Abstract:
A document shredder is disclosed including a paper receptacle for receiving a load of paper and a shredding assembly. A metering assembly is interposed between the paper receptacle and the shredding assembly and is configured to separate a portion of the load of paper from the load of paper and permit the portion of the load of paper to move into the shredding assembly. The metering assembly may include a stop plate secured thereto and defining a lifting portion on a perimeter portion thereof. The lifting portion is configured to engage a lower edge of the portion of the load of paper upon rotation of the stop plate and lift the paper over the stop plate. The lifting portion may include a flange, which may be a portion of a cone, formed on a perimeter portion of the wheel and occupying a sector of the perimeter of less than 60 degrees.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to a document shredder. The invention relates more particularly to a paper feeding portion of the document shredder. 
     BACKGROUND OF THE INVENTION 
     Document shredders are used to shred confidential or private documents to prevent unwanted viewing of the document by another. Document shredders are available in various feed capacities. For a small volume of documents to be shredded, a document shredder which accepts a single document to be shredded at a time may be satisfactory. For a larger volume of documents to be shredded, a document shredder that may accept more than one document at a time may be preferable. Document shredders that may accept more than one document at a time may have paper feeding mechanisms that feed more than one document at a time to the shredder. However, document shredders that may accept more than one document at a time may be prone to jams in the shredder portion of the document shredder due to improper feeding of the documents to be shredded. Jams in the shredder portion of the document shredder may be caused by attempting to feed more documents at one time than the document shredder is capable of shredding, or by attempting to shred documents at a faster rate than the document shredder is capable of shredding. Therefore, a need exists in the art for a feeding mechanism for a document shredder that feeds documents to be shredded at a volume and rate that does not exceed the shredding capacity of the document shredder. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for feeding a controlled amount of documents to be shredded into a document shredder at a controlled rate. The controlled, or desired amount of documents to be shredded is an amount of documents to be fed into a shredder mechanism of a document shredder that will not normally cause jamming of the shredder mechanism of the document shredder. In some embodiments, a shredder includes a paper receptacle for receiving a load of paper and a shredding assembly. A metering assembly is interposed between the paper receptacle and the shredding assembly. The metering assembly is configured to separate a portion of the load of paper from the load of paper and permit the portion of the load of paper to move into the shredding assembly. For example, the paper receptacle may be at a higher elevation than the shredding assembly. 
     In another aspect of the invention, the paper receptacle defines a ridge that engages a lower edge portion of the load of paper. The metering assembly may be configured to urge the portion of the load of paper over the ridge. The paper receptacle may include a base positioned to support lower edges of sheets of the load of paper. A support may extend upwardly from a rear portion of the base and the lip may be secured to a forward portion of the base. The paper receptacle may further include a biasing member positioned to urge the load of paper toward the metering assembly. 
     In another aspect of the invention, the metering assembly includes a metering shaft having an axis of rotation oriented perpendicular to lower edges of sheets in the load of paper. A stop plate is secured to the metering shaft and defines a lifting portion on a perimeter portion thereof. The lifting portion is configured to engage a lower edge of the portion of the load of paper. In some embodiments, the stop plate is embodied as a wheel and the lifting portion includes flange secured to a perimeter portion of the wheel. The flange may be embodied as a portion of a cone concentric with an axis of rotation of the wheel. In some embodiments, the lifting portion lies entirely in a sector of the stop plate smaller than 60 degrees with respect to an axis of rotation of the metering shaft. 
     In another aspect of the invention, a shaft support engages the metering shaft having the stop plate positioned between the shaft support and the paper receptacle. The shaft support may further include a ramp secured thereto and defining a ramp surface sloping downwardly from the metering shaft. 
     In some embodiments, the shredding assembly includes two cutting blade assemblies and a motor coupled to the cutting shafts. The motor, or a different motor, is also coupled to the metering shaft. The cutting blade assemblies may shred paper of length L with a linear feed rate F and be able, or rated, to simultaneously shred a maximum number of sheets M. The metering assembly may be configured to separate portions of paper of at most N sheets from the load of paper with a period T. The values of T and N may be configured such that N*ceiling(L/(F*T)) is less than M. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative examples of the present invention are described in detail below with reference to the following drawings: 
         FIG. 1  illustrates a top plan view of a document shredder in accordance with an embodiment of the present invention; 
         FIG. 2  illustrates an isometric view of a drive mechanism for the document shredder including a metering assembly in accordance with an embodiment of the present invention; 
         FIGS. 3A through 3C  illustrate a metering assembly in accordance with an embodiment of the present invention; 
         FIG. 4  is an isometric view of a drive mechanism for a metering assembly in accordance with an embodiment of the present invention; 
         FIG. 5  is a partial isometric view of a metering assembly having a shaft support in accordance with an embodiment of the present invention; and 
         FIGS. 6A and 6B  illustrate metered release of paper using a metering assembly in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates an embodiment of a document shredder  10 . The document shredder  10  includes a feeder portion  12  and a shredding portion  14 . The feeder portion  12  includes a paper tray  16  and a biasing plate  18 . The feeder portion  12  and shredding portion  14  may be secured to and/or housed within a housing  20 . 
     Referring to  FIG. 2 , the shredding assembly  14  may include a motor  22  for driving the shredding assembly  14 . The motor  22  may output power to a gear assembly  24  and a gear assembly  26 . As is apparent in  FIG. 2 , the gear assemblies  24 ,  26  are located on opposite sides of the cutting blade assemblies  28 . The cutting blade assemblies  28  may each include shafts having a number of blades secured thereto and interleaved with the blades of the opposing cutting blade assembly  28 . The cutting blades may be configured according to any embodiment known in the art. In some embodiments, gear assembly  26  is driven by the motor  22  by means of the cutting blade assemblies  28 . The manner in which the motor  22  drives the cutting blade assemblies  28  and the configuration of the gear assemblies  24 ,  26  may be according to any embodiment known in the art. 
     In some embodiments, the motor  22  may drive a gear  30  that actuates a metering assembly  32  for dispensing paper within the paper tray  16 . Alternatively, the metering assembly  32  may be actuated by a different motor. In the illustrated embodiment, the gear  30  is driven by gear assembly  26 . However, in other embodiments, the gear  30  may engage the gear assembly  24  or be coupled to the motor  22  by some other gear assembly or other actuation means. 
     As will be described in greater detail below, the metering assembly  32  dispenses paper  38  from the tray  16  in a controlled manner such that a user is relieved of the task of feeding paper into the shredding portion  14  and jamming of the shredding portion  14  is reduced or eliminated. In the illustrated embodiment, the paper tray  16  secures to a base  34 . The paper tray  16  may maintain the paper  38  in a substantially vertical orientation. For example, the tray  16  may be oriented, or selectively placed into an orientation, at an angle of less than 45 degrees, preferably less than 30 degrees, more preferably less than 15 degrees, with respect to vertical when the shredder  10  is resting on a flat surface. The base  34  may be substantially horizontal when the shredder  10  is resting on a flat surface, e.g. within +/−15 degrees of horizontal. 
     The paper  38  may be prevented from sliding off the base  34  in response to gravity and/or the action of the biasing plate (see  FIG. 1 ) by means of the metering assembly  32 . For example, the metering assembly  32  itself may be positioned at one side of the base  34  having the paper tray  16  extending from an opposing side such that a lower portion of the paper  38  is positioned between the metering assembly  32  and the paper tray  16 . In some embodiments, one or more ridges  36  are secured to the base  34 , such a portion of the base  34  extends between the one or more ridges  36  and the paper tray  16 . In this manner, the paper  38  is prevented from falling into the shredding portion  14  due to gravity and the action of the biasing plate  18 . In some embodiments, the metering assembly  32  may be operable to lift sheets of the paper  38  over the one or more ridges  36 . 
     Referring to  FIGS. 3A and 3B , the metering assembly  32  may include a stop plate  40  coupled to a shaft  42 . The stop plate  40  may be substantially planar in a plane perpendicular to the axis of rotation  44  of the shaft  42 . In the illustrated embodiment, the stop plate  40  has a round perimeter. However, other perimeter shapes may also be used. The stop plate  40  may define a lifting portion  46  operable to lift portions of a load of paper and allow the portions to fall into the shredder in response to rotation of the shaft  44 . The lifting portion  46  may lie in a sector of the stop plate  40 , with respect to the axis of rotation  44 , that is less than 60 degrees, e.g. between 45 and 60 degrees. In this manner, for a major portion of the period of rotation of the stop plate  40 , no paper is being lifted, thereby allowing a previous batch of paper to completely or partially pass through the shredding portion  14 . In some embodiments, multiple lifting portions  46  are distributed uniformly around the perimeter of the stop plate  40 . 
     In the illustrated embodiment, the lifting portion  46  is embodied as a flange  48  extending from a perimeter of the stop plate  40 . The flange  48  may be sector shaped in a plane perpendicular to the axis of rotation  44  (the plane of the page for  FIG. 3B ), the sector being centered on the axis or rotation  44 . As is apparent in  FIG. 3B , there is an abrupt radial step between the flange  48  and the perimeter of the wheel  44 . In other embodiments, a smoother transition between the larger radius of the flange  48  and the radius of the wheel  44  may be used. The angular width  50  occupied by the flange  48  is less than 180 degrees, preferably less than 90 degrees, and, more preferably, less than 60 degrees. For example, the angular width  50  may be between 45 and 60 degrees. In the illustrated embodiment, the angular width  50  is approximately 55 degrees. 
     Referring specifically to  FIG. 3C , as noted above, the flange  48  may be embodied a portion of a conical surface, such as a portion of a cone secured to the perimeter of the stop plate  40 , the cone defined by an outer surface at an angle  52  relative to the axis of rotation  44  and symmetrical about the axis of rotation  44 . In some embodiments, the inner surface of the flange  48  may be oriented at the same angle relative to the axis of rotation  44  as the outer surface. In other embodiments, the inner surface defines a greater angle such that the flange  48  tapers with distance from the axis of rotation  44 . 
     In some embodiments, the angle  52  may be substantially equal to an angle defined by paper stacked in a shredder with respect to the axis of rotation  44 . For example, the angle  52  may be such that when the metering assembly is positioned within the shredder  10 , the angle  52  is equal to the angle defined by the intersection between paper within the shredder  10  and a vertical plane intersecting the axis of rotation  44 . In this manner, the flange  48  may more easily slide between sheets of paper when dispensing paper. 
     The outer perimeter of the stop plate  40  may have a radius  54   a  and the outer perimeter (relative to the axis of rotation  44 ) of the flange  48  may have a radius  54   b . The difference between radius  54   a  and radius  54   b  may be selected to lift a desired number of sheets per revolution of the stop plate  40 . 
     Referring to  FIG. 5 , as noted above, the shaft  42  may be rotated by the motor  22 . For example, the gear  30  engaging the gear assembly  26  may rotate a lateral shaft  58 . The lateral shaft  58  may drive the shaft  42  by engagement of a bevel gear  60   a  secured to the shaft  58  with a bevel gear  60   b  secured to the shaft  42 . As is apparent in  FIG. 5 , the rate of rotation of the shaft  42  and stop plate  40  relative to the rotation of the cutting blade assemblies  28  is determined by some or all of the gear assembly  24 , gear assembly  26 , gear  30 , and bevel gears  60   a ,  60   b . A desired relative rate of rotation of the shaft  42  and cutting blade assemblies  28  may also be achieved by other means, including electronic control of separate motors or some other means. In some embodiments, a controller may be operably coupled to the motor  22  and to a sensor  61  positioned adjacent the shaft  42  and operable to sense a rotational speed of the shaft  42 , such as by means of optically detecting one or more optically detectable markings on the shaft  42 , detecting variation in a magnetic field from a magnet attached to the shaft  42 , mechanical actuation of a switch by the shaft  42  for each rotation, or any means known in the art for detecting rotational speed. 
     Referring to  FIG. 5 , in some embodiments a portion of the shaft  42  projects forwardly from the stop plate  40 , e.g. away from the base  34 . This portion may be engaged by a shaft support  62  defining an aperture  64  for receiving the portion of the shaft  42 . The shaft support may be secured to the base  34  or to some other structure that is secured to the base  34 , such as the housing  20  or paper tray  16  (See  FIG. 1 ). In some embodiments, the shaft support  62  may be configured to facilitate movement of paper  38  past the shaft support  62 . For example, the shaft support  62  may define an angled face  66  that slopes outwardly from the stop plate  40  with distance downward from the stop plate  40 . The face  66  may define a plane that intersects the stop plate  40 , such that paper sliding off the stop plate  40  will not catch on any horizontal or other surface of the shaft support  62 . The face  66  may be defined by areas of the shaft support  62  surrounding the aperture  64 . 
       FIGS. 6A and 6B  illustrate the manner of operation of the metering assembly  32 . Referring specifically to  FIG. 6A , as the stop plate  40  rotates, the flange  48  secured to the stop plate  40  engage the lower edge of a portion  38   a  of a load of paper thereby separating the portion  38   a  from the rest of the paper  38   b . As the leading edge of the flange  48  rises to the apex of its rotation, shown in  FIG. 7A , the paper  38   a  is lifted above any ridges  36 . Referring specifically to  FIG. 6B , as the stop plate  40  continues to rotate the portion  38   a  of the paper is allowed to fall past the stop plate  40  and any ridges  36  into the cutting blade assemblies  28 . In particular, the portion  38   a  of paper may be allowed to fall at some point after the leading edge of the flange  48  begins to descend past the apex of its rotation. As noted above, the biasing plate  18  urges the remaining paper  38   b  against one or both of the ridges  36  and the stop plate  40  ready to be lifted by the flange  48  as the stop plate  40  continues to rotate. 
     As noted above, the stop plate  40  and cutting blade assemblies  28  may be constrained to rotate at a fixed relative rate of rotation. The rate of rotation of the cutting blade assemblies  28  may be effective to achieve a linear feed rate F (e.g. length per unit time) of paper through the cutting blade assemblies. The linear feed rate F may be the linear feed of the cutting blade assemblies when shredding a maximum number of sheets M. In some embodiments, M is the maximum permissible number of sheets that can be shredded simultaneously between the cutting blade assemblies  28  at one time without causing jamming of the cutting blade assemblies  28 , failure of the motor  22 , or other malfunction of the shredding assembly  14 . The value M may be the value specified by the manufacturer of the shredding assembly as the maximum capacity, which may be some tolerance below the actual maximum simultaneous sheet limit for the shredding mechanism  14 . 
     The stop plate  40  may rotate with a period T for the feed rate F such that a new portion  38   a  of paper drops into the cutting blade assemblies every period T. The period T may be such that for pages having a maximum length L multiple portions  38   a  of paper may be simultaneously present between the cutting blade assemblies. The number of portions  38   a  that will be simultaneously between the cutting blade assemblies may be equal to up to Ceiling(L/(F*T)). As noted above, the configuration of the flange  48  (See  FIGS. 3A-3C ) may determine the largest possible number (N) of sheets that may be lifted by the stop plate  40  per revolution. Accordingly, the largest possible number N of sheets and period T may be selected relative to the feed rate F such that N*Ceiling(L/(F*T)) is less than M. 
     While the preferred embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, although the feeder portion  12  is shown operating in combination with a shredding assembly  12 , other sheets of material may be processed according by other material processing apparatus. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.