JPH09320844A - Detecting-method for load weight of lifting electromagnet and automatic correcting-method for centroid position by use of this detected result - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detecting method for the load weights of lifting electromagnets and an automatic correcting method for a centroid position by the use of this detected result. SOLUTION: Each lifting electromagnet 2a, 2b is suspended through a load cell 4a, 4b, and the quantity of a load to be sucked by the lifting electromagnet 2a, 2b to be linked to this load cell 4a, 4b is judged from a value measured by each load cell 4a, 4b. In this case, if it is found that a load weight exceeding the permissible value of an arbitrary lifting electromagnet 2a, 2b by the measured value (detected result) is burdened and sucked, it is desirable to raise a specified alarm. Besides, it is desirable that the direction and the amount of deviation between the current position of the centroid of a load to be sucked by individual lifting electromagnets 2a, 2b and the position of the centroid of the load whose weight should be distributed to each lifting electromagnet 2a, 2b, so as to be within the permissible value of each lifting electromagnet 2a, 2b, should be automatically calculated and displayed by using the measured value of each load cell 4a, 4b. Moreover, it is possible to correct the above-mentioned amount of deviation, if a specified means could be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation / control method for maintaining safety of a lifting electromagnet used when a steel material is transported in a steel mill or the like, and more particularly to a load amount suspended by each lifting electromagnet. The present invention relates to a method for detecting a load weight of a hoisting electromagnet that is optimal for balancing the load and a method for automatically correcting the position of the center of gravity using the detection result.

[0002]

2. Description of the Related Art For transporting steel products in steelworks, etc., a lifting electromagnet device for suspending a suspension electromagnet operated by a crane on a suspension beam and turning on / off a current to the suspension electromagnet to attract a steel product to be transported. Is used. In such a hoisting electromagnet device, one electromagnet may be used for one crane when suspending steels, but when carrying an iron plate or steel material having a large area formed as a product, it is appropriate to use it. In many cases, one steel plate or steel material and a processed product are carried by a plurality of hoisting electromagnets arranged.

[0003]

By the way, in the case of the lifting electromagnet apparatus as described above, the operator visually confirms the arrangement of the plurality of lifting electromagnets and the shape of the steel material corresponding to the shape of the steel material to be transported. The suction position is determined correspondingly. Therefore, when adsorbing irregular-shaped steel material, even if the adsorption position is improper because the position of the center of gravity is not clear, the carrying posture becomes unstable unless the operator notices the improper position. Dangerous cases occur. That is, it is necessary to carry out transportation work so that the deviation amounts of the center of the plurality of hoisting electromagnets and the center of gravity of the steel material fall within the reference values allowed for the respective hoisting electromagnets. In the case of irregularly shaped steel, it is difficult for the operator to adjust the position of the center of gravity so as to be appropriate. When such an operation is required, the operator's experience and skill have conventionally been used, and therefore, there is a tendency that the carrying work time is extended and the carrying is not performed accurately. The present invention solves the above-mentioned problems (problems) of the conventional one, and even a person with little experience in crane operation can surely adjust the center of gravity, and even an irregular-shaped steel material can easily perform the center of gravity surely. It is an object of the present invention to provide an automatic center-of-gravity position correction method using the detection result.

[0004]

In order to solve the above-mentioned problems, a method for detecting a load weight of a hoisting electromagnet according to the present invention is a hoisting electromagnet apparatus provided with a plurality of hoisting electromagnets for adsorbing and suspending and transporting steel materials. Is suspended through one to several or one to several pairs of load cells in the width direction of the steel material, and the amount of load adsorbed by the lifting electromagnet coupled to the load cells is determined from the measured values of the respective load cells. I chose In this case, the amount of load adsorbed to the lifting electromagnet coupled to the load cell is determined from the measured values of the respective load cells, and if any lifting electromagnet bears the load weight exceeding the allowable value, the predetermined value is determined. It is desirable to send an alarm. Also, using the values measured by each load cell, the deviation between the current position of the load center of gravity adsorbed to each hoisting electromagnet and the position of the load center of gravity for each hoisting electromagnet to which the load weight should be distributed within the allowable value of each hoisting electromagnet. It is desirable to automatically calculate and display the unit and direction. The attraction position of each lifting electromagnet may be manually or automatically corrected using the load amount detected by any of the above methods. Furthermore, by using the measured values by the respective load cells described above, the current position of the load center of gravity adsorbed to each lifting electromagnet and the position of the load center of gravity for each lifting electromagnet to which the load weight should be distributed within the allowable value of each lifting electromagnet, It is also possible to calculate the deviation amount and the direction and move the lifting electromagnet in the direction for correcting the deviation to re-adsorb the load, thereby automatically correcting the adsorption position of each lifting electromagnet. As described above, if the load weight of the hoisting electromagnet is detected and the center of gravity position is corrected, even an inexperienced operator can properly adsorb to the hoisting electromagnet regardless of the shape of the steel material.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings. First Embodiment: The first embodiment shows the basic functions of the present invention. A hoisting electromagnet device for adsorbing and carrying one steel material by two hoisting electromagnets will be described with reference to FIGS. 1 and 2. In FIG. 1, 1A is a suspension beam connected to a crane (not shown), and the suspension beam 1A has a first suspension electromagnet 2 at a predetermined interval.
a, the second hoisting electromagnet 2b is suspended, and the steel material 3A is adsorbed by these two hoisting electromagnets 2a, 2b.
Reference numerals 4a and 4b denote first and second load cells, respectively. The first load cell 4a is between the suspension beam 1A and the first suspension electromagnet 2a, and the second load cell 4b is the suspension beam 1.
A is coupled between A and the second lifting electromagnet 2b,
The load cell 4a and the second load cell 4b measure the weight of the steel material to which load is distributed respectively to the lifting electromagnets 2a and 2b to which they are coupled.

FIG. 2 shows a load weight detection method using a load cell according to the present invention and a center of gravity position correction method by an operator using the detection result. In FIG. 2, 4
a and 4b show the first and second load cells, 5a and 5a.
Reference characters b indicate the first and second measurement value display functions, respectively. The measurement output of the first load cell 4a is input to the first measurement value display function 5a, and the measurement output of the second load cell 4b is the second.
Is input to the measured value display function 5b. The operator
The lifting beam 1A in FIG. 1 is moved by a crane to move the first lifting electromagnet 2a and the second lifting electromagnet 2b.
Is activated to adsorb the steel material 3A to be conveyed, and then the suspension beam 1A is slightly raised. The operator determines whether each display value is within the reference value from the display value of the first measurement value display function 5a and the display value of the second measurement value display function 5b, and the display of any measurement value display function is displayed. If the value is larger than the reference value set corresponding to the characteristics of the lifting electromagnet, the center of gravity position G of the loaded steel material and the first lifting electromagnet 2
The approximate value of the distance δ between a and the middle of the second lifting electromagnet 2b is calculated, and depending on the conditions, the lifting beam 1A is lowered by the raised distance, and then the attraction force of the lifting electromagnet is temporarily released. After slightly raising the suspension beam 1A, the suspension beam 1A is moved by a distance δ to perform re-adsorption. The display value of the first measurement value display function 5a and the display value of the second measurement value display function 5b are read again, it is confirmed that both are within the reference value, and the transportation work is executed. However, if the display value of the first measurement value display function 5a and the display value of the second measurement value display function 5b are read again and the display value of any of the measurement value display functions is outside the reference value, the above work is performed. repeat.

Second Embodiment: A system in which the above-mentioned operator's correction work is automated, that is, a structure having an automatic calculation function for correcting the center of gravity using the detection result of the load weight detection method using a load cell. Will be described with reference to FIG. In FIG. 3, the measurement output of the first load cell 4a and the measurement output of the second load cell 4b are input to the arithmetic function 6A, and the output of the arithmetic function 6A is input to the alarm / display function 5c. The calculation function 6A has a function of automatically executing the operation performed by the operator based on the display values of the measurement value display functions 5a and 5b shown in the first embodiment, and the alarm / display function 5c is It has a function of displaying the calculation result. That is, the arithmetic function 6A is the first load cell 4a.
It is determined whether or not any of the measured values is within the reference value from the measured value of No. 2 and the measured value of the second load cell 4b, and the measured value of any of the measured value display functions is set corresponding to the characteristics of the lifting electromagnet. If the value is larger than the reference value, the first lifting electromagnet 2a and the second lifting electromagnet 2a are determined from the distance between the first lifting electromagnet 2a and the second lifting electromagnet 2b and the current measured value ratio of each load cell. The distance δ to be moved by the lifting electromagnet 2b is calculated, and a predetermined alarm and the distance δ to be moved are displayed on the alarm / display function 5c.

Third Embodiment: In the hoisting electromagnet device shown in FIG. 1 described above, a gravity center position compensating device for automatically compensating the adsorption position of the hoisting electromagnet, that is, a load weight detection result using a load cell is used. An embodiment of a center-of-gravity position correction apparatus to which the conventional center-of-gravity position correction method is applied will be described with reference to FIGS. 4 and 5. In FIG. 4, the measurement output of the first load cell 4a and the measurement output of the second load cell 4b are input to the signal processing function 6B, and the output of the signal processing function 6B is input to the crane control function 7. The crane control function 7 is provided with a signal line 7a for outputting each operation signal to each operation device, including an operation function of each hoisting electromagnet, each arm of the crane, an operation function of booms, a manual operation function, and the like. The signal processing function 6B and the crane control function 7 input a predetermined signal from a host control function (not shown) depending on the hoisting electromagnet device, and output a predetermined signal to the host control function (not shown). An input / output function (not shown) is provided.

The operation of the above-described center-of-gravity position correcting device will be described with reference to the flow chart shown in FIG. 5 in addition to FIGS. FIG.
At the time when the operator starts carrying work (S
0), the operator visually confirms the shape and position of the steel material 3A to be transported. When the signal processing function 6B and / or the crane control function 7 is provided with a signal input function from a host control function (not shown), the steel material information from the host control function is the signal processing function 6B and / or the crane control function. 7
(S1). While driving the crane, the lifting electromagnets 2a and 2b are excited to apply the electromagnets 2a and 2b to the steel material 3A to adsorb the steel material 3A (S2). Operate the crane to lift the suspension beam 1A, and thus each electromagnet 2a, 2
By slightly increasing b, each load cell 4a, load cell 4b is made to bear the total weight of the steel material 3A, and first the measured value G1 of the first load cell 4a and the preset limit value WC are compared by the signal processing function 6B. If the measured value G1 of the first load cell 4a is equal to or smaller than the limit value WC (S3), the measured value G2 of the second load cell 4b and the preset limit value WC are set to the signal processing function 6B. (S4), if the measured value G2 of the second load cell 4b is equal to or smaller than the limit value WC, the crane is raised to a predetermined height and then moved laterally to move the steel material 3A to a predetermined position. Proceed to the next step of transporting to.

As a result of comparing the measured value G1 of the first load cell 4a and the preset limit value WC by the signal processing function 6B, if the measured value G1 of the first load cell 4a is larger than the limit value WC (S3). (No portion), the deviation value between the measured value G1 of the first load cell 4a and the limit value WC, that is, the excess load is calculated (S6). In this case, the unillustrated data is also received, and the weight of the steel material 3A calculated by the sum of the measurement value G1 of the first load cell 4a and the measurement value G2 of the second load cell 4b and the electromagnet coupled to the suspension beam 1A. The position of the center of gravity G of the steel material 3A from the distance from 2a or 2b, the load weight ratio between the measured value G1 of the first load cell 4a and the measured value G2 of the second load cell 4b, and the lifting electromagnet 2a coupled to the hanging beam 1A. From the current center of gravity eccentricity position calculated from the distance between each of the hoisting electromagnets 2a and 2b, the eccentricity amount of the center of gravity for correcting the adsorption position of the steel material 3A between the hoisting electromagnets 2a and 2b, that is, each electromagnet 2a, 2b should be moved. The distance δ and the direction are calculated (S7). In this case, the suspension beam 1A is lowered to the original position to release the attraction force of each electromagnet 2a, 2b (S8), and the crane is slightly raised to a predetermined amount of eccentricity, that is, the movement distance δ of the electromagnet. The electromagnets 2a and 2b are moved in the direction (S9), and the process returns to step S2. As a result, step S3 and step S4 should be satisfied, so that the process proceeds to step S5 and the steel material transportation operation is executed.

As a result of comparing the measured value G1 of the first load cell 4a with the preset limit value WC by the signal processing function 6B, the measured value G1 of the first load cell 4a is equal to or smaller than the limit value WC ( S3) and if the measured value G2 of the second load cell 4b is larger than the limit value WC (S4)
No), the deviation value between the measured value G2 of the second load cell 4b and the limit value WC, that is, the excess load is calculated and calculated (S10). In this case as well, the data (not shown) is received and the same calculation as above is performed to make the steel material 3 by the electromagnets 2a and 2b.
An eccentricity amount δ and a direction for correcting the suction position of A are calculated (S7). As a result, after the suspension beam is lowered by the crane and the attraction force of each electromagnet 2a, 2b is released (S
8) Then, the crane is slightly raised to move in the predetermined direction by the amount of eccentricity δ (S9), and the process returns to step S2. as a result,
Steps S3 and S4 should be satisfied, so
Moving to step S5, the work of transporting the steel material 3A is executed.

The above-mentioned hoisting electromagnet is erroneously operated to correct the adsorption position, and the steel material load of the first hoisting electromagnet 2a or the second hoisting electromagnet 2b is larger than the set value.
That is, when the measured value G1 of the first load cell 4a or the measured value G2 of the second load cell 4b is larger than the limit value WC, the above steps are repeated. The crane operation described above is performed under the control of the host controller by providing the NC function in the crane control function 7 even if the operator manually operates by displaying the processing result on the signal processing function 6B. It may be configured automatically.

Fourth Embodiment: FIG. 6 shows a form of a hoisting electromagnet apparatus using a plurality of load cells for the hoisting electromagnet. In FIG. 6, 1B is a hanging hook connected to the crane, 2 is a lifting electromagnet, 4
c and 4d are load cells and 3B is a steel material attracted to the lifting electromagnet 2. This embodiment can be regarded as the same as the first embodiment shown in FIG. 1 in which two lifting electromagnets are brought close to each other and combined. Therefore, since the operation may be performed according to the first embodiment or the second embodiment described above, detailed description of the operation will be omitted.

Fifth Embodiment: Next, a large hoisting electromagnet device for carrying a large steel material will be described with reference to FIGS. 7 to 9. In FIG. 7 (A), 1C is suspended beam coupled to the crane, 2e ₁ ~2e _n denotes the lifting electromagnet to adsorb each steel 3C. Again 4
e ₁ ~4e _n is a load cell that measures the amount of load each respective lifting electromagnet share. The same figure (B) is the same figure (A)
Side shows a situation as seen from the direction, 2e ₁ represents one left of the lifting electromagnet 2e ₁ ~2e _n described above, 4e
_1a, 4e _1b, both load cells 4e ₁ ~4e _n described above, it indicates that the two load cells are formed become respectively a pair of electromagnets 2e ₁ lifting of the load cell 4e ₁ ~4e _n Only the load cell to be connected to is shown as a representative.

The functional configuration and operation of this embodiment will be described with reference to FIGS. 8 and 9. In FIG. 8 showing the schematic configuration of the control function, each load cell 4e _1a , 4e _{1b to} 4e _na ,
The output of 4e _nb is input to the measurement signal processing function 4A, and the output of the result of the measurement signal processing function 4A executing the processing described later is input to the operation / control function 10 of the lifting electromagnet device, and the operation / control of the lifting electromagnet device is performed. The output of the control function 10 is input to the crane operation / control function 11, and the output of the crane operation / control function 11 is output to the mechanism drive function 12 and the electromagnetic coil of the lifting electromagnet that collectively show each mechanism drive function of the crane. It is input to the excitation function 13 that comprehensively shows the drive function of supplying a predetermined current. An operation / control function 10 of the hoisting electromagnet apparatus is connected to an interpersonal interface function 10a having an operation / command signal input function for an operator to operate and a display function. Further, in accordance with the conditions of the lifting electromagnet device, the operation / control function 10 of the lifting electromagnet device measures the input line of the command signal to the measurement signal processing function 4A, each beam of the crane and the position of the lifting electromagnet, and the command is issued. An NC function or the like for automatically moving to a destination address is provided.

The operation of the above configuration will be described with reference to the schematic flow chart shown in FIG. When the operator starts work (S
0), the operator visually confirms the shape and position of the steel material 3C to be transported. An operation or an automatic control signal is input by the interpersonal interface function 10a, or steel material information from a host control function (not shown) is input to the operation / control function 10 of the lifting electromagnet device (S1). Electromagnet 2e lifting and moving the hanging beam 1C crane by an operator manipulation or preset program _{1 ~2e n}
After adsorbing the steel material 3C to be transported by operating the (S
2) Slightly raise the suspension beam 1C. The suspension beam 1C is lifted to raise the load cells 4e _1a , 4e _{1b to} 4e.
_na , 4e _nb (hereinafter abbreviated as 4e _{1 to} 4e _n ) is loaded with the total weight of the steel material 3C, and predetermined data of this lifting electromagnet device and position signals of respective parts obtained by a measurement sensor (not shown) during operation are displayed. Referring to the current position of the center of gravity corresponding to each lifting electromagnet of this steel material 3C,
Each load cell 4e ₁ ~4e _n corresponding to the shape of the steel material to calculate the position of the should illustrating an appropriately measured value balance as a normal center-of-gravity position (S3, S4). An eccentricity amount δ indicating the calculated distance between both gravity centers, that is, a deviation value and a deviation direction are calculated (S5). It is determined whether the calculated eccentricity amount δ is within the reference value (S6), and if it is within the reference value, the crane ascending operation is continued to perform the moving work (S7), and the steel material 3C is transported to the predetermined position. Proceed to the next step. Calculated eccentricity δ
There it is judged whether reference values (S6), If it is other than the reference value, a is lowered by a distance raised hanging beam 1C corresponds to the condition suction force of each lifting electromagnet 2e ₁ ~2e _n After releasing (S8), the suspension beam 1C is slightly raised as necessary to move in a direction for correcting the eccentricity amount δ,
If necessary, the pair of load cells of each hoisting electromagnet, for example, in the case of the hoisting electromagnet 4e ₁ , turns so that the measured values of the load cells 4e _1a and 4e _1b become equal (S9) and returns to step S2. As a result, step S6
Must be satisfied, the process proceeds to step S7 to carry out the steel material transportation work. Although it has been described that the eccentricity amount δ is compared with the reference value in order to detect the eccentricity state of the center of gravity described above, the measured value of each load cell is compared with the reference value as in the third embodiment described above. However, if it exceeds, the calculation and control processing for the eccentricity correction described above may be executed.

The above-described steps are repeated if the correction of the adsorption position by the lifting electromagnet is erroneously operated and the center of gravity position is calculated again and the result of determination is that the amount of eccentricity δ is larger than the reference value. In the above-described crane operation, even if the operator manually displays the processing result of the measurement signal processing function 4A on the interpersonal interface function 10a and the operator manually operates, the NC function is added to the crane operation / control function 11 and the mechanism drive function 12. It may be provided and may be configured completely automatically including the function of automatically operating the exciting function 13 for the coil of the lifting electromagnet. or,
The above-described third embodiment can be regarded as a special state of the fifth embodiment.

FIG. 10 shows an irregular shaped steel material applicable to each of the above-described embodiments of the present invention, and when applied to a case where a steel material whose center of gravity is indeterminate is adsorbed and conveyed. good. That is, as the steel material adsorbed by the lifting electromagnet, the one shown in FIG. 10 is targeted. FIG.
In the figures, (A), (B) and (C) are plan views of steel materials to be transported, respectively, and (D), (E) and (F) are the same.
Shows a side view of the steel material corresponding to FIGS. 8A, 8B and 8C respectively, and G shows the position of the center of gravity.

The above description shows a basic configuration for implementing the technical idea of the present invention and an embodiment for explaining its function. For example, the configuration of the main functions shown in FIG. 3 and FIG. In the block diagram, the calculation function based on the measurement signal of the load cell and the operation / control function of the hoisting electromagnet device are described as being separately configured for convenience of description, but an appropriate interface is provided between each measurement function and drive function. Are provided so that they can be executed by software processing on the same computer. For example, each function may be appropriately configured in accordance with the scale and the required function of the lifting electromagnet device.

[0020]

According to the present invention, the load weight distribution of the hoisting electromagnet is automatically detected by the above-described method, and the position of the center of gravity is automatically corrected using the detection result. Has excellent effect. Even an inexperienced operator can safely and surely apply the lifting electromagnet to the position of the center of gravity of the steel material that is the load to attract it. This can be similarly applied to the irregularly shaped steel material. Therefore, there is no risk of accidents during crane operation, and the steel material can be transported efficiently and safely.

[Brief description of drawings]

FIG. 1 is a front view showing a configuration of a lifting electromagnet device for explaining first to third embodiments of the present invention.

FIG. 2 is a block diagram showing a processing circuit by a load cell for explaining the first embodiment according to the present invention.

FIG. 3 is a block diagram showing a measurement signal processing circuit by a load cell for explaining a second embodiment according to the present invention.

FIG. 4 is a block diagram showing a processing circuit by a load cell for explaining a third embodiment according to the present invention.

FIG. 5 is a flowchart illustrating the operation of the third embodiment according to the present invention.

FIG. 6 is a front view showing a configuration of a hoisting electromagnet device for explaining a fourth embodiment according to the present invention.

FIG. 7 is a diagram showing a configuration of a lifting electromagnet device for explaining a fifth embodiment according to the present invention, the diagram (A).
Is a front view, and FIG.

FIG. 8 is a block diagram showing a processing circuit by a load cell for explaining a fifth embodiment according to the present invention.

FIG. 9 is a flowchart illustrating the operation of the fifth embodiment according to the present invention.

FIG. 10 is an outline view showing an example of the shape of a steel material to be conveyed to which the respective embodiments of the present invention are applied, and each of the drawings (A), (B) and (C) is a plan view. The figures, (D), (E) and (F) are respectively the same figure (A),
The side view of (B) and (C) is shown.

[Explanation of symbols]

1A, 1C: hanging beam 1B: hanging hooks _{2,2a, 2d, 2e 1 ~2 n} ,: lifting electromagnets 3A, 3B, 3C: steel _{4a~4d, 4e 1 ~4e n, 4e} 1a, 4e 1b: load cells 4A : Measurement signal processing function 5a, 5b: Measurement value display function 5c: Alarm / display function 6A: Calculation function 6B: Signal processing function 7: Crane control function 10: Lifting electromagnet device operation / control function 10a: Interpersonal interface function 11 : Crane operation / control function 12: Mechanism drive function 13: Excitation function

Claims (5)

[Claims] 1. A hoisting electromagnet device comprising a plurality of hoisting electromagnets for adsorbing and hoisting and transporting steel materials. In the hoisting electromagnet apparatus, each hoisting electromagnet is one to several or one in the width direction of the steel material.
Or a load weight detection method for a lifting electromagnet, which is suspended through several pairs of load cells, and a load amount adsorbed by a lifting electromagnet coupled to the load cell is determined from a measured value by each load cell. . 2. A hoisting electromagnet device comprising a plurality of hoisting electromagnets for adsorbing and hoisting and transporting steel materials, wherein each hoisting electromagnet is one to several or one in the width direction of the steel material.
Or, suspend the load through several pairs of load cells, judge the load amount adsorbed to the lifting electromagnets connected to the load cells from the measured values of each load cell, and any lifting electromagnet bears the load weight exceeding the allowable value. A load weight detection method, characterized in that a predetermined alarm is issued when adsorbed. 3. A hoisting electromagnet device comprising a plurality of hoisting electromagnets for adsorbing and hoisting and transporting steel materials. In the hoisting electromagnet apparatus, one to several or one or more hoisting electromagnets are provided in the width direction of the steel material.
Or, suspend the load through several pairs of load cells, and use the measured values of each load cell to distribute the load weight within the current position of the load center of gravity adsorbed to each lifting electromagnet and the allowable value of each lifting electromagnet. A load weight detection method characterized in that a deviation amount and a direction from a load gravity center position with respect to a hoisting electromagnet are automatically calculated and displayed. 4. The position of the center of gravity of the lifting electromagnet, which is adapted to manually or automatically correct the adsorption position of each lifting electromagnet by using the load amount detected by the method according to claim 1. Automatic correction method. 5. The method according to claim 3, wherein the deviation amount and the direction of the load gravity center position for each hoisting electromagnet are calculated, and the hoisting electromagnet is moved in a direction to correct the deviation to re-adsorb the load. By doing so, a method for automatically correcting the position of the center of gravity of each lifting electromagnet so that the attraction position of each lifting electromagnet is automatically corrected.