JP2024065148A - Chair and fitting degree relaxation structure - Google Patents

Abstract

[Problem] To provide a chair with a structure that can suitably release the engagement between the upper part of the leg support and the engagement hole of the support base. [Solution] A chair comprising a leg A having a leg support a2 extending in the vertical direction, a support base B having an engagement hole Ba that penetrates in the vertical direction and engages with the upper part of the leg support a2, and a seat C disposed on the support base B, in which a screw threading hole n4 having a threaded groove is disposed on the engagement hole Ba in the support base B, and configured so that the upper part of the leg support a2 can be pressed downward by a screw v4 that is screwed into the screw threading hole n4. [Selected drawing] Fig. 66

Description

The present invention relates to a chair and a fitting degree relaxation structure.

There is a known chair that has legs with leg supports extending in the vertical direction, a support base with fitting holes that penetrate in the vertical direction and fit into the upper parts of the leg supports, and a seat that is disposed on the support base (see, for example, Patent Document 1).

The legs are generally not lightweight and have a certain weight, so if the legs were to come loose from the support base when the user lifts the seat, this could lead to serious problems such as injury. Therefore, in this type of chair, the legs and support base are usually connected by a tight fit.

On the other hand, when it was necessary to disassemble the chair, it was necessary to use special tools to separate the legs from the support base, which required applying dangerously excessive force to the legs and support base.

In other words, with conventional chairs, separating the legs from the support base required a great deal of effort that could be dangerous.

JP 2021-065624 A

The present invention was made in consideration of the above circumstances, and aims to provide a chair and a fitting degree relaxation structure that has a configuration that can preferably release the fitting state between at least the upper part of the leg support and the fitting hole of the support base.

That is, the present invention has the following configuration.

The invention described in claim 1 is a chair comprising legs with leg supports extending in the vertical direction, a support base having a fitting hole penetrating in the vertical direction that fits into the upper part of the leg support, and a seat disposed on the support base, in which a screw-receiving hole having a threaded groove is disposed above the fitting hole in the support base, and the chair is configured so that the upper part of the leg support can be pressed downward by a screw that is screwed into the screw-receiving hole.

The invention described in claim 2 is the chair described in claim 1, in which the screw-threading hole penetrates in a substantially vertical direction.

The invention described in claim 3 is a chair according to claim 1, in which the leg support includes a gas cylinder capable of adjusting the vertical position of the seat, the gas cylinder includes a cylinder portion, a lifting rod capable of moving up and down relative to the cylinder portion, and an actuating member that protrudes from the upper end of the lifting rod and causes the lifting rod to move up and down when pressed downward, and the screw that is screwed into the screw-receiving hole can press the upper end of the lifting rod downward.

The invention described in claim 4 is the chair described in claim 1, in which the support base is made of metal and has a bottom wall portion in which the fitting hole is formed, and a rising structure portion having the screw-threading hole is integrally provided on the periphery of the fitting hole.

The invention described in claim 5 is the chair described in claim 4, in which the rising structure is provided in front of the fitting hole.

The invention described in claim 6 is the chair described in claim 4, in which the rising structure includes a rising portion that rises to partially surround the fitting hole in a plan view, and a horizontal portion that is installed between the rising portions so as to be located directly above the fitting hole, and the screw-threading hole is provided in the horizontal portion.

The invention described in claim 7 is a fitting degree relaxation structure that is provided on a chair having legs with leg supports extending in the vertical direction and a support base having a fitting hole that penetrates in the vertical direction and fits into the upper part of the leg support, and that relaxes the degree of fitting between the leg support and the support base, and a screw-receiving hole having a threaded groove is disposed above the fitting hole in the support base, and the upper part of the leg support can be pressed downward by a screw that is screwed into the screw-receiving hole.

As described above, the present invention provides a chair and a fitting degree relaxation structure that are at least configured to suitably release the fitting state between the upper part of the leg support and the fitting hole of the support base.

FIG. 1 is a perspective view showing an embodiment of the present invention. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. 15 is an enlarged view of the lower part of FIG. FIG. FIG. 2 is a rear view of the embodiment with a portion of the back upholstery broken away. FIG. 2 is a front view of the back upholstery in the same embodiment with a portion thereof broken away. FIG. 4 is a perspective view of first and second belt-shaped members in the embodiment. FIG. FIG. FIG. FIG. 4 is a plan view for explaining the operation of the operating member in the embodiment. FIG. 4 is a plan view for explaining the operation of the operating member in the embodiment. 5 is a cross-sectional plan view for explaining the operation of the operating member in the embodiment. FIG. 5 is a cross-sectional plan view for explaining the operation of the operating member in the embodiment. FIG. 5 is a view taken in the direction of the arrow X in FIG. 4 . FIG. FIG. FIG. 4 is an enlarged perspective view of a rear portion of the seat support in the embodiment. FIG. FIG. FIG. FIG. FIG. 4 is a perspective view of the seat body from below in the same embodiment. FIG. 4 is a central cross-sectional view of the seat body in the embodiment. FIG. FIG. FIG. FIG. FIG. FIG. FIG. 4 is a cross-sectional view for explaining attachment of the seat body to the seat support in the embodiment. FIG. 4 is a cross-sectional view for explaining attachment of the seat body to the seat support in the embodiment. FIG. 4 is a cross-sectional view for explaining attachment of the seat body to the seat support in the embodiment. FIG. 4 is a cross-sectional plan view illustrating the attachment of the seat body to the seat support in the embodiment. FIG. 4 is a cross-sectional plan view illustrating the attachment of the seat body to the seat support in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. FIG. 4 is an enlarged view of the embodiment after the opening is formed. FIG. 4 is a right side view of the embodiment (with the seat back tilted). FIG. FIG. FIG. FIG. 3 is a left side view of the support base in the embodiment; FIG. FIG. FIG. FIG. FIG. FIG. 4 is a partially enlarged vertical cross-sectional view of the leg and support base in the embodiment. FIG. 4 is a partially enlarged vertical cross-sectional view of the leg and support base in the embodiment. FIG. 4 is a partially enlarged vertical cross-sectional view of the leg and support base in the embodiment. FIG. 4 is a partially enlarged vertical cross-sectional view of a reaction force generating body and a support member in the embodiment. FIG. 68 is a partially enlarged longitudinal sectional view corresponding to the cutting position of FIG. 67 in the same embodiment. FIG. 4 is an exploded perspective view of the reaction force generator and the support member in the embodiment. FIG. 4 is a rear perspective view of the support member in the embodiment. FIG. 4 is a cross-sectional view illustrating the legs, the support base, and the lifting operation lever in the embodiment. FIG. 4 is a cross-sectional view illustrating the legs, the support base, and the lifting operation lever in the embodiment. 3 is a cross-sectional view taken along line AA in FIG. 2. FIG. 74 is a vertical cross-sectional view of the embodiment when the seat back is tilted backward, corresponding to the cut position of FIG. 73. FIG. 74 is a vertical cross-sectional view of the embodiment when seated in a forward leaning position corresponding to the cut-away position of FIG. 73 . Cross-sectional view of line BB in Figure 29. FIG. 77 is a cross-sectional view of the embodiment when seated in a forward leaning position corresponding to the cut position of FIG. 76 . FIG. FIG. 79 is a vertical cross-sectional view of the embodiment when seated in a forward leaning position corresponding to the cut position of FIG. 78 . Cross-sectional view of line CC in Figure 84. FIG. 81 is a cross-sectional view of the embodiment when seated in a forward leaning position corresponding to the cutting position of FIG. 80 . FIG. FIG. FIG. FIG. FIG. 87 is a central vertical cross-sectional view corresponding to the cutting position in FIG. 86 for explaining a process of removing the intermediate member in this embodiment. FIG. FIG. FIG. FIG. FIG. FIG. FIG. A longitudinal sectional view of the seat in the lifted position corresponding to the cutting position of Figure 78 in this embodiment. 79 is a vertical cross-sectional view of the seat in a popped-up position corresponding to the cut position in FIG. 78 in the same embodiment, and of the seat being detached from the support base.

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

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

The seat C is disposed on the support base B and is configured to be able to take a normal position (ps), a forward-leaning position (pf) which is more forward than the normal position (ps), and a backward-leaning position (pr) which is more rearward than the normal position (ps). Between the support base B and the back support L, a reaction force generating body R is provided which can bias the back support L in the direction of the normal position (ps).

The backrest M is supported so as to be able to tilt backward via the back support L with respect to the support base B. In other words, the backrest M and the back support L can take a normal position (ps) with respect to the support base B, and a backward tilt position (pr) which is tilted further backward than the normal position (ps).

The chair is equipped with a weight-sensing rocking mechanism that is configured to lift the front and central portion of the seat C upward in response to the backward tilting movement of the back support L linked to the backrest M, and to tilt and move the entire seat C backward.

The chair is provided with a seat forward tilting mechanism that shifts the seating load to the front part of the seat C, i.e., the part of the seat C in front of the front axis j2, thereby rotating the seat C forward around the front axis j2 and transitioning it to a forward tilted position (pf).

The individual components of the chair in this embodiment are described in detail below.

<<Leg A>>
The leg A has a plurality of leg blades a1 with casters at their lower ends, and a leg support a2 that stands up from the portion where the upper ends of the leg blades a1 come together.

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

<Leg support a2>
The leg support a2 is configured to be extendable and contractible in the vertical direction.

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

The gas cylinder ag is of a known configuration, comprising a cylinder section a21 provided at the bottom of the leg support a2, a lifting rod a22 that can be raised and lowered relative to the cylinder section a21, and an actuating member a23 that is protruding from the upper end of the lifting rod a22 so that it can be extended and retracted in the vertical direction and that, when pressed downward, causes the gas sealed inside to become flowable, thereby enabling the lifting rod a22 to be raised and lowered.

The lifting rod a22 is cylindrical. The outer circumferential surface of the upper part of the lifting rod a22, which is the upper part of the leg support a2, is tapered. In other words, the upper part of the lifting rod a22 is formed so that the diameter gradually decreases toward the top.

The upper part of the lifting rod a22 is adapted to fit into the fitting hole Ba, which is the leg connection part of the support base B. The fitting hole Ba of the support base B, into which the lifting rod a22 is fitted, is shaped so that it can fit tightly around the upper part of the lifting rod a22.

The operating member a23 can be pressed downward by the lift operation lever V, which is an operation lever rotatably supported on the lever support part b13 of the support base B.

<<Support Base B>>
A support base B is attached to the top of leg A.

The support base B is supported by legs A so that it can be moved up and down and can rotate. The support base B is molded as a single piece from metal. The support base B is shaped like a box that is long in the front-to-rear direction and open at the top.

The support base B has a bottom wall 2 having a downward surface and integrally formed with a mounting portion 2T for supporting the rear end of the reaction force generator R, left and right side walls b1 that are erected upward from both the left and right ends of the bottom wall 2, a rear wall b2 erected at the rear end of the bottom wall 2 and connecting the rear ends of the left and right side walls b1, and an extension flange b3 that extends outward from the rear of the left and right side walls b1.

<Bottom wall portion 2>
The bottom wall portion 2 comprises a foundation bottom wall 21 having a substantially horizontal bottom surface and a fitting hole Ba, which is a leg connecting portion that fits into the upper part of the leg support a2, an inclined bottom wall 22 extending diagonally upward and rearward from the rear end of the foundation bottom wall 21, a front bottom wall 23 extending forward from the front end of the foundation bottom wall 21 and positioned gradually upward as it moves forward, and a rear bottom wall 24 extending substantially horizontally rearward from the rear end of the inclined bottom wall 22.

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

[Foundation bottom wall 21]
A boss portion 211 is provided on the base bottom wall 21 and has a fitting hole Ba extending vertically therethrough to fit over the upper portion of the leg support b2.

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

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

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

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 an attachment portion 2T for a support member W that supports the rear end portion of the reaction force generating body R.

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

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

The rising structure 2S is adjacent to and rises up from the front side of the fitting hole Ba. The rising structure 2S is made of metal and is integral with the boss portion 211 of the foundation bottom wall 21 that forms the fitting hole Ba.

The rising structure 2S has rising parts 25 that rise up so as to partially surround the front of the fitting hole Ba in a plan view, and a horizontal part 26 that is installed between the rising parts 25 so as to be located directly above the fitting hole Ba.

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

In other words, the rear of the standing portion 25 is shaped so that a space is provided directly above the fitting hole Ba, and the cross-bridge portion 26 can be integrally disposed above that space.

The horizontal portion 26 has a screw hole n4 that penetrates in a substantially vertical direction. The horizontal portion 26 is integrally connected to the upright portion 25.

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

The worker can use a standard tool to screw a screw v4 of a size that matches the screw hole n4 provided in the cross section 26 of the rising structure section 2S from above downward.

The upper part of the leg support b2, which is disposed directly below the screw hole n4, is configured to be pressed downward by a screw v4 that screws into and enters downward while using the rising structure 2S, which is integrally formed with the support base B, as a foothold.

More specifically, the screw v4 screwed into the screw hole n4 is guided by the thread groove of the screw hole n4 and rotates and descends, so that the lower end of the screw v4 can press downward against the outer periphery of the upper end of the lifting rod a22 that constitutes the leg support b2.

The rising structure 2S is used when the leg A is detached from the support base B. When the chair is in a completed state, the fitting hole Ba of the support base B and the upper part of the lifting rod a22, which is the upper part of the leg support a2, are firmly fitted together.

In this embodiment, the pressing force of the screw v4, which can be screwed into the screw-receiving hole n4 of the rising structure 2S, is used to eliminate or ease the tight fit between the fitting hole Ba and the lift rod a22.

The screw v4, which rotates and descends along the screw groove, can apply a strong and continuous pressing force to the lift rod a22, which can effectively eliminate or alleviate the tight fit between the fitting hole Ba and the lift rod a22.

In other words, the chair of this embodiment is provided with a fit relaxation structure that relaxes the fit between the leg support a2 and the support base B. The fit relaxation structure is such that a screw thread hole n4 having a threaded groove is disposed above the fit hole Ba in the support base B, and the upper part of the leg support a2 can be pressed downward by a screw v4 that is screwed into the screw thread hole n4.

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

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

The mounting portion 2T includes a rear bottom wall 24, which is a bottom wall portion having a first screw insertion hole v5 through which a screw v5 for mounting the support member W is inserted, a rear wall portion 27 erected upward from the rear of the rear bottom wall 24 and having a rearwardly inclined front surface nm, and left and right side wall portions 28 extending forward from both the left and right ends of the rear wall portion 27 and erected upward from both the left and right sides of the rear wall 24.

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

The rear bottom wall 24 is abutted against the bottom wall portion w11 of the support member W, which is pulled toward the rear bottom wall 24 by the movement of the hexagonal nut n5 that is screwed onto the screw v5.

The rear wall portion 27 is in the form of an upright plate and is erected so as to be tilted backward with respect to the rear bottom wall 24. The front surface of the rear wall portion 27 is an inclined surface nm against which the rear wall portion w13 of the support member W abuts.

The inclined surface nm is set so 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) tightened against the rear bottom wall 24 toward the anti-fixed position, i.e., upward from the lower position.

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

<Left and right side walls b1>
The left and right side walls b1 are erected from both left and right ends of the bottom wall portion 2, i.e., the foundation bottom wall 21, the inclined bottom wall 22, the front bottom wall 23, and the rear bottom wall 24. The left and right side walls b1 extend substantially linearly in the front-to-rear direction.

The left and right side walls b1 are provided with an axle hole b11 penetrating in the left-right direction, which is provided at a front-to-back position corresponding to the rear of the base bottom wall 21 and can rotatably hold the main axle j1, a long hole b12 penetrating in the left-right direction, which is provided at a front-to-back position corresponding to the front of the front bottom wall 23 and can hold the front axle j2 for supporting the front part of the seat C so that it can slide forward and backward and up and down, a lever support b13 provided only on the left side wall b1 and can rotatably support the lifting operation lever V for raising and lowering the seat C, a groove b14 provided in front of the long hole b12 and along the long hole b12 and open toward the outside, and an axle movement restricting part b15 provided at the upper end of the middle part in the front-to-back direction so as to protrude in a mountain shape and which prohibits the seat engagement axle j3 provided on the back support L from moving forward and downward.

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

The left and right side walls b1 are integrally provided with boss-like portions b4 that protrude outward and form part of the shaft hole b11. By providing the boss-like portions b4 on the left and right side walls b1 in relation to the shaft hole b11, a left-right area capable of directly supporting the main shaft j1 is ensured that is longer than the width dimension of the left and right side walls b1. The boss-like portions b4 are connected to the front end of the extension flange b3.

[Long hole b12]
The long hole b12 extends obliquely so that the lower end side is located forward of the upper end side in a side view. A sleeve member gs made of synthetic resin is fitted into the long hole b12 so as to easily slide on the front axle j2. The front axle j2 is supported by the long hole b12 via the sleeve member gs.

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

[Lever support portion b13]
The lever support b13 pivotally supports the lift control lever V so as to be capable of flapping. The lift control lever V acts on the gas cylinder ag to extend and retract the leg support a2 in the vertical direction.

The lever support b13 includes a pair of front and rear support walls b15 that protrude outward from the left side wall b1 in a direction generally perpendicular to the left side wall b1, and a pair of shafts j4 that protrude in mutually approaching directions from the inner faces of the pair of support walls b15 that face each other.

A space is formed between the pair of front and rear support walls b15 in which the lift control lever V is disposed.

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

[Groove portion b14]
The groove portion b14 is provided extending in the same direction as the long hole b12, that is, in an oblique direction so that the lower end side is located forward of the upper end side in a side view.

A restricting protrusion 1t on the seat support 1 is arranged in the groove b14 to restrict the position of the seat support 1 relative to the support base B.

<Rear wall b2>
The rear wall b2 stands upright from the rear end of the rear bottom wall 24. The rear wall b2 connects the rear ends of the left and right side walls b1. A left-right intermediate portion of the rear wall b2 constitutes a rear wall portion 27 of the mounting portion 2T for mounting the support member W.

<Extended flange b3>
The extending flange b3 extends outward beyond the left and right side walls b1.

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

The lower front part of the support base B having the above configuration is covered by a support base cover X1 made of synthetic resin.

<<Lift operation lever V>>
The lift control lever V is a single unit made of synthetic resin and is configured so as to be attachable to the lever support portion b13 of the support base B without using any fasteners such as screws.

The lifting/lowering lever V is rotatably supported on the support base B. More specifically, the lifting/lowering lever V is rotatably supported on the lever support b13 provided on the left side wall b1 of the support base B.

The lifting/lowering lever V can be operated by the user to make the leg support a2 of the leg A extendable and retractable in the vertical direction in order to raise and lower the seat C.

When the user moves the operating end vc side of the lift lever V upward, it rotates around the shaft j4 of the support base B with which the bearing vb engages, and the rotating end va moves downward to press down the operating member a23 located at the upper end of the leg support a2.

The lifting lever V is a plate-like lever body vh extending in the left-right direction and having an operating end vc at its tip, a base end erection part vi extending upward from the base end of the lever body vh, an inward extension part vm extending inward from the upper end of the base end erection part vi and having a pivot end va at its tip that can come into contact with the leg support a2, and a bearing part vb provided between the base end erection part vi and the inward extension part vm.

<Lever body vh>
The lever body vh is curved to fit the outer surface of the seat support 1, i.e., curved in a partial arc shape that is convex downward when viewed from the front. The tip of the lever body vh is the operating end vc that mainly receives the operating force from the user's fingers. When not receiving the operating force from the user, the operating end vc is configured to be located at the lowest position by its own weight.

<Base end erection portion vi>
The base end erection portion vi is a generally square prism-shaped member erected from the base end portion of the lever main body vh.

<Inward extension portion vm>
The inward extension portion vm is supported by the base end erection portion vi in a cantilever manner. The base end portion of the inward extension portion vm has substantially the same width as the base end erection portion vi, and the width of the inward extension portion vm is gradually reduced toward the tip side located inside the support base B.

The tip of the inward extension vm is a pivot end va that can press down the actuating member a23 provided on the leg support a2.

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

The bearings vb are provided in pairs on both sides of the lift lever V, i.e., on the front and rear. One of the bearings vb faces forward, and the other faces rearward. The bearings vb are provided near the inner edge of the boundary between the base end erection portion vi and the inward extension portion vm.

The pair of front and rear bearings vb are recessed in opposite directions. The pair of front and rear bearings vb engage with a pair of front and rear shafts j4 that protrude in opposite directions from the lever support b13 of the support base B, allowing the entire lift operation lever V to rotate around the shafts j4.

The pair of front and rear bearings vb are provided with cutouts vd, which are escape passages through which the pair of front and rear shafts j4 can escape by moving the lift control lever V only when the lift control lever V is in a specified releasable position (SR).

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 lever support v13 to pass through. On the other hand, the notch vd is set to a width dimension that does not allow the wide portion j42 of the shaft j4 to pass through.

In this embodiment, the notch vd is provided at a position where the shaft j4 can move linearly relative to the bearing vb in the vertical direction and disengage from the bearing vb to the outside when the lift lever V is in the releasable position (SR).

<<Attachment of the lift operation lever V to the support base B>>
The mounting structure of the lift control lever V for mounting the lift control lever V to the support base B constituting the chair will now be described.

In this embodiment of the chair, the lifting lever V can take a detachable position (SR) in which it can be detached from the support base B, and a non-detachable position (SH) in which it cannot be detached from the support base B.

<About the SH (Short-Headed Position)>
The lifting/lowering lever V can only take a non-detachable position (SH) in which it cannot be detached from the support base B when the leg A, which is an obstructing member, is fitted inside the support base B.

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

The chair supports the lifting operation lever V on the lever support b13 of the support base B, and then attaches the leg support a2 of the leg A, which acts as an obstructing member, to the support base B. This restricts the range of rotation of the lifting operation lever V by the presence of the upper part of the leg support a2.

The lift control lever V can only rotate within the range of the non-releasable position (SH) by the upper part of the leg support a2, and as a result, any further rotation is prevented, so that the lift control lever V cannot assume the releasable position (SR).

In other words, when leg A is attached to support base B, the pivot end va of lift control lever V comes into contact with the upper part of leg support a2 in the non-detachable position (SH), and further downward movement of said pivot end va is prevented by the presence of leg support a2. For this reason, lift control lever V cannot be detached from support base B unless leg A is removed from support base B.

<About the ready-return position (SR)>
The lifting/lowering control lever V can take a detachable position (SR) in which it can be detached from the support base B only when the leg A, which is an obstructing member, is not fitted inside the support base B.

The chair is configured so that by removing the leg support a2 of the leg A from the support base B on which the lift control lever V is supported, the rotational range of the lift control lever V is no longer restricted by the upper part of the leg support a2, and the lift control lever V can be changed to a releasable position (SR).

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

The lift control lever V in the detachable position (SR) can be moved by the user in a direction away from the support base B (upward vertical direction) so that the narrow portion j41 of the shaft j4 can pass through the notch vd of the bearing portion vb, allowing the lift control lever V to be detached from the support base B.

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

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

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

In this embodiment, the reaction force generator R uses the support base B as a foothold to urge the left-right center of the seat engagement shaft j3 forward. The seat engagement shaft j3 abuts against the shaft movement restricting portions b15 of the left and right side walls b1 of the support base B, and is prohibited from moving further forward and downward.

In other words, when the seat engagement axis j3 hits the support base B, the back support L is prohibited from rotating forward around the main axis j1, and the normal position (ps) of the back support L is determined.

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

The reaction force generating body R is mainly composed of a metallic coil spring r1 (compression coil spring), which is a spring material.

In this embodiment, the seat occupant's weight is used to support the reaction force in the normal position (ps) direction against the backward tilting of the backrest M, based on the structure of a weight-sensing locking mechanism in which the seat occupant presses the seat engagement shaft j3 forward and downward via the seat C. For this reason, a relatively small and lightweight coil spring r1 is used for the reaction force generating body R in this embodiment.

The reaction force generator R comprises a coil spring r1 made of metal, a front member r2 attached to the front of the coil spring r1, a rear member r3 attached to the rear of the coil spring r1, and a position holding shaft r4 whose front portion is inserted into a holding hole provided in the front member r2 and whose rear portion is inserted into a holding hole provided in the rear member r3, thereby holding the positions of the front member r2 and the rear member r3.

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

The rear end of the rear member r3 is supported by the support base B via the support member W. The rear end of the rear member r3 is connected to the support member W so as to be capable of relative rotation. The rear end of the rear member r3 is provided with an engagement recess r31 extending in the left-right direction, and a pair of upper and lower vertical engagement recesses r32 that are aligned with the upper and lower parts of the engagement recess r31 in the left-right direction.

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

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

Note that the front member r2 and the rear member r3 have different postures, but are the same shape.

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

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

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

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

[Bottom wall portion w11]
The bottom wall portion w11 is provided with a second screw insertion hole h52 having an elongated hole shape in the front-rear direction in the left-right central portion. The lower surface of the bottom wall portion w11 is adapted to abut against the rear bottom wall 24 of the mounting portion 2T in the fixed position.

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

The front wall portion w12 has a pair of left and right shaft protrusions w15 protruding from the vertical middle portion so as to engage with the engagement recesses r31 of the rear member r3, and a mountain-shaped protrusion w16 protruding from the horizontal middle portion so as to engage with the vertical engagement recesses r32 of the rear member r3.

The rear wall portion w13 is inclined backwards in a side view. The inclined back surface portion wm of the rear wall portion w13 facing backwards is inclined so that it is gradually positioned rearward as it goes upwards.

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

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

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

Hexagonal nut n5 engages with peripheral wall portion w12 to restrict left-right movement and horizontal rotation, and also engages with peripheral wall portion w12 to permit forward-rearward movement.

<Operation of the support member W for mounting the reaction force generating body R>
The support member W for mounting the reaction force generating body R is attached to the mounting portion 2T in the following manner.

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

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

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

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

Next, the screw v5 threaded into the hexagonal nut n5 is rotated in the first direction (tightening direction).

When the screw v5 is rotated in the first direction, the hexagonal nut n5 held by the support member body w1 moves downward together with the support member body w1. In other words, the support member W moves toward the rear bottom wall 24 of the mounting portion 2T by the operator rotating the screw v5.

At this time, as the support member W moves downward, the reaction force generator R gradually increases its force backward. In other words, as the support member W descends, it is guided by the inclined surface nm of the mounting portion 2T and moves downward and forward, so that the reaction force generator R is gradually compressed between the seat engagement shaft j3 and the support member W, and the force gradually increases.

As the screw v5 continues to rotate, the support member W moves smoothly forward and downward while being guided by the inclined surface nm against the biasing force of the reaction force generating body R, and finally reaches a predetermined fixed position.

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

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

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

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

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

Seat C comprises a seat support 1 and a seat body D that has an upward facing seat surface and is detachable from seat support 1.

The outer periphery of seat C, i.e., the outer periphery of seat support 1 and seat body D, is smoothly continuous to form a partial sphere.

<Regarding the forward tilting configuration of the seat C>
The front part of the seat C is supported via a front shaft j2 so as to be rotatable and vertically movable with respect to the support base B. The rear part of the seat C is supported by a seat engagement shaft j3, which is a seat engagement part of the back support L, which is a structure supported by the support base B in the normal posture (ps). Here, the "rear part of the seat C" supported by the back support L means "behind the front part of the seat C."

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

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

The engaged portion 1k of the seat C is adapted to engage with the seat engagement shaft j3 so as to rest on the seat engagement shaft j3 when the normal posture (ps) and the backward tilt posture (pr) are adopted. The engaged portion 1k of the seat C is adapted to move upward away from the seat engagement shaft j3 when the forward tilt posture (ps) is adopted.

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

The seat support 1 is made of synthetic resin and formed into a shell shape. The seat support 1 has a partially spherical shape. The outer peripheral surface of the seat support 1 that is visible to the user is formed to have a spherical surface shape.

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

The seat support 1 is provided with a front axle holder 1m that can hold both ends of the front axle j2 supported by the support base B.

The seat support body 1 has a recess 11 that is open downward and in which the support base B and back support L are arranged, a shell body arrangement part 12 that is the seat body mounting part provided on the upper surface, a recess 13 that is open upward and provided in the left-right center part in which the intermediate member U and coil spring Y are arranged, and an arm passage hole 14 that is a vertical communication hole provided between the recess 13 and the recess 11 and through which the arm part u2 of the intermediate member U can pass.

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

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

At a location facing the recessed space of the recess 11 in the seat support 1, there are provided a front axle holding portion 1m capable of holding the front axle j2, an engaged portion 1k disposed behind the front axle holding portion 1m, which engages with the seat engagement shaft j3 in the normal position (ps) and the rearward tilted position (pr) and is spaced apart from the seat engagement shaft j3 in the forward tilted position (pf), and a restricting protrusion 1t disposed in a groove portion b14 provided in the support base B.

The recess 11 comprises a recess top wall portion 111 having an engaged portion 1k on the underside facing the recess space and engaging with the seat engagement shaft j3, a recess front wall portion 112 and a recess rear wall portion 113 extending downward from the front and rear parts of the recess top wall portion 111, respectively, and left and right recess side wall portions 114 extending downward from the left and right side parts of the recess top wall portion 111, respectively.

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

[Front axle holding portion 1m]
The front axle holders 1m protrude downward from the front of the recessed top wall 111. The front axle holders 1m are provided in pairs on both the left and right sides of the recessed top wall 111. The left and right front axle holders 1m are shaped to hold both the left and right ends of the front axle j2. The left and right front axle holders 1m are adjacent to each other with axle passages 1r through which the front axle j2 can pass when the front axle j2 is attached or detached.

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

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 approximately L-shaped.

The engaged portion 1k is configured to be able to move toward and away from the seat engagement axis j3 as the position of the seat C changes.

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

[Regulation protrusion 1t]
The restricting protrusion 1t is intended to prevent the seat body 1 from coming off the front axle j2 unless the seat support 1 takes the jumped-up position (ph), which is the position for releasing the seat support 1 from the front axle j2.

In other words, the restricting protrusion 1t engages with the groove b14 of the support base B, and can restrict the forward movement of the seat body 1 relative to the front axis j2 when the seat body 1 is in a position other than the specified raised position (ph).

The restricting protrusions 1t are provided in pairs on the left and right in front of the recess 11 of the seat support body 1. The restricting protrusions 1t protrude inward from a location on the seat support body 1 that corresponds to the groove b14 of the support base B. The restricting protrusions 1t are inclined so that they are positioned gradually higher toward the rear. The restricting protrusions 1t protrude from the inner parts of the left and right front axle holders 1m.

<Shell body installation section 12>
The shell body mounting portion 12 has a connecting portion with the shell body 3 of the seat main body D, and is provided on the upper portion of the seat support 1, i.e., the portion of the seat support 1 facing upward.

A notch 122 is provided at the rear end of the shell body mounting section 12 to avoid interference with the operating lever k2 provided on the shell body 3.

As will be described in detail later, the shell body mounting section 12 is provided with shaped parts that form a detachable engagement structure (central positioning section G, vertical engagement mechanism H, horizontal engagement mechanism I, and reverse restriction mechanism K) that allows the seat body D to be detached.

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

The upper end of the seat support peripheral wall portion 121, which is erected inside the outer peripheral edge 1e of the seat support 1, is arranged to extend in a substantially horizontal direction when viewed from the front, back, and side.

<Recess 13>
The recess 13 is provided in the upper portion of the seat receiving body 1 for disposing the intermediate member U and the coil spring Y. The recess 13 is provided in the vicinity of the engaged portion 1k which engages with the seat engaging shaft j3.

The recess 13 is recessed downward from the central top wall portion 123, which is the upper surface portion of the seat support body 1 constituting the shell body mounting portion 12. The recess 13 is open upward and includes the other spring support portion 13a that faces upward to receive the lower portion of the coil spring Y.

The recess 13 defines an arrangement space 13s in which the intermediate member body u1 and the coil spring Y are arranged.

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

The bottom wall 131 of the recess 13 is spaced apart on the left and right so that the arm portion u2 of the intermediate member U can be disposed on the recess 11 side. In other words, the bottom wall 131 of the recess 13 is spaced apart on the left and right through the arm passage hole 14.

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

<Configuration for easily attaching and detaching the seat support 1 to and from the support base B>
The seat support 1 is rotatable about the front shaft j2 so that the rear end portion thereof can be lifted up after the intermediate member U is released. The front shaft holding portion 1m is configured to be detachable from the front shaft j2 only when the seat support 1 is changed to a predetermined lifted position (ph).

A pair of grooves b14 are provided on the left and right sides of the front of the left and right side walls b1 of the support base B, extending vertically and opening outward.

The seat support 1 is provided with a pair of inwardly protruding restricting protrusions 1t on the left and right at locations corresponding to the grooves b14 of the support base B. The restricting protrusions 1t protrude from the inner parts of the left and right front axle retaining portions 1m provided on the seat support 1.

When the seat support 1 is restricted from disengaging by the intermediate member U (i.e., when the intermediate member U is interposed between the seat support 1 and the seat engagement shaft j3), the restricting protrusion 1t is positioned within the groove b14, and the front axle holding portion 1m is configured to be unable to disengage forward from the front axle j2.

Even if the intermediate member U is not interposed between the seat receiving body 1 and the seat engagement shaft j3, if the specified jump-up position (ph) is not taken, the restricting protrusion 1t and the groove portion b14 will engage, and the front axle holding portion 1m will not be able to disengage from the front axle j2.

When the seat support 1 assumes a predetermined raised position (ph), the position is changed so that the restricting protrusion 1t is positioned outside the groove portion b14, and the front axle holding portion 1m can be released forward from the front axle j2.

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

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

A pair of coil springs Y, which are spring members, are installed on the left and right between the seat support body 1 and the intermediate member U.

The intermediate member U is disposed between the seat engagement axis j3 of the back support L, which is rotatably supported on the support base B, and the rear of the seat C, i.e., the portion near the engaged portion 1k.

The intermediate member U has a portion that engages with the seat engagement shaft j3 and a portion that engages with the seat support 1 via the coil spring Y. The intermediate member U can limit the distance of the engaged portion 1k from the seat engagement shaft j3 in the forward tilted position (ps).

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

[Intermediate member body u1]
The intermediate member body u1 is a plate-like member having a horizontally long rectangular shape as a whole. The intermediate member body u1 is provided with one spring receiving portion u11 that faces downward.

That is, a pair of spring receiving portions u11 are provided on the underside of the intermediate member body u1 to receive the upper ends of the pair of left and right coil springs Y.

[Arm portion u2]
The arm portion u2 has a downward extension portion u21 that extends downward from the front portion of the intermediate member main body u1, and a hook-shaped portion u22 that curves forward from the lower portion of the downward extension portion u21 and can engage with the lower portion of the extension seat engagement shaft j3.

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

The coil spring Y biases the intermediate member U upward using the seat support 1 as a foothold. In other words, the coil spring Y biases the intermediate member U in the direction in which it engages with the seat engagement shaft j3.

<Attachment/detachment structure of intermediate member U>
The intermediate member U can restrict the separation of the seat support body 1 from the back support body L. In other words, the intermediate member U is interposed between the back support body L and the seat support body 1 so that the rear part of the seat support body 1 does not move away from the seat engagement axis j3 by more than a certain distance.

The arm portion u2 of the intermediate member U engages with the lower portion of the seat engagement shaft j3 on the back support L, and the intermediate member body u1 of the intermediate member U engages with the seat support body 1 via the coil spring Y.

The intermediate member U is configured to be detachable at a predetermined position between the back support L and the seat support 1 without using a fastener.

In other words, the intermediate member U can be disengaged from the seat engagement shaft j3 by being pressed in a direction against the biasing force of the coil spring Y, and is configured to be removable from between the seat engagement shaft j3 and the seat support 1 when the engagement is released.

By following the steps described above in reverse, the intermediate member U can be placed at a predetermined position between the back support L and the seat support 1 without using a fastener.

<Seat body D>
The seat body D includes a seat cushion Dq, a shell body 3 for supporting the cushion, which is a support member attached to the underside of the seat cushion Dq, and a seat upholstery Dh that covers the upper part and peripheral part of the seat cushion Dq and covers the peripheral part of the shell body 3. The seat body D is provided with a seat surface on the upper surface that is substantially circular in plan view.

[Seat cushion Dq]
The seat cushion Dq is mainly made of a urethane foam material. The seat cushion Dq is formed so that the width dimension gradually increases toward the top. The lower surface of the seat cushion Dq is attached to the shell body 3.

The seat cushion Dq is shaped to fit over the shell body 3 from above. When viewed from the bottom, the seat cushion Dq is larger than the shell body 3. The dimensions of the seat cushion Dq in the front-rear and left-right directions are set to be longer than the dimensions of the shell body 3 in the front-rear and left-right directions.

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

The shell body 3 comprises a shell body main body 31 having a disk-shaped portion whose upper surface is bonded to the underside of the seat cushion Dq, a support wall portion 33 that is connected to extend downward from the peripheral edge of the shell body main body 31 and whose outer surface is in contact with the inner surface of the peripheral portion of the seat cushion Dq, an end wall portion 34 that extends diagonally upward and outward from the lower end of the support wall portion 33 and supports the lower end of the peripheral portion of the seat cushion Dq, and a peripheral wall portion 32 that is suspended downward from the underside of the peripheral portion of the shell body main body 31 inside the support wall portion 33.

The lower end of the peripheral wall portion 32 is arranged to extend substantially horizontally when viewed from the front, rear, and side.

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

The shell body main body 31 has a central protrusion g1 that protrudes downward from the center in the front-rear and left-right directions. The shell body main body 31 has a plurality of locking projection engagement portions hk that are spaced at regular intervals in the circumferential direction on the inside of the peripheral wall portion 32.

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

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

The peripheral wall portion 32 is arranged in a substantially circular ring shape when viewed from the bottom. In other words, the peripheral wall portion 32 is arranged continuously on a circular path, except for one location at the rear where the operating lever k2 is arranged, so that the peripheral wall portion 32 is located on a virtual circumferential line that forms a perfect circle centered on the central protrusion g1 when viewed from the bottom.

The peripheral wall 32 has outward extensions 321 that extend outward and restrict the downward movement of the edge de of the seating material Dh. The outward extensions 321 are protruding pieces arranged at regular intervals around the peripheral wall 32.

The peripheral wall 32 has an inwardly protruding portion it on the inner surface at three locations on the front end and both left and right end portions, i.e., the inner surface at the center of the front part of the peripheral wall 32 in the left-right direction, and the inner surface at the center of the front-rear direction on both left and right end portions of the peripheral wall 32. The inwardly protruding portion it constitutes the horizontal engagement mechanism I, which will be described in detail later.

Ribs rv are connected to the inner surface of the peripheral wall 32, which are vertically attached to the shell body main body 31 and extend outward from the center of the shell body main body 31. The ribs rv are arranged radially on the underside of the shell body main body 31.

The operating lever k2 is supported on one side by the shell body main body 31. In other words, the shell body 3 is provided with the operating lever k2, which is a cantilevered lever member that engages with the seat support 1. The operating lever k2 has a wall-like portion k21 that constitutes part of the peripheral wall portion 32 and stands upright from the base end portion of the operating end portion k22.

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

Between the base end ke and the operating end k22, the operating lever k2 has a downwardly protruding protrusion kt that can engage with the upward recess k1 provided in the seat support 1. The recess k1 of the seat support 1 and the protrusion kt of the operating lever k2 constitute the reverse movement prevention mechanism K, which will be described in detail later.

The lower end edge 3e of the support wall portion 33 of the shell body 3 is formed so as to be gradually positioned downward (so as to be convex downward) from both the left and right ends toward the center in the left-right direction in front and rear views. Also, the lower end edge 3e of the support wall portion 33 of the shell body 3 is formed so as to be gradually positioned upward (so as to be convex upward) from both the front and rear ends toward the center in the front-to-rear direction in side views.

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

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

The seating fabric Dh has a ring-shaped edge portion de. The seating fabric Dh is configured in a bag shape that is open downward. The seating fabric Dh is provided with a string-like member (not shown) for reducing the diameter of the edge portion de and bringing the edge portion de into contact with the outward surface 32m of the peripheral wall portion 32 of the shell body 3.

<<Attachment/detachment structure of seat body D to seat support 1>>
The seat body D is configured to be horizontally rotatable around a common axis cj relative to the seat support 1 between a retracted position (E) in which it can be detached from the seat support 1 and an attached position (F) in which it is attached to the seat support 1.

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

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

<Central positioning part G>
The central positioning portion G is capable of positioning the seat support 1 and the shell body 3 of the seat main body D so that they approximately coincide with the common axis cj.

The central positioning portion G is cylindrical and has a downwardly protruding central protrusion g1 provided at the center of the shell body 3 of the seat body D, and a hole-shaped central protrusion engagement portion g2 provided at the center of the seat support body 1 with which the central protrusion g1 engages so as to be able to rotate relative to the seat body D.

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

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

The seat body D can take the mounting position (F) by tightly engaging the locking protrusion hp and the locking protrusion engagement portion hk.

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

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

The locking protrusion hp can engage in the vertical direction with the guide inclined surface hm provided on the locking protrusion engagement portion hk. More specifically, the locking protrusion hp can press the guide inclined surface hm of the locking protrusion engagement portion hk downward. In other words, the locking protrusion hp moves the seat body D downward during the process of the seat body D rotating from the retracted position (E) to the attached position (F).

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

The locking projection engagement portion hk includes a support wall hs that hangs downward from the shell body main body 31, and an engagement portion main body hg that is supported by the support wall hs and has an upwardly facing guide inclined surface hm on its upper surface.

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

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

The engagement body hg is a plate-like member that is in a fallen position and extends in the circumferential direction. The inner edge and base edge of the engagement body hg are connected to the support wall hs. The upward guide inclined surface hm on the engagement body hg is inclined so as to be positioned gradually upward from the tip side toward the base end side. Here, the tip side of the engagement body hg refers to the edge side that forms the tip of the direction in which it advances when rotating from the retracted position (E) to the attached position (F).

The locking protrusions hp and guide inclined surfaces hm of the vertical engagement mechanism H configured as described above are configured to gradually increase in close contact as the seat body D rotates from the retracted position (E) to the attached position (F).

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

First, as shown in FIG. 43, the seat body D is moved downward from a position spaced above the seat support 1 while its horizontal position is positioned on the common axis cj by the central positioning part G.

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

After that, as shown in FIG. 45, when the seat body D reaches the mounting position (F), the locking protrusion hp and the locking protrusion engagement portion hk are engaged so as to be in close contact with each other in the vertical direction.

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

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

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

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

In addition, from the portion of the peripheral wall 32 where the inward protrusion it is provided, an outward extension 321 extends in the opposite direction, i.e., outward, to engage with the edge de of the seating material Dh.

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

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

The inward protrusion it and outward guide inclined surface im of the horizontal engagement mechanism I configured as described above are configured to gradually increase the degree of intimacy as the seat body D rotates clockwise from the retracted position (E) to the attached position (F).

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

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

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

The protrusion kt of the reversal prevention mechanism K is provided on a cantilever-shaped operating lever k2 provided on the shell body 3. The protrusion kt of the operating lever k2 is disengaged from the recess k1 provided on the seat support 1 by moving the operating end k22, which receives the operating force from the user's fingers, upward using the elastic deformation of the member, and the seat body D can be rotated from the mounting position (F) to the retracted position (E).

The upper surface of the rear end of the seat support 1 is provided with a guide inclined surface km adjacent to the recessed portion k1, which can engage with the protruding portion kt of the operating lever k2. The guide inclined surface km is inclined so that it gradually rises upward as it approaches the recessed portion k1. The top of the inclined surface is set to be located above the bottom of the recessed portion k1.

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

When the seat body D moves from the retracted position (E) to the attached position (F), the protruding portion kt overcomes the guide inclined surface km and engages with the recessed portion k1 due to the elastic return force of the operating lever k2.

In this embodiment, when the reversal prevention mechanism K moves from the retracted position (E) to the attached position (F), the protrusion kt is raised by the pivoting movement of the shell body 3, running up the inclined guide surface km of the seat support body 1, so there is no need to apply an operating force to the operating lever k2. At this time, when the protrusion kt of the operating lever k2 has climbed up the inclined guide surface km, the elastic return force of the operating lever k2 automatically fits into the recess k1. In other words, no special operation of the operating lever k2 is required for the reversal prevention mechanism K in the process of moving from the retracted position (E) to the attached position (F).

In addition, on both sides of the peripheral wall 32 of the shell body 3 adjacent to the operating lever k2, downward protrusions 32t are provided that extend downward to the same position as the lower end position of the operating lever k2.

These downward protrusions 32t are designed to prevent the operating lever k2 from being pushed upward by the placement surface when the seat body D or the shell body 3 is placed independently on a placement surface such as a floor surface for the purpose of using it as a replacement part, etc.

In other words, the downward protrusions 32t provided on the left and right sides of the operating lever k2 can suppress the operating lever k2 from being pushed up by the placement surface, which can effectively prevent the operating lever k2 from developing a bending tendency that would impair the intended elastic deformation.

The back support L of this embodiment is described in detail below.

<<Back support L>>
The back support L is interposed between the support base B and the backrest M. The back support L can operably support the backrest M between a normal position (ps) and a rearward tilted position (pr) tilted further backward than the normal position (ps).

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

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

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

The back support L supports left and right operating members p1 that can be changed between an engagement position (U) in which the backrest M is engaged and a retracted position (N) in which the backrest M is retracted. The left and right operating members p1 constitute a disengagement prevention mechanism P, which will be described in detail later.

<Back support base 4>
The back support base 4 comprises a pair of left and right arms 41 each having an upright plate shape extending in the front-to-rear direction and rotatably supported on the support base B via a main shaft j1 which is an axis, a connecting member 42 having an upright plate shape connecting the rear portions of the pair of left and right arms 41, and a seat engagement shaft j3 extending in the left-right direction and supported at a position forward of the main shaft insertion hole 41a of the pair of left and right arms 41.

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

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

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

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

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

The connecting member 42 is provided with a nut portion n3 into which a screw v3 for attaching the back support body 5 is screwed. 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 connecting member 42, and is fastened by the screw v3.

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

The seat engagement shaft j3 is disposed in front of and above the main shaft j1. The seat engagement shaft j3 pushes up the middle part of the seat C in the front-rear direction upward and backward 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 part of the seat C is lifted upward by the pushing action of the seat engagement shaft j3 on the seat C.

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

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

When the backrest M tilts backward due to the weight of the seated person, the back support L7 supporting the backrest E rotates around the main axis j1 supported by the support base B.

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

The seat engagement shaft j3, which is connected to the upper part of the left and right front arm sections 412, moves upward and backward in the same manner as the left and right front arm sections 412 move.

The seat engagement shaft j3 moves upward and backward to lift the seat C upward against the seating load of the seated person.

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

The base end 51 is equipped with a back support base connecting part 5a that is connected to the back support base 4, and left and right arm parts 5d that form an inward channel shape that extends linearly forward from both the left and right sides of the back support base connecting part 5a and can restrict the outward movement of the main shaft j1 at the front.

The back support base connecting portion 5a is provided with a pair of left and right fitting holes 5b which are open forward and engage with the rearward protruding portion 41b protruding from the rear end portion of the back support base 4, and a connecting wall 5c which is disposed between the pair of left and right fitting holes 5b and is attached to the connecting member 42 of the back support base 4.

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

The left and right arm portions 5d extend in the front-rear direction along the outer side of the arm body 411 of the back support base 4. The front portions of the left and right arm portions 5d are located outside the axial direction of the main shaft j1 that protrudes outward from the left and right side walls b1 of the support base B. The left and right arm portions 5d regulate the main shaft j1 so that it does not slip out of the support base B.

The main shaft j1 is simply a cylindrical shape extending in the left-right direction. In this embodiment, the main shaft j1 is not directly provided with a positioning means (for example, a retaining ring attached to the end of the shaft, or a flange-shaped portion formed on one end of the shaft), but is simply positioned relative to the support base B using the arm portion 5d of the back support body 5 of the back support L.

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

The upper frame portion 53 is partially annular and curved to form a convex rearward shape in plan view. The upper frame portion 53 cooperates with the cover member 6 that forms the upper half of the half-split shape that corresponds to the upper frame portion 53 to form a circular shape with both left and right end faces facing forward, and the overall outer shape is a cylinder curved into a partially annular shape.

In other words, the upper frame portion 53 constitutes the lower half of a cylindrical exterior shape curved in a partially annular shape. In other words, the upper frame portion 53 and the cover member 6 constitute the upper frame body 5a, which has circular forward end faces at both the left and right ends, is curved to be convex rearward in a plan view, and has an overall generally cylindrical shape curved in a partially annular shape.

The upper frame portion 53 is provided with a number of screw insertion holes h1 through which screws v1 are inserted to attach the cover member 6 to the upper frame portion 53, penetrating vertically.

The rear side of the upper frame portion 53 is provided with a rear biasing member engaging portion 532 having a recessed shape that supports the rear portion of a coil spring p3, which is a biasing member that biases the operating member p1 forward, i.e., in the direction of the engaged posture (U).

A boss portion 533 is provided on the upper frame portion 53, and a screw member v2 is screwed into the boss portion 533 to regulate the vertical movement of the operating member p1. The boss portion 533 and the screw member v2 constitute the vertical movement regulation portion 53k.

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

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

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

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

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

The front side of the cover member 6 is provided with a notch 6k for exposing the operated portion p13 of the operating member p1. The notch 6k is provided adjacent to the inside of the window frame portion 6w.

The back support L having the above configuration is covered and concealed by a front back support cover X2 and a rear back support cover X3 made of synthetic resin.

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

The rear support cover X3 is attached so that the screw v3 for attaching the back support body 5 to the back support base 4 is not exposed on the rear side. The rear support cover X3 covers the rear of the back support base connecting part 5a located between the left and right standing frame parts 52 and provided at the base end part 51 of the back support body 5. Both side ends of the rear support cover X3 are designed to be connected to the rear ends of the front support cover X2.

The backrest M of this embodiment is described in detail below.

<<Backrest M>>
The backrest M is a generally horizontally elongated rectangular shape with both left and right ends rounded. The backrest M has a backrest surface on the front side against which the back of a seated person can abut. The backrest M in this embodiment is configured to be detachable from the back support L by a simple operation by the user. The backrest M has a backrest main body 7, which is a structural body, and a back upholstery 8, which is a covering body that can cover the backrest main body 7.

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

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

The inside of the accommodation groove 7m, i.e., the inner surfaces of the pair of groove forming walls 7f, 7r, are provided with a number of engagement protrusions t(f), t(r). Both of the pair of groove forming walls 7f, 7r are provided with engagement protrusions t(f), t(r) that protrude forward or backward.

In this embodiment, the engagement protrusions t(f), t(r) are provided alternately on both groove forming walls 7f, 7r arranged to face each other in the extension direction of the accommodation groove 7m. In other words, the engagement protrusions t(f) of one groove forming wall 7f and the engagement protrusions t(r) of the other groove forming wall 7r are provided alternately from one end to the other end in the longitudinal direction of the accommodation groove 7m so that they do not collide.

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

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

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

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

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

A space capable of accommodating the backrest body 7 is formed inside the back upholstery body 80. A lower opening 8k is formed at the lower end of the back upholstery body 80, i.e., between the lower end of the front covering part 8f and the lower end of the back covering part 8r, and is open downwards to allow the backrest body 7 to be inserted into the internal space.

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

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

Through holes 8t are formed at two locations on the left and right of the rear covering portion 8r, at positions corresponding to the protrusions q1 protruding from the rear side of the backrest body 7.

The ring-shaped member T is made of a flexible synthetic resin sheet material in the shape of a square frame with a hole th in the center. The ring-shaped member T is configured to be flexible. The ring-shaped member T is sewn to the through-hole periphery 8e in the back-side covering portion 8r. In the installation completion position (Ta), the back-side covering portion 8r covers the ring-shaped member T so that everything except the hole th cannot be seen from the outside.

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

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

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

The first and second belt-shaped members 81, 82 are overlapped with each other and inserted together into the storage groove 7m.

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

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

In addition, the engagement protrusions t(f) protruding from one groove forming wall 7f and the engagement protrusions t(r) protruding from the other groove forming wall 7r are arranged alternately along the extension direction of the storage groove 7m, so that the first and second belt-shaped members 81, 82 can be smoothly inserted into the storage groove 7m without excessive interference from the engagement protrusions t(f), t(r).

<<Method of forming opening 8s in back upholstery 8 (covering body)>>
An opening 8s is provided in the back upholstery 8. The opening 8s includes a back covering portion 8r, which is a fabric material having a through hole 8t, and an annular member T that has a continuous ring shape and is attached to the through hole peripheral portion 8e and is disposed so as not to be visible from the outside without impairing the front-rear communication function of the hole portion th.

In this embodiment, the opening 8s in the back upholstery 8 is formed through a preparation process S1, an outer surface side attachment process S2 of the annular member, a first annular member inversion process S3, and a second annular member inversion process S4, as shown below.

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

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

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

In this embodiment, the annular member T in the initial position (Tb) is sewn to the through-hole peripheral portion 8e while being pressed against the outer surface of the through-hole peripheral portion 8e. In other words, the annular member T in the initial position (Tb) is fixed to the outer surface of the through-hole peripheral portion 8e via the sewn portion tx.

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

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

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

In this embodiment, by going through the method of forming the opening 8s in the back upholstery 8 (covering body) that includes each of the steps described above, an opening 8s is formed in the rear covering portion 8r of the back upholstery 8, reinforced by the annular member T in the installation completion position (Ta) that is inverted 360° from the initial position (Tb).

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

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

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

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

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

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

The protrusion q1 is provided with a wall-shaped engaging portion q11 that extends vertically in rear view, with the width dimension gradually decreasing downward and positioned gradually rearward in side view, and a connecting portion q12 that connects the backrest body 7 and the left-right middle portion of the wall-shaped engaging portion q11 and is provided so that the front-rear dimension gradually increases downward. The upper end of the wall-shaped engaging portion q11 is connected to the backrest body 7.

The protrusion q1 is provided below the engaged portion p2 that constitutes the anti-detachment mechanism P recessed in the backrest body 7.

[Recess q2]
The recess q2 is provided on the front side of the upper end of the left and right standing frame parts 52 constituting the back support L. The recess q2 is open upward. The recess q2 is designed to fit the protrusion q1 of the backrest M inserted from above.

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

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

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

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

<Release prevention mechanism P>
The separation prevention mechanism P is provided between the back support L and the backrest M and prevents the backrest M from separating from the back support L.

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

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

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

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

The position of the operating member p1 can be changed from the engaged position (U) to the retracted position (N) by pressing the operated part p13 backward with the user's finger. In other words, the user can move the operating member p1 to the retracted position (N) by pressing the operated part p13 backward like a push button.

As shown in FIG. 27, a space sp is provided between the back support L and the backrest M into which fingers can be inserted. The operated part p13 is disposed in a position facing the space between the back support L and the backrest M. This allows the user to effortlessly press the operated part p13 like a push button.

In addition, 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 L and the backrest M. In other words, the outer surface of the operated portion p13 and the outer surface of the cover member 6 are configured to be substantially flush with each other. Therefore, although the operated portion p13 is arranged so as to be operable from the outside, it is arranged in an inconspicuous location and has a substantially flush form so as to be less noticeable in relation to the cover member 6.

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

The engaged parts p2 are provided in pairs on the left and right sides of the backrest M. The engaged parts p2 are recessed on the back side of the backrest main body 7 so as to open backward. The engaged parts p2 recessed in the backrest main body 7 are exposed to the outside through an opening 8s in the back upholstery 8.

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

After the backrest M is positioned in the correct mounting position by the positioning mechanism Q, when the engaging portion p11 of the operating member p1 engages with the engaged portion p2, the backrest M cannot move upward relative to the back support L, and as a result, it is prohibited from being detached from the back support L.

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

The weight-sensing rocking mechanism includes a mechanism for lifting the seat C upward against the weight of the seated person, so a backward tilt load proportional to the seated person's weight is required to tilt the backrest M backward.

The weight-sensing rocking mechanism is mainly composed of a support base B supported by legs A, a seat C arranged on the support base B and supported at its front by the support base B via a front axle j2, a back support L rotatably supported on the support base B via a main axle j1 and arranged in front of and above the main axle j1, having a seat engagement axle j3 that can engage with the front-to-rear center of the seat C and is biased forward by a reaction force generator R, a backrest M supported by the back support L, and a reaction force generator R that is arranged between the support base B and the back support L and can apply a reaction force to the backward tilting movement of the backrest M.

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

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

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

In addition, in the above-described embodiment, the seat body D is configured to be horizontally rotatable about the common axis cj relative to the seat support 1 between a retracted position (E) in which the seat body D can be detached from the seat support 1 and an attachment position (F) in which the seat body D is attached to the seat support 1. This makes it possible to provide a chair with a suitable configuration in which the seat body D can be easily attached and detached from the seat support 1 without using special tools.

In the above-described embodiment, the peripheral wall portion 32 is provided on the periphery of the shell body 3 and has an outward surface 32m against which the edge portion de of the seating fabric Dh can abut, and is arranged in a substantially annular shape when viewed from the bottom. This makes it possible to provide a chair in which the edge portion de of the seating fabric Dh covering the seat cushion Dq can be suitably abutted against the peripheral wall portion 32 of the shell body 3 with a substantially uniform pressing force.

In the above-described embodiment, the backrest body 7, which is the main structure, is provided with a storage groove 7m with engaging protrusions t(f), t(r), and the back upholstery 8 is provided with first and second belt-shaped members 81, 82 with through holes 81a, 82a that engage with the engaging protrusions t(f), t(r) of the storage groove 7m. This makes it possible to provide a chair with a configuration that allows the edge of the back upholstery 8 to be easily and less likely to come loose and be attached to the storage groove 7m of the backrest body 7, which is the main structure.

The above-described embodiment can provide a method for suitably forming a reinforced opening 8s with a desirable appearance in the back upholstery 8, which is a covering that can cover a member. The above-described embodiment can provide a chair that is applicable to the back upholstery 8, etc., and has a covering with a reinforced opening 8s with a desirable appearance.

In the above-described embodiment, the front part of the seat C can rotate relative to the support base B so that it can take a normal position (ps) and a forward-leaning position (pf), and an intermediate member U is provided between the back support L supported by the support base B and the rear part of the seat C (the part behind the front part of the seat C) to limit the distance between them.

As a result, it is possible to provide a chair that is configured so that the seat C can suitably assume a normal position (ps) and a forward-leaning position (pf) without providing a complex mechanism at the front of the seat C.

In the above-described embodiment, a reaction force generating body R capable of directly biasing the seat engagement shaft j3 forward is disposed between the seat engagement shaft j3 and the support base B, and this reaction force generating body R is set to assume a substantially horizontal position extending in the front-to-rear direction in the normal position (ps). As a result, it is possible to provide a chair that allows excellent design freedom for miniaturizing the support base B and the seat C in a chair that can perform rocking motion between the normal position (ps) and the backward tilt position (pr).

In addition, in the above-described embodiment, the intermediate member U that can prevent the seat support 1 from coming off the back support L is detachably arranged without using a fastener. This makes it possible to provide a chair in which the seat support 1 can be easily attached and detached from the support base B.

In addition, in the above-described embodiment, when the support member W supporting one end of the reaction force generating body R is removed from the support base B using the screw v5, the reaction force generating body R is gradually weakened as it moves while being guided by the inclined surface nm, making it possible to provide a chair that allows the reaction force generating body R to be conveniently attached to and detached from the support base B.

In the above-described embodiment, a screw hole n4 having a threaded groove is disposed above the fitting hole Ba in the support base B, and the screw v4 screwed into the screw hole n4 is configured to press the upper part of the leg support a2 downward. This makes it possible to provide a chair with a configuration that can suitably release the fitting state between the upper part of the leg support a2 and the fitting hole Ba of the support base B.

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

As described above, the chair according to this embodiment comprises a leg A having a leg support a2 extending in the vertical direction, a support base B having a fitting hole Ba passing through in the vertical direction that fits into the upper part of the leg support a2, and a seat C disposed on the support base B.

The chair is configured such that a screw-receiving hole n4 having a threaded groove is disposed above the fitting hole Ba in the support base B, and the upper part of the leg support a2 can be pressed downward by a screw v4 that is screwed into the screw-receiving hole n4.

Therefore, this embodiment can provide a chair with a configuration that can suitably release or relax the tight fit between the upper part of the leg support a2 and the fitting hole Ba of the support base B by using the screw v4 to thread in and out.

The screw hole n4 penetrates in a substantially vertical direction.

As a result, the screw v4 screwed into the screw hole n4 is preferably screwed in and enters vertically downward, so that the upper part of the leg support a2 can be preferably pressed in the vertical direction, which tends to release or relax the tight fit with the fitting hole Ba.

The leg support a2 is configured to include a gas cylinder ag that can adjust the vertical position of the seat C.

The gas cylinder ag is provided with a cylinder portion a21, a lifting rod a22 that can be raised and lowered relative to the cylinder portion a21, and an actuating member a23 that protrudes from the upper end of the lifting rod a22 and causes the lifting rod a22 to be able to be raised and lowered when pressed downward.

The screw v4 screwed into the screw hole n4 can press downward on the upper end of the lifting rod a22, which is the upper part of the leg support a2.

As a result, the screw v4 presses down on the lifting rod a22 on the leg support a2, which is configured to be vertically extendable and contractible, and can suitably release or relax the engagement between the upper part of the leg support a2 and the engagement hole Ba of the support base B.

The support base B is made of metal and has a bottom wall portion 2 in which a fitting hole Ba is formed, and a rising structure portion 2S having a screw-threading hole n4 is integrally provided on the periphery of the fitting hole Ba.

For this reason, the metallic raised structure 2S having the screw hole n4 has a rigidity that makes it difficult for it to move relative to the bottom wall 2, and it can suitably support the screw v4 screwed into the screw hole n4.

The rising structure 2S is provided in front of the fitting hole Ba.

For this reason, the rising structure 2S is provided in a suitable position that can easily avoid various components (e.g., reaction force generator R, back support L, etc.) that are likely to be arranged at the rear of the fitting hole Ba in the support base B.

The rising structure 2S has a rising portion 25 that rises so as to partially surround the fitting hole Ba in a plan view, and a horizontal portion 26 that is installed between the rising portions 25 so as to be located directly above the fitting hole Ba. A screw-threading hole n4 is provided in the horizontal portion 26 of the rising structure 2S.

For this reason, the screw-in hole n4 is preferably located directly above the fitting hole Ba.

In this embodiment, a fit relief structure is provided that reduces the fit between the leg support a2 and the support base B.

The fitting degree relaxation structure is such that a screw hole n4 having a threaded groove is disposed above the fitting hole Ba in the support base B, and the upper part of the leg support a2 can be pressed downward by a screw v4 screwed into the screw hole n4.

Therefore, this embodiment can provide a structure that can suitably alleviate the tight fit between the upper part of the leg support a2 and the fitting hole Ba of the support base B.

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

Of course, any tool can be used to thread the screw into the screw hole.

The screw threading hole only needs to be disposed above the fitting hole in the support base, and various specific configurations for disposing it above the fitting hole can be set.

For example, a raised structure with a screw hole may be provided so as to straddle the fitting hole of the support base.

The screw that is screwed into the screw hole only needs to be capable of pressing the upper part of the leg support downward, and the specific location can be set as appropriate.

The screw threading hole may penetrate in the vertical direction, but may not penetrate in an approximately vertical direction.

The leg support may not be configured to be extendable in the vertical direction.

The leg support does not have to include a gas cylinder that can adjust the vertical position of the seat.

The specific structure of the raised structure can be set as appropriate.

For example, the rising structure may be made separately from the support base. In other words, the rising structure may be provided separately from the support base, and the rising structure may be configured to be attached to the support base during dismantling.

Furthermore, the specific configuration of each part is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention.

A...Leg B...Support base C...Seat a2...Leg support Ba...Fitting hole 2s...Rising structure n4...Screw hole v4...Screw

Claims (7)

A chair comprising legs having leg supports extending in the vertical direction, a support base provided with a fitting hole passing through in the vertical direction and fitting into an upper portion of the leg support, and a seat disposed on the support base,
a screw hole having a thread groove is disposed on the fitting hole of the support base,
The chair is configured so that the upper part of the leg support can be pressed downward by a screw screwed into the screw hole. The chair according to claim 1, wherein the screw hole penetrates in a substantially vertical direction. The leg support is configured to include a gas cylinder capable of adjusting the vertical position of the seat,
the gas cylinder comprises a cylinder portion, a lifting rod capable of moving up and down relative to the cylinder portion, and an actuating member that is protruding from an upper end of the lifting rod and that, when pressed downward, causes the lifting rod to be in a state capable of moving up and down;
2. The chair according to claim 1, wherein a screw screwed into the screw hole can press an upper end of the lift rod downward. the support base is made of metal and has a bottom wall portion in which the fitting hole is formed,
2. The chair according to claim 1, wherein a raised structure having said screw hole is integrally provided on the periphery of said fitting hole. The chair according to claim 4, wherein the raised structure is provided in front of the fitting hole. the rising structure portion includes a rising portion rising so as to partially surround the fitting hole in a plan view, and a horizontal portion bridged between the rising portions so as to be located directly above the fitting hole,
5. The chair according to claim 4, wherein the screw holes are provided in the cross members. A fitting degree relaxation structure is provided on a chair including a leg having a leg support extending in a vertical direction and a support base having a fitting hole penetrating in a vertical direction that fits into an upper portion of the leg support, the fitting degree relaxation structure relaxing the fitting degree between the leg support and the support base,
A screw-receiving hole having a threaded groove is arranged above the fitting hole in the support base, and a screw that is screwed into the screw-receiving hole can press the upper part of the leg support downward.This is a fitting degree relaxation structure.

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