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

Abstract

The application provides a kind of five-axis force sensor based on fiber grating and manufacturing method, including base ring, spiral beam and stress ring, the spiral beam connects base ring and stress ring, three roots are arranged at equal intervals between base ring and stress ring, at least two cavities for accommodating optical fiber are arranged in any spiral beam;At least two Bragg fiber gratings are arranged on any optical fiber in the spiral beam. By adopting spiral beam structure and fiber grating sensing technology, the sensor has five-axis external force sensing capability in the case of small size, and also has a large internal cavity reserved for external instruments, such as external instruments through continuum cavity and sensor cavity to intervene in the human body. 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.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and more specifically, to a five-axis force sensor based on a fiber Bragg grating and its manufacturing method. Background Technology

[0002] A force sensor is a device that converts the magnitude of force into a corresponding electrical signal. Force is the direct cause of changes in the motion of matter. Force sensors can detect mechanical quantities such as tension, strain, pressure, weight, torque, internal stress, and strain. Specific devices include metal strain gauges and pressure sensors, and they have become indispensable core components in power equipment, engineering machinery, various machine tools, and industrial automation systems.

[0003] A Chinese patent application with publication number CN115839792A discloses a three-dimensional force sensor for laparoscopic minimally invasive surgical instruments and its usage method, comprising a strain elastomer and a fiber optic grating sensor. The strain elastomer is a one-piece structure made of elastic material, comprising an upper disk, a lower disk, and three helical beams. The top end of the helical beams is connected to the bottom end of the upper disk, and the bottom end of the helical beams is connected to the top end of the lower disk. The three helical beams are distributed at 120-degree intervals on the circumference of the upper and lower disks. The fiber optic grating sensor comprises a first fiber optic grating, a second fiber optic grating, a third fiber optic grating, and a fourth fiber optic grating connected in sequence. The first, second, and third fiber optic gratings are respectively disposed on the inclined surfaces of the helical beams, and the fourth fiber optic grating is disposed on the surface of the lower disk.

[0004] Existing force sensors are three-dimensional force sensors, which cannot realize the sensing of five-axis external forces. There is an urgent need in the market for a five-axis force sensor that has the ability to sense external forces in a small size, while also having a large internal cavity reserved for external instruments. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this invention is to provide a five-axis force sensor based on fiber Bragg grating and its manufacturing method.

[0006] A five-axis force sensor based on fiber Bragg gratings according to the present invention includes a base ring, a helical beam, and a force-bearing ring. The helical beam connects the base ring and the force-bearing ring. Three helical beams are equally spaced between the base ring and the force-bearing ring. Each helical beam contains at least two cavities for accommodating optical fibers. Each optical fiber in the helical beam contains at least two Bragg fiber gratings.

[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 Bragg fiber gratings on the two optical fibers on any one of the spiral beams are symmetrically distributed along the centerline of the spiral beam.

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

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

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

[0012]

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

[0014] Preferably, the five-axis forces are predicted using machine learning. The input to the prediction network is the wavelength of 12 gratings after temperature compensation, and the output is three-axis forces Fx, Fy, and Fz, as well as two radial moments Mx and My.

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

[0016] Step S1: Fabricate preforms according to the size and cavity distribution of the target product;

[0017] Step S2: The preform is stretched by heating and stretching.

[0018] Step S3: Cut out a sensor body with three straight beams from the stretched preform;

[0019] Step S4: Twist the sensor body;

[0020] Step S5: Heat and shape the twisted sensor body.

[0021] Preferably, in step S3, the three straight beam structures are distributed along the circumference of the sensor body, and any two adjacent straight beam structures are spaced 120° apart.

[0022] Preferably, in step S4, the spiral fixing body and at least three spiral fixing blocks are assembled onto the sensor body having a three-straight beam structure, and the three-straight beam structure is rotated to form a spiral state.

[0023] For step five, during the heating and shaping process, the assembly with 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 removed from the oven, and the spiral fixing body and all the spiral fixing blocks are removed to obtain the sensor spiral beam body.

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

[0025] 1. This invention employs a spiral beam structure and fiber optic grating sensing technology, enabling the sensor to have five-axis external force sensing capabilities in a small size, while also having a large internal cavity reserved for external instruments, such as external instruments that can be inserted into the human body through the continuum cavity and sensor cavity.

[0026] 2. This invention achieves temperature compensation for the sensor by circumferentially distributing the FBG on the spiral beam, overcoming the influence of temperature changes on sensor measurement and improving the sensor's measurement accuracy.

[0027] 3. This invention takes into account that when the outer diameter of the sensor is as small as millimeters, the spiral structure and the cavity inside the spiral structure are difficult to manufacture by conventional 3D printing, machining and other methods. The invention solves the manufacturing problem by using hot drawing and hot twisting.

[0028] 4. This invention, through the design of the cavity, arranges the optical fiber inside the cavity, which can protect the optical fiber and improve the service life of the sensor. Attached Figure Description

[0029] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 This is a schematic diagram illustrating the overall structure of the sensor body, which is the main feature of this invention.

[0031] Figure 2 This is a schematic diagram illustrating the overall cross-sectional structure of the sensor body, which is the main feature of this invention.

[0032] Figure 3 This is a schematic diagram illustrating the stretching of the preform.

[0033] Figure 4 This is a schematic diagram illustrating the overall structure of the sensor body before twisting, which is the main feature of this invention.

[0034] Figure 5 This is a schematic diagram illustrating the torsion of the sensor body, which is the main feature of this invention.

[0035] As shown in the figure:

[0036] Sensor body 1, force ring 103

[0037] Base ring 101 Fiber grating 2

[0038] Spiral beam 102, spiral fixing block 8 Detailed Implementation

[0039] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within 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 according to the present invention includes a base ring 101, a helical beam 102, and a force-receiving ring 103. The helical beam 102 connects the base ring 101 and the force-receiving ring 103. Three helical beams 102 are equally spaced between the base ring 101 and the force-receiving ring 103. Each helical beam 102 has at least two cavities for accommodating optical fibers. Each optical fiber within the helical beam 102 has at least two Bragg fiber gratings 2.

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

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

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

[0044]

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

[0046] Since each helical beam 102 has two optical fibers, and the arrangement of the six optical fibers and the positions of the two Bragg fiber gratings 2 on each fiber are related, a five-axis force can be predicted using machine learning based on the arrangement of the six optical fibers and the positional relationship of the two Bragg fiber gratings 2 on each fiber. The input to the prediction network is the temperature-compensated wavelength of the 12 gratings, and the output is the three-axis forces Fx, Fy, and Fz, as well as two radial moments Mx and My. It should be noted that the machine learning prediction network can use a backpropagation (BP) neural network for learning and computation. Using the temperature-compensated wavelength of the 12 gratings as the input to the BP neural network, the output is the three-axis forces Fx, Fy, and Fz, as well as the two radial moments Mx and My.

[0047] Furthermore, both the base ring 101 and the force-receiving ring 103 are provided with through holes in their middle portions, and the three helical beams 102 are all arranged on the circumference of the base ring 101 and the force-receiving ring 103. This allows the sensor to have a large internal cavity reserved for external instruments, such as external instruments that can be inserted into the human body through the continuum cavity and the sensor cavity.

[0048] More specifically, the Bragg fiber grating 2 is fixed within the cavity of the helical beam 102 of the sensor body 1. Each helical beam 102 has two cavities, each cavity fixing an optical fiber. Each optical fiber has two Bragg fiber gratings 2, and the wavelength of the Bragg fiber grating 2 changes with the deformation of the helical beam 102. When the force-bearing ring 103 of the sensor body 1 interacts with the outside world and is subjected to external force, the helical beam 102 will undergo a certain strain, thereby causing a change in the wavelength of the optical fiber. The assembled sensor... Figure 1 As shown, Figure 2 The figures show the cross-sectional and bottom views of the sensor. Since each beam has two Bragg fiber gratings (FBGs), the radial forces Fx and Fy, as well as the two radial moments Mx and My, can be quickly calculated by the arrangement of the six fibers and the positional relationship of the two FBGs on each fiber.

[0049] When the sensor is subjected to axial force, the compression or elongation of all beams is consistent. This application's technical solution decouples the axial force on the sensor using a helical beam 102. The two cavities on the helical beam 102 are symmetrically distributed along the beam's centerline, and after assembly, the Bragg fiber gratings 2 on the optical fibers within the two cavities are also symmetrically distributed along the beam's centerline. When the sensor is subjected to axial force, the wavelength changes of the symmetrically arranged FBGs on each bent beam are the same in magnitude and opposite in direction; therefore, this feature can be used to decouple the axial force Fz.

[0050] Furthermore, after assembly, the corresponding FBGs on the three helical beams 102 are distributed along the circumference of the sensor. This feature can further decouple the effect of temperature changes on sensor measurements, as the wavelength change caused by temperature variations is...

[0051] Wherein, Δλ in the formula i The wavelength that varies for each grating.

[0052] It should be noted that, before the three beams are twisted, the sensor body 1 has three beams distributed along the circumference of the sensor, with a 120° interval between them.

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

[0054] Step S1: Fabricate preforms according to the size and cavity distribution of the target product.

[0055] Step S2: The preform is stretched by heating and stretching.

[0056] Step S3: Cut out a sensor body 1 with three straight beams from the stretched preform. In step S3, the three straight beams are distributed along the circumference of the sensor body 1, with any two adjacent straight beams spaced 120° apart.

[0057] Step S4: Twist the sensor body 1. For step S4, assemble the spiral fixing body 12 and at least three spiral fixing blocks 8 onto the sensor body 1, which has a three-straight-beam structure, and rotate it so that the three-straight-beam structure forms a spiral shape.

[0058] For step five, during heat setting, the assembly with the spiral fixing body 12 and at least three spiral fixing blocks 8 is placed in an oven for heat setting. After a preset time, the assembly is removed from the oven, and the spiral fixing body 12 and all the spiral fixing blocks 8 are removed to obtain the sensor spiral beam 102 body. The sensor manufacturing process includes hot drawing and hot twisting.

[0059] Step S5: Heat and shape the twisted sensor body 1.

[0060] Hot drawing is used to draw a large-sized multi-cavity tube into a target small-sized multi-cavity tube through heating and drawing. Then, femtosecond laser cutting technology is used to cut out a sensor body 1 with a three-straight beam structure. Next, the straight beam sensor body 1 is twisted, and a spiral fixing body 12 and a spiral fixing block 8 are assembled onto the sensor body 1 to form a spiral state of the three beams. Finally, the assembly is placed in an oven for heating to twist and set its shape. After a certain period of time, it is removed and 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 fabricated based on the expected target size and cavity distribution after drawing. Then, a large-sized multi-cavity tube is drawn into a target small-sized multi-cavity tube using a heated drawing forming method, such as... Figure 3 As shown; secondly, the sensor body 1 with a three-straight-beam structure is cut out using femtosecond laser cutting technology, as shown. Figure 4 As shown; next, the sensor body 1 is twisted to assemble the spiral fixing body 12 and the spiral fixing block 8 onto the straight beam sensor body 1, so that the three beams form a spiral state, as shown. Figure 5 As shown; finally, the assembly is placed in an oven for heating and shaping. 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 employing a helical beam 102 structure and fiber optic grating (FBG) sensing technology, the sensor achieves five-axis external force sensing capability within a small size, while also possessing a large internal cavity reserved for external instruments, such as those inserted into the human body through continuum channels and sensor channels. The circumferential distribution of FBGs on the helical beam 102 enables temperature compensation for the sensor, overcoming the influence of temperature changes on sensor measurements and improving measurement accuracy. Considering that when the sensor's outer diameter is as small as millimeters, the helical structure and its internal cavities are difficult to manufacture using conventional 3D printing and machining methods, hot drawing and hot torsion techniques were employed to solve the manufacturing problem.

[0063] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0064] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A five-axis force sensor based on a fiber Bragg grating, characterized in that, It includes a base ring, a helical beam, and a force-bearing ring. The helical beam connects the base ring and the force-bearing ring. Three helical beams are equally spaced between the base ring and the force-bearing ring. Each of the helical beams has at least two cavities for accommodating optical fibers. At least two Bragg fiber gratings are provided on each optical fiber within the spiral beam.

2. The five-axis force sensor based on fiber Bragg grating as described in 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 as described in claim 1, characterized in that, The Bragg fiber gratings on the two optical fibers on any one of the spiral beams are symmetrically distributed along the centerline of the spiral beam.

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

5. The five-axis force sensor based on fiber Bragg grating as described in claim 1, characterized in that, Both the base ring and the force-bearing ring have through holes in their middle parts, and the three spiral beams are arranged on the circumference of the base ring and the force-bearing ring.

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

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

8. A method for manufacturing a five-axis force sensor based on a fiber Bragg grating, characterized in that, The manufacturing method for the five-axis force sensor based on fiber Bragg grating as described in any one of claims 1-7 includes the following steps: Step S1: Fabricate preforms according to the size and cavity distribution of the target product; Step S2: The preform is stretched by heating and stretching. Step S3: Cut out a sensor body with three straight beams from the stretched preform; Step S4: Twist the sensor body; Step S5: Heat and shape the twisted sensor body.

9. The manufacturing method of the five-axis force sensor based on fiber Bragg grating as described in claim 8, characterized in that, For step S3, the three straight beam structures are distributed along the circumference of the sensor body, and any two adjacent straight beam structures are spaced 120° apart.

10. The method for manufacturing a five-axis force sensor based on a fiber Bragg grating as described in claim 8, characterized in that, For step S4, the spiral fixing body and at least three spiral fixing blocks are assembled onto the sensor body with a three-straight beam structure, and rotated to form a spiral state for the three-straight beam structure. For step five, during the heating and shaping process, the assembly with 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 removed from the oven, and the spiral fixing body and all the spiral fixing blocks are removed to obtain the sensor spiral beam body.

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