Magnetic fastening device

Abstract

Provided is a magnetic fastening device in which the power consumption of a magnetizing coil of a magnet material having reversible polarity is reduced. A magnetic fastening device (10) is provided with: a neodymium magnet (18); the polarity of the aluminum-nickel-cobalt magnet (16) can be reversed through the magnetizing coil (17); a controller (7); a rectifier circuit (31); and a first circulation circuit (32). A rectifier circuit (31) half-wave rectifies an AC power source, supplies a positive-side pulse to a magnetizing coil (17) for a predetermined period when magnetization of the magnetizing coil (17) is instructed by a controller (7), and supplies a negative-side pulse to the magnetizing coil (17) for a predetermined period when demagnetization is instructed. In the first circulation circuit (32), a diode (34) and a switch (35) are connected in series, when the controller (7) instructs magnetization, the switch (35) is turned on, a closed circuit is formed with the magnetizing coil (17), and current caused by counter electromotive force is circulated, and when the controller (7) instructs demagnetization of the magnetizing coil (17), the switch (35) is turned off.

Description

Technical Field

[0001] The invention relates to a magnetic fastening device which utilizes magnetic adsorption force for fastening / releasing. Background Art

[0002] In a magnetizer that magnetizes a magnet raw material to produce a magnet, a magnetic field is generated inside the coil by passing an electric current through the coil, and the magnet raw material is supplied into the coil, thereby magnetizing the magnet raw material. The direction of the magnetic field is determined by the direction of the current flowing through the coil, and the intensity of the magnetic field is determined by the intensity of the current flowing through the coil. In the magnetizer that magnetizes the magnet raw material, "saturation magnetization" is performed, that is, magnetization is performed until the magnet raw material has a limit point "saturation point" of magnetism. In Patent Document 1, a capacitor type magnetizer is disclosed as an example of such a magnetizer.

[0003] In the capacitor-type magnetizer of Patent Document 1, the alternating current from the high-frequency transformer is double-wave rectified to form a pulsating current, and the charging capacitor is charged 10mV each time. When the charge reaches 2.5kV, the current of the charging capacitor is passed to drive the magnetizing coil. The series circuit of the SCR and the magnetizing coil, which are the switching elements for magnetization, is connected to the charging capacitor, and the freewheeling diode is connected in parallel to the series circuit. When the magnet raw material is inserted into the magnetizing coil and the SCR is arced, a magnetizing current of, for example, about 10kA is instantaneously supplied to the magnetizing coil. Through the resonance of the magnetizing coil and the charging capacitor, after the current reaches a peak value, the SCR is arced due to the reverse voltage and discharged through the freewheeling diode. By sequentially transporting the magnet raw material to the magnetizing coil, the magnet raw material is magnetized to mass-produce permanent magnets.

[0004] As a device for magnetizing a magnet raw material, in addition to a magnetizer that passes the magnet raw material through a coil to produce a magnet, a magnetic fastening device that winds a coil around the magnet raw material and switches magnetization / demagnetization is also known. For example, in a magnetic fastening device for magnetically fixing a mold shown in Patent Document 2, there is a magnet with irreversible polarity and a magnet raw material (aluminum nickel cobalt magnet) with reversible polarity, and the magnetic polarity of the aluminum nickel cobalt magnet is controlled by a magnetizing coil that surrounds the aluminum nickel cobalt magnet, so that it is possible to switch between a released state and a locked state, the released state is a state in which the mold is separated by forming a magnetic circuit in which the irreversible polarity magnet and the reversible polarity magnet are closed in series, and the locked state is a state in which the mold is fastened by forming a magnetic circuit in which the irreversible polarity magnet and the reversible polarity magnet are connected in parallel and in series with the mold.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2006-230124

[0008] Patent Document 2: International Publication No. WO2019 / 202957 Summary of the invention

[0009] In the capacitor magnetizer of Patent Document 1, the unmagnetized magnetic raw material is magnetized, and the current accumulated in the charging capacitor is instantaneously passed through once for magnetization. In contrast, in the magnetic fastening device, the polarity-reversible magnetic raw material (aluminum nickel cobalt magnet) not only reverses the polarity it maintains, but also cancels the magnetic flux flowing in from the adjacent non-reversible polarity magnet. To this end, sufficient current must be continuously passed through the coil wound around the alnico magnet until the magnetic pole of the alnico magnet is reversed and the magnetic flux is saturated. However, a large DC current source that can maintain a DC value at a certain time interval is expensive.

[0010] Therefore, in the magnetic fastening device, half-wave rectification of the AC power supply is performed. For example, when fastening, a half-sine wave on the upper side is supplied to the magnetizing coil, and when releasing, a half-sine wave on the lower side is supplied to the magnetizing coil, thereby controlling the direction of the current to reduce the cost of the power supply. A half-sine wave is a waveform of only the positive side or the negative side after rectification of the AC power supply. The length of one wave of the half-sine wave (called a "pulse") is about 10ms. Multiple half-sine waves are applied to the magnetizing coil to generate magnetic flux. The magnetic flux held by the Alnico magnet and the magnetic flux flowing from the magnet whose polarity cannot be reversed are added to the generated magnetic flux. By applying several pulses, the polarity of the Alnico magnet is gradually reversed, and finally the saturation magnetic flux is reached. Therefore, only the number of pulses applied until the magnetic flux is saturated is consumed.

[0011] The present invention provides a magnetic fastening device which reduces power consumption by reducing the number of pulses applied to a magnetizing coil of a magnetic material whose polarity can be reversed.

[0012] The magnetic fastening device of the present invention comprises: a controller; a rectifier circuit that performs half-wave rectification on an AC power supply, and supplies positive pulses to the magnetizing coil of a reversible magnet during a specified period when the controller instructs the magnetizing coil to be magnetized, and supplies a specified number of negative pulses to the magnetizing coil of the reversible magnet when the controller instructs demagnetization; and a first circulating current circuit in which a diode and a switch are connected in series, and during a period when the controller instructs the magnetizing coil to be magnetized, the switch is turned on to form a closed circuit with the magnetizing coil so that a current caused by a back electromotive force generated by the magnetizing coil circulates, and during a period when the controller instructs the magnetizing coil to be demagnetized, the switch is turned off.

[0013] According to the present invention, even if the magnetizing force of the magnet block weakens, as long as the mold is fastened to the magnet block in the initial position, the mold can be closed and magnetized again, thereby resuming the operation in a short time. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a figure explaining an injection molding machine and a magnetic fastening device. Figure 1 A is the overall picture of the injection molding machine. Figure 1 B is a view of the magnetic fastening device 10 as viewed from the side on which the mold is installed. Figure 1 C is a diagram showing the situation when the magnetic fastening device is in a demagnetized state, Figure 1 D is a diagram showing the state when the magnetic fastening device is in a magnetized state.

[0015] Figure 2 is a diagram illustrating a circuit of a magnetic fastening device. Figure 2 A is a diagram showing a power supply 30 for the magnetizing coil, Figure 2 B-2D is a diagram showing a waveform.

[0016] Figure 3 is a diagram showing the change in magnetic flux, Figure 3 A is a comparative example, Figure 3 B is a diagram showing the situation of this embodiment.

[0017] Figure 4 is a diagram showing the change in magnetic flux, Figure 4 A is a comparative example, Figure 4 B is a diagram showing the situation of this embodiment.

[0018] Figure 5 It is a diagram showing changes in magnetic flux.

[0019] Figure 6 It is a figure which shows the application example of a magnetic fastening device.

[0020] (Explanation of Reference Numerals)

[0021] 1: injection molding machine; 2, 3: pressing plate; 4: main body; 7: controller; 8: ejector rod; 9: guide rod; 10, 20: magnetic fastening device; 11: magnetic block; 12: proximity sensor; 13: through hole; 16: Alnico magnet; 17: magnetizing coil; 18: neodymium magnet; 30: power supply; 31: rectifier circuit; 32: first circulating circuit; 33: second circulating circuit; 34, 36: diode; 35, 37: switch; 38: arc starting circuit; 39, 40: thyristor. DETAILED DESCRIPTION

[0022] Hereinafter, an example of an embodiment of the present invention will be described. In the following description, the magnetic fastening devices 10 and 20 mounted on the injection molding machine 1 are described as an example.

[0023] Figure 1 1 is a diagram for explaining an injection molding machine 1 and magnetic fastening devices 10 and 20. Figure 1 In A, the injection molding machine 1 is provided with: left and right opposing platens 2 and 3; and a guide rod 9 for guiding and supporting the left platen 2 so that it can move forward and backward freely in the left and right directions. Magnetic fastening devices 10 and 20 for magnetically adsorbing the mold are respectively installed on the platens 2 and 3. Reference numeral 6 denotes a nozzle for injecting resin, 7 denotes a controller with an input unit and a liquid crystal display screen, and 8 denotes an ejector rod for extruding the injection molded product from the mold. The controller 7 controls the magnetic fastening devices 10 and 20.

[0024] Figure 1 B is a diagram of the magnetic fastening device 10 as viewed from the side on which the mold is installed. The main body 4 of the magnetic fastening device 10 includes a ferromagnetic body. A plurality of magnetic blocks 11 including a ferromagnetic body are embedded on the surface side of the main body 4. In addition, a proximity sensor 12 and a coil (not shown) for detecting changes in magnetic flux are provided. The ejector rod 8 is inserted into the through hole 13. The magnetic fastening device 20 is substantially the same as the magnetic fastening device 10, and the description thereof is omitted. The same applies below.

[0025] Figure 1 C shows the situation when the magnetic fastening device 10 is in a demagnetized state. The neodymium magnet (irreversible magnet) 18 surrounds the outer periphery of the magnetic block 11, and the side facing the magnetic block 11 is, for example, the S pole, and the side facing the main body 4 is the N pole. The alnico magnet (reversible magnet) 16 is a permanent magnet with the surface side facing the magnetic fastening device 10 (the upper side in the figure) set as the N pole and the side facing the back side set as the S pole. When the magnetic flux passes through the surface of the magnetic fastening device 10 in the magnetic circuit formed by the neodymium magnet 18, the main body 4, the alnico magnet 16, and the magnetic block 11, the magnetic flux will not leak out and the mold will not be adsorbed.

[0026] Figure 1 D shows the state when the magnetic fastening device 10 is in a magnetized state. By passing a positive current through the magnetizing coil 17, the magnetic pole of the Alnico magnet 16 is reversed. The Alnico magnet 16 is magnetized to form a permanent magnet with the surface of the magnetic fastening device 10 as the S pole and the back side as the N pole.

[0027] On the surface side of the magnetic fastening device 10, both the neodymium magnet 18 and the alnico magnet 16 are combined with the magnetic block 11 as the S pole. When the mold M is pressed against the surface of the magnetic fastening device 10, these magnetic fluxes pass through the mold M. As a result, a magnetic circuit consisting of the neodymium magnet 18, the magnetic block 11, the mold M, and the main body 4 and a magnetic circuit consisting of the alnico magnet 16, the magnetic block 11, the mold M, and the main body 4 are formed. Once this state is reached, the magnetic circuit continues to be maintained even if the current of the magnetizing coil is cut off. In order to make the magnetic fastening device 10 demagnetized from this state, the alnico magnet 16 is demagnetized by passing a current on the negative side.

[0028] Figure 2 1 is a diagram for explaining the circuit of the magnetic fastening device 10 . Figure 2 A shows a power supply 30 for the magnetizing coil, and the power supply 30 is controlled by control signals s0-s3 of the controller 7. When the controller 7 instructs the power supply 30 to magnetize the magnetizing coil 17, control signals s0 and s2 are generated, and when the controller 7 instructs the power supply 30 to demagnetize the magnetizing coil 17, control signals s1 and s3 are generated. The power supply 30 is connected to a commercial AC power supply PS supplied for industrial use, and includes a rectifier circuit 31, a first circulating circuit 32, and a second circulating circuit 33. The rectifier circuit 31 is a circuit for half-wave rectification of AC, and includes an arc starting circuit 38 and thyristors 39 and 40. When the control signal s0 is instructing the magnetization of the magnetic fastening device 10, the arc starting circuit 38 sends a trigger signal to the thyristor 39. The arc starting angle is set so that a positive half-sine wave pulse is generated during the rising edge of the voltage from the AC power supply PS increasing from 0V to the positive side. As a result, positive pulses are continuously generated during the rising period of the control signal s0. When the demagnetization of the magnetic fastening device 10 is instructed by the control signal s1, the arcing circuit 38 sends a trigger signal to the thyristor 40. The arcing angle is set to generate a negative half-sine wave pulse during the falling edge of the voltage from the AC power supply PS increasing from 0V to the negative side. As a result, negative pulses are continuously generated during the rising period of the control signal s1. By controlling the rising period of the control signals s0 and 1, the number of consecutive positive or negative pulses is controlled.

[0029] The pulse generated by the rectifier circuit 31 is applied to the magnetizing coil 17 as it is. In the capacitor type magnetizer, the pulse is stored in the capacitor and then supplied to the magnetizing coil, but the difference in this embodiment is that it is directly supplied to the magnetizing coil 17. The first circulating circuit 32 and the second circulating circuit 33 are respectively connected in parallel to the magnetizing coil 17. In the first circulating circuit 32, the diode 34 is connected in series with the switch 35, and in the second circulating circuit 33, the diode 36 is connected in series with the switch 37. The diode 34 and the diode 36 have opposite polarities with the anode and the cathode facing each other. In addition, as the diode 34 and the diode 36, a fast recovery diode (FRD) is used. The switch 35 and the switch 37 are controlled to be turned on and off by the control signals S2 and S3, respectively. The control signal S2 turns on the switch 35 when the magnetic fastening device 10 is magnetized. The control signal S3 turns on the switch 37 when the magnetic fastening device 10 is demagnetized. As the switch 35 and the switch 37, a relay circuit is used.

[0030] Figure 2 B is the waveform of the voltage v across the magnetizing coil 17 during magnetization, the current i flowing through the magnetizing coil 17, and the control signals s0 and s2. The switch 35 is turned on by the control signal s2 (the switch 37 remains off). The positive pulse v1 is generated by the rectifier circuit 31 by the control signal s0. The first circulating circuit 32 and the magnetizing coil 17 form a closed circuit by the control signal s2. During the period when the controller 7 indicates magnetization and the voltage between each pulse v1 disappears, the current i1 that is intended to continue to flow due to the back electromotive force of the inductance component of the magnetizing coil also circulates in the closed circuit and is consumed by the resistance component of the magnetizing coil 17 and attenuated. If the inductance component of the magnetizing coil 17 is large, the attenuation of the current i1 becomes gentle, and a large current value can continue to flow even when the voltage of the pulse v1 disappears. This means that the magnetic flux generated by the magnetizing coil 17 is maintained at a high level.

[0031] Figure 2 C shows the waveform of demagnetization of the magnetizing coil 17. During the period when the controller 7 instructs demagnetization, the switch 37 is turned on by the control signal s3 (the switch 35 remains off), and the rectifier circuit 31 generates a negative pulse v2 by the control signal s1. When the magnetizing coil 17 is demagnetized, a closed circuit that blocks the magnetizing coil 17 is formed by the second circulating current circuit 33, and the current i2 flows in the opposite direction to the magnetization case.

[0032] Figure 2D shows the waveform of magnetization when the first circulating circuit 32 and the second circulating circuit 33 do not exist. In this case, during the period when the voltage between each pulse v1 disappears, the current i3 tends to flow continuously for a certain period of time due to the back electromotive force of the inductance component of the magnetizing coil 17, and a negative voltage appears. However, this current i3 penetrates into the rectifying circuit 31 and cannot circulate in the magnetizing coil 17 to continuously generate magnetic flux.

[0033] Furthermore, it is needless to say that during magnetization of the magnetic fastening device 10 , the switch 37 is turned off, and during demagnetization of the magnetic fastening device 10 (demagnetization of the magnetizing coil 17 ), the switch 35 is turned off.

[0034] Figure 3 The magnetic flux density measured by the Tesla meter in the mold-mounted surface of the magnetic fastening device 10 is shown. If the magnetic flux density remaining after the current flowing through the magnetizing coil 17 disappears is measured as the saturation magnetic flux φs, the magnetic fastening device 10 is considered to be normally magnetized.

[0035] (Experimental Example 1)

[0036] Figure 3 A is a case where the first circulating circuit 32 and the second circulating circuit 33 are not provided (comparative example). Figure 3 B is a case where the first circulating current circuit 32 and the second circulating current circuit 33 are provided (Example). When the magnetic fastening device 10 is magnetized, 40 pulses are supplied to the magnetizing coil 17. It can be seen that the final remaining saturation magnetic flux φs (read as about 0.05 mT by the Tesla meter) is the same, but Figure 3 The rate of increase of the magnetic flux density in B is faster, and it reaches the upper limit of the rise in the second half. In particular, the difference in magnetic flux density from the application of the last pulse to the saturation magnetic flux φs is observed. Figure 3 The difference d2 of B relative to Figure 3 The difference d1 of A is significantly larger, and a strong magnetic flux is applied to the Alnico magnet 16 .

[0037] In addition, during demagnetization, 40 pulses were supplied to the magnetizing coil 17, but no significant difference was found between the two.

[0038] (Experimental Example 2)

[0039] Figure 4 A is a case where the first circulating circuit 32 and the second circulating circuit 33 are not provided (comparative example). Figure 4 B is a case where the first circulating current circuit 32 and the second circulating current circuit 33 are provided (an embodiment). 30 pulses are supplied to the magnetizing coil 17. The residual saturation magnetic flux φs is the same, but the differences d1 and d2 are reduced. Figure 4 The difference d1 observed in A does not have a sufficient margin as a product.

[0040] In addition, during demagnetization, 30 pulses were supplied to the magnetizing coil 17, but no significant difference was found between the two.

[0041] (Experimental Example 3)

[0042] Figure 5 This is the case where the first circulating current circuit 32 and the second circulating current circuit 33 are provided (Example). 20 pulses are supplied to the magnetizing coil 17. The residual magnetic flux density does not reach the saturation magnetic flux φs of Experimental Examples 1 and 2.

[0043] In addition, demagnetization was possible even when 20 pulses were supplied. Although not shown in the figure, it was also confirmed that demagnetization was possible even when 10 pulses were supplied.

[0044] According to the above experimental example, when magnetizing, if the first circulating current circuit 32 and the second circulating current circuit 33 are not provided, magnetization with a margin cannot be performed unless 40 pulses are supplied to the magnetizing coil 17. On the other hand, if the first circulating current circuit 32 and the second circulating current circuit 33 are provided, magnetization with a margin can be performed even if 30 pulses are supplied. Reducing the number of pulses from 40 to 30 reduces the current consumption by 25%.

[0045] On the other hand, during demagnetization, no significant difference was found between the presence or absence of the first circulating current circuit 32 and the second circulating current circuit 33 .

[0046] Therefore, in the case where it is desired to suppress the power consumption of the magnetizing coil 17, at least the first circulating circuit 32 of the first circulating circuit 32 and the second circulating circuit 33 is provided, and the switch 35 of the first circulating circuit 32 is turned on during magnetization and turned off during demagnetization. In addition to this, the number of pulses supplied to the magnetizing coil 17 during demagnetization can be reduced compared to the number of pulses during magnetization. Furthermore, the second circulating circuit 33 can also be increased. In addition, during demagnetization and during periods other than demagnetization, the rectifier circuit 31 does not generate pulses, so the switches 35 and 37 can be either on or off.

[0047] According to this embodiment, by turning on the first circulating circuit 32 at least during the magnetization period and turning it off at least during the demagnetization period, a closed circuit including the magnetizing coil 17 can be formed, and during the period when the pulse disappears, the current using the electromotive force of the magnetizing coil 17 is caused to circulate and continue to flow in the magnetizing coil 17, so that the magnetic flux used for magnetization can be maintained in a high state. As a result, there is an effect of reducing the power consumption during magnetization.

[0048] Furthermore, by reducing the number of pulses supplied to the magnetizing coil 17 during demagnetization compared to the number of pulses during magnetization, power consumption can be reduced.

[0049] Figure 6An application example of the present embodiment is shown. This application example is an example of a case where a plurality of magnetizing coils 17 are arranged in the magnetic fastening device 10, 20 and one power supply system cannot supply current. A power supply 30 is provided in which the power supply system from the rectifier circuit 31 is set to four systems. The first circulating circuit 32 and the second circulating circuit 33 are connected in series with the magnetizing coils 17 to which power is applied in each system, so that a closed circuit can be formed. The first circulating circuit 32 and the second circulating circuit 33 of each system are controlled in common by control signals s1 and s2, respectively.

[0050] In the above embodiment, the arc starting circuit 38 is provided in the rectifier circuit 31, but the controller 7 may directly apply a trigger signal to the thyristors 39 and 40 to directly control the number of pulses on the positive side or the negative side. In addition, the thyristors 39 and 40 are used in the rectifier circuit 31, but other switching elements may also be used.

Claims

1. A magnetic fastening device, comprising: a plurality of magnetic blocks having irreversible magnets and reversible magnets whose polarity can be reversed by a magnetizing coil, arranged on the surface of a plate containing a magnetic body for magnetically fastening a mold in a magnetized state, wherein: The magnetic fastening device has: Controller; a rectifier circuit that performs half-wave rectification on an AC power source, supplies positive pulses to the magnetizing coil of the reversible magnet for a specified period when the controller instructs the magnetizing coil to be magnetized, and supplies a specified number of negative pulses to the magnetizing coil of the reversible magnet when the controller instructs the magnetizing coil to be demagnetized; as well as A first circulating current circuit, in which a diode and a switch are connected in series, and when the controller instructs the magnetizing coil to be magnetized, the switch is turned on to form a closed circuit with the magnetizing coil so that a current caused by a back electromotive force generated by the magnetizing coil circulates, and when the controller instructs the magnetizing coil to be demagnetized, the switch is turned off.

2. The magnetic fastening device according to claim 1, characterized in that: The number of positive-side pulses generated by the rectifying circuit is greater than the number of negative-side pulses.

3. The magnetic fastening device according to claim 1, characterized in that: A second circulating current circuit is provided in which a diode and a switch are connected in series. When the controller instructs the demagnetization of the magnetizing coil, the switch is turned on to form a closed circuit with the magnetizing coil so that a current caused by a back electromotive force generated by the magnetizing coil circulates. When the controller instructs the magnetization of the magnetizing coil, the switch is turned off. The polarities of the diodes in the first circulating current circuit and the second circulating current circuit are opposite to each other.

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