Steel plate lifting method, lifting device, and steel plate manufacturing method

Abstract

To provide a method and a device for lifting a thin steel plate, which can stably lift a thin steel plate, and a method for manufacturing a steel plate, which can improve the work efficiency of manufacturing the steel plate.SOLUTION: A steel plate lifting method using a lifting magnet with a magnetic pole and an electromagnetic coil to lift at least one steel plate from a stack of a plurality of steel plates as an object to be lifted includes a lifting process in which a voltage is applied to the electromagnet coil so that the magnetic pole magnetic flux density becomes the target magnetic flux density, and the lifting magnet is raised to lift the object to be lifted. The steel plate lifting method includes a holding process of holding the object to be lifted by increasing the voltage applied to the electromagnetic coil when the decrease in a second magnetic flux density, which is the magnetic pole flux density in the state after the lifting magnet start to rise relative to a first magnetic flux density, which is the magnetic flux density of the magnetic poles in the state before the lifting magnets start to rise when the object to be lifted is attracted to the magnetic poles is equal to or greater than a dynamic lift off detection threshold.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for lifting a steel plate, and a method for manufacturing a steel plate including a step of conveying the lifted steel plate.

Background Art

[0002] A thick plate plant in a steelworks generally includes a rolling facility (rolling process) for rolling a massive steel plate to a desired thickness, a finishing facility (finishing process) for cutting to a shipping size, removing burrs at the ends, cleaning surface defects, or inspecting internal defects, and a product warehouse for storing steel plates awaiting shipment. Steel plates that are work-in-progress in the finishing process or steel plates awaiting shipment in the product warehouse are stored stacked in several to a dozen sheets due to space constraints. When rearranging or shipping the stacked steel plates, they are moved by lifting one to several steel plates to be moved using an electromagnetic lifting magnet attached to a crane.

[0003] A method (Patent Document 1) has been proposed for controlling the current applied to the coil based on the relationship between the current applied to the coil of the lifting magnet and the total thickness of the adsorbed steel plates in order to lift and move a predetermined number of steel plates.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the method of Patent Document 1, the amount of output magnetic flux is controlled by controlling the coil current in order to change the penetration depth of the magnetic flux. The coils of lifting magnets commonly used in steel mills' thick plate factories are designed to apply a large amount of magnetic flux to a steel plate in order to lift a large steel plate with a thickness of 100 mm or more. When using such a coil to lift a single thin steel plate with a thickness of 10 mm or less, it is necessary to control the magnetic flux density by applying a very small voltage to the coil.

[0006] However, when lifting thin steel plates, a gap may occur between the coil and the steel plate due to the deflection of the steel plate. The gap between the coil and the steel plate reduces the magnetic flux applied to the steel plate, reducing the adhesive force of the steel plate and causing the steel plate to fall. There is a need to stably lift thin steel plates. There is also a need to improve steel plate production efficiency by reducing the frequency of steel plate falls.

[0007] In view of the above, the present disclosure aims to provide a steel plate lifting method and apparatus capable of stably lifting thin steel plates, and a steel plate manufacturing method capable of improving the work efficiency of steel plate manufacturing. [Means for solving the problem]

[0008] (1) A method for lifting a steel plate according to one embodiment of the present disclosure is a method for lifting a steel plate, which uses a lifting magnet having a magnetic pole and an electromagnetic coil configured to be able to control a voltage for exciting the magnetic pole, and lifts at least one steel plate from among a plurality of stacked steel plates as a lifting target, a lifting process of lifting the object to be lifted by applying a voltage to the electromagnetic coil and raising the lifting magnet so that the magnetic flux density of the magnetic pole becomes a target magnetic flux density required for the magnetic pole to lift the object to be lifted; A holding step of increasing the voltage applied to the electromagnetic coil to hold the object to be lifted when the decrease amount of the second magnetic flux density, which is the magnetic flux density of the magnetic pole in a state where the object to be lifted is adsorbed to the magnetic pole and before the lifting magnet starts to rise, with respect to the first magnetic flux density, which is the magnetic flux density of the magnetic pole in a state before the lifting magnet starts to rise, is equal to or greater than the ground cutting detection threshold value. It includes.

[0009] (2) As an embodiment of the present disclosure, in the lifting step of (1) above, the voltage applied to the electromagnetic coil may be controlled so that the difference between the first magnetic flux density and the target magnetic flux density becomes equal to or less than the lifting control threshold value.

[0010] (3) As an embodiment of the present disclosure, the method for lifting a steel plate may further include a determination step of determining the number of steel plates lifted by being adsorbed to the lifting magnet based on the third magnetic flux density, which is the magnetic flux density of the magnetic pole in a state where the steel plate is lifted, in (1) or (2) above.

[0011] (4) As an embodiment of the present disclosure, in any one of (1) to (3) above, the ground cutting detection threshold value may be a value within a range of 0.01 or more and 0.20 T or less.

[0012] (5) As an embodiment of the present disclosure, in the holding step of any one of (1) to (4) above, the voltage applied to the electromagnetic coil may be increased to hold the object to be lifted after a waiting time has elapsed since it was determined that the decrease amount of the second magnetic flux density with respect to the first magnetic flux density is equal to or greater than the ground cutting detection threshold value. The waiting time may be a time within a range of 0.1 second or more and 2.0 seconds or less.

[0013] (6) As an embodiment of the present disclosure, in the lifting step of any one of (1) to (5) above, the target magnetic flux density may be calculated based on the respective plate thicknesses and saturation magnetic flux densities of at least one steel plate as the object to be lifted and the dimensions of the magnetic pole.

[0014] (7) The steel plate lifting device according to an embodiment of the present disclosure is a steel plate lifting device that lifts at least one steel plate as a lifting target from a plurality of stacked steel plates, and includes: a lifting magnet having a magnetic pole and an electromagnet coil configured to be able to control a voltage for exciting the magnetic pole; a voltage application device that applies a voltage to the electromagnet coil; a magnetic flux sensor that measures the magnetic flux density of the magnetic pole; a control device that controls the voltage applied to the electromagnet coil so that the magnetic flux density of the magnetic pole becomes a target magnetic flux density required for the magnetic pole to lift the lifting target. The steel plate lifting device is provided with: The magnetic flux sensor measures the magnetic flux density of the magnetic pole in a state where the lifting target is attracted to the magnetic pole and before the lifting magnet starts to rise as a first magnetic flux density, and measures the magnetic flux density of the magnetic pole in a state after the lifting magnet starts to rise as a second magnetic flux density. When the decrease amount of the second magnetic flux density with respect to the first magnetic flux density is equal to or greater than a ground cut detection threshold value, the control device increases the voltage applied to the electromagnet coil.

[0015] (8) As an embodiment of the present disclosure, in the above (7), the control device may control the voltage applied to the electromagnet coil so that the difference between the first magnetic flux density and the target magnetic flux density becomes equal to or less than a lifting control threshold value.

[0016] (9) As an embodiment of the present disclosure, in the above (7) or (8), the control device may determine the number of steel plates adsorbed and lifted by the lifting magnet based on the second magnetic flux density.

[0017] (10) As an embodiment of the present disclosure, in any one of the above (7) to (9), the ground cut detection threshold value may be a value within a range of 0.01 or more and 0.20 T or less.

[0018] (11) As one embodiment of the present disclosure, in any one of (7) to (10) above, when it is determined that the decrease amount of the second magnetic flux density with respect to the first magnetic flux density is equal to or greater than the ground cut detection threshold, the voltage applied to the electromagnetic coil may be increased after the elapse of the standby time. The standby time may be a time within a range of 0.1 second or more and 2.0 seconds or less.

[0019] (12) As one embodiment of the present disclosure, in any one of (7) to (11) above, the control device may calculate the target magnetic flux density based on the respective plate thicknesses and saturation magnetic flux densities of at least one steel plate as the lifting target and the dimensions of the magnetic poles.

[0020] (13) As one embodiment of the present disclosure, a method for manufacturing a steel plate includes a step of lifting and transporting at least one steel plate as a lifting target using the steel plate lifting device according to any one of (7) to (12) above.

Advantages of the Invention

[0021] According to the present disclosure, there are provided a steel plate lifting device and a lifting method capable of stably lifting a thin steel plate, and a steel plate manufacturing method capable of improving the production efficiency of the steel plate.

Brief Description of the Drawings

[0022] [Figure 1] It is a block diagram showing a configuration example of a steel plate lifting device according to the present disclosure. [Figure 2] It is a cross-sectional view showing a configuration example of a lifting magnet. [Diagram 3] It is a schematic diagram explaining a falling mechanism when lifting a steel plate with a lifting magnet. [Figure 4] It is a cross-sectional view explaining the magnitude of magnetic flux in each steel plate when adsorbing a plurality of steel plates with a lifting magnet. <able> [Figure 5] It is a flowchart showing a procedure example of the steel plate lifting method according to the present disclosure. [Figure 6]A graph showing the change in magnetic flux density when lifting a steel plate by the lifting method according to the present disclosure. [Figure 7] A graph showing the change in magnetic flux density when lifting a steel plate by the lifting method according to the comparative example.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments of a steel plate lifting device, a steel plate lifting method, and a steel plate manufacturing method according to the present disclosure will be described with reference to the drawings. Each drawing is schematic and may differ from reality. Further, the following embodiments illustrate an apparatus or method for embodying the technical idea of the present disclosure, and do not specify the configuration to the following. That is, various modifications can be made to the technical idea of the present disclosure within the technical scope described in the claims.

[0024] (Embodiment) A steel plate lifting device 10 (see FIG. 1) according to an embodiment of the present disclosure described below adsorbs a steel plate as a lifting object 20 (see FIG. 3) with a lifting magnet 1 (see FIG. 1 etc.). The steel plate lifting device 10 lifts the steel plate adsorbed by the lifting magnet 1 by raising the lifting magnet 1 with a crane 8 (see FIG. 1). Hereinafter, a configuration example and an operation example of the steel plate lifting device 10 according to the present embodiment will be described.

[0025] <Configuration Example of Steel Plate Lifting Device 10> As shown in FIG. 1, a steel plate lifting device 10 according to an embodiment of the present disclosure includes a lifting magnet 1, a control device 5, a voltage application device 6, and a crane 8. The crane 8 holds the lifting magnet 1 and is configured to raise, lower, or traverse the lifting magnet 1. The crane 8 may be configured to raise the lifting magnet 1 by winding up a wire.

[0026] <<Lifting Magnet 1>> As shown in FIGS. 1 and 2, the lifting magnet 1 includes an electromagnet coil 2, a magnetic pole 3, and a yoke 7. The lifting magnet 1 may include a plurality of units combining the electromagnet coil 2, the magnetic pole 3, and the yoke 7, as illustrated in FIG. 2.

[0027] The electromagnet coil 2 may be configured as a ring-shaped exciting coil obtained by winding an enameled copper wire a large number of times and performing insulation treatment. The diameter of the portion where the copper wire is wound in the electromagnet coil 2 may be from 100 mm to several hundred mm. When a voltage is applied to the electromagnet coil 2 from a voltage application device 6 described later, a current corresponding to the applied voltage flows through the copper wire. A magnetic flux is generated by the current flowing through the copper wire. The greater the voltage applied to the electromagnet coil 2, the greater the current flowing through the copper wire, and the greater the magnetic flux generated by the electromagnet coil 2. When the voltage application device 6 is off and no voltage is applied, the electromagnet coil 2 does not generate a magnetic flux. That is, the electromagnet coil 2 is configured to be controllable between an on state and an off state. Further, the electromagnet coil 2 is configured to be able to control the magnitude of the magnetic flux generated according to the magnitude of the applied voltage.

[0028] A magnetic pole 3 is disposed inside an electromagnet coil 2. The magnetic pole 3 functions as a magnetic core of the electromagnet coil 2. Let the diameter of the magnetic pole 3 be represented by D. The electromagnet coil 2 excites the magnetic pole 3. In other words, the electromagnet coil 2 is configured to be able to control a voltage for exciting the magnetic pole 3. A yoke 7 is disposed on the upper end side of the magnetic pole 3 and outside the electromagnet coil 2. Assume that the electromagnet coil 2 is wound around the magnetic pole 3 inside the yoke 7. That is, assume that the electromagnet coil 2 is wound between the magnetic pole 3 and the yoke 7. When viewed in the direction of the axis around which the electromagnet coil 2 is wound, the electromagnet coil 2 and the yoke 7 may be arranged concentrically around the magnetic pole 3. The shapes of the magnetic pole 3, the electromagnet coil 2, and the yoke 7 when viewed in the direction of the axis around which the electromagnet coil 2 is wound may be circular, rectangular, or various other shapes. Assume that the yoke 7 is configured such that its cross section is U-shaped. Assume that the yoke 7 is configured such that its cross section combined with the magnetic pole 3 is E-shaped. The magnetic pole 3 and the yoke 7 protrude more than the electromagnet coil 2 in cross section, and adsorb a steel plate at the tip of the protruding portion.

[0029] The magnetic pole 3 and the yoke 7 may be configured to include a soft magnetic material such as soft steel. Part or all of the magnetic pole 3 and the yoke 7 may be configured as an integral member. The magnetic pole 3 and the yoke 7 may be configured as separate members and combined. In order to fix the electromagnet coil 2 between the magnetic pole 3 and the yoke 7, a non-magnetic material such as resin may be filled.

[0030] The lifting magnet 1 further includes a magnetic flux sensor 4. The magnetic flux sensor 4 is installed on the magnetic pole 3 and measures the magnetic flux density of the magnetic flux passing through the magnetic pole 3. The magnetic flux density of the magnetic flux passing through the magnetic pole 3 is also referred to as the magnetic pole magnetic flux density. The magnetic pole magnetic flux density is determined based on the amount of magnetic flux generated by the electromagnet coil 2 and the cross-sectional area of the magnetic pole 3 in a cross section whose normal is the direction of the axis around which the electromagnet coil 2 is wound.

[0031] The magnetic flux sensor 4 may be configured to include, for example, a search coil or a Hall element. In the present embodiment, it is assumed that the magnetic flux sensor 4 is configured by a search coil. The installation position of the magnetic flux sensor 4 is not particularly limited as long as it can measure the magnetic pole magnetic flux density. In the present embodiment, it is assumed that the magnetic flux sensor 4 is installed at the lower end of the outer circumference of the magnetic pole 3. A plurality of magnetic flux sensors 4 may be installed at different positions of the magnetic pole 3.

[0032] <<Voltage application device 6>> The voltage application device 6 applies a voltage so as to pass an electric current through the electromagnet coil 2. The voltage application device 6 may be configured as a voltage source capable of controlling the voltage. The voltage application device 6 may be replaced with a current source capable of controlling the current.

[0033] <<Control device 5>> As shown in FIG. 1, the control device 5 is connected to the voltage application device 6 and controls the magnitude of the voltage applied by the voltage application device 6 to the electromagnet coil 2. The control device 5 acquires the measured value of the magnetic pole magnetic flux density by the magnetic flux sensor 4. The control device 5 may be connected to the crane 8 and configured to be able to control the lifting and lowering of the lifting magnet 1 by the crane 8.

[0034] The control device 5 may be configured to include at least one processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). The control device 5 may be configured by one processor or a plurality of processors. The processor constituting the control device 5 may realize the functions of the steel plate lifting device 10 by reading and executing a program stored in a storage unit described later.

[0035] The control device 5 may include a storage unit. The storage unit stores various types of information, data, etc. The storage unit may store, for example, a program executed in the control device 5, or data or processing results used in the processing executed in the control device 5. Further, the storage unit may function as a work memory of the control device 5. The storage unit may be configured to include, for example, a semiconductor memory, etc., but is not limited thereto. For example, the storage unit may be configured as an internal memory of a processor used as the control device 5, or may be configured as a hard disk drive (HDD) accessible from the control device 5. The storage unit may be configured as a non-temporary readable medium. The storage unit may be configured integrally with the control device 5, or may be configured separately from the control device 5.

[0036] The control device 5 may include a communication unit. The communication unit may be configured to include a communication interface for communicating with other devices by wire or wirelessly. The communication interface may be configured to be able to communicate with other devices via a network. The communication unit may be configured to include an input / output port for inputting / outputting data to / from other devices. The communication unit transmits and receives necessary data and signals to / from a process computer or a higher-level system. The communication unit may communicate based on a wired communication standard, or may communicate based on a wireless communication standard. For example, the wireless communication standard may include communication standards for cellular phones such as 3G, 4G, and 5G. Also, for example, the wireless communication standard may include IEEE802.11 and Bluetooth (registered trademark), etc. The communication unit may support one or more of these communication standards. The communication unit is not limited to these examples, and may communicate with other devices or input / output data based on various standards. The communication unit may be configured integrally with the control device 5, or may be configured separately from the control device 5.

[0037] The control device 5 may be configured to include an input device that receives input of information, data, etc. from an operator using the steel plate lifting device 10. The input device may be configured to include, for example, a touch panel or touch sensor, or a pointing device such as a mouse. The input device may be configured to include physical keys. The input device may be configured to include a voice input device such as a microphone. The control device 5 may be configured to be connectable to an external input device. The control device 5 may be configured to be able to acquire information or data input to the external input device from the external input device.

[0038] The control device 5 may be configured to include an output device that outputs information, data, etc. to the operator. The output device may include, for example, a display device that outputs visual information such as images, characters, or graphics. The display device may be configured to include, for example, an LCD (Liquid Crystal Display), an organic EL (Electro-Luminescence) display, an inorganic EL display, or a PDP (Plasma Display Panel), etc. The display device is not limited to these displays and may be configured to include various other types of displays. The display device may be configured to include a light emitting device such as an LED (Light Emitting Diode) or an LD (Laser Diode). The display device may be configured to include various other devices. The output device may include, for example, a voice output device such as a speaker that outputs auditory information such as voice. The output device is not limited to these examples and may include various other devices. The control device 5 may be configured to be connectable to an external output device. The control device 5 may be configured to be able to output information or data to the external output device.

[0039] <Operation Example of Steel Plate Lifting Device 10> The steel plate lifting device 10 according to this embodiment lifts a steel plate by adsorbing at least one steel plate from among a plurality of stacked steel plates with the lifting magnet 1 and raising the lifting magnet 1 with the crane 8.

[0040] When lifting the steel plate adsorbed by the lifting magnet 1, there is a difference between the force acting on the portion of the steel plate adsorbed by the lifting magnet 1 and the force acting on the portion not adsorbed by the lifting magnet 1 among the steel plates to be lifted. As illustrated in FIG. 3, the steel plate to be lifted 20 can be deformed due to the elasticity of the steel plate when grooved. After the steel plate is deformed when grooved, it can vibrate due to elasticity ((1) in FIG. 3). Due to the deformation or vibration of the steel plate, a gap may be generated between the lifting magnet 1 and the steel plate of the object to be lifted 20 ((2) in FIG. 3). The magnetic resistance increases due to the gap between the lifting magnet 1 and the steel plate of the object to be lifted 20, and the magnetic pole magnetic flux density decreases. When the magnetic pole magnetic flux density decreases, the force with which the lifting magnet 1 adsorbs the steel plate weakens, and at least a part of the steel plate to be lifted 20 may fall ((3) in FIG. 3).

[0041] Therefore, the control device 5 controls the voltage applied to the electromagnet coil 2 of the lifting magnet 1 so as to enhance the adsorption stability of the steel plate when lifting the steel plate. Hereinafter, an operation example of the control device 5 when adsorbing and lifting the steel plate with the lifting magnet 1 will be described.

[0042] <<Control of the Amount of Adsorbed Steel Plates>> The control device 5 can control the number of steel plates adsorbed by the lifting magnet 1 by controlling the voltage applied to the electromagnet coil 2. The process until starting to adsorb and lift the steel plate is also referred to as the lifting process.

[0043] When the lifting magnet 1 attracts a steel plate, a magnetic circuit through which magnetic flux passes is formed so as to link with the electromagnetic coil 2 through the magnetic pole 3, the yoke 7, and the attracted steel plate. As the amount of the attracted steel plates increases, the magnetic resistance of the magnetic circuit decreases, and the amount of magnetic flux passing through the magnetic circuit increases. The control device 5 can calculate the amount of the attracted steel plates based on the amount of magnetic flux passing through the magnetic circuit, that is, the magnetic flux density of the magnetic flux passing through the magnetic pole 3. The control device 5 may acquire a measured value of the magnetic pole magnetic flux density from the magnetic flux sensor 4 and calculate the amount of the attracted steel plates based on the measured value of the magnetic pole magnetic flux density. The control device 5 may calculate the amount of the attracted steel plates as the total thickness of a plurality of steel plates. When the thickness of each steel plate is the same or substantially the same, the control device 5 may calculate the amount of the attracted steel plates as the number of steel plates.

[0044] The control device 5 may acquire information specified by an operator on the number of steel plates to be attracted or the total thickness of the steel plates to be attracted. The control device 5 calculates a target value of the magnetic pole magnetic flux density necessary for attracting the specified amount of steel plates with the lifting magnet 1. The target value of the magnetic pole magnetic flux density is also referred to as the target magnetic flux density. Let the target magnetic flux density be represented as Br.

[0045] The total thickness of the steel plates attracted by the lifting magnet 1 is determined by the depth to which magnetic flux penetrates the steel plates (magnetic flux penetration depth). The lifting magnet 1 can control the number of steel plates attracted by controlling the magnetic flux penetration depth. The control device 5 may determine the target magnetic flux density based on the relationship between the magnetic pole magnetic flux density and the magnetic flux penetration depth.

[0046] The control device 5 attracts the specified amount of steel plates with the lifting magnet 1 by controlling the voltage application device 6 so that the magnetic pole magnetic flux density becomes the target magnetic flux density. The control device 5 may calculate the target magnetic flux density based on the plate thickness of the steel plates to be lifted 20 and the saturation magnetic flux density of the steel plates. The control device 5 can automatically control the number of steel plates to be lifted by feedback controlling the voltage applied to the electromagnetic coil 2 so that the magnetic pole magnetic flux density becomes the target magnetic flux density based on the diameter of the magnetic pole 3 and the magnetic pole magnetic flux density measured by the magnetic flux sensor 4.

[0047] Specifically, the control device 5 calculates the target magnetic flux density based on the diameter (D) of the magnetic pole 3 of the lifting magnet 1, that is, the dimension of the magnetic pole 3, and the respective plate thicknesses (t1 to t n ) of the n steel plates to be lifted 20, and the saturation magnetic flux densities (Bs1 to Bs n ) of the respective steel plates by the following formula (1).

Equation

[0048] Here, the target magnetic flux density of the magnetic pole 3 is derived from the following theory. As shown by the white arrow in FIG. 4, the magnetic flux generated by the lifting magnet 1 flows into the region 141 directly below the magnetic pole 3 from the upper surface of the steel plate to be lifted 20 and flows out from the side surface of the region 141. The magnetic flux outflow amount (Φ k ) in the k-th steel plate from the side close to the electromagnet coil 2 is based on the side area πD·t k and the saturation magnetic flux density Bs k and is calculated as Φ k =πD·Bs k ·t k .

[0049] Then, when n steel plates are to be lifted 20 from the side close to the electromagnet coil 2, the target magnetic flux (Φr) for passing the magnetic flux through the n-th steel plate is calculated by the following formula (2).

Equation

[0050] Furthermore, using the fact that the cross-sectional area (A) of the magnetic pole 3 is expressed as A = πD 2 / 4, the target magnetic flux density (Br) of the magnetic pole 3 is calculated by the following formula (3).

Equation

[0051] The control device 5 acquires the magnetic pole flux density of the magnetic pole 3 measured by the magnetic flux sensor 4 and calculates the difference between the magnetic pole flux density and the target magnetic flux density. Here, the magnetic pole flux density being adjusted to attract the steel plate is also referred to as the first magnetic flux density and is represented by Ba1. The control device 5 calculates the difference as |Ba1 - Br|. The control device 5 determines whether the difference is equal to or less than the lifting control threshold. The lifting control threshold is represented by B1. If the difference is greater than the lifting control threshold, i.e., |Ba1 - Br| > B1, the control device 5 feedback-controls the voltage application device 6 to adjust the voltage applied to the electromagnetic coil 2 so that the difference is equal to or less than the lifting control threshold. If the difference is equal to or less than the lifting control threshold, i.e., |Ba1 - Br| ≦ B1, the control device 5 may start raising the lifting magnet 1 using the crane 8.

[0052] As a comparative example, when an operator manually controls a lifting magnet, it is difficult to precisely control the magnetic flux penetration depth and operate the lifting magnet so that it can attract and lift the desired number of steel plates from the beginning. For this reason, a method is used in which more steel plates than the desired number are initially attracted and lifted, and then the excess steel plates are dropped by adjusting the current of the lifting magnet, thereby adjusting the number of attracted steel plates. However, this method of attracting a larger number of steel plates and then dropping the excess steel plates requires repeated adjustments of the number of attracted steel plates. The number of attempts required to successfully perform the task varies depending on the operator's skill. In other words, work efficiency depends on the operator's skill.

[0053] In contrast to the comparative example, the steel plate lifting device 10 according to this embodiment can automatically control the lifting of the steel plate, thereby improving work efficiency so that it does not depend on the skill of the worker.

[0054] <<Control when lifting steel plates>> As described above, when the steel plate to be lifted 20 is cut from the ground, the steel plate may fall due to deformation or vibration of the steel plate. Therefore, in the steel plate lifting device 10 according to the present embodiment, the control device 5 controls the magnetic pole magnetic flux density when lifting the steel plate based on the amount of decrease in the magnetic pole magnetic flux density when the steel plate is cut from the ground so that the steel plate to be lifted 20 can be stably lifted. The process after starting to lift the steel plate is also referred to as the holding process.

[0055] Specifically, the control device 5 calculates the amount of decrease in the magnetic pole magnetic flux density of the magnetic pole 3 when the lifting magnet 1 rises and the steel plate to be lifted 20 is cut from the ground. Here, the magnetic pole magnetic flux density before the lifting magnet 1 starts to rise is represented by Ba1. The magnetic pole magnetic flux density after the lifting magnet 1 starts to rise is also referred to as the second magnetic flux density and is represented by Ba2. The amount of decrease in the magnetic pole magnetic flux density is represented by Ba1 - Ba2. The control device 5 determines whether the amount of decrease in the magnetic pole magnetic flux density is equal to or greater than the ground cutting detection threshold value. The ground cutting detection threshold value is represented by B2. When the amount of decrease in the magnetic pole magnetic flux density is less than the ground cutting detection threshold value, that is, when Ba1 - Ba2 < B2, the control device 5 does not need to change the voltage applied to the electromagnetic coil 2 from the voltage application device 6. When the amount of decrease in the magnetic pole magnetic flux density is equal to or greater than the ground cutting detection threshold value, that is, when Ba1 - Ba2 ≧ B2, the control device 5 controls the voltage application device 6 to increase the voltage applied to the electromagnetic coil 2. By doing so, it becomes difficult for the steel plate to fall when the steel plate is cut from the ground.

[0056] After determining that the decrease amount of the magnetic pole magnetic flux density is equal to or greater than the ground cutting detection threshold, the control device 5 may control the voltage application device 6 to increase the voltage applied to the electromagnetic coil 2 after the elapse of the standby time. If the time until the voltage applied to the electromagnetic coil 2 is increased is too short, a number of steel plates greater than the number of steel plates to be lifted may be adsorbed. The standby time may be set with a lower limit of, for example, 0.1 seconds. The standby time may be set with a lower limit of 0.2 seconds. Conversely, if the time until the voltage applied to the electromagnetic coil 2 is increased is too long, at least a part of the steel plate to be lifted may fall. The standby time may be set with an upper limit of, for example, 2.0 seconds. The standby time may be set with an upper limit of 1.0 seconds. The lower limit or upper limit of the standby time is not limited to the exemplified values and may be determined as appropriate. By increasing the voltage applied to the electromagnetic coil 2 after the elapse of the appropriately set standby time, the possibility of successfully lifting the specified number of steel plates is increased.

[0057] The ground cutting detection threshold may be set as appropriate. However, if the ground cutting detection threshold is too small, although the possibility of the steel plate falling is low, a number of steel plates greater than the number of steel plates to be lifted may be adsorbed by increasing the voltage applied to the electromagnetic coil 2. Conversely, if the ground cutting detection threshold is too large, the possibility of the steel plate falling may be overlooked and the steel plate may fall as it is. The ground cutting detection threshold may be set with a lower limit of, for example, 0.01 T (tesla). The ground cutting detection threshold may be set with a lower limit of 0.02 T. The ground cutting detection threshold may be set with an upper limit of 0.2 T. The ground cutting detection threshold may be set with an upper limit of 0.1 T. The lower limit or upper limit of the ground cutting detection threshold is not limited to the exemplified values and may be determined as appropriate. By increasing the voltage applied to the electromagnetic coil 2 when the decrease amount of the magnetic pole magnetic flux density is equal to or greater than the appropriately set ground cutting detection threshold, the possibility of successfully lifting the specified number of steel plates is increased.

[0058] [[Determination of the number of lifted steel plates]] After the steel plate is cut by the ground cutter, the control device 5 determines the number of steel plates lifted based on the measured value of the magnetic pole magnetic flux density of the magnetic pole 3. The control device 5 may determine the number of steel plates lifted after the lifting of the lifting magnet 1 by the crane 8 is completed. This process is also referred to as the determination process.

[0059] Specifically, the control device 5 acquires from the magnetic flux sensor 4 the measured value of the magnetic pole magnetic flux density in the state where the steel plate is lifted. The magnetic pole magnetic flux density in the state where the steel plate is lifted is also referred to as the third magnetic flux density and is represented by Ba3. The control device 5 calculates the difference between the magnetic pole magnetic flux density in the state where the steel plate is lifted and the target magnetic flux density. The control device 5 can calculate the difference as |Ba3 - Br|. The control device 5 determines whether the difference is less than or equal to the lifting control threshold. When the difference is less than or equal to the lifting control threshold, that is, when |Ba3 - Br| ≤ B1, the control device 5 determines that the number of steel plates lifted is the specified number, and conveys the steel plate as it is.

[0060] When the difference is greater than the lifting control threshold, that is, when |Ba3 - Br| > B1, the control device 5 determines that the number of steel plates lifted is excessive or insufficient with respect to the specified number. When the control device 5 determines that the number of steel plates lifted is excessive or insufficient, it lowers the lifting magnet 1 to lower the steel plate, changes the target magnetic flux density, and lifts the steel plate again. The control device 5 may determine the change amount of the target magnetic flux density based on the value of Ba3 - Br. The control device 5 may change the target magnetic flux density by subtracting the value of Ba3 - Br from the original value. The control device 5 may change the target magnetic flux density by subtracting the value obtained by multiplying the value of Ba3 - Br by a predetermined coefficient from the original value. The predetermined coefficient may be a value less than 1 or a value greater than 1.

[0061] <<Example of flowchart>> The control device 5 may execute a method for lifting a steel plate including the procedure of the flowchart illustrated in FIG. 5. The method for lifting a steel plate may be realized as a steel plate lifting program to be executed by a processor included in the control device 5. The steel plate lifting program may be stored in a non-transitory computer-readable medium.

[0062] The control device 5 sets a target magnetic flux density (Br) according to the number of steel plates designated to be lifted (step S1). The control device 5 determines the voltage (coil voltage) to be applied to the electromagnet coil 2 based on the target magnetic flux density, and controls the voltage application device 6 to apply the coil voltage to the electromagnet coil 2 (step S2). The control device 5 measures the magnetic pole magnetic flux density (Ba1) by the magnetic flux sensor 4 (step S3).

[0063] The control device 5 determines whether the difference between the magnetic pole magnetic flux density and the target magnetic flux density is equal to or less than the lifting control threshold (step S4). That is, the control device 5 determines whether |Ba1 - Br| ≤ B1. When the difference is not equal to or less than the lifting control threshold (step S4: NO), that is, when the difference is greater than the lifting control threshold, the control device 5 returns to the procedure of step S2 and re-determines the coil voltage.

[0064] When the difference is equal to or less than the lifting control threshold (step S4: YES), the control device 5 determines that the designated number of steel plates are adsorbed and raises the lifting magnet 1 by the crane 8 (step S5). The control device 5 measures the magnetic pole magnetic flux density (Ba2) after the lifting magnet 1 starts to rise by the magnetic flux sensor 4 (step S6).

[0065] The control device 5 calculates the decrease amount of the magnetic pole flux density after starting the ascent of the lifting magnet 1 with respect to the magnetic pole flux density before starting the ascent of the lifting magnet 1, and determines whether the decrease amount has become equal to or greater than the ground cut detection threshold (step S7). That is, the control device 5 determines whether Ba1 - Ba2 ≥ B2. If the decrease amount of the magnetic pole flux density has not become equal to or greater than the ground cut detection threshold until the ascent of the lifting magnet 1 is completed (step S7: NO), that is, if the decrease amount of the magnetic pole flux density is less than the ground cut detection threshold, the process proceeds to the procedure of step S9.

[0066] If the decrease amount of the magnetic pole flux density becomes equal to or greater than the ground cut detection threshold during the ascent of the lifting magnet 1 (step S7: YES), the control device 5 controls the voltage application device 6 to increase the coil voltage (step S8). The control device 5 measures the magnetic pole flux density (Ba3) in the state where the ascent of the lifting magnet 1 is completed (step S9).

[0067] The control device 5 determines whether the difference between the magnetic pole flux density and the target flux density in the state where the ascent of the lifting magnet 1 is completed is equal to or less than the lifting control threshold (step S10). That is, the control device 5 determines whether |Ba3 - Br| ≤ B1. If the difference is equal to or less than the lifting control threshold (step S10: YES), it is determined that the specified number of steel plates to be lifted have been adsorbed and the lifting is completed, and the execution of the procedure of the flowchart in FIG. 5 is terminated. The control device 5 may cause the crane 8 to traverse the lifting magnet 1 to convey the steel plate.

[0068] If the difference is not equal to or less than the lifting control threshold (step S10: NO), that is, if the difference is greater than the lifting control threshold, the control device 5 adjusts the target flux density (step S11). After lowering the steel plate and releasing the adsorption, the control device 5 returns to the procedure of step S2 and starts over from the procedure of applying the coil voltage with the target flux density adjusted in the procedure of step S11.

[0069] <Method for manufacturing steel plate> The steel plate lifting device 10 may be used in the process of transporting steel plates in the manufacture of steel plates. As an embodiment, a method for manufacturing steel plates may be implemented, which includes a step of lifting and transporting at least one steel plate as a lifting target 20 by using the steel plate lifting device 10 according to the above-described embodiment.

[0070] <Parentheses> As described above, the control device 5 can stably lift the steel plate while automatically controlling the number of steel plates to be lifted by performing feedback control on the voltage applied to the electromagnet coil 2. By doing so, the number of steel plates to be lifted is controlled with high precision. By controlling the number of steel plates to be lifted with high precision, the number of times of redoing the lifting operation is reduced. As a result, the efficiency of the operation of lifting and transporting the steel plates is increased. Also, the production efficiency of the steel plates is increased.

[0071] (Example) Hereinafter, an example of the steel plate lifting device 10 according to an embodiment of the present disclosure will be described.

[0072] <Test on Control of Lifting Number> In order to evaluate the accuracy of controlling the number of steel plates lifted by the steel plate lifting device 10 according to an embodiment of the present disclosure, the following test was executed. In the lifting magnet 1 used in the test, the diameter of the magnetic pole 3 was set to 150 mm. The outer diameter of the yoke 7 was set to 350 mm. The thickness of the yoke 7 was set to 20 mm. The height (length in the direction along the winding axis) of the electromagnet coil 2 was set to 150 mm. The test was executed using a steel plate called SS400 (Structural Steel) whose saturation magnetic flux density is 1.5 T as the lifting target 20. The plate thickness of the steel plate used as the lifting target 20 was set to 4.5 mm. The number of plates to be lifted was set from 1 to 6. The lifting control threshold (B1) was set to 0.1 T. The ground cutting detection threshold (B2) was set to 0.1 T. The change amount of the target magnetic flux density was set to 0.1 T. The standby time was set to 0.2 seconds. The target magnetic flux density was set to 0.1 × the number of plates to be lifted (T).

[0073] The test results under the above-mentioned conditions are shown in Table 1 and Figure 6.

[0074]

Table 1

[0075] As shown in Table 1, by controlling the applied voltage based on the actual value of the pole magnetic flux density with respect to the target magnetic flux density, the number of lifted sheets was accurately controlled under any condition from 1 to 6 sheets. Also, as shown in Figure 6, although the pole magnetic flux density decreased by 0.1 T at the start of the ascent of the lifting magnet 1 when the number of lifted sheets was 1, it increased due to the increase in the coil voltage. As a result, even when the number of lifted sheets was 1, the steel plate was stably lifted without falling.

[0076] As a comparative example, the control accuracy of the number of lifted steel plates was evaluated when the amount of decrease in the pole magnetic flux density was not measured when lifting the steel plate. The test results of the comparative example are shown in Table 2 and Figure 7.

[0077]

Table 2

[0078] As shown in Table 2, the number of lifted sheets was accurately controlled under the conditions from 2 to 6 sheets. However, the lifting failed under the condition of 1 lifted sheet. As shown in Figure 7, since the pole magnetic flux density decreased at the start of the ascent of the lifting magnet 1, the steel plate fell as it was.

[0079] <Test on the setting range of the ground cut detection threshold> As described above, the ground-cut detection threshold may be set with a lower limit of 0.01T. The ground-cut detection threshold may be set with an upper limit of 0.2T. Furthermore, the ground-cut detection threshold may be set to an even narrower range, with a lower limit of 0.02T and an upper limit of 0.1T. To verify the validity of these ground-cut detection threshold settings, a lifting test was conducted 10 times under conditions where the ground-cut detection threshold was set to various values, in the case where the lifting failed in the comparative example described above and only one sheet was lifted. The test results are shown in Table 3. In Table 3, results for the ground-cut detection threshold range from 0.01T to 0.2T are enclosed in a bold box.

[0080] [Table 3]

[0081] As shown in Table 3, when the ground-cut detection threshold was set to 0.005T, the number of successful lifts when lifting one steel plate, which was the case in the comparative example described above where lifting failed, was only one. In other words, the success rate was only 10%. On the other hand, when the ground-cut detection threshold was set to 0.01T, the number of successful lifts increased to five. In other words, the success rate increased to 50%. Therefore, by setting the ground-cut detection threshold to 0.01T as the lower limit, the number of steel plates lifted can be controlled with high precision even when lifting only one steel plate.

[0082] Furthermore, when the ground-cut detection threshold was set to 0.25T, the number of successful lifts when lifting one steel plate, which was the case in the comparative example described above where lifting failed, was only one. In other words, the success rate was only 10%. On the other hand, when the ground-cut detection threshold was set to 0.2T, the number of successful lifts increased to six. In other words, the success rate increased to 60%. Therefore, by setting the ground-cut detection threshold to an upper limit of 0.2T, the number of steel plates that can be lifted can be controlled with high precision even when lifting only one steel plate.

[0083] Furthermore, when the ground-cut detection threshold was set to 0.02T, the number of successful attempts was greater than when it was set to 0.01T. Furthermore, when the ground-cut detection threshold was set to 0.1T, the number of successful attempts was greater than when it was set to 0.2T. Therefore, by setting the ground-cut detection threshold in an even narrower range, with a lower limit of 0.02T and an upper limit of 0.1T, the number of steel plates lifted can be controlled with even greater precision, even when lifting only one steel plate.

[0084] <Testing the setting range of the waiting time> As described above, the waiting time may be set with a lower limit of 0.1 seconds. The waiting time may be set with an upper limit of 2 seconds. Furthermore, the waiting time may be set in an even narrower range with a lower limit of 0.2 seconds and an upper limit of 1 second. To confirm the validity of these waiting time settings, a lifting test was conducted 10 times under conditions in which the waiting time was set to various values, in the case where the lifting failed in the comparative example described above and only one sheet was lifted. The test results are shown in Table 4. In Table 4, results for waiting times ranging from 0.1 seconds to 2 seconds are surrounded by a thick box.

[0085] [Table 4]

[0086] As shown in Table 4, when the waiting time was set to 0.05 seconds, the number of successful lifts when lifting one steel plate, which was the case in the comparative example described above where lifting failed, was only one. In other words, the success rate was only 10%. On the other hand, when the waiting time was set to 0.1 seconds, the number of successful lifts increased to six. In other words, the success rate increased to 60%. Therefore, by setting the waiting time to 0.1 seconds as the lower limit, the number of steel plates that can be lifted can be controlled with high precision even when lifting only one steel plate.

[0087] Furthermore, when the waiting time was set to 2.5 seconds, the number of successful lifts when lifting one steel plate, which was a failure in the comparative example described above, was only two. In other words, the success rate was only 20%. On the other hand, when the waiting time was set to 2 seconds, the number of successful lifts increased to five. In other words, the success rate increased to 50%. Therefore, by setting the waiting time to an upper limit of 2 seconds, the number of steel plates that can be lifted can be controlled with high precision even when lifting only one steel plate.

[0088] Furthermore, when the waiting time was set to 0.2 seconds, the number of successes was higher than when the waiting time was set to 0.1 seconds. Furthermore, when the waiting time was set to 1 second, the number of successes was higher than when the waiting time was set to 2 seconds. Therefore, by narrowing the waiting time range even further, with 0.2 seconds as the lower limit and 1 second as the upper limit, the number of steel plates lifted can be controlled with even greater precision, even when lifting only one steel plate.

[0089] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art could make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure. For example, the functions included in each component or step can be rearranged so as not to cause logical inconsistencies, and multiple components or steps can be combined or divided into one. The embodiments of the present disclosure can also be realized as a program executed by a processor included in an apparatus or a storage medium on which a program is recorded. It should be understood that these are also included within the scope of the present disclosure. [Explanation of symbols]

[0090] 10 Steel plate lifting device (5: control device, 6: voltage application device, 8: crane) 1 Lifting magnet (2: Electromagnet coil, 3: Magnetic pole, 4: Magnetic flux sensor, 7: Yoke) 20 Lifting Object (141: Area)

Claims

1. A method for lifting steel plates, which uses a lifting magnet having magnetic poles and an electromagnet coil configured to be able to control the voltage for exciting the magnetic poles, and lifts at least one steel plate out of a plurality of stacked steel plates as a lifting target, comprising: a lifting step of applying a voltage to the electromagnet coil so that the magnetic flux density of the magnetic poles becomes a target magnetic flux density required for the magnetic poles to lift the lifting target, and lifting the lifting target by raising the lifting magnet; a holding step of increasing the voltage applied to the electromagnet coil to hold the lifting target when the decrease amount of the second magnetic flux density, which is the magnetic flux density of the magnetic poles in a state where the lifting target is adsorbed to the magnetic poles and before the lifting magnet starts to rise, with respect to the first magnetic flux density, which is the magnetic flux density of the magnetic poles in a state after the lifting magnet starts to rise, is equal to or greater than a shear detection threshold; The method for lifting steel plates, comprising the above steps.

2. The method for lifting steel plates according to claim 1, wherein in the lifting step, the voltage applied to the electromagnet coil is controlled so that the difference between the first magnetic flux density and the target magnetic flux density is equal to or less than a lifting control threshold.

3. The method for lifting steel plates according to claim 1, further comprising a determination step of determining the number of steel plates lifted by being adsorbed to the lifting magnet based on the third magnetic flux density, which is the magnetic flux density of the magnetic poles in a state where the steel plates are lifted.

4. The method for lifting steel plates according to any one of claims 1 to 3, wherein the shear detection threshold is a value within a range of 0.01 or more and 0.20 T or less.

5. In the holding step, after a waiting time has elapsed since it is determined that the decrease amount of the second magnetic flux density with respect to the first magnetic flux density is equal to or greater than the shear detection threshold, the voltage applied to the electromagnet coil is increased to hold the lifting target. The method for lifting steel plates according to any one of claims 1 to 3, wherein the waiting time is a time within a range of 0.1 second or more and 2.0 seconds or less.

6. The method for lifting steel plates according to any one of claims 1 to 3, wherein in the lifting step, the target magnetic flux density is calculated based on the respective plate thicknesses and saturation magnetic flux densities of at least one steel plate as the lifting target and the dimensions of the magnetic poles.

7. A steel plate lifting device for lifting at least one steel plate from a plurality of stacked steel plates as a lifting target, A lifting magnet having a magnetic pole and an electromagnet coil configured to be able to control a voltage for exciting the magnetic pole, A voltage application device for applying a voltage to the electromagnet coil, A magnetic flux sensor for measuring the magnetic flux density of the magnetic pole, A control device for controlling the voltage applied to the electromagnet coil so that the magnetic flux density of the magnetic pole becomes a target magnetic flux density required for the magnetic pole to lift the lifting target, Comprising, The magnetic flux sensor measures the magnetic flux density of the magnetic pole in a state where the lifting target is adsorbed to the magnetic pole and before the lifting magnet starts to rise as a first magnetic flux density, and measures the magnetic flux density of the magnetic pole in a state after the lifting magnet starts to rise as a second magnetic flux density, When the decrease amount of the second magnetic flux density with respect to the first magnetic flux density is equal to or greater than a ground cutting detection threshold, the control device increases the voltage applied to the electromagnet coil, Steel plate lifting device.

8. The control device controls the voltage applied to the electromagnet coil so that the difference between the first magnetic flux density and the target magnetic flux density becomes equal to or less than a lifting control threshold. The steel plate lifting device according to claim 7.

9. The control device determines the number of steel plates adsorbed and lifted by the lifting magnet based on a third magnetic flux density which is the magnetic flux density of the magnetic pole in a state where the steel plate is lifted. The steel plate lifting device according to claim 7.

10. The ground cutting detection threshold is a value within a range of 0.01 or more and 0.20 T or less. The steel plate lifting device according to any one of claims 7 to 9.

11. When it is determined that the decrease amount of the second magnetic flux density with respect to the first magnetic flux density is equal to or greater than a ground cutting detection threshold, the control device increases the voltage applied to the electromagnet coil after a standby time has elapsed, The standby time is a time within a range of 0.1 second or more and 2.0 seconds or less. The steel plate lifting device according to any one of claims 7 to 9.

12. The control device calculates the target magnetic flux density based on the respective plate thicknesses and saturation magnetic flux densities of at least one steel plate as the lifting target and the dimensions of the magnetic pole. The steel plate lifting device according to any one of claims 7 to 9.

13. A method for manufacturing a steel sheet, comprising a step of lifting and conveying at least one steel sheet as a lifting target using the steel sheet lifting device according to any one of claims 7 to 9.

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