Lifting electromagnet control device and lifting electromagnet device equipped with the same

Abstract

To provide a control device for lifting electromagnet which can accurately detect drop of a steel sheet lifted by a lifting electromagnet without influence on a skill of an operator.SOLUTION: A control device 1 for lifting electromagnet controls an electric circuit 4 which drives a lifting electromagnet 2 that lifts a steel sheet with the electromagnetic force. A control device 1 for lifting electromagnet comprises: a current control unit 10 which controls the current flowing in an electric circuit 4 so as to reduce an excitation current flowing in a lifting electromagnet 2 when dropping a steel sheet lifted by the lifting electromagnet 2; an excitation current detection unit 20 which detects the excitation current flowing in the lifting electromagnet 2 when controlling the current flowing in the electric circuit 4 by the current control unit 10; and a steel sheet drop detection unit 30 which detects the drop of the steel sheet lifted by the lifting electromagnet 2 on the basis of the excitation current detected by the excitation current detection unit 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lifting electromagnet control device that controls an electric circuit that drives a lifting electromagnet that lifts a steel plate by electromagnetic force, and a lifting electromagnet device equipped with the same. [Background technology]

[0002] A lifting electromagnet control device is known that controls an electric circuit that drives a lifting electromagnet that lifts a steel plate by electromagnetic force. For example, Patent Document 1 discloses a lifting electromagnet steel plate attraction / detachment detection device that detects attraction and detachment of the steel plate by using the detection output of a magnetic flux detector that detects magnetic flux in a magnetic circuit formed in the lifting electromagnet and the steel plate lifted by the lifting electromagnet.

[0003] The steel plate attraction / detachment detection device includes an attraction / detachment determination circuit which counts pulse signals obtained by differentiating the detection output of the magnetic flux detector according to their polarities, thereby determining the number of attracted or detached steel plates.

[0004] This makes it possible to perform easier and more accurate control than in the past, where the selection control of the number of attracted sheets or the suspension failure correction control between each lifting electromagnet were dependent on the operator's intuition, and is expected to improve safety and work efficiency. In addition, since the attraction and release of steel plates can be detected automatically without the operator having to visually check, it is possible to confirm the change in the number of attracted steel plates. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 59-24717 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, when a steel plate attracted to a lifting electromagnet falls, the magnetic flux of the magnetic circuit formed by the lifting electromagnet changes at the time when the steel plate starts to separate from the lifting electromagnet. Therefore, the change in magnetic flux in the magnetic circuit occurs before the steel plate falls. In addition, the change in magnetic flux that occurs when the steel plate separates from the lifting electromagnet is gradual, and it is difficult to accurately detect the change in magnetic flux. Therefore, with the steel plate attraction / detachment detection device of Patent Document 1, it is difficult to accurately detect the fall of the steel plate from the lifting electromagnet at the time when the steel plate falls.

[0007] Here, when a lifting electromagnet is lifting multiple steel plates and only the lowest steel plate is to be dropped onto the lifting electromagnet, it is necessary to lower the excitation current flowing through the lifting electromagnet to drop the lowest steel plate, and then to pass a predetermined excitation current through the lifting electromagnet to generate a magnetic flux so that the other steel plates are attracted to the lifting electromagnet again. Therefore, it is necessary to predict the timing at which the steel plates will drop from the lifting electromagnet and pass an excitation current through the lifting electromagnet, which requires the skill of an operator who operates the lifting electromagnet device.

[0008] In response to this, there is a demand for a device that can accurately detect the falling of steel plates so that the number of steel plates being lifted by the hoisting electromagnet can be accurately controlled without being affected by the skill of the operator.

[0009] An object of the present invention is to provide a control device for a lifting electromagnet that can accurately detect the fall of a steel plate lifted by the lifting electromagnet without being affected by the skill of the operator. [Means for solving the problem]

[0010] A lifting electromagnet control device according to one embodiment of the present invention is a lifting electromagnet control device that controls an electric circuit that drives a lifting electromagnet that lifts a steel plate by electromagnetic force. This lifting electromagnet control device has a current control unit that controls the current flowing in the electric circuit so as to reduce the excitation current flowing in the lifting electromagnet when a steel plate lifted by the lifting electromagnet is dropped, an excitation current detection unit that detects the excitation current flowing in the lifting electromagnet when the current control unit controls the current flowing in the electric circuit, and a steel plate drop detection unit that detects the drop of the steel plate lifted by the lifting electromagnet based on the excitation current detected by the excitation current detection unit (first configuration).

[0011] When the steel plate suspended by the lifting electromagnet is dropped, the current control unit reduces the excitation current flowing through the lifting electromagnet. When the steel plate is dropped relative to the lifting electromagnet, an induced current flows through the lifting electromagnet in association with a change in magnetic flux, so that the excitation current flowing through the lifting electromagnet temporarily increases. This change in excitation current occurs when the steel plate is dropped, and is larger than the change in magnetic flux caused by the drop of the steel plate.

[0012] Therefore, the change in excitation current as described above is detected by the excitation current detection unit, and the steel plate drop detection unit detects the drop of the steel plate based on the detected excitation current, thereby making it possible to accurately detect the drop of the steel plate relative to the lifting electromagnet.

[0013] Furthermore, the fall of the steel plate relative to the lifting electromagnet can be detected by detecting changes in the excitation current flowing through the lifting electromagnet, so the fall of the steel plate can be detected without being affected by the skill of the operator operating the lifting electromagnet device.

[0014] Therefore, with the above-described configuration, the fall of the steel plate lifted by the lifting electromagnet can be detected with high accuracy, without being affected by the skill of the operator.

[0015] In the first configuration, the steel plate drop detection unit detects the drop of the steel plate being lifted by the lifting electromagnet when the polarity of the change in the amount of change per unit time of the excitation current changes or when the peak value of the excitation current is detected (second configuration).

[0016] This makes it possible to accurately detect a change in the excitation current flowing through the lifting electromagnet, and therefore to accurately detect the drop of the steel plate relative to the lifting electromagnet using the excitation current flowing through the lifting electromagnet.

[0017] In the first or second configuration, the current control unit forms a discharge circuit in the electrical circuit that reduces the excitation current of the lifting electromagnet when dropping the steel plate lifted by the lifting electromagnet (third configuration).

[0018] As a result, when the steel plate lifted by the lifting electromagnet is dropped, the excitation current of the lifting electromagnet can be reduced by the discharge circuit, and therefore, a configuration for reducing the excitation current of the lifting electromagnet can be realized with a simple configuration.

[0019] In the first or second configuration, the current control unit adjusts the current supplied to the electrical circuit so as to reduce the excitation current of the lifting electromagnet when dropping the steel plate lifted by the lifting electromagnet (fourth configuration).

[0020] As a result, when the steel plate lifted by the lifting electromagnet is dropped, the excitation current of the lifting electromagnet can be easily reduced by adjusting the current supplied to the electric circuit.

[0021] In any one of the first to fourth configurations, the excitation current detection unit detects an excitation current flowing through one of a plurality of lifting electromagnets electrically connected in parallel to a power source via the electric circuit, and the steel plate drop detection unit detects the drop of the steel plate lifted by the one lifting electromagnet based on the excitation current detected by the excitation current detection unit (fifth configuration).

[0022] When multiple lifting electromagnets are electrically connected in parallel to a power source in this manner, variations in the electrical resistance of the multiple lifting electromagnets occur due to temperature variations in the multiple lifting electromagnets, which causes variations in the excitation current flowing through the multiple lifting electromagnets. As a result, the magnetic flux generated by the multiple lifting electromagnets also varies for each lifting electromagnet, causing variations in the attraction force of the steel plate by the multiple lifting electromagnets.

[0023] In such a case, the above-mentioned configuration detects the excitation current flowing through one of the plurality of lifting electromagnets, and detects the drop of the steel plate lifted by the one lifting electromagnet based on the detected excitation current. This makes it possible to accurately detect the drop of the steel plate in the plurality of lifting electromagnets according to the variation in electrical resistance of each of the lifting electromagnets.

[0024] A lifting electromagnet device according to one embodiment of the present invention comprises a lifting electromagnet control device having any one of the first to fifth configurations described above, the lifting electromagnet, and the electric circuit (sixth configuration).

[0025] This provides a lifting electromagnet device that can accurately detect the fall of a steel plate relative to the lifting electromagnet. Effect of the Invention

[0026] A control device for a lifting electromagnet according to one embodiment of the present invention comprises a current control unit that controls the current flowing in an electrical circuit so as to reduce the excitation current flowing in the lifting electromagnet when a steel plate lifted by the lifting electromagnet is dropped, an excitation current detection unit that detects the excitation current flowing in the lifting electromagnet when the current flowing in the electrical circuit is controlled by the current control unit, and a steel plate drop detection unit that detects the drop of the steel plate lifted by the lifting electromagnet based on the excitation current detected by the excitation current detection unit.

[0027] With this, the excitation current detection unit detects a change in the excitation current that occurs when the steel plate falls relative to the hoisting electromagnet, and the steel plate drop detection unit detects the drop of the steel plate based on the excitation current detected by the excitation current detection unit. Therefore, the drop of the steel plate relative to the hoisting electromagnet can be detected with high accuracy without being affected by the skill of the operator. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a control circuit diagram showing a schematic configuration of a hoisting electromagnet device equipped with a hoisting electromagnet control device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing changes in the excitation current flowing through the lifting electromagnet and changes in the magnetic flux when a steel plate attracted to the lifting electromagnet falls. [Diagram 3] FIG. 3 is a diagram showing the relationship between the changes in the excitation current and magnetic flux and the behavior of the steel plate when the steel plate falls from the hoisting electromagnet. [Figure 4] FIG. 4 is a flowchart showing the operation of the lifting electromagnet control device to detect the drop of a steel plate. [Diagram 5] FIG. 5 is a control circuit diagram showing a schematic configuration of a hoisting electromagnet device including a hoisting electromagnet control device according to the second embodiment. [Figure 6] FIG. 6 is a control circuit diagram showing a schematic configuration of a hoisting electromagnet device including a hoisting electromagnet control device according to the third embodiment. [Figure 7]FIG. 7 is a control circuit diagram showing a current flow when a lifting electromagnet control device according to a modification of the third embodiment supplies power from a power source to the lifting electromagnet. [Figure 8] FIG. 8 is a control circuit diagram showing a current flow when the lifting electromagnet control device according to the modified example of the third embodiment is discharging the lifting electromagnet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and the description thereof will not be repeated.

[0030] (Embodiment 1) 1 is a control circuit diagram showing a schematic configuration of a lifting electromagnet device X1 equipped with a lifting electromagnet control device 1 according to a first embodiment of the present invention. The lifting electromagnet device X1 is a device for attracting a steel plate M or the like (see FIG. 4) to a lifting electromagnet 2 by a magnetic flux generated by the lifting electromagnet 2.

[0031] 1, in the lifting electromagnet device X, power is supplied from a power source 3 to a lifting electromagnet 2 by controlling the operation of an electric circuit 4 by a lifting electromagnet control device 1. In the lifting electromagnet device X1, the magnetic flux generated in the lifting electromagnet 2 is controlled by controlling the power supplied to the lifting electromagnet 2. Therefore, the magnetic attraction force of the lifting electromagnet 2 is controlled by controlling the operation of the electric circuit 4 by the lifting electromagnet control device 1.

[0032] The lifting electromagnet device X1 of this embodiment includes a lifting electromagnet 2, an electric circuit 4 that controls the power supply to the lifting electromagnet 2, and a lifting electromagnet control device 1 that controls the driving of the electric circuit 4.

[0033] The electric circuit 4 electrically connects the power source 3 and the lifting electromagnet 2. The electric circuit 4 has a pair of switches 41, 42, a discharge circuit 43, and a current detector 44. The power source 3 outputs DC power of a predetermined voltage.

[0034] The pair of switches 41, 42 are, for example, electromagnetic switches or electromagnetic contactors. One switch 41 of the pair of switches 41, 42 electrically connects or disconnects the power supply line P on the positive side of the power supply 3 and the lifting electromagnet 2, and the other switch 42 electrically connects or disconnects the power supply line N on the negative side of the power supply 3 and the lifting electromagnet 2. The pair of switches 41, 42 simultaneously perform opening and closing operations in response to a drive signal output from the lifting electromagnet control device 1.

[0035] When the pair of switches 41, 42 are closed, DC power is supplied from the power source 3 to the lifting electromagnet 2 via the electric circuit 4. When the pair of switches 41, 42 are open, DC power is not supplied from the power source 3 to the lifting electromagnet 2. Therefore, the pair of switches 41, 42 control the supply of DC power from the power source 3 to the lifting electromagnet 2.

[0036] The discharge circuit 43 is provided so as to electrically connect the power supply lines P, N between the pair of switches 41, 42 and the lifting electromagnet 2. The discharge circuit 43 is electrically connected in parallel to the power supply 3 and the lifting electromagnet 2.

[0037] The discharge circuit 43 has a discharge circuit switch 45 and a resistor 46. When the pair of switches 41, 42 are in an open state and the discharge circuit switch 45 is in a closed state, the discharge circuit 43 forms a closed circuit with the lifting electromagnet 2, and consumes the power stored in the lifting electromagnet 2 by the resistor 46. In other words, the discharge circuit 43 discharges the lifting electromagnet 2.

[0038] The discharge circuit switch 45 is, for example, an electromagnetic switch or an electromagnetic contactor. The open / close state of the discharge circuit switch 45 is controlled by the lifting electromagnet control device 1. The discharge circuit switch 45 is in a closed state when the pair of switches 41, 42 are in an open state and the lifting electromagnet 2 is discharged.

[0039] The resistor 46 has a resistance value within 10 times the resistance value of the lifting electromagnet 2. This allows the excitation current flowing through the lifting electromagnet 2 to be reduced relatively slowly rather than immediately. Therefore, when multiple steel plates are being attracted by the lifting electromagnet 2, it is possible to prevent the excitation current flowing through the lifting electromagnet 2 from being reduced suddenly, causing the multiple steel plates to fall all at once.

[0040] The current detector 44 detects the current flowing through the lifting electromagnet 2. Specifically, the current detector 44 detects a change in current caused by electromagnetic induction occurring in the lifting electromagnet 2 when the steel plate attracted to the lifting electromagnet 2 falls from the lifting electromagnet 2. The output of the current detector 44 is input to the lifting electromagnet control device 1.

[0041] The output of the current detector 44 may be used to control the power supply from the power source 3 to the hoisting electromagnet 2.

[0042] The lifting electromagnet control device 1 controls the driving of the electric circuit 4, thereby controlling the driving of the lifting electromagnet 2. The lifting electromagnet control device 1 controls the driving of a pair of switches 41, 42 in the electric circuit 4, and a discharge circuit switch 45, respectively.

[0043] Specifically, the lifting electromagnet control device 1 controls the drive of a pair of switches 41, 42 to control the power supply from the power source 3 to the lifting electromagnet 2. The lifting electromagnet control device 1 also controls the drive of a discharge circuit switch 45 to control the discharge of the lifting electromagnet 2. Furthermore, the lifting electromagnet control device 1 detects the drop of the steel plate attracted by the lifting electromagnet 2 based on the excitation current of the lifting electromagnet 2 detected by the current detector 44 during the discharge of the lifting electromagnet 2 by the discharge circuit 43.

[0044] In detail, the lifting electromagnet control device 1 has a current control unit 10, an excitation current detection unit 20, and a steel plate drop detection unit 30.

[0045] The current control unit 10 controls the driving of the pair of switches 41, 42 and the discharge circuit switch 45. The current control unit 10 generates and outputs driving signals to the pair of switches 41, 42 and the discharge circuit switch 45. The current control unit 10 controls the opening and closing of the pair of switches 41, 42 to control the power supply from the power source 3 to the lifting electromagnet 2. When the pair of switches 41, 42 are in the open state, the current control unit 10 closes the discharge circuit switch 45 to discharge the lifting electromagnet 2 by the discharge circuit 43. That is, the current control unit 10 controls the current flowing in the electric circuit 4 so as to reduce the excitation current flowing in the lifting electromagnet 2 by the discharge circuit 43.

[0046] The excitation current detection unit 20 acquires the value of the excitation current detected by the current detector 44 while the current control unit 10 is controlling the excitation current flowing through the hoisting electromagnet 2. Furthermore, the excitation current detection unit 20 uses the value of the excitation current acquired from the current detector 44 to determine the amount of change in the excitation current per unit time (the differential value of the excitation current).

[0047] The steel plate drop detection unit 30 detects the drop of the steel plate M attracted to the lifting electromagnet 2 based on the value of the excitation current acquired by the excitation current detection unit 20. Specifically, the steel plate drop detection unit 30 detects that the steel plate M attracted to the lifting electromagnet 2 is dropping when the polarity of the differential value of the excitation current obtained by the excitation current detection unit 20 changes from positive to negative. The steel plate drop detection unit 30 may also detect that the steel plate M attracted to the lifting electromagnet 2 is dropping when the polarity of the differential value of the excitation current changes from negative to positive.

[0048] As described above, when the steel plate drop detection unit 30 detects that the steel plate M has fallen from the lifting electromagnet 2, a signal may be output to the outside of the lifting electromagnet control device 1 to notify a worker or the like. The lifting electromagnet control device 1 may perform a screen display or the like based on the output signal.

[0049] Fig. 2 is a diagram showing changes in the excitation current and magnetic flux flowing through the lifting electromagnet 2 when a steel sheet M attracted to the lifting electromagnet 2 falls. Note that the example shown in Fig. 2 shows changes in the excitation current and magnetic flux when three steel sheets M are attracted to the lifting electromagnet 2 and fall from the lifting electromagnet 2 in order.

[0050] 2, when the steel sheet M falls from the lifting electromagnet 2, the excitation current flowing through the lifting electromagnet 2 temporarily increases. At times other than when the steel sheet M falls from the lifting electromagnet 2, the excitation current gradually decreases.

[0051] On the other hand, the magnetic flux generated in the lifting electromagnet 2 changes before the steel sheet M falls from the lifting electromagnet 2 (see P1 to P3 in FIG. 2). In this way, the timing at which the magnetic flux generated in the lifting electromagnet 2 changes does not closely match the timing at which the steel sheet M falls from the lifting electromagnet 2. Moreover, the change in the magnetic flux generated in the lifting electromagnet 2 is slight, and is much more difficult to distinguish than the change in the excitation current flowing through the lifting electromagnet 2.

[0052] In this way, by using the excitation current flowing through the lifting electromagnet 2 to determine the fall of the steel plate M, rather than magnetic flux, which makes it difficult to determine the fall of the steel plate M, the fall of the steel plate M from the lifting electromagnet 2 can be detected with high accuracy.

[0053] 3 is a diagram showing the relationship between the changes in the excitation current and magnetic flux and the behavior of the steel sheet M when the steel sheet M falls from the lifting electromagnet 2. When the pair of switches 41, 42 in the electric circuit 4 are in the open state and the discharge circuit switch 45 is in the closed state, the excitation current flowing through the lifting electromagnet 2 decreases as shown in FIG. 3, and the power stored in the lifting electromagnet 2 is consumed by the discharge circuit 43, which is a regeneration mode. After the regeneration mode, the excitation current flowing through the lifting electromagnet 2 increases, and the period until the polarity of the differential value of the excitation current changes from positive to negative (until the peak of the excitation current) is a separation mode in which the steel sheet M is separated from the lifting electromagnet 2. The steel sheet M falls from the lifting electromagnet 2 after the separation mode.

[0054] Fig. 4 is a flow chart showing the operation of detecting the drop of a steel plate by the lifting electromagnet control device 1. When the flow shown in Fig. 4 starts (START), first in step S1, the lifting electromagnet control device 1 judges whether or not a drop command has been input. If it is judged in step S1 that a drop command has been input (YES), the process proceeds to step S2, where the current control unit 10 opens the pair of switches 41, 42 and closes the discharge circuit switch 45.

[0055] On the other hand, if it is determined in step S1 that a drop command has not been input (NO), the determination in step S1 is repeated until a drop command is input to the hoisting electromagnet control device 1.

[0056] In the following step S3, the excitation current detection unit 20 acquires the value of the excitation current detected by the current detector 44, and calculates the derivative value of the acquired excitation current. In the next step S4, the steel plate drop detection unit 30 determines whether the polarity of the calculated derivative value of the excitation current has changed from positive to negative.

[0057] In step S4, if it is determined that the polarity of the calculated differential value of the excitation current has changed from positive to negative (YES), then in step S5, the steel plate drop detection unit 30 determines that the steel plate M has dropped from the lifting electromagnet 2. After that, in step S6, the lifting electromagnet control device 1 outputs a signal indicating that the steel plate M has dropped, and then ends this flow (END).

[0058] On the other hand, if it is determined in step S4 that the polarity of the calculated differential value of the excitation current has not changed from positive to negative (NO), the process returns to step S3, where the excitation current detection unit 20 again acquires the value of the excitation current detected by the current detector 44 and calculates the differential value of the acquired excitation current.

[0059] The lifting electromagnet control device 1 of this embodiment controls an electric circuit 4 that drives a lifting electromagnet 2 that lifts a steel plate M by electromagnetic force. The lifting electromagnet control device 1 has a current control unit 10 that controls the current flowing in the electric circuit 4 to reduce the excitation current flowing in the lifting electromagnet 2 when the steel plate M lifted by the lifting electromagnet 2 is dropped, an excitation current detection unit 20 that detects the excitation current flowing in the lifting electromagnet 2 when the current control unit 10 controls the current flowing in the electric circuit 4, and a steel plate drop detection unit 30 that detects the drop of the steel plate M lifted by the lifting electromagnet 2 based on the excitation current detected by the excitation current detection unit 20.

[0060] When the steel sheet M lifted by the lifting electromagnet 2 is dropped, the current control unit 10 reduces the excitation current flowing through the lifting electromagnet 2. When the steel sheet M drops relative to the lifting electromagnet 2, an induced current flows through the lifting electromagnet 2 in association with a change in magnetic flux, so that the excitation current flowing through the lifting electromagnet 2 temporarily increases. This change in excitation current occurs when the steel sheet M drops, and is larger than the change in magnetic flux caused by the drop of the steel sheet M.

[0061] Therefore, the change in excitation current as described above is detected by the excitation current detection unit 20, and the steel plate drop detection unit 30 detects the drop of the steel plate based on the detected excitation current, thereby making it possible to accurately detect the drop of the steel plate M relative to the lifting electromagnet 2.

[0062] Furthermore, the fall of the steel plate M relative to the lifting electromagnet 2 can be detected by detecting changes in the excitation current flowing through the lifting electromagnet 2, so the fall of the steel plate M can be detected without being affected by the skill of the operator operating the lifting electromagnet device X1.

[0063] Therefore, with the above-mentioned configuration, the drop of the steel plate M lifted by the lifting electromagnet 2 can be detected with high accuracy, without being affected by the skill of the operator.

[0064] In this embodiment, the steel plate drop detection unit 30 detects the drop of the steel plate M lifted by the lifting electromagnet 2 when the polarity of the change in the excitation current per unit time (the differential value of the excitation current) changes.

[0065] In this way, by detecting the change in polarity of the differential value of the excitation current flowing through the lifting electromagnet 2, the change in the excitation current can be detected with high accuracy. Therefore, the drop of the steel sheet M relative to the lifting electromagnet 2 can be detected with high accuracy using the excitation current flowing through the lifting electromagnet 2.

[0066] In addition, in this embodiment, the current control unit 10 forms a discharge circuit 43 in the electric circuit 4 that reduces the excitation current of the lifting electromagnet 2 when the steel plate M lifted by the lifting electromagnet 2 is dropped.

[0067] As a result, when the steel plate M lifted by the lifting electromagnet 2 is dropped, the excitation current of the lifting electromagnet 2 can be reduced by the discharge circuit 43. Therefore, a configuration for reducing the excitation current of the lifting electromagnet 2 can be realized with a simple configuration.

[0068] (Embodiment 2) 5 is a control circuit diagram showing a schematic configuration of a lifting electromagnet device X2 equipped with a lifting electromagnet control device 100 according to embodiment 2. The configuration of this embodiment differs from that of embodiment 1 in that the lifting electromagnet device X2 has a plurality of electric circuits 4a, 4b, and 4c. In the following, the same components as those in embodiment 1 are given the same reference numerals and their explanation is omitted, and only the components different from embodiment 1 will be explained.

[0069] As shown in FIG. 5, the lifting electromagnet device X2 has a plurality of electric circuits 4a, 4b, 4c electrically connected in parallel, and a plurality of lifting electromagnets 2a, 2b, 2c supplied with power from a power source 3 by the plurality of electric circuits 4a, 4b, 4c.

[0070] The configurations of the multiple electric circuits 4a, 4b, and 4c are similar to that of the electric circuit 4 in embodiment 1. In addition, the configurations of the multiple lifting electromagnets 2a, 2b, and 2c are similar to that of the lifting electromagnet 2 in embodiment 1. Therefore, detailed descriptions of the configurations of the multiple electric circuits 4a, 4b, and 4c and the multiple lifting electromagnets 2a, 2b, and 2c will be omitted.

[0071] The lifting electromagnet control device 100 controls the driving of the multiple lifting electromagnets 2a, 2b, and 2c by controlling the driving of the multiple electric circuits 4a, 4b, and 4c. The lifting electromagnet control device 100 is configured to be able to selectively control the driving of at least one of the multiple electric circuits 4a, 4b, and 4c.

[0072] Specifically, the lifting electromagnet control device 100 has a lifting electromagnet selection unit 110. The lifting electromagnet selection unit 110 selects at least one of the multiple electric circuits 4a, 4b, 4c in response to a signal input to the lifting electromagnet control device 100, and permits signal output from the current control unit 10 only to the selected electric circuit. This allows the lifting electromagnet control device 100 to control the drive of the electric circuit selected from the multiple electric circuits 4a, 4b, 4c, and control the drive of the lifting electromagnet driven by the selected electric circuit.

[0073] The drive control of the multiple electric circuits 4a, 4b, 4c by the lifting electromagnet control device 100 is similar to the drive control of the electric circuit 4 by the lifting electromagnet control device 1 in embodiment 1. Therefore, a detailed description of the lifting electromagnet control device 100 will be omitted.

[0074] With the configuration of this embodiment, it is not necessary to connect a power source to each of the multiple lifting electromagnets 2a, 2b, and 2c, so that a compact and low-cost lifting electromagnet device X2 can be obtained.

[0075] Moreover, as described above, when the lifting electromagnet device X2 has multiple lifting electromagnets 2a, 2b, and 2c, the temperatures of the lifting electromagnets may differ depending on the frequency of use of each lifting electromagnet and the environment. In such a case, since the electric resistances of the multiple lifting electromagnets 2a, 2b, and 2c are different, even if the same voltage is applied to the multiple lifting electromagnets 2a, 2b, and 2c, the current flowing through each lifting electromagnet is different. This causes variation in the magnetic flux generated in the multiple lifting electromagnets 2a, 2b, and 2c. Therefore, variation also occurs in the number of steel plates M attracted by the multiple lifting electromagnets 2a, 2b, and 2c.

[0076] In contrast, since the lifting electromagnet control device 100 has a lifting electromagnet selection unit 110 and a configuration similar to the lifting electromagnet control device 1 of embodiment 1, it is possible to drop the steel plate M from one of the multiple lifting electromagnets 2a, 2b, and 2c, and to accurately detect the drop of the steel plate M.

[0077] Specifically, in this embodiment, the excitation current detection unit 20 detects an excitation current flowing through one of the multiple lifting electromagnets 2a, 2b, 2c electrically connected in parallel via electric circuits 4a, 4b, 4c to the power source 3. The steel plate drop detection unit 30 detects the drop of the steel plate M lifted by the one lifting electromagnet, based on the excitation current detected by the excitation current detection unit 20.

[0078] This allows the multiple lifting electromagnets 2a, 2b, and 2c to accurately detect the drop of the steel sheet M in accordance with the variations in electrical resistance of each of the multiple lifting electromagnets 2a, 2b, and 2c. Therefore, it becomes possible to accurately adjust the number of steel sheets M attracted by the multiple lifting electromagnets 2a, 2b, and 2c.

[0079] In addition, the lifting electromagnet control device 100 may be configured to control the operation of two or more electrical circuits and detect the fall of the steel plate M from two or more lifting electromagnets based on the excitation current flowing through those lifting electromagnets.

[0080] (Embodiment 3) 6 is a control circuit diagram showing a schematic configuration of a lifting electromagnet device X3 equipped with a lifting electromagnet control device 200 according to embodiment 3. The configuration of this embodiment differs from that of embodiment 1 in that, instead of a discharge circuit, an excitation current flowing through the lifting electromagnet 2 is controlled by a power source 230. In the following, the same components as those in embodiment 1 are given the same reference numerals and their explanation is omitted, and only the components different from embodiment 1 will be explained.

[0081] 6, the lifting electromagnet device X3 includes a lifting electromagnet 2, an electric circuit 240, and a lifting electromagnet control device 200. The electric circuit 240 is the same as the electric circuit 4 of the first embodiment except that it does not have a discharge circuit. Therefore, a detailed description of the electric circuit 240 will be omitted.

[0082] The lifting electromagnet control device 200 has a current control unit 210 , an excitation current detection unit 20 , and a steel plate drop detection unit 30 .

[0083] The current control unit 210 controls the current flowing through the lifting electromagnet 2 by controlling the driving of the thyristors T constituting a forward excitation thyristor circuit 233 and a reverse excitation thyristor circuit 234 of the power source 230, which will be described later.

[0084] In detail, the current control unit 210 controls the drive of the thyristor T constituting the forward excitation thyristor circuit 233, thereby passing an excitation current through the lifting electromagnet 2 to generate a magnetic flux. On the other hand, the current control unit 210 controls the drive of the thyristor T constituting the reverse excitation thyristor circuit 234, thereby reducing the excitation current flowing through the lifting electromagnet 2. In this way, the current control unit 210 can also control the discharge of the lifting electromagnet 2 by controlling the drive of the thyristor T constituting the reverse excitation thyristor circuit 234.

[0085] The power supply 230 has an AC power supply 231, a circuit breaker 232, a positive excitation thyristor circuit 233, and a reverse excitation thyristor circuit 234. The positive excitation thyristor circuit 233 has three pairs of thyristors T electrically connected in series. The positive excitation thyristor circuit 233 is a circuit in which three pairs of thyristors T are electrically connected in parallel, and the midpoint of each pair of thyristors T is electrically connected to the AC power supply 231. The reverse excitation thyristor circuit 234 has two pairs of thyristors T electrically connected in series. The reverse excitation thyristor circuit 234 is a circuit in which two pairs of thyristors T are electrically connected in parallel, and the midpoint of each pair of thyristors T is electrically connected to the AC power supply 231 and each midpoint of the two pairs of thyristors T of the positive excitation thyristor circuit 233.

[0086] In the forward excitation thyristor circuit 233, a cathode of the thyristor T is connected to a power supply line P. In the reverse excitation thyristor circuit 234, a cathode of the thyristor T is connected to a power supply line N.

[0087] As in this embodiment, instead of a discharge circuit, the excitation current of the lifting electromagnet 2 may be reduced by the power source 230. That is, the current control unit 210 of this embodiment adjusts the current supplied to the electric circuit 240 so as to reduce the excitation current of the lifting electromagnet 2 when the steel plate M lifted by the lifting electromagnet 2 is dropped. As a result, by adjusting the current supplied to the electric circuit 240 when the steel plate M lifted by the lifting electromagnet 2 is dropped, the excitation current of the lifting electromagnet 2 can be easily reduced. Moreover, since a discharge circuit as in the first embodiment is not necessary, the electric circuit 240 can be configured compactly.

[0088] (Modification of the third embodiment) In the above embodiment, the power supply 230 has the forward excitation thyristor circuit 233 and the reverse excitation thyristor circuit 234. However, the power supply may have another configuration as long as it is capable of reducing the excitation current of the lifting electromagnet 2.

[0089] 7, the power supply 330 may have a circuit using a switching element such as an IGBT. Specifically, the power supply 330 has an AC power supply 331, a first switching circuit 332, and a second switching circuit 333.

[0090] The first switching circuit 332 has three pairs of switching elements SW electrically connected in series. The first switching circuit 332 is a circuit in which the three pairs of switching elements SW are electrically connected in parallel, and the midpoint of each pair of switching elements SW is electrically connected to the AC power supply 331. A diode is connected in anti-parallel to each switching element SW. In the following description, one side of the midpoint of each pair of switching elements SW is referred to as an upper arm, and the other side of the midpoint of each pair of switching elements SW is referred to as a lower arm.

[0091] The second switching circuit 333 has three pairs of switching elements SW electrically connected in series. The second switching circuit 333 is a circuit in which the three pairs of switching elements SW are electrically connected in parallel, and the midpoints of two pairs of switching elements SW are electrically connected to the lifting electromagnet 2. A diode is connected in anti-parallel to each switching element SW. In the following description, one side of the midpoint of each pair of switching elements SW is referred to as an upper arm, and the other side of the midpoint of each pair of switching elements SW is referred to as a lower arm.

[0092] The first switching circuit 332 and the second switching circuit 333 are electrically connected in parallel. A smoothing capacitor 334 is electrically connected in parallel to the first switching circuit 332 and the second switching circuit 333.

[0093] The first switching circuit 332 and the second switching circuit 333 configured as described above are driven and controlled by the lifting electromagnet control device 300. The lifting electromagnet control device 300 has a current control unit 310, an excitation current detection unit 20, and a steel plate drop detection unit 30. The current control unit 310 controls the driving of the switching elements SW of the first switching circuit 332 and the second switching circuit 333, thereby controlling the excitation current flowing through the lifting electromagnet 2.

[0094] In detail, the current control unit 310 controls the driving of the switching elements SW of the first switching circuit 332 and the second switching circuit 333 as follows.

[0095] When supplying power from the AC power supply 331 to the lifting electromagnet 2, the current control unit 310 turns on the upper arm and lower arm switching elements SW one by one out of the multiple switching elements SW constituting the first switching circuit 332, and turns on the upper arm and lower arm switching elements SW one by one out of the multiple switching elements SW constituting the second switching circuit 333. Thereby, a current flows from the AC power supply 331 to the lifting electromagnet 2, for example, as shown by the thick line in FIG.

[0096] When discharging the lifting electromagnet 2, the current control unit 310 turns on one of the switching elements SW of either the upper arm or the lower arm among the multiple switching elements SW constituting the second switching circuit 333. As a result, a current flows through the switching element SW that has been turned on and a diode connected in anti-parallel to the other switching element SW, forming a closed circuit for the lifting electromagnet 2, for example as shown by the thick line in Fig. 8. Therefore, the excitation current flowing through the lifting electromagnet 2 can be gradually reduced, and the lifting electromagnet 2 can be discharged.

[0097] In addition, similar to the current control unit 10 of the first embodiment, when a drop command is input to the lifting electromagnet control device 300, the current control unit 310 drives and controls the switching elements SW of the first switching circuit 332 and the second switching circuit 333 so as to reduce the excitation current flowing through the lifting electromagnet 2. This allows the steel plate M to be dropped from the lifting electromagnet 2.

[0098] As in this modified example, the exciting current flowing through the lifting electromagnet 2 can be controlled by a circuit using the switching element SW, thereby controlling the drop of the steel plate M relative to the lifting electromagnet 2.

[0099] (Other embodiments) Although the embodiment of the present invention has been described above, the above-mentioned embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-mentioned embodiment, and it is possible to carry out the above-mentioned embodiment by appropriately modifying it within the scope of the gist of the present invention.

[0100] In the first embodiment, the discharge circuit 43 has a discharge circuit switch 45 and a resistor 46. However, the discharge circuit may have a diode instead of the discharge circuit switch and resistor. By having the discharge circuit have a diode in this way, when power is supplied from a power source to the lifting electromagnet, a discharge circuit can be formed when the lifting electromagnet is discharged while suppressing current flow through the discharge circuit. Note that when the discharge circuit has a diode, the lifting electromagnet discharges due to the resistance of the lifting electromagnet.

[0101] In the first embodiment, the steel plate drop detection unit 30 of the lifting electromagnet control device 1 detects the drop of the steel plate M based on a change in polarity of the amount of change per unit time of the excitation current flowing through the lifting electromagnet 2 (the differential value of the excitation current). However, the steel plate drop detection unit may detect the drop of the steel plate M by detecting the peak value of the excitation current flowing through the lifting electromagnet 2.

[0102] In the second embodiment, the lifting electromagnet device X2 has three lifting electromagnets 2a, 2b, and 2c and three electric circuits 4a, 4b, and 4c. However, the lifting electromagnet device may have two lifting electromagnets and two electric circuits. Also, the lifting electromagnet device may have four or more lifting electromagnets and four or more electric circuits.

[0103] In the third embodiment, a circuit using a thyristor T or a circuit using a switching element SW such as an IGBT has been described as an example of the power supply that controls the current flowing through the lifting electromagnet 2. However, the power supply may be a power supply circuit having another configuration as long as it is capable of controlling the current flowing through the lifting electromagnet 2. [Industrial Applicability]

[0104] INDUSTRIAL APPLICABILITY The present invention can be used in a lifting electromagnet device having a lifting electromagnet that lifts a steel plate by electromagnetic force. [Explanation of symbols]

[0105] X, X1, X2, X3, X4 Lifting electromagnet device 1, 100, 200, 300 Lifting electromagnet control device 2, 2a, 2b, 2c lifting electromagnet 3, 230, 330 power supply 4, 4a, 4b, 4c, 240 Electrical circuits 10, 210, 310 Current control section 20 Excitation current detection section 30 Steel plate drop detector 41, 42 Switchgear 43 Discharge circuit 44 Current detector 45 Discharge circuit switch 46 resistor 110 Lifting electromagnet selection section 231, 331 AC power supply 232 Circuit Breaker 233 Positive excitation thyristor circuit 234 Thyristor circuit for reverse excitation 332 First switching circuit 333 Second switching circuit P Positive power line N Negative power supply line T Thyristor SW Switching element

Claims

1. A lifting electromagnet control device that controls an electric circuit that drives a lifting electromagnet that lifts a steel plate by electromagnetic force, a current control unit that controls a current flowing through the electric circuit so as to reduce an excitation current flowing through the lifting electromagnet when the steel plate lifted by the lifting electromagnet is dropped; an excitation current detection unit that detects an excitation current flowing through the lifting electromagnet when the current flowing through the electric circuit is controlled by the current control unit; a steel plate drop detection unit that detects the drop of the steel plate hoisted by the hoisting electromagnet based on the excitation current detected by the excitation current detection unit; having the steel plate drop detection unit detects a drop of the steel plate hoisted by the hoisting electromagnet when a polarity of a change amount per unit time of the excitation current changes or when a peak value of the excitation current is detected. Control device for lifting electromagnets.

2. The lifting electromagnet control device according to claim 1, The current control unit forms a discharge circuit in the electric circuit so as to reduce the excitation current of the lifting electromagnet when the steel plate lifted by the lifting electromagnet is dropped. Control device for lifting electromagnets.

3. The lifting electromagnet control device according to claim 1, the current control unit adjusts the current supplied to the electric circuit so as to reduce the excitation current of the lifting electromagnet when dropping the steel plate lifted by the lifting electromagnet. Control device for lifting electromagnets.

4. A control device for a lifting electromagnet that controls an electric circuit that drives a lifting electromagnet that lifts a steel plate by electromagnetic force, comprising: a current control unit that controls a current flowing through the electric circuit so as to reduce an excitation current flowing through the lifting electromagnet when the steel plate lifted by the lifting electromagnet is dropped; an excitation current detection unit that detects an excitation current flowing through the lifting electromagnet when the current flowing through the electric circuit is controlled by the current control unit; a steel plate drop detection unit that detects the drop of the steel plate hoisted by the hoisting electromagnet based on the excitation current detected by the excitation current detection unit; having the excitation current detection unit detects an excitation current flowing through one of a plurality of lifting electromagnets electrically connected in parallel to a power source via the electric circuit; The steel plate drop detection unit detects a drop of the steel plate hoisted by the one lifting electromagnet based on the excitation current detected by the excitation current detection unit. Control device for lifting electromagnets.

5. A lifting electromagnet control device according to any one of claims 1 to 4, The lifting electromagnet; The electrical circuit; Equipped with Hanging electromagnet device.

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