Chair

Abstract

The invention provides a chair, wherein a seat bearing body can be simply assembled and disassembled relative to a supporting base part. To this end, a seat receiving body (1) of a chair is provided with a front axle holding part capable of holding a front axle (j2), and an engaged part (1k) that is disposed further toward the rear than the front axle holding part and that engages with a back support body (L), which is a structure supported by a support base (B), and that holds the front axle (j2) between the back support body (L) and the seat receiving body (1). An intermediate member (U) capable of limiting the separation of the seat receiving body (1) from the back support body (L) is detachably arranged without using a fixed mounting member. According to the structure, the seat bearing body (1) can be simply assembled and disassembled relative to the supporting base part (B).

Description

Technical Field

[0001] The invention relates to a chair. Background Art

[0002] In recent industries, especially with the efforts towards SDGs, there is a demand for the development of environmentally friendly products based on easily decomposable structures, and the field of chairs is no exception.

[0003] In addition, from the perspective of suppressing the spread of infectious diseases such as the new coronavirus, many users use the chair for work at home, and there is a demand for individuals to be able to easily disassemble the structure of the chair.

[0004] Conventionally, in order to enable classified disposal in consideration of the environment, inventions have been made in which the parts constituting a chair are configured to be easily disassembled (for example, see Patent Document 1).

[0005] However, conventional chairs require the removal of screws in order to be disassembled, or excessive force, which is dangerous, is required to separate components, so that it is not possible for anyone to disassemble the chair easily.

[0006] Prior Art Literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent No. 2895402 Summary of the invention

[0009] [Problems to be solved by the invention]

[0010] The present invention has been made in view of the above situation, and provides a chair in which at least a seat receiving body can be easily attached and detached from a supporting base.

[0011]

Means for solving the problem

[0012] That is, the present invention has the following structure:

[0013] The invention described in technical solution 1 is a chair, which includes a supporting base supported on the legs and a seat supported on the above-mentioned supporting base via a front axle; it is characterized in that the above-mentioned seat includes a seat body with a seat surface and a seat receiving body supporting this seat body, and the above-mentioned seat receiving body includes a front axle retaining portion and a clamping portion, and the front axle retaining portion can retain the above-mentioned front axle; the clamping portion is arranged at the rear compared with the front axle retaining portion, and is clamped relative to the above-mentioned supporting base or the structure supported on the above-mentioned supporting base, and an intermediate component that can limit the detachment of the above-mentioned seat receiving body relative to the above-mentioned supporting base or the above-mentioned structure is arranged between the above-mentioned supporting base or the above-mentioned structure and the above-mentioned seat receiving body so that it can be loaded and unloaded without using a fixed mounting part.

[0014] The invention described in technical solution 2 is a chair according to technical solution 1, characterized in that a spring member is sandwiched between the above-mentioned seat receiving body and the above-mentioned intermediate member, and the above-mentioned spring member is loaded in a direction to engage the above-mentioned intermediate member with respect to the above-mentioned support base or the above-mentioned structure.

[0015] The invention described in Technical Solution 3 is a chair according to Technical Solution 2, characterized in that the intermediate member is constructed so that, by being pushed in the direction of resisting the loading force of the spring member, the intermediate member can be released from the engagement with the supporting base or the structure, and can be detached from between the supporting base or the structure and the seat receiving body in the state in which the engagement is released.

[0016] The invention described in Technical Solution 4 is a chair according to Technical Solution 3, characterized in that the seat support body can rotate around the front axle in a manner in which the rear end jumps up after the intermediate component is detached; the front axle retaining portion can be detached from the front axle only when the seat support body changes its posture to a specified jumping posture.

[0017] The invention described in Technical Solution 5 is a chair according to Technical Solution 4, characterized in that grooves are provided in pairs on the left and right sides of the above-mentioned support base, the grooves extend in the up-down direction and are open toward the outside, and limiting protrusions protruding toward the inside are provided in pairs on the left and right sides of the above-mentioned seat support body, and the above-mentioned seat support body is constructed so that when the above-mentioned intermediate member restricts the disengagement, the above-mentioned limiting protrusions are located in the above-mentioned grooves, and the above-mentioned front axle retaining portion cannot be disengaged forwardly relative to the above-mentioned front axle, and the above-mentioned seat support body is constructed so that when the above-mentioned specified jumping posture is adopted, the above-mentioned limiting protrusions are located outside the above-mentioned grooves, and the above-mentioned front axle retaining portion can be disengaged forwardly relative to the above-mentioned front axle.

[0018] The invention described in technical solution 6 is a chair according to technical solution 1, characterized in that the above-mentioned structure is a back support body supported to be rotatable relative to the above-mentioned support base, the above-mentioned engaged portion is engaged with the seat engaging portion provided on the above-mentioned back support body, and the above-mentioned intermediate member is arranged between the above-mentioned back support body and the above-mentioned seat receiving body.

[0019] The invention described in technical solution 7 is a chair according to technical solution 1, characterized in that the seat is configured to be tiltable and rotatable around the front axis between a normal posture and a forward tilted posture that is more forward than the normal posture, and the engaged portion is engaged relative to the supporting base or the structure when the normal posture is adopted.

[0020] The invention described in Technical Solution 8 is a chair according to Technical Solution 2, characterized in that the intermediate member comprises an intermediate member body and an arm portion, the intermediate member body is provided with a spring receiving portion on one side for receiving one end portion of the spring member; the arm portion is extended from the intermediate member body and can be engaged with the supporting base or structure, and a spring receiving portion on the other side for receiving the other end portion of the spring member is provided on the seat receiving body, the spring receiving portion on the one side is provided downward, and the spring receiving portion on the other side is provided upward.

[0021] The invention described in technical solution 9 is a chair according to technical solution 8, characterized in that a recess is provided on the seat receiving body, the recess is open upward, includes the spring receiving portion of the other side, and forms a space for arranging the intermediate component body.

[0022] The invention described in technical solution 10 is a chair according to technical solution 9, characterized in that a recess is provided on the seat support body, the recess is open downward, and the supporting base is provided; an arm passage hole through which the arm can pass is provided between the recesses.

[0023] Effects of the Invention

[0024] As described above, according to the present invention, there is provided a chair in which at least a seat receiving body can be easily attached to and detached from a supporting base. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a perspective view showing one embodiment of the present invention.

[0026] Figure 2 It is a front view in this embodiment.

[0027] Figure 3 It is a rear view in this embodiment.

[0028] Figure 4 It is a left side view in this embodiment.

[0029] Figure 5 It is a right side view in this embodiment.

[0030] Figure 6 It is a top view in this embodiment.

[0031] Figure 7 It is a bottom view in this embodiment.

[0032] Figure 8 It is an exploded perspective view in this embodiment.

[0033] Fig. 9 It is an exploded perspective view in this embodiment.

[0034] Fig.10 This is a perspective view of this embodiment as seen from the rear.

[0035] Fig.11 1 is a rear view of the backrest in this embodiment.

[0036] Fig.12 It is a left side view of the backrest in this embodiment.

[0037] Fig.13 It is a bottom view of the backrest in this embodiment.

[0038] Fig.14 It is a central longitudinal sectional view of the backrest in this embodiment.

[0039] Fig.15 yes Fig.14 The lower enlarged image in .

[0040] Fig.16 It is an exploded perspective view of the backrest in this embodiment.

[0041] Fig.17 This is a rear view showing a portion of the back fabric in this embodiment in section.

[0042] Fig.18 This is a front view with a portion of the back fabric in this embodiment cut away.

[0043] Fig.19 It is a perspective view of the first and second belt-shaped members in this embodiment.

[0044] Fig. 20 It is a bottom view of the backrest body in this embodiment.

[0045] Fig.21 It is a perspective view of the back support body in this embodiment.

[0046] Fig. 22 It is an exploded perspective view of the back support body in this embodiment.

[0047] Fig.23 It is a plan view for explaining the operation of the operating member in this embodiment.

[0048] Fig.24 It is a plan view for explaining the operation of the operating member in this embodiment.

[0049] Fig.25 It is a top cross-sectional view for explaining the operation of the operating member in this embodiment.

[0050] Fig.26It is a top cross-sectional view for explaining the operation of the operating member in this embodiment.

[0051] Fig. 27 yes Figure 4 Arrow in the X direction view.

[0052] Fig.28 It is a perspective view of the seat receiving body in this embodiment.

[0053] Fig.29 It is a top view of the seat receiving body in this embodiment.

[0054] Fig.30 It is an enlarged perspective view of the rear portion of the seat receiving body in this embodiment.

[0055] Fig.31 It is a front view of the seat receiving body in this embodiment.

[0056] Fig.32 It is a rear view of the seat receiving body in this embodiment.

[0057] Fig.33 It is a left side view of the seat receiving body in this embodiment.

[0058] Fig.34 It is a right side view of the seat receiving body in this embodiment.

[0059] Fig.35 This is a perspective view of the seat body in this embodiment as seen from below.

[0060] Fig.36 It is a central cross-sectional view of the seat body in this embodiment.

[0061] Fig.37 It is a central longitudinal sectional view of the seat body in this embodiment.

[0062] Fig.38 1 is a top view of the housing in this embodiment.

[0063] Fig.39 It is a bottom view of the housing in this embodiment.

[0064] Fig.40 It is a front view of the shell in this embodiment.

[0065] Fig.41 1 is a rear view of the housing in this embodiment.

[0066] Fig.42 It is a right side view of the housing in this embodiment.

[0067] Fig.43 It is a cross-sectional view for explaining the attachment of the seat body to the seat receiving body.

[0068] Fig.44 It is a cross-sectional view for explaining the attachment of the seat body to the seat receiving body.

[0069] Fig.45 It is a cross-sectional view for explaining the attachment of the seat body to the seat receiving body.

[0070] Fig.46 It is a top cross-sectional view for explaining the attachment of the seat body to the seat receiving body.

[0071] Fig.47 It is a top cross-sectional view for explaining the attachment of the seat body to the seat receiving body.

[0072] Fig.48 It is an explanatory diagram of a method for forming an opening in this embodiment.

[0073] Fig.49 It is an explanatory diagram of a method for forming an opening in this embodiment.

[0074] Fig.50 It is an explanatory diagram of a method for forming an opening in this embodiment.

[0075] Fig.51 It is an explanatory diagram of a method for forming an opening in this embodiment.

[0076] Fig.52 It is an explanatory diagram of a method for forming an opening in this embodiment.

[0077] Fig.53 This is an enlarged view after the opening portion is formed in this embodiment.

[0078] Fig.54 It is a right side view (backrest tilted posture) in this embodiment.

[0079] Fig.55 It is a right plan view (seat forward tilting posture) in this embodiment.

[0080] Fig.56 It is a top view of the support base in this embodiment.

[0081] Fig.57 It is a bottom view of the support base in this embodiment.

[0082] Fig.58 1 is a left side view of the support base in this embodiment

[0083] Fig.59 It is a right side view of the support base in this embodiment.

[0084] Fig.60It is a perspective view of the support base in this embodiment.

[0085] Fig.61 It is an exploded perspective view in this embodiment.

[0086] Fig.62 It is an exploded perspective view in this embodiment.

[0087] Fig.63 It is a top view in this embodiment.

[0088] Fig.64 It is a partially enlarged longitudinal sectional view of the leg and the support base in this embodiment.

[0089] Fig.65 It is a partially enlarged longitudinal sectional view of the leg and the support base in this embodiment.

[0090] Fig.66 It is a partially enlarged longitudinal sectional view of the leg and the support base in this embodiment.

[0091] Fig.67 It is a partially enlarged longitudinal sectional view of the reaction force generating body and the supporting member in this embodiment.

[0092] Fig.68 In this embodiment, Fig.67 An enlarged longitudinal sectional view of the portion corresponding to the cutting position.

[0093] Fig.69 It is an exploded perspective view of the reaction force generating body and the supporting member in this embodiment.

[0094] Fig.70 This is a perspective view of the support member as seen from the rear.

[0095] Fig.71 It is a cross-sectional view for explaining the leg, the support base, and the lifting and lowering operation rod in this embodiment.

[0096] Fig.72 It is a cross-sectional view for explaining the leg, the support base, and the lifting and lowering operation rod in this embodiment.

[0097] Fig.73 yes Figure 2 AA line section view in.

[0098] Fig.74 In this embodiment, Fig.73 A longitudinal sectional view of the seat back when the cutting position corresponds to the rearward tilting posture.

[0099] Fig.75 In this embodiment, Fig.73 A longitudinal sectional view of the seat when the seat is in a forward tilted position corresponding to the cutting position in the figure.

[0100] Fig.76 yes Fig.29 BB line section view in.

[0101] Fig.77 In this embodiment, Fig.76 The cross-sectional view of the seat when the seat is tilted forward corresponds to the cutting position in the figure.

[0102] Fig.78 It is a longitudinal sectional view in this embodiment.

[0103] Fig.79 In this embodiment, Fig.78 A longitudinal sectional view of the seat when the seat is in a forward tilted position corresponding to the sectional position.

[0104] Fig.80 yes Fig.84 CC line section view in.

[0105] Fig.81 In this embodiment, Fig.80 The cross-sectional view of the seat when the seat is tilted forward corresponds to the cutting position in the figure.

[0106] Fig.82 It is an exploded perspective view in this embodiment.

[0107] Fig.83 It is a partially enlarged top view of this embodiment.

[0108] Fig.84 It is a bottom view in this embodiment.

[0109] Fig.85 It is a perspective view in this embodiment.

[0110] Fig.86 It is a central longitudinal sectional view in this embodiment.

[0111] Fig.87 It is used to explain the process of separating the intermediate member in this embodiment. Fig.86 The central longitudinal section view corresponding to the cutting position in .

[0112] Fig.88 It is a front view of the intermediate member in this embodiment.

[0113] Fig.89 It is a rear view of the intermediate member in this embodiment.

[0114] Fig.90 It is a top view of the intermediate member in this embodiment.

[0115] Fig.91 It is a bottom view of the intermediate member in this embodiment.

[0116] Fig.92 It is a right side view of the intermediate member in this embodiment.

[0117] Fig.93 It is a perspective view of the intermediate member in this embodiment.

[0118] Fig.94 In this embodiment, Fig.78 A longitudinal sectional view of the seat in the pop-up posture corresponding to the cutting position.

[0119] Fig.95 In this embodiment, Fig.78 A longitudinal sectional view showing the pop-up posture of the seat corresponding to the cutting position and the state in which the seat is separated from the supporting base. DETAILED DESCRIPTION

[0120] Modes for carrying out the invention

[0121] The following reference Figure 1 to Figure 95 One embodiment of the present invention will be described.

[0122] The chair includes 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.

[0123] The seat C is configured to be able to take a normal posture (ps) disposed on the support base B, a forward-leaning posture (pf) leaning forward from the normal posture (ps), and a backward-leaning posture (pr) leaning backward from the normal posture (ps). A reaction force generating body R is provided between the support base B and the back support body L, which can load the back support body L in the direction of the normal posture (ps).

[0124] The backrest M is supported via the back support body L so as to be able to tilt backward relative to the support base B. That is, the backrest M and the back support body L can take a normal posture (ps) relative to the support base B and a tilted posture (pr) tilted backward relative to the normal posture (ps).

[0125] The chair is provided with a body weight sensing locking mechanism, which is configured to lift the front portion and the front-rear center portion of the seat C upwards as the back support body L linked to the backrest M tilts backwards, and to tilt and move the entire seat C backwards.

[0126] The chair is provided with a seat forward tilting mechanism which can rotate the seat C forward about the front axis j2 and transition to a forward tilting posture (pf) by offsetting the seating load relative to the front part of the seat C, i.e., the part forward of the front axis j2 in the seat C.

[0127] The following describes in detail each structure of the chair in this embodiment.

[0128] <<Foot A>>

[0129] The leg A includes a plurality of leg blades a1 having casters at the lower ends thereof, and a leg support a2 rising from a portion where the upper ends of the leg blades a1 are gathered.

[0130] The foot A of this embodiment constitutes a blocking member that blocks the rotation of the lifting operation rod V for vertically extending and retracting the foot support a2 in a predetermined direction relative to the support base B so as not to take a detachable posture (SR) from the support base B.

[0131] <Foot support a2>

[0132] The foot support a2 is configured to be extendable in the up-down direction.

[0133] The foot support a2 extends in the up-down direction and includes a cylinder ag that can adjust the position of the seat C in the up-down direction.

[0134] The cylinder ag is a known structure having a cylinder portion a21, a lifting rod a22 and a working component a23, wherein the cylinder portion a21 is arranged at the lower portion of the foot support a2; the lifting rod a22 can perform lifting movements relative to the cylinder portion a21; the working component a23 is protrudingly arranged at the upper end portion of the lifting rod a22 so that it can protrude and sink in the up and down directions, and when pushed downward, the lifting rod a22 is made to be in a state where it can perform lifting movements by making the gas sealed inside flowable.

[0135] The lifting rod a22 is cylindrical. The outer peripheral surface of the upper portion of the lifting rod a22, which is the upper portion of the foot support a2, is tapered. In other words, the upper portion of the lifting rod a22 is formed so that the diameter gradually decreases toward the upper side.

[0136] The upper portion of the lift rod a22 is fitted into the fitting hole Ba as the leg connection portion of the support base B. The fitting hole Ba of the support base B into which the lift rod a22 is fitted is shaped so as to be tightly fitted to the upper portion of the lift rod a22.

[0137] The actuating member a23 is configured to be pressed downward by a lifting and lowering operating lever V which is an operating lever rotatably supported by the support base B relative to the lever supporting portion b13.

[0138] <<Support base B>>

[0139] The support base B is mounted on the upper part of the foot A.

[0140] The support base B is supported so that the upper and lower positions can be changed and the support base B can be rotated by the legs A. The support base B is a structure formed integrally of metal. The support base B is box-shaped as a whole, long in the front-back direction, and open upward.

[0141] The supporting base B includes a bottom wall portion 2, left and right side walls b1, a rear wall b2 and an extended flange b3. The bottom wall portion 2 has a downward surface and is integrally provided with a mounting portion 2T for supporting the rear end portion of the reaction force generating body R; the left and right side walls b1 are in the form of upright walls that are continuously arranged upward from the left and right end portions of the bottom wall portion 2 respectively; the rear wall b2 is uprightly arranged at the rear end portion of the bottom wall portion 2, connecting the rear end portions of the left and right side walls b1; the extended flange b3 is extended outward from the rear portion of the left and right side walls b1.

[0142] <Bottom wall part 2>

[0143] The bottom wall portion 2 includes a basic bottom wall 21, an inclined bottom wall 22, a front bottom wall 23 and a rear bottom wall 24. The basic bottom wall 21 has a bottom surface that is approximately horizontal and is provided with a fitting hole Ba that serves as a foot connecting portion that is fitted into the upper portion of the foot support a2; the inclined bottom wall 22 extends from the rear end portion of the basic bottom wall 21 toward the upper and oblique rear; the front bottom wall 23 extends forward from the front end portion of the basic bottom wall 21 and is arranged to be gradually located upward as it moves toward the front; and the rear bottom wall 24 extends approximately horizontally from the rear end portion of the inclined bottom wall 22 toward the rear.

[0144] The bottom wall portion 2 is provided with a rising structure portion 2S provided to rise near the fitting hole Ba and a mounting portion 2T to which a support member W engaged with a rear end portion of the reaction force generating body R is mounted.

[0145] [Foundation bottom wall 21]

[0146] A boss portion 211 is provided upright on the base bottom wall 21 , and a fitting hole Ba is formed in the boss portion 211 and penetrates in the up-down direction and is fitted in the upper portion of the foot support b2 .

[0147] [Inclined bottom wall 22]

[0148] The inclined bottom wall 22 is inclined so as to gradually move upward from the rear end of the base bottom wall 21. Since the inclined bottom wall 22 extends upward and rearward from the base bottom wall 21, it can be well disposed on the rear bottom wall 24 where the mounting portion 2T is arranged at a position higher than the base bottom wall 21.

[0149] [Front bottom wall 23]

[0150] The front bottom wall 23 extends forward from the front end of the base bottom wall 21. The front bottom wall 23 is provided with a front shaft j2 inserted into the long hole b12 of the left and right side walls b1.

[0151] [Rear bottom wall 24]

[0152] The rear bottom wall 24 is extended substantially horizontally rearward from the rear end of the inclined bottom wall 24. The middle portion in the left-right direction of the rear bottom wall 24 constitutes a bottom wall portion of the mounting portion 2T for mounting the support member W.

[0153] The rear bottom wall 24 is disposed at a position higher than the base bottom wall 21. The rear bottom wall 24 is provided with a mounting portion 2T of a support member W that supports a rear end portion of the reaction force generating body R.

[0154] That is, by providing the rear bottom wall 24 at a position higher than the base bottom wall 21 , it is possible to preferably adopt a structure in which the reaction force generating body R is disposed in a horizontal posture.

[0155] [Rising structure 2s]

[0156] The rising structure 2S includes a screw connection hole n4 having a screw groove provided in the fitting hole Ba.

[0157] The rising structure 2S is provided adjacently so as to rise in front of the fitting hole Ba. The rising structure 2S is a metal structure, and is provided integrally with the boss portion 211 of the base bottom wall 21 forming the fitting hole Ba.

[0158] The rising structure 2S includes a rising portion 25 rising so as to partially surround the front portion of the fitting hole Ba in a plan view, and a horizontal frame portion 26 spanning between the rising portions 25 so as to be located directly above the fitting hole Ba.

[0159] The rising portion 25 is integrally provided continuously at the front portion of the boss portion 211 in which the fitting hole Ba is formed. The rising portion 25 has a shape in which the center portion in the left-right direction of the rear side is recessed forward.

[0160] That is, the rear portion of the rising portion 25 is set in a shape such that a space is provided in a portion immediately above the fitting hole Ba, and the horizontal frame portion 26 can be integrally arranged in the space.

[0161] The horizontal frame portion 26 is provided with a screw hole n4 penetrating in a substantially vertical direction. The horizontal frame portion 26 is provided continuously with the rising portion 25 in an integral manner.

[0162] The rising structure 2S provided on the chair of the present embodiment is provided specifically for enabling the operator to perform the work of separating the leg A and the support base B safely.

[0163] The operator can use a common tool to screw a screw v4 having a size matching that of the screw hole n4 into the screw hole n4 provided in the horizontal frame portion 26 of the ascending structure 2S from above toward below.

[0164] Furthermore, the upper portion of the foot support b2 disposed immediately below the screw connection hole n4 is configured to be pushed downward by the screw v4 that is threadedly engaged while using the ascending structure 2S provided integrally with the support base B as a foothold.

[0165] More specifically, the screw v4 threadedly engaged with the threaded connection hole n4 is guided in the threaded groove of the threaded connection hole n4 while rotating and descending, and the lower end of the screw v4 can push downward the outer peripheral edge portion of the upper end of the lifting rod a22 constituting the foot support b2.

[0166] The ascending structure 2S is used when the leg A is detached from the support base B. When the chair is completed, the fitting hole Ba of the support base B is firmly fitted to the upper portion of the lifting rod a22 as the upper portion of the leg support a2.

[0167] In this embodiment, the strong fitting state between the fitting hole Ba and the lifting rod a22 is eliminated or relaxed by the pressing force of the screw v4 that can be threadedly engaged with the threaded connection hole n4 of the rising structure 2S.

[0168] Since the screw v4 that descends while rotating along the thread groove can apply a strong and continuous pressing force to the elevating rod a22, the firm fitting state between the fitting hole Ba and the elevating rod a22 can be effectively eliminated or relaxed.

[0169] In other words, the chair of this embodiment is provided with a fitting degree easing structure for easing the fitting degree between the foot support a2 and the support base B. The fitting degree easing structure is provided with a threaded connection hole n4 having a thread groove on the fitting hole Ba in the support base B, and the upper part of the foot support a2 can be pushed downward by a screw v4 threadedly engaged with the threaded connection hole n4.

[0170] In addition, the screw v4 only needs to have the same specifications as the threaded connection hole n4 and have a certain length in the vertical direction. In this embodiment, in a place where the chair is disassembled, after removing the screw v5 for fixing the support member W relative to the mounting portion 2T of the support base B, the screw v5 can be used as a screw v4 that enters the threaded connection hole n4 of the ascending structure 2S without changing its thread.

[0171] [Mounting part 2T]

[0172] The mounting portion 2T is provided at the rear portion of the support base B. The mounting portion 2T constitutes a portion where a support member W that supports the rear end portion of the reaction force generating body R is mounted.

[0173] The mounting portion 2T includes a rear bottom wall 24 as a bottom wall portion, a rear wall portion 27, and left and right side wall portions 28. The bottom wall portion has a first screw insertion hole v5 for inserting a screw v5 for mounting the supporting member W; the rear wall portion 27 is uprightly arranged upward from the rear of the rear bottom wall 24, and the front is formed into a backward inclined surface nm; the left and right side wall portions 28 extend forward from the left and right end portions of the rear wall portion 27, and are uprightly arranged upward from the left and right side portions of the rear wall 24.

[0174] The rear bottom wall 24 is in a substantially horizontal plate shape. A first screw insertion hole h51 as a screw insertion hole penetrating in the vertical direction is provided in the left-right center of the rear bottom wall 24. The first screw insertion hole h51 is formed in a long hole shape that is long in the front-rear direction.

[0175] The bottom wall portion w11 of the support member W abuts against the rear bottom wall 24 , and the bottom wall portion w11 of the support member W is pulled toward the rear bottom wall 24 by the movement of the hexagonal nut n5 threadedly engaged with the screw v5 .

[0176] The rear wall portion 27 is in the shape of a standing plate and is provided upright in a posture tilted backward relative to the rear bottom wall 24. The front surface of the rear wall portion 27 serves as an inclined surface nm with which the rear wall portion w13 of the support member W abuts.

[0177] The inclined surface nm is set in such a manner that it gradually moves 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 a fixed position (lower position) fastened relative to the rear bottom wall 24 toward a direction opposite to the fixed position, i.e., upward compared to the lower position.

[0178] The left and right side wall portions 28 are erected on the rear bottom wall 24, and the rear portions thereof are connected to the rear wall portion 27. The left and right side wall portions 28 play a role in defining the left and right positions of the support member W, and play a role in ensuring the strength of the rear wall portion 27, which serves as a foothold for receiving the load force generated by the reaction force generating body R.

[0179] <Left and right side walls b1>

[0180] The left and right side walls b1 are erected from the left and right ends of the bottom wall portion 2, namely, 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-rear direction.

[0181] The left and right side walls b1 have an axial hole b11, a long hole b12, a rod support portion b13, a groove portion b14 and an axial movement limiting portion b15. The axial hole b11 is set at a front-to-back position corresponding to the rear portion of the base bottom wall 21, and penetrates in the left-to-right direction so as to keep the main shaft j1 rotatable; the long hole b12 is set at a front-to-back position corresponding to the front portion of the front bottom wall 23, and penetrates in the left-to-right direction so as to keep the front shaft j2 for supporting the front portion of the seat C slidable forward and backward and up and down; the rod support portion b13 is only set on the left side wall b1, and can support the lifting and lowering operating rod V for lifting and lowering the seat C so as to be rotatable; the groove portion b14 is set along the long hole b12 and in front of the long hole b12, and is open to the outside; the axial movement limiting portion b15 is set at the upper end portion of the middle portion in the front-to-back direction in a mountain-shaped protruding manner, prohibiting the forward and downward movement of the seat engaging shaft j3 set on the back support body L.

[0182] [Shaft hole b11]

[0183] The shaft hole b11 is used to support a main shaft j1 that supports the back support body L relative to the support base B so as to be rotatable.

[0184] The left and right side walls b1 are integrally provided with a boss-shaped portion b4 that protrudes outward and forms a part of the shaft hole b11. By providing the boss-shaped portion b4 on the left and right side walls b1 in association with the shaft hole b11, the left-right direction area that can directly support the main shaft j1 is ensured to be longer than the width dimension of the left and right side walls b1. The boss-shaped portion b4 is continuously provided at the front end portion of the extended flange b3.

[0185] [Slotted hole b12]

[0186] The long hole b12 extends in an oblique direction so that the lower end side is located forward compared to the upper end side in a side view. A sleeve member gs made of synthetic resin is embedded in the long hole b12 so as to facilitate sliding relative to the front axle j2. The front axle j2 is supported in the long hole b12 via the sleeve member gs.

[0187] In other words, a long hole-shaped front axle support portion is provided in the support base B. The long hole-shaped front axle support portion is composed of a long hole b12 and a sleeve member gs with excellent sliding properties installed in the long hole b12, and can support the front axle j2 to be slidable.

[0188] [Rod support portion b13]

[0189] The rod support b13 is a structure that rotatably supports the lifting operation rod V so as to be able to perform a hinge action. The lifting operation rod V can act on the cylinder ag to extend and retract the foot support a2 in the vertical direction.

[0190] The rod supporting portion b13 includes a pair of front and rear supporting wall portions b15 and a pair of shaft portions j4. The pair of front and rear supporting wall portions b15 protrude outward from the left side wall b1 in a direction approximately perpendicular to the left side wall b1; and the pair of shaft portions j4 protrude from the inner surfaces of the pair of supporting wall portions b15 that are in a face-to-face relationship in directions approaching each other.

[0191] A space for arranging the lifting and lowering operation rod V is formed between the pair of front and rear support walls b15.

[0192] A pair of shaft portions j4 are protruded in mutually opposite directions, that is, directions in which the axes are aligned and approach each other. The shaft portion j4 has a narrow width portion j41 having a narrow width in the left-right direction, which is a direction perpendicular to the axis, and a wide width portion j42 having a wide width (wider than the narrow width portion j41) in the up-down direction, which is a direction perpendicular to the axis. In other words, the shaft portion j4 is configured so that the lateral width is shorter than the longitudinal width.

[0193] [Groove b14]

[0194] The groove portion b14 is provided to extend in the same direction as the long hole b12, that is, in an oblique direction such that the lower end side is located forward of the upper end side when viewed from the side.

[0195] A restriction protrusion 1t provided on the seat receiving body 1 to restrict the position of the seat receiving body 1 relative to the support base B is disposed in the groove portion b14.

[0196] <Back wall b2>

[0197] The rear wall b2 is erected from the rear end of the rear bottom wall 24. The rear wall b2 connects the rear ends of the left and right side walls b1. The middle portion of the rear wall b2 in the left-right direction constitutes a rear wall portion 27 for mounting the mounting portion 2T of the support member W.

[0198] <Extended flange b3>

[0199] The extended flange b3 is extended outward from the left and right side walls b1.

[0200] The extension portion b3 is provided with a damper mounting portion b31 for mounting a damper gx that abuts against the back support body base 4 when the back support body L is tilted backward. The damper gx mounted on the damper mounting portion b31 can be engaged with the engaging protrusions 41c protruding inwardly from the upper ends of the left and right arm bodies 411, respectively.

[0201] The front lower portion of the support base B constructed as described above is covered with a support base cover X1 made of synthetic resin.

[0202] <<Lifting lever V>>

[0203] The lifting operation rod V is a single structure formed integrally of synthetic resin and is configured to be attachable to the rod support portion b13 of the support base B without using fixing members such as screws.

[0204] The lifting operation lever V is rotatably supported with respect to the support base B. More specifically, the lifting operation lever V is rotatably supported with respect to a lever support portion b13 provided on the left side wall b1 of the support base B.

[0205] The lifting operation lever V can be operated by the user to make the foot support a2 of the foot A extendable in the vertical direction in order to lift the seat C.

[0206] If the user moves the operating end vc upward, the lifting operating lever V rotates around the shaft j4 of the support base B engaged with the bearing vb, and the rotating end va moves downward to push down the working member a23 arranged at the upper end of the foot support a2.

[0207] The lifting operation rod V includes a rod body vh, a base end upright setting part vi, an inner extension setting part vm and a bearing part vb. The rod body vh is in the shape of a plate extending in the left and right directions, and has an operating end vc at the front end; the base end upright setting part vi extends upward from the base end of the rod body vh; the inner extension setting part vm extends inward from the upper end of the base end upright setting part vi, and has a rotating end va at the front end that can abut against the foot support a2; the bearing part vb is arranged between the base end upright setting part vi and the inner extension setting part vm.

[0208] <Rod body vh>

[0209] The rod body vh is bent along the outer surface of the seat receiving body 1, that is, it is bent into a partial arc shape so as to be convex downward in the front view. The front end of the rod body vh becomes the operating end vc that mainly receives the operating force operated by the user's finger. The operating end vc is configured to be located at the lower limit position by its own weight when not receiving the operating force operated by the user.

[0210] <Base end upright setting part vi>

[0211] The base end upright portion vi is a substantially quadrangular column-shaped structure that is upright from the base end portion of the rod body vh.

[0212] <Inner extension part vm>

[0213] The inner extension vm is supported by the base end upright portion vi in ​​a cantilever manner. The inner extension vm is formed so that the base end portion has substantially the same width as the base end upright portion vi and the width gradually shortens toward the front end side located inside the support base B.

[0214] The front end portion of the inner extension portion vm serves as a rotation end portion va that can push down the operating member a23 provided on the foot support a2.

[0215] <Bearing part vb>

[0216] The bearing portion vb is provided so that the front portion and the rear portion of the boundary portion between the base end upright portion vi and the inner extending portion vm face in opposite directions.

[0217] The bearings vb are arranged in pairs on both sides of the lifting operation rod V, i.e., front and rear. One of the bearings vb faces forward, and the other faces rearward. The bearings vb are arranged near the inner edge of the boundary between the base end upright portion vi and the inner extension portion vm.

[0218] The front and rear bearings vb are recessed in opposite directions and engage with the front and rear shafts j4 protruding in the rod support b13 of the support base B, so that the lifting lever V can rotate around the shafts j4 as a whole.

[0219] The pair of front and rear bearing portions vb are provided with a notch portion vd as a pull-out passage. The notch portion vd allows the pair of front and rear shaft portions j4 to be pulled out by moving the lift operating lever V only when the lift operating lever V takes a predetermined detachable posture (SR).

[0220] The notch vd of the bearing vb is set to a width dimension that allows the narrow width portion j41 of the shaft j4 of the rod support v13 to pass through. On the other hand, the notch vd is set to a width dimension that does not allow the wide width portion j42 of the shaft j4 to pass through.

[0221] In this embodiment, the cutout portion vd is provided at a position where, when the lift operating lever V is in the detachable posture (SR), the shaft portion j4 can move linearly relative to the vertical direction and can detach from the inside of the bearing portion vb to the outside.

[0222] <<Regarding the Installation of the Lifting Operation Rod V to the Support Base B>>

[0223] A mounting structure of the lift operation rod V for mounting the lift operation rod V to the support base B constituting the chair will be described.

[0224] The chair of this embodiment is a chair in which the lifting operation rod V can take a detachable posture (SR) in which it is detachable from the support base B, and a non-detachable posture (SH) in which it is non-detachable from the support base B.

[0225] <About the Inseparable Posture (SH)>

[0226] When the leg A as the blocking member is fitted inside the support base B, the lifting operation rod V can only take a non-detachable posture (SH) in which it cannot be detached from the support base B.

[0227] That is, when the leg A is normally mounted on the support base B, the lift operation lever V cannot take the detachable posture (SR).

[0228] After the lift rod V is supported by the rod support b13 of the support base B, the foot support a2 of the foot A as a blocking member is installed on the support base B, so that the rotatable range of the lift rod V is limited by the existence of the upper part of the foot support a2.

[0229] The lifting operation lever V cannot take the detachable posture (SR) as a result of the upper portion of the foot support a2 being able to rotate only within the range of the non-detachable posture (SH) and being prevented from further rotation.

[0230] That is, when the foot A is attached to the support base B, the rotating end va of the lift operating rod V abuts against the upper part of the foot support a2 in the non-detachable posture (SH), and the rotating end va is prevented from further moving downward by the foot support a2. Therefore, the lift operating rod V cannot be detached from the support base B unless the foot A is removed from the support base B.

[0231] <About detachable posture (SR)>

[0232] The lifting operation rod V can take a detachable posture (SR) in which it can be detached from the support base B only when the leg A serving as an obstacle is not fitted inwardly with respect to the support base B.

[0233] The chair is configured such that by removing the foot support a2 of the foot A from the support base B supporting the lift lever V, the rotatable range of the lift lever V is not limited by the upper portion of the foot support a2, and the posture of the lift lever V can be changed to a detachable posture (SR).

[0234] That is, when the foot A is detached from the support base B, the rotation end va of the lift operation rod V can enter the inside of the fitting hole Ba until it can take the detachable posture (SR).

[0235] Moreover, the lifting operating rod V can be detached from the supporting base B by being relatively moved by the user in a direction away from the supporting base B (upward vertical direction), so that the narrow width portion j41 of the shaft portion j4 can pass through the cutout portion vd of the bearing portion vb.

[0236] <<Reaction Force Generator R>>

[0237] 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 to be extendable and retractable in the front-rear direction.

[0238] The reaction force generating body R is a compression spring type, one end, namely the rear end, is mounted on the support base B via the support member W, and the other end, namely the front end, is mounted relative to the seat engagement shaft j3 of the back support body L.

[0239] The reaction force generating body R can directly load the seat engagement axis j3 forward. The reaction force generating body R is set to be in a substantially horizontal posture extending in the front-rear direction when the seat C and the back support body L are in a normal posture (ps). The reaction force generating body R is in a horizontal posture between the support base B and the seat engagement axis j3 of the back support body L in the normal posture (ps).

[0240] In this embodiment, the reaction force generating body R can load the left-right center of the seat engagement axis j3 forward with the support base B as a foothold. The seat engagement axis j3 abuts against the axial movement limiting portion b15 of the left and right side walls b1 of the support base B, and is prohibited from further moving forward and downward.

[0241] That is, the seat engagement shaft j3 contacts the support base B, thereby prohibiting the back support body L from rotating forward about the main axis j1, thereby defining the normal posture (ps) of the back support body L.

[0242] Furthermore, as the back support body L and the seat C transition from the normal posture (ps) to the rearwardly inclined posture (pr), the reaction force generating body R gradually inclines rearwardly while being compressed in the front-rear direction as the seat engagement axis j3 moves rearward.

[0243] The reaction force generating body R is mainly composed of a metal coil spring r1 (compression coil spring) as a spring material.

[0244] In this embodiment, based on the structure of the body weight-sensitive locking mechanism in which the seat occupant pushes the seat engagement shaft j3 forward and downward through the seat C, the seat occupant assists the reaction force in the direction of the normal posture (ps) of the backrest M relative to the rearward tilting action. Therefore, as the reaction force generating body R of this embodiment, a relatively small and lightweight coil spring r1 is used.

[0245] The reaction force generating body R includes a coil spring r1 made of metal; a front member r2 installed in front of the coil spring r1; a rear member r3 installed in the rear of the coil spring r1; and a posture retaining shaft r4 that can maintain the postures of the front member r2 and the rear member r3 by inserting the front portion into a retaining hole provided on the front member r2 and the rear portion into a retaining hole provided on the rear member r3.

[0246] The front end of the front member r2 is connected to the seat engagement shaft j3 so as to be relatively rotatable. The front end of the front member r2 is provided with an engagement recess r21 extending in the left-right direction so as to be fitted onto the cylindrical seat engagement shaft j3.

[0247] The rear end of the rear member r3 is supported on the support base B via the support member W. The rear end of the rear member r3 is connected to the support member W so as to be relatively rotatable. The rear end of the rear member r3 is provided with a locking recess r31 extending in the left-right direction, and a pair of upper and lower longitudinal locking recesses r32 provided so that the positions in the left-right direction coincide with the upper and lower parts of the locking recess r31.

[0248] The engagement recess r31 of the rear member r3 engages with a pair of left and right shaft projections w15 projecting from the middle of the front wall portion w12 in the support member body w1. The pair of left and right shaft projections w15 project forward in a partially disc-like shape in side view.

[0249] The vertical engagement recess r32 of the rear member r3 engages with a mountain-shaped protrusion w16 provided protrudingly at the left-right center of the front wall portion w12 of the support member body w1. The mountain-shaped protrusion w16 is provided to extend in the up-down direction.

[0250] Furthermore, although the front member r2 and the rear member r3 have different postures relative to each other, they each use a structure of the same shape.

[0251] <<Supporting member W>>

[0252] The supporting member W includes a supporting member body w1 and a hexagonal nut n5. The supporting member body w1 is formed of synthetic resin and has a portion on the front side that can be engaged with the reaction force generating body R, and has an inclined back side portion wm on the rear side; the hexagonal nut n5 is a nut that can be movably arranged inside the supporting member body w1.

[0253] The support member W is fixed with respect to the mounting portion 2T having the first screw insertion hole h51 provided at the rear portion of the support base B by the screw v5.

[0254] 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 as the bottom wall portion of the mounting portion 2T of the support base B at a predetermined fixed position.

[0255] <Supporting member body w1>

[0256] The supporting member body w1 has a bottom wall portion w11 and a peripheral wall portion ws. The bottom wall portion w11 has a second screw insertion hole h52 for inserting the screw v5. The peripheral wall portion ws is vertically arranged upward from the peripheral edge of the bottom wall portion w11, and a nut installation space wk for accommodating the hexagonal nut n5 is arranged inside.

[0257] [Bottom wall portion w11]

[0258] The bottom wall portion w11 is provided with a second screw insertion hole h52 having a long hole shape in the front-rear direction at the center in the left-right direction. The bottom surface of the bottom wall portion w11 abuts against the rear bottom wall 24 of the mounting portion 2T at a fixed position.

[0259] [Surrounding wall ws]

[0260] The surrounding wall portion ws includes a front wall portion w12 that engages with the rear member r3 of the reaction force generating body R; a rear wall portion w13 of an inclined back portion wm that can slide in contact with the inclined surface nm of the rear wall portion 27 in the supporting 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.

[0261] The front wall portion w12 includes a pair of left and right axial protrusions w15 and a mountain-shaped protrusion w16. The pair of left and right axial protrusions w15 are protrudingly arranged in the middle portion in the left-right direction in a manner that allows them to engage with the engaging recess r31 of the rear member r3; the mountain-shaped protrusion w16 is protrudingly arranged in the middle portion in the left-right direction in a manner that allows them to engage with the longitudinal engaging recess r32 of the rear member r3.

[0262] The rear wall portion w13 is a rearwardly inclined structure when viewed from the side. The rearwardly inclined back surface portion wm of the rear wall portion w13 is inclined so as to gradually move backward toward the upper side.

[0263] The left and right side wall portions w14 each include an outer wall wa and an inner wall wb disposed inside the outer wall wa. The nut arrangement space wk is formed by the front wall portion w12 and the rear wall portion w13 of the peripheral wall portion ws and the inner wall wb of the left and right side wall portions w14.

[0264] The hexagonal nut n5 disposed in the nut disposing space wk of the peripheral wall portion w12 is engaged with the inner peripheral surface of the peripheral wall portion w12 in a manner that suppresses left-right movement and horizontal rotation. In addition, since the nut disposing space wk is formed so that the dimension in the front-back direction gradually increases upward, it becomes a structure that allows the hexagonal nut n5 to move in the front-back direction.

[0265] <Hexagonal nut n5 (nut)>

[0266] The hexagonal nut n5 is a nut of a known structure held on the supporting base body w1. The hexagonal nut n5 is threadedly matched with a screw v5 inserted into a first screw insertion hole h51 provided in the supporting base B having a thread groove and a second screw insertion hole h52 provided in the bottom wall portion w11 of the supporting member body w1.

[0267] The hexagonal nut n5 is engaged with the peripheral wall portion w12 so as to suppress movement in the left-right direction and horizontal rotation, and is engaged with the peripheral wall portion w12 so as to allow movement in the front-rear direction.

[0268] <About the Operation of the Supporting Member W for Attaching the Reaction Force Generating Body R>

[0269] The support member W for mounting the reaction force generating body R is mounted on the mounting portion 2T in the following manner.

[0270] First, the front member r2 of the reaction force generating body R is engaged with the seat engaging shaft j3, and the rear member r3 is engaged with the front wall portion w12 of the supporting member main body w1.

[0271] Next, the screws v5 inserted from bottom to top in the order of the first screw insertion holes h51 of the support base B and the second screw insertion holes h52 of the support member body w1 are connected (threadedly engaged) to the hexagonal nuts n5 provided inside the support base body w1.

[0272] At this time, the support member W is connected to the rear portion of the reaction force generating body R in a state that is not compressed in the front-rear direction. In other words, the support member W is located above and behind the fixed position. The screw v5 inserted into the first and second screw insertion holes h51 and h52 in the shape of long holes can be easily tilted backward in order to threadably engage with the hexagonal nut n5.

[0273] After the above steps, the operator can complete the installation work only by rotating the screw v5 without directly contacting the reaction force generating body R which is prone to danger or the supporting member W connected to the reaction force generating body R.

[0274] Next, the screw v5 threadedly engaged with the hexagonal nut n5 is rotated in the first direction (tightening direction).

[0275] When the screw v5 is rotated in the first direction, the hexagonal nut n5 held on the supporting member body w1 moves downward together with the supporting member body w1. That is, the supporting member W moves toward the rear bottom wall 24 of the mounting portion 2T by the operator's rotation of the screw v5.

[0276] At this time, as the support member W gradually moves downward, it is gradually loaded from behind by the reaction force generating body R. That is, as the support member W is guided by the inclined surface nm of the mounting portion 2T as it descends, it moves downward and forward, so the reaction force generating body R is gradually compressed between the seat engagement shaft j3 and the support member W, and its loading force gradually increases.

[0277] If the screw v5 is further rotated, the support member W is guided to the inclined surface nm while resisting the biasing force of the reaction force generating body R, and at the same time, gradually moves smoothly forward and downward, and finally reaches a predetermined fixed position.

[0278] As described above, the mounting of the support member W to the mounting portion 2T is completed.

[0279] The operation of removing the reaction force generating body R and the supporting member W can be carried out very safely by following the above-mentioned reverse steps.

[0280] That is, the support member W can be guided to move (rise) in the direction of the counter-fixed position while engaging with the inclined surface nm by rotating the screw v5 in the second direction. At this time, the support member W is guided by the inclined surface nm and moves upward and backward as the hexagonal nut n5 rises, weakening the loading force of the reaction force generating body R.

[0281] The operator can complete the initial step of disassembling the reaction force generating body R and the supporting member W, which are prone to be dangerous, simply by rotating the screw v5 in the second direction without touching the reaction force generating body R and the supporting member W.

[0282] <<Seat C>>

[0283] The seat C is supported by a support base B provided on the leg 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.

[0284] The seat C includes a seat receiving body 1 and a seat main body D having a seat surface facing upward and being attachable to and detachable from the seat receiving body 1 .

[0285] 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 in a partial spherical shape.

[0286] <Regarding the forward-tilting structure of seat C>

[0287] The front part of the seat C is supported via the front shaft j2 to be rotatable and movable in the up-down direction relative to the support base B. The rear part of the seat C is supported on the seat engagement shaft j3, which is the seat engagement part of the back support body L as a structure supported on the support base B in the normal posture (ps). Here, the "rear end of the seat C" supported on the back support body L means "the part behind the front part of the seat C".

[0288] The seat C is configured to be tiltably rotatable about a front axis j2 supported by the support base B between a normal posture (ps) and a forward-leaning posture (pf) that is tilted forward relative to the normal posture (ps).

[0289] The seat C is provided with an engaged portion 1 k that can come into contact with a seat engagement shaft j3 that is a seat engagement portion provided on the support base B.

[0290] The engaged portion 1k of the seat C is engaged with the seat engagement axis j3 so as to be placed on the seat engagement axis j3 in the normal posture (ps) and the rearwardly inclined posture (pr). The engaged portion 1k of the seat C is configured to be separated upward relative to the seat engagement axis j3 in the forwardly inclined posture (ps).

[0291] <Seat support 1>

[0292] The seat receiving body 1 supports the seat main body D. The upper surface of the seat receiving body 1 is engaged with the housing 3 constituting the seat main body D. That is, the housing 3 is placed on the upper surface of the seat receiving body 1 .

[0293] The seat receiving body 1 is formed of a synthetic resin in a shell shape. The seat receiving body 1 is in a partially spherical shape. The outer peripheral surface of the seat receiving body 1 recognized by the user or the like is formed in a spherical surface shape.

[0294] The outer peripheral surface of the front portion of the seat receiving body 1 is configured to be smoothly continuous with the lower surface of the front portion of the support base B. In addition, the outer peripheral surface of the seat receiving body 1 is configured to be smoothly continuous with the outer peripheral surface of the seat body D.

[0295] The seat receiving body 1 is provided with a front axle holding portion 1m which can hold both end portions of the front axle j2 supported by the support base B.

[0296] The seat support body 1 includes a recess 11, a shell mounting portion 12, a recess 13 and an arm through hole 14. The recess 11 is open downward and is equipped with a supporting base B and a back support body L; the shell mounting portion 12 is a seat body mounting portion arranged on the upper portion; the recess 13 is arranged in the central portion in the left-right direction and is open to the upper side where the intermediate member U and the coil spring Y are arranged; the arm through hole 14 is arranged between the recess 13 and the recess 11, and is a vertical connecting hole through which the arm u2 of the intermediate member U can pass.

[0297] <Recess 11>

[0298] The recess 11 is provided at the lower portion of the center portion in the left-right direction of the seat receiving body 1 and is open to a downward direction where the support base B can be disposed.

[0299] The recessed portion 11 forms a recessed space in which the support base B and the back support body L are disposed.

[0300] In the recessed space facing the recess 11 in the seat supporting body 1, a front axle retaining portion 1m, a clamped portion 1k and a limiting protrusion 1t are provided. The front axle retaining portion 1m can retain the front axle j2; the clamped portion 1k is arranged at the rear compared to the front axle retaining portion 1m, and is engaged with the seat engaging axis j3 in the normal posture (ps) and the rearward tilted posture (pr), and is separated from the seat engaging axis j3 in the forward tilted posture (pf); the limiting protrusion 1t is arranged in the groove portion b14 provided in the supporting base B.

[0301] The recess 11 includes a recess top wall portion 111, a recess front wall portion 112, a recess rear wall portion 113 and a recess side wall portion 114. The recess top wall portion 111, whose lower side faces the recessed space, has a clamping portion 1k, which is a portion that is engaged with the seat clamping axis j3; the recess front wall portion 112 and the recess rear wall portion 113 are respectively extended downward from the front and rear portions of the recess top wall portion 11; the left and right recess side wall portions 114 are respectively extended downward from the left and right side portions of the recess top wall portion 111.

[0302] The distance between the inner surfaces of the left and right recess side wall portions 114 is set to be longer than the left-right dimension of the seat engaging axis j3.

[0303] [Front axle holding part 1m]

[0304] The front axle holding portion 1m is protruded downward from the front portion of the recessed top wall portion 111. The front axle holding portions 1m are provided in pairs at the left and right sides of the recessed top wall portion 111. The left and right front axle holding portions 1m are shaped to hold the left and right side ends of the front axle j2. The left and right front axle holding portions 1m are adjacently provided with an axle passage 1r through which the front axle j2 can pass when the front axle j2 is mounted or unmounted.

[0305] [Engaged portion 1k]

[0306] The engaged portion 1k is engaged with the seat engagement shaft j3 of the back support body L rotatably supported by the support base B. The engaged portion 1k is provided on the recessed top wall 111. The engaged portion 1k is provided in pairs on the left and right sides of the front lower portion of the recessed portion 13.

[0307] 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.

[0308] The engaged portion 1k is configured to be contactable and separable with respect to the seat engagement axis j3 in accordance with a change in the posture of the seat C.

[0309] The engaged portion 1k is engaged with the seat engagement axis j3 when the seat C takes the normal posture (ps) and the rearwardly inclined posture (pr), and is separated from the seat engagement axis j3 only when the seat C takes the forwardly inclined posture (pf). In other words, the engaged portion 1k is not in a form that normally holds the seat engagement axis j3 in a non-detachable manner, but is configured to be contactable and separable with respect to the seat engagement axis j3.

[0310] [Limiting protrusion 1t]

[0311] The restricting protrusion 1t is a structure for preventing the seat body 1 from being separated from the front shaft j2 unless the seat body 1 is in a jumping posture (ph) which is a posture for separating the seat receiving body 1 from the front shaft j2.

[0312] That is, the restriction protrusion 1t engages with the groove b14 of the support base B, and when the seat body 1 is in a posture other than the predetermined jumping posture (ph), the forward movement of the seat body 1 relative to the front axis j2 can be restricted.

[0313] The limiting protrusions 1t are provided in pairs on the left and right sides at the front part of the recess 11 of the seat receiving body 1. The limiting protrusions 1t protrude inwardly at the position corresponding to the groove b14 of the support base B in the seat receiving body 1. The limiting protrusions 1t are inclined so as to be gradually located upward toward the rear. The limiting protrusions 1t are provided protrudingly at the inner side parts of the left and right front axle retaining parts 1m.

[0314] <Casing Arrangement Section 12>

[0315] The housing arrangement portion 12 has a connection portion with the housing 3 of the seat body D, and is provided on an upper portion of the seat receiving body 1 , that is, a portion of the seat receiving body 1 that faces upward.

[0316] A cutout portion 122 is provided at the rear end portion of the housing installation portion 12 to avoid interference with the operation lever k2 provided on the housing 3 .

[0317] The shell installation portion 12 is provided with a shape portion constituting a detachable engagement structure (central positioning portion G, vertical engagement mechanism H, horizontal engagement mechanism I, reverse return restriction mechanism K) for detachably attaching the seat body D as described in detail later.

[0318] The outer peripheral edge 1e of the seat receiving body 1 is formed so that it is gradually located downward (concave downward) from the left and right ends toward the center in the left-right direction when viewed in the front view and the rear view. In addition, the outer peripheral edge 1e of the seat receiving body 1 is formed so that it is gradually located upward (convex upward) from the front and rear ends toward the center in the front-back direction when viewed in the side view.

[0319] The upper end of the seat receiving body peripheral wall portion 121 disposed on the inner side than the outer peripheral edge 1e of the seat receiving body 1 is disposed so as to extend in a substantially horizontal direction when viewed in the front view, the rear view, and the side view.

[0320] <Concave 13>

[0321] The recessed portion 13 is provided in the upper portion of the seat receiving body 1 in order to arrange the intermediate member U and the coil spring Y. The recessed portion 13 is provided in the vicinity of the engaged portion 1k engaged with the seat engaging axis j3.

[0322] The recess 13 is provided so as to be recessed downward relative to the central top wall portion 123 which is the upper portion of the seat receiving body 1 constituting the housing arrangement portion 12. The recess 13 is open upward and includes another spring receiving portion 13a disposed upward for receiving the lower portion of the coil spring Y.

[0323] In the recessed portion 13 , a placement space 13 s in which the intermediate member body u1 and the coil spring Y are placed is formed.

[0324] The recess 13 includes a bottom wall 131 on which a spring receiving portion 13a facing upward is provided; a front wall 132 connecting the front end portion of the bottom wall 131 and the central top wall portion 123; a rear wall 133 connecting the rear end portion of the bottom wall 131 and the central top wall portion 123; and an outer wall 134 connecting the outer end portion of the bottom wall 131 and the central top wall portion 123.

[0325] The bottom wall 131 of the recess 13 is separated from the left and right sides so that the arm u2 of the intermediate member U is disposed on the recess 11 side. That is, the bottom wall 131 of the recess 13 is separated from the left and right sides through the arm through hole 14.

[0326] <Arm through hole 14>

[0327] The arm through hole 14 is a structure through which the arm portion u2 of the intermediate member u2 can pass. The arm through hole 14 is provided between the recess 13 and the recess 11. The arm portion u2 of the intermediate member U is disposed in the arm through hole 14. The arm through hole 14 allows the intermediate member U held in the recess 13 to move in the up-down direction.

[0328] <Structure for Easy Installation and Removal of Seat Receiving Body 1 with Respect to Support Base B>

[0329] The seat receiving body 1 can rotate around the front axle j2 in a manner that the rear end jumps upward after the intermediate member U is separated. Moreover, the front axle holding portion 1m is configured to be detachable from the front axle j2 only when the posture of the seat receiving body 1 is changed to a predetermined jumping posture (ph).

[0330] In front portions of the left and right side walls b1 of the support base B, grooves b14 are provided in pairs on the left and right sides. The grooves b14 extend in the up-down direction and are open toward the outside.

[0331] The seat receiving body 1 is provided with a pair of left and right restricting protrusions 1t protruding inwardly at locations corresponding to the grooves b14 of the support base B. The restricting protrusions 1t are provided protrudingly at inner sides of left and right front axle holding portions 1m provided on the seat receiving body 1 .

[0332] The seat receiving body 1 is constructed so that when the intermediate component U restricts the disengagement (i.e., when the intermediate component U is clamped between the seat receiving body 1 and the seat engaging axis j3), the restricting protrusion 1t is located in the groove b14, keeping the front axle holding portion 1m from disengaging forward relative to the front axle j2.

[0333] Even when the intermediate member U is not sandwiched between the seat receiving body 1 and the seat engaging shaft j3, when the prescribed jumping posture (ph) is not taken, the front axle retaining portion 1m cannot be separated from the front axle j2 because the limiting protrusion 1t and the groove portion b14 are also engaged.

[0334] The seat receiving body 1 is configured so that, when taking a predetermined jumping posture (ph), the posture is changed so that the restriction protrusion 1t is located outside the groove portion b14 and the front axle holding portion 1m can be separated forwardly from the front axle j2.

[0335] That is, in this embodiment, the following structure is provided: without using a special tool, the seat body 1 can be easily separated from the front shaft j2 (support base B) by making it into a predetermined jumping posture (ph). On the other hand, since the seat body 1 cannot be separated from the front shaft j2 (support base B) unless the seat body 1 is made into a predetermined jumping posture (ph), a structure for stably supporting the seat body 1 is realized.

[0336] <Intermediate Component U>

[0337] The intermediate member U is formed of a synthetic resin and is provided between the seat receiving body 1 and the seat engagement shaft j3 serving as the seat engagement portion of the back support body L.

[0338] Between the seat receiving body 1 and the intermediate member U, left and right pairs of coil springs Y are interposed as spring members.

[0339] The intermediate member U is disposed between the seat engagement axis j3 of the back support body L rotatably supported with respect to the support base B and the rear portion of the seat C, that is, the vicinity of the engaged portion 1k.

[0340] The intermediate member U includes a portion engaged with the seat engagement axis j3 and a portion engaged with the seat receiving body 1 via the coil spring Y. The intermediate member U can limit the separation distance of the engaged portion 1k from the seat engagement axis j3 in the forward tilted posture (ps).

[0341] The intermediate member includes an intermediate member body u1 and a pair of left and right arm portions u2. The intermediate member body u1 is provided with an upper end portion receiving one end portion of a coil spring Y. The pair of left and right arm portions u2 extend from the intermediate member body u1 and can be engaged with a seat engaging shaft j3 as a seat engaging portion.

[0342] [Intermediate member main body u1]

[0343] The intermediate member body u1 is a rectangular plate-shaped structure as a whole and is long in the horizontal direction. The intermediate member body u1 is provided with a spring receiving portion u11 which is arranged downward.

[0344] That is, on the lower surface of the intermediate member body u1, spring receiving portions u11 for receiving one of the upper end portions of the pair of left and right coil springs Y are provided in pair on the left and right sides.

[0345] [Arm u2]

[0346] The arm portion u2 includes a downward extending portion u21 extending downward from the front portion of the intermediate member body u1 and a hook-shaped portion u22 extending forwardly from the lower portion of the downward extending portion u21 and engageable with the lower portion of the seat engagement shaft j3.

[0347] <Coil spring Y (spring member)>

[0348] The coil springs Y are interposed between the seat receiving 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 posture that can be extended and retracted in the up-and-down direction.

[0349] The coil spring Y urges the intermediate member U upward with the seat receiving body 1 as a foothold. That is, the coil spring Y urges the intermediate member U in a direction in which the intermediate member U engages with the seat engagement axis j3.

[0350] <Loading and Removing Structure of Intermediate Member U>

[0351] The intermediate member U can restrict the seat receiving body 1 from separating from the back supporting body L. That is, the intermediate member U is interposed between the back supporting body L and the seat receiving body 1 so that the rear portion of the seat receiving body 1 does not separate from the seat engagement axis j3 by a certain distance or more.

[0352] The arm portion u2 of the intermediate member U is engaged with the lower portion of the seat engagement shaft j3 in the back support body L, and the intermediate member body u1 of the intermediate member U is engaged with the seat receiving body 1 via the coil spring Y.

[0353] The intermediate member U is configured to be attachable and detachable to a predetermined position between the back support body L and the seat receiving body 1 without using a fixing member.

[0354] That is, the intermediate member U is constructed so that it can be disengaged from the seat engagement shaft j3 by being pushed in the direction resisting the biasing force of the coil spring Y, and can be detached from between the seat engagement shaft j3 and the seat receiving body 1 in the disengaged state.

[0355] Furthermore, if the above-mentioned steps are reversed, the intermediate member U can be disposed at a predetermined position between the back support body L and the seat receiving body 1 without using a fixing member.

[0356] <Seat body D>

[0357] The seat body D includes a seat cushion Dq, a cushion support housing 3 as a support member attached to the bottom of the seat cushion Dq, and a seat surface fabric Dh covering the upper portion and the peripheral portion of the seat cushion Dq and the peripheral portion of the housing 3. The seat body D has a substantially circular seat surface on the upper portion thereof when viewed from above.

[0358] [Seat cushion Dq]

[0359] The seat cushion Dq is mainly formed of a polyurethane foam material as a foaming material. The seat cushion Dq is formed so that the width thereof gradually increases upward. The lower surface of the seat cushion Dq is attached to the housing 3.

[0360] The seat cushion Dq is fitted from the upper side to the housing 3. The seat cushion Dq is larger than the housing 3 in a bottom view. The dimensions of the seat cushion Dq in the front-rear direction and the left-right direction are set longer than those of the housing 3 in the front-rear direction and the left-right direction.

[0361] [Shell 3]

[0362] The housing 3 is attached to the lower surface of the seat cushion Dq and has a substantially disc shape. The housing 3 is integrally formed of synthetic resin.

[0363] The shell 3 includes a shell body 31, a supporting wall portion 33, an end wall portion 34 and a peripheral wall portion 32. The shell body 31 has a circular plate-shaped portion with the upper surface bonded to the lower surface of the seat cushion Dq; the supporting wall portion 33 is continuously arranged in a manner extending downward from the peripheral end edge of the shell body 31, and the outer surface is attached to the inner surface of the peripheral portion of the seat cushion Dq; the end wall portion 34 extends from the lower end portion of the supporting wall portion 33 to the oblique upper and outer side, and supports the lower end portion of the peripheral portion of the seat cushion Dq from below; the peripheral wall portion 32 is vertically arranged downward from the lower surface of the peripheral portion of the shell body 31 which is on the inner side compared to the supporting wall portion 33.

[0364] The lower end of the peripheral wall portion 32 is provided so as to extend in a substantially horizontal direction when viewed in a front view, a rear view, and a side view.

[0365] An operating lever k2 is integrally provided on the housing 3. The operating lever k2 is cantilevered and has a convex portion kt that is engaged with the seat receiving body 1 so as to prevent relative rotation from the mounting posture (F).

[0366] The housing body 31 has a central protrusion g1 protruding downward in the center in the front-rear and left-right directions. The housing body 31 has a plurality of locking protrusion engagement portions hk provided inside the peripheral wall portion 32 at regular intervals in the circumferential direction.

[0367] The central convex portion g1 constitutes a central positioning portion G, and the locking protrusion engaging portion hk constitutes a vertical engagement mechanism H, which will be described in detail later.

[0368] The peripheral wall portion 32 is disposed at the peripheral edge of the housing 3. More specifically, the peripheral wall portion 32 is disposed on the central side of the support wall portion 33 of the housing 3. The peripheral wall portion 32 has an outward surface 32m against which the edge de of the seat fabric Dh surrounding the seat cushion pad Dq can abut.

[0369] That is, the peripheral wall portion 32 is continuously arranged on a perfect circular track except for a portion where the rear portion of the operating rod k2 is arranged, so as to be located on an imaginary circumference of a perfect circle centered on the central protrusion g1 in a top view.

[0370] The peripheral wall 32 has an outwardly extending portion 321 extending outwardly to restrict downward movement of the edge de of the seat fabric Dh. The outwardly extending portion 321 is a plurality of protruding pieces arranged at regular intervals in the peripheral direction of the peripheral wall 32.

[0371] In addition, an inner protrusion it bulging inward is provided on the inner surface side of three locations of the front end portion and the left and right side ends of the peripheral wall portion 32, that is, on the inner surface side of the left and right central portion of the front portion of the peripheral wall portion 32 and on the inner surface side of the front and rear central portions of the left and right side portions of the peripheral wall portion 32. The inner protrusion it constitutes a horizontal engagement mechanism I described in detail later.

[0372] Ribs rv, which are vertically provided on the case body 31 and extend outward from the center of the case body 31, are connected to the inner side surface of the peripheral wall portion 32. The ribs rv are radially arranged on the lower surface of the case body 31.

[0373] The operating rod k2 is a structure that is cantilever-supported relative to the housing body 31. That is, the housing 3 is provided with the operating rod k2, which is a rod member that is cantilever-shaped and engaged with the seat receiving body 1. The operating rod k2 has a wall-shaped portion k21 that constitutes a part of the peripheral wall portion 32, which is upright from the base end portion of the operating end portion k22.

[0374] The operating rod k2 is disposed at the rear of the housing body 31. The operating rod k2 has a base end ke connected to the housing body 31 as a whole, and an operating end k22 for receiving an operating force from a user's finger is provided at the outer end.

[0375] On the operating rod k2, a convex portion kt is provided between the base end portion ke and the operating end portion k22 to protrude downward, and the convex portion kt can be engaged with the upward concave portion k1 provided on the seat receiving body 1. The concave portion k1 of the seat receiving body 1 and the convex portion kt of the operating rod k2 constitute a reverse return limiting mechanism K described in detail later.

[0376] The lower edge 3e of the supporting wall portion 33 in the housing 3 is formed so as to be gradually located downward (protrudes downward) from the left and right ends toward the center in the left-right direction when viewed in the front view and the rear view. The lower edge 3e of the supporting wall portion 33 in the housing 3 is formed so as to be gradually located upward (protrudes upward) from the front and rear ends toward the center in the front-back direction when viewed in the side view.

[0377] The lower edge 3e of the support wall portion 33 in the housing 3 is set to follow the outer peripheral edge 1e of the seat receiving body 1 when the seat body D is in the mounting posture (F).

[0378] [Seat fabric Dh]

[0379] The seat fabric Dh is mainly composed of stretchable fabric that covers the seat cushion Dq.

[0380] The seat fabric Dh has an annular edge portion de. The seat fabric Dh is formed into a bag shape that is open downward. The seat fabric Dh is provided with a belt-shaped member (not shown) for reducing the diameter of the edge portion de so that the edge portion de abuts against the outward surface 32m of the peripheral wall portion 32 of the housing 3.

[0381] <<Attachment and Removal Structure of Seat Main Body D with Respect to Seat Receiving Body 1>>

[0382] The seat body D is configured to be horizontally rotatable about the common axis cj relative to the seat receiving body 1 between a retracted posture (E) in which it is detachable from the seat receiving body 1 and an attached posture (F) in which it is attached to the seat receiving body 1 .

[0383] The chair of this embodiment is constructed so that the seat body D can be easily mounted and removed from the seat receiving body 1 by not only the manufacturer but also the end user (user) without using tools, which helps facilitate maintenance such as cleaning and replacement, storage and transportation.

[0384] A central positioning portion G is provided between the seat support body 1 and the seat main body D for positioning the seat main body D in a manner that the axis thereof is aligned with the axis thereof relative to the seat support body 1; a vertical locking mechanism H for tightly locking the seat support body 1 and the shell 3 in the vertical direction when the seat main body D is in the installation posture (F); a horizontal locking mechanism I for tightly locking the seat support body 1 and the shell 3 in the horizontal direction when the seat main body D is in the installation posture (F); and a reverse return limiting mechanism K for limiting the seat main body D in the installation posture (F) from returning to the direction of the retreat posture (E).

[0385] <Central positioning part G>

[0386] The central positioning portion G can position the seat receiving body 1 and the housing 3 of the seat main body D so that they can be substantially aligned with the common axis cj.

[0387] The central positioning portion G includes a central protrusion g1 and a central protrusion snap-fitting portion g2. The central protrusion g1 is cylindrical and arranged in the central portion of the shell 3 in the seat body D, protruding downward; the central protrusion snap-fitting portion g2 is arranged in the central portion of the seat supporting body 1, and the central protrusion g1 can be relatively rotatably snap-fitted and is in the shape of a hole.

[0388] <Up and down direction engagement mechanism H>

[0389] The vertical engagement mechanism H engages the seat receiving body 1 and the housing 3 of the seat main body D in the vertical direction so as to close each other.

[0390] The vertical engagement mechanism H includes a locking protrusion hp as a first engagement portion provided on the seat receiving body 1 and a locking protrusion engagement portion hk as a second engagement portion provided on the housing 3 and engageable with the locking protrusion hp of the seat receiving body 1 .

[0391] The seat body D can take the installation posture (F) by tightly engaging the locking protrusion hp with the locking protrusion engaging portion hk.

[0392] A plurality of the locking protrusions hp of the seat receiving body 1 and the locking protrusion engaging portions hk of the housing 3 are arranged at regular intervals along an imaginary circular line centered on the common axis cj.

[0393] [Locking protrusion hp (first engaging portion)]

[0394] The locking protrusion hp is a protruding structure protruding in a direction intersecting the common axis cj. The locking protrusion hp is protruding approximately horizontally from a standing wall-like seat receiving body peripheral wall portion 121 of a substantially annular seat receiving body 1 disposed upright on the periphery of the seat receiving body 1 toward the inner side, i.e., the center direction where the common axis cj is located, in a top view.

[0395] The locking protrusion hp can be engaged with the guide inclined surface hm provided in the locking protrusion engaging portion hk in the up-down direction. More specifically, the locking protrusion hp can push the guide inclined surface hm of the locking protrusion engaging portion hk downward. That is, the locking protrusion hp moves the seat body D downward during the process of rotating the seat body D from the retreat posture (E) to the installation posture (F).

[0396] [Engaging tab engagement portion hk (second engagement portion)]

[0397] The locking protrusion engaging portion hk has an upward guide inclined surface hm, which is a portion that the locking protrusion hp can engage with. The locking protrusion engaging portion hk is provided to protrude downward from the housing body 31 having a circular plate shape.

[0398] The locking protrusion engaging portion hk includes a support wall hs vertically provided downward from the housing body 31 and an engaging portion main body hg supported by the support wall hs and having an upward guide inclined surface hm provided on the upper surface.

[0399] The support wall hs includes a first support wall portion ha extending in the circumferential direction, and a second support wall portion hb provided continuously from the first support wall portion ha and extending in a direction substantially orthogonal to the first support wall portion ha.

[0400] The first support wall ha is connected to the inner edge of the engagement portion body hg extending in the circumferential direction. The second support wall hb is shorter in width than the first support wall ha and is connected to one circumferential end edge of the engagement portion body hg.

[0401] [The main body hg of the engaging part is a plate-like structure that is in a lying posture and extends in the circumferential direction. The inner edge and the base end edge of the main body hg of the engaging part are connected to the supporting wall hs. The upward guiding inclined surface hm provided on the main body hg of the engaging part is inclined in a manner that gradually moves upward from the front end side toward the base end side. Here, the front end side of the main body hg of the engaging part refers to the edge side of the front end that becomes the direction of travel when the swing action is performed from the retreat posture (E) to the installation posture (F).

[0402] The locking protrusion hp and the guide inclined surface hm of the vertical engagement mechanism H having the above structure are configured so that the degree of close contact gradually increases as the seat body D rotates from the retreat posture (E) to the mounting posture (F).

[0403] The procedure for mounting the seat body D to the seat receiving body 1 is as follows.

[0404] First, if Fig.43 As shown, the seat body D is moved downward while being separated from the upper side of the seat receiving body 1 and being positioned horizontally on the common axis cj by the central positioning portion G.

[0405] Then, if Fig.44 As shown in FIG. 1 , the seat body 43 moved downward is caused to rotate around the common axis cj.

[0406] Then, if Fig.45 As shown, when the seat body D reaches the mounting posture (F), the locking protrusion hp and the locking protrusion engaging portion hk are engaged with each other in close contact in the up-down direction.

[0407] <Horizontal engagement mechanism I>

[0408] The horizontal engagement mechanism I engages the seat receiving body 1 and the housing 3 of the seat main body D in the horizontal direction.

[0409] The horizontal locking mechanism I has an inner protrusion it and an outward guiding inclined surface im, wherein the inner protrusion it is a second locking portion arranged on the shell 3; the outward guiding inclined surface im is arranged on the seat supporting body 1, and is a first locking portion that can be engaged with the inner protrusion it of the shell 3 as a horizontal protrusion.

[0410] A plurality of the inward protruding portions it of the housing 3 and the outward guiding inclined surfaces im of the seat receiving body 1 are arranged at predetermined intervals along an imaginary circular line centered on the common axis cj.

[0411] [Inward protrusion it (second engagement portion)]

[0412] The inner protrusion it constitutes a protruding structure protruding in a direction intersecting the common axis cj. The inner protrusion it, in a top view, protrudes from a hanging wall-like peripheral wall portion 32 erected on the housing 3 in a substantially annular manner toward the inner direction, that is, the common axis cj.

[0413] Furthermore, an outward extending portion 321 for engaging the edge portion de of the seat fabric Dh is extended outward in the opposite direction from the portion of the peripheral wall portion 32 where the inward protruding portion it is provided.

[0414] The inner protrusion it can be engaged in the horizontal direction with respect to the outward guiding inclined surface im provided on the seat receiving body 1. More specifically, the inner protrusion it can push the outward guiding inclined surface im of the seat receiving body peripheral wall portion 121 provided in the seat receiving body toward the inside.

[0415] [Outward guiding inclined surface im (first engaging portion)]

[0416] The outward guiding inclined surface im is provided on the outer peripheral surface of the peripheral wall portion 121 of the seat receiving body 1 as a vertical wall provided upright at the peripheral edge portion of the seat receiving body 1. The outward guiding inclined surface im faces the outer side, which is a horizontal direction that can be engaged with the inner protruding portion it. The outward guiding inclined surface is inclined in a manner that gradually moves to the outer side as it moves in the clockwise direction.

[0417] The inward protrusion it and the outward guiding inclined surface im of the horizontal locking mechanism I of the above structure are constructed so that the degree of close contact gradually increases as the seat body D rotates clockwise from the retreat posture (E) to the installation posture (F).

[0418] <Reverse return restriction mechanism K>

[0419] The reverse return restriction mechanism K is provided between the seat body D and the housing 3 of the seat receiving body 1, and restricts the seat body D in the mounting posture (F) from reversely returning to the retreat posture (E).

[0420] On the other hand, the reverse return limiting mechanism K can release the non-rotatable state of the seat body D relative to the seat receiving body 1 by operating the operating rod k2 in a manner that deforms upward against the elastic restoring force of the shell 3, and can rotate the seat body D in the installation posture (F) to the retreat posture (E) to disengage from the seat receiving body 1.

[0421] The reverse return limiting mechanism K comprises a recessed portion k1 provided on the upper surface of the rear end portion of the seat receiving body 1, and an operating lever k2 provided on the housing 3 and having a protruding portion kt engageable with the recessed portion k1 only in the mounting posture (F).

[0422] The convex portion kt of the reverse return limiting mechanism K is provided on the operating lever k2, which is provided on the housing 3 in a cantilevered shape. The convex portion kt of the operating lever k2 uses elastic deformation of the member to move the operating end portion k22 receiving the operating force from the user's finger upward, thereby releasing the engagement state with the concave portion k1 provided on the seat receiving body 1, and rotating the seat body D from the installation posture (F) to the retreat posture (E).

[0423] Furthermore, a guide inclined surface km that can engage with the convex portion kt of the operating lever k2 is provided on the upper surface of the rear end portion of the seat receiving body 1 in a manner adjacent to the concave portion k1. The guide inclined surface km is inclined in a manner that gradually moves upward as it approaches the concave portion k1. The uppermost portion of the inclined surface is set to be located above the bottom of the concave portion k1.

[0424] When the seat body D is in the retreat posture (E), the convex portion kt of the operating rod k2 is arranged at the lowest position in the inclined surface. Furthermore, if the seat body D is rotated from the retreat posture (E) to the installation posture (F), the convex portion kt is gradually pushed upward by the guide inclined surface km against the elastic restoring force of the operating rod k2.

[0425] When the seat body D reaches the mounting position (F) from the retreat position (E), the convex portion kt goes over the guide inclined surface km and engages with the concave portion k1 by the elastic restoring force of the operating rod k2.

[0426] In this embodiment, when the reverse return limiting mechanism K moves from the retreat posture (E) to the installation posture (F), since the convex portion kt is lifted by the rotation of the housing 3 so as to run onto the inclined guide surface km of the seat receiving body 1, it is not necessary to apply an operating force to the operating rod k2. At this time, when sitting on the inclined guide surface km, the convex portion kt of the operating rod k2 is automatically embedded in the concave portion k1 by the elastic restoring force of the operating rod k2. That is, in the process of the reverse return limiting mechanism K reaching the installation posture (F) from the retreat posture (E), no special operation of the operating rod k2 is required.

[0427] Furthermore, downward protrusions 32t are provided on both side portions of the peripheral wall portion 32 of the housing 3 adjacent to the operating rod k2. The downward protrusions 32t extend downward until they reach the same position as the lower end position of the operating rod k2.

[0428] These downward protrusions 32t can prevent the operation rod k2 from being pushed upward from the placement surface when the seat body D and the housing 3 are independently placed on a placement surface such as a floor surface for the purpose of replacing components.

[0429] That is, since the lower protrusions 32t provided on the left and right sides of the operating rod k2 can suppress the operating rod k2 from being pushed up by the placement surface, it is possible to effectively avoid adding a bending tendency that impairs the desired elastic deformation to the operating rod k2.

[0430] The back support body L of this embodiment will be described in detail below.

[0431] <Back support body L>>

[0432] The back support body L is interposed between the support base B and the backrest M. The back support body L can support the backrest M so as to be movable between a normal posture (ps) and a rearwardly inclined posture (pr) that is tilted rearward from the normal posture (ps).

[0433] The backrest M supported by the back support body L is biased by a reaction force generating body R provided between the support base B and the seat engagement shaft j3 of the back support body L in a direction in which the backrest M can take a normal posture (ps).

[0434] The back support body L is also interposed between the support base B and the seat C. That is, the back support body L also functions as a seat support body supporting the seat C. The back support body L includes a seat engagement shaft j3 extending in the left-right direction and engaging with an engaged portion 1k provided on the seat receiving body 1 of the seat C.

[0435] The back support body L includes a back support body base 4, a back support body main body 5 and a cover member 6. The back support body base 4 is a metal structure supported to be rotatable relative to the support base B via a main axis j1; the back support body main body 5 is installed relative to the back support body base 4; and the cover member 6 is installed relative to the back support body main body 5.

[0436] The back support body L supports left and right operating members p1 that can change their positions between an engaged position (U) with respect to the backrest M and a retracted position (N) with respect to the backrest M. The left and right operating members p1 constitute a disengagement prevention mechanism P described in detail later.

[0437] <Back support base 4>

[0438] The back support body base 4 includes a pair of left and right arms 41, a connecting member 42 and a seat engaging shaft j3. The pair of left and right arms 41 are in the shape of an upright plate extending in the front-to-back direction and are rotatably supported on the support base B via a main shaft j1 serving as an axis; the connecting member 42 connects the rear portions of the pair of left and right arms 41 and is in the shape of an upright plate; the seat engaging shaft j3 is supported at the front side compared to the main shaft insertion hole 41a in the pair of left and right arms 41 and extends in the left-right direction.

[0439] [right and left arms 41]

[0440] The left and right arms 41 are made of metal. The left and right arms 41 have left and right arm bodies 411 in the form of upright walls, and the left and right arm bodies 411 are parts extending long in the front-back horizontal direction. The left and right arms 41 are arranged outside the left and right side walls b1 in the support base B.

[0441] The left and right arms 41 include left and right arm bodies 411, left and right forearm portions 412 and a main shaft insertion hole 41a. The left and right arm bodies 41 extend approximately linearly in the front-to-back direction and can support the main shaft j1 at the front end portion. The left and right forearm portions 412 extend integrally from the front end portion of the left and right arm bodies 411 obliquely forward and upward and support a seat engaging shaft j3 engaged with the seat C at the upper end portion. The main shaft insertion hole 41a is provided between the left and right arm bodies 411 and the left and right forearm portions 412 and penetrates in the left-right direction to maintain the main shaft j1.

[0442] The rear parts of the left and right arm bodies 411 are connected by a connecting member 42. The rear end parts of the left and right arm bodies 411 protrude rearwardly compared with the connecting member 42. The rear protruding parts 41b of the left and right arm bodies 411 that protrude rearwardly compared with the connecting member 42 are embedded in the fitting holes 5b of the back support body base connecting part 5a provided at the base end part 51 of the back support body main body 5.

[0443] The left and right front arms 412 extend integrally from the front ends of the left and right arm bodies 411 toward the obliquely forward upper direction. The seat engagement axis j3 extending in the left-right direction that can engage with the seat C is rigidly connected to the front ends or upper ends of the left and right front arms 412.

[0444] [Joining member 42]

[0445] The connecting member 42 is a metal structure. The connecting member 42 is in the shape of a standing plate extending in the left-right direction. The left and right ends of the connecting member 42 are rigidly connected to the inner side parts of the left and right arm bodies 411 by welding.

[0446] The coupling member 42 is provided with a nut portion n3, which is threadedly fitted with a screw v3 for mounting the back support body main body 5. A connecting wall 5c of a back support body base connecting portion 52 provided at a base end portion 51 of the back support body main body 5 is attached to the back side of the coupling member 42 and fixedly mounted by the screw v3.

[0447] [Seat engagement shaft j3]

[0448] The seat engagement axis j3 extends in the left-right direction and is connected to the upper ends of the left and right front arms 412. The seat engagement axis j3 is located above the left and right side walls b1 of the support base B and extends outward from both sides of the support base B.

[0449] The seat engagement axis j3 is arranged in front and above the main axis j1. The seat engagement axis j3 pushes up the middle part of the seat C in the front-to-back direction upward and backward in association with the backward tilting action of the back support body L. In other words, the chair is configured such that when the back support body L tilts backward, the front part of the seat C is lifted upward by the pushing action of the seat C by the seat engagement axis j3.

[0450] 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 disposed with the support base B as a foothold. The seat engagement shaft j3 is pressed forward by the reaction force generating body R.

[0451] Here, the movement of the back support body base 4 when the backrest M is tilted rearward will be described.

[0452] When the backrest M receives the load of the seated person and tilts backward, the back support body L7 supporting the backrest E rotates around the main axis j1 supported by the support base B.

[0453] At this time, the left and right arm bodies 411 of the back support body base 4 move downward and forward, and the left and right front arm parts 412 of the back support body base 4 move upward and backward.

[0454] The seat engagement shaft j3 connected to the upper portion of the left and right front arm parts 412 moves upward and rearward in the same manner as the movement of the left and right front arm parts 412 .

[0455] The seat engagement shaft j3 moves upward and rearward to lift the seat C upward against the seat load of the seated person.

[0456] [Back support body main body 5]

[0457] The back support body main body 5 includes a base end portion 51, left and right upright frame portions 52 and an upper frame portion 53. The base end portion 51 is fixed relative to the back support body base 4; the left and right upright frame portions 52 are continuously arranged with the base end portion 51 and extend in pairs in the up and down directions; the upper frame portion 53 extends in a substantially horizontal direction and is connected to the upper ends of the left and right upright frame portions 52.

[0458] The base end portion 51 includes a back support body base connecting portion 5a and left and right arm portions 5d, wherein the back support body base connecting portion 5a is connected to the back support body base 4; the left and right arm portions 5d extend linearly from the left and right side portions of the back support body base connecting portion 5a toward the front, forming an inward channel shape, which can limit the outward movement of the main axis j1 at the front.

[0459] The back support body base connecting portion 5a includes a pair of left and right interlocking holes 5b and a connecting wall 5c. The pair of left and right interlocking holes 5b are open to the front and are interlocked in the rear protruding portion 41b protrudingly arranged at the rear end portion of the back support body base 4; the connecting wall 5c is arranged between the pair of left and right interlocking holes 5b and is installed on the connecting component 42 of the back support body base 4.

[0460] The connecting wall 5c is provided with a screw insertion hole h3 penetrating in the front-rear direction. The back support body main body 5 is mounted to the back support body base 4 by threading a screw v3 inserted in the screw insertion hole h3 with a nut n3 provided on the connecting member 42 .

[0461] The left and right arm portions 5d extend in the front-to-back direction along the outer side of the arm body 411 of the back support body base 4. The front portions of the left and right arm portions 5d are located outside the axial direction of the main shaft j1 protruding outward from the left and right side walls b1 in the support base B. Moreover, the left and right arm portions 5d are restricted in a manner that the main shaft j1 does not pull out to the outside relative to the support base B.

[0462] The spindle j1 is simply cylindrical and extends in the left-right direction. The spindle j1 of this embodiment is not directly provided with a positioning component (for example, a ring for preventing slippage installed at the end of the shaft, or a structure in which a flange-shaped portion is formed at one end of the shaft), but the arm portion 5d of the back support body main body 5 of the back support body L is used to position the spindle j1 relative to the support base B.

[0463] A recess q2 constituting the positioning mechanism Q is provided on the front side of the upper ends of the left and right upright frame portions 52, that is, on the front side of the connection portion between the left and right upright frame portions 52 and the upper frame portion 53. The recess q2 will be described in detail later.

[0464] The upper frame portion 53 is in a partially circular ring shape, which is curved in a convex manner toward the rear in a plan view. The upper frame portion 53 cooperates with the upper cover member 6 that constitutes a half-cut shape corresponding to the upper frame portion 53, and is in a circular shape with both end surfaces facing forward, and as a whole, has a cylindrical shape that is curved into a partially circular shape.

[0465] That is, the upper frame portion 53 constitutes the lower half of the cylindrical outer shape bent into a partial ring shape. In other words, the upper frame portion 53 and the cover member 6 have forward end faces that are circular at both left and right ends, and are convexly curved toward the rear in a top view, and as a whole constitute the upper frame body 5a that is substantially cylindrical and bent into a partial ring shape.

[0466] The upper frame portion 53 is provided with a plurality of screw insertion holes h1 penetrating in the up-down direction and through which screws v1 for attaching the cover member 6 to the upper frame portion 53 are inserted.

[0467] A rear biasing member engaging portion 532 having a concave shape is provided on the rear side of the upper frame portion 53. The rear biasing member engaging portion 532 supports the rear portion of the coil spring p3 which is a biasing member biasing the operation member p1 forward, i.e., in the direction of the engaging posture (U).

[0468] A boss portion 533 is vertically provided on the upper frame portion 53. A screw member v2 that can restrict the vertical movement of the operating member p1 is threadedly mounted on the boss portion 533. The boss portion 533 and the screw member v2 constitute a vertical movement restricting portion 53k.

[0469] The boss 533 is disposed in the long hole p14 provided at the rear of the engagement portion p11 of the operating member p1. The screw member v2 is engaged near the upper opening edge of the long hole p14 in the operating member p1 to prevent its head from moving upward of the operating member p1.

[0470] [Cover member 6]

[0471] The cover member 6 constitutes a substantially upper half of the upper frame body 5a having a curved cylindrical shape. The cover member 6 is attached to the upper frame portion 53 by screws v1 so as to cover the left and right operation members p1.

[0472] The cover member 6 covers the operation member p1 so that only the engaging portion p11 and the operated portion p13 provided on the operation member p1 can be exposed to the outside.

[0473] The cover member 6 is provided with a window frame portion 6w surrounding the engaging portion p11 of the operating member p1 that 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 engaging portion p11 of the operating member p1, and side wall portions 62 that partially cover the left and right sides.

[0474] Furthermore, the window frame portion 6w can cooperate with the outer peripheral wall q21 of the recessed portion q2 constituting the positioning mechanism Q to form a window frame-shaped portion that is rectangular in a front view.

[0475] In addition, a cutout portion 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 portion 6k is provided adjacent to the inner side of the window frame portion 6w.

[0476] The back support body L having the above structure is covered with a front back support body cover X2 and a rear back support body cover X3 formed of synthetic resin.

[0477] The front back support body cover X2 mainly covers the lower part and the outer side of the back support body base 4. The front back support body cover X2 is attached to the arm part 5d of the back support body main body 5.

[0478] The back support body cover X3 is mounted so that the screws v3 for mounting the back support body main body 5 to the back support body base 4 are not exposed on the back side. The back support body cover X3 is provided at the base end 51 of the back support body main body 5, and covers the back support body base connection portion 5a located between the left and right upright frame portions 52. Both side ends of the back support body cover X3 are connected to the rear end of the front back support body cover X2.

[0479] The backrest M of this embodiment will be described in detail below.

[0480] <Backrest M>>

[0481] The backrest M is a rectangular shape with rounded left and right ends as a whole and is approximately horizontally long. The backrest M has a backrest surface on the front against which the back of the seated person can abut. The backrest M of this embodiment is configured to be attachable to and detachable from the back support body L by a simple operation performed by the user. The backrest M has a backrest body 7 as a main structure and a back surface fabric 8 as a covering body that can cover the backrest body 7.

[0482] <Backrest body 7>

[0483] The backrest body 7 comprises a backrest base 71 formed of synthetic resin and having a substantially horizontally long rectangular shape, and a backrest pad 72 attached to the front of the backrest base 71. A single receiving groove 7m opening downward and extending in the left-right direction is provided at the lower end of the backrest base 71 in the backrest body 7.

[0484] The receiving groove 7m is composed of a pair of front and rear groove forming walls 7f and 7r, and the front and rear groove forming walls 7f and 7r are arranged so that the inner surfaces face each other in the front-back direction. The first and second belt-shaped members 81 and 82 provided at the lower edge of the back surface fabric 8 covering the backrest body 7 are inserted into the single receiving groove 7m.

[0485] A plurality of engaging protrusions t(f) and t(r) are provided inside the receiving groove 7m, that is, on each inner surface of a pair of groove forming walls 7f and 7r. Engaging protrusions t(f) and t(r) protruding forward or backward are provided on both sides of the pair of groove forming walls 7f and 7r.

[0486] In this embodiment, the engaging protrusions t(f) and t(r) are alternately provided with respect to the groove forming walls 7f and 7r arranged to face each other in the front and rear directions along the extending direction of the receiving groove 7m. That is, in the receiving groove 7m, the engaging protrusions t(f) of the groove forming wall 7f on one side and the engaging protrusions t(r) of the groove forming wall 7r on the other side are alternately provided to protrude from one end toward the other end in the longitudinal direction so as not to conflict with each other.

[0487] On the back side of the backrest base 71 constituting the backrest body 7, an engaged portion p2 and a protruding portion q1 are provided as a connecting structure for connecting with the back support body L. The engaged portion p2 constitutes the disengagement prevention mechanism P. The protruding portion q1 constitutes the positioning mechanism Q.

[0488] <Back fabric 8 (cover)>

[0489] The back fabric 8 includes a front cover portion 8f covering the front side of the backrest body 7 and a back cover portion 8r covering the back side of the backrest body 7, and includes a bag-shaped back fabric body 80 opened downward and first and second belt-shaped members 81 and 82 arranged at the lower open end of the back fabric body 80.

[0490] The back fabric 8 includes a front covering portion 8f, an inner covering portion 8r, a first belt-like member 81, and a second belt-like member 82. The front covering portion 8f covers the front side which is the front side of the backrest body 7; the inner covering portion 8r covers the back side which is the inner side of the backrest body 7; the first belt-like member 81 is sewn to the lower end portion which is one end of the front covering portion 8f and is inserted into the receiving groove 7m of the backrest body 7; the second belt-like member 82 is sewn to the lower end portion which is one end of the inner covering portion 8r and is inserted into the receiving groove 7m of the backrest body 7.

[0491] The back fabric 8 exposes the engaged portion p2 and the protruding portion q1 as the connecting structure provided in the backrest body 7 to the outside through the opening portions 8s provided in pairs on the left and right sides on the back side.

[0492] [Back fabric body 80]

[0493] The back fabric main body 80 is formed into a bag shape that opens downward by sewing the peripheral edges of the front cover 8f and the back cover 8r made of stretchable fabric except for the lower ends.

[0494] A space capable of accommodating the back fabric body 7 is formed inside the back fabric body 80. A lower opening 8k is formed between the lower end of the back fabric body 80, that is, the lower end of the front cover 8f and the lower end of the back cover 8r. The lower opening 8k opens downward and is used to insert the back fabric body 7 into the internal space.

[0495] In this embodiment, the back cover 8r, which is the back side of the back fabric body 80, is provided with a pair of left and right openings 8s for exposing the engaged portions p2 and the protruding portions q1 of the backrest body 7 to the outside.

[0496] The opening portion 8s is mainly composed of a through hole 8t, a through hole peripheral portion 8e and an annular member T. The through hole 8t is provided in the inner covering portion 8r which is a fabric material; the through hole peripheral portion 8e is the peripheral area portion of the through hole 8t in the inner covering portion 8r; the annular member T is a continuous ring, is installed on the through hole peripheral portion 8e by sewing, and is an annular member made of synthetic resin.

[0497] Through holes 8 t are formed at two left and right locations of the back cover portion 8 r at positions corresponding to the protrusions q1 protrudingly provided on the back side of the backrest body 7 .

[0498] The annular member T is formed into a square frame shape by a thin sheet material made of a synthetic resin as a flexible raw material, and has a hole portion th in the center. The annular member T is configured to be able to bend and deform. The annular member T is sewn to the through hole peripheral portion 8e in the inner side covering portion 8r. In the installation completion posture (Ta), the annular member T is covered by the inner side covering portion 8r so that the portion other than the hole portion th cannot be seen from the outside.

[0499] In this embodiment, the entire area of ​​the outer portion t1, the entire area of ​​the inner end t2, and at least a portion of the inner surface t3 of the annular member T in the installation completion posture (Ta) are covered by the through-hole peripheral portion 8e adjacent to the through-hole 8t in the inner side covering portion 8r, and only the through-hole peripheral portion 8e is fixed relative to the inner surface t3 of the annular member T in the installation completion posture (Ta).

[0500] [First and second belt-shaped members 81, 82]

[0501] The first and second belt-shaped members 81 and 82 are structures made of synthetic resin and are belt-shaped and extend in the left-right direction. In this embodiment, the first and second belt-shaped members 81 and 82 have substantially the same structure. In each of the first and second belt-shaped members 81 and 82, a plurality of through holes 81a and 82a are arranged to engage with the engaging protrusions t(f) and t(r).

[0502] [Regarding the Engagement of the First and Second Belt-Shaped Members 81 and 82 with the Accommodating Grooves 7m of the Backrest Body 7]

[0503] The first belt-shaped member 81 sewn to the lower end of the front cover 8 f and the second belt-shaped member 82 sewn to the lower end of the back cover 8 r are inserted into a single receiving groove 7 m provided at the lower end of the backrest body 7 .

[0504] The first and second belt-shaped members 81 and 82 are inserted into the receiving groove 7m in a state of overlapping each other.

[0505] When the first and second belt-shaped members 81 and 82 are inserted to the predetermined positions in the receiving groove 7m, the engaging protrusions t(f) and t(r) protruding from the groove forming walls 7f and 7r of the receiving groove 7m can be engaged with the through holes 81a and 82a provided on the belt-shaped members 81 and 82. More precisely, only the through holes 81a and 82a of the inserted first and second belt-shaped members 81 and 82a at the positions corresponding to the engaging protrusions t(f) and t(r) can be engaged with the engaging protrusions t(f) and t(r).

[0506] As a result, the first and second belt-shaped members 81, 82 constituting the end edge portions of the back fabric 8 are restricted from moving downward (reverse return, extraction) by the engaging protrusions t(f) and t(r) after entering into a predetermined position in the single receiving groove 7m, and are thus difficult to be easily extracted to the outside even when subjected to a pulling force from the back fabric body 80.

[0507] In addition, since the engaging protrusions t(f) protruding from the groove forming wall 7f on one side and the engaging protrusions t(r) protruding from the groove forming wall 7r on the other side are alternately arranged along the extension direction of the receiving groove 7m, the first and second belt-like members 81 and 82 can be smoothly inserted into the receiving groove 7m without being excessively hindered by the engaging protrusions t(f) and t(r).

[0508] <<Method for Forming Opening 8s in Back Fabric 8 (Cover)>>

[0509] An opening 8s is provided on the back fabric 8. The opening 8s includes an inner cover 8r and an annular member T. The inner cover 8r is a fabric material provided with a through hole 8t. The annular member T is in a continuous ring shape and is mounted on the through hole peripheral portion 8e. The front and rear communication function of the hole th is not impaired and is arranged so as not to be visible from the outside.

[0510] The opening 8s of the back fabric 8 in this embodiment is formed through a preparation step S1, an annular member outer side mounting step S2, a first annular member inverting step S3, and a second annular member inverting step S4 as described below.

[0511] <Preparation process S1>

[0512] Preparation step S1, such as Fig.48 As shown in FIG. 1 , a back fabric main body 80 as a fabric material constituting the back fabric 8 for forming the opening 8s and a ring-shaped member T in an initial posture (Tb) are prepared.

[0513] The through hole 8t is formed by an appropriate method in the back cover portion 8r of the back fabric body 80. The annular member T is a flexible thin plate frame structure that can be sewn to the back fabric body 80. In this embodiment, the annular member T is a synthetic resin structure formed into a substantially rectangular ring shape.

[0514] <Annular member outer side installation step S2>

[0515] The next step in the preparation process, such as Fig.49 and Fig.50 As shown, a step of attaching the annular member T in the initial posture (Tb) to the outer side of the through hole peripheral edge portion 8e in the back cover portion 8r which is a fabric material (annular member outer side attaching step S2) is performed.

[0516] In this embodiment, the annular member T in the initial position (Tb) is sewed relative to the through hole peripheral portion 8e in a state of being attached to the outer side of the through hole peripheral portion 8e. In other words, the annular member T in the initial position (Tb) is fixed to the outer side of the through hole peripheral portion 8e via the sewed portion tx.

[0517] That is, in the annular member outer side attaching step S2, the annular member T is sewn to the outer side of the through hole peripheral edge portion 8e which is the edge portion of the through hole 8t.

[0518] <First annular member reversing step S3>

[0519] The next step in the ring component installation process is Fig.51As shown, the following process is performed: the annular member T in the initial posture (Tb) as a state installed on the outer side of the peripheral edge portion 8e of the through hole is flexibly deformed in a manner so that the inner peripheral edge side is rotated toward the inner surface side of the inner cover portion 8r, and the annular member T is reversed front to back, and the annular member T is arranged on the inner surface side of the inner cover portion 8r (first annular member reversal process S3).

[0520] <Second Ring Component Reversal Process S4>

[0521] The next step of the first annular member reversing step S3 is as follows. Fig.52 As shown, the following process is performed: the annular member T in the intermediate posture (Tc) is further bent and deformed on the inner end edge side toward the inner surface side of the inner side covering portion 8r, and is reversed front to back so that the entire annular member T is covered by the inner side covering portion 8r from the outer side (second annular member reversal process S4).

[0522] In this embodiment, by a method for forming an opening 8s in the back fabric 8 (covering body) formed through the above-mentioned steps, an opening 8s reinforced by the annular member T in the mounting completion posture (Ta) reversed 360° from the initial posture (Tb) is formed in the back covering portion 8r of the back fabric 8.

[0523] Furthermore, the first and second annular member inverting steps S3 and S4 are smoothly and continuously performed by the bending deformation of the annular member T.

[0524] <<Attachment and Removal Structure of Backrest M with Respect to Back Support Body L>>

[0525] The chair of this embodiment is constructed so that the backrest M can be easily attached and detached from the back support body L by not only the manufacturer but also the end user (user) without using tools, which helps facilitate maintenance such as cleaning and replacement, storage and transportation.

[0526] The attachment and detachment structure of the backrest M includes a positioning mechanism Q for positioning the backrest M relative to the back support body L and a separation inhibition mechanism P for inhibiting the backrest M positioned in a normal mounting position by the positioning mechanism Q from being separated from the back support body L.

[0527] <Positioning mechanism Q>

[0528] The positioning mechanism Q positions the backrest M relative to the back support body L at a predetermined installation position.

[0529] The positioning mechanism Q includes a protrusion q1 provided on the backrest M and a recess q2 provided on the back support body L and into which the protrusion q1 can engage. The protrusion q1 provided on the backrest body 7 and the recess q2 provided on the back support body L can engage in the vertical direction.

[0530] [Protrusion q1]

[0531] The protrusions q1 are provided in pairs on the left and right sides of the backrest M. The protrusions q1 are provided to protrude on the back surface side of the backrest body 7 , and are exposed to the outside through the opening 8 s of the back surface fabric 8 .

[0532] The protrusion q1 includes a wall-shaped locking portion q11 and a connecting portion q12. The wall-shaped locking portion q11 extends in the vertical direction in a rear view, and its width dimension is gradually shortened toward the bottom, and is arranged to be gradually located toward the back in a side view. The connecting portion q12 connects the backrest body 7 and the middle portion of the wall-shaped locking portion q11 in the left-right direction, and is arranged to have a dimension in the front-to-back direction gradually become longer toward the bottom. The upper end of the wall-shaped locking portion q11 is connected to the backrest body 7.

[0533] The protrusion q1 is provided below the engaged portion p2 constituting the disengagement prevention mechanism P which is recessed in the backrest body 7 .

[0534] [Concave q2]

[0535] The recessed portion q2 is provided at the front side of the upper end portion of the left and right upright frame portions 52 constituting the back support body L. The recessed portion q2 is open upward. The recessed portion q2 can be externally fitted with the protruding portion q1 of the backrest M inserted from the upper side.

[0536] The recessed portion q2 is provided inside the outer peripheral wall q21 protruding forward from the upper end of the left and right upright frame portions 52. The recessed portion q2 is composed of the outer peripheral wall q21 and a pair of left and right front wall portions q22. The outer peripheral wall q21 has a bottom wall portion qt and left and right side wall portions qs erected upward from the left and right side edges of the bottom wall portion qt; the pair of left and right front wall portions q22 are erected in front of the bottom wall portion qt.

[0537] The recessed portion q2 has a pair of left and right front wall portions q22 erected on the bottom wall portion qt in a manner separated from each other, and a front recessed portion qm having a first space qa disposed therebetween. The first space qa is provided with a connecting portion q12 of the protruding portion q1.

[0538] In addition, the recess q2 has a rear recessed portion qr in which a second space qb is provided. The second space qb is formed at the rear of the front recessed portion qm, that is, behind a pair of front wall portions q22, and a wall-shaped locking portion q11 of the protrusion q1 is arranged between the left and right side wall portions qs upright on the bottom wall portion qt.

[0539] In this embodiment, the protrusion q1 of the backrest M constituting the positioning mechanism Q is engaged with the recess q2 of the back support body L while moving in the up-down direction, more precisely, from the oblique front upper direction to the oblique rear lower direction. The backrest load of the seated person acts in the upper, rear and lower directions, and hardly acts in the front direction. Therefore, by configuring the protrusion q1 to be inserted into the recess q2 from the oblique front upper direction to the oblique rear lower direction, the backrest M is difficult to be pulled out from the back support body L, and the backrest M can be reliably fixed to the back support body L.

[0540] <Leaving the Prohibited Institution P>

[0541] The separation prevention mechanism P is provided between the back support body L and the backrest M, and prevents the backrest M from being separated from the back support body L.

[0542] The disengagement prevention mechanism P includes an operating member p1 and an engaged portion p2. The operating member p1 is arranged on the back support body L, and can be reversibly moved between an engaged posture (U) that prohibits the backrest M from disengaging and a retreat posture (N) that allows the backrest M to disengage by human operating force, that is, it can be rotated in the forward and backward directions; the engaged portion p2 is arranged on the backrest M, and in the engaged posture (U), the engaged portion p11 arranged on the operating member p1 can be engaged.

[0543] [Operation member p1]

[0544] The operation member p1 prohibits vertical movement of the backrest M relative to the back support body L in the engagement position (U). The operation member p1 is rotatably supported by the upper frame portion 53 of the back support body main body 5. The operation member p1 is provided on the left and right of the back support body L in pairs.

[0545] The operating member p1 includes an axial hole pa, an engaging portion p11, a loading member engaging portion p12, an operated portion p13 and a long hole portion p14, wherein the axial hole pa is provided at the inner end portion serving as the base end portion, and is inserted into the axial portion 531 uprightly provided on the upper frame portion 53, and penetrates in the up-down direction; the engaging portion p11 is provided at the outer end portion serving as the front end portion protruding forward; the loading member engaging portion p12 is provided at the rear side between the axial hole pa and the engaging portion p11, and is the loading member engaging portion before the front portion of the coil spring p3 serving as the loading member is engaged; the operated portion p13 is provided at the front side between the axial hole pa and the engaging portion p11, and directly receives the operating force of a person, i.e., the pushing operating force performed by a finger toward the rear when moving from the engaging posture (U) to the retreat posture (N); the long hole portion p14 is provided at the rear of the engaging portion p11, and is engaged with the up-and-down movement limiting portion 53k provided on the upper frame portion 53.

[0546] The operating member p1 is biased in the direction of the normal engagement posture (U) by the coil spring p3. The user can change the posture of the operating member p1 to the retreat posture (N) by pushing the operated portion p13 of the operating member p1 in the engagement posture (U) in the direction of the retreat posture (N) (the direction in which the engagement portion p11 as the rotation end moves backward) against the bias of the coil spring p3.

[0547] The user can change the position of the operation member p1 from the engaged position (U) to the retracted position (N) by pushing the operated portion p13 backward with a finger of the user. That is, the user can move the operation member p1 to the retracted position (N) by pushing the operated portion p13 backward like pressing a button.

[0548] like Fig. 27 As shown, a space sp into which a finger can be inserted is provided between the back support body L and the backrest M. The operated portion p13 is disposed at a position facing the space between the back support body L and the backrest M. Therefore, the user can easily push the operated portion p13 like pressing a button.

[0549] Moreover, only the outer surface of the operated portion p13 of the operating member p1 in the engaged posture (U) is exposed between the back support body L and the backrest M. In other words, the outer surface of the operated portion p13 is substantially flush with the outer surface of the cover member 6. Therefore, although the operated portion p13 is arranged so as to be operable from the outside, it is arranged at an inconspicuous position and is substantially flush with the cover member 6 in a manner that is not conspicuous.

[0550] [Engaged portion p2]

[0551] The engaged portion p2 has a portion that can be engaged with the engaging portion p11 of the operating member p1 supported by the back support body L. The engaging portion p11 of the operating member p1 in the engaging posture (U) is engaged with the engaged portion p2.

[0552] The engaged portions p2 are provided in pairs on the left and right sides of the backrest M. The engaged portions p2 are provided on the back side of the backrest body 7 in a manner open to the rear and have a recessed shape. The engaged portions p2 recessed on the backrest body 7 are exposed to the outside through the opening 8s of the back fabric 8.

[0553] The engaged portion p2 is provided on a protruding portion q1 constituting a positioning mechanism Q provided to protrude from the backrest body 7 .

[0554] After the backrest M is positioned in the normal installation position by the positioning mechanism Q, if the engaging portion p11 of the operation 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, is prohibited from being separated from the back support body L.

[0555] <<Weight-sensing locking mechanism>>

[0556] The weight-sensitive locking mechanism has a structure that can tilt and rotate the backrest M according to the weight of the seat occupant sitting on the seat C. The weight-sensitive locking mechanism is configured to move the seat C backward while resisting the load of the seat occupant and lifting the seat C upward as the backrest M tilts backward.

[0557] The weight-sensitive locking mechanism includes a structure for lifting the seat C upward against the load of the seat occupant, and therefore requires a backward tilting load proportional to the seat occupant's weight in order to tilt the backrest M backward.

[0558] The body weight-sensing locking mechanism is mainly composed of a supporting base B, a seat C, a back support body L, a backrest M and a reaction force generating body R, wherein the supporting base B is supported on the foot A; the seat C is arranged on the supporting base B, and the front part is supported on the supporting base B via the front axis j2; the back support body L is rotatably supported on the supporting base B via the main axis j1, and has a seat engaging axis j3, which is arranged in the front and above compared with the main axis j1, can be engaged with the central part of the seat C in the front-to-back direction, and is loaded forward by the reaction force generating body R; the backrest M is supported on the back support body L; the reaction force generating body R is arranged between the supporting base B and the back support body L, and can provide the backrest M with a reaction force relative to the rearward tilting action.

[0559] <Seat tilt mechanism>>

[0560] The seat forward tilting mechanism can change the posture of the seat C, which is rotatably supported relative to the support base B via the front axis j1, between a normal posture (ps) and a forward tilting posture (pf).

[0561] The seat forward tilting mechanism is mainly composed of a supporting base B, a seat C, a back support body L, and an intermediate component U, wherein the supporting base B is supported on the leg A; the seat C is arranged on the supporting base B, and the front part is supported on the supporting base B via the front axis j2; the back support body L has a seat engaging axis j3 which engages with the engaged part 1k of the seat C in the normal posture (ps); the intermediate component U, whose lower part is engaged with the seat engaging axis j3, and whose upper part is engaged with the seat C via the coil spring Y, limits the separation distance of the engaged part 1k relative to the seat engaging axis j3 in the forward tilting posture (pf).

[0562] According to the above-described embodiment, it is possible to provide a chair having a favorable structure in which the backrest M can be easily attached to and detached from the back support body L using the operating member p1 that can be reversibly moved by a human operating force.

[0563] In addition, according to the above-mentioned embodiment, the seat body D is configured to be horizontally rotatable about the common axis cj relative to the seat receiving body 1 between the retreat posture (E) in which the seat receiving body 1 can be detached and the installation posture (F) in which the seat receiving body 1 is installed. Therefore, it is possible to provide a chair having a good structure in which the seat body D can be easily attached and detached from the seat receiving body 1 without using special tools.

[0564] In addition, according to the above-mentioned embodiment, the peripheral wall portion 32 is provided at the peripheral portion of the housing 3, and the peripheral wall portion 32 has an outward surface 32m with which the edge portion de of the seat fabric Dh can abut, and is arranged in a substantially annular shape when viewed from below. Therefore, it is possible to provide a chair in which the edge portion de of the seat fabric Dh covering the seat cushion Dq can be well abutted against the peripheral wall portion 32 of the housing 3 by a substantially uniform pressing force.

[0565] In addition, according to the above-mentioned embodiment, the receiving groove 7m is provided on the backrest body 7 as the main structure, and the receiving groove 7m is provided with the engaging protrusions t(f) and t(r), and the first and second belt-shaped members 81 and 82 are provided with the through holes 81a and 82a engaged with the engaging protrusions t(f) and t(r) of the receiving groove 7m on the back fabric 8. Therefore, it is possible to provide a chair having a structure in which the edge of the back fabric 8 can be easily and hardly removed from the receiving groove 7m of the backrest body 7 as the main structure.

[0566] In addition, according to the above-mentioned embodiment, a method can be provided that can well form a reinforced opening 8s with a good appearance on the back fabric 8 of the cover body as a coverable member. In addition, according to the above-mentioned embodiment, a chair can be provided that is suitable for the back fabric 8 and the like, has a cover body, and has an opening 8s that is a reinforced opening with a good appearance.

[0567] In addition, according to the above-mentioned embodiment, the seat C can be rotated relative to the support base B in a manner such that the front portion can assume a normal posture (ps) and a forward tilted posture (pf), and an intermediate component U that can limit the separation distance is provided between the back support body L supported on the support base B and the rear portion of the seat C (the rear portion compared to the front portion of the seat C).

[0568] Therefore, a chair is provided which is configured as follows: without arranging a bulky mechanism in front of the seat C, the seat C can well take the normal posture (ps) and the forward leaning posture (pf).

[0569] In addition, according to the above-mentioned embodiment, a reaction force generating body R that can directly load the seat engagement shaft j3 forward is provided between the seat engagement shaft j3 and the support base B, and the reaction force generating body R is set to be in a substantially horizontal posture extending in the front-rear direction in the normal posture (ps). Therefore, it is possible to provide a chair that can be locked between the normal posture (ps) and the rearwardly inclined posture (pr) and has excellent design freedom for miniaturizing the support base B and the seat C.

[0570] According to the above embodiment, the intermediate member U that can restrict the seat receiving body 1 from being separated from the back support body L is provided so as to be attachable and detachable without using a fixing member. Therefore, a chair in which the seat receiving body 1 can be easily attached and detached from the support base B can be provided.

[0571] In addition, according to the above-mentioned embodiment, because it is a structure in which, when the supporting member W supporting one end of the reaction force generating body R is removed from the supporting base B using the screw v5, the loading force of the reaction force generating body R is gradually weakened while being guided to move by the inclined surface nm, a chair can be provided that allows the reaction force generating body R to be well installed and detached relative to the supporting base B.

[0572] Furthermore, according to the above-mentioned embodiment, a threaded connection hole n4 having a thread groove is provided above the fitting hole Ba in the support base B, and the foot support a2 can be pushed downward by the screw v4 threadedly engaged with the threaded connection hole n4. Therefore, a chair having a structure that can well release the fitting state between the upper part of the foot support a2 and the fitting hole Ba of the support base B can be provided.

[0573] Furthermore, according to the above-mentioned embodiment, the foot support a2 of the foot A is attached to the support base B as a blocking member, and the blocking member blocks the lifting operation rod V as the operation rod from taking the detachable posture (SR), and the lifting operation rod V can take the detachable posture (SR) only when the foot support a2 is removed from the support base B. Therefore, a chair in which the lifting operation rod V can be well attached to the support base B can be provided.

[0574] As described above, the chair according to the present embodiment includes the support base B supported by the legs A and the seat C supported by the support base B via the front axis j2.

[0575] Moreover, the seat C includes a seat body D having a seat surface and a seat receiving body 1 supporting the seat body D, the seat receiving body 1 including a front axle retaining portion 1m capable of retaining the front axle j2; and an engaged portion 1k which is arranged at the rear compared to the front axle retaining portion 1m and is engaged with a back support body L which is a structure supported on the support base B.

[0576] An intermediate member U that can restrict the seat receiving body 1 from being separated from the back receiving body L is disposed between the back receiving body L and the seat receiving body 1 so as to be attachable and detachable without using a fixing member.

[0577] Therefore, a chair in which the seat receiving body 1 can be easily attached to and detached from the support base B can be provided.

[0578] That is, in this chair, an intermediate member U is provided between the back support body L and the seat support body 1, and the intermediate member U is configured so as to be attachable and detachable only by manual work without using a tool without using a fixing member.

[0579] Since the intermediate member U is arranged to be detachable without using a fixing member, the intermediate member U can be removed from between the back support body L and the seat receiving body 1 and arranged between the back support body L and the seat receiving body 1 by the user using only fingers.

[0580] After the intermediate member U is removed from between the back support body L and the seat receiving body 1 , the seat receiving body 1 can be easily removed from the support base B by performing an operation to release the engagement between the seat receiving body 1 and the front shaft j2 .

[0581] In addition, in this chair, the seat receiving body 1 can be easily attached to the support base B and the back support body L by taking the reverse procedure to the operation of detaching the seat receiving body 1 described above.

[0582] A coil spring Y as a spring member is interposed between the seat receiving body 1 and the intermediate member U. The coil spring Y is biased in a direction in which the intermediate member U is engaged with the back support body L.

[0583] Therefore, the intermediate member U is normally well engaged with the back support body L by the coil spring Y. Meanwhile, the intermediate member U receives the operation force of the user against the biasing force of the coil spring Y, and is easily disengaged from the back support body L and the seat receiving body 1 .

[0584] Furthermore, the intermediate member U can also be easily interposed between the back support body L and the seat receiving body 1 by receiving the operating force of the user against the biasing force of the coil spring Y.

[0585] The intermediate member U is configured to be disengaged from the back support body L by being pressed in a direction resisting the biasing force of the coil spring Y and to be removed from between the back support body L and the seat receiving body 1 in the disengaged state.

[0586] Therefore, the intermediate member U has a structure that can be well separated from between the back support body L and the seat receiving body 1.

[0587] The seat receiving body 1 can rotate around the front axle j2 in a manner that the rear end jumps upward after the intermediate member U is detached. The front axle holding portion 1m can be detached from the front axle j2 only when the seat receiving body 1 changes its posture to a predetermined jumping posture (ph).

[0588] Therefore, the seat receiving body 1 can be separated from the front shaft j2 only under predetermined conditions, and thus has a structure excellent in safety of disassembly.

[0589] The support base B is provided with a pair of grooves b14 extending in the vertical direction and opening outward. In addition, the seat receiving body 1 is provided with a pair of restricting protrusions 1t protruding inwardly.

[0590] Furthermore, the seat receiving body 1 is configured such that, when the intermediate member U restricts the seat receiving body 1 from coming off, the restricting projection 1t is located in the groove b14 and the front axle holding portion 1m cannot be disengaged forwardly relative to the front axle j2.

[0591] On the other hand, the seat receiving body 1 is configured such that, when taking a predetermined jumping posture (ph), the restricting projection 1t is located outside the groove portion b14 and the front axle holding portion 1m can be separated forwardly from the front axle j2.

[0592] Therefore, the seat support body 1 adopts the following structure with excellent safety in disassembly: by engaging the limiting protrusion 1t with the groove b14 of the supporting base B, the front axle retaining portion 1m can be detached from the front axle j2 only under specified conditions.

[0593] The back support body L is a structure rotatably supported relative to the support base B. The engaged portion 1k of the seat receiving body 1 is engaged with the seat engaging shaft j3 as a seat engaging portion provided on the back support body L. The intermediate member U is disposed between the back support body L and the seat receiving body 1.

[0594] Therefore, the intermediate member U is interposed between the back support body L and the seat receiving body 1 in a favorable manner.

[0595] The seat C is configured to be tiltable about the front axis j2 between a normal posture (ps) and a forward-leaning posture (pf) that is tilted forward of the normal posture (ps). The engaged portion 1k is engaged with the back support body L in the normal posture (ps).

[0596] Therefore, the seat C can take not only the normal posture (ps) but also the forward tilted posture (pf) in which the seat C is tilted and rotated about the front axis j2.

[0597] The intermediate member U includes an intermediate member body u1 and an arm u2. The intermediate member body u1 is provided with a spring receiving portion u11 on one side for receiving one end of a coil spring Y as a spring member. The arm u2 is extended from the intermediate member body u1 and can be engaged with the back support body L. In addition, the seat support body 1 is provided with a spring receiving portion 13a on the other side for receiving the other end of the coil spring Y. The spring receiving portion u1 on one side is provided downward, and the spring receiving portion 13a on the other side is provided upward.

[0598] Therefore, the intermediate member U has a favorable structure interposed between the seat receiving body 1 and the back support body L.

[0599] Furthermore, when the intermediate member main body u1 is pushed downward against the biasing force of the coil spring Y, the engagement between the intermediate member U and the back support body L is released, so that the operation is easy for the user.

[0600] The seat receiving body 1 is provided with a recessed portion 13 which is open upward and includes the other spring receiving portion 13a, thereby forming a placement space 13s for placing the intermediate member main body u1.

[0601] Therefore, the seat receiving body 1 has a good structure in which the intermediate member U can be disposed.

[0602] The seat receiving body 1 is provided with a recess 11 which is open downward and in which the support base B is disposed. An arm through hole 14 through which the arm u2 can pass is provided between the recess 13 and the recess 11 .

[0603] Therefore, the seat receiving body 1 has a favorable structure in which the intermediate member U having the arm portion u2 is interposed between the seat receiving body 1 and the back support body L.

[0604] In addition, the present invention is not limited to the embodiments described in detail above.

[0605] The seat may be configured to be capable of being in a normal posture, that is, the seat may be configured to be capable of being in a posture that does not lean forward or backward.

[0606] The front portion of the seat may be configured to be rotatably supported relative to the support base via the front shaft, and any appropriate configuration may be employed as a specific configuration.

[0607] The rear portion of the seat may be any structure as long as it is supported on the support base or on a structure supported by the support base in a normal posture.

[0608] The structure is not limited to the back support body, and any structure may be used as long as it is supported by the support base.

[0609] The shape of the intermediate member may be any structure as long as it can restrict the separation distance of the rear portion of the seat from the support base or the structure in the forward-leaning posture, and the specific structure thereof may be an appropriate structure.

[0610] The seat engaging portion is not limited to a shaft-shaped structure, and any mechanism may be used as long as it is a structure that engages with the rear portion of the seat in a normal posture.

[0611] The spring member is not limited to the coil spring, and any spring member may be used as long as it can be interposed between the seat receiving body and the intermediate member to exert a biasing force.

[0612] For example, the spring member may also be made of a rubber material.

[0613] The seat receiving body may be configured so that the front axle holding portion can be detached from the front axle only when the seat receiving body changes its posture to a predetermined jumping posture.

[0614] For example, the front axle holding portion may be detached from the front axle when the intermediate member U is detached before the seat body reaches the predetermined jumping posture.

[0615] The support base may be provided with a restricting protrusion, and the seat receiving body may be provided with a groove that engages with the restricting protrusion of the support base.

[0616] A structure in which one spring receiving portion provided on the intermediate member is provided upward and the other spring receiving portion provided on the seat receiving body is provided downward may be adopted.

[0617] The arm passage hole provided in the seat receiving body may be provided between the recessed portion and the recessed part so as to allow the arm portion of the intermediate member to pass therethrough, and its specific shape may be appropriately set.

[0618] In addition, the specific configuration of each part is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

[0619]

Explanation of symbols

[0620] A: Feet

[0621] B: Support base

[0622] C: Seat

[0623] 1: Seat support

[0624] L: Back support (structure)

[0625] U: Intermediate component

[0626] j2: front axle.

Claims

1. A chair comprising a support base supported on the legs and a seat supported on the support base via a front axle; characterized in that: The seat comprises a seat body having a seat surface and a seat receiving body supporting the seat body, the seat receiving body comprises a front axle holding portion and a clamping portion, the front axle holding portion can hold the front axle; the clamping portion is arranged at the rear compared to the front axle holding portion, and is clamped relative to the support base or a structure supported by the support base, An intermediate member capable of restricting the seat receiving body from being separated from the support base or the structure is detachably provided between the support base or the structure and the seat receiving body without using a fixing member.

2. The chair according to claim 1, characterized in that: A spring member is interposed between the seat receiving body and the intermediate member. The spring member biases the intermediate member in a direction to engage the intermediate member with the support base or the structure.

3. The chair according to claim 2, characterized in that: The intermediate member is configured to be released from engagement with the support base or the structure by being pushed in a direction resisting the biasing force of the spring member, and to be detached from between the support base or the structure and the seat receiving body in the released state.

4. The chair according to claim 3, characterized in that: The seat receiving body can rotate around the front shaft in a manner that the rear end thereof jumps up after the intermediate member is separated; The front axle holding portion can be detached from the front axle only when the seat receiving body changes its posture to a predetermined jumping posture.

5. The chair according to claim 4, characterized in that: The support base is provided with grooves in pairs on the left and right sides, the grooves extending in the up-down direction and opening toward the outside. The seat receiving body is provided with a pair of restricting protrusions protruding inwardly on the left and right sides. The seat receiving body is configured such that, when the intermediate member is used to restrict the disengagement, the restricting protrusion is located in the groove portion, and the front axle holding portion cannot be disengaged forward relative to the front axle. The seat receiving body is configured such that, when the seat receiving body takes the predetermined jumping posture, the restricting protrusion is located outside the groove portion and the front axle holding portion can be separated forwardly from the front axle.

6. The chair according to claim 1, characterized in that: The structure is a back support body rotatably supported relative to the support base. The engaged portion is engaged with a seat engaging portion provided on the back support body. The intermediate member is disposed between the back support body and the seat receiving body.

7. The chair according to claim 1, characterized in that The seat is configured to be tiltable and rotatable about the front axis between a normal posture and a forward-leaning posture that is tilted forward of the normal posture. The engaged portion is engaged with the support base or the structure when taking the normal posture.

8. The chair according to claim 2, characterized in that: The intermediate member comprises an intermediate member body and an arm portion, wherein the intermediate member body is provided with a spring receiving portion for receiving one end portion of the spring member; the arm portion is extended from the intermediate member body and can be engaged with the support base or the structure. The seat receiving body is provided with another spring receiving portion for receiving the other end portion of the spring member. The one spring receiving portion is disposed downward, and the other spring receiving portion is disposed upward.

9. The chair according to claim 8, characterized in that The seat receiving body is provided with a recessed portion which is open upward and includes the other spring receiving portion to form a placement space for placing the intermediate member body.

10. The chair according to claim 9, characterized in that A recess is provided on the seat receiving body, the recess is open downward, and the supporting base is arranged therein; an arm through hole through which the arm can pass is provided between the recesses.

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