A compact structural glueless capacitive displacement sensor and method of assembly thereof

Abstract

The application discloses a compact structural glue-free capacitive displacement sensor and an assembling method thereof, and belongs to the technical field of precise geometric quantity measurement. The compact structural glue-free capacitive displacement sensor comprises a measuring electrode, three coaxial electric wires, an insulating film layer, a shell, a shell bottom cover and a protection ring. The shell is provided with the shell bottom cover at one end. The inner and outer surfaces of the protection ring are covered with the insulating film layer. The protection ring is arranged in the other end of the shell. The measuring electrode is arranged in the protection ring. The measuring electrode is connected with the three coaxial electric wires at one end. The other end of the three coaxial electric wires is sequentially arranged through the protection ring and the shell and is arranged out of the shell bottom cover. The interference fit is adopted between the shell and the protection ring and between the protection ring and the measuring electrode. The problem of the reduction of the measurement precision caused by the separation of the connection due to the long-term use of the adhesive in the prior art is solved. The practicability and the detection precision are improved.

Description

Technical Field

[0001] This invention relates to the field of precision geometric measurement technology, specifically to a compact, adhesive-free capacitive displacement sensor and its assembly method. Background Technology

[0002] Capacitive displacement sensors are widely used in lithography machines, precision machine tools, and aerospace. Traditional coaxial capacitive sensors typically employ a three-layer structure of "protective ring-insulating ring-measuring electrode." Current technologies mainly rely on adhesives such as epoxy resin to bond the ceramic insulating ring to the metal electrode. However, existing technologies have significant drawbacks. First, organic adhesives can creep under long-term stress or temperature changes, leading to micro- and nano-scale structural drift and compromising measurement accuracy. Second, adhesive assembly makes it difficult to ensure the coaxiality of the three cylinders, and uneven adhesive layer thickness can result in asymmetrical electric field distribution. Finally, the thickness of the solid ceramic ring is difficult to reduce to less than 0.5 mm, limiting the extreme miniaturization of the sensor.

[0003] Therefore, how to provide a compact, adhesive-free capacitive displacement sensor and its assembly method to solve the defects in the existing capacitive displacement sensor structure is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address this issue, the present invention provides a compact, adhesive-free capacitive displacement sensor and its assembly method, thereby solving the problem of reduced measurement accuracy caused by the long-term use of adhesives leading to connection separation in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the invention, This invention discloses a compact, structurally adhesive-free capacitive displacement sensor, comprising: The outer casing has a bottom cover installed at one end; A protective ring, with an insulating film layer covering its inner and outer surfaces, is installed inside the other end of the outer casing; A measuring electrode is installed in the protective ring. One end of the measuring electrode is connected to a three-coaxial wire, and the other end of the three-coaxial wire passes through the protective ring and the outer shell in sequence and exits from the bottom cover of the outer shell. The outer shell and the protective ring, and the protective ring and the measuring electrode, are fitted with an interference fit.

[0006] In one possible implementation, the housing includes: The installation ring has a partition installed inside, and an annular pad is installed at one end of the partition. One end of the bottom cover of the outer shell abuts against the annular pad. The other end of the partition plate forms an installation space with the interior of the mounting ring, and the protective ring is interference-fitted into the installation space.

[0007] In one possible implementation, the protection ring includes: A connecting ring is connected to a circular sealing plate at one end. The connecting ring and the circular sealing plate form a bowl-shaped structure. An arc-shaped chamfer is opened on the outer wall of one end of the circular sealing plate. The outer and inner walls of the connecting ring are covered with the insulating film layer. A circular hole is formed in the circular sealing plate, and an inner chamfer is formed at the other end of the circular sealing plate, the inner chamfer being located on the outside of the circular hole.

[0008] In one possible implementation, the insulating film layer is made of diamond carbon and has a thickness of 2 μm-50 μm.

[0009] In one possible implementation, the measuring electrode includes: The electrode body has a mounting hole on one end surface. The outer wall of the electrode body is press-fitted with the inner wall of the connecting ring. One end of the three coaxial wires is welded into the mounting hole. An outer chamfer is formed on the outer surface of one end of the electrode body. The mounting hole and the outer chamfer are located on the same side, and the outer chamfer is located outside the mounting hole.

[0010] In one possible implementation, the bottom cover of the housing has a perforation at its center, through which the other end of the three coaxial wires passes.

[0011] According to a second aspect of the invention, This invention discloses a method for assembling a compact, adhesive-free capacitive displacement sensor, which utilizes the aforementioned compact, adhesive-free capacitive displacement sensor and includes the following steps: S1: The insulating thin film layer is grown in situ on the inner and outer surfaces of the protective ring using physical or chemical vapor deposition processes; S2: Weld the core wire ends of the three coaxial wires to one end of the measuring electrode; S3: Using a cold-fitting process, the measuring electrode is interference-fitted into the protective ring, and the inner shielding layer of the three coaxial wires is welded to the metal welding area at the axial wire hole of the protective ring. S4: Using a heat-fitting process, the protective ring is interference-fitted into one end of the housing, and the three coaxial wires are passed through the housing; S5: Pass one end of the three coaxial wires through the bottom cover of the housing, and then fix the bottom cover of the housing to the other end of the housing.

[0012] In one possible implementation, the cold-loading process in S3 specifically includes the following steps: S301: Place the measuring electrode with the welded core wire in a cryogenic environment to cause it to shrink; S302: Quickly insert the shrunken measuring electrode into the protective ring, which is at room temperature and has been coated with an insulating film layer; S303: Pass the three coaxial wires through the protective ring; S304: After the measuring electrode recovers and expands, it forms a first-stage interference fit with the protection ring.

[0013] In one possible implementation, the hot-fitting process in S4 specifically includes the following steps: S401: Heat the outer shell to a set temperature to cause it to expand; S402: Push the assembled protective ring into the outer casing; S403: After the outer shell cools and shrinks, it forms a second-level interference fit with the protective ring.

[0014] This invention utilizes cold and hot fitting processes to achieve an interference fit between the measuring electrode, protective ring, and outer shell. This ensures connection strength while significantly improving the rigidity of the structural sensor. Furthermore, this cold and hot fitting interference fit prevents drift under long-term temperature and stress, significantly extending the service life. Adding an insulating film layer to the protective ring achieves the insulation effect previously only achievable with a thicker ceramic ring, enabling the fabrication of ultra-micro probes smaller than 3mm. Moreover, the use of vapor deposition allows the insulating film layer to grow in situ from the protective ring, facilitating the formation of micron-level insulation layers and enabling the fabrication of sensors with higher detection precision. Attached Figure Description

[0015] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0016] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0017] Figure 1 A three-dimensional view of the compact, adhesive-free capacitive displacement sensor provided by the present invention; Figure 2 A perspective view of the outer casing provided for this invention; Figure 3 A perspective view of the ring, partition, and installation space provided by the present invention; Figure 4 A perspective view of the protective ring provided by the present invention; Figure 5 A perspective view of the connecting ring, circular hole, and inner chamfer provided by the present invention; Figure 6 A three-dimensional view of the measuring electrode provided by the present invention; Figure 7 A perspective view of the bottom cover of the outer casing provided for this invention; Figure 8 A flowchart illustrating the assembly method for a compact, glue-free capacitive displacement sensor provided by this invention. Figure 9 The S3 cold packing process flow diagram provided by this invention; Figure 10 The S4 hot-charging process flow diagram provided by the present invention; In the diagram: 1 Measuring electrode; 11 Outer chamfer; 12 Electrode body; 13 Mounting hole; 2 Triaxial wire; 3 Insulating film layer; 4 Housing; 41 Mounting ring; 42 Partition plate; 43 Annular pad; 44 Mounting space; 5 Housing bottom cover; 51 Perforation; 6 Protective ring; 61 Arc chamfer; 62 Circular sealing plate; 63 Connecting ring; 64 Circular hole; 65 Inner chamfer. Detailed Implementation

[0018] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please refer to Figures 1-6 The present invention will now describe a compact, adhesive-free capacitive displacement sensor, as disclosed in this invention. Figure 1The sensor comprises a measuring electrode 1, a triaxial cable 2, an insulating film layer 3, a housing 4, a bottom cover 5, and a protective ring 6. The bottom cover 5 is mounted on one end of the housing 4. The inner and outer surfaces of the protective ring 6 are covered with the insulating film layer 3, and the protective ring 6 is installed inside the other end of the housing 4. The measuring electrode 1 is installed within the protective ring 6, and one end of the measuring electrode 1 is connected to the triaxial cable 2. The other end of the triaxial cable 2 passes sequentially through the protective ring 6 and the housing 4, and exits from the bottom cover 5. An interference fit is used between the housing 4 and the protective ring 6, and between the protective ring 6 and the measuring electrode 1. The bottom cover 5 can be screwed or welded to the housing 4. The interference fit between the housing 4 and the protective ring 6 is 5-10 μm, while the interference fit between the protective ring 6 and the measuring electrode 1 is 3-6 μm. This interference fit enables the sensor to generate an axial holding force of 500 N. The protective ring 6 is made of titanium alloy.

[0020] In a specific embodiment, such as Figures 2-3 The outer casing 4 includes a mounting ring 41, a partition 42, an annular pad 43, and a mounting space 44. The partition 42 is installed inside the mounting ring 41, and the annular pad 43 is installed at one end of the partition 42. One end of the outer casing bottom cover 5 rests against the annular pad 43. The other end of the partition 42 and the interior of the mounting ring 41 form the mounting space 44. A protective ring 6 is interference-fitted into the mounting space 44. The partition 42 separates the protective ring 6 from the outer casing bottom cover 5 and can block the electric field signal generated by the measuring electrode 1. The mounting space 44 is used to place the protective ring 6, and the inner wall of the mounting ring 41 is interference-fitted with the outer wall of the protective ring 6.

[0021] In a specific embodiment, such as Figures 4-5 The protective ring 6 includes an arc-shaped chamfer 61, a circular sealing plate 62, a connecting ring 63, a circular hole 64, and an inner chamfer 65. One end of the connecting ring 63 is connected to the circular sealing plate 62, forming a bowl-shaped structure. An arc-shaped chamfer 61 is formed on the outer wall of one end of the circular sealing plate 62. An insulating film layer 3 covers both the outer and inner walls of the connecting ring 63. The circular hole 64 is located on the circular sealing plate 62, and an inner chamfer 65 is formed at the other end of the circular sealing plate 62, located outside the circular hole 64. The arc-shaped chamfer 61 guides the installation of the protective ring 6 and protects the insulating film layer 3 from damage. The circular hole 64 allows the triaxial wire 2 to pass through and is used for welding to the triaxial wire 2, fixing it in place. The surface roughness of the connecting ring 63 is Ra≤0.1μm, reducing wear on the insulating film layer 3 during assembly and facilitating in-situ growth of the insulating film layer 3.

[0022] In one specific embodiment, the insulating film layer 3 is made of diamond carbon, and its thickness is 2μm-50μm. The insulating film layer 3 can also be made of materials such as alumina or aluminum nitride, with a Vickers hardness greater than 2500HV and an insulation resistance greater than 10 Ω·cm.12 Ω, and this method of using vapor deposition to create the insulating thin film layer 3 allows for insulation without the need for thicker walls like ceramic structures, making it easier to manufacture ultra-miniature probes with a diameter of less than 3mm.

[0023] In a specific embodiment, such as Figure 6 The measuring electrode 1 includes an outer chamfer 11, an electrode body 12, and a mounting hole 13. The mounting hole 13 is formed on one end surface of the electrode body 12. The outer wall of the electrode body 12 is press-fitted with the inner wall of the connecting ring 63. One end of the triaxial wire 2 is soldered into the mounting hole 13. The outer chamfer 11 is formed on the outer surface of one end of the electrode body 12. The mounting hole 13 and the outer chamfer 11 are located on the same side, with the outer chamfer 11 positioned outside the mounting hole 13. The outer chamfer 11 is used to guide the installation of the measuring electrode 1.

[0024] In a specific embodiment, such as Figure 7 The bottom cover 5 of the outer casing has a through hole 51 in the center, through which the other end of the triaxial cable 2 passes. The through hole 51 is used to fix the triaxial cable 2.

[0025] In use, this invention employs physical or chemical vapor deposition to grow an insulating thin film layer 3 in situ on the outer and inner walls of the connecting ring 63 of the fabricated protective ring 6. Then, utilizing the thermal expansion and contraction of metals, the measuring electrode 1, connected to the triaxial wire 2, is immersed in a cryogenic environment, typically -196°C liquid nitrogen. This causes the measuring electrode 1 to contract upon cooling. After contraction, the measuring electrode 1 is removed from the liquid nitrogen and quickly inserted into the bowl-shaped structure. When the measuring electrode 1 is at room temperature, its temperature rises rapidly, causing it to expand due to heat. The measuring electrode 1, during its fabrication... When the outer diameter is slightly larger than the inner diameter of the connecting ring 63, the measuring electrode 1 will be interference-fitted into the connecting ring 63 after expansion and will be limited in the connecting ring 63. After the measuring electrode 1 is connected, the outer shell 4 is heated to 250°C, and then the protective ring 6 is quickly pushed into the outer shell 4. The heating is stopped, and the outer shell 4 is allowed to cool to room temperature. As it cools, it contracts and locks the protective ring 6, thus completing the limitation. During assembly, the fixed triaxial wire 2 is passed through the protective ring 6 and the outer shell 4 in sequence, and when the bottom cover 5 of the outer shell is installed, the triaxial wire 2 is allowed to extend out from the through hole 51. After assembly, connect the other end of the three coaxial wires 2 to the power supply. During testing, position the measuring electrode 1 directly in front of the liquid container. Then, detect the liquid level through the electric field generated by the measuring electrode 1. The measuring electrode 1, the outer shell 4, and the protective ring 6 are connected by interference fit. Compared with bonding, this connection method is less likely to delaminate when heated, thus preventing drift problems. Moreover, it makes the sensor as a whole like a solid metal rod with an extremely high natural frequency and excellent vibration resistance.

[0026] Based on the same inventive concept, such as Figure 8 The present invention also discloses a method for assembling a compact, adhesive-free capacitive displacement sensor, comprising a compact, adhesive-free capacitive displacement sensor, and further comprising the following steps: S1: An insulating thin film layer 3 is grown in situ on the inner and outer surfaces of the protective ring 6 using physical or chemical vapor deposition processes; S2: Solder the end of the core wire of the triaxial wire 2 to one end of the measuring electrode 1; S3: Using a cold-fitting process, the measuring electrode 1 is interference-fitted into the protective ring 6, and the inner shielding layer of the triaxial wire 2 is welded to the metal welding area at the axial wire hole of the protective ring 6. S4: Using a heat-fitting process, the protective ring 6 is interference-fitted into one end of the outer casing 4, and the three coaxial wires 2 are passed out from the outer casing 4; S5: Pass one end of the three coaxial wires 2 through the bottom cover 5 of the outer casing, and then fix the bottom cover 5 to the other end of the outer casing 4.

[0027] In a specific embodiment, such as Figure 9 The cold-loading process in S3 specifically includes the following steps: S301: Place the measuring electrode 1 with the soldered core wire in a cryogenic environment to cause it to shrink; S302: Quickly insert the shrunken measuring electrode 1 into the protective ring 6, which is at room temperature and has been coated with an insulating thin film layer 3; S303: Pass the triaxial cable 2 through the protective ring 6; S304: After the measuring electrode 1 expands due to temperature recovery, it forms a first-stage interference fit with the guard ring 6.

[0028] In a specific embodiment, such as Figure 10 The hot-charging process in S4 specifically includes the following steps: S401: Heat the outer casing 4 to a set temperature to cause it to expand; S402: Push the assembled protective ring 6 into the outer casing 4; S403: After the outer casing 4 cools and shrinks, it forms a second-stage interference fit with the protective ring 6.

[0029] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A compact, structurally adhesive-free capacitive displacement sensor, characterized in that, include: The outer casing (4) has a bottom cover (5) installed at one end. The protective ring (6) has an insulating film layer (3) covering its inner and outer surfaces, and the protective ring (6) is installed inside the other end of the outer shell (4); Measuring electrode (1) is installed in the protective ring (6). One end of the measuring electrode (1) is connected to a three-coaxial wire (2). The other end of the three-coaxial wire (2) passes through the protective ring (6) and the outer shell (4) in sequence and exits from the bottom cover (5) of the outer shell. The outer shell (4) and the protective ring (6) are fitted with an interference fit, and the protective ring (6) and the measuring electrode (1) are fitted with an interference fit.

2. The compact, adhesive-free capacitive displacement sensor as described in claim 1, characterized in that, The outer casing (4) includes: The mounting ring (41) has a partition (42) installed inside. One end of the partition (42) is fitted with an annular pad (43), and one end of the bottom cover (5) of the outer shell abuts against the annular pad (43). The other end of the partition (42) and the interior of the mounting ring (41) form an installation space (44), and the protective ring (6) is interference-fitted into the installation space (44).

3. The compact, adhesive-free capacitive displacement sensor as described in claim 1, characterized in that, The protective ring (6) includes: A connecting ring (63) is connected to a circular sealing plate (62) at one end. The connecting ring (63) and the circular sealing plate (62) form a bowl-shaped structure. An arc-shaped chamfer (61) is opened on the outer wall of one end of the circular sealing plate (62). The outer and inner walls of the connecting ring (63) are covered with the insulating film layer (3). A circular hole (64) is formed on the circular sealing plate (62), and an inner chamfer (65) is formed at the other end of the circular sealing plate (62). The inner chamfer (65) is located outside the circular hole (64).

4. The compact, adhesive-free capacitive displacement sensor as described in claim 1, characterized in that, The insulating film layer (3) is made of diamond carbon and has a thickness of 2μm-50μm.

5. The compact, adhesive-free capacitive displacement sensor as described in claim 3, characterized in that, The measuring electrode (1) includes: The electrode body (12) has a mounting hole (13) on one end surface. The outer wall of the electrode body (12) is press-fitted with the inner wall of the connecting ring (63). One end of the three coaxial wires (2) is welded in the mounting hole (13). An outer chamfer (11) is formed on the outer surface of one end of the electrode body (12). The mounting hole (13) and the outer chamfer (11) are located on the same side, and the outer chamfer (11) is located outside the mounting hole (13).

6. The compact, adhesive-free capacitive displacement sensor as described in claim 1, characterized in that, The bottom cover (5) of the outer casing has a perforation (51) in the center, and the other end of the triaxial wire (2) passes through the perforation (51).

7. A method for assembling a compact, adhesive-free capacitive displacement sensor, comprising the compact, adhesive-free capacitive displacement sensor as described in claim 1, characterized in that, Includes the following steps: S1: The insulating thin film layer (3) is grown in situ on the inner and outer surfaces of the protective ring (6) using physical or chemical vapor deposition process. S2: Weld the core wire end of the three coaxial wire (2) to one end of the measuring electrode (1); S3: Using a cold-fitting process, the measuring electrode (1) is interference-fitted into the protective ring (6), and the inner shielding layer of the triaxial wire (2) is welded to the metal welding area at the axial wire hole of the protective ring (6); S4: Using a heat-fitting process, the protective ring (6) is press-fitted into one end of the outer shell (4), and the triaxial wire (2) is passed out from the outer shell (4); S5: Pass one end of the three coaxial wires (2) through the bottom cover of the outer casing (5), and then fix the bottom cover of the outer casing (5) in the other end of the outer casing (4).

8. The assembly method for the compact, adhesive-free capacitive displacement sensor as described in claim 7, characterized in that, The cold-loading process in S3 specifically includes the following steps: S301: Place the measuring electrode (1) with the welded core wire in a cryogenic environment to shrink it; S302: Quickly insert the shrunken measuring electrode (1) into the protective ring (6) which is at room temperature and has been coated with an insulating thin film layer (3); S303: Pass the three coaxial wires (2) through the protective ring (6); S304: After the measuring electrode (1) has recovered and expanded, it forms a first-stage interference fit with the protective ring (6).

9. The assembly method for the compact, adhesive-free capacitive displacement sensor as described in claim 7, characterized in that, The hot-fitting process in S4 specifically includes the following steps: S401: Heat the outer shell (4) to a set temperature to cause it to expand; S402: Push the assembled protective ring (6) into the outer shell (4); S403: After the outer shell (4) cools and shrinks, it forms a second-level interference fit with the protective ring (6).

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