Optical fiber force sensor and decoupling method

Abstract

The invention relates to the technical field of medical instruments, in particular to an optical fiber force sensor and a decoupling method.The optical fiber force sensor comprises a base, a top cover and a hollow tubular elastic body, the two ends of the elastic body are connected with the base and the top cover respectively, and an optical fiber is arranged in the elastic body; the first optical fiber is engraved with an optical fiber grating, and the two ends of the first optical fiber are connected with the base and the top cover respectively; and the first end of the second optical fiber is provided with a temperature measuring element, and the second end of the second optical fiber is connected with the base / top cover. Through the arrangement, the optical fiber force sensor can resist transverse force in all directions, the interference caused by temperature change is overcome, and the measurement precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and in particular to an optical fiber force sensor and a decoupling method. Background Art

[0002] During robot-assisted minimally invasive surgery, surgeons will lose tactile information because they do not have direct contact with the patient. Real-time force feedback is very important for surgeons' diagnosis. The information of contact force ensures the safety of surgery and improves the success rate of surgery. Therefore, contact force sensors play a vital role here. They can provide surgeons with real-time force feedback when micro medical instruments interact with tissues.

[0003] Compared with electrical force sensors, optical force sensors have many unique advantages, such as strong anti-electromagnetic interference ability, easier compatibility with radiofrequency ablation devices, small size, good flexibility, high sensitivity and good physiological compatibility. In optical force sensors, wavelength modulation sensors modulate force information into the light beam by changing the wavelength in the optical fiber. Fiber Bragg grating (FBG) is the most commonly used wavelength modulation sensor. Using optical fiber engraved with FBG as a sensing element can overcome the limitations of light intensity fluctuations and phase discontinuity, and has high sensitivity and good biocompatibility.

[0004] However, since FBG sensors are very sensitive to temperature and strain, temperature changes will interfere with the measurement of force, resulting in large errors in the measurement results and low measurement accuracy. Summary of the invention

[0005] In order to solve the defects of the existing FBG sensor that the measurement accuracy is low and the measurement result error is large due to the influence of temperature, the present invention proposes an optical fiber force sensor and a decoupling method.

[0006] The technical solution adopted by the present invention is a fiber optic force sensor, comprising a base, a top cover and a hollow tubular elastomer, wherein the two ends of the elastomer are respectively connected to the base and the top cover, and the elastomer is provided with: a first optical fiber on which a fiber grating is engraved, and the two ends of the first optical fiber are respectively connected to the base and the top cover; a second optical fiber, a temperature measuring element is provided at the first end, and the second end of the second optical fiber is connected to the base / top cover.

[0007] Preferably, the temperature measuring element is one of a gallium arsenide crystal, a silicon boride crystal, a platinum crystal or a fluorescent temperature measuring element.

[0008] Preferably, the first optical fiber is arranged along the axis of the elastomer, and the surface of the elastomer is provided with a plurality of hollow structures arranged in an alternating manner along its circumference.

[0009] Preferably, the cross-sectional shape of the hollow structure is an inclined parallelogram, and the inclination directions of the plurality of hollow structures are not completely the same.

[0010] Preferably, the inclination directions of the hollow structures at different positions along the axial direction of the elastomer are different.

[0011] Preferably, the elastic body is made of stainless steel or epoxy resin.

[0012] Preferably, the base / top cover is bonded / welded and fixed to the elastomer, the first optical fiber and the second optical fiber respectively.

[0013] The present invention also proposes a sensor decoupling method, based on the above-mentioned optical fiber force sensor, the method includes: obtaining the central wavelength offset of the optical fiber Bragg grating; using a temperature measuring element to obtain the ambient temperature change; constructing a first relationship between the central wavelength offset of the optical fiber Bragg grating and the external force value and the ambient temperature change; substituting the central wavelength offset and the ambient temperature change into the first relationship to obtain the external force value.

[0014] Preferably, the temperature measuring element is a gallium arsenide crystal, and the method of obtaining the ambient temperature change by using the temperature measuring element specifically includes: obtaining the wavelength of intrinsic absorption of the gallium arsenide crystal; constructing a second relationship between the wavelength of intrinsic absorption of the gallium arsenide crystal and the real-time temperature; substituting the wavelength of intrinsic absorption of the gallium arsenide crystal into the second relationship to obtain the real-time temperature; and obtaining the ambient temperature change according to the real-time temperature at different times.

[0015] Preferably, the method of constructing the first relationship between the central wavelength offset of the fiber Bragg grating and the external force value and the ambient temperature change also includes: calibrating the force sensitivity coefficient and the temperature sensitivity coefficient of the fiber Bragg grating.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The optical fiber force sensor of the present invention decouples the external force value by setting a first optical fiber with an optical fiber grating, and performs temperature compensation through a temperature measuring element, thereby reducing the influence of temperature changes on the measurement results, improving the measurement accuracy, and reducing the measurement error. The temperature measuring element is connected to the optical sensor through a second optical fiber, and the stability and robustness are greatly improved. The second optical fiber with a temperature measuring element is directly connected to the elastic body that fixes the first optical fiber, and is fixed to the base together with the first optical fiber. There is no need to increase the length of the sensor, and no other complex parts and structures are required. It is easy to produce and assemble, has low cost, small size, and is easy to promote and apply;

[0018] 2. The first optical fiber is arranged along the axis of the elastomer, and a plurality of hollow structures arranged in an alternating manner are arranged on the surface of the elastomer along its circumferential direction. The plurality of hollow structures arranged in an alternating manner reduce the conduction effect of the lateral force, and the lateral force applied from the outside will be dispersed to each groove on the surface of the elastomer. This dispersion effect prevents the lateral force from being excessively concentrated on a small part of the elastomer, but is evenly distributed on the entire surface, thereby improving the sensor's resistance to lateral force, effectively reducing the impact of lateral force on the sensor, overcoming the requirement that the sensor must be perpendicular to the tissue surface during palpation, and improving the feasibility of the sensor's application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is described in detail below with reference to the embodiments and accompanying drawings, wherein:

[0020] Figure 1 is a schematic diagram of a fiber optic force sensor;

[0021] Figure 2 This is the internal structure diagram of the fiber optic force sensor;

[0022] Figure 3 It is a schematic diagram of the hollow structure on the elastomer.

[0023] 1. Top cover; 2. Elastic body; 3. Base; 4. First optical fiber; 5. Second optical fiber;

[0024] 3.1. Fiber Bragg grating; 3.2. Temperature measuring element. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar components or components with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0026] In one embodiment, Figure 1 As shown, a fiber optic force sensor includes a base 3, a top cover 1 and an elastic body 2. The elastic body 2 is a hollow tube. The two ends of the elastic body 2 are connected to the base 3 and the top cover 1 respectively. A first optical fiber 4 and a second optical fiber 5 are arranged in the elastic body 2. A fiber grating 3.1 is engraved on the first optical fiber 4. The two ends of the first optical fiber 4 are connected to the base 3 and the top cover 1 respectively. The first optical fiber 4 is fixed in the elastic body 2 by the base 3 and the top cover 1. The fiber grating 3.1 on the first optical fiber 4 is suspended inside the elastic body 2. The two ends of the second optical fiber 5 are a first end and a second end respectively. The second end is connected to the base 3, and the first end is suspended in the elastic body 2. A temperature measuring element 3.2 is arranged on the first end.

[0027] The optical fiber force sensor in this embodiment decouples the external force value through the first optical fiber 4 provided with the optical fiber grating 3.1, and performs temperature compensation through the temperature measuring element 3.2, thereby reducing the influence of temperature change on the measurement result, improving the measurement accuracy, and reducing the measurement error. The temperature measuring element 3.2 is connected to the optical sensor through the second optical fiber 5, and the stability and robustness are greatly improved. The second optical fiber 5 provided with the temperature measuring element 3.2 is directly connected to the elastic body 2 that fixes the first optical fiber 4, and is fixed on the base 3 together with the first optical fiber 4, without the need to increase the length of the sensor, and without other complex parts and structures, it is easy to produce and assemble, with low cost, small size, and easy to promote and apply.

[0028] In other embodiments, the second end of the second optical fiber 5 may be connected to the top cover 1 , which can also ensure that the first end of the second optical fiber 5 is suspended in the elastic body 2 .

[0029] In one embodiment, the first optical fiber 4 and the second optical fiber 5 are arranged in parallel to avoid interference between the two and simplify the calculation of the external force value.

[0030] In one embodiment, the temperature measuring element 3.2 is one of gallium arsenide crystal, silicon boride crystal, platinum crystal or fluorescent temperature measuring element 3.2. Among them, gallium arsenide crystal has the advantages of fast response speed, high stability, high sensitivity, good linear characteristics, stable chemical properties, etc., and is suitable for a variety of usage scenarios.

[0031] The FBG sensor is a one-dimensional force sensor that needs to be palpated perpendicular to the tissue surface, which is difficult to control in practical applications, resulting in low measurement accuracy.

[0032] In one embodiment, the first optical fiber 4 is arranged along the axis of the elastomer 2, and the surface of the elastomer 2 is provided with a plurality of hollow structures arranged in an staggered manner along its circumference. The plurality of hollow structures arranged in an staggered manner reduce the conduction effect of the lateral force, and the lateral force applied from the outside will be dispersed to each groove on the surface of the elastomer 2. This dispersion effect prevents the lateral force from being overly concentrated on a small part of the elastomer 2, but is evenly distributed on the entire surface, thereby improving the sensor's resistance to lateral force and effectively reducing the impact of the lateral force on the sensor.

[0033] Specifically, the cross-sectional shape of the hollow structure is an inclined parallelogram, and the inclination directions of the multiple hollow structures are not exactly the same, so the lateral force applied by the outside can be evenly distributed to the four sides without being overly concentrated in a small part, thereby improving the stability and reliability of the sensor. Furthermore, the inclination directions of the hollow structures at different positions along the axial direction of the elastic body 2 are different, which greatly reduces the influence of the lateral force on the sensor, and has strong robustness and anti-interference capabilities.

[0034] like Figure 2-3As shown, the length of the hollow elastic body is L and the diameter is d. The staggered structure used to resist lateral forces is shown in Figure 3 As shown, the length, width and angle of the inclined parallelogram are a, b and c respectively. The values ​​of the above dimensions L, d, a, b and c can be designed according to the size of the instrument to which the sensor is connected and the accuracy and sensitivity of the force to be measured. At the same time, the material of the elastomer can also be selected according to the actual application scenario.

[0035] In one embodiment, the material of the elastomer can be stainless steel, such as 304 stainless steel, which has good biocompatibility. The material of the elastomer can also be epoxy resin, such as using medical epoxy resin glue (EP42HT-2Med) for 3D printing to reduce production costs.

[0036] In one embodiment, the connection between the base, the top cover, the elastic body and the first optical fiber, and the connection between the base and the second optical fiber can be fixed by bonding with medical-grade glue, and the medical glue can specifically be medical instant glue, medical epoxy resin glue or medical UV glue, etc. In other embodiments, welding, mechanical clamping and other methods can also be used to fix the connection.

[0037] In one embodiment, a sensor decoupling method is provided, based on the optical fiber force sensor in the above embodiment, and the method comprises:

[0038] Obtaining the central wavelength offset of the fiber Bragg grating;

[0039] The change of ambient temperature is obtained by using the temperature measuring element;

[0040] Constructing a first relational expression between the central wavelength offset of the fiber Bragg grating and the external force value and the ambient temperature change;

[0041] Substitute the center wavelength offset and the ambient temperature change into the first equation to obtain the external force value.

[0042] The first relationship between the center wavelength offset of the fiber Bragg grating and the external force value and the ambient temperature change is constructed, and further includes:

[0043] Calibrate the force sensitivity coefficient and temperature sensitivity coefficient of the fiber Bragg grating. F and K T are the force sensitivity coefficient and temperature sensitivity coefficient of FBG, which can be obtained during the calibration process. Equation (1) is the first relational formula for constructing the central wavelength offset of the fiber Bragg grating with the external force value and the ambient temperature change.

[0044] Specifically, according to the sensing principle of FBG, under the simultaneous action of temperature and force, the optical fiber will produce strain and temperature changes accordingly. At this time, the central wavelength of FBG will drift as follows:

[0045]

[0046] Where Δλ is the Bragg center wavelength offset, λ is the Bragg center wavelength, and ρ e is the effective photoelastic coefficient of the sensing fiber, Δε is the strain of the FBG under the axial force, and α f is the thermal expansion coefficient of the sensing fiber, ξ f is the thermo-optical coefficient of the sensing fiber, and ΔT is the change in ambient temperature of the object being measured.

[0047] Equation (1) can be simplified to:

[0048] Δλ=K F F+K T ΔT (2)

[0049] Among them, K F and K T are the force sensitivity coefficient and temperature sensitivity coefficient of FBG, which can be obtained during the calibration process. Equation (1) is the first relational formula for constructing the central wavelength offset of the fiber Bragg grating with the external force value and the ambient temperature change.

[0050] In one embodiment, the temperature measuring element is a gallium arsenide crystal, and obtaining the ambient temperature change using the temperature measuring element specifically includes:

[0051] Obtain the wavelength of intrinsic absorption of GaAs crystal;

[0052] Construct a second relationship between the intrinsic absorption wavelength of the gallium arsenide crystal and the real-time temperature;

[0053] Substitute the wavelength of intrinsic absorption of the gallium arsenide crystal into the second equation to obtain the real-time temperature;

[0054] The change in ambient temperature is obtained based on the real-time temperature at different times.

[0055] Specifically, the bandgap width E of GaAs material is g Determines the absorption edge wavelength λ g The smaller the bandgap width, the larger the absorption edge wavelength. Let E g (T) is a function of temperature. When the temperature increases, E g (T) decreases monotonically, and its relationship with temperature in the range of -253.15℃~699.85℃(20K-973K) is as follows:

[0056]

[0057] Where E g (0) = 1.522 eV, which is the bandgap width E when the ambient temperature is 0 K genergy; γ and β are two constants, which are the inherent properties of GaAs materials. γ=5.8×10-4eV / K,β=300K. The wavelength λ of intrinsic absorption of GaAs crystal g The relationship between (T) and temperature T can be written as:

[0058]

[0059] Where h is Planck's constant and c is the speed of light. The real-time temperature T can be measured by wavelength drift, and the force value at the decoupling temperature can be obtained by substituting the temperature change ΔT into formula (2).

[0060] The sensor decoupling method in the above embodiment mainly measures the temperature change through the gallium arsenide crystal, and calculates the contact force and temperature change information after decoupling. The optical fiber force sensor used has a simple structure, is easy to assemble, and is convenient to integrate. It can resist lateral forces in all directions, overcomes the requirement that it must be perpendicular to the tissue surface during palpation, and improves the feasibility of sensor application. It can also effectively overcome the interference caused by temperature changes and improve the measurement accuracy during palpation.

[0061] The optical fiber force sensor and decoupling method in the present invention can be used not only for force sensing in minimally invasive surgical palpation, but also for force sensing in interventional catheter surgery and other scenarios.

[0062] In the description of this specification, if the terms "embodiment one", "this embodiment", "in an embodiment" and the like appear, it means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in the invention or at least one embodiment or example of the invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example; moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in an appropriate manner.

[0063] In the description of this specification, the terms "connect", "install", "fix", "set", "have", etc. are all understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0064] In the description of this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0065] The above description of the embodiments is to facilitate ordinary technicians in the technical field to understand and apply the technology of this case. People familiar with the technology in this field can obviously easily make various modifications to these examples and apply the general principles described here to other embodiments without creative work. Therefore, this case is not limited to the above embodiments. Modifications to the following situations should all be within the scope of protection of this case: ① A new technical solution implemented based on the technical solution of the present invention and combined with existing common knowledge, the technical effect produced by the new technical solution does not exceed the technical effect of the present invention; ② The equivalent replacement of some features of the technical solution of the present invention by using known technology, the technical effect produced is the same as the technical effect of the present invention; ③ The technical solution of the present invention can be expanded, and the substantive content of the expanded technical solution does not exceed the technical solution of the present invention; ④ The equivalent transformation made by using the contents of the description and drawings of the present invention is directly or indirectly applied to other related technical fields.

Claims

1. An optical fiber force sensor, characterized in that: It includes a base, a top cover and a hollow tubular elastic body, the two ends of the elastic body are respectively connected to the base and the top cover, and the elastic body is provided with: A first optical fiber, on which an optical fiber Bragg grating is engraved, and two ends of the first optical fiber are respectively connected to the base and the top cover; A second optical fiber has a temperature measuring element disposed at a first end thereof, and a second end of the second optical fiber is connected to the base / top cover.

2. The optical fiber force sensor according to claim 1, characterized in that: The temperature measuring element is one of a gallium arsenide crystal, a silicon boride crystal, a platinum crystal or a fluorescent temperature measuring element.

3. The optical fiber force sensor according to claim 1, characterized in that: The first optical fiber is arranged along the axis of the elastic body, and a plurality of staggered hollow structures are arranged on the surface of the elastic body along its circumference.

4. The optical fiber force sensor according to claim 3, characterized in that: The cross-sectional shape of the hollow structure is an inclined parallelogram, and the inclination directions of the plurality of hollow structures are not completely the same.

5. The optical fiber force sensor according to claim 4, characterized in that: The inclination directions of the hollow structures at different positions along the axial direction of the elastic body are different.

6. The optical fiber force sensor according to any one of claims 1 to 5, characterized in that: The elastic body is made of stainless steel or epoxy resin.

7. The optical fiber force sensor according to any one of claims 1 to 5, characterized in that: The base / top cover is respectively bonded / welded and fixed to the elastomer, the first optical fiber and the second optical fiber.

8. A sensor decoupling method, based on the optical fiber force sensor according to any one of claims 1 to 7, characterized in that: The method comprises: Obtaining the central wavelength offset of the fiber Bragg grating; The change of ambient temperature is obtained by using the temperature measuring element; Constructing a first relational expression between the central wavelength offset of the fiber Bragg grating and the external force value and the ambient temperature change; Substitute the center wavelength offset and the ambient temperature change into the first relationship to obtain the external force value.

9. The sensor decoupling method according to claim 8, characterized in that: The temperature measuring element is a gallium arsenide crystal, and obtaining the ambient temperature change by using the temperature measuring element specifically includes: Obtaining the wavelength of intrinsic absorption of the gallium arsenide crystal; Constructing a second relationship between the intrinsic absorption wavelength of the gallium arsenide crystal and the real-time temperature; Substituting the wavelength of intrinsic absorption of the gallium arsenide crystal into the second relationship to obtain the real-time temperature; The ambient temperature change is obtained according to the real-time temperature at different times.

10. The sensor decoupling method according to claim 8, characterized in that: The first relationship between the central wavelength offset of the fiber grating and the external force value and the ambient temperature change is constructed, and further includes: The force sensitivity coefficient and temperature sensitivity coefficient of the fiber Bragg grating are calibrated.

Images