chair

Abstract

To provide a chair capable of excellently mounting and removing a reaction generator relative to a support base part.SOLUTION: A bearing member W supporting a reaction generator R can move to a prescribed fixed position while engaging an inclined plane nm by rotating a screw v5 inserted in a first screw insertion hole h51 of a support base part B in a first direction, and can move in an unfixing position direction while engaging the inclined plane nm by rotating the screw v5 in a second direction. The inclined plane nm is set to gradually move away from another end part, the more it approaches the direction of the unfixing position from the fixing position.SELECTED DRAWING: Figure 68

Description

[Technical Field]

[0001] The present invention relates to a chair. [Background technology]

[0002] BACKGROUND ART Various chairs with backrests that can be tilted backward have been known (see, for example, Patent Document 1).

[0003] Recently, in the industrial world, there has been a demand for the development of environmentally friendly products, especially in line with the SDGs. The chair sector is no exception, and one example of this is a structure that can be easily disassembled.

[0004] Additionally, in order to curb the spread of infectious diseases such as COVID-19, many users are using chairs at home to work, and there is a demand for chairs that can be easily disassembled by individuals.

[0005] However, most conventional chairs require disassembly by removing multiple screws, or require the application of dangerously large force when removing components, and are not something that anyone can easily disassemble.

[0006] In particular, the reaction force generating element that generates a reaction force against the backward tilting of the backrest is inherently dangerous when disassembled, and until now it has been extremely difficult to do so without using special tools. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5386071 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and aims to provide a chair in which at least a reaction force generating body can be suitably attached to and detached from a support base. [Means for solving the problem]

[0009] That is, the present invention has the following configuration.

[0010] The invention described in claim 1 is a chair comprising legs, a support base supported by the legs, and a back support supported on the support base so as to be rotatable relative to the support base between a normal position and a backward-inclined position that is tilted further back than the normal position, wherein a reaction force generating body is provided between the support base and the back support, which can urge the back support toward the normal position, the reaction force generating body being a compression spring type having one end attached to the support base via a support member and the other end attached to the back support, the support base being provided with a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member, the support member being able to move to a predetermined fixed position while engaging with the inclined surface by rotating the screw inserted into the first screw insertion hole in a first direction, and being able to move toward a counter-fixed position while engaging with the inclined surface by rotating the screw in a second direction, the inclined surface being set to gradually move away from the other end as it moves from the fixed position toward the counter-fixed position.

[0011] A second aspect of the present invention is the chair according to the first aspect, wherein a mounting portion to which the support member is attached is provided at the rear of the support base.

[0012] The invention described in claim 3 is a chair described in claim 2, in which the mounting portion comprises at least a bottom wall portion having the first screw insertion hole and a rear wall portion erected upward from the rear end of the bottom wall portion and having the inclined surface on its front surface.

[0013] The invention described in claim 4 is a chair described in claim 2, wherein the mounting portion comprises a bottom wall portion having the first screw insertion hole, a rear wall portion erected upward from the rear of the bottom wall portion and having the inclined surface on its front surface, and left and right side wall portions erected upward from both the left and right sides of the bottom wall portion and having their rear portions connected to the rear wall portion.

[0014] The invention described in claim 5 is the chair described in claim 4, wherein the support member is surrounded by the bottom wall portion, the rear wall portion, and the left and right side wall portions at the fixed position.

[0015] The invention described in claim 6 is a chair described in claim 1, in which the support member comprises a support member main body and a nut arranged inside the support member main body, the support base has a bottom wall portion having a second screw insertion hole through which the screw is inserted, and a peripheral wall portion erected upward from the peripheral edge of the bottom wall portion, and the nut is threaded onto the screw inserted through the first and second screw insertion holes.

[0016] The invention described in claim 7 is a chair described in claim 6, in which the nut engages with the surrounding wall portion so as to suppress left-right movement and horizontal rotation, and engages with the surrounding wall portion so as to allow forward-backward movement.

[0017] An invention recited in claim 8 is the chair recited in claim 1, wherein the first screw insertion hole is an elongated hole extending in the front-rear direction.

[0018] The invention described in claim 9 is a chair comprising legs, a support base supported by the legs, and a back support supported on the support base so as to be rotatable relative to the support base between a normal position and a backward tilted position tilted further back than the normal position, wherein a reaction force generating body is provided between the support base and the back support, which is capable of urging the back support toward the normal position, the reaction force generating body being a tension spring having one end attached to the support base via a support member and the other end attached to the back support, the support base being provided with a first screw insertion hole through which a screw for attaching the support member is inserted and an inclined surface that engages with the support member, the support member being capable of moving to a predetermined fixed position while engaging with the inclined surface by rotating the screw inserted into the first screw insertion hole in a first direction, and the support member being capable of moving in a direction opposite to the fixed position while engaging with the inclined surface by rotating the screw in a second direction, The inclined surface is set so as to gradually approach the other end portion as it moves from the fixed position toward the anti-fixed position. [Effects of the Invention]

[0019] As described above, the present invention can provide at least a chair in which the reaction force generating body can be suitably attached to and detached from the support base. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a perspective view showing an embodiment of the present invention; [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8]FIG. [Figure 9] FIG. [Figure 10] FIG. [Figure 11] FIG. [Figure 12] FIG. [Figure 13] FIG. [Figure 14] FIG. [Figure 15] Enlarged view of the bottom of Figure 14. [Figure 16] FIG. [Figure 17] FIG. 2 is a rear view of the back upholstery in the same embodiment with a portion thereof broken away. [Figure 18] FIG. 2 is a front view of the back upholstery in the same embodiment with a portion thereof broken away. [Figure 19] FIG. 2 is a perspective view of first and second belt-shaped members in the embodiment. [Figure 20] FIG. [Figure 21] FIG. [Figure 22] FIG. [Figure 23] FIG. 4 is a plan view illustrating the operation of the operating member in the embodiment. [Figure 24] FIG. 4 is a plan view illustrating the operation of the operating member in the embodiment. [Figure 25] FIG. 4 is a cross-sectional plan view illustrating the operation of the operating member in the embodiment. [Figure 26] FIG. 4 is a cross-sectional plan view illustrating the operation of the operating member in the embodiment. [Figure 27] 5 is a view taken in the direction of the arrow X in FIG. 4. [Figure 28] FIG. [Figure 29] FIG. [Figure 30]FIG. 4 is an enlarged perspective view of a rear portion of the seat support in the embodiment. [Figure 31] FIG. [Figure 32] FIG. [Figure 33] FIG. [Figure 34] FIG. [Figure 35] FIG. 2 is a perspective view of the seat body from below in the same embodiment. [Figure 36] FIG. [Figure 37] FIG. [Figure 38] FIG. [Figure 39] FIG. [Figure 40] FIG. [Figure 41] FIG. [Figure 42] FIG. [Figure 43] FIG. 4 is a cross-sectional view illustrating the attachment of the seat body to the seat receiver in the embodiment. [Figure 44] FIG. 4 is a cross-sectional view illustrating the attachment of the seat body to the seat receiver in the embodiment. [Figure 45] FIG. 4 is a cross-sectional view illustrating the attachment of the seat body to the seat receiver in the embodiment. [Figure 46] FIG. 4 is a cross-sectional plan view illustrating the attachment of the seat body to the seat receiver in the embodiment. [Figure 47] FIG. 4 is a cross-sectional plan view illustrating the attachment of the seat body to the seat receiver in the embodiment. [Figure 48] 5A to 5C are explanatory views of a method for forming an opening in the embodiment. [Figure 49] 5A to 5C are explanatory views of a method for forming an opening in the embodiment. [Figure 50] 5A to 5C are explanatory views of a method for forming an opening in the embodiment. [Figure 51] 5A to 5C are explanatory views of a method for forming an opening in the embodiment. [Figure 52] 5A to 5C are explanatory views of a method for forming an opening in the embodiment. [Figure 53] FIG. 10 is an enlarged view of the embodiment after the openings are formed. [Figure 54] FIG. 2 is a right side view of the embodiment (with the seat back tilted backward). [Figure 55] FIG. 2 is a right side view of the embodiment (seat in a forward-leaning position). [Figure 56] FIG. [Figure 57] FIG. [Figure 58] FIG. 10 is a left side view of the support base in the same embodiment. [Figure 59] FIG. [Figure 60] FIG. [Figure 61] FIG. [Figure 62] FIG. [Figure 63] FIG. [Figure 64] FIG. 3 is a partially enlarged longitudinal cross-sectional view of the leg and support base in this embodiment. [Figure 65] FIG. 3 is a partially enlarged longitudinal cross-sectional view of the leg and support base in this embodiment. [Figure 66] FIG. 3 is a partially enlarged longitudinal cross-sectional view of the leg and support base in this embodiment. [Figure 67] FIG. 3 is a partially enlarged vertical cross-sectional view of a reaction force generating body and a support member in this embodiment. [Figure 68] FIG. 68 is a partially enlarged longitudinal cross-sectional view corresponding to the cutting position of FIG. 67 in the same embodiment. [Figure 69] FIG. 2 is an exploded perspective view of the reaction force generator and the support member in this embodiment. [Figure 70] FIG. 4 is a perspective view of the support member in the same embodiment, seen from the rear. [Figure 71] FIG. 3 is a cross-sectional view illustrating the legs, the support base, and the lifting operation lever in this embodiment. [Figure 72] FIG. 3 is a cross-sectional view illustrating the legs, the support base, and the lifting operation lever in this embodiment. [Figure 73] Cross-sectional view taken along line AA in Figure 2. [Figure 74] 74 is a longitudinal cross-sectional view of the embodiment when the seat back is tilted backward, corresponding to the cutting position of FIG. 73. [Figure 75] FIG. 74 is a longitudinal cross-sectional view of the same embodiment when the seat is in a forward tilted position, corresponding to the cut position of FIG. 73. [Figure 76] 29 along line BB. [Figure 77] 77 is a cross-sectional view of the same embodiment when the seat is in a forward tilted position, corresponding to the cutting position of FIG. 76. FIG. [Figure 78] FIG. [Figure 79] FIG. 79 is a longitudinal cross-sectional view of the same embodiment when the seat is in a forward tilted position, corresponding to the cutting position of FIG. 78. [Figure 80] Cross section of line CC in Figure 84. [Figure 81] 81 is a cross-sectional view of the same embodiment when the seat is in a forward tilted position, corresponding to the cutting position of FIG. 80. [Figure 82] FIG. [Figure 83] FIG. [Figure 84] FIG. [Figure 85] FIG. [Figure 86] FIG. [Figure 87] 87 is a central vertical cross-sectional view corresponding to the cutting position of FIG. 86 for explaining the process of removing the intermediate member in this embodiment. [Figure 88] FIG. [Figure 89] FIG. [Figure 90] FIG. [Figure 91] FIG. [Figure 92]FIG. [Figure 93] FIG. [Figure 94] FIG. 79 is a longitudinal cross-sectional view of the seat in the lifted position corresponding to the cutting position of FIG. 78 in the same embodiment. [Figure 95] 79 is a longitudinal cross-sectional view of the seat in the lifted position corresponding to the cut position of FIG. 78 in the same embodiment, and the seat in the detached state from the support base. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, one embodiment of the present invention will be described with reference to FIGS.

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

[0023] The seat C is disposed on a support base B and is configured to be able to assume a normal position (ps), a forward-leaning position (pf) that is leaning further forward than the normal position (ps), and a backward-leaning position (pr) that is leaning further back 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 so as to be able to tilt backward relative to the support base B via the back support member L. In other words, the backrest M and the back support member L can take a normal position (ps) relative to the support base B and a backward tilt position (pr) that is tilted further backward than the normal position (ps).

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

[0026] The chair is provided with a seat forward tilting mechanism that can shift the seating load to the front of the seat C, i.e., the part of the seat C in front of the front axis j2, thereby rotating the seat C forward around the front axis j2 and transitioning it to a forward tilting posture (pf).

[0027] Each component of the chair in this embodiment will be described in detail below.

[0028] <<Legs A>> The leg A has a plurality of leg blades a1 with casters at their lower ends, and a leg support a2 that stands up from the area where the upper ends of the leg blades a1 gather.

[0029] In this embodiment, the leg A constitutes an obstructing member that can obstruct rotation in a predetermined direction relative to the support base B so that the lifting / lowering operating lever V, which extends and retracts the leg support a2 in the vertical direction, cannot assume a detachable position (SR) in which it can be detached from the support base B.

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

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

[0032] The gas cylinder ag has a known configuration and includes a cylinder portion a21 provided at the bottom of the leg support a2, a lifting rod a22 that can move up and down relative to the cylinder portion a21, and an operating member a23 that is protruded from the upper end of the lifting rod a22 so that it can move up and down in the vertical direction and that, when pressed downward, causes the gas sealed inside to become flowable, thereby enabling the lifting rod a22 to move up and down.

[0033] The lifting rod a22 is cylindrical. The outer circumferential 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 the diameter gradually decreases toward the top.

[0034] The upper part of the lifting rod a22 is adapted to fit into a fitting hole Ba, which is a 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 so that it can fit tightly around the upper part of the lifting rod a22.

[0035] The operating member a23 can be pressed downward by an elevation operation lever V, which is an operation lever rotatably supported on a 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 legs A so that it can be moved up and down and can rotate. The support base B is molded as a single piece from metal. The support base B is shaped like a box that is long in the front-to-rear direction and open at the top.

[0038] The support base B comprises a bottom wall portion 2 having a downward surface and integrally formed with an attachment portion 2T for supporting the rear end portion of the reaction force generating body R, left and right side walls b1 which are erected walls extending upward from both the left and right ends of the bottom wall portion 2, a rear wall b2 which is erected from the rear end portion of the bottom wall portion 2 and connects the rear ends of the left and right side walls b1, and extended flanges b3 which extend outward from the rear portions of the left and right side walls b1.

[0039] <Bottom wall part 2> The bottom wall portion 2 comprises a foundation bottom wall 21 having a substantially horizontal bottom surface and a fitting hole Ba, which is a leg connecting portion that fits into the upper part of the leg support a2; an inclined bottom wall 22 extending diagonally upward and rearward 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 gradually upward as it moves forward; and a rear bottom wall 24 extending substantially horizontally from the rear end of the inclined bottom wall 22 toward the rear.

[0040] The bottom wall 2 is provided with a rising structure 2S provided to rise 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 generator R is attached.

[0041] [Foundation bottom wall 21] A boss portion 211 is provided on the base bottom wall 21, and has a fitting hole Ba formed therein that penetrates in the vertical direction and fits onto the upper portion of the leg support b2.

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

[0043] [Front bottom wall 23] The front bottom wall 23 extends forward from the front end of the base bottom wall 21. A front shaft j2 is disposed on the front bottom wall 23 and inserted into the long holes b12 in the left and right side walls b1.

[0044] [Rear bottom wall 24] The rear bottom wall 24 extends rearward and substantially horizontally from the rear end of the inclined bottom wall 24. The left-right intermediate portion of the rear bottom wall 24 forms the bottom wall portion of the mounting portion 2T for mounting the support member W.

[0045] The rear bottom wall 24 is disposed at a position higher than the base bottom wall 21. On the rear bottom wall 24, a mounting portion 2T of a support member W that supports the rear end portion of the reaction force generator R is provided.

[0046] That is, by providing the rear bottom wall 24 at a position higher than the base bottom wall 21, a configuration can be suitably adopted in which the reaction force generating body R is disposed in a horizontal position.

[0047] [Rising structure 2S] The rising structure 2S is configured to include a screw hole n4 having a thread groove disposed above the fitting hole Ba.

[0048] The rising structure 2S is provided adjacent to and rises in front of the fitting hole Ba. The rising structure 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 a rising portion 25 that rises so as to partially surround the front of the fitting hole Ba in a plan view, and a horizontal portion 26 that is installed between the rising portions 25 so as to be positioned directly above the fitting hole Ba.

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

[0051] That is, the rear part of the standing part 25 is shaped so that a space is provided directly above the fitting hole Ba, and the horizontal part 26 can be integrally disposed above the space.

[0052] The horizontal portion 26 is provided with a screw hole n4 penetrating in a substantially vertical direction. The horizontal portion 26 is integrally connected to the upright portion 25.

[0053] The rising structure 2S provided on the chair of this embodiment is provided solely to enable an operator to separate the leg A from the support base B safely.

[0054] Using ordinary tools, an operator can insert a screw v4 of a size that matches the screw threading hole n4 from above downward into the screw threading hole n4 provided in the horizontal portion 26 of the rising structure portion 2S.

[0055] The upper part of the leg support b2, which is arranged directly below the screw threading hole n4, is configured to be pressed downward by a screw v4 that threads downward while using the rising structure part 2S, which is integrally formed with the support base B, as a foothold.

[0056] More specifically, the screw v4 threaded into the screw hole n4 rotates and descends while being guided by the thread groove of the screw hole n4, so that the lower end of the screw v4 can press downward against the outer peripheral edge portion of the upper end of the lifting rod a22 that constitutes the leg support b2.

[0057] The rising structure 2S is used when the leg A is to be detached 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 tightly fitted together.

[0058] In this embodiment, the pressing force of the screw v4 that can be screwed into the screw hole n4 of the rising structure 2S is used to release or relax the tight fit between the fit hole Ba and the lift 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 eliminating or alleviating the tight engagement between the engagement hole Ba and the lifting rod a22.

[0060] In other words, the chair of this embodiment is provided with a fit relaxation structure that relaxes the fit between the leg support a2 and the support base B. The fit relaxation structure has a screw threaded hole n4 disposed above the fit hole Ba in the support base B, and is designed so that the upper part of the leg support a2 can be pressed downward by a screw v4 threadedly inserted into the screw threaded hole n4.

[0061] The screw v4 may be any type as long as it conforms to a standard that matches the screw insertion hole n4 and has a certain length in the vertical direction. In this embodiment, when disassembling the chair, for example, the screw v5 used to fix the support member W to the mounting portion 2T of the support base B is removed, and then the screw v5 can be reused as the screw v4 to be threaded into the screw threading hole n4 of the rising structure 2S.

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

[0063] The mounting portion 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 mounting the support member W is inserted; a rear wall portion 27 which extends upward from the rear of the rear bottom wall 24 and has a rearwardly inclined inclined surface nm on its front surface; and left and right side wall portions 28 which extend forward from both left and right ends of the rear wall portion 27 and which extend upward from both left and right sides of the rear wall 24.

[0064] The rear bottom wall 24 has a generally horizontal plate shape. A first screw insertion hole h51, which is a screw insertion hole that penetrates in the vertical direction, is provided in the center of the rear bottom wall 24 in the left-right direction. The first screw insertion hole h51 is formed in the shape of an elongated hole that is elongated in the front-rear direction.

[0065] The rear bottom wall 24 is adapted to come into contact with the bottom wall portion w11 of the support member W, which is drawn toward the rear bottom wall 24 by the movement of a hexagonal nut n5 threaded onto the screw v5.

[0066] The rear wall portion 27 is shaped like an upright plate and is erected so as to be tilted backward relative to the rear bottom wall 24. The front surface of the rear wall portion 27 forms an inclined surface nm with which the rear wall portion w13 of the support member W abuts.

[0067] The inclined surface nm is set so as 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) tightened against the rear bottom wall 24 toward the anti-fixed position, i.e., above the lower position.

[0068] The left and right side wall portions 28 are erected on the rear bottom wall 24, and their rear portions are connected to the rear wall portion 27. The left and right side wall portions 28 play a role in determining the left-right position of the support member W, and also in ensuring the strength of the rear wall portion 27, which serves as a foothold for receiving the urging force of the reaction force generating body R.

[0069] <Left and right side walls b1> The left and right side walls b1 are erected from the left and right end portions of the bottom wall portion 2, i.e., the base 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 substantially linearly in the front-to-rear direction.

[0070] The left and right side walls b1 are provided with an axle hole b11 penetrating in the left-right direction, which is provided at a front-to-back position corresponding to the rear of the base bottom wall 21 and which can rotatably hold the main axle j1, a long hole b12 penetrating in the left-to-right direction, which is provided at a front-to-back position corresponding to the front of the front bottom wall 23 and which can hold the front axle j2 for supporting the front part 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 and which can rotatably support a lifting operation lever V for raising and lowering the seat C, a groove portion b14 provided in front of the long hole b12 and along the long hole b12 and which is open outward, and an axle movement restricting portion b15 which is provided at the upper end of the middle part in the front-to-back direction so as to protrude in a mountain shape and which prohibits the seat engagement axle j3 provided on the back support body L from moving forward and downward.

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

[0072] The left and right side walls b1 are integrally provided with boss-like portions b4 that protrude outward and 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 left-right region capable of directly supporting the main shaft j1 is ensured that is longer than the width of the left and right side walls b1. The boss-like portions b4 are connected to the front end of the extension flange b3.

[0073] [Long hole b12] The long hole b12 extends obliquely so that its lower end is located forward of its upper end in side view. A sleeve member gs made of synthetic resin is fitted into the long hole b12 to allow easy sliding on the front shaft j2. The front shaft j2 is supported by the long hole b12 via the sleeve member gs.

[0074] In other words, the support base B is provided with a long hole-shaped front shaft support portion that is composed of a long hole b12 and a sleeve member gs with excellent sliding properties that is attached to the long hole b12 and can support the front shaft j2 in a slidable manner.

[0075] [Lever support b13] The lever support portion b13 pivotally supports the lift control lever V so that it can perform a flap operation. The lift control lever V acts on the gas cylinder ag to operate the leg support a2 to extend and retract in the vertical direction.

[0076] The lever support portion b13 comprises a pair of front and rear support wall portions b15 protruding outward from the left side wall b1 in a direction approximately perpendicular to the left side wall b1, and a pair of shaft portions j4 protruding in directions approaching each other from the inner surfaces of the pair of support wall portions b15 that face each other.

[0077] A space in which the lifting operation lever V is disposed is formed between the pair of front and rear support wall portions b15.

[0078] The pair of shaft portions j4 protrude in opposite directions, i.e., in directions approaching each other with their axes aligned. Each shaft portion j4 has a narrow portion j41 that is narrow in the left-right direction, which is a direction perpendicular to the axis, and a wide portion j42 that is wider in the up-down direction, which is a direction perpendicular to the axis (wider than the narrow portion j41). In other words, the horizontal width of the shaft portion j4 is shorter than its vertical width.

[0079] [Groove b14] The groove b14 extends in the same direction as the long hole b12, that is, in a diagonal direction so that the lower end side is positioned forward of the upper end side in a side view.

[0080] In order to regulate the position of the seat receiver 1 relative to the support base B, a regulating protrusion 1t provided on the seat receiver 1 is arranged in the groove b14.

[0081] <Back wall b2> The rear wall b2 stands upright 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. A left-right intermediate portion of the rear wall b2 forms a rear wall portion 27 of the mounting portion 2T for mounting the support member W.

[0082] <Extended tsuba b3> The extending flanges b3 extend outward beyond the left and right side walls b1.

[0083] The extension b3 is provided with a damper mounting portion b31 for mounting a damper gx against which the back support base 4 abuts when the back support L tilts backward. The damper gx mounted on the damper mounting portion b31 can be engaged with an engaging protrusion 41c that protrudes inward from the upper end of each of the left and right arm bodies 411.

[0084] The lower front portion of the support base B having the above-described configuration is covered with a support base cover X1 made of synthetic resin.

[0085] <<Lifting operation lever V>> The lifting operation lever V is a single unit made of synthetic resin. The lifting operation lever V is configured to be attachable to the lever support portion b13 of the support base B without using fasteners such as screws.

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

[0087] The lifting / lowering operation lever V is operable by the user to make the leg support a2 of the leg A extendable and retractable in the vertical direction so as to raise and lower the seat C.

[0088] When the user moves the part of the lifting operation lever V on the operating end vc side upward, the lever rotates around the axis j4 of the support base B with which the bearing portion vb is engaged, and the rotating end va moves downward to press down the operating member a23 arranged at the upper end of the leg support a2.

[0089] The lifting operation lever V comprises a lever body vh in the shape of a plate extending in the left-right direction and having an operating end vc at its tip, a base end erection portion vi extending upward from the base end of the lever body vh, an inward extension portion vm extending inward from the upper end of the base end erection portion vi and having a rotating end va at its tip that can abut against the leg support a2, and a bearing portion vb provided between the base end erection portion vi and the inward extension portion vm.

[0090] <Lever body vh> The lever body vh is curved to fit the outer surface of the seat support body 1, i.e., curved in a partial arc shape that convexly extends downward when viewed from the front. The tip of the lever body vh is the operating end vc, which is primarily subjected to the operating force from the user's fingers. When not subjected to the operating force from the user, the operating end vc is configured to be located at its lowest position due to its own weight.

[0091] <Proximal end section vi> The base end erected portion vi is a generally square pillar-shaped member erected from the base end portion of the lever main body vh.

[0092] <Inward extension part vm> The inward extending portion vm is cantilevered by the base end erecting portion vi. The base end portion of the inward extending portion vm has substantially the same width as the base end erecting portion vi, and the width of the inward extending portion vm gradually decreases toward the tip end located inside the support base B.

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

[0094] <Bearing part vb> The bearing portions vb are provided at the front and rear of the boundary between the base end upright portion vi and the inward extending portion vm so as to face in opposite directions.

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

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

[0097] The pair of front and rear bearing portions vb are provided with a cutout portion vd, which is an escape passage through which the pair of front and rear shaft portions j4 can escape by moving the lifting operation lever V only when the lifting operation lever V takes on a predetermined releasable position (SR).

[0098] The notch vd of the bearing vb is set to a width that allows the narrow portion j41 of the shaft j4 of the lever support v13 to pass through, while the notch vd is set to a width that does not allow the wide portion j42 of the shaft j4 to pass through.

[0099] In this embodiment, the notch vd is located at a position where, when the lifting operation lever V is in the releasable position (SR), the shaft j4 can move linearly relative to the bearing portion vb and be released from the inside to the outside.

[0100] <<Installation of lift control lever V to support base B>> The mounting structure of the lifting operation lever V for mounting the lifting operation lever V to the support base B that constitutes the chair will be described.

[0101] In the chair of this embodiment, the lifting operation lever V can take 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] <About the no-escape position (SH)> When the leg A, which is an obstructing member, is fitted into the support base B, the lifting operation lever V can only take a non-detachable position (SH) in which it cannot be detached from the support base B.

[0103] That is, when the leg A is attached to the support base B in the normal state, the lifting operation lever V cannot take the releasable position (SR).

[0104] The chair supports the lifting operation lever V on the lever support part b13 of the support base B, and then attaches the leg support a2 of the leg A, which acts as an obstructing member, to the support base B, so that the range of rotation of the lifting operation lever V is restricted by the presence of the upper part of the leg support a2.

[0105] The lifting operation lever V can only be rotated within the range of the non-releasable position (SH) by the upper part of the leg support a2, and as a result, any further rotation is prevented, so that it cannot assume the releasable position (SR).

[0106] That is, when the leg A is attached to the support base B, the rotation end va of the lift control lever V abuts against the upper part of the leg support a2 in the non-detachment position (SH), and further downward movement of the rotation end va is prevented by the presence of the leg support a2. Therefore, the lift control lever V cannot be detached from the support base B unless the leg A is detached from the support base B.

[0107] <About the Release Position (SR)> The lifting operation lever V can take a detachable position (SR) in which it can be detached from the support base B only when the leg A, which is an obstructing member, is not fitted inside the support base B.

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

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

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

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

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

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

[0114] In this embodiment, the reaction force generator R is capable of biasing the center portion of the seat engagement shaft j3 in the left-right direction forward, using the support base B as a foothold. The seat engagement shaft j3 abuts against the shaft movement restricting portions b15 on the left and right side walls b1 of the support base B, and is prohibited from further forward and downward movement.

[0115] That is, when the seat engagement shaft j3 abuts against the support base B, the back support L is prohibited from rotating forward about the main shaft j1, and as a result, the normal posture (ps) of the back support L is determined.

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

[0117] The reaction force generating body 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 locking mechanism in which the seat occupant presses the seat engagement shaft j3 forward and downward via the seat C, the weight of the seat occupant assists in generating a reaction force in the normal posture (ps) direction against the backward tilting of the backrest M. For this reason, a relatively small and lightweight coil spring r1 is applied to 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 part of the coil spring r1, a rear member r3 attached to the rear part of the coil spring r1, and a posture holding shaft r4 whose front part is inserted into a holding hole provided in the front member r2 and whose rear part is inserted into a holding hole provided in the rear member r3, thereby holding the posture of the front member r2 and the rear member r3.

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

[0121] The rear end of the rear member r3 is supported on the support base B via a 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 the support member W. 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 at the upper and lower parts of the engagement recess r31 so as to match their left-right positions.

[0122] The engaging recesses r31 of the rear member r3 are adapted to engage with a pair of left and right shaft protrusions w15 protruding from the vertical middle of the front wall portion w12 of the support member main body w1. The pair of left and right shaft protrusions w15 are protruding forward so as to form a partial disk shape in side view.

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

[0124] Although the front member r2 and the rear member r3 have different postures, they have the same shape.

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

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

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

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

[0129] [Bottom wall part w11] The bottom wall portion w11 has a second screw insertion hole h52 that is elongated in the front-rear direction and is provided in the center in the left-right direction. The lower surface of the bottom wall portion w11 is configured to abut against the rear bottom wall 24 of the mounting portion 2T at the fixed position.

[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 surface wm that can slide against the inclined surface nm of the rear wall portion 27 of the support base B, and left and right side wall portions w14 that connect the left and right side portions of the front wall portion w12 and the rear wall portion w13.

[0131] The front wall portion w12 has a pair of left and right axial protrusions w15 protruding from the middle portion in the vertical direction so as to be able to engage with the engagement recess r31 of the rear member r3, and a mountain-shaped protrusion w16 protruding from the middle portion in the horizontal direction so as to be able to engage with the vertical engagement recess r32 of the rear member r3.

[0132] The rear wall portion w13 is inclined backward in a side view. The inclined back surface portion wm of the rear wall portion w13 facing rearward is inclined so as to be positioned gradually rearward as it extends upward.

[0133] The left and right side wall portions w14 each have an outer wall wa and an inner wall wb disposed inward of the outer wall wa. The nut installation space wk is defined by the front wall portion w12 and the rear wall portion w13 of the peripheral wall portion ws, and the inner walls wb of the left and right side wall portions w14.

[0134] The hexagonal nut n5 disposed in the nut disposition space wk of the peripheral wall portion w12 engages with the inner peripheral surface of the peripheral wall portion w12 so as to restrict left-right movement and horizontal rotation. In addition, the nut disposition space wk is formed so that the dimension in the front-rear direction gradually increases toward the top, allowing the hexagonal nut n5 to move in the front-rear direction.

[0135] <Hexagon nut n5 (nut)> The hexagonal nut n5 has a known configuration and is held by the support base main body w1. The hexagonal nut n5 has a threaded groove and is threaded onto a screw v5 that is inserted into 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 main body w1.

[0136] The hexagonal nut n5 engages with the peripheral wall portion w12 so as to restrict left-right movement and horizontal rotation, and also engages with the peripheral wall portion w12 so as to allow forward-backward movement.

[0137] <Operation of the support member W for mounting the reaction force generating body R> The support member W for mounting the reaction force generating body R is attached to the attachment portion 2T as follows.

[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 main body w1.

[0139] Next, the screw v5 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 main body w1, and is connected (screwed) to the hexagonal nut n5 arranged inside the support base main 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-to-rear direction. In other words, the support member W is located above and rearward of the fixed position. The screw v5 inserted through the first and second elongated screw insertion holes h51 and h52 can easily assume a rearward tilted position in order to screw into the hexagonal nut n5.

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

[0142] Next, the screw v5 threaded into the hexagonal nut n5 is rotated 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 toward the rear bottom wall 24 of the mounting portion 2T as a result of the worker's rotation of the screw v5.

[0144] At this time, as the support member W moves downward, the reaction force generator R applies a gradually increasing rearward force to the support member W. That is, as the support member W descends, it is guided by the inclined surface nm of the mounting portion 2T and moves downward and forward, so that the reaction force generator R is gradually compressed between the seat engagement shaft j3 and the support member W, and the biasing force gradually increases.

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

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

[0147] The reaction force generating body R and the support member W can be removed extremely safely by reversing the above-described procedure.

[0148] That is, by rotating the screw v5 in the second direction, the support member W can be moved (raised) in the direction opposite to the fixed position while being guided while engaging with the inclined surface nm. At this time, the support member W moves upward and rearward while being guided by the inclined surface nm while weakening the biasing force of the reaction force generating body R as the hexagonal nut n5 rises.

[0149] The worker can complete the initial step of disassembling the reaction force generating body R and the support member W, which can be dangerous, by simply rotating the screw v5 in the second direction without touching the reaction force generating body R or the support member W.

[0150] <<Location C>> The seat C is supported by a support base B disposed on the legs A. The lower surface of the support base B and the outer peripheral surface of the seat C are configured to be smoothly continuous when viewed from the front.

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

[0152] The outer peripheral surface of the seat C, that is, the outer peripheral surfaces of the seat receiving body 1 and the seat main body D, are smoothly continuous so as to form a partial sphere.

[0153] <About the forward tilting configuration of seat C> The front part of the seat C is supported via a front axis j2 so as to be rotatable and movable up and down relative to the support base B. The rear part of the seat C is supported by a seat engagement axis j3, which is the seat engagement part of the back support L, a structure supported by the support base B in the normal posture (ps). Here, the "rear part of the seat C" supported by the back support L means "behind the front part of the seat C."

[0154] The seat C is configured to be tiltable around a front axis j2 supported by the support base B between a normal position (ps) and a forward tilted position (pf) tilted further forward than the normal position (ps).

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

[0156] The engaged portion 1k of the seat C is adapted to engage with the seat engaging shaft j3 so as to rest on the seat engaging shaft j3 when the seat is in the normal posture (ps) or the backward tilted posture (pr). The engaged portion 1k of the seat C is adapted to move upward away from the seat engaging shaft j3 when the seat is in the forward tilted posture (ps).

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

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

[0159] The outer peripheral surface of the front part of the seat support body 1 is configured to smoothly connect to the underside of the front part of the support base B. In addition, the outer peripheral surface of the seat support body 1 is configured to smoothly connect to the outer peripheral surface of the seat main body D.

[0160] The seat receiving 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 has a recess 11 that is open downward and in which the support base B and back support body L are arranged, a shell body arrangement section 12 that is a seat body mounting section provided on the upper surface section, a recess 13 that is open upward and provided in the center in the left-right direction in which an intermediate member U and a coil spring Y are arranged, and an arm passage hole 14 that is a vertical communication hole that is provided between the recess 13 and the recess 11 and through which the arm portion u2 of the intermediate member U can pass.

[0162] <Recess 11> The recess 11 is provided in the lower part of the center in the left-right direction of the seat receiving body 1, and is open downward so that the support base B can be disposed therein.

[0163] The recess 11 has a recessed space in which the support base B and the back support L are disposed.

[0164] At a location facing the recessed space of the recess 11 in the seat support body 1, there are provided a front axle holding portion 1m capable of holding the front axle j2, an engaged portion 1k arranged behind the front axle holding portion 1m and engaging with the seat engaging axis j3 in the normal position (ps) and the rearward tilted position (pr) and separating from the seat engaging axis j3 in the forward tilted position (pf), and a regulating protrusion 1t arranged in a groove portion b14 provided in the support base B.

[0165] The recess 11 comprises a recess top wall portion 111 having an engaging portion 1k on the underside facing the recess space and which is the portion with which the seat engagement axis 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 side portions 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 shaft j3.

[0167] [Front shaft holding part 1m] The front axle holders 1m protrude downward from the front of the recess top wall 111. The front axle holders 1m are provided in pairs on both the left and right sides of the recess top wall 111. The left and right front axle holders 1m are shaped to hold both the left and right ends of the front axle j2. Adjacent to the left and right front axle holders 1m are shaft passages 1r through which the front axle j2 can pass when attaching or detaching the front axle j2.

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

[0169] The engaged portion 1k has an upper contact portion 1ku that can contact the upper portion of the seat engagement shaft j3 and a rear contact portion 1kr that can contact the rear portion 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 be able to move toward and away from the seat engaging shaft j3 as the position of the seat C changes.

[0171] The engaged portion 1k engages with the seat engaging shaft j3 when the seat C is in the normal position (ps) or the backward tilted position (pr), and is configured to separate from the seat engaging shaft j3 only when the seat C is in the forward tilted position (pf). In other words, the engaged portion 1k is not configured to constantly hold the seat engaging shaft j3 so that it does not come off, but is configured to be able to come into contact with and separate from the seat engaging shaft j3.

[0172] [Regulating protrusion 1t] The restricting projection 1t is intended to prevent the seat body 1 from separating from the front axis j2 unless the seat body 1 takes the jumped-up position (ph), which is the position for separating the seat support body 1 from the front axis j2.

[0173] In other words, the regulating protrusion 1t engages with the groove portion b14 of the support base B and can regulate 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 the predetermined bounced-up position (ph).

[0174] The restricting protrusions 1t are provided in pairs on the left and right in front of the recess 11 of the seat support body 1. The restricting protrusions 1t protrude inward at locations on the seat support body 1 that correspond to the groove portions b14 of the support base B. The restricting protrusions 1t are inclined so that they are positioned gradually upward toward the rear. The restricting protrusions 1t protrude from the inside of the left and right front axle holding portions 1m.

[0175] <Shell body installation section 12> The shell body mounting portion 12 has a connecting portion with the shell body 3 of the seat main body D, and is provided in the upper portion of the seat receiving body 1, that is, in the portion of the seat receiving body 1 facing upward.

[0176] The rear end of the shell body installation portion 12 is provided with a notch 122 for avoiding interference with the operating lever k2 provided on the shell body 3.

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

[0178] The outer peripheral edge 1e of the seat support 1 is formed so as to be gradually positioned downward (concave downward) from both left and right ends toward the center in the left-right direction when viewed from the front and back. Also, the outer peripheral edge 1e of the seat support 1 is formed so as to be gradually positioned upward (convex upward) from both front and rear ends toward the center in the front-to-rear direction when viewed from the side.

[0179] The upper end of the seat receiver peripheral wall portion 121 erected inside the outer peripheral edge 1e of the seat receiver 1 is provided so as to extend in a substantially horizontal direction when viewed from the front, back, and side.

[0180] <Recess 13> The recess 13 is provided in the upper part of the seat receiving body 1 in order to accommodate 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 engaging shaft j3.

[0181] The recess 13 is recessed downward relative to the central top wall portion 123, which is the upper surface portion of the seat support body 1 that constitutes the shell body installation portion 12. The recess 13 is open upward and includes the other spring support portion 13a that is provided facing upward to receive the lower portion of the coil spring Y.

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

[0183] The recess 13 includes a bottom wall 131 having the other spring receiving portion 13a facing upward on its 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 provided spaced apart on the left and right so that the arm portion u2 of the intermediate member U can be disposed on the recess 11 side. That is, the bottom wall 131 of the recess 13 is provided spaced apart on the left and right via the arm passing hole 14.

[0185] <Arm passage hole 14> The arm passing hole 14 allows the arm portion u2 of the intermediate member u2 to pass through. The arm passing hole 14 is provided between the recess 13 and the recess 11. The arm portion u2 of the intermediate member U is arranged in the arm passing hole 14. The arm passing hole 14 allows the intermediate member U held in the recess 13 to move in the up and down direction.

[0186] <Configuration for easily attaching and detaching the seat support body 1 to and from the support base B> The seat support 1 is rotatable around the front axis j2 so that its rear end portion bounces up after the intermediate member U is released. The front axis holding portion 1m is configured to be detachable from the front axis j2 only when the seat support 1 is changed to a predetermined bounced-up position (ph).

[0187] A pair of grooves b14 extending in the vertical direction and opening outward are provided on the left and right sides of the front portions of the left and right side walls b1 of the support base B.

[0188] The seat support body 1 is provided with a pair of inwardly protruding restriction protrusions 1t on the left and right at locations corresponding to the groove portions b14 of the support base B. The restriction protrusions 1t are provided on the inner sides of the left and right front axle holding portions 1m provided on the seat support body 1.

[0189] When the seat support 1 is restricted from coming off by the intermediate member U (i.e., when the intermediate member U is interposed between the seat support 1 and the seat engagement axis j3), the restricting protrusion 1t is positioned within the groove portion b14, and the front axle holding portion 1m is configured to be unable to come off forward relative to the front axle j2.

[0190] Even if the intermediate member U is not interposed between the seat receiving body 1 and the seat engagement axis j3, if the predetermined jump-up posture (ph) is not taken, the regulating protrusion 1t and the groove portion b14 will engage, and the front axle holding portion 1m will not be able to disengage from the front axle j2.

[0191] When the seat support body 1 takes a predetermined jump-up position (ph), the position is changed so that the regulating protrusion 1t is positioned outside the groove portion b14, and the front axle holding portion 1m can be released forward from the front axle j2.

[0192] That is, in this embodiment, the seat body 1 can be easily separated from the front axis j2 (support base B) by placing it in a predetermined jump-up position (ph) without using any special tools. On the other hand, the seat body 1 cannot be separated from the front axis j2 (support base B) unless it is placed in the predetermined jump-up position (ph), so a configuration is realized in which the seat body 1 is stably supported.

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

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

[0195] The intermediate member U is disposed between the seat engaging shaft j3 of the back support L rotatably supported on the support base B and the rear part of the seat C, that is, the part near the engaged part 1k.

[0196] The intermediate member U has a portion that engages with the seat engagement shaft j3 and a portion that engages with the seat support body 1 via the coil spring Y. The intermediate member U can limit the distance that the engaged portion 1k is separated from the seat engagement shaft j3 in the forward tilt posture (ps).

[0197] The intermediate member comprises an intermediate member body u1 having a spring support portion u11 that supports the upper end portion, 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 the seat engagement shaft j3, which is the seat engagement portion.

[0198] [Intermediate member body u1] The intermediate member main body u1 is a horizontally long rectangular plate as a whole, and is provided with one spring receiving portion u11 that faces downward.

[0199] That is, a pair of spring receiving portions u11 for receiving the upper ends of the pair of left and right coil springs Y are provided on the lower surface of the intermediate member main body u1.

[0200] [Arm part u2] The arm portion u2 has a downward extension portion u21 that extends downward from the front of the intermediate member main body u1, and a hook-shaped portion u22 that extends 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 axis j3.

[0201] <Coil spring Y (spring material)> The coil springs Y are interposed between the seat support body 1 and the intermediate member U. The coil springs Y are arranged in pairs on the left and right. 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 receiving body 1 as a foothold. That is, the coil spring Y biases the intermediate member U in a direction in which it engages with the seat engaging shaft j3.

[0203] <Detachable structure of intermediate member U> The intermediate member U can restrict the separation of the seat support body 1 from the back support body L. In other words, the intermediate member U is interposed between the back support body L and the seat support body 1 so that the rear part of the seat support body 1 does not move away 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 portion of the seat engagement shaft j3 of the back support L, and the intermediate member body u1 of the intermediate member U engages with the seat receiving body 1 via the coil spring Y.

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

[0206] In other words, the intermediate member U can be pressed in a direction against the spring force of the coil spring Y to release the engagement of the intermediate member U with the seat engagement axis j3, and is configured to be able to separate from between the seat engagement axis j3 and the seat support 1 when the engagement is released.

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

[0208] <Seat body D> The seat body D includes a seat cushion Dq, a cushion-supporting shell body 3 that is a support member attached to the underside of the seat cushion Dq, and a seat upholstery Dh that covers the upper and peripheral edge of the seat cushion Dq and also covers the peripheral edge of the shell body 3. The seat body D has a seat surface on the upper surface that is approximately circular in plan view.

[0209] [Seat cushion Dq] The seat cushion Dq is made mainly of urethane foam, which is a foam material. The seat cushion Dq is formed so that its width gradually increases toward 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 over the shell body 3. When viewed from the bottom, the seat cushion Dq is larger than the shell body 3. The dimensions of the seat cushion Dq in the front-rear and left-right directions are set longer than the dimensions of the shell body 3 in the front-rear and left-right directions.

[0211] [Shell body 3] The shell body 3 is a generally disk-shaped body attached to the underside of the seat cushion Dq and is integrally formed from synthetic resin.

[0212] The shell body 3 comprises a shell body main body 31 having a disk-shaped portion whose upper surface is adhered to the underside of the seat cushion Dq; a support wall portion 33 that is connected to and extends downward from the peripheral edge of the shell body main body 31 and whose outer surface is in contact with the inner surface of the peripheral edge of the seat cushion Dq; an end wall portion 34 that extends diagonally upward and outward from the lower end of the support wall portion 33 and supports the lower end of the peripheral edge of the seat cushion Dq; and a peripheral wall portion 32 that is suspended downward from the underside of the peripheral edge of the shell body main body 31, more inward than 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 when viewed from the front, rear, and side.

[0214] The shell body 3 is integrally provided with an operating lever k2 that is cantilevered and has a protrusion kt that is a portion that engages with the seat receiving body 1 to prevent relative rotation from the mounting position (F).

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

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

[0217] The peripheral wall 32 is disposed on the peripheral edge of the shell body 3. More specifically, the peripheral wall 32 is disposed closer to the center than the support wall 33 of the shell body 3. The peripheral wall 32 has an outward surface 32m against which the edge de of the seat upholstery Dh that encases the seat cushion Dq can come into contact.

[0218] The peripheral wall portion 32 is disposed in a substantially annular shape in bottom view. That is, the peripheral wall portion 32 is disposed continuously on a perfect circular path except for one location at the rear where the operating lever k2 is disposed, so as to be located on an imaginary circumferential line that forms a perfect circle centered on the central protrusion g1 in bottom view.

[0219] The peripheral wall 32 has outward extensions 321 that extend outward and restrict downward movement of the edge de of the seat upholstery Dh. The outward extensions 321 are protruding pieces that are arranged at regular intervals around the circumferential direction of the peripheral wall 32.

[0220] Inward protrusions it are provided on the inner surface of three locations on the front end and both left and right end portions of the peripheral wall portion 32, namely, on the inner surface of the central portion in the left-right direction of the front portion of the peripheral wall portion 32 and on the inner surface of the central portions in the front-rear direction of both left and right portions of the peripheral wall portion 32. The inward protrusions it constitute a horizontal engagement mechanism I, which will be described in detail later.

[0221] Ribs rv are connected to the inner surface of the peripheral wall portion 32. The ribs rv are vertically attached to the shell body main body 31 and extend outward from the center of the shell body main body 31. The ribs rv are radially arranged on the lower surface of the shell body main body 31.

[0222] The operating lever k2 is supported in a cantilevered manner on the shell body main body 31. That is, the shell body 3 is provided with the operating lever k2, which is a cantilevered lever member that engages with the seat support body 1. The operating lever k2 has a wall-like portion k21 that constitutes part of the peripheral wall portion 32 and stands upright from the base end portion of the operating end portion k22.

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

[0224] The operating lever k2 has a downwardly projecting convex portion kt between the base end portion ke and the operating end portion k22, which can be engaged with an upwardly facing concave portion k1 provided in the seat support body 1. The concave portion k1 of the seat support body 1 and the convex portion kt of the operating lever k2 constitute a reverse restriction mechanism K, which will be described in detail later.

[0225] The lower edges 3e of the support wall portions 33 of the shell body 3 are formed so as to be gradually positioned downward (so as to be convex downward) from both left and right ends toward the center in the left-right direction in front and rear views. Also, the lower edges 3e of the support wall portions 33 of the shell body 3 are formed so as to be gradually positioned upward (so as to be convex upward) from both front and rear ends toward the center in the front-rear direction in side view.

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

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

[0228] The seat upholstery Dh has a ring-shaped edge portion de. The seat upholstery Dh is configured in a bag-like shape that is open downward. The seat upholstery Dh is provided with a string-like member (not shown) that reduces the diameter of the edge portion de and causes the edge portion de to abut against the outward surface 32m of the peripheral wall portion 32 of the shell body 3.

[0229] <<Attachment / detachment structure of the seat body D to the seat support body 1>> The seat body D is configured to be horizontally rotatable 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.

[0230] The chair of this embodiment is configured so that the seat body D can be easily attached and detached to the seat support 1 without the use of tools, not only by the manufacturer but also by the end user, to facilitate maintenance such as cleaning and replacement, as well as storage and transportation.

[0231] Between the seat support 1 and the seat body D, there are provided a central positioning section G that positions the seat body D so that its axis coincides with that of the seat support 1, a vertical engagement mechanism H that tightly engages the seat support 1 and the shell body 3 in the vertical direction when the seat body D is in the mounting position (F), a horizontal engagement mechanism I that tightly engages the seat support 1 and the shell body 3 in the horizontal direction when the seat body D is in the mounting position (F), and a reversal prevention mechanism K that prevents the seat body D in the mounting position (F) from moving backward toward the retracted position (E).

[0232] <Central positioning part G> The central positioning portion G is capable of positioning the seat receiving body 1 and the shell body 3 of the seat main body D so that they can be approximately aligned with the common axis cj.

[0233] The central positioning portion G is cylindrical and includes a downwardly protruding central convex portion g1 provided in the center of the shell body 3 of the seat main body D, and a hole-shaped central convex portion engagement portion g2 provided in the center of the seat receiving body 1 with which the central convex portion g1 engages so as to be able to rotate relative to the seat main body D.

[0234] <Vertical engagement mechanism H> The vertical engagement mechanism H engages the seat receiving body 1 and the shell body 3 of the seat main body D in the vertical direction so as to draw them together.

[0235] The vertical engagement mechanism H has a locking protrusion hp, which is a first engagement portion provided on the seat support 1, and a locking protrusion engagement portion hk, which is a second engagement portion provided on the shell body 3 and can engage with the locking protrusion hp of the seat support 1.

[0236] The seat body D can take the mounting position (F) by tightly engaging the locking projection hp with the locking projection engagement portion hk.

[0237] The locking projections hp of the seat receiving body 1 and the locking projection engaging portions hk of the shell body 3 are arranged at regular intervals along an imaginary circumferential line centered on the common axis cj.

[0238] [Latching protrusion hp (first engagement part)] The locking protrusions hp constitute a protruding structure protruding in a direction intersecting the common axis cj. The locking protrusions hp protrude approximately horizontally inward, i.e., toward the center of the common axis cj, from the seat support peripheral wall 121, which is erected in a substantially annular shape in plan view on the periphery of the seat support 1.

[0239] The locking protrusion hp can be engaged in the vertical direction with the guide inclined surface hm provided on the locking protrusion engagement portion hk. More specifically, the locking protrusion hp can press the guide inclined surface hm of the locking protrusion engagement portion hk downward. In other words, the locking protrusion hp moves the seat body D downward when the seat body D is rotated from the retracted position (E) to the attached position (F).

[0240] [Latching protrusion engaging part hk (second engaging part)] The locking projection engaging portion hk has an upwardly facing guide inclined surface hm with which the locking projection hp can engage. The locking projection engaging portion hk is provided to protrude downward from the shell body main body 31, which is in the shape of a circular plate.

[0241] The locking projection engaging portion hk comprises a support wall hs extending downward from the shell body main body 31, and an engaging portion main body hg supported by the support wall hs and having an upwardly 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 approximately perpendicular to the first support wall portion ha.

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

[0244] The engagement body hg is a plate-like member that is in a laid-down position and extends in the circumferential direction. The inner edge and base edge of the engagement body hg are connected to the support wall hs. The upward guide inclined surface hm provided on the engagement body hg is inclined so as to be positioned gradually upward from the tip side toward the base side. Here, the tip side of the engagement body hg refers to the edge side that forms the tip of the direction of travel when pivoting from the retracted position (E) to the attached position (F).

[0245] The locking protrusion hp and guide inclined surface hm of the vertical engagement mechanism H configured as described above are configured so that the degree of contact gradually increases as the seat body D rotates from the retracted position (E) to the attached position (F).

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

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

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

[0249] Thereafter, as shown in FIG. 45, when the seat body D reaches the mounting position (F), the locking projection hp and the locking projection engagement portion hk are engaged so as to come into close contact with each other in the vertical direction.

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

[0251] The horizontal engagement mechanism I comprises an inward protrusion it, which is a second engagement portion provided on the shell body 3, and an outward guide inclined surface im, which is a first engagement portion provided on the seat support body 1 and can engage with the inward protrusion it, which is a horizontal protrusion of the shell body 3.

[0252] The inward protrusion it of the shell body 3 and the outward inclined guide surface im of the seat support body 1 are arranged at regular intervals along an imaginary circumferential line centered on the common axis cj.

[0253] [Inwardly protruding part it (second engaging part)] The inward protrusion it constitutes a protruding structure protruding in a direction intersecting the common axis cj. The inward protrusion it protrudes inward, i.e., in the direction of the common axis cj, from the peripheral wall portion 32, which is a hanging wall-like wall erected on the shell body 3 so as to form a substantially annular shape in a plan view.

[0254] In addition, from the portion of the peripheral wall 32 where the inward protrusion it is provided, an outward extending portion 321 extends in the opposite direction, i.e., outward, to engage with the edge portion de of the seat upholstery Dh.

[0255] The inward protrusion it can be horizontally engaged with the outward inclined guide surface im provided on the seat support 1. More specifically, the inward protrusion it can press the outward inclined guide surface im provided on the seat support peripheral wall portion 121 of the seat support 1 inward.

[0256] [Outward guide inclined surface im (first engagement portion)] The outward inclined guide surface im is provided on the outer peripheral surface of the seat support peripheral wall portion 121, which is an upright wall erected on the peripheral edge portion of the seat support 1. The outward inclined guide surface im faces outward, which is the horizontal direction in which it can engage with the inward protrusion it. The outward inclined surface is inclined so that it is positioned gradually outward as it moves clockwise.

[0257] The inward protrusion it and outward guide inclined surface im of the horizontal engagement mechanism I configured as described above are configured so that the degree of close contact gradually increases as the seat body D rotates clockwise from the retracted position (E) to the attached position (F).

[0258] <Reverse control mechanism K> The reversal prevention mechanism K is provided between the seat body D and the shell body 3 of the seat support 1, and prevents the seat body D from moving back in the mounting position (F) toward the retracted position (E).

[0259] On the other hand, the reverse restriction mechanism K can release the state in which the seat body D cannot rotate relative to the seat support body 1 by operating the operating lever k2 so as to deform it upward against the elastic return force of the shell body 3, and the seat body D can be rotated from the mounting position (F) to the retracted position (E) and separated from the seat support body 1.

[0260] The reverse restriction mechanism K comprises a recess k1 provided on the upper surface of the rear end of the seat support body 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 restriction mechanism K is provided on a cantilevered operating lever k2 provided on the shell body 3. When the operating end k22 of the operating lever k2, which receives the operating force from the user's fingers, is moved upward by utilizing the elastic deformation of the member, the protrusion kt of the operating lever k2 is released from the engagement with the recess k1 provided in the seat support body 1, and the seat body D can be rotated from the attached position (F) to the retracted position (E).

[0262] In addition, a guide inclined surface km that can engage with the protrusion kt of the operating lever k2 is provided on the upper surface of the rear end of the seat support body 1, adjacent to the recess k1. The guide inclined surface km is inclined so that it gradually rises as it approaches the recess k1. The top of the inclined surface is set to be located 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 located at the lowest position on the inclined surface. When the seat body D rotates from the retracted position (E) to the attached 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] When the seat body D moves from the retracted position (E) to the attached position (F), the convex portion kt climbs over the guide inclined surface km and engages with the concave portion k1 due to the elastic restoring force of the operating lever k2.

[0265] In this embodiment, when the reverse-back limiting mechanism K moves from the retracted position (E) to the attached position (F), the pivoting movement of the shell body 3 causes the convex portion kt to rise up the inclined guide surface km of the seat support body 1, eliminating the need to apply an operating force to the operating lever k2. At this time, once the convex portion kt of the operating lever k2 has climbed up the inclined guide surface km, the elastic restoring force of the operating lever k2 automatically fits into the concave portion k1. In other words, no special operation of the operating lever k2 is required for the reverse-back limiting mechanism K to move from the retracted position (E) to the attached position (F).

[0266] The peripheral wall 32 of the shell body 3 is provided on both sides adjacent to the operating lever k2 with downward protrusions 32t 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 supporting surface when the seat body D or the shell body 3 is placed independently on a supporting surface such as the floor for the purpose of using it as a replacement part, etc.

[0268] In other words, the downward protrusions 32t provided on the left and right sides of the operating lever k2 can suppress the operating lever k2 from being pushed up by the placing surface, thereby making it possible to preferably prevent the operating lever k2 from developing a bending tendency that would impair the 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 can operably support the backrest M between a normal position (ps) and a backward tilted position (pr) that is tilted further back 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 an engagement 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 relative to the support base B via the main axis j1, a back support main body 5 attached to the back support base 4, and a cover member 6 attached to the back support main body 5.

[0274] The back support L supports left and right operating members p1 that can change their position between an engagement 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 detachment 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 each having an upright plate shape extending in the front-to-rear direction and rotatably supported on the support base B via a main shaft j1, an upright plate-shaped connecting member 42 connecting the rear portions of the pair of left and right arms 41, and a seat engagement shaft j3 extending in the left-to-right direction and supported at a position forward of the main shaft insertion hole 41a of the pair of left and right arms 41.

[0276] [Left and right arms 41] The left and right arms 41 are made of metal. The left and right arms 41 are shaped like upright walls having left and right arm bodies 411 that extend longitudinally in the front-to-rear horizontal direction. The left and right arms 41 are disposed outside the left and right side walls b1 of the support base B.

[0277] The left and right arms 41 include left and right arm bodies 411 that extend in a substantially straight line in the front-to-rear direction and can support the main shaft j1 at their front end portions, left and right forearm sections 412 that extend diagonally upward and forward from the front end portions of the left and right arm bodies 411 and support, at their upper end portions, a seat engagement shaft j3 that engages with the seat C, and a main shaft insertion hole 41a that is provided between the left and right arm bodies 411 and the left and right forearm sections 412 and penetrates in the left-to-right direction and can hold the main shaft j1.

[0278] The rear portions of the left and right arm bodies 411 are connected by a connecting member 42. The rear end portions of the left and right arm bodies 411 protrude rearward beyond the connecting member 42. Rearward protruding portions 41b of the left and right arm bodies 411 protruding rearward beyond the connecting member 42 are adapted to fit into fitting holes 5b of back support body base connecting portions 5a provided at the base end portion 51 of the back support body body 5.

[0279] The left and right front arm portions 412 are integrally extended diagonally upward and forward from the front ends of the left and right arm bodies 411. A seat engagement shaft j3 extending in the left-right direction and capable of engaging with the seat C is rigidly connected to the distal ends, i.e., the upper ends, 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 has an upright plate shape that extends in the left-right direction. The left and right ends of the connecting member 42 are rigidly connected to the inner sides of the left and right arm bodies 411 by welding.

[0281] The connecting member 42 is provided with a nut portion n3 onto which a screw v3 for attaching the back support body 5 is threaded. A connecting wall 5c of the back support body base connecting portion 52 provided at 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 forearm 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 beyond both sides of the support base B.

[0283] The seat engagement shaft j3 is disposed in front of and above the main shaft j1. The seat engagement shaft j3 pushes up the middle part of the seat C in the front-rear direction upward and rearward as the back support L tilts backward. In other words, this chair is configured so that when the back support L tilts backward, the seat engagement shaft j3 pushes up the seat C, lifting the front part 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 disposed using the support base B as a foothold. The seat engagement shaft j3 is pressed forward by the reaction force generating body R.

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

[0286] When the backrest M is tilted backward by the weight of the seated person, the back support L7 supporting 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 of the back support base 4 move downward and forward, and the left and right front arm portions 412 of the back support base 4 move upward and backward.

[0288] The seat engagement shaft j3 connected to the upper portions of the left and right front arm portions 412 moves upward and backward in the same manner as the left and right front arm portions 412 move.

[0289] The seat engaging shaft j3 moves upward and backward to lift the seat C upward against the seating load of the seated person.

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

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

[0292] The back support base connecting portion 5a is a pair of left and right connectors that are open forward and engage with rearward protruding portions 41b that protrude from the rear end of the back support base 4. Fitting hole 5b and a connecting wall 5c disposed between the 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 has a screw insertion hole h3 penetrating in the front-to-rear direction. The back support body main body 5 is attached to the back support body base 4 by threading a screw v3 inserted into 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 sides of the arm body 411 of the back support base 4. The front portions of the left and right arm portions 5d are located outside in the axial direction 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 slipping out of the support base B.

[0295] The main shaft j1 is simply a cylindrical shape extending in the left-right direction. The main shaft j1 in this embodiment 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 is simply positioned relative to the support base B using the arm portion 5d of the spine support body 5 of the spine support L.

[0296] A recess q2 that constitutes the positioning mechanism Q is provided on the front side of the upper end of the left and right standing frame portions 52, i.e., on the front side of the connecting portion between the left and right standing frame portions 52 and the upper frame portion 53. The recess q2 will be described in detail later.

[0297] The upper frame portion 53 has a partially annular shape that is curved so as to convex backward in a plan view. The upper frame portion 53 cooperates with the cover member 6 that forms the upper half of the split shape corresponding to the upper frame portion 53 to form a circular shape with both left and right end faces facing forward, and has an overall cylindrical outer shape that is partially annularly curved.

[0298] In other words, the upper frame portion 53 constitutes the lower half of a cylindrical outer shape curved in a partially annular shape. In other words, the upper frame portion 53 and the cover member 6 constitute the upper frame body 5a that has circular forward end faces at both left and right ends, has a curved shape that is convex rearward in plan view, and has a generally cylindrical shape curved in a partially annular shape as a whole.

[0299] The upper frame portion 53 is provided with a plurality of screw insertion holes h1 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 provided a rear biasing member engaging portion 532 having a recessed shape that supports the rear portion of a coil spring p3, which is a biasing member that biases the operating member p1 forward, i.e., in the direction of the engagement posture (U).

[0301] A boss portion 533 into which a screw member v2 capable of restricting the up and down movement of the operating member p1 is screwed is provided upright on the upper frame portion 53. The boss portion 533 and the screw member v2 constitute a up and down movement restricting portion 53k.

[0302] The boss portion 533 is disposed in an elongated hole portion p14 provided at the rear of the engagement portion p11 of the operating member p1. The head of the screw member v2 can engage near the upper opening edge of the elongated hole portion p14 of the operating member p1 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 with screws v1 so as to cover the left and right operating members p1.

[0304] The cover member 6 covers the operating member p1 so 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 engagement portion p11 of the operating member p1, which can be protruded and retracted 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 engagement portion p11 of the operating member p1, and side wall portions 62 that partially cover both the left and right sides.

[0306] The window frame portion 6w cooperates with the outer peripheral wall q21 that constitutes the recess q2 of the positioning mechanism Q to form a rectangular window frame-shaped portion when viewed from the front.

[0307] Furthermore, a cutout 6k for exposing the operated portion p13 of the operating member p1 is provided on the front side of the cover member 6. The cutout 6k is provided adjacent to the inner side of the window frame portion 6w.

[0308] The back support member L having the above-described structure is covered and hidden by a front support member cover X2 and a rear support member cover X3 made of synthetic resin.

[0309] The front and back support cover X2 mainly covers the lower and outer sides of the back support base 4. The front and 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 screw v3 for attaching the back support main body 5 to the back support base 4 is not exposed on the rear side. The rear support cover X3 covers the rear of the back support base connecting part 5a which is provided at the base end part 51 of the back support main body 5 and located between the left and right standing frame parts 52. Both side ends of the rear support cover X3 are designed to be 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 generally horizontally elongated rectangular shape with rounded left and right ends. The backrest M has a backrest surface at the front against which the back of a seated person can rest. The backrest M of this embodiment is configured to be detachable from the back support L with a simple operation by the user. The backrest M has a backrest main body 7, which is the structural main body, and a back upholstery 8, which is a covering that can cover the backrest main body 7.

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

[0314] The accommodation groove 7m is composed of a pair of front and rear groove-forming walls 7f, 7r arranged so that their inner surfaces face each other in the front-rear direction. The single accommodation groove 7m is designed to receive first and second belt-shaped members 81, 82 attached to the lower edge of the back upholstery 8 covering the backrest body 7.

[0315] A plurality of engagement protrusions t(f), t(r) are provided inside the accommodation groove 7m, i.e., on the inner surfaces of the pair of groove forming walls 7f, 7r. Both of the pair of groove forming walls 7f, 7r are provided with engagement protrusions t(f), t(r) that protrude forward or backward.

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

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

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

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

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

[0321] [Back upholstery body 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, except for the lower ends.

[0322] A space capable of accommodating the backrest main body 7 is formed inside the back upholstery main body 80. A lower opening 8k that is open downward and allows the backrest main body 7 to be inserted into the internal space is formed at the lower end of the back upholstery main body 80, i.e., between the lower end of the front covering portion 8f and the lower end of the back covering portion 8r.

[0323] In this embodiment, the back side of the back upholstery main body 80, i.e., the back side covering portion 8r, has a pair of openings 8s on the left and right sides that expose the engaging portion p2 and protruding portion q1 of the backrest main 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 ring-shaped member T made of synthetic resin, which forms a continuous ring and is attached to the through hole peripheral portion 8e by sewing.

[0325] At two locations on the left and right of the rear cover portion 8r, through holes 8t are formed at positions corresponding to the protrusions q1 protruding from the rear side of the backrest main body 7.

[0326] The annular member T is formed in a rectangular frame shape from a flexible synthetic resin sheet material with a hole th in the center. The annular member T is configured to be flexible and deformable. The annular member T is sewn to the through-hole periphery 8e of the back-side covering portion 8r. In the installation completion position (Ta), the annular member T is covered by the back-side covering portion 8r so that all parts of the annular member T except for the hole th are invisible 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 installation completion position (Ta) are covered by the through hole peripheral portion 8e adjacent to the through hole 8t in the back side covering portion 8r, and the through hole peripheral portion 8e is fixed only to the inner surface t3 of the annular member T in the installation completion position (Ta).

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

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

[0330] The first and second belt-shaped members 81, 82 are inserted together into the receiving groove 7m in a state where they are overlapped with each other.

[0331] When the first and second belt-shaped members 81 and 82 are inserted to predetermined positions within the accommodating groove 7m, the engaging protrusions t(f) and t(r) protruding from the groove-forming walls 7f and 7r of the accommodating groove 7m can engage with the through holes 81a and 82a formed in the belt-shaped members 81 and 82. More precisely, only the through holes 81a and 82a located at positions corresponding to the engaging protrusions t(f) and t(r) of the inserted first and second belt-shaped members 81 and 82 can be locked by the engaging protrusions t(f) and t(r).

[0332] As a result, after the first and second belt-shaped members 81, 82 that form the edge portions of the back upholstery 8 have penetrated to a specified depth in the single storage groove 7m, their downward movement (reverse movement / slip-out) is restricted by the engaging protrusions t(f), t(r), and they are unlikely to easily slip out to the outside even when subjected to a pulling force from the back upholstery main body 80.

[0333] Furthermore, the engaging protrusions t(f) protruding from one groove forming wall 7f and the engaging protrusions t(r) protruding from the other groove forming wall 7r are arranged alternately along the extension direction of the storage groove 7m, so that the first and second strip-shaped members 81, 82 can be inserted smoothly and effortlessly into the storage groove 7m without being excessively hindered by the engaging protrusions t(f), t(r).

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

[0335] In this embodiment, the opening 8s in the back upholstery 8 is formed by going through a preparation process S1, a process S2 for attaching the outer surface of the annular member, a process S3 for inverting the first annular member, and a process S4 for inverting the second annular member, as shown below.

[0336] <Preparation process S1> As shown in FIG. 48, the preparation step S1 involves preparing a back upholstery main body 80, which is a fabric material constituting the back upholstery 8 in which the opening 8s is to be formed, and a ring-shaped member T in the initial position (Tb).

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

[0338] <Annular member outer surface side mounting step S2> Following the preparation process, as shown in Figures 49 and 50, a process (annular member outer surface side mounting process S2) is performed in which a ring-shaped member T in an initial position (Tb) is attached to the outer surface side of the through-hole peripheral portion 8e of the back side covering portion 8r, which is made of the base material.

[0339] In this embodiment, the annular member T in the initial position (Tb) is sewn to the through-hole peripheral portion 8e in a state where it is in contact with the outer surface of the through-hole peripheral portion 8e. In other words, the annular member T in the initial position (Tb) is fixed to the outer surface of the through-hole peripheral portion 8e via the sewn portion tx.

[0340] That is, the annular member outer surface side attaching step S2 is to sew the annular member T to the outer surface side of the through-hole peripheral portion 8e, which is the edge portion of the through-hole 8t.

[0341] <First annular member inversion step S3> After the annular member mounting process, as shown in Figure 51, the annular member T in its initial position (Tb), which is attached to the outer surface of the through-hole peripheral portion 8e, is flexibly deformed so as to rotate its inner peripheral edge toward the inner surface of the back side covering portion 8r, and then inverted back and forth to arrange the annular member T on the inner surface of the back side covering portion 8r (first annular member inversion process S3).

[0342] <Second annular member inversion step S4> After the first annular member inversion process S3, as shown in Figure 52, a process (second annular member inversion process S4) is performed in which the annular member T in the intermediate position (Tc) is inverted back and forth while further bending and deforming the inner edge side toward the inner surface side of the back side covering portion 8r, so that the entire annular member T is covered from the outer surface side by the back side covering portion 8r.

[0343] In this embodiment, by going through a method for forming an opening 8s in the back upholstery 8 (covering body) that includes each of the steps described above, an opening 8s reinforced by a ring-shaped member T in a completed installation position (Ta) that is inverted 360° from the initial position (Tb) is formed in the back covering portion 8r of the back upholstery 8.

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

[0345] <<Detachable structure of the backrest M relative to the back support L>> The chair of this embodiment is configured so that the backrest M can be easily attached and detached to and from the back support L without the use of tools, not only by the manufacturer but also by the end user, to facilitate maintenance such as cleaning and replacement, as well as storage and transportation.

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

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

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

[0349] [Protrusion q1] The protrusions q1 are provided in pairs on the left and right sides of the backrest M. The protrusions q1 protrude from the back side of the backrest main body 7 and are exposed to the outside through openings 8s in the back upholstery 8.

[0350] The protrusion q1 includes a wall-like engaging portion q11 that extends vertically in rear view, gradually narrows in width as it goes downward, and is positioned gradually further rearward as it goes downward as it goes sideways, and a connecting portion q12 that connects the backrest main body 7 and the left-right intermediate portion of the wall-like engaging portion q11 and is provided so that its front-to-rear dimension gradually gets longer as it goes downward. The upper end of the wall-like engaging portion q11 is connected to the backrest main body 7.

[0351] The protrusion q1 is provided below an engaged portion p2 that constitutes a separation 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 standing frame portions 52 that constitute the back support L. The recess q2 is open upward. The recess q2 is designed to fit over the protrusion q1 of the backrest M inserted from above.

[0353] The recess q2 is provided inside an 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 the outer peripheral wall q21, which has a bottom wall portion qt and left and right side wall portions qs that extend upward from both left and right edges of the bottom wall portion qt, and a pair of left and right front wall portions q22 that extend 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 on the left and right, and is provided with a front recess portion qm in which a first space qa is provided between the pair of front wall portions q22 in which the connecting portion q12 of the protrusion q1 is arranged.

[0355] In addition, the recess q2 has a rear recess qr in which a second space qb is provided, in which the wall-like engaging portion q11 of the protrusion q1 is arranged between left and right side wall portions qs formed behind the front recess qm, i.e., behind the pair of front wall portions q22 and erected on the bottom wall portion qt.

[0356] In this embodiment, the protrusion q1 of the backrest M constituting the positioning mechanism Q moves in the vertical direction, more precisely, from the diagonally upper-front direction to the diagonally lower-rear direction, while engaging with the recess q2 of the back support L. Since the load of the seated person on the backrest acts upward, backward, and downward, but hardly acts forward, by configuring the protrusion q1 to be inserted into the recess q2 from the diagonally upper-front direction to the diagonally lower-rear direction, the backrest M is less likely to come off the back support L, and the backrest M can be reliably fixed to the back support L.

[0357] <Release Prevention Mechanism P> The separation prevention mechanism P is provided between the back support L and the backrest M, and prevents the backrest M from separating from the back support L.

[0358] The detachment prevention mechanism P comprises an operating member p1 which is provided on the back support L and can be reversibly operated, i.e., rotated in the forward and backward directions, by human operating force between an engagement position (U) which prevents the backrest M from detaching and a retracted position (N) which allows the backrest M to detach, and an engaged portion p2 which is provided on the backrest M and can engage with an engaging portion p11 provided on the operating member p1 in the engagement position (U).

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

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

[0361] The operating member p1 is constantly biased toward the engaged position (U) by a coil spring p3. A 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), toward the retracted position (N) (the direction in which the engaging portion p11, which is the rotation end, moves backward) against the biasing force of the coil spring p3.

[0362] The operating member p1 can be changed from the engaged position (U) to the retracted position (N) by pressing the operated part p13 backward with the user's finger. 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] 27, a space sp into which fingers can be inserted is provided between the back support L and the backrest M. The operated part p13 is disposed in a position facing the space between the back support L and the backrest M. This allows the user to easily press the operated part p13 like a push button.

[0364] Moreover, only the outer surface of the operated portion p13 of the operating member p1 in the engagement position (U) is exposed between the back support L and the backrest M. 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 with each other. Therefore, although the operated portion p13 is arranged so as to be operable from the outside, it is arranged in an inconspicuous location and has a substantially flush form with the cover member 6 so as to be inconspicuous.

[0365] [Engaged part p2] The engaged portion p2 forms a portion that can be engaged with the engaging portion p11 of the operating member p1 supported by the back support member L. The engaged portion p2 is adapted to be engaged with the engaging portion p11 of the operating member p1 in the engaging posture (U).

[0366] The engaging portions p2 are provided in pairs on the left and right sides of the backrest M. The engaging portions p2 are recessed and open to the rear on the back side of the backrest main body 7. The engaging portions p2 recessed in the backrest main body 7 are exposed to the outside through openings 8s in the back upholstery 8.

[0367] The engaged portion p2 is provided on a protruding portion q1 that constitutes a positioning mechanism Q protruding from the backrest main body 7.

[0368] After the backrest M is positioned in the correct 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 cannot move upward relative to the back support body L, and as a result, it is prohibited from being detached from the back support body L.

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

[0370] The weight-sensing rocking mechanism includes a mechanism for lifting the seat C upward against the weight of the occupant, and is configured to require a backward tilting load proportional to the weight of the occupant in order to tilt the backrest M backward.

[0371] The weight-sensing rocking mechanism is mainly composed of a support base B supported by legs A, a seat C arranged on top of the support base B and supported at its front by the support base B via a front axis j2, a back support L rotatably supported on the support base B via a main axis j1 and having a seat engagement axis j3 arranged in front of and above the main axis j1 and capable of engaging with the front-to-rear center of the seat C and urged forward by a reaction force generating body R, a backrest M supported by the back support L, and a reaction force generating body R arranged between the support base B and the back support L and capable of applying a reaction force to the backward tilting movement of the backrest M.

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

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

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

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

[0376] Furthermore, in the above-described embodiment, the peripheral wall 32, which has an outward surface 32m against which the edge portion de of the seat upholstery Dh can abut, and is arranged in a substantially annular shape when viewed from the bottom, is provided at the periphery of the shell body 3. This makes it possible to provide a chair in which the edge portion de of the seat upholstery Dh covering the seat cushion Dq can be brought into favorable abutment against the peripheral wall 32 of the shell body 3 with a substantially uniform pressing force.

[0377] Furthermore, in the above-described embodiment, the backrest main body 7, which is the main structure, is provided with a storage groove 7m with engaging protrusions t(f), t(r), and the back upholstery 8 is provided with first and second belt-shaped members 81, 82 with through-holes 81a, 82a that engage with the engaging protrusions t(f), t(r) of the storage 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 attached to the storage groove 7m of the backrest main body 7, which is the main structure, without it coming loose.

[0378] Furthermore, the above-described embodiment can provide a method for suitably forming reinforced openings 8s with a desirable appearance in the back upholstery 8, which is a covering that can cover a member. Furthermore, the above-described embodiment can be applied to the back upholstery 8, etc., and can provide a chair having a covering with reinforced openings 8s with a desirable appearance.

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

[0380] This makes it possible to provide a chair that is configured so that the seat C can suitably assume a normal posture (ps) and a forward-leaning posture (pf) without providing a large-scale mechanism at the front of the seat C.

[0381] Furthermore, in the above-described embodiment, a reaction force generating body R that can directly bias the seat engagement shaft j3 forward is disposed between the seat engagement shaft j3 and the support base B, and this reaction force generating body R is set to assume a substantially horizontal position extending in the front-to-rear direction in the normal position (ps). Therefore, it is possible to provide a chair that can rock between the normal position (ps) and the backward tilted position (pr), and that has excellent design freedom for reducing the size of the support base B and the seat C.

[0382] In the above-described embodiment, the intermediate member U, which can prevent the seat support body 1 from being separated from the back support body L, is detachably disposed without using a fastener. Therefore, it is possible to provide a chair in which the seat support body 1 can be easily attached and detached to the support base B.

[0383] Furthermore, in the above-described embodiment, when the support member W supporting one end of the reaction force generating body R is removed from the support base B using the screw v5, the reaction force generating body R moves while being guided by the inclined surface nm while gradually weakening its spring force, so that a chair can be provided in which the reaction force generating body R can be conveniently attached to and detached from the support base B.

[0384] Furthermore, in the above-described embodiment, a screw hole n4 having a thread groove is disposed above the fitting hole Ba in the support base B, and a screw v4 threadedly inserted into the screw hole n4 can press the upper part of the leg support a2 downward. This makes it possible to provide a chair having a configuration that can suitably release the fitting state between the upper part of the leg support a2 and the fitting hole Ba of the support base B.

[0385] Furthermore, in the above-described embodiment, the leg support a2 of the leg A, which is an inhibiting member that can inhibit the lift operation lever V, which is an operating lever, from taking the releasable position (SR), is attached to the support base B, and the lift operation lever V can take the releasable position (SR) only when the leg support a2 is detached from the support base B. Therefore, it is possible to provide a chair in which the lift operation lever V can be suitably attached to the support base B.

[0386] As described above, the chair of this embodiment comprises a leg A, a support base B supported by the leg A, and a back support L supported rotatably relative to the support base B between a normal position (ps) and a backward tilted position (pr) that is tilted further back than the normal position (ps).

[0387] Between the support base B and the back support L, a reaction force generating body R is provided, which can bias the back support L in the direction of the normal posture (ps).

[0388] The reaction force generator R is a compression spring type whose rear end is attached to the support base B via a support member W and whose front end is attached to the back support L.

[0389] The support base B is provided with a first screw insertion hole h51 through which a screw v5 for attaching the support member W is inserted, and an inclined surface nm that engages with the support member W. The support member W can be moved to a predetermined fixed position while engaging with the inclined surface nm by rotating the screw v5 inserted into the first screw insertion hole h51 in a first direction, and can be moved in the direction opposite to the fixed position while engaging with the inclined surface nm by rotating the screw v5 in a second direction.

[0390] The inclined surface nm is set so as to gradually move away from the front end of the reaction force generating body R as it moves from the fixed position toward the anti-fixed position.

[0391] Therefore, when the support member W, which supports the rear end portion, which is one end portion of the reaction force generating body R, is removed from the support base B using the screw v5, it is guided by the inclined surface nm and moves while gradually weakening the spring force of the reaction force generating body R.

[0392] Therefore, in this embodiment, a chair having a configuration that allows the reaction force generator R to be suitably detached from the support base B can be provided.

[0393] Conversely, this embodiment can provide a chair having a configuration in which the reaction force generating body R can be suitably attached to the support base B.

[0394] At the rear of the support base B, a mounting portion 2T to which a support member W is attached is provided.

[0395] Therefore, the support member W can be attached to the support base B at a suitable location.

[0396] The mounting portion 2T comprises at least a rear bottom wall 24, which is a bottom wall portion having a first screw insertion hole h51, and a rear wall portion 27 that stands upward from the rear end of the rear bottom wall 24 and has an inclined surface nm on its front surface.

[0397] Therefore, the support member W is suitably supported by the rear bottom wall 24 and the rear wall portion 27 having the inclined surface nm that constitute the mounting portion 2T.

[0398] The mounting portion 2T comprises a rear bottom wall 24, which is a bottom wall portion having a first screw insertion hole h51, a rear wall portion 27 erected upward from the rear portion of the rear bottom wall 24 and having a front surface which is an inclined surface nm, and left and right side wall portions 28 erected upward from both the left and right sides of the rear bottom wall 24 and whose rear portions are connected to the rear wall portion 27.

[0399] Therefore, the support member W is suitably supported by the rear bottom wall 24 constituting the mounting portion 2T, the rear wall portion 27 having the inclined surface nm, and the left and right side wall portions 28 that support the rear wall portion 27. In particular, since the rear wall portion 27 having the inclined surface nm is urged rearward by the reaction force generating body R, the rear wall portion 27 is suitably reinforced by the left and right side wall portions 28.

[0400] The support member W is surrounded by the rear bottom wall 24, the rear wall portion 27, and the left and right side wall portions 28 in the fixed position.

[0401] Therefore, the support member W is surrounded by the rear bottom wall 24, the rear wall portion 27, and the left and right side wall portions 28 at the fixed position, and is therefore suitably supported by the attachment portion 2T.

[0402] The support member W includes a support member main body w1 and a hexagonal nut n5 disposed inside the support member main body w1. The support base W includes a bottom wall portion w11 having a second screw insertion hole h52 through which the screw v5 is inserted, and a peripheral wall portion ws extending upward from the peripheral edge of the bottom wall portion w11.

[0403] The hexagonal nut N5 is threaded onto the screw V5 that is inserted through the first and second screw insertion holes H51 and H52.

[0404] Therefore, since the support member W comprises a support member body w1 and a hexagonal nut n5, the support member body w1 is configured to be able to move suitably along the inclined surface nm.

[0405] The hexagonal nut n5 engages with the peripheral wall portion ws so as to restrict left-right movement and horizontal rotation, and engages with the peripheral wall portion ws so as to allow forward-backward movement.

[0406] In other words, the hexagonal nut n5 is disposed so as to be freely movable in the front-to-rear direction relative to the support member body w1, and therefore, the hexagonal nut n5 can adopt a suitable inclined posture inside the support member body w1, which moves up and down along the inclined surface nm, so that it can be threaded onto the screw v5.

[0407] The first screw insertion hole h51 of the support base B is an elongated hole extending in the front-rear direction.

[0408] Therefore, the screw v5 inserted into the first screw insertion hole h51, which has the shape of a long hole, can take on a suitable inclined posture in response to the support member main body w1 and the hexagonal nut n5, which move up and down while tilting along the inclined surface nm.

[0409] The present invention is not limited to the above-described embodiment.

[0410] The reaction force generator may be a tension spring type, one end of which is attached to the support base via a support member and the other end of which is attached to the back support. In this case, the inclined surface is set so as to gradually approach the other end as it moves from the fixed position toward the anti-fixed position. Even with this configuration, the desired purpose can be achieved.

[0411] The other end of the reaction force generator may be attached to the back support via some other member.

[0412] The support base needs to be provided with at least a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member. In other words, the support base does not need to be provided with a screw insertion hole as long as a nut portion is integrally formed with the support member W. Furthermore, the inclined surface may be provided on one surface of the block-shaped portion, and does not need to be provided on one surface of the upright wall-shaped portion.

[0413] The mounting portion to which the support member is attached may be provided at a portion other than the rear portion of the support base.

[0414] The mounting portion may have at least a bottom wall portion having a first screw insertion hole and a rear wall portion extending upward from the rear end of the bottom wall portion and having an inclined front surface. In other words, the mounting portion may not have left and right side walls.

[0415] The support member may be configured such that the support member body and the nut are integrally provided. In other words, the support member does not have to be configured such that the nut is disposed freely relative to the support member body.

[0416] The first screw insertion hole of the support base does not have to be an elongated hole extending longitudinally in the front-rear direction.

[0417] The specific configuration of each part is not limited to the above embodiment. Various modifications are possible within the scope of the present invention. [Explanation of symbols]

[0418] A...legs B...Support base R...Reaction force generator W...Support member L...back support (structure) 2T...Mounting part

Claims

1. A chair comprising legs, a support base supported by the legs, and a back support supported rotatably with respect to the support base between a normal position and a backward tilted position tilted further backward than the normal position, a reaction force generating body is provided between the support base and the back support body, the reaction force generating body being capable of urging the back support body in the direction of the normal posture; the reaction force generating body is a compression spring type having one end attached to the support base via a support member and the other end attached to the back support body, the support base is provided with a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member, the support member can be moved to a predetermined fixed position while engaging with the inclined surface by rotating the screw inserted into the first screw insertion hole in a first direction, and can be moved in a direction opposite to the fixed position while engaging with the inclined surface by rotating the screw in a second direction, The inclined surface is set so as to gradually move away from the other end as it moves from the fixed position toward the anti-fixed position.

2. 2. The chair according to claim 1, wherein a mounting portion for mounting the support member is provided at the rear of the support base.

3. 3. The chair of claim 2, wherein the mounting portion comprises at least a bottom wall portion having the first screw insertion hole and a rear wall portion extending upward from the rear end of the bottom wall portion and having the inclined surface on its front surface.

4. 3. The chair of claim 2, wherein the mounting portion comprises a bottom wall portion having the first screw insertion hole, a rear wall portion extending upward from the rear of the bottom wall portion and having the inclined surface on its front surface, and left and right side wall portions extending upward from both left and right sides of the bottom wall portion and having their rear portions connected to the rear wall portion.

5. 5. The chair according to claim 4, wherein the support member is surrounded by the bottom wall portion, the rear wall portion, and the left and right side wall portions at the fixed position.

6. The support member includes a support member body and a nut disposed inside the support member body, the support base has a bottom wall portion having a second screw insertion hole through which the screw is inserted, and a peripheral wall portion erected upward from a peripheral edge portion of the bottom wall portion, 2. The chair according to claim 1, wherein the nut is threaded onto the screw inserted through the first and second screw insertion holes.

7. 7. The chair according to claim 6, wherein the nut engages with the peripheral wall portion so as to restrict left-right movement and horizontal rotation, and engages with the peripheral wall portion so as to allow forward-backward movement.

8. 2. The chair according to claim 1, wherein the first screw insertion hole is an elongated hole extending in the front-rear direction.

9. A chair comprising legs, a support base supported by the legs, and a back support supported rotatably with respect to the support base between a normal position and a backward tilted position tilted further backward than the normal position, a reaction force generating body is provided between the support base and the back support body, the reaction force generating body being capable of urging the back support body in the direction of the normal posture; the reaction force generating body is a tension spring type having one end attached to the support base via a support member and the other end attached to the back support body, the support base is provided with a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member, the support member can be moved to a predetermined fixed position while engaging with the inclined surface by rotating the screw inserted into the first screw insertion hole in a first direction, and can be moved in a direction opposite to the fixed position while engaging with the inclined surface by rotating the screw in a second direction, The inclined surface is set to gradually approach the other end as it moves from the fixed position toward the anti-fixed position.

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