Abstract:
A chair having a backrest with a Y-shaped member. The member being affixed to the center of the top rail of the backrest frame at one end. The other end of the Y-shaped member connects to backrest fabric, pulls it rearward, and holds the backrest fabric in tension using a pair of retractors. The backrest fabric is secured to the retractors by a welt cord contained within a chamber formed in each retractor. The welt cord is sewn into a fabric sheath that is, in turn, stitched to the backrest fabric. The member is biased to flex rearward when the backrest fabric moves rearward from an at-rest position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. provisional patent application No. 60/579,437, filed Jun. 14, 2004 (now expired). 

   BACKGROUND OF THE INVENTION 
   The invention relates generally to chairs, and more particularly to a retractor structure for a chair backrest and a height-adjustable chair arm. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will hereinafter be described in conjunction with the appended drawing figures wherein like numerals denote like elements. 
       FIG. 1  is a perspective view of a chair showing the backrest and adjustable arm of the present invention. 
       FIG. 2  is an enlarged perspective view of the right arm. 
       FIG. 3  is an enlarged perspective view of the armrest frame for the right arm. 
       FIG. 4  is an exploded view, taken from the right-front side, of the right arm. 
       FIG. 5  is an exploded view, taken from the right-rear side, of the left arm. 
       FIG. 6  is a partial view of the lower portion of the retractor structure of the backrest. 
       FIG. 7  is an enlarged front partial view of the barrel portion of the retractor structure. 
       FIG. 8  is a sectional view of the retractor structure shown in an extended position (in tension). 
       FIG. 9  is a sectional view of the retractor structure shown in a retracted position (tension relieved). 
       FIG. 10  is a perspective view of one assembled pull and plunger. 
       FIG. 11  is a partial sectional view of the male pull. 
       FIG. 12  is a partial sectional view of the female pull and plunger. 
       FIG. 13  is a perspective view of the welt cord and enveloping fabric. 
       FIG. 14  is an end view showing the welt cord and fabric sheath with the fabric sheath is sewn to the backrest fabric. 
       FIG. 15  is an end view showing the welt cord contained within the assembled male and female pulls. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The ensuing detailed description provides preferred exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention, as set forth in the appended claims. 
   To aid in describing the invention, directional terms are used in the specification and claims to describe portions of the chair  10  of the present invention (e.g., upper, lower, left, right, etc.). These directional definitions are merely intended to assist in describing and claiming the invention and are not intended to limit the invention in any way. In addition, reference numerals that are introduced in the specification in association with a drawing figure may be repeated in one or more subsequent figures without additional description in the specification in order to provide context for other features. 
     FIG. 1  shows a preferred embodiment of the chair  10  of the present invention, which includes a base  12 , a seat  14 , left and right arms  16 ,  18  and a backrest  20 . The base  12  and seat  14  are conventional. The backrest  20  defines an opening that is covered by a backrest fabric  122 , which is preferably an expanded mesh material that is see-through. It should be understood that any features described in relation to the right arm  18  are also present as a mirror image in the left arm  16  and vice-versa. 
   Referring now to  FIG. 2 , the right arm  18  includes an armrest  22  and an arm support  24 , which is connected to the armrest  22  by a height-adjustment structure  26 . As will be discussed in greater detail herein, the armrest  22  is height-adjustable relative to the seat  14 . The armrest support  24  includes a lateral portion  23  that is rigidly affixed to the base  16  and an upright portion  25  that extends upwardly from the lateral portion  23 . Rigidity for the armrest  22  is provided by an armrest frame  30  (see  FIG. 3 ), which is connected to the height-adjustment structure  26  via a bracket  32 . 
   Referring now to  FIGS. 4 and 5 , the height-adjustment structure  26  will be described in detail. The armrest  22  is connected to the support  24  by two linkages  44 ,  46 . The linkages  44 ,  46  pivot relative to the support  24  and the armrest frame bracket  32  (see  FIG. 3 ), so that the armrest maintains a substantially level (i.e., remains in substantially the same rotational orientation) as the linkages  44 ,  46  move the armrest  22  up and down through the armrest&#39;s  22  range of motion. In this embodiment, the linkages  44 ,  46  are of equal length and are arranged to remain parallel when pivoting. Linkage  44  will be referred to herein as the drive linkage  44  and linkage  46  will be referred to herein as the non-drive linkage  46 . This portion of the height-adjustment structure  26  is sometimes referred to in the art as a four-bar linkage. 
   The linkages  44 ,  46  are sandwiched between a boss plate  48  and the support  24  and are pivotally attached to the boss plate  48  by linkage posts  50 ,  52  located on the inner side of the boss plate  48 . The linkage post  50  for the drive linkage  44  is preferably located along a central axis  9  of the height-adjustment structure  26  and the linkage post  52  for the non-drive linkage  46  is located above the linkage post  50  for the drive linkage  44  and vertically aligned therewith. A third post  54  is included to provide stability. Each of the three posts  50 ,  52 ,  54  is aligned with a respective hole located in the support  24  and is secured to the support  24  with a screw or any other suitable fastener. The outer diameter of each of the linkage posts  50 ,  52  is sized to allow a lower hole of the respective linkage  44 ,  46  to rotate about the post, while minimizing “play” in the linkage  44 ,  46 . Similarly, the length of each of the posts  50 ,  52 ,  54  is sized to allow the linkages  44 ,  46  to rotate freely about the posts  50 ,  52 , while minimizing “play” from side-to-side. 
   An eccentric shaft  56  is located on the outer side of the boss plate  48 . Moving from the outside end to the inside end, the eccentric shaft  56  includes a gear  58  that engages a knob  28 , a non-eccentric bearing surface  60  that rotates within a bearing plate  64 , and an eccentric bearing surface  62  that rotates within an axial hole  65  of an inner gear  66 . Both bearing surfaces  60 ,  62  are cylindrical in shape. The non-eccentric bearing surface  60  is centered about the central axis  9  and the eccentric bearing surface  62  is off-center from the central axis  9 . In this embodiment, the eccentric bearing surface  62  is off-center by about 0.070 inches. 
   Six posts  68  extend outwardly from the boss plate  48 . Each of the six posts  68  is located along a circular path and is evenly-spaced along the path. Both the bearing plate  64  and the inner gear  66  include six holes formed therein that are positioned and spaced to slide over the six posts  68  in the boss plate  48  so that the bearing plate  64  and the inner gear  66  cannot rotate relative to the boss plate  48 . Each of the six holes located in the inner gear  66  is 0.070 inches larger in radius than each of the posts  68  to allow lateral movement of the inner gear when the eccentric shaft  56  is rotated. In this embodiment, lateral movement of the inner gear  66  follows a circular path as the eccentric shaft  56  is rotated. An outer gear  70  is sandwiched between the bearing plate  64  and the boss plate  48 . 
   Referring now to  FIGS. 1 and 6 , the backrest  20  will be described in greater detail. The backrest  20  includes a top rail  29  having an inverted Y-shaped member  74  that is attached to the top rail  29  at an upper end  77  and terminates at two lower ends  76 ,  78 . A retractor  80 ,  82  is located on the inner side of each of the lower ends  76 ,  78 . The left and right retractors  80 ,  82  work in conjunction with the Y-shaped member  74  to pull the backrest fabric (the fabric against which rests the back of a person sifting in the chair) rearward along two seams. As will be explained herein, the retractor  80 ,  82  places the backrest fabric under tension, which provides a firm, comfortable surface for the user. In addition, the retractor  80 ,  82  is designed to “give”, which adds to the comfort of the user. The Y-shaped member  74  may also flex slightly to provide additional “give” to the backrest fabric. 
   When the eccentric shaft  56  is rotated a full revolution (i.e., 360 degrees), the eccentric bearing surface  62  moves the inner gear  66  through one cycle of lateral movement, which causes the outer gear to rotate the width of one tooth (about fifteen degrees in this embodiment). The outer gear  70  includes a slot  72  that engages the drive linkage  44 . Thus, rotation of the outer gear  70  causes the drive linkage  44  to rotate in the same direction. This structure also provides a mechanical advantage between rotation of the knob  28  and change in height of the armrest  22 . 
   As noted above, the larger relative size of the post-engaging holes of the inner gear  66  allows lateral movement of the inner gear  66  relative to the outer posts  68  of the boss plate  48 . The magnitude of the difference in radius between the post-engaging holes of the inner  66  and the outer posts  68  of the boss plate is equal to the offset of the eccentric bearing surface  62  and is equal to 50–55% of the tooth depth of the inner gear  66 . This enables sufficient lateral movement of the inner gear  66  to allow the teeth of the inner gear  66  to engage and disengage the teeth of the outer gear  70  as the eccentric shaft  56  is rotated. In addition, it ensures that at least one of the outer posts  68  will be engaged with the wall of the post-engaging hole located therein. This minimizes rotation of the inner gear  66  and enables the inner gear  66  “bind”, which prevents rotation of the outer gear  70  when the eccentric shaft  56  is not being rotated by the knob  28 . Covers  40  and  42  shroud and protect the mechanical components of the height adjustment structure  26 . 
   Referring now to  FIGS. 8 and 9 , one can see that the pull  84  is slender and elongated. The inner edge of the pull  84  has a slight concave curvature of radius R, where R is between 20 and 30 inches, preferably 24 inches. This curvature is intended to more closely follow the natural curvature of the user&#39;s back, and therefore, make the backrest  20  more comfortable. The plunger  86  is affixed to the outer surface of the pull  84 , preferably midway between the top and bottom of the pull  84 . The plunger  86  includes a base  92  which engages the pull  84 , a slender, cylindrical body  94  and a tapered head  90  that is designed to be inserted through a radial array of fingers  96  (see also  FIG. 7 ). The fingers  96  flex outwardly as the head  90  is pushed through, then return to their original position. A lip  93  that defines the transition between the head  90  and the body  94  prevents the head  90  from being pulled back through the fingers  96 . 
   Most of the components of the height adjustment structure  26  are formed of metal or a durable, rigid polymer. Smooth and reliable operation has been achieved by forming the bearing plate  64 , inner gear  58  and outer gear  60  from nylon, Delrin® brand plastic, manufactured by E. I. DuPont Nemours and Company, or other rigid, non-binding polymers. 
   Referring now to  FIGS. 1 and 6 , the backrest  20  will be described in greater detail. The backrest  20  includes a top rail  29  having an inverted Y-shaped member  74  that is attached to the top rail  29  at an upper end  77  and terminates at two lower ends  76 ,  78 . A retractor  80 ,  82  is located on the inner side of each of the lower ends  76 ,  78 . The left and right retractors  80 ,  82  work in conjunction with the Y-shaped member  74  to pull the backrest fabric  122  (the fabric against which rests the back of a person sitting in the chair) rearward along two seams. As will be explained herein, the retractor  80 ,  82  places the backrest fabric  122  under tension, which provides a firm, comfortable surface for the user. In addition, the retractor  74  is designed to “give”, which adds to the comfort of the user. The Y-shaped member  74  may also flex slightly to provide additional “give” to the backrest fabric  122 . 
   In the context of the parts of the backrest  20 , including backrest fabric  122 , the Y-shaped member  74  and the retractors  80 , 82 , the terms “front,” “frontward” or “front side” are intended to refer to the side of any of these parts which faces a person sitting in the chair. Conversely, the terms “rear,” “rearward” or “rear side” are intended to refer to the side of any of the parts of the backrest  20  opposite the front side (i.e., facing way from a person sitting in the chair). 
   The left and right retractors  80 ,  82  are mirror-images of each-other. It should be understood that any features described in relation to the left retractor  80  are also present as a mirror image in the right retractor  82  and vice-versa. The retractor  80  includes a pull  84 , a plunger  86  and a barrel  88 . 
   Referring now to  FIGS. 8 and 9 , one can see that the pull  84  is slender and elongated. The inner edge of the pull  84  has a slight concave curvature of radius R, where R is between 20 and 30 inches, preferably 24 inches. This curvature is intended to more closely follow the natural curvature of the user&#39;s back, and therefore, make the backrest  20  more comfortable. The plunger  86  is affixed to the outer surface of the pull  84 , preferably midway between the top and bottom of the pull  84 . The plunger  86  includes a base  92  which engages the pull  84 , a slender, cylindrical body  94  and a tapered head  90  that is designed to be inserted through a radial array of fingers  96  (see also  FIG. 7 ). The fingers  96  flex outwardly as the head  90  is pushed through, then return to their original position. A lip  96  that defines the transition between the head  90  and the body  94  prevents the head  90  from being pulled back through the fingers  96 . 
   Optionally, an opaque fabric member can be provided which is positioned in front of the backrest fabric  122 . The opaque fabric member is preferably sewn to the backrest fabric  122  around its perimeter and along or near the seam  120  which attaches that backrest fabric  122  to the fabric sheath  116 . The opaque member is designed to provide additional padding, and a more traditional appearance from the front side of the chair  10 . The opaque fabric member could be formed from any conventional material, such as padded core sandwiched between layers of a polyester or polyester-blend material. 
   In this embodiment, the pull  84  is comprised of two halves: a male half  98  and a female half  100 , as shown in  FIGS. 10–12 . Use of male and female halves  98 ,  100  simplifies assembly. The male and female halves  98 ,  100  include structures to retain the plunger  86 , in this embodiment mating half-cylinders  102 ,  104  each having a centrally located half-circle  106 ,  108  are provided. Alternatively, the plunger  86  could be molded as part of one of the male and female halves  98 ,  100 . In addition, the male and female halves  98 ,  100  include a fastening structure that prevents the halves  98 ,  100  from separating once assembled. In this embodiment latches  110  located along the male half  98  mate with locks  112  located along the female half  100 . Any suitable fastening structure could be used, as could adhesives (either alone or as a supplement to the fasteners). 
   Referring now to  FIGS. 13–15 , the structure for attaching the backrest fabric  122  to the retractor is shown. A fabric sheath  116  is sewn around a welt cord  114 , leaving a flap  118  of excess fabric. The welt cord  114  is preferably slightly shorter in length than the pull  84  and may optionally have the same curvature (or radius R) as the inner surface of the pull  84 . The welt cord  114  is preferably formed of a polymeric material that will provide some longitudinal flexibility, but strong cross-sectional rigidity. The fabric sheath  116  is preferably a durable fabric having a dense weave. 
   The fabric sheath  116  is sewn to backrest fabric  122  along a seam  120  that is located where the welt cord  114  and fabric flap  118  meet. After the backrest fabric  122  is sewn to the fabric sheath  116 , the welt cord  114  and fabric sheath  116  are enclosed within a chamber  124  formed within the pull  84 . Preferably, the welt cord  114  is drawn into the chamber  124  sufficiently far so that the seam  120  cannot be felt by the user. 
   When being assembled, the welt cord  114  and fabric sheath  116  are inserted into the chamber  124 , then the male and female halves  98 ,  100  are assembled. An elongated slot  126  (see also  FIG. 6 ) allows the male and female halves  98 ,  100  to be more easily assembled and prevents pinching of the backrest fabric  122 . 
   Optionally, an opaque fabric member can be provided which is positioned in front of the backrest fabric  122 . The opaque fabric member is preferably sewn to the backrest fabric  122  around its perimeter and along or near the seam  120  which attaches that backrest fabric  122  to the fabric sheath  116 . The opaque member is designed to provide additional padding, and a more traditional appearance from the font side of the chair  10 . The opaque fabric member could be formed from any conventional material, such as padded core sandwiched between layers of a polyester or polyester-blend material. 
   While the principles of the invention have been described above in connection with preferred embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of the invention.