A high linearity LVDT sensor

Abstract

The present invention discloses a high-linearity LVDT sensor, which relates to the field of LVDT technology and includes a housing assembly, a connecting rod, an iron core, a skeleton, a primary coil, a first secondary coil, and a second secondary coil. The skeleton is nested within the housing assembly, and the iron core is movably disposed within the skeleton along its length. One end of the connecting rod is connected to one end of the iron core, and the other end extends from the housing assembly. The primary coil is wound around the skeleton. The first secondary coil and the second secondary coil are wound around the primary coil. The primary coil includes a primary main coil and two primary compensation coils. The two primary compensation coils are symmetrically arranged on either side of the primary main coil, with a gap between the primary compensation coils. One primary compensation coil, the primary main coil, and the other primary compensation coil are sequentially connected in series. The present invention can further reduce the overall length while maintaining the same linearity, or further improve the linearity while maintaining the same overall length.

Description

Technical Field

[0001] The present invention relates to the technical field of LVDT, in particular to a high-linearity LVDT sensor. Background Art

[0002] LVDT is the abbreviation of Linear Variable Differential Transformer, which is a linear displacement sensor. LVDT has extremely high resolution and reliability, simple structure and low cost, and is widely used in hydraulic and pneumatic fields. However, to ensure good linearity of current large-scale LVDTs, the sensor coil length usually needs to be more than three times the range. The resulting long length brings difficulties to layout and application. Therefore, it is necessary to improve the existing LVDT and shorten the coil length while ensuring linearity. Summary of the Invention

[0003] The purpose of the present invention is to provide a high-linearity LVDT sensor to solve the problems existing in the above-mentioned prior art, further reduce the overall length while ensuring the linearity remains unchanged, or further improve the linearity while ensuring the overall length remains unchanged.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] The present invention provides a high-linearity LVDT sensor, comprising: a housing assembly, a connecting rod, an iron core, a skeleton, a primary coil, a first secondary coil and a second secondary coil; the skeleton is nested in the housing assembly, and the iron core is movably arranged in the skeleton along the length direction; one end of the connecting rod is connected to one end of the iron core, and the other end extends from the housing assembly; the primary coil is wound on the skeleton; the first secondary coil and the second secondary coil are wound on the primary coil to form a two-section laminated LVDT; the primary coil comprises a primary main coil and two primary compensation coils; the two primary compensation coils are symmetrically arranged on both sides of the primary main coil, with a gap between the primary compensation coils and the primary main coils, and one primary compensation coil, the primary main coil and the other primary compensation coil are connected in series in sequence.

[0006] Preferably, two sections of primary coil separation rings are sleeved on the skeleton; the two sections of the primary coil separation rings are respectively arranged between the two sections of the primary compensation coils and the primary main coil.

[0007] Preferably, a wire groove or a wire hole is provided on the primary coil separation ring, and the wire connecting the primary main coil and the primary compensation coil passes through the wire groove or the wire hole.

[0008] Preferably, a secondary coil separation ring is further sleeved on the skeleton; the secondary coil separation ring is located between the first secondary coil and the second secondary coil.

[0009] Preferably, the secondary coil separation ring and the two primary coil separation rings are an integral structure with the skeleton.

[0010] Preferably, the first secondary coil and the second secondary coil are connected in reverse series.

[0011] Preferably, the height of the primary coil separation ring protruding from the surface of the skeleton is the same as the radial thickness of the primary coil.

[0012] Preferably, the shell assembly includes a first end cover, a magnetic shell and a second end cover; the magnetic shell is a sleeve-shaped structure with openings at both ends; the first end cover and the second end cover are respectively covered at both ends of the magnetic shell, the skeleton is nested in the magnetic shell, and the connecting rod extends from the middle of the first end cover.

[0013] Preferably, the wire groove or wire hole is extended along a first straight line, and the first straight line is parallel to the axis of the iron core.

[0014] Preferably, the length of the primary main coil is 1 to 1.2 times the length of the iron core, the interval between the primary compensation coil and the primary main coil is 0.3 to 0.4 times the length of the iron core, and the overall length of the primary coil is L f The sum of the lengths of the first secondary coil and the second secondary coil is also L f , the L f It is 1.9 to 2.1 times the length of the core.

[0015] Compared with the prior art, the present invention has achieved the following technical effects:

[0016] The high-linearity LVDT sensor provided by the present invention can further reduce the overall length while ensuring the linearity remains unchanged, or further improve the linearity while ensuring the overall length remains unchanged.

[0017] The present invention only requires a small amount of improvement on the basis of the original two-section stacking structure design, without adding any additional parts, and the improvement cost is low.

[0018] The present invention can also be directly applied to an existing two-section laminated LVDT to expand its effective measuring range.

[0019] The present invention provides approximate ratios of key parameters, greatly reducing the difficulty of design. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 This is the basic principle diagram of the two-dimensional axisymmetric high linearity LVDT sensor;

[0022] Figure 2 This is a schematic diagram of the key dimension symbols of the high linearity LVDT sensor;

[0023] Figure 3 This is the basic circuit diagram of the LVDT sensor;

[0024] Figure 4 Comparison curve of displacement output characteristics between a conventional LVDT sensor and the high-linearity LVDT sensor provided by the present invention;

[0025] Figure 5 It is a structural diagram of a high linearity LVDT sensor;

[0026] Figure 6 for Figure 5 Schematic diagram of the structure of the mesoskeleton;

[0027] Figure 7 for Figure 6 Middle AA section view;

[0028] In the figure: 1-connecting rod; 2-first end cover; 3-magnetic conductive shell; 4-skeleton; 5-iron core; 6-first secondary coil; 7-primary coil; 8-second secondary coil; 9-second end cover; 10-primary coil separation ring; 11-primary compensation coil; 12-primary main coil; 13-secondary coil separation ring; 14-wire slot. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The following combination Figures 1 to 7, describing embodiments of the present invention.

[0032] The present invention provides a high linearity LVDT sensor, hereinafter referred to as LVDT sensor. Figure 1 as well as Figures 5 to 7 The LVDT sensor includes: a housing assembly, a connecting rod 1, an iron core 5, a skeleton 4, a primary coil 7, a first secondary coil 6 and a second secondary coil 8; the skeleton 4 is nested in the housing assembly, and the iron core 5 is movably arranged in the skeleton 4 along the length direction; one end of the connecting rod 1 is connected to one end of the iron core 5, and the other end extends from the housing assembly; the primary coil 7 is wound on the skeleton 4; the first secondary coil 6 and the second secondary coil 8 are wound on the primary coil 7 to form a two-section laminated LVDT; the primary coil 7 includes a primary main coil 12 and two primary compensation coils 11; the two primary compensation coils 11 are symmetrically arranged on both sides of the primary main coil 12, with a gap between the primary compensation coils 11 and the primary main coil 12, and one primary compensation coil 11, the primary main coil 12 and the other primary compensation coil 11 are connected in series in sequence.

[0033] The present invention generally adopts a two-section stacked arrangement scheme. The secondary coil is wound outside the primary coil 7, which can effectively reduce the overall length of the LVDT sensor. The primary coil 7 is divided into three sections, namely a primary main coil 12 and two primary compensation coils 11. The three sections of the primary coil 7 are connected in series to form a whole. The two secondary coils are connected in reverse series to form a whole. The primary coil 7 inputs external sinusoidal excitation, and the secondary coil outputs the induction signal, such as Figure 3 As shown. The initial position of the core 5 is as follows Figure 1 The center of the primary coil 7 is shown as the zero point of the LVDT sensor output. The core 5 can move left and right. Depending on the direction of movement, the secondary coil can obtain output signals of opposite positive and negative directions, which is convenient for judging the displacement direction.

[0034] The principle of the high-linearity LVDT sensor provided by the present invention being able to further reduce the overall length while maintaining the same linearity, or further improve the linearity while maintaining the same overall length, is as follows:

[0035] First, let’s explain the design criteria for the range limit of LVDT sensors. Figure 2 As shown, in order to facilitate the explanation of the dimensional relationship of each part, the relevant dimensions are represented by letter abbreviations, L f Represents the length of the primary coil 7, i.e. the effective length of the LVDT sensor, l c Represents the length of the core 5, L f1 Represents the length of the primary main coil 12, L f2Represents the total length of the primary coil 7 after removing the primary compensation coils 11 on both sides. Considering the symmetry of the LVDT sensor and the total length of the first secondary coil 6 and the second secondary coil 8 is equal to the total length of the primary coil 7, the length of the first secondary coil 6 and the second secondary coil 8 are both L f / 2. Also based on the symmetrical design, the two primary coil separation rings 10 are arranged symmetrically about the central symmetry axis, so the primary compensation coils 11 on both sides are respectively arranged about the central symmetry axis L f2 / 2, the two end surfaces of the primary main coil 12 are respectively about the central symmetry axis L f1 / 2, and further we can get the length of the primary coil separation ring 10 is (L f2 -L f1 ) / 2, the length of the primary compensation coil 11 on both sides is (L f -L f2 ) / 2. The number of turns of the primary coil 7 projected onto the iron core 5 is C f The number of turns of the first secondary coil 6 and the second secondary coil 8 projected onto the iron core 5 are C s1 、C s2 .

[0036] LVDT sensor maximum range maxL and core length l c Need to meet:

[0037] l c +maxL<=L f (1)

[0038] maxL<=l c (2)

[0039] Combining equations (1) and (2), we can get:

[0040] 2*maxL<=L f (3)

[0041] Formulas (1), (2), and (3) are the limit design criteria for LVDT sensors. Compared with the design criteria of the traditional two-section stacked LVDT design method, the design criteria must ensure that L f >=3*maxL to ensure its linearity. The present invention divides the primary coil 7 into three sections to achieve the minimum limit length of the LVDT sensor, namely L f =2*maxL. The basic principle of the present invention to achieve high linearity is variable gain compensation of the primary coil 7.

[0042] The traditional LVDT primary coil couples the primary magnetic field to the two secondary coils through the iron core. The degree of coupling between the primary coil and the iron core remains basically unchanged, that is, C f is a constant. Due to the displacement of the core, the coupling degree between the primary coil and the two secondary coils is different, that is, Cs1 、C s2 The number of turns is different, and the LVDT can be regarded as two transformers. The output signal is the difference between the secondary outputs of the two transformers. The difference in secondary output is basically linearly proportional to the core displacement. However, when the core displacement of the traditional LVDT is close to the two ends of the primary coil, the gain will drop significantly due to the end effect, which leads to a decrease in the overall output linearity of the LVDT. In the present invention, there is a gap between the primary compensation coil 11 and the primary main coil 12, which leads to the core 5 displacement process C f It is not a constant. Through reasonable design and layout, the transformation ratio of the two equivalent transformers can be further increased when the core 5 is close to the two ends of the primary coil 7, compensating for the linearity decline of the traditional LVDT, thereby shortening L under the condition of ensuring linearity. f , so that it reaches the design limit 2*maxL.

[0043] Through simulation calculation and theoretical analysis, it is concluded that the key structural parameters of the LVDT sensor have the following approximate relationship:

[0044] L f =2*l c ;

[0045] l c =maxL;

[0046] L f1 =1.1*l c ;

[0047] L f2 =1.8*l c .

[0048] In some embodiments, two primary coil separation rings 10 are mounted on the frame 4; the two primary coil separation rings 10 are respectively disposed between the two primary compensation coils 11 and the primary main coil 12. The primary coil separation rings 10 are provided with wire slots 14 or wire holes, through which the wires connecting the primary main coil 12 and the primary compensation coil 11 pass.

[0049] In this embodiment, the primary compensation coil 11 and the primary main coil 12 are isolated by the primary coil separation ring 10 to prevent the length of the separation therebetween from changing during use, thereby improving stability during use.

[0050] In some embodiments, a secondary coil separation ring 13 is further sleeved on the skeleton 4 ; the secondary coil separation ring 13 is located between the first secondary coil 6 and the second secondary coil 8 , and a wire groove 14 or a wire hole is also provided on the secondary coil separation ring 13 .

[0051] In this embodiment, it can be ensured that the first secondary coil 6 and the second secondary coil 8 are distributed symmetrically on the left and right.

[0052] In some embodiments, the secondary coil separation ring 13 and the two primary coil separation rings 10 are integrated with the frame 4 .

[0053] This embodiment improves the structural stability of the skeleton 4 .

[0054] In some embodiments, the first secondary coil 6 and the second secondary coil 8 are connected in reverse series.

[0055] In some embodiments, the height of the primary coil separation ring 10 protruding from the surface of the frame 4 is the same as the radial thickness of the primary coil 7 . The primary coil can be arranged in a single layer or multiple layers along the radial direction.

[0056] This embodiment enables the outer surface of the primary coil separation ring 10 and the outer edge of the primary coil 7 to be on the same cylindrical surface, so as to facilitate the subsequent winding of the first secondary coil 6 and the second secondary coil 8 on the cylindrical surface.

[0057] In some embodiments, the shell assembly includes a first end cover 2, a magnetic shell 3 and a second end cover 9; the magnetic shell 3 is a sleeve-shaped structure with openings at both ends; the first end cover 2 and the second end cover 9 are respectively covered at both ends of the magnetic shell 3, the skeleton 4 is nested in the magnetic shell 3, and the connecting rod 1 extends from the middle of the first end cover 2.

[0058] In some embodiments, the wire slot 14 or the wire hole extends along a first straight line, and the first straight line is parallel to the axis of the iron core 5 .

[0059] In some embodiments, the length of the primary main coil 12 is 1 to 1.2 times the length of the core 5, the interval between the primary compensation coil 11 and the primary main coil 12 is 0.3 to 0.4 times the length of the core 5, and the overall length of the primary coil 7 is L f， The sum of the lengths of the first secondary coil 6 and the second secondary coil 8 is also L f , L f It is 1.9 to 2.1 times the length of the iron core 5.

[0060] This embodiment realizes that the measuring range of the LVDT sensor is approximately equal to the length of the core 5, that is, 0.5 times the L f .

[0061] The original LVDT sensor displacement output characteristic curve obtained by the same analysis method and the LVDT sensor provided by the embodiment of the present invention are shown in the attached figure. Figure 4 As shown, the output nonlinearity of the LVDT sensor provided by the present application is reduced by about 50.7% compared with the original nonlinearity.

[0062] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A high linearity LVDT sensor, characterized in that: include: A shell assembly, a connecting rod, an iron core, a skeleton, a primary coil, a first secondary coil and a second secondary coil; the skeleton is nested in the shell assembly, and the iron core is movably arranged in the skeleton along the length direction; one end of the connecting rod is connected to one end of the iron core, and the other end extends from the shell assembly; the primary coil is wound on the skeleton; the first secondary coil and the second secondary coil are wound on the primary coil; the primary coil includes a primary main coil and two primary compensation coils; the two primary compensation coils are symmetrically arranged on both sides of the primary main coil, and there is a gap between the primary compensation coil and the primary main coil, and one primary compensation coil, the primary main coil and the other primary compensation coil are connected in series in sequence; the first secondary coil and the second secondary coil are connected in reverse series; the length of the primary main coil is 1~1.2 times the length of the iron core, the length of the gap between the primary compensation coil and the primary main coil is 0.3~0.4 times the length of the iron core, and the overall length of the primary coil is L f The sum of the lengths of the first secondary coil and the second secondary coil is also L f , the L f It is 1.9~2.1 times the length of the iron core; the initial position of the iron core is at the center of the primary coil.

2. The high linearity LVDT sensor according to claim 1, wherein: Two sections of primary coil separation rings are sleeved on the skeleton; the two sections of the primary coil separation rings are respectively arranged between the two sections of the primary compensation coils and the primary main coil.

3. The high linearity LVDT sensor according to claim 2, wherein: The primary coil separation ring is provided with a wire groove or a wire hole, and the wire connecting the primary main coil and the primary compensation coil passes through the wire groove or the wire hole.

4. The high linearity LVDT sensor according to claim 2, wherein: A secondary coil separation ring is also sleeved on the skeleton; the secondary coil separation ring is located between the first secondary coil and the second secondary coil.

5. The high linearity LVDT sensor according to claim 4, characterized in that: The secondary coil separation ring and the two primary coil separation rings are an integrated structure with the frame.

6. The high linearity LVDT sensor according to claim 2, wherein: The height of the primary coil separation ring protruding from the surface of the skeleton is the same as the radial thickness of the primary coil.

7. The high linearity LVDT sensor according to claim 1, wherein: The shell assembly includes a first end cover, a magnetic conductive shell and a second end cover; the magnetic conductive shell is a sleeve-shaped structure with openings at both ends; the first end cover and the second end cover are respectively covered at both ends of the magnetic conductive shell, the skeleton is nested in the magnetic conductive shell, and the connecting rod extends from the middle of the first end cover.

8. The high linearity LVDT sensor according to claim 3, wherein: The wire groove or wire hole is extended along a first straight line, and the first straight line is parallel to the axis of the iron core.

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