Patent Publication Number: US-8970334-B2

Title: Magnetic substance holding device using permanent magnet energy control

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 2013-0065478 filed on Jun. 7, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetic substance holding device, and more particularly, to a magnetic substance holding device that controls permanent magnet energy with which it is possible to obtain a strong holding force with a simple structure and to change from holding to releasing and vice versa by using only a low current. 
     2. Description of the Related Art 
     A magnetic substance holding device such as a permanent magnet workholding device is used to attach a target made of a magnetic material such as iron by using a magnetic force, and is widely used in various areas as an internal device attached to a die clamp of an injection molding machine, a die clamp of a press, a chuck of a machine tool, or the like, nowadays. 
     Basically, the magnetic substance holding device attaches the target formed of a magnetic substance to a holding face by using a strong magnetic force of a permanent magnet. When releasing the target, the magnetic substance holding device separates the target from the holding face by controlling a magnetic flow from the permanent magnet so as not to form the magnetic flow to the holding face. 
     As a method of controlling the magnetic flow from the permanent magnet, a method of controlling the magnetic flow by rotating another permanent magnet that is rotatably disposed and a method of controlling the magnetic flow by using a separate electromagnet may be used. 
     The applicant(s) has proposed a magnetic substance holding device using a separate electromagnet (see Patent Literature 1). 
     Patent Literature 1 
     International Patent Publication No. WO2012/039548A1 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a magnetic substance holding device capable of obtaining a strong holding force with a simple structure by disposing a coil on a pole piece without using a separate electromagnet and controlling the magnetic force of a permanent magnet by using even a low current only when changing from holding to releasing and vice versa. 
     Another object of the present invention is to provide a magnetic substance holding device capable of exhibiting a strong magnetic force in an optimum area by implementing a structure that can minimize remaining magnetism when releasing a target. 
     The objects of the present invention are not limited to the aforementioned objects, and other objects, which are not mentioned above, will be apparent to those skilled in the art from the following description. 
     In order to obtain the object, a magnetic substance holding device that controls permanent magnet energy includes an N pole piece formed of a magnetic substance, wherein the N pole piece has a holding face to which a target formed of a magnetic substance is attached and a base attachment face at a side different from the holding face; an S pole piece formed of a magnetic substance, wherein the S pole piece has a holding face to which the target is attached and a base attachment face at a side different from the holding face; a permanent magnet that is disposed such that the N pole thereof comes in contact with the N pole piece and the S-pole thereof comes in contact with the S pole piece; a coil that is wound around at least one of the N pole piece and the S pole piece; a base that is movable between a first position at which the base does not come in contact with both of the base attachment face of the N pole piece and the base attachment face of the S pole piece and a second position at which the base comes in contact with both of the base attachment face of the N pole piece and the base attachment face of the S pole piece; and a control device that controls a current applied to the coil, in which the target is held or released by applying a current to the coil through the control device such that at least one of the N pole piece and the S pole piece is magnetized. 
     According to another characteristic of the present invention, the base is movable between a first position at which the base does not come in contact with both of the base attachment face of the N pole piece and the base attachment face of the S pole piece and a second position at which the base comes in contact with both of the base attachment face of the N pole piece and the base attachment face of the S pole piece, the device further includes an elastic member that provides an elastic force in a direction in which the base is away from the N pole piece and the S pole piece; when the base is disposed at the first position, the target is attached to the holding faces of the N pole piece and the S pole piece; and the target is released from the holding faces of the N pole piece and the S pole piece by applying a current to the coil to generate a magnetic flow through the base attachment face of the N pole piece and the base attachment face of the S pole piece and by moving the base to the second position by a magnetic force. 
     According to still another characteristic of the present invention, the coil is wound around only the N pole piece and is positioned closer to the base than the permanent magnet. 
     According to still another characteristic of the present invention, the coil is wound around only the N pole piece and is positioned further from the base than the permanent magnet, and the sum of an area of the base attachment face of the N pole piece and an area of the base attachment face of the S pole piece is larger than that the sum of an area of the holding face of the N pole piece and an area of the holding face of the S pole piece. 
     According to still another characteristic of the present invention, the device further includes a yoke that has an empty space therein and an opening, in which the base is disposed within the empty space and the holding faces of the N pole piece and the S pole piece are exposed to the outside through the opening, and a first reinforced permanent magnet is disposed between the yoke and the N pole piece such that the N pole thereof comes in contact with the N pole piece and the S-pole thereof comes in contact with the yoke, or a second reinforced permanent magnet is disposed between the yoke and the S pole piece such that the S-pole thereof comes in contact with the S pole piece and the N pole thereof comes in contact with the yoke. 
     According to still another characteristic of the present invention, the S pole piece is a first S pole piece and the permanent magnet is a first permanent magnet, the device further includes: a second S pole piece formed of a magnetic substance, that has a holding face to which the target is attached and a base attachment face at a side different from the holding face; and a second permanent magnet that is disposed such that the N pole thereof comes in contact with the N pole piece and the S-pole thereof comes in contact with the second S pole piece, in which the coil is wound around the N pole piece, and the base extends to face the base attachment face of the second S pole piece. 
     According to still another characteristic of the present invention, the N pole piece is a first N pole piece and the permanent magnet is a first permanent magnet, the device further includes: a second N pole piece formed of a magnetic substance, that has a holding face to which the target formed of a magnetic substance is attached and a base attachment face at a side different from the holding face; and a second permanent magnet that is disposed such that the S-pole thereof comes in contact with the S pole piece and the N pole thereof comes in contact with the second N pole piece, in which the coil is wound around the S pole piece, and the base extends to face the base attachment face of the second N pole piece. 
     According to still another characteristic of the present invention, the N pole piece is a first N pole piece, the S pole piece is a first S pole piece, the permanent magnet is a first permanent magnet, the base is a first base, and the elastic member is a first elastic member, the device further includes: a second N pole piece formed of a magnetic substance, that has a holding face to which a target formed of a magnetic substance is attached and a base attachment face at a side different from the holding face; a second S pole piece formed of a magnetic substance, that has a holding face to which the target formed of a magnetic substance is attached and a base attachment face at a side different from the holding face; a second permanent magnet that is disposed such that the N pole thereof comes in contact with the second N pole piece and the S-pole thereof comes in contact with the second S pole piece; a second base formed of a magnetic substance, that is movable between a first position at which the second base does not come in contact with both of the base attachment face of the second N pole piece and the base attachment face of the second S pole piece and a second position at which the base comes in contact with both of the base attachment face of the second N pole piece and the second base attachment face of the second S pole piece; and a second elastic member that provides an elastic force pushing the second base in a direction in which the second base is away from the second N pole piece and the second S pole piece, in which the first N pole piece and the second N pole piece face each other but are spaced from each other, and the coil is disposed to surround both of the first N pole piece and the second N pole piece. 
     According to still another characteristic of the present invention, the N pole piece is a first N pole piece, the S pole piece is a first S pole piece, the permanent magnet is a first permanent magnet, the base is a first base, and the elastic member is a first elastic member, the device further includes: a second N pole piece formed of a magnetic substance, that has a holding face to which a target formed of a magnetic substance is attached and a base attachment face at a side different from the holding face; a second S pole piece formed of a magnetic substance, that has a holding face to which the target formed of a magnetic substance is attached and a base attachment face at a side different from the holding face; a second permanent magnet that is disposed such that the N pole thereof comes in contact with the second N pole piece and the S-pole thereof comes in contact with the second S pole piece; a second base formed of a magnetic substance, that is movable between a first position at which the second base does not come in contact with both of the base attachment face of the second N pole piece and the base attachment face of the second S pole piece and a second position at which the second base comes in contact with both of the base attachment face of the second N pole piece and the base attachment face of the second S pole piece: and a second elastic member that provides an elastic force in a direction in which the second base is away from the second N pole piece and the second S pole piece, in which the first S pole piece and the second S pole piece face each other but are spaced from each other, and the coil is disposed to surround both of the first S pole piece and the second S pole piece. 
     According to still another characteristic of the present invention, the target and one or more of the holding face of the N pole piece and the holding face of the S pole piece are fitted to each other, and the one or more of the holding face of the N pole piece and the holding face of the S pole piece is held at a predetermined position of the target when holding. 
     According to a magnetic substance holding device of the present invention, it is possible to obtain a strong holding force with a simple structure by disposing a coil on a pole piece without using a separate electromagnet, and to control the magnetic force of a permanent magnet by using even a low current only when changing from holding to releasing and vice versa. 
     Further, it is possible to minimize remaining magnetism when releasing the target. 
     Further, it is possible to achieve a stronger holding force even using a small space by using a plurality of magnetic substance holding devices that is separately provided. 
     Further, the device can be used for die clamps, locking devices, connection devices for passenger cars of a train, and roll lifting by changing the shape of the holding faces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view schematically showing a magnetic substance holding device according to an exemplary embodiment of the present invention; 
         FIG. 2A  is a schematic cross-sectional view when the magnetic substance holding device shown in  FIG. 1  holds a target, and  FIG. 2B  is a schematic cross-sectional view when the magnetic substance holding device shown in  FIG. 1  releases the target; 
         FIG. 3A  is a schematic cross-sectional view when a magnetic substance holding device according to another exemplary embodiment of the present invention holds the target, and  FIG. 3B  is a schematic cross-sectional view when the magnetic substance holding device shown in  FIG. 3A  releases the target; 
         FIG. 4  is a schematic cross-sectional view of a magnetic substance holding device according to still another exemplary embodiment of the present invention; 
         FIG. 5  is a schematic cross-sectional view of a magnetic substance holding device according to still another exemplary embodiment of the present invention; 
         FIGS. 6A and 6B  are schematic cross-sectional views of magnetic substance holding devices according to still other exemplary embodiments of the present invention; 
         FIG. 7  is a schematic cross-sectional view of a magnetic substance holding device according to still another exemplary embodiment of the present invention; and 
         FIG. 8  shows a schematic front view and a left side view of a magnetic substance holding device according to still another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Various advantages and features of the present invention and methods accomplishing thereof will become apparent from the following description of embodiments with reference to the accompanying drawings. However, the present invention is not limited to exemplary embodiment disclosed herein but will be implemented in various forms. The exemplary embodiments are provided by way of example only so that a person of ordinary skilled in the art can fully understand the disclosures of the present invention and the scope of the present invention. Therefore, the present invention will be defined only by the scope of the appended claims. 
     Indicating that elements or layers are “on” other elements or layers include both a case in which the corresponding elements are just above other elements and a case in which the corresponding elements are intervened with other layers or elements. Although first, second, and the like are used in order to describe various components, the components are not limited by the terms. The above terms are used only to discriminate one component from the other component. Therefore, a first component mentioned below may be a second component within the technical spirit of the present invention. 
     The same reference numerals indicate the same elements throughout the specification. 
     In the drawings, size and thickness of each element are arbitrarily illustrated for convenience of description, and the present invention is not necessarily limited to those illustrated in the drawings. 
     Respective features of various exemplary embodiments of the present invention can be partially or totally joined or combined with each other and as sufficiently appreciated by those skilled in the art, various interworking or driving can be technologically achieved and the respective exemplary embodiments may be executed independently from each other or together executed through an association relationship. 
     Hereinafter, magnetic substance holding devices according to exemplary embodiments of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a perspective view schematically showing a magnetic substance holding device according to an exemplary embodiment of the present invention,  FIG. 2A  is a schematic cross-sectional view when the magnetic substance holding device shown in  FIG. 1  holds a target, and  FIG. 2B  is a schematic cross-sectional view when the magnetic substance holding device shown in  FIG. 1  releases the target. 
     The configuration of a magnetic substance holding device  100  according to an exemplary embodiment of the present invention is described with reference to  FIGS. 1 ,  2 A, and  2 B. 
     Referring to  FIGS. 1 ,  2 A, and  2 B, the magnetic substance holding device  100  according to an exemplary embodiment of the present invention includes an N pole piece  110 , an S pole piece  120 , a permanent magnet  130 , a coil  140 , a base  150 , springs  160 , and a control device  170 . 
     The N pole piece  110  has a holding face  111  to which a target  1  as a magnetic substance is attached and a base attachment face  112  at a different side from the holding face  111 . The N pole pieced is a magnetic substance. 
     The S pole piece  120  has a holding face  121  to which the target  1  as a magnetic substance is attached and a base attachment face  122  at a different side from the holding face  121 . The S pole piece is a magnetic substance. 
     The permanent magnet  130  is disposed such that the N pole comes in contact with the N pole piece  110  and the S pole comes in contact with the S pole piece  120 . The number or the shape of the permanent magnet  130  may be freely determined, as long as the permanent magnet is disposed between the N pole piece  110  and the S pole piece  120 . 
     The coil  140  is disposed so as to be wound around at least one of the N pole piece  110  and the S pole piece  120 . In the exemplary embodiment, the coil  140  is wound around only the N pole piece  110  and is positioned closer to the base  150  than the permanent magnet  130 . However, the arrangement of the coil  140  is not limited to the aforementioned arrangement, and the coil may be wound around only the S pole piece  120 , or may be wound around both of the N pole piece  110  and the S pole piece  120 . Alternatively, the coil may be wound around any one of the portions upper and lower than the permanent magnet  130 . 
     The base  150  is a magnetic substance. The base can move between a first position (the position in  FIG. 2A ) where the base is not in contact with both of the base attachment face  112  of the N pole piece  110  and the base attachment face  122  of the S pole piece  120 , and a second position (the position in  FIG. 2B ) where the base is in contact with both of the base attachment face  112  of the N pole piece  110  and the base attachment face  122  of the S pole piece  120 . 
     Referring to  FIGS. 2A and 2B , the base  150  is guided to slide by bolts  151  fixed to the N pole piece  110  and the S pole piece  120  through the base  150  and receives a force applied upward by the springs  160  that are elastic members to be described below. Since counterbores  153  are formed at the base  150 , the distance by which the base is separated from the N pole piece  110  and the S pole piece  120  can be limited by heads  152  of the bolts  151 , even if the base  150  is pushed upward by the springs  160 . 
     The springs  160  are a type of elastic members that apply an elastic force to the base  150  in a direction in which the base is away from the N pole piece  110  and the S pole piece  120 . Elastic bodies such as rubber or polyurethane may be used as the elastic member in addition to the springs  160  of the exemplary embodiment. 
     It is preferable that the springs  160  and the bolts  151  be non-magnetic substances without influencing a magnetic flow between the N pole piece  110  and the base  150  and between the S pole piece  120  and the base. 
     The control device  170  controls the target  1  to be attached or released by controlling a current applied to the coil  140 . For reference, the control device is provided in the following exemplary embodiments but the control device not shown in the figures. 
     The principle of holding and releasing the target  1  formed of a magnetic substance by the magnetic substance holding device  100  having the configuration described above is described hereafter. 
     Referring to  FIG. 2A , by magnetizing the N pole piece  110  and the S pole piece  120  by using the permanent magnet  130  while a current is not applied to the coil  140 , attraction is generated between the N pole piece  110  and the target  1  and between the S pole piece  120  and the target, so that the target  1  is finally attached to the holding faces  111  and  121 . 
     After the target is attached to the holding faces, since the base  150  is spaced from the N pole piece  110  and the S pole piece  120  by the springs  160 , the magnetic flow from the permanent magnet  130  does not flow to the base  150  and the magnetic flow shown by the dotted line in  FIG. 2A  is generated, so that the target  1  is firmly fixed. 
     Once the magnetic flow shown by the dotted line is generated through the target  1 , since the entire magnetic flows move as shown by the dotted line, no magnetic force is generated through the base  150 . Therefore, the magnetic force of the permanent magnet  130  can be used to hold the target  1  without a loss of the magnetic force, so that an efficient holding force can be achieved. 
     Further, in order to increase the strength of attachment, a current is applied to the coil  140  such that an N pole is formed downward in  FIG. 2A . When a current is applied to the coil  140 , the N pole piece  110  is magnetized by electromagnetic induction as in an electromagnet, so that a stronger magnetic force can be produced. 
     Releasing the target  1  from the magnetic substance holding device  100  is described with reference to  FIG. 2B . 
     As shown in  FIG. 2B , when a current is applied to the coil  140  such that an S pole is formed toward the permanent magnet  130 , the magnetic force that attracts the base  150  increases and the base  150  is attached to the base attachment faces  112  and  122  against the elastic force of the springs  160 . That is, the base  150  moves to the second position. 
     As the base  150  is attached to the base attachment faces  112  and  122 , magnetic flow is formed along the path of permanent magnet  130 -N pole piece  110 -base  150 -S pole piece  120 -permanent magnet  130  and the magnetic flow of the permanent magnet  130  is induced to not the target  1  but the base  150  by the coil  140 , so that magnetic flow is not formed into the target  1 . 
     Accordingly, the target  1  can be released from the holding face  111  of the N pole piece  110  and the holding face  121  of the S pole piece  120 . Thereafter, even if the current applied to the coil  140  is stopped, since the base  150  does not return to the first position and the magnetic flow through the base  150  is maintained, so that the target  1  cannot be attached to the holding faces  111  and  121 . 
     In order to hold the target  1  again, it is required to return the base  150  to the first position shown in  FIG. 2A  by the elastic force of the springs  160  by allowing a current to flow in the coil  140  in a direction opposite to that of  FIG. 2B . That is, it is possible to return the base  150  to the first position by decreasing the magnitude of the magnetic flow shown by the dotted line in  FIG. 2B  by the coil  140 . 
     A noticeable point in the this configuration is that once the closed-loop magnetic flow is formed, as depicted by the dotted lines in  FIGS. 2A and 2B , even if another closed-loop path is formed by a magnetic substance, the magnetic flow keeps the direction in which the closed-loop magnetic flow is formed and magnetic flow is not formed along the another closed-loop path. That is, as shown in  FIG. 2B , when the base  150  is attached to the N pole piece  110  and the S pole piece  120  and the magnetic flow shown by the dotted line is formed, little or no magnetic flow is generated through the target  1 , even if the target  1  comes in contact with the holding faces  111  and  121 . Accordingly, it is possible to control magnetic flow to the holding faces  111  and  121  by using the base  150  that comes in contact with or does not comes in contact with the N pole piece  110  and the S pole piece  120 . Therefore, it is exemplified in the exemplary embodiment that the base  150  can move between the first position and the second position. 
     On the other hand, there is a need to appropriately adjust the modulus of elasticity of the springs  160 . For example, when the modulus of elasticity of the springs  160  is too small, it is required to supply a large amount of current to the coil  140  in order to return the base  150  to the first position, after the base  150  is attached to the N pole piece  110  and the S pole piece  120  as shown in  FIG. 2B . In contrast, when the modulus of elasticity of the springs  160  is too large, since it is required to a large amount of current to the coil  140  in order to attach the base  150  to the base attachment faces  112  and  122  when releasing the target  1 , this is not preferable. The modulus of elasticity of the springs  160  may be determined by experiences or experiments in consideration of the magnitude of the magnetic force that can be induced to the coil  140 . 
     Further, as well as the modulus of elasticity of the springs  160 , the distance by which the base  150  disposed at the first position is separated from the base attachment faces  112  and  122  should also be appropriately determined. This is because when the distance is too long, the base  150  may not be attached to the base attachment faces  112  and  122 , even if a current is applied to the coil  140 , whereas when the distance is too short, the base  150  may be attached to the base attachment faces  112  and  122 , even if a current is not applied to the coil  140 . Accordingly, in consideration of this point, only when a predetermined amount of current is applied to the coil  140 , the separation distance between the base  150  disposed at the first position and the base attachment faces  112  and  122  should be adjusted such that the base  150  can be attached to the base attachment faces  112  and  122 . The adjustment may be performed by experiences or experiments in consideration of the magnitude of the magnetic force that can be induced to the coil  140  and the modulus of elasticity of the springs  160 . 
     Further, the separation distance may be easily adjusted by the bolts  151  fastened to the N pole piece  110  and the S pole piece  120 . 
       FIG. 3A  is a schematic cross-sectional view when a magnetic substance holding device according to another exemplary embodiment of the present invention holds the target, and  FIG. 3B  is a schematic cross-sectional view when the magnetic substance holding device shown in  FIG. 3A  releases the target. 
     Referring to  FIGS. 3A and 3B , a magnetic substance holding device  200  according to another exemplary embodiment of the present invention includes an N pole piece  210 , an S pole piece  220 , a permanent magnet  230 , a coil  240 , a base  250 , springs  260 , and a control device (not shown). 
     The magnetic substance holding device  200  of the exemplary embodiment follows the same principle as that of the magnetic substance holding device  100  shown in  FIGS. 1 to 2B  and thus only the differences there between are described in detail. 
     In the magnetic substance holding device  200  of the exemplary embodiment, unlike the magnetic substance holding device  100  shown in  FIGS. 1 to 2B , the permanent magnet  230  is positioned close to the base  250  and the coil  240  is positioned close to a holding face  211 . That is, the coil  240  is positioned further from the base  250  than the permanent magnet  230 . 
     Further, in the magnetic substance holding device  200  of the exemplary embodiment, the sum of an area of a base attachment face  212  of the N pole piece  210  and an area of a base attachment face  222  of the S pole piece  220  is larger than the sum of an area of the holding face  211  of the N pole piece  210  and an area of a holding face  221  of the S pole piece  220 . 
     Accordingly, the magnetic force of the permanent magnet  230  can be efficiently induced to the base  250 , when the target  1  is released, so that the remaining magnetism that may be generated on the holding faces  211  and  221  can be minimized. 
       FIG. 4  is a schematic cross-sectional view of a magnetic substance holding device according to still another exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , a magnetic substance holding device  300  according to still another exemplary embodiment of the present invention includes an N pole piece  310 , an S pole piece  320 , a permanent magnet  330 , a coil  340 , a base  350 , and a control device (not shown). 
     The magnetic substance holding device  300  of the exemplary embodiment is different from the magnetic substance holding devices  100  and  200  in that the springs are not used as the elastic members and the base  350  is fixed so as to come in contact with a base attachment face  312  of the N pole piece  310  and a base attachment face  322  of the S pole piece  320 , and the other configurations are all the same. 
     In the magnetic substance holding device  300  of the exemplary embodiment, when holding the target, the direction of the magnetic flow through the base  350  is changed by applying a current to the coil  340  through the control device (not shown) such that the magnetic flow from the N pole of the permanent magnet  330  moves to a holding face  311  of the N pole piece  310 . Accordingly, the target  1  can be attached to holding faces  311  and  321 . 
     In contrast, when releasing the target, the direction of the magnetic flow through the target  1  is changed by applying a current to the coil  340  through the control device (not shown) such that the magnetic flow from the N pole of the permanent magnet  330  moves to the base attachment faces  312  of the N pole piece  310 . Accordingly, the target  1  can be released from the holding faces  311  and  321 . 
       FIG. 5  is a schematic cross-sectional view of a magnetic substance holding device according to still another exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , a magnetic substance holding device  400  according to the exemplary embodiment further includes a yoke  480 , a first reinforced permanent magnet  490 , and a second reinforced permanent magnet  495 , in addition to the configuration of the magnetic substance holding device  100  shown in  FIGS. 1 to 2B . 
     The yoke  480  has an empty space therein and an opening  482  formed toward the outside. The yoke is a magnetic substance. 
     The base  150  is disposed in the empty space  481  of the yoke  480  and the holding faces  111  and  121  of the N pole piece  110  and the S pole piece  120  are exposed to the outside through the opening  482 . 
     The first reinforced permanent magnet  490  may be disposed between the yoke  480  and the N pole piece  110  such that the N pole comes in contact with the N pole piece  110  and the S-pole comes in contact with the yoke  480 . Further, the second reinforced permanent magnet  495  may be disposed between the yoke  480  and the S pole piece  120  such that the S-pole comes in contact with the S pole piece  120  and the N pole comes in contact with the yoke  480 . In this configuration, both or only any one of the first reinforced permanent magnet  490  and the second reinforced permanent magnet  495  may be provided. 
     In the exemplary embodiment, it is exemplified that the yoke  480 , the first reinforced permanent magnet  490 , and the second reinforced permanent magnet  495  are added to the magnetic substance holding device  100  shown in  FIGS. 1 to 2B , but the present invention is not limited thereto and the yoke  480 , the first reinforced permanent magnet  490 , and the second reinforced permanent magnet  495  may be added to the magnetic substance holding device  200  shown in  FIGS. 3A and 3B  and the magnetic substance holding device  300  shown in  FIG. 4 . Those configurations are not described in detail. 
     According to the magnetic substance holding device  400  of the exemplary embodiment, since the permanent magnets are further attached to the N pole piece  110  and the S pole piece  120 , a large attaching force can be achieved even at a limited occupying area, the yoke  480  functions as a case, and excellent esthetic appearance can be expected. 
       FIGS. 6A and 6B  are schematic cross-sectional views of magnetic substance holding devices  500   a  and  500   b  according to still other exemplary embodiments of the present invention. 
     Referring to  FIG. 6A , the magnetic substance holding device  500   a  according to the exemplary embodiment further includes a second S pole piece  520  and a second permanent magnet  530 , in addition to the configuration of the magnetic substance holding device  100  shown in  FIGS. 1 to 2B . 
     The second S pole piece  520  has a holding face  521  to which the target  1  is attached and a base attachment face  522  at the different side from the holding face  521 . The second S pole piece is a magnetic substance. 
     The second permanent magnet  530  is disposed such that the N pole comes in contact with the N pole piece  110  and the S-pole comes in contact with the second S pole piece  520 . 
     The coil  140  is preferably wound around the N pole piece  110  in order to effectively control magnetic flow and in order not to expose the coil  140 , but the present invention is not limited thereto, and the coil may be wound around other pole pieces  120  and  520 . 
     The magnetic substance holding device  500   b  shown in  FIG. 6B  is different from the magnetic substance holding device  500   a  shown in  FIG. 6A  in that an S pole piece  120  is disposed at the middle portion, an N pole piece  110  and a second N pole piece  510  are disposed at both sides thereof, and a second permanent magnet  530  is disposed such that the S-pole comes in contact with the S pole piece  120  and the N pole comes in contact with the second N pole piece  510 . The basic principle of the magnetic substance holding device  500   b  shown in  FIG. 6B  is the same as that of the magnetic substance holding device  500   a  shown in  FIG. 6A , so that the detailed description thereof is not provided. 
     The bases  150  and  550  of the magnetic substance holding devices  500   a  and  500   b  shown in  FIGS. 6A and 6B  extend to be able to come in contact with all of three pole pieces. 
       FIG. 7  is a schematic cross-sectional view of a magnetic substance holding device  600  according to still another exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , the magnetic substance holding device  600  according to the exemplary embodiment is implemented by arranging two or more of the magnetic substance holding device  100  shown in  FIGS. 1 to 2B . 
       FIG. 7  shows an example with a case where two magnetic substance holding devices  100  are arranged, and N pole pieces  110  and  110 ′ are disposed so as to face each other, but may be spaced from each other. It is preferable that a coil  640  surround all of the N pole pieces  110  and  110 ′, as shown in  FIG. 7 . However, the present invention is not limited thereto, and the N pole pieces  110  and  110 ′ may be individually equipped with a coil. 
     Unlike the configuration shown in  FIG. 7 , S pole pieces  120  and  120 ′ may be disposed so as to face each other, but may be spaced from each other, and the coil  640  may surround all of the S pole pieces  120  and  120 ′. 
     Other configurations are the same as the configurations of the magnetic substance holding device  100  shown in  FIGS. 1 to 2B , and thus the detailed descriptions thereof are not provided. 
       FIG. 8  shows a schematic front view and a left side view of a magnetic substance holding device  700  according to still another exemplary embodiment of the present invention. 
     Referring to  FIG. 8 , a target  2  and one or more of a holding face  711  of an N pole piece  710  and a holding face  721  of an S pole piece  720  may be fitted to each other. In  FIG. 8 , the target  2  is formed such that three flat faces form two edges and the N pole piece  710  and the S pole piece  720  respectively have the holding faces  711  and  721  so as to be in contact with all of the three flat faces. 
     Accordingly, when holding the target, the holding faces  711  and  721  hold the target  2  at specific positions. That is, according to that the exemplary embodiment shown in  FIG. 8 , the target  2  is held such that the edges formed by the three flat faces are positioned so as to face edges of the holding faces  711  and  712 . 
     On the other hand, the magnetic substance holding device may be configured such that any one of the N pole piece  710  and the S pole piece  720  may be fitted to the target  2  and the other one is not fitted. Those various items of application may be achieved by changing the holding faces and the target in various ways. 
     When the magnetic substance holding device  700  of the exemplary embodiment is used, the target is held at an accurate position. Further, the sides of the target  2  are held by a magnetic force and the portion where the force is applied (the side perpendicular to the gravitational direction in (a) of  FIG. 8  is held, so that a large holding force can be effectively provided by the shape of the holding faces in addition to the magnetic force. 
     Since the magnetic substance holding device  700  of the exemplary embodiment has the structure that is fixed to a certain portion and held in the direction of force, the magnetic substance holding device can be used to pull or fix a certain target. For example, the magnetic substance holding device may be used for die clamps, locking devices, connection devices of passenger cars of a train, and roll lifting. In particular, the magnetic substance holding device may be fixed to a certain position by being connected through the connection link shown by the dotted line in (a) of  FIG. 8 . 
     The exemplary embodiments of the present invention have been described in more detail with reference to the accompanying drawings, but the present invention is not limited to the exemplary embodiments. It will be apparent to those skilled in the art that various modifications can be made without departing from the technical sprit of the invention. Accordingly, the exemplary embodiments disclosed in the present invention are used not to limit but to describe the technical spirit of the present invention, and the technical spirit of the present invention is not limited to the exemplary embodiments. Therefore, the exemplary embodiments described above are considered in all respects to be illustrative and not restrictive. The protection scope of the present invention must be interpreted by the appended claims and it should be interpreted that all technical spirits within a scope equivalent thereto are included in the appended claims of the present invention. 
     For example, the structure of fixing the base  350  in the magnetic substance holding device  300  shown in  FIG. 4  may be used for all of other exemplary embodiments.