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CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of and claims priority to U.S. patent application Ser. No. 13/492,358, filed Jun. 8, 2012, which, in turn, claims the benefit of U.S. Provisional Application Ser. No. 61/526,479, filed Aug. 23, 2011, the entire contents of each of the afore-mentioned applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to safety equipment, and in particular, to a magnetic latch and switch combination highly resistant to generating false “door closed” signals and that may be flexibly employed in a variety of safety situations. 
         [0003]    Many industrial processes present risks to human operators during one or more operating phases. These risks may be reduced through the use of “safety systems” which provides specialized computers and sensors that help ensure the safety of human operators in such environments. 
         [0004]    The safety system may monitor operation of the industrial process and detect risk to human operators within a risk zone at certain times during that process by monitoring or controlling the position of the human operators through the use of various sensing systems and barricades. Common sensor systems include pressure mats and light curtains. Highest security is provided by mechanical barriers, such as gates having switches indicating whether the gate is open and access to the risk zone is possible. 
         [0005]    In the latter case, it is important that the switches on such gates be highly resistant to failures that incorrectly indicate that the gate is closed, when the gate is open, whether the failure is caused by normal wear, damage, environmental contamination, or tampering. 
         [0006]    One method of producing such reliable switches employs a “radio-frequency identification” RFID tag positioned on one component of the gate and an RFID tag sensor on another component of the gate, such that the sensor and tag are separated when the gate is open. Positive indication of gate closure requires not only detection of proximity of the RFID tag (which may only be sensed at close ranges) but that a numeric code embedded in the RFID tag be the correct numeric code for the gate, preventing tampering through the use of different RFID tags. 
         [0007]    Ideally, this RFID sensor system might be incorporated into a latch used to hold the gate closed to be automatically positioned near to elements of the gate which separate when the gate is opened. The wide variety of different types of latches intended for gates of different sizes dimensions and operation, make incorporating an RFID sensor system into the latch difficult. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides an extremely versatile latch system incorporating RFID sensing. The latch is a magnetic style latch that may work in a large variety of different gate holding applications and in contaminating environments. In some embodiments, the latch is configured to permit use for both rolling or swinging gate configurations and the latching-force of magnetic attraction provided by the latch may be adjusted. 
         [0009]    Specifically then, the present invention provides a magnetic latch for safety applications having a magnet assembly providing a housing presenting a mounting surface for attaching the housing to a gate, the housing holding a permanent magnet flanked by ferromagnetic pole pieces extending out of the housing. A keeper plate of ferromagnetic material provides a first and second area displaced from each other each with different magnetic permeability and each sized to receive the ferromagnetic pole pieces thereagainst. 
         [0010]    It is thus a feature of at least one embodiment of the invention to permit adjustment of the magnetic attraction force between the magnet assembly and the keeper plate permitting versatile use of a single latch design in multiple safety applications. 
         [0011]    The keeper plate may have a series of holes in the ferromagnetic material in the first area decreasing its average permeability with respect to the second area. 
         [0012]    It is thus a feature of at least one embodiment of the invention to provide a simple method of changing the permeability of a mechanically integrated ferromagnetic plate. 
         [0013]    The holes may be filled with a nonmetallic material. 
         [0014]    It is thus a feature of at least one embodiment of the invention to provide a method of controlling permeability that is easy to manufacture and resistant to environmental contamination. 
         [0015]    The keeper plate may be overmolded with a polymer material outside of the first and second areas. 
         [0016]    It is thus a feature of at least one embodiment of the invention to provide a simple method of incorporating an RFID tag into a magnetic keeper plate through an over molding encapsulation. 
         [0017]    The pole pieces may be fixed with respect to the housing and sealed at a point of exit from the housing. 
         [0018]    It is thus a feature of at least one embodiment of the invention to provide a magnetic latch that is better resistant to environmental contamination. 
         [0019]    The housing may provide a cantilevered portion extending from the mounting surface in a direction of egress of the pole pieces from the housing. 
         [0020]    It is thus a feature of at least one embodiment of the invention to provide a housing form factor that permits application to a variety of different gate configurations including rolling or sliding gates and swinging or hinging gates. 
         [0021]    The ferromagnetic pole pieces may extend in a direction perpendicular to the mounting surface out of the cantilevered portion and extend in a direction parallel to the mounting surface out of the cantilevered portion. 
         [0022]    It is thus a feature of at least one embodiment of the invention to provide magnetic latching surfaces suited for different gate configurations. 
         [0023]    The housing may further hold an RFID reader and the keeper plate may hold an RFID tag. 
         [0024]    It is thus a feature of at least one embodiment of the invention to provide a highly secure gate switch for use in industrial environments. 
         [0025]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a fragmentary perspective view of the magnetic latch of the present invention, including a magnet assembly and keeper plate as installed on a hinging-style gate; 
           [0027]      FIG. 2  is a figure similar to that of  FIG. 1  showing the magnetic latch as installed on a rolling-style gate; 
           [0028]      FIG. 3  is a cross-sectional view of the magnet assembly and keeper plate of the magnetic latch of the present invention, along a vertical plane as positioned in opposition for a rolling-style gate of  FIG. 2  showing a permanent magnet internal to a housing of the magnet assembly having flanking pole pieces extending outside of the housing and sealed with respect to the housing with an internal RFID reader, and showing a ferromagnetic bar of the keeper plate with cylinders of nonferrous material in one section for reducing magnetic attraction as overmolded with a polymer retaining an internal RFID tag; 
           [0029]      FIGS. 4   a  and  4   b  are respectively a perspective view of the magnet assembly and keeper plate in a first orientation for maximum magnetic attraction, and a fragmentary vertical cross-section through the pole pieces of the magnet assembly showing conduction of magnetic flux lines through a first area of the keeper plate for maximum magnetic attraction; 
           [0030]      FIGS. 5   a  and  5   b  are figures similar to that of  FIGS. 4   a  and  4   h  showing positioning of the magnet assembly and keeper plate in a second configuration for intermediate magnetic attraction; 
           [0031]      FIGS. 6   a  and  6   b  are figures similar to that of  FIGS. 4   a  and  4   b  showing adjustment of the magnet assembly and keeper plate in a third configuration for minimum magnetic attraction; 
           [0032]      FIG. 7  is a perspective view of the keeper plate showing the first and second areas; and 
           [0033]      FIG. 8  is a perspective view of the magnet assembly showing to perpendicular surfaces for hinging-style or rolling-style door operation. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    Referring now to  FIG. 1 , a magnetic latch  10  of the present invention may provide for a separate, interengaging keeper plate  12  and magnet assembly  14  that may be attached to different respective portions of an operable gate  16  and a supporting gate frame  18 . 
         [0035]    As depicted, the keeper plate  12  may be attached to a front surface of a vertical stationary stile  19  of the supporting gate frame  18  and the magnet assembly  14  may be attached to a movable edge  20  of the swinging gate  16 , the swinging gate  16  pivoting generally about a vertical axis  25  located at an edge of the gate  16  opposite a vertically extending movable edge  20 . When the gate  16  is open, the keeper plate  12  and magnet assembly  14  are separated and when the gate  16  is closed, the keeper plate  12  and magnet assembly  14  are inter-engaging. 
         [0036]    Referring to  FIGS. 1 ,  7  and  8 , the magnet assembly  14  may have a rear mounting surface  36  which may abut and be attached to a front surface of the movable edge  20  and the keeper plate  12  may have a rear surface  64  that may abut and the attached to a front edge of the stationary stile  19 . When the gate  16  is closed, and the magnet assembly  14  and keeper plate  12  are inter-engaging, the front edges of the movable edge  20  and stationary stile  19  may be adjacent and parallel. In this state, a portion  22  of the magnet assembly  14  will extend over a front surface of the keeper plate  12  in cantilevered fashion, and a rear surface of the magnet assembly  14  will abut the front surface of the keeper plate  12 . 
         [0037]    An electrical cable  26  may extend from the magnet assembly  14  to carry signals from and power to a RFID tag reader (to be described below) contained in the magnet assembly  14 . The signals may be provided to a remote industrial control system not shown) managing a safety protocol 
         [0038]    Referring now to  FIG. 2 , in an alternative configuration, the magnet assembly  14  may be mounted on a stationary stile  19  of a gate frame  18  so that movable edge  20  of the gate  30  may approach stationary stile  19  of the gate frame  18  along a linear trajectory  32 . In this case, the magnet assembly  14  is mounted with its rear mounting surface  24  against a front surface of the stationary stile  19 . The keeper plate  12  maybe rotated 90 degrees to extend perpendicularly from the front face of the movable edge  20  as held by a support block  34 . Thus, when the gate  30  is closed against the gate frame  18  with the movable edge  20  abutting the stationary stile  19  and their front face is substantially coplanar, a side surface of the cantilevered portion  22  of the magnet assembly  14  abuts the front surface of the keeper plate  12 . Again, a cable  26  may extend from the magnet assembly  14  to carry signals from and power to a RFID tag reader to a remote industrial control system. 
         [0039]    Referring again to  FIG. 8 , the mounting surface  24  of the magnet assembly  14  may present a relatively planar rear mounting surface  36  flanked by slotted holes  38  allowing the mounting surface  36  to be attached to a planar surface of the movable edge  20  or stationary stile  19  and retained there by machines screws or the like, while permitting horizontal adjustment (as depicted). The cantilevered portion  22  has a rear overhang surface  39  displaced forward with respect to the mounting surface  36  to be removed from the movable edge  20  or stile  19  and to extend help therefrom. Pole pieces  40   a  and  40   b  project from the cantilevered portion  22  to provide for rear engaging surfaces  42  on a rear face of the cantilevered portion  22  and side engaging surfaces  44  on a side face of the cantilevered portion. The rear engaging surfaces  42  may engage corresponding surfaces of the keeper plate  12  in the configuration shown in  FIG. 1  and the side engaging surfaces  44  may engage corresponding surfaces of the keeper plate  12  in the configuration shown in  FIG. 2 . 
         [0040]    Referring now generally to  FIGS. 3 and 8 , the magnet assembly  14  may include a housing  50 , for example, constructed of a non-ferromagnetic metal or high-strength thermoplastic holding therein a permanent magnet  52 , for example, a rare earth magnet. The magnet  52  may be flanked by generally planar and rectangular ferromagnetic pole pieces  40   a  and  40   b  that serve to conduct the flux of the magnet  52  from inside the housing  50  to outside of the housing  50  through a housing wall. Outside the housing wall, the pole pieces  40   a  and  40   b  provide the exposed rear engaging surfaces  42  and side engaging surfaces  44  of the pole pieces  40  described above. 
         [0041]    The housing  50  may include a transparent portion  56  through which may be viewed indicator lights  58  of an RFID reader  60  contained in the housing  50 . 
         [0042]    The outer surface of the housing  50  may be sealed, for example, with an overmolded polymer material  62  preventing the ingress of contaminants into the housing  50 . Electrical cable  26 , providing power to and signals from the RFID reader  60 , may pass through a grommet  63  through the housing  50  and thereby be sealed as well. 
         [0043]    Referring now generally to  FIGS. 3 and 7 , the keeper plate  12  may provide for a generally rectangular form providing a rear surface  64  that may be mounted against a support surface. The rear surface  64  may be flanked by slotted holes  66  extending generally across the longest dimension of the keeper plate  12  and generally parallel to the slotted holes  38  of the magnet assembly  14  in the mounting system of  FIG. 1 , allowing the proximity of the two to be freely adjusted. 
         [0044]    The keeper plate  12  may include a ferromagnetic core  67 , for example, a martensitic stainless steel material having a plateau portion  68  rising from its front surface and presenting a first area  70   a  and second area  70   b , either of which may be engaged by the pole pieces  40   a  and  40   b  depending on the relative alignment between the magnet assembly  14  and the keeper plate  12 . The outer surface of the keeper plate  12  may be overmolded with a polymer material  72  similar to polymer material  62  used with the magnet assembly  14   
         [0045]    The first area  70   a  may be perforated by a series of holes  71  filled with the overmolded material and the second area  70   b  may be free of such perforations. As will be described below, depending on the alignment of the pole pieces  40   a  and  40   b  with the first area  70   a  or the second area  70   b  different levels of magnetic attraction may be obtained. 
         [0046]    An RFID tag  76  may fit within a pocket on the front surface of the ferromagnetic core  67  to be readable by the RFID reader  60  for all relative orientations of the magnet assembly  14  and keeper plate  12 . 
         [0047]    Referring now to  FIGS. 4   a  and  4   b , a high degree of magnetic attraction between the magnet assembly  14  and keeper plate  12  may be attained by aligning the pole pieces  40   a  and  40   b  to both abut the second area  70   b . In this orientation magnetic flux  80  between the pole pieces  40  is largely contained within the ferromagnetic core  67  increasing the flux density and hence magnetic attractive force between the pole pieces  40  and the ferromagnetic core  67 . 
         [0048]    Referring to  FIGS. 5   a  and  5   b , conversely a low degree of magnetic attraction between the magnet assembly  14  and keeper plate  12  may be obtained by aligning the pole pieces  40   a  and  40   b  to both abut the first area  70   a . In this orientation, magnetic flux between the pole pieces  40  is not fully contained within the ferromagnetic core  67  decreasing the flux density and magnetic attractive force between the pole pieces  40  and the ferromagnetic core  67 . 
         [0049]    Referring to  FIGS. 6   a  and  6   b , a position halfway between the two positions of  FIGS. 5 and 4  may also be employed providing an intermediate level of force in which the magnetic flux  80  is only partially contained in the ferromagnetic core  67  as they pass between pole pieces  40 . 
         [0050]    In these figures, the magnetic latch  10  is mounted on channels  77  forming the stile  19  and movable edge  20  allowing ready repositioning of the magnet assembly  14  and keeper plate  12 . 
         [0051]    Although the terms “safety”, “reliable”, “safety system”, “safety controller”, and other related terms may be used herein, the usage of such terms is not a representation that the present invention will make an industrial or other process safe or absolutely reliable, or that other systems will produce unsafe operation. Safety in an industrial or other process depends on a wide variety of factors outside of the scope of the present invention including, for example: design of the safety system; installation and maintenance of the components of the safety system; the cooperation and training of individuals using the safety system; and consideration of the failure modes of the other components being utilized. Although the present invention is intended to be highly reliable, all physical systems are susceptible to failure and provision must be made for such failure. 
         [0052]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0053]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0054]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.

Summary:
A magnetic latch for industrial environments includes fixed magnetic pole pieces that may be sealed within a housing to resist environmental contamination and which provide for perpendicular engagement faces for use with gates having a rolling or swinging configuration. An RFID tag reader may be incorporated into the magnet assembly of the latch for reading a specially encoded RFID tag in a keeper portion of the magnetic latch.