Reaction force adjustment mechanism of the backrest reaction force mechanism of the chair

Abstract

To enable weight saving and down-sizing for a reaction force adjustment mechanism in a chair backrest reaction force mechanism.SOLUTION: A chair backrest reaction force mechanism generates, by compression of a reaction force spring, a force for pushing back a backrest linked with backward tilting of the backrest. In connection with this mechanism, a reaction force adjustment mechanism includes: a reaction force adjustment cam 51 which provides displacement in stretching direction for the reaction force spring; and a reaction force adjustment operation shaft 7 (70) which rotates the reaction force adjustment cam 51 to change over a cam displacement amount that is provided for the reaction force spring. Also, a reaction force adjustment mechanism is provided in which, by the rotation operation of the reaction force adjustment operation shaft 7 (70), the cam displacement amount provided by the reaction force adjustment cam 51 is switched, with the initial compression amount of the reaction force spring adjusted. The reaction force adjustment cam 51 has a cam basic circle 51a that is smaller in diameter than the minimum shaft diameter of the shaft of the reaction force adjustment operation shaft 7 (70), for example, the shaft diameter of a tip end shaft part 55, with the position of the cam basic circle 51a made a starting point or a terminal point.SELECTED DRAWING: Figure 14

Description

Technical Field

[0001] The present invention relates to a reaction force adjustment mechanism of a backrest reaction force mechanism of a chair. More specifically, the present invention relates to a reaction force adjustment mechanism of a backrest reaction force mechanism of a chair that adjusts the initial compression amount of a reaction force spring using a cam mechanism.

Background Art

[0002] Conventionally, there are chairs whose locking reaction force can be adjusted. There are those that change the initial compression amount of a spring by rotating a cam to adjust the reaction force (for example, Patent Document 1), and those that change the initial compression amount of a spring by sliding a cam in the lateral direction (for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, all of them are composed of two members, an iron operation lever and a cam member through which the operation lever passes inside. In such a structure, a surface (cam contour surface) that abuts against a spring-side member that becomes a driven joint is provided at a position protruding outside the shaft diameter of the operation lever in a cross-sectional view. That is, the cam member becomes large. And when the cam member is large, the surface (cam contour surface) that abuts against the spring-side member that becomes the driven joint moves away from the rotation center, so a large force is required to turn the operation lever, it is necessary to move the operation lever greatly, it is difficult to make multi-stage adjustments, and the reaction force adjustment part itself becomes large, etc.

[0005] The present invention aims to provide a reaction force adjustment mechanism for a chair backrest reaction force mechanism that enables weight reduction and miniaturization of the mechanism. [Means for solving the problem]

[0006] To achieve this objective, the present invention provides a chair backrest reaction force mechanism that generates a force that pushes the backrest back in conjunction with the backward tilt of the backrest by compressing a reaction spring, and includes a reaction force adjustment cam that applies displacement in the expansion and contraction direction to the reaction spring, and a reaction force adjustment operating shaft that rotates the reaction force adjustment cam to switch the amount of cam displacement applied to the reaction spring, and a reaction force adjustment mechanism that adjusts the initial compression amount of the reaction spring by rotating the reaction force adjustment operating shaft to switch the amount of cam displacement applied by the reaction force adjustment cam, the reaction force adjustment cam has a cam base circle with a diameter smaller than the minimum shaft diameter of the shaft portion of the reaction force adjustment operating shaft, and the position of the cam base circle is the starting point or ending point.

[0007] Furthermore, in the chair backrest reaction force mechanism of the present invention, it is preferable that the reaction force adjustment operating shaft is integrally molded with the reaction force adjustment cam using synthetic resin.

[0008] Furthermore, in the chair backrest reaction force mechanism of the present invention, it is preferable that the reaction force adjustment mechanism is arranged such that the reaction force adjustment operating shaft and the reaction force spring are in a positional relationship perpendicular to each other, and that the reaction force adjustment cam of the reaction force adjustment operating shaft provides cam displacement in the direction of expansion and contraction of the reaction force spring.

[0009] Furthermore, in the chair backrest reaction force mechanism of the present invention, the reaction force adjustment mechanism is configured such that the reaction force adjustment cam is a planar cam forming a polygonal cam contour in which multiple stages of cam displacement can be switched in steps, and the starting or ending cam surface is a flat surface that is tangent to a cam base circle with a diameter smaller than the shaft diameter of the minimum shaft portion of the reaction force adjustment operation shaft, and the amount of cam displacement provided by the cam surface that is switched in accordance with the rotation of the reaction force adjustment operation shaft is preferably increased or decreased in steps.

[0010] Furthermore, in the chair backrest reaction force mechanism of the present invention, it is preferable that the reaction force adjustment mechanism has two reaction force adjustment cams spaced apart on the reaction force adjustment operating shaft.

[0011] Furthermore, it is preferable that the reaction force adjustment mechanism of the chair backrest reaction force mechanism of the present invention is provided with an intermediate bearing portion that supports the intermediate shaft portion between the two reaction force adjustment cams of the reaction force adjustment operating shaft, at least in the expansion direction of the reaction force spring.

[0012] Furthermore, in the chair backrest reaction force mechanism of the present invention, it is preferable that a left-right wobble prevention part that engages axially with an intermediate bearing part is provided between the two reaction force adjustment cams.

[0013] Furthermore, in the chair backrest reaction force mechanism of the present invention, it is preferable that the reaction force adjustment mechanism is rotatably supported on both sides of the reaction force adjustment cam by an outer bearing portion that supports the outer shaft portion of the reaction force adjustment cam and an inner bearing portion that supports the inner shaft portion of the reaction force adjustment cam.

[0014] Furthermore, it is preferable that the backrest reaction force adjustment mechanism of the chair of the present invention is used in conjunction with a weight-sensitive reaction force application mechanism that makes the resistance to back rocking proportional to the user's weight by linking the backrest reaction force mechanism to lift the seat when the backrest tilts backward.

[0015] Furthermore, it is preferable that the chair of the present invention is equipped with a reaction force adjustment mechanism for the backrest reaction force mechanism of the chair described in any one of claims 1 to 8. [Effects of the Invention]

[0016] According to the reaction force adjustment mechanism for the chair backrest reaction force mechanism described in claim 1, the reaction force adjustment cam has a cam base circle with a smaller diameter than the minimum shaft diameter of the shaft portion of the reaction force adjustment operating shaft, and the position of the cam base circle is used as the starting point or ending point. Therefore, the reaction force adjustment cam itself can be made compact while setting the cam displacement in multiple stages, and the force required to rotate the reaction force adjustment cam is small.

[0017] That is, the reaction force adjustment operation shaft can be rotated with a smaller force. Further, there is no need to move it significantly, and it becomes possible to create a multi-stage adjustment mechanism. In addition, the reaction force adjustment mechanism itself can be miniaturized.

Brief Description of the Drawings

[0018] [Figure 1] It is a perspective view showing one embodiment of a chair to which the present invention is applied, from the bottom surface. [Figure 2] It is an exploded perspective view showing one embodiment of a seat, a backrest, and a backrest reaction force applying mechanism. [Figure 3] It is a central longitudinal sectional view showing one embodiment of a backrest reaction force mechanism, its reaction force adjustment mechanism, and a locking range adjustment mechanism for regulating the locking range of the backrest. [Figure 4] It is a perspective view showing one embodiment of a backrest reaction force mechanism, its reaction force adjustment mechanism, and a locking range adjustment mechanism for regulating the locking range of the backrest. [Figure 5] It is a longitudinal sectional view showing one embodiment of the reaction force adjustment mechanism along the axis center (the cross-section location is shown in color). [Figure 6] It is a partial longitudinal sectional perspective view showing the relationship between the reaction force adjustment operation shaft, the operation shaft retainer, and the main frame of the reaction force adjustment mechanism centered on the regulating projection (the cross-section location is shown in color). [Figure 7] It is a partial longitudinal sectional perspective view showing the relationship between the reaction force adjustment operation shaft, the operation shaft retainer, and the main frame of the reaction force adjustment mechanism centered on the intermediate bearing portion (the cross-section location is shown in color). [Figure 8] It is a perspective view showing the relationship between the backrest reaction force mechanism and the reaction force adjustment mechanism with the operation shaft retainer removed. [Figure 9] It is a perspective view showing the relationship between the backrest reaction force mechanism and the reaction force adjustment mechanism. [Figure 10] It is a perspective view showing the operation shaft retainer from below. [Figure 11] It is a perspective view showing a partial cross-section of the operation shaft retainer along the axis center. [Figure 12] It is an explanatory view showing the relationship between the reaction force adjustment cam and the slider of the reaction force adjustment operation shaft. [Figure 13] This is a perspective view showing one embodiment of the reaction force adjustment operating shaft. [Figure 14] This is a side view showing the tip of the reaction force adjustment shaft from the shaft side. [Figure 15] This is a perspective view showing one embodiment of a mainframe from the upper left rear. [Figure 16] This is a perspective view showing one embodiment of a mainframe from the upper right rear. [Figure 17] This is a perspective view showing one embodiment of a backrest support member from an oblique angle above and in front. [Figure 18] This is a perspective view showing one embodiment of the outer shell of the seat, viewed from a diagonal downward and rearward angle. [Figure 19] This is a perspective view showing the relationship between the outer shell of the seat, the main frame, and the seat's rotation axis, partially cross-sectionally along the axis (the cross-sectional area is colored). [Figure 20] This is a perspective view showing one embodiment of a mechanism to prevent the seat rotation shaft from coming loose (cross-sectional areas are shown in color). [Figure 21] This is a perspective view showing a partial cross-section of the outer shell before the retaining member is inserted into the vertical hole (the cross-sectional area is colored). [Figure 22] This is a perspective view showing one embodiment of the backrest rocking range adjustment mechanism, viewed from diagonally below and to the rear. [Figure 23] This is a perspective view showing one embodiment of a locking block that constitutes a locking range adjustment mechanism. [Figure 24] This is a perspective view of the locking block from the opposite end of the shaft. [Figure 25] This is a perspective view showing one embodiment of a fixed block that constitutes a locking range adjustment mechanism. [Figure 26] This is a perspective view of the same fixed block from the opposite side. [Figure 27] This is a perspective view showing one embodiment of the rotation axis of a locking block. [Figure 28] This is a perspective view showing another embodiment of the reaction force adjustment mechanism for the chair backrest reaction force mechanism according to the present invention. [Figure 29]This is a perspective view of the reaction force adjustment mechanism's reaction force adjustment shaft, as seen from the handle side. [Figure 30] This is a perspective view of the reaction force adjustment mechanism's reaction force adjustment shaft, seen from the tip side. [Figure 31] This is a perspective view showing the main frame of the reaction force adjustment mechanism from the upper right rear. [Figure 32] This is a longitudinal cross-sectional view of the main frame, looking at the peripheral wall side (the cross-sectional area is colored to indicate its position). [Modes for carrying out the invention]

[0019] The configuration of the present invention will now be described in detail based on the embodiments shown in the drawings. In this specification, "front" or "forward" refers to the front or forward direction for the chair and the person seated on the chair, respectively, and "rear" or "backward" similarly refers to the rear or back direction for the chair and the person seated. Furthermore, the direction perpendicular to the front-to-back direction in the horizontal plane refers to the left-to-right direction or width direction for the person seated or the chair, respectively, for the seat and backrest. Also, in the seat and backrest, "inside" refers to the side toward the person seated or toward the vertical plane in the front-to-back direction passing through the center of the chair, and "outside" refers to the side away from the person seated or away from the vertical plane in the front-to-back direction passing through the center of the chair. Furthermore, "up" and "down" refer to the top and bottom of the chair and the person seated, respectively, for the armrest, seat, and backrest, and are top and bottom in the vertical plane.

[0020] Figures 1 and 2 show an embodiment of a chair to which the present invention is applied. This chair has, for example, legs 1 equipped with casters, a main frame (support base) 2 supported by the legs 1, and a seat 3 and backrest 4 that are pivotably supported on the main frame 2 and move in conjunction with each other. On the front side of the main frame 2, there is a reaction force adjustment mechanism 6 and its reaction force adjustment operating shaft 7 that allow adjustment of the initial reaction force of the backrest reaction force mechanism 5, and on the rear side, there is a rocking range adjustment mechanism 8 that restricts the rocking range of the backrest 4 and an operating shaft (hereinafter referred to as the rocking range switching operating shaft 9) that switches the rocking range, both of which protrude outward from the side of the main frame 2. In addition, a cover member 10 is provided between the back frame of the backrest 4 and the main frame 2.

[0021] In this embodiment, the main frame 2 is molded from a synthetic resin. To ensure the structural mechanical rigidity, it is preferable to use a rigid synthetic resin such as glass fiber reinforced nylon, like PA6-GF (polyamide 6). Of course, it is not limited to this; the main frame 2 may also be constructed by forming a box shape or other shapes from aluminum die-cast or steel materials by welding.

[0022] The main frame 2 of this embodiment is box-shaped, as shown in Figures 15 and 16, for example, in order to increase the mechanical rigidity of the structure, particularly torsional rigidity, and to accommodate a reaction force adjustment mechanism 6 inside, and to increase the mechanical rigidity of the structure, particularly torsional rigidity, and to house a reaction force adjustment mechanism 6 inside, and to increase the mechanical rigidity of the structure, particularly torsional rigidity. It has front and rear side peripheral walls 2A, a bottom wall 2B, a partition wall 2C arranged in the front and rear direction, and reinforcing ribs 2D connecting them. The rear side of the main frame 2 is further provided with a rear leg support cylinder 2E into which the gas spring of the leg is fitted, and a recess 19 for attaching a buffer block 41.

[0023] Furthermore, on the front side of the main frame 2, an intermediate bearing portion 11 is provided between the left and right partition walls 2C to support the intermediate shaft portion 52 of the reaction force adjustment operating shaft 7, at least in the expansion direction of the reaction spring, i.e., the compression coil spring 65. Since a large force is applied to the compression coil spring 65 of the backrest reaction force mechanism 5, the shaft that receives the compression coil spring 65, i.e., the reaction force adjustment operating shaft 7 in this embodiment, is required to have rigidity. For this reason, metal members such as iron are usually used, but from the viewpoint of reducing the weight of the chair and promoting separate disposal, there is a demand for resin parts. However, even if the parts are molded from a synthetic resin with sufficient rigidity, such as glass fiber reinforced nylon such as PA6-GF (polyamide 6), in order to ensure the mechanical rigidity of the structure, the problem arises that they are more prone to bending than metal shafts. Therefore, it is preferable to provide an intermediate bearing portion 11 that supports the intermediate shaft portion 52 of the reaction force adjustment operating shaft 7 at least in the expansion direction of the compression coil spring 65, thereby supporting the intermediate shaft portion 52 of the reaction force adjustment operating shaft 7 at three points together with the bearing portions at both ends, making it less prone to bending.

[0024] The intermediate bearing section 11 supports at least the force of the compression coil spring 65, and in this embodiment, it is composed of a semicircular open bearing that opens toward the compression coil spring 65. For example, it is composed of left and right vertical walls 11A and a front wall 11B that serve as both the bearing section and a rib, and an overhang section 11C that protrudes toward the rear of the main frame. The bearing section 11D is formed by the left and right vertical walls 11A being carved out in a semicircular shape. The overhang section 11C supports the upward force of the compression coil spring 65 acting on the reaction force adjustment operating shaft 7. In this embodiment, the vertical walls 11A and the front wall 11B, and the overhang section 11C are integrally molded with the bottom wall section 2B of the main frame 2, so that they stand upright from the bottom wall section 2B. Of course, the intermediate bearing section 11 may be formed separately from the main frame 2 and fixed to the bottom wall section 2B by screws or welding.

[0025] The left and right side walls 2A of the front of the main frame 2 are provided with elongated holes 12 that are inclined towards the rear when viewed from below, and are provided so as to allow a seat rotation shaft 42, which rotatably connects the outer shell 71 and the main frame 2, to pass through.

[0026] Furthermore, a circular through-hole (referred to as a circular hole 13) is provided in one peripheral wall portion 2A of the main frame 2, for example, the right peripheral wall portion 2A, for inserting the reaction force adjustment operating shaft 7 of the reaction force adjustment mechanism 6 from the side. Inside this hole, the partition wall 2C is provided with a semicircular open bearing portion 14 with a notched upper edge. In addition, the partition wall 2C on the opposite side is also provided with a semicircular open bearing portion 14 with a notched upper edge. Therefore, the reaction force adjustment operating shaft 7 inserted into the main frame 2 is supported by the circular hole 13 and the semicircular open bearing portion 14 of the partition wall 2C. At the same time, the upper half of the reaction force adjustment operating shaft 7 is supported by the operating shaft retainer 43 shown in Figure 8, and the reaction force adjustment operating shaft 7 is rotatably clamped between the retainer and the open bearing portion 14 of the partition wall 2C, and is held in place so as not to come loose in the axial direction.

[0027] Here, the operating shaft retainer 43 is provided with semicircular bearing portions (open bearing portions 44) at both ends, as shown in Figures 10 and 11, for example, to support the shaft portions 55 and 59 of the reaction force adjustment operating shaft 7. By pressing down on the shaft portions 56 and 59 of the reaction force adjustment operating shaft 7 from above, the reaction force adjustment operating shaft 7 is rotatably supported between the semicircular open bearing portions 14 of the partition wall 2C. In addition, the inner circumferential surface of the operating shaft retainer 43 is provided with a restricting projection (stopper) 49 that contacts the restricting projection (stopper) 54 of the reaction force adjustment operating shaft 7 and restricts the rotation of the reaction force adjustment operating shaft 7 to within a certain range (for example, a range of approximately 270°) (see Figure 6). As a result, the reaction force adjustment operating shaft 7 is mounted to the main frame 2 so as to be able to swing within a certain range.

[0028] Furthermore, in this embodiment, the operating shaft retainer 43 is provided with a slider housing 50 that houses a slider 66 and guides it in the spring axis direction, positioned opposite the reaction force adjustment cam 51 of the reaction force adjustment operating shaft 7. This slider housing 50 is, for example, a rectangular cylindrical case, positioned to straddle the portion that covers the left and right partition walls 2C, and is integrally molded with the operating shaft retainer 43. Of course, the slider housing 50 is not limited to being integrally molded with the operating shaft retainer 43; it may also be molded separately and assembled to the operating shaft retainer 43, or assembled to the main frame 2 or integrally molded with the main frame 2.

[0029] Furthermore, the operating shaft retainer 43 is provided with a pair of protrusions 45 positioned to fit over the left and right partition walls 2C of the main frame 2, with a spacing approximately equal to the thickness of the partition walls 2C, thereby forming a recess 48 into which the partition walls 2C are sandwiched. In addition, a U-shaped mounting seat portion 47 is formed on the base end side (seat rotation shaft 42 side) of the operating shaft retainer 43, which is fitted from above to surround the boss portion of the main frame 2 that has screw holes 15. Therefore, the mounting seat portion 47 can be placed over the boss portion with screw holes 15, and the partition walls 2C can be fitted into the recess 48 between the pair of protrusions 45, and screws can be screwed into the screw holes 15 through the four through holes 46 on the front, back, left, and right sides to secure it without any wobbling.

[0030] Furthermore, as shown in Figure 16, a round hole 16 is provided in one of the rear side walls of the main frame 2, for example, the left side wall 2A, through which the rocking range switching operation shaft 9 of the rocking range adjustment mechanism 8 passes. The other side wall, the right side wall 2A, and the partition wall 2C are provided with a semicircular bearing 17 that supports the tip of the rocking range switching operation shaft 9 and a round hole 18 through which the tip passes. The recess 19 that houses the buffer block 41 (resin damper) is a recess surrounded by the side walls of the main frame 2, and a hole 20 is provided on the bottom surface for fitting the pin portion 41a of the buffer block 41. The buffer block 41 is fixed to the main frame 2 by being fitted into the recess 19 and the pin portion 41a is fitted into the hole 20 at the bottom.

[0031] Inside the main frame 2, specifically inside the left and right partition walls 2C, a cavity 2F is formed to house a reaction force mechanism 60 including a compression coil spring 65. This cavity can accommodate the spring receiving arm 21B of the backrest support member (also called a back support rod) 21, which is pivotably supported by the main frame 2, the reaction force adjustment operating shaft 7, which is rotatably supported by the main frame 2, and a means, such as a compression coil spring 65, which is positioned between them and generates a force that pushes the backrest 4 back in conjunction with the backward tilt of the backrest 4.

[0032] In this embodiment, the main frame 2 is connected to the leg column (in other words, the gas spring) at the rear leg column support cylinder portion 2E and is rotatably supported in the horizontal plane, while its front is rotatably connected to the outer shell 71 of the seat 3 via the seat rotation axis 42, and is engaged with the seat support axis 21D of the backrest support member 21 behind the point where the seat 3 is connected by the seat rotation axis 42, so that the seat 3 and backrest 4 are supported by the main frame 2 so that they can swing in conjunction. In other words, the seat 3 is supported so that it is pulled diagonally backward and lifted in conjunction with the swinging of the backrest support member 21 via the backrest rotation axis 25. This constitutes a weight-sensitive (or sensing) reaction force application mechanism 61 that makes the resistance to back rocking proportional to the user's weight by linking the lifting of the seat 3 when the backrest 4 is tilted backward.

[0033] (Backrest) In this embodiment, the backrest 4, as shown in Figures 1 and 2, for example, consists of a back frame 4a that forms a rectangular frame in front view with an internal cavity, and a mesh upholstery (not shown) stretched across the back frame 4a to form the backrest surface, and is pivotably mounted on the main frame 2 via a backrest support member 21. To ensure the mechanical rigidity of the structure, the back frame 4a is preferably molded from a rigid synthetic resin such as glass fiber reinforced nylon, such as PA6-GF (polyamide 6).

[0034] In this embodiment, the back frame 4a has, for example, a recess 90 on the front side of its base that accommodates the rear part of the back support member 21. With the rear part of the back support member 21 fitted into the recess 90, the back frame 4a is connected to the back support member 21 by fastening screws to the nuts 24 of the back plate 21C, passing through the base of the back frame 4a from the rear of the back support member 21. As a result, the back frame 4a is fixed to the back support member 21 without rattling in the front, back, left, right, up, and down directions.

[0035] The backrest support member 21 is pivotably attached to the main frame 2 by a backrest rotation shaft 25 that penetrates the main frame 2 laterally. The backrest 4 is attached to the backrest support member 21 behind the backrest rotation shaft 25, and the backrest support member 21 is linked to the seat 3 in front of the backrest rotation shaft 25, so as the backrest 4 tilts backward, it raises the seat 3. Specifically, for example, the plate member 21A of the backrest support member 21 has a roughly V-shaped bend, with the edge in front of the through-hole 21F inclined diagonally upwards relative to the edge behind the through-hole 21F through which the backrest rotation axis 25 passes. In the initial position (when no one is seated), the seat 3 and backrest 4 are kept in their initial positions, and the positional relationship is set such that when the backrest 4 tilts backward, a force is applied to the seat 3 that lifts the seat 3.

[0036] Specifically, in this embodiment, as shown in Figure 17, the backrest support member 21 is composed of a pair of plate members 21A arranged on both sides of the main frame 2, a seat support shaft portion 21D connecting them at the front, a back mounting plate 21C connecting them at the rear, and a spring support arm 21B that receives and supports one end of the compression spring mechanism of the reaction force mechanism. In this embodiment, the spring support arm 21B is, for example, roughly triangular (L-shaped), with the seat support shaft portion 21D passing through the corner portion of the vertex, and a spring support shaft 21E for engaging the rear spring mount 63 is provided at the end of one side that is hanging down (the position corresponding to the vertex), and a through hole 21F for passing the backrest rotation shaft 25 is provided at the end of the other side that is inclined diagonally downward and rear (the position corresponding to the vertex). In other words, the backrest support member 21 and the spring receiving arm 21B are rotatably supported with respect to the main frame 2, and are arranged to swing simultaneously around the backrest rotation axis 25 as the center of rotation while maintaining a constant angular relationship between them.

[0037] The portion of the backrest support member 21 to which the back frame 4a is attached (i.e., the backrest mounting seat) is composed of a lateral connecting plate 21C positioned to cross between the plate members 21A on both sides of the backrest support member 21, as shown in Figure 17. Screw holes are provided in the lateral connecting plate 21C by welding nuts 24 to it. The rear portions of the plates 21A on both sides of the backrest support member 21, including the lateral connecting plate 21C, are fitted into a recess (backrest support member mounting seat) 90 that opens in front of the bottom edge of the back frame 4a. With the lateral connecting plate 21C and the backrest support member mounting seat in place, fastening screws are screwed in from behind the back frame 4a, thereby integrating the backrest support member 21 and the back frame 4a. Furthermore, the holes (not shown) for inserting fastening screws that appear on the back of the bottom portion of the back frame 4a are covered by fitting a cover plate 91 after the fastening screws are tightened, so that they do not appear to the outside. The cover plate 91 has, for example, a locking claw, and is easily attached and detached by hooking the locking claw into a notch in a recess on the back of the bottom portion of the back frame.

[0038] (Location structure) The seat 3 is not limited to a specific structure and shape, but in this embodiment, as shown in Figure 2, it is composed of an outer shell 71, an inner shell 72, a urethane foam cushion 73, and an upholstery (not shown), and is mounted on the main frame 2 so as to be able to swing around the seat rotation axis 42 by connecting the outer shell 71 to the main frame 2 via the seat rotation axis 42. The seat 3 is mounted on the main frame 2 so as to be able to swing while moving vertically and horizontally within a certain range via the outer shell 71 by making the hole 12 in the main frame 2 that supports the front seat rotation axis 42 an elongated hole that is inclined toward the rear when viewed from below.

[0039] In this embodiment, the outer shell 71 is provided with a U-shaped peripheral wall portion 74 surrounding the main frame 2, projecting downwards, as shown in Figure 18, for example. The main frame 2 and the backrest support member 21 are housed in a recess 75 on the inside of the peripheral wall portion 74. A vertically cut slit 76 is provided on the backrest-side surface of the peripheral wall portion 74, and care is taken to prevent interference between the backrest support member 21 and the outer shell 71 by allowing the backrest support member 21 to pass through the slit 76. The seat rotation shaft 42 is positioned to pass through the main frame 2 and the peripheral wall portion 74 housed in the recess 75, thereby rotatably connecting and supporting the outer shell 71 to the main frame 2. The outer shell 71 has bearing portions formed in the peripheral wall portion 74 to support both ends of the seat rotation shaft 42. In this embodiment, the peripheral wall portion 74 is composed of a double-wall structure consisting of an inner wall portion and an outer wall portion that are continuously formed, for example, by folding back at the bottom, and a bearing portion is formed between them to support both ends by straddling the seat rotation shaft 42. The bearing portion has, for example, a blind circular hole 77 in one side of the peripheral wall portion and a through circular hole 78 in the other side of the peripheral wall portion.

[0040] A window-shaped opening (hereinafter referred to as the opening 80) for inserting the seat rotation shaft 42 is provided in the outer wall portion of the peripheral wall portion 74 at the position of the round hole 78. After the seat rotation shaft 42 is inserted so as to straddle the main frame 2 and the outer shell 71, this opening 80 is closed by a retaining member 81. The shape and structure of the outer shell 71 are designed as appropriate as needed, but it is preferable that at least the left and right peripheral wall portions 2A of the main frame 2 are provided with a bearing portion, for example, a peripheral wall portion 74 that overlaps with the bearing portion, for example horizontally (lateral direction) on one axis and is interconnected via the seat rotation shaft 42, and that the bearing portion has an opening 80 for inserting the seat rotation shaft 42 from the side and a structure for installing a retaining member 81 to prevent the seat rotation shaft 42 from coming out. In this embodiment, one of the bearing portions is a blind hole, but it is not limited to this, and both may be provided with openings 80 as through-holes and closed by fitting the retaining member 81 into them.

[0041] Outside the through hole 78 that supports the seat rotation shaft 42, that is, between the through hole 78 in the peripheral wall portion 74 of the outer shell 71 and the opening 80, a retaining member insertion hole 79 is formed, as shown in Figures 19 to 20, into which a retaining member 81 is fitted. This retaining member insertion hole 79 is a vertical hole that is positioned, for example, to intersect with the seat rotation shaft 42 and opens to the upper surface of the outer shell 71 (i.e., the surface on which the inner shell and urethane foam are placed), and a stepped portion (overhang) 83 that catches against upward pulling is formed on the inner surface of the outer wall portion of the peripheral wall portion 74 above the opening 80. On the other hand, the retaining member 81 abuts against the end face of the seat rotation shaft 42, which is inserted so as to straddle the main frame 2 and the outer shell 71, and prevents axial movement. In this embodiment, the retaining member 81 has rigidity and spring elasticity to prevent the seat rotation shaft 42 from coming loose. For example, it is made of a resin plate with a vertical cross-section shape of L-shape and equipped with a return 82 as shown in Figure 21. When the return 82 is inserted into the retaining member insertion hole 79, the tip of the return 82 bends inward, and after overcoming the stepped portion 83, it returns to its original shape and settles into the recess below the stepped portion 83, and at the same time catches on the stepped portion 83. In this embodiment, the return 82 is composed of an inclined surface portion 86 that fits into the opening 80 and a locking portion 87 that rises vertically and abuts against the stepped portion 83. Therefore, when the return (reverse hook) 82 portion of the retaining member 81 approaches the stepped portion 83, the locking portion 87 of the return 82 enters due to spring elasticity and catches on the stepped portion 83, thereby engaging the retaining member 81 so that it does not come out of the retaining member insertion hole 79. Furthermore, the rear end of the retaining member 81 is provided with a hook portion 85 that abuts against the edge of the retaining member insertion hole 79, preventing it from becoming submerged in the retaining member insertion hole 79. The planar shape of the retaining member insertion hole 79 is not particularly limited, but in this embodiment it is a rectangular hole when viewed from above.

[0042] Since the retaining member insertion hole 79 communicates with the opening 80 of the peripheral wall portion 74, when the retaining member 81 is inserted, the inclined surface portion 86 of the return 82 is exposed on the surface. In this embodiment, the area of ​​the inclined surface portion 86 of the return 82 of the retaining member 81 is set to be slightly smaller than the opening area of ​​the opening 80, so that when the retaining member 81 is pushed into the retaining member insertion hole 79, the locking portion 87 of the return 82 fits under the stepped portion 83 on the inner surface of the outer wall portion, and at the same time the inclined surface portion 86 of the return 82 fits into and closes the opening 80. This makes it possible to push the inclined surface portion 86 of the return 82 that is exposed inside the opening 80 from the outside of the peripheral wall portion 74 of the outer shell 71 with a finger and disengage it from the stepped portion 83.

[0043] Furthermore, as shown in Figure 3, the seat 3 is supported by a locking member of the outer shell 71, such as a claw-shaped engaging portion 84, which hooks onto the seat support shaft portion 21D of the backrest support member 21 at the midpoint of the seat 3 in the front-to-back direction, located behind the seat rotation axis 42 and in front of the backrest rotation axis 25.

[0044] Here, the rear connection point of the outer shell 71 to the backrest support member 21 is located on the seat support shaft portion 21D, which is forward of the rotation axis (backrest rotation axis 25) of the backrest support member 21. This position allows the seat 3 to be lifted by the seat support shaft portion 21D on the tip side of the backrest support member 21 when the backrest support member 21 tilts backward. In other words, the seat 3 is lifted as the backrest 4 tilts backward, and a portion of the seater's weight acts as resistance to the backward tilting movement of the backrest 4 (the rocking resistance is weight-sensitive), thus constituting a weight-sensitive reaction force application mechanism. Therefore, when a seated person leans back on the backrest 4, the backrest support member 21 rotates so as to tilt backward around the backrest rotation axis 25, causing the seat 3 to be pulled diagonally backward, thereby lifting the rear side of the seat 3 and applying a reaction force to the backrest 4 via the backrest support member 21 that is proportional to the seated person's weight.

[0045] The outer shell 71 is not limited to a specific material or structure, but in this embodiment, it is molded from a rigid synthetic resin such as glass fiber reinforced nylon, and is reinforced by appropriately employing a rib structure. The connection structure between the outer shell 71 and the inner shell is well known and therefore not shown in detail, but for example, the T-shaped locking claws, which have locking heads distributed at four locations on the upper surface of the outer shell 71, are fixed to each other by engaging them with T-shaped slits that extend in the front-rear direction when viewed from above on the inner shell, that is, by passing the heads of the T-shaped locking claws through the T-shaped slits and then sliding them in the front-rear direction.

[0046] The assembly of the seat 3 and the main frame 2 is performed by placing the outer shell 71 over the main frame 2 so that it fits into the recess 75 of the outer shell 71, aligning the elongated hole 12 of the main frame 2 with the rotation shaft hole (opening 80, through hole 78, and blind round hole 77) of the outer shell 71, and inserting the seat rotation shaft 42 from the outside of the outer shell 71 through the opening 80. Then, the seat rotation shaft 42 is pushed in until its tip abuts against the blind round hole 77 of the outer shell 71. After that, the retaining member 81 is inserted into the retaining member insertion hole 79 from the top surface of the outer shell 71, and pushed in until the return 82 is under the stepped portion 83 while contacting the rear end surface of the seat rotation shaft 42. Once the retaining member 81 is installed in the retaining member insertion hole 79, the shaft end surface of the seat rotation shaft 42 abuts against the retaining member 81 and is fixed in place. After that, the inner shell 72 and cushion 73 are placed on top of the outer shell 71 and then covered with the upholstery. Next, the claw-shaped bearing portion 84 in the middle of the outer shell 71 is placed against the seat support shaft 21D of the backrest support member 21 and pressed down from above, thereby rotatably fitting the claw-shaped bearing portion 84 and the seat support shaft 21D. As a result, the backrest support member 21 swings around the backrest rotation shaft 25, and the seat 3 is supported so that it is pulled diagonally backward and lifted.

[0047] In this embodiment, for example, the outer shell 71 is rotatably connected to the front of the main frame 2 via the seat rotation shaft 42, then the retaining member 81 is inserted, the inner shell is placed on top, the cushion is placed on top of that, and then it is wrapped and secured with the upholstery. Therefore, once the seat 3 is assembled to the main frame 2, the seat rotation shaft 42 will not fall out. On the other hand, if it becomes necessary to separate the seat 3 from the main frame 2, with the upholstery, urethane foam cushion and inner shell removed, the return 82 of the retaining member 81 exposed at the opening 80 in the outer peripheral wall of the outer shell 71 can be pushed in to dislodge the return 82 from the stepped portion 83, allowing the retaining member 81 to be removed upwards from the outer shell, thus allowing the seat rotation shaft 42 to be removed and the seat 3 from the main frame 2 to be separated. In this embodiment, the retaining member insertion hole 79 is a vertical hole into which the retaining member 81 is inserted from the upper surface of the outer shell 71. However, the embodiment is not limited to this, and for example, the retaining member insertion hole 79 and the stepped portion 83 may be formed horizontally so that the retaining member 81 is inserted from the front of the outer shell 71. The retaining member insertion hole 79 only needs to be provided in a direction intersecting the shaft 42. In this case as well, by pushing in the return 82 of the retaining member 81 that is exposed in the opening 80, the return 82 can be removed from the stepped portion 83, allowing the retaining member 81 to be removed upwards from the outer shell, and thus the seat rotation shaft 42 can be removed to separate the seat 3 from the main frame 2.

[0048] (Backrest reaction mechanism) The backrest reaction force mechanism 5 is not limited to a specific type, but in this embodiment, as shown in Figure 3, a reaction force mechanism 60 using a spring is used to obtain a force (reaction force) that compresses the spring when the backrest 4 tilts backward, attempting to push the backrest 4 back to its initial position, and a weight-sensitive (or sensing) reaction force application mechanism 61 is used in conjunction with the backrest 4 to lift the seat 3 when the backrest 4 is tilted backward, thereby making the resistance to back rocking proportional to the user's weight. Of course, depending on the embodiment, only one of the reaction force mechanisms may be used.

[0049] Specifically, a weight-sensitive reaction force application mechanism 61 and a spring-based reaction force mechanism 60 are incorporated in front of the backrest rotation axis 25 of the backrest support member 21, and are provided between the backrest support member 21 and the reaction force adjustment operating shaft 7 of the main frame 2 to generate a force (reaction force) that attempts to push back the backrest 4 in conjunction with the backward tilt of the backrest 4.

[0050] Here, the spring-type reaction force mechanism 60 is provided by interposing a reaction spring, for example, a single compression coil spring 65, between the spring support shaft 21E of the backrest support member 21 and the reaction force adjustment operating shaft 7, which is a fixed shaft attached to the main frame 2. This spring-type reaction force mechanism 60, including the compression coil spring 65, is provided so as to generate a force between the backrest support member 21, which is pivotably supported by the main frame 2, and the fixed shaft on the front side of the main frame 2, for example, the reaction force adjustment operating shaft 7, that tries to push the backrest 4 back in conjunction with the backward tilt of the backrest 4.

[0051] The compression coil spring 65 is mounted between a fixed shaft, such as the reaction force adjustment operating shaft 7, and the spring support shaft 21E of the arm portion 21B of the backrest support member 21, via a front spring mount 62 and a rear spring mount 63. Mounting pins 64 are inserted between the front and rear spring mounts 62 and 63 to prevent buckling of the compression coil spring 65.

[0052] The front spring mount 62 and rear spring mount 63 are known mechanical elements and therefore will not be described in detail, but they have, for example, a shaft portion that fits inside the spring and a seat that receives the end of the spring, and are equipped with means for engaging with a fixed shaft, such as the reaction force adjustment operating shaft 7, or a movable shaft, such as the spring support shaft 21E, such as a recess, a protrusion, or a hook portion. In this embodiment, since the reaction force mechanism is equipped with an initial reaction force adjustment mechanism 6, it abuts against the fixed shaft, the reaction force adjustment operating shaft 7, via a slider 66. Therefore, on the surfaces of the slider 66 and the front spring mount 62 that come into contact with each other, for example, a semicircular convex portion 62a and a concave portion 66b are formed, having an axis (horizontal axis) parallel to the backrest rotation axis 25. By fitting the concave portion 66b and the convex portion 62a together, a universal joint is formed that allows the angle (formed by the slider 66 and the front spring mount 62) to be varied in a plane perpendicular to the backrest rotation axis 25, and the front spring mount 62 is supported so as to be able to swing freely relative to the slider 66.

[0053] Furthermore, the rear spring mount 63 is equipped with a hook on its rear side that hooks onto the spring support shaft 21E, and a shaft portion that protrudes laterally from the hook and acts as a spacer between the arm portion 21B. The arm portion 21B is supported so as to be able to swing by being hooked onto the spring support shaft 21E in such a way that lateral (widthwise) movement is prevented.

[0054] Therefore, as the backrest 4 tilts backward, the arm portion 21B rotates around the backrest rotation axis 25 and is pushed forward, compressing the compression coil spring 65 via the rear spring mount 63. At the same time, the seat support shaft 21D at the tip of the backrest support member 21 is lifted, raising the rear of the seat 3. Since the front end of the seat 3 is housed in the rearward-tilting elongated hole 12 of the main frame 2 via the rotation axis, this lifts the seat 3 slightly diagonally backward. As a result, the seat support shaft 21D at the tip of the backrest support member 21 bears the weight of the person sitting on the seat 3. In other words, a force proportional to the weight of the person sitting is applied to the tip of the backrest support member, and a reaction force is applied to the backrest 4 via the arm portion 21B of the backrest support member 21.

[0055] (Initial reaction force adjustment mechanism for the reaction force mechanism) The backrest reaction force application mechanism 5 is equipped with a reaction force adjustment mechanism 6 that allows adjustment of the initial reaction force (the rebound force of the compression coil spring 65 applied in the initial position).

[0056] The reaction force adjustment mechanism 6 adjusts the amount of compression of the compression coil spring 65 at the initial position (i.e., the initial compression amount) by changing the position in which one end of the compression coil spring 65 contacts a fixed member on the main frame 2 side. As shown in Figure 8, the reaction force adjustment mechanism 6 of this embodiment changes the amount of compression of the compression coil spring 65 at the initial position by using a cam mechanism to impart displacement in the expansion and contraction direction of the compression coil spring 65, and consists of a reaction force adjustment cam 51 that rotates by the reaction force adjustment operating shaft 7 and a slider 66 as a driven link.

[0057] In this embodiment, the reaction force adjustment cam 51 is integrally molded with the reaction force adjustment operating shaft 7 from a rigid synthetic resin, such as glass fiber reinforced nylon such as PA6-GF (polyamide 6). As shown in Figure 14, the reaction force adjustment cam 51 has a cam base circle 51f with a diameter smaller than the minimum shaft diameter of the reaction force adjustment operating shaft 7, for example, the shaft diameter of the tip shaft portion 55 in this embodiment, and the position of the cam base circle 51f is the starting point or ending point. In the case of the reaction force adjustment cam 51 of this embodiment, it is configured as a planar cam with a polygonal cam contour that allows the amount of cam displacement to be switched in multiple stages, for example, about 4 stages, within the swing range of the reaction force adjustment operating shaft 7 (the swingable range restricted between the regulating projection 49 of the operating shaft retainer 43 and the regulating projection 54 of the reaction force adjustment operating shaft 7).

[0058] Here, the starting or ending cam surface 51a consists of a flat surface that is tangent to the cam base circle 51f, which has a smaller diameter than the minimum shaft diameter of the reaction force adjustment operating shaft 7. The cam surfaces 51b, 51c, and 51d, which are switched as the reaction force adjustment operating shaft 7 rotates, gradually increase or decrease the displacement applied to the slider 66. As a result, the reaction force adjustment cam itself can be made compact while setting the cam displacement in multiple stages, and the cam can be operated with light force due to the relationship between force moment and torsional moment. Moreover, when not in a switching operation state, the force from the compression coil spring 65 acts perpendicular to the surface due to the contact between the flat surfaces, providing stability, and when switching the initial compression amount of the compression coil spring, a clicking sensation is generated as the displacement gradually increases as it moves over the switching section 51e.

[0059] Of course, the cam contour surface of the reaction force adjustment cam 51 is not limited to the polygonal, intermittent flat end surface shown in the figure, but may also be a cam contour consisting of a continuous curved surface that provides stepless displacement, so that the displacement applied to the compression coil spring 65, i.e., the initial compression amount, can be changed steplessly by operating the reaction force adjustment operating shaft 7. In this case as well, by making the cam base circle 51f smaller in diameter than the shaft diameter of the smallest part of the reaction force adjustment operating shaft 7, the reaction force adjustment cam itself can be made compact while setting the cam displacement in multiple stages, and the cam can be operated with light force due to the relationship between force moment and torsional moment.

[0060] In this embodiment, as shown in Figure 13, a pair of reaction force adjustment cams 51 are provided spaced apart on the reaction force adjustment operating shaft 7. In this case, as shown in Figure 9, the reaction force adjustment cams 51 operate by pressing the slider 66 at two separate points, which makes it less likely for the movement of the slider 66 to become uneven and makes it easy to move it in parallel without twisting.

[0061] As shown in Figure 13, an intermediate shaft portion 52 is formed between the pair of reaction force adjustment cams 51, supported by an intermediate bearing portion 11. In addition, a shaft portion 53 with a circular cross-section is provided on the outside of each reaction force adjustment cam 51 (away from the central intermediate shaft portion 52). The shaft portion 53 and the intermediate shaft portion 52 are, for example, axes of a circle (i.e., shaft diameter) that enclose the vertex of the contour portion that gives the maximum displacement of the reaction force adjustment cam 51, and are provided to prevent the slider 66 that is in contact with the reaction force adjustment cam 51 from swinging outward or inward (left-right direction) and deviating. Furthermore, on the outer side of each shaft portion 53, there is a restricting projection (stopper) 54 that restricts the rotation of the reaction force adjustment operating shaft 7, and a shaft portion 56 of a certain diameter that allows relative circumferential movement (rotation) of the restricting projection (stopper) 49 that protrudes from the inner circumferential surface of the operating shaft retainer 43 toward the axis center. The restricting projection 49 of the operating shaft retainer 43 and the restricting projection 54 around the shaft portion 56 are arranged to restrict the rotation of the reaction force adjustment operating shaft 7 to within a certain range (approximately 270°) (see Figure 6).

[0062] Further outside each shaft portion 56, there is a tip shaft portion 55 supported by a semicircular open bearing portion 14 of the partition wall 2C on the far side when viewed from the round hole 13, which is the insertion hole for the reaction force adjustment operating shaft 7, and a front shaft portion 57 supported by a semicircular open bearing portion 14 of the partition wall 2C on the near side. Here, the regulating projection 54 on the far side is at the same height (i.e., the same diameter) as the shaft portion 53, and the regulating projection 54 on the near side is at the same height (i.e., the same diameter) as the shaft portion 57. Also, on the outside of the shaft portion 57 supported by the open bearing portion 14 of the partition wall 2C, there is a shaft portion 59 with a diameter similar to that of the shaft portion 56, which forms a groove between the shaft portion 58 supported by the round hole 13 of the peripheral wall portion 2A into which the open bearing portion 44 of the edge of the operating shaft retainer 43 is fitted.

[0063] In other words, the reaction force adjustment operating shaft 7 of this embodiment is formed such that the tip shaft portion (referred to as the tip shaft portion 55) is the smallest in diameter among the shaft portions inserted into the main frame, the shaft portion 53 and the intermediate shaft portion 52 are circles (i.e., shaft diameters) that enclose the vertex of the contour portion that gives the maximum displacement amount of the reaction force adjustment cam 51, and the shaft portions 57 and 58 are formed as shaft portions with a larger diameter than the shaft portion 53 and a diameter that allows them to pass through the round hole 13 with sufficient clearance. In short, the reaction force adjustment operating shaft 7 of this embodiment is formed so that the shaft diameter increases sequentially from the tip, and the reaction force adjustment operating shaft 7 can be inserted straight into the round hole 13 using an assembly robot or the like.

[0064] As shown in Figure 5, the reaction force adjustment operating shaft 7 is supported so that it can rotate freely while preventing axial movement, as the tip shaft portion 55 and shaft portion 57 are supported by the semicircular open bearing portion 14 of the rear and front (left and right) partition walls 2C, and at the same time, the shaft portion 59 and tip shaft portion 55 are pressed down from above by the open bearing portion 44 on the edge of the operating shaft retainer 43. In addition, the shaft portion 58 is supported by the round hole 13 of the peripheral wall portion 2A, and the outer flange 7B abuts against the peripheral wall portion 2A, thereby positioning the reaction force adjustment operating shaft 7 for insertion into the main frame 2.

[0065] On the other hand, in this embodiment, the slider 66 that contacts the reaction force adjustment cam 51 is housed in a slider housing 50 integrally molded with the operating shaft retainer 43, thereby being held to move linearly along a single axis connecting the reaction force adjustment operating shaft 7 and the spring support shaft 21E at the tip of the spring receiving arm 21B of the backrest support member 21 in its initial position (when no one is seated). Therefore, the slider 66 applies the same amount of compression to the compression coil spring 65 as the cam displacement applied by the reaction force adjustment cam 51 via the rear front spring mount 62.

[0066] As shown in Figure 9, the slider 66 has cam receiving surfaces (contacts) 66a that protrude forward at both the left and right ends and contact the reaction force adjustment cams 51. Here, the cam receiving surfaces (contacts) 66a of the slider 66 that contact the reaction force adjustment cams 51 are flat surfaces (i.e., flat-end contacts), and are formed as a roughly H-shaped block with the cam receiving surfaces 66a at both ends protruding so as to face a pair of reaction force adjustment cams 51 that are spaced apart with the intermediate shaft portion 52 in between. In addition, a slight protrusion 66c that functions as a rail is formed on the side surface of the slider 66, and is fitted into a groove on the inner surface of the slider 66 to support sliding in the front-rear direction, i.e., in the direction of expansion and contraction of the spring. Note that in this embodiment, the cam receiving surfaces (contacts) 66a are flat ends, but depending on the circumstances, they may be pointed ends or rounded ends.

[0067] According to the initial reaction force adjustment mechanism of the reaction force mechanism described above, by rotating the reaction force adjustment operating shaft 7, the cam surface that contacts the slider 66 of the reaction force adjustment cam 51 is switched, increasing or decreasing the amount of displacement applied to the compression coil spring 65, thereby switching the initial compression amount of the compression coil spring 65. Moreover, since the reaction force adjustment cam 51 starts or ends at the position of the cam base circle 51f, which has a smaller diameter than the minimum shaft diameter of the reaction force adjustment operating shaft 7, the switching operation can be performed with less force when turning the handle 7A of the reaction force adjustment operating shaft 7 due to the shorter diameter. Furthermore, the sensitivity of the reaction force mechanism can be switched to gradually lighter or heavier by rotating the handle grip 7A that can adjust the initial reaction force of the spring. In particular, in the case of a chair that uses a weight-sensitive reaction force application mechanism as a backrest reaction force mechanism, as in this embodiment, the weight of the sitter can be used as part of the reaction force when the backrest tilts backward. Therefore, the compression coil spring 65 used as the spring that applies the reaction force can be a spring with a small reaction force. As a result, the force applied to the reaction force adjustment operating shaft 7 is not as large as in a backrest reaction force mechanism consisting only of a reaction force mechanism 60 that uses a spring that compresses when the backrest 4 tilts backward to obtain a reaction force, and sufficient durability can be obtained even if the reaction force adjustment operating shaft 7 is made of resin. That is, by turning the handle 7A of the reaction force adjustment operating shaft 7, the feeling that allows adjustment of the stiffness of the reaction force of the weight-sensing mechanism can be changed.

[0068] Figures 28 to 32 also show other embodiments of the initial reaction force adjustment mechanism. In this initial reaction force adjustment mechanism, the reaction force adjustment operating shaft 70 is rotatably supported by an intermediate bearing portion 11 and an outer bearing portion 67 provided on the bottom wall portion 2B of the main frame 2, utilizing the biasing force of the reaction force spring 65, while rotation is restricted between the main frame 2 and the reaction force adjustment operating shaft 70. In other words, the reaction force adjustment operating shaft 70 is rotatably supported on both sides of the reaction force adjustment cam 51 by the outer bearing portion 67 which supports the outer shaft portion of the reaction force adjustment cam 51 and the inner bearing portion (i.e., the intermediate bearing portion 11) which supports the inner shaft portion of the reaction force adjustment cam 51, and the vicinity of each reaction force adjustment cam 51 is rotatably supported. That is, the reaction force adjustment cam 51 is supported at both ends over a short distance. Therefore, even if the surrounding shafts of the reaction force adjustment operating shaft 70, including the reaction force adjustment cam 51, are thin, the structure can be made less prone to bending because both sides close to the reaction force adjustment cam 51 are supported.

[0069] As shown in Figures 29 and 30, the reaction force adjustment operating shaft 70 comprises a handle (also called a grip) 70A, a flange portion 70B, a shaft portion 93, a reaction force adjustment cam 51, an intermediate shaft portion 92, a left-right wobble prevention portion 94, a reaction force adjustment cam 51, and a tip shaft portion 95. The shaft portion 93 and shaft portion 92 beyond the flange portion 70B are formed to have the same shaft diameter, while the tip shaft portion 95 has the smallest shaft diameter. In this embodiment, the reaction force adjustment operating shaft 70 and the reaction force adjustment cam 51 are integrally molded from a rigid synthetic resin such as glass fiber reinforced nylon such as PA6-GF (polyamide 6), but are not particularly limited to this, and may be made of metal, or may be made of two components: a metal shaft and a plastic cam member.

[0070] On the other hand, in this embodiment, the outer bearing portion 67 is integrally formed to rise from the bottom wall portion 2B of the main frame 2, similar to the vertical wall 11A of the intermediate bearing portion 11, and a semicircular open bearing portion 69 is provided concentrically with the semicircular open bearing portion 11D of the intermediate bearing portion 11. The open bearing portion 69 is open toward the compression coil spring 65 side. Therefore, the front half of the reaction force adjustment operating shaft 70 inserted into the main frame 2 is supported by the semicircular open bearing portion 11D of the intermediate bearing portion 11 and the semicircular open bearing portion 69 of the outer bearing portion 67. In addition, the reaction force adjustment operating shaft 70 is constantly biased by the force of the reaction force spring, i.e., the compression coil spring 65 of the backrest reaction force mechanism 5, via the slider 66. As a result, the reaction force adjustment operating shaft 70 is constantly pressed against the intermediate bearing portion 11 and the outer bearing portion 67 and is supported at four points. Therefore, the reaction force adjustment operating shaft 70 is held rotatably without being clamped between the operating shaft retainer 43 and the semicircular open bearing portion 14 of the left and right partition walls 2C, as shown in the embodiments in Figures 3 to 16. The intermediate bearing portion 11 and the outer bearing portion 67 may be formed separately from the main frame 2 and fixed to the bottom wall portion 2B by screws or welding.

[0071] Furthermore, as shown in Figures 29 and 30, the reaction force adjustment shaft 7 is supported by the semicircular open bearing portion 69 of the rear outer bearing portion 67, with the tip shaft portion 95 supported by the semicircular open bearing portion 69 of the front outer bearing portion 67, while the flange portion 70B abuts against the edge of the insertion hole 98 (i.e., the peripheral wall portion 2A), thereby preventing axial movement while allowing rotational support and positioning for insertion into the main frame 2.

[0072] Although not shown in the figures, it is desirable that the slider 66, which is positioned opposite the reaction force adjustment cam 51 of the reaction force adjustment operating shaft 70, be held on the main frame 2 so as to be movable in the expansion and contraction direction of the reaction force spring in the initial position of the reaction force application mechanism. Therefore, for example, as shown in the embodiments in Figures 3 to 16 (although not shown), the slider 66 is housed in a slider housing 50 which is integrally molded with the operating shaft retainer 43 and fixed to the left and right partition walls 2C. Of course, the slider housing 50 is not limited to being integrally molded with the operating shaft retainer 43; it may also be a separately molded part assembled to the operating shaft retainer 43, or assembled to the main frame 2 or integrally molded with the main frame 2.

[0073] In this embodiment, the reaction force adjustment operating shaft 70 has a portion, such as the reaction force adjustment cam 51 and the lateral vibration prevention portion 94, which have a larger diameter than the shaft diameters of the shaft portions 93 and 92 beyond the flange portion 70B. Therefore, it cannot be inserted into a circular hole with a shaft diameter slightly larger than the shaft diameters of the shaft portions 93 and 92. Furthermore, if one attempts to insert it concentrically with the outer bearing portion 67 and the bearing portions 11D and 69 of the intermediate bearing portion 11, the reaction force adjustment cam 51 and the lateral vibration prevention portion 94 will interfere with the outer bearing portion 67 and the intermediate bearing portion 11. Therefore, in this embodiment, the through hole (referred to as the insertion hole 98) for inserting the reaction force adjustment operating shaft 70 of the reaction force adjustment mechanism 6, which is opened in one peripheral wall portion 2A of the main frame 2, for example, the right peripheral wall portion, is formed in an elliptical shape with its long axis generally oriented in the front-rear direction. At the same time, the diameter of the insertion hole 98 on the side of the main frame in the short axis direction is made larger than the maximum dimension of the part inserted into the main frame 2 (the distance from the axis to the shaft diameter of the left-right wobble prevention part 94 or the maximum contour position of the reaction force adjustment cam 51). This allows the reaction force adjustment operating shaft 70 to be inserted at a position away from the bearing center (original installation position) of the outer bearing part 67 and the intermediate bearing part 11, and then shifted and set to the original installation position (called shift insertion). Therefore, it becomes possible to insert and install the reaction force adjustment cam 51 and the left-right wobble prevention part 94 in the predetermined position while avoiding interference with the outer bearing part 67 and the intermediate bearing part 11.

[0074] Furthermore, in this embodiment, the insertion hole 98 also functions as a means for restricting the swing range of the reaction force adjustment operating shaft 70. A projection 97 corresponding to the restricting projection 49 of the operating shaft retainer 43 in the above-described embodiment is formed on the front end side of the insertion hole 98 in the longitudinal axis direction, projecting toward the rear. On the other hand, a projection 96 corresponding to the restricting projection 54 in the above-described embodiment is formed on the reaction force adjustment operating shaft 70. This allows the reaction force adjustment operating shaft 70 to swing until the projection 96 of the reaction force adjustment operating shaft 70 contacts the projection 97 of the insertion hole 98 in the main frame 2. The reaction force adjustment operating shaft 70 is provided with a flange 70B, and the flange 70B is provided to contact the periphery of the hole 98 (i.e., the peripheral wall portion 2A) to position the insertion position into the main frame 2. In this embodiment, the reaction force adjustment operating shaft 70 is provided so as to be able to swing within a certain range, and the cam surface 51A that provides the smallest amount of cam displacement is set as the starting or ending point. However, it is not limited to this, and it may be provided so as necessary to rotate one or more times, that is, so that the switching of the amount of cam displacement cycles. This is also the case in the embodiments shown in Figures 3 to 16.

[0075] As described above, the reaction force adjustment cam 51 has a cam base circle 51f with a diameter smaller than the minimum shaft diameter of the reaction force adjustment operating shaft 70, for example, the shaft diameter of the tip shaft portion 95 in this embodiment, and the position of the cam base circle 51f is used as the starting point or ending point (see Figure 14).

[0076] Here, the starting or ending cam surface 51a consists of a flat surface that is tangent to the cam base circle 51f, which has a smaller diameter than the minimum shaft diameter of the reaction force adjustment operating shaft 70. It is configured as a planar cam with a polygonal cam contour that allows the amount of cam displacement to be switched in multiple stages, for example, about four stages, within the oscillation range of the reaction force adjustment operating shaft 70. Therefore, the cam surfaces 51b, 51c, and 51d that are switched as the reaction force adjustment operating shaft 70 rotates gradually increase or decrease the displacement applied to the slider 66. As a result, the reaction force adjustment cam itself can be made compact while setting the cam displacement in multiple stages, and the cam can be operated with light force due to the relationship between force moment and torsional moment.

[0077] Of course, the cam contour surface of the reaction force adjustment cam 51 is not limited to the polygonal, intermittent flat end surface shown in the figure, but may also be a cam contour consisting of a continuous curved surface that provides stepless displacement, so that the displacement applied to the compression coil spring 65, i.e., the initial compression amount, can be changed steplessly by operating the reaction force adjustment operating shaft 70. In this case as well, by making the cam base circle 51f smaller in diameter than the shaft diameter of the minimum shaft portion of the reaction force adjustment operating shaft 7, the reaction force adjustment cam itself can be made compact while setting the cam displacement in multiple stages, and the cam can be operated with light force due to the relationship between force moment and torsional moment.

[0078] As shown in Figure 28, a pair of reaction force adjustment cams 51 are provided on the reaction force adjustment operating shaft 70 at a distance from each other, and are designed to apply cam displacement by pressing the slider 66 at two separate points. This makes it less likely for the movement of the slider 66 to become uneven, and makes it easy to move it in parallel without twisting.

[0079] As shown in Figure 28, an intermediate shaft portion 92 is formed between the pair of reaction force adjustment cams 51, supported by the intermediate bearing portion 11. Furthermore, a lateral wobble prevention portion 94, which has a larger diameter than the intermediate shaft portion 92, is formed inside the area supported by the left and right vertical walls 11A of the intermediate bearing portion 11, for example, in the central part of the intermediate shaft portion 92. This lateral wobble prevention portion 94 engages axially with a projection 68 that protrudes upward from the tip edge of the overhang portion 11C of the main frame 2, for example, the intermediate bearing portion 11, toward the intermediate shaft portion 92. This creates a structure that makes it difficult for the reaction force adjustment operating shaft 70 and, consequently the reaction force adjustment cam 51 to move in the left-right direction (width direction), that is, a lateral wobble prevention structure that prevents misalignment between the reaction force adjustment cam 51 and the contact surface 66a of the slider 66, which is the driven link.

[0080] In this embodiment, the shaft diameter of the reaction force adjustment operating shaft can be made smaller, allowing the reaction force adjustment to be operated with less force. In particular, in the case of a chair that uses a weight-sensitive reaction force application mechanism as a backrest reaction force mechanism, the weight of the sitter can be used as part of the reaction force when the backrest tilts backward, so the compression coil spring 65 used as the spring that applies the reaction force can be a spring with a smaller reaction force. As a result, the force applied to the reaction force adjustment operating shaft 7 does not become larger than in a backrest reaction force mechanism consisting only of a reaction force mechanism 60 that uses a spring that compresses when the backrest 4 tilts backward to obtain a reaction force, and sufficient durability can be obtained even if the reaction force adjustment operating shaft 7 is made of resin.

[0081] (Backrest rocking range adjustment mechanism) Between the main frame 2 and the backrest 4, as shown in Figures 3 and 22, there is a rocking range adjustment mechanism 8 that allows adjustment of the maximum reclined position in which the backrest 4 can rock by constraining the movement of a member that is linked to the backrest 4, such as the backrest support member 21.

[0082] This rocking range adjustment mechanism 8 restricts and adjusts the maximum reclining position in which the backrest 4 can rock by changing the position in which a member that works in conjunction with the backrest 4, such as a backrest support member 21, contacts the main frame 2. It consists of a locking block (a so-called reclining range restricting member) 26 that moves with the backrest 4 and contacts the main frame 2 to prevent the backrest 4 from tilting backward, and a fixed block 34 that fixes the position of the locking block 26 relative to the backrest 4. Here, it is preferable that at least one of the movable member, the locking block 26, and the fixed member, the fixed block 34, is made of a resin material, such as polyacetal resin (POM) with high sliding properties. Furthermore, a buffer block 41 is provided on the main frame 2 side as needed to reduce the impact and collision noise when the locking block 26 contacts the frame.

[0083] In this embodiment, as shown in Figure 22, the locking block 26 is fixed to a rocking range switching operation shaft 9 attached to a backrest support member 21, and is provided to swing together with the backrest support member 21, and to rotate coaxially with the rotation of the rocking range switching operation shaft 9. This locking block 26 has a plurality of stepped portions, for example, four stepped portions 28A to 28D of varying lengths, that contact the buffer block 41 of the main frame 2 at different positions from the center of the rocking range switching operation shaft 9, in order to change the maximum reclining position in which the backrest can be rocked in stages. For example, as shown in Figure 24, the locking block 26 has a semi-fan-shaped lever-shaped locking portion 28 having a plurality of stepped portions 28A to 28D of varying lengths, for example, four, from the center of the rocking range switching operation shaft 9, i.e., the center of rotation.

[0084] Specifically, as shown in Figures 23 and 24, the locking block 26 has a cylindrical portion 27 through which the locking range switching operation shaft 9 passes, a lever-shaped locking portion 28 protruding radially outward from the cylindrical portion 27, a spring housing portion 32 at one end of the cylindrical portion 27 for housing a compression coil spring (not shown) that constantly biases the locking block 26 toward the other end, and a protrusion 30 at the other end of the cylindrical portion 27 that fits into a recess 36 of the fixed block 34. The locking block 26 is positioned by being pressed against the fixed block 34 fixed to the main frame 2 on the other end of the locking range switching operation shaft 9 by the spring force of the compression coil spring (not shown) housed at one end.

[0085] The shapes of the protrusions 30 and 36 on the fixed block 34 and the locking block 26 are not limited to a specific shape, as long as they interlock with each other in the axial direction of the locking range switching operation shaft 9 and can be overcome in the circumferential direction when a certain amount of rotation is applied. In this embodiment, for example, it consists of a combination of a convex protrusion and a concave recess in the shape of a kamaboko (a semicircular shape, with a raised center and a crescent-shaped cross-section). In this embodiment, one kamaboko-shaped protrusion 30 is provided on the other end of the cylindrical portion 27 of the locking block 26. On the other hand, as shown in Figure 25, the fixed block 34 has multiple, for example, four, kamaboko-shaped concave recesses 36 arranged in a fan shape around the locking range switching operation shaft 9 (more precisely, the hole 38 through which the locking range switching operation shaft 9 passes).

[0086] In other words, the locking range adjustment mechanism 8 in this embodiment is provided to be switchable in four stages at arbitrary intervals, for example, at 6° intervals from a reference position (0°). Furthermore, at both ends of a group of recesses 36 arranged in a fan shape on the fixed block 34 at the same intervals (outside the region where the recesses 36 are continuously formed), restricting blocks 35 are formed at each degree that restricts the swing range. These restricting blocks 35 abut against the side surface of the fixed base 29 of the locking block 26, thereby preventing the movement of the locking block 26. The rigidity of the fixed base 29 and the lever-shaped locking portion 28 is increased by providing ribs. In addition, the other end face of the cylindrical portion 27 of the locking block 26 is provided with a sliding projection 31 that is lower than the projection 30 and contacts the surrounding surface 37 of the recess 36 of the fixed block 34, thereby reducing the contact area between the fixed block 34 and the locking block 26 and reducing the force required for the rotation of the locking block 26.

[0087] The lever-shaped locking portion 28 is formed in stages, for example, around the central axis of the cylindrical portion 27, divided into four stages at arbitrary intervals, for example, at 6° intervals from a reference position (0°), such that the length from the center of rotation becomes progressively shorter or longer. In this embodiment, a semi-fan-shaped lever-shaped locking portion 28 having four stages of stepped length is formed by continuously forming levers of four stages of length. In this embodiment, the lever-shaped locking portion 28 is provided in pairs at intervals in the middle of the cylindrical portion 27, for example, and is connected to each other by ribs to increase rigidity, thereby increasing mechanical rigidity and making it resistant to twisting. Of course, the lever-shaped locking portion 28 may also be provided in one place, for example, in the center of the cylindrical portion 27. Furthermore, the lever-shaped locking portion 28 is not particularly limited to a fan shape having four stages of stepped length on the same plane, and in some cases, the four stages of stepped length may be formed on four different planes.

[0088] The cylindrical portion 27 is provided with a shaft hole 33 in which a keyway is formed. On the other hand, the locking range switching operation shaft 9 is also provided with a key 9A, which is supported so as to be movable in the axial direction when the locking range switching operation shaft 9 is inserted through the cylindrical portion 27, and is also designed to rotate together in the rotational direction.

[0089] As shown in Figure 27, the locking range switching operation shaft 9 is divided into two parts: a short first shaft portion 9G having a cylindrical receiving portion 9E and a flange 9F, and a long second shaft portion 9H having a key portion 9A and a flange 9D. The second shaft portion 9H is inserted through one plate 21A of the backrest support member 21 from the outside and near the other plate 21A, while the first shaft portion 9G is inserted through the other plate 21A of the backrest support member 21 from the outside, and the tip of the second shaft portion 9H is fitted into the cylindrical receiving portion 9E near the other plate 21A to connect them. As a result, the two flanges 9D and 9F are positioned so that they abut against the outer surfaces of the plates 21A on both sides of the backrest support member 21. The two divided locking range switching operation shaft 9 is integrated by press-fitting or crimping after assembly. An operating lever 9B is fitted and screwed into a second shaft portion 9H that protrudes outward from the backrest support member 21. The operating lever 9B and the locking range switching operating shaft 9 are connected in the rotational direction by the fitting of a key 9A and a keyway (not shown). The flange 9D, which is made of a washer, is provided to prevent it from coming off by a retaining protrusion 9C formed by partially crushing the shaft portion.

[0090] The through holes 22 in the plates 21A on both sides of the backrest support member 21 are each provided with grooves for passing the key 9A through. This allows the second shaft portion 9H to be inserted from either side of the plate 21A.

[0091] As shown in Figure 25, the fixing block 34 is provided with a projection-shaped claw 39 that engages with the hole 23 of the plate 21A and a plate-shaped claw 40 that fits against the lower edge of the plate 21A and catches on the side opposite to the side with the fan-shaped recess 36 (the so-called surface). The projection-shaped claw 39 is a claw member with a barb that deforms to narrow as it passes through the hole 23 and returns to its original shape after passing through to engage with the plate 21A. This allows the fixing block 34 to be easily attached by pushing the claw portion 39 into the pair of holes 23 drilled around the through hole 22 of the backrest support member 21 and fitting the claw portion 40 against the lower edge of the plate 21A. Simultaneously with the attachment of the fixing block 34 to the backrest support member 21, the hole 38 through which the locking range switching operation shaft 9 passes and the hole 22 of the plate 21A are aligned.

[0092] The recesses 36 of the fixed block 34 are arranged in a fan shape with semicircular recesses at the same pitch as the protrusions 30 of the locking block 26. As a result, the boundaries between the recesses 36 have apex points with small radii of curvature, and the protrusions 30 of the locking block 26, which are pressed by a spring (not shown), cannot remain near the apex and fall into one of the bottoms. This ensures reliable switching. However, the recesses 36 of the fixed block 34 and the protrusions 30 of the locking block 26 are not limited to the semicircular recesses described above; for example, they may be hemispherical recesses or other shapes.

[0093] In this embodiment, the buffer block 41 provided on the main frame 2 is, for example, a semi-circular resin block exhibiting rubber elasticity, and is housed in a recess 19 surrounded by side walls formed at the rear end of the main frame 2. A push-in pin portion 41a is integrally molded on the bottom surface of the resin block 41, and it is fixed to the main frame 2 by fitting the push-in pin portion 41a into the hole 20 on the bottom surface of the recess 19. This buffer block 41 mitigates the impact and noise when the lever-shaped locking portion 28 of the locking block 26 strikes the main frame 2, and may be omitted in some cases, or may be provided on the stepped portion of the lever-shaped locking portion 28 itself.

[0094] With the locking range adjustment mechanism 8 of this embodiment configured as described above, by rotating the locking range switching operation shaft 9, the stepped portion of the lever-shaped locking portion 28 that contacts the buffer block 41 of the main frame 2 is selected from among the multiple stepped portions 28A to 28D. In this case, the convex portion 30 of the locking block 26 is fitted into the corresponding recess 36 of the fixed block 34, and the inclination angle of the lever-shaped locking portion 28 is fixed. Therefore, when the backrest 4 attempts to tilt backward, the stepped portion of the lever-shaped locking portion 28 at the corresponding angle (any of 28A to 28D) contacts the buffer block 41 of the main frame 2, preventing further locking of the backrest.

[0095] The above-described embodiment is merely one example of a preferred embodiment of the present invention and is not limited thereto. Various modifications can be made without departing from the spirit of the invention. For example, in the above-described embodiment, a pair of reaction force adjustment cams 51 are provided on the reaction force adjustment operating shafts 7 and 70 at intervals, and intermediate shaft portions 52 and 92 and an intermediate bearing portion 11 are provided between the pair of cams 51. However, the cam support structure is not particularly limited to this, and one reaction force adjustment cam 51 may be provided, with a pair of backup portions on either side of it so as to sandwich the reaction force adjustment cam 51. For example, the reaction force adjustment cam 51 may be positioned between the left and right vertical walls 11A of the intermediate bearing portion 11, or a pair of bearing portions that are independent of each other may be provided, as shown in Figure 31 with respect to the outer bearing portion 97. In this case, a flat surface that contacts the reaction force adjustment cam 51 will be formed on the front surface of the slider 66, for example, in the center.

[0096] Furthermore, in the above-described embodiment, the reaction force adjustment operating shafts 7, 70 and the reaction force adjustment cam 51 are integrally molded from synthetic resin, but the invention is not limited to this, and may be made from integrally machined parts made by machining or forging metal, or in some cases, from two or more components.

[0097] Furthermore, in the above-described embodiment, the backrest is exemplified as being composed of a frame-shaped back frame and mesh-like upholstery stretched over it, but the backrest structure is not particularly limited to this, and other backrest structures such as a backrest structure in which a perforated shell is fixed to a frame-shaped back frame or a back structure in which a cushion is fixed to a backboard and covered with upholstery are also acceptable.

[0098] Furthermore, in the above-described embodiment, the backrest reaction force application mechanism 5 is equipped with a reaction force adjustment mechanism 6 that allows adjustment of the initial reaction force (the repulsive force of the compression coil spring 65 applied in the initial position). However, when it is not necessary to provide the reaction force adjustment mechanism 6, it may be configured between the backrest and the fixed shaft of the main frame 2.

[0099] Furthermore, in the above-described embodiment, an example is given in which a compression coil spring acting in the axial direction of the cylindrical portion 27 is used as a means of constantly biasing the locking block 26 toward the fixed block 34, but this is not particularly limited to this, and a leaf spring may be incorporated, or other spring-elastic materials such as a ball plunger may be used on the protrusion 30 of the locking block 26 as a substitute.

[0100] Furthermore, in the above-described embodiment, we mainly explained an example in which the rocking range adjustment mechanism 8, which adjusts the maximum reclined position in which the backrest 4 can rock by constraining the movement of a member that works in conjunction with the backrest 4, such as the backrest support member 21, as a mechanism for fixing the position between two relatively rotating members, is applied as a positioning member for the rocking range switching operation shaft. However, it is not limited to this, and can be implemented as an operating member that enables the chair to function, and can be applied as a positioning member between the back frame and the headrest, for example.

[0101] Furthermore, in the above-described embodiment, the retaining member 81 is positioned at one end of the seat rotation shaft 42, but this is not the only way to go. It is also possible to use through holes for both the bearing holes supporting the seat rotation shaft 42 and insert the retaining members 81 at both ends of the seat rotation shaft 42 to prevent it from coming loose.

[0102] Furthermore, in the above-described embodiment, an example of a structure to prevent the shaft from coming loose connecting two relatively rotating members was mainly explained by describing its application to a seat rotation shaft 42 connecting the seat outer shell and the main frame. However, it is not limited to this, and it can also be applied to other connecting structures between chair components, such as the connecting structure between the seat outer shell 71 and the back support member 21, the connecting structure between the headrest and the back frame, or a structure to prevent the shaft from coming loose connecting two members that do not rotate relative to each other. [Explanation of symbols]

[0103] 1 leg 2 Mainframe 3 seats 4 Backrest 5. Backrest reaction mechanism 6. Reaction force adjustment mechanism 7. Reaction force adjustment operating shaft 8. Locking range adjustment mechanism 9. Locking range switching operation axis 10 Cover component 11 Intermediate bearing section 12 long hole 13 round holes 14 Open-type bearing section 15 screw holes 16 round holes 17 Bearing section 18 round holes 19. Dent 20 pin holes 21 Backrest support member 22 holes 23 holes 24 nuts 25 Backrest rotation axis 26 Locking block 27 Cylinder part 28 Lever-shaped locking part 29 Fixed base 30 Convex part 31 Sliding protrusion 32 Spring housing 33 Operating shaft holes with keyways 34 Fixed Blocks 35 regulatory blocks 36 recesses 37 Edge 38 holes 39 Nails 40 Claw part 41 Buffer Block 42-seat rotation axis 43 Operating shaft retainer 44 Bearing section 45. Protrusions (spanning the partition wall) 46 through holes 47. Fixing part through which screws are inserted. 48. Groove (through the partition wall) 49. Restrictive protrusion (stopper) 50 Slider Housing 51 Reaction force adjustment cam 51f Cam base circle 51a, 51b, 51c, 51d Cam surface 52 Intermediate shaft section 53 Shaft 54. Restrictive protrusion (stopper) 55 Tip shaft 56 Shaft 57 Shaft 58 Shaft 59 Shaft 60. Spring-type backrest reaction mechanism 61 Weight-sensitive reaction force application mechanism 62 Front spring mount 63 Rear spring mount 64 mounting pins 65 Compression coil spring 66 Slider 66a Cam receiving surface (contact element) 67 Outer bearing section 68 Protrusions that extend toward the intermediate shaft 69 Semicircular open bearing section 70 Reaction force adjustment operating shaft 71 Outer Shell 72 Inner Shell 73 Cushions 74 Peripheral wall portion of the bottom surface of the outer shell 75 recess 76 slits 77. Blind round hole (bearing for the seat rotation axis) 78 Through hole (bearing for the seat rotation shaft) 79 vertical holes 80 Opening (for inserting the seat rotation axis) 81 Retaining member 82 Return 83 Multilayered section 84 Claw-shaped bearing part 85. Hook portion of the retaining member 86. Inclined surface portion (retaining member) 87 Locking part 90 recess 91 Blind Plate 92 Intermediate shaft section 93 Shaft 94. Anti-left-right sway section 95 Tip shaft 96 Protrusion of the reaction force adjustment operating shaft 97. Protrusion of the insertion hole 98 Insertion holes

Claims

1. A chair backrest reaction mechanism that generates a force pushing back the backrest in conjunction with the backward tilt of the backrest by compressing a reaction spring, a reaction force adjustment mechanism including a reaction force adjustment cam that applies a displacement to the reaction force spring in an expansion / contraction direction, and a reaction force adjustment operation shaft that rotates the reaction force adjustment cam to change the amount of cam displacement applied to the reaction force spring, wherein the amount of cam displacement applied by the reaction force adjustment cam is changed by rotating the reaction force adjustment operation shaft, and the reaction force adjustment mechanism adjusts the amount of initial compression of the reaction force spring; The reaction force adjusting cam has a cam base circle whose diameter is smaller than the smallest shaft diameter of the shaft portion of the reaction force adjusting operation shaft, and the position of the cam base circle is used as the starting point or the ending point. A reaction force adjustment mechanism for a chair back reaction force mechanism characterized by the above.

2. 2. The reaction force adjusting mechanism for a chair backrest reaction force mechanism according to claim 1, wherein said reaction force adjusting operation shaft is made of synthetic resin and is integrally formed with said reaction force adjusting cam.

3. The reaction force adjustment mechanism for a chair backrest reaction force mechanism according to claim 1 or 2, characterized in that the reaction force adjustment operating shaft and the reaction force spring are arranged in a perpendicular positional relationship, and the reaction force adjustment cam of the reaction force adjustment operating shaft applies cam displacement in the extension / contraction direction of the reaction force spring.

4. 4. The reaction force adjustment mechanism for a chair back reaction force mechanism according to claim 1, wherein the reaction force adjustment cam is configured as a planar cam with a polygonal cam contour that allows the cam displacement amount to be switched in stages in multiple steps, and the cam surface that serves as the starting point or ending point is made of a flat surface that is tangent to a cam base circle that has a diameter smaller than the shaft diameter of the smallest shaft part of the reaction force adjustment operating shaft, and the cam displacement amount provided by the cam surface that is switched in accordance with the rotation of the reaction force adjustment operating shaft increases or decreases in stages.

5. 5. The reaction force adjusting mechanism for a chair backrest reaction force mechanism according to claim 1, wherein the reaction force adjusting cam is provided at two positions spaced apart on the reaction force adjusting operation shaft.

6. 6. The reaction force adjustment mechanism for a chair backrest reaction force mechanism according to claim 5, characterized in that an intermediate bearing portion is provided to support an intermediate shaft portion between the reaction force adjustment cams at two locations on the reaction force adjustment operating shaft at least in the expansion direction of the reaction force spring.

7. The reaction force adjustment mechanism for a chair backrest reaction force mechanism as described in claim 6, characterized in that a left-right sway prevention part that engages with the intermediate bearing part in the axial direction is provided between the two reaction force adjustment cams.

8. 8. A reaction force adjustment mechanism for a chair backrest reaction force mechanism according to claim 1, wherein the reaction force adjustment operating shaft is rotatably supported at both ends of the reaction force adjustment cam by an outer bearing portion that supports the outer shaft portion of the reaction force adjustment cam and an inner bearing portion that supports the inner shaft portion of the reaction force adjustment cam.

9. A reaction force adjustment mechanism for a chair backrest reaction force mechanism described in any one of claims 1 to 8, characterized in that the backrest reaction force mechanism is used in combination with a weight-sensitive reaction force applying mechanism that makes resistance to back rocking proportional to the user's weight by linking it to lift the seat when the backrest is tilted backward.

10. A chair comprising a reaction force adjusting mechanism for a chair backrest reaction force mechanism according to any one of claims 1 to 9.

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