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RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Ser. No. 61/032,880, filed Feb. 29, 2008, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure is generally directed to filtration systems for a mobile surface maintenance machine. More specifically, the present disclosure is directed to a filtration system utilizing a filter shaker assembly for periodically removing debris from a filter surface. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to a filtration system for a mobile surface maintenance machine utilizing a filter shaker for periodically removing debris from a filter surface. The filtration system is preferably vacuum-based. In one embodiment, a filter stage is provided along with a debris hopper to allow dust and debris to be removed from a filter surface via activation of a filter shaker. Loosened dust and debris is deposited within the debris hopper. A preferred form of the invention utilizes a cylindrical pleated media filter. 
     A conventional forward throw cylindrical broom sweeper will be used by way of example in the following description of the invention. However, it should be understood that, as already stated, the invention could as well be applied to other types of mobile surface maintenance machines, such as, for example, other types of cylindrical broom sweepers and other machines such as sacrificers and various types of vacuum sweepers. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  is a perspective illustration of one embodiment of a cleaning machine utilizing a filter cleaning system in accordance with the present invention. 
         FIG. 2  is a perspective illustration of a hopper assembly and filter box of the cleaning machine of  FIG. 1 . 
         FIG. 3  is a perspective illustration of a hopper assembly and filter box of the cleaning machine of  FIG. 1 . 
         FIG. 4  illustrates a cross-sectional view of the hopper assembly and filter box of  FIG. 2 . 
         FIG. 5  illustrates a cross-sectional view of the hopper assembly and filter box of  FIG. 2 . 
         FIG. 6  illustrates a cross-sectional view of the hopper assembly and filter box of  FIG. 2 . 
         FIG. 7  illustrates a cross-sectional view of the hopper assembly and filter box of  FIG. 2 . 
         FIG. 8  illustrates a cross-sectional view of the hopper assembly and filter box of  FIG. 2 . 
         FIG. 9  illustrates a cross-sectional view of the hopper assembly and filter box of  FIG. 2 . 
         FIG. 10  is a perspective view of a filter and filter shaker components of the embodiment of  FIG. 2 . 
         FIG. 11  is a perspective view of a filter and filter shaker components of the embodiment of  FIG. 2 . 
         FIG. 12  is a perspective view of a filter shaker frame of the embodiment of  FIG. 2 . 
         FIG. 13  is a perspective view of the shaker plate of  FIG. 2 . 
         FIG. 14  is a detailed cross sectional view of the filter and filter shaker components of the embodiment of  FIG. 2 . 
         FIG. 15  is a detailed cross sectional view of the filter and filter shaker components of the embodiment of  FIG. 2 . 
         FIG. 16  is a top view of the main cover of the embodiment of  FIG. 2 . 
         FIG. 17  is a bottom view of the main cover of the embodiment of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , there is shown an industrial sweeping machine  10 . As shown, it is a forward throw sweeper. However, it could as well be an over-the-top, rear hopper sweeper, a type which is also well known in the art. It has a rotating cylindrical brush  12  for sweeping debris from a floor or other surface into a debris hopper assembly  14 . Hopper arms (not shown) allow hopper assembly  14  to be lifted during a dumping procedure. The broom chamber may be enclosed by skirts which come down nearly to the floor. The skirts largely contain within the broom chamber any dust stirred up by the broom. To complete the dust control there is a suction blower or vacuum fan  16  which exhausts air from the broom chamber to the atmosphere. Prior to exhaust, the air passes through hopper assembly  14  containing a filter module. Vacuum fan  16  maintains a sub-atmospheric pressure within the broom chamber so that air is drawn in under the skirts and through the filter module prior to exhaust. As a result, relatively little dust escapes from the broom chamber to the external environment. Various components of machine  10  have been left out of  FIG. 1 , e.g., the drive engine and engine have been omitted to improve understanding of the aspects of the present invention. Additional aspects of machine  10  are disclosed in U.S. Pat. No. 5,940,928, said patent being incorporated by reference herein. 
     As shown in  FIG. 2 , hopper assembly  14  of machine  10  includes air/debris inlet  20  through which air-entrained dust and debris enters via a mechanical throwing action by brush  12  and a vacuum action generated by vacuum fan  16  during a sweeping operation of machine  10 . Hopper assembly includes air outlet  22  through which filtered air is drawn by operation of vacuum fan  16 . During a hopper dumping procedure, dust and debris within hopper assembly  14  exits debris inlet  20 . Attached to hopper assembly  14  is a filter module including main cover  24 , filter cover  25  and tray  26 . 
       FIG. 3  depicts the hopper assembly of  FIG. 2  with main cover  24  and filter cover  25  removed. A portion of cylindrical filter  28  is exposed. Dust is retained on outer surfaces of filter  28  as air is drawn toward the filter&#39;s center by action of vacuum fan  16 . Air at the center of filter  28  is then directed out of air outlet  22  of filter cover  25  and toward vacuum fan  16 . 
       FIG. 4  is a cross-sectional view of hopper assembly  14  of  FIG. 2 . In the illustrated embodiment, a filter module includes three different filter sections for removing dust and debris from an air stream, namely prefilter  32 , cyclonic filters/vortex separators  34  and a cylindrical filter  28 . The arrows in  FIG. 4  generally depict air flow through hopper assembly  14  during machine operation. This filter system removes dust from the air stream so the vacuum fan will exhaust relatively clean air to the atmosphere. The filter module includes a bank of cyclonic filters  34  through which dusty air passes causing separation and retention of at least some of the larger dust particles and debris. Dust and debris exiting the bottom apertures of cyclonic filters  34  is deposited on collection surface  35  of the filter module. During a sweeping operation, dust and debris remains on surface  35  as an outlet is sealed by flexible seal  36  by way of vacuum action. Dust and debris on surface  35  is periodically removed during a hopper dumping procedure. During such a procedure, with the vacuum fan  16  uncoupled to hopper assembly  14 , seal  36  is free to swing open allowing dust and debris to pass through the outlet previously blocked by seal  36 . 
     During machine operation, air enters the filter module through prefilters  32  and passes through the vortex separators  34  prior to being filtered by the cylindrical filter. A vortex is created by the channels and conical sections below the channels as air spirals in a path moving downward and inward, then upward in a helical path to exit at an upper opening. The centrifugal acceleration due to rapid rotation of the air causes dense particles to be forced outward to the wall of the cones of vortex separators  34 . The dense particles are transported in a slow moving boundary layer downward toward the apex openings  38 . During operation, air passes from vortex separators  34  through openings  39  to the cylindrical filter for subsequent filtering. 
       FIG. 5  is another cross-sectional view of hopper assembly  14 . Cylindrical filter  28  is shown in cross section with a shaker motor  40  positioned within the central open interior of filter  28 . Filter  28  and shaker motor  40  are supported above collection surface  42  by support frame  44 . Shaker motor  40  is coupled to a pair of eccentric masses  46 ,  48  which are periodically rotated by motor  40  to impart a shaking action to filter  28 . Dust and debris removed from outer surfaces of filter  28  via a filter shaking procedure drops onto collection surface  42 . During a sweeping operation, flexible seal  49  is held closed by vacuum action thereby retaining debris on collection surface  42 . During a hopper dumping procedure with vacuum fan  16  uncoupled, flexible seal  49  opens to release debris on collection surface  42  for passage out of hopper assembly  14  at inlet opening  20 . 
     In one preferred embodiment of the invention, cylindrical filter  28  includes a pleated media filter, such as are manufactured, for example, by Donaldson Company, Inc. of Minneapolis, Minn. In one embodiment, filter  28  has a pleated media, with the pleats running parallel to the centerline of the cylinder, which makes them vertical when installed as shown. The pleated media is surrounded with a perforated metal sleeve for structural integrity. Outside the metal sleeve may be provided a fine mesh sleeve (not shown) woven from a slippery synthetic filament which stops the coarser dust and sheds it easily during a filter cleaning cycle. Other types of filter technologies may be applicable for implementation within filter  28 . 
       FIG. 6  is a cross-sectional view of hopper assembly components. Flexible seals  36 ,  49  are shown in this drawing. Collection surface  35  is separated from collection surface  42  by wall  51 . A pressure differential may exist across wall  51  as pressure within the vortex separator section may be different than pressure within the cylindrical filter section. 
       FIG. 7  depicts cylindrical filter  28  held between filter cover  25  and a filter support frame  44  above debris collection surface  42 . The filter support frame  44  includes a pair of frame arms attached to base  62 . The filter support frame  44  is secured via fasteners  63  passing through frame arm ends to a rigid portion of the hopper assembly. As a result, the filter support frame  44  is substantially secured against movement within the hopper assembly  14 . 
       FIGS. 8 and 9  are cross sectional views of filter  28 , shaker mechanism components and the filter support frame  44 . Shaker mechanism includes a pair of eccentric masses  46 ,  48  mounted to shaft  74  of motor  40 . Motor  40  may be electric or hydraulic-based. Motor  40  is secured to shaker plate  77  via, for example, threaded fasteners. Upon activation of motor  40 , the weights  46 ,  48  rotate and vibrate shaker plate  77  and filter  28  at a frequency dependent on motor speed. In a preferred embodiment of the invention, an electric motor  40  is entirely received within a center cavity of cylindrical filter  28 . As shown in  FIG. 9 , shaker plate  77  includes filter support  78  which engages a bottom surface of filter  28  and limits a degree of gasket compression as described in more detail below. 
       FIG. 10  illustrates cylindrical filter  28  and support frame  44 . A flexible gasket  79  engages shaker plate  77  and another gasket  79  engages the underside of cover  25  (not shown) during operation. Together the gaskets  79  seal the interior of filter  28  and prevent air leakage around filter  28 . Filter support  78  controls the position of filter  28  relative to shaker plate  77  and thus limits the degree of gasket  79  compression. 
       FIG. 11  is a perspective view of components of the filter support frame and shaker mechanism. Shaker plate  77  is supported upon a slide bearing  80 , which is supported upon support plate  62 . During shaker mechanism operation, shaker plate  77  slides upon bearing  80  in response to movement of eccentric masses  46 ,  48 . The rotational range of motion of shaker plate  77  is limited by pins  82  attached to the frame base plate  62 . Pins  82  may engage edges of apertures  84  during motor  40  start up or during machine operation to prevent further rotation of shaker plate  77 . Reinforcement structure, in this example welded stops, are provided around apertures  84  to minimize wear to shaker plate  77 , base plate  62  and/or pins  82 . Together the pins  82  and apertures  84  cooperate to limit the rotational range of motion of shaker plate  77  relative to the filter support frame  44 . In the illustrated embodiment as shown in  FIG. 12 , a pair of pins  82  are connected to base plate  62 . A third pin  82  is connected to shaker plate  77 . As shown in  FIG. 13 , a pair of slot apertures  84  are defined on shaker plate  77  and a third slot aperture  84  is defined on base plate  62 . This arrangement of pins  82  and apertures  84  prevents the shaker assembly from being assembled improperly during manufacturing or use. 
       FIG. 12  is a perspective view of frame support arms of the filter support frame  44  and base plate  62 . In a preferred embodiment, tabs and slots  85  are defined in frame support arms of the filter support frame  44  and base plate  62  to aid in alignment, durability and/or manufacturability of the filter support frame  44 . Base plate  62  includes a center aperture  100  defined by a circular edge  102 . 
       FIG. 13  is a perspective view of shaker plate  77 . Apertures  120  receive fasteners to secure electric motor  40  to shaker plate  77 . Wiring for electric motor  40  passes through aperture  124 . Motor shaft  74  passes through aperture  123 . 
       FIGS. 14-15  are cross sectional views of the shaker mechanism components and filter  28 . The shaker mechanism includes a pair of cylindrical rings  90 ,  92  which are secured to shaker plate  77 . Cylindrical ring  90  is sized in relation to the inside diameter of filter  28  so as to snuggly engage and retain filter  28  against shaker plate  77 . Cylindrical ring  92  is sized in relation to the diameter of center aperture  100  of base plate  62 . The size difference (or clearance) between ring  92  and aperture  100  is shown by dimension, DP. Ring  92  has a smaller diameter than that of aperture  100  so that shaker plate  77  can slide/rotate relative to base plate  62 . During operation, ring  92  may contact the edge  102  of aperture  100  so as to limit the range of shaker motion. In a preferred embodiment, ring  92  is sized relative to aperture  100  so as to provide sufficient movement of shaker plate  77  in order to generate impulses upon contact between ring  92  and edge  102 . In other embodiments, ring  92  may engage a differently configured structure of support plate  62 . For example, edge  102  include additional support material provide additional durability. As a result, ring  92  and aperture  100  cooperate to limit the range of motion of shaker plate  77  relative to the filter support frame. 
     The control of filter shaker mechanism is via an on-board controller of machine  10 . The controller may automatically activate the electric motor  40  of the shaker mechanism after a period of time has elapsed or upon receipt of a signal from a pressure switch indicating that the filter has become occluded. A differential pressure sensor/switch may be used across filter  28  to detect filter condition. As dust gradually accumulates on filter  28 , the differential pressure will rise. When it reaches a predetermined value the pressure switch will close, which will initiate an automatic filter cleaning cycle. The time period during which electric motor  40  is activated may be predetermined. Alternatively, activation of the electric motor  40  to perform a filter shake procedure may be via a manual switch utilized by a machine operator. 
       FIG. 16  is a top perspective view of main cover  24  showing filter opening  141  through which filter  28  can be accessed during inspection, replacement, etc. The filter cover  25  (not shown) is secured to main cover  24  by threaded fasteners (not shown) engaging threaded components  142 . Main cover  24  defines an air conduit  143  through which filtered air travels toward vacuum fan  16 . Conduit  143  includes a mating surface  144  which is sealed against a surface of filter cover  25 . 
       FIG. 17  is a bottom perspective view of main cover  24  showing a plenum portion  151  connected to a plurality of vortex-forming spiral walls  152 . Some of the walls  152  spiral in one direction and other walls  152  spiral in an opposite direction. A lower surface  153  of main cover  24  engages tray  26  (shown in  FIG. 4 ) of the filter assembly. Dusty air from the hopper assembly enters plenum  151  at plenum entrance  154 . Plenum  151  effectively distributes airflow across the various spiral walls  152  so as to maintain a balanced dust removal among the vortex separators. Air exits this portion of main cover  24  through openings  156  and passes into a generally enclosed volume of cover  24 . 
     Advantages of a shaker mechanism in accordance with the present invention include: a cleaner operating environment for shaker motor  40  as motor  40  is position inside cylindrical filter  28 ; the pair of eccentric masses  46 ,  48  tend to provide a balanced, radial shaking motion to filter  28 ; filter  28  durability may be improved by providing a balanced, radial shaking motion; and noise generated during shaker mechanism operation can be minimized by providing a balanced shaker assembly. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Summary:
A filter shaking assembly for a floor surface maintenance machine including a filter assembly in fluid communication with the debris hopper and having a cylindrical filter held against a shaker plate. The shaker plate is vibrated by a shaker motor at least partially positioned within an interior of the filter and eccentric mass to remove an accumulation of debris from the surface of the filter. The eccentric mass may include two eccentric masses positioned on a common shaft of the shaker motor.