Patent Publication Number: US-6215381-B1

Title: Magnetic lock device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a magnetic lock device including two separate elements that arc capable of being detachably coupled together by attracting each other magnetically under the magnetic interaction of two permanent magnets, and more particularly to a magnetic lock device that may be used with an article, such as bags, that usually includes two integral parts, such as a flap and a body, for detachably coupling those two parts together, and may also be used with clothing or clothes that usually require the regular or frequent washing or cleaning treatment. 
     DESCRIPTION OF THE PRIOR ART 
     In the prior art, there is a conventional magnetic lock device that takes advantage of the magnetic attracting action of a permanent magnet, and is used with an article such as a bag, for example, for detachably coupling the body and flap of the bag. It is known that this device performs well for the above purpose. The conventional magnetic lock device is known in different types and constructions. Typically and basically, it has the construction that is described below. 
     The magnetic lock device essentially includes a first element and a second element that are capable of being detachably coupled together by utilizing the magnetic interaction between a permanent magnets and a ferromagnetic plate. Specifically, for one part, the first element includes an annular permanent magnet having a center bore through it, and a first ferromagnetic disk-like plate disposed to make contact with the non-attracting side of the annular permanent magnet that is located on the side opposite the attracting side of the magnet, and a first ferromagnetic projecting member extending from the center of the first ferromagnetic disk-like plate and through the said center bore of the permanent magnet toward the attracting side of the annular permanent magnet. The annular permanent magnet and the first ferromagnetic disk-like plate having the first ferromagnetic projecting member are packaged as a single unit within a non-magnetic covering. The first element thus formed acts as the attracting unit. 
     For the other part, the second clement, which acts as the unit to be attracted by the first element or attracting unit, includes a second ferromagnetic disk-like plate that is to be attached to the attracting side of the annular permanent magnet of the first element. As the annular permanent magnet and the first ferromagnetic disk-like plate comprising the first element arc packaged by the non-magnetic covering, when the second ferromagnetic disk-like plate of the second element is attached to the attracting side of the annular permanent magnet of the first element by and under the magnetic force of the annular permanent magnet, the upper horizontal part of the non-magnetic covering, which covers the attracting side of the annular permanent magnet, is sandwiched between the second ferromagnetic disk-like plate and the annular permanent magnet. 
     The second ferromagnetic disk-like plate of the second element can be attached to the annular permanent magnet of the first clement by and under the magnetic force of the annular permanent magnet, also the second ferromagnetic disk-like plate can be detached from the annular permanent against the magnetic force of the annular permanent magnet. 
     The second ferromagnetic disk-like plate of the second element has a second ferromagnetic projecting member which extends from the center of the second ferromagnetic disk-like plate, and, when the second ferromagnetic disk-like plate of the second element is attached to the annular permanent magnet of the first element, extends through the center bore of the annular permanent magnet toward the first ferromagnetic disk-like plate of the first element. 
     The second ferromagnetic projecting member on the second element can engage the first ferromagnetic projecting member on the first ferromagnetic disk-like plate through the center bore of the permanent magnet when the second ferromagnetic disk-like plate is attached to the annular permanent magnet. Thus, the first and second elements may be coupled together magnetically under the action of the permanent magnet, which is enclosed in the first element, as they are brought closer to each other, so that a magnetic circuit can be concluded through the first and second ferromagnetic projecting members, the first and second ferromagnetic disk-like plates, and the annular permanent magnet. This permits the first and second elements to be coupled securely. 
     When the first and second elements are to be detached, this may be accomplished simply by moving them laterally relative to each other with a certain angle with regard to the interface between the first and second elements as coupled, and thus disconnecting the path of the magnetic circuit principally formed by the first and second ferromagnetic projecting members. 
     This device is of a compact size, and provides powerful magnetic attracting force that can keep them locked securely. Attaching and detaching the two elements may be accomplished very easily. The magnetic lock device described above is disclosed in Japanese patent application No. H2 (1990)-205503, for example. 
     It should be noted, however, that according to the conventional magnetic lock device described above, there is a gap between the outer peripheral wall of the first ferromagnetic projecting member and the inner peripheral wall of the center bore of the permanent magnet. The space formed by the gap may easily introduce particles such as dust, particularly ferromagnetic particles like iron. Those ferromagnetic particles may create a short magnetic circuit between the inner peripheral wall of the center bore of the permanent magnet and the outer peripheral wall of the first ferromagnetic projecting member. When this situation occurs, the magnetic circuit formed by the first and second ferromagnetic projecting members, the first and second ferromagnetic plates and the permanent magnet may become weaker, which may reduce the magnetic interaction between the first and second elements when they are coupled. Therefore, in the conventional magnetic lock device as before described, it is necessary to take care that any particle can not enter into the gap between the inner peripheral wall of the center bore of the annular permanent magnet and the outer peripheral wall of the first ferromagnetic projecting member. 
     But when the conventional magnetic lock device is used with clothing or clothes that may usually require the regular or frequent washing or cleaning treatment or that may often be put on the ground or make contact with other various objects, it is likely that particles such as dust, particularly ferromagnetic particles like iron, will enter the gap or space between the inner peripheral wall of the center bore of the permanent magnet and the outer peripheral wall of the first ferromagnetic projecting member. For this reason, the conventional magnetic lock device has principally been used with bags, rather than clothing or clothes. 
     It should also be noted that the conventional magnetic lock device includes the first and second ferromagnetic plates that are made of iron that may easily gather rust when exposed to water or moisture. This is another reason why the conventional device has not been used with the clothing or clothes. 
     SUMMARY OF THE INVENTION 
     The present invention provides a new magnetic lock device which can eliminate the problems associated with the conventional magnetic lock device as described above. According to the present invention, a magnetic lock device includes a first element and a second element that are capable of being detachably coupled, and each of the first and second elements has an annular permanent magnet enclosed therein such that one permanent magnet and the other permanent magnet have the opposed polarities on the side facing opposite each other, wherein each of the first and second elements may entirely be covered with any suitable non-magnetic, synthetic resin film, sheet, covering and casing or may entirely have a coating of the non-magnetic, synthetic resin layer formed thereon, or alternatively may be covered with any suitable non-magnetic, synthetic resin film, sheet, covering and casing or may have a coating of the nonmagnetic, synthetic resin layer formed thereon, with the ends of the ferromagnetic projecting members engaging each other being uncovered or exposed. 
     It may be appreciated from the detailed description presented so far that the magnetic lock device according to the particular preferred embodiments and variation thereof has advantages over the conventional magnetic lock device whose usage is limited to bags, in that the magnetic lock device according to the present invention can be used not only with bags, but also with clothes that require regular and frequent washing or cleaning treatment. To provide those advantages, each of the first element and the second element may have an annular permanent magnet enclosed therein such that the permanent magnet and the other permanent magnet have the opposed polarities on the side facing opposite each other. And the first element may totally be covered with the non-magnetic, synthetic resin film, sheet, covering or casing or coated with the non-magnetic, synthetic resin layer. Alternatively, the first element and the second element may be covered with the non-magnetic, synthetic resin film, sheet, covering or casing or coated with the non-magnetic, synthetic resin layer, such that the ends of the first and second ferromagnetic projecting members engaging each other remain uncovered or exposed. Thereby, the gaps or spaces that are present between the inner peripheral wall of the center bore in the annular permanent magnet and the outer peripheral wall of the ferromagnetic projecting member extending through the center bore can be protected against any foreign matter such as dust, particularly magnetic particles like iron, that might otherwise enter the gaps or spaces. All of the metal component parts including the ferromagnetic plates, projecting members, etc. can also be protected against any possible rust that might occur if water or moisture should enter there. 
     In addition, the magnetic lock device according to the present invention has the advantage in that the first element and the second element can be coupled more securely and more stably by the increased magnetic interaction of the first and second annular permanent magnets of opposed polarities facing each other, coupled with the magnetic circuit formed by the individual ferromagnetic component parts packaged in the respective first and second elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 ( a ), FIG.  1 ( b ) and FIG.  1 ( c ) illustrate a first preferred embodiment of the present invention, in which FIG.  1 ( a ) is a cross sectional view of first and second elements that are separated from each other, FIG.  1 ( b ) is a cross sectional view of the first and second elements that are coupled, and FIG.  1 ( c ) is a plan view of the second element; 
     FIG.  2 ( a ), FIG.  2 ( b ) and FIG.  2 ( c ) illustrate second preferred embodiment of the present invention, in which FIG.  2 ( a ) is a cross sectional view of first and second elements that are separated from each other, FIG.  2 ( b ) is a cross sectional view of the first and second elements that are coupled, and FIG.  2 ( c ) is a plan view of the second element; 
     FIG.  3 ( a ), FIG.  3 ( b ), FIG.  3 ( c ) and FIG.  3 ( d ) illustrate a third preferred embodiment of the present invention, in which FIG.  3 ( a ) is a cross sectional view of first and second elements that arc separated from each other, FIG.  3 ( b ) is a cross sectional view of the first and second elements that are coupled, FIG.  3 ( c ) is a plan view of the second element, and FIG.  3 ( d ) is a plan view of the first element; 
     FIG.  4 ( a ), FIG.  4 ( b ), FIG.  4 ( c ) and FIG.  4 ( d ) illustrate a fourth preferred embodiment of the present invention, in which FIG.  4 ( a ) is a cross sectional view of first and second elements that are separated from each other, FIG.  4 ( b ) is a cross sectional view of the first and second elements that are coupled, FIG.  4 ( c ) is a plan view of the second element, and FIG.  4 ( d ) is a plan view of the first element; 
     FIG. 5 illustrates a fifth preferred embodiment of the present invention, showing the cross section of first and second elements that are separated from each other; 
     FIG.  6 ( a ) and FIG.  6 ( b ) illustrate a sixth preferred embodiment of the present invention, in which FIG.  6 ( a ) is a cross sectional view of a second element and FIG.  6 ( b ) is a plan view of the second element; 
     FIG.  7 ( a ) and FIG.  7 ( b ) illustrate a seventh preferred embodiment of the present invention, in which FIG.  7 ( a ) is a cross sectional view of a second element and FIG.  7 ( b ) is a plan view of the second element; and 
     FIG. 8 illustrates an eighth preferred embodiment of the present invention, showing the cross section of first and second elements that are separated from each other. 
    
    
     DETAILS OF THE PREFERRED EMBODIMENTS 
     The present invention is now described in further detail with reference to several preferred embodiments shown in the drawings. 
     Referring first to FIG. 1, the magnetic lock device includes a first element  1  and a second element  11  that are capable of being detachably coupled together by the magnetic action. Specifically, the first element  1  includes a first annular permanent magnet  2  having a center bore  3  through it, a first ferromagnetic disk-like plate  4  that is provided to engage the non-attracting side of the first annular permanent magnet  2 , and a first ferromagnetic projecting member  5  extending from the center of the first ferromagnetic disk-like plate  4  through the center bore  3  of the first annular permanent magnet  2  until it reaches the plane flush with the plane on the attracting side  9  of the first annular permanent magnet  2 . Those component parts are incorporated as a single unit within a synthetic resin covering  21 . 
     The second element  11  includes a second annular permanent magnet  12  having a center bore  13  through it and disposed to provide the polarity opposite to the polarity of the attracting side  9  of the first annular permanent magnet  2  such that the second and first annular permanent magnets can magnetically attract each other on the sides  19  and  9  thereof facing opposite each other. A second ferromagnetic disk-like plate  14  is disposed to engage the non-attracting side of the second annular permanent magnet  12  opposite the attracting side  19 , and a second ferromagnetic projecting member  15  extends from the center of the second ferromagnetic disk-like plate  14  through the center bore  13  of the second annular permanent magnet  12  until it reaches the plane flush with the plane on the attracting side  19  of the second annular permanent magnet  12 . These component parts are incorporated as a single unit within a synthetic resin covering  22 . 
     For the first element  1 , the gap or space that is present between the outer peripheral wall of the first ferromagnetic projecting member  5  and the inner peripheral wall of the center bore  3  of the annular permanent magnet  2  is shielded from the outside by the synthetic resin covering  21  on the side  10  engaging the corresponding side of the second element  11  so that any foreign matter such as dust, particularly ferromagnetic particles like iron, cannot enter the gap or space. 
     Similarly, for the second element  11 , the gap or space that is present between the outer peripheral wall of the second ferromagnetic projection member  15  and the inner peripheral wall of the center bore  13  of the annular permanent magnet  12  is shielded from the outside by the synthetic resin covering  22  on the side  20  engaging the corresponding said  10  of the first element  1  so that any foreign matter such as dust, particularly ferromagnetic particles like iron, cannot enter the gap or space. 
     As both the first element  1  and the second element  11  are entirely shielded by the synthetic resin coverings  21 ,  22 , respectively, there is no risk of any water or moisture entering into the elements. As a result, no rust gathers on the metallic component parts inside the elements. Thus, the first and second elements can serve as a fastener for clothing or clothes that usually require the regular or frequent washing or cleaning treatment. 
     In the example shown in FIG. 1, the first and second ferromagnetic projecting members  5 ,  15  have an extension  7 ,  17  on the rear end thereof, respectively, and the first and second ferromagnetic disk-like plates  4 ,  14  have a center bore  6 ,  16  through it, respectively. The extensions  7 ,  17  are passed through the center bores  6 ,  16 , respectively, and the portions  8 ,  18  of the extensions  7 ,  17  that project through the center bores  6 ,  16  may be pressed against the ferromagnetic plates  4 ,  14 , respectively. In this way, the projecting members  5 ,  15  can be secured to the ferromagnetic plates  4 ,  14 , respectively. 
     Alternatively, the projecting members  5 ,  15  may be formed as an integral part of the respective ferromagnetic plates  4 ,  14 . 
     Alternatively, the ferromagnetic plates may have no center bore. In this case, the projecting members  5 ,  15  may be secured at the rear ends thereof to the ferromagnetic plates  4 ,  14 , respectively, by means of fusion or bonding. 
     The synthetic resin covering  21 ,  22  may be made of any synthetic resin materials that are not magnetized in nature. 
     The sides of the first and second elements  1  and  11  on which they are to be fastened to the corresponding separate parts  24  and  27  of an article such as clothing or clothes, respectively, may slightly protrude toward the parts  24  and  27  because of the presence of the rear ends  8  and  18  on the first and second ferromagnetic projecting members  5  and  15 . To mitigate this effect, the synthetic resin coverings  21  and  22  may be made of any synthetic resin film or sheet that is flexible enough to absorb such protrusion and to permit the first and second elements  1  and  11  to be fastened to the corresponding parts  24  and  27  of the article by sewing threads. For example, this may be accomplished by sewing threads  25 ,  28  directly into the marginal edges  23 ,  26  around the periphery of the first and second elements  1 ,  11  on the side on which the elements are to be fastened to the corresponding parts  24 ,  27 , although this is not shown. 
     The synthetic resin covering  21 ,  22  may also be made of any hard or rigid materials that can be formed to accept the protrusion that occurs slightly toward the parts  24 ,  27  due to the presence of the rear ends  8 ,  18  on the first and second ferromagnetic projecting members  5 ,  15  on the respective sides of the first and second elements  1 ,  11  on which the elements are to be fastened to the corresponding parts  24 ,  27 . In this case, the first and second elements  1 ,  11  may be fastened to the corresponding parts  24 ,  27  by providing thread holes  32   a ,  32   b ,  34   a ,  34   b  on the marginal edges  23 ,  26  around the periphery of the first and second elements  1 ,  11 , respectively, through which threads may be sewn to fasten them to the corresponding parts  24 ,  27 . This is represented in FIGS. 6 and 7. Specifically, the second elements  11 ,  41  that are shown in FIGS. 1 and 2, respectively, may be varied to have the thread holes  32   a ,  32   b ,  34   a ,  34   b  around the marginal edge  26  through which threads may be sewn to fasten the second elements  11 ,  41  to the parts  24 ,  27 . The first elements  1 ,  31  may be varied in the same manner as for the second elements, respectively. FIG.  6 ( a ) and FIG.  6 ( b ) show the variation of the second element shown in FIG. 1, wherein the marginal edge  26  is modified as shown, and FIG.  7 ( a ) and FIG.  7 ( b ) show the variation of the second element shown in FIG. 2, wherein the marginal edge  26  is modified as shown. 
     For each of the first and second elements, all of the metallic component parts including the annular permanent magnet, ferromagnetic disk-like plate and ferromagnetic projecting member may be covered with the covering  21 ,  22  that may be made of any suitable synthetic resin film or sheet, and the exposed portion of the covering may be closed by fusion or bonding. 
     Alternatively, all of the metallic component parts including the annular permanent magnet, ferromagnetic disk-like plate and ferromagnetic projecting member may be enclosed within the synthetic resin cylindrical casing, which is open on one side (the top, for example) and closed on the other side (the bottom, for example). Within the cylindrical casing, the permanent magnet  2 ,  12  may be disposed with its non-attracting side on the open side, and the ferromagnetic disk-like plate  4 ,  14  may be disposed in such a way that it can engage the non-attracting side of the permanent magnet  2 ,  12  by inserting the ferromagnetic projecting member  5 ,  15  through the center bore  3 ,  13  from the top open side of the casing. In this case, the cylindrical casing may have an inner diameter equal to the outer diameter of the annular permanent magnet  2 ,  12  and ferromagnetic disk-like plate  4 ,  14 , and may have an inner height equal to the sum of the thickness of the permanent magnet  2 ,  12  plus the thickness of the disk-like plate  4 ,  14 , respectively. The top open side of the casing may be covered with any suitable synthetic resin film or sheet, and may be closed by fusion or bonding. 
     According to the magnetic lock device as described above, when the first element  1  and the second element  11  may attract each other magnetically as shown in FIG.  1 ( b ), the respective coverings  21  and  22 , are present between the ferromagnetic projecting members  5  and  15 . As described, however, the first element  1  and the second element  11  contain the respective annular permanent magnets  2  and  12  that are disposed to provide the opposed polarities on the respective sides  9  and  19  of the first and second elements  1  and  11  that are to engage each other. In the example shown in FIG. 1, the polarity on the side  9  is assumed to be S while the polarity on the side  19  is assumed to be N. This may be reversed. As shown in FIG. 1, the first and second elements  1  and  11  may attract each other, as shown by arrows  52   a ,  52   b , under the magnetic interaction of the permanent magnets  2  and  12  that produce the magnetic lines of force that, beginning with the permanent magnet  2 , pass through the first ferromagnetic disk-like plate  4 , the first ferromagnetic projecting member  5  and then through the second ferromagnetic projecting member  15 , the second ferromagnetic disk-like plate  14 , finally reaching the permanent magnet  12 . The magnetic circuit thus generated is coupled with the magnetic interaction between the permanent magnets  2  and  12 , as shown by the arrows  52   a ,  52   b , thereby increasing the magnetic force that can keep the first and second elements  1  and  11  coupled securely. Thus, the first and second elements  1  and  2  cannot slide laterally relative to each other, as shown by arrows  29 ,  30  in FIG.  1 ( b ), when an attempt is made to slide them laterally relative to each other. 
     The magnetic interaction between the permanent magnets  2  and  12  as shown by arrows  52   a ,  52   b , coupled with the magnetic lines of force through the first and second ferromagnetic projecting members  5  and  15 , enables the first and second projecting members  5 ,  15  to be aligned with each other. Thus, the first and second elements  1  and  11  can accurately face each other, and can then be coupled. 
     The first and second annular permanent magnets  2  and  12  that can be utilized for the purpose of the present invention may include Nd—Fe—B group sintered magnets, rare earth magnets such as neodymium group bond magnets, or even any other conventional ferrite magnets that provide a powerful magnetic force. By using those magnets, powerful magnets may be obtained although they are compact and thin. 
     For the magnetic lock device according to the present invention, for example, the first and second annular permanent magnets  2 ,  12  may have a diameter of between 10 mm and 20 mm and the thickness of between 0.5 mm and 2.0 mm, the center bores  3 ,  13  for the permanent magnets may have a diameter of between 5 mm and 10 mm, the first and second ferromagnetic projecting members  5 ,  15  may have a maximum diameter of between 5 mm and 10 mm, and the synthetic resin coverings  21 ,  22  may have a thickness of between 0.05 mm and 0.5 mm. 
     When the magnetic lock device is specifically designed for use with bags or clothes, the specific values that are given above for each of the individual component parts including the permanent magnet, etc. may be chosen so that the before described appropriate dimensional relationship among the individual component parts can be maintained, by considering the total size of the first or second element. 
     The first and second ferromagnetic disk-like plates  4 ,  14  and the first and second ferromagnetic projecting members  5 ,  15  may be formed from iron, for example. 
     The magnetic lock device that has been described so far may be modified as shown in FIG.  2 ( a ), FIG.  2 ( b ) and FIG.  2 ( c ). Specifically, the first element shown in FIG.  1 ( a ), FIG.  1 ( b ) and FIG.  1 ( c ) may be modified in such a way that the synthetic resin covering  21  has a center bore  50  on the side on which the first element  31  is to engage the second element  41 , and the first ferromagnetic projecting member  33  that extends from the center of the first ferromagnetic disk-like plate  4  and through the center bore  3  in the first annular permanent magnet  2  has the length sufficient to permit it to extend further through the center bore  50  on the covering  21  by making intimate contact with the inner wall of the center bore  50  until it reaches the side  44  of the covering  21 , while the synthetic resin covering  22  has a center bore  51  on the side on which the second element  41  is to engage the first element  31 , and the second ferromagnetic projecting member  35  that extends from the center of the second ferromagnetic disk-like plate  14  and through the center bore  13  in the second annular permanent magnet  12  has the length sufficient to permit it to extend further through the center bore  51  on the covering  22  by making intimate contact with the inner wall of the center bore  51  until it reaches the side  45  of the covering  22 . For the first and second elements  31  and  41 , all of the individual component parts are covered with any suitable non-magnetic, synthetic resin film, sheet, covering or casing, or have a coating of any suitable non-magnetic, synthetic resin layer, except for the ends of the first and second projecting members  33 ,  35  engaging each other that remain uncovered or exposed. Otherwise, the magnetic lock device shown in FIG.  2 ( a ), FIG.  2 ( b ) and FIG.  2 ( c ) is similar to that shown in FIG.  1 ( a ), FIG.  1 ( b ) and FIG.  1 ( c ). 
     Similarly to the magnetic lock device shown in FIG.  1 ( a ), FIG.  1 ( b ) and FIG.  1 ( c ), the gap or space that is present between the outer peripheral wall of the first ferromagnetic projecting member  33  and the inner peripheral wall of the center bore  3  in the annular permanent magnet  2  may be shielded from the outside by the side  44  of the covering  21  engaging the covering  22 , and the gap or space that is present between the outer peripheral wall of the second ferromagnetic projecting member  35  and the inner peripheral wall of the center bore  13  in the annular permanent magnet  12  may be shielded from the outside by the side  45  of the covering  22  engaging the covering  21 . Thus, for each of the first and second elements, any foreign matter such as dust, particularly magnetic particles like iron, cannot enter the gap or space from the outside. 
     In the embodiment shown in FIG.  2 ( a ), FIG.  2 ( b ) and FIG.  2 ( c ), the ends of the first ferromagnetic projecting member  33  and second ferromagnetic projecting member  35  that arc to engage each other when the first element  1  and the second element  11  are actually coupled together remain uncovered, and may make contact with each other directly but not through the respective non-magnetic, synthetic resin coverings  21  and  22 , and the magnetic circuit formed by the first and second ferromagnetic projecting members, the first and second ferromagnetic plates, and the first and second annular permanent magnets may produce a more powerful magnetic force. Thus, when the first element  31  and the second element  41  are coupled, they will never slide laterally relative to each other as shown by arrows  29 ,  30  in FIG.  2 ( b ) when any external sliding force is applied. In addition, as the first and second ferromagnetic projecting members  33  and  35  can be aligned with each other correctly when the first and second elements  31  and  41  are to be coupled by attracting each other magnetically, the first and second elements  31  and  41  can be coupled securely. 
     In the embodiment shown in FIG.  2 ( a ), FIG.  2 ( b ) and FIG.  2 ( c ), it is possible that any foreign matter such as iron particles may be attached to the ends of the first and second ferromagnetic projecting members  33  and  35  that are to engage each other, because those ends remain uncovered or are exposed to the outside as described above. If this should occur, however, those iron particles may easily be removed from the ends by gently wiping them off. As the gap or space between the inner peripheral wall of the center bore in the permanent magnet and the outer peripheral wall of the ferromagnetic projecting member for each of the first and second elements is protected against any foreign matter or iron particles, the magnetic force from the magnetic circuit will never be weakened. 
     As described later, the ends of the first and second ferromagnetic projecting members  33  and  35  that are to engage each other may have a coating of any nonmagnetic material that protects those ends against any possible rust that may gather thereon. 
     It may be appreciated from the foregoing description that the principal object of the present invention is to protect the gap or space between the inner peripheral wall of the center bore in the annular permanent magnet and the outer peripheral wall of the ferromagnetic projecting member against the entry of the iron particles or other foreign matter such as dust, or to cover the portions of the metal component parts that are exposed to the outside in order to prevent any rust gathering there. For this purpose, each of the individual metal component parts, including the first ferromagnetic projecting member  5 ,  33 , second ferromagnetic projecting member  15 ,  35 , first and second annular permanent magnets  2 ,  12 , and first and second ferromagnetic disk-like plates  4 ,  14 , or the exposed portions of the respective metal component parts as assembled in the first and second elements, or the whole first and second elements incorporating the respective metal component parts as assembled, may be covered by applying a coating or spray coating of non-magnetic materials such as polyamide, epoxy resin or by the electro-deposition process. The gap or space that is present between the inner peripheral wall of the center bore in the annular permanent magnet and the outer peripheral wall of the ferromagnetic projecting member may be filled with the same materials as the above coating materials (not shown), and the respective sides of the first elements  1 ,  31  and the second elements  11 ,  41  on which the first and second elements are to be fastened to an article  24 ,  27  such as clothes, respectively, may be covered with any synthetic resin sheet or film forming the marginal edge  23 ,  26  by attaching it to the respective sides by means of bonding. 
     The magnetic lock devices shown in FIGS.  1 ( a ), FIG.  1 ( b ) and FIG.  1 ( c ) and FIG.  2 ( a ), FIG.  2 ( b ) and FIG.  2 ( c ) may be modified as shown in FIGS.  3 ( a ) to FIG.  3 ( d ) and FIG.  4 ( a ) to FIG.  4 ( d ), respectively. 
     Specifically, as shown in FIG.  3 ( a ) to FIG.  3 ( d ), the first element  1  shown in FIG.  1 ( a ), FIG.  1 ( b ) and FIG.  1 ( c ) may be modified such that the synthetic resin covering  21  is equipped with an annular rising flange  36  around the peripheral edge thereof on the side  10  on which the first element  1  is to engage the second element  11  so that the annular rising flange  36  can accept the peripheral edge of the second element  11  on the side  20  on which the first element  1  is to engage the second element  11 , when they have actually engaged each other. Similarly, as shown in FIG.  4 ( a ) to FIG.  4 ( d ), the first element  31  shown in FIG.  2 ( a ) to FIG.  2 ( c ) may be modified such that the synthetic resin covering  32  is equipped with an annular rising flange  37  around the peripheral edge thereof on the side  44  on which the first element  31  is to engage the second element  41  so that the annular rising flange  37  can accept the peripheral edge of the second element  41  on the side  45  on which the first element  31  is to engage the second element  41 , when they have actually engaged each other. 
     According to the magnetic lock devices of FIG.  1 ( a ) to FIG.  1 ( c ) and FIG.  2 ( a ) to FIG.  2 ( c ) including the first element as modified as shown in FIGS.  3 ( a ) to FIG.  3 ( d ) and  4 ( a ) to FIG.  4 ( d ), respectively, the respective annular rising flange  36 ,  37  on the first element  1  can accept the second element  11  when they have actually engaged each other, and can prevent them from sliding laterally relative to each other, as shown by arrows  29 ,  30  in FIG.  3 ( b ) and FIG.  4 ( b ), respectively. The first and second elements can thus be coupled in their proper positions. 
     It should be noted that the annular rising flanges  36  and  37  shown in FIGS.  3 ( a ) to FIG.  3 ( d ) and  4 ( a ) to FIG.  4 ( d ) do not have to be provided around the total peripheral edge of the respective synthetic resin coverings  21 ,  32 . Instead, the flanges  36 ,  37  may be provided on half the peripheral edge of the respective coverings  21 ,  32 . In this way, the first and second elements can be disengaged easily when they are engaged. 
     The present invention may be modified in other different manners. FIG. 5 represents one example of those possible modifications. 
     The magnetic lock device shown in FIG. 5 is essentially the same as that shown in FIG.  1 ( a ) to FIG.  1 ( c ), except that the second ferromagnetic projecting member  67  on the second element  54  has a larger diameter, and has a center recess  60  while the synthetic resin covering  59  on the first element  53  has a boss  62  on the center that engages the recess  60  on the second element  54  when the first and second elements engage each other. 
     Specifically, for the magnetic lock device shown in FIG. 5, the first element  53  includes a first annular permanent magnet  55  having a center bore  56  through it, a first ferromagnetic disk-like plate  58  in contact with the non-attracting side of the first annular permanent magnet  55 , and a first ferromagnetic projecting member  57  extending from the center of the first ferromagnetic disk-like plate  58  and through the center bore  56  in the first annular permanent magnet  55  until it reaches the plane flush with the plane of the attracting side  63  of the first annular permanent magnet  55  opposite the non-attracting side, all of which are packaged as a single unit within a synthetic resin covering  59 . 
     On the other hand, the second element  54  includes a second annular permanent magnet  65  having a center bore  66  and disposed to provide a polarity opposed to that of the first annular permanent magnet  55  on the attracting side  64  on which the second element  54  engages the first element  53 , a second ferromagnetic disk-like plate  68  in contact with the non-attracting side of the second annular permanent magnet  65  opposite the attracting side  64 , and a second ferromagnetic projecting member  67  extending from the second ferromagnetic disk-like plate  68  and through the center bore  66  in the second annular permanent magnet  65  until it reaches the plane flush with the plane on the attracting side  64  of the second annular permanent magnet  65 , all of which are packaged as a single unit within a synthetic resin covering  69 . 
     As shown in FIG. 5, the second ferromagnetic projecting member  67  has a recess  60  at the center, and the synthetic resin covering  69  that covers the entire second element  54  is also formed to have a recess at the center to conform with the recess  60 . Thus, the second element  54  has a recess  61  at the center. On the other hand, the synthetic resin covering  59  that covers the entire first element  53  has a projection  62  at the center on the side on which the first element  53  is to engage the second element  54 . The projection  62  can engage the recess  61  when the first and second elements  53  and  54  engage each other. 
     When an attempt is made to couple the first element  53  and the second element  54  together, the respective annular permanent magnets  55  and  65  in the first and second elements, which provide the opposite polarities facing each other, will magnetically attract each other, while at the same time, a magnetic circuit is concluded which, starting at the upper part of the first annular permanent magnet  55 , passes through the first ferromagnetic disk-like plate  58  to the first ferromagnetic projecting member  57  and then through the second ferromagnetic projecting member  67  to the second ferromagnetic disk-like plate  68  until finally it reaches the lower part of the second annular permanent magnet  65 . The magnetic attraction between the first and second magnets, coupled with the magnetic attraction provided by the magnetic circuit as well as the recess  61  and projection  62  engaging each other, will make the first and second elements  53  and  54  coupled more securely, without sliding laterally relative to each other. 
     FIG. 8 represents another embodiment of the magnetic lock device. The magnetic lock device shown in FIG. 8 is specifically designed for use with clothes. It includes a first element and a second element, both of which may be mounted between the front side cloth  70  and back side cloth  71 , and may be sewn by threads  73  into the front side cloth  70  and back side cloth  71 , keeping the first and second elements aligned. The magnetic lock device shown in FIG. 8 is essentially the same as that shown in FIG.  1 ( a ) to FIG.  1 ( c ), except that there are no such annular marginal edges  23 ,  26  as found on the magnetic lock device of FIG.  1 ( a ) to FIG.  1 ( c ). In the embodiment shown in FIG. 8, the first and second elements may be mounted between the front side cloth  70  and back side cloth  71 , and may be sewn by threads  73  into the front side cloth and back side cloth, without having to rely on the marginal edges  23 ,  26 . The first and second elements, which are embedded between the front side cloth and back side cloth, maybe coupled together in a secure manner, by permitting the annular permanent magnets  2  and  12  of opposite polarities facing each other to attract each other. 
     Although the present invention has been described with reference to several particular preferred embodiments thereof, it should be understood that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.