JP2018011433A - Magnetic field generation device for plastic magnet injection molder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic field generation device for controlling an inverter by digital control, capable of performing demagnetization by generating an AC current attenuating precisely.SOLUTION: A magnetic field generation device (10) for plastic magnet injection molder consisting of a coil (13), an inverter (11) for supplying a current thereto, and a controller (14) for controlling the inverter performs digital control of the inverter (11). Between the inverter (11) and coil (13), first and second current detectors (19, 20) having different detection ranges are provided. When the controller (14) performs feedback control by a measurement current so that the current flowing through the coil (13) becomes a predetermined target current, the measurement current is inputted from the first and second current detectors (19, 20) while being switched according to the magnitude thereof.SELECTED DRAWING: Figure 2

Description

  In the present invention, a resin containing magnetic powder is injected into a mold, a magnetic field is generated by generating a magnetic field in one direction, and an alternating magnetic field that attenuates when the molded product cools and solidifies is applied to remove the resin. The present invention relates to a magnetic field generator for generating a magnetic field in a plastic magnet injection molding machine adapted to carry out magnetism to obtain a plastic magnet molded product.

  Plastic magnets are made of a resin mixed with magnetic powder, have a high degree of freedom in shape, and have high dimensional accuracy, and are used in various fields. Molded products made of plastic magnets include so-called isotropic plastic magnets in which powdered magnetic materials are randomly oriented and distributed in the molded product, or different in which magnetic materials are oriented in a predetermined direction. There are also anisotropic plastic magnets. Any of them can be molded by injection molding, but the latter anisotropic plastic magnet is excellent because it can give a strong magnetic force. A molded product made of an anisotropic plastic magnet is molded as follows by an injection molding machine equipped with a magnetic field generator. The mold is clamped by the mold clamping device of the injection molding machine. The injection device is driven to inject a molten resin containing magnetic powder into a mold that has been clamped. The magnetization process is performed by the magnetic field generator. That is, a direct current is passed through the coil provided on the mold platen of the mold clamping device, a unidirectional magnetic field is applied to the molded product in the mold, and the powdery magnetic material is oriented. When the molded product is solidified, a demagnetizing step is performed by a magnetic field generator. That is, an alternating current that decays with time is passed through the coil, and an alternating magnetic field that attenuates is applied to the molded product. Then, the molded product is demagnetized. Open the mold clamping device and eject the molded product. If necessary, the molded product is conveyed to a predetermined magnetizing device and magnetized in the magnetizing device.

JP-A-6-254933

  Although not directly related to the present invention, Patent Document 1 also describes an injection molding machine that molds an anisotropic plastic magnet. In such an injection molding machine, in order to apply a large magnetic field to the molded product, it is necessary to pass a large current such as several tens of amperes through the coil of the magnetic field generator. If the value is large, the coating of the coil may be deteriorated or disconnection may occur. In the injection molding machine described in Patent Document 1, the resistance of the coil is measured after completion of the demagnetization process, and compared with a preset resistance value, a temperature abnormality occurs if the measured resistance is large. It comes to judge that it is doing. According to this method, it is not necessary to provide a temperature sensor in the coil, and it is possible to detect a temperature abnormality at low cost and prevent deterioration of the coil coating or disconnection. According to Patent Document 1, when the detected resistance is very large, it is determined that the coil is disconnected.

  As described above, it is necessary to supply a direct current or a decaying alternating current to the coil of the magnetic field generator, and a desired current is generated by an inverter constituting the magnetic field generator. The inverter is controlled by a pulse width modulation method, that is, PWM, and feedback-controlled from the measured current so that the current flowing through the coil becomes a desired target current. Conventionally, this feedback control is performed by analog control. However, an analog board for performing analog control has a problem that control characteristics change under the influence of temperature. Therefore, in recent years, an inverter is digitally controlled by a controller made of a digital board that is not easily affected by temperature.

  If the inverter is digitally controlled in the magnetic field generator, it is excellent in that a desired direct current or alternating current can be generated accurately and supplied to the coil without being affected by temperature. However, there are also problems to be solved. Specifically, when generating an alternating current in the demagnetization process, it is a problem that a small alternating current cannot be generated with high accuracy, and therefore, a decaying alternating current cannot be generated with high accuracy. This is because the accuracy of the measurement current data is reduced by digital conversion. Feedback control is performed so that the target current flows through the coil, but when the measurement current is input to the controller, it is converted into digital data of a predetermined number of bits. Since the magnetic field generator needs to handle a relatively large current, the digital data needs to have a large detection range so that it can handle a large current, but this reduces accuracy when handling a small current. If the accuracy of the small current is reduced, it is not possible to accurately generate a small current. If it does so, the alternating current which attenuate | damps with time cannot be produced | generated accurately, and demagnetization cannot fully implement in a demagnetizing process. There is also a method of selecting the detection range so as to increase the accuracy of the small current. This is because a small alternating current can be generated with high accuracy. However, in this case, a large current cannot be handled and cannot be used as a magnetic field generator. By the way, in a relatively general digital substrate, the measurement current is converted into, for example, 10-bit digital data by digital conversion. Therefore, for example, increasing the number of bits may solve the accuracy problem. However, in order to be able to handle digital data having a large number of bits, the cost of the digital board increases, which is not preferable.

  There are other problems with magnetic field generators. As described above, the magnetic field generator includes the coil provided on the template, but the insulation may be broken and a ground fault may occur in the coil. Since the magnetic field generator is also supplied with electric power from the injection molding machine like the other apparatuses, if a ground fault occurs, this can be detected by the power supply breaker of the injection molding machine. However, since it is not possible to identify in which device the ground fault has occurred, there is a problem that the solution of the failure is delayed. For example, a ground fault of a coil can be detected by providing a zero-phase current transformer, that is, ZCT, on an electric wire connecting an inverter of a magnetic field generator and a coil. However, there is a problem that the cost increases.

  An object of the present invention is to provide a magnetic field generator for a plastic magnet injection molding machine that solves the above-described problems. Specifically, in a magnetic field generator configured to supply current to a coil by PWM control of an inverter by feedback control including digital control, an alternating current that attenuates with high accuracy can be generated. It aims at providing the magnetic field generator for plastic magnet injection molding machines which can carry out a process appropriately. It is another object of the present invention to provide a magnetic field generator for a plastic magnet injection molding machine that can detect a ground fault in a coil of a magnetic field generator at a low cost.

  In order to achieve the above object, the present invention provides a magnetic field generator for a plastic magnet injection molding machine comprising a coil, an inverter for supplying current to the coil, and a controller for controlling the inverter. The target is a magnetic field generator to be controlled. The first and second current detectors having different detection ranges are provided between the inverter and the coil. When the controller performs feedback control with the measurement current so that the current flowing through the coil becomes a predetermined target current, the measurement current is switched and input from the first and second current detectors depending on the magnitude of the current. The first and second current detectors are provided on one terminal side and the other terminal side of the coil, and the controller monitors the deviation of the current detected by the first and second current detectors. If a predetermined threshold value is exceeded, it is determined that a ground fault has occurred.

That is, in order to achieve the above object, the invention according to claim 1 provides a coil for applying a magnetic field to a resin molded product containing magnetic powder injected into a mold, and supplies a direct current or an alternating current to the coil. And a controller that performs PWM control of the inverter by digital control, wherein first and second current detectors having different detection ranges are provided between the inverter and the coil, When the controller feedback-controls the current flowing through the coil with the measured current so as to be a predetermined target current, the measured current is switched and input from the first and second current detectors depending on the magnitude of the current. It is comprised as a magnetic field generator for a plastic magnet injection molding machine, characterized by being.
According to a second aspect of the present invention, in the magnetic field generator according to the first aspect, the first and second current detectors are provided on one terminal side and the other terminal side of the coil, and the controller The plastic magnet injection is characterized in that a deviation in current detected by the first and second current detectors is monitored and it is determined that a ground fault has occurred if a predetermined threshold value is exceeded. It is configured as a magnetic field generator for a molding machine.
According to a third aspect of the present invention, in the magnetic field generator according to the first or second aspect, the inverter includes a servo amplifier that generates a three-phase AC voltage, and the U phase, the V phase output from the servo amplifier, A direct current or an alternating current is generated by any two phases of the W phase, and the first and second current detectors are two current transformers provided in the servo amplifier. It is comprised as a magnetic field generator for the plastic magnet injection molding machine characterized by this.

  As described above, the present invention provides a coil for applying a magnetic field to a resin molded product containing magnetic powder injected into a mold, an inverter for supplying a direct current or an alternating current to the coil, and PWM controlling the inverter by digital control. It is intended for a magnetic field generator comprising a controller to be controlled. According to the present invention, the first and second current detectors having different detection ranges are provided between the inverter and the coil, and the controller controls the feedback of the current flowing through the coil with the measured current so that the current flows through the coil. When the measurement current is switched from the first and second current detectors according to the magnitude of the current, the measurement current is input. In other words, the first and second current detectors are different in the range of currents to be detected, one being able to cover a large current and the other being able to detect a small current with high accuracy. Since the measurement current is switched from the first and second current detectors according to the magnitude of the current and input to the controller, the controller can handle a large current and can accurately handle a small current. Can be handled. Therefore, an alternating current that decays with time can be generated with high accuracy, and the demagnetization step can be appropriately performed when a molded product of a plastic magnet is obtained. According to another invention, the first and second current detectors are provided on one terminal side and the other terminal side of the coil, and the controller calculates the deviation of the current detected by the first and second current detectors. It is configured to monitor and determine that a ground fault has occurred when a predetermined threshold value is exceeded. When a ground fault occurs, a part of the current flowing from the inverter toward the coil does not return to the inverter, so that the current flowing from the coil toward the inverter decreases. This deviation is monitored to monitor a ground fault in the coil. According to the present invention, it becomes easy to detect a ground fault generated in the coil. According to still another invention, the inverter includes a servo amplifier that generates a three-phase AC voltage, and a DC current or an AC current is generated by any two phases of the U phase, the V phase, and the W phase output from the servo amplifier. The first and second current detectors are configured to be two current transformers provided in the servo amplifier. Servo amplifiers that generate a three-phase AC voltage are provided with U, V, and W phase wires, and at least two phase wires are provided with current transformers that detect current. If it does so, even if it does not provide a current transformer exceptionally, the effect that this invention can be implemented only by using the servo amplifier which produces | generates a three-phase alternating voltage is acquired.

It is a circuit diagram which shows the electric power supply system and magnetic field generator in the plastic magnet injection molding machine which concern on embodiment of this invention. It is a circuit diagram which shows the magnetic field generator of the plastic magnet injection molding machine which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below. The injection molding machine 1 according to the embodiment of the present invention is also provided with a mold clamping device for clamping a mold, and an injection device for melting and injecting a resin consisting of a heating cylinder and a screw, as in the case of a conventionally known injection molding machine. , Etc. FIG. 1 shows servo motors M, M,... That drive these devices, and a power supply system 2 for supplying power to these servo motors M, M,. That is, like the conventional electric injection molding machine, the injection molding machine 1 is provided with a converter, that is, an AC / DC transformer 3, so that the three-phase AC voltage supplied from the factory power supply 5 is converted into a DC voltage. Yes. The DC voltage line 6 to which the converted DC current is supplied is provided with inverters that drive the servo motors M, M,..., That is, servo amplifiers 7, 7,. These servo amplifiers 7, 7,... Generate a three-phase AC voltage from the DC voltage and drive the servo motors M, M,.

  In the injection molding machine 1 according to the present embodiment, the magnetic field generator 10 is provided on the DC voltage line 6 of such a power supply system 2. The magnetic field generator 10 according to the present embodiment is shown in detail in FIG. 2, and controls the coil 13, the servo amplifier 11 that supplies a direct current or a single-phase alternating current to the coil 13, and the servo amplifier 11. The controller 14 is configured roughly. Although not shown in the drawing, the coil 13 is provided on a mold platen of the mold clamping device, and applies a magnetic field to a mold clamped by the mold clamping device. Since the current supplied to the coil 13 is a direct current and a single-phase alternating current, in general, the current may be supplied by an inverter that generates a single-phase alternating current. In other words, it suffices to generate current by using four IGBTs and four diodes. However, in the present embodiment, the servo amplifier 11 for three-phase AC voltage is used. Accordingly, the servo amplifier 11 is composed of six IGBTs 16, 16,... And six diodes 17, 17,... As known in the art, and converts the DC voltage supplied from the DC voltage line 6 to the U phase, V It is designed to output as a three-phase AC voltage of three phases of phase and W phase. In the present embodiment, a DC current or a single-phase AC current is generated and supplied to the coil 13 using only the U phase and the V phase of the servo amplifier 11 as described above.

  In this embodiment, there is an advantage by adopting the servo amplifier 11 for generating a three-phase AC voltage. Two current detectors are required to implement the present invention, but a general three-phase AC voltage generating servo amplifier is provided with at least two current detectors to detect a three-phase current. This is because they can be used. In the present embodiment, the first current detector 19 is interposed in a wire connecting the U phase of the servo amplifier 11 and one end of the coil 13, and the second current detector 20 is connected to the servo amplifier 11. An electric wire that connects the V-phase and the other end of the coil 13 is interposed. The first and second current detectors 19 and 20 are each composed of a current transformer, but one current transformer has a larger number of turns than the other. In the present embodiment, the first current detector 19 has more turns than the second current detector 20. As a result, the first current detector 19 can detect a current more accurately with respect to a small current, whereas the second current detector 20 can also detect a large current.

  The controller 14 is composed of a digital board and controls the servo amplifier 11 by software operating on this board. That is, the servo amplifier 11 is digitally controlled. The controller 14 is given a target current for generating a DC current or a single-phase AC current, and controls the servo amplifier 11 so as to be the target current. The target current is implemented as software in the controller 14. Is input to the comparison unit 25. In the comparison unit 25, as will be described below, data of the measured current flowing through the coil 13 is input, and these deviations are calculated and input to the current controller 26. The current controller 26 calculates an operation amount by feedback control so that there is no deviation, and the PWM signal generator 28 generates an ON / OFF signal, that is, a PWM signal. The IGBTs 16, 16,... Are driven by this PWM signal. That is, the servo amplifier 11 is controlled.

  The controller 14 is supplied with the measured current of the coil 13 detected via the first and second current detectors 19 and 20. Specifically, currents detected by the first and second current detectors 19 and 20 are converted into digital data by A / D converters 21 and 21 in the controller 14. In either case, the bit length of the digital data is the same, but the digital data converted from the current of the first current detector 19 has a narrow current range. In other words, the detection range is narrow and small currents can be handled with high accuracy. On the other hand, digital data converted from the current of the second current detector 20 has a wide current range. In other words, the detection range is wide, and the current accuracy is rough, but it can handle large currents. The current composed of these digital data is input to the switch 23 implemented as software, and one of the first and second current detectors 19 and 20 is selected by the switch 23 and input to the comparator 25. Is done. The switch 23 is switched by a current controller 26. Specifically, when the target current is relatively large, it is necessary to handle a large current. Since the measured current increases, the switch 23 is switched so that the current from the second current detector 20 is selected. On the other hand, when the target current is small, it is necessary to accurately handle a small current. Accordingly, at this time, the switch 23 is switched so that the current from the first current detector 19 is selected as the measurement current.

  The magnetic field generation apparatus 10 according to the present embodiment can also detect a ground fault generated in the coil 13. The controller 14 is provided with a comparator 31. The measured currents detected by the first and second current detectors 19 and 20 are compared, and the deviation is input to the ground fault monitor 32.

  The operation of the injection molding machine 1 provided with the magnetic field generator 10 according to the present embodiment will be described. In order to obtain a plastic magnet molded product in the injection molding machine 1, it is as follows. The mold clamping device is driven to clamp the mold. The injection device is driven to inject a resin containing magnetic powder into the mold. A magnetizing step for orienting the magnetic material is performed. That is, the controller 14 sets a target current for allowing a predetermined direct current to flow. Since the direct current flowing through the coil 13 is relatively large, the switch 23 of the controller 14 is switched to select the current from the second current detector 20 having a large detection range and to the comparison unit 25 as a measurement current. To be entered. The servo amplifier 11 is driven by processing by the current controller 26 and the PWM signal generator 28, and a direct current flows through the coil 13. When a direct current flows through the coil 13, a magnetic field is generated in one direction. The magnetic powder in the molded product is oriented. When the molded product is cooled and solidified, the magnetization process is terminated. Next, a demagnetizing step is performed. That is, a single-phase alternating current that decays with time is supplied to the coil 13. The controller 14 changes the target current so as to obtain such a single-phase AC current. Since it is not attenuated at the beginning, the target current is relatively large. Accordingly, the switch 23 of the controller 14 selects the current of the second current detector 20 having a large detection range and inputs it to the comparison unit 25 as the measurement current. The servo amplifier 11 is controlled so that a predetermined amount of alternating current flows through the coil 13. The target current is changed so that the alternating current is attenuated. When the target current becomes smaller, the switch 23 of the controller 14 is switched. That is, the current of the first current detector 19 having a small detection range is selected and input to the comparison unit 25 as a measurement current. The current of the first current detector 19 is digital data with high accuracy for a small current. Therefore, when the servo amplifier 11 is feedback-controlled using this as a measurement current, a smooth alternating current can be generated and supplied to the coil 13 even with a small current. When an alternating current is supplied to the coil 13, an alternating magnetic field is generated. When this is attenuated, the alternating magnetic field gradually decreases. As a result, the plastic magnet molded product is demagnetized. The demagnetization process is terminated. The mold clamping device is driven to open the mold to obtain a plastic magnet molded product.

  Thus, when molding a plastic magnet molded product, the ground fault monitor 32 monitors the ground fault. When a ground fault occurs in the coil 13, the magnitude of the current flowing from one end of the coil 13 to the coil 13 and the current flowing from the other end of the coil 13 do not match. This will be detected. Specifically, the ground fault monitor 32 receives the current deviation from the first and second current detectors 19 and 20 as described above. The ground fault monitor 32 compares the deviation with a predetermined threshold value. When the deviation is smaller than the threshold value, it is determined to be normal. However, if the deviation exceeds the threshold value, it is determined that a ground fault has occurred.

DESCRIPTION OF SYMBOLS 1 Injection molding machine 3 Electric power supply system 3 AC direct current transformer 5 Factory power supply 6 DC voltage line 7 Servo amplifier 10 Magnetic field generator 11 Servo amplifier 13 Coil 14 Controller 19 1st current detector 20 2nd current detector 23 Switching 25 Comparison unit 26 Current controller 28 PWM signal generator 32 Ground fault monitor

Claims (3)

Magnetic field generation comprising a coil for applying a magnetic field to a resin molded product containing magnetic powder injected into a mold, an inverter for supplying a direct current or an alternating current to the coil, and a controller for PWM control of the inverter by digital control A device,
First and second current detectors having different detection ranges are provided between the inverter and the coil, and when the controller performs feedback control with a measured current so that the current flowing through the coil becomes a predetermined target current, The magnetic field generator for a plastic magnet injection molding machine, wherein the measurement current is switched and inputted from the first and second current detectors according to the magnitude of the current.   2. The magnetic field generator according to claim 1, wherein the first and second current detectors are provided on one terminal side and the other terminal side of the coil, and the controller includes the first and second current detectors. A magnetic field generator for a plastic magnet injection molding machine, wherein a deviation in current detected in a container is monitored to determine that a ground fault has occurred when a predetermined threshold value is exceeded.   3. The magnetic field generator according to claim 1, wherein the inverter includes a servo amplifier that generates a three-phase AC voltage, and direct current is generated by any two phases of U phase, V phase, and W phase output from the servo amplifier. A plastic magnet injection molding machine characterized in that a current or an alternating current is generated, and the first and second current detectors are two current transformers provided in the servo amplifier. Magnetic field generator.

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