 are symmetrically distributed along the center line of the spiral beam 102. The Bragg fiber gratings 2 on the two optical fibers on any spiral beam 102 are symmetrically distributed along the center line of the spiral beam 102. The Bragg fiber gratings 2 located in the same cross section on the three spiral beams 102 are distributed along the circumference of the sensor. By designing the cavity, the optical fiber is arranged in the cavity, which can protect the optical fiber and improve the service life of the sensor.

[0042] Specifically, the base ring 101 is used to fix the sensor, for example, to fix the sensor to the end of the surgical connector robot. The spiral beam 102 is composed of three independent beams. The pitch and spiral angle of each spiral beam 102 are the same, and each spiral beam 102 has two cavities inside for placing optical fibers. The force ring 103 is used to withstand external forces and interact with the external environment. There are six optical fibers in total, each of which has two Bragg fiber gratings 2 (FBGs). Every two optical fibers are assembled in a spiral beam 102 and fixed to the spiral beam 102.

[0043] The wavelength change of the fiber Bragg grating 2 caused by temperature change can be calculated from the wavelength changes of the 12 gratings as follows:

[0044]

[0045] Where: Δλ in the formula iThe wavelength changed for each grating.

[0046] Since there are two optical fibers on each spiral beam 102, there is a certain relationship between the arrangement of the six optical fibers and the position of the two Bragg fiber gratings 2 on each optical fiber. The five-axis force can be predicted by the arrangement relationship between the six optical fibers and the position relationship of the two Bragg fiber gratings 2 on each optical fiber through the machine learning method. The input of the prediction network is the wavelength of the 12 gratings after temperature compensation, and the output is the three-axis force Fx, Fy and Fz, and two radial moments Mx and My. It should be noted that the prediction network of machine learning can be learned and calculated using a BP neural network. The wavelength of the 12 gratings after temperature compensation is used as the input of the BP neural network, and the output is the three-axis force Fx, Fy and Fz, and two radial moments Mx and My.

[0047] Furthermore, the middle of the base ring 101 and the force ring 103 are both provided with through holes, and the three spiral beams 102 are all arranged on the circumference of the base ring 101 and the force ring 103. The sensor has a large inner cavity reserved for external instruments, such as external instruments inserted into the human body through the continuous body cavity and the sensor cavity.

[0048] More specifically, the fiber Bragg grating 2 is fixed in the cavity of the spiral beam 102 of the sensor body 1. Each spiral beam 102 has two cavities, each cavity fixes an optical fiber, and each optical fiber has two fiber Bragg gratings 2. The wavelength of the fiber Bragg grating 2 will change with the deformation of the spiral beam 102. When the force ring 103 of the sensor body 1 interacts with the outside world and is acted upon by external forces, the spiral beam 102 will be strained to a certain extent, thereby causing the wavelength of the optical fiber to change. The assembled sensor is as follows: Figure 1 As shown, Figure 2 Since there are two Bragg fiber gratings 2 on each beam, the radial forces Fx and Fy, as well as the two radial moments Mx and My, can be quickly solved through the arrangement relationship between the six optical fibers and the position relationship between the two FBGs on each optical fiber.

[0049] When the sensor is subjected to axial force, the compression or extension of all beams is consistent. The technical solution of the present application decouples the axial force of the sensor by means of a spiral beam 102. The two cavities on the spiral beam 102 are symmetrically distributed along the center line of the beam, and after assembly, the Bragg fiber gratings 2 on the optical fibers in the two cavities are also symmetrically distributed along the center line of the beam. When the sensor is subjected to axial force, the wavelength change values ​​of the FBGs symmetrically arranged on each curved beam are the same in magnitude and opposite in direction, so the axial force Fz can be decoupled through this feature.

[0050] In addition, after assembly, the FBGs at corresponding positions on the three spiral beams 102 are distributed along the circumference of the sensor. This feature can further decouple the effect of temperature change on sensor measurement. The wavelength change caused by temperature change is

[0051] Among them, Δλ in the formula i The wavelength changed for each grating.

[0052] It should be noted that, before the three beams of the sensor body 1 are twisted, the three beams are distributed along the circumference of the sensor and are spaced 120 degrees apart from each other.

[0053] According to a method for manufacturing a five-axis force sensor based on a fiber Bragg grating 2 provided by the present invention, Figure 3 , Figure 4 as well as Figure 5 As shown, the manufacturing method comprises the following steps:

[0054] Step S1, manufacturing a preform according to the size and cavity distribution of a target product.

[0055] Step S2, stretching the preform rod by heating and drawing.

[0056] Step S3, cutting out a sensor body 1 having three straight beam structures from the stretched preform rod. In step S3, the three straight beam structures are distributed along the circumference of the sensor body 1, and any two adjacent straight beam structures are spaced 120 degrees apart from each other.

[0057] Step S4, twisting the sensor body 1. With respect to step S4, assembling the spiral fixing body 12 and at least three spiral fixing blocks 8 onto the sensor body 1 having three straight beam structures, and rotating the three straight beam structures to form a spiral state;

[0058] For step five, during heating and shaping, the assembly having the spiral fixing body 12 and at least three spiral fixing blocks 8 is placed in an oven for heating and shaping, and after reaching a preset time, the assembly is taken out of the oven and the spiral fixing body 12 and all the spiral fixing blocks 8 are taken out to obtain the sensor spiral beam 102 body. The manufacturing process of the sensor includes hot drawing and hot twisting.

[0059] Step S5, heating and shaping the twisted sensor body 1.

[0060] The hot drawing method uses a heating and drawing method to draw a large-sized multi-lumen tube into a target small-sized multi-lumen tube. Then, the sensor body 1 with three straight beam structures is cut out using femtosecond laser cutting technology. Next, the straight beam sensor body 1 is twisted, and the spiral fixing body 12 and the spiral fixing block 8 are assembled to the sensor body 1 so that the three beams form a spiral state. Finally, the assembly is placed in an oven for heating to twist and shape it. After a certain period of time, it is taken out and the excess parts are removed to form the sensor spiral beam 102 body.

[0061] Specifically, the sensor manufacturing process includes hot drawing and hot twisting. First, a preform is designed and manufactured according to the target size and cavity distribution after drawing; then, a large-sized multi-cavity tube is drawn into a target small-sized multi-cavity tube by heating and drawing. Figure 3 As shown; secondly, the sensor body 1 having three straight beam structures is cut out by using femtosecond laser cutting technology, as shown Figure 4 Again, the sensor body 1 is twisted, the spiral fixing body 12 and the spiral fixing block 8 are assembled to the straight beam sensor body 1 so that the three beams form a spiral state, such as Figure 5 As shown; finally, the assembly is placed in an oven for heating and shaping, and after a certain period of time, it is taken out and excess parts are removed to form the sensor spiral beam 102 body.

[0062] By adopting the spiral beam 102 structure and the fiber Bragg grating 2 sensing technology, the sensor has five-axis external force sensing capability in a small size, and also has a large inner cavity reserved for external instruments, such as external instruments inserted into the human body through the continuous body cavity and the sensor cavity. Through the circumferential distribution of FBG on the spiral beam 102, the temperature compensation of the sensor is achieved, the influence of temperature change on the sensor measurement is overcome, and the measurement accuracy of the sensor is improved. Considering that when the outer diameter of the sensor is as small as the millimeter level, the spiral structure and the cavity in the spiral structure are difficult to manufacture by conventional 3D printing, machining and other methods, the manufacturing problem is solved by hot drawing and hot torsion.

[0063] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application 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 should not be understood as a limitation on the present application.

[0064] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A five-axis force sensor based on fiber Bragg grating, characterized in that: It comprises a base ring, a spiral beam and a stress ring, wherein the spiral beam connects the base ring and the stress ring, three spiral beams are arranged at equal intervals between the base ring and the stress ring, and any of the spiral beams is provided with at least two cavities for accommodating optical fibers; At least two Bragg fiber gratings are arranged on any optical fiber in the spiral beam.

2. The five-axis force sensor based on fiber Bragg grating according to claim 1, characterized in that: The spiral beam is provided with two cavities for accommodating optical fibers, and the two cavities on the spiral beam are symmetrically distributed along the center line of the spiral beam.

3. The five-axis force sensor based on fiber Bragg grating according to claim 1, characterized in that: The fiber Bragg gratings on the two optical fibers on any one of the spiral beams are symmetrically distributed along the center line of the spiral beam.

4. The five-axis force sensor based on fiber Bragg grating and the manufacturing method according to claim 1, characterized in that: The fiber Bragg gratings located in the same cross section on the three spiral beams are distributed along the circumference of the sensor.

5. The five-axis force sensor based on fiber Bragg grating according to claim 1, characterized in that: The middle parts of the base ring and the stress ring are both provided with through holes, and the three spiral beams are all arranged on the circumference of the base ring and the stress ring.

6. The five-axis force sensor based on fiber Bragg grating according to claim 1, characterized in that: The wavelength change of the fiber Bragg grating caused by temperature change can be calculated from the wavelength change of the 12 gratings as follows: Where: Δλ in the formula i The wavelength changed for each grating.

7. The five-axis force sensor based on fiber Bragg grating according to claim 1, characterized in that: The five-axis force is predicted by machine learning. The input of the prediction network is the wavelength of 12 gratings after temperature compensation, and the output is three-axis forces Fx, Fy and Fz, and two radial moments Mx and My.

8. A method for manufacturing a five-axis force sensor based on fiber grating, characterized in that: A five-axis force sensor based on fiber grating as claimed in any one of claims 1 to 7 is manufactured by a manufacturing method comprising the following steps: Step S1, manufacturing a preform according to the size and cavity distribution of a target product; Step S2, stretching the preform rod by heating and drawing; Step S3, cutting out a sensor body having three straight beam structures from the stretched preform rod; Step S4, twisting the sensor body; Step S5, heating and shaping the twisted sensor body.

9. The method for manufacturing a five-axis force sensor based on fiber Bragg grating according to claim 8, characterized in that: With respect to step S3, three straight beam structures are distributed along the circumference of the sensor body, and any two adjacent straight beam structures are spaced 120 degrees apart from each other.

10. The method for manufacturing a five-axis force sensor based on fiber Bragg grating according to claim 8, characterized in that: With respect to step S4, the spiral fixing body and at least three spiral fixing blocks are assembled onto the sensor body having three straight beam structures, and the three straight beam structures are rotated to form a spiral state; For step five, during heating and shaping, the assembly having the spiral fixing body and at least three spiral fixing blocks is placed in an oven for heating and shaping. After the preset time is reached, the assembly is taken out of the oven and the spiral fixing body and all the spiral fixing blocks are taken out to obtain the sensor spiral beam body.

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