JP4006919B2 - Permeability measuring device and permeability measuring method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic permeability measuring apparatus and a magnetic permeability measuring method.
[0002]
[Prior art]
For example, Japanese Patent Application Laid-Open No. 3-255380 discloses a device that accurately measures the magnetic permeability of a small component such as a micro shaft of a video tape recorder. As shown in FIG. 12, an exciting coil 92 is wound around the outer periphery of a rod-shaped magnetic core 91 made of a ferromagnetic material having both end surfaces formed into spherical surfaces, and this is connected to an AC power source 93. A pair of detection coils 94A and 94B that constitute a differential coil are wound around the upper and lower positions. As shown in FIG. 12, the end surface of the magnetic core 91 is brought into contact with the material 3 to be measured, and the output signals of the detection coils 94A and 94B at this time are subjected to phase analysis based on the rotation of the reference vector to correspond to the magnetic permeability obtained thereby. The electrical signal to be displayed is displayed. Such a magnetic permeability measuring device can measure the local magnetic permeability of small parts non-destructively by reducing the outer diameter of the magnetic core 91, and can easily know material defects and the like. it can.
[0003]
[Problems to be solved by the invention]
By the way, the magnetic circuit of the conventional apparatus is composed of the magnetic core 91, the material to be measured 3, and the air layer, and the magnetic resistance Rm of the magnetic circuit is expressed by the following equation (1).
[0004]
Rm = L1 / (μ1 · S) + L2 / (μ2 · S) + L3 / (μ3 · S) (1)
[0005]
Here, L1, L2, and L3 are the lengths of the magnetic paths of the magnetic core 91, the material to be measured 3, and the air layer, and μ1, μ2, and μ3 are the magnetic permeability of the magnetic core, the material to be measured, and the air layer, respectively. S is the cross-sectional area of the magnetic path.
[0006]
Here, since the permeability μ3 of the air layer is two orders of magnitude or more smaller than the permeability μ1 and μ2 of the magnetic core 91 and the measured material 3, the magnetic resistance of the magnetic circuit is air in the region where the measured material 3 has a large permeability. The characteristics are saturated by being almost equal to the magnetoresistance of the layer. For this reason, there existed a problem that the measurable range was restricted to the range with a small magnetic permeability.
[0007]
The present invention solves such a problem, and it is possible to easily and accurately measure the magnetic permeability of a small component or the like in a wide range from a small value to a large value by eliminating the influence of the magnetic permeability of an air layer or the like. An object of the present invention is to provide a magnetic permeability measuring device and a magnetic permeability measuring method.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the magnetic permeability measuring apparatus according to the first aspect of the present invention includes a rod-shaped first magnetic core (1A) whose end face is in contact with the material to be measured (3), and a winding around the outer periphery of the first magnetic core. A second magnetic core (1B) having the same shape as the first magnetic core having its end face brought into contact with the rotated first exciting coil (2A) and a reference material (4) having a sufficiently high permeability as compared with the material to be measured ), A second excitation coil (2B) wound around the outer periphery of the second magnetic core, an energization circuit (5A) for energizing the first excitation coil (2A) with a constant voltage, and a second excitation coil (2B) The difference between the second energization circuit (5B) energizing with a constant voltage to the first excitation coil (2A) and the output according to the energization current to the second excitation coil (2B). And an arithmetic circuit (81, 83) for calculating the magnetic permeability of the material to be measured based on the reciprocal of.
[0009]
In the present invention, if the difference in output according to the energization current of the first energization circuit and the second energization circuit is taken, the permeability of the air layer and the magnetic core is canceled in this difference output, so that the air layer has a small permeability. There is no problem that the measurement range of the magnetic permeability of the material to be measured is limited by the influence of the magnetic permeability. Since the magnetic permeability of the reference material is sufficiently larger than the magnetic permeability of the material to be measured, the magnetic permeability of the material to be measured is uniquely determined as a value proportional to the reciprocal of the difference current. Furthermore, it is possible to measure the local permeability of small parts by reducing the outer diameter of the magnetic core, and only the exciting coil needs to be wound around the magnetic core. The overall structure is simplified.
[0010]
The first invention can also be realized as a measurement method having the following configuration. That is, in the magnetic permeability measuring method of the present invention, the end surface of the rod-shaped magnetic core (1A) wound with the exciting coil (2A) is contacted with the material to be measured (3) and the exciting coil (2B) is disposed on the outer periphery. The end face of another rod-shaped magnetic core (1B) of the same shape as that of the magnetic core (1A) wound around is brought into contact with a reference material (4) having a sufficiently high permeability as compared with the measured material (3). Then, AC excitation is performed on each of the exciting coils (2A, 2B) at a constant voltage, and the permeability of the material to be measured (3) is calculated from the reciprocal of the difference between the energization currents at this time.
[0011]
The magnetic permeability measuring apparatus according to the second aspect of the present invention includes a rod-shaped first magnetic core (1A), a first excitation coil (2A) wound around the outer periphery of the first magnetic core (1A), and a first excitation coil. A first energizing circuit (5A) for energizing AC at a constant voltage to (2A), and a reference material (4) having a sufficiently large permeability at the end face of the first magnetic core (1A) compared to the material to be measured (3) A pseudo output generating circuit (85) for generating an output corresponding to an energization current when the first energizing coil (2A) is AC-energized by the first energizing circuit (5A) and the first magnetic core (1A) The output corresponding to the energization current and the output of the pseudo output generation circuit (85) when the first energization circuit (5A) is energized to the first excitation coil (2A) with the end face in contact with the material to be measured (3) An arithmetic circuit (81, 83) for calculating the magnetic permeability of the material to be measured (3) based on the reciprocal of the difference between It is provided.
[0012]
In the second aspect of the invention, in addition to the effect of the first aspect of the invention, the provision of the pseudo output generation circuit eliminates the need to provide the reference material in the measuring apparatus, thereby simplifying the apparatus configuration.
[0013]
In the third aspect of the invention, the pseudo output generating circuit (85) in the second aspect of the invention is wound around the outer periphery of the rod-shaped second magnetic core (1B) having the same shape as the first magnetic core (1A). A second energization circuit (5B) for energizing with a constant voltage is connected to the second excitation coil (2B).
[0014]
In the third invention, by providing a circuit similar to the first magnetic core side on the input side of the pseudo output generation circuit, the first excitation accompanying the temperature change when the subsequent differential output is taken. Coil impedance fluctuations, drift fluctuations in the first energization circuit, etc. can be offset and compensated.
[0015]
In addition, this 2nd invention is realizable also as a measuring method which has the following structures. That is, in the magnetic permeability measurement method of the present invention, the end surface of the rod-shaped magnetic core (1A) in which the excitation coil (2A) is wound around the outer periphery is a reference having a sufficiently large magnetic permeability as compared with the measured material (3). The pseudo output generation circuit (85) generates an output corresponding to an energization current when the material is in contact with the material (4) and AC current is applied to the excitation coil (2A) at a constant voltage, and the magnetic core (1A) is connected to the material to be measured. The excitation coil (2A) is contacted with AC at a constant voltage in contact with (3), and the material to be measured (3) is obtained from the reciprocal of the difference between the output corresponding to the energized current and the output of the pseudo output generation circuit (85). ) Is calculated. Also, means (9, 86, 87) for detecting the inclination of the magnetic core (1A) from the vertical direction and correcting the output current of the exciting coil (2A) can be provided.
[0016]
The reference numerals in the parentheses indicate the correspondence with specific means described in the embodiments described later.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
In FIG. 1, the whole structure of the magnetic permeability measuring apparatus of this invention is shown. In the figure, a magnetic core 1A made of a round bar-shaped permalloy or the like whose upper and lower end surfaces are spherical surfaces is provided, and its lower end portion 11 is in contact with the surface of the material 3 to be measured whose magnetic permeability is to be measured. An example of the material to be measured 3 is a carbon steel material. An excitation coil 2A is wound around the outer periphery of the magnetic core 1A, for example, 160 times, and this excitation coil 2A is connected to a constant voltage AC power source (for example, 1 KHz) 6 by an energization circuit 5A. The energization circuit 5A is provided with a current-voltage converter 7A that generates a voltage corresponding to the energization current flowing therethrough. On the other hand, a reference material 4 having a sufficiently large permeability compared to the expected permeability of the material 3 to be measured is provided, and an excitation coil 2B having the same structure as described above is provided on the surface thereof. The lower end 11 of the wound magnetic core 1B is in contact. Examples of the reference material 4 include ferrite and permalloy. The exciting coil 2B is connected to the AC power source 6 by an energizing circuit 5B, and the energizing circuit 5B is provided with a current-voltage converter 7B.
[0018]
As shown in FIG. 2, the magnetic cores 1A and 1B are actually housed in a cylindrical sensor case 12 that exposes only the lower end portion 11 and opens downward, and the sensor case 12 opens downward. It is stored in a cylindrical holder 13. A coil spring 14 is disposed between the top wall of the sensor case 12 and the top wall of the holder 13, and urges the sensor case 12 in a direction protruding from the holder 13. With this structure, as shown in FIG. 2, when the opening end surface 131 of the holder 13 is brought into contact with the surface of the material to be measured 3 or the reference material 4, the magnetic cores 1 </ b> A and 1 </ b> B The vertical posture is maintained with respect to the surface, and the lower end surface thereof is brought into contact with the surface of the material to be measured 3 or the reference material 4 with a constant force by a spring force. As a result, during the measurement of the magnetic permeability, stable measurement can be performed without causing a change in the posture of the magnetic cores 1A and 1B with respect to the measured material 3 and the like and a change in contact pressure.
[0019]
In FIG. 1, the outputs of the current-voltage converters 7A and 7B are input to a differential amplifier 81, and a difference ΔI between energization currents Ia and Ib flowing in both energization circuits 5A and 5B is obtained. The current difference signal is input to the next stage AC-DC converter 82 to be converted into a DC voltage signal, and then input to the reciprocal calculator 83 to output a signal corresponding to the reciprocal of the current difference (1 / ΔI). The A signal corresponding to the reciprocal of the current difference (1 / ΔI) is proportional to the magnetic permeability μ 2 of the material 3 to be measured as will be described later, and is measured on the display 84 by multiplying by a predetermined coefficient. The magnetic permeability μ2 of the material 3 is displayed.
[0020]
In the magnetic permeability measuring apparatus having the above-described configuration, the magnetic circuit formed by the magnetic core 1A and the material to be measured 3 can be expressed by a model as shown in FIG. Rm is represented by the above equation (1) as described in the prior art. When an energizing current Ia having a frequency f is passed through the exciting coil 2A having N turns, the voltage V across the exciting coil 2A (that is, the voltage of the AC power supply 6) is expressed by the following equation (2).
[0021]
V = 2π · f · N ² · Ia / Rm (2)
[0022]
Therefore, the conduction current Ia is expressed by the equation (3) from the equations (1) and (2).
[0023]
Ia = (V / 2π · f · N ² ) {(L1 / (μ1 · S) + L2 / (μ2 · S) + L3 / (μ3 · S)}} (3)
[0024]
On the other hand, the energization current Ib to the exciting coil 2B (the number of turns N) of the magnetic core 1B brought into contact with the reference material 4 having a magnetic permeability μ4 is expressed by the following equation (4) by the same relationship as described above.
[0025]
Ib = (V / 2π · f · N ² ) {(L1 / (μ1 · S) + L2 / (μ4 · S) + L3 / (μ3 · S)}} (4)
[0026]
When the difference ΔI of the energizing current is obtained by the differential amplifier 81, it is as shown in Equation (5), and since μ2 << μ4 as described above, the reciprocal calculator 83 calculates the reciprocal of ΔI (1 / ΔI). Then, this becomes proportional to the magnetic permeability μ 2 of the material 3 to be measured, as shown in Expression (6). Therefore, the permeability μ 2 of the material to be measured 3 can be obtained by multiplying the reciprocal of the difference current (1 / ΔI) by an appropriate coefficient.
[0027]
ΔI = Ia−Ib = (V · L 2) (1 / μ 2 −1 / μ 4) / (2π · f · N ² · S) (5)
[0028]
μ 2 = {(V · L 2) / (2π · f · N ² · S)} · (1 / ΔI) (6)
[0029]
FIG. 4 shows the relationship between the relative permeability of the material 3 to be measured and the output of the reciprocal calculator 83. As is apparent from the figure, since the measurement apparatus of the present embodiment eliminates the influence of the permeability of the air layer R and the magnetic cores 1A and 1B, the output of the reciprocal calculator 83 is to some extent as the permeability increases. Shows a tendency of saturation, but the magnetic permeability of the material to be measured can be accurately measured without causing saturation in the output in a wide range from a small magnetic permeability to a large magnetic permeability as compared with the conventional apparatus. In the measuring apparatus of the present embodiment, the local permeability of a small component can be measured by reducing the outer diameter of the magnetic cores 1A and 1B, and the detection coil is wound around the magnetic core as in the past. There is no need to do this, and only the exciting coil needs to be wound, so that the structure of the entire measuring unit including the magnetic core is simplified.
[0030]
(Second Embodiment)
In the present embodiment, the configuration of a magnetic permeability measuring apparatus that does not require the reference material 4 in the apparatus as in the first embodiment will be described. That is, in FIG. 5, unlike the first embodiment, the magnetic core 1 </ b> B is entirely disposed in the air without the lower end portion 11 being brought into contact with the surface of the reference material 4. Then, a pseudo output generation circuit 85 is provided after the current-voltage converter 7B provided in the energization circuit 5B for energizing the magnetic core 1B, and its output is input to the differential amplifier 81, where the energization circuit 5A The difference from the output of the provided current-voltage converter 7A is calculated. The pseudo output generation circuit 85 can arbitrarily change the amplitude and phase of the AC signal input thereto, and the other device configuration is the same as that of the first embodiment.
[0031]
In the magnetic permeability measuring apparatus having such a configuration, prior to measuring the magnetic permeability of the material 3 to be measured, the lower end 11 of the magnetic core 1A is brought into contact with the reference material 4 as shown in FIG. The amplitude and phase of the output of the pseudo output generation circuit 85 are adjusted so that the output of the differential amplifier 81 becomes zero. In this case, the current flowing through the energizing circuit 5A is Ib equal to the current flowing through the energizing circuit 5B in the first embodiment, and the output of the current-voltage converter 7A corresponds to the current Ib. Therefore, the output of the pseudo output generation circuit 85 is equal to the voltage output corresponding to the current Ib flowing through the energization circuit 5B when the lower end portion 11 of the magnetic core 1B is brought into contact with the reference material 4.
[0032]
After setting the output of the pseudo output generating circuit 85 as described above, the lower end 11 of the magnetic core 1A is brought into contact with the surface of the material 3 to be measured as shown in FIG. By comparing the output of the current-voltage converter 7A corresponding to the output of the pseudo output generation circuit 85 with the differential amplifier 81, the magnetic core brought into contact with the material to be measured 3 as in the first embodiment. A current difference signal ΔI between the current Ia flowing through the exciting coil 2A of 1A and the current Ib flowing through the exciting coil 2B of the magnetic core 1B virtually brought into contact with the reference material 4 is obtained. Hereinafter, the same as in the first embodiment Thus, the magnetic permeability μ 2 of the measured material 3 can be obtained from the reciprocal of the current difference (1 / ΔI). In the present embodiment, since the pseudo output generation circuit is provided and the output is set to the output corresponding to the reference material contact as described above, it is not necessary to provide the reference material 3 in the measuring device, and the device configuration is simplified. Is done.
[0033]
(Third embodiment)
In the second embodiment, the reason for providing the magnetic core 1B that does not actually contact the reference material 4 and the material 3 to be measured, the energizing circuit 2B, and the current-voltage converter 7B is as follows. This is because the differential amplifier 81 cancels and compensates for the impedance fluctuation of the exciting coil 2A and the drift fluctuation of the current-voltage converter 7A due to the temperature change by providing a circuit similar to the above-mentioned side.
[0034]
Therefore, when the impedance fluctuation or drift fluctuation is not so much of a problem, the pseudo output generation circuit 85 is directly connected to the power source 6 as shown in FIG. 7, and the magnetic core 1B and the energization circuit 5B in the second embodiment are connected. And the current-voltage converter 7B can be omitted. Thereby, the apparatus configuration can be further greatly simplified.
[0035]
(Fourth embodiment)
In the first embodiment, the holder 12 and the sensor case 13 are used so that the lower end 11 of the magnetic core 1A is brought into contact with the surface of the material 3 to be measured in a vertical posture, but the posture of the magnetic core 1A is inclined from the vertical. FIG. 8 shows a configuration in which the output of the reciprocal calculator 83 is corrected to minimize the occurrence of errors in the case where the error occurs.
[0036]
In FIG. 8, a tilt sensor 9 is provided in the magnetic core 1 </ b> A in which the lower end portion 11 is brought into contact with the material to be measured 3, and the output thereof is input to the tilt measuring circuit 86. The output of the inclination measuring circuit 86 is input to a sensitivity correction circuit 87 provided at the subsequent stage of the reciprocal calculator 83, where the output of the reciprocal calculator 83 is described later according to the degree of inclination of the magnetic core 1A. It is corrected. Other configurations are the same as those of the first embodiment already described.
[0037]
As shown in FIG. 9, the tilt sensor 9 is provided with Hall elements 91 at four circumferential positions at equal intervals in the outer periphery of the magnetic core 1 </ b> A. The magnetic flux that passes through the outer periphery of the magnetic core 1 </ b> A in the radial direction by these Hall elements 91. Density is measured. As shown in FIG. 10, the inclination measuring circuit 86 calculates the difference (B1−B2) (B3−B4) between the magnetic flux density outputs B1 to B4 of the Hall elements 91 provided at the opposing positions, and based on these, The magnetic flux density difference Bx and the magnetic flux density difference By in the y direction perpendicular to the x direction are obtained, and the mean square value of the magnetic flux density differences Bx and By is calculated. Since the mean square value θv is proportional to the inclination angle of the magnetic core 1A from the vertical line, the output of the reciprocal calculator 83 is corrected by inputting this to the sensitivity correction circuit 87. An example is shown in FIG. When the magnetic core 1A is held in a vertical posture, the output characteristic of the reciprocal calculator 83 with respect to the relative permeability of the material 3 to be measured is indicated by a line x, whereas the inclination angle of the magnetic core 1A is At 10 °, the output characteristic becomes a small value as a whole as shown by the line y. Therefore, by multiplying the output of the reciprocal computing unit 83 at this time by a predetermined constant according to the tilt angle of the magnetic core 1A, the output characteristic of the reciprocal computing unit 83 shown by the line y is substantially linear as shown by the line z. It is corrected to a characteristic along the output characteristic indicated by x.
[0038]
In the second embodiment and the third embodiment, the reference material 4 is actually brought into contact with the magnetic core 2A, and in this state, the output of the pseudo output generation circuit 85 is set so that the output of the differential amplifier 81 becomes zero. If the output is adjusted, but the output of the current-voltage converter 7A when the reference material 4 is brought into contact with the magnetic core 2A can be predicted, the predicted value is directly output directly without using the reference material 4 at all. The generation circuit 85 may be set. Various modifications can be made without departing from the spirit of the present invention.
[0039]
【The invention's effect】
As described above, according to the magnetic permeability measuring apparatus and the magnetic permeability measuring method of the present invention, the magnetic permeability of small parts and the like can be reduced over a wide range from a small value to a large value by eliminating the influence of the magnetic permeability of the air layer or the like. Simple and accurate measurement is possible.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of a magnetic permeability measuring apparatus according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of a magnetic core holder.
FIG. 3 is a model diagram showing a magnetic circuit of a magnetic core.
FIG. 4 is a graph showing the relationship between the relative permeability of the material to be measured and the output of the reciprocal calculator.
FIG. 5 is a block diagram showing an overall configuration of a magnetic permeability measuring device in a second embodiment of the present invention.
FIG. 6 is a partial cross-sectional side view of a state in which a magnetic core is in contact with a reference material.
FIG. 7 is a block diagram showing an overall configuration of a magnetic permeability measuring device in a third embodiment of the present invention.
FIG. 8 is a block diagram showing a main configuration of a magnetic permeability measuring device according to a fourth embodiment of the present invention.
FIG. 9 is a partial cross-sectional side view of a magnetic core.
FIG. 10 is a block diagram showing a calculation procedure in the inclination measuring circuit.
FIG. 11 is an output characteristic diagram with respect to relative permeability.
FIG. 12 is a schematic side view of a magnetic core used in a conventional magnetic permeability measuring apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1A, 1B ... Magnetic core, 2A, 2B ... Excitation coil, 3 ... Material to be measured, 4 ... Reference material, 5A, 5B ... Current supply circuit, 81 ... Differential amplifier, 83 ... Reciprocal calculator, 85 ... Pseudo output generation circuit .

Claims (5)

A rod-shaped first magnetic core whose end face is in contact with the material to be measured, a first excitation coil wound around the outer periphery of the first magnetic core, and a reference having a sufficiently high permeability as compared with the material to be measured A second magnetic core having the same shape as the first magnetic core with the end face in contact with the material, a second excitation coil wound around the outer periphery of the second magnetic core, and alternating current energization with a constant voltage to the first excitation coil A first energizing circuit, a second energizing circuit for energizing the second exciting coil with a constant voltage at a constant voltage, an output according to the energizing current to the first exciting coil, and an energizing current to the second exciting coil A magnetic permeability measuring apparatus comprising: an arithmetic circuit that calculates the magnetic permeability of the material to be measured based on the reciprocal of the difference in output. The end surface of a rod-shaped magnetic core having an excitation coil wound around its outer periphery is brought into contact with the material to be measured, and the end surface of another rod-shaped magnetic core having the same shape as the magnetic core having the excitation coil wound around its outer periphery The magnetic permeability of the material to be measured is determined from the reciprocal of the difference in output according to the current applied at this time, by contacting a reference material having a sufficiently high permeability compared to A magnetic permeability measuring method, characterized by: A rod-shaped first magnetic core; a first excitation coil wound around the outer periphery of the first magnetic core; a first energization circuit for energizing the first excitation coil with a constant voltage; and A pseudo output generation circuit that generates an output corresponding to an energization current when the end surface is brought into contact with a reference material having a sufficiently large permeability as compared with the material to be measured and the first energization coil is energized by the first energization circuit. And an output corresponding to the energized current when the first energizing circuit energizes the first exciting coil with the end face of the first magnetic core in contact with the material to be measured, and the output of the pseudo output generating circuit And an arithmetic circuit for calculating the magnetic permeability of the material to be measured based on the reciprocal of the difference. A second energization circuit for energizing at a constant voltage to a second excitation coil wound around the outer periphery of a rod-shaped second magnetic core having the same shape as the first magnetic core is connected to the input side of the pseudo output generation circuit. The magnetic permeability measuring apparatus according to 1. The end face of a rod-shaped magnetic core with an excitation coil wound around its outer periphery is brought into contact with a reference material having a sufficiently high permeability compared to the material to be measured, and the current applied when AC current is supplied to the excitation coil at a constant voltage. A corresponding output is generated in the pseudo output generating circuit, and the magnetic core is brought into contact with the material to be measured, and the exciting coil is energized with a constant voltage, and the output corresponding to the energizing current and the pseudo output are generated. A magnetic permeability measuring method, wherein the magnetic permeability of the material to be measured is calculated from the reciprocal of the difference in output of the circuit.

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