Reaction force mechanism and chair using same

A pivot shaft (10) which is a first shaft member coupled to a supporting member, an inner cylinder (12) which is a second shaft member coupled to a supported member, and an outer cylinder (14) which is a third shaft member are disposed to be approximately coaxial with each other and disposed radially in multiple layers. The pivot shaft (10) and the inner cylinder (12) are coupled to each other through a first rubber-like elastic member (11), and the inner cylinder (12) and the outer cylinder (14) are coupled to each other through a second rubber-like elastic member (13). The total reaction force is increased by restricting the rotation of the outer cylinder (14) by means of an operating pin (19) which is a reaction force adjusting part and thereby adding a reaction force resulting from the second rubber-like elastic member (13) to a base reaction force resulting from the first rubber-like elastic member (11).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of International Patent Application No. PCT/JP2016/050112, filed Jan. 5, 2016, which claims the benefit of Japanese Patent Application No. 2015-006878, filed Jan. 16, 2015, the contents of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a reaction force mechanism capable of adjusting a reaction force acting between a supporting member and a supported member, and a chair using the same.

Priority is claimed on Japanese Patent Application No. 2015-006878 filed Jan. 16, 2015, the content of which is incorporated herein by reference.

BACKGROUND ART

Among chairs used in offices and the like, there are chairs in which a backrest is tiltably attached to a support structure. Further, as a chair of this type, a chair in which a support structure which is a supporting member and a backrest which is a supported member are connected via a reaction force mechanism capable of adjusting a reaction force is known (for example, refer to Patent Document 1).

The reaction force mechanism disclosed in Patent Document 1 has a structure in which a plurality of unit biasing parts are provided in a pivotally connecting portion between a supporting member (support structure) and a supported member (backrest) in an axial direction of a pivot shaft and a combination of the unit biasing parts which causes a reaction force to be effective between the supporting member and the supported member can be selected by an operation lever. The reaction force mechanism is a mechanism which adjusts the reaction force acting between the supporting member and the supported member by switching the effective combination of the unit biasing parts. Therefore, as compared with a mechanism which adjusts the reaction force by changing an initial load of a single biasing part, it is possible to reduce an operation force required to adjust the reaction force.

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

However, in the reaction force mechanism disclosed in Patent Document 1, when an axial length of the pivot shaft is limited, the axial length of the unit biasing part should be shortened and a switching mechanism should also be arranged within the limited axial length due to a structure in which the plurality of unit biasing parts are arranged in the axial direction of the pivot shaft. Accordingly, strict design accuracy is required, which may increase manufacturing cost.

Therefore, an object of the present invention is to provide a reaction force mechanism which does not require a high degree of design accuracy and in which a reaction force acting between a supporting member and a supported member can be easily changed, and a chair using the same.

Solution to Problem

In order to achieve the aforementioned objects, according to an aspect of the present invention, there is provided a reaction force mechanism which is provided between a supporting member and a supported member supported by the supporting member to be tiltable and is capable of adjusting a reaction force resulting from the tilting movement of the supported member with respect to the supporting member, including a plurality of shaft members including a first shaft member connected to the supporting member, a second shaft member connected to the supported member and a third shaft member other than the first shaft member and the second shaft member and disposed coaxially and radially in multiple layers; a plurality of biasing members configured to connect the shaft members adjacent to each other in a radial direction; and a reaction force adjusting part configured to increase the reaction force against a base reaction force resulting from the biasing member interposed between the first shaft member and the second shaft member by restricting rotation of the third shaft member with respect to the first shaft member or the second shaft member.

Due to such a constitution, when the reaction force acting between the supporting member and the supported member is adjusted, the reaction force can be increased against the base reaction force resulting from the biasing member interposed between the first shaft member and the second shaft member by restricting the rotation of the third shaft member by means of the reaction force adjusting part.

Since the first shaft member, the second shaft member and the third shaft member are approximately coaxial with each other and disposed radially in multiple layers, even when an axial space is limited, an axial length of each of the shaft members and the biasing member interposed between the adjacent shaft members can be sufficiently secured.

The first shaft member may be constituted by a shaft member in an innermost layer, the second shaft member may be constituted by a shaft member disposed radially outside the first shaft member to be adjacent thereto, the third shaft member may be constituted by a shaft member disposed radially outside the second shaft member to be adjacent thereto, and the reaction force adjusting part capable of adjusting rotation of the third shaft member may be provided at the supporting member.

In this case, in a state in which the reaction force adjusting part does not restrict the rotation of the third shaft member, the third shaft member is rotated and displaced following the adjacent second shaft member, and the biasing member interposed between the second shaft member and the third shaft member does not generate a reaction force. Therefore, when the supported member is tilted with respect to the supporting member in this state, only a base reaction force of the biasing member interposed between the first shaft member and the second shaft member acts. Meanwhile, in a state in which the reaction force adjusting part restricts the rotation of the third shaft member, when the supported member is tilted with respect to the supporting member, the second shaft member rotates relative to the first shaft member and the third shaft member, and the reaction force of the biasing member interposed between the second shaft member and the third shaft member is added to that of the biasing member interposed between the first shaft member and the second shaft member. As a result, the reaction force between the supported member and the supporting member is adjusted to be increased.

The second shaft member may be constituted by a shaft member in an innermost layer, the third shaft member may be constituted by a shaft member disposed radially outside the second shaft member to be adjacent thereto, the first shaft member may be constituted by a shaft member disposed radially outside the third shaft member to be adjacent thereto, and the reaction force adjusting part capable of adjusting rotation of the third shaft member may be provided at the supporting member.

In this case, when the supported member is tilted with respect to the supporting member in a state in which the reaction force adjusting part does not restrict the rotation of the third shaft member, the third shaft member is rotated and replaced following the adjacent second shaft member, and the biasing member between the second shaft member and the third shaft member and the biasing member between the third shaft member and the first shaft member are connected in series and generate the base reaction force. Meanwhile, when the reaction force adjusting part restricts the rotation of the third shaft member, the relative rotation does not occur between the first shaft member and the third shaft member. Accordingly, when the supported member is tilted with respect to the supporting member in this state, the biasing member between the second shaft member and the third shaft member generates the reaction force by itself. As a result, the reaction force between the supported member and the supporting member is adjusted to be increased.

An axial length of one of the plurality of shaft members which is disposed radially inward may be set to be longer than that of the shaft member which is disposed radially outward.

In this case, the shaft member disposed inward in the radial direction protrudes outward from an axial end of the shaft member disposed outward in the radial direction. Accordingly, the shaft member disposed inward in the radial direction can be easily positioned with respect to the supported member or the supporting member.

The biasing member may be a rubber-like elastic member which is filled between the shaft members radially adjacent to each other and bonded to the shaft members disposed radially inward and outward.

In this case, when the relative rotation occurs between the shaft members adjacent to each other in the radial direction, the entire rubber-like elastic member is approximately evenly twisted and deformed. Therefore, a stable reaction force can be obtained while a compact structure is provided.

An outer end surface of the rubber-like elastic member in an axial direction may be inclined axially outward with respect to a direction orthogonal to the axial direction.

In this case, since an axial cross section of the rubber-like elastic member between the shaft members disposed radially outward and inward has an approximate trapezoidal shape, axial misalignment of the shaft members hardly occurs. Therefore, even when the relative rotation occurs between the shaft members adjacent to each other in the radial direction, the reaction force can be more stably obtained.

In order to achieve the aforementioned objects, according to another aspect of the present invention, there is provided a chair in which a backrest is attached to a support structure to be tilted, wherein the backrest is attached to the support structure via any one of the above-described reaction force mechanisms.

Advantageous Effects of Invention

According to the present invention, the first shaft member, the second shaft member and the third shaft member are approximately coaxial with each other and are disposed radially in multiple layers, and the rotation of the third shaft member is restricted by the reaction force adjusting part. Therefore, since the total reaction force can be adjusted by increasing the reaction force against the base reaction force, an axial length of each of the shaft members and the biasing member can be sufficiently secured even when an axial space is limited. Therefore, the reaction force acting between the supporting member and the supported member can be easily changed without a high degree of design accuracy.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described on the basis of the accompanying drawings. Further, in the following description of each embodiment, forward, backward, upward, downward, left and right directions are directions seen by a user seated in a chair unless otherwise specified. Furthermore, in each embodiment described below, the same reference numerals are provided for the same parts, and repeated description thereof will be omitted.

First, a first embodiment shown inFIGS. 1 to 10will be described.

FIG. 1is a perspective view of a chair1according to a first embodiment of the present invention as seen from a front surface side thereof, andFIG. 2is a perspective view of the chair1according to the first embodiment of the present invention as seen from a rear surface side thereof.

The chair1according to the embodiment includes a leg portion2which is placed on a placement surface such as a floor, a support base3which is installed at an upper end of the leg portion2, a seat4which is attached to an upper portion of the support base3and supports a user's buttocks and thighs, a backrest5which is attached to the support base3and supports a user's back on a rear side of the seat4and an armrest6which is supported by the support base3via the backrest5and on which a distal end of a user's arm rests. Also, in the embodiment, the support base3constitutes a main part of a support structure in the chair1.

The leg portion2includes multiple legs2a, each of which has a caster2a1at a lower end thereof, and a leg post2bwhich stands upright from a center of the multiple legs2a. The leg post2bis constituted by a gas spring which has an outer cylinder2b1and a rod2b2capable of advancing and retracting in the outer cylinder2b1. An upper end of the rod2b2is coupled to the support base3in a state in which a part thereof is disposed in the support base3. A push valve2b3(refer toFIG. 7) for supplying/discharging gas (air) in the gas spring is provided on the upper end of the rod2b2. In the leg post2b, when the push valve2b3is pressed, the rod2b2is allowed to move upward and downward in the outer cylinder2b1, and when the pressing against the push valve2b3is released, the upward and downward movement of the rod2b2is locked. Therefore, the seat4and the backrest5supported by the leg post2bvia the support base3can be controlled to move upward and downward by pressing the push valve2b3.

The support base3attached to the leg portion2supports the seat4from a lower side thereof and supports the backrest5to be tilted backward and downward. A detailed structure of the support base3will be described in detail later.

FIG. 3is a view showing a state in which a connection portion between the support base3and the backrest5is disassembled.

As shown in the drawing, the backrest5includes a frame5awhich is a strength member having a load receiving portion in the form of a rectangular frame, a first upholstery5bwhich is stretched on the frame5ato adjacent an opening of the load receiving portion of the frame5a, and a second upholstery5cwhich covers an outer side of the first upholstery5b.

The frame5aof the backrest5includes a pair of left and right forward rods5a1which extend from a lower end of the load receiving portion toward the support base3, and a connecting portion5a2which connects the left and right forward rods5a1and to which a connection portion15cof a torsion unit7to be described later is connected. Further, the armrest6is fixed to an outer side surface of each of left and right lower edges of the frame5aof the backrest5.

Also, the torsion unit7is provided at a connection portion between the support base3and the backrest5and applies a predetermined reaction force to the backrest5in a direction of an initial position thereof when the backrest5is tilted backward and downward with respect to the support base3. Further, the torsion unit7can adjust the reaction force applied to the backrest5in two strong and weak stages and can lock rotation of the backrest5at the initial position. The torsion unit7constitutes the reaction force mechanism according to the embodiment.

Next, a detailed structure of the support base3and the torsion unit7will be described.

FIG. 4is an exploded perspective view of a part of the support base3and the torsion unit7as seen from a lower side of a rear portion thereof, andFIG. 5is an exploded perspective view of the support base3and the torsion unit7as seen from an upper side of a front portion thereof. Also,FIG. 6is a view of a central region on an upper surface side of the support base3,FIG. 7is a cross-sectional view of the support base3and the torsion unit7corresponding to a cross section along VII-VII ofFIG. 6, andFIG. 8is a cross-sectional view of the support base3and the torsion unit7corresponding to a cross section along VIII-VIII ofFIG. 7.

The support base3has a base member3awhich is a strength member fixed to an upper end portion of the rod2b2of the leg post2b. In the base member3a, an accommodation recess portion20which has an approximately rectangular shape in a plane view is provided in a central region of an upper surface thereof, and a pair of backward rods3a5which extend backward and a pair of arms3a1which extend toward a front upper side thereof are provided on left and right side walls forming the accommodation recess portion20. The pair of backward rods3a5form a recess portion3a2recessed forward in a concave shape between the backward rods3a5and a main body of the base member3ain which the accommodation recess portion20is formed.

An inside of the accommodation recess portion20of the base member3ais partitioned into an upper accommodation chamber20aand a lower accommodation chamber20bby a partition member23.

The rod2b2of the leg post2bis attached to a central portion of the base member3a, and the upper end of the rod2b2including the push valve2b3protrudes into the lower accommodation chamber20bof the accommodation recess portion20as shown inFIG. 7. A swing lever27for pressing the push valve2b3is pivotally supported on a lower surface side of the partition member23. One end side of the swing lever27is connected to a lifting wire30(refer toFIG. 6), and the other end side thereof faces the push valve2b3to be capable of performing a pressing operation. The lifting wire30is drawn out from the partition member23to the upper accommodation chamber20aside and is routed to an outside of the support base3via a wire guide25. The lifting wire30drawn out from the support base3is connected to a lifting operation lever8a(refer toFIG. 2) of an operation unit8provided on a right side portion of the seat4. The lifting wire30is pulled by a pushing-up operation of the lifting operation lever8aand thus rotates the swing lever27so that the push valve2b3is pressed.

A pair of holding holes3dwhich pass through in a forward and backward direction are formed in a rear wall20cof the accommodation recess portion20of the base member3ato be spaced apart from each other in a left and right direction. An operation pin19which is elongated in an advancing and retracting direction is slidably fitted in each of the holding holes3d. The operation pin19includes a large diameter portion19bwhich is slidably fitted in the holding holes3d, a small diameter portion19awhich protrudes from the large diameter portion19btoward the torsion unit7side, and a locking portion19cwhich protrudes from the large diameter portion19btoward the inside of the accommodation recess portion20. The operation pin19performs adjustment of the reaction force of the torsion unit7acting on the backrest5and tilt lock of the backrest5according to an advancing and retracting position in the forward and backward direction. In this embodiment, the operation pin19constitutes a reaction force adjusting part in the torsion unit7(reaction force mechanism).

Further, an interlocking member24to which each of the locking portions19cof the left and right operation pins19is connected, and a pair of coil springs28which are disposed coaxially with the left and right operation pins19and are biasing parts for biasing the interlocking member24toward a rear side (the torsion unit7side) are accommodated in the upper accommodation chamber20aof the accommodation recess portion20. Therefore, the left and right operation pins19are biased toward the torsion unit7side by the coil spring28via the interlocking member24. Further, a backrest operating wire31is connected to the interlocking member24. The backrest operating wire31is routed to the outside of the support base3via the wire guide25. The backrest operating wire31drawn out from the support base3is connected to a backrest operating lever8b(refer toFIG. 2) of the operation unit8provided on a right side portion of the seat4. The backrest operating wire31is pulled by a rotating operation of the backrest operating lever8band thus the left and right operation pins19are retracted against a biasing force of the coil springs28. In the case of the embodiment, a rotational position of the backrest operating lever8bcan be changed to any of three positions. Therefore, the left and right operation pins19can be changed to any of the three positions in the forward and backward direction according to the rotational position of the backrest operating lever8b.

Each distal end of the left and right arms3a1which extends toward a front upper side of the base member3ais directly fixed to a lower surface of the seat4. Further, the torsion unit7is accommodated in the recess portion3a2on a rear side of the base member3a. A fitting groove3a4for fitting a pivot shaft10of the torsion unit7is provided in two facing inner side surfaces of the recess portion3a2. Also, a separation distance between the backward rods3a5is set to be approximately equal to that between the above-described left and right forward rods5a1of the backrest5.

Further, as shown inFIGS. 4 and 5, a restriction protrusion33is provided on a wall portion of the base member3awhich faces a rear side in the recess portion3a2. The restriction protrusion33protrudes backward at an approximate intermediate position between the left and right operation pins19. As will be described in detail later, the restriction protrusion33restricts a tilt range of the backrest5and applies an initial load to the torsion unit7.

However, as shown inFIGS. 7 and 8, the torsion unit7includes the metal pivot shaft10which is a shaft member of an innermost layer, an inner cylinder12which is disposed radially outside the pivot shaft10to be adjacent thereto via a first rubber-like elastic member11(biasing member), an outer cylinder14which is disposed radially outside the inner cylinder12to be adjacent thereto via a second rubber-like elastic member13(biasing member), and a housing15which covers an outer side of the outer cylinder14. Further, in the embodiment, the pivot shaft10, the inner cylinder12and the outer cylinder14constitute a plurality of shaft members which are arranged approximately coaxially and radially in a multilayered manner.

The pivot shaft10is formed so that both axial ends10ahave a rectangular cross section, and both ends10aprotrude to an outside of the housing15. The ends10aof the pivot shaft10which protrude outward from the housing15are fitted and fixed in the fitting groove3a4provided in the recess portion3a2of the support base3in a state in which rotation thereof is restricted. Therefore, the pivot shaft10is fixed to prevent rotation relative to the base member3aof the support base3.

The inner cylinder12is formed of a rigid body such as a metal or a hard resin. The inner cylinder12is formed so that an axial length thereof is shorter than that of the housing15. Therefore, the axial length of the inner cylinder12is set to be shorter than that of the pivot shaft10.

The first rubber-like elastic member11is formed in an approximately cylindrical shape, and an inner circumferential surface and an outer circumferential surface thereof are vulcanization-bonded to an outer circumferential surface of the pivot shaft10and an inner circumferential surface of the inner cylinder12. Both axial end surfaces of the first rubber-like elastic member11are inclined with respect to a direction orthogonal to the axial direction so that a radially inner side thereof expands outward in the axial direction.

Like the inner cylinder12, the outer cylinder14is formed of a rigid body such as a metal or a hard resin. The outer cylinder14is formed so that an axial length thereof is sufficiently shorter than that of the inner cylinder12. In the case of the embodiment, the axial length of the outer cylinder14is set to a length of about ⅓ of the axial length of the inner cylinder12. The outer cylinder14is arranged in an approximate central region of the inner cylinder12in the axial direction.

The second rubber-like elastic member13is formed in an approximate cylindrical shape, and an inner circumferential surface and an outer circumferential surface thereof are vulcanization-bonded to an outer circumferential surface of the inner cylinder12and an inner circumferential surface of the outer cylinder14. Both axial end surfaces of the second rubber-like elastic member13are inclined with respect to a direction orthogonal to the axial direction so that a radially inner side thereof expands outward in the axial direction.

Further, a lock hole12b(refer toFIG. 8) for restricting relative rotation with respect to the housing15is provided in a region of a circumferential wall of the inner cylinder12which protrudes axially outward from the outer cylinder14.

A fitting convex portion15dwhich is fitted in the lock hole12bis provided inside the housing15.

The housing15has an upper member15aand a lower member15bwhich cover upper sides and lower sides of the outer cylinder14and the inner cylinder12from a radial outside of the pivot shaft10. Additionally, the housing15is locked to prevent rotation relative to the inner cylinder12by fitting the fitting convex portion15dinto the lock hole12bof the inner cylinder12as described above. However, the housing15is separated from the outer cylinder14with a predetermined gap.

Further, the connection portion15cwhich expands backward is provided at a rear side of the housing15. The connection portion15cis connected to the backrest5by a bolt fastening method or the like. Therefore, the housing15and the inner cylinder12locked in the housing15are connected to prevent rotation relative to the backrest5.

Furthermore, in the embodiment, the pivot shaft10constitutes a first shaft member connected to the support base3which is the support structure (supporting member), and the inner cylinder12constitutes a second shaft member connected to the backrest5(supported member). Also, the outer cylinder14constitutes a third shaft member which is a shaft member other than the first shaft member and the second shaft member.

In addition, the restriction protrusion33which protrudes backward from the support base3, and an opening15e(refer toFIGS. 3, 5, and 7) which allows the pair of operation pins19to enter the housing15is formed on a front side wall of the housing15. At a most retracted position (displaced in the forward direction) of the operation pin19shown inFIG. 7, a distal end of the small diameter portion19ais disposed in the opening15e. The opening15eof the housing15is formed to have a vertical width which may prevent interference with the operation pin19within the tilt range of the backrest5.

Here, a pair of fitting holes14aare formed in the outer cylinder14of the torsion unit7to be spaced apart from each other in the left and right direction. In each of the fitting holes14a, the small diameter portions19aof the left and right operation pins19held on the support base3side may be fitted in the axial direction. When the operation pins19are fitted in the fitting holes14a, relative rotation of the outer cylinder14with respect to the support base3is locked.FIG. 9is a cross-sectional view which is the same as that ofFIG. 7and shows a state in which the small diameter portions19aof the operation pins19are fitted in only the fitting holes14aof the outer cylinder14.

A pair of fitting holes12aare formed in the inner cylinder12of the torsion unit7to be spaced apart from each other in the left and right direction. The small diameter portions19aof the operation pins19may be fitted in the fitting holes12ain the axial direction. When the operation pins19are fitted in the fitting holes12a, relative rotation of the inner cylinder12with respect to the support base3is locked.

Also, escape holes13aand11afor allowing advancing and retracting displacement of the operation pins19are provided in the second rubber-like elastic member13which connects the outer cylinder14and the inner cylinder12and the first rubber-like elastic member11which connects the inner cylinder12and the pivot shaft10. The fitting hole14aof the outer cylinder14and the fitting hole12aof the inner cylinder12are set to be coaxial with each other when the backrest5is in an initial position (maximally standing initial rotating posture). Therefore, when the backrest5is in the initial position, the operation pins19can be fitted into the fitting holes14aon the outer cylinder14side and the fitting holes12aon the inner cylinder12side.FIG. 10is a cross-sectional view which is the same as that ofFIG. 7and shows a state in which the small diameter portions19aof the operation pins19are fitted in the fitting holes14aof the outer cylinder14and the fitting holes12aof the inner cylinder12.

Here, the restriction protrusion33which protrudes from the support base3is arranged in the opening15eof the housing15of the torsion unit7and restricts the tilt range of the backrest5integrally formed with the housing15by coming in contact with an upper side surface or a lower side surface of the opening15e.

Further, when the torsion unit7is assembled to the support base3, both ends10aof the pivot shaft10are fitted in the corresponding fitting groove3a4on the support base3side to prevent relative rotation, as described above. Then, the housing15integrally formed with the inner cylinder12is rotated in a direction in which the backrest5is inclined backwards to twist the first rubber-like elastic member11by a predetermined amount, and in this state, the restriction protrusion33on the support base3side is fitted into the opening15eof the housing15. Accordingly, the upper side surface of the opening15eof the housing15receives the reaction force of the first rubber-like elastic member11and comes in contact with an upper surface of the restriction protrusion33. Therefore, when the torsion unit7is assembled in this way, the rotation of the backrest5is restricted in the initial position (initial posture) while the first rubber-like elastic member11is twisted and thus the initial reaction force is stored.

The left and right operation pins19held by the support base3may be changed to the three positions in the forward and backward direction according to the rotational position of the backrest operating lever8bas described above, but the three positions are the following positions.

(1) First Biasing Force Adjustment Position A1

This is a most retracted position (refer toFIG. 7) in which the operation pins19are not engaged (fitted) with either of the outer cylinder14which is the third shaft member and the inner cylinder12which is the second shaft member.

(2) Second Biasing Force Adjustment Position A2

This is an intermediate advancing and retracting position (refer toFIG. 9) in which the operation pins19are engaged (fitted) only with the outer cylinder14which is the third shaft member.

This is a most advanced position (refer toFIG. 10) in which the operation pins19are engaged (fitted) not only with the outer cylinder14which is the third shaft member but also with the inner cylinder12which is the second shaft member.

Next, adjustment of a tilt reaction force of the backrest5and tilt lock of the backrest5of the chair1according to the embodiment will be described.

To set the tilt reaction force of the backrest5to “weak,” a user grips the backrest operating lever8bof the operation unit8and rotates the backrest operating lever8bto a “weak” position. At this time, the backrest operating wire31is maximally retracted, and the operation pins19supported by the support base3advance or retract to the first biasing force adjustment position A1shown inFIG. 7. At this time, since the operation pins19are not engaged with either of the outer cylinder14and the inner cylinder12, the rotation of the outer cylinder14becomes free without being restricted by the support base3side.

In this state, when the user leans on the backrest5and the backrest5is tilted backward and downward, the inner cylinder12integrally formed with the backrest5rotates relative to the pivot shaft10integrally formed with the support base3, the first rubber-like elastic member11interposed between the pivot shaft10and the inner cylinder12is twisted, and the first rubber-like elastic member11generates the reaction force at this time. At this point, since the outer cylinder14rotates following the rotation of the inner cylinder12, the second rubber-like elastic member13interposed between the inner cylinder12and the outer cylinder14does not generate the reaction force. Therefore, at this time, only a base reaction force resulting from the first rubber-like elastic member11acts on the backrest5.

Further, to set the tilt reaction force of the backrest5to “strong,” the user grips the backrest operating lever8bof the operation unit8and rotates the backrest operating lever8bto a “strong” position. At this time, the backrest operating wire31is retracted relatively little, and the operation pins19supported by the support base3advance or retract to the second biasing force adjustment position A2shown inFIG. 9. At this time, since the operation pins19are engaged with the outer cylinder14, the rotation of the outer cylinder14is restricted by the support base3.

In this state, when the user leans on the backrest5and the backrest5is tilted backward and downward, the inner cylinder12integrally formed with the backrest5rotates relative to the pivot shaft10integrally formed with the support base3, and the first rubber-like elastic member11interposed between the pivot shaft10and the inner cylinder12is twisted. Also, at this point, since the rotation of the outer cylinder14is restricted by the support base3, the second rubber-like elastic member13interposed between the inner cylinder12and the outer cylinder14is also twisted. As a result, both of the first rubber-like elastic member11and the second rubber-like elastic member13generate the reaction force, a reaction force resulting from the second rubber-like elastic member13is added to the base reaction force resulting from the first rubber-like elastic member11, and thus the total reaction force acts on the backrest5.

Meanwhile, to lock the tilt of the backrest, the user grips the backrest operating lever8bof the operation unit8and rotates the backrest operating lever8bto a “lock” position. At this time, the retracting of the backrest operating wire31is released, and the operation pins19supported by the support base3receive the biasing force of the coil springs28and advance or retract to the lock position A3shown inFIG. 10. At this time, since the operation pins19are engaged with not only the outer cylinder14but also the inner cylinder12, the rotation of the backrest5is locked by the operation pins19.

As described above, in the torsion unit7(reaction force mechanism) of the chair1according to the embodiment, the pivot shaft10, the inner cylinder12and the outer cylinder14are disposed approximately coaxially and radially in the multilayered manner. Also, since the first rubber-like elastic member11and the second rubber-like elastic member13respectively connect between the pivot shaft10and the inner cylinder12and between the inner cylinder12and the outer cylinder14and the rotation of the outer cylinder14which is not directly coupled to the support base3or the backrest5is restricted by the operation pins19which are the reaction force adjusting parts, the reaction force acting on the backrest5can be increased. That is, in the torsion unit7according to the embodiment, the rotation of the outer cylinder14is restricted by displacing the operation pins19from the first biasing force adjustment position A1to the second biasing force adjustment position A2, and the reaction force resulting from the second rubber-like elastic member13is added to the base reaction force resulting from the first rubber-like elastic member11, and thus the reaction force acting on the backrest5can be increased. Therefore, even when an axial space which can be secured by the torsion unit7is limited, the axial length of each of the first rubber-like elastic member11, the inner cylinder12, the second rubber-like elastic member13and the outer cylinder14can be sufficiently secured. Accordingly, the torsion unit7which can easily change the reaction force can be obtained without a high degree of design accuracy.

Also, particularly, in the torsion unit7according to the embodiment, the pivot shaft10which is the shaft member of the innermost layer is coupled to the support base3, and the inner cylinder12which is arranged radially outside the pivot shaft10to be adjacent thereto is connected to the backrest5. Further, the outer cylinder14is disposed radially outside the inner cylinder12, and the operation pins19which are the reaction force adjusting parts advance and retract between the first biasing force adjustment position A1and the second biasing force adjustment position A2. Therefore, the reaction force when the operation pins19are operated to the second biasing force adjustment position A2(“strong” position) can be relatively easily set to a desired reaction force. That is, in the case of the embodiment, the total reaction force can be easily set by simply adding the reaction force resulting from the second rubber-like elastic member13to the reaction force resulting from the first rubber-like elastic member11.

Also, in the torsion unit7according to the embodiment, the axial length of the inner cylinder12which is disposed radially inward is set to be longer than that of the outer cylinder14disposed radially outside, and both axial ends of the inner cylinder12protrude axially outward from the outer cylinder14. Therefore, the inner cylinder12which is disposed inside the outer cylinder14can be easily positioned in the housing15or the like by using both axial protruding portions of the inner cylinder12, for example, by providing the lock hole12bengaged with the fitting convex portion15d.

Also, in the torsion unit7according to the embodiment, the biasing members interposed between the pivot shaft10and the inner cylinder12and between the inner cylinder12and the outer cylinder14are constituted with the rubber-like elastic member (first rubber-like elastic member11and second rubber-like elastic member13) which is vulcanization-bonded to each of the circumferential surfaces thereof. Therefore, when the relative rotation occurs between the pivot shaft10and the inner cylinder12or between the inner cylinder12and the outer cylinder14, the rubber-like elastic member is twisted and deformed approximately evenly over an entire region thereof. Accordingly, the stable tilt reaction force can be obtained while the entire torsion unit7has a compact structure.

Further, in the case of the embodiment, the axial outer end surfaces of the first rubber-like elastic member11and the second rubber-like elastic member13are formed to be inclined axially outward with respect to a direction orthogonal to the axial direction, and thus a cross section of each of the rubber-like elastic members in the axial direction has an approximate trapezoidal shape. Therefore, axial misalignment of the shaft members disposed radially inside and outside each of the rubber-like elastic members can be efficiently restricted by the rubber-like elastic members. Accordingly, in the torsion unit7according to the embodiment, the stable reaction force can always be obtained.

Next, a second embodiment shown inFIGS. 11 to 13will be described. Also,FIG. 11is a view corresponding toFIG. 7of the first embodiment,FIG. 12is a view corresponding toFIG. 9of the first embodiment, andFIG. 13is a view corresponding toFIG. 10of the first embodiment.

In a chair101according to the second embodiment like in the first embodiment, a torsion unit107which is a reaction force mechanism includes a pivot shaft10, an inner cylinder12, an outer cylinder14and a housing15, the pivot shaft10and the inner cylinder12are connected by a first rubber-like elastic member11, and the inner cylinder12and the outer cylinder14are connected by a second rubber-like elastic member13. However, the pivot shaft10is integrally coupled to a backrest (not shown), and the outer cylinder14is integrally coupled to a support base3. Additionally, fitting holes14aand12ainto which small diameter portions19aof operation pins19can be fitted as reaction force adjusting parts are formed in the outer cylinder14and the inner cylinder12, respectively, and a lock hole35into which a distal end of the small diameter portion19aof the operation pin19can be fitted is formed in the pivot shaft10. Further, the operation pin19is held in the support base3to be able to advance and retract, like in the first embodiment.

In the case of the embodiment, the outer cylinder14constitutes a first shaft member, the pivot shaft10constitutes a second shaft member, and the inner cylinder12constitutes a third shaft member.

The operation pin19is operated to advance and retract among a first biasing force adjustment position A11(refer toFIG. 11) in which the operation pin is not engaged with either of the inner cylinder12and the pivot shaft, a second biasing force adjustment position A12(refer toFIG. 12) in which the operation pins are fitted into the fitting hole12aof the inner cylinder12, and a lock position (refer toFIG. 13) in which the operation pins are fitted into the lock hole35of the pivot shaft10.

When the tilt reaction force of the backrest is set to “weak,” the operation pin19supported by the support base3is operated to advance and retract to the first biasing force adjustment position A11shown inFIG. 11. At this time, since the operation pin19is not engaged with either of the inner cylinder12and the pivot shaft10, the inner cylinder12rotates and is displaced following the pivot shaft10which is adjacent thereto via the first rubber-like elastic member11when the pivot shaft10rotates together with the backrest, and a base reaction force is generated in a state in which the first rubber-like elastic member11between the pivot shaft10and the inner cylinder12and the second rubber-like elastic member13between the inner cylinder12and the outer cylinder14are connected in series. Therefore, the reaction force generated at this time is relatively small compared with a case in which the first rubber-like elastic member11or the second rubber-like elastic member13is separately twisted and the reaction force is generated. As a result, a relatively small reaction force acts on the backrest5.

When the tilt reaction force of the backrest is set to “strong,” the operation pin19supported by the support base3is operated to advance and retract to the second biasing force adjustment position A12shown inFIG. 12. At this time, since the operation pin19is engaged with the fitting hole12aof the inner cylinder12, the rotation of the inner cylinder12is locked by the operation pin19. Therefore, at this time, when the pivot shaft10rotates together with the backrest, only the first rubber-like elastic member11between the pivot shaft10and the inner cylinder12is twisted and deformed, and a reaction force larger than the above-described base reaction force is generated. As a result, a relatively large reaction force acts on the backrest5.

Further, when the tilt reaction force of the backrest is locked, the operation pin19supported by the support base3is operated to advance and retract to the lock position A13shown inFIG. 13. At this time, since the operation pin19is engaged with not only the fitting hole12aof the inner cylinder12but also the lock hole35of the pivot shaft10, the rotation of the pivot shaft10is restricted by the operation pin19. As a result, the tilt of the backrest is locked.

As described above, the torsion unit107used in the chair101according to the second embodiment generates the reaction force in a state in which the first rubber-like elastic member11and the second rubber-like elastic member13are connected in series when the operation pin19is in the first biasing force adjustment position A11. Additionally, when the operation pin19is operated from this state to the second biasing force adjustment position A12and restricts the rotation of the inner cylinder12, only the first rubber-like elastic member11generates a reaction force. Therefore, when the operation pin19is operated from the first biasing force adjustment position A11to the second biasing force adjustment position A12, the reaction force acting on the backrest can be increased with respect to the base reaction force generated in a state in which the first rubber-like elastic member11and the second rubber-like elastic member13are in a series state.

Therefore, also in the torsion unit107according to the second embodiment, even when an axial space to be secured is limited, an axial length of each of the first rubber-like elastic member11, the inner cylinder12, the second rubber-like elastic member13and the outer cylinder14can be sufficiently secured. Therefore, the torsion unit107which can easily change the reaction force can be obtained without a high degree of design accuracy.

Next, a third embodiment shown inFIGS. 14 to 23will be described. Also,FIG. 14is an exploded view of a torsion unit7and a part of a support base3as seen from a front side, andFIGS. 15, 17 and 19are cross-sectional views corresponding toFIGS. 7, 9 and 10of the first embodiment. Also,FIG. 16is a cross-sectional view corresponding to a cross section along XVI-XVI ofFIG. 15, andFIGS. 18 and 20are views corresponding to a cross section along XVIII-XVIII ofFIG. 17and a cross section along XX-XX ofFIG. 19. Also,FIG. 21is a cross-sectional view corresponding to a cross section along XXI-XXI ofFIG. 20, andFIGS. 22 and 23are cross-sectional views corresponding to a cross section along XXII-XXII ofFIG. 16.

A chair201according to the third embodiment has the same basic constitutions as the first embodiment in which a torsion unit7(reaction force mechanism) includes a pivot shaft10, an inner cylinder12, an outer cylinder14and a housing15, the pivot shaft10and the inner cylinder12are connected by a first rubber-like elastic member11, the inner cylinder12and the outer cylinder14are connected by a second rubber-like elastic member13, the pivot shaft10is integrally coupled to the support base3side, the inner cylinder12is integrally coupled to the backrest side via the housing15, and so on.

The third embodiment is different from the first embodiment in that one operation pin219is provided and the operation pin219has a different shape. However, like in the first embodiment, the operation pin219is operated to advance and retract among a first biasing force adjustment position A1(refer toFIGS. 15 and 16) in which the operation pin is not engaged with either of the inner cylinder12and the outer cylinder14, a second biasing force adjustment position A2(refer toFIGS. 17 and 18) in which the operation pin219is fitted into only the outer cylinder14and a lock position A3(refer toFIGS. 19 and 20) in which rotation of the inner cylinder12is locked.

A major difference between the first embodiment and the third embodiment is that, when the operation pin219is operated to the lock position A3, the operation pin219is fitted to the housing15formed integrally with the inner cylinder12and the rotation of the inner cylinder12is locked.

A holding hole203dhaving an approximately rectangular shape (approximately rectangular shape of which corners and side portions on both sides are rounded) which is elongated in the left and right direction to slidably hold the operation pin219is formed in a rear wall220cof the support base3. Also, a pair of displacement restricting protrusions40which protrude backward are formed to protrude from left and right sides thereof with the holding hole203dof the rear wall220cinterposed therebetween. The displacement restricting protrusions40are formed to have an approximate rectangular shape of which a cross section in a direction orthogonal to a protruding direction is vertically elongated. The rear wall220cis fixed to a main body of the support base3by a bolt41.

The operation pin219includes an enlarged width portion219bof which a cross section is approximately the same as that of the holding hole203d, a small diameter portion219awhich coaxially protrudes from one axial end of the enlarged width portion219b, and a locking portion219cwhich protrudes coaxially from the other axial end of the enlarged width portion219b. The enlarged width portion219bis slidably held in the holding hole203dof the rear wall220c. The small diameter portion219ais formed to have a circular cross section which has a diameter smaller than a smallest width portion (width portion in a height direction) of the enlarged width portion219b. Also, the small diameter portion219aprotrudes toward the torsion unit7side and may enter radially inside the torsion unit7. An interlocking member24which is biased toward the torsion unit7by a pair of coil springs28is connected to the locking portion219c. A backrest operating wire (not shown) is connected to the interlocking member24like the first embodiment.

Meanwhile, an approximately rectangular fitting hole42which is elongated laterally and into which the enlarged width portion219bof the operation pin219can be fitted is formed in a front surface of the housing15of the torsion unit7. As precisely shown inFIG. 14, in the fitting hole42, a caved portion42awhich is caved downward in an approximately semicircular shape is continuously provided in a central region on a lower side of a rectangular portion having approximately the same shape as a cross section of the enlarged width portion219bof the operation pin219. Since the small diameter portion219aof the operation pin219is smaller than a minimum width portion of the enlarged width portion219b, the small diameter portion219acan be freely inserted into the fitting hole42when the backrest5is in an initial position (in an initial posture). However, the caved portion42ais provided to prevent the small diameter portion219aof the operation pin219from interfering with the housing15when the backrest5is tilted largely backward and downward. As shown inFIG. 21, in the housing15of the torsion unit7, the rotation thereof with respect to the support base3is locked by fitting the enlarged width portion219bof the operation pin219into the fitting hole42.

Further, locking holes43in which the left and right displacement restricting protrusions40of the rear wall220con the support base3side are inserted are formed at right and left side positions of the side surface of the housing15with the fitting hole42interposed therebetween. A separation width in a vertical direction inside the locking hole43is set to be sufficiently larger than a height of the displacement restricting protrusion40. As shown inFIGS. 22 and 23, when the housing15is largely rotated and displaced vertically together with the backrest, the displacement restricting protrusion40is in contact with an inner surface of the locking hole43, and thus the locking hole43restricts the tilt of the backrest5. Further,FIG. 22shows a state in which the backrest5rotates maximally in a direction of the initial position (direction of a standing posture) and an upper side surface43aof the locking hole43is in contact with an upper surface of the restriction protrusion33.FIG. 23shows a state in which the backrest5rotates maximally backward and downward and a lower side surface43bof the locking hole43is in contact with a lower surface of the restriction protrusion33.

Further, when the torsion unit7is assembled to the support base3, both ends10aof the pivot shaft10of the torsion unit7are fitted into the fitting groove3a4corresponding to the support base3side to prevent relative rotation. Then, the first rubber-like elastic member11is twisted by a predetermined amount by rotating the housing15formed integrally with the inner cylinder12in a direction in which the backrest5is tilted backward, and in this state, the displacement restricting protrusion40on the support base3side is fitted into the locking hole43of the housing15. Accordingly, as shown inFIG. 22, the upper side surface43aof the locking hole43of the housing15receives the reaction force of the first rubber-like elastic member11and comes in contact with the upper surface of the displacement restricting protrusion40. When the torsion unit7is assembled in this way, the rotation of the backrest5is restricted in the initial position (initial posture) in a state in which the first rubber-like elastic member11is twisted and the initial reaction force is stored.

Fitting holes14aand12ainto which small diameter portions219aof operation pins219can be fitted are formed in the outer cylinder14and the inner cylinder12of the torsion unit7, respectively. Also, escape holes13aand11afor allowing the small diameter portion219aof the operation pin219to enter are formed in the second rubber-like elastic member13and the first rubber-like elastic member11.

Further, in the third embodiment, since the operation pin219is fitted into the housing15and thus the tilt of the backrest is locked as will be described later in detail, the fitting hole12aof the inner cylinder12may have a diameter slightly larger than that of the small diameter portion219aof the operation pin219. Also, when the small diameter portion219aof the operation pin219has a length which does not interfere with an outer surface of the inner cylinder12and the small diameter portion219awhen the operation pin219protrudes maximally, the fitting hole12amay not be provided in the inner cylinder12.

In the case of the embodiment, the pivot shaft10constitutes a first shaft member, the inner cylinder12and the housing15constitute a second shaft member, and the outer cylinder14constitutes a third shaft member.

When the tilt reaction force of the backrest is set to “weak,” the operation pin219supported by the support base3is operated to advance and retract to a first biasing force adjustment position A1shown inFIGS. 15 and 16. At this time, since the operation pin219is not engaged with either of the outer cylinder14and the inner cylinder12, the first rubber-like elastic member11interposed between the pivot shaft10and the inner cylinder12is twisted when the housing15and the inner cylinder12rotate together with the backrest, and at this time, the first rubber-like elastic member11generates the reaction force. Further, at this time, since the outer cylinder14should follow the rotation of the inner cylinder12, the second rubber-like elastic member13interposed between the inner cylinder12and the outer cylinder14does not generate the reaction force. Therefore, only a base reaction force resulting from the first rubber-like elastic member11acts on the backrest.

Further, when the tilt reaction force of the backrest is set to “strong,” the operation pin219supported by the support base3is operated to advance and retract to a second biasing force adjustment position A2shown inFIGS. 17 and 18. At this time, since the operation pin219is fitted into the fitting hole14aof the outer cylinder14, the rotation of the outer cylinder14is restricted. Therefore, when the backrest is tilted, the inner cylinder12rotates relative to the pivot shaft10of which the rotation is stopped and the outer cylinder14, and the first rubber-like elastic member11and the second rubber-like elastic member13are twisted and deformed. As a result, the reaction force resulting from the second rubber-like elastic member13is added to the base reaction force resulting from the first rubber-like elastic member11, and thus the total reaction force acts on the backrest.

Further, when the tilt of the backrest is locked, the operation pin219supported by the support base3is operated to advance and retract to a lock position A3shown inFIGS. 19 and 20. At this time, the small diameter portion219aof the operation pin219is fitted into the fitting hole12aof the inner cylinder12and the fitting hole14aof the outer cylinder14, and the enlarged width portion219bis fitted into the fitting hole42of the housing15. As a result, the tilt of the backrest formed integrally with the housing15is locked.

As described above, like in the first embodiment, the torsion unit7used in the chair201according to the third embodiment restricts the rotation of the outer cylinder14by displacing the operation pin219from the first biasing force adjustment position A1to the second biasing force adjustment position A2. Therefore, the reaction force resulting from the second rubber-like elastic member13is added to the base reaction force resulting from the first rubber-like elastic member11, and thus the reaction force acting on the backrest5can be increased. Therefore, even when an axial space secured by the torsion unit7is limited, an axial length of each of the first rubber-like elastic member11, the inner cylinder12, the second rubber-like elastic member13and the outer cylinder14can be sufficiently secured, and the torsion unit7which can easily change the reaction force can be obtained without a high degree of design accuracy.

However, since the torsion unit7according to the third embodiment has a structure in which the tilt of the backrest is locked by fitting the operation pin219into the housing15located at an outermost circumference of the torsion unit7, an excessive load can be prevented in advance from acting on the inner cylinder12having a small diameter. Therefore, performance of the torsion unit7at the time of shipment can be maintained over a long period of time.

Next, a fourth embodiment shown inFIG. 12will be described.

FIG. 24is a view showing a cross section of a torsion unit307(reaction force mechanism) according to a fourth embodiment which is cut in an axial direction.

In the torsion unit307according to the fourth embodiment, an inner cylinder12is disposed radially outside of a pivot shaft10, and two outer cylinders14A and14B are arranged radially outside the inner cylinder12in parallel with each other in the axial direction. The pivot shaft10and the inner cylinder12are connected by the first rubber-like elastic member11, and the inner cylinder12and each of the outer cylinders14A and14B are connected by second rubber-like elastic members13A and13B.

Two operation pins19A and19B constituting a reaction force adjusting part are provided to correspond to the outer cylinders14A and14B. Fitting holes14Aa and14Ba in which the operation pins19A and19B can be fitted are formed in the outer cylinders14A and14B, respectively, and fitting holes12Aa and12Ba in which the operation pins19A and19B can be fitted are formed in the inner cylinder12.

For example, the torsion unit307according to the fourth embodiment is used in a state in which the pivot shaft10is integrally coupled to a support structure (supporting member) such as a support base and the inner cylinder12is integrally coupled to the backrest (supported member).

In the torsion unit307, when a weak reaction force is obtained, the operation pins19A and19B are displaced at positions at which the operation pins are not engaged with either of the inner cylinder12and the outer cylinders14A and14B. When a medium reaction force is obtained, one operation pin19A is displaced to a position in which the one operation pin19A is fitted to the fitting hole14Aa of the outer cylinder14A. When a stronger reaction force is obtained, the two operation pins19A and19B are displaced at positions in which the two operation pins are fitted into the fitting holes14Aa and14Ba of the corresponding outer cylinders14A and14B.

That is, when the operation pins19A and19B are in positions in which the operation pins are not engaged with either of the outer cylinders14A and14B and the inner cylinder12, the first rubber-like elastic member11generates a base reaction force by itself.

When the one operation pin19A is in the position in which the one operation pin is fitted into the fitting hole14Aa of the outer cylinder14A, rotation of one outer cylinder14A is locked, and one second rubber-like elastic member13A generates the reaction force. As a result, a base reaction force resulting from one second rubber-like elastic member13A is added to that resulting from the first rubber-like elastic member11.

When the two operation pins19A and19B are in positions in which the two operation pins are fitted into the fitting holes14Aa and14Ba of the corresponding outer cylinders14A and14B, rotation of the two outer cylinders14A and14B is locked, and the two second rubber-like elastic members13A and13B generate the reaction force. As a result, the base reaction force resulting from the two second rubber-like elastic members13A and13B is added to that of the first rubber-like elastic member11.

Therefore, the torsion unit307according to the fourth embodiment can adjust the reaction force in three stages without an increase in an axial length or an outer diameter.

Also, in the case of the torsion unit307, the tilt of the backrest can be locked by fitting at least one of the operation pins19A and19B into the fitting holes12Aa and12Ba of the inner cylinder.

Finally, a fifth embodiment shown inFIG. 25will be described.

FIG. 25is a view showing a cross section of a torsion unit407(reaction force mechanism) according to a fifth embodiment which is cut in an axial direction.

In the torsion unit407according to the fifth embodiment, an inner cylinder12is coupled to an outside of a pivot shaft10in a radial direction via a first rubber-like elastic member11, and a second rubber-like elastic member13is coupled to an outside of the inner cylinder12in a radial direction. For example, the torsion unit407is used in a state in which the pivot shaft10is coupled to a support structure (supporting member) such as a support base and the inner cylinder12is coupled to the backrest (supported member). Additionally, gear teeth12eand14eare provided on an outer circumferential surface of the inner cylinder12and an outer circumferential surface of the outer cylinder14, respectively, and an operation gear (restriction protrusion)33which can be displaced forward and backward and an operation gear (reaction force adjusting part)34may be engaged with the gear teeth12eand14e.

In the torsion unit407according to the fifth embodiment, when a weak reaction force is obtained, the operation gears33and34are separated from the inner cylinder12and the outer cylinder14. Accordingly, the outer cylinder14rotates following the inner cylinder12, and the first rubber-like elastic member11generates a base reaction force by itself.

Further, when a strong reaction force is obtained, the operation gear34is engaged with the gear teeth14eof the outer cylinder14. Therefore, rotation of the outer cylinder14is locked, and the second rubber-like elastic member13also generates the reaction force together with the first rubber-like elastic member11.

Further, when the tilt of the backrest is locked, the operation gear33is engaged with the gear teeth12eof the inner cylinder12. Therefore, relative rotation between the pivot shaft10and the inner cylinder12is locked.

In addition, the present invention is not limited to the above-described embodiments, and various design changes are possible without departing from the gist thereof. For example, although the pivot, the inner cylinder and the outer cylinder constitute a three-layer shaft member in the embodiments, the number of the shaft members arranged in the radial direction may be more if three or more layers are provided.

INDUSTRIAL APPLICABILITY

According to the present invention, a reaction force mechanism which does not require a high degree of design accuracy and in which the reaction force acting between a supporting member and a supported member can be easily changed, and a chair using the same can be provided.

REFERENCE SIGNS LIST