Fiber grating based force vector measurement device

Abstract

The application discloses a force vector measurement device based on fiber grating, which comprises a flexible entity and a fiber grating sensor array, wherein the fiber grating sensor array is arranged inside the flexible entity; the flexible entity contains a hollow spherical cavity, and the flexible entity is arranged in a square shape; the fiber grating sensor array comprises a first fiber grating string and a second fiber grating string, and the first fiber grating string and the second fiber grating string are embedded inside the flexible entity and located below the hollow spherical cavity; the force vector measurement device based on fiber grating does not need to arrange a fiber grating sensor on the Z axis, has a simple structure, can realize force vector measurement by arranging sensors in a two-dimensional plane, improves force vector measurement precision, has small mutual influence between strains of the two groups of fiber grating strings, improves the accuracy of single-dimension measurement, and reduces coupling interference between dimensions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fiber grating sensors, in particular to a force vector measurement device based on fiber grating. BACKGROUND

[0002] Multi-dimensional force sensors are produced along with the development of robot technology, and are loaded on robot joints, wrists and fingertips, etc. The multi-dimensional force sensors can sense the force information of the environment in which the robot is located in real time and feed back to the control system or the operator, so as to assist the robot to complete the work such as packaging, stacking, injection molding and polishing and welding. The multi-dimensional force sensor can detect force information in multiple directions at the same time, and is one of the core instruments of the robot control system. The existing multi-dimensional force sensors are mostly designed based on traditional sensitive elements such as resistance strain gauges and piezoelectric films. These sensitive elements use weak current as the sensing signal, and have the problems of signal susceptible to electromagnetic interference, temperature zero drift, large number of lead wires, large volume, difficult to be integrated with small surgical arms such as minimally invasive surgical robots, etc. The fiber grating is a new type of passive optical device that uses the photosensitive characteristics of optical fiber to establish a periodic refractive index distribution on the fine fiber core, so as to control the propagation mode of light in the area. The fiber grating has the advantages of non-electric detection, immunity to electromagnetic interference, high temperature resistance, no zero drift, high precision, small volume, and multiple gratings can be connected in series on one optical fiber, etc., and has shown its advantages in the field of robot sensing.

[0003] The existing device pastes the fiber grating sensor on the multi-dimensional force sensor on the surface of the cross beam structure through an adhesive. Influenced by factors such as manufacturing and installation errors, there is coupling interference between the dimensions, which affects the accuracy and reliability of the sensor. The multi-dimensional force sensor that encapsulates the fiber grating through a polymer entity has low sensitivity and limited measurement range. Therefore, we propose a force vector measurement device based on fiber grating. SUMMARY

[0004] The main purpose of the present application is to provide a force vector measurement device based on fiber grating, which can effectively solve the problems in the background art.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] The force vector measurement device based on fiber grating comprises a flexible entity and a fiber grating sensing array, the fiber grating sensing array is arranged inside the flexible entity, the flexible entity contains a hollow spherical cavity, and the flexible entity is arranged in the form of a cube, the fiber grating sensing array comprises a first fiber grating string and a second fiber grating string, the first fiber grating string and the second fiber grating string are embedded inside the flexible entity and located below the hollow spherical cavity.

[0007] The first fiber grating string comprises a first fiber, a first fiber grating and a second fiber grating, the first fiber grating and the second fiber grating are arranged on the first fiber parallel to the Y axis, and the first fiber grating and the second fiber grating are located on both sides of the hollow spherical cavity for more accurate sensing of the Y axis stress.

[0008] The second fiber grating string comprises a second fiber, a third fiber grating and a fourth fiber grating, the third fiber grating and the fourth fiber grating are arranged on the second fiber parallel to the X axis, and the third fiber grating and the fourth fiber grating are located on both sides of the hollow spherical cavity for more accurate sensing of the X axis stress.

[0009] The first fiber and the second fiber are arranged in the same plane at 90° and the intersection point is located on the line connecting the center of the bottom surface of the flexible entity and the center of the hollow spherical cavity.

[0010] Further, the first fiber grating and the second fiber grating, the third fiber grating and the fourth fiber grating are arranged in a central symmetric manner about the intersection point of the first fiber and the second fiber, the central symmetric relationship is maintained, the same sign / different sign equivalent of the measurement data can be realized, and subsequent demodulation processing is facilitated.

[0011] Further, the distance between the first fiber grating and the second fiber grating, the third fiber grating and the fourth fiber grating is greater than the radius of the hollow spherical cavity and less than the side length of the flexible entity.

[0012] Further, the diameter of the hollow spherical cavity is less than the side length of the flexible entity, the flexible entity is preformed by pouring a silica gel solution into a mold, and the silica gel material is soft and has a protective effect on the fiber grating.

[0013] Further, the device and a broadband light source, a 3dB coupler, a fiber grating sensing demodulator and a computer can constitute a measurement system, and the use steps are as follows:

[0014] Step one: the light emitted by the broadband light source is divided into two paths after passing through the 3dB coupler and enters the fiber grating sensing array composed of the first fiber grating string and the second fiber grating string;

[0015] Step two: after being measured by the fiber grating sensing array, the reflected light carrying the measurement information returns to the 3dB coupler again and enters the fiber grating sensing demodulator;

[0016] Step three: the computer obtains the strain and center wavelength change information of the fiber grating in the fiber grating sensing array detected through communication with the fiber grating sensing demodulator, and calculates and displays the size and direction of the force borne by the fiber grating sensing array in the computer by using a corresponding demodulation matrix.

[0017] The present application has the following beneficial effects:

[0018] Compared with the prior art, the fiber grating sensor does not need to be arranged in the Z axis, the device structure is simple, wiring is easy, force vector measurement can be realized only by arranging the sensor in a two-dimensional plane, force vector measurement precision is improved, the strain between the two groups of fiber grating sensors has little mutual influence, the accuracy of single-dimension measurement is improved, and the coupling interference between dimensions is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the technical description of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and all other drawings obtained by those skilled in the art without creative labor on the basis of these drawings are also within the protection scope of the present application.

[0020] Figure 1 It is a structural schematic diagram of the force vector measurement device based on fiber grating of the present application.

[0021] Figure 2 It is a measurement system principle diagram of the force vector measurement device based on fiber grating of the present application.

[0022] Figure 3 It is an X, Y axis strain distribution simulation diagram when the fiber grating sensing array is applied with stress along the Y axis.

[0023] Figure 4 It is an X, Y axis strain distribution simulation diagram when the fiber grating sensing array is applied with stress along the Z axis.

[0024] In the figure: 1, flexible entity; 2, hollow spherical cavity; 3, first fiber grating string; 301, first optical fiber; 302, first fiber grating; 303, second fiber grating; 4, second fiber grating string; 401, second optical fiber; 402, third fiber grating; 403, fourth fiber grating. DETAILED DESCRIPTION

[0025] The present application will be further described below in combination with specific embodiments, wherein the drawings are only used for exemplary description, and the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation of the present patent. In order to better illustrate the specific embodiments of the present application, some components of the drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product. It is understandable for those skilled in the art that some known structures and their descriptions in the drawings can be omitted. On the basis of the specific embodiments in the present application, all other specific embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0026] As Figures 1-4As shown, the fiber grating-based force vector measurement device comprises a flexible entity and a fiber grating sensor array arranged inside the flexible entity 1; the flexible entity 1 contains a hollow spherical cavity 2, and the flexible entity 1 is arranged in a square shape, and the fiber grating sensor array comprises a first fiber grating string 3 and a second fiber grating string 4, both of which are embedded inside the flexible entity 1 and located below the hollow spherical cavity 2.

[0027] The first fiber grating string 3 comprises a first optical fiber 301, a first fiber grating 302 and a second fiber grating 303, the first fiber grating 302 and the second fiber grating 303 are mounted on the first optical fiber 301 parallel to the Y-axis, and the first fiber grating 302 and the second fiber grating 303 are located on both sides of the hollow spherical cavity 2 for more accurate sensing of Y-axis stress.

[0028] The second fiber grating string 4 comprises a second optical fiber 401, a third fiber grating 402 and a fourth fiber grating 403, the third fiber grating 402 and the fourth fiber grating 403 are mounted on the second optical fiber 401 parallel to the X-axis, and the third fiber grating 402 and the fourth fiber grating 403 are located on both sides of the hollow spherical cavity 2 for more accurate sensing of X-axis stress.

[0029] The first optical fiber 301 and the second optical fiber 401 are arranged vertically in the same plane at 90° and the intersection point is located on the line connecting the center of the bottom surface of the flexible entity 1 and the center of the hollow spherical cavity 2.

[0030] The first fiber grating 302 and the second fiber grating 303, the third fiber grating 402 and the fourth fiber grating 403 are arranged in a central symmetric manner about the intersection point of the first optical fiber 301 and the second optical fiber 401, maintaining a central symmetric relationship, which can realize the same sign / different sign equivalent of the measurement data, facilitating subsequent demodulation processing.

[0031] The distance between the first fiber grating 302 and the second fiber grating 303, the third fiber grating 402 and the fourth fiber grating 403 is greater than the radius of the hollow spherical cavity 2 and less than the length of the flexible entity 1.

[0032] The diameter of the hollow spherical cavity 2 is smaller than the length of the flexible entity 1, and the flexible entity 1 is preformed by pouring silica gel solution into a mold, and the silica gel material is soft and has a protective effect on the fiber grating.

[0033] The device, together with a broadband light source, a 3dB coupler, a fiber grating sensor demodulator and a computer, can constitute a measurement system, and the use steps are as follows:

[0034] Step one: the light emitted by the broadband light source is divided into two paths after passing through the 3dB coupler, and enters the fiber grating sensor array composed of the first fiber grating string 3 and the second fiber grating string 4;

[0035] Step two: after measurement by the fiber grating sensor array, the reflected light carrying the measurement information returns to the 3dB coupler and enters the fiber grating sensor demodulator again;

[0036] Step three: the computer obtains the strain and central wavelength change information of the fiber gratings in the fiber grating sensor array through communication with the fiber grating sensor demodulator, and calculates and displays the size and direction of the force acting on the fiber grating sensor array in the computer by using the corresponding demodulation matrix.

[0037] The force vector decoupling model constructed by the above device is as follows:

[0038] ε y = ε1- ε2 (1)

[0039] ε x = ε3- ε4 (2)

[0040] ε z = (ε1+ ε2) / 2 = (ε3+ ε4) / 2 (3)

[0041] Wherein, ε represents strain, ε1 is the strain measurement value of the first fiber grating, ε2 is the strain measurement value of the second fiber grating, ε3 is the strain measurement value of the third fiber grating, and ε4 is the strain measurement value of the fourth fiber grating. x , ε y , ε z respectively represent the strain values acting on the X, Y and Z axes.

[0042] The ε x , the ε y , the ε z are brought into the following demodulation matrix to obtain F x , F y , F z .

[0043]

[0044] Wherein, F represents the external force acting on the fiber grating sensor array, F x , F y , F z respectively represent the component forces of the external force acting on the fiber grating sensor array in the X, Y and Z directions, K xx , K xy , K xz respectively represent ε xCorrection coefficients in the X, Y, and Z directions. Similarly, K yx , K yy , K yz Represents ε y Correction coefficient in X, Y, and Z directions, K zx , K zy , K zz Represents ε z Correction coefficients in the X, Y, and Z directions.

[0045] The F is ultimately composed of the F x 、The F y 、The F z Perform vector synthesis, and the positive or negative value represents the same or opposite direction as the specified coordinate axis.

[0046] Figure 3 and Figure 4 The following are simulation results based on the case where the side length of the flexible entity 1 is 2 cm and the diameter of the hollow sphere is 1 cm, and stress is applied to the Y and Z axes respectively:

[0047] Depend on Figure 3 The simulation results show that when negative stress is applied along the Y-axis, the strain of the Y-axis is symmetrically distributed with different signs and equal values. Compared with the strain value of the Y-axis, the strain of the X-axis is very small, indicating that the strain sensitivity of the two axes does not cross, which helps to improve the measurement accuracy of a single dimension. By subtracting the strain values ​​measured by the two fiber grating sensors on the Y-axis, the strain magnitude of the Y-axis can be obtained, that is, ε y =ε1-ε2. The simulation results of stress applied along the X-axis are similar to those along the Y-axis and will not be repeated here.

[0048] Depend on Figure 4 The simulation results show that when negative stress is applied along the Z axis, the strains of the X and Y axes are symmetrically distributed with the same sign and value. Therefore, the strain value of the Z axis is half of the sum of the strain values ​​of one axis, that is, ε z =(ε1+ε2) / 2=(ε3+ε4) / 2.

[0049] Compared with the existing fiber Bragg grating force vector measurement device, the present invention reduces the fiber Bragg grating arranged on the Z axis and can achieve force vector measurement only by arranging the fiber Bragg grating on the X and Y axes. It has a simple structure, high measurement accuracy, simple wiring, and can be widely used in the field of tactile perception of manipulators.

[0050] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A fiber Bragg grating (FBG)-based force vector measurement device, comprising a flexible body and a fiber Bragg grating (FBG) sensor array, characterized in that: The fiber Bragg grating sensing array is arranged inside the flexible entity (1), the flexible entity (1) contains a hollow spherical cavity (2), and the flexible entity (1) is arranged in a cube shape. The fiber Bragg grating sensing array includes a first fiber Bragg grating string (3) and a second fiber Bragg grating string (4), and the first fiber Bragg grating string (3) and the second fiber Bragg grating string (4) are both embedded inside the flexible entity (1) and located below the hollow spherical cavity (2); The first fiber Bragg grating string (3) comprises a first optical fiber (301), a first fiber Bragg grating (302), and a second fiber Bragg grating (303), wherein the first fiber Bragg grating (302) and the second fiber Bragg grating (303) are arranged on the first optical fiber (301) parallel to the Y axis, and the first fiber Bragg grating (302) and the second fiber Bragg grating (303) are located on both sides of the hollow spherical cavity (2) and are distributed in a centrally symmetrical manner; The second fiber Bragg grating string (4) comprises a second optical fiber (401), a third optical fiber Bragg grating (402) and a fourth optical fiber Bragg grating (403), wherein the third optical fiber Bragg grating (402) and the fourth optical fiber Bragg grating (403) are arranged on the second optical fiber (401) parallel to the X-axis, and the third optical fiber Bragg grating (402) and the fourth optical fiber Bragg grating (403) are located on both sides of the hollow spherical cavity (2) and are distributed in a centrally symmetrical manner; The first optical fiber (301) and the second optical fiber (401) are arranged perpendicularly at 90 degrees in the same plane, and the intersection point is located on the line connecting the center of the bottom surface of the flexible entity (1) and the center of the hollow spherical cavity (2).

2. The fiber Bragg grating-based force vector measurement device according to claim 1, characterized in that: The first fiber grating (302) and the second fiber grating (303), the third fiber grating (402) and the fourth fiber grating (403) are centrally symmetrically arranged about the intersection of the first optical fiber (301) and the second optical fiber (401).

3. The fiber Bragg grating-based force vector measurement device according to claim 1, characterized in that: The distance between the first fiber grating (302) and the second fiber grating (303), and the distance between the third fiber grating (402) and the fourth fiber grating (403) is greater than the radius of the hollow spherical cavity (2) and less than the side length of the flexible entity (1).

4. The fiber Bragg grating-based force vector measurement device according to claim 1, characterized in that: The diameter of the hollow spherical cavity (2) is smaller than the side length of the flexible entity (1), and the flexible entity (1) is prefabricated by pouring a silica gel solution into a mold.

5. The fiber Bragg grating-based force vector measurement device according to any one of claims 1 to 4, characterized in that: The steps for using the device are as follows: Step 1: Light emitted from a broadband light source is divided into two paths after passing through a 3dB coupler and enters a fiber Bragg grating sensor array composed of a first fiber Bragg grating string (3) and a second fiber Bragg grating string (4); Step 2: After being measured by the fiber Bragg grating sensor array, the reflected light carrying the measurement information returns to the 3dB coupler again and enters the fiber Bragg grating sensor demodulator; Step 3: The computer communicates with the fiber Bragg grating sensor demodulator to obtain the detected strain and center wavelength change information of the fiber Bragg grating in the fiber Bragg grating sensor array, and uses the corresponding demodulation matrix in the computer to calculate and display the magnitude and direction of the force applied to the fiber Bragg grating sensor array.

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