Mechanical retention optical fiber Fabry-Perot liquid level sensor capable of calibrating cavity length and method

Abstract

The invention discloses a mechanical retention optical fiber Fabry-Perot liquid level sensor capable of calibrating the cavity length and a method. The sensor comprises a base, an inner conical surface fixing nut, a ceramic ferrule, an adjusting rod, a viscoelastic damping block, a high-reflectivity sensitive diaphragm, a diaphragm fixing screw, a diaphragm fixing block and an F-P cavity. The adjusting rod and the ceramic ferrule are tightly connected through interference fit. A conical surface self-locking jacket is arranged in the base and is matched with an inner conical surface fixing nut to form an axial adjusting and fixing assembly, and accurate mechanical fixing and radial fixing of the ceramic ferrule at any axial position are achieved. Meanwhile, a square notch is reserved in the other end of the base and used for installing the high-reflectivity sensitive diaphragm assembly. According to the sensor structure, the ceramic ferrule and the base can be coaxial, mechanical retention is stabilized, the parallelism of the end face of the ceramic ferrule and the sensitive diaphragm is guaranteed, and the multi-application-scene adaptability of the sensor is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensor technology, specifically relating to a calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor and method. Background Technology

[0002] Fiber optic FP sensors are widely used in chemical, petroleum, and aerospace fields due to their characteristics such as corrosion resistance, small size, high sensitivity, high precision, and resistance to electromagnetic interference.

[0003] Currently, fiber optic sensors are developing towards lower cost, harsher environments, and miniaturization. However, most common fiber optic sensors are fabricated using methods such as MEMS and femtosecond lasers, which not only have high processing requirements and costs but also poor parameter adjustability. Limited by the precision of processing and core-aligning equipment, traditional diaphragm-type fiber optic FP level sensors typically use a precision displacement platform to adjust the cavity length and fix the fiber end and the sensitive diaphragm using an adhesive curing process. This results in poor cavity length consistency and susceptibility to external forces, leading to cavity length drift or sensor damage, which seriously affects sensor use, subsequent information demodulation, and data calibration.

[0004] Therefore, designing a calibrable cavity length mechanical fixation structure is expected to improve the sensor manufacturing requirements and cavity length calibration, enhance the consistency reliability of multiple sensors, and broaden their application scenarios. Summary of the Invention

[0005] To achieve the above objectives, this invention aims to design a calibrable, mechanically fixed fiber optic Fabry-Perot level sensor and method. The ceramic ferrule and adjusting rod are encased in a conical self-locking sleeve, achieving mechanical fixation of the ceramic ferrule's axial and radial positions. This design effectively avoids problems such as fiber misalignment caused by adhesive fixation.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution: A calibrable cavity-length mechanically fixed fiber optic Fabry-Perot level sensor includes: The base has a tapered self-locking sleeve at end a and a ceramic ferrule through hole, FP cavity hole and square slot at end b along the axial direction. The inner conical surface fixing nut is connected to end a of the base by threads, and its inner conical surface mates with the conical surface of the conical self-locking sleeve; The adjusting rod has a ceramic insert coaxially connected at the lower end and an extension rod at the upper end for connecting to an external displacement platform. The conical self-locking sleeve is composed of multiple conical support blocks evenly distributed in the circumference, forming a two-stage radial positioning for the ceramic ferrule. The first-stage radial positioning is achieved by the through hole of the ceramic ferrule, and the second-stage radial positioning is achieved by the deformation and wrapping of the conical self-locking sleeve. The bottom end of the adjusting rod is provided with a positioning protrusion arranged radially. The positioning protrusion is used to insert into the gap between the multiple conical support blocks to restrict the rotation of the ceramic insert. The viscoelastic damping block, placed in the central hole of the conical self-locking jacket, can axially wrap the ceramic ferrule, providing vibration buffering and space for fine adjustment of the FP cavity length; A high-reflectivity sensitive diaphragm is installed inside a square slot; A membrane fixing block is positioned above the high-reflectivity sensitive membrane; The diaphragm fixing screw is connected to end b of the base via threads, and compresses the diaphragm fixing block; The conical self-locking sleeve is deformed inward by the inner conical fixing nut, wrapping and fixing the adjusting rod and the ceramic insert; the end face of the ceramic insert and the high reflectivity sensitive diaphragm form an intrinsic FP cavity in the FP cavity hole.

[0007] Beneficial effects: The calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor proposed in this invention has the following technical advantages: First, this invention utilizes a type of expansion screw structure, employing the radial deformation fit between the inner conical fixing nut and the conical self-locking sleeve, to effectively fix the axial position of the ceramic ferrule, thus achieving effective fixation of the fiber optic ceramic ferrule. Compared to traditional adhesive curing methods, this design improves the stability and accuracy of fiber optic ceramic ferrule fixation, reduces operational difficulty, and enhances the consistency of multi-sensor fabrication and calibration.

[0008] Secondly, the through hole of the ceramic ferrule forms a first-level radial positioning for the ceramic ferrule, and the tapered self-locking sleeve forms a second-level radial positioning for the ceramic ferrule, effectively preventing radial displacement of the ceramic ferrule.

[0009] Third, the bottom of the adjusting rod is provided with a positioning protrusion, which can effectively prevent the optical fiber from being damaged by large-scale rotation of the ceramic ferrule when the adjusting rod is inserted into the conical self-locking sleeve.

[0010] Fourth, the viscoelastic damping block is made of high-damping viscoelastic vibration reduction material, which can effectively reduce and isolate external mechanical vibration, improve the signal-to-noise ratio of the FP cavity interference signal, and ensure the stability of liquid level measurement under complex working conditions; moreover, the elastic deformation characteristics of the viscoelastic damping block can compensate for assembly tolerances and provide adjustment margins for the ceramic insert.

[0011] In one optional embodiment, the diaphragm fixing block has a first annular groove on its side for installing a second sealing ring, and the square groove has rounded corners and a chamfer at the top; the second sealing ring is pressed into the square groove through the chamfer and forms a radial seal with the inside of the groove.

[0012] Beneficial effects: The square groove has large rounded corners, avoiding high stress at right angles and low compression rate of the sealing ring.

[0013] In one optional embodiment, the bottom surface of the diaphragm fixing block is provided with a second annular groove for installing the first sealing ring; when the diaphragm fixing screw squeezes the diaphragm fixing block, the first sealing ring deforms and increases the contact area with the high reflectivity sensitive diaphragm, forming an axial seal.

[0014] In one optional embodiment, the diaphragm fixing block is a rounded square structure, and both the diaphragm fixing block and the diaphragm fixing screw have through holes at their centers. The diameter of the through holes is larger than that of the FP cavity hole to ensure that the pressure is transmitted to the sensitive diaphragm.

[0015] In one optional embodiment, the bottom end of the adjusting rod has a slot of the same shape as the middle section of the ceramic insert, so as to achieve an interference fit between the two.

[0016] In one optional embodiment, the base, inner conical fixing nut, adjusting rod, diaphragm fixing screw, and diaphragm fixing block are all made of stainless steel.

[0017] This invention further discloses a method for fine-tuning the FP cavity length of the calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor, comprising the following steps: (a) A base with a high-reflectivity sensitive film is fixed to an external clamp; (b) Connect the upper extension rod of the adjusting rod to the corresponding fixture of the three-axis precision displacement platform; (c) Drive the triaxial precision displacement platform to move the ceramic insert axially and adjust the initial cavity length between its end face and the high reflectivity sensitive diaphragm; (d) Monitor the FP cavity interference spectrum signal in real time using optical detection equipment, and stop the displacement when the spectral characteristics reach the target value; (e) Tighten the inner conical surface fixing nut to deform and lock the ceramic insert in place with the self-locking sleeve of the conical surface; (f) Based on the elastic deformation characteristics of the viscoelastic damping block, an axial fine-tuning external force is applied to the adjusting rod to compensate for assembly tolerances or environmental disturbances, thereby achieving sub-micron level calibration of the cavity length.

[0018] This invention further discloses a method for fabricating the calibrable cavity-length mechanically fixed fiber optic Fabry-Perot level sensor, comprising the following steps: S1. Base forming and finishing: The base is integrally formed by metal 3D printing and includes a conical self-locking sleeve, a ceramic ferrule through hole, an FP cavity hole and a square slot. The following parts are precision machined by CNC: the inner conical surface accuracy of the self-locking conical sleeve; the diameter tolerance of the ceramic ferrule through hole; the mating thread of the base a end with the inner conical surface fixing nut, and the mating thread of the base b end with the diaphragm fixing screw. S2. Enhanced sealing treatment: Apply thread-locking adhesive evenly to the threaded surfaces of the mating thread at end a of the base and the diaphragm fixing screw at end b of the base, and then assemble. S3. Assembly of key components: Press the viscoelastic damping block into the central hole of the conical self-locking jacket; The ceramic ferrule passes through the viscoelastic damping block and the through hole of the ceramic ferrule, and its rotational freedom is restricted by the positioning protrusion of the adjusting rod; Tighten the inner conical surface fixing nut to drive the inner conical surface to press against the conical surface self-locking sleeve, causing the sleeve to deform inward and wrap around the ceramic insert and adjusting rod.

[0019] In summary, the mechanically fixed fiber optic Fabry-Perot level sensor of the present invention has a simple structure and is easy to install. It is an effective means of achieving level measurement and avoids the positional displacement and fixed model differences of the traditional adhesive-fixed sensitive diaphragm under pressure. Attached Figure Description

[0020] Figure 1 This is a three-dimensional view of the overall structure of the universal effective cavity length adjustable fiber optic FP liquid level sensor of the present invention; Figure 2 This is a frontal view of the overall structure of the present invention. The components include: 1. Inner conical surface fixing nut; 2. Adjusting rod; 3. Ceramic insert; 4. Viscoelastic damping block; 5. Base; 6. High reflectivity sensitive diaphragm; 7. First sealing ring; 8. Diaphragm fixing block; 9. Second sealing ring; 10. Diaphragm fixing screw. Figure 3 This is a structural diagram of end a of the base; Among them, 13 is a conical self-locking sleeve; 15 is a ceramic ferrule through hole; and 18 is a conical surface. Figure 4 This is a schematic diagram of the structural fit of the parts at end a of the base; Among them, 11 is the extension rod; 12 is the positioning protrusion; Figure 5 This is a structural diagram of end b of the base; Among them, 14 is a chamfer; 19 is a square groove; Figure 6 This is a schematic diagram showing the fit between the first sealing ring, the second sealing ring, and the diaphragm fixing block. Wherein, 20 is the second annular groove; 21 is the first annular groove; Figure 7 This is a schematic diagram of the structural fit of the parts at end b of the base; Figure 8 This is a right-side view of the overall structure of the present invention. Figure 9 This is a disassembled view of the overall structure of the present invention from the left side. Detailed Implementation

[0021] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings to provide a clearer understanding of the purpose and features of the invention. The present invention is embodied through various embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0022] like Figure 1-2 As shown, the present invention discloses a calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor, the main body of which includes an inner conical fixing nut 1, an adjusting rod 2, a ceramic ferrule 3, a viscoelastic damping block 4, a base 5, a high reflectivity sensitive diaphragm 6, a first sealing ring 7, a diaphragm fixing block 8, a second sealing ring 9, and a diaphragm fixing screw 10; wherein the inner conical fixing nut 1, the adjusting rod 2, the ceramic ferrule 3, the diaphragm fixing block 8, and the diaphragm fixing screw 10 are all coaxial with the base 5.

[0023] like Figure 3 As shown, a conical self-locking sleeve 13 is provided on surface a of base 5, which is composed of circumferentially distributed conical support blocks with a cylindrical hole in the center and gaps between the support blocks. Trapezoidal threads are arranged on the inner circumference of surface a of base 5 to engage with the external threads of the insert fixing nut 1. Ends a and b of base 5 are connected by a ceramic insert through hole 15.

[0024] like Figure 4 As shown, the upper end of the adjusting rod 2 is provided with an extension rod 11 that matches the shape of the clamp, for connecting with an external precision displacement platform. The lower end has a slot of the same shape as the middle section of the ceramic ferrule 3, realizing an interference fit between the two. The bottom end is provided with a positioning protrusion 12. The ferrule fixing nut 1 has an external thread and its interior is a through hole structure, with a tapered surface at the bottom through hole. The viscoelastic damping block 4 is installed in the central cylindrical hole of the conical self-locking sleeve 13 inside the base 5. The ceramic ferrule 3 and the adjusting rod 2 are combined and installed in the central cylindrical hole of the conical self-locking sleeve 13, placed above the viscoelastic damping block 4. At this time, the positioning protrusion 12 is located in the adjacent gap of the conical self-locking sleeve 13, effectively avoiding fiber optic entanglement damage caused by large-scale rotation of the ceramic ferrule 3.

[0025] Finally, the ferrule fixing nut 1 is threaded to the base a end, and the inner conical surface 17 contacts the conical surface 18, causing the conical self-locking sleeve 13 to deform inward and wrap around the adjusting rod 2. At this time, the ceramic ferrule enters the FP cavity hole 16 through the ceramic ferrule through hole 15, realizing the coaxial mechanical fixation of the ceramic ferrule 3 and the base.

[0026] The ceramic ferrule through-hole 15 and the conical self-locking sleeve 13 provide two levels of radial position fixation for the ceramic ferrule. The viscoelastic damping block 4 forms an axial wrap around the ceramic ferrule 3, effectively protecting it and reducing the interference of external vibrations; moreover, the deformation characteristics of the viscoelastic damping block 4 provide a finer adjustment space for the FP cavity length, thus playing a limiting role.

[0027] like Figure 5 As shown, the base 5 has a square slot 19, an FP cavity 16, and a ceramic insert hole 15 on its b-side. The square slot 19 has large rounded corners to avoid high stress at right angles and low compression ratio of the sealing ring, and a chamfer 14 at the top. The base 5 has trapezoidal threads on its inner circumference that mate with the external threads of the diaphragm fixing screw 10.

[0028] like Figure 6 As shown, the diaphragm fixing block 8 has a first annular groove 21 on its side for installing the second sealing ring 9; the diaphragm fixing block 8 has a second annular groove 20 on its upper surface for installing the first sealing ring 7.

[0029] like Figure 7 As shown, the first sealing ring 7 and the second sealing ring 9 are installed onto the diaphragm fixing block 8 to form an integral sealed installation structure. Using a vacuum pen, the high-reflectivity sensitive diaphragm 6 is placed in the square slot 19 on the b-side of the base 5. The size of the FP cavity 16 is the actual working size of the high-reflectivity sensitive diaphragm 6. Then, the diaphragm fixing block 8 is placed above the high-reflectivity sensitive diaphragm 6. The diaphragm fixing screw 10 engages with the base 5 via a trapezoidal thread. Rotating the diaphragm fixing screw 10 causes axial movement, which in turn moves the diaphragm fixing block 8 to fix the high-reflectivity sensitive diaphragm 6.

[0030] The second sealing ring 9, after being chamfered by the chamfer 14, deforms under the compression of the diaphragm fixing screw 10 and enters the square slot 19. Simultaneously, the contact area between the first sealing ring 7 and the high-reflectivity sensitive diaphragm 6 gradually increases under compression, firmly fixing the high-reflectivity sensitive diaphragm 6 and effectively preventing damage to the diaphragm due to high shear stress. Both the diaphragm fixing block 8 and the diaphragm fixing screw 10 are circular through-hole structures with a diameter larger than the FP cavity 16, effectively transmitting external pressure to the high-reflectivity sensitive diaphragm 6.

[0031] like Figure 8-9 As shown, the present invention provides a calibrable cavity length mechanically fixed fiber optic Fabry-Perot liquid level sensor. Its overall component distribution and assembly structure are simple and easy to operate, enabling the effective functioning of the liquid level sensor and the effective axial fixation of the fiber optic ceramic ferrule.

[0032] The FP cavity length fine-tuning method for the calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor of the present invention includes the following steps: (a) A base with a high-reflectivity sensitive film is fixed to an external clamp; (b) Connect the upper extension rod of the adjusting rod to the corresponding fixture of the three-axis precision displacement platform; (c) Drive the triaxial precision displacement platform to move the ceramic insert axially and adjust the initial cavity length between its end face and the high reflectivity sensitive diaphragm; (d) Monitor the FP cavity interference spectrum signal in real time using optical detection equipment, and stop the displacement when the spectral characteristics reach the target value; (e) Tighten the inner conical surface fixing nut to deform and lock the ceramic insert in place with the self-locking sleeve of the conical surface; (f) Based on the elastic deformation characteristics of the viscoelastic damping block, an axial fine-tuning external force is applied to the adjusting rod to compensate for assembly tolerances or environmental disturbances, thereby achieving sub-micron level calibration of the cavity length.

[0033] The method for fabricating the calibrable cavity-length mechanically fixed fiber optic Fabry-Perot level sensor of the present invention includes the following steps: S1. Base forming and finishing: The base is integrally formed by metal 3D printing and includes a conical self-locking sleeve, a ceramic ferrule through hole, an FP cavity hole and a square slot. The following parts are precision machined by CNC: the inner conical surface accuracy of the self-locking conical sleeve; the diameter tolerance of the ceramic ferrule through hole; the mating thread of the base a end with the inner conical surface fixing nut, and the mating thread of the base b end with the diaphragm fixing screw. S2. Enhanced sealing treatment: Apply thread-locking adhesive evenly to the threaded surfaces of the mating thread at end a of the base and the diaphragm fixing screw at end b of the base, and then assemble. S3. Assembly of key components: Press the viscoelastic damping block into the central hole of the conical self-locking jacket; The ceramic ferrule passes through the viscoelastic damping block and the through hole of the ceramic ferrule, and its rotational freedom is restricted by the positioning protrusion of the adjusting rod; Tighten the inner conical surface fixing nut to drive the inner conical surface to press against the conical surface self-locking sleeve, causing the sleeve to deform inward and wrap around the ceramic insert and adjusting rod.

[0034] Therefore, the calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor of the present invention effectively achieves tight fixation of the fiber optic ceramic ferrule in any axial and radial position through a conical self-locking sleeve and a conical fixing nut, and introduces a viscoelastic damping block for protection, limiting, and vibration reduction. Effective sealing of the sensitive diaphragm end is achieved through a two-stage sealing ring.

[0035] Finally, it should be noted that the above embodiments are only used to describe the technical solutions of the present invention in detail, and are not intended to limit it. It should be understood that those skilled in the art can make many modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of the prior art should be within the scope of protection defined by the claims.

Claims

1. A calibrable cavity-length mechanically fixed fiber optic Fabry-Perot level sensor, characterized in that, include: The base has a tapered self-locking sleeve at end a and a ceramic ferrule through hole, FP cavity hole and square slot at end b along the axial direction. The inner conical surface fixing nut is connected to end a of the base by threads, and its inner conical surface mates with the conical surface of the conical self-locking sleeve; The adjusting rod has a ceramic insert coaxially connected at the lower end and an extension rod at the upper end for connecting to an external displacement platform. The conical self-locking sleeve is composed of multiple conical support blocks evenly distributed in the circumference, forming a two-stage radial positioning for the ceramic ferrule. The first-stage radial positioning is achieved by the through hole of the ceramic ferrule, and the second-stage radial positioning is achieved by the deformation and wrapping of the conical self-locking sleeve. The bottom end of the adjusting rod is provided with a positioning protrusion arranged radially. The positioning protrusion is used to insert into the gap between the multiple conical support blocks to restrict the rotation of the ceramic insert. The viscoelastic damping block, placed in the central hole of the conical self-locking jacket, can axially wrap the ceramic ferrule, providing vibration buffering and space for fine adjustment of the FP cavity length; A high-reflectivity sensitive diaphragm is installed inside a square slot; A membrane fixing block is positioned above the high-reflectivity sensitive membrane; The diaphragm fixing screw is connected to end b of the base via threads, and compresses the diaphragm fixing block; The conical self-locking sleeve is deformed inward by the inner conical fixing nut, wrapping and fixing the adjusting rod and the ceramic insert; the end face of the ceramic insert and the high reflectivity sensitive diaphragm form an intrinsic FP cavity in the FP cavity hole.

2. The calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor according to claim 1, characterized in that, The diaphragm fixing block has a first annular groove on its side for installing a second sealing ring. The square groove has rounded corners and a chamfer at the top. The second sealing ring is pressed into the square groove through the chamfer and forms a radial seal with the inside of the groove.

3. The calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor according to claim 1, characterized in that, The diaphragm fixing block has a second annular groove on its bottom surface for installing the first sealing ring; when the diaphragm fixing screw squeezes the diaphragm fixing block, the first sealing ring deforms and increases the contact area with the high reflectivity sensitive diaphragm, forming an axial seal.

4. The calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor according to claim 1, characterized in that, The diaphragm fixing block has a rounded square structure, and both it and the diaphragm fixing screw have through holes at their centers. The diameter of the through holes is larger than that of the FP cavity hole to ensure that the pressure is transmitted to the sensitive diaphragm.

5. The calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor according to claim 1, characterized in that, The bottom end of the adjusting rod has a slot of the same shape as the middle section of the ceramic insert, so as to achieve an interference fit between the two.

6. The calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor according to claim 1, characterized in that, The base, inner conical surface fixing nut, adjusting rod, diaphragm fixing screw, and diaphragm fixing block are all made of stainless steel.

7. The method for fine-tuning the cavity length of the FP cavity of the mechanically fixed fiber optic Fabry-Perot level sensor according to any one of claims 1 to 6, characterized in that, Includes the following steps: (a) A base with a high-reflectivity sensitive film is fixed to an external clamp; (b) Connect the upper extension rod of the adjusting rod to the corresponding fixture of the three-axis precision displacement platform; (c) Drive the triaxial precision displacement platform to move the ceramic insert axially and adjust the initial cavity length between its end face and the high reflectivity sensitive diaphragm; (d) Monitor the FP cavity interference spectrum signal in real time using optical detection equipment, and stop the displacement when the spectral characteristics reach the target value; (e) Tighten the inner conical surface fixing nut to deform and lock the ceramic insert in place with the self-locking sleeve of the conical surface; (f) Based on the elastic deformation characteristics of the viscoelastic damping block, an axial fine-tuning external force is applied to the adjusting rod to compensate for assembly tolerances or environmental disturbances, thereby achieving sub-micron level calibration of the cavity length.

8. The method for manufacturing a calibrable cavity length mechanically fixed fiber optic Fabry-Perot level sensor according to any one of claims 1 to 6, characterized in that, Includes the following steps, S1. Base forming and finishing: The base is integrally formed by metal 3D printing and includes a conical self-locking sleeve, a ceramic ferrule through hole, an FP cavity hole and a square slot. The following parts are precision machined by CNC: the inner conical surface accuracy of the self-locking conical sleeve; the diameter tolerance of the ceramic ferrule through hole; the mating thread of the base a end with the inner conical surface fixing nut, and the mating thread of the base b end with the diaphragm fixing screw. S2. Enhanced sealing treatment: Apply thread-locking adhesive evenly to the threaded surfaces of the mating thread at end a of the base and the diaphragm fixing screw at end b of the base, and then assemble. S3. Assembly of key components: Press the viscoelastic damping block into the central hole of the conical self-locking jacket; The ceramic ferrule passes through the viscoelastic damping block and the through hole of the ceramic ferrule, and its rotational freedom is restricted by the positioning protrusion of the adjusting rod; Tighten the inner conical surface fixing nut to drive the inner conical surface to press against the conical surface self-locking sleeve, causing the sleeve to deform inward and wrap around the ceramic insert and adjusting rod.

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