chair

Abstract

To provide a chair in which a seat support part can be easily attached / detached to / from a support base part.SOLUTION: A seat support part 1 of a chair includes: a front shaft holding part for holding a front shaft j2; and an engaged part 1k that engages with a back support part L which is a structure provided on a back of the front shaft holding part and supported to a support base part B. Between the back support part L and the seat support part 1, an intermediate member U for restricting detachment of the seat support part 1 from the back support part L is provided in an attachable / detachable manner without using a stopper. With this configuration, the seat support part 1 can be easily attached / detached to / from the support base part B.SELECTED DRAWING: Figure 87

Description

Technical Field

[0001] The present invention relates to a chair.

Background Art

[0002] In recent industries, especially in accordance with the efforts towards SDGs, product development friendly to the global environment based on a configuration that can be easily disassembled is required, and the field of chairs is no exception.

[0003] Also, from the perspective of suppressing the spread of infectious diseases such as the novel coronavirus, there are many users who work using a chair at home, and a configuration that allows an individual to easily disassemble the chair is required.

[0004] Conventionally, in order to enable separate disposal considering the environment, etc., inventions have been made in which the components constituting the chair are configured to be easily disassembled (for example, see Patent Document 1).

[0005] However, those with conventional configurations actually required operations such as removing screws for disassembly or applying excessive force that involves danger during the operation of detaching members, and it could not be said that anyone could easily disassemble it.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made paying attention to the above circumstances, and at least, an object thereof is to provide a chair in which a seating body can be easily attached to and detached from a support base.

Means for Solving the Problems

[0008] In other words, the present invention has the following configuration.

[0009] The invention described in claim 1 is a chair comprising a support base supported by legs and a seat supported by the support base via a front axis, wherein the seat comprises a seat body having a seat surface and a seat support body that supports the seat body, the seat support body comprises a front axis holding portion capable of holding the front axis and an engaged portion disposed after the front axis holding portion and engaging with the support base or a structure supported by the support base, and an intermediate member capable of restricting the seat support body from detaching from the support base or the structure is detachably disposed between the support base or the structure and the seat support body without the use of fasteners.

[0010] The invention described in claim 2 is the chair according to claim 1, wherein a spring member is interposed between the seat support and the intermediate member, and the spring member biases the intermediate member in a direction that engages with the support base or the structure.

[0011] The invention described in claim 3 is a chair according to claim 2, wherein the intermediate member can be released from engagement with the support base or the structure by being pressed in a direction opposite to the biasing force of the spring member, and is configured to be detachable from the support base or the structure and the seat support when the engagement is released.

[0012] The invention described in claim 4 is the chair according to claim 3, wherein the seat support is rotatable around the front axis such that its rear end springs up after the intermediate member is detached, and the front axis holding portion is detachable from the front axis only when the seat support is changed to a predetermined springed-up position.

[0013] The invention described in claim 5 is a chair according to claim 4, wherein the support base is provided with a pair of grooves on the left and right sides that extend in the vertical direction and are open toward the outside, the seat support is provided with a pair of restricting protrusions on the left and right sides that protrude toward the inside, the seat support is configured such that when the seat support is restricted from detaching by the intermediate member, the restricting protrusions are located within the grooves and the front shaft holding portion cannot be detached forward relative to the front shaft, and the seat support is configured such that when the seat support assumes the predetermined flipped-up position, the restricting protrusions are located outside the grooves and the front shaft holding portion can be detached forward relative to the front shaft.

[0014] The invention described in claim 6 is the chair according to claim 1, wherein the structure is a back support rotatably supported with respect to the support base, the engaged portion engages with a seat engaging portion provided on the back support, and the intermediate member is disposed between the back support and the seat support.

[0015] The invention described in claim 7 is the chair according to claim 1, wherein the seat is configured to be tiltable around the front axis between a normal position and a forward-leaning position that is more tilted forward than the normal position, and the engaged portion engages with the support base or the structure when the normal position is adopted.

[0016] The invention described in claim 8 is the chair according to claim 2, wherein the intermediate member comprises an intermediate member body having one spring receiving portion that receives one end of the spring member, and an arm portion extending from the intermediate member body and capable of engaging with the support base or the structure, the seat receiving body having another spring receiving portion that receives the other end of the spring member, the one spring receiving portion being provided facing downward, and the other spring receiving portion being provided facing upward.

[0017] The invention described in claim 9 is the chair according to claim 8, wherein the seat support is provided with a recess that is open upward and includes the other spring support portion, forming a space in which the intermediate member body is disposed.

[0018] The invention according to claim 10 is a chair in which the seating body is provided with a recess that is open downward and in which the support base is disposed, and an arm passage hole through which the arm portion can pass is provided between the recess and the recess. The chair according to claim 9.

Effect of the Invention

[0019] As described above, according to the present invention, it is possible to provide at least a chair in which the seating body can be easily attached to and detached from the support base.

Brief Description of the Drawings

[0020] [Figure 1] Perspective view showing an embodiment of the present invention. [Figure 2] Front view of the embodiment. [Figure 3] Rear view of the embodiment. [Figure 4] Left side view of the embodiment. [Figure 5] Right side view of the embodiment. [Figure 6] Plan view of the embodiment. [Figure 7] Bottom view of the embodiment. [Figure 8] Exploded perspective view of the embodiment. [Figure 9] Exploded perspective view of the embodiment. [Figure 10] Perspective view from the rear of the embodiment. [Figure 11] Rear view of the backrest in the embodiment. [Figure 12] Left side view of the backrest in the embodiment. [Figure 13] Bottom view of the backrest in the embodiment. [Figure 14] Central longitudinal sectional view of the backrest in the embodiment. [Figure 15] Enlarged view of the lower part in FIG. 14. [Figure 16] Exploded perspective view of the backrest in the embodiment. [Figure 17] A rear view of the same embodiment, with a portion of the back upholstery cut away. [Figure 18] A front view showing a portion of the back upholstery in the same embodiment, with a section cut away. [Figure 19] Perspective views of the first and second strip-shaped members in the same embodiment. [Figure 20] A bottom view of the backrest body in the same embodiment. [Figure 21] A perspective view of the back support in the same embodiment. [Figure 22] An exploded perspective view of the back support in the same embodiment. [Figure 23] A plan view illustrating the operation of the operating member in the same embodiment. [Figure 24] A plan view illustrating the operation of the operating member in the same embodiment. [Figure 25] A plan view illustrating the operation of the operating member in the same embodiment. [Figure 26] A plan view illustrating the operation of the operating member in the same embodiment. [Figure 27] View in the direction of the arrow in the X direction in Figure 4. [Figure 28] A perspective view of the seat support in the same embodiment. [Figure 29] A plan view of the seat support in the same embodiment. [Figure 30] An enlarged perspective view of the rear of the seat support in the same embodiment. [Figure 31] Front view of the seat support in the same embodiment. [Figure 32] Rear view of the seat support in the same embodiment. [Figure 33] Left side view of the seat support in the same embodiment. [Figure 34] Right side view of the seat support in the same embodiment. [Figure 35] A perspective view from below of the seat body in the same embodiment. [Figure 36] A central cross-sectional view of the seat body in the same embodiment. [Figure 37] A central vertical cross-sectional view of the seat body in the same embodiment. [Figure 38]A plan view of the shell body in the same embodiment. [Figure 39] A bottom view of the shell body in the same embodiment. [Figure 40] Front view of the shell body in the same embodiment. [Figure 41] Rear view of the shell body in the same embodiment. [Figure 42] Right side view of the shell body in the same embodiment. [Figure 43] A cross-sectional view illustrating the mounting of the seat body to the seat support in the same embodiment. [Figure 44] A cross-sectional view illustrating the mounting of the seat body to the seat support in the same embodiment. [Figure 45] A cross-sectional view illustrating the mounting of the seat body to the seat support in the same embodiment. [Figure 46] A plan cross-sectional view illustrating the mounting of the seat body to the seat support in the same embodiment. [Figure 47] A plan cross-sectional view illustrating the mounting of the seat body to the seat support in the same embodiment. [Figure 48] A diagram illustrating the method for forming an opening in the same embodiment. [Figure 49] A diagram illustrating the method for forming an opening in the same embodiment. [Figure 50] A diagram illustrating the method for forming an opening in the same embodiment. [Figure 51] A diagram illustrating the method for forming an opening in the same embodiment. [Figure 52] A diagram illustrating the method for forming an opening in the same embodiment. [Figure 53] An enlarged view of the same embodiment after the opening has been formed. [Figure 54] Right side view of the same embodiment (back and seat tilted backward). [Figure 55] Right side view of the same embodiment (seat tilted forward). [Figure 56] A plan view of the support base in the same embodiment. [Figure 57] A bottom view of the support base in the same embodiment. [Figure 58] Left side view of the support base in the same embodiment [Figure 59] Right side view of the support base in the same embodiment. [Figure 60] A perspective view of the support base in the same embodiment. [Figure 61] An exploded perspective view of the same embodiment. [Figure 62] An exploded perspective view of the same embodiment. [Figure 63] A plan view of the same embodiment. [Figure 64] A partially enlarged longitudinal cross-sectional view of the leg / support base in the same embodiment. [Figure 65] A partially enlarged longitudinal cross-sectional view of the leg / support base in the same embodiment. [Figure 66] A partially enlarged longitudinal cross-sectional view of the leg / support base in the same embodiment. [Figure 67] A partially enlarged longitudinal cross-sectional view of the reaction force generating body and support member in the same embodiment. [Figure 68] A partially enlarged longitudinal section view corresponding to the cutting position in Figure 67 in the same embodiment. [Figure 69] An exploded perspective view of the reaction force generating body and support member in the same embodiment. [Figure 70] A rearward perspective view of the support member in the same embodiment. [Figure 71] A cross-sectional view illustrating the legs, support base, and lifting / lowering operation lever in the same embodiment. [Figure 72] A cross-sectional view illustrating the legs, support base, and lifting / lowering operation lever in the same embodiment. [Figure 73] Cross-sectional view of line AA in Figure 2. [Figure 74] A longitudinal cross-sectional view of the back and seat in a reclined position, corresponding to the cutting position in Figure 73 of the same embodiment. [Figure 75] A longitudinal cross-sectional view of the seated forward-tilting posture corresponding to the cutting position in Figure 73 of the same embodiment. [Figure 76] Cross-sectional view of line BB in Figure 29. [Figure 77] A cross-sectional view of the seated forward-leaning posture corresponding to the cutting position in Figure 76 of the same embodiment. [Figure 78] A longitudinal cross-sectional view of the same embodiment. [Figure 79] A longitudinal cross-sectional view of the seated forward-tilting posture corresponding to the cutting position in Figure 78 of the same embodiment. [Figure 80] Cross-sectional view of line CC in Figure 84. [Figure 81] A cross-sectional view of the seated forward-leaning posture corresponding to the cutting position in Figure 80 of the same embodiment. [Figure 82] An exploded perspective view of the same embodiment. [Figure 83] A partially enlarged plan view of the same embodiment. [Figure 84] A bottom view of the same embodiment. [Figure 85] A perspective view of the same embodiment. [Figure 86] A central longitudinal section view of the same embodiment. [Figure 87] A central vertical cross-sectional view corresponding to the cutting position in Figure 86, illustrating the process of detaching the intermediate member in the same embodiment. [Figure 88] Front view of the intermediate member in the same embodiment. [Figure 89] Rear view of the intermediate member in the same embodiment. [Figure 90] A plan view of the intermediate member in the same embodiment. [Figure 91] A bottom view of the intermediate member in the same embodiment. [Figure 92] A right side view of the intermediate member in the same embodiment. [Figure 93] A perspective view of the intermediate member in the same embodiment. [Figure 94] A longitudinal cross-sectional view of the seat in the flipped-up position corresponding to the cutting position in Figure 78 of the same embodiment. [Figure 95] Figure 78 shows the flipped-up position of the seat corresponding to the cutting position in the same embodiment, and a vertical cross-sectional view of the seat detached from the support base. [Modes for carrying out the invention]

[0021] One embodiment of the present invention will be described below with reference to Figures 1 to 95.

[0022] The chair comprises legs A, a support base B supported by legs A, a seat C supported by support base B, a back support L supported by support base B, and a backrest M supported by back support L.

[0023] The seat C is positioned on the support base B and is configured to be able to assume a normal position (ps), a forward-leaning position (pf) that is more inclined forward than the normal position (ps), and a backward-leaning position (pr) that is more inclined backward than the normal position (ps). A reaction force generating body R is provided between the support base B and the back support L, which can bias the back support L in the direction of the normal position (ps).

[0024] The backrest M is supported on the support base B via a back support L so as to be able to tilt backward. That is, the backrest M and the back support L can assume a normal position (ps) and a tilted position (pr) that is more backward than the normal position (ps) relative to the support base B.

[0025] The chair is equipped with a weight-sensing rocking mechanism that, in conjunction with the backward tilting movement of the back support L linked to the backrest M, can lift the front and front-to-back center of the seat C upward, and can also tilt and move the entire seat C backward.

[0026] The chair is equipped with a seat tilt mechanism that allows the seat to be rotated forward around the front axis j2 by shifting the seating load towards the front part of the seat C, that is, the part of the seat C in front of the front axis j2, thereby transitioning to a forward-leaning posture (pf).

[0027] The following describes in detail each component of the chair in this embodiment.

[0028] <<Legs A>> Leg A comprises multiple leg blades a1 equipped with casters at their lower ends, and a leg support column a2 that rises from the point where the upper ends of the leg blades a1 converge.

[0029] In this embodiment, leg A is configured with an obstructing member that can prevent rotation in a predetermined direction relative to the support base B, so that the lifting operation lever V for extending and retracting the leg column a2 in the vertical direction cannot assume a detachable position (SR) that allows it to detach from the support base B.

[0030] <Leg support a2> The leg support column a2 is configured to be extendable and retractable in the vertical direction.

[0031] The leg support a2 extends vertically. The leg support a2 includes a gas cylinder ag that can adjust the vertical position of the seat C.

[0032] The gas cylinder ag has a known configuration, comprising a cylinder portion a21 provided at the lower part of the leg support column a2, a lifting rod a22 that can move up and down relative to the cylinder portion a21, and an operating member a23 that protrudes from the upper end of the lifting rod a22 so as to be able to extend and retract in the vertical direction, and when pressed downward, makes the gas sealed inside flowable, thereby making the lifting rod a22 able to move up and down.

[0033] The lifting rod a22 is cylindrical in shape. The outer surface of the upper part of the lifting rod a22, which is the upper part of the leg support a2, is tapered. That is, the upper part of the lifting rod a22 is formed so that its diameter gradually decreases towards the top.

[0034] The upper part of the lifting rod a22 is designed to fit into the fitting hole Ba, which is the leg connecting part of the support base B. The fitting hole Ba of the support base B into which the lifting rod a22 is fitted is shaped to allow for a tight fit over the upper part of the lifting rod a22.

[0035] The operating member a23 can be pressed downward by the lifting / lowering operation lever V, which is an operating lever rotatably supported on the lever support portion b13 of the support base B.

[0036] <<Support base B>> Support base B is attached to the top of leg A.

[0037] The support base B is supported by the leg A so that its vertical position can be changed and it can also rotate. The support base B is integrally molded from metal. The support base B as a whole has a box shape that is elongated in the front-to-back direction and is open to the top.

[0038] The support base B comprises a bottom wall portion 2 having a downward-facing surface and integrally provided with a mounting portion 2T for supporting the rear end of the reaction force generating body R; left and right side walls b1 that are vertical wall-like and are connected upward from both left and right ends of the bottom wall portion 2; a rear wall b2 erected at the rear end of the bottom wall portion 2 and connecting the rear ends of the left and right side walls b1; and an extended flange b3 extending outward from the rear of the left and right side walls b1.

[0039] <Bottom wall section 2> The bottom wall section 2 comprises a foundation bottom wall 21 with a substantially horizontal bottom surface and a fitting hole Ba which is a leg connecting part that fits into the upper part of the leg support column a2; an inclined bottom wall 22 extending diagonally upward and backward from the rear end of the foundation bottom wall 21; a front bottom wall 23 extending forward from the front end of the foundation bottom wall 21 and positioned to gradually move upward as it moves forward; and a rear bottom wall 24 extending substantially horizontally backward from the rear end of the inclined bottom wall 22.

[0040] The bottom wall portion 2 is provided with a rising structure portion 2S that rises up near the fitting hole Ba, and a mounting portion 2T to which a support member W that engages with the rear end of the reaction force generating body R is attached.

[0041] [Foundation base wall 21] A boss portion 211 is erected on the foundation base wall 21, having a vertically penetrating fitting hole Ba that fits into the upper part of the leg support b2.

[0042] [Sloped bottom wall 22] The inclined bottom wall 22 is provided at an angle so as to be gradually positioned upward toward the rear from the rear end of the foundation bottom wall 21. Because the inclined bottom wall 22 extends upward and backward from the foundation bottom wall 21, it is possible to suitably provide a rear bottom wall 24 at a position higher than the foundation bottom wall 21, where the mounting portion 2T is located.

[0043] [Anterior bottom wall 23] The front bottom wall 23 extends forward from the front end of the foundation bottom wall 21. The front shaft j2, which is inserted into the elongated holes b12 of the left and right side walls b1, is positioned on top of the front bottom wall 23.

[0044] [Rear bottom wall 24] The rear bottom wall 24 extends approximately horizontally to the rear from the rear end of the inclined bottom wall 24. The middle portion of the rear bottom wall 24 in the left-right direction constitutes the bottom wall portion of the mounting section 2T for attaching the support member W.

[0045] The rear bottom wall 24 is positioned higher than the foundation bottom wall 21. The rear bottom wall 24 is provided with an attachment portion 2T for a support member W that supports the rear end of the reaction force generating body R.

[0046] In other words, by positioning the rear bottom wall 24 higher than the foundation bottom wall 21, a configuration for positioning the reaction force generating body R in a horizontal position can be suitably adopted.

[0047] [Rising structure part 2S] The rising structural part 2S is composed of a screw thread hole n4 having a screw groove, which is disposed above the fitting hole Ba.

[0048] The rising structural part 2S is installed adjacent to the front side of the fitting hole Ba so as to rise up. The rising structural part 2S is made of metal and is provided integrally with the boss portion 211 of the foundation bottom wall 21 that forms the fitting hole Ba.

[0049] The rising structure 2S comprises an upright portion 25 that rises up to partially enclose the front part of the fitting hole Ba in a plan view, and a horizontal portion 26 that is installed between the upright portions 25 so as to be located directly above the fitting hole Ba.

[0050] The upright portion 25 is integrally connected to the front of the boss portion 211, which has a fitting hole Ba formed therein. The upright portion 25 has a shape in which the central part in the left-right direction on the rear side is recessed forward.

[0051] In other words, the rear of the upright portion 25 is shaped such that a space is provided directly above the fitting hole Ba, and the horizontal portion 26 can be integrally disposed on top of this space.

[0052] The horizontal section 26 is provided with screw holes n4 that penetrate in a substantially vertical direction. The horizontal section 26 is integrally connected to the upright section 25.

[0053] The standing structure 2S provided in the chair of this embodiment is provided solely to enable the worker to safely perform the task of separating the leg A and the support base B.

[0054] The worker can insert a screw v4 of a size that matches the screw hole n4 into the horizontal portion 26 of the vertical structure 2S by screwing it in from above downwards using a general tool.

[0055] Furthermore, the upper part of the leg support b2, which is positioned directly below the screw hole n4, is configured to be pressed downward by a screw v4 that screws in and enters downward, using the rising structure 2S, which is integrally provided with the support base B, as a foothold.

[0056] More specifically, the screw v4, which is screwed into the screw hole n4, rotates and descends guided by the screw groove of the screw hole n4, so that the lower end of the screw v4 can press downwards against the outer peripheral edge of the upper end of the lifting rod a22 that constitutes the leg support b2.

[0057] The rising structure 2S is used to detach the leg A from the support base B. When the chair is completed, the fitting hole Ba of the support base B and the upper part of the lifting rod a22, which is the upper part of the leg support a2, are firmly fitted together.

[0058] In this embodiment, the pressing force of the screw v4, which can screw into the screw threading hole n4 of the rising structure 2S, is used to relieve or alleviate the tight fit between the fitting hole Ba and the lifting rod a22.

[0059] The screw v4, which rotates and descends along the screw groove, can apply a strong and continuous pressing force to the lifting rod a22, thereby effectively disabling or easing the tight fit between the fitting hole Ba and the lifting rod a22.

[0060] In other words, the chair of this embodiment is provided with a fitting degree relaxation structure that relaxes the degree of fitting between the leg support a2 and the support base B. The fitting degree relaxation structure is provided with a screw thread hole n4 having a screw groove on the fitting hole Ba of the support base B, and the screw v4 screwed into the screw thread hole n4 can press the upper part of the leg support a2 downward.

[0061] The screw v4 can be any screw that conforms to the specifications of the screw insertion hole n4 and has a certain length in the vertical direction. In this embodiment, when the chair is disassembled, the screw v5 used to fix the support member W to the mounting part 2T of the support base B can be removed and then reused as a screw v4 to be screwed into the screw threading hole n4 of the rising structure part 2S.

[0062] [Mounting part 2T] The mounting portion 2T is located at the rear of the support base B. The mounting portion 2T is the part to which the support member W that supports the rear end of the reaction force generating body R is attached.

[0063] The mounting section 2T comprises a rear bottom wall 24 which is a bottom wall portion having a first screw insertion hole v5 through which a screw v5 for attaching the support member W is inserted; a rear wall portion 27 which is erected upward from the rear of the rear bottom wall 24 and has an inclined surface nm with its front surface tilted backward; and left and right side wall portions 28 which extend forward from both left and right ends of the rear wall portion 27 and are erected upward from both left and right sides of the rear wall 24.

[0064] The rear bottom wall 24 is roughly in the shape of a horizontal plate. The rear bottom wall 24 is provided with a first screw insertion hole h51, which is a screw insertion hole that penetrates vertically through the center in the left-right direction. The first screw insertion hole h51 is formed as an elongated hole that is longitudinal in the front-rear direction.

[0065] The bottom wall portion w11 of the support member W, which is pulled toward the rear bottom wall 24 by the movement of the hexagonal nut n5 screwed onto the screw v5, comes into contact with the rear bottom wall 24.

[0066] The rear wall portion 27 is in the shape of an upright plate and is erected so as to be inclined backward relative to the rear bottom wall 24. The front surface of the rear wall portion 27 is an inclined surface nm that abuts against the rear wall portion w13 of the support member W.

[0067] The inclined surface nm is set to gradually move away from the other end of the reaction force generating body R, i.e., the front end of the front member r2, as it moves from the fixed position (lower position) where it is tightened against the rear bottom wall 24 towards the non-fixed position, i.e., upward from the lower position.

[0068] The left and right side wall sections 28 are erected on the rear bottom wall 24 and their rear ends are connected to the rear wall section 27. The left and right side wall sections 28 play a role in defining the left-right position of the support member W and in ensuring the strength of the rear wall section 27, which serves as a footing that receives a biasing force from the reaction force generating body R.

[0069] <Left and right side walls b1> The left and right side walls b1 are erected from both the left and right ends of the bottom wall section 2, namely the foundation bottom wall 21, the inclined bottom wall 22, the front bottom wall 23, and the rear bottom wall 24. The left and right side walls b1 extend in a substantially straight line in the front-to-back direction.

[0070] The left and right side walls b1 are provided with a shaft hole b11 that penetrates in the left-right direction and is located at a front-rear position corresponding to the rear of the foundation bottom wall 21, capable of rotatably holding the main shaft j1; an elongated hole b12 that penetrates in the left-right direction and is located at a front-rear position corresponding to the front of the front bottom wall 23, capable of holding the front shaft j2 for supporting the front of the seat C so that it can slide back and forth and up and down; a lever support portion b13 provided only on the left side wall b1, capable of rotatably supporting a lifting operation lever V for raising and lowering the seat C; a groove portion b14 provided in front of the elongated hole b12 along the elongated hole b12 and open outward; and an axis movement restricting portion b15 provided at the upper end of the intermediate part in the front-rear direction so as to protrude in a mountain shape, which prohibits the forward and downward movement of the seat engagement shaft j3 provided on the back support L.

[0071] [Shaft hole b11] The axial hole b11 is for supporting the main shaft j1, which rotatably supports the back support L relative to the support base B.

[0072] The left and right side walls b1 are integrally provided with outwardly projecting boss-like portions b4 that form part of the shaft hole b11. By providing the boss-like portions b4 on the left and right side walls b1 in relation to the shaft hole b11, a region in the left-right direction that can directly support the main shaft j1 is secured that is longer than the width dimension of the left and right side walls b1. The boss-like portions b4 are connected to the front end of the extended flange b3.

[0073] [Long hole b12] The elongated hole b12 extends diagonally such that, in a side view, its lower end is positioned in front of its upper end. A sleeve member g, made of synthetic resin, is fitted into the elongated hole b12 to allow for smooth sliding against the front shaft j2. The front shaft j2 is supported by the elongated hole b12 via the sleeve member g.

[0074] In other words, the support base B is provided with an elongated hole b12 and a sleeve member g with excellent sliding properties fitted into the elongated hole b12, which allows the front shaft j2 to be supported in a slidable manner.

[0075] [Lever support part b13] The lever support b13 pivotally supports the lifting operation lever V so that it can be operated like a flap. The lifting operation lever V acts on the gas cylinder ag, allowing the leg support column a2 to be extended and retracted in the vertical direction.

[0076] The lever support portion b13 comprises a pair of front and rear support wall portions b15 projecting outward from the left side wall b1 in a manner substantially perpendicular to the left side wall b1, and a pair of shaft portions j4 projecting in directions toward each other from the opposing inner surfaces of the pair of support wall portions b15.

[0077] A space is formed between the front and rear support wall sections b15 for which a lifting operation lever V is installed.

[0078] The pair of shaft portions j4 are positioned to protrude in opposite directions, that is, in directions that are aligned and approaching each other. Each shaft portion j4 has a narrow portion j41 that is narrow in the left-right direction, which is perpendicular to the axis, and a wide portion j42 that is wider in the up-down direction, which is also perpendicular to the axis (wider than the narrow portion j41). In other words, the shaft portion j4 is configured so that its width is shorter than its height.

[0079] [Groove b14] The groove b14 is provided extending diagonally in the same direction as the elongated hole b12, that is, in a side view, the lower end is positioned in front of the upper end.

[0080] A regulating projection 1t is provided on the seating body 1 in order to regulate the position of the seating body 1 relative to the support base B in the groove b14.

[0081] <Back wall b2> The rear wall b2 is erected from the rear end of the rear bottom wall 24. The rear wall b2 connects the rear ends of the left and right side walls b1. The middle section of the rear wall b2 in the left-right direction constitutes the rear wall portion 27 of the mounting section 2T for attaching the support member W.

[0082] <Extended tsuba b3> The extended flange b3 extends outward beyond the left and right side walls b1.

[0083] The extension portion b3 is provided with a damper mounting portion b31 for attaching a damper gx that the back support base 4 contacts when the back support L is tilted backward. The damper gx attached to the damper mounting portion b31 can be engaged with engaging projections 41c that protrude inward from the upper ends of the left and right arm bodies 411, respectively.

[0084] The front lower part of the support base B, which has the above configuration, is covered by a support base cover X1 made of synthetic resin.

[0085] <<Lifting / Lowering Operation Lever V>> The lifting / lowering lever V is a single unit integrally formed from synthetic resin. The lifting / lowering lever V is configured to be attachable to the lever support portion b13 of the support base B without the use of fasteners such as screws.

[0086] The lifting lever V is rotatably supported with respect to the support base B. More specifically, the lifting lever V is rotatably supported with respect to a lever support portion b13 provided on the left side wall b1 of the support base B.

[0087] The lifting lever V allows the user to extend or retract the leg support a2 of leg A in the vertical direction in order to raise or lower the seat C.

[0088] The lifting lever V is configured such that when the operating end vc is moved upward by the user, the bearing vb rotates around the shaft j4 of the support base B with which it is engaged, and the rotating end va moves downward to push down the operating member a23 located at the upper end of the leg support a2.

[0089] The lifting and lowering lever V comprises a lever body vh which is plate-shaped and extends in the left-right direction and has an operating end vc at its tip, a base end upright portion vi which extends upward from the base end of the lever body vh, an inward extension portion vm which extends inward from the upper end of the base end upright portion vi and has a rotating end va at its tip which can abut against the leg support column a2, and a bearing portion vb provided between the base end upright portion vi and the inward extension portion vm.

[0090] <Lever body vh> The lever body vh has a curved shape that follows the outer surface of the seating body 1, that is, a partially arc-shaped curve that is convex downwards when viewed from the front. The tip of the lever body vh is the operating end vc, which is mainly subjected to the operating force from the user's fingers. When not subjected to operating force from the user, the operating end vc is configured to be in the lower limit position due to its own weight.

[0091] <Proximal end section vi> The base-end erection portion vi is a roughly rectangular prism-shaped structure erected from the base end portion of the lever body vh.

[0092] <Inward extension part vm> The inwardly extending portion vm is cantilevered to the base-end upright portion vi. The inwardly extending portion vm has approximately the same width dimension as the base-end upright portion vi at its base end, and is formed so that its width gradually decreases towards the tip end located inside the support base B.

[0093] The tip of the inwardly extending portion vm is a pivot end portion va that can press down on the operating member a23 provided on the leg support column a2.

[0094] <Bearing part vb> The bearing portion vb is provided at the front and rear of the boundary portion between the base end erect portion vi and the inwardly extending portion vm, facing in opposite directions.

[0095] The bearing portions vb are provided in pairs on both sides, i.e., front and rear, of the lifting operation lever V. One bearing portion vb faces forward, and the other bearing portion vb faces rear. The bearing portions vb are provided near the inner edge of the boundary portion between the base end erected portion vi and the inwardly extended portion vm.

[0096] The front and rear bearing portions vb are recessed in opposite directions. The front and rear bearing portions vb engage with a pair of front and rear shaft portions j4 that protrude toward each other at the lever support portion b13 of the support base B, thereby allowing the entire lifting operation lever V to rotate around the shaft portion j4.

[0097] The front and rear pair of bearing sections vb are provided with notches vd, which are escape passages that allow the front and rear pair of shaft sections j4 to be removed only when the lifting operation lever V takes a predetermined detachable position (SR) by moving the lifting operation lever V.

[0098] The notch vd in the bearing portion vb is set to a width dimension that allows the narrow portion j41 of the shaft portion j4 of the lever support portion v13 to pass through. On the other hand, the notch vd is set to a width dimension that prevents the wide portion j42 of the shaft portion j4 from passing through.

[0099] In this embodiment, the notch vd is positioned so that when the lifting operation lever V takes a detachable position (SR), the shaft portion j4 can move linearly relative to it in the vertical direction and detach from the bearing portion vb to the outside.

[0100] <<Regarding the attachment of the lifting / lowering lever V to the support base B>> This section describes the mounting structure for the lifting lever V, which is attached to the support base B that constitutes the chair.

[0101] In this embodiment, the chair's lifting lever V can assume a detachable position (SR) in which it can be detached from the support base B, and a non-detachable position (SH) in which it cannot be detached from the support base B.

[0102] <Regarding the Non-Detachable Posture (SH)> The lifting lever V is designed to only be able to assume a non-detachable position (SH) relative to the support base B when the obstructing member, leg A, is fitted into the support base B.

[0103] In other words, the lifting lever V cannot assume a detachable position (SR) when leg A is properly attached to support base B.

[0104] The chair is configured such that, after the lifting lever V is supported by the lever support b13 of the support base B, the leg support a2 of the leg A, which is an obstructing member, is attached to the support base B, thereby restricting the range of rotation of the lifting lever V due to the presence of the upper part of the leg support a2.

[0105] The lifting lever V is restricted by the upper part of the leg support column a2 to only rotate within the range of the non-detachable position (SH), and as a result of being prevented from rotating further, it is not possible to assume the detachable position (SR).

[0106] In other words, when the leg A is attached to the support base B, the pivot end va of the lifting operation lever V will come into contact with the upper part of the leg support a2 in the non-detachable position (SH), and the pivot end va will be prevented from moving any further downward by the presence of the leg support a2. For this reason, the lifting operation lever V cannot be detached from the support base B unless the leg A is removed from the support base B.

[0107] <Regarding the detachable posture (SR)> The lifting lever V can only assume a detachable position (SR) that allows it to detach from the support base B if the obstructing member, leg A, is not fitted into the support base B.

[0108] The chair is configured such that by removing the leg support column a2 of the leg A from the support base B on which the lifting operation lever V is supported, the range of rotation of the lifting operation lever V is no longer restricted by the upper part of the leg support column a2, and the lifting operation lever V can be changed to a detachable position (SR).

[0109] In other words, when the leg A is detached from the support base B, the rotating end va of the lifting operation lever V can enter the inside of the fitting hole Ba until it can assume a detachable position (SR).

[0110] Furthermore, when the lifting lever V in the detachable position (SR) is moved relative to the support base B by the user in a direction away from it (upward vertical direction), the narrow portion j41 of the shaft portion j4 can pass through the notch vd of the bearing portion vb, and the lifting lever V can be detached from the support base B.

[0111] <<Reaction force generator R>> The reaction force generating element R, also known as a reaction spring, is interposed between the support base B and the back support L. The reaction force generating element R is arranged to be expandable and contractible in the front-rear direction.

[0112] The reaction force generating element R is a compression spring type in which one end, i.e., the rear end, is attached to the support base B via a support member W, and the other end, i.e., the front end, is attached to the seat engagement axis j3 of the back support L.

[0113] The reaction force generating body R can directly bias the seat engagement axis j3 forward. The reaction force generating body R is set to assume a substantially horizontal position extending in the front-rear direction when the seat C and back support L are in the normal position (ps). In the normal position (ps), the reaction force generating body R is in a horizontal position between the support base B and the seat engagement axis j3 of the back support L.

[0114] In this embodiment, the reaction force generating body R can use the support base B as a base to bias the left-right central portion of the seat engagement shaft j3 forward. The seat engagement shaft j3 abuts against the axial movement restricting portions b15 of the left and right side walls b1 of the support base B, preventing it from moving further forward and downward.

[0115] In other words, the contact of the seat engagement axis j3 with the support base B prevents the forward rotation of the back support L around the main axis j1, thereby defining the normal position (ps) of the back support L.

[0116] Furthermore, the reaction force generating body R is gradually compressed in the front-rear direction and tilts backward as the seat engagement axis j3 moves rearward and upward as the back support L and seat C transition from the normal position (ps) to the reclined position (pr).

[0117] The reaction force generating element R is mainly composed of a metal coil spring r1 (compression coil spring), which is a spring material.

[0118] In this embodiment, based on the structure of a weight-sensing rocking mechanism in which the seated person presses the seat engagement axis j3 forward and downward through the seat C, the seated person's weight assists the reaction force in the normal posture (ps) direction against the backward tilting movement of the backrest M. For this reason, a relatively small and lightweight coil spring r1 is used as the reaction force generating body R in this embodiment.

[0119] The reaction force generating body R comprises a coil spring r1 made of metal, a front member r2 attached to the front of the coil spring r1, a rear member r3 attached to the rear of the coil spring r1, and a posture-holding shaft r4 whose front end is inserted into a holding hole provided in the front member r2 and whose rear end is inserted into a holding hole provided in the rear member r3, thereby being able to hold the posture of the front member r2 and the rear member r3.

[0120] The tip of the front member r2 is connected to the seat engagement shaft j3 so as to be rotatable relative to it. The tip of the front member r2 is provided with an engagement recess r21 that extends in the left-right direction so as to be fitted onto the cylindrical seat engagement shaft j3.

[0121] The rear end of the rear member r3 is supported by the support base B via the support member W. The rear end of the rear member r3 is connected to the support member W so as to be rotatable relative to it. The rear end of the rear member r3 is provided with an engagement recess r31 extending in the left-right direction, and a pair of upper and lower vertical engagement recesses r32 provided above and below the engagement recess r31, with their left-right positions aligned.

[0122] The engaging recess r31 of the rear member r3 engages with a pair of left and right axial protrusions w15 that protrude from the upper and lower middle portion of the front wall portion w12 of the support member body w1. The pair of left and right axial protrusions w15 protrude forward in a partially disc shape when viewed from the side.

[0123] The vertical engagement recess r32 of the rear member r3 engages with a mountain-shaped projection w16 that protrudes from the left-right center of the front wall portion w12 of the support member body w1. The mountain-shaped projection w16 is provided to extend in the vertical direction.

[0124] Although the front member r2 and the rear member r3 are in different orientations, they are of the same shape.

[0125] <<Support member W>> The support member W comprises a support member body w1 made of synthetic resin, having a portion on the front side that can engage with the reaction force generating body R and an inclined rear portion wm on the rear side, and a hexagonal nut n5 which is a nut that is freely disposed inside the support member body w1.

[0126] The support member W is fixed by a screw v5 to the mounting portion 2T which has a first screw insertion hole h51 provided at the rear of the support base B.

[0127] The support member W is configured to be surrounded at a predetermined fixed position by the rear bottom wall 24, the rear wall portion 27, and the left and right side wall portions 28 of the mounting portion 2T of the support base B.

[0128] <Support member body w1> The support member body w1 has a bottom wall portion w11 having a second screw insertion hole h52 through which a screw v5 is inserted, and a peripheral wall portion ws that is erected upward from the peripheral edge of the bottom wall portion w11 and has a nut arrangement space wk inside which a hexagonal nut n5 is housed.

[0129] [Bottom wall part w11] The bottom wall portion w11 is provided with a second screw insertion hole h52 in the center in the left-right direction, which is elongated in the front-rear direction. The lower surface of the bottom wall portion w11 is in contact with the rear bottom wall 24 of the mounting portion 2T when it is fixed in place.

[0130] [Peripheral wall ws] The peripheral wall portion ws comprises a front wall portion w12 that engages with the rear member r3 of the reaction force generating body R, a rear wall portion w13 having an inclined back portion wm that can slide against the inclined surface nm of the rear wall portion 27 at the support base B, and left and right side wall portions w14 that connect the left and right sides of the front wall portion w12 and the rear wall portion w13.

[0131] The front wall portion w12 includes a pair of left and right axial protrusions w15 projecting from the upper and lower intermediate portion so as to engage with the engagement recess r31 of the rear member r3, and a mountain-shaped protrusion w16 projecting from the left and right intermediate portion so as to engage with the vertical engagement recess r32 of the rear member r3.

[0132] The rear wall portion w13 is tilted backward in a side view. The rearward-facing inclined rear portion wm of the rear wall portion w13 is tilted so as to gradually move backward towards the top.

[0133] Each of the left and right side wall sections w14 comprises an outer wall wa and an inner wall wb positioned inside the outer wall wa. The nut placement space wk is composed of the front wall section w12 and the rear wall section w13 of the peripheral wall section ws, and the inner walls wb of the left and right side wall sections w14.

[0134] The hexagonal nut n5, positioned in the nut mounting space wk of the peripheral wall portion w12, is configured to engage with the inner surface of the peripheral wall portion w12 in such a way that lateral movement and horizontal rotation are suppressed. Furthermore, the nut mounting space wk is formed such that its length in the front-to-back direction gradually increases towards the top, thus allowing for front-to-back movement of the hexagonal nut n5.

[0135] <Hexagonal nut n5 (nut)> The hexagonal nut n5 is a known configuration held in the support base body w1. The hexagonal nut n5 has a screw groove and is screwed onto a screw v5 inserted through a first screw insertion hole h51 provided in the support base B, and a second screw insertion hole h52 provided in the bottom wall portion w11 of the support member body w1.

[0136] The hexagonal nut n5 engages with the circumferential wall portion w12 in such a way that movement in the left-right direction and horizontal rotation are suppressed, and also engages with the circumferential wall portion w12 in such a way that movement in the front-rear direction is permitted.

[0137] <Regarding the operation of the support member W for attaching the reaction force generating body R> The support member W for mounting the reaction force generating body R is attached to the mounting portion 2T in the following manner.

[0138] First, the front member r2 of the reaction force generating body R is engaged with the seat engagement shaft j3, and the rear member r3 is engaged with the front wall portion w12 of the support member body w1.

[0139] Next, the screw v5, which is inserted from bottom to top through the first screw insertion hole h51 of the support base B and the second screw insertion hole h52 of the support member body w1, is connected (screwed) to the hexagonal nut n5 located inside the support base body w1.

[0140] At this time, the support member W is connected to the rear of the reaction force generating body R, which is not compressed in the front-rear direction. In other words, the support member W is located above and behind the fixed position. The screws v5 inserted through the elongated first and second screw insertion holes h51 and h52 can easily assume a backward-tilted position in order to screw into the hexagonal nut n5.

[0141] After completing the above steps, the worker can complete the installation process simply by rotating the screw v5, without directly touching the potentially dangerous reaction force generating body R or the support member W connected to the reaction force generating body R.

[0142] Next, rotate the screw v5, which is screwed into the hexagonal nut n5, in the first direction (tightening direction).

[0143] When the screw v5 is rotated in the first direction, the hexagonal nut n5 held by the support member body w1 moves downward together with the support member body w1. In other words, the support member W moves towards the rear bottom wall 24 of the mounting portion 2T due to the operator's rotation of the screw v5.

[0144] At this time, as the support member W moves downward, it is biased backward by the reaction force generating body R in such a way that the biasing force gradually increases. That is, as the support member W moves downward and forward, guided by the inclined surface nm of the mounting portion 2T, the reaction force generating body R is gradually compressed between the seat engagement shaft j3 and the support member W, and its biasing force gradually increases.

[0145] As the rotation of the screw v5 continues, the support member W moves smoothly forward and downward, guided by the inclined surface nm while resisting the biasing force of the reaction force generating body R, and eventually reaches a predetermined fixed position.

[0146] In this way, the attachment of the support member W to the mounting portion 2T is completed.

[0147] The removal of the reaction force generating body R and the support member W can be carried out very safely by following the reverse procedure described above.

[0148] In other words, the support member W can be guided and moved (upward) in the non-fixed position direction by rotating the screw v5 in the second direction, engaging with the inclined surface nm. At this time, the support member W moves upward and backward while being guided by the inclined surface nm, as the biasing force of the reaction force generating body R weakens as the hexagonal nut n5 rises.

[0149] The operator can complete the initial steps for disassembling the potentially dangerous reaction force generating element R and support member W simply by rotating the screw v5 in the second direction, without touching the reaction force generating element R or support member W.

[0150] <<Location C>> The seat C is supported by a support base B, which is positioned on top of the leg A. The lower surface of the support base B and the outer circumferential surface of the seat C are configured to be smoothly continuous when viewed from the front.

[0151] The seat C comprises a seat support 1 and a seat body D having an upward-facing seat surface and being detachable from the seat support 1.

[0152] The outer circumferential surfaces of seat C, that is, the outer circumferential surfaces of seat support 1 and seat body D, are smoothly continuous, forming a partially spherical shape.

[0153] <Regarding the forward-tilting configuration of seat C> The front of seat C is supported on the support base B via the front axis j2 so as to be rotatable and movable in the vertical direction. The rear of seat C is supported on the seat engagement axis j3, which is the seat engagement portion of the back support L, a structure supported on the support base B in the normal position (ps). Here, "rear of seat C" supported on the back support L means "behind the front of seat C".

[0154] The seat C is configured to be able to tilt around a front axis j2 supported by the support base B, between a normal position (ps) and a forward-leaning position (pf) that is more tilted forward than the normal position (ps).

[0155] The seat C is provided with an engaged portion 1k that can abut against the seat engaging shaft j3, which is a seat engaging portion provided on the support base B.

[0156] The engaged portion 1k of seat C engages with the seat engagement axis j3 so that it rests on the seat engagement axis j3 when the seat is in the normal position (ps) and the reclined position (pr). The engaged portion 1k of seat C is configured to be spaced upward from the seat engagement axis j3 when the seat is in the forward-tilted position (ps).

[0157] <Seat receiver 1> The seat support body 1 supports the seat body D. The upper surface of the seat support body 1 is configured to engage with the shell body 3 that constitutes the seat body D. In other words, the shell body 3 is mounted on the upper surface of the seat support body 1.

[0158] The seat support body 1 is formed in a shell shape from synthetic resin. The seat support body 1 has a partially spherical shape. The outer surface of the seat support body 1, which is visible to the user, is formed to have a spherical surface shape.

[0159] The outer circumferential surface of the front portion of the seat support 1 is configured to smoothly connect with the lower surface of the front portion of the support base B. Furthermore, the outer circumferential surface of the seat support 1 is configured to smoothly connect with the outer circumferential surface of the seat body D.

[0160] The seat support body 1 is provided with a front shaft holding portion 1m capable of holding both ends of the front shaft j2 supported by the support base B.

[0161] The seat support body 1 includes a recess 11 that is open downwards and in which the support base B and back support L are disposed, a shell body mounting portion 12 which is a seat body mounting portion provided on the upper surface, an upwardly open recess 13 provided in the center in the left-right direction in which the intermediate member U and coil spring Y are disposed, and an arm passage hole 14 which is a vertical communication hole provided between the recess 13 and the recess 11 through which the arm portion u2 of the intermediate member U can pass.

[0162] <Recess 11> The recess 11 is located at the lower part of the center of the seating body 1 in the left-right direction and is open downwards, allowing for the placement of the support base B.

[0163] A recessed space is formed in the recess 11, in which the support base B and the back support L are arranged.

[0164] In the seat support body 1, facing the recessed space of the recess 11, there is a front shaft holding portion 1m capable of holding the front shaft j2, an engaged portion 1k disposed behind the front shaft holding portion 1m that engages with the seat engagement shaft j3 in the normal position (ps) and the reclined position (pr), and separates from the seat engagement shaft j3 in the forward-tilted position (pf), and a regulating projection 1t disposed within the groove b14 provided in the support base B.

[0165] The recess 11 comprises a recess top wall portion 111 having an engaged portion 1k on its lower side that faces the recessed space and into which the seat engagement shaft j3 engages; a recess front wall portion 112 and a recess rear wall portion 113 extending downward from the front and rear of the recess top wall portion 111, respectively; and left and right recess side wall portions 114 extending downward from both the left and right sides of the recess top wall portion 111, respectively.

[0166] The distance between the inner surfaces of the left and right recess side walls 114 is set to be longer than the left-right dimension of the seat engagement axis j3.

[0167] [Front shaft holding part 1m] The front axle holding portion 1m protrudes downward from the front of the recessed top wall portion 111. The front axle holding portions 1m are provided in pairs on both the left and right sides of the recessed top wall portion 111. The left and right front axle holding portions 1m are shaped to hold both the left and right ends of the front axle j2. The left and right front axle holding portions 1m are adjacent to each other, with an axle passage 1r through which the front axle j2 can pass when attaching or detaching the front axle j2.

[0168] [Engaged part 1k] The engaged portion 1k engages with the seat engagement axis j3 of the back support L, which is pivotally supported by the support base B. The engaged portion 1k is provided on the top wall portion 111 of the recess. The engaged portions 1k are provided in pairs on the left and right sides of the front lower part of the recess 13.

[0169] The engaged portion 1k has an upper contact portion 1ku that can contact the upper part of the seat engagement shaft j3 and a rear contact portion 1kr that can contact the rear part of the seat engagement shaft j3. The left and right engaged portions 1k are substantially L-shaped.

[0170] The engaged portion 1k is configured to move toward and away from the seat engagement axis j3 in accordance with the change in the orientation of the seat C.

[0171] The engaged portion 1k engages with the seat engagement shaft j3 when the seat C is in its normal position (ps) and reclined position (pr), and separates from the seat engagement shaft j3 only when the seat C is in a forward-tilted position (pf). In other words, the engaged portion 1k is not designed to constantly hold the seat engagement shaft j3 in an unseparated manner, but is configured to be able to move toward and away from the seat engagement shaft j3.

[0172] [Restrictive protrusion 1t] The restricting projection 1t is designed to prevent the seat body 1 from detaching from the front axis j2 unless it adopts the upward-swinging position (ph), which is the position that detaches the seat support 1 from the front axis j2.

[0173] In other words, the restricting projection 1t engages with the groove b14 of the support base B, and can restrict the forward movement of the seat body 1 relative to the front axis j2 when the seat body 1 is in a position other than a predetermined flipped-up position (ph).

[0174] The restricting projections 1t are provided in pairs on the left and right sides at the front of the recess 11 of the seat support body 1. The restricting projections 1t protrude inward at the location corresponding to the groove b14 of the support base B of the seat support body 1. The restricting projections 1t are inclined so as to be positioned gradually upward toward the rear. The restricting projections 1t are provided protruding from the inner parts of the left and right front axle holding parts 1m.

[0175] <Shell body arrangement section 12> The shell mounting section 12 has a connection part with the shell body 3 of the seat body D, and is provided on the upper part of the seat support 1, that is, the upward-facing part of the seat support 1.

[0176] The rear end of the shell body mounting section 12 is provided with a notch 122 to avoid interference with the operating lever k2 provided on the shell body 3.

[0177] The shell mounting section 12 is provided with a shaped portion that constitutes a detachable engagement structure (central positioning section G, vertical engagement mechanism H, horizontal engagement mechanism I, and reverse return restricting mechanism K) that allows the seat body D to be attached and detached, as will be described in detail later.

[0178] The outer edge 1e of the seat support body 1 is formed so that, in front and rear views, it is gradually positioned downward from both the left and right ends toward the center in the left-right direction (forming a concave shape downwards). In addition, in side views, the outer edge 1e of the seat support body 1 is formed so that it is gradually positioned upward from both the front and rear ends toward the center in the front-rear direction (forming a convex shape upwards).

[0179] The upper end of the seat support periphery wall portion 121, which is erected inward from the outer peripheral edge 1e of the seat support 1, is provided to extend substantially horizontally in the front view, rear view, and side view.

[0180] <Recess 13> The recess 13 is provided on the upper part of the seating body 1 for arranging the intermediate member U and the coil spring Y. The recess 13 is provided in the vicinity of the engaged portion 1k that engages with the seat engagement shaft j3.

[0181] The recess 13 is provided so as to be recessed downward from the central top wall portion 123, which is the upper surface portion of the seating body 1 that constitutes the shell body arrangement portion 12. The recess 13 is open upward and includes the other spring receiving portion 13a which is provided upward for receiving the lower part of the coil spring Y.

[0182] The recess 13 has a space 13s in which the intermediate member body u1 and the coil spring Y are arranged.

[0183] The recess 13 comprises a bottom wall 131 on which the other spring receiving portion 13a facing upward is provided on the upper surface, a front wall 132 connecting the front end of the bottom wall 131 and the central top wall portion 123, a rear wall 133 connecting the rear end of the bottom wall 131 and the central top wall portion 123, and an outer wall 134 connecting the outer end of the bottom wall 131 and the central top wall portion 123.

[0184] The bottom wall 131 of the recess 13 is spaced apart on the left and right so that the arm portion u2 of the intermediate member U can be positioned on the recess 11 side. That is, the bottom wall 131 of the recess 13 is spaced apart on the left and right via the arm passage hole 14.

[0185] <Arm passage hole 14> The arm passage hole 14 is through which the arm portion u2 of the intermediate member u2 can pass. The arm passage hole 14 is provided between the recess 13 and the recess 11. The arm portion u2 of the intermediate member U is positioned in the arm passage hole 14. The arm passage hole 14 allows the intermediate member U, which is held in the recess 13, to move in the vertical direction.

[0186] <Regarding the configuration of the seating body 1 for easy attachment and detachment from the support base B> The seat support 1 is rotatable around the front shaft j2 so that its rear end springs upward after the intermediate member U is detached. The front shaft holding part 1m is configured to detach from the front shaft j2 only when the seat support 1 is changed to a predetermined upward position (ph).

[0187] On the front of the left and right side walls b1 of the support base B, there are pairs of grooves b14 on the left and right sides that extend vertically and open outwards.

[0188] The seat support body 1 has a pair of restrictive projections 1t on the left and right sides, which protrude inward at locations corresponding to the grooves b14 of the support base B. The restrictive projections 1t are located on the inner sides of the left and right front shaft holding portions 1m provided on the seat support body 1.

[0189] When the seat support 1 is restricted from detaching by the intermediate member U (i.e., when the intermediate member U is interposed between the seat support 1 and the seat engagement shaft j3), the restricting projection 1t is located within the groove b14, and the front shaft holding portion 1m is configured to be unable to detach forward relative to the front shaft j2.

[0190] Even if the intermediate member U is not interposed between the seating body 1 and the seating shaft j3, if the predetermined upward position (ph) is not adopted, the regulating projection 1t and the groove b14 will engage, preventing the front shaft holding portion 1m from detaching from the front shaft j2.

[0191] The seat support 1 is configured such that when it adopts a predetermined upward-bending position (ph), the regulating projection 1t is positioned outside the groove b14, and the front shaft holding portion 1m is detached forward from the front shaft j2.

[0192] In other words, this embodiment has a configuration that allows the seat body 1 to be easily separated from the front axle j2 (support base B) by placing it in a predetermined flipped-up position (ph) without using any special tools. On the other hand, the configuration is such that the seat body 1 cannot be separated from the front axle j2 (support base B) unless it is placed in the predetermined flipped-up position (ph), thus realizing a configuration in which the seat body 1 is stably supported.

[0193] <Intermediate member U> The intermediate member U is made of synthetic resin. The intermediate member U is provided between the seat receiver 1 and the seat engagement shaft j3, which is the seat engagement portion of the back support L.

[0194] Between the seat support 1 and the intermediate member U, a pair of coil springs Y, which are spring members, are interposed on the left and right sides.

[0195] The intermediate member U is positioned between the seat engagement axis j3 of the back support L, which is rotatably supported with respect to the support base B, and the rear portion of the seat C, i.e., the portion near the engaged portion 1k.

[0196] The intermediate member U comprises a portion that engages with the seat engagement shaft j3 and a portion that engages with the seat receiving body 1 via a coil spring Y. The intermediate member U can limit the distance between the engaged portion 1k and the seat engagement shaft j3 in the forward-tilted position (ps).

[0197] The intermediate member comprises an intermediate member body u1 having a spring receiving portion u11 that receives the upper end, which is one end of the coil spring Y, and a pair of left and right arm portions u2 that extend from the intermediate member body u1 and can engage with a seat engagement shaft j3, which is a seat engagement portion.

[0198] [Intermediate component body u1] The intermediate member body u1 is a horizontally elongated rectangular plate in shape. The intermediate member body u1 is provided with one spring receiving portion u11 facing downwards.

[0199] In other words, on the lower surface of the intermediate member body u1, there are two spring receiving portions u11, one on each side, for receiving the upper ends of a pair of left and right coil springs Y.

[0200] [Arm section u2] The arm portion u2 includes a downward extension portion u21 extending downward from the front of the intermediate member body u1, and a hook-shaped portion u22 that extends forward from the lower part of the downward extension portion u21 so as to curve forward and can engage with the lower part of the seat engagement shaft j3.

[0201] <Coil spring Y (spring component)> The coil spring Y is interposed between the seat support 1 and the intermediate member U. The coil springs Y are arranged in pairs on the left and right sides. The coil springs Y are in a position that allows them to expand and contract in the vertical direction.

[0202] The coil spring Y biases the intermediate member U upward using the seat support 1 as a base. In other words, the coil spring Y biases the intermediate member U in a direction that engages with the seat engagement axis j3.

[0203] <Attachment and detachment structure of intermediate member U> The intermediate member U can restrict the detachment of the seating body 1 from the back support L. That is, the intermediate member U is interposed between the back support L and the seating body 1 so that the rear part of the seating body 1 does not separate from the seat engagement axis j3 by more than a certain distance.

[0204] The arm portion u2 of the intermediate member U engages with the lower part of the seat engagement axis j3 in the back support L, and the intermediate member body u1 of the intermediate member U engages with the seat receiver 1 via a coil spring Y.

[0205] The intermediate member U is configured to be detachable from a predetermined position between the back support L and the seat support 1 without the use of fasteners.

[0206] In other words, the intermediate member U can be released from its engagement with the seat engagement shaft j3 by being pressed in a direction opposite to the biasing force of the coil spring Y, and is configured to be detachable from the seat engagement shaft j3 and the seat receiving body 1 from the released state.

[0207] Furthermore, by following the reverse procedure described above, the intermediate member U can be positioned at a predetermined location between the back support L and the seat support 1 without using any fasteners.

[0208] <Seat body D> The seat body D comprises a seat cushion Dq, a support shell 3 attached to the underside of the seat cushion Dq, and seat upholstery Dh covering the upper part and peripheral edge of the seat cushion Dq and the peripheral edge of the shell 3. The seat body D has a seat surface on its upper surface that is approximately circular in shape when viewed from above.

[0209] [Seat cushion Dq] The seat cushion Dq is primarily made of polyurethane foam. The seat cushion Dq is shaped so that its width gradually increases towards the top. The underside of the seat cushion Dq is attached to the shell body 3.

[0210] The seat cushion Dq is shaped to fit onto the shell body 3 from above. When viewed from below, the seat cushion Dq is larger than the shell body 3. The dimensions of the seat cushion Dq in the front-to-back and left-to-right directions are set to be longer than the dimensions of the shell body 3 in the front-to-back and left-to-right directions.

[0211] [Shell Body 3] The shell body 3 is a roughly disc-shaped object attached to the underside of the seat cushion Dq. The shell body 3 is integrally formed from synthetic resin.

[0212] The shell body 3 includes a shell body main body 31 having a disk-like portion whose upper surface is adhered to the lower surface of the seat cushion Dq, a support wall portion 33 that extends downward from the peripheral edge of the shell body main body 31 and whose outer surface is attached to the inner surface of the peripheral portion of the seat cushion Dq, an end wall portion 34 that extends obliquely upward and outward from the lower end portion of the support wall portion 33 and supports the lower end portion of the peripheral portion of the seat cushion Dq, and a peripheral wall portion 32 that is vertically provided downward from the lower surface of the peripheral portion of the shell body main body 31 inside the support wall portion 33.

[0213] The lower end of the peripheral wall portion 32 is provided so as to extend in a substantially horizontal direction in a front view, a rear view, and a side view.

[0214] The shell body 3 is integrally provided with an operation lever k2 having a convex portion kt that is in a cantilever shape and engages with a portion that can prevent relative rotation from the mounting posture (F) with respect to the seat receptor 1.

[0215] The shell body main body 31 is provided with a central convex portion g1 that protrudes downward at the center in the front-rear direction and the left-right direction. The shell body main body 31 is provided with a plurality of locking projection engaging portions hk at regular intervals in the circumferential direction inside the peripheral wall portion 32.

[0216] The central convex portion g1 constitutes a central positioning portion G, and the locking projection engaging portion hk constitutes a vertical engagement mechanism H, which will be described in detail later.

[0217] The peripheral wall portion 32 is disposed at the peripheral portion of the shell body 3. More specifically, the peripheral wall portion 32 is disposed closer to the center side than the support wall portion 33 of the shell body 3. The peripheral wall portion 32 has an outer surface 32m against which the edge portion de of the seat covering Dh that wraps the seat cushion Dq can abut.

[0218] The peripheral wall portion 32 is arranged in a substantially annular shape when viewed from below. That is, the peripheral wall portion 32 is continuously arranged on a circular trajectory, except for one point at the rear where the operating lever k2 is located, so that when viewed from below, it is located on a virtual circumference that forms a perfect circle with the central protrusion g1 at its center.

[0219] The peripheral wall portion 32 is provided with outwardly extending portions 321 that extend outward and can restrict the downward movement of the edge portion de of the upholstery Dh. The outward extending portions 321 are multiple projections arranged at regular intervals in the circumferential direction on the peripheral wall portion 32.

[0220] Furthermore, inwardly bulging inward protrusions it are provided on the inner surfaces of three locations on the peripheral wall portion 32: the front end and both left and right ends, specifically the inner surface of the central left-right portion of the front of the peripheral wall portion 32, and the inner surface of the central front-rear portions of both left and right sides of the peripheral wall portion 32. These inward protrusions it constitute the horizontal engagement mechanism I, which will be described in detail later.

[0221] Ribs rv are attached to the inner surface of the peripheral wall portion 32, perpendicular to the shell body 31 and extending outward from the central part of the shell body 31. The ribs rv are arranged radially on the lower surface of the shell body 31.

[0222] The operating lever k2 is cantilevered to the shell body 31. That is, the shell body 3 is provided with an operating lever k2, which is a lever member that is cantilevered and engages with the seating body 1. The operating lever k2 has a wall-like portion k21 that extends from the base portion of the operating end portion k22 and forms part of the peripheral wall portion 32.

[0223] The operating lever k2 is located at the rear of the shell body 31. The base end ke of the operating lever k2 is integrally connected to the shell body 31, and the outer end is provided with an operating end k22 that receives the operating force from the user's fingers.

[0224] The operating lever k2 has a protrusion kt projecting downward between its base end ke and operating end k22, which can engage with an upward-facing recess k1 provided in the seating body 1. The recess k1 of the seating body 1 and the protrusion kt of the operating lever k2 constitute the reverse-reverse restricting mechanism K, which will be described in detail later.

[0225] In the shell body 3, the lower edge 3e of the support wall portion 33 is formed so as to be gradually positioned downward from both the left and right ends toward the center in the left-right direction when viewed from the front and rear (convex downward). In addition, in the shell body 3, the lower edge 3e of the support wall portion 33 is formed so as to be gradually positioned upward from both the front and rear ends toward the center in the front-rear direction when viewed from the side (convex upward).

[0226] The lower end edge 3e of the support wall portion 33 in the shell body 3 is set to follow the outer peripheral end edge 1e of the seat support body 1 when the seat body D is in the mounting position (F).

[0227] [Sitting area Dh] The seat upholstery Dh is primarily composed of a stretchable fabric that covers the seat cushion Dq.

[0228] The seat upholstery Dh has an annular edge portion de. The seat upholstery Dh is constructed in a bag-like shape that is open downwards. The seat upholstery Dh is provided with a string-like member (not shown) that reduces the diameter of the edge portion de and brings the edge portion de into contact with the outward-facing surface 32m of the peripheral wall portion 32 of the shell body 3.

[0229] <<Attachment and detachment structure of the seat body D to the seat support 1>> The seat body D is configured to be able to rotate horizontally around a common axis cj relative to the seat support 1, between a retracted position (E) in which it is detachable from the seat support 1 and an attached position (F) in which it is attached to the seat support 1.

[0230] The chair of this embodiment is configured such that not only the manufacturer but also the end user (user) can easily attach and detach the seat body D to and from the seat receiver 1 without using tools, for the convenience of maintenance such as cleaning and replacement, as well as storage and transportation.

[0231] Between the seat receiver 1 and the seat body D, there are provided a central positioning portion G for positioning such that the axis of the seat body D coincides with the axis of the seat receiver 1, an up-and-down engagement mechanism H in which the seat receiver 1 and the shell body 3 are closely engaged in the up-and-down direction when the seat body D takes the attachment posture (F), a horizontal engagement mechanism I in which the seat receiver 1 and the shell body 3 are closely engaged in the horizontal direction when the seat body D takes the attachment posture (F), and a reverse return regulation mechanism K for regulating the reverse return of the seat body D in the attachment posture (F) in the retreat posture (E) direction.

[0232] <Central positioning portion G> The central positioning portion G is capable of positioning the seat receiver 1 and the shell body 3 of the seat body D so as to substantially coincide with the common axis cj.

[0233] The central positioning portion G includes a central convex portion g1 projecting downward provided at the central portion of the shell body 3 in the seat body D having a cylindrical shape, and a central convex portion engaging portion g having a hole shape provided at the central portion of the seat receiver 1 and engaging with the central convex portion g1 so as to be relatively rotatable.

[0234] <Up-and-down engagement mechanism H> The up-and-down engagement mechanism H engages the seat receiver 1 and the shell body 3 of the seat body D in the up-and-down direction so as to attract each other.

[0235] The up-and-down engagement mechanism H includes a locking projection piece hp which is a first engagement portion provided on the seat receiver 1, and a locking projection piece engaging portion hk which is a second engagement portion provided on the shell body 3 and capable of engaging with the locking projection piece hp of the seat receiver 1.

[0236] The seat body D is configured to be able to take the attachment posture (F) when the locking projection piece hp and the locking projection piece engaging portion hk are closely engaged.

[0237] Multiple locking projections hp of the seating body 1 and locking projection engagement portions hk of the shell body 3 are arranged at regular intervals along a virtual circumference centered on the common axis cj.

[0238] [Locking projection hp (first engagement part)] The locking projection hp constitutes a protruding structure that is provided in a direction intersecting the common axis cj. The locking projection hp is provided approximately horizontally inward, that is, towards the center where the common axis cj is located, from the upright wall-shaped seat body peripheral wall portion 121, which is erected on the periphery of the seat body 1 in a substantially annular shape in a plan view.

[0239] The locking projection hp can engage in the vertical direction with the guide inclined surface hm provided on the locking projection engagement portion hk. More specifically, the locking projection hp can press the guide inclined surface hm of the locking projection engagement portion hk downwards. In other words, the locking projection hp moves the seat body D downwards during the process of the seat body D being rotated from the retracted position (E) to the mounted position (F).

[0240] [Latching protrusion engaging part hk (second engaging part)] The locking projection engagement portion hk has an upward-facing guide inclined surface hm that can engage with the locking projection hp. The locking projection engagement portion hk protrudes downward from the circular plate-shaped shell body 31.

[0241] The locking projection engagement portion hk comprises a support wall hs that is suspended downward from the shell body 31, and an engagement portion body hg that is supported by the support wall hs and has an upward-facing guide inclined surface hm on its upper surface.

[0242] The support wall hs comprises a first support wall portion ha extending in the circumferential direction and a second support wall portion hb connected to the first support wall portion ha and extending in a direction substantially perpendicular to the first support wall portion ha.

[0243] The first support wall portion ha is connected to the inner edge of the engagement portion body hg, which extends in the circumferential direction. The second support wall portion hb has a shorter width dimension than the first support wall portion ha and is connected to the base edge, which is one circumferential edge of the engagement portion body hg.

[0244] The engaging part body hg is a plate-like structure that extends circumferentially in a reclined position. The inner edge and base edge of the engaging part body hg are connected to the support wall hs. The upward-facing guide inclined surface hm provided on the engaging part body hg is inclined so as to be gradually positioned upward from the tip side to the base side. Here, the tip side of the engaging part body hg refers to the edge side that forms the tip in the direction of movement when rotating from the retracted position (E) to the mounted position (F).

[0245] The locking projection hp and guide inclined surface hm of the vertical engagement mechanism H, which has the above configuration, are configured such that the degree of contact gradually increases as the seat body D pivots from the retracted position (E) to the mounted position (F).

[0246] The procedure for attaching the seat body D to the seat support 1 is as follows:

[0247] First, as shown in Figure 43, the seat body D is moved downward from a position separated above the seat support 1, while the central positioning unit G positions it horizontally on the common axis cj.

[0248] Next, as shown in Figure 44, the seat body 43, which has been moved downward, is rotated around the common axis cj.

[0249] Subsequently, as shown in Figure 45, when the seat body D reaches the mounting position (F), the locking projection hp and the locking projection engagement portion hk engage so that they are in close contact in the vertical direction.

[0250] <Horizontal engagement mechanism I> The horizontal engagement mechanism I engages the seat support 1 and the shell 3 of the seat body D in the horizontal direction.

[0251] The horizontal engagement mechanism I comprises an inward projection it, which is a second engagement portion provided on the shell body 3, and an outward-facing guide inclined surface im, which is a first engagement portion provided on the seating body 1 and capable of engaging with the inward projection it, which is a horizontal projection portion of the shell body 3.

[0252] Multiple inwardly protruding portions it of the shell body 3 and outwardly oriented guide inclined surfaces im of the seating body 1 are arranged at regular intervals along a virtual circumference centered on the common axis cj.

[0253] [Inwardly protruding part it (second engaging part)] The inward projection it constitutes a protruding structure that extends in a direction intersecting the common axis cj. In a plan view, the inward projection it extends inward, that is, toward the common axis cj, from a hanging wall-shaped peripheral wall portion 32 that is erected on the shell body 3 in a substantially annular shape.

[0254] Furthermore, an outward extension 321 extends from the peripheral wall portion 32, where the inward projection it is provided, in the opposite direction, i.e., outward, to which the edge portion de of the upholstery Dh is locked.

[0255] The inward projection it can engage horizontally with the outward-facing guide inclined surface im provided on the seating body 1. More specifically, the inward projection it can press inward against the outward-facing guide inclined surface im provided on the seating body peripheral wall portion 121 of the seating body 1.

[0256] [Outward-facing guide inclined surface im (first engagement portion)] The outward-facing guide inclined surface im is provided on the outer circumferential surface of the seat-receiving body periphery wall portion 121, which is an upright wall erected on the periphery of the seat-receiving body 1. The outward-facing guide inclined surface im faces outward, which is the horizontal direction that allows it to engage with the inward projection portion it. The outward-facing inclined surface is inclined so that it gradually moves outward as it moves clockwise.

[0257] The inward projection it and outward guide inclined surface im of the horizontal engagement mechanism I, which has the above configuration, are configured such that the degree of contact gradually increases as the seat body D rotates clockwise from the retracted position (E) to the mounted position (F).

[0258] <Reverse Regulatory Mechanism K> The reverse movement restriction mechanism K is provided between the seat body D and the shell body 3 of the seat support 1, and restricts the seat body D from moving backward in the retracted position (E) direction from the mounting position (F).

[0259] On the other hand, the reverse-returning restraint mechanism K can release the state in which the seat body D is unable to rotate relative to the seat support 1 by operating the operating lever k2 so as to deform upward against the elastic restoring force of the shell body 3, thereby allowing the seat body D from the mounting position (F) to be rotated to the retracted position (E) and detached from the seat support 1.

[0260] The reverse-reverse restricting mechanism K comprises a recess k1 provided on the upper surface of the rear end of the seat support 1, and an operating lever k2 provided on the shell body 3 and having a protrusion kt that can engage with the recess k1 only in the mounting position (F).

[0261] The protrusion kt of the reverse-reverse regulating mechanism K is provided on the cantilevered operating lever k2 provided on the shell body 3. The protrusion kt of the operating lever k2 releases the engagement with the recess k1 provided on the seat support body 1 by using the elastic deformation of the material to move the operating end k22, which receives the operating force from the user's fingers, upward, thereby allowing the seat body D to rotate from the mounting position (F) to the retracted position (E).

[0262] Furthermore, the upper rear end surface of the seat support 1 is provided with a guide inclined surface km adjacent to the recess k1, which can engage with the protrusion kt of the operating lever k2. The guide inclined surface km is inclined so as it approaches the recess k1, gradually rising upwards. The uppermost part of the inclined surface is set to be above the bottom of the recess k1.

[0263] When the seat body D is in the retracted position (E), the protrusion kt of the operating lever k2 is positioned at the lowest point on the inclined surface. Then, when the seat body D rotates from the retracted position (E) to the mounted position (F), the protrusion kt is gradually pushed upward by the guide inclined surface km against the elastic restoring force of the operating lever k2.

[0264] Furthermore, when the seat body D moves from the retracted position (E) to the mounted position (F), the protruding portion kt overcomes the guide inclined surface km and engages with the recessed portion k1 by the elastic restoring force of the operating lever k2.

[0265] In this embodiment, when the reverse-return restricting mechanism K moves from the retracted position (E) to the mounted position (F), the rotational movement of the shell body 3 causes the protrusion kt to climb up the inclined guide surface km of the seating body 1, thus eliminating the need to apply any operating force to the operating lever k2. At this point, once it has climbed over the inclined guide surface km, the protrusion kt of the operating lever k2 automatically engages with the recess k1 due to the elastic restoring force of the operating lever k2. In other words, the reverse-return restricting mechanism K does not require any special operation of the operating lever k2 during the process from the retracted position (E) to the mounted position (F).

[0266] Furthermore, downward projections 32t are provided on both sides of the peripheral wall portion 32 of the shell body 3 adjacent to the operating lever k2, extending downward to the same position as the lower end of the operating lever k2.

[0267] These downward protrusions 32t are designed to prevent the operating lever k2 from being pushed upward by the mounting surface when the seat body D or shell body 3 is placed independently on a mounting surface such as the floor for purposes such as replacement parts.

[0268] In other words, the downward protrusions 32t provided on the left and right sides of the operating lever k2 can suppress the upward pushing of the operating lever k2 by the mounting surface, thereby effectively preventing the operating lever k2 from developing a bending tendency that would impair its intended elastic deformation.

[0269] The back support L of this embodiment will be described in detail below.

[0270] <<Back support L>> The back support L is interposed between the support base B and the backrest M. The back support L is capable of supporting the backrest M so as to be movable between a normal position (ps) and a reclined position (pr) that is more reclined than the normal position (ps).

[0271] The backrest M, supported by the back support L, is biased in a direction that allows it to assume the normal posture (ps) by a reaction force generating body R provided between the support base B and the seat engagement axis j3 of the back support L.

[0272] The back support L is also interposed between the support base B and the seat C. In other words, the back support L also functions as a seat support that supports the seat C. The back support L is equipped with a seat engagement shaft j3 that extends in the left-right direction and engages with the engaged portion 1k provided on the seat receiving body 1 of the seat C.

[0273] The back support L comprises a back support base 4, which is a metal structure rotatably supported on a support base B via a main shaft j1; a back support body 5 attached to the back support base 4; and a cover member 6 attached to the back support body 5.

[0274] The back support L supports left and right operating members p1 that can change their position between an engaged position (U) in which they engage with the backrest M and a retracted position (N) in which they are retracted from the backrest M. The left and right operating members p1 constitute a release prevention mechanism P, which will be described in detail later.

[0275] <Back support base 4> The back support base 4 comprises a pair of left and right arms 41 that are rotatably supported on the support base B via a main shaft j1 which is an upright plate shape extending in the front-rear direction, a connecting member 42 which is an upright plate shape connecting the rear parts of the pair of left and right arms 41, and a seat engagement shaft j3 that extends in the left-right direction and is supported at the part of the pair of left and right arms 41 that is in front of the main shaft insertion hole 41a.

[0276] [Left and right arms 41] The left and right arms 41 are made of metal. The left and right arms 41 have an upright wall shape with left and right arm bodies 411 that extend longitudinally in the front-to-back horizontal direction. The left and right arms 41 are positioned outside the left and right side walls b1 of the support base B.

[0277] Each of the left and right arms 41 comprises left and right arm bodies 411 that extend substantially linearly in the front-rear direction and can support the main spindle j1 at their front ends, left and right front arm portions 412 that extend integrally from the front ends of the left and right arm bodies 411 diagonally forward and upward and support a seat engagement shaft j3 that engages with a seat C at its upper end, and a main spindle insertion hole 41a that penetrates in the left-right direction and is provided between the left and right arm bodies 411 and the left and right front arm portions 412, and can hold the main spindle j1.

[0278] The rear ends of the left and right arm bodies 411 are connected by a connecting member 42. The rear ends of the left and right arm bodies 411 protrude behind the connecting member 42. The rear protruding portions 41b of the left and right arm bodies 411 that protrude behind the connecting member 42 are fitted into the fitting holes 5b of the back support base connecting portion 5a provided at the base end 51 of the back support body 5.

[0279] The left and right front arm portions 412 are integrally extended from the front ends of the left and right arm bodies 411 diagonally upward and forward. A seat engagement shaft j3 extending in the left-right direction, capable of engaging with the seat C, is rigidly connected to the tip, i.e., the upper end, of the left and right front arm portions 412.

[0280] [Connecting member 42] The connecting member 42 is made of metal. The connecting member 42 is in the shape of an upright plate extending in the left-right direction. Both the left and right ends of the connecting member 42 are rigidly connected to the inner parts of the left and right arm bodies 411 by welding.

[0281] The connecting member 42 is provided with a nut portion n3 into which a screw v3 for attaching the back support body 5 is screwed. The connecting wall 5c of the back support base connecting portion 52, which is provided on the base end portion 51 of the back support body 5, is attached to the back side of the connecting member 42 and is fastened with the screw v3.

[0282] [Seat engagement axis j3] The seat engagement shaft j3 extends in the left-right direction and is connected to the upper ends of the left and right front arm portions 412. The seat engagement shaft j3 is located above the left and right side walls b1 of the support base B and extends outward from both sides of the support base B.

[0283] The seat engagement axis j3 is positioned in front of and above the main axis j1. The seat engagement axis j3 pushes the middle portion of the seat C in the front-to-back direction upward and backward in conjunction with the backward tilting movement of the back support L. In other words, this chair is configured such that when the back support L tilts backward, the upward pushing action of the seat C by the seat engagement axis j3 lifts the front portion of the seat C upward.

[0284] The seat engagement shaft j3 is directly pressed forward by the reaction force generating body R. The seat engagement shaft j3 is directly connected to one end of the reaction force generating body R, which is positioned using the support base B as a base. The seat engagement shaft j3 is pressed forward by the reaction force generating body R.

[0285] Here, we will explain the movement of the back support base 4 when the backrest M is tilted backward.

[0286] When the backrest M tilts backward under the weight of the seated person, the back support L7 that supports the backrest E rotates around the main axis j1 supported by the support base B.

[0287] At this time, the left and right arm bodies 411 on the back support base 4 move downward and forward, and the left and right front arm portions 412 on the back support base 4 move upward and backward.

[0288] The seat engagement shaft j3, connected to the upper part of the left and right front arm sections 412, will move upward and backward in the same way as the movement of the left and right front arm sections 412.

[0289] The seat engagement axis j3 moves upward and backward, thereby lifting the seat C upward against the seated load of the person sitting on it.

[0290] [Back support body 5] The back support body 5 comprises a base end 51 fixed to the back support base 4, left and right upright frame portions 52 connected to the base end 51 and extending vertically in pairs, and an upper frame portion 53 extending substantially horizontally and connected to the upper ends of the left and right upright frame portions 52.

[0291] The base portion 51 includes a back support base connecting portion 5a connected to the back support base 4, and left and right arm portions 5d that are inwardly channel-shaped and extend linearly forward from both the left and right sides of the back support base connecting portion 5a, and can restrict the outward movement of the main shaft j1 at the front.

[0292] The back support base connecting portion 5a is open to the front and fits into a pair of left and right rearward protruding portions 41b that protrude from the rear end of the back support base 4. Fitting hole 5b It also includes a connecting wall 5c which is disposed between a pair of left and right fitting holes 5b and attached to the connecting member 42 of the back support base 4.

[0293] The connecting wall 5c is provided with a screw insertion hole h3 that penetrates in the front-to-back direction. The back support body 5 is attached to the back support base 4 by screwing a screw v3 inserted through the screw insertion hole h3 into a nut n3 provided on the connecting member 42.

[0294] The left and right arm portions 5d extend in the front-rear direction along the outer part of the arm body 411 of the back support base 4. The front parts of the left and right arm portions 5d are located outside the axis of the main shaft j1 that protrudes outward from the left and right side walls b1 of the support base B. The left and right arm portions 5d restrict the main shaft j1 from coming out of the support base B.

[0295] The main shaft j1 has a simple cylindrical shape that extends in the left-right direction. In this embodiment, the main shaft j1 is not directly provided with a positioning means (for example, a retaining ring attached to the end of the shaft, or a flange-like portion formed on one end of the shaft), but rather the main shaft j1 is positioned relative to the support base B by utilizing the arm portion 5d of the back support body 5 of the back support L.

[0296] Recesses q2, which constitute the positioning mechanism Q, are provided on the front side of the upper ends of the left and right upright frame sections 52, that is, on the front side of the connection portion between the left and right upright frame sections 52 and the upper frame section 53. The recesses q2 will be described in detail later.

[0297] The upper frame portion 53 has a partially annular shape that curves to convex towards the rear in a plan view. The upper frame portion 53 works in cooperation with the cover member 6, which forms the upper half of the upper frame portion 53, to form a circular shape with both left and right end faces facing forward, and the overall shape is a cylindrical shape that is curved in a partially annular manner.

[0298] In other words, the upper frame portion 53 constitutes the lower half of a cylindrical outer shape that is partially curved in an annular shape. To put it another way, the upper frame portion 53 and the cover member 6 have circular forward-facing end faces at both the left and right ends, and have a curved shape that is convex to the rear in a plan view, and as a whole constitute an upper frame body 5a that is partially curved in an annular shape.

[0299] The upper frame portion 53 is provided with a plurality of screw insertion holes h1 that penetrate vertically and through which screws v1 for attaching the cover member 6 to the upper frame portion 53 are inserted.

[0300] On the rear side of the upper frame portion 53, there is a rear biasing member engagement portion 532 which has a recessed shape and supports the rear of a coil spring p3, which is a biasing member that biases the operating member p1 forward, i.e., in the engagement position (U) direction.

[0301] A boss portion 533 is erected on the upper frame portion 53, to which a screw member v2 capable of restricting the vertical movement of the operating member p1 is screwed. The boss portion 533 and the screw member v2 constitute the vertical movement restricting portion 53k.

[0302] The boss portion 533 is disposed within the elongated hole portion p14 provided at the rear of the engaging portion p11 of the operating member p1. The screw member v2 is configured such that its head can engage with the vicinity of the upper opening edge of the elongated hole portion p14 of the operating member p1 in order to prevent the operating member p1 from moving upward.

[0303] [Cover member 6] The cover member 6 constitutes approximately the upper half of the curved cylindrical upper frame body 5a. The cover member 6 is attached to the upper frame portion 53 by screws v1 so as to cover the left and right operating members p1.

[0304] The cover member 6 covers the operating member p1 such that only the engaging portion p11 and the operated portion p13 provided on the operating member p1 are exposed to the outside.

[0305] The cover member 6 is provided with a window frame portion 6w that surrounds the engaging portion p11 of the operating member p1, which can extend and retract from the upper frame portion 53. The window frame portion 6w has an upper wall portion 61 that partially covers the upper side of the engaging portion p11 of the operating member p1, and side wall portions 62 that partially cover both the left and right sides.

[0306] Furthermore, the window frame portion 6w can cooperate with the outer peripheral wall q21 that constitutes the recess q2 of the positioning mechanism Q to form a rectangular window frame shape when viewed from the front.

[0307] Furthermore, a notch 6k is provided on the front side of the cover member 6 to expose the operated portion p13 of the operating member p1. The notch 6k is located adjacent to the inside of the window frame portion 6w.

[0308] The back support L, which has the above configuration, is covered by a front back support cover X2 and a rear back support cover X3, both made of synthetic resin.

[0309] The front back support cover X2 primarily covers the lower and outer parts of the back support base 4. The front back support cover X2 is attached to the arm portion 5d of the back support body 5.

[0310] The rear support cover X3 is attached so that the screws v3 for attaching the back support body 5 to the back support base 4 are not exposed on the back side. The rear support cover X3 is provided at the base end 51 of the back support body 5 and covers the back of the back support base connecting portion 5a located between the left and right upright frame portions 52. Both ends of the rear support cover X3 are connected to the rear ends of the front support cover X2.

[0311] The backrest M of this embodiment will be described in detail below.

[0312] <<Backrest M>> The backrest M has a roughly elongated rectangular shape overall, with rounded ends on both sides. The backrest M has a backrest surface on its front that can come into contact with the back of the person sitting. In this embodiment, the backrest M is configured to be easily attached to and detached from the back support L by a simple operation by the user. The backrest M has a backrest body 7, which is the main structure, and a back upholstery 8, which is a covering that can cover the backrest body 7.

[0313] <Backrest body 7> The backrest body 7 comprises a roughly horizontally elongated rectangular backrest base 71 made of synthetic resin and a back cushion 72 attached to the front surface of the backrest base 71. At the lower end of the backrest base 71 of the backrest body 7, a single storage groove 7m is provided, which opens downward and extends in the left-right direction.

[0314] The storage groove 7m is composed of a pair of front and rear groove-forming walls 7f and 7r arranged so that their inner surfaces face each other in the front-to-back direction. The first and second strip-shaped members 81 and 82, which are provided at the lower edge of the back upholstery 8 that covers the backrest body 7, are inserted into a single storage groove 7m.

[0315] Multiple engaging protrusions t(f) and t(r) are provided inside the accommodating groove 7m, that is, on the inner surfaces of the pair of groove-forming walls 7f and 7r. Engaging protrusions t(f) and t(r) are provided on both the pair of groove-forming walls 7f and 7r, projecting either forward or backward.

[0316] In this embodiment, the engaging protrusions t(f) and t(r) are alternately provided on both groove-forming walls 7f and 7r, which are arranged to face each other front and back along the extension direction of the accommodating groove 7m. In other words, the engaging protrusions t(f) on one groove-forming wall 7f and the engaging protrusion t(r) on the other groove-forming wall 7r are arranged to protrude alternately from one end to the other in the longitudinal direction of the accommodating groove 7m so as not to collide.

[0317] On the back side of the backrest base 71, which constitutes the backrest body 7, there is an engaging portion p2 and a protruding portion q1, which are connecting structures for connecting to the back support L. The engaging portion p2 constitutes a detachment prevention mechanism P. The protruding portion q1 constitutes a positioning mechanism Q.

[0318] <Back upholstery 8 (covering body)> The back upholstery 8 comprises a back upholstery body 80 which is a bag-like structure open downwards and includes a front covering portion 8f that covers the front side of the backrest body 7 and a back covering portion 8r that covers the back side of the backrest body 7, and first and second strip-shaped members 81 and 82 disposed at the lower open end of the back upholstery body 80.

[0319] The back upholstery 8 comprises a front covering portion 8f that covers the front side of the backrest body 7, a back covering portion 8r that covers the rear side of the backrest body 7, a first strip-shaped member 81 that is sewn to the lower end of one end of the front covering portion 8f and inserted into the storage groove 7m of the backrest body 7, and a second strip-shaped member 82 that is sewn to the lower end of one end of the back covering portion 8r and inserted into the storage groove 7m of the backrest body 7.

[0320] The back upholstery 8 exposes the engaging portion p2 and the protruding portion q1, which are connecting structures provided on the backrest body 7, to the outside through openings 8s provided on the left and right sides of the back side.

[0321] [Back upholstery fabric 80] The back upholstery body 80 is formed into a bag-like shape that is open downwards by sewing together the peripheral edges of the front covering portion 8f and the back covering portion 8r, which are made of stretchable fabric, excluding the lower ends.

[0322] A space is formed inside the back upholstery body 80 that can accommodate the backrest body 7. Between the lower end of the back upholstery body 80, that is, the lower end of the front covering portion 8f and the lower end of the back covering portion 8r, a lower opening 8k is formed that opens downwards and allows the backrest body 7 to be inserted into the internal space.

[0323] In this embodiment, the back of the back upholstery body 80, i.e., the back covering portion 8r, is provided with a pair of openings 8s on the left and right sides that expose the engaged portion p2 and the protruding portion q1 of the backrest body 7 to the outside.

[0324] The opening 8s is mainly composed of a through hole 8t provided in the back covering portion 8r which is made of fabric material, a through hole peripheral portion 8e which is the peripheral region of the through hole 8t in the back covering portion 8r, and a synthetic resin annular member T which forms a continuous ring and is attached to the through hole peripheral portion 8e by sewing.

[0325] Through holes 8t are formed at two locations on the left and right sides of the back covering portion 8r, corresponding to the protruding portion q1 that is provided on the back side of the backrest body 7.

[0326] The annular member T is formed in a rectangular frame shape from a flexible synthetic resin sheet material and has a hole th in the center. The annular member T is configured to be deformable by bending. The annular member T is sewn to the peripheral edge 8e of the through hole in the back covering portion 8r. In the completed mounting position (Ta), the annular member T is covered by the back covering portion 8r so that everything except the hole th is not visible from the outside.

[0327] In this embodiment, the entire outer surface t1, the entire inner end t2, and at least a portion of the inner surface t3 of the annular member T in the completed mounting position (Ta) are covered by the through-hole periphery 8e adjacent to the through-hole 8t in the back covering portion 8r, and the through-hole periphery 8e is fixed only to the inner surface t3 of the annular member T in the completed mounting position (Ta).

[0328] [First and second strip-shaped members 81, 82] The first and second strip-shaped members 81 and 82 are made of synthetic resin, are strip-shaped, and extend in the left-right direction. In this embodiment, the first and second strip-shaped members 81 and 82 have substantially the same structure. Each of the first and second strip-shaped members 81 and 82 is provided with a plurality of through holes 81a and 82a arranged in a row, into which the engaging projections t(f) and t(r) can engage.

[0329] [Regarding the relationship between the first and second strip-shaped members 81 and 82 and the storage groove 7m of the backrest body 7] The first strip-shaped member 81, sewn to the lower end of the front covering portion 8f, and the second strip-shaped member 82, sewn to the lower end of the back covering portion 8r, are inserted into a single storage groove 7m provided at the lower end of the backrest body 7.

[0330] The first and second strip-shaped members 81 and 82 are superimposed on each other and inserted together into the 7m storage groove.

[0331] When the first and second strip-shaped members 81 and 82 are inserted to their predetermined positions within the housing groove 7m, the engaging projections t(f) and t(r) protruding from the groove-forming walls 7f and 7r of the housing groove 7m can engage with the through holes 81a and 82a provided in the respective strip-shaped members 81 and 82. More precisely, when the first and second strip-shaped members 81 and 82 are inserted, only the through holes 81a and 82a located at positions corresponding to the engaging projections t(f) and t(r) can be locked against the engaging projections t(f) and t(r).

[0332] As a result, the first and second strip-shaped members 81 and 82 that constitute the edges of the back upholstery fabric 8 are restricted from moving downward (reverse / coming out) by the engaging projections t(f) and t(r) after they have entered the predetermined depth of the single storage groove 7m, making it difficult for them to easily come out even when subjected to tensile force from the back upholstery fabric body 80.

[0333] Furthermore, since the engaging projection t(f) protruding from one groove-forming wall 7f and the engaging projection t(r) protruding from the other groove-forming wall 7r are arranged alternately along the extension direction of the accommodating groove 7m, the first and second strip-shaped members 81 and 82 can be inserted smoothly and without force into the accommodating groove 7m without being excessively obstructed by the engaging projections t(f) and t(r).

[0334] <<Method for forming an opening 8s in the backing fabric 8 (covering)>> The back upholstery 8 is provided with an opening 8s. The opening 8s comprises a back covering portion 8r, which is a fabric material with a through hole 8t, and an annular member T that forms a continuous ring and is attached to the peripheral edge 8e of the through hole, and is arranged so as not to be visible from the outside without impairing the front-to-back communication function of the hole th.

[0335] In this embodiment, the opening 8s of the backing fabric 8 is formed by going through the following steps: preparation step S1, annular member outer surface attachment step S2, first annular member inversion step S3, and second annular member inversion step S4.

[0336] <Preparation process S1> Preparation step S1, as shown in Figure 48, involves preparing the back upholstery body 80, which is the fabric material that constitutes the back upholstery 8 in which the opening 8s is to be formed, and the annular member T in the initial position (Tb).

[0337] A through-hole 8t is provided in the back covering portion 8r of the back upholstery body 80 by an appropriate method. The annular member T is a flexible, thin plate frame that can be sewn to the back upholstery body 80. In this embodiment, the annular member T is made of synthetic resin and is formed in a substantially rectangular annular shape.

[0338] <Attachment process S2 to the outer surface of the annular member> Following the preparation process, as shown in Figures 49 and 50, the annular member T in its initial position (Tb) is attached to the outer surface of the through-hole periphery 8e of the back covering portion 8r, which is the fabric material (annular member outer surface attachment process S2).

[0339] In this embodiment, the annular member T in the initial position (Tb) is attached to the outer surface of the through-hole periphery 8e and is sewn to the through-hole periphery 8e. In other words, the annular member T in the initial position (Tb) is fixed to the outer surface of the through-hole periphery 8e via the sewing portion tx.

[0340] In other words, the annular member outer surface attachment process S2 involves sewing the annular member T to the outer surface of the through-hole peripheral edge 8e, which is the edge portion of the through-hole 8t.

[0341] <First annular member inversion process S3> Following the annular member mounting process, as shown in Figure 51, the annular member T, which is in its initial position (Tb) attached to the outer surface of the through-hole periphery 8e, is reversed front to back while being deformed so that its inner periphery rotates toward the inner surface of the back covering portion 8r, thereby positioning the annular member T on the inner surface of the back covering portion 8r (first annular member reversal process S3).

[0342] <Second annular member inversion process S4> Following the first annular member inversion step S3, as shown in Figure 52, the annular member T in the intermediate position (Tc) is inverted front to back while further bending and deforming its inner edge toward the inner surface of the back covering portion 8r, thereby covering the entire annular member T from the outer surface with the back covering portion 8r (second annular member inversion step S4).

[0343] In this embodiment, by going through the method for forming an opening 8s in the back covering fabric 8 (covering body) which includes the steps described above, an opening 8s is formed in the back covering portion 8r of the back covering fabric 8, which is reinforced by an annular member T in the completed mounting position (Ta) that has been reversed 360° from the initial position (Tb).

[0344] Furthermore, the first and second annular member inversion processes S3 and S4 are carried out smoothly and continuously due to the bending deformation of the annular member T.

[0345] <<Detachable structure of back support M to back support L>> In this embodiment, the chair is configured so that the backrest M can be easily attached to and detached from the back support L by both the manufacturer and the end user (user) without the use of tools, which facilitates maintenance such as cleaning and replacement, as well as storage and transportation.

[0346] The attachment and detachment structure of the backrest M includes a positioning mechanism Q for positioning the backrest M relative to the back support L, and a detachment prevention mechanism P for preventing the backrest M, which has been positioned in the correct mounting position by the positioning mechanism Q, from detaching from the back support L.

[0347] <Positioning mechanism Q> The positioning mechanism Q positions the backrest M to a predetermined mounting position relative to the back support L.

[0348] The positioning mechanism Q comprises a protrusion q1 provided on the backrest M and a recess q2 provided on the back support L into which the protrusion q1 can engage. The protrusion q1 provided on the backrest body 7 and the recess q2 provided on the back support L can engage in the vertical direction.

[0349] [Protrusion q1] The protruding parts q1 are provided in pairs on the left and right sides of the backrest M. The protruding parts q1 are located on the back side of the backrest body 7 and are exposed to the outside through the opening 8s in the back upholstery 8.

[0350] The protruding portion q1 comprises a wall-like locking portion q11 that extends vertically in a rear view, gradually decreasing in width towards the bottom, and positioned to gradually move backward towards the bottom in a side view, and a connecting portion q12 that connects the backrest body 7 and the left-right intermediate portion of the wall-like locking portion q11, and is provided so as to gradually increase in length in the front-rear direction towards the bottom. The upper end of the wall-like locking portion q11 is connected to the backrest body 7.

[0351] The protruding portion q1 is located below the engaged portion p2, which constitutes the detachment prevention mechanism P recessed in the backrest body 7.

[0352] [Recess q2] The recess q2 is provided on the front side of the upper end of the left and right upright frame portions 52 that constitute the back support L. The recess q2 is open upward. The recess q2 is designed so that the protruding portion q1 of the backrest M, which is inserted from above, can be fitted into it.

[0353] The recess q2 is provided inside the outer peripheral wall q21 that protrudes forward from the upper ends of the left and right upright frame portions 52. The recess q2 is composed of an outer peripheral wall q21 having a bottom wall portion qt and left and right side wall portions qs erected upward from both left and right edges of the bottom wall portion qt, and a pair of left and right front wall portions q22 erected in front of the bottom wall portion qt.

[0354] The recess q2 has a pair of left and right front wall portions q22 erected on the bottom wall portion qt so as to be spaced apart from each other, and a front recess portion qm is provided between the pair of front wall portions q22, with a first space qa where the connecting portion q12 of the protruding portion q1 is disposed.

[0355] Furthermore, the recess q2 is formed behind the front recess portion qm, i.e., behind the pair of front wall portions q22, and includes a rear recess portion qr, which is provided with a second space qb between the left and right side wall portions qs erected on the bottom wall portion qt, where the wall-like locking portion q11 of the protruding portion q11 is disposed.

[0356] In this embodiment, the protrusion q1 of the backrest M, which constitutes the positioning mechanism Q, moves vertically, or more precisely, from diagonally forward-upward to diagonally rear-downward, while engaging with the recess q2 of the back support L. Since the backrest load of the seated person acts upward, backward, and downward, but hardly acts forward, by configuring the protrusion q1 to be inserted into the recess q2 from diagonally forward-upward to diagonally rear-downward, the backrest M becomes difficult to detach from the back support L, and the backrest M can be securely fixed to the back support L.

[0357] <Withdrawal Prevention Mechanism P> The detachment prevention mechanism P is provided between the back support L and the backrest M and prevents the backrest M from detaching from the back support L.

[0358] The detachment prevention mechanism P comprises an operating member p1 provided on the back support L that is reversibly operable by human operating force between an engaged position (U) that prohibits the detachment of the backrest M and a retracted position (N) that allows the detachment of the backrest M, i.e., rotatable in the front-rear direction, and an engaged portion p2 provided on the backrest M that can engage with an engaging portion p11 provided on the operating member p1 in the engaged position (U).

[0359] [Operating component p1] The operating member p1 prevents vertical movement of the backrest M relative to the back support L in the engaged position (U). The operating member p1 is rotatably supported on the upper frame portion 53 of the back support body 5. The operating members p1 are arranged in pairs on the left and right sides of the back support L.

[0360] The operating member p1 comprises a shaft hole pa that penetrates vertically and is inserted into a shaft portion 531 erected on the upper frame portion 53, which is provided at the inner end which is the base end; an engaging portion p11 that protrudes forward at the outer end which is the tip end; a biasing member engaging portion p12 provided on the rear side between the shaft hole pa and the engaging portion p11, which engages with the front part of the coil spring p3, which is a biasing member; an operated portion p13 provided on the front side between the shaft hole pa and the engaging portion p11, which directly receives the operating force of a person, i.e., the backward pressing force by the fingers, when moving from the engaged position (U) to the retracted position (N); and an elongated hole p14 provided at the rear of the engaging portion p11 that engages with the vertical movement restricting portion 53k provided on the upper frame portion 53.

[0361] The operating member p1 is constantly biased in the engaged position (U) direction by a coil spring p3. The user can change the position of the operating member p1 to the retracted position (N) by pressing the operated portion p13 of the operating member p1, which is in the engaged position (U), against the biasing force of the coil spring p3 in the retracted position (N) direction (the direction in which the engaging portion p11, which is the rotating end, moves backward).

[0362] The change in the position of the operating member p1 from the engaged position (U) to the retracted position (N) is performed by pressing the operated part p13 backward with the user's fingers. In other words, the user can move the operating member p1 to the retracted position (N) by pressing the operated part p13 backward like a push button.

[0363] As shown in Figure 27, a space sp into which fingers can be inserted is provided between the back support L and the backrest M. The operable part p13 is positioned facing the space between the back support L and the backrest M. Therefore, the user can easily press the operable part p13 like a push button.

[0364] Furthermore, the back support L and the backrest M are configured to expose only the outer surface of the operated portion p13 of the operating member p1 in the engagement position (U). In other words, the outer surface of the operated portion p13 and the outer surface of the cover member 6 are configured to be substantially flush. Therefore, although the operated portion p13 is provided to be operable from the outside, it is provided in an inconspicuous location and is configured to be substantially flush with the cover member 6 so as not to be conspicuous.

[0365] [Engaged part p2] The engaged portion p2 is the part that the engaging portion p11 of the operating member p1, which is supported by the back support L, can engage with. The engaging portion p11 of the operating member p1, which is in the engaged position (U), engages with the engaged portion p2.

[0366] The engaging portions p2 are provided in pairs on the left and right sides of the backrest M. The engaging portions p2 have a recessed shape that is provided on the back side of the backrest body 7 so as to open to the rear. The engaging portions p2 recessed in the backrest body 7 are exposed to the outside through the opening 8s in the back upholstery 8.

[0367] The engaged portion p2 is located on a protruding portion q1 that constitutes a positioning mechanism Q, which is projected from the backrest body 7.

[0368] After the backrest M is positioned in its proper mounting position by the positioning mechanism Q, when the engaging portion p11 of the operating member p1 engages with the engaged portion p2, the backrest M becomes unable to move upward relative to the back support L, and as a result, detachment from the back support L is prohibited.

[0369] <<Weight-sensing locking mechanism>> The weight-sensing rocking mechanism is configured to tilt the backrest M in accordance with the weight of the person sitting on the seat C. The weight-sensing rocking mechanism is configured to move the seat C backward in conjunction with the backward tilting of the backrest M, while simultaneously lifting the seat C against the weight of the person sitting on it.

[0370] The weight-sensing rocking mechanism includes a mechanism that lifts the seat C upward against the weight of the sitter, and therefore requires a backward tilting load proportional to the sitter's weight in order to tilt the backrest M backward.

[0371] The weight-sensing rocking mechanism mainly consists of a support base B supported by the legs A, a seat C disposed on the support base B and with its front end supported by the support base B via a front axis j2, a back support L rotatably supported by the support base B via a main axis j1 and having a seat engagement axis j3 disposed in front of and above the main axis j1 that can engage with the center of the seat C in the front-rear direction and is biased forward by a reaction force generating body R, a backrest M supported by the back support L, and a reaction force generating body R provided between the support base B and the back support L that can provide a reaction force against the backward tilting movement of the backrest M.

[0372] <<Seat forward tilt mechanism>> The seat tilt mechanism allows the seat C, which is rotatably supported on a support base B via a front axis j1, to change its orientation between a normal position (ps) and a tilted position (pf).

[0373] The seat tilt mechanism mainly consists of a support base B supported by legs A, a seat C disposed on the support base B with its front end supported by the support base B via a front axis j2, a back support L having a seat engagement axis j3 that engages with the engaged portion 1k of the seat C in the normal position (ps), and an intermediate member U whose lower part engages with the seat engagement axis j3 and whose upper part engages with the seat C via a coil spring Y, thereby limiting the distance between the engaged portion 1k and the seat engagement axis j3 in the tilted position (pf).

[0374] In the embodiment described above, it is possible to provide a chair having a suitable configuration in which the backrest M can be easily attached to and detached from the back support L using an operating member p1 that can be reversibly operated by human force.

[0375] Furthermore, in the embodiment described above, the seat body D is configured to be able to rotate horizontally around a common axis cj relative to the seat support 1, between a retracted position (E) in which it can be detached from the seat support 1 and an attached position (F) in which it is attached to the seat support 1. Therefore, it is possible to provide a chair with a suitable configuration that allows the seat body D to be easily attached to and detached from the seat support 1 without the use of any special tools.

[0376] Furthermore, in the embodiment described above, the shell body 3 is provided with a peripheral wall portion 32 that has an outward-facing surface 32m to which the edge portion de of the upholstery Dh can abut, and is arranged in a substantially annular shape when viewed from the bottom. Therefore, it is possible to provide a chair that can suitably abut the edge portion de of the upholstery Dh covering the seat cushion Dq against the peripheral wall portion 32 of the shell body 3 with substantially uniform pressure.

[0377] Furthermore, in the above-described embodiment, the backrest body 7, which is the main structural body, is provided with a receiving groove 7m having engaging protrusions t(f) and t(r), and the back upholstery 8 is provided with first and second strip-shaped members 81 and 82, which have through holes 81a and 82a that engage with the engaging protrusions t(f) and t(r) of the receiving groove 7m. Therefore, it is possible to provide a chair with a configuration that allows the edge of the back upholstery 8 to be easily and securely attached to the receiving groove 7m of the backrest body 7, which is the main structural body.

[0378] Furthermore, according to the above-described embodiment, it is possible to provide a method for suitably forming a reinforced opening 8s having a suitable appearance in the back upholstery 8, which is a covering body that can cover the member. Furthermore, according to the above-described embodiment, it is possible to provide a chair having a covering body that is applicable to the back upholstery 8, etc., and has a reinforced opening 8s having a suitable appearance.

[0379] Furthermore, in the embodiment described above, the seat C is rotatable at its front relative to the support base B so that it can assume a normal posture (ps) and a forward-tilted posture (pf), and an intermediate member U is provided between the back support L supported by the support base B and the rear of the seat C (the part behind the front of the seat C) that can limit the distance between them.

[0380] Therefore, it is possible to provide a chair in which the seat C can suitably adopt both a normal posture (ps) and a forward-leaning posture (pf) without having to install a large-scale mechanism at the front of the seat C.

[0381] Furthermore, in the embodiment described above, a reaction force generating body R is provided between the seat engagement shaft j3 and the support base B, which can directly bias the seat engagement shaft j3 forward. This reaction force generating body R is set to be in a substantially horizontal position extending in the front-rear direction in the normal position (ps). Therefore, in a chair that can rock between the normal position (ps) and the reclined position (pr), it is possible to provide a chair that offers excellent design freedom for miniaturizing the support base B and the seat C.

[0382] Furthermore, in the embodiment described above, an intermediate member U that can restrict the detachment of the seat support 1 from the back support L is detachably provided without the use of fasteners. Therefore, it is possible to provide a chair in which the seat support 1 can be easily attached to and detached from the support base B.

[0383] Furthermore, in the embodiment described above, when the support member W that supports one end of the reaction force generating body R is removed from the support base B using a screw v5, the biasing force of the reaction force generating body R is gradually weakened as it moves while being guided along the inclined surface nm. This configuration makes it possible to provide a chair that can suitably attach and detach the reaction force generating body R from the support base B.

[0384] Furthermore, in the embodiment described above, a screw threaded hole n4 is provided above the fitting hole Ba in the support base B, and the screw v4 screwed into the screw threaded hole n4 can press the upper part of the leg support a2 downward. Therefore, it is possible to provide a chair with a configuration that can suitably release the fitted state between the upper part of the leg support a2 and the fitting hole Ba of the support base B.

[0385] Furthermore, in the embodiment described above, a leg support a2 of leg A, which is an obstructing member that can prevent the lifting operation lever V, which is the operating lever, from assuming a detachable position (SR), is attached to the support base B. The lifting operation lever V can assume a detachable position (SR) only when the leg support a2 is removed from the support base B. Therefore, it is possible to provide a chair in which the lifting operation lever V can be suitably attached to the support base B.

[0386] As described above, the chair according to this embodiment comprises a support base B supported by legs A, and a seat C supported by the support base B via a front axis j2.

[0387] The seat C comprises a seat body D having a seat surface and a seat support 1 that supports the seat body D, the seat support 1 comprising a front shaft holding portion 1m capable of holding the front shaft j2 and an engaged portion 1k that engages with a back support L, which is a structure disposed behind the front shaft holding portion 1m and supported by a support base B.

[0388] An intermediate member U is detachably disposed between the back support L and the seat support 1 without the use of fasteners, which can restrict the seat support 1 from detaching from the back support L.

[0389] Therefore, it is possible to provide a chair in which the seat support 1 can be easily attached to and detached from the support base B.

[0390] In other words, this chair is equipped with an intermediate member U between the back support L and the seat support 1, which is configured to be attachable and detachable solely by hand without the use of fasteners or tools.

[0391] Since the intermediate member U is provided so that it can be attached and detached without the use of fasteners, the user can detach the intermediate member U from between the back support L and the seat support 1 and also place the intermediate member U between the back support L and the seat support 1 simply by using their fingers.

[0392] After the intermediate member U is detached from the back support L and the seat support 1, the seat support 1 can be easily detached from the support base B by performing an operation to release the engagement between the seat support 1 and the front shaft j2.

[0393] Furthermore, this chair allows the seat support 1 to be easily attached to the support base B and back support L by following the reverse procedure of the action of detaching the seat support 1 as described above.

[0394] A coil spring Y, which is a spring member, is interposed between the seating body 1 and the intermediate member U. The coil spring Y biases the intermediate member U in a direction that engages with the back support L.

[0395] Therefore, the intermediate member U is normally well engaged with the back support L by the coil spring Y. On the other hand, the intermediate member U can easily release its engagement with the back support L and the seat support 1 by receiving the user's operating force against the biasing force of the coil spring Y.

[0396] Furthermore, the intermediate member U receives the user's operating force against the biasing force of the coil spring Y, making it easy to interpose it between the back support L and the seat support 1.

[0397] The intermediate member U can be released from its engagement with the back support L by being pressed in a direction opposite to the biasing force of the coil spring Y, and is configured to be detachable from the back support L and the seating body 1 from the released state.

[0398] Therefore, the intermediate member U is configured to be suitably detachable from the back support L and the seat support 1.

[0399] The seat support 1 is rotatable around the front shaft j2 such that its rear end springs upward after the intermediate member U is detached, and the front shaft holding part 1m can only be detached from the front shaft j2 when the seat support 1 is changed to a predetermined springed-up position (ph).

[0400] Therefore, the seat support 1 is designed to be detachable from the front shaft j2 only under predetermined conditions, resulting in a configuration that offers excellent safety during disassembly.

[0401] The support base B is provided with a pair of grooves b14 on the left and right sides that extend vertically and are open outwards. The seating body 1 is also provided with a pair of restrictive projections 1t on the left and right sides that protrude inwards.

[0402] Furthermore, when the seat support 1 is restricted from detaching by the intermediate member U, the restricting projection 1t is located within the groove b14, and the front shaft holding portion 1m is configured to be unable to detach forward relative to the front shaft j2.

[0403] On the other hand, when the seat support 1 adopts a predetermined upward position (ph), the regulating projection 1t is located outside the groove b14, and the front shaft holding portion 1m is configured to detach forward from the front shaft j2.

[0404] Therefore, the seating body 1 is designed to have excellent safety for disassembly, by engaging a restricting projection 1t with the groove b14 of the support base B, so that the front shaft holding part 1m can be detached from the front shaft j2 only under predetermined conditions.

[0405] The back support L constitutes a structure that is rotatably supported on the support base B, and the engaged portion 1k of the seating body 1 engages with the seating shaft j3, which is a seating engagement portion provided on the back support L. The intermediate member U is disposed between the back support L and the seating body 1.

[0406] Therefore, the intermediate member U is preferably interposed between the back support L and the seat support 1.

[0407] The seat C is configured to be tiltable around the front axis j2 between a normal position (ps) and a forward-leaning position (pf) that is more tilted forward than the normal position (ps), and the engaged portion 1k engages with the back support L when the normal position (ps) is adopted.

[0408] Therefore, seat C can adopt not only the normal posture (ps) but also a forward-tilted posture (pf) that tilts around the front axis j2.

[0409] The intermediate member U comprises an intermediate member body u1 having one spring receiving portion u11 that receives one end of a coil spring Y, which is a spring member, and an arm portion u2 that extends from the intermediate member body u1 and can engage with the back support L. The seating body 1 is provided with another spring receiving portion 13a that receives the other end of the coil spring Y. One spring receiving portion u1 is positioned downwards, and the other spring receiving portion 13a is positioned upwards.

[0410] Therefore, the intermediate member U is preferably configured to be interposed between the seat support 1 and the back support L.

[0411] Furthermore, the intermediate member U is designed to be easy for the user to operate, as pressing the intermediate member body u1 downwards against the biasing force of the coil spring Y will release its engagement with the back support L.

[0412] The seat support body 1 is provided with a recess 13 in which a space 13s is formed, which is open upward and includes the other spring support portion 13a, and in which the intermediate member body u1 is disposed.

[0413] Therefore, the seat support 1 has a suitable configuration that allows for the placement of the intermediate member U.

[0414] The seating body 1 is provided with a recess 11 that is open downwards and into which the support base B is disposed, and an arm passage hole 14 is provided between the recess 13 and the recess 11 through which the arm portion u2 can pass.

[0415] Therefore, the seat support 1 has a suitable configuration in which an intermediate member U having an arm portion u2 is interposed between it and the back support L.

[0416] However, the present invention is not limited to the embodiments described in detail above.

[0417] The seat only needs to allow for a normal posture. In other words, the seat may not be designed to allow for a forward-leaning or backward-leaning posture.

[0418] The front part of the seat only needs to be rotatably supported with respect to the support base via a front axle, and the specific configuration can be any as appropriate.

[0419] The rear of the seat should, in its normal position, be supported by a support base or a structure supported by a support base.

[0420] The structure is not limited to a back support; it can be anything that is supported by a support base.

[0421] The shape of the intermediate member only needs to be such that it can limit the distance between the rear of the seat and the support base or structure when the seat is tilted forward, and its specific configuration can be any as appropriate.

[0422] The seat engagement portion is not limited to an axial shape; it may have any configuration as long as it engages with the rear of the seat in its normal position.

[0423] The spring member is not limited to a coil spring; any member that can be interposed between the seating body and the intermediate member and exert a biasing force is acceptable.

[0424] For example, the spring component may be made of rubber.

[0425] The seat support does not need to be designed so that the front axle holding portion can detach from the front axle only when its orientation is changed to a predetermined flipped-up position.

[0426] For example, the front shaft holding portion may be configured to detach from the front shaft if the intermediate member U detaches even though the seat body has not reached a predetermined flipped-up position.

[0427] The support base may be provided with a restricting projection, and the seating body may be provided with a groove that engages with the restricting projection of the support base.

[0428] The configuration may also include one spring receiving portion on the intermediate member facing upwards, and the other spring receiving portion on the seating body facing downwards.

[0429] The arm passage hole provided in the seat support only needs to be located between recesses and recesses so that the arm portion of the intermediate member can pass through, and it goes without saying that its specific shape can be set as appropriate.

[0430] Furthermore, the specific configuration of each part is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Explanation of Symbols]

[0431] A...legs B...Support base C…za 1...Seat receptor L...back support (structure) U...Intermediate member j2…front axis

Claims

1. A chair comprising a support base supported by legs and a seat supported by the support base via a front axis, The aforementioned seat comprises a seat body having a seat surface and a seat support that supports the seat body. The seating body comprises a front shaft holding portion capable of holding the front shaft, and an engaged portion disposed behind the front shaft holding portion and engaging with the support base or a structure supported by the support base. A chair in which an intermediate member capable of restricting the detachment of the seat support from the support base or the structure is detachably disposed between the support base or the structure and the seat support without the use of fasteners.

2. A spring member is interposed between the seat support and the intermediate member. The chair according to claim 1, wherein the spring member biases the intermediate member in a direction that engages it with the support base or the structure.

3. The chair according to claim 2, wherein the intermediate member can be released from its engagement with the support base or the structure by being pressed in a direction opposite to the biasing force of the spring member, and is configured to be detachable from the support base or the structure and the seat support when the engagement is released.

4. The seating body is rotatable around the front axis such that its rear end springs up after the intermediate member is detached. The chair according to claim 3, wherein the front shaft holding portion can be detached from the front shaft only when the seat support changes its position to a predetermined flipped-up position.

5. The support base is provided with a pair of grooves on the left and right sides that extend vertically and are open to the outside, The aforementioned seating body is provided with a pair of regulating protrusions on the left and right sides that project inward. The seating body is configured such that, when detachment is restricted by the intermediate member, the restricting projection is located within the groove, and the front shaft holding portion cannot be detached forward relative to the front shaft. The chair according to claim 4, wherein the seat support is configured such that when the predetermined flipped-up posture is adopted, the regulating projection is located outside the groove and the front shaft holding portion is detached forward from the front shaft.

6. The structure is a back support that is rotatably supported with respect to the support base, The engaged portion engages with a seated engaging portion provided on the back support, The chair according to claim 1, wherein the intermediate member is disposed between the back support and the seat support.

7. The aforementioned seat is configured to be able to tilt around the front axis between a normal position and a forward-leaning position that is more tilted forward than the normal position. The chair according to claim 1, wherein the engaged portion engages with the support base or the structure when the chair is in the normal position.

8. The intermediate member comprises an intermediate member body having one spring receiving portion that receives one end of the spring member, and an arm portion extending from the intermediate member body and capable of engaging with the support base or the structure. The seating body is provided with another spring receiving portion that receives the other end of the spring member. The chair according to claim 2, wherein one of the spring receiving portions is provided facing downward and the other spring receiving portion is provided facing upward.

9. The chair according to claim 8, wherein the seat support is provided with a recess that is open upward and includes the other spring support portion, forming a space in which the intermediate member body is disposed.

10. The aforementioned seating body is provided with a recess that is open downwards and into which the support base is disposed. The chair according to claim 9, wherein an arm passage hole is provided between the recess and the recess through which the arm portion can pass.

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