CN113483816B - Shape-position-force composite sensing unit and measuring method thereof - Google Patents
Shape-position-force composite sensing unit and measuring method thereof Download PDFInfo
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- G—PHYSICS
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35309—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
- G01D5/35316—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Bragg gratings
Abstract
The invention relates to a form and position force composite sensing unit and a measuring method thereof. When the elastic three-dimensional force measuring unit is subjected to axial force and radial force, the upper cover plate, the lower cover plate and the elastic body deform, the internal fiber grating is stretched or compressed, the reflection wavelength of light passing through the grating changes, and the magnitude and the direction of the stress are obtained through a force sensing calibration algorithm. The part for detecting the shape in the invention adopts four optical fibers which are arranged orthogonally, and the shape measurement reconstruction and the temperature compensation of the sensor can be realized through the parameter solution of the redundant optical fibers.
Description
Technical Field
The invention relates to the technical field of sensors for detecting force and shape, in particular to a sensor which can detect three-dimensional force and simultaneously detect bent shape based on FBG grating optical fiber, and the sensor is mainly applied to occasions needing to detect the three-dimensional force and the bent shape, such as: the method is applied to the fields of three-dimensional force of surgical instruments, detection of bent shapes and the like.
Background
In the diagnosis and treatment process of modern medicine, in order to meet the requirements of small operation wound, light pain, quick postoperative recovery, attractive appearance and the like, minimally invasive surgery plays an increasingly important role in the field of medical surgery. With the advent of minimally invasive surgical robots, doctors can achieve minimally invasive, accurate, and efficient stereotactic surgery with the help of the robots. For the minimally invasive surgery robot system, a doctor controls the front-end surgical instrument to simulate the flexible actions of the arm and the wrist of the doctor through the operating console, so that the minimally invasive surgery robot has higher design requirements on the surgical instrument. Compared with the traditional surgical instruments, the surgical instruments used in the minimally invasive surgery have the advantages that the measurement requirements of miniaturization, light weight, multiple degrees of freedom, flexible operation, convenience in installation and the like on the contact force are met, the measurement requirements are universal, the significance is high, the contact state of the tool and the external environment can be obtained, on one hand, the task safety is guaranteed, the tool is prevented from being damaged, or the influence on the environment is avoided; on the other hand, to ensure the effectiveness of the task, the contact force detection is used as feedback to control the contact state. The detection of the shape is also of great significance to tools which can deform, and the relative position relation between the tool and the environment can be known by using the feedback of the shape, and the shape can also be used as a reference for the active control of the tool. For example, in the field of minimally invasive surgery, the operation force of the distal end of the surgical instrument and the shape detection of the flexible surgical instrument have important significance on the safety of soft tissue operation and the control precision of the deformation of the surgical instrument.
At present, most of contact force detection utilizes a special elastic component to convert an external acting force into local micro deformation, and a sensing component of strain or micro displacement is embedded in an elastic body, so that acquired information is processed to acquire contact force information. The sensing component can adopt a strain gauge, a magnetic coupling coil, a Bragg grating optical fiber and the like. The FBG optical fiber-based sensor has the advantages of interference resistance, stable sensing and the like, and is researched and applied more. The design of the elastic component and the combination mode of the sensing component are the key for realizing the force detection. At present, under a smaller scale, multi-dimensional accurate force detection is still difficult, and some schemes adopt complex structures to realize axial force measurement and radial force measurement decoupling, so that the problems of difficult assembly, unstable use and the like are solved. In addition, under the condition of needing shape perception, a plurality of sensing devices are often independent equipment, the whole integration is complex, the space utilization rate is low, and the like. Sensors for measuring force and for measuring bending shape are separate sensing devices, which are particularly disadvantageous for installation and use in miniaturized surgical instruments.
Disclosure of Invention
The invention aims to provide a multifunctional composite sensing device capable of realizing force and simultaneously realizing bending shape detection. According to the invention, based on a plurality of FBG optical fibers, grating nodes on the front part of the optical fibers are matched with an elastic body with a spiral groove for detecting three-dimensional force, and a plurality of subsequent grating nodes are matched with an elastic tube for detecting the bending shape, so that the FBG sensor is calibrated by using the same optical fiber passage for measuring force and shape through a force sensing calibration algorithm and a shape reconstruction and calibration algorithm.
The invention can realize the detection of three-dimensional shape and multi-dimensional force on the basis of sharing a detection channel, improve the complexity of the sensor and reduce the complexity of the whole sensor. The elastomer with a plurality of spiral grooves can realize better matched axial rigidity and radial rigidity. The three-dimensional force measuring device is simple in overall structure, few in number of adopted parts, simple and convenient to assemble, large in force measuring range and capable of achieving accurate three-dimensional force detection. The part for detecting the shape in the invention adopts four optical fibers which are arranged orthogonally, and the shape measurement reconstruction and the temperature compensation of the sensor can be realized through the parameter solution of the redundant optical fibers.
The technical scheme adopted by the invention for realizing the purpose is as follows: a three-dimensional force measurement unit comprising: the optical fiber connector comprises an upper cover plate, a lower cover plate, an elastic body and an optical fiber;
the elastic body forms a side wall and is fixed between the upper cover plate and the lower cover plate to form a hollow structure; the optical fiber penetrates into the hollow structure from the lower cover plate and is fixedly connected with the upper cover plate;
the optical fibers are multiple, and the tail ends connected with the upper cover plate are uniformly arranged along the geometric center of the upper cover plate;
the upper cover plate and the lower cover plate are respectively provided with an optical fiber fixing hole, and the positions of the optical fiber fixing holes correspond to those of the optical fibers, so that the optical fibers are parallel to the axis of the hollow structure in the hollow structure.
The elastic body is provided with spiral cutting grooves which are distributed along the axial direction of the axis of the elastic body at equal angles.
A plurality of Bragg gratings are arranged on the optical fiber; a plurality of optical fibers outside the hollow structure are glued inside the elastic outer tube, symmetrically distributed around the central axis of the elastic outer tube at equal intervals and connected with an optical fiber demodulator.
A form and position force composite sensing unit comprises a three-dimensional force measuring unit, an optical fiber demodulator and a calculating unit which are sequentially connected;
three-dimensional force measuring unit for produce deformation when receiving external force, include: the optical fiber connector comprises an upper cover plate, a lower cover plate, an elastic body and an optical fiber;
the elastic body forms a side wall and is fixed between the upper cover plate and the lower cover plate to form a hollow structure; the optical fiber penetrates into the hollow structure from the lower cover plate and is fixedly connected with the upper cover plate;
the optical fibers are multiple, and the tail ends connected with the upper cover plate are uniformly arranged along the geometric center of the upper cover plate;
the upper cover plate and the lower cover plate are respectively provided with an optical fiber fixing hole, and the positions of the optical fiber fixing holes correspond to those of the optical fibers, so that the optical fibers are parallel to the axis of the hollow structure in the hollow structure.
The optical fiber demodulator is used for converting optical signals generated by the optical fiber when the three-dimensional force measuring unit deforms into wavelengths;
and the calculation unit is used for obtaining the wavelength offset of each optical fiber according to the wavelength of the optical fibers, and obtaining the magnitude and the direction of acting force of each fiber grating node of the three-dimensional force measurement unit and the curvature and the flexibility of each grating node of the shape sensing section formed by the hollow-structure external optical fibers according to the wavelength offset.
The elastic body is provided with a spiral cutting groove which is distributed along the axial direction of the axis of the elastic body at equal angles.
A plurality of Bragg gratings are arranged on the optical fiber; a plurality of optical fibers outside the hollow structure are arranged inside the elastic hose in an adhesive mode and connected with the optical fiber demodulation instrument.
A method of force measurement of a three-dimensional force measurement unit, comprising the steps of:
when the three-dimensional force measuring unit is subjected to axial force, the upper cover plate and the lower cover plate deviate, and the reflection wavelength of the internal fiber bragg grating changes; when the three-dimensional force measuring unit is subjected to radial force, the elastic body deforms, and the internal optical fiber bends or stretches, so that the reflection wavelength of the grating changes;
the magnitude and direction of the acting force are obtained according to the change of the reflection wavelength.
A method of force measurement of a three-dimensional force measurement unit, comprising the steps of:
1) and (3) calculating the temperature according to the wavelength variation of the four optical fibers:
Δt＝(Δt1+Δt2+Δt3+Δt4)/(4×Kt)
wherein, delta t is the integral temperature variation of the four optical fibers; Δ tiThe temperature variation of the ith fiber grating node is obtained; ktThe influence coefficient of temperature change on the wavelength;
2) according to (
) For each two optical fibers in orthogonal relationship according to
) Calculating to obtain the shape description parameters of the grating points (
) (ii) a Wherein r represents the distance from the optical fiber to the geometric center of the section of the elastic outer tube theoretically, and theta represents the included angle between the plane of the central axis of the elastic outer tube and the X axis of the coordinate system of the section of the elastic outer tube; k is a coefficient representing a change in the deformation amount of the optical fiber to the wavelength, Delta lambda iThe Bragg wavelength variation quantity of the ith fiber grating node is obtained; alpha (alpha) ("alpha")iThe angle between the line connecting the ith optical fiber and the central axis of the elastic outer tube and the X axis is shown; theta.theta.iThe included angle is formed by the connecting line of the ith fiber grating point and the center of the cross section and the X axis; r isiThe distance from the ith optical fiber to the geometric center of the section of the elastic outer tube is represented;
the coordinate system of the section of the elastic outer tube is a two-dimensional coordinate system which is constructed by taking the center of the section of the elastic outer tube as an origin and taking the perpendicular direction of the connecting line of two adjacent optical fibers as the direction of the X, Y axis;
3) four groups of shape description parameters are obtained once according to the arrangement of four optical fibers in the elastic hose: r is a radical of hydrogeniAnd thetai。
A method of force measurement of a three-dimensional force measurement unit, comprising the steps of:
obtaining a real force reference value by adopting a measuring tool; when the three-dimensional force measuring unit is subjected to forces in different directions and different magnitudes, a force reference value and an optical fiber wavelength change value are simultaneously acquired;
the optical fiber wavelength change value is used as input data of an SVM model, the obtained force reference value is used as output data of the SVM model, and a mapping relation between the optical fiber wavelength change value and the force data is obtained through model training;
when the force is measured by the three-dimensional force measuring unit, a force measurement value is obtained according to the mapping relation between the optical fiber wavelength change value and the force data.
A calibration method of a three-dimensional force measurement unit comprises the following steps:
calibrating a geometric center: stretching the elastic hose into a linear state, and recording the optical fiber shape description parameter riAnd thetaiThen, sequentially placing the single optical fiber separated from the hollow structure in two grooves on a double-sided orthogonal calibration tool, so that the same optical fiber completes a semicircular state with the same shape on two planes which are orthogonal in space; respectively obtaining the wavelength variation of the single optical fiber twice, and obtaining the installation error of the geometric center of each optical fiber according to the following formula;
wherein K represents a coefficient of a change in the deformation amount of the optical fiber to the wavelength; r isxRepresents the distance of the optical fiber from the X axis; r isyThe distance from the optical fiber to the Y axis of the section coordinate system of the elastic outer tube is represented;
represents the average value of the two wavelength offsets in the X direction;
an average value of two wavelength shifts in the Y direction; mounting error r according to geometric center of each optical fiberxAnd ryCorrecting the actual installation position of the optical fiber;
individual fiber installation error calibration: sequentially embedding an elastic hose in two grooves of a double-sided orthogonal calibration tool, and recording the wavelength parameter of each optical fiber grating point:
calculating the installation error parameter of each optical fiber to obtain the optical fiber shape description parameter r iAnd thetaiCompensating for shape reconstruction errors caused by installation errors
Wherein K represents a coefficient of deformation amount to wavelength change; delta lambdaixThe wavelength offset of the ith optical fiber in the X-axis direction is shown; delta lambdaiyThe wavelength offset of the ith optical fiber in the Y-axis direction is shown; alpha is alphaiRepresenting the angle between the line connecting the ith optical fiber with the central axis and the X axis; r represents the distance from the optical fiber to the geometric center of the section of the elastic outer tube theoretically; r isiThe distance from the ith optical fiber to the geometric center of the section of the elastic outer tube is represented; Δ riRepresenting the difference between the theoretical distance and the actual distance; i denotes the serial number of the optical fiber.
The double-sided orthogonal calibration tool is composed of two mutually perpendicular calibration plates, and arc-shaped grooves are formed in the two calibration plates respectively; the arc-shaped grooves are the same in shape and size.
The invention has the following beneficial effects and advantages:
the invention combines the sensing of measuring three-dimensional force based on the FBG and the sensing of measuring the bending shape based on the FBG, and the two adopt the same optical fiber path, thereby reducing the usage amount of the optical fiber path and reducing the complexity of the whole sensor.
The part for detecting the three-dimensional force adopts a mode of cutting a plurality of spiral grooves on the elastic body, so that the elastic body has better matched axial rigidity and radial rigidity. The three-dimensional force sensor has the advantages of simple integral structure, fewer parts, simple and convenient assembly and large force measuring range, and can realize accurate three-dimensional force detection by adopting a force sensing calibration algorithm and a shape reconstruction and calibration algorithm for calibration.
Drawings
FIG. 1 is a schematic diagram of an overall configuration of a form and position force sensor according to the present invention;
FIG. 2a is a schematic structural diagram of a terminal three-dimensional elastic force measuring unit of a form and position force sensor according to the present invention;
FIG. 2b is a schematic structural diagram of a terminal three-dimensional elastic force measuring unit of a form and position force sensor according to the present invention;
wherein, 1-1, an upper cover plate; 1-2, an elastomer; 1-3, a lower cover plate; 1-4, optical fiber; 1-1-4, grating nodes;
FIG. 3a is a schematic structural diagram of an upper cover plate of a form and position force sensor according to the present invention;
FIG. 3b is a schematic diagram of a lower cover plate structure of a form and position force sensor according to the present invention;
1-1-1, and optical fiber fixing holes; 1-1-2, drive channel holes;
FIG. 4 is a schematic diagram of an elastomer structure of a form and position force sensor according to the present invention;
wherein, 1-2-1, spirally cutting grooves; 1-2, elastomers
FIG. 5 is a schematic view of a curved shape sensing internal fiber layout for a one-form force sensor of the present invention;
wherein, 2-1, an elastic hose; 1-4, optical fiber; 5-1, colloid;
FIG. 6 is a schematic view of an angle deviation double-sided correction plate according to the present invention;
FIG. 7 is a schematic diagram of deformation of an optical fiber;
FIG. 8a is a schematic view of the position of the optical fibers inside the multi-core optical fiber;
FIG. 8b is a schematic view of a curved planar projection of an optical fiber inside a multi-core optical fiber.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The invention relates to the technical field of sensors for detecting force and shape, and the main structure of the sensor comprises a three-dimensional elastic force measuring unit, a multi-core optical fiber, an elastic hose, a calculating unit and four optical fiber demodulators.
The FBG (fiber Bragg grating) sensor can simultaneously realize shape sensing and force sensing, when the FBG sensor is subjected to axial force and radial force, the upper cover plate, the lower cover plate and the elastic body deform through an elastic three-dimensional force measuring unit, the internal fiber Bragg grating is stretched or compressed, the reflection wavelength changes when light passes through the grating, the magnitude and the direction of the stress are obtained through a force sensing calibration algorithm, four Bragg grating optical fibers are fixed in the elastic hose at the rear end through glue pouring, when the hose deforms under stress, the internal optical fibers also deform, shape description parameters of each point are obtained through calculation according to the reflection wavelength offset of grating nodes on the optical fibers and an orthogonal optical fiber shape reconstruction algorithm, and continuous deformation bodies are obtained through integral reconstruction of deformation of each point. The shape measurement calibration algorithm uses a calibration tool to obtain information about the sensor reference and obtain specific parameters of the sensor to calibrate errors generated during the sensor manufacturing process.
A shape and position force composite sensor comprises a three-dimensional elastic force measuring unit, a three-dimensional shape measuring unit, an optical fiber demodulator and a calculating unit, wherein the three-dimensional force measuring unit consists of an upper cover plate, a lower cover plate, an elastic body and the optical fiber, a multi-core optical fiber is adopted, and one division is four at the force sensing part of an elastic probe: the three-dimensional shape measuring unit consists of an elastic outer tube and four optical fibers, wherein a plurality of Bragg gratings are arranged on the optical fibers (the optical fibers in the hollow structure need to be arranged, and the optical fibers in the shape sensing section need to be arranged), the four optical fibers are glued inside the elastic hose, and the other end of the four optical fibers is connected with an optical fiber demodulator. The function of simultaneously measuring force and three-dimensional shape and position by using the same optical fiber channel can be realized. Four optical fibers are distributed in the elastic hose at equal angles, and the optical fiber data can be read by four optical fiber demodulators.
When the three-dimensional elastic force probe measuring unit is stressed, the upper cover plate, the lower cover plate and the elastic body are stressed and deformed, the internal optical fiber is also deformed, the reflection wavelength of the grating is changed, and the magnitude and the direction of the acting force are obtained through a force sense calibration algorithm; when the elastic outer tube is deformed under stress, the multiple multi-core optical fibers glued in the elastic outer tube deform along with the deformation, and the final shape description parameters can be solved through a shape reconstruction and calibration algorithm.
When the three-dimensional force measuring unit is subjected to axial force, the upper cover plate and the lower cover plate are deviated, the reflection wavelength of the internal fiber bragg grating is changed, and the magnitude and the direction of acting force can be calculated; when the force probe is stressed by radial force, the elastic body is deformed, the internal optical fiber is bent or stretched, and the magnitude and the direction of the acting force can be obtained according to the reflection wavelength of the grating. The upper cover plate and the lower cover plate are provided with optical fiber fixing holes, and the distance of the optical fiber fixing holes can be changed, so that the strain sensitivity of the grating when the elastic body is subjected to radial force is changed. The plurality of spiral cutting grooves are distributed along the circumferential direction of the central shaft of the elastic body at equal angles, and the radial rigidity and the axial rigidity of the elastic body can be balanced.
A plurality of multi-core optical fibers are adopted, the optical fibers are folded together, one section of the three-dimensional elastic force measuring unit is divided into four sections, the four sections are fixed through four optical fiber fixing holes, and the four optical fibers are glued around the central axis in the flexible pipe.
As shown in fig. 8a and 8b, the calibration method includes geometric center calibration and single fiber parameter calibration. A. Calibrating geometric center, stretching the flexible hose to be in a linear state, recording linear state parameters of the optical fiber, respectively completing semicircles with the same shape on two planes which are orthogonal in space by the shape measuring unit, respectively calculating wavelength offset of the geometric center of the shape sensor under two angles, according to (A), (B) and (C) 
) The installation error of the geometric center of the four optical fibers can be obtained; B. calibrating the installation error of the single optical fiber, respectively embedding the elastic hoses in two orthogonal calibration grooves by using a double-sided orthogonal calibration tool, and recording the wavelength parameter of each optical fiber grating point according to
) The installation error parameter of each optical fiber can be calculated (
) (ii) a (K represents a coefficient of deformation amount to wavelength change). According to the installation error parametersWhen the shape is reconstructed, the optical fibers are considered to be equidistantly and symmetrically distributed around the central axis of the section of the elastic hose, so that the offset and the offset angle of the central distance are compensated. Delta lambdaix、ΔλiyRespectively representing the wavelength offset of the ith fiber grating point in the X-axis direction and the Y-axis direction, namely mapping of the wavelength variation in the X, Y-axis direction;
and (3) realizing the shape reconstruction algorithm by using redundant optical fibers. The method includes a, calculating a temperature (Δ t ═ Δ t) from the total strain amount of the four optical fibers1+Δt2+Δt3+Δt4)/(4×Kt) ); B. according to (
) Every two optical fibers in orthogonal relationship (two optical fibers forming a right angle with the central axis) can be obtained according to (
) Calculating to obtain the shape description parameters of the grating points (
) (ii) a C. Four groups of shape description parameters can be obtained at one time according to the arrangement mode of the four redundant optical fibers, and the final shape description parameters are obtained by adopting an averaging method. The solving method includes, but is not limited to, calculating an average value, weighted averaging, particle swarm filtering, and the like.
The force sense calibration algorithm is as follows: the method comprises the steps of obtaining a true force reference value by adopting a measuring tool such as a standard force sensor or an electronic scale, simultaneously collecting the force reference value and an FBG optical fiber wavelength change value when the force sensor is subjected to forces in different directions and different magnitudes, obtaining a nonlinear model of the sensor by adopting a Support Vector Machine (SVM) so as to calibrate the sensor, specifically, taking the FBG optical fiber wavelength change value as input data of the SVM model, taking obtained force data as output data of the SVM, obtaining a mapping relation between the FBG optical fiber wavelength change value and the force data through model training so as to calibrate the force sensor, and finally evaluating a calibration result through a K-fold cross-validation method.
The shape and position force are transmitted compositelyThe method for acquiring the space temperature by the sensor comprises the following steps: taking a group of optical fiber grating points as a measuring unit, recording wavelength information of the four grating points at a reference temperature, measuring wavelength offset of the four grating points when measuring the temperature, calculating average wavelength offset as temperature difference offset of the temperature measuring unit, calibrating the temperature difference offset according to a check parameter of the optical fiber in front, and calibrating the temperature difference offset according to a Bragg grating wavelength offset relation (delta lambda)B＝Kεεx+KTΔ T), the amount of offset from the reference temperature can be solved. (Delta lambda) BRepresenting a bragg wavelength variation; kεRepresenting the influence coefficient of strain on the wavelength; epsilonxAxial stress is represented; kTRepresents the influence coefficient of temperature on the wavelength; Δ T represents the influence coefficient of temperature on wavelength. )
The first embodiment is described with reference to fig. 1, fig. 2a to fig. 2b, fig. 3a to fig. 3b, and fig. 5: a three-dimensional force and shape sensing composite sensor based on FBG grating optical fibers is integrally formed.
The main structure of the three-dimensional force and shape sensing composite sensor comprises a tail end three-dimensional force measuring unit (1) and a bent shape sensing part (2), wherein the tail end three-dimensional force measuring unit and the bent shape sensing part share four optical fibers and acquire data through a four-channel optical fiber demodulator (3); the tail end three-dimensional force measuring unit (1) comprises an upper cover plate (1-1), an elastic body (1-2), a lower cover plate (1-3) and an optical fiber (1-4); the curved shape sensing part (2) comprises an elastic outer tube (2-1) and an optical fiber (1-4); the tail end three-dimensional force measuring unit (1) can detect three-dimensional force, and the bent shape sensing part (2) at the tail part of the tail end can detect a space three-dimensional bent shape.
The second embodiment is described with reference to fig. 2a, 2b to 4: the tail end three-dimensional force probe.
The three-dimensional force measuring unit comprises an upper cover plate (1-1), an elastic body (1-2), a lower cover plate (1-3) and an optical fiber (1-4); the elastic body can be axially deformed under the action of axial external force, the distance between the upper cover plate and the lower cover plate is slightly changed, so that the fiber bragg grating between the upper cover plate and the lower cover plate is driven to be deformed, and the reflection wavelength of the grating is changed and is measured by the fiber optic demodulator; the elastic body can generate tiny bending deformation under the action of radial external force, and the bending deformation of the elastic body can cause the upper cover plate and the lower cover plate to be unparallel to generate a deflection angle, so that part of the grating is compressed by the elongated part of the grating; the acting direction and the acting force magnitude of the external force can be solved by a force sense calibration algorithm by analyzing the reflection wavelength changes of the four gratings;
Four optical fiber fixing holes (1-1-1) on the upper (lower) cover plate (1-1) are distributed along the circumferential direction of the central axis of the upper (lower) cover plate by 90 degrees, and the distance of the optical fiber fixing holes can be adjusted during processing so as to change the strain sensitivity of the grating when the elastic body bears radial force; the elastic body (1-2) is provided with a plurality of spiral cutting grooves (1-2-1) which are distributed along the circumferential direction of the central shaft of the elastic body at equal angles, and the radial rigidity and the axial rigidity of the elastic body can be balanced.
The third embodiment is described with reference to fig. 1 and 5: the curved shape sensing portion is formed.
The bending shape sensing part comprises an elastic outer tube (2-1) and optical fibers (1-4), wherein 4 optical fibers in the optical fibers (1-4) are glued in the elastic outer tube and distributed around a central axis; when the elastic outer tube is bent and deformed, the optical fiber inside the elastic outer tube is compressed or stretched, the grating reflection wavelength on the optical fiber is changed, the curvature of each grating point position and the relative angle of a bending plane can be obtained by analyzing the reflection wavelength of each part of the grating node, and the bending shape of the elastic outer tube is reconstructed through shape reconstruction and a calibration algorithm.
The fourth embodiment is illustrated in conjunction with fig. 5-7: a method for using an orthogonal correction plate.
The angle deviation orthogonal correction plate (figure 6) is composed of an orthogonal plate, each plate is provided with an arc-shaped groove, in the correction process, the root of the sensor is fixed, the optical fibers (1-4) are respectively bent and placed in the arc-shaped grooves of two orthogonal planes, the wavelength offset of the geometric center of the shape sensing under the two bending states is respectively calculated, and the wavelength offset is calculated according to the formula (A) 
) Obtaining the offset between the geometric centers of the four optical fibers and the center of the cross section of the hose; when correcting the deviation of a single optical fiber, one end of the elastic hose is fixed on the extension line of the intersection line of two planes of the correction plateThen placing the optical fiber in the arc groove on one side, then straightening the elastic hose, placing the elastic hose in the groove on the other side, and respectively recording the wavelength parameters of each optical fiber grating point at two positions according to
) The installation error parameters of each optical fiber can be calculated.
The fifth specific embodiment is described with reference to fig. 5 to 7: shape reconstruction algorithm
The shape reconstruction algorithm obtains the integral strain quantity of the four optical fibers through an optical fiber demodulator (4), and calculates the temperature (delta t ═ delta t)1+Δt2+Δt3+Δt4)/(4×Kt) According to (a)
) Each two optical fibers in orthogonal relationship of
) Solving the shape description parameters of the raster points in the deformation diagram (FIG. 7) ((
) Four groups of shape description parameters can be obtained at one time according to the arrangement mode of the four redundant optical fibers, and the final shape description parameters are obtained by means of averaging, weighted averaging, particle swarm filtering and the like.
Shape description parameters of each grating point include curvature and bending angle of the bending plane once the curvature and bending angle are determined, the shape of the space curve is also determined. Under the Frenet frame, based on Frenet theorem, a differential geometry method is adopted, the tangent vector at a discrete point is calculated by utilizing the collected curvature and deflection data, and the reconstruction of the shape of a continuum is completed based on the integral of the tangent vector. Finally, space shape perception based on discrete point curvature and flexibility information is achieved through computer image programming and a data interface according to a space curve Frenet integral equation, and coordinate description of the space curve can be obtained.
The sixth specific embodiment is described with reference to fig. 2a, 2b to 4: calibration method of force sensor
The force sensing calibration algorithm is characterized in that the magnitude of a known acting force is obtained through a measuring tool such as a standard force sensor or an electronic scale, the known acting force is applied to different positions and different directions on an upper cover plate (1-1), an elastic body (1-2) and a lower cover plate (1-3), a force reference value and an FBG optical fiber wavelength change value are collected, a Support Vector Machine (SVM) is adopted to obtain a nonlinear model of the sensor so as to calibrate the sensor, specifically, the FBG optical fiber wavelength change value is used as input data of the SVM model, the obtained force data is used as output data of the SVM, a mapping relation between the FBG optical fiber wavelength change value and the force data is obtained through model training, so that the force sensor is calibrated, and finally a calibration result is evaluated through a K-fold cross-validation method.
The seventh embodiment is explained with reference to fig. 2, fig. 5 and fig. 7: method for obtaining ambient temperature
The method for obtaining the environmental temperature comprises the steps of taking a group of optical fiber grating points as a measuring unit through a measuring elastic hose (figure 5), recording wavelength information of the four grating points at a reference temperature, measuring wavelength offset of the four grating points during temperature measurement, calculating average wavelength offset to serve as temperature difference offset of the temperature measuring unit, calibrating the temperature difference offset according to a check parameter of a front optical fiber, and calibrating the temperature difference offset according to a Bragg grating wavelength offset relation (delta lambda) B＝Kεεx+KTΔ T), the amount of offset from the reference temperature can be solved.
In this specification, the invention has been described with reference to specific embodiments thereof. The above embodiments are preferred embodiments of the present invention, and are not intended to limit the scope 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 modifications, changes, combinations, substitutions and the like without departing from the principle of the present invention, and the scope of the present invention is defined by the appended claims.
Claims (4)
1. A force measuring method of a shape and position force composite sensing unit is realized based on a shape and position force composite sensing unit, and the shape and position force composite sensing unit comprises a three-dimensional force measuring unit, an optical fiber demodulator and a calculating unit which are sequentially connected;
three-dimensional force measuring unit for produce deformation when receiving external force, include: the optical fiber connector comprises an upper cover plate, a lower cover plate, an elastic body and an optical fiber;
the elastic body is provided with a spiral cutting groove which is distributed along the axial direction of the axis of the elastic body at equal angles;
the elastic body forms a side wall and is fixed between the upper cover plate and the lower cover plate to form a hollow structure; the optical fiber penetrates into the hollow structure from the lower cover plate and is fixedly connected with the upper cover plate;
The optical fibers are multiple, and the tail ends connected with the upper cover plate are uniformly arranged along the geometric center of the upper cover plate;
the upper cover plate and the lower cover plate are respectively provided with optical fiber fixing holes, and the positions of the optical fiber fixing holes correspond to those of the optical fibers, so that the optical fibers are parallel to the axis of the hollow structure in the hollow structure;
the optical fiber demodulator is used for converting optical signals generated by optical fibers when the three-dimensional force measuring unit deforms into wavelengths; the calculating unit is used for obtaining the wavelength offset of each optical fiber according to the wavelength of the optical fibers, and obtaining the magnitude and the direction of acting force of each fiber grating node of the three-dimensional force measuring unit and the curvature and the flexibility of each grating node of the shape sensing section formed by the hollow-structure external optical fibers according to the wavelength offset, and is characterized by comprising the following steps of:
when the three-dimensional force measuring unit is subjected to axial force, the upper cover plate and the lower cover plate deviate, and the reflection wavelength of the internal fiber bragg grating changes;
when the three-dimensional force measuring unit is subjected to radial force, the elastic body deforms, and the internal optical fiber bends or stretches, so that the reflection wavelength of the grating changes;
obtaining the magnitude and direction of the acting force according to the change of the reflection wavelength;
the calibration method of the three-dimensional force measuring unit comprises the following steps:
Calibrating a geometric center: stretching the elastic hose into a linear state, and recording the optical fiber shape description parameter riAnd thetaiThen, the single optical fiber separated from the hollow structure is sequentially arranged on the double-sided orthogonal calibrationTwo grooves on the quasi-tool enable the same optical fiber to complete a semicircular state with the same shape on two planes which are orthogonal in space; respectively obtaining the wavelength variation of the single optical fiber twice, and obtaining the installation error of the geometric center of each optical fiber according to the following formula;
wherein K represents a coefficient of a change in the deformation amount of the optical fiber to the wavelength; r isxRepresents the distance of the optical fiber from the X axis; r isyThe distance from the optical fiber to the Y axis of the section coordinate system of the elastic outer tube is represented;
represents the average value of the two wavelength offsets in the X direction;
an average value of two wavelength shifts in the Y direction; mounting error r according to geometric center of each optical fiberxAnd ryCorrecting the actual installation position of the optical fiber;
individual fiber installation error calibration: sequentially embedding an elastic hose in two grooves of a double-sided orthogonal calibration tool, and recording the wavelength parameter of each optical fiber grating point:
calculating the installation error parameter of each optical fiber to obtain the optical fiber shape description parameter riAnd thetaiCompensating for shape reconstruction errors caused by installation errors
Wherein K represents a coefficient of a change in the deformation amount of the optical fiber to the wavelength; delta lambdaixThe wavelength offset of the ith optical fiber in the X-axis direction is shown; delta lambdaiyThe wavelength offset of the ith optical fiber in the Y-axis direction is shown; alpha is alphaiRepresenting the angle between the line connecting the ith optical fiber with the central axis and the X axis; r represents the distance from the optical fiber to the geometric center of the section of the elastic outer tube theoretically; r isiThe distance from the ith optical fiber to the geometric center of the section of the elastic outer tube is represented; Δ riRepresenting the difference between the theoretical distance and the actual distance; i represents the serial number of the optical fiber;
the double-sided orthogonal calibration tool is composed of two mutually perpendicular calibration plates, and arc-shaped grooves are formed in the two calibration plates respectively; the arc-shaped grooves are the same in shape and size.
2. A method of force measurement of a form and position force composite sensing unit according to claim 1, comprising the steps of:
1) and (3) calculating the temperature according to the wavelength variation of the four optical fibers:
Δt＝(Δt1+Δt2+Δt3+Δt4)/(4×Kt)
wherein, delta t is the integral temperature variation of the four optical fibers; Δ tiThe temperature variation of the ith fiber grating node is obtained; ktThe influence coefficient of temperature change on the wavelength;
2) according to
For each two optical fibers in orthogonal relationship, according to
Solving to obtain the shape description parameters of the grating points
Wherein r represents the distance from the optical fiber to the geometric center of the section of the elastic outer tube theoretically, and theta represents the included angle between the plane of the central axis of the elastic outer tube and the X axis of the coordinate system of the section of the elastic outer tube; k is a coefficient representing the change of the deformation amount of the optical fiber to the wavelength, Delta lambda iThe variable quantity of Bragg wavelength of the ith fiber grating node is obtained; alpha (alpha) ("alpha")iTo representThe angle between the connecting line of the ith optical fiber and the central axis of the elastic outer tube and the X axis; thetaiThe included angle is formed by the connecting line of the ith fiber grating point and the center of the cross section and the X axis; r isiThe distance from the ith optical fiber to the geometric center of the section of the elastic outer tube is represented;
the coordinate system of the section of the elastic outer tube is a two-dimensional coordinate system which is constructed by taking the center of the section of the elastic outer tube as an origin and taking the perpendicular direction of the connecting line of two adjacent optical fibers as the direction of the X, Y axis;
3) four groups of shape description parameters are sequentially obtained according to the arrangement of the four optical fibers in the elastic hose: r isiAnd thetai。
3. The method for measuring force of a form and position force composite sensing unit of claim 1, wherein the magnitude and direction of the applied force are obtained according to the change of the reflection wavelength, comprising the following steps:
obtaining a real force reference value by adopting a measuring tool;
when the three-dimensional force measuring unit is subjected to forces in different directions and different magnitudes, a force reference value and an optical fiber wavelength change value are simultaneously acquired;
the optical fiber wavelength change value is used as input data of an SVM model, the obtained force reference value is used as output data of the SVM model, and a mapping relation between the optical fiber wavelength change value and the force data is obtained through model training;
When the force is measured by the three-dimensional force measuring unit, a force measurement value is obtained according to the mapping relation between the optical fiber wavelength change value and the force data.
4. A method for measuring force of a form and position force composite sensing unit according to claim 1, characterized in that a plurality of bragg gratings are arranged on the optical fiber; a plurality of optical fibers outside the hollow structure are glued inside the elastic hose and connected with the optical fiber demodulator.
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