Compact LVDT with multi-layer structure

Abstract

This invention discloses a compact LVDT with a multi-layer structure, relating to the field of sensor technology. The LVDT includes a magnetic core, a frame, a primary coil, a secondary coil, a first insulating layer, a compensation layer, and a second insulating layer. A through-hole is axially formed at the center of the frame, and the magnetic core is movably disposed within the through-hole. The primary coil is wound around the outer surface of the frame. The first insulating layer is disposed outside the primary coil. The compensation layer is disposed outside the first insulating layer, and the second insulating layer is disposed outside the compensation layer; the compensation layer is made of a magnetically conductive material. The secondary coil is wound around the outer surface of the second insulating layer. This invention, by incorporating a tapered compensation layer made of magnetically conductive material, forms a magnetic field compensation structure between the primary and secondary coils, effectively improving the uniformity of the magnetic field distribution within the compact LVDT and enhancing the magnetic induction intensity in the central region. This improves the linearity and sensitivity of the sensor while maintaining the miniaturization advantages of a compact structure.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, specifically relating to a multi-layered compact LVDT (Linear Variable Differential Transformer). Background Technology

[0002] A linear variable differential transformer (LVDT) is a sensor that achieves precise displacement measurement based on the principle of electromagnetic induction. Due to its outstanding advantages such as non-contact measurement, unlimited mechanical life, high resolution, and excellent repeatability, it has been widely used in industrial automation, aerospace, military equipment, hydraulic servo control, power generation, and structural health monitoring. In typical servo valve spool displacement control, the LVDT, as a core sensing element, can achieve micron-level displacement detection, providing crucial displacement feedback signals for the closed-loop control system and directly determining the system's response speed and control accuracy. In the aerospace field, LVDTs are used in critical components such as wing flap control and landing gear position monitoring; in the power industry, LVDTs are used in steam turbine valve control, often requiring tolerance to extreme environments such as high temperatures and radiation.

[0003] In existing technologies, traditional LVDTs typically consist of a primary coil and two secondary coils, with the secondary coils divided into two segments and wound on either side of the primary coil. This segmented winding design helps to achieve a more uniform magnetic field distribution, reduce leakage flux, and thus improve the linearity of the sensor. Simultaneously, the induced electromotive force change in each secondary coil is more pronounced, enhancing the sensor's sensitivity to displacement changes. Furthermore, improving the sensor's frame structure or adding a magnetic ring to the frame can also optimize the magnetic field distribution to some extent, further improving sensor performance. However, to meet the growing demand for miniaturization, compact LVDTs have gradually been adopted, where the secondary coils are wound directly above the primary coils, significantly reducing the sensor's axial dimensions and resulting in a simpler and lower-cost structure. However, this compact structure also introduces new technical challenges: the uneven magnetic field distribution after coil stacking affects the sensor's linearity and sensitivity. Traditional compensation methods for improving magnetic field uniformity, such as magnetic rings or frame structure improvements, are difficult to implement effectively in this multi-layered compact structure.

[0004] While existing technologies can achieve miniaturization or high static characteristics respectively, there are inherent limitations between the two. Traditional structures can achieve high linearity and sensitivity through segmented winding or magnetic ring compensation, but they are difficult to meet the miniaturization requirements with limited installation space. While compact LVDTs achieve miniaturization, their linearity and sensitivity are often inferior to traditional structures due to the non-uniform magnetic field caused by the coil stacking structure, making it impossible to simultaneously meet the application requirements of high precision and long stroke. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a compact LVDT with a multilayer structure. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a compact LVDT with a multilayer structure, comprising: a magnetic core, a frame, a primary coil, a secondary coil, a first insulating layer, a compensation layer, and a second insulating layer; wherein, The frame has a through hole along the axial direction at its center, and the magnetic core is movably disposed in the through hole; The primary coil is wound around the outer surface of the skeleton; the first insulating layer is disposed on the outside of the primary coil; The compensation layer is disposed on the outside of the first insulating layer; the second insulating layer is disposed on the outside of the compensation layer; the secondary coil is wound on the outer surface of the second insulating layer.

[0006] In one embodiment of the present invention, the outer wall of the skeleton is provided with a winding groove, and the primary coil is embedded in the winding groove.

[0007] In one embodiment of the present invention, the compensation layer is a cylindrical magnetically conductive interlayer sleeved on the outside of the insulating layer, and the compensation layer has a tapered cross section in the axial direction.

[0008] In one embodiment of the present invention, the compensation layer includes two symmetrically arranged compensation half-layers, with the thicker ends of the two compensation half-layers close to each other, such that the thickness of the compensation layer in the axial central region is greater than the thickness of the two end regions.

[0009] In one embodiment of the present invention, the thickness of the compensation layer is 0.1-1 mm.

[0010] In one embodiment of the present invention, the compensation layer is indirectly connected to the secondary coil through the second insulating layer, wherein the second insulating layer is a thin layer of thermally conductive epoxy resin.

[0011] In one embodiment of the present invention, the compensation layer and the magnetic core are made of the same magnetically conductive material, namely permalloy.

[0012] In one embodiment of the present invention, the secondary coil includes a primary coil and a secondary coil that are identical in structure and connected in reverse series.

[0013] In one embodiment of the present invention, both the primary coil and the secondary coil adopt a multi-layer close-wound structure.

[0014] In one embodiment of the present invention, the skeleton is a cylindrical structure with end caps at both ends for limiting the axial movement of the coil.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The multi-layered compact LVDT of the present invention includes a compensation layer made of magnetically conductive material between the primary and secondary coils. When the primary coil is energized and generates a magnetic field, the compensation layer can be magnetized, forming an additional magnetic field component. This component superimposes on the original magnetic field, effectively improving the uniformity of the magnetic field distribution along the axial direction. In the compact structure, since the secondary coil directly covers the primary coil, the magnetic field tends to attenuate in the regions at both ends of the coil. The presence of the compensation layer is equivalent to introducing additional magnetomotive force compensation in the magnetic field attenuation region, making the change in magnetic induction intensity at various points along the axial direction more gradual, thereby significantly improving the linear relationship between the induced voltage of the secondary coil and the displacement of the iron core. At the same time, the improved magnetic field uniformity also reduces leakage flux and improves the sensitivity of the sensor.

[0016] 2. The multi-layer compact LVDT of the present invention adopts a multi-layer stacked structure. This radial stacking layout significantly shortens the axial dimension of the sensor. Compared with the traditional structure in which the secondary coil is wound in segments on both sides of the primary coil, the present invention achieves significant miniaturization and can adapt to more compact installation space requirements.

[0017] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a multi-layered compact LVDT provided in an embodiment of the present invention.

[0019] Icons: 1-Skeleton; 2-Primary coil; 3-Secondary coil; 4-First insulation layer; 5-Magnetic core; 6-Compensation layer; 7-Second insulation layer. Detailed Implementation

[0020] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of a multi-layered compact LVDT based on the present invention is provided in conjunction with the accompanying drawings and specific embodiments.

[0021] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0022] This invention provides a compact LVDT with a multi-layer structure; please refer to [link / reference]. Figure 1 , Figure 1 This is a structural schematic diagram of a multi-layered compact LVDT provided in an embodiment of the present invention, as shown below. Figure 1 As shown, the compact LVDT with a multi-layer structure in this embodiment includes: a frame 1, a primary coil 2, a secondary coil 3, a first insulating layer 4, a magnetic core 5, a compensation layer 6, and a second insulating layer. The frame 1 has a through-hole along its axial direction at its center, and the magnetic core 5 is movably disposed within the through-hole. The primary coil 2 is wound around the outer surface of the frame 1. The first insulating layer 4 is disposed outside the primary coil 2. The compensation layer 6 is disposed outside the first insulating layer 4. The second insulating layer 7 is disposed outside the compensation layer 6. The secondary coil 3 is wound around the outer surface of the second insulating layer 7.

[0023] Optionally, the frame 1 can be made of a non-magnetic material, such as stainless steel or engineering plastic, and has an overall cylindrical structure with a through hole in its center along the axial direction. The magnetic core is slidably disposed in this through hole. The magnetic core can be made of a high-permeability material such as permalloy. In this embodiment, the frame 1 has end caps at both ends for limiting the axial movement of the coil.

[0024] In an optional embodiment, the outer wall of the frame 1 is provided with a winding groove, and the primary coil 2 is embedded in the winding groove. The primary coil is positioned and fixed by the winding groove structure combined with the end caps at both ends of the frame 1, preventing axial or radial displacement of the coil during use, avoiding the adverse effects of coil loosening or displacement on the magnetic field distribution, and ensuring the reliability of the sensor in long-term use or vibration environment.

[0025] In this embodiment, the frame 1 and the first insulating layer 4 are fixedly connected by pins. This connection method ensures the relative positional accuracy between the frame 1 and the first insulating layer 4, and improves the stability of the multilayer structure under vibration.

[0026] Optionally, the first insulating layer 4 can be made of polyimide material and tightly wrap around the outside of the skeleton 1 of the wound primary coil 2.

[0027] In an optional embodiment, the compensation layer 6 is a cylindrical magnetically conductive interlayer sleeved outside the first insulating layer 4, and the compensation layer 6 has a tapered cross-section in the axial direction. Specifically, the compensation layer 6 includes two symmetrically arranged compensation half-layers, with the thicker ends of the two compensation half-layers close to each other, such that the thickness of the compensation layer 6 in the axial central region is greater than the thickness of the end regions.

[0028] In this embodiment, the compensation layer 6 adopts a tapered cross-section design, with the thicker end of each of the two compensation halves facing the central region. From an electromagnetic principle perspective, the tapered compensation layer, on the one hand, increases the magnetic cross-sectional area of ​​the central region through a variable cross-section magnetic path, thereby enhancing the magnetic induction intensity of the central linear measurement region and effectively improving the sensor's sensitivity within the core working range; on the other hand, the tapered structure causes the radial gap between the secondary coil 3 and the magnetic core 5 to gradually vary along the axial direction. This variable gap structure can actively compensate for the non-uniform magnetic field distribution caused by the coil end effect, further optimizing the linearity of the output signal. Compared with traditional uniform thickness compensation layers, the tapered compensation layer achieves higher sensitivity gain and better linearity performance with the same amount of material.

[0029] Optionally, the compensation layer 6 is made of the same magnetic material as the magnetic core 5, such as permalloy. The thickness of the compensation layer 6 is 0.1-1 mm, with a thicker central region and thinner end regions, forming a tapered, gradually changing cross-section. The length of the compensation layer 6 is slightly longer than the winding range of the secondary coil 3.

[0030] Understandably, permalloy possesses high permeability and low coercivity, effectively improving magnetic field uniformity. The compensation layer 6 and the magnetic core 5 utilize the same permalloy material, optimizing the continuity of the magnetic circuit and ensuring a smooth closed path of magnetic field lines between the core, air gap, and compensation layer, reducing the nonlinear effects of reluctance variations. The identical material properties contribute to a matched magnetic field distribution, further enhancing the compensation effect.

[0031] In this embodiment, the secondary coil 3 includes a primary coil and a secondary coil with identical structures but connected in reverse series. The primary coil and the secondary coil are wound in axial segments on the outer surface of the compensation layer 6, with gaps between them, and connected in reverse series.

[0032] In this embodiment, the compensation layer 6 and the secondary coil 3 are indirectly connected through the second insulating layer 7. The second insulating layer 7 is a thin layer of thermally conductive epoxy resin, which serves both fixing and thermal conduction functions. When the secondary coil 3 is wound around the outer surface of the second insulating layer 7, the second insulating layer 7, the compensation layer 6, the first insulating layer 4, and the frame 1 are pressed and fixed by the winding tension to form an integrated multi-layer structure. The thermally conductive epoxy resin of the second insulating layer 7 can quickly conduct the heat generated by the secondary coil 3 during operation to the compensation layer 6, and utilize the large area of ​​the metal surface of the compensation layer 6 for heat dissipation, effectively reducing the impact of coil temperature rise on sensor performance.

[0033] Optionally, both the primary coil 2 and the secondary coil 3 employ a multi-layered, densely wound structure. Multi-layered, dense winding increases the number of coil turns within a limited space, thereby enhancing the strength of the induced electromotive force. In other optional embodiments, the primary coil 2 and the secondary coil 3 are wound using a segmented winding method.

[0034] This embodiment of a compact LVDT with a multilayer structure generates an alternating magnetic field inside and around the frame 1 when an AC excitation voltage is applied to the primary coil 2. The magnetic core 5 is disposed within the central through-hole of the frame 1, and its axial position moves with the object being measured. The magnetic core 5 has high magnetic permeability, which can change the magnetic reluctance distribution in the magnetic circuit, thereby affecting the magnetic flux through the secondary coil 3. The secondary coil 3 includes two identical coils connected in reverse series. When the magnetic core 5 is in the center position, the electromotive forces induced in the two secondary coils are equal in magnitude and opposite in phase, and the differential output voltage is zero. When the magnetic core 5 deviates from the center position, the electromotive forces induced in the two secondary coils are no longer equal, and the differential output voltage is linearly related to the displacement of the magnetic core. The magnitude of the displacement can be determined by detecting this output voltage.

[0035] In the multilayer structure of this embodiment, the compensation layer 6 plays a crucial role in optimizing the magnetic field distribution. From an electromagnetic perspective, the compensation layer 6 is made of the same magnetically conductive material as the magnetic core 5, effectively adding a magnetically conductive path around the primary coil 2. When the primary coil 2 is energized and generates a magnetic field, the compensation layer 6 is magnetized, forming an additional magnetic field surrounding the primary coil 2. This additional magnetic field is superimposed on the original magnetic field generated by the primary coil 2.

[0036] Specifically, the compensation layer 6 adopts a tapered cross-section design, with the thicker end of each of the two compensation half-layers facing the central region. This structure offers two beneficial effects: firstly, the variable cross-section magnetic path increases the magnetic cross-sectional area of ​​the central region, thereby enhancing the magnetic induction intensity of the central linear measurement region and effectively improving the sensor's sensitivity within its core operating range; secondly, the tapered structure causes the radial gap between the secondary coil 3 and the magnetic core 5 to gradually change along the axial direction, with a smaller gap in the central region and larger gaps at both ends. This variable gap structure actively compensates for the uneven magnetic field distribution caused by the coil end effect, further optimizing the linearity of the output signal.

[0037] In this embodiment, the presence of compensation layer 6 makes the magnetic field distribution more uniform along the axial direction. In a compact LVDT without compensation layer, secondary coil 3 directly covers primary coil 2, causing the magnetic field to decay rapidly at both ends, forming a nonlinear region. In this embodiment, compensation layer 6 is equivalent to introducing an additional magnetomotive force source in the magnetic field decay region, compensating for the insufficient magnetic field at the ends, making the change in magnetic induction intensity at each point along the axial direction more gradual, thereby significantly improving the linearity between the induced voltage of secondary coil 3 and the magnetic core displacement.

[0038] Secondly, the compensation layer 6 reduces leakage flux and improves the sensor's sensitivity. Since the compensation layer 6 surrounds the primary coil 2, it forms a low-resistivity magnetic circuit channel, guiding magnetic lines of force that would otherwise leak into the external space into the compensation layer 6, allowing them to pass through the secondary coil 3 more extensively. This increase in magnetic flux directly enhances the induced electromotive force of the secondary coil 3, making the sensor more sensitive to minute displacements. Furthermore, the compensation layer 6 and the magnetic core 5 use the same magnetically conductive material, ensuring good continuity in the magnetic circuit. Magnetic lines of force originate from the magnetic core 5, pass through the air gap to the frame 1, then through the insulating layer 4 into the compensation layer 6, and finally return to the magnetic core 5, forming a closed loop. This continuous magnetic circuit design reduces the nonlinear effects caused by sudden changes in reluctance, further improving the sensor's output characteristics.

[0039] Furthermore, in this embodiment, the second insulating layer 7 is a thin layer of thermally conductive epoxy resin, which has better thermal conductivity than traditional insulating materials. The heat generated during the operation of the secondary coil 3 is rapidly conducted to the compensation layer 6 through the second insulating layer 7. The large metal surface of the compensation layer 6 then radiates heat, effectively reducing the impact of coil temperature rise on the sensor's output characteristics and improving the sensor's temperature stability. Simultaneously, the second insulating layer 7 serves to fix and compress the secondary coil 3 during winding, eliminating the need for additional fasteners and simplifying the assembly process.

[0040] The multi-layer compact LVDT of the present invention, through ingenious multi-layer structure design and introduction of magnetic compensation layer, achieves a compact structure while effectively improving the uniformity of magnetic field distribution, thereby enhancing the linearity and sensitivity of LVDT, and solving the problem of miniaturization and high static characteristics that are difficult to achieve simultaneously in the prior art.

[0041] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0042] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0043] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A compact LVDT of multi-layer construction, characterized in that, include: Magnetic core, frame, primary coil, secondary coil, first insulating layer, compensation layer, and second insulating layer; wherein, The frame has a through hole along the axial direction at its center, and the magnetic core is movably disposed in the through hole; The primary coil is wound around the outer surface of the skeleton; the first insulating layer is disposed on the outside of the primary coil; The compensation layer is disposed on the outside of the first insulating layer; the second insulating layer is disposed on the outside of the compensation layer; the secondary coil is wound on the outer surface of the second insulating layer.

2. A compact multi-layer LVDT according to claim 1, wherein, The outer wall of the frame is provided with a winding groove, and the primary coil is embedded in the winding groove.

3. The compact LVDT with a multi-layer structure according to claim 1, characterized in that, The compensation layer is a cylindrical magnetically conductive interlayer sleeved on the outside of the insulating layer, and the compensation layer has a tapered cross section in the axial direction.

4. A compact LVDT with a multi-layer structure according to claim 1, characterized in that, The compensation layer includes two symmetrically arranged compensation half-layers, with the thicker ends of the two compensation half-layers close to each other, so that the thickness of the compensation layer in the axial central region is greater than the thickness of the two end regions.

5. A compact multi-layer LVDT according to claim 1, wherein, The thickness of the compensation layer is 0.1-1 mm.

6. A compact multi-layer LVDT according to claim 1, wherein, The compensation layer is indirectly connected to the secondary coil through the second insulating layer, which is a thin layer of thermally conductive epoxy resin.

7. A compact multi-layer LVDT according to claim 1, wherein, The compensation layer and the magnetic core are made of the same magnetically conductive material, namely permalloy.

8. A compact multi-layer LVDT according to claim 1, wherein, The secondary coil includes a primary coil and a secondary coil that are identical in structure and connected in reverse series.

9. A compact multi-layer LVDT according to claim 1, wherein, Both the primary coil and the secondary coil employ a multi-layered, tightly wound structure.

10. A compact multi-layer LVDT according to claim 1, wherein, The frame is a cylindrical structure with end caps at both ends to restrict the axial movement of the coil.

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