Chair

Abstract

A chair in which a seat can assume a normal position and a forward position without providing a bulky mechanism to the front of the seat. To this end, the chair is provided with: a support base (B) supported on legs (A); and a seat (C) that is disposed on the support base (B) and that can assume a normal posture (ps) and a forward-tilting posture (pf) that tilts more forward than the normal posture (ps), in which the front portion of the seat (C) is rotatably supported with respect to the support base (B), the rear portion of the seat (C) is supported in the normal posture (ps) on a back support body (L) supported by the support base (B), and in the forward-tilting posture (pf), the seat (C) is separated upward with respect to the back support body (L). An intermediate member (U) capable of limiting the separation distance of the rear portion of the seat (C) with respect to the back support (L) in the forward leaning posture (pf) is provided.

Description

Technical Field

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

[0002] Conventionally, various chairs having seats configured to be tiltable forward are known (for example, see Patent Document 1).

[0003] However, in conventional chairs, the structure for placing the seat in a forward-leaning posture is a bulky structure, which is one of the reasons why the entire front portion of the seat is enlarged.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-093091 Summary of the Invention

[0007] [Problems to be Solved by the Invention]

[0008] The present invention has been made in view of the above-mentioned situation, and provides a chair in which the seat is structured so as to be able to be satisfactorily positioned in a normal posture and a forward leaning posture without providing a bulky mechanism at least in the front portion of the seat.

[0009]

Means for solving the problem

[0010] That is, the present invention has the following structure.

[0011] The invention described in technical solution 1 is a chair, which has a support base supported on the feet; a seat arranged on this support base and can adopt a normal posture and a forward-leaning posture that is more inclined forward than the normal posture, characterized in that the front part of the above-mentioned seat is supported relative to the above-mentioned support base so as to be rotatable, the rear part of the above-mentioned seat is supported on the above-mentioned support base or on a structure supported by the above-mentioned support base in the above-mentioned normal posture, and is separated upward relative to the above-mentioned support base or the above-mentioned structure in the above-mentioned forward-leaning posture, and an intermediate member is arranged between the above-mentioned support base and the rear part of the above-mentioned seat, which can limit the separation distance of the rear part of the above-mentioned seat relative to the above-mentioned support base or the above-mentioned structure in the above-mentioned forward-leaning posture.

[0012] Here, the "rear portion of the seat" refers to "a portion that is rearward compared to the front portion of the seat."

[0013] The invention described in claim 2 is the chair according to claim 1 , wherein the front portion of the seat is rotatably supported relative to the support base via a front shaft.

[0014] The invention described in Technical Solution 3 is a chair according to Technical Solution 1, characterized in that the rear part of the seat is supported on a structure supported by the support base in the normal posture, and is separated upward relative to the structure in the forward-leaning posture; the structure is a back support body supported so as to be rotatable relative to the support base.

[0015] The invention described in claim 4 is a chair according to claim 3, characterized in that a seat engaging portion is provided on the back support body for engaging with the rear portion of the seat in the normal posture.

[0016] The intermediate member is provided between the seat engaging portion and the seat.

[0017] The invention described in technical solution 5 is a chair according to technical solution 4, characterized in that the seat includes a seat body having a seat surface and a seat receiving body supporting the seat body, and the intermediate member is arranged between the seat receiving body and the seat engaging portion.

[0018] The invention described in claim 6 is the chair according to claim 5 , characterized in that a spring member is interposed between the seat receiving body and the intermediate member.

[0019] The invention described in Technical Solution 7 is a chair according to Technical Solution 6, characterized in that the above-mentioned intermediate member includes an intermediate member body and an arm portion, and the intermediate member body is provided with a spring receiving portion on one side of one end portion of the above-mentioned spring member; the arm portion extends from this intermediate member body and can be engaged with the above-mentioned seat engaging portion.

[0020] The invention described in claim 8 is the chair according to claim 7 , wherein the one spring receiving portion is arranged downward, and the other spring receiving portion is arranged 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 other spring receiving portion, and forms an arrangement space for arranging the intermediate member 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, the support base is provided, and 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 the seat is structured so as to be able to take both a normal posture and a forward leaning posture well without providing a bulky mechanism at least in the front portion of the seat. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] Figure 2 This is a front view of this embodiment.

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

[0033] Figure 9 It is an exploded perspective view of this embodiment.

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

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

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

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

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

[0039] Figure 15 yes Figure 14 The lower part of the enlarged figure.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0064] Figure 40 It is a front view of the housing in this embodiment.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0085] Figure 61 It is an exploded perspective view of this embodiment.

[0086] Figure 62 It is an exploded perspective view of this embodiment.

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

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

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

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

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

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

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

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

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

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

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

[0098] Figure 74 In this embodiment, Figure 73 A longitudinal sectional view of the seat with the backrest tilted back corresponding to the cutting position.

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

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

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

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

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

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

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

[0106] Figure 82 It is an exploded perspective view of this embodiment.

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

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

[0109] Figure 85 It is a perspective view of this embodiment.

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

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

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

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

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

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

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

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

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

[0119] Figure 95 In this embodiment, Figure 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 support base. DETAILED DESCRIPTION

[0120] Modes for carrying out the invention

[0121] The following reference Figures 1 to 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 capable of assuming a normal posture (ps) disposed on a support base B, a forward-leaning posture (pf) tilted forward of the normal posture (ps), and a rearward-leaning posture (pr) tilted rearward of the normal posture (ps). A reaction force generator R is provided between the support base B and the back support L to bias the back support L toward the normal posture (ps).

[0124] The backrest M is supported by the back support body L so as to be tiltable 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 rearward 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-to-back center portion of the seat C upward as the back support body L linked to the backrest M tilts backward, and can tilt and move the entire seat C backward.

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

[0127] The following describes in detail the various structures of the chair in this embodiment.

[0128] <<Foot A>>

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

[0130] The foot A of this embodiment constitutes an obstruction member that obstructs 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 to prevent the foot support a2 from taking a detachable posture (SR).

[0131] <Foot support a2>

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

[0133] The foot support a2 extends in the vertical direction and includes an air cylinder ag that can adjust the vertical position of the seat C.

[0134] The cylinder ag is a known structure having a cylinder portion a21, a lifting rod a22 and a working component a23. The cylinder portion a21 is arranged at the lower part of the foot support a2; the lifting rod a22 can be lifted and lowered 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. When pushed downward, the lifting rod a22 is made to be in a state where it can be lifted and lowered 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 serving 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 fit tightly against the upper portion of the lift rod a22.

[0137] The actuating member a23 is configured to be pressed downward by a lifting operation lever V which is an operation lever rotatably supported by the support base B relative to the lever support 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 by the legs A so that the vertical position can be changed and the support base B can be rotated. The support base B is a structure formed integrally of metal. The support base B is generally box-shaped, elongated in the front-to-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 continuously arranged upward from the left and right end portions of the bottom wall portion 2; 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 roughly horizontal and is provided with a fitting hole Ba that serves as a foot connecting portion that is fitted into the upper part of the foot support a2; the inclined bottom wall 22 extends from the rear end portion of the basic bottom wall 21 obliquely upward and rearward; the front bottom wall 23 extends forward from the front end portion of the basic bottom wall 21 and is arranged to gradually be located upward as it goes forward; and the rear bottom wall 24 extends roughly 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 the 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 toward the rear. Since the inclined bottom wall 22 extends upward and rearward from the base bottom wall 21, it can be conveniently positioned on the rear bottom wall 24 where the mounting portion 2T is provided 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 that is inserted into the long holes b12 of the left and right side walls b1.

[0151] [Rear bottom wall 24]

[0152] The rear bottom wall 24 extends rearward and substantially horizontally from the rear end of the inclined bottom wall 24. The left-right middle portion 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 arranged 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 adjacent to and rising 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 rising portions 25 rising to partially surround the front portion of the fitting hole Ba in a plan view, and a horizontal bridge portion 26 spanning between the rising portions 25 to be located directly above the fitting hole Ba.

[0159] The rising portion 25 is integrally and continuously provided 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 shaped so as to provide a space 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 substantially in the vertical direction. The horizontal frame portion 26 is provided continuously with the upright portion 25 as a whole.

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

[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 threadedly engaged while using the ascending structure 2S integrally provided 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 the outer peripheral edge portion of the upper end of the lifting rod a22 constituting the foot support b2 downward.

[0166] The lifting 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 with the upper portion of the lifting rod a22, which is 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 lifting 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 fit-relaxing structure that eases the fit between the foot support a2 and the support base B. This fit-relaxing structure comprises a threaded connection hole n4 having a thread groove provided in the fitting hole Ba in the support base B. A screw v4 threadedly engaged with the threaded connection hole n4 presses the upper portion of the foot support a2 downward.

[0170] Furthermore, the screw v4 only needs to have the same specifications as the threaded connection hole n4 and a certain length in the vertical direction. In this embodiment, after removing the screw v5 used to secure the support member W to the mounting portion 2T of the support base B in a location such as where the chair is being disassembled, the screw v5 can be reused as the screw v4 that is threadedly engaged with the threaded connection hole n4 of the rising structure 2S.

[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 installing the supporting member W; the rear wall portion 27 is upright upward from the rear of the rear bottom wall 24, and the front is made 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 upright 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 is provided at the center of the rear bottom wall 24 in the left-right direction. The first screw insertion hole h51 is formed in a long hole shape extending in the front-back 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 movement of the hexagonal nut n5 threadedly engaged with the screw v5 .

[0176] The rear wall portion 27 is in the shape of a rising plate and is provided upright in a posture tilted rearward 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 the fixed position (lower position) fastened relative to the rear bottom wall 24 toward the direction opposite to the fixed position, i.e., upward compared to the lower position.

[0178] Left and right side wall portions 28 are provided upright on the rear bottom wall 24, and their rear portions are connected to the rear wall portion 27. The left and right side wall portions 28 serve to define the left-right position of the support member W and to ensure 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] Left and right side walls b1 are erected from both 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 provided at a front-to-back position corresponding to the rear portion of the base bottom wall 21, and passes through in the left-to-right direction so as to keep the main shaft j1 rotatable; the long hole b12 is provided at a front-to-back position corresponding to the front portion of the front bottom wall 23, and passes through 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 provided only on the left side wall b1, and can support the lifting operating rod V for lifting and lowering the seat C so as to be rotatable; the groove portion b14 is provided along the long hole b12 in front of the long hole b12 and is open toward the outside; the axial movement limiting portion b15 is provided 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 provided 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 formed with outwardly projecting bosses b4 that form part of the shaft hole b11. Providing bosses b4 on the left and right side walls b1 in conjunction with the shaft hole b11 ensures a horizontal area longer than the width of the left and right side walls b1 that can directly support the spindle j1. The bosses b4 continue to the front end of the extended flange b3.

[0185] [Slotted hole b12]

[0186] The elongated hole b12 extends obliquely, with its lower end positioned forward relative to its upper end in a side view. A sleeve member gs made of synthetic resin is embedded within the elongated hole b12 to facilitate sliding relative to the front axle j2. The front axle j2 is supported within the elongated 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, which can support the front axle j2 so that it can slide.

[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 capable of hinge operation. The lifting operation rod V can act on the air cylinder ag to extend and retract the leg support a2 in the vertical direction.

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

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

[0192] The pair of shaft portions j4 protrude in opposite directions, that is, in directions that align their axes and approach each other. The shaft portion j4 includes a narrow portion j41, which is narrow in the horizontal direction (a direction perpendicular to the axis), and a wide portion j42, which is wide in the vertical direction (a width wider than the narrow portion j41). In other words, the shaft portion j4 is configured so that its lateral width is shorter than its 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 portion is located forward of the upper end portion when viewed from the side.

[0195] A restriction protrusion 1 t provided on the seat receiving body 1 to restrict the position of the seat receiving body 1 relative to the support base B is provided 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 extension flange b3 is provided to extend 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 against which the back support base 4 abuts when the back support L tilts rearward. The damper gx mounted on the damper mounting portion b31 is engageable with engaging tabs 41c projecting 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 operating 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 leg 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, pushing down the working member a23 arranged at the upper end of the foot support a2.

[0207] The lifting operating 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 lever body vh is curved along the outer surface of the seat support 1, that is, it is curved into a partial arc shape, convex downward in a front view. The tip of the lever body vh serves as the operating end vc, which primarily receives operating force from the user's finger. The operating end vc is configured to be positioned at the lower limit position due to its own weight when no operating force is applied by the user.

[0210] <Base end upright setting portion 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 section vm>

[0213] The inner extension vm is supported on 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 decreases toward the front end side located inside the support base B.

[0214] The front end portion of the inward extending portion vm serves as a rotating 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 inward extending portion vm face in opposite directions.

[0217] A pair of bearings vb are provided on either side of the lift lever V, i.e., on the front and rear sides. One bearing vb faces forward, while the other faces rearward. The bearings vb are located near the inner edge of the boundary between the base upright portion vi and the inwardly extending portion vm.

[0218] The front and rear bearings vb are recessed in opposite directions. These bearings vb engage with a pair of front and rear shafts j4 protruding toward each other on the rod support b13 of the support base B, allowing the entire lift lever V to rotate about the shafts j4.

[0219] The front and rear bearings vb are provided with cutouts vd serving as extraction paths. The cutouts vd allow the lift lever V to be moved and the front and rear shafts j4 to be extracted only when the lift lever V assumes a predetermined detachable posture (SR).

[0220] The notch vd of the bearing vb is set to a width dimension that allows the narrow portion j41 of the shaft j4 of the rod support v13 to pass through, while the notch vd is set to a width dimension that prevents the wide portion j42 of the shaft j4 from passing through.

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

[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 position (SR) in which it is detachable from the support base B, and a non-detachable position (SH) in which it is non-detachable from the support base B.

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

[0226] When the leg A, which serves as an obstruction member, is fitted inwardly into 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 attached to the support base B, the lifting operation lever V cannot take the detachable posture (SR).

[0228] After the lift lever V is supported by the lever support b13 of the support base B, the foot support a2 of the foot A serving as a blocking member is attached to the support base B. The upper portion of the foot support a2 limits the rotatable range of the lift lever V.

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

[0230] Specifically, when the foot A is attached to the support base B, the pivoting end va of the lift operating lever V abuts against the upper portion of the foot support a2 in the non-detachable position (SH). The pivoting end va is prevented from further downward movement by the foot support a2. Therefore, the lift operating lever 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 be inserted into the fitting hole Ba until it can take the detachable posture (SR).

[0235] Moreover, the lifting operating rod V in the detachable posture (SR) can be moved relative to the support base B by the user (upward vertical direction), so that the narrow width portion j41 of the shaft portion j4 can pass through the notch portion vd of the bearing portion vb, and the lifting operating rod V can be detached from the support base B.

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

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

[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 tilts rearward 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, the seat occupant utilizes a weight-sensitive locking mechanism in which the seat engaging shaft j3 is pushed forward and downward via the seat C. This assists the seat occupant in generating a reaction force in the direction of the normal posture (ps) of the backrest M relative to the rearward tilting movement. Therefore, a relatively small and lightweight coil spring r1 is used as the reaction force generator R in this embodiment.

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

[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 an engaging recess r31 extending in the left-right direction, and a pair of upper and lower longitudinal engaging recesses r32 provided so that their left-right positions coincide with the upper and lower portions of the engaging recess r31.

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

[0249] The longitudinal engagement recess r32 of the rear member r3 engages with a mountain-shaped protrusion w16 provided protruding from 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 vertical direction.

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

[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 portion wm on the rear side; the hexagonal nut n5 is a nut that is movably arranged inside the supporting member body w1.

[0253] The support member W is fixed 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 27 , and the left and right side walls 28 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 upright upward from the peripheral edge of the bottom wall portion w11 and has a nut mounting space wk inside for accommodating the hexagonal nut n5.

[0257] [Bottom wall portion w11]

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

[0259] [Surrounding wall ws]

[0260] The peripheral 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 configured to be rearwardly inclined in a side view. The rearwardly inclined back portion wm of the rear wall portion w13 is inclined so as to gradually become rearwardly located 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 inward of the outer wall wa. The nut placement space wk is formed by the front wall portion w12 and 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, located in the nut-receiving space wk of the peripheral wall portion w12, engages with the inner circumferential surface of the peripheral wall portion w12 to inhibit left-right movement and horizontal rotation. Furthermore, the nut-receiving space wk is configured to gradually increase in length in the front-to-back direction toward the upper side, thereby allowing for front-to-back movement of the hexagonal nut n5.

[0265] <Hexagonal nut n5 (nut)>

[0266] The hexagonal nut n5 is a known nut secured to the support base body w1. It is threadably engaged with a screw v5, which is inserted into a first screw insertion hole h51 provided in the threaded groove of the support base B and a second screw insertion hole h52 provided in the bottom wall w11 of the support member body w1.

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

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

[0269] The support member W for attaching the reaction force generating body R is attached to the attachment portion 2T in the following manner.

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

[0271] Next, the screws v5 inserted from bottom to top in the order of the first screw insertion hole h51 of the support base B and the second screw insertion hole 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 point, the support member W is connected to the rear portion of the reaction force generating body R, which is not compressed in the front-to-back direction. In other words, the support member W is positioned above and rearward of its fixed position. The screws v5 inserted into the first and second elongated screw insertion holes h51 and h52 can be tilted back in a relaxed manner to threadably engage the hexagonal nuts n5.

[0273] After the above steps, the operator can complete the installation work simply 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 support member body w1 moves downward together with the support member body w1. That is, the support 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. Specifically, as the support member W is guided by the inclined surface nm of the mounting portion 2T as it descends, moving downward and forward, the reaction force generating body R is gradually compressed between the seat engagement axis j3 and the support member W, and the 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 forward and downward smoothly, finally reaching 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 steps in reverse.

[0280] In other words, by rotating the screw v5 in the second direction, the support member W can be guided to move (rise) toward the anti-fixed position while engaging with the inclined surface nm. At this time, as the hexagonal nut n5 rises, the support member W weakens the loading force of the reaction force generating body R while being guided by the inclined surface nm and moving upward and rearward.

[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 danger, 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 partially spherical shape.

[0286] <Regarding the Forward-Tiltable Structure of Seat C>

[0287] The front portion of the seat C is supported by a front axis j2 for rotation and vertical movement relative to the support base B. The rear portion of the seat C is supported by a seat engagement axis j3, which is the seat engagement portion of the back support body L, which is supported by the support base B in the normal posture (ps). Here, the "rear end of the seat C" supported by the back support body L means "the portion rearward of the front portion 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 , which is capable of coming into contact with a seat engagement shaft j3 , which 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 engaging axis j3 so as to be placed on the seat engaging axis j3 when the seat C is in the normal posture (ps) and the rearwardly tilted posture (pr). The engaged portion 1k of the seat C is configured to separate upward from the seat engaging axis j3 when the seat C is in the forwardly tilted posture (ps).

[0291] <Seat support 1>

[0292] The seat receiving body 1 supports the seat body D. The upper surface portion of the seat receiving body 1 is engaged with the housing 3 constituting the seat body D. That is, the housing 3 is placed on the upper surface portion 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 has a partially spherical shape. The outer peripheral surface of the seat receiving body 1 recognized by the user 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. 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 and support both end portions of the front axle j2 supported by the support base B.

[0296] The seat support body 1 has a recess 11, a shell arrangement portion 12, a recess 13 and an arm through hole 14. The recess 11 is open to the bottom and is equipped with a support base B and a back support body L; the shell arrangement portion 12 is a seat body mounting portion arranged on the upper part; the recess 13 is arranged in the central part in the left and right directions and is open to the top 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 downwardly where the support base B can be disposed.

[0299] A recessed space in which the support base B and the back support body L are disposed is formed in the recess 11 .

[0300] In the recessed space facing the recess 11 in the seat support 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 clamping axis j3 in the normal posture (ps) and the rearward tilted posture (pr), and is separated from the seat clamping axis j3 in the forward tilted posture (pf); the limiting protrusion 1t is arranged in the groove portion b14 provided on the support 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 has its lower side facing the recessed space and has a clamped portion 1k, which is the 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 sides 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 retaining portion 1m]

[0304] A front axle retaining portion 1m protrudes downward from the front of the recessed top wall 111. A pair of front axle retaining portions 1m are provided on the left and right sides of the recessed top wall 111. The left and right front axle retaining portions 1m are shaped to retain the left and right ends of the front axle j2. Axle passages 1r are provided adjacent to the left and right front axle retaining portions 1m, allowing the front axle j2 to pass through during installation and removal.

[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 engages with the seat engagement axis j3 when the seat C is in the normal position (ps) and the rearwardly tilted position (pr), and is separated from the seat engagement axis j3 only when the seat C is in the forwardly tilted position (pf). In other words, the engaged portion 1k is not configured to normally retain the seat engagement axis j3, but is configured to be able to engage and disengage with respect to the seat engagement axis j3.

[0310] [Restriction 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 adopts the 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 to restrict forward movement of the seat body 1 relative to the front axle j2 when the seat body 1 is in a posture other than the predetermined jumping posture (ph).

[0313] A pair of restricting protrusions 1t are provided in front of the recess 11 of the seat support body 1. The restricting protrusions 1t project inward at locations corresponding to the grooves b14 of the support base B in the seat support body 1. The restricting protrusions 1t are inclined so as to gradually move upward toward the rear. The restricting protrusions 1t project from the inner sides of the left and right front axle retaining portions 1m.

[0314] <Casing Arrangement Section 12>

[0315] The housing mounting 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, on an upwardly directed portion of the seat receiving body 1 .

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

[0317] The shell arrangement 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 will be described in detail later.

[0318] The outer peripheral edge 1e of the seat receiving body 1 is formed so as to gradually be positioned downward (concave downward) from the left and right end portions toward the center portion in the left-right direction when viewed in the front view and the rear view. Furthermore, the outer peripheral edge 1e of the seat receiving body 1 is formed so as to gradually be positioned upward (convex upward) from the front and rear end portions toward the center portion in the front-back direction when viewed in the side view.

[0319] The upper end of the seat receiving body peripheral wall portion 121 provided on the inner side than the outer peripheral edge 1e of the seat receiving body 1 is provided 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 on the upper portion of the seat receiving body 1 for arranging 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 a central top wall portion 123, which is an upper portion of the seat receiving body 1 constituting the housing mounting portion 12. The recess 13 is open upward and includes another spring receiving portion 13a, which is positioned upward and is configured to receive the lower portion of the coil spring Y.

[0323] The recessed portion 13 has an arrangement space 13 s in which the intermediate member body u1 and the coil spring Y are arranged.

[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 into left and right sides so that the arm u2 of the intermediate member U is disposed on the recess 11 side.

[0326] <Arm Through Hole 14>

[0327] The arm hole 14 is a structure through which the arm portion u2 of the intermediate member u2 can pass. The arm 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 hole 14. The arm hole 14 allows the intermediate member U, which is held in the recess 13, to move in the vertical direction.

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

[0329] The seat receiving body 1 can rotate about the front axle j2 by jumping the rear end 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 open outward.

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

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

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

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

[0335] That is, this embodiment has a structure in which the seat body 1 can be easily separated from the front axle j2 (support base B) by placing the seat body 1 in a predetermined jumping posture (ph) without using special tools. On the other hand, since the seat body 1 cannot be separated from the front axle j2 (support base B) unless the seat body 1 is placed in the predetermined jumping posture (ph), a structure that stably supports the seat body 1 is achieved.

[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 relative to the support base B and the rear portion of the seat C, namely, the vicinity of the engaged portion 1 k.

[0340] The intermediate member U includes a portion engaging with the seat engagement axis j3 and a portion engaging 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 for 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 serving as a seat engaging portion.

[0342] [Intermediate member body u1]

[0343] The intermediate member body u1 is a horizontally long rectangular plate-shaped structure as a whole. The intermediate member body u1 is provided with a downwardly directed spring receiving portion u11.

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

[0345] [Arm u2]

[0346] The arm portion u2 includes a downward extending portion u21 extending downward from the front 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 sides. The coil springs Y are in a posture capable of stretching and contracting in the vertical direction.

[0349] The coil spring Y urges the intermediate member U upward with the seat receiving body 1 as a foothold. In other words, 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] <Attachment and Removal Structure of Intermediate Member U>

[0351] The intermediate member U can restrict the seat receiving body 1 from separating from the back support body L. That is, the intermediate member U is interposed between the back support 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 distance greater than a certain distance.

[0352] The arm portion u2 of the intermediate member U engages 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 engages with the seat receiving body 1 via the coil spring Y.

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

[0354] That is, the intermediate member U is constructed so that it can be released from the engagement with the seat engagement shaft j3 by being pushed in the direction resisting the loading 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 released state.

[0355] Furthermore, if the above 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 comprises a seat cushion Dq; a cushion-supporting housing 3 attached to the bottom surface of the seat cushion Dq and serving as a supporting member; and a seat fabric Dh that covers the upper portion and peripheral edge of the seat cushion Dq and the peripheral edge of the housing 3. The seat body D has a generally circular seat surface formed on its upper surface when viewed from above.

[0358] [Seat cushion Dq]

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

[0360] The seat cushion Dq is fitted onto the housing 3 from above. The seat cushion Dq is larger than the housing 3 in a bottom view. The front-to-back and left-to-right dimensions of the seat cushion Dq are longer than those of the housing 3.

[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 its 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 its outer surface is attached to the inner surface of the peripheral portion of the seat cushion Dq; the end wall portion 34 extends obliquely upward and outward from the lower end portion of the supporting wall portion 33, supporting 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 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 substantially horizontally when viewed in front, rear, and side views.

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

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

[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 on the peripheral edge of the housing 3. More specifically, the peripheral wall portion 32 is disposed closer to the center of the supporting 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 Dq can abut.

[0369] The peripheral wall portion 32 is arranged in a substantially annular shape when viewed from below. That is, the peripheral wall portion 32 is continuously arranged on a perfect circular track, except for a portion where the rear portion of the operating rod k2 is arranged, so that it is located on an imaginary circumference of a perfect circle centered on the central protrusion g1 when viewed from above.

[0370] The peripheral wall 32 has an outwardly extending portion 321 that extends outward and restricts downward movement of the edge de of the seat fabric Dh. The outwardly extending portion 321 is a plurality of protruding tabs arranged at regular intervals in the peripheral direction of the peripheral wall 32.

[0371] Furthermore, inwardly bulging inwardly projecting portions it are provided on the inner surfaces of three locations: the front end portion and the left and right side ends of the peripheral wall portion 32. Specifically, inwardly bulging inwardly are provided on the inner surfaces of the left-right center portion of the front portion of the peripheral wall portion 32 and on the inner surfaces of the front-back center portions of the left and right side ends of the peripheral wall portion 32. The inwardly projecting portions it constitute a horizontal engagement mechanism I, which will be described in detail later.

[0372] Ribs rv, which are vertically provided on the housing body 31 and extend outward from the center of the housing 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 housing body 31.

[0373] The operating lever k2 is cantilevered relative to the housing body 31. Specifically, the operating lever k2 is provided on the housing 3 as a cantilevered lever member that engages with the seat support 1. The operating lever k2 has a wall-like portion k21 extending from the base end of an operating end portion k22, forming part of the peripheral wall portion 32.

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

[0375] The operating lever k2 has a downwardly projecting protrusion kt between its base end k1 and its operating end k22. This protrusion kt engages with an upwardly directed recess k1 provided on the seat support 1. The recess k1 of the seat support 1 and the protrusion kt of the operating lever k2 constitute a reverse return limiting mechanism K, which will be described in detail later.

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

[0377] The lower edge 3 e of the support wall portion 33 in the housing 3 is set so as to follow the outer peripheral edge 1 e 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 end edge de. The seat fabric Dh is formed into a downwardly open bag. A belt-shaped member (not shown) is provided on the seat fabric Dh to reduce the diameter of the end edge de so that the end edge de contacts the outward-facing surface 32m of the peripheral wall 32 of the housing 3.

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

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

[0383] The chair of this embodiment is constructed so that not only the manufacturer but also the end user (user) can easily load and unload the seat body D relative to the seat support body 1 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 such 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 takes 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 takes 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 Portion 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 part G has a central convex part g1 and a central convex part engaging part g2. The central convex part g1 is cylindrical and is arranged in the central part of the shell 3 in the seat body D, protruding downward; the central convex part engaging part g2 is arranged in the central part of the seat supporting body 1, and the central convex part g1 can be relatively rotatably engaged 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 them to each other.

[0390] The vertical engagement mechanism H includes a first engagement portion, a locking protrusion hp provided on the seat receiving body 1 , and a second engagement portion, a locking protrusion engagement portion hk, 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 projecting in a direction intersecting the common axis cj. The locking protrusion hp protrudes generally horizontally from a seat support body peripheral wall portion 121, which is a vertically disposed, generally annular seat support body 1, on its peripheral edge, inwardly, toward the center of the common axis cj, as viewed in a top view.

[0395] The locking tab hp engages vertically with the inclined guide surface hm provided on the locking tab engaging portion hk. More specifically, the locking tab hp pushes the inclined guide surface hm of the locking tab engaging portion hk downward. In other words, the locking tab hp causes the seat body D to move downward as the seat body D rotates from the retracted position (E) to the installed position (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 upwardly directed guide inclined surface hm provided on its 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 circumferentially extending engagement portion body hg. 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 portion is a plate-like structure that is in an inverted position and extends in the circumferential direction. The inner edge and base end edge of the main body hg of the engaging portion are connected to the support wall hs. The upward guide inclined surface hm provided on the main body hg of the engaging portion is inclined so as to gradually move upward from the front end side toward the base end side. Here, the front end side of the main body hg of the engaging portion refers to the edge side of the front end that becomes the direction of travel when rotating from the retreat position (E) to the installation position (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 pivots from the retreat position (E) to the mounting position (F).

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

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

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

[0406] Then, if Figure 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 vertical 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 inward protruding portions it of the housing 3 and outward guiding inclined surfaces im of the seat receiving body 1 are arranged at regular intervals along an imaginary circular line centered on the common axis cj.

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

[0412] The inward protrusion it constitutes a protruding structure that protrudes in a direction intersecting the common axis cj. In a top view, the inward protrusion it protrudes inward, that is, in the direction of the common axis cj, from a peripheral wall portion 32 that is vertically provided on the housing 3 in a generally annular shape.

[0413] Furthermore, an outward extending portion 321 for engaging the end edge de of the seat fabric Dh is provided extending in the opposite direction, that is, outward, 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 Section)]

[0416] The outward-guiding inclined surface im is provided on the outer circumferential surface of a peripheral wall portion 121 of the seat support body 1, which serves as an upright wall and is provided upright on the peripheral edge of the seat support body 1. The outward-guiding inclined surface im faces outward, which is a horizontal direction that allows engagement with the inward protrusion it. The outward-guiding inclined surface is inclined so as to gradually move outward 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 seat body D from the non-rotatable state relative to the seat supporting body 1 by operating the operating rod k2 in a manner that resists 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) and detach from the seat supporting body 1.

[0421] The reverse return limiting mechanism K comprises a recess 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 protrusion kt engageable with the recess k1 only in the mounting position (F).

[0422] The convex portion kt of the reverse return limiting mechanism K is provided on an operating lever k2, which is cantilevered and mounted on the housing 3. The convex portion kt of the operating lever k2 utilizes elastic deformation to cause an operating end portion k22, which receives operating force from a user's finger, to move upward, thereby releasing the engagement with the concave portion k1 provided on the seat support 1 and rotating the seat body D from the installed position (F) to the retracted position (E).

[0423] Furthermore, a guide inclined surface km is provided on the upper surface of the rear end of the seat support 1, adjacent to the recess k1, to engage with the protrusion kt of the operating lever k2. The guide inclined surface km is inclined so as to gradually move upward as it approaches the recess k1. The uppermost portion of the inclined surface is positioned above the bottom of the recess k1.

[0424] When the seat body D is in the retracted position (E), the protrusion kt of the operating lever k2 is located at the lowest position on the inclined surface. Furthermore, as the seat body D pivots from the retracted position (E) toward the installed position (F), the protrusion kt is gradually pushed upward by the guide inclined surface km against the elastic restoring force of the operating lever k2.

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

[0426] In this embodiment, when the reverse return limiting mechanism K moves from the evacuated position (E) to the installed position (F), the protrusion kt is lifted by the rotation of the housing 3, resting on the inclined guide surface km of the seat support 1. Therefore, no operating force is required on the operating lever k2. At this point, when the operator sits on the inclined guide surface km, the protrusion kt of the operating lever k2 automatically retracts into the recess k1 due to the elastic restoring force of the operating lever k2. In other words, the reverse return limiting mechanism K does not require any special operation of the operating lever k2 when moving from the evacuated position (E) to the installed position (F).

[0427] Furthermore, downward protrusions 32t are provided on both sides 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 of the operating rod k2.

[0428] These downward protrusions 32t can prevent the operating 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 left and right lower protrusions 32t 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. In other words, 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 axis 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 that is supported relative to the support base B via the main axis j1 so that it can rotate; 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 be changed between an engaged position (U) for engaging with the backrest M and a retracted position (N) for retracting from the backrest M. The left and right operating members p1 constitute a disengagement prevention mechanism P, which will be 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 the main shaft j1 serving as an axis; the connecting member 42 connects the rear parts 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] [Left and right arms 41]

[0440] The left and right arms 41 are made of metal. They have left and right arm bodies 411, which are upright wall-like structures extending horizontally in the front-back direction. The left and right arms 41 are positioned outward from the left and right side walls b1 of 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 in a roughly linear shape 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 the 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 passes through in the left and right directions to maintain the main shaft j1.

[0442] The rear portions of the left and right arm bodies 411 are connected by a coupling member 42. The rear ends of the left and right arm bodies 411 protrude rearwardly relative to the coupling member 42. The rear protruding portions 41b of the left and right arm bodies 411, which protrude rearwardly relative to the coupling member 42, are fitted into the fitting holes 5b of the back support base connecting portion 5a provided at the base end portion 51 of the back support body main body 5.

[0443] The left and right forearms 412 extend integrally from the front ends of the left and right arm bodies 411 toward the obliquely forward upper direction.

[0444] [Joint member 42]

[0445] The connecting member 42 is a metal structure. The connecting member 42 is in the shape of an upright plate extending in the left-right direction. The left and right ends of the connecting member 42 are rigidly connected to the inner side 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 attaching the back support body 5. A connecting wall 5c of the back support base connecting portion 52 provided at the base end portion 51 of the back support body 5 is attached to the back side of the coupling member 42 and fixedly mounted with the screw v3.

[0447] [Seat clamping 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 positioned forward and upward relative to the main axis j1. The seat engagement axis j3 pushes the front-to-back middle portion of the seat C upward and rearward as the back support L tilts backward. In other words, this chair is configured so that when the back support L tilts backward, the front portion of the seat C is lifted upward by the seat engagement axis j3 pushing the seat C forward.

[0450] The seat engagement shaft j3 is directly pressed forward by the reaction force generator R. The seat engagement shaft j3 is directly connected to one end of the reaction force generator R disposed on the support base B. The seat engagement shaft j3 is pressed forward by the reaction force generator R.

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

[0452] When the backrest M tilts backward under the load of the seated person, the back support body L7 supporting the backrest E rotates about 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 base 4 move downward and forward, and the left and right front arm portions 412 of the back support base 4 move upward and backward.

[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 seating load of the seated person.

[0456] [Back support 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 upper and lower 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 has 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 shaft j1 at the front.

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

[0460] The back support body 5 is mounted on the back support body base 4 by screws v3 inserted into the screw holes h3 and nuts 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 sides of the arm main body 411 of the back support base 4. The front portions of the left and right arm portions 5d are located outside the axis of the main shaft j1 that protrudes outward from the left and right side walls b1 of the support base B. Furthermore, the left and right arm portions 5d are restrained so that the main shaft j1 does not extend outward from the support base B.

[0462] The spindle j1 has a simple cylindrical shape extending in the left-right direction. In this embodiment, the spindle j1 is not directly provided with a positioning component (for example, a retaining ring attached to the end of the shaft, or a structure with a flange-shaped portion formed at one end of the shaft). Instead, the spindle j1 is positioned relative to the support base B using the arm portion 5d of the back support body 5 of the back support body L.

[0463] A recess q2 constituting the positioning mechanism Q is provided on the front sides of the upper ends of the left and right upright frame portions 52, that is, on the front sides of the connection portions 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 has a partially annular shape that is curved convexly toward the rear when viewed from above. The upper frame portion 53, in conjunction with the cover member 6, which forms the upper portion of the half-cut shape corresponding to the upper frame portion 53, has a circular shape with both left and right end surfaces facing forward, and as a whole has a cylindrical outer shape that is curved into a partially annular shape.

[0465] In other words, the upper frame portion 53 forms the lower half of the cylindrical outer shape that is bent into a partial annular shape. In other words, the upper frame portion 53 and the cover member 6 have rounded front end surfaces at both left and right ends, and are curved in a convex manner toward the rear when viewed from above. As a whole, they form the upper frame body 5a, which is a generally cylindrical shape that is bent into a partial annular shape.

[0466] The upper frame portion 53 is provided with a plurality of screw insertion holes h1 that penetrate 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 concave rear biasing member engaging portion 532 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 that biases the operating member p1 forward, i.e., in the engaging position (U) direction.

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

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

[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 are exposed to the outside.

[0473] The cover member 6 is provided with a window frame portion 6w that surrounds the engaging portion p11 of the operating member p1, which can be moved forward and backward by protruding and retracting from the upper frame portion 53. The window frame portion 6w includes 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 recess q2 constituting the positioning mechanism Q to form a window frame-shaped portion that is rectangular in a front view.

[0475] Furthermore, 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-described structure is covered with a front back support body cover X2 and a rear back support body cover X3 , and the front back support body cover X2 and the rear back support body cover X3 are formed of synthetic resin.

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

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

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

[0480] <Backrest M>>

[0481] The backrest M has a generally horizontally elongated rectangular shape with rounded left and right ends. The backrest M has a backrest surface on the front against which the user's back rests. The backrest M of this embodiment is designed to be attachable to and detachable from the back support L through simple user manipulation. The backrest M comprises a backrest body 7 as the main structure and a back fabric 8 as a covering that covers the backrest body 7.

[0482] <Backrest body 7>

[0483] The backrest body 7 includes 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 surface of the backrest base 71. A single receiving groove 7m is provided at the lower end of the backrest base 71 in the backrest body 7. The receiving groove 7m is open downward and extends in the left-right direction.

[0484] The receiving groove 7m is formed by a pair of front and rear groove-forming walls 7f and 7r, which are arranged so that their inner surfaces face each other in the front-to-back direction. First and second belt-shaped members 81 and 82, which are provided at the lower edge of the back 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 the inner surfaces of the pair of groove forming walls 7f and 7r. Engaging protrusions t(f) and t(r) are provided on both sides of the pair of groove forming walls 7f and 7r to protrude forward or backward.

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

[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 connecting structures for connecting to 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. The back fabric 8 includes a bag-shaped back fabric body 80 open downward, and first and second belt-shaped members 81 and 82 provided at the lower open end of the back fabric body 80.

[0490] The back fabric 8 includes a front covering portion 8f, a back covering portion 8r, a first strip-shaped member 81, and a second strip-shaped member 82. The front covering portion 8f covers the front side serving as the front side of the backrest body 7; the back covering portion 8r covers the back side serving as the back side of the backrest body 7; the first strip-shaped member 81 is sewn onto the lower end portion of one end portion of the front covering portion 8f and is inserted into the receiving groove 7m of the backrest body 7; the second strip-shaped member 82 is sewn onto the lower end portion of one end portion of the back covering portion 8r and is inserted into the receiving groove 7m of the backrest body 7.

[0491] The back fabric 8 exposes the engaged portions p2 and the protruding portions q1 , which are connecting structures provided on the backrest body 7 , to the outside through openings 8 s 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 open downward by sewing together the peripheral edges of the front cover 8f and the back cover 8r made of stretchable fabric, excluding the lower ends.

[0494] A space for 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. This lower opening 8k opens downward and is used to insert the back fabric body 7 into the internal space.

[0495] Furthermore, in this embodiment, a pair of left and right openings 8s are provided on the back side of the back fabric main body 80 , namely, on the back cover 8r , for exposing the engaged portion p2 and the protruding portion q1 of the backrest main 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 side covering portion 8r which is a fabric material; the through hole peripheral portion 8e is the peripheral area of ​​the through hole 8t in the inner side covering portion 8r; the annular member T is a continuous annular member made of synthetic resin and is attached to the through hole peripheral portion 8e by sewing.

[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 protruding from the back side of the backrest body 7 .

[0498] The annular member T is formed into a square frame shape from a flexible synthetic resin sheet material and has a hole th in its center. The annular member T is configured to bend and deform. The annular member T is sewn to the peripheral edge 8e of the through-hole in the rear cover 8r. In the fully installed position (Ta), the annular member T is covered by the rear cover 8r so that the portion other than the hole th is not visible from the outside.

[0499] In this embodiment, the entire area of ​​the outer portion t1, the entire area of ​​the inner end portion 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 the through-hole peripheral portion 8e is fixed only 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 made of synthetic resin 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. Each of the first and second belt-shaped members 81 and 82 has a plurality of through-holes 81a and 82a arranged in a row, into which the engaging projections t(f) and t(r) engage.

[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 member 81 sewn to the lower end of the front cover 8 f and the second belt 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 strip-shaped members 81 and 82 are inserted into the receiving groove 7m at predetermined positions, the engaging projections t(f) and t(r) protruding from the groove-forming walls 7f and 7r of the receiving groove 7m engage with the through-holes 81a and 82a provided in the strip-shaped members 81 and 82, respectively. More specifically, only the through-holes 81a and 82a of the inserted first and second strip-shaped members 81 and 82 located at positions corresponding to the engaging projections t(f) and t(r) engage with the engaging projections t(f) and t(r).

[0506] As a result, the first and second belt-shaped members 81 and 82 constituting the end edges of the back fabric 8 are restricted from downward movement (reverse return, extraction) by the engaging protrusions t(f) and t(r) after entering the predetermined position in the single receiving groove 7m, and thus cannot 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 in the back fabric 8. The opening 8s comprises a back cover 8r made of fabric material with a through hole 8t formed therein, and an annular member T. The back cover 8r is a continuous ring-shaped member attached to the through hole periphery 8e and is arranged so as not to be visible from the outside, without compromising the front-to-back communication function of the hole th.

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

[0511] <Preparatory Work S1>

[0512] Preparation step S1, such as Figure 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] Through-holes 8t are formed in the back cover portion 8r of the back fabric main body 80 by an appropriate method. The annular member T is a flexible, thin plate frame structure that can be sewn to the back fabric main body 80. In this embodiment, the annular member T is made of synthetic resin and formed into a substantially rectangular ring shape.

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

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

[0516] In this embodiment, the annular member T in the initial position (Tb) is sewn to the outer side of the through-hole peripheral portion 8e while 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 sewn 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 8 e which is the edge portion of the through-hole 8 t.

[0518] <First annular member reversing step S3>

[0519] The next step in the ring member installation process is Figure 51 As shown, the following process is performed: the annular member T in the initial posture (Tb) of the state of being installed on the outer side of the peripheral edge portion 8e of the through hole is flexed and deformed in a manner so that its 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 reversal step S3 is as follows: Figure 52 As shown, the following process is performed: the annular member T in the intermediate posture (Tc) is further bent and deformed so that the inner end edge side is toward the inner surface side of the inner covering part 8r, and is reversed front to back so that the entire annular member T is covered by the inner covering part 8r from the outside (second annular member reversal process S4).

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

[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 not only the manufacturer but also the end user (user) can easily attach and detach the backrest M relative to the back support body L 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 detachment inhibition mechanism P for inhibiting the backrest M positioned in the normal attachment position by the positioning mechanism Q from detaching 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, into which the protrusion q1 engages. 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 on the back side of the backrest body 7 and are exposed to the outside through the opening 8s of the back fabric 8.

[0532] The protrusion q1 includes a wall-like locking portion q11 and a connecting portion q12. The wall-like locking portion q11 extends vertically in a rear view, its width gradually decreasing downward, and is positioned gradually downward and rearward in a side view. The connecting portion q12 connects the backrest body 7 to the left-right intermediate portion of the wall-like locking portion q11, with its front-to-back dimension gradually increasing downward. The upper end of the wall-like 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 seat back main body 7 .

[0534] [Concave q2]

[0535] The recess q2 is provided on the front side of the upper end portion of the left and right upright frame portions 52 constituting the back support body L. The recess q2 is open upward and can fit the protrusion q1 of the backrest M inserted from above.

[0536] The recessed portion q2 is formed within an outer peripheral wall q21 that projects forward from the upper ends of the left and right upright frame portions 52. The recessed portion q2 is formed by the outer peripheral wall q21, which includes a bottom wall portion qt and left and right side wall portions qs extending upward from the left and right edges of the bottom wall portion qt; and a pair of left and right front wall portions q22 that are formed upright 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 with a first space qa provided between the pair of front wall portions q22. The connecting portion q12 of the protruding portion q1 is provided in the first space qa.

[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 a protrusion q1 is provided 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, which constitutes the positioning mechanism Q, engages with the recess q2 of the back support body L while moving in the vertical direction, more precisely, from the obliquely upper front direction to the obliquely lower rear direction. The backrest load of the seated person acts in the upward, rearward, and downward directions, but hardly in the forward direction. Therefore, by inserting the protrusion q1 into the recess q2 from the obliquely upper front direction to the obliquely lower rear direction, the backrest M is less likely to be removed from the back support body L, and the backrest M can be securely fixed to the back support body L.

[0540] <Leaving the Prohibited Institution P>

[0541] The detachment prevention mechanism P is provided between the back support body L and the backrest M, and prevents the backrest M from detaching 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 provided on the back support body L and can be reversibly moved between an engaged posture (U) that prohibits the disengagement of the backrest M and a retreat posture (N) that allows the disengagement of the backrest M by human operating force, that is, it can be rotated in the forward and backward directions; the engaged portion p2 is provided on the backrest M, and in the engaged posture (U), the engaging portion p11 provided on the operating member p1 can be engaged.

[0543] [Operation member p1]

[0544] The operating member p1 prohibits vertical movement of the backrest M relative to the back support body L in the engaged position (U). The operating member p1 is rotatably supported by the upper frame portion 53 of the back support body 5. The operating member p1 is provided on the left and right sides 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, the axial hole pa being provided at the inner end portion serving as the base end portion, and being inserted into the axial portion 531 uprightly provided on the upper frame portion 53, and passing through in the up-down direction; the engaging portion p11 being provided at the outer end portion serving as the front end portion protruding forward; the loading member engaging portion p12 being provided at the rear side between the axial hole pa and the engaging portion p11, and being 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 being provided at the front side between the axial hole pa and the engaging portion p11, and directly receiving the human operating force, i.e., the rearward pushing operating force performed by the finger, when moving from the engaging posture (U) to the retreat posture (N); the long hole portion p14 being provided at the rear portion of the engaging portion p11, and engaging with the up-and-down movement limiting portion 53k provided on the upper frame portion 53.

[0546] The operating member p1 is biased toward the normal engaged position (U) by a coil spring p3. The user can change the position of the operating member p1 to the retracted position (N) by pushing the operated portion p13 of the operating member p1 in the engaged position (U) against the bias of the coil spring p3 toward the retracted position (N) (the direction in which the engaging portion p11, which serves as the pivoting end, moves rearward).

[0547] Furthermore, the position of the operating member p1 can be changed from the engaged position (U) to the retracted position (N) by pushing the operated portion p13 rearward with the user's finger. In other words, the user can move the operating member p1 to the retracted position (N) by pushing the operated portion p13 rearward like a button.

[0548] like Figure 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 facing the space between the back support body L and the backrest M. Therefore, the user can easily push the operated portion p13 as if pressing a button.

[0549] Furthermore, only the outer surface of the operated portion p13 of the operating member p1 in the engaged position (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 operable from the outside, it is positioned in an inconspicuous location and is substantially flush with the cover member 6 so as to be inconspicuous.

[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 so as to open rearward and have a recessed shape. The engaged portions p2 recessed in 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 protruding 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 operating member p1 engages with the engaged portion p2, the backrest M cannot move upward relative to the back support body L, and as a result, 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 occupant sitting on the seat C. The weight-sensitive locking mechanism is configured to move the seat C backward as the backrest M tilts backward while resisting the load of the occupant and lifting the seat C upward.

[0557] The weight-sensitive locking mechanism includes a structure for lifting the seat C upward against the load of the seated person. Therefore, in order to tilt the backrest M backward, a tilting load proportional to the seated person's weight is required.

[0558] The weight-sensing locking mechanism is mainly composed of a support base B, a seat C, a back support body L, a backrest M and a reaction force generating body R, wherein the support base B is supported on the foot A; the seat C is arranged on the support base B, and the front part is supported on the support base B via the front axis j2; the back support body L is rotatably supported on the support base B via the main axis j1, and has a seat engaging axis j3, which is arranged in front and above compared with the main axis j1, can be engaged with the central part of the seat C in the front and rear directions, 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 support 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 that engages with the engaged part 1k of the seat C in the normal posture (ps); the intermediate component U, whose lower part engages with the seat engaging axis j3, and the upper part engages with the seat C via the coil spring Y, limiting 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, a chair having an excellent 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 operated by a human operating force can be provided.

[0563] Furthermore, according to the above-described embodiment, the seat body D is configured to be horizontally rotatable relative to the seat body 1 about the common axis cj between a retracted position (E) in which the seat body D can be detached from the seat body 1 and an attached position (F) in which the seat body D is attached to the seat body 1. Therefore, a chair having an excellent structure can be provided in which the seat body D can be easily attached to and detached from the seat body 1 without the use of special tools.

[0564] Furthermore, according to the above-described embodiment, a peripheral wall portion 32 is provided on the peripheral edge of the housing 3. This peripheral wall portion 32 has an outward-facing surface 32m with which the end edge de of the seat fabric Dh abuts, and is arranged in a generally annular shape when viewed from below. Consequently, a chair can be provided in which the end edge de of the seat fabric Dh covering the seat cushion Dq can be brought into good contact with the peripheral wall portion 32 of the housing 3 with a generally uniform pressing force.

[0565] Furthermore, according to the above-described embodiment, the backrest body 7, which serves as the main structure, is provided with a receiving groove 7m, which is provided with engaging protrusions t(f) and t(r), and the back fabric 8 is provided with first and second strip-shaped members 81 and 82, each having through-holes 81a and 82a that engage with the engaging protrusions t(f) and t(r) of the receiving groove 7m. Therefore, a chair can be provided in which the edge of the back fabric 8 can be easily and reliably attached to the receiving groove 7m of the backrest body 7, which serves as the main structure.

[0566] Furthermore, according to the above embodiment, a method can be provided for forming a well-designed reinforced opening 8s on the back fabric 8 of a cover body as a coverable member. Furthermore, according to the above embodiment, a chair can be provided that is suitable for the back fabric 8 and the like, and includes a cover body having 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 normal posture (ps) and a forward-leaning posture (pf) at the front, 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 part of the seat C (the rear part compared to the front part of the seat C).

[0568] Therefore, a chair is provided which is configured such that the seat C can be satisfactorily positioned in the normal posture (ps) and the forward leaning posture (pf) without providing a bulky mechanism in front of the seat C.

[0569] Furthermore, according to the above-described embodiment, a reaction force generator R is provided between the seat engagement axis j3 and the support base B, which can directly bias the seat engagement axis j3 forward. This reaction force generator R is positioned so as to assume a substantially horizontal position extending in the front-to-rear direction in the normal posture (ps). Consequently, a chair can be provided that is capable of locking between the normal posture (ps) and the rearwardly tilted posture (pr), and that offers excellent design freedom for miniaturizing the support base B and seat C.

[0570] Furthermore, according to the above embodiment, the intermediate member U that restricts 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 fixing parts. 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, since it is a structure in which, when the supporting member W supporting one end portion 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 by the inclined surface nm, a chair can be provided in which the reaction force generating body R can be well attached to and detached from the supporting base B.

[0572] Furthermore, according to the above-described embodiment, a threaded hole n4 having a threaded groove is provided above the fitting hole Ba in the support base B. The foot support a2 is pushed downward by a screw v4 threadedly engaged with the threaded hole n4. Consequently, a chair having a structure that allows for the upper portion of the foot support a2 to be easily released from the fitting hole Ba in the support base B can be provided.

[0573] Furthermore, according to the above-described embodiment, the foot support a2 of the foot A is attached to the support base B as an obstruction member. This obstruction member prevents the lift operating lever V, which serves as an operating lever, from assuming the detachable position (SR). The lift operating lever V can assume the detachable position (SR) only when the foot support a2 is removed from the support base B. Therefore, a chair can be provided in which the lift operating lever V can be properly attached to the support base B.

[0574] As described above, the chair of this embodiment includes a support base B and a seat C, wherein the support base B is supported on the legs A; the seat C is arranged on the support base B and can adopt a normal posture (ps) and a forward-leaning posture (pf) that is more forward than the normal posture (ps).

[0575] Moreover, the front part of the seat C is supported so as to be rotatable relative to the support base B, and the rear part of the seat C is supported on the back support body L, and is separated upward relative to the back support body L in the forward leaning posture (pf). The back support body L is a structure supported on the support base B in the normal posture (ps).

[0576] An intermediate member U is provided between the support base B and the rear portion of the seat C. The intermediate member U regulates the separation distance of the rear portion of the seat C from the back support L in the forward-leaning posture (pf).

[0577] Therefore, according to the above embodiment, a chair can be provided in which the seat C can well take the normal posture (ps) and the forward leaning posture (pf) without providing a bulky mechanism in front of the seat C.

[0578] That is, the seat C has a structure in which the front portion can be rotated relative to the support base B in a manner that allows it to take a normal posture (ps) and a forward-leaning posture (pf), and the rear portion can be jumped relative to the back support body L.

[0579] In this chair, an intermediate member U is provided between the back support L and the seat C. The intermediate member U limits the distance of separation of the rear portion of the seat C from the back support L (the range in which the seat C can jump up).

[0580] Therefore, according to the above-mentioned embodiment, by utilizing the upward movement range limiting function of the rear part of the seat C performed by the intermediate member U as a single component, the seat C can be well changed to the forward tilting posture (pf) without providing a large structure for tilting the seat C forward at the front part of the seat C.

[0581] The front portion of the seat C is rotatably supported relative to the support base B via the front shaft j2.

[0582] Therefore, by interposing the front shaft j2, the front portion of the seat C is supported relative to the support base B so as to be rotatable.

[0583] The rear portion of the seat C is supported on a back support body L and separated upward from the back support body L in the forward-leaning posture (pf). The back support body L is a structure supported on a support base B in the normal posture (pf). The back support body L is rotatably supported relative to the support base B.

[0584] Therefore, by having the back support body L support the rear portion of the seat C, the seat C can be favorably changed to a forward-leaning posture (pf).

[0585] The back support body L is provided with a seat engagement shaft j3 as a seat engagement portion that engages with the rear portion of the seat C in the normal posture (ps), and an intermediate member U is provided between the seat engagement shaft j3 and the seat C.

[0586] Therefore, by disposing the intermediate member U between the seat engagement shaft j3 and the seat C, a favorable structure is achieved in which the seat C can take the forward-leaning posture (pf).

[0587] The seat C includes a seat body D having a seat surface and a seat receiving body 1 that supports the seat body D. The intermediate member U is provided between the seat receiving body 1 and the seat engagement shaft j3.

[0588] Therefore, the intermediate member U is well provided between the seat receiving body 1 and the seat engagement shaft j3.

[0589] A coil spring Y serving as a spring member is interposed between the seat receiving body 1 and the intermediate member U.

[0590] Therefore, when the seat C changes its posture between the normal posture (ps) and the forward-leaning posture (pf), the unpleasant bottoming feeling easily caused by the coil spring Y can be suppressed, and good cushioning performance based on the biasing force of the coil spring Y can be obtained.

[0591] The intermediate member U comprises an intermediate member body u1 provided with a spring receiving portion u11 for receiving one end of the coil spring Y; and an arm portion u2 extending from the intermediate member body u1 and engageable with a seat engagement shaft j3 serving as a seat engagement portion. Furthermore, the seat receiving body 1 is provided with another spring receiving portion 13a for receiving the other end of the coil spring Y.

[0592] Therefore, the coil spring Y is well supported by the one spring receiving portion u11 provided on the intermediate member U and the other spring receiving portion 13 a provided on the seat receiving body 1 .

[0593] That is, since the seat C is engaged with the intermediate member U via the coil spring Y, good cushioning performance can be obtained by the coil spring Y in the center.

[0594] One spring receiving portion u11 is positioned downward, and the other spring receiving portion 13a is positioned upward.

[0595] Therefore, a structure for sandwiching the coil spring Y between the intermediate member U and the seat receiving body 1 is preferably achieved.

[0596] The seat receiving body 1 is provided with a recessed portion 13 . The recessed portion 13 is open upward and includes the other spring receiving portion 13 a , thereby forming a placement space 13 s for placing the intermediate member main body u1 .

[0597] Therefore, a favorable structure for disposing the intermediate member U is provided on the seat receiving body 1 .

[0598] The seat receiving body 1 is provided with a recess 11 that opens downward and is provided with the support base B. An arm through hole 14 is provided between the recess 13 and the recess 11 so that the arm u2 of the intermediate member U can pass therethrough.

[0599] Therefore, the seat receiving body 1 has a favorable structure in which the intermediate member U is supported by the support base B and is engaged with the back support body L located below the seat receiving body 1 .

[0600] In addition, the present invention is not limited to the embodiments described in detail above.

[0601] The seat can be in a normal position and a forward-leaning position that is tilted forward than the normal position. That is, the seat can also be configured not to be in a rearward-leaning position.

[0602] Any structure may be employed as long as the front portion of the seat is rotatably supported relative to the support base, and any appropriate structure may be employed as a specific structure.

[0603] The rear portion of the seat only needs to be rearward compared to the front portion of the seat.

[0604] The rear portion of the seat can be supported on a supporting base or a structure supported by the supporting base under a normal posture. The structure is not limited to a back support body and can be any structure as long as it is supported on the supporting base.

[0605] The shape of the intermediate member may be any shape as long as it can regulate the separation distance between the rear portion of the seat and the support base or the structure in the forward-leaning posture, and the specific structure thereof may be an appropriate one.

[0606] The seat engaging portion is not limited to a shaft-shaped structure, and may have any structure as long as it engages with the rear portion of the seat in the normal posture.

[0607] The spring member is not limited to a coil spring. Any structure that can be sandwiched between the seat support body and the intermediate member to exert a biasing force may be used. For example, the spring member may be a structure made of a rubber material.

[0608] Alternatively, the following structure may be adopted: 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.

[0609] The arm passage hole provided in the seat receiving body may be provided between the recesses so as to allow the arm portion of the intermediate member to pass therethrough, and its specific shape may be appropriately set.

[0610] Furthermore, the specific configuration of each portion is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0611]

Explanation of symbols

[0612] A: Feet

[0613] B: Support base

[0614] C: Block

[0615] 1: Seat support

[0616] 11: Recess

[0617] 13: concave part

[0618] 14: Arm through hole

[0619] U: Intermediate component

[0620] Y: Coil spring (spring component)

[0621] u1: Intermediate component body

[0622] u2: arm

[0623] u11: One side spring receiving part

[0624] (ps):Usually

[0625] (pf): Forward leaning posture.

Claims

1. A chair comprising a support base supported on the legs; a seat disposed on the support base and capable of taking a normal posture and a forward-leaning posture leaning forward from the normal posture, characterized in that: The front portion of the seat is supported rotatably relative to the support base, The rear portion of the seat is supported on the support base or on a structure supported by the support base in the normal posture, and is separated upward relative to the support base or the structure in the forward tilted posture. An intermediate member is provided between the support base and the rear portion of the seat, and the intermediate member can limit a separation distance of the rear portion of the seat from the support base or the structure in the forward-leaning posture.

2. The chair according to claim 1, characterized in that: The front portion of the seat is rotatably supported relative to the support base via a front shaft.

3. The chair according to claim 1, characterized in that: The rear portion of the seat is supported on a structure supported by the support base in the normal posture, and is separated upward relative to the structure in the forward tilted posture; The structure is a back support body rotatably supported relative to the support base.

4. The chair according to claim 3, characterized in that: The back support body is provided with a seat engaging portion that engages with the rear portion of the seat in the normal posture. The intermediate member is provided between the seat engaging portion and the seat.

5. The chair according to claim 4, characterized in that: The seat includes a seat body having a seat surface and a seat receiving body supporting the seat body, and the intermediate member is provided between the seat receiving body and the seat engaging portion.

6. The chair according to claim 5, characterized in that: A spring member is interposed between the seat receiving body and the intermediate member.

7. The chair according to claim 6, characterized in that The intermediate member includes an intermediate member body and an arm portion. 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 seat engaging portion.

8. The chair according to claim 7, characterized in that The spring receiving portion of the above-mentioned one side is arranged downward, 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 and forms a placement space for placing the intermediate member body.

10. The chair according to claim 9, characterized in that The seat receiving body is provided with a recess which is open downward and in which the supporting base is disposed, and an arm passage hole through which the arm can pass is provided between the recess.

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