JP2014174114A - Displacement sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a displacement sensor capable of easily performing downsizing with a simple circuit configuration.SOLUTION: A displacement sensor 100 includes: a cylindrical coil 10; a soft magnetic material 30 that moves by strokes inside the coil 10 in conjunction with the displacement of a moving body 20; a power supply unit 40 for energizing the coil 10; a detection element 50 that is arranged such that a detection direction is along the axial direction of the coil 10 outside the radial direction of the coil 10 to detect the intensity of the surrounding magnetic field of the coil 10; a stroke arithmetic unit 60 for calculating the amount of stroke of the moving body 10 based on detection results of the detection element 50.

Description

  The present invention relates to a displacement sensor that detects the amount of displacement of a moving body that moves in a stroke.

  As a technique for detecting the amount of displacement of a moving body that moves in a stroke, there is a technique described in Patent Documents 1-4, for example. Patent Document 1 discloses a floated magnetic body that moves in response to a change in the liquid level, a detection coil unit that is wound so that the pitch gradually decreases, and detects a change in a magnetic field accompanying the movement of the floated magnetic body. A liquid level sensor is provided. In this liquid level sensor, the floated magnetic body moves in the vicinity of the detection coil or in the detection coil according to the change in the liquid level, and the liquid level sensor is changed by the change in the inductance of the detection coil according to the position of the float magnetic body. Detect faces. Moreover, the detection coil of this liquid level sensor can also be configured with a primary coil and a secondary coil. In such a configuration, an AC voltage is applied to the primary coil, and the liquid level is detected according to the induced electromotive force generated in the secondary coil as the floated magnetic body moves according to the change in the level of the liquid level. .

  In Patent Document 2, a magnetic ball is enclosed in an arcuate guide tube in a movable state, and a coil having a sparse winding portion and a dense portion is provided around the guide tube. A tilt angle sensor is disclosed. In the tilt angle sensor, when the guide tube is inclined in the outer peripheral direction, the magnetic ball moves inside the guide tube, and the positional relationship with the coil changes. As a result, since the magnetic resistance of the coil changes, the inclination angle of the guide cylinder is measured by detecting the change of the magnetic resistance.

  Patent Document 3 discloses a flow meter including a fluid circulation pipe, a float having a magnetic body provided in the fluid circulation pipe, and a coil wound around the fluid circulation pipe. The coil has a coil length that covers the position detection range of the magnetic material, and includes an excitation coil to which an AC voltage is applied, and a search coil that divides the position detection range into a plurality of parts and corresponds to each range. A voltage corresponding to the position of the magnetic body is output from the plurality of search coils. Thereby, the liquid level is detected.

  Patent Document 4 discloses a differential transformer having a primary coil and a secondary coil, and a movable magnetic core fixed to a drive shaft. This working transformer is provided with a pair of secondary coils on both sides in the drive axis direction of the primary coil, and detects the displacement amount of the movable magnetic core from the voltage difference generated in the pair of secondary coils according to the movement of the movable magnetic core. To do.

JP 2001-194213 A JP-A-5-34152 Japanese Patent Laid-Open No. 3-188324 JP 2000-213956 A

Since the technique described in Patent Documents 1-4 described above detects a change in impedance or a change in induced electromotive force, the voltage applied to the excitation coil and the primary coil needs to be an alternating current. For example, when detecting a change in impedance, a conversion circuit that converts the change in impedance into a change in voltage is required. In addition, when detecting a change in induced electromotive force, a detection circuit is required. For this reason, in the techniques described in Patent Documents 1-4, the circuit configuration becomes complicated and the scale thereof becomes large. In addition, since an AC magnetic field is required as a detection principle, there are limitations on the specification environmental conditions such as difficulty in installation inside a metal cylinder.
In the technique described in Patent Document 4, since the primary coil and the secondary coil are arranged in series in the displacement direction of the drive shaft, the movable magnetic core, which is a movable part, needs to be longer than the detection range. Become. For this reason, the length of a primary coil and a secondary coil requires the length more than double of a detection range, and size reduction is difficult.

  In view of the above problems, an object of the present invention is to provide a displacement sensor that can be easily miniaturized with a simple circuit configuration.

  In order to achieve the above object, the displacement sensor according to the present invention is characterized by a cylindrical coil, a soft magnetic body that moves in a stroke in conjunction with a moving body that is a displacement detection target, A power supply unit that energizes the coil, a detection element that is arranged on the outer side in the radial direction of the coil so that a detection direction is along the axial direction of the coil, and detects the strength of a magnetic field around the coil; and the detection element And a stroke amount calculation unit that calculates the stroke amount of the moving body based on the detection result of the above.

  With such a characteristic configuration, the soft magnetic body can be moved in a stroke on the radially inner side of the coil in conjunction with the moving body. Therefore, since the magnetic field outside the coil in the radial direction can be changed according to the stroke amount, the displacement amount of the moving body can be calculated according to the detection result of the detection element. Further, with this configuration, it is only necessary to arrange the coil so as to surround the soft magnetic material and provide the detection element on the outer side in the radial direction of the coil, so that the size can be reduced with a simple circuit configuration.

  Further, it is preferable that the coil is formed such that a pitch of windings forming the coil is gradually narrowed from one end portion in the axial direction of the coil toward the other end portion.

  With such a configuration, the strength with which the soft magnetic material is magnetized can be changed according to the position where the soft magnetic material has reached the stroke with the moving material. Therefore, the intensity of the magnetic field on the outer side in the radial direction of the coil can be changed according to the stroke amount, so that the detection sensitivity can be increased.

  In addition, it is preferable that the detection element is arranged on the side of the end portion in the axial direction where the pitch of the winding of the coil becomes narrow.

  With such a configuration, when the soft magnetic material is in a narrow pitch region and the soft magnetic material is strongly magnetized, the soft magnetic material and the detection element are close to each other, and the magnetic field in the vicinity of the detection element becomes stronger, and the soft magnetic material is soft. When the magnetic body is in a wide pitch area and the soft magnetic body is weakly magnetized, the soft magnetic body and the detection element are separated from each other, and the magnetic field near the detection element becomes weaker. Therefore, it is possible to further increase the detection sensitivity.

  The coil is a first coil, and the cylindrical second coil formed so that the pitch of the winding gradually increases from one end in the axial direction to the other end, It is preferable that the first coil and the first coil are provided so as to overlap with each other in the axial direction.

  With such a configuration, for example, currents are passed through the first coil and the second coil in different directions, or the winding directions of the first coil and the second coil are wound in different directions. By doing so, it is possible to configure so that the non-linearities of the respective magnetic fields of the first coil and the second coil cancel each other. Therefore, since the linearity of detection sensitivity can be improved, robustness can be improved.

  Further, it is preferable that the power supply unit is a DC power supply.

  With such a configuration, an AC magnetic field is not generated from the coil and the soft magnetic material, so that no eddy current is generated. Therefore, for example, even when the moving body is made of metal, eddy current loss does not occur. Therefore, the influence of eddy current on the magnetic field can be eliminated, and errors related to detection of displacement can be suppressed. Further, it is preferable that the current flowing through the coil is a current that changes in a staircase pattern having at least a binary value. By using such a current, an output in which the influence of disturbance is reduced can be obtained from the difference in output at different currents.

  The detection element is preferably provided with yokes on both sides along the axial direction of the coil.

  With such a configuration, the magnetic field generated from the coil can be collected by the yoke, and the collected magnetic field can be input to the detection element. Therefore, detection sensitivity can be increased.

It is a figure which shows typically the structure of the displacement sensor which concerns on 1st Embodiment. It is a figure which shows the detection form of the detection element which concerns on 1st Embodiment. It is a figure which shows typically the structure of the displacement sensor which concerns on 2nd Embodiment. It is a figure which shows typically the structure of the displacement sensor which concerns on 3rd Embodiment.

1. First Embodiment A displacement sensor according to the present invention is configured to be able to detect a displacement amount of a moving body that moves in a stroke. Hereinafter, the displacement sensor 100 of the present embodiment will be described in detail. FIG. 1 is a schematic diagram showing the configuration of the displacement sensor 100. As shown in FIG. 1, the displacement sensor 100 according to the present embodiment includes a coil 10, a moving body 20, a soft magnetic body 30, a power supply unit 40, a detection element 50, a stroke amount calculation unit 60, and functional units of a yoke 70. It is configured with. The stroke amount calculation unit 60 uses the CPU as a core member, and the above-described functional units for performing various processes for detecting the displacement amount related to the stroke of the moving body 20 are constructed by hardware and / or software.

  The coil 10 is formed in a cylindrical shape by winding the windings forming the coil 10 at a predetermined pitch like a so-called air-core coil. In the present embodiment, the winding pitch is formed so as to gradually narrow from one end of the coil 10 in the axial direction toward the other end. The pitch of the winding is an interval between windings adjacent to each other along the axial direction when the direction in which the cylindrical axis extends is the axial direction. Further, one axial end portion of the coil 10 corresponds to one axial end portion in a cylindrical shape, and in FIG. 1 corresponds to the end portion 10A side. The other end portion of the coil 10 corresponds to an end portion on the opposite side along the axial direction with respect to the end portion on one side in the axial direction described above, and corresponds to the end portion 10B side in FIG. Therefore, as shown in FIG. 1, the coil 10 according to the present embodiment has a shape in which the spring is extended near the end portion 10A and a shape in which the spring is contracted on the side close to the end portion 10B. The

  The soft magnetic body 30 moves in a stroke within the coil 10 in conjunction with the moving body 20. The moving body 20 corresponds to a detection target of the displacement sensor 100. The inside of the coil 10 is the radially inner side of the coil 10 formed in a cylindrical shape. In the present embodiment, the soft magnetic body 30 moves in a stroke along the axial direction of the coil 10. Therefore, the soft magnetic body 30 is provided on the radially inner side of the coil 10 so as to be relatively movable along the axial direction. Such a soft magnetic body 30 is provided so as to extend along the axial direction of the coil 10.

  Although details will be described later, the soft magnetic body 30 functions to change a magnetic field generated when the coil 10 is energized. Such a soft magnetic body 30 moves in a radial direction inside the coil 10 in conjunction with the moving body 20. In FIG. 1, the moving body 20 is integrated with the soft magnetic body 30 and moves in a stroke within the coil 10. However, the soft magnetic body 30 may move in a stroke in conjunction with the moving body 20, and the moving body may be moved by a mechanism such as a link. It is only necessary that the movement of 20 can be converted into the stroke movement of the soft magnetic body 30, and the movement of the moving body 20 is not limited to the stroke movement. As the soft magnetic body 30, it is preferable to use ferrite, soft iron, silicon steel, permalloy, sendust, permendur, or the like.

  The power supply unit 40 energizes the coil 10. In the present embodiment, the power supply unit 40 is constituted by a DC power supply. Therefore, a direct current from the power supply unit 40 is supplied to the coil 10, and a magnetic field corresponding to the direct current is generated from the coil 10.

  The detection element 50 is disposed outside the coil 10 in the radial direction so that the detection direction is along the axial direction of the coil 10, and detects the strength of the magnetic field around the coil 10. The radially outer side of the coil 10 is the radially outer side of the cylindrical coil 10. When a current flows through the cylindrical coil 10, a magnetic field is generated according to the magnitude of the current. Also in FIG. 1, a magnetic field is generated according to the direction of the energized current. The magnetic flux forming such a magnetic field is such that it returns from the one side in the cylindrical axial direction to the other side through the radially outer side. The detection element 50 is arranged so that the detection direction coincides with the direction of the magnetic field. Thereby, it is possible to effectively detect the strength of the magnetic field formed on the radially outer side of the coil 10.

  In the present embodiment, the detection element 50 is disposed on the side of the axial end where the winding pitch of the coil 10 is reduced.

  In the present embodiment, the detection element 50 has the yokes 70 arranged on both sides along the axial direction of the coil 10. Such a yoke 70 is preferably configured using a soft magnetic material. As a result, the magnetic field outside the coil 10 in the radial direction can be collected by the yoke 70, and the magnetic field thus collected can be input to the detection element 50, so that the detection sensitivity of the detection element 50 can be increased. . The detection result of such a detection element 50 is shown in FIG.

  In FIG. 2, the vertical axis represents the strength of the magnetic field, and the horizontal axis represents the stroke amount. Here, the strength of the magnetic field from the winding of the coil 10 depends on the magnitude of the current flowing through the coil 10 (winding). On the other hand, the soft magnetic body 30 provided on the radially inner side of the coil 10 is magnetized by such a magnetic field. Thereby, magnetic poles appear on both sides in the axial direction of the soft magnetic body 30 along the cylindrical axial direction, and a magnetic field is further generated by the magnetic poles. Since the magnetic field distribution by the magnetized soft magnetic body 30 varies depending on the stroke position of the soft magnetic body 30, the magnetic field penetrating the detection element 50 also varies depending on the position of the soft magnetic body, and the soft magnetic body 30 is closer to the detection element 50. Sometimes a strong magnetic field penetrates the detection element 50 when it is far away.

  On the other hand, the soft magnetic body 30 moves together with the moving body 20 along the radial direction of the coil 10 wound so that the pitch gradually increases from the end portion 10B toward the end portion 10A. The magnetization of the soft magnetic body 30 corresponds to the strength of the magnetic field where the soft magnetic body 30 is placed. Therefore, when the pitch is narrow, the magnetization of the soft magnetic body 30 becomes strong, and the magnetic field from the soft magnetic body 30 also becomes strong. On the other hand, when the pitch is wide, the magnetization of the soft magnetic body 30 is weakened, and the magnetic field from the soft magnetic body 30 is also weakened. Therefore, as shown in FIG. 2, the detection result (magnetic field strength) of the detection element 50 changes according to the stroke amount. The detection result of such a detection element 50 is output to a stroke amount calculation unit 60 described later.

  The stroke amount calculation unit 60 calculates the stroke amount of the moving body 20 based on the detection result of the detection element 50. For example, the stroke amount calculation unit 60 uses the strength of the magnetic field when the moving body 20 is not moving as a reference, and calculates the difference between the strength of the magnetic field that is the reference and the strength of the magnetic field obtained from the detection element 50. It is also possible to calculate and calculate the stroke amount. Alternatively, a map that defines the relationship between the stroke amount of the moving body 20 and the strength of the magnetic field is stored in advance, and the stroke amount is calculated by fitting the strength of the magnetic field obtained from the detection element 50 to the map. It is also possible to configure.

2. Second Embodiment Next, a second embodiment according to the present invention will be described. In the said 1st Embodiment, although the coil 10 was one, it differs from 1st Embodiment by the point by which the two coils 10 which concern on this embodiment are provided. Hereinafter, different points will be mainly described. FIG. 3 is a schematic diagram illustrating a configuration of the displacement sensor 100 according to the present embodiment.

  As shown in FIG. 3, the displacement sensor 100 according to the present embodiment includes a first coil 71 and a second coil 72. The first coil 71 corresponds to the coil 10 according to the first embodiment. Accordingly, the first coil 71 is formed in a cylindrical shape, and is formed so that the pitch of the winding gradually becomes narrower from the one end portion 10A in the axial direction toward the other end portion 10B.

  On the other hand, the second coil 72 is wound in such a manner that the winding pitch gradually increases from one end portion 10A to the other end portion 10B, and is formed into a cylindrical shape. Therefore, the second coil 72 and the first coil 71 are formed so that the density of the winding pitch at each end is different from each other. Similarly to the first coil 71, the second coil 72 is also configured in a cylindrical shape. The second coil 72 is provided coaxially with the first coil 71 and so as to overlap each other in the axial direction.

  Further, the currents that flow through the first coil 71 and the second coil 72 are such that the magnetic fields generated when the currents flow are in different directions in the first coil 71 and the second coil 72, respectively. Is energized. Such a magnetic field is preferably canceled out in the radial direction outside of the first coil 71 and the second coil 72 at the center position between the one end 10A and the other end 10B. In the present embodiment, the currents flowing through the first coil 71 and the second coil 72 are always set to have the same magnitude. Thereby, the linearity of the characteristic which prescribes | regulates the relationship between the strength of an electric field and stroke amount can be improved. Therefore, robustness can be improved.

  In the example of FIG. 3, the detection element 50 is shown to be arranged on the outer side in the radial direction of the first coil 71 and the second coil 72 and in the central portion in the axial direction. This is merely an example, and the detection element 50 can be disposed at any position along the axial direction as long as it is radially outside the first coil 71 and the second coil 72.

3. Third Embodiment Next, a third embodiment according to the present invention will be described. In the second embodiment, the first coil 71 and the second coil 72 are provided, and the power supply unit 40 always supplies the same current so that the directions of the magnetic fields generated when the current flows are different from each other. It has been described that power is supplied and the stroke amount calculation unit 60 calculates the stroke amount according to the detection result of the detection element 50. The power supply unit 40 in the present embodiment is different from the second embodiment in that the current of the same magnitude does not always flow through the first coil 71 and the second coil 72. Hereinafter, different points will be mainly described. FIG. 4 is a schematic diagram illustrating a configuration of the displacement sensor 100 according to the present embodiment.

  As shown in FIG. 4, the displacement sensor 100 according to the present embodiment includes a first coil 71 and a second coil 72. Also in the present embodiment, as in the second embodiment, the first coil 71 is configured in a cylindrical shape, and the winding pitch gradually increases from one end 10A in the axial direction toward the other end 10B. It is formed to be narrow.

  In the present embodiment, the detection result of the detection element 50 is transmitted to the power supply unit 40. The power supply unit 40 energizes each of the first coil 71 and the second coil 72 so that the directions of magnetic fields generated when current flows are opposite to each other. In addition, the power supply unit 40 includes the first coil 71 so that the strength of the magnetic field at the position where the detection element 50 is disposed becomes zero regardless of whether the moving body 20 and the soft magnetic body 30 have moved by a stroke. And the current of the second coil 72 are adjusted. Specifically, the power supply unit 40 adjusts the currents of the first coil 71 and the second coil 72 so that the detection result detected by the detection element 50 becomes zero. The value of the current adjusted by the power supply unit 40 is transmitted to the stroke amount calculation unit 60.

  The stroke amount calculation unit 60 calculates the stroke amounts of the moving body 20 and the soft magnetic body 30 based on the ratio of the currents flowing through the first coil 71 and the second coil 72 transmitted from the power supply unit 40. To do. Such calculation is based on, for example, the ratio of the current when the moving body 20 is not moving in a stroke, and the ratio of the reference current and the ratio obtained from the value of the current transmitted from the power supply unit 40. It is also possible to calculate the stroke and calculate the stroke amount. Alternatively, a map that defines the relationship between the current ratio and the stroke amount is stored in advance, and the stroke amount is calculated by fitting the ratio calculated by the current transmitted from the power supply unit 40 to the map. Is also possible.

4). Other Embodiments In the above embodiment, the coil 10 is formed such that the pitch of the windings forming the coil 10 is gradually narrowed from one end 10A in the axial direction of the coil 10 toward the other end 10B. It was explained as being. However, the scope of application of the present invention is not limited to this. The coil 10 can naturally be formed so that the pitch of the windings forming the coil 10 is uniform along the axial direction.

  In the above-described embodiment, the detection element 50 has been described as being disposed on the side of the axial end where the winding pitch of the coil 10 is reduced. However, the scope of application of the present invention is not limited to this. The detection element 50 can be arranged on the side of the end portion in the axial direction where the pitch of the winding of the coil 10 is widened, and is arranged on the outer side in the radial direction of the coil 10 regardless of the pitch of the winding of the coil 10. Of course it is also possible.

  In the above embodiment, the second coil 72 has been described as being provided coaxially with the first coil 71 and so as to overlap each other in the axial direction. However, the scope of application of the present invention is not limited to this. It is also possible to provide the first coil 71 and the second coil 72 on different axes.

  In the above embodiment, the first coil 71 and the second coil 72 have been described as being energized so that the directions of the magnetic fields generated when energized are opposite to each other. However, the scope of application of the present invention is not limited to this. When the winding directions of the first coil 71 and the second coil 72 are made different from each other, it is naturally possible to make the energization directions the same. Even in such a case, the directions of the magnetic fields generated when energized can be different from each other.

  In the above embodiment, the power supply unit 40 has been described as a DC power supply. However, the scope of application of the present invention is not limited to this. Of course, an AC power source may be used as the power source unit 40.

  In the above embodiment, the detection element 50 has been described on the assumption that the yokes 70 are arranged on both sides along the axial direction of the coil 10. However, the scope of application of the present invention is not limited to this. It is possible to arrange the yoke 70 only on one side of the detection element 50 along the axial direction of the coil 10, and naturally it is possible to adopt a configuration in which the yoke 70 is not arranged.

  In addition, the current flowing through the coil may be a current that changes in a stepped manner having at least a binary value. By using such a current, an output in which the influence of disturbance is reduced can be obtained from the difference in output at different currents. For example, the time for which the current takes a binary value of 0 A and a predetermined direct current and has a periodic rectangular wave shape and maintains a constant current value is set to be longer than the time for which the magnetic field penetrating the detection element changes and stabilizes due to the current change. As a result, an output in which the influence of the disturbance is reduced is obtained from the difference between the output due to the disturbance detected at 0A and the output at the time of energization.

  The present invention can be used in a displacement sensor that detects the amount of displacement of a moving body that moves in a stroke.

10: Coil 10A: One axial end 10B: The other end (the other axial end)
20: moving body 30: magnetic body 40: power supply unit 50: detection element 60: stroke amount calculation unit 70: yoke 71: first coil 72: second coil 100: displacement sensor

Claims (6)

A cylindrical coil;
A moving body that is a displacement detection target and is displaced on a straight line or a curve;
A soft magnetic body that moves in a stroke in the coil in conjunction with the displacement of the moving body;
A power supply for energizing the coil;
A detection element that is arranged on the outer side in the radial direction of the coil so that the detection direction is along the axial direction of the coil, and detects the strength of the magnetic field around the coil;
Based on the detection result of the detection element, a stroke amount calculation unit for calculating the displacement amount of the moving body;
A displacement sensor comprising:   2. The displacement sensor according to claim 1, wherein the coil is formed such that a pitch of windings forming the coil is gradually narrowed from one end portion in the axial direction of the coil toward the other end portion.   The displacement sensor according to claim 2, wherein the detection element is disposed on an axial end side where a winding pitch of the coil is narrowed. The coil is a first coil,
A cylindrical second coil formed so that the pitch of the winding gradually increases from one end in the axial direction toward the other end, is coaxial with the first coil, and 4. The displacement sensor according to claim 2, wherein the displacement sensors are provided so as to overlap each other in the axial direction.   The displacement sensor according to claim 1, wherein the power supply unit is a DC power supply.   The displacement sensor according to any one of claims 1 to 5, wherein yokes are arranged on both sides of the detection element along an axial direction of the coil.

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