JP2008232894A - Displacement sensor using helmholtz coil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a great displacement by making a measuring range of a displacement sensor using a Hermholtz coil not limited within a range of a uniform magnetic field of the Helmholtz coil. <P>SOLUTION: This displacement sensor has, as constitutive elements, a set of two air-cored transformers 15a, 15b formed of the Hermholtz coil 10 and a detecting coil 20, a core 30 for detecting a displacement accompanying a shaft 40, and a magnetic shielding body 50 comprising a set of two nonmagnetic metals, an unnecessary magnetic flux is eliminated by the magnetic shielding body 50 to secure a moving space, the core is thereafter displaced in the uniform magnetic field of the Helmholtz coil 10 and across the center axis c1, while bringing the core 30 into a shape of point symmetric to the shaft 40, and is functioned as displaced along the center axis c1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to improvement of Japanese Patent Application Laid-Open No. 2001-66103 “Displacement detector using Helmholtz coil”.

  A Helmholtz coil is made by matching the central axes of two coils of the same shape, facing each other at equal intervals to their radii, and connecting them so that the magnetic fields generated by both coils are added to each other. A portion having a uniform magnetic field strength is generated as a combined magnetic field in the middle portion, which is called an equal magnetic field. Among analog AC / DC electric meters, it is a coil used for measuring voltage, current, and power as a current force meter.

  8 to 11 are explanatory diagrams of JP 2001-66103 A related to the present invention. FIG. 8 is an explanatory diagram showing the principle of the Helmholtz coil. Of the equal magnetic fields generated by the Helmholtz coil, the practical equal magnetic field range (hereinafter simply referred to as the equal magnetic field range) is a flat cylindrical shape. As an image. The range is about 1/3 of the coil diameter (2 × r) in the radial direction of the coil on the central axis cl of the Helmholtz coil, and about 1/3 of the coil interval d in the axial direction (direction along the magnetic field). Occupies a flat cylindrical space. The term “degree” is used here because it depends on how precise the range of the equal magnetic field is defined.

  FIG. 9 is a graph showing the magnetic field generated by the Helmholtz coil, including the magnetic field h generated by each coil. The X axis is a displacement and the Helmholtz coil radius r is 1, and the Y axis is a magnetic field strength and the maximum value of the magnetic field strength h generated by each coil is 1. Show. According to such an expression, it is well known that the relative magnetic field strength of the equal magnetic field he that is the combined magnetic field is 1.43. Note that the gradient magnetic field hg indicated by the dotted line is another characteristic of the Helmholtz coil and indicates the difference in the generated magnetic field h of each coil.

  FIG. 10 is a perspective view showing the basic configuration of Japanese Patent Application Laid-Open No. 2001-66103. A displacement detection core 3 is provided through a shaft 4 in an equal magnetic field of the Helmholtz coil 1, and its movement is detected by the detection coil 2. Detected. FIG. 11 is a connection diagram of the Helmholtz coil 1 and the detection coil 2. The black dots in the figure indicate the start of winding of each coil. In the Helmholtz coil 1, the same current flows in the same direction, and each magnetic field is added to the detection coil. 2 represents a state in which each output is subtracted.

  Now, when the core 3 is displaced along the magnetic field in the uniform magnetic field via the shaft 4 in accordance with the displacement dm of the measured object (not shown), the detection coil 2 is caused to eddy by the eddy current effect or magnetic induction effect of the core 3. Generates an AC differential output e1-e2 corresponding to the displacement.

  In this case, if the eddy current effect is used, the core 3 is preferably a non-magnetic metal having a small specific resistance, and the excitation frequency of the Helmholtz coil 1 is set to about several tens kHz or more (referred to as an eddy current mode). If the magnetic induction effect is used, the core 3 is preferably a magnetic metal having a high magnetic permeability, and the excitation frequency is about 10 kHz (referred to as a magnetic induction mode).

  Since the amplitude of the AC differential output e1-e2 thus obtained is proportional to the magnitude of the displacement dm and the phase indicates the direction of the displacement dm, the magnitude of the displacement dm is simply measured with an AC voltmeter. I only know. For this reason, the AC differential outputs e1-e2 know the magnitude and direction of the displacement dm using a signal conditioner incorporating a phase discrimination circuit or the like.

  In addition, in the description of the effect of the invention in Japanese Patent Laid-Open No. 2001-66103, there is a description (page 5, paragraph number 0030, not shown) that the rotation angle can be measured, and the common axis of the Helmholtz coil and the detection coil (In the present invention, it is referred to as “center axis”), it is described that an eccentric core is inserted through a shaft from a perpendicular direction, and the shaft can be rotated to measure an angle. In this case, the movement of the core is decentered (displaced) along the common axis in the uniform magnetic field, that is, along the magnetic field so as to cross the central axis and the equal magnetic field of the Helmholtz coil as in the present invention. Is not displaced.

Since the displacement detector of Japanese Patent Laid-Open No. 2001-66103 is based on such a configuration and action, its measurement range is limited to the range of the equal magnetic field of the Helmholtz coil (in this case, the common axis direction along the magnetic field). Basically, it becomes a small displacement detector. For example, when measuring a small displacement of 1 mm or less, the range of the equal magnetic field is 1 mm, the diameter of the Helmholtz coil is 6 mm (in principle, about 6 times the measurement range is required), and the interval is 3 mm (in principle, the measurement range It is about 3 times necessary), and it does not have a large shape like the coil of the differential transformer including the detection coil, and the response is fast. In addition, when incorporated in another physical quantity sensor as a displacement detector, a smaller displacement measurement may be used, which is advantageous because a shape effect is further exhibited. On the other hand, when measuring displacement of 50 mm, the range of the equal magnetic field is 50 mm, the diameter of the Helmholtz coil is 300 mm, and the interval is 150 mm. Cannot be overcome and is not suitable for measuring large displacements.
JP 2001-66103 A

  The measurement range of the displacement sensor using the Helmholtz coil is not restricted by the range of the equal magnetic field of the Helmholtz coil, and a large displacement can be measured.

  In order to solve this problem, the invention of claim 1 includes a pair of air-core transformers formed by matching the center axes of a Helmholtz coil and a pair of detection coils, and a pair of non-core transformers. As a constituent element, a magnetic shielding body made of magnetic metal and a core for displacement detection in which a pair of two nonmagnetic metal plates that are asymmetric in the longitudinal direction are fixed at point-symmetrical positions on both sides of the shaft, Exciting the Helmholtz coil at a high frequency at which eddy current effects can be expected, eliminating unnecessary magnetic flux by magnetic shielding, and displacing the core so that it crosses the magnetic field in a uniform magnetic field, the point-symmetrical shape of the core To make the core function as if it were displaced along an equal magnetic field so that a pair of differential eddy current effects occur in the core. Combined with differential feeding to air core transformer And a means for solving the problem, will be described below step by step operation thereof.

  For a set of two air-core transformers, the Helmholtz coil specification is first determined, and then the arrangement of the detection coil is determined. At this time, it may be considered almost the same as the design of a general air core transformer for electronic equipment, but the coil positional relationship (up, down, left, right, etc.) and spacing in each air core transformer are related to the coupling coefficient. Pay attention to the symmetry of each pair.

  In Japanese Patent Laid-Open No. 2001-66103, the terms “air core transformer” and “coupling coefficient” are not used, but are used in the present invention. The reason why the “air core” is used while using the displacement detection core is as follows. In a general electronic device transformer, the entire magnetic path is formed of a magnetic core, and the coupling coefficient between the primary and secondary coils is close to 1. In contrast, in the present invention, the entire magnetic path is not formed by a magnetic core, and the coupling coefficient between the Helmholtz coil and the detection coil is smaller than 1. On the contrary, the eddy current effect of the core apparently reduces the coupling coefficient of the coil itself, and it can be seen that AC differential output is obtained by differentially controlling the degree of the reduction. This is because it was thought that it would be useful for the accurate understanding and explanation of the invention to adopt a simple concept.

  Although magnetic shielding is generally considered one of the difficulties, there is a further requirement in the present invention to reduce only the strength without disturbing the magnetic field (flux flow). In view of this, a magnetic shield made of a pair of non-magnetic metals uses a magnetic shield utilizing an eddy current effect in an unequal magnetic field (unnecessary magnetic flux flow) around an equal magnetic field. The principle of magnetic shielding is an application of a phenomenon in which when an unnecessary magnetic flux passes through a magnetic shield, a new magnetic flux is generated in a direction that cancels the original magnetic flux that has passed through due to an eddy current. As a result, even if the core is inserted / removed so as to cross the central axis of the Helmholtz coil, the core can be displaced under the influence of only the equal magnetic field without being exposed to the unequal magnetic field.

  The role of the core in the equal magnetic field is to act so as to generate an AC differential output in the detection coil forming a pair of air core transformers. For that purpose, when the core is displaced so as to cross the magnetic field in the equal magnetic field, it is necessary to behave as if it is displaced along the equal magnetic field. One means is to use two non-magnetic metal plates in the form of elongated arrows, align both ends in a staggered fashion, and attach them to symmetrical positions on both the left and right sides to attach to one axis. It has a simple shape.

  Considering the case where the eddy current effect generated in the core acts differentially on a pair of air core transformers according to the displacement of the object to be measured, it appears that it is closer to the core (in the equal magnetic field) Air core transformer with larger core area) core eddy current increases → magnetic flux cancellation increases → magnetic flux linkage number decreases → apparent coupling coefficient decreases → detection coil output decreases at the same time With an air-core transformer, the core eddy current decreases → magnetic flux cancellation decreases → magnetic flux linkage number increases → apparent coupling coefficient increases → the output of the detection coil increases differentially. Thus, the AC differential output obtained in the detection coil forming the air-core transformer can know the magnitude and direction of the displacement of the measured object using a signal conditioner incorporating a phase discrimination circuit and the like.

  By the means described above, it is released from the restriction due to the range of the equal magnetic field of the Helmholtz coil, and the maximum factor is that the factor that determines the measurement range of the displacement is not the range of the equal magnetic field but the length of the core. It is characterized by.

  The invention of claim 2 for solving this problem solves the problem using the magnetic induction effect instead of the eddy current effect generated in the core. That is, a pair of air core transformers formed by aligning the center axes of the Helmholtz coil and the pair of detection coils, a pair of non-magnetic metal magnetic shields, and one by two Helmetholtz with a low-frequency that is expected to have a magnetic induction effect, with a displacement detection core that is fixed in a point-symmetrical position on both sides of the shaft with a magnetic metal plate that is asymmetric in the longitudinal direction. Exciting the coil, eliminating unnecessary magnetic flux by magnetic shielding, displacing the core across the magnetic field in an equal magnetic field, utilizing a point-symmetric shape of the core, a pair of differential Combines the function of the core as if it were displaced along an equal magnetic field so that a magnetic induction effect occurs, and the differential induction of the core's magnetic induction effect to a pair of air-core transformers. Means for solving problems And which is hereinafter described difference in action between the case of using the eddy current effects of claim 1.

  The eddy current effect of the non-magnetic metal core according to claim 1 acts without disturbing the flow of the surrounding magnetic flux, and the differential output of the detection coil forming the air core transformer apparently decreases closer to the core. Increased on the other. On the other hand, the magnetic induction effect of the magnetic metal core according to claim 2 acts to attract the surrounding magnetic flux (however, the equal magnetic field does not collapse). The air core transformer with the larger core area) increases magnetic induction → increases the number of flux linkages → apparently increases the coupling coefficient → increases the output of the detection coil, and at the same time, the other air core transformer Induction decreases → Magnetic flux linkage number decreases → Apparent coupling coefficient decreases → Differential detection coil output decreases.

  Therefore, when the eddy current effect of claim 1 is used and when the magnetic induction effect of claim 2 is used, the polarity of the AC differential output is reversed, so that a signal conditioner with a built-in phase discrimination circuit or the like is used. Consider in the combination stage.

  In order to solve this problem, the invention of claim 3 is characterized in that, in the configuration of claims 1 and 2, the central axis of the Helmholtz coil is set together with the shape of the core for the purpose of simplifying and downsizing the shape of the displacement detecting core. It is characterized in that the insertion / removal position so as to cross is biased to one of a set of two air core transformers.

  The shape of the core is asymmetric with respect to the longitudinal direction (axial direction), for example, a simple non-magnetic or magnetic metal plate having an elongated arrow shape. The reason why the core has such a shape is that it is displaced to one of a pair of air core transformers and displaced across the magnetic field in a uniform magnetic field. By the way, when the core of this shape is displaced so that it crosses the magnetic field in the middle of an equal magnetic field, the coupling coefficient of the pair of air core transformers appears to be always the same, and the AC differential is applied to the detection coil. No output can be obtained.

  When it is biased to one of a pair of air core transformers and an elongated arrow-shaped non-magnetic or magnetic metal core is inserted into or removed from a uniform magnetic field so as to cross the magnetic field, a nearby air core transformer is coupled. The coefficient changes greatly, and the other coupling coefficient changes small. This bias in the coupling coefficient appears as a fixed output biased as an AC differential output to the detection coil forming the air-core transformer and finally as a DC differential output of the signal conditioner.

  In this state, when the core is displaced so as to cross the magnetic field in an equal magnetic field according to the displacement of the measured object, the measured displacement changes up and down with the biased fixed output as the base point. In a signal conditioner with a built-in phase discriminator, etc., displacement can be measured by correcting the biased fixed output with zero adjustment to simplify and downsize the core.

  The displacement sensor of the present invention uses a Helmholtz coil to measure the displacement while crossing the equal magnetic field by inserting / removing the displacement measurement core into the equal magnetic field from the outside of the equal magnetic field. Compared to the sensor, it is advantageous in the following points.

  Since the Helmholtz coil is used, the number of turns of the coil can be reduced, and a planar coil, a printed wiring coil, an IC coil, etc. can be used. Since the measurement range of the displacement does not depend on the range of the equal magnetic field, the measurement range can be determined by the length of the core, and the coil does not become long like a differential transformer. Since both the eddy current effect and the magnetic induction effect can be used, the selection range of the core shape and material is wide, and no special material is required. Measurements can be made regardless of static or dynamic displacement from millimeter to metric displacement. Since the core can be freely inserted and removed, it can be replaced to change the displacement measurement range. The eddy current effect has other interesting properties. It is a displacement sensor using magnetism, but it can be used even in a static magnetic field where the differential transformer becomes inoperable, and the measurement reaction force is extremely small. Can also be zero. Basically, it has a simple structure mainly composed of a coil with a small number of turns and a core, so there is no zero point variation like a strain gauge using a Wheatstone bridge circuit. In addition, there are advantages such as no contact / abrasion between the coil and the core, resistance to bad environments such as oil and water, and low cost.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  In a displacement sensor using magnetism, the displacement detection core is usually displaced along the magnetic field, so the measurement range cannot avoid the restriction of the magnetic field. On the other hand, in the present invention, the displacement detection core is displaced so as to cross the magnetic field in an equal magnetic field, and the point-symmetric core shape is used as if it were displaced along the central axis. By making it function, the displacement measurement range can be expanded.

  FIG. 1 is a perspective view showing the basic configuration of the present invention, wherein 10 is a Helmholtz coil (d = r where r is a radius and d is a distance), 15a and 15b are a pair of air core transformers, A set of two detection coils, 30 is a core for detecting displacement, 40 is a shaft, and 50 is a set of two magnetic shields made of nonmagnetic metal. dm indicates the displacement of the core 30 according to the displacement of the measured object (not shown).

  The center axes cl of the Helmholtz coil 10 and the detection coil 20 are made to coincide with each other and the two coils are brought close together to form a pair of symmetrical air-core transformers 15a and 15b. At this time, pay attention to the symmetry of each pair. Further, the coupling coefficient may be a bifilar winding in which the wires of both coils are wound at the same time, even if they are wound slightly apart, overlapped, or wound, based on the same idea as an ordinary air core transformer for electronic equipment.

  The range in which the equal magnetic field he of the Helmholtz coil 10 is generated is a flat cylindrical shape having a coil diameter (2 × r) and a distance d of about 1/3 at the central portion on the central axis cl of the Helmholtz coil 10. ing. In the vicinity of the equal magnetic field he, the intensity of the magnetic field is reduced and the magnetic field becomes unequal as it goes in any direction, and naturally, unnecessary magnetic flux exists (see FIG. 8 for explaining the background art). Image, see graph in FIG. 9).

  In order to eliminate the unnecessary magnetic flux and allow the displacement detection core 30 to be displaced only under the influence of the equal magnetic field he, the magnetic shield 50 is emptied from the direction crossing the central axis cl of the Helmholtz coil 10. Between the core transformers 15a and 15b, a magnetic shield is provided by passing through the central axis cl. At this time, the direction crossing the central axis cl is basically a perpendicular direction, but a slight inclination is not a problem.

  The magnetic shielding effect by the eddy current becomes more effective when the Helmholtz coil 10 is excited by using a nonmagnetic metal having as small a specific resistance as possible to form the magnetic shielding body 50 and using a frequency as high as possible. For this reason, it is preferable that the magnetic shield 50 be made of copper, aluminum, or the like, and the excitation frequency of the Helmholtz coil 10 be about several tens kHz or higher. The same can be said for the eddy current effect of the core 30. Although the operation is possible even at a low excitation frequency lower than around several tens of kHz, the eddy current effect tends to decrease.

  Thus, a magnetic shielding space of the displacement detection core 30 that can be inserted into and removed from the equal magnetic field he together with the shaft 40 is ensured. However, unlike the magnetic shielding using a ferromagnetic material, the flow of the surrounding magnetic flux does not change. It can be said that it is a magnetic shielding according to the invention.

  On the other hand, the shape of the core 30 is important in conjunction with the displacement so as to cross the magnetic field in the equal magnetic field he. After using a non-magnetic metal, such as copper or aluminum, to align both ends alternately using a pair of arrow-shaped metal plates, the symmetrical shape on the left and right sides of the shaft 40 as shown in FIG. It is attached at a certain position and has a point-symmetric shape. At this time, the interval between the pair of metal plates may be appropriately determined in the equal magnetic field he.

  When the core 30 is displaced with the shaft 40 in the equal magnetic field he and across the central axis cl, the core 30 is not displaced in the direction of the central axis cl, but functions as if it is displaced along the central axis cl. Show. That is, assuming that the core 30 is present in the equal magnetic field he, and there is a difference in the area occupied by the two point-symmetric non-magnetic metal plates in the equal magnetic field he, There are many eddy currents, canceling out many magnetic fluxes, the number of magnetic flux linkages of the detection coil 20 decreases, and the output decreases. The output of the detection coil 20 having the larger area of the metal plate is assumed to be e2.

  At the same time, the non-magnetic metal plate having the smaller area has less eddy current, less magnetic flux cancellation, increases the number of flux linkages of the detection coil 20, and increases its output. If the output of the detection coil 20 having the smaller metal plate area is assumed to be e1, an AC differential output e1-e2 is obtained. A series of these operations are repeated without interruption along with the displacement dm of the object to be measured, which is the function that characterizes the present invention most.

  Here, consider a case where only the core 30 is changed from a non-magnetic metal to a magnetic metal. The magnetic field generated by the Helmholtz coil 10 is attracted to the core 30 as in the case of the differential transformer, and the core 30 is displaced while attracting the surrounding magnetic flux. For this reason, if there is a difference in area between the two magnetic metal plates in the core 30 remaining in the equal magnetic field he, a large amount of magnetic flux is attracted to the larger magnetic metal plate, and the detection coil 20 The number of flux linkages increases and the output increases. This is assumed to be e2. At the same time, the magnetic metal plate having the smaller area has less magnetic flux attraction, the number of magnetic flux linkages of the detection coil 20 is reduced, and the output is reduced. If this is assumed to be e1, an AC differential output e2-e1 is obtained. It is done.

  Therefore, when the core 30 is made of a non-magnetic metal and a magnetic metal, the polarity of the AC differential output e1-e2 with respect to the displacement dm is reversed. Therefore, the signal conditioner 70 incorporating the phase discriminating circuit 71 and the like. It is necessary to consider at the combination stage. Normally, regardless of the material of the core 30, if the rightward displacement dm is determined to be positive and the leftward displacement dm is determined to be negative, the polarity of the DC differential output Eo of the signal conditioner 70 is adjusted to that.

   FIG. 2 is a perspective view in which the shape of the magnetic shield 50 of FIG. 1 is changed, and is a magnetic shield 50a having a pair of discs. The structure is simplified, multifunctional, and cost-reduced. Etc. can be selected according to the purpose.

  By simplifying the structure, it is easy to integrate the Helmholtz coil 10, the detection coil 20, and the magnetic shield 50a, and the movement space of the core 30 is released, so that the degree of design freedom is also increased. In addition, the core 30 may be a functional type that uses a curve in whole or in part, that is, the AC differential output e1-e2 with respect to the displacement may have a fixed functional relationship, or non-linearity may be improved. It becomes easy to realize multi-functionality such as preparing and replacing only a few of 30. In order to make FIG. 2 easier to understand, the magnetic shield 50a is highlighted with a larger hole diameter, a smaller outer diameter, and a wider interval than the actual shape.

   FIG. 3 is a connection diagram of the Helmholtz coil 10 and the detection coil 20. The black dots attached to the coils in the figure indicate the beginning of winding of the coils. When the excitation voltage ev is applied to the Helmholtz coil 10, the same current flows in the two coils in the same direction, and the generated magnetic field is added. This shows that an equal magnetic field he is obtained. If one of the Helmholtz coils 10 is connected in reverse polarity, the Helmholtz coil is reversely connected to obtain a gradient magnetic field hg as shown in FIG. However, this will be separately described later. On the other hand, the detection coil 20 represents that the outputs of the two coils are subtracted to become an AC differential output e1-e2. The core 30 and the shaft 40 are shown in a simplified form in consideration of the relationship between the displacement dm and the AC differential output e1-e2.

  FIG. 4 is a partial perspective view of a simplified example of the core 30 of FIGS. 1 and 2 for the purpose of simplifying the structure, reducing the weight, reducing the cost, and the like. A position where the core 30a is displaced to one of the pair of air core transformers 15a and 15b and is displaced across the magnetic field in the equal magnetic field he is shown together with an image of the equal magnetic field he.

  Since the shape of the core 30a is a single long and thin arrow-shaped metal plate that is asymmetric in the axial direction, the core 30a is temporarily in the middle of a uniform magnetic field he having a length s on the central axis cl (point of s1 = s2). Is displaced, the pair of air core transformers 15a and 15b can no longer have a magnetically differential effect, and an AC differential output e1-e2 is obtained at the detection coil 20. Absent.

  Therefore, the core 30a having this shape needs to be displaced to one of a pair of air core transformers and displaced so as to cross the magnetic field in the equal magnetic field he, and the axial length s of the equal magnetic field he. S1 and s2 are appropriately determined as points that divide s1 into s2. That is, one of s1 and s2 is made small and the others are made large so that the core 30a can be inserted / removed close to one end of the equal magnetic field he.

  In this way, when the core 30a is displaced across the magnetic field in the equal magnetic field he near one end of the equal magnetic field he, the coupling coefficient changes greatly in the air core transformer 15a or 15b on the side closer to the core 30a. The other air core transformer 15b or 15a changes slightly. By giving the bias of the coupling coefficient, the displacement dm of the core 30a first produces the AC differential output e1-e2, and the measured displacement dm goes up and down around the bias of the coupling coefficient.

  Further, since the bias of the coupling coefficient appears as a fixed output biased to the AC differential outputs e1-e2 of the detection coil 20, it is combined with the signal conditioner 70 having a built-in phase discriminating circuit 71 and the like to adjust the zero point. Make necessary corrections before use. The core 30a may be made of either a non-magnetic metal or a magnetic metal. However, it should be noted that the polarities of both AC differential outputs e1-e2 are inverted as described above.

  FIG. 5 is a partial perspective view of an example in which the core 30 of FIGS. 1 and 2 is changed to a tape measure, and is an example in which the displacement space of the core 30b itself is changed to be small. That is, since the core 30b has a long and narrow arrow shape and is wound in the case with the entire tape measure (the spring for winding is not shown), it is limited to static displacement measurement, but it is large in a narrow space. Can also handle displacement measurement. The position of the core displaced in the equal magnetic field is the same as that described in FIG.

  FIG. 6 is a block diagram in which a displacement measuring device is configured by combining the displacement sensor 60 of the present invention and the signal conditioner 70. FIG. 7 is a graph showing the AC differential output e1-e2 of the detection coil 20 with respect to the displacement dm, the phase discrimination output Es of the signal conditioner 70, the DC differential output Eo, and the like. The displacement sensor 60 receives the excitation output ev of the oscillation circuit 74 and generates an AC differential output e1-e2 having a displacement magnitude and direction according to the displacement dm of the measured object.

  The AC differential outputs e1-e2 have V-shaped characteristics as shown in FIG. 7, and have the same value as long as the absolute value of the displacement is the same regardless of the direction of the displacement dm. Now, if an AC voltmeter is used to know this value, the magnitude of the displacement is known from the magnitude of the voltage, but the direction of the displacement is unknown, so a function called phase discrimination is necessary. .

  The phase discriminating circuit 71 detects and smoothes the AC differential differential outputs e1-e2, and as the phase discrimination output Es, as shown in FIG. 7, the magnitude of the displacement is a DC voltage and the direction of the displacement is added. Make it possible to identify with a minus sign. Since the phase discrimination output Es has a low voltage level and requires zero point adjustment and sensitivity adjustment, the amplification circuit / output circuit appropriately amplifies and makes necessary adjustments, and finally a DC difference indicating the magnitude and direction of the displacement dm. The dynamic output is Eo.

  The present invention is not limited to the above description, and many changes can be made without departing from the scope of the invention.

  For example, the above-described reversely connected Helmholtz coil can also be applied to the present invention. If one of the Helmholtz coils is reversely connected and the detection coil is reversely connected, displacement measurement can be performed as described above.

  Also, move the point symmetry center of the core to an arbitrary point on or off the axis of the core, use a combination of multiple asymmetric metal plates for the core in the longitudinal direction, and cantilever the axis If there are restrictions on mounting, the shaft should be the central axis of the Helmholtz coil. It is also possible to insert it consciously tilted from the right angle direction.

  Further, the core can be made lighter and more lightweight by making it an elongated right triangle. When the core has such a shape, it becomes easier to insert and remove it into the equal magnetic field with the core surface in the horizontal direction. In addition, it is possible to arbitrarily change the AC differential output with respect to the displacement by providing a hole or notch in a part of the core.

  It is also possible to increase the magnetic shielding effect by configuring the magnetic shielding body with a plurality of different metals.

  In addition, a Helmholtz coil, two detection coils, and two magnetic shields are manufactured as an integral structure on the central axis, and in contrast to the measurement of displacement, they are generated by external electrical signals. A function that generates a certain displacement along the central axis is given in advance so that the measured object is in a stationary state, and the operation inspection and displacement calibration are performed. It is also possible.

It is a perspective view which shows the basic composition of this invention. It is the perspective view which changed the shape of the magnetic shielding body of FIG. It is a connection diagram of a Helmholtz coil and a detection coil. FIG. 3 is a partial perspective view of a simplified example of the core of FIGS. 1 and 2. It is a partial perspective view of the example which made the core of FIG. 1 and FIG. 2 into the tape measure shape. It is the block diagram which comprised the displacement measuring apparatus combining this invention displacement sensor and the signal conditioner. It is a graph which shows the alternating current differential output, direct current differential output, etc. with respect to a displacement. It is explanatory drawing of Unexamined-Japanese-Patent No. 2001-66103 relevant to this invention. It is explanatory drawing of Unexamined-Japanese-Patent No. 2001-66103 relevant to this invention. It is explanatory drawing of Unexamined-Japanese-Patent No. 2001-66103 relevant to this invention. It is explanatory drawing of Unexamined-Japanese-Patent No. 2001-66103 relevant to this invention.

Explanation of symbols

1, 10 Helmholtz coil 2, 20 Detection coil 3, 30, 30a, 30b Core 4, 40, 40a, 40b Shaft 50, 50a Magnetic shield 60 Displacement sensor 70 Signal conditioner 71 Phase discrimination circuit 72 Amplification circuit 73 Output circuit 74 Oscillation circuit 75 Power supply circuit cl Center axis of Helmholtz coil and detection coil d Helmholtz coil interval dm displacement e1, e2 Detection coil output e1-e2 AC differential output ev Excitation voltage Es Phase discrimination output Eo DC differential output he Range of equal magnetic field r Helmholtz coil radius s Axial magnetic field length

Claims (3)

  A Helmholtz coil, a set of two detection coils, a magnetic shield made of a pair of nonmagnetic metals, and a displacement detection core made of a nonmagnetic metal fixed to a shaft, The center axis of the Helmholtz coil and the detection coil are aligned and spaced apart to form a pair of air core transformers, and the magnetic shield passes through the center axis between the air core transformers. Providing a magnetic shielding space in which the core can move, and at the same time, the shape of the core is a pair of metal plates that are asymmetric in the longitudinal direction, and is symmetrical in the axial direction on both sides of the shaft. A displacement sensor that is fixed at a position and can be inserted into and removed from the magnetic shielding space, and that measures displacement using an AC differential output generated in the detection coil by using an eddy current effect of the core.   A Helmholtz coil, a set of two detection coils, a magnetic shield made of a pair of non-magnetic metals, and a displacement detection core made of a magnetic metal fixed to a shaft; A central axis of the coil and the detection coil are aligned and spaced apart to form a pair of air core transformers, and the magnetic shield passes through the central axis between the air core transformers. By providing, a magnetic shielding space in which the core can move is formed, and at the same time, the shape of the core is a set of two metal plates that are asymmetric in the longitudinal direction. A displacement sensor that is fixed to the magnetic shield space so that it can be inserted into and removed from the magnetic shielding space and that measures displacement using an AC differential output generated in the detection coil by using the magnetic induction effect of the core.   The displacement sensor according to claim 1, wherein the core that can be inserted and removed in the magnetic shielding space is provided to be biased to one of a pair of air core transformers as asymmetric in the longitudinal direction.

Images