Weight distribution measurement method of laminated steel sheet

Abstract

To provide a weight distribution measurement method of a laminated steel sheet by which a weight distribution of a laminated steel sheet formed by laminating a plurality of steel sheets can be measured.SOLUTION: Provided is a weight distribution measurement method of a laminated steel sheet 1 produced by laminating a plurality of steel sheets 2 in the sheet thickness direction of the steel sheets 2. In the measurement method, a measurement tool 9 including a yoke 4 having a U-shaped cross section whose tip surface is formed in a shape along the outer surface of the laminated steel sheet 1, and an excitation coil 5 and a detection coil 6 wound around the yoke 4 is disposed at a predetermined distance from the outer surface of the laminated steel sheet 1. A weight of the laminated steel sheet 1 at a position facing the yoke 4 is measured based on a voltage detected by the detection coil 6 when the excitation coil 5 is energized. A weight distribution in the circumferential direction of the laminated steel sheet 1 is measured by moving the measurement tool 9 by a predetermined interval in the circumferential direction of the laminated steel sheet 1 and measuring the weight of each part in the circumferential direction of the laminated steel sheet 1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the weight distribution of a steel plate laminate in which steel plates are stacked. [Background technology]

[0002] Patent Document 1 describes a method for measuring the thickness of a corroded steel plate without removing corrosion products or irregularities caused by corrosion. Specifically, an excitation coil is placed at a predetermined distance from one side of the steel plate, and a detection coil is placed on the other side of the steel plate. A step-like current is applied to the excitation coil. The voltage generated in the detection coil is measured. The delay time, which is the difference between an initial peak and a subsequent peak in the measured voltage, is then calculated, and the thickness of the steel plate is calculated based on the measured delay time and a predetermined relational expression representing the relationship between the delay time and the thickness of the steel plate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-056202 Summary of the Invention [Problem to be solved by the invention]

[0004] The method for measuring the thickness of steel plates described in Patent Document 1 can measure thicknesses of steel plates up to approximately 20 mm. However, because motor rotor cores and the like are made by stacking multiple steel plates in the axial direction, the total thickness (hereinafter referred to as the thickness of the laminated steel plate) after the steel plates are stacked and assembled into a unit is large. Therefore, the measurement method described in Patent Document 1 may not be able to measure the thickness of the laminated steel plate. Furthermore, air gaps may be present between the stacked steel plates due to coatings such as insulating materials, surface shapes, or caulking, and these air gaps cause magnetic resistance. Furthermore, when magnetic flux flows perpendicular to the plate surface, eddy currents are generated in a direction that cancels out the magnetic flux. Due to the generation of such magnetic resistance and eddy currents, magnetic flux is unlikely to flow in the axial direction of the laminated steel plate (thickness direction of the laminated steel plate), which may make it impossible to measure the thickness of the laminated steel plate. Therefore, it may be impossible to properly measure the thickness distribution (i.e., weight distribution) of the laminated steel plate in the circumferential direction.

[0005] The present invention has been made in light of the above-mentioned technical problems, and aims to provide a method for measuring the weight distribution of a laminated steel plate, which is capable of measuring the weight distribution of a laminated steel plate formed by stacking multiple steel plates. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides a method for measuring the weight distribution of a laminated steel plate formed by stacking a plurality of steel plates in the thickness direction of the steel plates, characterized in that a measuring jig comprising a yoke with a U-shaped cross section whose tip surface is shaped to follow the outer surface of the laminated steel plate, an excitation coil wound at a predetermined position on the yoke, and a detection coil wound at a position on the yoke different from the excitation coil is positioned at a predetermined distance from the outer surface of the laminated steel plate, and the weight of the laminated steel plate at a position opposite the yoke is measured based on the voltage detected by the detection coil when current is applied to the excitation coil, and the measuring jig is moved at predetermined intervals in the circumferential direction of the laminated steel plate to measure the weight distribution in the circumferential direction of the laminated steel plate. [Effects of the Invention]

[0007] According to the present invention, a measuring jig is positioned at a predetermined distance from the outer surface of the laminated steel sheet. The measuring jig includes a yoke with a U-shaped cross section, whose tip end conforms to the outer surface of the laminated steel sheet, an excitation coil wound at a predetermined position on the yoke, and a detection coil wound at a different position on the yoke from the excitation coil. Therefore, by passing current through the excitation coil, a magnetic circuit is formed that passes through the yoke and the laminated steel sheet. The detection coil is located on the magnetic circuit, allowing for detection of a voltage corresponding to the amount of magnetic flux passing through the magnetic circuit. That is, the total thickness (lamination thickness) of the base steel in the portion through which the magnetic flux passes can be measured, taking into account the effects of coatings and air gaps. Since the lamination thickness is proportional to the weight of the portion through which the magnetic circuit passes, determining the lamination thickness allows for measurement of the weight of that portion. Therefore, by moving the measuring jig at predetermined intervals around the circumferential direction of the laminated steel sheet and measuring the weight of each portion around the circumferential direction of the laminated steel sheet, the circumferential weight distribution of the laminated steel sheet can be measured, even for laminated steel sheet with air gaps formed between the steel sheets. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view schematically illustrating an example of a laminated steel sheet according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram schematically illustrating an example of a measuring jig according to an embodiment of the present invention. [Figure 3] FIG. 1 is a diagram schematically illustrating an example in which a measuring jig is arranged to measure the plate thickness of a laminated steel plate. [Figure 4] FIG. 10 is a diagram showing the relationship between the voltage of the detection coil and the thickness (weight) of the laminated steel plate. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described based on the embodiments shown in the drawings. Note that the embodiments described below are merely examples of specific embodiments of the present invention and are not intended to limit the present invention.

[0010] Fig. 1 shows a schematic diagram of an example of a laminated steel sheet according to an embodiment of the present invention. The laminated steel sheet 1 shown in Fig. 1 is used as a rotor provided in a permanent magnet synchronous motor serving as a driving force source for a vehicle, and is formed by laminating annular steel sheets 2 made of silicon steel, which is made by adding silicon to iron, in the axial direction (thickness direction). Note that each steel sheet 2 may have a coating material, such as an insulating material, applied to its surface.

[0011] In the laminated steel plate 1 shown in Fig. 1, through holes 3 for embedding permanent magnets (not shown) are formed at predetermined intervals in the circumferential direction of the laminated steel plate 1 on the outer periphery in the radial direction of the laminated steel plate 1. Specifically, the laminated steel plate 1 shown in Fig. 1 has a two-split eight-pole structure, and therefore eight pairs of V-shaped through holes 3 are formed in the circumferential direction. In other words, the laminated steel plate 1 is formed by stacking the steel plates 2 with the phases (positions in the rotational direction) of the steel plates 2 aligned so that the positions of the through holes 3 are aligned.

[0012] When the laminated steel plate 1 configured as described above is used as a rotor, if the weight of each part of the laminated steel plate 1 in the direction of rotation is uneven, vibrations may occur when the laminated steel plate 1 rotates (spins) due to eccentricity between the central axis of rotation and the center of gravity of the laminated steel plate 1. The weight of each part of this laminated steel plate 1 is the sum of the weights of the members provided in that part, so if each steel plate 2 is completely unattached, the height and weight of that part will be proportional.

[0013] However, each steel plate 2 is coated, and due to the surface shape such as flatness of the steel plate 2, and the provision of caulking, etc., air spaces and the like are present between the base steel of the steel plates 2. Therefore, even if the height (thickness) of each part of the laminated steel plate 1 is measured, there is a possibility that the height and weight of that part will not necessarily be in a proportional relationship due to the influence of the intervening air spaces and the like.

[0014] Therefore, the method for measuring the weight distribution of a laminated steel sheet according to an embodiment of the present invention is configured to measure the total thickness (hereinafter referred to as the lamination thickness) of the steel sheets 2 (base steel) at positions corresponding to each pole, and to measure the weight distribution of the laminated steel sheet 1 based on the measured value. Specifically, as shown in Fig. 2, the weight of a predetermined portion of the laminated steel sheet 1 is measured using a measuring jig 9 that is configured of a yoke 4, an excitation coil 5, a detection coil 6, a voltmeter 7 that measures the voltage of the detection coil 6, and a controller 8 that calculates the lamination thickness based on a signal from the voltmeter 7 and calculates the weight from the lamination thickness.

[0015] The yoke 4 is formed by laminating non-oriented electromagnetic steel sheets or by integrating a wound iron core of oriented electromagnetic steel sheets using an impregnation bonding method or the like. The yoke 4 shown in FIG. 2 is formed in a U-shape having a linear base portion 4a, a first protrusion 4b protruding from one end of the base portion 4a, and a second protrusion 4c protruding from the other end of the base portion 4a in the same direction as the first protrusion 4b. The tip surface of each of the protrusions 4b and 4c is formed into a concave arc-shaped cross section that conforms to the outer surface of the laminated steel sheet 1. The distance between the protrusions 4b and 4c is approximately the same as the distance between the pair of through holes 3.

[0016] Like a coil provided in an electromagnet, the excitation coil 5 generates a magnetic force (magnetic flux) in its axial direction when a current flows through it, and is configured by winding a conductor in the thickness (or height) direction of the yoke 4. In the example shown in Fig. 2, the excitation coil 5 is wound around the base portion 4a. The excitation coil 5 is configured so that a direct current is passed through it from a power source (not shown).

[0017] Similar to the exciting coil 5, the detection coil 6 is also formed by winding a conductor in the thickness (or height) direction of the yoke 4. In the example shown in Fig. 2, the detection coil 6 is wound around the second protruding portion 4c.

[0018] The voltmeter 7 is configured to measure the voltage generated in the detection coil 6 by electromagnetic induction caused by magnetic flux flowing through the yoke 4, as described below, and the controller 8 is configured to calculate the stack thickness based on the voltage value detected by the voltmeter 7, and to calculate the weight of the measured portion of the laminated steel plate 1 based on the stack thickness.

[0019] Fig. 3 is a schematic diagram illustrating a method for measuring the thickness and weight of a predetermined portion of the laminated steel plate 1. In the example shown in Fig. 3, the laminated steel plate 1 and a measuring jig 9 are arranged so that the pair of through holes 3 and the respective protrusions 4b, 4c are aligned in phase in the circumferential direction of the laminated steel plate 1, and a predetermined distance is left between the outer surface of the laminated steel plate 1 and the tip end faces of the respective protrusions 4b, 4c.

[0020] Next, a direct current is passed from the power supply to the excitation coil 5. By passing current through the excitation coil 5 in this manner, a magnetic circuit is formed in which magnetic flux passes through the yoke 4 and the steel plate 2 (base steel), as shown in Figure 3. The amount of magnetic flux passing through this magnetic circuit is determined from the electromotive force generated by passing current through the excitation coil 5, the magnetic resistance of the yoke 4, the air gap between the yoke 4 and the laminated steel plate 1, and the magnetic resistance (composite magnetic resistance) of the laminated steel plate 1.

[0021] The magnetic resistance is determined by the magnetic permeability, cross-sectional area, and average magnetic path, and the magnetic resistance of the yoke 4 and the air layer is constant. In addition, the materials and outer diameter dimensions of the laminated steel sheets 1 are considered to be constant. Therefore, the amount of magnetic flux changes depending on the stacking thickness. Specifically, the thicker the stacking thickness, the smaller the magnetic resistance, and as a result, the greater the amount of magnetic flux.

[0022] Furthermore, when a magnetic circuit is formed by energizing the excitation coil 5 as described above, magnetic flux passes through the inside of the detection coil 6, generating an electromotive force in the detection coil 6 according to the rate of change of the magnetic flux amount and the number of turns of the detection coil 6. In other words, a potential difference occurs across the detection coil 6. As described above, the amount of magnetic flux passing through the magnetic circuit changes depending on the stack thickness, and therefore the electromotive force (voltage) also changes according to the rate of change of the magnetic flux amount. Specifically, as shown in Figure 4, the voltage value increases as the stack thickness increases. Therefore, the voltage of the detection coil 6 is detected by a voltmeter 7.

[0023] The voltage value detected as described above is input to controller 8. Controller 8 stores a map that has been constructed by previously determining the relationship between stack thickness and electromotive force through experiments or the like, or stores a function (arithmetic formula) for calculating stack thickness using electromotive force as a variable, and is configured to determine the stack thickness from the voltage value input from voltmeter 7 and the map or arithmetic formula. Then, the weight of the portion of laminated steel sheet 1 where the magnetic circuit is formed is determined by multiplying the stack thickness by a predetermined coefficient that takes into account the specific gravity of steel sheet 2 and the surface area of ​​the portion through which the magnetic circuit passes.

[0024] After measuring the weight at a position corresponding to one pole as described above, the measuring jig 9 is rotated 45 degrees relative to the laminated steel plate 1, or the laminated steel plate 1 is rotated 45 degrees, and the weight of the portion (pole) adjacent to the previously measured portion (pole) is measured in the same manner as described above. By measuring the weight at the positions corresponding to each pole in turn in this manner, the variation in the weight distribution of the laminated steel plate 1 can be found.

[0025] When the variation in weight distribution is determined as described above, if the variation (for example, the difference between the maximum weight and the minimum weight) is greater than or equal to a predetermined value, the variation in weight distribution is reduced by, for example, changing the phase of a predetermined number of steel plates 2 that make up the laminated steel plate 1.

[0026] As described above, the measuring jig 9 includes a U-shaped yoke 4 with its tip end shaped to fit the outer surface of the laminated steel sheet 1, and excitation coil 5 and detection coil 6 wound around the yoke 4. The measuring jig 9 is positioned at a predetermined distance from the outer surface of the laminated steel sheet 1. Therefore, when current is applied to the excitation coil 5, a magnetic circuit is formed between the yoke 4 and the laminated steel sheet 1. The detection coil 6 is located on the magnetic circuit, allowing for detection of a voltage corresponding to the amount of magnetic flux passing through the magnetic circuit. In other words, the total thickness (lamination thickness) of the base steel in the area through which the magnetic flux passes can be measured, taking into account the effects of coatings and air gaps. Since the lamination thickness is proportional to the weight of the area through which the magnetic circuit passes, determining the lamination thickness allows for the weight of that area to be measured. Therefore, by moving the measuring jig 9 at predetermined intervals around the circumferential direction of the laminated steel sheet 1 and measuring the weight of each area around the circumferential direction of the laminated steel sheet 1, the weight distribution of the laminated steel sheet 1 in the circumferential direction can be measured, even for laminated steel sheet 1 with air gaps formed between the steel sheets 2.

[0027] As described above, the stack thickness is determined based on the yoke 4, the air layer between the yoke 4 and the laminated steel sheet 1, and the magnetic resistance of the laminated steel sheet 1. Among the areas that act as magnetic resistance, the magnetic permeability of the air layer is much smaller than the magnetic permeability of other areas. Therefore, if the gap between the laminated steel sheet 1 and the measuring jig 9 is small, the voltage value detected by the voltmeter 7 will vary greatly. Conversely, if the gap between the laminated steel sheet 1 and the measuring jig 9 is large, the voltage level detected by the voltmeter 7 will be extremely small, and the measurement accuracy of the stack thickness and weight will deteriorate.

[0028] Therefore, it is preferable to appropriately determine the relative position between the laminated steel plate 1 and the measuring jig 9. Specifically, for example, it is preferable to position the laminated steel plate 1 by providing a positioning pin at a predetermined distance from the measuring jig 9 and bringing the outer peripheral surface of the laminated steel plate 1 into contact with the positioning pin or by fitting the through hole 3 into the positioning pin, so that the relative position between the laminated steel plate 1 and the measuring jig 9 is a predetermined position. [Explanation of symbols]

[0029] 1 Laminated steel plate 2 steel plate 3 Through holes 4 York 4a Base 4b,4c protrusion 5 Excitation coil 6 Detection coil 7. Voltmeter 8 Controller 9 Measuring Jig

Claims

[Claim 1] A method for measuring weight distribution of a laminated steel plate formed by stacking a plurality of steel plates in a plate thickness direction of the steel plates, a measuring tool including a yoke having a U-shaped cross section whose tip end surface is formed in a shape that follows the outer surface of the laminated steel plate, an excitation coil wound at a predetermined position of the yoke, and a detection coil wound at a position of the yoke different from that of the excitation coil, is disposed at a predetermined distance from the outer surface of the laminated steel plate; measuring a weight of the laminated steel plate at a position facing the yoke based on a voltage detected by the detection coil when the excitation coil is energized; The measuring jig is moved at predetermined intervals in the circumferential direction of the laminated steel plate, and the weight of each portion in the circumferential direction of the laminated steel plate is measured, thereby measuring the weight distribution in the circumferential direction of the laminated steel plate. A method for measuring weight distribution of laminated steel sheets.

Images