JP2013000446A - Chair - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chair for obtaining a normal posture, a straight backward reclining posture, and a horizontally backward reclining posture without employing a complicated rocking mechanism and being much influenced by a weight difference of a sitting person.SOLUTION: The chair includes a leg body 2, a seat support part supported by the leg body 2, and a seat 4 positioned at the seat support part. The seat support part is pivotally supported by the leg body 2 so as to allow a balancing motion to take place around a single axis core 20 extending in a horizontal direction. The chair includes a turning restriction mechanism for restricting the balancing motion of the seat support part to be within a fixed range. The seat 4 is configured to allow the rear area 9 to sink downward by elastic deformation with respect to a front area 8 beyond a turnable range of the balancing motion of the seat support part.

Description

  The present invention relates to a chair suitably used for school or office use.

  Conventionally, as this type of chair, various types of seats that allow the seat to tilt backward have been developed in order to give a reclining feeling (see, for example, Patent Document 1).

  However, the conventional one employs a complicated locking mechanism to cause the seat to tilt backward, and has a problem that the configuration is complicated and the number of parts increases.

  Further, as a simple configuration, there is also known a configuration in which only the front portion of the seat is supported by a support, and the seat is tilted backward using elastic deformation of the seat or the support. In such a case, for example, each part of the chair has to be set so that the entire chair has rigidity so that it can withstand even when a heavy load is applied due to the seating of a heavy person. However, in such a case, there is a problem that a sufficient reclining feeling cannot be obtained when a light weight person is seated.

JP 2000-342377 A

  The present invention has been made paying attention to the above circumstances, and does not require a complicated locking mechanism, and is not affected by the difference in weight of the seated person so that the normal posture, right behind, and right and left rearward. It is an object to provide a chair that can take a reclining posture.

  The present invention employs the following configuration in order to solve the above-described problems. That is, the chair according to the present invention comprises a leg, a seat support portion supported by the leg, and a seat positioned on the seat support portion, wherein the seat support portion is , Which is pivotally supported by the leg body so as to be able to perform a balance operation integrally around a single axial center extending in the left-right direction, and restricting the rotation of the seat support portion within a certain range Provided with a mechanism, wherein the seat is configured to be capable of sinking by elastic deformation downward with respect to its front region beyond the range of rotation by the balance operation of the seat support portion. Features.

  Here, the “legs” are, for example, those having a four-legged frame made of pipe material, those having a cantilever type frame made of pipe material, and swivel chair type leg feathers. In addition to things that can be carried and casters such as those provided with leg posts and support bases, they may be of a type fixed to the floor such as legs extending from the floor surface or standing wall.

  The “seat support portion” is a concept including a portion formed mainly by a seat support member such as a frame, a portion formed integrally with another member such as a seat, and the like.

  The “seat” means, for example, a mesh-like stretch fabric between frames, a plate-like shell or the like, a slit or groove made into the shell for easy bending, or a cushioning material on the shell Etc. are provided.

  The “balance operation” refers to an operation in which the seat is tilted backward and the rear end side is lowered and the front end side is raised while the load of the seated person is applied rearward around the axis.

  “To allow the balance operation” may be considered when a part or all of the seat is deformed or when the joint between the seat and the frame part is loose. As an example of the case where the coupling portion between the seat and the frame portion moves, there is one that slides.

  The “front region” indicates a region formed on the front side of an arbitrary portion between the front end and the rear end of the seat, and the seat is supported by the support body in an unloaded state, As long as it is a region where it can be seated stably, its size, shape, attachment method to the support, etc. may be any. In addition, the “rear region” indicates a region formed on the rear side of an arbitrary portion between the front end and the rear end of the seat, and the seat is directly supported by the support body in an unloaded state. It refers to a non-existing area, and its size, shape, sinking amount, etc. may be anything.

  In this case, “front”, “rear”, “left”, and “right” mean “front”, “rear”, “left” as viewed from the seated person in a state where the seated person is seated on the chair according to the present invention. ”And“ right ”.

  In such a case, it is not necessary to use a complicated locking mechanism, and the normal posture and the reclining posture to the rear and right and left rear can be taken without being greatly affected by the difference in weight of the seated person.

  As a preferred aspect of the seat support portion, the seat support portion has rigidity, and the front region of the seat is supported so as not to tilt relative to the seat support portion in the front-rear direction, and the rear region of the seat Only when a load is applied to the rear support region, the rear region sinks into the seat support portion.

  It is preferable that the seating surface of the rear region of the seat is configured to be inclined in the left-right direction by elastic deformation of the seat.

  As a preferred embodiment of the seat, a stretch fabric is stretched between the left and right frame parts that can be elastically deformed, and the left and right frame parts sink independently of the seat support part. Things.

  As another preferred aspect of the seat support portion, the seat support portion is elastically deformable, and the rear portion corresponding to the rear region of the seat exceeds the rotation range by the balance operation of the seat support portion. The part is configured to be able to sink downward by its own deformation with respect to the front part corresponding to the front part region of the seat.

  It is preferable to include a return mechanism that biases the seat support portion forward.

  As a preferred aspect of the return mechanism, there may be mentioned one constituted mainly of a single leaf spring that urges the seat support portion to rotate forward.

  Since the present invention is configured as described above, it is not necessary to use a complicated locking mechanism, and the normal posture and the reclining posture to the rear and right and left rear are taken without being greatly affected by the weight difference of the seated person. Can provide a chair that can.

The whole perspective view showing the chair of one embodiment of the present invention. The front view which shows the chair of the embodiment. XX sectional drawing in FIG. The right view which shows the chair of the embodiment. The right view which shows the sinking state of the chair of the embodiment. The YY sectional view taken on the line in FIG. Explanatory drawing which shows typically the rotation control mechanism of the embodiment. Explanatory drawing which shows typically the rotation control mechanism of the modification of this invention. The right view which shows the chair of the further another modification of this invention. The right view which shows the subsidence state of the chair of the modification.

  First, an embodiment of the present invention will be described with reference to FIGS.

  In this embodiment, the present invention is applied to an office swivel chair. As shown in FIGS. 1 to 6, the chair 1 is positioned on a leg 2, left and right frames 3 </ b> A and 3 </ b> B as seat support portions supported by the leg 2, and the left and right frames 3 </ b> A and 3 </ b> B. A seat 4 and a backrest 5 supported by the seat 4.

  As shown in FIGS. 1 to 6, the leg body 2 is supported by a leg blade 21 having a caster attached to the tip, a leg column 22 standing from the leg blade 21, and an upper end of the leg column 22. A support base 23 that can pivot about the axis of the leg support 22 is provided, and the left and right frames 3A and 3B are supported on the support base 23 so as to be able to perform a balance operation. The leg support 22 is constituted by a gas spring, and the support base 23 is fixed to the upper end of the cylinder shaft 24 of the gas spring. The support base 23 includes a support base body 25 fixed to the cylinder shaft 24 and arms 26 erected upward from both left and right ends of the support base body 25. It can turn in the horizontal direction. Left and right support shafts 27 are provided at the upper ends of the left and right arms 26 so that the shaft centers 20 coincide with each other, and the left and right frames 3A and 3B are supported on the support shafts 27 so that the balance operation is possible. Yes. Here, the “balance operation” refers to an operation about the support shaft 27 as a center, when the seated person's load is applied to the rear, the seat 4 tilts backward, the rear end side lowers, and the front end side rises. In this embodiment, this balance operation is an operation in which the seat 4 returns to the initial state (f) when the load of the seated person is applied forward, with the support shaft 27 as the center, and the front end side is lowered and the rear end side is raised. Also included. The shaft center 20 extends in the left-right direction of the chair 1.

  As shown in FIGS. 1 to 6, the left and right frames 3A and 3B are pivotally supported by the leg 2 so as to be able to perform a balance operation around the single axis 20 extending in the left-right direction. For example, it is made of a synthetic resin reinforced with fibers. These left and right frames 3A and 3B are each provided with a frame main body 3A1 and 3B1, and fixed arms 3A2 and 3B2 extending downward from the center of the frame main bodies 3A1 and 3B1, respectively. The fixed arms 3A2 and 3B2 are integrally formed. The left and right frame bodies 3A1 and 3B1 respectively have a front portion 91 extending substantially horizontally from the front end toward the front-rear intermediate portion of the seat 2, and a rear portion from the rear end of the front portion 91 while being gradually separated from the lower surface of the seat 2. And a rear portion 93 extending in the direction. In this embodiment, the rear portion 93 has an inclined portion 90 that gradually separates rearward from the seat 2 below the rear region 9 of the seat 4. When a load is applied, the rear region 9 sinks and the seat 4 is deformed along the inclined portion 90.

  As shown in FIGS. 1 to 6, the seat 4 has a mesh-like stretch fabric 41 stretched between the left and right seat frames 4A and 4B. The seat 4 includes a front region 8 on the front side of the axis 20 and a rear region 9 on the rear side of the axis 20. The left and right seat frames 4A and 4B are elastically deformable bowls made of synthetic resin or the like, and their front regions 8 are supported by the left and right frames 3A and 3B as the seat support portions, The rear region 9 can be submerged between an initial state (f) before subsidence and a subsidence state (s) most subsidized. That is, the rear region 9 is separated from the upper surfaces of the left and right frames 3A and 3B in the initial state (f), and appropriately sinks using elastic deformation of the seat 4 according to the load acting on the seat surface. It is like that. The rear region 9 is configured to come into contact with the upper surfaces of the left and right frames 3A and 3B in the most depressed state (s). That is, the seat frames 4A and 4B, which are the left and right frame portions of the present invention, are sunk independently with respect to the left and right frames 3A and 3B which are the seat support portions. It is comprised so that the seat surface of can be inclined also in the left-right direction. In FIG. 4, the initial state (f) taken in the office posture is indicated by a solid line, and the rear region 9 of the seat 4 sinks into the front region 8 beyond the rotation range by the balance operation (explanation) For the sake of convenience, a balance operation is not performed). Further, in FIG. 5, the subsidence state (s) in which the balance operation that is performed in the reclining posture and the operation in which the rear region 9 of the seat 4 sinks beyond the rotation range by the balance operation is simultaneously performed is indicated by a solid line, The state (f) is indicated by a two-dot chain line.

  As shown in FIGS. 1 to 6, the backrest 5 is formed by stretching a mesh-like tension fabric 51 between the left and right back frames 5A and 5B formed integrally with the left and right seat frames 4A and 4B. is there. The left and right seat frames 4A and 4B and the left and right back frames 5A and 5B are integrally formed of, for example, synthetic resin reinforced with fibers. The chair 1 according to this embodiment is configured such that the backrest 5 and the seat 4 are interlocked. Specifically, the seat 4 is tilted in accordance with the backward tilting operation of the backrest 5 while the front side is raised. It is a weight-sensing type that can be moved.

  The chair 1 also includes a rotation restricting mechanism 6 that restricts the balance operation of the left and right frames 3A and 3B within a certain range. As shown in FIG. 7, the rotation restricting mechanism 6 is provided with a slot-like recess 61 provided in the arm 26 of the support base 23 and the fixing arms 3A2 and 3B2 of the left and right frames 3A and 3B. 61 in the initial state (f) before the rear end side of the seat 4 sinks, the protrusion 62 is locked to the one end 63 side of the recess 61, In the subsidence state (s) in which the rear end side of the seat 4 is most depressed, the protrusion 62 is locked to the other end 64 side of the recess 61.

  Further, as shown in FIGS. 1 to 6, the chair 1 is provided with the left and right frames 3A, 3B pivoted forward so that the left and right frames 3A, 3B can rotate integrally. A return mechanism 7 is provided. The return mechanism 7 is mainly composed of a single leaf spring that pivotally biases the left and right frames 3A and 3B as the seat support portions forward. That is, the return mechanism 7 includes a resin spring 73 in which one end 71 is continued to the intermediate portion of the left and right frames 3A and 3B via the horizontal member 33 and the other end 72 is supported by the leg body 2. Is. More specifically, the resin spring 73 is provided in a J-shape as viewed from the side with the middle portion curved forward, and one end 71 of the resin spring 73 is continuous with the horizontal center of the horizontal member 33. I am letting. The horizontal member 33 is continuous with the left and right frames 3A and 3B so that the left and right frames 3A and 3B tilt at the same angle, that is, in synchronization with the left and right.

  In the case of such a chair 1, when sitting on the seat 4 in the office posture, the load caused by the weight of the seated person acts on the front region 8 of the seat 4, so that the left and right frames 3 </ b> A and 3 </ b> B tilt. Instead, the seat 4 is supported in a stable state. When the seated person leans on the backrest 5 and the load moves to the rear area 9 of the seat 4, the left and right frames 3A and 3B rotate by the same angle to perform a balance operation, and the rear area of the seat 4 9 will sink.

  When the reclining operation is performed in a state where the seated person is tilted to the right, the right seat frame 4A is more elastically deformed than the left seat frame 4B, and the right seat frame 4A comes into contact with the frame 3A. The seat is tilted to the right. Similarly, when the reclining operation is performed with the seated person tilted leftward, the left seat frame 4B is more elastically deformed than the right seat frame 4A, and the left seat frame 4B is placed on the frame 3B. The seating surface tilts to the left until it touches.

  When the seat occupant moves the load to the front region 8 of the seat 4 and returns to the office posture, the left and right frames 3A and 3B perform a balance operation forward, and the rear region 9 of the seat 4 is in an initial state before sinking. Self-return to (f).

  As described above, the chair 1 according to this embodiment includes the leg 2, the left and right frames 3A and 3B as seat support portions supported by the leg 2, and the seat 4 positioned on the left and right frames 3A and 3B. The left and right frames 3A, 3B are pivotally supported by the leg 2 so as to be able to perform a balance operation integrally around a single axis 20 extending in the left-right direction. And a rotation restricting mechanism 6 for restricting the balance operation of the left and right frames 3A and 3B within a certain range, and the seat 4 is a rotation range by the balance operation of the left and right frames 3A and 3B. Since the rear region 9 is configured to be able to sink downward by elastic deformation with respect to the front region 8, it is not necessary to use a complicated locking mechanism, and it has a simple structure and a suitable reclining feeling. Can be obtained. In addition, the rotation support portion for the balance operation is in the center portion in the front-rear direction of the seat 4, and the center of gravity of the load by the seated person is concentrated on the front region 8 during the work posture, so that the work posture can be stably maintained and rest Since the center of gravity of the load by the seated person concentrates on the rear region 9 in the posture, the rear region 9 of the seat 4 falls downward, so that a suitable reclining posture can be taken. That is, the chair 1 has a structure like a seesaw in which the front side is raised when the rear side of the seat 4 is lowered, and the front side of the seat 4 is lowered and returned to the original position. It can be said that.

  In this embodiment, in particular, the left and right frames 3A and 3B, which are seat support portions, have rigidity, and the front region 8 of the seat 4 does not tilt relative to the frames 3A and 3B in the front-rear direction. Since the rear region 9 sinks with respect to the frames 3A and 3B only when a load is applied to the rear region 9 of the seat 4, the frames 3A and 3B It will play a role as a receiving part that controls the sinking operation of the rear region 8. That is, since the seat frames 4A and 4B are elastically deformed along the inclined portion 90 in the rear portion 93 of the frames 3A and 3B, the seat 4 can be prevented from being tilted more than necessary, and a sense of security can be given to the seated person. .

  Since the chair 1 of this embodiment is provided with the back frames 5A and 5B in succession to the seat frames 4A and 4B, the seat 4 and the backrest 5 can perform a series of tilting operations. That is, when the seated person takes a reclining posture, the rear region 9 of the seat 4, which is a region on the rear side of the axis 20, is elastically deformed and sinks downward. The backrest 5 also tilts backward. Note that the rear region 9 of the seat 4 of the present embodiment is such that the entire left and right seat frames 4A and 4B are elastically deformed and self-recovered by this elastic restoring force. May be a rigid body that does not deform, and another return mechanism for elastically deforming the seat may be provided, and the seat may be elastically deformed by the action of the return mechanism.

  Such a balance operation is performed without being significantly affected by the difference in weight of the seated person. Conventionally, when the stability of the seat 4 in the working posture is obtained, the seat 4 is firmly supported by the leg body 2 and there is a problem that it is difficult to take a reclining posture. For example, when the back side of the seat 4 is lowered, the front side is raised, and conversely, the front side is lowered, and when the seat 4 is returned to the original position, the rear side is raised and returned to the original position. The reclining feeling can be exhibited stably.

  Further, when returning from the reclining posture to the stable posture, the place where the seated person's load concentrates gradually moves from the rear region 9 to the front region 8, but the seating surface elastically deforms following this, 4, the rear region 8 is elastically returned to the normal posture according to the consciousness of the seated person. In other words, when returning to the working posture again, the center of gravity of the load of the seated person moves to the front region 5 of the seat 2, so that it can be naturally shifted to the working posture. That is, in this case as well, the seat surface naturally follows the posture change of the seated person without being greatly affected by the weight of the seated person. Therefore, a feeling that the inclination of the seat 2 can be changed at the will of the seated person is obtained.

  Furthermore, since the chair 1 of this embodiment is provided with the rotation control mechanism 6, even if the seat 4 is supported so as to rotate around the single axis 20, the rearward is unlimited. The fall is regulated and the seated person can take a reclining posture with peace of mind.

  In addition, in the chair 1, when the seated person leans to the backrest 5 or to the left or right of the seat 4, the seat frames 4A and 4B corresponding to the rear region 9 of the seat 4 are elastically deformed in the thickness direction. As a result, the backrest 5 and the seat 4 on the curled side perform a tilting action larger than the backrest 5 and the seat 4 on the opposite side and sink downward. That is, the seat surface and the backrest surface are twisted by tilting left and right, and the seat frames 4A and 4B and the back frames 5A and 5B can be tilted rearward independently on the left and right. Therefore, the seat 4 and the backrest 5 can easily follow the tilting motion of the seated person to the rear left and right. In other words, the left and right frames 3A and 3B can be operated at the same left and right angles, and the rear sides of the seat frames 4A and 4B can be independently elastically deformed in the front-rear direction. It is also easy to perform a sinking operation in the front-rear direction. In particular, since the chair 1 performs a balance operation around the central portion of the seat 4 in the front-rear direction, the amount of sinking of the rear end portion of the rear region 9 of the seat 4 can be increased.

  Since the chair 1 includes the return mechanism 7 that urges the left and right frames 3A and 3B forward at once, the backward tilt of the seat 4 can be restricted to a certain amount. In particular, in this embodiment, the return mechanism 7 includes a single resin spring 73 in which one end 71 is connected to the left and right frames 3A and 3B and the other end 72 is supported by the leg 2. Therefore, the return mechanism 7 is arranged on the lower surface side of the seat 4, and the aesthetic appearance of the entire chair 1 can be improved. The resin spring 73 also serves as a positioning mechanism for determining the position of the seat 4 in a no-load state where no load is applied to the seat surface.

  The left and right seat frames 4A and 4B and the left and right back frames 5A and 5B are made of synthetic resin, and the left and right frames 4A and 4B and the left and right back frames 5A and 5B themselves are elastically deformed. Depending on how the load is applied, it can be tilted back and forth and tilted backward.

  The present invention is not limited to the embodiment described above.

  The rotation restricting mechanism is not limited to the one shown in the present embodiment, and various shapes and dimensions can be changed. As another example of the rotation restricting mechanism, there is a mechanism provided with a recess provided between a plurality of spaced protrusions as shown in FIG. In FIG. 8, parts corresponding to the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Furthermore, a protrusion may be provided on the support base side and a recess may be provided on the frame side. Further, the concave portion is not limited to a bottomed hole shape, and may be a through hole shape, a gap provided between a plurality of spaced protrusions, or the like.

  Further, as shown in FIGS. 9 and 10, the left and right frames that are seat support portions have portions beyond the axis 20 beyond the rotation range by the balance operation of the left and right frames 3A and 3B. It may be configured to be able to sink downward by its own deformation with respect to a portion in front of the axis 20. 9 and 10, parts corresponding to the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Here, in FIG. 9, the initial state (f) taken in the office posture is indicated by a solid line, and the rear region 9 of the seat 4 sinks with respect to the front region 8 beyond the rotation range by the balance operation ( For convenience of explanation, the balance operation is indicated by a two-dot chain line. Further, in FIG. 10, the subsidence state (s) in which the balance operation performed in the reclining posture and the operation in which the rear region 9 of the seat 4 sinks beyond the rotation range by the balance operation is simultaneously performed is indicated by a solid line, The state (f) is indicated by a two-dot chain line. In the chair 1 shown in FIGS. 9 and 10, the left and right frames 3A and 3B, which are the seat support portions, can be elastically deformed, and beyond the rotation range by the balance operation of the left and right frames 3A and 3B, The rear portion corresponding to the rear region 9 of the seat 4 is configured to be able to sink downward by its own deformation with respect to the front portion corresponding to the front region 8 of the seat 4. That is, the rear region 9 of the seat 4 is also supported by the frames 3A and 3B. Specifically, in the initial state (f), the rear portion of the frames 3A and 3B is brought into contact with the lower surfaces of the seat frames 4A and 4B. Touching. If it is such, the effect according to the effect of this embodiment is acquired. When the seat support portion is also elastically deformed in this way, it is preferable to provide a stopper for determining the lower limit position of the seat support portion at an appropriate location.

  The seat support portion is not limited to a frame-like one, and can be changed in various ways, but it supports the front edge side in the front region of the seat across the left and right and supports the rear edge side only near the center in the left-right direction. If there is, it is easy to incline the rear end side of the seat in the left-right direction. Therefore, it is possible to follow the twisting motion of the seated person. Further, the fixed arm provided integrally from the seat support portion may be provided integrally with the frame, or may be formed separately from the frame. Further, the fixed arm may extend in an oblique direction as viewed from the side, in addition to the one extending in the vertical direction of the seat support portion. That is, the position of the fixed arm attached to the spindle and the position continuous with the seat support portion may be different in the front-rear direction.

  The left and right back frames may be connected by a horizontal member. The horizontal member preferably has elasticity that allows the left and right back frames to tilt at different angles.

  The shaft may be any shaft as long as it has a single axis and extends in the left-right direction, and is not limited to the shaft spaced apart from the left and right as in this embodiment. If they are separated from each other on the left and right, they can be formed integrally with the support base and the frame, so that the number of parts and man-hours can be reduced. On the other hand, if the support shaft is continuous in the left-right direction, the load on the seated person can be shared even with the support shaft, so that the rigidity of the chair can be increased. That is, if the support shaft is separated from the left and right, the support shaft is provided at the tip end that is cantilevered, so that it is difficult to maintain the strength, but the support shaft is a single shaft that is continuous in the left-right direction. With this configuration, the rigidity of the support shaft itself can be increased, and the shaft center can be stabilized on the left and right. In the above-described embodiment, the support shaft is formed integrally with the leg-side member. However, the support shaft is not limited to this, and for example, the support shaft is formed integrally with the frame-side member, or the support shaft is connected to the leg or the frame. May be configured separately.

  The return mechanism may use a metal coil spring, a leaf spring, or the like in addition to the above-described resin spring. The return mechanism may be attached at any position on the front, center and rear of the seat. For example, even when the return mechanism is attached to the front portion of the seat, various changes can be made such as adjusting the repulsive force by changing the position of one end of the resin spring shown in the present embodiment. That is, the total length distance between one end of the resin spring and the leg to which the other end of the resin spring is attached can be set short or long.

  The left and right frames 3A and 3B may be tilted at different angles. In this case, it is preferable that the horizontal member provided between the left and right frames has elasticity that allows the left and right frames 3A and 3B to tilt at different angles. In such a case, if the reclining operation is performed in a state where the seated person is tilted to the right, the right frame 3A performs a greater scale operation than the left frame 3B, and the rear region 9 of the seat 4 The amount of subsidence on the right side can be greater than the amount of subsidence on the left side. Similarly, if the reclining operation is performed in a state where the seated person is tilted to the left, the left frame 3B performs a balance operation more greatly than the right frame 3A, and the left side of the rear region 9 of the seat 4 sinks. The amount can be greater than the amount of sinking on the right side.

  In addition, various changes may be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Chair 2 ... Leg body 20 ... Axes 3A, 3B ... Frame 4 ... Seat 6 ... Rotation restricting mechanism 7 ... Return mechanism 8 ... Front area 9 ... Rear area

Claims (7)

A chair comprising a leg, a seat support portion supported by the leg, and a seat positioned on the seat support portion,
The seat support portion is pivotally supported by a leg so that the balance support operation can be integrally performed around a single axis extending in the left-right direction, and the balance operation of the seat support portion is within a certain range. It is provided with a restricting mechanism for restricting, and the seat is configured such that the rear region can sink downward by elastic deformation with respect to the front region beyond the rotational range by the balance operation of the seat support portion. The chair is characterized by being. The seat support portion has rigidity, the front region of the seat is supported so as not to tilt relative to the seat support portion in the front-rear direction, and a load is applied to the rear region of the seat. The chair according to claim 1, wherein the rear region sinks with respect to the seat support portion only when. The chair according to claim 1 or 2, wherein a seating surface in a rear region of the seat is configured to be inclined in the left-right direction by elastic deformation of the seat. 3. The seat according to claim 1, 2, or 3, wherein a stretched fabric is stretched between left and right frame portions that can be elastically deformed, and the left and right frame portions sink independently of the seat support portion. 3. The chair according to 3. The seat support portion is elastically deformable, and the rear portion corresponding to the rear region of the seat exceeds the rotation range by the balance operation of the seat support portion and corresponds to the front region of the seat. The chair according to claim 1, wherein the chair is configured to be able to sink downward by its own deformation with respect to the portion. 6. The chair according to claim 1, further comprising a return mechanism that urges the seat support portion to rotate forward. The chair according to claim 6, wherein the return mechanism is mainly composed of a single leaf spring that biases the seat support portion forward.

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