Patent Publication Number: US-8991932-B2

Title: Backrest mechanism for chair

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase of PCT/JP2011/060883 filed May 11, 2011, and is related to Japanese Patent Application No. 2009-258539 filed Nov. 12, 2009 each of which is incorporated by reference herewith. 
     FIELD 
     The present invention relates to a backrest mechanism for a chair, in which opposing surfaces of left and right side rods of a backrest are connected via a back plate. 
     BACKGROUND 
     A certain backrest among backrests for office chairs is configured such that, for example, the entire backrest is integrally formed with synthetic resin and a plurality of openings are formed in a back plate for back support, so that the back plate can appropriately bend backward to provide a comfortable sitting feeling when a person leans on the backrest (see, for example, Patent Literatures 1 to 3). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-open No. 2009-112729 
     Patent Literature 2: Japanese Patent No. 4295266 
     Patent Literature 2: Japanese Patent No. 4238122 
     SUMMARY 
     Technical Problem 
     In each of the backrests for chairs disclosed in Patent Literatures 1 to 3 as described above, a flexible back plate is provided on the inside surrounded by a back casing (back frame) that has large rigidity and a rectangular shape when viewed from the front. Therefore, if the backrest is reclined and the upper body is largely leaned back, a lateral casing oriented in the left-right direction in the upper end of the back casing prevents an upper portion of the back plate from bending backward, so that the upper back cannot be supported comfortably. 
     Furthermore, a certain chair among the chairs disclosed in Patent Literatures as described above is configured such that an intermediate portion of the back frame and the back plate in the up-down direction is folded in a laid-V shape when viewed from the side to provide comfortable support around lumbar by the lumbar support effect. However, the lumbar support effect is reduced in a lower portion of the back plate because almost the entire surface of the back plate surrounded by the back casing is made flexible. 
     The present invention has been made in view of the above circumstances, and an object thereof is to provide a backrest mechanism for a chair, in which upper and lower portions of a back plate are distinctly separated as a flexible portion and an inflexible portion in order to give a sitting person comfortable support at and around his or her back and lumbar. 
     Solution to Problem 
     According to the present invention, the above object is accomplished by the following aspects. 
     (1) A backrest includes a pair of left and right side rods, each having a folded portion in a laid-V shape in a side view at a portion for supporting a sitting person around his or her lumbar; and a back plate that connects opposing surfaces of the side rods, wherein an upper portion of the back plate above the folded portions serves as a flexible portion that is elastically deformable in a backward direction and that has smaller rigidity than the left and right side rods, and a lower portion of the back plate below the flexible portion serves as an inflexible portion that has greater rigidity than the flexible portion. 
     According to the above-described configuration, the back plate is distinctly separated into the upper flexible portion and the lower inflexible portion across the folded portions of the side rods, and the upper flexible portion, which is located above the folded portions of the side rods and which supports the back of a sitting person, is connected to the opposing surfaces of the pair of the left and right side rods that have greater rigidity than the upper flexible portion, unlike a conventional configuration in which the upper end of the flexible portion is surrounded by a back frame. Therefore, when the backrest is reclined, the flexible portion effectively bends backward and provides comfortable back support. 
     In contrast, the lower portion of the back plate below the flexible portion serves as the inflexible portion with greater rigidity than the flexible portion, and is less likely to bend backward. Therefore, the lumbar support effect is exerted and a sitting person can be supported comfortably around his or her lumbar. 
     (2) In the above-described aspect (1), a center portion of the inflexible portion in a left-right direction is connected to a backrest support rod that stands upward at a rear of a seat. 
     According to the above-described configuration, the center portion in the left-right direction of the inflexible portion with large rigidity is connected to the backrest support rod. Therefore, the flexible portion that is not connected to the backrest support rod can more easily bend backward in more upper portions, so that it becomes possible to comfortably support the back. 
     (3) In the above-described aspect (1) or (2), a plurality of elongated holes elongated in an up-down direction and arranged in up-down and left-right directions are provided in the flexible portion. 
     According to the above-described configuration, it becomes possible to bend the flexible portion in a backward convex arc shape in a planer view, about the elongated holes that are arranged in the up-down and the left-right directions, so that the flexible portion can fit the back. 
     (4) In the above-described aspect (1), the flexible portion and the inflexible portion are connected to the opposing surfaces of the left and right side rods such that the flexible portion is located anteriorly relative to the inflexible portion, a lower end of the flexible portion and an upper end of the inflexible portion are continued via a step portion, and a grid-like rib is arranged so as to protrude from a front surface of the inflexible portion and so as to be continued to the step portion. 
     According to the above-described configuration, the flexible portion is located anteriorly relative to the inflexible portion and the grid-like rib is arranged so as to protrude from the inflexible portion. Therefore, the bending rigidity of the inflexible portion is increased relative to that of the flexible portion and the lumbar support effect is improved, so that it becomes possible to provide comfortable support around the lumbar. 
     Furthermore, the lower end of the flexible portion and the upper end of the inflexible portion are continued via the step portion, and the upper end of the grid-like rib is continued to the step portion. Therefore, the strength at the boundary between the flexible portion and the inflexible portion of the back plate can hardly be reduced. 
     (5) In the above-described aspect (4), a front surface plate is attached to the front surface of the inflexible portion across the grid-like rib. 
     According to the above-described configuration, the grid-like rib can be covered by the front surface plate in a dressed-up manner, and the front surface plate can be reinforced by the grid-like rib provide on the rear surface thereof and can function as the inflexible portion with large rigidity. Therefore, it becomes possible to provide comfortable support by the front surface plate around the lumbar. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a backrest mechanism for a chair, in which upper and lower portions of a back plate are distinctly separated as a flexible portion and an inflexible portion in order to give a sitting person comfortable support at and around his or her back and lumbar by the flexible portion and the inflexible portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of a chair provided with an embodiment of the present invention. 
         FIG. 2  is a side view of the embodiment. 
         FIG. 3  is an exploded perspective view of backrest support rods and a backrest mounted on the backrest support rods of the embodiment. 
         FIG. 4  is front view of a back plate of the embodiment. 
         FIG. 5  is an enlarged transverse cross-sectional plan view taken along line V-V of  FIG. 4 . 
         FIG. 6  is an enlarged transverse cross-sectional plan view taken along line VI-VI of  FIG. 4 . 
         FIG. 7  is an enlarged longitudinal cross-sectional side view of a mounting portion of the backrest on the backrest support rods. 
         FIG. 8  is an enlarged transverse cross-sectional plan view taken along line VIII-VIII of  FIG. 7 . 
         FIG. 9  is an enlarged transverse cross-sectional plan view taken along line IX-IX of  FIG. 7 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
       FIG. 1  is a front view of a chair provided with an embodiment of the present invention,  FIG. 2  is a side view of the embodiment, and  FIG. 3  is an exploded perspective view of main components of the embodiment. The chair includes a leg body  3  having radial five leg rods  2 , each having a caster  1  at a leading end thereof. A retractable leg column  4  that includes a gas spring (not illustrated) is vertically installed in the center of the leg body  3 , and a rear portion of a support base  5  is fixedly mounted on an upper end of the leg column  4 . 
     The support base  5  has a substantially hollow box shape with an upper surface open, and an opening of the upper surface is covered by a detachable cover  5   a . A pair of left and right armrests  6  and  6  are mounted on both side surfaces of the support base  5 . 
     While a biasing means configured to bias a backrest  7  in a standing direction, i.e., a forward direction, and a biasing means configured to bias a seat supported by the support base  5  in the forward direction (neither illustrated) are installed in the support base  5 , these are not directly related to the present invention, and therefore, illustration and detailed description thereof will be omitted. 
     The backrest  7  is configured such that opposing surfaces at an intermediate curved portion are connected via a connecting plate  9  that is oriented in the left-right direction, and an upper half is mounted on a pair of left and right backrest support rods  10  and  10  that stand upward at the rear of the seat  8  and that has an L-shape when viewed from the side (details will be described later). 
     Front ends of the left and right backrest support rods  10  and  10  are pivotally mounted on the support base  5  via a left-right directional shaft  11 , and the backrest support rods  10  and  10  and the backrest  7  can rotate in a front-back direction about the shaft  11  or can stop at a predetermined backward-tilt angle by the operation of a gas spring  12  whose front and rear ends are connected to a rear end of the support base  5  and the connecting plate  9 . 
     The backrest  7  includes a pair of left and right side rods  13  and  13 , which are folded in a laid-V shape in a side view at intermediate portions in the up-down direction, that is, portions at a height near the lumbar of a sitting person, and a back plate  14  that connects opposing surfaces of both of the side rods  13  and that has a smaller thickness than a front-back dimension of each of the side rods  13 . A left-right dimension and the front-back dimension of the left and right side rods  13  and  13  are gradually reduced in the upward direction. Incidentally, the left and right side rods  13  and  13  and the back plate  14  are integrally formed with synthetic resin. 
     A portion of the back plate  14  for supporting the back of a sitting person, that is, a portion slightly above folded portions  13   a  of the side rods  13  serves as a flexible portion  14   a , and a lower half for supporting a portion around and below the lumbar of the sitting person serves as an inflexible portion  14   b . The flexible portion  14   a  is formed at the intermediate portions of the opposing surfaces of both of the side rods  13  and the inflexible portion  14   b  is formed at rear edges of both of the side rods  13  in a continuous manner, so that a step portion  15  that is recessed backward and that has a horizontal cross-section is formed at an intermediate portion being a connection portion of the flexible portion and the inflexible portion in the up-down direction (see  FIG. 7 ). Furthermore, a concave portion  16  that is recessed backward and opened downward is formed on the front surface of the back plate  14  below the step portion  15  because the front surface of the inflexible portion  14   b  is located posteriorly relative to the front surface of the flexible portion  14   a.    
     A lower edge of the flexible portion  14   a  and a lower surface of the step portion  15  are curved, in a downward arc shape, toward the vicinity of the folded portions  13   a  of the side rods  13 . 
     A pair of front and rear concave grooves  17  and  18 , the former of which is recessed backward, the latter of which is recessed forward, and both of which are oriented in the up-down direction, are respectively formed in front and rear surfaces of each of the left and right side rods  13  and  13  such that the grooves are aligned in the front-back direction. A horizontal cross-section of a portion of each of the side rods  13  in which the concave grooves  17  and  18  are provided has a substantially H-shape (see  FIG. 5 ). The concave grooves  17  and  18  are used to mount a not-shown optional member on the backrest  7 . 
     As illustrated in enlarged views in  FIG. 4  and  FIG. 5 , a plurality of elongated holes  19  elongated in the up-down direction and arranged in the up-down and the left-right directions are provided in almost the entire surface of the flexible portion  14   a  of the back plate  14  except for the lower end portion, such that the elongated holes are arranged adjacent to each other in a zigzag manner in the left-right direction. This makes the flexible portion  14   a  to easily bend in a backward convex arc shape when viewed in the planer view, about the elongated holes  19  arranged in the up-down direction, so that the back of a sitting person can be supported comfortably. A plurality of ribs  20  that are oriented in the up-down direction are arranged so as to protrude from the rear surface of the flexible portion  14   a , so that the bending rigidity of the flexible portion  14   a  in a direction perpendicular to the elongated holes  19  increases. Incidentally, the thickness of the flexible portion  14   a  is approximately uniform, and only the front-back dimensions of the ribs  20  are gradually reduced in the upward direction (see  FIG. 7 ). 
     Grid-like ribs  21 , upper ends of which are continued to the step portion  15 , are arranged so as to protrude from both sides of the front surface of the inflexible portion  14   b  of the back plate  14 , and the bending rigidity of the inflexible portion  14   b  is made greater than the bending rigidity of the flexible portion  14   a , so that a portion for supporting a sitting person around and below his or her lumbar becomes less likely to bend backward. Incidentally, a front surface plate  28  made of synthetic resin, which will be described later, is attached to the front surface of the inflexible portion  14   b . The front surface plate  28  is attached across the ribs  21 , so that the front surface plate has a function as the inflexible portion for supporting a sitting person around his or her lumbar. 
     As illustrated in  FIG. 4  and  FIG. 6  to  FIG. 8 , tubular holding portions  22  and  22 , which can hold the backrest  7  while determining the positions of the upper ends of the left and right backrest support rods  10  and which are opened downward, are integrally formed so as to protrude downward from the lower surfaces of both sides of the step portion  15  of the back plate  14 . The rear surface and a part of the lateral outer surface of each of the holding portions  22  are respectively connected to the front surface of the inflexible portion  14   b  and a horizontal piece of each of the grid-like ribs  21 , and the front outer surface of each of the holding portions  22  and the lower front surface of the flexible portion  14   a  are connected to each other via vertical ribs  23  and  23 , so that the left and right holding portions  22  and  22  are reinforced. 
     To mount the backrest  7  on the left and right backrest support rods  10  and  10 , first, the left and right holding portions  22  and  22  protruding from the lower surface of the step portion  15  of the back plate  14  are fitted, from above, to the upper ends of the left and right backrest support rods  10  and  10  that are inserted in the concave portion  16  between the left and right grid-like ribs  21  and  21  on the front surface of the inflexible portion  14   b  of the back plate  14 , so that the backrest  7  is temporarily held by the left and right backrest support rods  10  and  10 . 
     Subsequently, as illustrated in  FIG. 9 , a front surface of a left-right directional fixing piece  24  protruding forward from the center portion of the lower front surface of the inflexible portion  14   b  of the back plate  14  is brought into contact with the rear surface of the upper end of the connecting plate  9  that is fixed to the opposing surfaces of the left and right backrest support rods  10  and  10 . Subsequently, the connecting plate  9  and the fixing piece  24  are fixed with fixing screws  26  and  26  that are inserted, from the front surface side, into two left and right through holes  25  and  25  provided on the connecting plate  9  and the fixing piece  24 , and with nuts  27  and  27 . Therefore, the inflexible portion  14   b  of the back plate  14  is firmly mounted on the left and right backrest support rods  10  and  10 . 
     By mounting the back plate  14  on the left and right backrest support rods  10  and  10  as described above, the tubular holding portions  22  and  22  are fitted to the upper ends of both of the backrest support rods  10 , so that the upper ends of the backrest support rods  10  are prevented from moving forward. Therefore, when the backrest  7  is reclined, moment in a direction away from the back plate  14  is not applied to the fixed portion in the lower portion of the back plate  14 . Therefore, it becomes less necessary to increase the fixing strength of the lower portion of the back plate  14 . 
     Incidentally, in some cases, the through holes  25  of the fixing piece  24  may be formed as female screws and the nuts  27  may be omitted. 
     Upper portions of the backrest support rods  10  and the front surface of the inflexible portion  14   b  of the back plate  14  are covered by the front surface plate  28 , which is mounted on the front portion of the inflexible portion  14   b , which is made of hard synthetic resin in approximately the same shape as the inflexible portion, and which has large bending rigidity. 
     The front surface plate  28  is, as illustrated in  FIG. 8 , fixedly attached so as to be aligned with the same plane as the front surface of the flexible portion  14   a  by press fitting four tubular protrusions  29 , which protrude backward from the top, bottom, left, and right of the rear surface thereof, into appropriate four of fitting holes  30  (see  FIG. 4 ) formed at the intersections of the grid-like ribs  21 . Incidentally, an upper portion of the front surface plate  28 , that is, a portion for supporting a sitting person around his or her lumbar is curved in a laid-V shape when viewed from the side (see  FIG. 7 ). 
     The front surface of the front surface plate  28 , the front surface of the flexible portion  14   a  of the back plate  14 , and the rear surface of the flexible portion  14   a  of the back plate  14  are covered by a cushion material  31  that is folded in half. 
     As described above, according to the chair of the embodiment, the concave portion  16  that is opened downward is provided below the intermediate portion of the front surface of the back plate  14  in the up-down direction, and, the tubular holding portions  22  and  22 , which protrude downward from the lower surface of the step portion  15  and which are opened downward, are fitted to the upper ends of the left and right backrest support rods  10  and  10  that are inserted in the concave portion  16 . Therefore, it is possible to easily determine the position of the back plate  14  and temporarily hold the back plate  14 , with respect to both of the backrest support rods  10 . 
     Therefore, fixing operation of the lower portion of the back plate  14 , that is, screwing operation between the fixing piece  24  protruding from the inflexible portion  14   b  and the connecting plate  9  connecting the left and right backrest support rods  10  and  10  can be made much easier. 
     Furthermore, the left and right tubular holding portions  22  and  22  are formed so as to be integrated with and continued to the step portion  15  and the front surface of the inflexible portion  14   b  of the back plate  14 , and the bending strength in the front-back and the left-right directions is increased. Therefore, even by only fitting both of the holding portions  22  and  22  to the upper ends of the left and right backrest support rods  10  and  10 , it becomes possible to stably hold the intermediate portion of the back plate  14  by the upper ends of the backrest support rods  10  and  10 . 
     Therefore, it becomes not necessary to fix the intermediate portion of the back plate  14  to the upper ends of the backrest support rods  10  by a fixing means, such as screws, and, it becomes possible to fully ensure the mounting strength of the back plate  14  with respect to the backrest support rods  10  even by fixing only the lower portion of the back plate  14  to the connecting plate  9  of the backrest support rods  10  with screws. Therefore, it becomes not necessary to use a special connecting member or to fix the back plate with screws at two portions at the top and bottom as in the conventional technology. As a result, the number of components and costs can be reduced. 
     The upper half of the back plate  14  for supporting the back of a sitting person is used as the flexible portion  14   a , a lower half including the front surface plate  28  for supporting the sitting person around and below the lumbar is used as the inflexible portion  14   b , the upper half and the lower half of the back plate  14  are distinctly separated as an easy-to-bend portion and a hard-to-bend portion, the concave portion  16  formed below the intermediate portion of the back plate  14  is supported by the backrest support rods  10 , and the flexible portion  14   a  and the inflexible portion  14   b  are continuously provided on the opposing surfaces of a pair of the left and right side rods  13  and  13 , each having a laid-V shape when viewed from the side and having higher rigidity. Therefore, the flexible portion  14   a  can more easily bend backward in more upper portions, so that it becomes possible to comfortably support the back of a sitting person via the cushion material  31  and to comfortably support the lumbar of the sitting person due to the lumbar support effect by the inflexible portion  14   b  having the higher rigidity than that of the flexible portion and by the front surface plate  28  on the front surface of the inflexible portion. 
     The present invention is not limited to the above embodiment. 
     In the embodiment, the concave portion  16  is formed in the front surface of the back plate  14 , and the holding portions  22  and  22  continued to the step portion  15 , which is formed on the upper surface of the concave portion and which is recessed backward, are fitted to the upper ends of the backrest support rods  10  and  10 . However, in contrast, a concave portion that is recessed forward and opened downward may be provided on the rear surface of the back plate  14 , and holding portions as described above may be formed in a continuous manner on a step surface, which is formed on the upper surface of the concave portion and which is recessed forward, such that the holding portions are fitted to the upper ends of the backrest support rods  10 . In this case, the front surface plate  28  is not needed, the lower half of the back plate  14  serves as the inflexible portion as it is, and a rear surface plate is fixedly attached to the rear surface of the concave portion that is recessed forward. 
     Furthermore, it may be possible to provide grid-like ribs protruding from the rear surface of the inflexible portion in the lower half in order to reinforce the lower half. 
     The present invention may be applied to a chair in which the cushion material  31  is not mounted on the backrest  7 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  CASTER 
               2  LEG ROD 
               3  LEG BODY 
               4  LEG COLUMN 
               5  SUPPORT BASE 
               5   a  COVER 
               6  ARMREST 
               7  BACKREST 
               8  SEAT 
               9  CONNECTING PLATE 
               10  BACKREST SUPPORT ROD 
               11  SHAFT 
               12  GAS SPRING 
               13  SIDE ROD 
               13   a  FOLDED PORTION 
               14  BACK PLATE 
               14   a  FLEXIBLE PORTION 
               14   b  INFLEXIBLE PORTION 
               15  STEP PORTION 
               16  CONCAVE PORTION 
               17  CONCAVE GROOVE 
               18  CONCAVE GROOVE 
               19  ELONGATED HOLE 
               20  RIB 
               21  RIB 
               22  HOLDING PORTION 
               23  RIB 
               24  FIXING PIECE 
               25  THROUGH HOLE 
               26  FIXING SCREW 
               27  NUT 
               28  FRONT SURFACE PLATE 
               29  TUBULAR PROTRUSION 
               30  FITTING HOLE 
               31  CUSHION MATERIAL