JP5259995B2 - Chair - Google Patents

Description

  The present invention relates to a chair that supports a seat body by a pair of left and right seat frames provided on the upper part of the leg body.

In a conventional chair, the left and right sides of the seat are supported by the upper surfaces of a pair of left and right brackets that are fixed to the upper part of the leg and facing the front and rear, and both sides of the seat are attached to the brackets by screws. Some are fixed (see, for example, Patent Document 1).
JP 2006-187534 A

  In the chair described in Patent Document 1, since the left and right sides of the seat body are supported and fixed by the pair of left and right brackets, the left and right sides of the seat body that are not supported by the left and right brackets. The central portion of the direction may be excessively bent downward, or a large load may be applied to the mounting portion between the bracket and the seat body.

In order to prevent this, increase the rigidity of the seat by increasing the thickness of the seat, especially the seat plate to which the cushioning material is attached, or by firmly attaching the seat plate to the bracket. It is necessary to increase the bending strength of the part.
However, if this is done, the thickness of the seat plate will increase, the vertical dimension of the entire seat body will increase, the appearance of the chair will be impaired, the manufacturing cost of the seat plate will increase, and the seat on the bracket will increase. This increases the man-hours for mounting the plate.

  The present invention has been made in view of the above problems, and without increasing the thickness of the seat plate or increasing the attachment strength to the seat frame that supports both sides of the seat plate. The object is to provide an inexpensive and good-looking chair that can increase the bending rigidity.

According to the present invention, the above problem is solved as follows.
(1) Both side end portions of the bottom plate are fixed to the upper surfaces of a pair of left and right seat frames facing the front-rear direction fixed to the legs, and on the upper surfaces of the left and right seat frames outside the fixed portions. The lower surface of both side ends of the flexible seat plate disposed above the bottom plate is placed, and the inner portion of the seat plate from the seat frame is fixed to the upper surface of the bottom plate.

(2) In the above item (1), a downward protruding portion whose lower end is in contact with the upper surface of the seat frame is provided on the lower surface of the side end portion of the seat plate.

(3) In the above item (1) or (2), a concave stepped portion that opens upward and inward is formed on the upper surfaces of the left and right seat frames, and a bottom plate is formed on the upper surface of the concave stepped portion. While fixing a side edge part, the side edge part of a seat board is fitted and mounted.

(4) In any one of the above items (1) to (3), a bolt inserted into the side end portion of the bottom plate from above is screwed into the screw hole to be provided on the upper surface of the seat frame. Fix the side edge of the bottom plate to the top surface.

(5) In any one of the above items (1) to (4), a protrusion having a female screw hole is provided on the lower surface of the seat plate, and a bolt inserted from below the bottom plate is inserted into the female screw hole. The seat plate is fixed to the bottom plate by screwing.

(6) In any one of the above items (1) to (5), a plurality of reinforcing ribs whose lower ends are in contact with the upper surface of the bottom plate protrude from the lower surface of the seat plate.

(7) In any one of the above items (1) to (6), the bottom plate is made of sheet metal, and the reinforcing plate is fixed to the center of the top surface.

According to the invention described in the above item (1), since the load applied to the seat plate is received and supported by the bottom plate, the bending rigidity of the central portion of the seat plate is increased, and the portion is excessively bent downward. Is prevented. Therefore, it is not necessary to increase the bending strength by increasing the thickness of the seat plate or to firmly fix the seat plate to the seat frame, and the manufacturing cost and the number of mounting steps of the seat plate are reduced.

Further, since the vertical dimension of the entire seat including the seat plate can be reduced, the appearance of the chair is improved.
Further, since the side edge of the seat plate is simply placed on the seat frame and is not fixed to the seat frame, the entire seat plate is easily bent downward, and the seating comfort is improved.
Since the bottom plate is separately fixed to the seat frame and the inner portion of the seat frame from the seat frame is separately fixed to the bottom plate, the load applied to the seat plate is distributed to the two mounting portions. Concentration on the location is prevented.
Since the left and right seat frames are connected by the bottom plate, the both seat frames are prevented from wobbling in the left-right direction.

According to the invention described in the above item (2) , the gap is formed between the lower surface inward of the downward projecting portion of the seat plate and the upper surface of the side end portion of the bottom plate. When the end portion is fixed to the upper surface of the seat frame using a bolt, the head portion of the bolt can be fixed without causing interference with the lower surface of the seat plate.

According to the invention described in (3) above , the seat plate is easily positioned in the left-right direction with respect to the seat frame, and the seat plate is not displaced in the left-right direction. The seat plate can be stably attached to the left and right seat frames.
In addition, since the side edges of the bottom plate and the seat plate are attached to the upper surface of the recessed stepped portion of the seat frame, the rear plate and the seat plate do not protrude significantly above the seat frame, improving the appearance. To do.

According to the invention described in the above item (4), since the side end portion of the bottom plate can be fixed only with bolts from above the seat frame, workability is good.

According to the invention described in (5) above , after the bottom plate is fixed to the seat frame, the seat plate can be easily fixed to the bottom plate with only the bolt inserted from below the bottom plate. Since the bolt head is located below the bottom plate, it is inconspicuous.
Even if a cushion material is attached to the upper surface of the seat plate, it can be conveniently screwed from below the bottom plate.

According to the invention described in the above item (6) , since the bending rigidity of the seat plate is increased, the entire thickness of the seat plate excluding the reinforcing rib can be reduced, and material costs and the like are saved.

According to the invention described in the above item (7) , since the central portion of the bottom plate is reinforced by the reinforcing plate and the bending rigidity is increased, an inexpensive bottom plate having a small thickness can be used and the weight can be reduced. Can be planned.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view of a lobby chair to which the present invention is applied and which includes a plurality of (in the embodiment, two) single chairs 1 (the right chair has a backrest with a backrest removed). These are the center longitudinal cross-section expansion side views of the single chair 1. FIG.

  A leg 2 supporting each chair 1 is formed between a pair of left and right support legs 3 and 3 made of an aluminum alloy having a mountain shape in a side view and expanding at an obtuse angle in the front-rear direction, and between the upper ends thereof. It consists of a horizontal rod 4 made of a horizontal steel tube. Openings at both side ends of the reed 4 are closed by the cap 5 in a good appearance.

  Each chair 1 stands upright with a seat frame 6a facing forward, a bent portion 6b having a concave curved shape in side view provided continuously at the rear end thereof, and tilted slightly rearward from the upper end of the bent portion 6b. A pair of left and right side frames 6, 6 having a substantially forward L-shape in a side view including a back frame 6 c bent backward is provided.

The seat frame 6a of each side frame 6 is gradually thickened toward the rear, and a mounting portion 7 protrudes downward from the lower surface of the rear end portion, and the lower end portion thereof has a U-shape that faces downward. A shaped fitting groove 8 is formed.
The outer side frame 6 in each chair 1 is coupled to the left and right support legs 3 and the reeds 4 in the leg 2 as follows.

  In the side frames 6 and 6 on the outer sides, the lower half portions of both ends of the horizontal bar 4 are fitted into fitting grooves 9 formed in the tops of the left and right support legs 3 in an upward U-shape. Fit the fitting groove 8 of the mounting portion 7 of the seat frame 6a into the upper half of both ends of the horizontal flange 4 so that a slight gap is formed between the top end of the support leg 3 and the lower end of the mounting portion 7. Combine.

  Next, the front and rear two bolts 10 and 10 inserted from below the top of the support leg 3 are screwed into the two front and rear female screw holes 11 and 11 provided in the mounting portion 7 of the seat frame 6a and tightened. As a result, the left and right support legs 3, 3, both side end portions of the reed 4, and the outer side frame 6 are integrally coupled.

  The side frames 6 and 6 on the inner side of each chair 1, after fitting the mounting portion 7 of the seat frame 6 a to the upper half of the horizontal frame 4, The fitting metal fitting 12 that is U-shaped when viewed from the side is tightened by screwing a bolt inserted from below the fitting metal fitting 12 into a female screw hole (both not shown) in the same manner as described above. Thus, it is fixed to the central portion of the reed 4 (see FIG. 1).

The bent portions 6b of the left and right side frames 6 and 6 in each chair 1 are connected by a connecting member 13 made of an aluminum alloy or the like as follows.
As shown in FIG. 2, the connecting member 13 faces the left and right directions and has a flat plate-like base piece 13a that is curved in a downwardly concave shape with substantially the same curvature as the bent portion 6b, and its front end edge faces slightly rearward and downward. It consists of a downwardly extending piece 13b provided continuously, and on the lower surface (only one is shown) of both end portions of the base piece 13a, two front and rear protrusions 14 and 14 facing obliquely backward and downward are integrally projected. It is installed.

  As shown in the enlarged cross-sectional view of FIG. 3, the left and right side frames 6 project in an opposing manner at an intermediate portion in the vertical direction of the inner surface of the bent portion 6 b (symmetrically and in the same shape, only one is shown). Mounting screws provided on both inwardly projecting pieces 15 and inserted into the through holes 16 from below with the upper ends of the two front and rear inwardly projecting pieces 15 and 15 in contact with the lower ends of the projecting parts 14 and 14. By screwing the upper end portion of 17 into the female screw hole 18 of the protrusion 14, both end portions of the connecting member 13 are formed on the upper surfaces of the bent portions 6 b of the left and right side frames 6 on their opposing surfaces. The bent portions 6 b of the left and right side frames 6 are connected to each other by the connecting member 13.

As described above, when the bent portions 6 b in the left and right side frames 6 are connected to each other by the connecting member 13, the bending load applied to the bent portion 6 b is also distributed and added to the connecting member 13. Accordingly, the bending rigidity of the bent portion 6b is increased, and even when a large bending load from the backrest 19 described later is applied to the bent portion 6b, the strength of the portion is sufficiently maintained, and the backrest 19 is supported by the left and right back frames 6c. Can be stably supported.
Further, since the inwardly protruding piece 15 of the bent portion 6b and the protruding portion 14 on the lower surface of the side end portion of the connecting member 13 are fixed by the mounting screw 17, the bent portion 6b and the side end portion of the connecting member 13 are fixed. The sectional shape of the portion becomes large, and the bending rigidity of the bent portion 6b can be further increased.

A backrest 19 is attached to the back frame 6 c of the left and right side frames 6 of each chair 1.
The backrest 19 includes a rear plate 20 made of a sheet metal punching plate, a synthetic resin back plate 21 that can be elastically deformed in the front-rear direction, and a backrest made of a cushion material attached to the front surface of the back plate 21. It consists of 22.

  The rear plate 20 is sized to block the rear portion between the opposing surfaces of the bent portion 6b and the back frame 6c in the left and right side frames 6, 6, and the left and right side end portions thereof are as shown in FIGS. The mounting groove 23 having an inwardly U-shaped cross-section in plan view and formed in the opposite surface of the bent portion 6b of the both side frames 6 and the back frame 6c and opening inwardly with a groove width larger than the plate thickness of the rear plate 20. It is attached so as to be sandwiched by both side frames 6 at the rear end portion between the left and right side frames 6, 6 by being fitted (symmetrically attached, only one is shown).

The back plate 21 is formed in a shape that conforms to the shape of the front surface of the side frame 6, and, as shown in FIG. 7, reinforcing ribs 24 that form a lattice shape project from the rear surface.
Further, in the central portion of the rear surface of the back plate 21, that is, the central portion slightly above the portion where the back of the seater hits strongly during normal use, and the left and right side portions near the upper end portion above it, Four protrusions 25 having a larger projecting dimension than the reinforcing ribs 24 and a pair of left and right protrusions 25 are provided so as to protrude rearward.
Further, as shown in FIG. 9, on the left and right sides of the rear surface of the back plate 21 on the upper side, downward hook-like locking hooks 26 and 26 that open to the left and right sides and downward (only one in FIG. 9). (Shown) is provided.
On both sides of the lower end of the back plate 21, a pair of left and right daruma-shaped engagement holes 27, 27 are formed (see FIG. 8).

The back plate 21 is attached to the front surfaces of the left and right side frames 6 as follows.
As shown in FIGS. 3 to 6, the inner upper surface of the bent portion 6b and the inner front surface of the back frame 6c in the left and right side frames 6 are L-shaped in plan view and are rearwardly downward and rearward. A recessed step 28 (symmetrically attached, only one side frame is shown) is formed continuously in the vertical direction. As shown in FIGS. 6 and 8, the recessed portion of the back frame 6c is recessed. A stepped screw 29 with an enlarged diameter head is screwed to the lower end of the stepped portion 28.
Further, as shown in FIG. 9, locking protrusions 30 project inwardly on the inner surface of the left and right side frames 6 (only one is shown) near the upper side of the back frame 6c.

  The left and right locking hooks 26 of the back plate 21 are engaged with the locking protrusions 30 of the left and right side frames 6 from above, and the back plate 21 is connected to the stepped screws 29 of the left and right side frames 6. The left and right engagement holes 27 are dropped and engaged, so that the back plate 21 and the backrest 22 are fitted to the recessed step portions 28 of the left and right side frames 6 at their both side ends. Installed.

  As shown in FIGS. 4 and 9, the setscrew 31 inserted from below into the rearward bent portion 6 d connected to the upper ends of the left and right side frames 6 is connected to the upper end of the back plate 21. The back plate 21 is prevented from coming off upward by being screwed into the female screw holes 32 on the lower surfaces of both end portions of the curved portion 21a. In addition, as shown in FIG. 1, the lower end front portion of the backrest 22 attached to the front surface of the back plate 21 is positioned in front of the upper end portion of the connecting member 13, thereby bending the left and right side frames 6. The open space formed between the upper end portions of the portion 6 b is closed by the upper end portion of the connecting member 13 and the lower end portion of the backrest 22.

  When the back plate 21 is attached to the left and right side frames 6 as described above, as shown in FIGS. 1 and 5, the rear ends of the plurality of protrusions 25 protruding from the rear surface of the back plate 21 are The back plate 21 is pressed against the front surface of the face plate 20 so that it is slightly pressed backward, and the rear surface of the other back plate 21 is separated from the front surface of the rear plate 20, and a gap S is formed between the opposing surfaces. It has become so.

In this case, the rear plate 20 is slightly pressed rearward by the protrusions 25, so that even if the groove width of the mounting groove 23 of the side frame 6 is larger than the plate thickness of the rear plate 20, In this case, it is possible to prevent the rear plate 20 from rattling in the front-rear direction and the occurrence of rattling between the rear plate 20 and the back plate 21 to generate contact noise or the like. Moreover, since the groove width of the attachment groove 23 is larger than the plate thickness of the rear plate 20, the rear plate 20 can be easily attached.
Further, the portion of the back plate 21 excluding the protrusion 25, particularly the back plate 21 slightly lower than the central portion where the back strongly contacts during normal use, is moderately rearward within the gap S. Since it can bend, a comfortable sitting comfort can be obtained.

Furthermore, since the load when the backrest 19 is strongly pressed by the entire back is received and supported by the rear plate 20 through each protrusion 25, the entire backrest 19 including the back plate 21 is excessively bent backward. There is no fear.
Since the pair of left and right protrusions 25 on the upper end are provided above the locking hook 26 and are pressed against the rear plate 20, the portion of the back plate 21 positioned above the locking hook 26 is It is prevented from rattling in the front-rear direction away from the rear plate 20.
That is, when the lower portion of the back plate 21 bends backward, the back plate 21 above the locking hook 26 part tends to float forward, but the protrusions are located above the locking hook 26. Since 25 is always in pressure contact with the rear plate 20, the upper portion of the back plate 21 is less likely to be separated from the front surface of the rear plate 20.

  The rear plate 20 is attached by fitting both end portions thereof to fitting grooves 23 formed on the opposing surfaces of the left and right side frames 6 and does not use fixing means such as screws. There is also good work efficiency when removing and separating.

  Since the back plate 21 and the backrest 22 are fitted in the recessed step portions 28 on the front surfaces of the left and right side frames 6, they are not displaced in the left and right directions. It can be installed stably.

A seat body 33 is attached to the seat frames 6 a of the left and right side frames 6 in each chair 1.
As shown in FIGS. 2 and 10 to 13, the seat body 33 is attached to the upper surface of the seat plate 35, the bottom plate 34 made of sheet metal, the seat plate 35 made of synthetic resin attached to the upper surface thereof, and the seat plate 35. The cushion material 36 is used.

As shown in the perspective view of FIG. 14, the bottom plate 34 is folded upward so that the front end portion (the upper left side is obliquely forward) is slightly inclined forward and downward, and the front end forms an inverted L-shape facing backward as viewed from the side. A curved flat plate is formed, and a reinforcing plate 37 is fixed to the center of the upper surface by spot welding or the like.
The left and right sides of the bottom plate 34 are bent slightly upward so that the lateral width gradually increases toward the rear end.

  The seat plate 35 has a left-right dimension and a front-rear dimension that are larger than those of the bottom plate 34, and downward projecting portions 35a, 35a are continuously provided in the front-rear direction on the lower surfaces of the left and right sides. In addition, a plurality of reinforcing ribs 38 that are parallel to each other and face in the front-rear direction, and an X-shaped reinforcing rib 39 that is continuous with each of the reinforcing ribs 38 on the bottom surface excluding the downward projecting portions 35a, It protrudes downward. It should be noted that the dimension between the opposing surfaces of both downward projections 35a is slightly larger than the lateral dimension of the bottom plate 34.

The bottom plate 34 is attached to the seat frame 6a in the left and right side frames 6 as follows.
As shown in FIGS. 11 to 13, the inner upper surface of the seat frame 6 a in the left and right side frames 6 is L-shaped in a front view that opens upward and inward, for supporting the seat body 33. A recessed step 40 (symmetrically attached to the same shape, only one of which is shown) is formed so as to be continuous with the recessed step 28, and is formed by the inner upper surface of the left and right recessed steps 40. In the state where both side end portions of the bottom plate 34 are supported, the front, rear, left and right four places are fixed by bolts 41.

  That is, as shown in FIGS. 11 and 13, the bolts 41 inserted from above into the mounting holes 42 (see FIG. 14) drilled in the four front and rear corners of the bottom plate 34 are recessed in the left and right seat frames 6a. The bottom plate 34 is fixed between the seat frames 6 a of the left and right side frames 6 by being screwed into the screw holes 43 to be provided at the front end portion and the rear end portion in the stepped portion 40. In addition, as shown in FIG. 12, the both side edge parts of the center part of the front-back direction of the baseplate 34 are received and supported by the inward support piece 44 which protruded inwardly of the recessed step part 40 of the seat frame 6a. Yes.

  As shown in FIGS. 11 and 14, on the lower surface of the seat plate 35, four front and rear cylindrical protrusions 46 having female screw holes 45 are provided so as to protrude downward. In the state supported by the four corners of the bottom plate 34, bolts 48 inserted from below into the through holes 47 provided at the four corners slightly inward of the mounting holes 42 are inserted into the female screw holes 45 of the respective projections 46. By screwing, the seat plate 35 has its lower end surface excluding the front end portion of the left and right downward projecting portions 35a in contact with the upper surface outside the mounting portion of the bottom plate 34 in the recessed stepped portion 40. Thus, it is attached to the upper surface of the bottom plate 34. After the seat plate 35 is attached, the lower ends of the ribs 38 and 39 on the lower surface thereof are in contact with or close to the upper surfaces of the bottom plate 34 and the reinforcing plate 37.

  As shown in FIG. 2, on the upper surface of the seat plate 35, the cushion material 36 makes the rear end lower part abut or approach the front end of the connecting member 13 provided on the bent part 6b of the side frame 6, and the rear part. The upper end portion is attached so as to be positioned in front of the base piece 13a of the connecting member 13. Therefore, the gap formed between the lower end of the backrest 22 in the backrest 19 and the rear end of the cushion 36 of the seat body 33 is closed with good appearance by the connecting member 13.

  As described above, the both side ends of the bottom plate 34 are fixed to the seat frames 6a of the left and right side frames 6, and the downward projections 35a of both side ends are placed on the upper surface of the seat frame 6a. When the seat plate 35 is attached to the upper surface of the bottom plate 34 that is inward of the seat frame 6a, the seat frame 6a in the left and right side frames 6 is strengthened by the bottom plate 34 and is prevented from wobbling in the left-right direction. At the same time, since the load applied to the seat plate 35 is received and supported by the bottom plate 34, the central portion of the entire seat body 33 is prevented from being excessively bent downward. Therefore, it is possible to form the seat plate 35 thinly, and material costs, mold manufacturing costs, and the like are saved, and the overall vertical dimension of the seat body 33 is reduced, so that the appearance of the chair is improved.

  Further, since the bottom plate 34 and the seat plate 35 are separately screwed to the seat frame 6a and the bottom plate 34 in the side frame 6, the load applied to the seat 33 is concentrated on one mounting portion. There is nothing. In addition, since the downward projections 35a on both side ends of the seat plate 35 are simply placed on the upper surface of the seat frame 6a and are not fixed, the entire seat plate 35 is easily bent downward and the seating comfort is improved. .

  Furthermore, since the both end portions of the seat plate 35 and the cushion material 36 are fitted and attached to the recessed step portions 40 of the seat frame 6a in the left and right side frames 6, they can be easily positioned in the left-right direction. In addition, since it is not displaced in the left-right direction, only the front, rear, left, and right portions of the seat plate 35 are fixed to the bottom plate 34 with the bolts 48, so that the seat frames 6a in the left and right side frames 6 are fixed. It can be installed stably.

  Like a chair in the above embodiment, the backrest 19 and the seat body 33 are placed on a pair of left and right side frames 6 and 6 that are L-shaped in a forward-facing L-shape and are directly fixed to the recumbent body 4 of the leg 2. If it attaches, the number of parts and the man-hour for attachment to a leg will be reduced, and cost reduction can be aimed at.

In the chair of the above embodiment, the cushion material 36 is attached to the upper surface of the seat plate 35, but the cushion material 36 may be omitted and only the seat plate 35 may be used.
In addition to the lobby chair, the present invention can be applied to a normal single chair.

It is a perspective view of the state which removed the back support of the chair of the right side in the lobby chair to which the present invention is applied. Similarly, it is a partially cutaway enlarged central longitudinal side view of the chair. It is the III-III line enlarged vertical front view of FIG. Similarly, it is an IV-IV line enlarged longitudinal end view. Similarly, it is a VV line expansion transverse end view. Similarly, it is a VI-VI line expansion transverse end view. It is a rear view of a back board. It is a perspective view before the backplate attachment to a side part frame. Similarly, it is the rear surface perspective view of the attachment part of the back plate upper part to the side part frame upper part. It is an expansion center vertical side view of a seat. It is the XI-XI line enlarged vertical end view of FIG. Similarly, it is an XII-XII line enlarged longitudinal end view. Similarly, it is an XIII-XIII line enlarged longitudinal end view. It is a bottom perspective view before attachment of a bottom board and a seat board.

DESCRIPTION OF SYMBOLS 1 Chair 2 Leg 3 Support leg 4 Recumbent 5 Cap 6 Side frame 6a Seat frame 6b Bending part 6c Back frame 6d Backward bending part
7 Mounting portion 8 Fitting groove 9 Fitting groove 10 Bolt 11 Female screw hole 12 Mounting bracket 13 Connecting member 13a Base piece 13b Downward piece 14 Protruding portion 15 Inwardly protruding piece 16 Through hole 17 Mounting screw 18 Female screw hole 19 Backrest 20 Back plate 21 Back plate 21a Backward bent portion 22 Back support 23 Mounting groove 24 Reinforcement rib 25 Protrusion 26 Locking hook 27 Engagement hole 28 Recessed stepped portion 29 Stepped screw 30 Locking protrusion 31 Stop screw 32 Female Screw hole 33 Seat body 34 Bottom plate 35 Seat plate 35a Downward projecting portion 36 Cushion material 37 Reinforcement plate 38 Reinforcement rib 39 Reinforcement rib 40 Recessed stepped portion 41 Bolt 42 Mounting hole 43 Female screw hole 44 Inward support piece 45 Female screw hole 46 Cylindrical protrusion 47 Through hole 48 Bolt S Clearance

Claims (6)

Both side ends of the bottom plate are fixed to the upper surfaces of a pair of left and right seat frames that are fixed to the legs and face in the front-rear direction, and on the upper surfaces of the left and right seat frames outside the fixing portions, placing the two side lower surface of the seat plate having an upwardly arranged flexible faceplate, and an inner portion than the seat frame in the seat plate, and fixed to the upper surface of the bottom plate, further, the right and left A recessed step portion that opens upward and inward is formed on the upper surface of the seat frame, and the side edge of the bottom plate is fixed to the upper surface of the recessed step portion, and the side edge of the seat plate is fixed. A chair characterized in that the parts are fitted and placed .   The chair according to claim 1, wherein a downward projecting portion whose lower end is in contact with the upper surface of the seat frame protrudes from the lower surface of the side end portion of the seat plate. A female screw hole provided on the upper surface of the seat frame, by screwing a bolt inserted from above into the side end portion of the bottom plate, formed of a fixed side edge portion of the bottom plate to the upper surface of the seat frame according to claim 1 or 2. The chair according to 2 . A projecting portion having a female screw hole is provided on the lower surface of the seat plate, and a bolt inserted from below the bottom plate is screwed into the female screw hole, thereby fixing the seat plate to the bottom plate. Item 4. The chair according to any one of Items 1 to 3 . The chair according to any one of claims 1 to 4, wherein a plurality of reinforcing ribs whose lower ends are in contact with the upper surface of the bottom plate are provided on the lower surface of the seat plate. The chair according to any one of claims 1 to 5 , wherein the bottom plate is made of sheet metal, and a reinforcing plate is fixed to a central portion of the top surface.

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