Abstract:
An improved attachment structure is provided for securing a cover in overlying covering relation to a seat cushion. In the chair, the chair comprises a seat/back assembly having a seat assembly and back assembly which are supported upon a load-bearing base adapted for support upon a floor. The attachment structure provides an improved method of securing a cover about its peripheral edge to an outer and inner shell on a seat assembly, wherein cooperating ribs and channel sections form convolutions in the fabric edge and hold the fabric edge between the inner and outer shells.

Description:
FIELD OF THE INVENTION 
     The invention relates to an improved seat assembly, and more particularly, to a seat assembly having an improved connector structure for securing a cushion-enclosing cover to a seat shell. 
     BACKGROUND OF THE INVENTION 
     Conventional office chairs use a variety of constructions for the seat assembly. Many such chairs use a sheet-like molded shell which mounts to a chair base wherein the shell supports a cushion and then a seat cover which overlies the cushion to provide the aesthetic finished appearance of the seat assembly. The cover may be formed from a variety of materials and often is formed of a fabric that can be selectively varied depending upon the pattern desired by a purchaser. In such chairs, it is necessary to secure the peripheral edge of the cover, often to the seat shell or other seat structure. In some chair constructions, separate fasteners such as staples and the like may be used to secure the peripheral edge to the inner shell. 
     It is an object of the invention to provide an improved seat assembly for a cushioned seat having an improved construction for securing the peripheral edge of the seat cover. 
     The invention relates to improved attachment structure for securing a cover in overlying covering relation to a seat cushion. In the chair of the invention, the chair comprises a seat/back assembly having a seat assembly and back assembly which are supported upon a load-bearing base adapted for support upon a floor. This base may include a tilt control mechanism wherein the seat assembly and back assembly are pivotally connected to the tilt control mechanism and rearwardly reclinable in operation. The seat assembly itself has front and rear seat portions that pivotally connect to the tilt control mechanism supported on the base. To support the seat loads, the seat assembly comprises a structurally rigid support plate which is horizontally enlarged and formed of a structurally rigid material such as metal, wherein the front and rear edge portions of the seat plate pivotally connect to the seat or to the tilt control mechanism so that the seat assembly is rearwardly tiltable in operation. 
     The seat assembly further comprises a horizontally enlarged, inner shell which has a bottom surface which is supported by the seat plate, and an upper surface which preferably is covered with a resiliently-compressible cushion. This cushion extends outwardly to the outer peripheral edge of the inner shell and in turn is enclosed by a seat cover, for example, formed of a fabric material, which seat cover is enlarged widthwise and in the front-to-back direction so as to hang over the sides of the cushion and wrap about the outer peripheral edge of the inner shell. As such, the peripheral cover edge is able to wrap about and extend partially underneath the bottom of the inner shell. In this edge region, the inner shell includes an edgewise-extending securement channel defined by parallel, downwardly-projecting channel walls. The inner channel wall includes spaced-apart teeth which preferably are tapered so as to facilitate compression of the cover material. 
     An annular outer shell is provided which mounts to the inner shell from the underside thereof and extends about the outer periphery of the inner shell. This outer shell includes an upstanding rib that extends edgewise about the periphery of the outer shell and preferably is formed of aligned ribs which are separated from each other by cross-windows. In this manner, the individual ribs are edgewise elongate so as to be generally parallel to the inner and outer channel walls of the outer shell while the individual ribs may also have some cross-wise flexure. The free ends of the ribs include additional teeth so that when the outer shell is pressed or fitted onto the inner shell from below, the peripheral cover edge follows a convoluted or treacherous path by wrapping about the outer edge of the inner shell and overlapping the underside of the inner shell, and then turning upwardly into the channel or valley as it wraps over the free ends of the ribs, and then turns downwardly out of the channel and finally extends over and terminates beyond the inner channel wall and the teeth thereof. 
     As the fabric passes cross-wise through this convoluted path, the cover is pinched at pinch points, wherein one pinch point preferably is located between the teeth at the upper ends of the ribs and the opposing bottom surface of the valley, and a further pinch point is located at the teeth on the inner channel wall which presses the fabric against an opposing inside surface of the outer shell. Hence, the cover material is pinched at multiple locations along the cross-wise extend of the convoluted path and thereby fixedly secured at the edge of the cover in compressed, pinched engagement between opposing surfaces of the outer shell and inner shell. 
     Additionally, the individual ribs are separated edge-wise by the cross-windows wherein the interior of the securement channel also includes upstanding cross-ribs which extend between the inner and outer channel walls in crosswise relation and fit into the cross-windows which thereby forces the soft cover material into the cross-windows and defines additional folds along the convoluted path of the cover material. This provides additional fixed securement of the cover when compressed between the outer shell and inner shell. 
     To potentially define an additional pinch point, the separation of the individual ribs from each other by the cross-windows preferably allows for outward flexing of the individual ribs when the cover material is pulled taut on the seat. Sufficient cross-wise deflection of the ribs will occur until the outer side surface of each rib contacts the interior face of the outer channel wall which thereby would serve to define an additional pinch point by pinching the cover material sidewardly or cross-wise between the rib and the outer channel wall. 
     The securement structure provides an improved method of securing a cover about its peripheral edge to an outer and inner shell on a seat assembly. While this structure is primarily provided for a seat assembly, a back assembly might also be configured using such securing structure. 
     Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a chair of the invention. 
         FIG. 2  is a side elevational view thereof. 
         FIG. 3  is an exploded view of the seat assembly. 
         FIG. 4  is a front cross-sectional view of the joined shells. 
         FIG. 5  is a side cross-sectional view thereof. 
         FIG. 6  is a plan view of a shell assembly. 
         FIG. 7  is a bottom view of an inner shell of the shell assembly. 
         FIG. 8  is an enlarged partial view of the inner shell. 
         FIG. 9  is a top perspective view of an outer shell. 
         FIG. 10  is an enlarged partial view of the inner and outer shells. 
         FIG. 11  is a side cross-sectional view of the joined shells. 
         FIG. 12  is a side cross-sectional view thereof. 
         FIG. 13  is an enlarged perspective view of the joined inner and outer shells taken from the front. 
         FIG. 14  is a partial side cross-sectional view taken at a rear of the chair. 
         FIG. 15  is a side cross-sectional view taken at the front of the chair. 
     
    
    
     Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , the invention relates to a chair  10  having a pedestal base  11  which comprises a tilt control mechanism  12  having a seat/back assembly  14  pivotally connected thereto. The seat/back assembly  14  comprises a pair of uprights or support arms  15  which are pivotally connected at their front ends to the tilt control mechanism  12 , and have rearward ends which support a back assembly  16  projecting vertically upwardly therefrom. Additionally, the seat/back assembly  14  includes a seat assembly  17  that is pivotally connected to the uprights  15  and the tilt control mechanism  12  so that the back assembly  16  and seat assembly  17  are rearwardly tiltable. The invention relates to improvements in the seat assembly  17 . 
     Referring to  FIGS. 2 and 3 , the seat assembly  17  is pivotally connected by its four corners to front pivot connections  18  to the tilt control mechanism  12 , and rear pivot connections  19  at the upper ends of upwardly extending support arms  20  ( FIG. 2 ) respectively provided on the uprights  15 . In particular, the seat assembly  17  comprises a horizontally enlarged rigid support plate  22  which is formed of a rigid metal construction and has rear pivot mounts  23  which interconnect to the rear pivot connectors  19  ( FIG. 2 ). The seat plate  22  also includes guide slots  24  which interconnect with the slidable pivot connectors  18  so that the front edge of the seat assembly  17  may displace rearwardly to a small extent therewith during rearward tilting of the uprights  15 . The support plate  22  has a generally rectangular, pan-like shape which provides a rigid support surface  22 A on the top thereof for carrying the loads of an occupant sitting on the seat assembly  17 . 
     In the chair  10  of the invention, the back assembly  16  preferably includes a thin, suspension membrane  24  that supports the back of a chair occupant. The seat assembly  17  has a different construction in that the seat assembly  17  includes a seat cushion  25  that is relatively thick and is compressible to conform to the contours of the chair occupant. 
     Referring to  FIG. 3 , this cushion  25  generally comprises an interior cushion layer  26  and a sheet-like flexible cover  27  that preferably is formed of a fabric material that defines a suitable exposed surface of the seat assembly  17 . The cover  27  is generally illustrated in  FIG. 3  and is shaped so as to overlie the cushion. This cover  27  comprises a central portion  28  and a peripheral cover edge  29  that is configured to extend over the peripheral cushion edge  30  of the cushion layer  26 . The peripheral cover edge  29  is configured to be fixedly secured to the seat assembly  17  in an improved manner which represents an inventive advantage over prior securement methods for fabric covers of this type. 
     More particularly, the seat assembly  17  comprises a horizontally enlarged inner shell  32  having a top surface  33  that is substantially covered by the cushion layer  26 . The inner shell  32  further defines a downward-facing bottom surface  34  which is configured to fit onto the support plate  22  and is supported by such support plate  22  in the central region thereof. The inner shell  32  further defines an outer peripheral shell edge  35  which generally conforms to the peripheral cushion edge  30  in its shape. The size of the cover  27  is oversized relative to the edges  30  and  35  so that the peripheral edge portion  29  of the cover  27  is able to wrap about and extend beneath the bottom shell surface  34  for subsequent connection thereto. 
     In this regard, the seat assembly  17  further comprises a ring-like outer shell  40  which is defined by an outer shell edge  41 , an inner shell edge  42  as well as top and bottom surfaces  43  and  44 . The outer shell edge  41  is shaped and sized so that it conforms closely to the shape and size of the cushion edge  30  and inner shell edge  34 . The interior shell edge  42  of the outer shell  40 , however, is dimensioned larger than the support plate  22  so that this interior shell edge  42  is spaced outwardly of the support plate  22  and the support plate  22  in turn is able to pivotally connect to the tilt control mechanism  12  and uprights  15  as described above. 
     Referring to  FIGS. 4 and 5 , the inner shell  32  includes the cushion layer  30  thereon as diagrammatically illustrated, and also includes the cover  27  which overlies the cushion material  30  and has its peripheral edge  29  wrapped downwardly around the outer shell edge  35  so as to thereby extend underneath the bottom shell surface  34  and be sandwiched between the inner shell  32  and the underlying outer shell  40  which is fitted below the bottom shell surface  34 . In particular, the outer shell edge  41  is disposed so as to be closely adjacent and contact the outer shell edge  35  so that the peripheral cover edge  29  can extend into the space and be completely hidden from the exterior of the chair  10  which provides a clean appearance to the overall seat construction. 
     In this regard, it is necessary to ensure that the peripheral cover edge  29  is not able to pull free from the inner shell  32 . In this regard, the peripheral cover edge  29  extends into the space between the inner shell  32  and outer shell  40  and extends along a torturous or convoluted path which securely engages the cover edge  29  so as to be compressed at one or more locations along such convoluted path to resist slippage of the cover edge  29  from the interface between the inner shell  32  and outer shell  40 . Further, as will be described in further detail hereinafter, the tortuous or convoluted path as defined by the inventive connector structure forms convolutions in both a crosswise direction of the cover edge  29  which can extend either widthwise across the lateral width or front to back width of the fabric, or edgewise along the edgewise-extending cover edge  29 . By forming convolutions in the crosswise and edgewise directions, the connection provides a strong interconnection with the cover edge  29  to prevent pulling separation of the cover  27  from the interface between the inner shell  32  and outer shell  40 . 
     As to the outer shell shown in  FIGS. 6-8 , this outer shell  32  is adapted to receive the outer shell  40  in facing relation on the underside  34  thereof. In this regard, the bottom shell side  34  includes upstanding connector posts  45  at spaced-apart locations about the outer shell edge  35  for fastening to the outer shell  40 . The inner shell  32  further comprises an edgewise-extending connector channel or valley  46  which is defined by front and back channel sections  46 A and  46 B as well as opposite side sections  46 C and  46 D. These channel sections  46 A- 46 D generally have similar constructions although the overall shape may vary depending upon the requirements and components provided in the seat assembly  17 . As seen in the enlarged view of  FIGS. 8 and 13 , the connector channel  46  is defined by inner and outer channel walls  47  and  48  and a bottom wall  49 . The channel  46  is continuous along the length of the entire channel  46  at least proximate the downward-opening mouth of the channel  46 . The bottom of the channel  46 , however, which is defined adjacent the bottom wall  49 , is segmented by cross-ribs  50  as seen generally in  FIG. 8 , and illustrated in greater detail in  FIGS. 11-13 . This forms a plurality of separated pockets  51  which are separated from each other by the cross-ribs  50 . The pockets  51  hereby are defined edgewise by the spaced-apart cross-ribs  50 , as well as crosswise by the inside faces of the inner and outer channel walls  47  and  48 . These pockets  51  and cross-ribs  50  help define the convoluted path and the convolutions thereof in the crosswise direction and the edgewise direction. Since the channel  46  extends about the entire periphery of the inner shell  35 , the crosswise direction extends between the inside faces of the inner and outer channel walls  47  and  48 . As such, the crosswise direction in channel sections  46 D and  46 C would extend widthwise, while the crosswise direction in the channel sections  46 A and  46 B would extend in the front-to-back directions. 
     To further affix the cover edge  29 , the middle edge  52  of the inner channel wall  47  is formed with a plurality of edgewise spaced projections or teeth  53  that preferably are formed as pointed or cone-shaped projections. As seen in  FIGS. 13-15 , the cover edge  29  extends over the wall edge  52  and is pinched by the projections  53  which project downwardly and are disposed closely adjacent if not disposed in contact with the inner face of the outer shell  40 . 
     More particularly as to the outer shell  40 , such shell  40  is formed with a peripheral rib structure  60  defined by front and rear rib sections  60 A and  608  and side rib sections  60 C and  60 D. These rib sections  60 A- 60 D of the rib structure  60  are each defined by separated, rectangular ribs  61  which project upwardly and are separated from each other by windows  62 .  FIGS. 11 and 12  clearly illustrate the individual ribs  61  and window  62  wherein the ribs  61  fit into the individual pockets  51  while the windows  62  accommodate the cross-ribs  50  described above. The individual ribs  60  also include upright conical or pointed teeth or projections  63 , which project upwardly and are disposed closely adjacent the bottom channel surface defined by the bottom channel wall  49 . These teeth  63  thereby pinch the cover  27  tightly against the channel bottom wall  49  while the inward section of the cover  27  also is pinched by the respective teeth  53  formed on the inner channel  47  as seen in  FIG. 13 . These structures thereby firmly secure the cover edge  29  in place. 
     In particular, the cover  27  follows a convoluted path in both the edgewise direction as seen in phantom outline in  FIG. 12  and also follows a convoluted path in the crosswise direction as seen in phantom outline in  FIG. 13 . These paths extend sidewardly but then turn vertically downwardly or upwardly and then reverse directions and turn in the opposite downward or upward direction until then again turning sidewardly or horizontally. In the edgewise direction, the convoluted path is generally U-shaped ( FIG. 12 ) as the cover  27  extends through each window  62  and around the bottom edge of the cross-ribs  50 . In  FIG. 13 , the convoluted path defines an inverted U shape as the fabric  27  extends upwardly over the top edge and teeth  63  provided on the ends of the ribs  61 . The crosswise convoluted path is also seen in  FIG. 14  at the rear edge of the seat assembly  17 , and in  FIG. 15  at the front edge of the seat assembly  17 . The edgewise convoluted path of  FIG. 12  is also created at the seat back edge ( FIG. 14 ) and at the seat front edge ( FIG. 15 ). 
     Additionally, the close engagement of the respective teeth  53  and  63  against opposing shell surfaces creates pinch points at at least two locations along the crosswise width of the edge portion  29 . When the seat assembly  17  is occupied, it is expected that this may thereby tension and pull the cover  27  outwardly in the direction of reference arrow  65  ( FIG. 13 ) which would tend to attempt to withdraw the fabric edge  29  from the above-described connector structure. However, the above-described tortuous or convoluted path of the fabric edge  29  in the crosswise and edgewise directions will prevent undesirable stretching of the cover  27  away from this connector structure. If some stretching or displacement of the fabric  27  does occur, it is anticipated that the ribs  61  may also deflect inwardly as diagrammatically seen in  FIG. 13  until the upper edge of the rib  61  contacts the inside face of the inner channel wall  48 . This is then expected to create a further pinch point at location  66  and the pinching force would increase in direct relation to the pulling force by which the cover  27  is subjected by occupant loads. In this manner, the above-described connector structure provides secure engagement of the cover  27  within the interface between the inner shell  32  and the outer shell  40 . 
     During assembly, the outer cover  40  also includes fastener holes  75  that align with the afore-mentioned posts  45  on the inner shell  32  so that the inner shell  32  and outer shell  40  are screwed together and tightly secure the fabric edge  29  as described above. This then forms a sub-assembly of the shells  32  and  40 , the cushion layer  30  and the cover  27  which in turn can be mounted to the support plate  22  by appropriate fasteners. 
     Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.