Linear Variable Differential Transformer

Abstract

To provide a linear variable differential transformer capable of suppressing decrease in magnetic flux density at an end portion of a position detection range more than before.SOLUTION: A linear variable differential transformer includes: a straight tubular primary coil: a pair of secondary coils taper-wound coaxially with the primary coil; and a probe provided inside the primary coil and the secondary coil, freely movable in a central axis direction of the primary coil and the secondary coil, and on which a magnetic core is mounted. An end portion having a smaller number of layers in the pair of the secondary coils is reversely wound.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a linear variable differential transformer. [Background technology]

[0002] The following Patent Document 1 describes a linear variable differential transformer (LVDT) used for measuring aircraft engines. This linear variable differential transformer is an inductive electric sensor for detecting the linear displacement of an object such as a variable stator vane, and includes a primary coil, a pair of secondary coils, and a central core provided in a probe, and detects the linear position of the object engaged with the tip of the probe based on a change in the differential voltage of the pair of secondary coils that depends on the linear displacement of the central core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2015-521747 Summary of the Invention [Problem to be solved by the invention]

[0004] The linear variable differential transformer described above has a primary coil that is a linear coil with a structurally finite length and whose moving direction of the central core is the central axis direction. At the end of the primary coil, the magnetic flux density of the magnetic flux penetrating the primary coil in the central axis direction drops sharply. The magnetic flux penetrating in the central axis direction is the magnetic flux that governs the differential voltage. Therefore, the linear variable differential transformer has a basic property that the detection accuracy of the linear displacement is easily deteriorated near the full stroke of the central core.

[0005] Conventionally, the only solution to this deterioration in detection accuracy was to set the coil length of the primary coil to a length with a sufficient margin relative to the operating range of the core, or to repeatedly rewind the primary coil until a predetermined detection accuracy was obtained. However, when the dimensional constraints on the length of the linear variable differential transformer are strict, it is difficult to set the coil length of the primary coil to a length with a sufficient margin. In addition, there is a problem that repeatedly rewinding the primary coil at the manufacturing site reduces production efficiency.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a linear variable differential transformer that can suppress the decrease in magnetic flux density at the ends of the position detection range more than ever before. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention employs, as a first solution for a linear variable differential transformer, a straight tubular primary coil, a pair of secondary coils that are tapered wound coaxially with the primary coil, and a probe that is provided inside the primary coil and the secondary coil and is movable in the central axial direction of the primary coil and the secondary coil and has a magnetic core attached, and the ends of the pair of secondary coils that have fewer layers are reverse wound.

[0008] The present invention employs a second solution for a linear variable differential transformer according to the first solution, in which the secondary coil has nine sections set in the central axis direction, and the two sections closest to the ends are reverse wound.

[0009] The present invention provides a third solution for a linear variable differential transformer according to the second solution, in which the secondary coil has a section with the greatest number of layers having six layers and a section with the least number of layers having one layer.

[0010] The present invention employs a fourth solution for a linear variable differential transformer according to any one of the first to third solutions, in which the primary coil has seven layers as a whole, the first to fifth layers closest to the probe being densely wound, the sixth layer being densely wound at both ends and with a spaced winding in the center, and the seventh layer being less densely wound at both ends and with a spaced winding in the center than the sixth layer.

[0011] The present invention employs, as a fifth solution relating to a linear variable differential transformer, any one of the first to fourth solutions described above, a solution in which the transformer is arranged coaxially with the rotating shaft inside the rotor of a rotating electric machine. Effect of the Invention

[0012] According to the present invention, it is possible to provide a linear variable differential transformer that can suppress the decrease in magnetic flux density at the ends of the position detection range more than ever before. [Brief description of the drawings]

[0013] [Figure 1] 1 is a front view showing the overall configuration of a linear variable differential transformer according to an embodiment of the present invention; [Diagram 2] 1 is a front view showing a configuration of a main part of a linear variable differential transformer according to an embodiment of the present invention; [Diagram 3] FIG. 2 is a schematic diagram showing the winding state of a primary coil and a secondary coil in one embodiment of the present invention. [Figure 4] FIG. 2 is a characteristic diagram showing the performance of the entire configuration of a linear variable differential transformer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A linear variable differential transformer A according to this embodiment is attached to an electric motor B as shown in FIG. 1, and is a substantially cylindrical displacement sensor for detecting the position of an object engaged with an end portion thereof.

[0015] The electric motor B corresponds to the rotating electric machine of the present invention. In addition, in Fig. 1 and Fig. 2, three orthogonal axes consisting of an X-axis, a Y-axis, and a Z-axis are added. Furthermore, the central axis direction of this linear variable differential transformer A is parallel to the Z-axis.

[0016] First, motor B is described. Motor B has a known configuration and includes a stator b1, a rotor b2, and a rotating shaft b3. Stator b1 includes a predetermined number of slots arranged in an annular shape. Each slot includes a stator core and a stator winding, and functions as a plurality of electromagnets that generate a rotating magnetic field.

[0017] The rotor b2 is an annular member fixed to a rotating shaft b3, and is disposed inside the stator b1. The outer periphery of the rotor b2 faces the tip of the slot across a small gap, and permanent magnets that form magnetic poles at predetermined electrical angles are disposed on the outer periphery. A rotational force acts on the rotor b2 by electromagnetic coupling with the stator b1.

[0018] The rotating shaft b3 is a rod-shaped metal member and is the output shaft of the electric motor B. That is, the rotating shaft b3 is a rod-shaped metal member that rotates by the rotational force acting on the rotor b2, and has a through hole b4 formed in the central axis direction. As shown in the figure, the linear variable differential transformer A according to this embodiment is a substantially rod-shaped member that is inserted into the through hole b4 with a certain gap therebetween.

[0019] As shown in Figures 1 and 2, this linear variable differential transformer A is arranged coaxially with a rotating axis b3 within the rotor of an electric motor B (rotating electric machine), and includes a housing 1, a bracket 2, a probe 3, a bobbin 4, a primary coil 5, a pair of secondary coils 6A, 6B, a magnetic core 7, and a guide member 8.

[0020] The housing 1 is a cylindrical member with a bottom, as shown in Figures 1 and 2. The housing 1 has a cylindrical side portion 1a and disk-shaped bottom portions 1b and 1c, and accommodates a part of the probe 3, a primary coil 5, a pair of secondary coils 6A and 6B, a magnetic core 7, and a guide member 8. In the housing 1, one of the bottom portions 1b is formed with a through hole h that passes through the center.

[0021] That is, in this embodiment, the housing 1 not only houses a part of the probe 3, the primary coil 5, a pair of secondary coils 6A, 6B, the magnetic core 7 and the guide member 8 as described above, but also has a through hole h through which one end of the probe 3 passes.

[0022] The bracket 2 is a metal member that contacts the periphery of the side portion 1a of the housing 1, and includes a tubular portion 2a and a flange portion 2b as shown in Fig. 2. The tubular portion 2a is a cylindrical portion whose inner peripheral surface contacts the side portion 1a of the housing 1. The flange portion 2b is a plate portion of a predetermined thickness provided on the outside of the tubular portion 2a, and has multiple mounting holes formed therein. These multiple mounting holes are screw holes for fixing the linear variable differential transformer A.

[0023] As shown in the figure, the probe 3 is a rod-shaped member provided coaxially with the bottomed cylindrical housing 1. That is, the probe 3 is provided in a state where it is inserted into a through hole h that passes through the center of the housing 1, and is freely movable in the direction of the central axis (direction parallel to the Z axis) of the housing 1 (i.e., the linear variable differential transformer A).

[0024] Such a probe 3 is provided with an engagement member 2a that engages with an object at one end (tip) in the direction of the central axis, i.e., the moving direction, of the linear variable differential transformer A. Also, at the rear end of this probe 3, a magnetic core 7 having a substantially cylindrical shape is fixed coaxially with the probe 3, as shown in FIG.

[0025] The bobbin 4 is a cylindrical member provided in the housing 1 coaxially with the housing 1 and the probe 3. The bobbin 4 is a cylindrical member of a predetermined length made of a non-magnetic material. That is, the bobbin 4 is accommodated in the housing 1 such that its inner surface (cylindrical surface) forms a certain gap with respect to the circumferential surface (cylindrical surface) of the magnetic core 7 fixed to the probe 3.

[0026] As shown in Fig. 3(a), the primary coil 5 is a straight-tube winding wound in multiple layers with a predetermined length in the central axis direction of the linear variable differential transformer A. An alternating current (excitation current) for exciting the pair of secondary coils 6A and 6B is supplied to this primary coil 5 from an external power source (not shown). An excitation magnetic field is generated around this primary coil 5 based on the excitation current.

[0027] As shown in Fig. 3(a), the pair of secondary coils 6A and 6B are straight-tube windings that are coaxial with the primary coil and tapered at a predetermined length. That is, of the pair of secondary coils 6A and 6B, one secondary coil 6A is wound in a tapered shape at a predetermined length on the surface of the primary coil 5 in the central axis direction, and the other secondary coil 6B is wound in a tapered shape at a predetermined length on the surface of the primary coil 5 in the central axis direction. On the surface of one of the secondary coils 6A It is wound in a reverse taper shape over a given length.

[0028] Such a pair of secondary coils 6A, 6B each outputs an induced voltage based on the excitation magnetic field generated by the primary coil 5. That is, the primary coil 5 and one of the secondary coils 6A, and the primary coil 5 and the other secondary coil 6A each constitute a transformer. The primary coil 5 and one of the secondary coils 6A constitute a first transformer, and the primary coil 5 and the other secondary coil 6A constitute a second transformer.

[0029] Here, Fig. 3(b) is a schematic diagram showing the winding state of the above-mentioned primary coil 5 and the pair of secondary coils 6A, 6B as a winding ratio. As shown in Fig. 3(b), the primary coil 5 is wound in seven layers as a whole on the outer circumferential surface of the bobbin 4. Furthermore, a total of nine sections are set in the primary coil 5 and the pair of secondary coils 6A, 6B in the central axis direction. In Fig. 3(b), the leftmost section with the smallest winding coordinate is the first section, and the rightmost section with the largest winding coordinate is the ninth section.

[0030] Of the seven layers in the primary coil 5, the first to fifth layers, which are close to the bobbin 4, i.e., the magnetic core 7, are densely wound in all sections as shown in Fig. 3(b), and in the sixth layer, the first and ninth sections at both ends are densely wound, and the second to eighth sections at the center are spaced apart. Furthermore, the seventh layer is wound so that the degree of dense winding at both ends and the degree of spaced winding in the center are lower than those of the sixth layer.

[0031] The dense winding is also called aligned winding, and is a winding state in which adjacent windings are in contact with each other. On the other hand, the spaced winding is a winding state in which adjacent windings are spaced apart from each other. In other words, the dense winding is a winding method in which the winding density is higher than that of the spaced winding, so the primary coil 5 is wound so that the winding density is higher in the center than at both ends in the central axial direction.

[0032] Of the pair of secondary coils 6A, 6B, one secondary coil 6A is wound so that the number of layers gradually increases in the Z-axis direction. That is, one secondary coil 6A is wound so that the number of layers is maximum at one end and minimum at the other end, that is, in a tapered shape.

[0033] More specifically, as shown in Fig. 3(b), one secondary coil 6A has six layers in the first section which has the greatest number of layers, and one layer in the ninth section which has the least number of layers. Also, the winding direction of the eighth and ninth sections of one secondary coil 6A is a negative value as shown in the figure. That is, in the first layer, the winding direction in the eighth and ninth sections is the opposite direction to the winding direction of the other sections, that is, reverse winding.

[0034] On the other hand, the secondary coil 6A is wound sequentially from the 9th section to the 1st section, but when the 9th and 8th sections are wound in a CCW (counterclockwise) direction, the winding is temporarily stopped to perform a loosening prevention process. Then, the 7th to 1st sections are wound in a CW (clockwise) direction, which is the opposite direction to the CCW (counterclockwise) direction.

[0035] With respect to the one secondary coil 6A, the other secondary coil 6B is wound so that the number of layers gradually decreases in the Z-axis direction. That is, the other secondary coil 6B is wound so that the number of layers is maximum at the other end and minimum at one end, that is, in a tapered shape in the opposite direction to the one secondary coil 6A.

[0036] As shown in Fig. 3(b), the other secondary coil 6B has six layers in the ninth section, which is the largest number of layers, and one layer in the first section, which is the smallest number of layers. The other secondary coil 6B has a negative winding direction in the first and second sections, as shown in the figure. That is, the winding direction in the first and second sections is opposite to the winding direction in the other sections, 3 to 9, that is, reverse winding.

[0037] That is, in the other secondary coil 6B, the wire is wound sequentially from the first section to the ninth section, but when the first and second sections are wound in a CW direction (clockwise), the winding is temporarily stopped to perform a loosening prevention process. Then, the third to ninth sections are wound in a CCW direction (counterclockwise), which is the opposite direction to the CW direction (clockwise).

[0038] Here, the reverse winding of the eighth and ninth sections in one secondary coil 6A and the reverse winding of the first and second sections in the other secondary coil 6B are important features of the linear variable differential transformer A according to this embodiment. As will be described later, this linear variable differential transformer A suppresses the decrease in magnetic flux density at both ends of the primary coil 5, i.e., at both ends of the pair of secondary coils 6A and 6B, more than in the past, by the reverse winding.

[0039] The magnetic core 7 is a cylindrical magnetic member fixed coaxially to the probe 3 at a midpoint of the probe 3. The length of the magnetic core 7 in the direction of the central axis of the probe 3 and the housing 1, i.e., the length of the magnetic core 7 in its own direction, is set to a predetermined length. Such a magnetic core 7 varies the coupling coefficients of the first transformer and the second transformer depending on the position in the direction of the central axis.

[0040] In the above-mentioned first and second transformers, the coupling coefficient changes according to the position of the magnetic core 7 which is movable in the central axis direction inside the bobbin 4. As a result, the change characteristic of the induced voltage (first induced voltage) output by one secondary coil 6A according to the position of the magnetic core 7 is the inverse characteristic of the change characteristic of the induced voltage (second induced voltage) output by the other secondary coil 6B according to the position of the magnetic core 7.

[0041] 2, the guide member 8 is provided in the housing 1 near the other bottom 1c. This guide member 8 is an assembly of multiple disk-shaped members arranged coaxially, and guides the lead wire of the primary coil 5 and the lead wires of the pair of secondary coils 6A, 6B. Although not shown, the lead wire of the primary coil 5 and the lead wires of the pair of secondary coils 6A, 6B are drawn from inside the housing 1 to outside the housing 1 via the guide member 8.

[0042] Next, the effects of the linear variable differential transformer A according to this embodiment will be described in detail with reference to the characteristic diagram of FIG.

[0043] In this linear variable differential transformer A, the excitation magnetic field generated by the primary coil 5 acts on the pair of secondary coils 6A, 6B via the magnetic core 7, thereby generating a first induced voltage in one of the secondary coils 6A and a second induced voltage in the other secondary coil 6B. The above excitation magnetic field passes through the primary coil 5, the pair of secondary coils 6A, 6B, and the magnetic core 7 mainly in the direction of the central axis (Z-axis direction).

[0044] The pair of secondary coils 6A, 6B generate a first induced voltage and a second induced voltage based on the excitation magnetic field passing mainly in the movable direction (Z-axis direction). That is, one secondary coil 6A generates a first induced voltage based on the excitation magnetic field passing in the movable direction (Z-axis direction), and the other secondary coil 6B generates a second induced voltage based on the excitation magnetic field passing in the movable direction (Z-axis direction).

[0045] Such a linear variable differential transformer A detects the position of the object in the central axis direction by the action of an excitation magnetic field passing in the movable direction (Z-axis direction). That is, since the magnetic core 7 is fixed to the probe 3 and the probe 3 is engaged with the object to be detected, the position of the magnetic core 7 in the movable direction (Z-axis direction) changes according to the position of the object to be detected in the central axis direction. The first induced voltage and the second induced voltage change according to the position of the magnetic core 7 in the movable direction (Z-axis direction).

[0046] Such a linear variable differential transformer A outputs the difference between the first induced voltage and the second induced voltage, which changes depending on the position in the central axis direction of the object, i.e., the differential voltage, as a detection signal indicating the position of the object in the movable direction (Z-axis direction).

[0047] In this embodiment, since the eighth and ninth sections of one secondary coil 6A and the first and second sections of the other secondary coil 6B are wound in reverse, the decrease in magnetic flux density at both ends of the position detection range of the linear variable differential transformer A can be suppressed more than in the conventional case.

[0048] That is, Fig. 4 is a characteristic diagram showing an example of the position detection accuracy of the linear variable differential transformer A according to this embodiment. As shown in Fig. 4, according to the linear variable differential transformer A according to this embodiment, the position detection accuracy is significantly improved over the conventional one over the entire region of the position detection range, and in particular, the position detection accuracy at both ends of the position detection range is significantly improved over the conventional one.

[0049] Therefore, according to this embodiment, since the ends of the pair of secondary coils 6A, 6B having fewer layers are wound in the opposite direction, it is possible to provide a linear variable differential transformer A that can suppress the decrease in magnetic flux density at the ends of the position detection range more than in the conventional art.

[0050] In this embodiment, the technical significance of reverse winding the end with fewer layers will be further explained. By reverse winding the end with fewer layers where winding is not usually performed, it is possible to increase the voltage gain (Vrms / mm) relative to the core position without changing the length of the winding area. As a result, it is possible to compensate for the decrease in magnetic flux density at the ends of the position detection range of the primary winding by the secondary winding. The improvement in position detection accuracy at both ends of the position detection range shown in Figure 4 is believed to be due to the increase in voltage gain (Vrms / mm) mentioned above.

[0051] From another perspective, when the magnetic flux generated by the primary winding is usually insufficient at the ends compared to the ideal voltage output specifications, and the position detection accuracy at the ends deteriorates, the voltage gain (Vrms / mm) for the core position is lowered or the winding area is lengthened to compensate for the decrease in magnetic flux density at the ends. However, in this embodiment, a high voltage gain (Vrms / mm) is achieved while the length of the winding area is suppressed by reverse winding at the end with fewer layers, thereby improving the position detection accuracy at both ends of the position detection range.

[0052] Furthermore, in this embodiment, in a special usage condition in which the linear variable differential transformer A is arranged coaxially with the rotating shaft b3 within the rotor b2 of the electric motor B (rotating electric machine), the position detection accuracy at both ends of the position detection range can be improved compared to the conventional case.

[0053] The present invention is not limited to the above-described embodiment, and the following modifications are possible. (1) In the above embodiment, the eighth and ninth sections of one secondary coil 6A and the first and second sections of the other secondary coil 6B are reversely wound, but the present invention is not limited to this. For example, the ninth section of one secondary coil 6A and the first section of the other secondary coil 6B may be reversely wound.

[0054] (2) In the above embodiment, an example of the number of layers and the number of turns of each section is shown in Fig. 3, but the present invention is not limited to this. The number of layers and the number of turns of each section may be appropriately changed as necessary.

[0055] (3) In the above embodiment, the linear variable differential transformer A is disposed coaxially with the rotating shaft b3 inside the rotor b2 of the electric motor B (rotating electric machine), but the present invention is not limited to this. In other words, the rotating electric machine of the present invention is not limited to the electric motor B, and may be, for example, a generator. [Explanation of symbols]

[0056] A Linear Variable Differential Transformer B Electric motor b1 Stator b2 rotor b3 Rotation axis b4 Through hole 1 Case 2 Bracket 3. Probe 4 Bobbin 5 Primary coil 6A, 6B Secondary coil 7 Magnetic Core 8 Guide member

Claims

1. A straight tubular primary coil; a secondary coil wound coaxially and tapered on a surface of the primary coil; Another secondary coil is wound around the surface of the one secondary coil in a reverse tapered shape; a probe provided inside the primary coil and the pair of secondary coils, movable in a central axis direction of the primary coil and the pair of secondary coils, and having a magnetic core attached thereto; 13. A linear variable differential transformer, comprising: a pair of secondary coils, each of which has a smaller number of layers at its two ends, each of which is wound in a reverse direction;

2. 2. The linear variable differential transformer according to claim 1, wherein the secondary coil has nine sections in the central axial direction, and the two sections closest to the ends are reverse wound.

3. 3. The linear variable differential transformer according to claim 2, wherein the section with the largest number of layers of the secondary coil has six layers, and the section with the smallest number of layers has one layer.

4. 4. The linear variable differential transformer according to claim 1, wherein the linear variable differential transformer is arranged coaxially with a rotation axis within a rotor of a rotating electric machine.

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