A magnetic latch mechanism and related process for easily and reliably performing a latch operation by moving a magnetically attractive catch plate into and out of engagement with a magnetic field. When in engagement, the latch is secured. When the catch plate is moved away from engagement, the latch can be opened. A magnetic latch for a marking system, particularly for panels covering paper path and jam clearance mechanisms.

FIELD OF INVENTION 
     The field of the invention is a latch apparatus and more particularly a latch apparatus suitable for securing a movable member such as an enclosure panel with a magnetic latch and, when desired, providing an easy release mechanism from the magnetic latch. 
     BACKGROUND AND SUMMARY 
     Magnetic latches are commonly used to seal doors on cabinets, appliances, and other applications where openings and closings are frequent. A magnetic latch provides an inexpensive, durable, and simple latch device. One disadvantage of magnetic latches is the “stickiness” of the latch when attempting to first budge it from the closed position. The reason is that the magnetic force is greatest when the magnet or its strike plates are in direct contact with the metallic catch plate to which the magnet is attracted. The intensity of the magnetic field dissipates rapidly as the catch plate is moved from the magnet during the process of opening. 
     For a typical door, the above “stickiness” when freeing the catch plate from the magnet is a minimal problem since a person opening the door typically has ample room to grasp a handle and pull. When a person has only a small space within which to reach and grasp a handle, however, the “stickiness” of a magnetic latch can be problematic. Worse, when a person must reach under or around an apparatus in order to grasp a handle, the person may have very little leverage or room, and the ‘stickiness” of the magnetic latch may require an awkward yank on the handle rather than a smooth and comfortable pull. 
     It would be advantageous to combine the inexpensiveness, durability, and simplicity of a magnetic latch with an easier method of freeing the catch plate from the magnet when opening the door. This advantage would be particularly desirable in those instances when a person has little room to reach a handle and must reach under or around encumbrances in order to exert force to open the door. Such a situation exists, for example, if the latch door opens downward within a small space that is lower than the level of an adult's comfortable reach. 
     One embodiment of the invention is a magnetic latch mechanism for removably latching a first member to a second member, comprising: a magnet emitting a magnetic field mounted to the first member; and a magnetically attractive catch plate mounted to the second member; wherein, prior to moving one member in relation to the other member, the position of the catch plate is moved in relation to the position of the magnet from a position strongly engaged with the magnetic field to a position weakly engaged with the magnetic field. 
     Another embodiment of the invention is a marking device, comprising: an enclosure panel for covering a space; a frame member proximate to an edge of the space; a magnet emitting a magnetic field mounted to the frame member; and a magnetically attractive catch plate mounted to the enclosure panel; wherein, prior to moving the enclosure panel covering the space, the position of the catch plate is moved in relation to the position of the magnet from a position strongly engaged with the magnetic field to a position weakly engaged with the magnetic field. 
     A process for unlatching one member from a second member, comprising: mounting a magnet emitting a magnetic field to the first member; mounting a magnetically attractive catch plate to the second member; prior to changing the position of one member in relation to the other, moving the position of the catch plate in relation to the position of the magnet from a position strongly engaged with the magnetic field to a position weakly engaged with the magnetic field; and changing the position of the first member in relation to the second member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevated cross-sectional view of an embodiment of the invention. 
         FIG. 2  is a plan view of the embodiment of the present invention shown in  FIG. 1  wherein the catch plate is in an engaged position. 
         FIG. 3  is a plan view of the embodiment of the invention shown in  FIG. 1  wherein the catch plate is in a disengaged position. 
         FIG. 4  is a plan view of another embodiment of the invention in which a rod comprises both magnetic and non-magnetic sections. 
         FIG. 5  is a plan view of yet another embodiment of the invention comprising a curved rod. 
         FIG. 6  is an elevated perspective view of an embodiment of the invention as used to latch a panel enclosure covering access mechanisms in which substrates may be jammed. 
     
    
    
     DETAILED DESCRIPTION 
     For a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. 
     Referring first to  FIG. 1 , a schematic cross sectional view is shown of one embodiment  100  of the invention. In this view, magnet  101  is shown with twin strike plates  102 . Strike plates  102  can be of any metallic or other material through which a magnetic field can be transmitted. Magnet  101  and strike plates  102  are mounted to an enclosure body by attachment to support member  104 . Support member  104  may be part of the enclosure that moves during opening or may be part of the enclosure body, and rod  110  may similarly be positioned opposite support member  104  on either the door or the enclosure body. Support bracket  130  is shown wrapping around rod  110  in order to slidably mount rod  110  in the panel or other member to be latched to member  104 . 
     The magnet and strike plate assembly is positioned such that in the door's closed position, at least one of the strike plates is in close proximity to bar or rod  110 , preferably touching. The cross section of rod  110  is shown in  FIG. 1  as a circular bar but may have any cross-sectional shape, including a square or rectangular shape. In this embodiment of the invention, rod  110  serves as the catch plate. As such, rod  110  in this embodiment should be of a suitable magnetically attractive material such as iron or steel. 
     Referring next to  FIG. 2 , a plan schematic view of latch system  100  is shown. In this view, magnet  101  and strike plate  102  are shown suspended from support member  104  and in contact with rod  110 . This configuration conforms to the configuration shown in  FIG. 1 . Additional features shown in  FIG. 2  include subparts of rod  110 . Specifically, section  111  of rod  110  is dimensioned to be in intimate proximity or contact to strike plates  102  when in latched position. In the embodiment shown, section  111  is the full diameter of rod  110 . In contrast, section  112  has been turned or otherwise machined or formed to be less than the diameter of section  111 . Although in this embodiment, section  112  is also comprised of a magnetically attractive material, its diameter is such that if moved laterally underneath strike plates  102 , the surface of section  112  would be sufficiently removed from strike plates  102  that the force of attraction would be extremely small. 
     Other elements shown in  FIG. 2  include a compression spring  120  for biasing or urging rod  110  into the position shown in  FIG. 2  in which section  111  is in contact with strike plates  102 . Also, retaining brackets  130  and  131  are shown in cross-section. In this embodiment, these brackets loop around rod  110  to hold it to the enclosure door or other member to be retained in position when strike plates  102  are in close proximity to section  111  of rod  110 . As shown in the perspective of  FIG. 2 , brackets  130  and  131  allow rod  110  to slide side-to-side along the magnet's length axis marked  132  but not up and down. Biasing spring  120  urges rod  110  toward the left in  FIG. 2 . To counteract biasing spring  120 , a force exertion member such as lever  140  is provided. Lever  140  can be any protrusion that enables fingers or machine parts to exert a force to the right, opposing and overcoming the biasing force of spring  120 . Instead of a lever such as  140 , force may also be employed by pushing or pulling other parts of rod  110 , including using the end regions of rod  110  as force exertion members for pushing or pulling of the rod. 
       FIG. 3  shows the state of the latch system once a force has been exerted to push rod  110  to the right. In this state, spring  120  has been compressed, and section  112  has been moved underneath strike plates  102 . The result is that close proximity between rod  110  and strike plates  102  has been lost. Negligible magnetic attraction force will be exerted upon rod  110 , thereby effectively “unlatching” rod  110  from housing  104 . If rod  110  is attached to a door or other member hung from the bottom of an enclosure, then such door or member is expected to move to its unlatched position. Similarly, if rod  110  is attached to a door or other member that is mounted essentially vertically, then release of latch mechanism  100  allows a pulling or other force to easily move the door or member to its open or removed unlatched position. 
     Referring to  FIG. 4 , another embodiment of latch mechanism is shown. In this embodiment, rod  210  is the same diameter throughout its length. However, section  212  is made of a non-magnetic material such as plastic. The result is the same as the mechanism shown in  FIGS. 2 and 3 . 
     Referring to  FIG. 5 , yet another of many possible embodiments is shown. In this embodiment  300 , rod  310  contains a U-shaped section  311 . When rotated appropriately, magnetically attractive section  311  becomes latched by contact with strike plates  302 . Instead of being pushed laterally, rod  310  operates as a latch by being rotated around its axis as shown by arrow  320 . The results are similar to those shown in  FIGS. 2 and 3 . Alternatively, rod  310  can be slidably mounted for movement along arrow  321 , in which case this embodiment will operate similarly to the embodiment shown in  FIGS. 1 and 2 . A square shaped rod may be particularly appropriate for a latch configured as shown in  FIG. 5 . 
     Referring to  FIG. 6 , application of an exemplary embodiment of the invention is shown as part of a jam clearing mechanism for a document feeder (“DF”) mounted on top of an electrostatographic imaging system. Such imaging systems are well known in the art. One electrostatographic imaging process is electrophotography. Generally, the process of electrophotographic reproduction is initiated by substantially uniformly charging a photoreceptive member, followed by exposing a light image of an original document thereon. Exposing the charged photoreceptive member to a light image discharges a photoconductive surface layer in areas corresponding to non-image areas in the original document, while maintaining the charge on image areas for creating an electrostatic latent image of the original document on the photoreceptive member. This latent image is subsequently developed into a visible image by a process in which a charged developing material is deposited onto the photoconductive surface layer, such that the developing material is attracted to the charged image areas on the photoreceptive member. Thereafter, the developing material is transferred from the photoreceptive member to a copy sheet or some other image support substrate to which the image may be permanently affixed for producing a reproduction of the original document. In a final step in the process, the photoconductive surface layer of the photoreceptive member is cleaned to remove any residual developing material therefrom, in preparation for successive imaging cycles. 
     The above described electrophotographic reproduction process is well known and is useful for both digital copying and printing as well as for light lens copying from an original. In many of these applications, the process described above operates to form a latent image on an imaging member by discharge of the charge in locations in which photons from a lens, laser, or LED strike the photoreceptor. Such printing processes typically develop toner on the discharged area, known as DAD, or “write black” systems. Light lens generated image systems typically develop toner on the charged areas, known as CAD, or “write white” systems. Embodiments of the present invention apply to both DAD and CAD systems. Since electrophotographic imaging technology is so well known, further description is not necessary. See, for reference, e.g., U.S. Pat. No. 6,069,624 issued to Dash, et al. and U.S. Pat. No. 5,687,297 issued to Coonan et al., both of which are hereby incorporated herein by reference. 
     Referring again to  FIG. 6 , the latch mechanism of  FIGS. 2 and 3  is shown as a latch that holds a jam clearance panel door  504  “up” against the bottom of DF body  500  during normal operations. DF  500  may take many forms, including without limitation, recirculating document feeders and simultaneous duplex document feeders. In the DF of  FIG. 5 , latch mechanism  100  is labeled as in  FIGS. 2 and 3 . In addition to lever  140  that is attached to rod  110 , a gripping fixture in the form of lever  150  is included. Lever  150  is fixedly attached to door  504  and is spaced apart from lever  140  at a distance that is conveniently spanned by a human hand. The result is that when DF  500  is lifted by its rear hinge (not shown) from the printer platen, an operator may reach under the body of DF  500  to grip levers  140  and  150  between thumb and index finger. By squeezing the hand, lever  140  with its attached rod  110  is moved from the position shown in  FIG. 2  to the position shown in  FIG. 3 . As discussed in relation to those figures, such shift moves section  112  of rod  110  underneath strike plates  102 , and the magnetic force holding door  504  in place snug against the body of DF  500  is released. As a result, door  504  is free to swing down from its hinge (not shown). The operator can then clear paper from the slot and mechanism exposed beneath door  504 . When cleared, the operator can lift door  504  back into its latched position. As soon as the operator released pressure from levers  140  and  150 , bias spring  120  shifted rod  110  back into the configuration shown in  FIG. 2 . The result is that when door  504  is lifted to its latched position, section  111  of rod  110  is one again in close proximity to strike plates  102 , and the door is latched in place. 
     In sum, the latch mechanism of the invention may have many embodiments. By using a magnet and a movable catch plate, the mechanism provides for a reliable, durable, inexpensive latch system that requires minimal force to open while virtually eliminating the “stickiness” of prying a catch plate away from a magnet. This amelioration of “stickiness” is particularly advantageous when, as shown in  FIG. 6 , the latch must be operated under conditions that constrain an operator's ability to apply ample force or that require handling in a confined space. 
     While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.