Patent Publication Number: US-7717513-B2

Title: Chair

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a chair whose backrest can be tilted rearward. 
   2. Description of the Related Art 
   Conventionally, there has been disclosed a chair in which a backrest surface is made up by extending an upholstery member between frame elements, which make a pair on both right and left sides. For example, there has been disclosed a chair employing a structure in which an upper portion of the backrest surface is supported by upper frame elements and a lower portion of the backrest surface is supported by lower frame elements, and these upper frame elements and lower frame elements are made independent to perform rotational operation around a horizontal axis, that is, rocking movement (for example, refer to Japanese Patent Application Laid-Open No. 2002-119375 and Japanese Patent Application Laid-Open No. 2002-119373). Furthermore, in the chair having such a constitution, by providing elastically biasing means that elastically biases the lower frame elements forward and elastically biasing means that biases the upper frame elements forward, independently of each other, the backrest surface capable of following, for example, a motion of the entire upper body of a sitter by the motion of his or her waist, and for example, a motion of only an upper portion of the upper body such as turning back and extending his or her arm laterally is realized. 
   In everyday life, when seated with his or her upper body standing in a chair, a sitter often turns back, extends his or her arm, twists himself or herself and so on. With respect to such motions of the sitter, in the chairs described in the Japanese Patent Application Laid-Open No. 2002-119375 and Japanese Patent Application Laid-Open No. 2002-119373, the upper frame elements follow the motions of the upper body of the sitter, particularly the upper portion with a required elastically biasing force. 
   However, when the sitter tilts his or her upper body rearward, the backrest is required to surely support the upper body of the sitter. That is, the elastically biasing force of such a degree that the upper frame elements of the backrest can move in accordance with the motion of the upper body of the sitter as described above does not allow the upper portion of the upper body to be stably supported. In such a chair, there may arise a defect that when the sitter inclines his or her upper body by tilting the lower frame elements of the backrest rearward, the sitter feels insecure. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in light of the above-described problem, and is intended to provide a chair that realizes a state preferably following a motion of a sitter in accordance with a posture of the relevant sitter and a state preferably supporting the sitter. 
   The present invention takes the following measures in order to the above-described object. That is, a chair according to the present invention is a chair having at least a leg body, a base supported by the leg body, and a back frame supported by the base, the aforementioned back frame comprising a lower frame portion supported so as to be capable of rocking between a standing position and a rearward tilting position with respect to the base, and an upper frame portion supported so as to be capable of rocking between a normal position and a rear end position with respect to the relevant lower frame portion, wherein upper frame portion biasing means that elastically biases the aforementioned upper frame portion from the aforementioned rear end position to the aforementioned normal position is provided, and the relevant upper frame portion biasing means is constituted so as to change an elastically biasing force to the aforementioned upper frame portion corresponding to a position with respect to the aforementioned base in the aforementioned rocking movement of the aforementioned lower frame portion. 
   Here, the present invention includes an aspect in which the elastically biasing force to the upper frame portion becomes weaker as the lower frame portion is tilted rearward, and an aspect in which the elastically biasing force to the upper frame portion becomes stronger. 
   With the above-described constitution, the elastically biasing force to the upper frame portion can be set in accordance with a posture of a sitter, particularly, a posture of the upper body. That is, in the case where a shape of a backrest of the chair is desired to follow the motion of the upper body of the sitter, the elastically biasing force to the upper frame portion is set weaker, and in the case where the upper body of the sitter is desired to be supported by the backrest, the elastically biasing force to the upper frame portion can be set stronger. As a result, the chair having the backrest serving differently in accordance with the posture of the sitter, particularly the posture of the upper body, can be provided. 
   In the posture in which the sitter raises his or her upper body, the elastically biasing force is set weaker to make it easy to follow the motion of the upper body of the sitter, while in the posture in which the sitter inclines his or her upper body, the elastically biasing force is set stronger to make it easy to support the upper body of the sitter. For this, the upper frame portion biasing means is preferably adapted such that the elastically biasing force is set stronger as the lower frame portion becomes closer to the rearward tilting position. 
   As a specific constitution for preferably making up the upper frame portion biasing means, there can be cited an aspect in which the upper frame portion biasing means is made of an elastic member provided between the upper frame portion and the lower frame portion, and an aspect in which the upper frame portion biasing means is made of an elastic member provided between the base and the upper frame portion. 
   As a more specific constitution in the former case, a constitution can be cited in which the elastic member is made of a torsion coil spring, whose one end side and another end side are locked in the upper frame portion and the lower frame portion, by which there is provided repulsive force changing means capable of changing an initial repulsive force of the torsion coil spring by changing a locking position of the torsion coil spring as the lower frame portion becomes closer to the rearward tilting position. The above-described constitution allows the upper frame portion biasing means to be provided compactly in a portion between the upper frame portion and the lower frame portion. 
   In the latter case, a constitution is realized in the elastically biasing force to the upper frame portion can be varied in accordance with a relative position between the lower frame portion and the base without providing special means. In both the former and latter cases, to provide the upper frame portion biasing means with a simple constitution, it is preferable that the elastic member is made of a frame-like spring. Here, “frame-like” refers to an aspect in which a spring extends along a frame to which the spring is attached, or stretches along the relevant frame. The “frame-like spring” may be a resin spring formed into a frame, or may be a spring steel plate cut into a frame. Also, a spring steel plate to which resin coating is applied is included. 
   Particularly, such a frame-like spring can be the elastic member capable of preferably exerting the elastically biasing force even when it is provided between the base and the upper frame, which are apart from each other via the lower frame portion, as described above. 
   As a specific desirable aspect of the upper frame portion biasing means in the case where the frame-like spring is employed, there can be cited an aspect in which supporting position changing means capable of changing a supporting position where the frame-like spring is supported corresponding to the rocking movement of the lower frame portion is provided. Furthermore, as another desirable aspect, there can be cited an aspect in which a supporting point forming member that comes into contact with an intermediate portion of a frame-like spring to change the elastic repulsive force of the frame-like spring, and supporting point changing means capable of changing a fixing position of the supporting point forming member corresponding to the rocking movement of the lower frame portion are provided. 
   For the constitution in which the motion of the upper body is not hindered when the sitter raises his or her body, and the upper body of the sitter is preferably supported when the sitter inclines his or her upper body rearward, it is preferably to further provide a movement range setting mechanism that sets a movement range of the upper frame portion narrower as the lower frame portion becomes closer to the rearward tilting position. Also, in this case, in order to preferably incline the upper body of the sitter when the lower frame portion is tilted, the movement range setting mechanism may be adapted such that the rear end portion of the upper frame portion becomes closer to the normal position as the lower frame portion becomes closer to the rearward tilting position. Here, the narrower movement range also includes an aspect in which the upper frame portion is fixed so as to be incapable of moving. That is, the movement range setting mechanism may be adapted to prohibit the movement of the upper frame portion in an arbitrary position while the lower frame portion is tilted from the standing position to the rearward tilting position. With such a constitution, the upper body of the sitter when inclined rearward can be preferably supported. 
   Moreover, as desired by the sitter, as a constitution in which the movement range setting mechanism can switch between on and off, a switching mechanism for temporarily stopping the function of the movement range setting mechanism is desirably provided. 
   Additionally, in order to make up the chair capable of faithfully moving in accordance with the motion of the upper body of the sitter, it is desirable that the upper frame portion has a pair of upper frame elements arranged on the right and left sides, and that the relevant pair of upper frame elements is supported so as to be capable of rocking independently of each other between the normal position and the rear end position with respect to the relevant lower frame portion. 
   According to the present invention, in the case where the shape of the backrest of the chair is desired to follow the motion of the upper body of the sitter, the elastically biasing force of the upper frame portion is set weaker, and in the case where the upper body of the sitter is desired to be supported by the backrest, the elastically biasing force to the upper frame portion can be set stronger. As a result, it can be provided a chair having a backrest serving in accordance with the posture of the sitter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an appearance view of a chair according to a first embodiment of the present invention; 
       FIG. 2  is an appearance view of the chair according to the first embodiment of the present invention. 
       FIG. 3  is a side view of the chair according to the first embodiment of the present invention; 
       FIG. 4  is a rear view of the chair according to the first embodiment of the present invention; 
       FIG. 5  is a top view of the chair according to the first embodiment of the present invention; 
       FIG. 6  is a view for explaining a movement, corresponding to  FIG. 3 ; 
       FIG. 7  is a view for explaining the movement, corresponding to  FIG. 2 ; 
       FIG. 8  is a view for explaining the movement, corresponding to  FIG. 5 ; 
       FIG. 9  is a view for explaining the movement, corresponding to  FIG. 3 ; 
       FIG. 10  is a side view showing a chair according to a second embodiment of the present invention; 
       FIG. 11  is a view for explaining a movement, corresponding to  FIG. 10 ; 
       FIG. 12  is a view for explaining the movement, corresponding to  FIG. 10 ; 
       FIG. 13  is a view for explaining a major portion according to the second embodiment of the present invention; 
       FIG. 14  is a view for explaining the major portion according to the second embodiment of the present invention; 
       FIG. 15  is a side view of a modified embodiment of the present invention; 
       FIG. 16  is a side view of the modified embodiment of the present invention; 
       FIG. 17  is a side view of another modified embodiment of the present invention; 
       FIG. 18  is a view for explaining a constitution according to a third embodiment of the present invention; 
       FIG. 19  is a view for explaining a movement according to the third embodiment of the present invention; 
       FIG. 20  is a view for explaining a constitution according to a fourth embodiment of the present invention, and 
       FIG. 21  is a view for explaining a movement according to the fourth embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, embodiments of the present invention are described with reference to the drawings. 
   First Embodiment 
   A first embodiment of the present invention is described with reference to the drawings. A chair C of the present embodiment, as shown in  FIGS. 1 to 5 , includes a leg body  4 , a base  2  supported by the leg body  4 , a seat  3  arranged on the base  2 , and a backrest  1  attached to the base  2  pivotally through a horizontal shaft  16 , and is capable of synchronous rocking movement in which the seat  3  and the backrest  1  are interlocked and tilted rearward. 
   In this case, the chair C according to the present embodiment includes a lower frame portion  13  supported so as to be capable of rocking between a standing position (S) and a rearward tilting position (T) with respect to the base  2 , and an upper frame portion  14  supported so as to be capable of rocking between a normal position (N) and a rear end position (E) with respect to the relevant lower frame portion  13 . Furthermore, upper frame portion biasing means X that elastically biases the upper frame portion from the rear end portion (E) toward the normal position (N) is provided. Moreover, this upper frame portion biasing means X is constituted so as to change an elastically biasing force to the upper frame portion  14  corresponding to a position in the rocking movement of the lower frame portion  13 . The relevant upper frame portion biasing means X will be described in detail later. 
   Hereinafter, respective components in the chair C are described in detail with reference to  FIGS. 1 to 9 . 
   The leg body  4 , as shown in  FIGS. 1 to 4 , is provided with a leg wing  41  with a plurality of casters mounted and a leg support pillar  42  rising from the center of the leg wing  41  substantially vertically, and the leg support pillar  42  can be projected or sunk vertically by expansion and contraction of a gas spring (not shown in the figure) arranged between the leg wing  41  and the leg support pillar  42 . 
   The base  2 , as shown in  FIGS. 1 to 4 , is fixed to an upper end of the leg support pillar  42  and height positions of the seat  3  and the backrest  1  can be adjusted through projecting and sinking movement of the leg support pillar  42 . On the lower surface side of the base  2 , there are provided base attaching portions  203   a ,  203   b  for attaching reactive force frame elements of a reactive force frame portion  15 , which will be described later. Moreover, the base  2  incorporates an elastically biasing mechanism (not shown in the figure) that biases forward the backrest  1  rotating around the horizontal shaft  16 , a fixing mechanism (not shown in the figure) that fixes a rocking angle of the backrest  1 , and the like. The elastically biasing mechanism mounts a coil spring or a gas spring to elastically bias a back frame  11 . The fixing mechanism fixes the rocking angle, for example, by selectively engaging a claw with any one of a plurality of steps of depressions provided on the back frame  11  side, and in the case where a push-lock type gas spring is used for the elastically biasing mechanism, an aspect in which a valve thereof is driven to prohibit expansion and contraction movement of the gas spring may be taken. 
   The seat  3 , as shown in  FIGS. 1 to 5 , is made up by mounting a cushion body  32  making up a seat surface on a seat receiver  31 . The cushion body  32  has, for example, a two-layer structure in which a urethane cushion material is superimposed on a double raschel mesh made of synthetic fiber, the mesh of the lower layer maintaining appropriate elasticity while absorbing impact, and the urethane cushion material of the upper layer maintaining the stability in style and shape. A front end portion of the seat  3  is supported slidably in an back and forth direction with respect to the base  2 , and a rear end portion of the seat  3  is attached to the lower frame portion  13  in the back frame  11  described below through hinges (not shown in the figure). 
   The backrest  1 , as shown in  FIGS. 1 to 5 , is made up by extending an upholstery member  12  making up a backrest surface in front of the back frame  11 . The back frame  11  includes the lower frame portion  13  jointed to the base  2  rotatably around the horizontal shaft  16 , the upper frame portion  14  jointed to upper ends of the lower frame portion  13  through hinges  17 , and the reactive force frame portion  15  supporting the upper frame portion  14  from the rear side. 
   In the lower frame portion  13 , right and left lower frame elements  131   a ,  131   b  arranged apart from each other in a width direction are jointed mutually through a rigid lateral bridging member  132 , as shown in  FIGS. 1 to 4 . The lower frame elements  131   a ,  131   b  and the rigid lateral bridging member  132  are, for example, rigid bodies made of metal. Each of the lower frame elements  131   a ,  131   b  extends rearward from a front end thereof where the horizontal shaft  16  is located, and forms a substantially L shape bent upward at a rear end thereof in a side view. 
   In the upper frame portion  14 , right and left upper frame elements  141   a ,  141   b  arranged apart from each other in the width direction are jointed mutually through an elastic lateral bridging member  142  as shown in  FIGS. 1 to 4 . The upper frame elements  141   a ,  141   b  are, for example, rigid bodies made of metal, while the elastic lateral bridging member  142  is, for example, an elastic body made of resin. Each of the upper frame elements  141   a ,  141   b  extends upward from a lower end thereof where the hinge  17  is located while curving moderately so as to be slightly depressed rearward, and forms an arc that swells forward again in the vicinity of an upper end thereof in a side view. 
   The reactive force frame portion  15 , as shown in  FIGS. 1 to 4 , is made of reactive force frame elements  151   a ,  151   b , which are the same number of frame-like springs supporting the upper frame elements  141   a ,  141   b , respectively. Upper portions  153   a ,  153   b , which are one-end portions of the reactive force frame elements  151   a ,  151   b , are connected to upper attachment portions  143   a ,  143   b  of the upper frame elements  141   a ,  141   b , and lower end portions  152   a ,  152   b , which are other-end portions, are connected to the base attachment portions  203   a ,  203   b  provided in a downside surface of the base  2 . However, as described later, the lower end portions  152   a ,  152   b  of the reactive force frame elements  151   a ,  151   b  are not hindered from being fixed to the base  2  supporting the seat  3  and the backrest  1 . The reactive force frame elements  151   a ,  151   b  are elastic bodies made of the same resin as that of the elastic lateral bridging member  142 , for example. In the present embodiment, the reactive force frame elements  151   a ,  151   b  are frame-like springs that extend along the lower frame elements  131   a ,  131   b  and the upper frame elements  141   a ,  141   b  so as to form a substantially L shape in a side view, and are formed such that a width dimension is almost the same as, or a little narrower than, that of the frame elements  131   a ,  131   b ,  141   a ,  141   b , and thicknesses of the longitudinal part and vertical part thereof are thinner than that of the frame elements  131   a ,  131   b ,  141   b ,  141   b  (in addition, it becomes gradually thinner away from the end portions where they are jointed to the base  2  and the upper frame elements  141   a ,  141   b ). With the above-described constitution, an appearance is formed as if the reactive force frame elements  151   a ,  151   b  are a part of the back frame  11 , which branches from the upper frame elements  141   a ,  141   b.    
   In a range of a vicinity of each of the hinges  17  pivotally supporting the lower frame elements  131   a ,  131   b  and the upper frame elements  141   a ,  141   b , more specifically, a range of a portion from the rear end of each of the lower frame elements  131 ,  131   b  to a vicinity of the upper end thereof, and a range of a vicinity of the lower end of each of the upper frame elements  141   a ,  141   b , a curve is formed such that a front surface of the frame swells forward in a side view. As described before, in the vicinity of the upper end of each of the upper frame elements  141   a ,  141   b , a curve is also formed so that the front surface of the frame swells forward in a side view. Thus, the upholstery member  12  is extended so as to bridge between the portions forming the above-described curves of the lower frame elements  131   a ,  131   b  and the upper frame elements  141   a ,  141   b.    
   The upholstery member  12 , as shown in  FIGS. 1 to 5 , is mainly made of an upholstery material having rich stretch properties. The upholstery material is obtained, for example, by further weaving an elastic thread such as an elastomer thread into double raschel mesh made of synthetic fiber, having both strength and cushioning properties. The upholstery material differs in appearance (color, pattern, luster or the like) between the front and the back sides. At an upper side and right and left sides of the upholstery material, the shape of the upholstery material is maintained by a backup member (not shown in the figure) forming a three-side frame or four-side frame in a front view. The backup member is, for example, a thin plate body made of resin, which particularly prevents the right and left sides of the upholstery material from sagging inward, and keeps the upholstery material strained. An upper end portion of the upholstery member  12  is attached to the right and left upper frame elements  141   a ,  141   b  to be supported, and a lower end portion is attached to the right and left lower frame elements  131   a ,  131   b  to be supported. At this time, the backup member acts as a plate spring, pushing the upholstery material forward to throw it out. 
   A lumber support belt  18  can also be laid in a position of a height corresponding to the waist of the sitter behind the upholstery member  12 . Even when the sitter leans his or her body against the backrest surface, the portion where the lumber support belt  18  is laid does not sink rearward at a depth larger than a depth in accordance with a length of the lumber support belt  18 . 
   The chair C of the present embodiment is capable of synchronous rocking movement in which the seat  3  and the backrest  1  are interlocked and tilted. As shown in  FIG. 6 , in the synchronous rocking movement, the rotation of the entire back frame  11  around the horizontal shaft  16  allows the backrest  1  to tilt back and forth. At the same time, the rear end portion of the seat  3  is interlocked with the back frame  11  to swing vertically, and the front end portion of the seat  3  slides back and forth. 
   With the above-described constitution, as shown in  FIGS. 7 and 8 , the chair C of the present embodiment is capable of movement in which only a left half portion or only a right half portion of an upper portion of the backrest surface is displaced rearward following the sitter&#39;s motion of turning back, extending his or her arm, or twisting his or her body while the sitter stays seated. In the upper frame portion  14  supporting the upper portion of the backrest surface, the upper fame elements  141   a ,  141   b  making a pair on both right and left sides move back and forth independently of each other. That is, the upper frame element  141   a  on the left side is jointed to the lower frame element  131   a  on the left side through the hinge  17 , the upper frame elements  141   b  on the right is jointed to the lower frame element  131   b  on the right side through the hinge  17 , and these upper frame elements  141   a ,  141   b  can rotate individually. 
   As shown in  FIG. 7 , when the upper frame elements  141   a ,  141   b  are tilted rearward around the hinges  17 , an area where the upholstery member  12  contacts the portions forming curves of the lower frame elements  131   a ,  131   b  and the upper frame elements  141   a ,  141   b  gradually increases, and the upholstery material stretches vertically while increasing tension. Furthermore, the reactive force frame elements  151   a ,  151   b  deform so as to increase the angle to accumulate reactive force to elastically bias the upper frame elements  141   a ,  141   b  in a direction in which the upper frame elements  141   a ,  141   b  are restored to the original positions, that is, forward. 
   One of the upper frame elements  141   a ,  141   b  is displaced relative to the other of the upper frame elements  141   a ,  141   b  in the backward and forward directions, by which the shape of the backrest surface can be changed three-dimensionally, as shown in  FIGS. 8 ,  9 . In this movement, the lower frame portion  13  is not necessarily driven. Furthermore, since the lower frame elements  131   a ,  131   b , which make a pair on the right and left sides, are rigidly jointed through the rigid lateral bridging member  132 , these lower frame elements  131   a ,  131   b  are always interlocked integrally. Therefore, a shape of a lower portion of the backrest surface, that is, portion lower than the waist of the sitter is always kept constant. 
   When one of the upper frame elements  141   a ,  141   b  moves back and forth relative to the other with a motion of the sitter, a distance between the right and left upper frame elements  141   a ,  141   b  increases. At this time, the elastic lateral bridging member  142  is deformed elastically so as to correspond to the increase in separate distance of both the upper frame elements  141   a ,  141   b . The elastic lateral bridging member  142  of the present embodiment joints the upper end portions of the upper frame elements  141   a ,  141   b  to each other, and is assembled in a state forming a curve depressed rearward in a plane view. A thickness in the back and forth direction of the elastic lateral bridging member  142  gradually becomes smaller toward the center in the width direction from both the end portions joining the upper frame elements  141   a ,  141   b , which makes a central portion easier to deform than both the end portions. This is intended to avoid concentration of load on the joining points between the upper frame elements  141   a ,  141   b  and the elastic lateral bridging member  142 . When one of the upper frame elements  141   a ,  141   b  moves back and forth relative to the other, the elastic lateral bridging member  142  deforms so as to reduce a curvature, thereby lengthening the distance between both the ends. 
   Additionally, the load of the sitter that the backrest surface receives acts on the upper frame elements  141   a ,  141   b  through the upholstery member  12 , and tries to bring the upper frame elements  141   a ,  141   b  down inward, which applies load to the hinges  17 . For the purpose of negating and reducing such load, the elastic lateral bridging member  142  is assembled in a state exerting an initial elastic force that sets apart the upper frame elements  141   a ,  141   b  in the width direction. 
   Also, the right and left upper frame elements  141   a ,  141   b  can be tilted together. In this case, for example, stretch enough to allow the sitter to largely bend himself or herself backward is possible. 
   Thus, the chair C according to the present embodiment is characterized in that the upper frame portion biasing means X is constituted so as to change the elastically biasing force to the upper frame portion  14  corresponding to the rocking movement of the lower frame portion  13 , as described above. 
   Hereinafter, a specific constitution of the upper frame portion biasing means X is described in detail with reference to  FIGS. 3 ,  6  and  9 . 
   First, in a posture shown in  FIGS. 3 and 6 , that is, when the lower frame portion  13  is in a standing position (S), the upper frame elements  141   a ,  141   b  are in the state where the predetermined elastically biasing force is applied by the reactive force frame elements  151   a ,  151   b . The lower frame portion  13  falls toward a rearward tilting position (T), and thereby, the upper attachment portions  143   a ,  143   b  of the upper frame elements  141   a ,  141   b  that attach the reactive force frame elements  151   a ,  151   b  and the base attachment portions  203   a ,  203   b  of the base  2  become closer in relative position, and the reactive force frame elements  151   a ,  151   b  enter an inflected state, thereby entering a state where an elastic repulsive force is increased. As shown in  FIG. 9 , when the lower frame portion  13  is located in the rearward tilting position (T), the upper attachment portions  143   a ,  143   b  and the base attachment portions  203   a ,  203   b  become the closest, and thus, the elastic repulsive force is accumulated most. Thus, the elastic repulsive force of the reactive force frame elements  151   a ,  151   b  increases as the lower frame portion  13  becomes closer to the rearward tilting position (T). In other words, the reactive force frame portion  15  is provided between the base  2  and the upper frame portion  14  to make up the upper frame portion biasing means X, which realizes the constitution in which the elastically biasing force of the reactive force frame elements  151   a ,  151   b  to the upper frame elements  141   a ,  141   b  is set stronger as the lower frame portion  13  becomes closer to the rearward tilting position (T). 
   As described above, in the chair C according to the present embodiment, since the relevant upper frame portion biasing means X is constituted so as to change the elastically biasing force to the upper frame portion  14  corresponding to the rocking movement of the lower frame portion  13 , the constitution is realized as described above, in which as the lower frame portion  13  becomes closer to the rearward tilting position (T) from the state where the lower frame portion  13  is in the standing position (S), the elastically biasing force of the reactive force frame elements  151   a ,  151   b  increases. This realizes the constitution in which the chair may be gradually changed from an aspect easy to follow the back of the sitter to an aspect easy to support the back. This allows for the constitution in which the backrest  1  matches the posture of the sitter. Specifically, in one and the same chair C can be preferably realized two contrary characteristics required to the backrest  1 ; in the state where the lower frame portion  13  is in the standing position (S), the backrest  1  preferably moves following the back, while in the state where the lower frame portion  13  is in the rearward tilting position (T), the backrest  1  preferably supports the back of the sitter. 
   The above-described upper frame portion biasing means X capable of changing such elastically biasing force to the upper frame elements  141   a ,  141   b  can be made up with the simple constitution in which the reactive force frame elements  151   a ,  151   b , which are elastic members, are attached between the base  2  and the upper frame portion  14 . More particularly, the constitution in which the elastically biasing force to the upper frame portion  14  is varied by utilizing the change in relative position of the lower frame portion  13  and the base  2  is preferably realized. Furthermore, by employing the reactive force frame elements  151   a ,  151   b  which are frame-like springs, the reactive force frame elements  151   a ,  151   b  can preferably exert the elastically biasing force even when they are provided between the base  2  and the upper frame elements  141   a    141   b  which are apart from each other through the lower frame portion  13 . 
   Furthermore, in the present embodiment, the upper frame portion  14  is made of the pair of upper frame elements  141   a ,  141   b  that can move independently, and particularly, when the lower frame portion  13  is in the standing position (S) or is located in the vicinity, the backrest  1  can move faithfully in accordance with the upper body of the sitter. 
   While in the foregoing, the first embodiment of the present invention is described, the specific constitutions of the respective components are not limited to only the above-described embodiment. 
   Hereinafter, another embodiment of the present invention is described, and components having actions similar to those of the above-described embodiment are indicated by like reference numerals, whose detailed description is omitted. 
   Second Embodiment 
   A chair C 2  according to a second embodiment of the present invention, as shown in  FIGS. 10 to 15 , is constituted such that upper frame portion biasing means X 1  is made of a torsion coil spring  17   sp , which is an elastic member, provided between the above-described upper frame portion  14  and lower frame portion  13 , and includes repulsive force changing means X 11 , described later, that can change an initial repulsive force of the torsion coil spring  17   sp  by changing a locking position of the relevant torsion coil spring  17   sp . Furthermore, a regulator  19  is mounted to provide a movement range setting mechanism A that can change a movement range of the upper frame portion  14  corresponding to the position of the lower frame portion  13 . 
   Hereinafter, a constitution of the chair C 2  according to this embodiment is described. 
   The regulator  19 , as shown in  FIGS. 10 to 12 , has regulating members  191   a ,  191   b  and link elements  192   a ,  192   b . The regulator  19  forms a substantially-L-shaped frames extending along the lower frame elements  131   a ,  131   b  and the upper frame elements  141   a ,  141   b  in a side view, in which the regulating members  191   a ,  191   b  are turnably attached to the base  2  at lower end portions, and are turnably attached to the link elements  192   a ,  192   b  in the vicinity of upper end portions thereof. The upper ends of the regulator  19  are contacting end portions  191   a   1 ,  191   b   1  that can contact the upper frame elements  141   a ,  141   b  to thereby determine the rear end position (E) of the upper frame portion  14 , or prohibit the rocking movement itself of the upper frame portion  14 . The link elements  192   a ,  192   b  are turnably attached to the hinges  17  and the regulating members  191   a ,  191   b  at both end portions thereof. With the above-described constitution, a so-called parallel link mechanism made of the regulating members  191   a ,  191   b , the link elements  192   a ,  192   b , the lower frame elements  131   a ,  131   b , and the base  2  is realized, by which the relevant movement range setting mechanism A is made up. 
   The upper frame portion biasing means X 1 , as shown in  FIGS. 13 and 14 , is adapted to set the elastically biasing force to the upper frame portion  14  stronger as the lower frame portion  13  becomes closer to the rearward tilting position (T). More specifically, the upper frame portion biasing means X 1 , as shown in the same figures, is mainly made of the torsion coil spring  17   sp , which is an elastic member, provided between the upper frame portion  14  and the lower frame portion  13 , that is, in the vicinity of the hinge  17 . One end  171   sp  of the relevant torsion coil spring  17   sp  is fixed to each of the upper frame elements  141   a ,  141   b , and another end  172   sp  is fixed to each of the link elements  192   a ,  192   b . That is, the relevant upper frame portion biasing means X 1  makes up the repulsive force changing means X 11  capable of changing the initial repulsive force of the above-described torsion coil spring  17   sp  by changing the locking position of the torsion coil spring  17   sp  by the torsion coil spring  17   sp , each of the link elements  191   a ,  191   b , and each of the upper frame elements  141   a ,  141   b.    
   Hereinafter, the change in the movement range of the upper frame portion  14  by the movement range setting mechanism A is described in detail. 
   As shown in  FIGS. 10 to 12 , as the lower frame portion  13  performs the rocking movement from the standing position (S) as shown in  FIG. 10  to an intermediate position (M) as shown in  FIG. 11  and the rearward tilting position (T) as shown in  FIG. 12 , the regulating members  191   a ,  191   b  gradually rise and become closer to the normal position (N) of the upper frame portion  14 , by which the movement range from the relevant normal position (N) to the rear end position (E) gradually becomes narrower ( FIG. 10 ), until the rocking movement is not activated in the rear end position (E) ( FIG. 12 ). Specifically, as the lower frame portion  13  is performing the rocking movement from the standing position (S), to the intermediate position (M) and the rearward tilting position (T), the contacting end portions  191   a   1 ,  191   b   1  of the regulating members  191   a ,  191   b  gradually rise closer to the upper frame elements  141   a ,  141   b , and in the rearward tilting position (T), the contacting end portions  191   a   1 ,  191   b   1  come into contact with the upper frame elements  141   a ,  141   b , which prohibits the rocking movement of the upper frame elements  141   a ,  141   b . In other words, in the rear end position (T) of the lower frame portion  13 , the contacting end portions  191   a   1 ,  191   b   1  come into contact with the upper frame element  141   a ,  141   b , and thereby, the normal position (N) and the rear end position (E) of the upper frame elements  141   a ,  141   b  are located in the same position. While each of the hinges  17  also has a forward contacting portion that determines the normal position (N) of the upper frame  14 , for a constitution for regulating the movement of the hinge  17  in the relevant normal position (N), various existing constitutions can be employed, and thus, a detailed description is omitted in the present embodiment. 
   In the upper frame portion biasing means X 1 , as shown in  FIGS. 13 and 14 , when the lower frame portion  13  performs the rocking movement toward the rearward tilting position (T) from the standing position (S) as shown in  FIG. 13  to the intermediate position (M) as shown in  FIG. 14 , a relative angle between the one end  171   sp  and the other end  172   sp  of the torsion coil spring  17   sp  changes with the change of a relative angle of each of the link elements  192   a ,  192   b  with respect to each of the upper frame elements  141   a ,  141   b . With this, the torsion strength of the torsion coil spring  17   sp  increases, which allows a stronger elastically-biasing-force to be applied to each of the upper frame elements  141   a ,  141   b.    
   Since the chair according to the second embodiment of the present invention as described above is provided with the movement range setting mechanism A, which sets the movement range of the upper frame elements  141 ,  141   b  narrower as the lower frame portion  13  become closer to the rearward tilting position (T), the chair is adapted such that the backrest  11  can follow the motion of the upper body of the sitter without disturbing it when the sitter raises his or her upper body during execution of business or the like, and that the upper frame elements  141   a ,  141   b  can preferably support the upper body of the sitter respectively when the lower frame portion  13  is tilted rearward by inclining the sitter&#39;s upper body when the sitter leaning against the backrest  11  or the like. 
   Furthermore, since the movement range setting mechanism A is adapted such that as the lower frame portion  13  becomes closer to the rearward tilting position (T), the above-described upper frame rear end position (E) becomes closer to the normal position (N), the lower frame portion  13  can be tilted rearward with the upper body stable. Moreover, in the present embodiment, since the movement range setting mechanism A is adapted so as to prohibit the movement of the upper frame elements  141   a ,  141   b  when the lower frame portion  13  reaches the rearward tilting position (T), the upper body of the sitter in the rearward tilting position (T) can be preferably supported. 
   In the present embodiment, specifically, by applying the regulator  19 , the contacting end portions  191   a   1 ,  191   b   1  of the regulating members  191   a ,  191   b  gradually become closer to the normal position (N) of the upper frame elements  141   a ,  141   b  corresponding to the rocking movement in which the lower frame portion  13  is tilted rearward, and come into contact with the upper frame elements  141   a ,  141   b  when the upper frame elements  141   a ,  141   b  are located in the rear end position (E) to prohibit the movement of the upper frame elements  141   a ,  141   b . With such a constitution, only by adding the two kinds of components of the regulating members  191   a ,  191   b  and the link elements  192   a ,  192   b , the movement range setting mechanism A capable of setting the movement range of the upper frame elements  141   a ,  141   b  in a continuous manner is preferably made up. 
   Moreover, by supporting the regulating members  191   a ,  191   b  by the base  2 , a parallel link structure is preferably made up to preferably correspond to the movement of the lower frame portion  13 . 
   As a modification of the present embodiment, for example, as shown in  FIG. 15 , a switching mechanism SW for temporarily stopping the above-described function of the movement range setting mechanism A may be provided. Specifically, a folding portion  193   b  in the vicinity of each of the contacting end portions  191   a   1 ,  191   b   1  of the regulating members  191   a ,  191   b  is provided, and rotating the relevant folding portion  193   b  as necessary allows switching between an on state (ON) in which each of the contacting end portions  191   a   1 ,  191   b   1  comes into contact with each of the upper frame elements  141   a ,  141   b , and an off state (OFF) indicated by a dashed line, in which each of the contacting end portions  191   a   1 ,  191   b   1  cannot come into contact with each of the upper frame elements  141   a ,  141   b.    
   Furthermore, as shown in  FIG. 16 , a projecting and sinking regulating member  194   b  may be provided in the vicinity of each of the contacting end portions  191   a   1 ,  191   b   1  of the regulating members  191   a ,  191   b , and by operating the projecting and sinking regulating member  194   b  as necessary to perform a projecting and sinking movement in each of the contacting end portions  191   a   1 ,  191   b   1 , switching can be performed between the on state (ON) in which each of the contacting end portions  191   a   1 ,  191   b   1  comes into contact with the upper frame elements  141   a ,  141   b , and the off state (OFF) indicated by a dashed line, in which each of the contacting end portions  191   a   1 ,  191   b   1  cannot come into contact with the each of the upper frame elements  141   a ,  141   b.    
   With the above-described constitution, the setting of the movement range setting mechanism A can be switched to temporarily stop the function of the relevant movement range setting mechanism A as desired by the sitter. 
   Furthermore, as another modification of the present embodiment, as shown in  FIG. 17 , instead of the torsion coil spring  17   sp , the reactive force frame portion  15  similar to that of the above-described first embodiment may be provided. With such a constitution, the movement range setting mechanism and the upper frame portion biasing means preferably act in combination. 
   With such a constitution, a constitution can be realized in which the upper body of the sitter is supported more stably, as the lower frame portion  13  is tilted rearward. 
   Third Embodiment 
   Next, a chair C 3  according to a third embodiment of the present invention is described. 
   In the chair C 3  according to the present embodiment, as shown in  FIGS. 18 ,  19 , upper frame portion biasing means X 2  is made up by providing the reactive force frame portion  15  made of reactive force frame elements A 151   a , A 151   b , which are resin springs, between the upper frame portion  14  and the lower frame portion  13 , as an elastic member. Further, there is provided supporting position changing means Y 1  capable of changing a supporting position where the reactive force frame elements A 151   a , A 151   b  are supported, corresponding to the rocking movement of the lower frame portion  13 . As a specific constitution of the supporting position changing means Y 1 , various mechanisms or structures such as position change by gear or position change employing a link mechanism can be employed. 
   With the above-described mechanisms or structures, the elastic repulsive force can preferably be applied to the reactive force frame elements A 151   a , A 151   b , and the relevant elastic repulsive force is surely changed, thereby changing the elastically biasing force of the reactive force frame elements A 151   a , A 151   b.    
   Fourth Embodiment 
   Next, a chair C 4  according to a fourth embodiment of the present invention is described. 
   In the chair C 4  according to the present embodiment, as shown in  FIGS. 20 ,  21 , the upper frame portion biasing means X 2  is made up by providing the reactive force frame portion  15  made of the reactive force frame elements B 151   a , B 151   b , which are resin springs, between the upper frame portion  14  and the lower frame portion  13 , as an elastic member. Moreover, interfering supporting point  21   a  that comes into contact with each of intermediate portions B 151   ay , B 151   by  of the reactive force frame elements B 151   a , B 151   b  when the relevant reactive force frame elements B 151   a , B 151   b  inflect is provided to thereby provide a supporting point forming member  21  that interferes with inflecting movement. Specifically, the supporting point forming member  21  is fixed to the base  2 , by which the position of the interfering supporting point  21   a  is changed relatively corresponding to the movement of the lower frame portion  13 . With such a constitution, the supporting point forming member  21  can simultaneously bring about an action of supporting point changing means Y 2  capable of changing the fixing position of the relevant supporting point forming member  21  with respect to each of the reactive force frame elements B 151   a , B 151   b  corresponding to the above-described rocking movement of the lower frame portion  13 . 
   The above-described constitution can also preferably change the elastic repulsive force of the reactive force frame elements B 151   a ,  151   b  corresponding to the movement of the lower frame portion  13 . 
   While in the foregoing, the respective embodiments of the present invention are described, the specific constitutions of the respective components are not limited to the above-described embodiments. For example, the above-described supporting position changing means and the supporting point changing means are not limited to the aspects used for the reactive force frame elements provided between the upper frame portion and the lower frame portion, but may be applied to the reactive force frame elements in the above-described first embodiment. 
   Additionally, the specific constitutions of the respective components are not limited to the above-described embodiments, but various modifications can be made within a range not departing from the gist of the present invention.