Lifting electromagnet control device

Abstract

To provide a control device for lifting electromagnet which can accurately detect a plate thickness of a steel sheet lifted by a lifting electromagnet.SOLUTION: A control device 1 for lifting electromagnet comprises: a plate thickness magnetic flux characteristic storage unit 30 which stores a plate thickness magnetic flux characteristic in which a magnetic flux generated by a lifting electromagnet 2a is associated with a plate thickness T of a steel sheet M for each excitation current; an excitation current detection unit 20 which detects the excitation current flowing in the lifting electromagnet 2a; a plate thickness magnetic flux characteristic acquisition unit 40 which acquires a plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit 20 out of the plate thickness magnetic flux characteristics stored in the plate thickness magnetic flux characteristic storage unit 30; a magnetic flux detection unit 50 which detects a magnetic flux generated by the lifting electromagnet 2a when making the excitation current flow in the lifting electromagnet 2a; and a plate thickness detection unit 60 which detects the plate thickness T corresponding to the magnetic flux detected by the magnetic flux detection unit 50 as the plate thickness of the steel sheet M by using the plate thickness magnetic flux characteristic acquired by the plate thickness magnetic flux characteristic acquisition unit 40.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control device for a lifting electromagnet that controls a lifting electromagnet that lifts a steel plate by electromagnetic force. [Background technology]

[0002] A lifting electromagnet control device that controls a lifting electromagnet that lifts a steel plate by electromagnetic force is known. 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] With this, when the number of steel plates hoisted by the hoisting electromagnet is different from the desired number, the addition or dropping of steel plates can be detected by detecting the magnetic flux with the magnetic flux detector while controlling the excitation current, so that the selection control of the number of steel plates to be attracted can be easily and accurately performed. [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, in order to perform the selective control of the number of steel plates to be attracted as in the cited document 1, it is first necessary to accurately detect the number of steel plates lifted by the lifting electromagnet. As a method for accurately detecting the number of steel plates lifted by the lifting electromagnet, a method using the relationship between the magnetic flux and the thickness of the steel plates has been proposed in the past.

[0007] Specifically, the relationship between the magnetic flux generated by the lifting electromagnet and the thickness of the steel plates is obtained in advance, and the plate thickness corresponding to the magnetic flux detected by the magnetic flux detector is obtained from the relationship. Then, the number of steel plates being lifted by the lifting electromagnet is calculated from the obtained plate thickness and the plate thickness per steel plate.

[0008] Furthermore, when lifting a steel plate by a lifting electromagnet as in the cited document 1, a plurality of lifting electromagnets may be used. In this case, by supplying power to each of the plurality of lifting electromagnets, the steel plate can be lifted by each of the lifting electromagnets.

[0009] The temperature of the lifting electromagnets when lifting a steel plate varies depending on the frequency of use, the environment, etc. When the temperatures of the multiple lifting electromagnets differ in this way, the electrical resistances of the multiple lifting electromagnets also differ. Therefore, even if the same voltage is applied to the multiple lifting electromagnets with different electrical resistances, the current flowing through each lifting electromagnet differs. This causes variation in the magnetic flux generated by the multiple lifting electromagnets.

[0010] In this way, when the magnetic flux generated by the multiple lifting electromagnets varies, if one tries to determine the thickness of the steel plate using the relationship between the magnetic flux and the thickness of the steel plate as described above, it is difficult to accurately determine the thickness of the steel plate because the thickness obtained varies for each lifting electromagnet.

[0011] An object of the present invention is to provide a control device for a lifting electromagnet that can accurately detect the thickness of a steel plate lifted by the lifting electromagnet. [Means for solving the problem]

[0012] A lifting electromagnet control device according to one embodiment of the present invention controls the drive of a lifting electromagnet that lifts a steel plate by electromagnetic force. The lifting electromagnet control device includes a thickness flux characteristic storage unit in which thickness flux characteristics, in which the magnetic flux generated by the lifting electromagnet and the thickness of the steel plate are associated, are stored for each excitation current, an excitation current detection unit that detects the excitation current flowing through the lifting electromagnet, a thickness flux characteristic acquisition unit that acquires the thickness flux characteristic corresponding to the excitation current detected by the excitation current detection unit from the thickness flux characteristics stored in the thickness flux characteristic storage unit, a magnetic flux detection unit that detects the magnetic flux generated by the lifting electromagnet when an excitation current is passed through the lifting electromagnet, and a thickness detection unit that detects the thickness corresponding to the magnetic flux detected by the magnetic flux detection unit as the thickness of the steel plate using the thickness flux characteristic acquired by the thickness flux characteristic acquisition unit (first configuration).

[0013] When there is variation in the excitation current flowing through the multiple lifting electromagnets, the magnetic flux generated by the multiple lifting electromagnets also differs for each of the lifting electromagnets, which causes variation in the attraction force of the multiple lifting electromagnets to the steel plate, resulting in a problem that when detecting the thickness of the steel plate using the magnetic flux generated by the multiple lifting electromagnets, the thickness detected by each lifting electromagnet differs.

[0014] In response to this, the lifting electromagnet control device having the above-mentioned configuration obtains the plate thickness magnetic flux characteristic corresponding to the excitation current flowing through the lifting electromagnet, and uses the obtained plate thickness magnetic flux characteristic to determine the plate thickness of the steel plate corresponding to the magnetic flux generated by the lifting electromagnet. This makes it possible to accurately detect the plate thickness of the steel plate lifted by the lifting electromagnet even if there is variation in the excitation current flowing through the multiple lifting electromagnets.

[0015] In the first configuration, the plate thickness magnetic flux characteristic storage unit stores the plate thickness magnetic flux characteristic for each excitation current as table data, and the plate thickness magnetic flux characteristic acquisition unit acquires the plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit from the table data (second configuration).

[0016] This makes it possible to select a plate thickness magnetic flux characteristic corresponding to the excitation current flowing through the lifting electromagnet from table data stored in advance in the plate thickness magnetic flux characteristic storage unit, and therefore makes it possible to accurately detect the plate thickness of the steel plate lifted by the lifting electromagnet based on the excitation current flowing through the lifting electromagnet.

[0017] In the first configuration, the plate thickness magnetic flux characteristic storage unit stores the plate thickness magnetic flux characteristic for each excitation current as an approximate expression. The plate thickness magnetic flux characteristic acquisition unit acquires the plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit from the approximate expression (third configuration).

[0018] This makes it possible to obtain the plate thickness magnetic flux characteristic corresponding to the excitation current flowing through the lifting electromagnet from the approximation formula stored in advance in the plate thickness magnetic flux characteristic storage unit, and therefore makes it possible to accurately detect the plate thickness of the steel plate lifted by the lifting electromagnet based on the excitation current flowing through the lifting electromagnet.

[0019] In any one of the first to third 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 an electric circuit. The plate thickness magnetic flux characteristic acquisition unit acquires the plate thickness magnetic flux characteristic stored in the plate thickness magnetic flux characteristic storage unit based on the excitation current flowing through the one lifting electromagnet. The magnetic flux detection unit detects a magnetic flux generated by the one lifting electromagnet (fourth configuration).

[0020] 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.

[0021] In such a case, the above-mentioned configuration detects the excitation current flowing through one of the plurality of lifting electromagnets, and detects the thickness of the steel plate lifted by the plurality of lifting electromagnets based on the detected excitation current, thereby making it possible to accurately detect the thickness of the steel plate lifted by the plurality of lifting electromagnets according to the variation in the excitation current flowing through each lifting electromagnet. Effect of the Invention

[0022] A lifting electromagnet control device according to an embodiment of the present invention acquires a thickness-flux characteristic that correlates the magnetic flux generated by the lifting electromagnet with the thickness of a steel plate according to an excitation current flowing through the lifting electromagnet. The lifting electromagnet control device also uses the acquired thickness-flux characteristic to determine the thickness of the steel plate that corresponds to the magnetic flux generated by the lifting electromagnet when an excitation current is passed through the lifting electromagnet.

[0023] This makes it possible to accurately detect the thickness of the steel plate lifted by multiple lifting electromagnets even if there is variation in the excitation current flowing through the multiple lifting electromagnets when the steel plate is lifted by the multiple lifting electromagnets. [Brief description of the drawings]

[0024] [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 one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the relationship between the magnetic flux generated by the lifting electromagnet and the plate thickness of the steel plate lifted by the lifting electromagnet. [Diagram 3] FIG. 3 is a flowchart showing a detection operation when the lifting electromagnet control device detects the thickness of a steel plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] 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.

[0026] 1 is a control circuit diagram showing a schematic configuration of a lifting electromagnet device X equipped with a lifting electromagnet control device 1 according to one embodiment of the present invention. This lifting electromagnet device X is a device for attracting a steel plate M or the like to a plurality of lifting electromagnets 2a, 2b, 2c by magnetic flux generated by the plurality of lifting electromagnets 2a, 2b, 2c.

[0027] As shown in Fig. 1, in the lifting electromagnet device X, the lifting electromagnet control device 1 controls the driving of the multiple electric circuits 3a, 3b, 3c, thereby supplying power from a power source 4 to the multiple lifting electromagnets 2a, 2b, 2c. In the lifting electromagnet device X, the magnetic flux generated in the multiple lifting electromagnets 2a, 2b, 2c is controlled by controlling the power supplied to the multiple lifting electromagnets 2a, 2b, 2c. Therefore, the magnetic attraction force of the multiple lifting electromagnets 2a, 2b, 2c is controlled by controlling the driving of the multiple electric circuits 3a, 3b, 3c with the lifting electromagnet control device 1.

[0028] In this embodiment, as described later, the lifting electromagnet control device 1 is configured to be able to selectively control the drive of at least one of the plurality of electric circuits 3a, 3b, and 3c.

[0029] The lifting electromagnet device X of this embodiment includes a plurality of lifting electromagnets 2a, 2b, and 2c, a plurality of electric circuits 3a, 3b, and 3c, and a lifting electromagnet control device 1.

[0030] The multiple lifting electromagnets 2a, 2b, and 2c are supplied with power from a power source 4 by multiple electric circuits 3a, 3b, and 3c electrically connected in parallel. Specifically, the lifting electromagnet 2a is supplied with power from the power source 4 by the electric circuit 3a. The lifting electromagnet 2b is supplied with power from the power source 4 by the electric circuit 3b. The lifting electromagnet 2c is supplied with power from the power source 4 by the electric circuit 3c. That is, the multiple lifting electromagnets 2a, 2b, and 2c are supplied with power from a common power source 4. In this embodiment, the multiple lifting electromagnets 2a, 2b, and 2c have the same configuration.

[0031] The plurality of lifting electromagnets 2a, 2b, and 2c each have a search coil 5a, 5b, and 5c. The search coil 5a detects the magnetic flux generated by the lifting electromagnet 2a. The search coil 5b detects the magnetic flux generated by the lifting electromagnet 2b. The search coil 5c detects the magnetic flux generated by the lifting electromagnet 2c.

[0032] The multiple electric circuits 3a, 3b, 3c electrically connect the multiple lifting electromagnets 2a, 2b, 2c to the power source 4. Specifically, the electric circuit 3a electrically connects the lifting electromagnet 2a to the power source 4. The electric circuit 3b electrically connects the lifting electromagnet 2b to the power source 4. The electric circuit 3c electrically connects the lifting electromagnet 2c to the power source 4. In this embodiment, the multiple electric circuits 3a, 3b, 3c have the same configuration. Therefore, hereinafter, only the electric circuit 3a will be described.

[0033] The electric circuit 3a has a pair of switches 31 and 32, a discharge circuit 33, and a current detector 34. The power source 4 outputs DC power of a predetermined voltage.

[0034] The pair of switches 31, 32 are, for example, electromagnetic switches or electromagnetic contactors. One switch 31 of the pair of switches 31, 32 electrically connects or disconnects the power supply line P on the positive side of the power supply 4 and the lifting electromagnet 2a, and the other switch 32 electrically connects or disconnects the power supply line N on the negative side of the power supply 4 and the lifting electromagnet 2a. The pair of switches 31, 32 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 31, 32 are closed, DC power is supplied from the power source 4 to the lifting electromagnet 2a via the electric circuit 3a. When the pair of switches 31, 32 are open, DC power is not supplied from the power source 4 to the lifting electromagnet 2a. Therefore, the pair of switches 31, 32 control the supply of DC power from the power source 4 to the lifting electromagnet 2a.

[0036] The discharge circuit 33 is provided so as to electrically connect the power supply lines P, N between the pair of switches 31, 32 and the lifting electromagnet 2a. The discharge circuit 33 is electrically connected in parallel to the power supply 4 and the lifting electromagnet 2a.

[0037] The discharge circuit 33 has a discharge circuit switch 35 and a resistor 36 having a predetermined resistance value. When the pair of switches 31, 32 are in an open state and the discharge circuit switch 35 is in a closed state, the discharge circuit 33 forms a closed circuit with the lifting electromagnet 2a, and the resistor 36 consumes the power stored in the lifting electromagnet 2a. In other words, the discharge circuit 33 discharges the lifting electromagnet 2a.

[0038] The discharge circuit switch 35 is, for example, an electromagnetic switch or an electromagnetic contactor. The open / close state of the discharge circuit switch 35 is controlled by the lifting electromagnet control device 1. The discharge circuit switch 35 is in a closed state when the pair of switches 31, 32 are in an open state and the lifting electromagnet 2a is discharged.

[0039] The current detector 34 detects the current flowing through the lifting electromagnet 2a. The output of the current detector 34 is input to the lifting electromagnet control device 1. The output of the current detector 34 may be used when controlling the power supply from the power source 4 to the lifting electromagnet 2a.

[0040] Next, the lifting electromagnet control device 1 will be described. As described above, the electric circuits 3a, 3b, and 3c and the lifting electromagnets 2a, 2b, and 2c have the same configuration. Therefore, the following describes a case where the lifting electromagnet control device 1 controls the operation of the electric circuit 3a to control the operation of the lifting electromagnet 2a. The lifting electromagnet control device 1 controls the operation of the pair of switches 31 and 32 and the discharge circuit switch 35 in the electric circuit 3a.

[0041] Specifically, the lifting electromagnet control device 1 controls the power supply from the power source 4 to the lifting electromagnet 2a by controlling the driving of a pair of switches 31, 32. The lifting electromagnet control device 1 also detects the plate thickness T of the steel plate M lifted by the lifting electromagnet device X based on the excitation current flowing through the lifting electromagnet 2a and the magnetic flux generated by the lifting electromagnet 2a. The lifting electromagnet control device 1 may also control the discharge of the lifting electromagnet 2a by controlling the driving of the discharge circuit switch 35.

[0042] In detail, the lifting electromagnet control device 1 has a current control unit 10, an excitation current detection unit 20, a plate thickness magnetic flux characteristic storage unit 30, a plate thickness magnetic flux characteristic acquisition unit 40, a magnetic flux detection unit 50, and a plate thickness detection unit 60.

[0043] The current control unit 10 controls the driving of the pair of switches 31, 32 and the discharge circuit switch 35. The current control unit 10 generates and outputs driving signals to the pair of switches 31, 32 and the discharge circuit switch 35. The current control unit 10 controls the opening and closing of the pair of switches 31, 32, thereby controlling the power supply from the power source 4 to the lifting electromagnet 2a. Note that when the pair of switches 31, 32 are in the open state, the current control unit 10 may close the discharge circuit switch 35 to discharge the lifting electromagnet 2a through the discharge circuit 33.

[0044] The excitation current detection unit 20 acquires the value of the excitation current detected by the current detector 34 when an excitation current flows through the lifting electromagnet 2a with the pair of switches 31, 32 in a closed state. That is, the excitation current detection unit 20 detects the excitation current flowing through the lifting electromagnet 2a in a state in which power is supplied from the power source 4 to the lifting electromagnet 2a and the steel plate M is lifted by the lifting electromagnet device X.

[0045] The plate thickness magnetic flux characteristic storage unit 30 stores plate thickness magnetic flux characteristics that associate the magnetic flux generated by the lifting electromagnet 2a with the total plate thickness T of the lifted steel plate M. The plate thickness magnetic flux characteristics differ depending on the excitation current flowing through the lifting electromagnet 2a. The plate thickness magnetic flux characteristic storage unit 30 stores plate thickness magnetic flux characteristics corresponding to a plurality of excitation currents. Hereinafter, the total plate thickness T of the steel plate M will also be simply referred to as the plate thickness of the steel plate M.

[0046] In this embodiment, the plate thickness magnetic flux characteristic storage unit 30 stores, for example, the plate thickness magnetic flux characteristic for each excitation current as table data. Specifically, the plate thickness magnetic flux characteristic storage unit 30 stores in advance, as table data, data of a graph as shown in FIG. 2. Here, FIG. 2 is a graph showing the relationship between the total plate thickness T of the steel plate M lifted by the lifting electromagnet device X and the magnetic flux (magnetic flux detector output) generated by the lifting electromagnet 2a. Each of the curves in FIG. 2 is a curve showing the relationship between the plate thickness T and the magnetic flux at each excitation current. That is, each of the curves in FIG. 2 is the plate thickness magnetic flux characteristic. In the example shown in FIG. 2, when the magnetic flux generated in the magnetic circuit formed by the lifting electromagnet 2a and the steel plate is the same, the smaller the excitation current, the larger the plate thickness T.

[0047] The plate thickness magnetic flux characteristic acquisition unit 40 acquires the plate thickness magnetic flux characteristic corresponding to the value of the excitation current acquired by the excitation current detection unit 20 from the plate thickness magnetic flux characteristics stored in the plate thickness magnetic flux characteristic storage unit 30. In this embodiment, since the table data is stored in the plate thickness magnetic flux characteristic storage unit 30, the plate thickness magnetic flux characteristic acquisition unit 40 acquires the plate thickness magnetic flux characteristic from the table data based on the value of the excitation current acquired by the excitation current detection unit 20. Specifically, the plate thickness magnetic flux characteristic acquisition unit 40 selects a curve corresponding to the excitation current acquired by the excitation current detection unit 20 from the graph in FIG. 2.

[0048] The magnetic flux detection unit 50 is a magnetic flux detector that detects magnetic flux generated in a magnetic circuit formed by the lifting electromagnet 2a and the steel sheet M. The magnetic flux detection unit 50 acquires the value of the induced voltage detected by the search coil 5a when the steel sheet M is lifted by the lifting electromagnet device X with the pair of switches 31, 32 in a closed state. The magnetic flux detection unit 50 then obtains the magnetic flux by integrating the value of the induced voltage acquired from the search coil 5a. In this manner, the magnetic flux detection unit 50 detects the magnetic flux generated by the lifting electromagnet 2a using the search coil 5a.

[0049] The plate thickness detection unit 60 detects the plate thickness T corresponding to the magnetic flux detected by the magnetic flux detection unit 50, using the plate thickness magnetic flux characteristics acquired by the plate thickness magnetic flux characteristics acquisition unit 40 from the plate thickness magnetic flux characteristics storage unit 30. In this embodiment, as described above, the plate thickness magnetic flux characteristics acquisition unit 40 selects a curve (see FIG. 2) corresponding to the excitation current detected by the excitation current detection unit 20 from the graph of FIG. 2 stored in the plate thickness magnetic flux characteristics storage unit 30. Therefore, the plate thickness detection unit 60 acquires the plate thickness T from the curve selected by the plate thickness magnetic flux characteristics acquisition unit 40.

[0050] In this embodiment, the lifting electromagnet control device 1 has a lifting electromagnet selection unit 70. The lifting electromagnet selection unit 70 selects one of the multiple lifting electromagnets 2a, 2b, and 2c in response to a signal input to the lifting electromagnet control device 1. The lifting electromagnet selection unit 70 also selects a current detector of an electric circuit corresponding to the selected lifting electromagnet. The lifting electromagnet control device 1 then detects the plate thickness T of the lifted steel plate M using the selected lifting electromagnet and a current detector that detects the current flowing through the selected lifting electromagnet.

[0051] With the configuration of this embodiment, whichever of the multiple lifting electromagnets is used, the plate thickness T of the steel plate M lifted by the lifting electromagnets can be detected with high accuracy. Moreover, in the configuration of this embodiment, the multiple electric circuits 3a, 3b, 3c and the multiple lifting electromagnets 2a, 2b, 2c are electrically connected in parallel to one power source 4. This eliminates the need to connect a power source to each of the multiple lifting electromagnets 2a, 2b, 2c, and therefore makes it possible to obtain a compact and low-cost lifting electromagnet device X.

[0052] 3 is a flowchart showing the detection operation of the lifting electromagnet control device 1 when detecting the thickness T of the steel sheet M lifted by the lifting electromagnet 2a. When detecting the thickness T of the steel sheet M, the current control unit 10 closes the pair of switches 31, 32 and opens the discharge circuit switch 35. In this state, the steel sheet M is lifted by the lifting electromagnet device X.

[0053] 3 starts (START), first in step S1, the lifting electromagnet control device 1 determines whether a plate thickness detection command has been input. If it is determined in step S1 that a plate thickness detection command has been input (YES), the process proceeds to step S2. In step S2, the lifting electromagnet selection unit 70 selects one lifting electromagnet to be used for detecting the plate thickness of the steel plate M from the multiple lifting electromagnets 2a, 2b, and 2c, and also selects a current detector corresponding to the selected lifting electromagnet.

[0054] On the other hand, if it is determined in step S1 that the plate thickness detection command has not been input (NO), the determination in step S1 is repeated until the plate thickness detection command is input to the lifting electromagnet control device 1.

[0055] In the next step S3, the excitation current detection unit 20 acquires the value of the excitation current detected by the current detector selected in step S2. In the next step S4, the plate thickness magnetic flux characteristic acquisition unit 40 acquires the plate thickness magnetic flux characteristic corresponding to the value of the excitation current acquired by the excitation current detection unit 20, with reference to information on a plurality of plate thickness magnetic flux characteristics previously stored in the plate thickness magnetic flux characteristic storage unit 30.

[0056] Then, in step S5, the magnetic flux detection unit 50 acquires the value of an induced voltage detected by the search coil of the selected lifting electromagnet, and obtains the magnetic flux by integrating the acquired value of the induced voltage. In the next step S6, the plate thickness detection unit 60 acquires the plate thickness T corresponding to the magnetic flux detected by the magnetic flux detection unit 50, using the plate thickness magnetic flux characteristics acquired by the plate thickness magnetic flux characteristic acquisition unit 40, and detects the acquired plate thickness T as the plate thickness of the steel plate M. Then, in step S7, the lifting electromagnet control device 1 outputs the plate thickness T of the steel plate M to a display unit such as a monitor, and then ends this flow (END).

[0057] The lifting electromagnet control device 1 in this embodiment has a plate thickness magnetic flux characteristic memory unit 30 in which plate thickness magnetic flux characteristics relating the magnetic flux generated by the lifting electromagnet 2a to the plate thickness T of the steel plate M are stored for each excitation current, an excitation current detection unit 20 that detects the excitation current flowing through the lifting electromagnet 2a, a plate thickness magnetic flux characteristic acquisition unit 40 that acquires the plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit 20 from the plate thickness magnetic flux characteristics stored in the plate thickness magnetic flux characteristic memory unit 30, a magnetic flux detection unit 50 that detects the magnetic flux generated by the lifting electromagnet 2a when an excitation current is passed through the lifting electromagnet 2a, and a plate thickness detection unit 60 that detects the plate thickness T corresponding to the magnetic flux detected by the magnetic flux detection unit 50 as the plate thickness of the steel plate M using the plate thickness magnetic flux characteristic acquired by the plate thickness magnetic flux characteristic acquisition unit 40.

[0058] When there is variation in the excitation current flowing through the multiple lifting electromagnets 2a, 2b, and 2c, the magnetic flux generated by the multiple lifting electromagnets 2a, 2b, and 2c also varies for each lifting electromagnet. This causes variation in the attraction force of the multiple lifting electromagnets 2a, 2b, and 2c for the steel sheet M, which causes a problem that when detecting the thickness T of the steel sheet M based on the magnetic flux generated by the lifting electromagnets 2a, 2b, and 2c, the thickness T detected for each lifting electromagnet differs.

[0059] In response to this, the lifting electromagnet control device 1 having the above-mentioned configuration acquires plate thickness magnetic flux characteristics corresponding to the excitation current flowing through the lifting electromagnet 2a, and acquires the plate thickness T corresponding to the magnetic flux generated by the lifting electromagnet 2a using the acquired plate thickness magnetic flux characteristics. This makes it possible to accurately detect the plate thickness T of the steel plate M lifted by the lifting electromagnets even if there is variation in the excitation current flowing through the multiple lifting electromagnets 2a, 2b, and 2c.

[0060] In this embodiment, the plate thickness magnetic flux characteristic for each excitation current is stored as table data in the plate thickness magnetic flux characteristic storage unit 30. The plate thickness magnetic flux characteristic acquisition unit 40 acquires the plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit 20 from the table data.

[0061] This makes it possible to select a plate thickness magnetic flux characteristic corresponding to the excitation current flowing through the lifting electromagnet 2a from table data previously stored in the plate thickness magnetic flux characteristic storage unit 30. Therefore, it is possible to accurately detect the plate thickness T of the steel plate M lifted by the lifting electromagnet 2a based on the excitation current flowing through the lifting electromagnet 2a.

[0062] In this embodiment, the excitation current detection unit 20 detects the excitation current flowing through one of the lifting electromagnets 2a among the multiple lifting electromagnets 2a, 2b, and 2c electrically connected in parallel to the power source 4 via the electric circuits 3a, 3b, and 3c. The plate thickness magnetic flux characteristic acquisition unit 40 acquires the plate thickness magnetic flux characteristics stored in the plate thickness magnetic flux characteristic storage unit 30 based on the excitation current flowing through the lifting electromagnet 2a. The magnetic flux detection unit 50 detects the magnetic flux generated by the lifting electromagnet 2a.

[0063] In this way, when the multiple lifting electromagnets 2a, 2b, 2c are electrically connected in parallel to the power source 4, the electrical resistance of the multiple lifting electromagnets 2a, 2b, 2c varies due to temperature variations in the multiple lifting electromagnets 2a, 2b, 2c, and the excitation current flowing through the multiple lifting electromagnets 2a, 2b, 2c varies. As a result, the magnetic flux generated by the multiple lifting electromagnets 2a, 2b, 2c also varies for each lifting electromagnet, and the adsorptive force of the multiple lifting electromagnets 2a, 2b, 2c on the steel plate M also varies.

[0064] In such a case, in the above-mentioned configuration, the excitation current flowing through one of the lifting electromagnets 2a among the multiple lifting electromagnets 2a, 2b, and 2c is detected, and the thickness T of the steel sheet M lifted by the lifting electromagnet 2a is detected based on the detected excitation current. This makes it possible to accurately detect the thickness T of the steel sheet M lifted by each lifting electromagnet according to the variation in the excitation current flowing through each lifting electromagnet.

[0065] (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.

[0066] In the embodiment, the thickness magnetic flux characteristic storage unit 30 stores in advance, as table data, thickness magnetic flux characteristics that associate the magnetic flux generated by the hoisting electromagnet 2a with the thickness T of the steel sheet M for each excitation current. The thickness magnetic flux characteristic acquisition unit 40 acquires the thickness magnetic flux characteristics corresponding to the excitation current flowing through the hoisting electromagnet 2a from the table data. However, the thickness magnetic flux characteristic acquisition unit may acquire the thickness magnetic flux characteristics corresponding to the excitation current flowing through the hoisting electromagnet by using an approximation formula stored in advance in the thickness magnetic flux characteristic storage unit.

[0067] Specifically, the thickness magnetic flux characteristic storage unit may store, for each excitation current, a thickness magnetic flux characteristic that correlates the magnetic flux generated by the hoisting electromagnet with the thickness T of the steel sheet M, as an approximate formula. In this case, the thickness magnetic flux characteristic acquisition unit acquires the thickness magnetic flux characteristic using the excitation current detected by the excitation current detection unit and the approximate formula.

[0068] This makes it possible to reduce the amount of data stored in the plate thickness-magnetic flux characteristic storage unit, as compared with the case where table data is stored in the plate thickness-magnetic flux characteristic storage unit.

[0069] The plate thickness-magnetic flux characteristic storage unit may store, as the approximation formula, a general formula of the plate thickness-magnetic flux characteristic, in which the excitation current is a variable.

[0070] In the above embodiment, the lifting electromagnet selection unit 70 selects one of the multiple lifting electromagnets 2a, 2b, and 2c, and selects a current detector that detects the current flowing through the selected lifting electromagnet. However, the lifting electromagnet selection unit may select two or more lifting electromagnets from the multiple lifting electromagnets, and select a current detector corresponding to each of the selected lifting electromagnets.

[0071] In the above embodiment, the timing for detecting the magnetic flux by the magnetic flux detection unit 50 is after the plate thickness magnetic flux characteristic acquisition unit 40 acquires the plate thickness magnetic flux characteristic from the plate thickness magnetic flux characteristic storage unit 30. However, the timing for detecting the magnetic flux by the magnetic flux detection unit may be before the plate thickness magnetic flux characteristic acquisition unit acquires the plate thickness magnetic flux characteristic from the plate thickness magnetic flux characteristic storage unit, or before the excitation current is detected by the excitation current detection unit.

[0072] In the above embodiment, the lifting electromagnet device X has three lifting electromagnets 2a, 2b, and 2c. However, the lifting electromagnet device may have two or less lifting electromagnets, or may have four or more lifting electromagnets.

[0073] In the above embodiment, the electric circuit 3a of the lifting electromagnet device X has the discharge circuit 33. However, the electric circuit of the lifting electromagnet device does not have to have the discharge circuit.

[0074] In the above embodiment, the lifting electromagnet control device 1 controls the driving of the pair of switches 31, 32 and the discharge circuit switch 35 of the discharge circuit 33. However, the lifting electromagnet device may have a control device that controls the driving of the pair of switches and the discharge circuit switch, separate from the lifting electromagnet control device that detects the plate thickness of the steel plate being lifted by the lifting electromagnet.

[0075] In the above embodiment, the electric circuits 3a, 3b, 3c and the lifting electromagnets 2a, 2b, 2c are electrically connected in parallel to one power source 4. However, only some of the electric circuits and the lifting electromagnets may be electrically connected in parallel to one power source. Also, the electric circuits and the lifting electromagnets may be connected to different power sources. [Industrial Applicability]

[0076] 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]

[0077] X Lifting electromagnet device 1. Lifting electromagnet control device 2a, 2b, 2c lifting electromagnet 3a, 3b, 3c electrical circuit 4 Power supply 5a, 5b, 5c search coils 31, 32 Switchgear 34 Current detector 10 Current control section 20 Excitation current detection section 30 Plate thickness magnetic flux characteristic memory section 40 Plate thickness magnetic flux characteristic acquisition section 50 Magnetic flux detector 60 Plate thickness detection unit 70 Lifting electromagnet selection section M steel plate P Positive power line N Negative power supply line T plate thickness

Claims

1. A lifting electromagnet control device that controls the drive of a lifting electromagnet that lifts a steel plate by electromagnetic force, a plate thickness magnetic flux characteristic storage unit in which plate thickness magnetic flux characteristics in which the magnetic flux generated by the hoisting electromagnet and the plate thickness of the steel plate are related to each other are stored for each excitation current; An excitation current detection unit that detects an excitation current flowing through the hoisting electromagnet; a plate thickness magnetic flux characteristic acquisition unit that acquires a plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit from among the plate thickness magnetic flux characteristics stored in the plate thickness magnetic flux characteristic storage unit; a magnetic flux detection unit that detects a magnetic flux generated by the lifting electromagnet when an excitation current is applied to the lifting electromagnet; a plate thickness detection unit that detects, as a plate thickness of the steel plate, a plate thickness corresponding to the magnetic flux detected by the magnetic flux detection unit, using the plate thickness magnetic flux characteristic acquired by the plate thickness magnetic flux characteristic acquisition unit; having The plate thickness magnetic flux characteristic storage unit stores the plate thickness magnetic flux characteristic for each excitation current as an approximation formula, The plate thickness magnetic flux characteristic acquisition unit acquires, from the approximation formula, a plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit. Control device for lifting electromagnets.

2. A control device for a lifting electromagnet that controls the drive of a lifting electromagnet that lifts a steel plate by electromagnetic force, comprising: a plate thickness magnetic flux characteristic storage unit in which plate thickness magnetic flux characteristics in which the magnetic flux generated by the hoisting electromagnet and the plate thickness of the steel plate are related to each other are stored for each excitation current; An excitation current detection unit that detects an excitation current flowing through the hoisting electromagnet; a plate thickness magnetic flux characteristic acquisition unit that acquires a plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit from among the plate thickness magnetic flux characteristics stored in the plate thickness magnetic flux characteristic storage unit; a magnetic flux detection unit that detects a magnetic flux generated by the lifting electromagnet when an excitation current is applied to the lifting electromagnet; a plate thickness detection unit that detects, as a plate thickness of the steel plate, a plate thickness corresponding to the magnetic flux detected by the magnetic flux detection unit, using the plate thickness magnetic flux characteristic acquired by the plate thickness magnetic flux characteristic acquisition 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 an electric circuit; the plate thickness magnetic flux characteristic acquisition unit acquires a plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit from the plate thickness magnetic flux characteristics stored in the plate thickness magnetic flux characteristic storage unit, The magnetic flux detection unit detects a magnetic flux generated by the one hoisting electromagnet. Control device for lifting electromagnets.

3. The lifting electromagnet control device according to claim 2, The plate thickness magnetic flux characteristic storage unit stores the plate thickness magnetic flux characteristic for each excitation current as table data, The plate thickness magnetic flux characteristic acquisition unit acquires, from the table data, a plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit. Control device for lifting electromagnets.

4. The lifting electromagnet control device according to claim 1, 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 an electric circuit; the plate thickness magnetic flux characteristic acquisition unit acquires a plate thickness magnetic flux characteristic corresponding to the excitation current detected by the excitation current detection unit from the plate thickness magnetic flux characteristics stored in the plate thickness magnetic flux characteristic storage unit, The magnetic flux detection unit detects a magnetic flux generated by the one hoisting electromagnet. Control device for lifting electromagnets.

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