Calibration method and calibration device of three-dimensional force sensor

Abstract

The invention provides a calibration method for a three-dimensional force sensor, and the method comprises the steps: enabling a to-be-calibrated three-dimensional force sensor to be fixedly connected with a standard force sensor, enabling the to-be-calibrated three-dimensional force sensor and the standard force sensor to have a fixed position relation in the calibration process, and enabling the to-be-calibrated three-dimensional force sensor and the standard force sensor to be kept still relative to a calibration platform; obtaining a transformation relation between the space three-dimensional coordinate systems of the standard force sensor and the three-dimensional force sensor; and applying contact forces with different magnitudes and directions to obtain wavelength data output by an optical demodulator connected with the three-dimensional force sensor and force data output by a standard sensor, thereby carrying out calibration. In addition, the invention further provides a calibration device which comprises the three-dimensional force sensor to be calibrated, the standard force sensor, the first clamp, the second clamp, the optical demodulator and the data processing unit, the three-dimensional force sensor to be calibrated does not need to be moved during calibration, a displacement table does not need to be used either, and the calibration device is simple in structure, easy and convenient to operate and high in practicability. And static loading calibration of the contact force at any angle can be realized.

Description

Technical Field

[0001] The present invention relates to the technical fields of force sensing, optical sensing, mechanical precision measurement, etc., and in particular to a calibration method and a calibration device for a three-dimensional force sensor. Background Art

[0002] A force sensor is a device used to detect the force exerted on an object. It can convert the force exerted on an object into an electrical signal, an optical signal or other forms of signals and output them, so that the magnitude and angle of the applied force can be quantified and recorded. Traditional force sensors mainly include electrical force sensors and optical force sensors. Electrical force sensors convert contact force into corresponding measurable electrical signals through sensitive elements, and obtain contact force information through circuit and software processing. They have the characteristics of high sensitivity, wide measurement range, strong customizability and high real-time performance. Optical force sensors mainly measure contact force based on the principle of optical modulation of optical fibers, and have the characteristics of high accuracy and wide measurement range.

[0003] Force sensors are widely used in many fields. For example, in industrial automation, force sensors are used to measure the motion force of robots and as load monitoring equipment; in the automotive industry, force sensors are used to measure braking force, suspension system load, engine force output, and collision test experiments; in medical equipment, surgical robots can use force sensors to accurately control the force, and rehabilitation technologies such as radiofrequency ablation rely on force sensors to characterize the degree of ablation; in aerospace, force sensors are used to evaluate the structural performance of aircraft; in addition, force sensors are also of great significance in sports science, environmental monitoring and other fields.

[0004] The calibration experiment of the force sensor is an experiment conducted to determine the relationship between the output signal of the force sensor and the contact force applied to the force sensor. By applying different contact forces to the force sensor, recording the output signals of the corresponding force sensor, and establishing a model of the relationship between the contact force and the output signal. The traditional static calibration method is to fix the standard force sensor and the multi-dimensional translation stage together, and then move the multi-dimensional translation stage to apply contact forces of different sizes and angles to the designed force sensor to perform a loading calibration experiment on the force sensor.

[0005] In the traditional force sensor calibration device, the standard force sensor is generally separated from the designed force sensor. The designed force sensor is fixed on the calibration platform, and the standard force sensor is fixed to the displacement table. By changing the position of the displacement table, the designed force sensor can be accurately controlled for multi-angle force loading. The traditional static calibration method of force sensors is too cumbersome. When changing the angle of contact force, the designed force sensor needs to be disassembled, and there may be limitations in complex nonlinear situations. To solve the above problems, Chinese utility model patent CN216081891U discloses a six-dimensional force sensor calibration platform, which changes the size of the contact force by changing the weight, thereby more easily realizing the loading calibration of the multi-dimensional force sensor. However, this solution is limited by the weight of the weight itself when collecting data, which will cause the step size of the calibrated data to be too large, which is not conducive to improving the calibration accuracy of the sensor. Chinese invention patent publication CN114088289A discloses a three-dimensional force sensor calibration device. In its implementation case, the angle of the contact force is changed by rotating the workbench, making it a three-dimensional force sensor calibration device with adjustable loading angle. However, this solution also has limitations: when changing the direction of the multi-dimensional force, the stroke and angle of the translation stage need to be manually adjusted to achieve contact forces at different specific angles, which brings certain complexity to the operation method, and when manually loading a force load in a fixed direction, there will inevitably be errors in the contact angle. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention designs a calibration method and a calibration device for a three-dimensional force sensor. The calibration method comprises the following steps performed in sequence:

[0007] S11: fixedly connecting the three-dimensional force sensor to be calibrated to the standard force sensor, wherein during the calibration process, the three-dimensional force sensor to be calibrated and the standard force sensor have a fixed positional relationship;

[0008] S12: The three-dimensional force sensor to be calibrated and the standard force sensor are fixedly connected to a calibration platform. During the calibration process, the three-dimensional force sensor to be calibrated and the standard force sensor remain stationary relative to the calibration platform.

[0009] S13: connecting the output end of the three-dimensional force sensor to be calibrated to an optical demodulator, and connecting the output end of the optical demodulator to a data processing unit; connecting the output end of the standard force sensor to the data processing unit;

[0010] S14: obtaining an input relationship between the standard force sensor and the three-dimensional force sensor to be calibrated for the same contact force;

[0011] S15: applying contact forces of different magnitudes and directions to the three-dimensional force sensor to be calibrated, and obtaining a first signal output by the optical demodulator and a second signal output by the standard force sensor;

[0012] S16: Obtaining first mechanical data according to the first signal;

[0013] S17: Obtain a correspondence between the first mechanical data and the second signal, and use the correspondence as calibration data of the three-dimensional force sensor to be calibrated.

[0014] Optionally, in step S11, a first clamp is used to fix the three-dimensional force sensor to be calibrated and the standard force sensor, and the three-dimensional force sensor, the standard force sensor and the first clamp all have an axisymmetric structure, and the longitudinal axis of the three-dimensional force sensor coincides with the longitudinal axis of the standard force sensor.

[0015] Optionally, in step S12, a second clamp is used to fix the standard force sensor to the calibration platform.

[0016] Optionally, the input relationship in step S14 includes a transformation relationship between the spatial three-dimensional coordinate systems of the standard force sensor and the three-dimensional force sensor to be calibrated. Through this transformation relationship, the three-dimensional spatial coordinate systems of the standard force sensor and the three-dimensional force sensor to be calibrated completely overlap with each other. For the same contact force input, the standard force sensor and the three-dimensional force sensor to be calibrated have the same spatial three-dimensional coordinates.

[0017] Optionally, the optical demodulator in step S15 is a fiber Bragg grating demodulator, the first signal is a fiber Bragg grating center wavelength drift signal, and the drift signal includes a first center wavelength drift amount, a second center wavelength drift amount, and a third center wavelength drift amount.

[0018] Optionally, in step S16, the first mechanical data includes the components of the contact force along three directions in space, and the first center wavelength drift, the second center wavelength drift and the third center wavelength drift respectively correspond to the components of the contact force along three directions in space; the first center wavelength drift, the second center wavelength drift and the third center wavelength drift are respectively linearly related to the corresponding components.

[0019] The present invention also provides a calibration device for a three-dimensional force sensor, which includes a three-dimensional force sensor to be calibrated, a standard force sensor, a first clamp, a second clamp, an optical demodulator and a data processing unit. The three-dimensional force sensor to be calibrated and the standard force sensor are fixedly connected by the first clamp. During the calibration process, the three-dimensional force sensor to be calibrated and the standard force sensor have a fixed positional relationship; the second clamp is used to fixedly connect the three-dimensional force sensor to be calibrated, the standard force sensor and a calibration platform, so that the three-dimensional force sensor to be calibrated and the standard force sensor remain stationary relative to the calibration platform during the calibration process; the three-dimensional force sensor to be calibrated includes an optical fiber, which is connected to the optical demodulator. When contact force is applied to the three-dimensional force sensor to be calibrated, the optical demodulator outputs a first signal and the standard force sensor outputs a second signal. The first signal and the second signal are input into the data processing unit.

[0020] Optionally, the three-dimensional force sensor to be calibrated, the standard force sensor and the first fixture all have an axisymmetric structure, and the longitudinal axis of the three-dimensional force sensor coincides with the longitudinal axis of the standard force sensor.

[0021] Optionally, the three-dimensional force sensor to be calibrated has an axisymmetric structure, comprising an elastic matrix, an optical fiber and a contact end; the optical fiber is located on the central axis and passes through the elastic matrix and the contact end; the elastic matrix includes a first region, a second region and a third region adjacent to each other along the axis direction, wherein the first region and the second region are cantilever beam structures, the cantilever beams are both thin-walled beams, and the extension direction of the first beam located in the first region is perpendicular to the extension direction of the second beam located in the second region; the third region is a thin-walled hollow tube structure.

[0022] Optionally, in the first region and the second region, the optical fiber is attached to the central axis of the surface of the first beam and the second beam, and has a first fiber grating and a second fiber grating respectively; in the third region, the optical fiber has a third fiber grating.

[0023] Optionally, the first fiber grating, the second fiber grating, and the third fiber grating are all fiber Bragg gratings, the optical demodulator is a fiber Bragg grating demodulator, the first signal is a fiber Bragg grating center wavelength drift signal, and the drift signal includes a first center wavelength drift amount, a second center wavelength drift amount, and a third center wavelength drift amount.

[0024] Optionally, the data processing unit calculates component force values ​​of the contact force applied to the contact end along three spatial directions according to the first center wavelength drift, the second center wavelength drift and the third center wavelength drift.

[0025] The calibration method of the three-dimensional force sensor of the present invention can realize the loading of contact forces at different angles without moving the three-dimensional force sensor to be calibrated, simplifies the operation method to the greatest extent, has a simple structure, and can realize static loading calibration of contact forces at any angle.

[0026] Furthermore, the calibration device of the three-dimensional force sensor of the present invention does not use a translation stage, but only uses a clamp to fix the three-dimensional force sensor and the standard force sensor, so the device is simpler and convenient for practical use.

[0027] Based on the detailed description of the specific embodiments of the present application in combination with the accompanying drawings below, those skilled in the art will become more aware of the above and other objects, advantages and features of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Hereinafter, some specific embodiments of the present application will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0029] Figure 1 It is a block diagram of the components of the calibration device of the three-dimensional force sensor of the present invention.

[0030] Figure 2 The present invention is a flow chart of a calibration method for a three-dimensional force sensor.

[0031] Figure 3 4 is a structural diagram of a three-dimensional force sensor to be calibrated according to an embodiment of the present invention.

[0032] Figure 4 is the force diagram of the thin-walled beam subjected to lateral force, where

[0033] Figure 4 (a) is the force diagram of the thin-walled beam B in the elastic base region 5.2 subjected to lateral force;

[0034] Figure 4 (b) is the force diagram of the thin-walled beam A in the elastic base region 5.1 subjected to lateral force.

[0035] Figure 5 This is a positional relationship diagram between the three-dimensional force sensor to be calibrated and the standard force sensor.

[0036] Figure 6 is the relationship between the FBG central wavelength drift and the contact force applied along the X, Y, and Z axes, where

[0037] Figure 6 (a) is a graph showing the relationship between the first central wavelength drift and the contact force applied along the X-axis direction;

[0038] Figure 6 (b) is a graph showing the relationship between the second center wavelength drift and the contact force applied along the Y-axis direction;

[0039] Figure 6 (c) is a graph showing the relationship between the third central wavelength drift and the contact force applied along the Z-axis direction.

[0040] Figure 7 is the relationship between the reference value and the predicted value of the contact force applied along the X, Y, and Z axes, where

[0041] Figure 7 (a) is the relationship between the reference value and the predicted value of the contact force applied along the X-axis direction;

[0042] Figure 7 (b) is the relationship diagram between the reference value and the predicted value of the contact force applied along the Y-axis direction;

[0043] Figure 7 (c) is the relationship diagram between the reference value and the predicted value of the contact force applied along the Z-axis direction.

[0044] The symbols contained in the above drawings are explained as follows: 1-three-dimensional force sensor; 2-first clamp; 3-standard force sensor; 4-second clamp; 5-elastic matrix; 6-optical fiber; 7-optical demodulator; 8-signal amplifier; 9-data processing unit; 10-contact end; 11-bending axis; A, B-thin-walled beam; FBG1, FBG2, FBG3-fiber Bragg grating. DETAILED DESCRIPTION

[0045] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present disclosure will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0046] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only embodiments of a part of the present disclosure, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0047] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so as to describe the embodiments of the present invention described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0048] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0049] Figure 1 The block diagram of each component of the calibration device of the three-dimensional force sensor of the present invention is given. The three-dimensional force sensor 1 to be calibrated has a fixed positional relationship with the standard force sensor 3, and this fixed positional relationship can be achieved by a certain mechanical connection, such as using a clamp to fix the two. The three-dimensional force sensor 1 contains an optical fiber, and a fiber grating is engraved on the optical fiber. The optical fiber is led outward from the end of the three-dimensional force sensor, and the led-out optical fiber is connected to the optical demodulator 7, and the optical demodulator 7 transmits the demodulated wavelength data to the data processing unit 9. If the fiber grating is a fiber Bragg grating (FBG), the optical demodulator 7 uses a fiber Bragg grating (FBG) type demodulator. When the three-dimensional force sensor 1 is touched by contact forces in different directions, the fiber grating on its internal optical fiber will produce strain, causing the central wavelength of the fiber grating to drift. According to the corresponding relationship between the demodulated wavelength data and the contact forces in different directions, the contact force is calculated by the data processing unit 9. However, at this time, the three-dimensional force sensor has not yet completed the calibration, and its output needs to establish a relationship with the output of the standard force sensor.

[0050] The output of the standard force sensor 3 is amplified by the signal amplifier 8 and then input to the data processing unit 9. It should be noted that the signal amplifier 8 is not necessary. When the output signal of the standard force sensor is strong enough, there is no need to use the signal amplifier 8 additionally. The data processing unit 9 can be a computer, which uses certain software platforms, such as LabView. On this software platform, the wavelength data output by the optical demodulator 7, the contact force output by the three-dimensional force sensor to be calibrated calculated by the wavelength data, and the force data output by the standard force sensor can be recorded simultaneously, thereby calibrating the three-dimensional force sensor.

[0051] Figure 2 The following is a flow chart of the calibration method of the three-dimensional force sensor of the present invention. When performing the calibration, the following steps are performed in sequence:

[0052] S11: The three-dimensional force sensor to be calibrated is fixedly connected to the standard force sensor so that they have a fixed positional relationship during the entire calibration process.

[0053] S12: The three-dimensional force sensor to be calibrated and the standard force sensor are fixedly connected to the calibration platform. During the calibration process, the three-dimensional force sensor to be calibrated and the standard force sensor remain stationary relative to the calibration platform.

[0054] S13: connecting the output end of the three-dimensional force sensor to be calibrated to the optical demodulator, and connecting the output end of the optical demodulator to the data processing unit; connecting the output end of the standard force sensor to the data processing unit.

[0055] In this step, preferably, the output end of the standard force sensor may be first connected to a signal amplifier, and the output end of the signal amplifier may be further connected to a data processing unit.

[0056] S14: Obtaining the input relationship between the standard force sensor and the three-dimensional force sensor to be calibrated for the same contact force.

[0057] S15: applying contact forces of different magnitudes and directions to the three-dimensional force sensor to be calibrated, and obtaining a first signal output by the optical demodulator and a second signal output by the standard force sensor.

[0058] S16: Obtain first mechanical data according to the first signal.

[0059] S17: Obtain a correspondence between the first mechanical data and the second signal, and use the correspondence as calibration data of the three-dimensional force sensor to be calibrated.

[0060] The input relationship described in step S14 includes the transformation relationship between the spatial three-dimensional coordinate systems of the standard force sensor 3 and the three-dimensional force sensor 1 to be calibrated. Through this transformation relationship, the three-dimensional spatial coordinate systems of the standard force sensor 3 and the three-dimensional force sensor 1 to be calibrated completely overlap with each other. For the same contact force input, the standard force sensor 3 and the three-dimensional force sensor 1 to be calibrated have the same spatial three-dimensional coordinates.

[0061] In step S15, the optical demodulator 7 can be a fiber Bragg grating (FBG) demodulator, and the first signal is a fiber Bragg grating (FBG) central wavelength drift signal, which includes a first central wavelength drift Δλ1, a second central wavelength drift Δλ2 and a third central wavelength drift Δλ3.

[0062] The first mechanical data in step S16 includes the components of the contact force F along three directions in space F x 、F y 、F z The first center wavelength drift Δλ1, the second center wavelength drift Δλ2 and the third center wavelength drift Δλ3 are respectively related to F x 、F y 、F z Corresponding.

[0063] Figure 3 The structure diagram of the three-dimensional force sensor to be calibrated of the present invention. The three-dimensional force sensor has a cylindrical axisymmetric structure, including an elastic matrix 5, an optical fiber 6 and a contact end 10. The elastic matrix 5 can be divided into three regions 5.1, 5.2 and 5.3. The contact end 10 is hemispherical and is located outside the region 5.3. There is an opening on the top, and the opening runs inward along the axis. The optical fiber 6 is arranged on the central axis of the cylinder of the entire three-dimensional force sensor and runs through regions 5.1, 5.2 and 5.3. The two ends of the optical fiber 6 are respectively fixed to the bottom side of region 5.1 and the top side of region 5.3, and can be fixed by glue. Fiber gratings are engraved on the parts of the optical fiber in regions 5.1, 5.2 and 5.3, respectively, which can be fiber Bragg gratings (FBGs). The optical fiber continues to extend outward from the top side of region 5.3 along the axis of the contact end 10, and is led outward from the opening at the top of the contact end 10. The contact end 10 may be made of stainless steel, which is deformed after being subjected to an external force and can recover quickly. The contact force F to be sensed is applied to the contact end 10 .

[0064] The elastic matrix 5 can be made of stainless steel material, which deforms and recovers quickly after being subjected to external force. The elastic matrix has different structural forms in regions 5.1, 5.2 and 5.3. In region 5.1, above the first base region of a certain thickness, the two opposite sides of the cylinder are grooved, wherein the groove on one side extends to the radius, and the groove depth on the other side is less than the radius, and finally a beam A with a specific thickness is formed. Region 5.2 has a structure similar to that of region 5.1, and the second base region is adjacent to beam A. Above the second base region, a groove similar to that of region 5.1 is formed, that is, the groove on one side extends to the radius, and the groove depth on the other side is less than the radius, and finally a beam B with a specific thickness is formed. The thickness of beam B is the same as that of beam A, set to d, and the extension direction of beam B is perpendicular to the extension direction of beam A. The d value is much smaller than the diameter of the cylinder, so that beams A and beam B are both thin-walled beams. When the diameter of the cylinder is 3mm, the d value should be taken as one order of magnitude less than it, that is, the d value should be less than 0.3mm. Regions 5.1 and 5.2 can be regarded as a cantilever beam structure, and the optical fiber is attached to the central axis of the cantilever beam surface. The thickness of the second base area can be the same as or different from the thickness of the first base area. In this embodiment, they are selected to be the same. Region 5.3 is a thin-walled hollow tube structure, that is, there is a cylindrical thin wall of a certain thickness radially inward along the side of the cylinder, and the inside of the thin wall is a hollow area. In this embodiment, the diameter of the outer circumferential surface of region 5.3 is 3mm, and the thickness of the thin wall is only 0.3mm. The optical fiber 6 is located on the central axis of the hollow area. A rectangular groove penetrating the thin wall is opened on the thin wall, where a2 represents the opening width of the rectangular groove along the circumference of the cylinder, a1 represents the opening width of the rectangular groove along the axial direction of the cylinder, and a3 represents the spacing between each rectangular groove along the axial direction of the cylinder. In this embodiment, a1, a2, and a3 are 0.1mm, 2.7mm, and 0.24mm respectively. The above structures of regions 5.1, 5.2 and 5.3 can decouple the contact force applied to the contact end 10 along the X, Y and Z directions, thereby obtaining the components of the contact force along the X, Y and Z directions.

[0065] The decoupling of contact force in regions 5.1, 5.2 and 5.3 is the sensing basis of the three-dimensional force sensor disclosed in the present invention, and its principle is described as follows. The direction along the axial direction of the elastic substrate 5 pointing to the contact end 10 is taken as the Z axis, the radial direction outward along the beam B is taken as the X axis, and the radial direction outward along the beam A is taken as the Y axis. When the contact force F is applied to the contact end 10, it is transmitted downward to regions 5.3, 5.2 and 5.1. The contact force F can be decomposed into the longitudinal force along the axial direction of the cylinder and the transverse force F along the cylindrical surface t ,in represents the unit vector along the Z axis. In area 5.3, since there is no beam structure distributed along the X and Y directions, the lateral force F t There is no force-bearing body in this area, so F tis zero, and region 5.3 only has longitudinal force along the axial direction of the cylinder The longitudinal force F z The optical fiber 6 has a fiber Bragg grating FBG3 inscribed on the region 5.3, and its central wavelength is λ3. After the strain is generated, the central wavelength of FBG3 drifts, and the drift amount is Δλ3. Figure 4 (a) Beam B in region 5.2 is subjected to a lateral force F t Force diagram of lateral force F t Applied to the end face of the cantilever beam B, due to the thin thickness of the cantilever beam, its end face (that is, the cross section of the cantilever beam) can be approximately regarded as a rectangular cross section, the lengths of the long side and short side of the end face are b and d respectively, d is also the thickness of the cantilever beam. t It can be decomposed into the component force F along the X direction x and the component force F along the Y direction y , where the component force F along the Y direction y The cantilever beam B is bent along the short side of the end face, with the bending axis 11 as the axis. The bending axis 11 is a straight line passing through the center of the short side, such as Figure 4 (a) As shown in the upper left figure. The bending of the cantilever beam causes strain in the optical fiber 6, and the strain can be calculated by the following formula:

[0066]

[0067] Where ε is strain, M is bending moment, r is the distance between the optical fiber and the bending axis, E is the elastic modulus of the cantilever beam, and I is the moment of inertia of the cantilever beam about the bending axis. Figure 4 (a) In the case shown in the upper left figure, the moment of inertia is:

[0068]

[0069] Lateral force F t Component force F along the X direction x The force acts along the long side of the end face, so that the cantilever beam B is bent with the bending axis 11 as the axis. At this time, the bending axis 11 is a straight line passing through the center of the long side, such as Figure 4 (a) As shown in the upper right figure. The bending of the cantilever beam causes strain in the optical fiber 6, and the strain magnitude is still calculated by equation (1), but for Figure 4 (a) In the case shown in the upper right figure, the moment of inertia is:

[0070]

[0071] Since b is much larger than d, I1 is much smaller than I2, so the optical fiber 6 Figure 4 (a) The strain generated in the upper left figure is much greater than Figure 4 (a) The strain generated in the upper right figure. And, Figure 4(a) In the upper right figure, the optical fiber 6 passes through the bending axis 11. At this time, r is zero, so the strain generated by the optical fiber is also zero. As for the longitudinal force in region 5.2 Since the longitudinal force is always along the axis, it does not bend the beam B, and the optical fiber 6 does not produce strain due to the longitudinal force. Therefore, for area 5.2, the strain produced by the optical fiber 6 is only the transverse force F t Component force F along the Y direction y The force F along the X direction is generated x and longitudinal force F z The optical fiber 6 has a fiber Bragg grating FBG2 inscribed in region 5.2, and its central wavelength is λ2. After the strain is generated, the central wavelength of FBG2 drifts by Δλ2.

[0072] The same lateral force F t After being transferred to area 5.1, since the extension direction of beam A is perpendicular to that of beam B, the force on the end face of cantilever beam A is the same as that on the end face of cantilever beam B. Figure 4 (a) Exactly swap, such as Figure 4 (b) is shown. Figure 4 The force component F in (a) y At this time, it acts along the long side of the end face, and Figure 4 The force component F in (a) x At this time, the effect is along the short side direction of the end face, as shown in Figure 4 (b) is shown in the upper left and upper right figures. From the previous analysis process, it is known that the strain on the optical fiber caused by the force acting along the long side of the end face is zero, and the strain of the optical fiber is only caused by the force acting along the short side of the end face. Similarly, in area 5.1, the optical fiber does not produce strain due to the longitudinal force. Therefore, for area 5.1, the strain generated by optical fiber 6 is only the transverse force F t Component force F along the X direction x The force F in the Y direction is generated. y and longitudinal force F z The optical fiber 6 has a fiber Bragg grating FBG1 inscribed on region 5.1, and its central wavelength is λ1. After the strain is generated, the central wavelength of FBG1 drifts by Δλ1.

[0073] The three-dimensional force sensor structure provided in the present disclosure decouples the contact force in regions 5.3, 5.2 and 5.1 along the Z, Y and X directions respectively, and detects the force components in these three directions respectively, that is, the magnitude and direction of the applied contact force are obtained.

[0074] The relationship between the center wavelength drift of FBG1, FBG2, and FBG3 and the force applied thereto is given below.

[0075] According to the working principle of FBG, when it is subjected to force, the central wavelength of FBG will drift:

[0076]

[0077] Where Δλ1, Δλ2, Δλ3 are the center wavelength drifts of FBG1, FBG2 and FBG3, λ1, λ2, λ3 are the center wavelengths of FBG1, FBG2 and FBG3, ρ e is the effective elastic-optical coefficient of the optical fiber, ε x , ε y , ε z The strains on FBG1, FBG2 and FBG3 caused by the forces in the X, Y and Z directions respectively.

[0078] From the stress formula σ=F / A and Hooke's law σ=Eε, the relationship between strain and force is obtained:

[0079]

[0080] Where σ is stress, ε is strain, E is elastic modulus, F is applied contact force, and A is cross-sectional area. Substitute equation (5) into equation (4) and let:

[0081]

[0082] The relationship between the force and the center wavelength drift is as follows:

[0083]

[0084] where F x 、F y 、F z They are the components of the contact force in the X, Y, and Z directions respectively.

[0085]

[0086] is the sensitivity matrix, K1, K2, and K3 are the force sensitivity coefficients of FBG1, FBG2, and FBG3, respectively.

[0087] After the demodulated wavelength data is obtained by the optical demodulator 7, the components F of the contact force in the X, Y, and Z directions can be calculated by formula (7): x 、F y 、F z .

[0088] After the size and direction of the contact force are obtained by the three-dimensional force sensor, the three-dimensional force sensor needs to be calibrated, that is, a corresponding relationship is established between the output of the three-dimensional force sensor and the output of the standard force sensor. Figure 5It is a position relationship diagram between the three-dimensional force sensor 1 to be calibrated and the standard force sensor 3. The standard force sensor 3 can be of different structural types. In this embodiment, an ATI six-axis torque sensor (Nano17 SI-12-0.12, USA) is used as the standard force sensor, which has a cylindrical structure. The three-dimensional force sensor 1 to be calibrated and the standard force sensor 3 are fixedly connected by the first clamp 2 so that the two have a fixed position relationship. Specifically, the three-dimensional force sensor 1 and the standard force sensor 3 are coaxially fixed by the first clamp 2, one end of the first clamp 2 is tightly connected to the three-dimensional force sensor 1, and the other end is tightly connected to the standard force sensor 3, and the tight connection can be achieved by screws or bolts. The first clamp 2 also has axial symmetry. During installation, it is necessary to ensure that the longitudinal axis of the three-dimensional force sensor 1 coincides with the longitudinal axis of the standard force sensor 3, and the X-axis and Y-axis of the three-dimensional force sensor 1 are parallel to the X-axis and Y-axis of the standard force sensor 3, respectively. After the above installation, the three-dimensional force sensor 1 and the standard force sensor 3 always have a fixed position relationship in the subsequent calibration process, and the spatial position coordinates of the two satisfy:

[0089]

[0090] Where x', y', z' are the spatial coordinates in the coordinate system of the three-dimensional force sensor 1, x, y, z are the spatial coordinates in the coordinate system of the standard force sensor 3, and z0 is the axial distance between the three-dimensional force sensor 1 and the standard force sensor 3. According to formula (9), the output result of the three-dimensional force sensor 1 can be matched with the output result of the standard force sensor 3.

[0091] Continue to use the second clamp 4 to fix the standard force sensor 3 to the calibration platform, so that the positional relationship between the three-dimensional force sensor 1, the standard force sensor 3 and the calibration platform is completely fixed. During the calibration process, the three-dimensional force sensor 1 and the standard force sensor 3 remain stationary relative to the calibration platform. The second clamp 4 is connected to the standard force sensor 3 and the calibration platform by screws or bolts. The material of the first clamp 2 and the second clamp 4 is generally made of hard materials with a high Young's modulus to ensure its rigidity, such as metal materials or high-hardness resins, to prevent the clamp from tilting when subjected to a large pressure, resulting in the actual applied contact force being inconsistent with the contact force output by the sensor.

[0092] After completing the above fixing operation and determining the coordinate transformation relationship of formula (9), the calibration operation can be performed. During calibration, a single-direction force can be applied along the X, Y, and Z axes of the three-dimensional force sensor 1, and the output of the single-direction force can be calibrated, and then the force at any angle can be calibrated. Figure 6(a), (b), and (c) are diagrams showing the relationship between the center wavelength drift and the contact force obtained by demodulating the optical demodulator 7 when contact forces are applied along the X, Y, and Z axes of the three-dimensional force sensor 1 using a standard force-applying component. Figure 6 (a) is a contact force applied by a standard force-applying component along the X-axis of the three-dimensional force sensor 1. When applying force, the standard force-applying component applies a force F to the contact end 10 of the three-dimensional force sensor 1 along the X-axis. x , the center wavelength drift of FBG1, FBG2 and FBG3 is output by the optical demodulator 7. It can be seen that the center wavelength drift Δλ1 output by FBG1 is related to F x There is a good linear relationship, and the linear slope obtained by fitting is in good agreement with the K1 value given by equation (6). FBG2 and FBG3 have a slight central wavelength drift, which is within the allowable error range. Figure 6 (b) and (c) are the situations where the standard force-applying component applies force along the Y-axis and Z-axis of the three-dimensional force sensor 1, respectively. It can be seen that the center wavelength drift Δλ2 output by FBG2 is related to F y There is a good linear relationship. The linear slope obtained by fitting is consistent with the K2 value given by equation (6). The center wavelength drift Δλ3 of FBG3 output is consistent with F z There is a good linear relationship, and the linear slope obtained by fitting is in good agreement with the K3 value given by equation (6). y When F is applied, the zero output of FBG3 is very stable, and FBG1 has a slight central wavelength drift, which can be eliminated through data calibration. z When the wavelength is 0, the zero output of FBG2 is very stable, and FBG1 has a slight center wavelength drift, which can also be eliminated through data calibration.

[0093] The standard force-applying components are used again to apply contact force F along the X, Y, and Z axis directions of the three-dimensional force sensor 1. x 、F y 、F z, the corresponding force value is read out by the standard force sensor 3 as the reference value (horizontal axis). In this embodiment, the output end of the standard force sensor 3 is connected to the signal amplifier 8, that is, the output signal of the standard force sensor 3 is amplified and then input into the data processing unit 9. The signal amplifier 8 in this embodiment is NetBox (9105-NETBA, USA), and the standard force sensor 3 is the ATI six-axis torque sensor (Nano17 SI-12-0.12, USA) mentioned above. It should be pointed out that the signal amplifier 8 is not required to be used. When the signal strength output by the standard force sensor 3 can meet the requirements of the calibration experiment, the signal amplifier can be omitted. The output force value of the three-dimensional force sensor 1 is obtained by the central wavelength drift obtained after demodulation by the optical demodulator 7 as the predicted value (vertical axis). After the coordinate transformation relationship (9), the relationship diagram between the contact force reference value and the predicted value is obtained, as shown Figure 7 shown. Figure 7 (a), (b), and (c) are the contact forces F x 、F y 、F z It can be seen that the output of the calibrated three-dimensional force sensor 1 is very consistent with the output of the standard force sensor 3.

[0094] For the case where the contact force is at any angle, a calibration process similar to the above can be performed. The contact force can be applied to the contact end 10 of the three-dimensional force sensor 1 at multiple different angles by holding a clamp by hand or using other appropriate methods, and the calibration data can be continuously collected to record the output signal of the three-dimensional force sensor 1 under different contact force loading conditions. Such a continuous touch and data collection process can cover the loading conditions of forces at various angles to obtain calibration data at multiple angles, and then calibrate the three-dimensional force sensor. When the contact force is at any angle, the amount of data during calibration is large. In order to improve the data fitting effect, a data-driven model can be obtained in a data-driven manner, and the collected data-driven model can be trained to automatically learn the complex mapping relationship between the input and output of the three-dimensional force sensor. By learning a large number of input-output data samples, a better data fitting effect can be obtained.

[0095] The three-dimensional force sensor calibration device designed by the present invention fixes the three-dimensional force sensor to be calibrated and the standard force sensor together. When applying contact forces of different angles and sizes, there is no need to move the three-dimensional force sensor or use a translation stage. The structure is simple and can realize static loading calibration of contact forces at any angle. Coordinate transformation ensures that the standard force sensor can sense the contact force of the same size and direction as the three-dimensional force sensor to be calibrated. The calibration operation is simple, the step distance is small, and accurate calibration is achieved.

[0096] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0097] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0098] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the devices or elements referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention. The directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0099] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A calibration method for a three-dimensional force sensor, characterized in that: The calibration method comprises the following steps performed in sequence: S11: fixedly connecting the three-dimensional force sensor to be calibrated to the standard force sensor, wherein during the calibration process, the three-dimensional force sensor to be calibrated and the standard force sensor have a fixed positional relationship; S12: The three-dimensional force sensor to be calibrated and the standard force sensor are fixedly connected to a calibration platform. During the calibration process, the three-dimensional force sensor to be calibrated and the standard force sensor remain stationary relative to the calibration platform. S13: connecting the output end of the three-dimensional force sensor to be calibrated to an optical demodulator, and connecting the output end of the optical demodulator to a data processing unit; connecting the output end of the standard force sensor to the data processing unit; S14: obtaining an input relationship between the standard force sensor and the three-dimensional force sensor to be calibrated for the same contact force; S15: applying contact forces of different magnitudes and directions to the three-dimensional force sensor to be calibrated, and obtaining a first signal output by the optical demodulator and a second signal output by the standard force sensor; S16: Obtaining first mechanical data according to the first signal; S17: Obtain a correspondence between the first mechanical data and the second signal, and use the correspondence as calibration data of the three-dimensional force sensor to be calibrated.

2. The calibration method according to claim 1, characterized in that: In step S11, a first clamp (2) is used to fix the three-dimensional force sensor to be calibrated and the standard force sensor, wherein the three-dimensional force sensor, the standard force sensor and the first clamp all have an axisymmetric structure, and the longitudinal axis of the three-dimensional force sensor coincides with the longitudinal axis of the standard force sensor.

3. The calibration method according to claim 2, characterized in that: In step S12, a second clamp (4) is used to fix the standard force sensor to the calibration platform.

4. The calibration method according to claim 3, characterized in that: The input relationship in step S14 includes the transformation relationship between the spatial three-dimensional coordinate systems of the standard force sensor and the three-dimensional force sensor to be calibrated. Through this transformation relationship, the three-dimensional spatial coordinate systems of the standard force sensor and the three-dimensional force sensor to be calibrated completely overlap with each other. For the same contact force input, the standard force sensor and the three-dimensional force sensor to be calibrated have the same spatial three-dimensional coordinates.

5. The calibration method according to claim 1, characterized in that: In step S15, the optical demodulator is a fiber Bragg grating demodulator, the first signal is a fiber Bragg grating center wavelength drift signal, and the drift signal includes a first center wavelength drift amount, a second center wavelength drift amount, and a third center wavelength drift amount.

6. The calibration method according to claim 5, characterized in that: In step S16, the first mechanical data includes the components of the contact force along the three directions of space, and the first center wavelength drift, the second center wavelength drift and the third center wavelength drift respectively correspond to the components of the contact force along the three directions of space; the first center wavelength drift, the second center wavelength drift and the third center wavelength drift are respectively linearly related to the corresponding components.

7. A calibration device for a three-dimensional force sensor, characterized in that: The calibration device comprises a three-dimensional force sensor to be calibrated (1), a standard force sensor (3), a first fixture (2), a second fixture (4), an optical demodulator (7) and a data processing unit (9); the three-dimensional force sensor to be calibrated (1) and the standard force sensor (3) are fixedly connected via the first fixture (2); during the calibration process, the three-dimensional force sensor to be calibrated (1) and the standard force sensor (3) have a fixed positional relationship; the second fixture (4) is used to calibrate the three-dimensional force sensor to be calibrated (1) and the standard force sensor (3) ) is fixedly connected to the calibration platform so that the three-dimensional force sensor (1) to be calibrated and the standard force sensor (3) remain stationary relative to the calibration platform during the calibration process; the three-dimensional force sensor (1) to be calibrated comprises an optical fiber (6), and the optical fiber (6) is connected to the optical demodulator (7). When a contact force is applied to the three-dimensional force sensor (1) to be calibrated, the optical demodulator (7) outputs a first signal and the standard force sensor (3) outputs a second signal. The first signal and the second signal are input to the data processing unit (9).

8. The calibration device according to claim 7, characterized in that: The three-dimensional force sensor (1) to be calibrated, the standard force sensor (3) and the first fixture (2) all have an axisymmetric structure, and the longitudinal axis of the three-dimensional force sensor coincides with the longitudinal axis of the standard force sensor.

9. The calibration device according to claim 7, characterized in that: The three-dimensional force sensor (1) to be calibrated has an axisymmetric structure, comprising an elastic matrix (5), an optical fiber (6) and a contact end (10); the optical fiber (6) is located on a central axis and penetrates the elastic matrix (5) and the contact end (10); the elastic matrix (5) comprises a first region (5.1), a second region (5.2) and a third region (5.3) which are adjacent in sequence along the axis direction, wherein the first region (5.1) and the second region (5.2) are cantilever beam structures, the cantilever beams are thin-walled beams, and the extension direction of the first beam (A) located in the first region is perpendicular to the extension direction of the second beam (B) located in the second region; and the third region (5.3) is a thin-walled hollow tube structure.

10. The calibration device according to claim 9, characterized in that: In the first region (5.1) and the second region (5.2), the optical fiber (6) is attached to the central axis of the surface of the first beam (A) and the second beam (B), and has a first fiber grating and a second fiber grating respectively; in the third region (5.3), the optical fiber (6) has a third fiber grating.

11. The calibration device according to claim 10, characterized in that: The first fiber grating, the second fiber grating, and the third fiber grating are all fiber Bragg gratings, the optical demodulator is a fiber Bragg grating demodulator, the first signal is a fiber Bragg grating central wavelength drift signal, and the drift signal includes a first central wavelength drift amount, a second central wavelength drift amount, and a third central wavelength drift amount.

12. The calibration device according to claim 11, characterized in that: The data processing unit (9) calculates the component force values ​​of the contact force applied to the contact end (10) along three spatial directions according to the first central wavelength drift, the second central wavelength drift and the third central wavelength drift.

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