Chair

A chair in which a biasing force acting on a back can be changed even if the stroke of a moving member is small, thereby enabling the device to be compact, and the biasing force can be steplessly adjusted with light force. A biasing force transmission member (41) reverses the biasing force of a biasing mechanism acting on a tip portion of the biasing force transmission member (41) which is a point of effort (Q) with a point abutting a fulcrum member (49) working as a fulcrum (P) for a lever, transmits the biasing force to a base end of the biasing force transmission member (41) which is a point load (R) to bias the back in an upright direction, and moves the fulcrum member (49) along a side edge of the biasing force transmission member (41) on a pressure receiving side to be able to adjust the biasing force.

TECHNICAL FIELD

This application is a National Stage completion of PCT/JP2012/078454 filed Nov. 2, 2012, which claims priority from Japanese patent application serial nos. 2012-215917 filed Sep. 28, 2012 and 2011-242881 filed Nov. 4, 2011.

The present invention relates to a chair in which the backrest is tilted backward wherein the chair is capable of adjusting a biasing force of biasing means for biasing the backrest toward an upright position.

BACKGROUND ART

There are conventional adjusting means for adjusting a biasing force of biasing means for biasing the backrest toward an upright position as below:

(A) At a winding end of the coil spring for biasing the backrest toward an upright position, the nut which engages with the thread of the adjusting rod is turned by the handle to change initial load of the coil spring in Patent Literature 1.

(B) A plurality of rubber torsion springs is arranged along the pivot shaft turning with the backrest, and biasing force of the rubber torsion spring selectively acts on the pivot shaft in Patent Literature 2.

(C) On the transmitting path of a biasing force, changing a position where the biasing force acts applies strength and weakness to the biasing force to be transmitted in Patent Literatures 3 and 4.

PRIOR ART

Patent Literatures

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

The adjusting means in (A) to (C) involves the following disadvantages:

(A) The biasing force of the coil spring directly acts on the operation of the handle, thereby causing operation of the handle to decrease.

(B) The biasing force for biasing the backrest toward an upright position can be adjusted merely stepwise to disable it to adjust minutely.

(C) A stroke of a moving member has to be increased. It may be necessary to change layout of the biasing means and other members or to get the whole device larger.

In view of the disadvantages in the prior art, it is an object of the present invention to provide a chair in which a moving member has a small stroke, wherein the biasing force for acting on the backrest and adjustable range are changed greatly to make the whole device smaller, the biasing force acting on the backrest being adjusted by a weak force continuously.

Means for Solving the Problems

According to the present invention, the foregoing problems are solved as below:

(1) There is provided a chair comprising:

a base supported by a leg unit;

a seat over the base;

a pivot shaft pivotally mounted to the base transversely of the chair;

a backrest fixed at a front end to the pivot shaft and standing at a rear end of the seat, the backrest turning between an upright position where the backrest is upright and a rearward-inclined position where the backrest is inclined rearward around an axis of the pivot shaft;

a rotary member fixed at a proximal end to the pivot shaft; a biasing-force transmitting member pivotally mounted at a proximal end to an eccentric portion of the rotary member via a shaft; biasing means disposed between the biasing-force transmitting member and part of the base and storing a reaction force by compression;

a fulcrum member in the base, the fulcrum member being capable of coming in contact with a middle of a pressed side of the biasing-force transmitting member and of moving along the pressed side; and

a moving member moving the fulcrum member along the pressed side of the biasing-force transmitting member,

wherein the biasing-force transmitting member acts as a lever having a contact portion with the fulcrum member as fulcrum to reverse a biasing force of the biasing means acting on a distal end as a point of effort whereby the proximal end as a point of action biases the rotary member in a direction where the backrest stands up.

The difference between a distance from the fulcrum to the point of effort and a distance from the fulcrum to the point of action becomes twice of a moving distance of the fulcrum member. Hence, the fulcrum member slightly moves, so that the biasing force acting on the backrest can be changed greatly, thereby making the device itself smaller. The biasing force acting on the backrest can continuously be adjusted.

(2) In the item (1), when the backrest is upright, the fulcrum member is spaced from the pressed side of the biasing-force transmitting member or is in contact with the pressed side so that a biasing force of the biasing means does not act on the fulcrum member.

The fulcrum member can be moved by a weak force thereby enhancing operation capability.

(3) In the item (1), the contact portion of the fulcrum member to the biasing-force transmitting member is arcuate viewed from the axis of the pivot shaft.

The biasing-force transmitting member can be turned on the contact portion with the fulcrum member smoothly. The contact portion moves along the arcuate surface depending on a rotary angle of the biasing-force transmitting member. Wear does not gather locally, thereby enhancing durability. By employing that the contact portion moves depending on the rotary angle of the biasing-force transmitting member, the biasing force transmitted to the backrest can be increased as the backrest is inclined backward.

(4) In item (1), between the pressed side of the biasing-force transmitting member and a wall of the base facing the fulcrum member, the fulcrum member slides along the wall.

Guide for guiding the fulcrum member to move can partially be omitted thereby simplifying the structure.

(5) In item (1), the moving member comprises a pair of vertical link arms supported by the base to move longitudinally of the chair, the fulcrum member being disposed between facing surfaces of the pair of link arms.

The fulcrum member is disposed at the upper end of the pair of link arms, and the lower ends of the link arms are moved thereby increasing vertical moving range of the fulcrum member. Thus, the adjustable range of the biasing force of the biasing means increases the biasing force acting on the backrest can be changed more greatly.

(6) In the item (5), lower parts of the pair of link arms are pivotally mounted to sides of the horizontally-moving member which is supported by the base to move longitudinally of the chair.

The lower parts of the pair of link arms can stably be moved longitudinally of the chair while they are held on the horizontally-moving member.

(7) In the item (6), the horizontally-moving member and a lower end of the link arm pivotally mounted to the horizontally-moving member are disposed behind and below the biasing means.

The lower ends of the horizontally-moving member and links arms can be moved longitudinally of the chair without contacting with the biasing means. The vertical distance of the link arm increases thereby increasing vertical moving range of the fulcrum member.

(8) In the item (6), a pair of guide shafts projects on the horizontally-moving member and a pair of guide members is provided to move the pair of guide shafts.

The horizontally-moving member can be moved stably and smoothly with the pair of guide members longitudinally of the chair.

(9) In item (6), the base has a sliding surface supporting the horizontally-moving member so that the horizontally-moving member slides longitudinally of the chair.

The horizontally-moving member can be carried on a broader area of the sliding surface and moves longitudinally of the chair, so that the pair of link arms can be moved more stably. Hence, the fulcrum member at the upper end of the pair of link arms moves up and down while held horizontally.

(10) In item (5), the fulcrum members in the pair of link arms comprise rollers rotating around a pivot shaft.

The fulcrum member moves up and down along the side edge of the pressed side of the biasing-force transmitting member while rotating around a transverse pivot shaft. Without sliding resistance, the biasing force can be adjusted by a weak force.

(11) In item (5), in the base there is provided a position-changing device for changing a longitudinal position of a horizontally-moving member and a lower part of the link arm and for stopping the horizontally-moving member and the lower part of the link arm.

By changing a lower longitudinal position of the horizontally-moving member and link arm pivotally mounted thereto, a vertical position of the fulcrum member can easily be adjusted and can be fixed at a certain vertical position, thereby preventing the biasing force of the biasing means from changing when the backrest is inclined.

Advantages of the Invention

According to the present invention, there is provided a chair wherein, even if a stroke of moving member is small, the biasing force acting on the backrest can be changed greatly thereby making a whole device smaller; whereby the biasing force acting on the backrest can be adjusted by a weak force continuously.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

One embodiment of the present invention will be described with respect to the drawings. In each view, the right and left are determined based on those viewed in a front elevational view.

The chair comprises a leg unit3comprising five radially-arranged legs2each of which has a caster1; a telescopic column5which stands on the leg unit3and houses a gas spring4therein (inFIGS. 3 and 14); a base6which is supported at the rear end on the column4and inclined forward and upward; a seat7supported as below; a pair of backrest support rods9,9pivotally mounted to the base6via a pair of pivot shafts8,8(inFIGS. 3 and 7) at the front end; and a backrest10supported by the rear ends of the backrest support rods9,9.

The backrest10is pivoted together with the right and left backrest support rods9,9and the pivot shafts8,8from an upright position on the rear of the seat7inFIG. 2to a suitable rearward-inclined position (not shown) about an axis of the pivot shafts8,8.

InFIGS. 4 to 21the base6made of rigid synthetic resin comprises a pentagonal base body11like a baseball home plate which is a bottom opening, and a lower cover made of rigid synthetic resin which detachably closes the lower opening of the base body11. Under the base body11, a number of parts are attached in the base6.

Through side portions11b,11bsuspending from an upper portion11aof the base body11, there are formed holes13,13in the same line at the rear part, and a bush14fits in the each of the holes13. The bush14is held with the upper portion11aof the base body11and a gland14ascrewed on the lower surface of the upper portion11a.

On the inner and outer ends of each of the pivot shaft8, there are formed rectangular portions8a,8b. The outer rectangular portion8aengages in a rectangular hole16at the front end of each of the backrest support rods9, and the inner rectangular portion8bengages in a rectangular hole17of each of a pair of rotary members16,16in the base6.

Each end of a connecting rod19fits in an engagement hole18over the rectangular hole17at an eccentric part of the rotary member16. Each end of the connecting rod19may turn in the engagement hole19or may be fixed to the rotary member16.

Thus, the backrest10, backrest support rods9,9, pivot shafts8,8, rotary members16,16and connecting rod19turn together around an axis of the pivots shafts8,8.

There is provided a pair of biasing means20,20for applying the rotary members16in a direction for standing up the backrest10or counterclockwise inFIG. 8between an eccentric portion in front of the rectangular hole17and the front part of the base11.

InFIGS. 4-13, the first biasing means20comprises a spring-guide plate24inclined forward and upward, the rear end of the plate24being coupled to the rotary member16with a transverse shaft21, a transverse shaft23in the base body11being disposed in an elongate hole22of the plate24; a spring-bearing plate25fixed to the rear end of the guide plate24; a spring retainer26in which the shaft23fits in through holes26c,26cof the side portions26b26bsuch that the spring guide plate24puts through a slit27(FIG. 20) in the middle of the spring-bearing surface26a; and a compression spring28compressed between the spring-bearing plate25and the spring-bearing surface26aof the spring retainer26and biasing the front end of the rotary member16backward and downward by storing a reaction force under compression.

The shaft23has a length approximately equal to a distance between the side portions11band11bof the base body11and engages in an inverted U-shaped groove29in two ribs11c,11clongitudinally on the lower surface of the upper portion11aof the base body11. The shaft23is attached with a shaft holder30on the front part in the base rotatably (unrotatably may be accepted) by holding it on the lower surface of each of the ribs11c.

InFIG. 12, when the shaft23is in contact with the front end of the elongate hole22of the spring-guide plate24, the rear end of the spring guide plate24does not move backward further, thereby preventing the rotary member16from turning counterclockwise inFIG. 12and the backrest10forward from the upright position. InFIG. 13, with backward inclination of the backrest10, the rotary member16is turned clockwise around the pivot shaft8, and the spring guide plate24is pushed up forward within the range in which the elongate hole22can move with respect to the shaft23. The compression spring28is compressed to apply a biasing force to the rotary member16in a direction where the backrest10is upright.

On the outer arcuate circumferential surface of the right and left rotary members16,16, there are formed teeth31like a part of a spur gear. With the teeth31of one of the rotary members16,16is provided a locking device32for the backrest10.

The locking device32comprises a locking member33having teeth33aon its lower surface. The teeth33acan engage with the teeth31of the right rotary member16viewed from front.

InFIGS. 10 and 11, the locking member33moves obliquely between a locked position in which the teeth33amesh with the teeth31of the rotary member16inFIG. 11and an unlocked position in which the teeth33aleave the teeth31of the rotary member16inFIG. 10along a guide portion11don the lower surface of the upper portion11aof the base body11.

The locking member33is connected to operating means (later described) via a Bowden cable.

The Bowden cable34comprises a flexible outer tube35mounted at one end outward and downward to the upper end of the guide portion11dand at the other end to a case of the operating means; and an inner wire36pulled out of one end of the outer tube35obliquely downward through a wire-through portion33bat the upper end of the locking member33and mounted to a wire end member36a.

Between the locking member33and one end of the outer tube35and between the locking member33and the wire end member36a, compression springs37,38, preferably having the same spring constant, are compressed to surround the inner wire36.

InFIG. 11when the locking member33is in the locking position, the inner and outer compression springs37,38are balanced to each other, and the locking member33is held in the locking position. When the inner wire36is pulled in by the operating means, the two compression springs37,38are compressed. When load is not applied to the backrest10, the locking member33is moved to the unlocking position inFIG. 10with balance of the forces by the compression springs37,38, so that the backrest10can be pivoted freely.

When load is applied to the backrest10not to disengage the teeth32of the locking member33from the teeth31of the rotary member16, the inner wire36is pulled by the operating means, and the outer compression spring38is only compressed. Thereafter, when the backrest is unloaded, the locking member33is moved by the force of the compression spring38to the unlocking position inFIG. 10balancing the forces of the compression springs37,38.

InFIGS. 6,7and14-19, between the connecting rod19and the base6, there is provided second biasing means40with biasing-force adjusting means for applying a biasing force to the connecting rod19and right and left rotary members between the right and left rotary members16and16and between the first biasing means20and20.

The second biasing means40is similar to the first biasing means20except the biasing-force adjusting means.

The second biasing means40comprises a biasing-force transmitting member41pivotally mounted to the connecting rod19and suspending therefrom as part of the biasing-force adjusting means39; a spring-guide plate44inclined forward and upward, engaging in a forked portion41aunder the lower end of the biasing-force transmitting member41with a shaft42, and having an elongate hole43at the front end in which the shaft23engages; a spring-bearing plate45fixed to the rear part of the spring guide plate44; a spring retainer46in which the shaft23engages in the through holes46c,46cof side portions46b,46bsuch that the spring guide plate44is disposed in a slit47(inFIG. 14) of a spring-retaining surface46a; and a compression spring48compressed between the spring-retaining plate45and spring-retaining surface46aof the spring retainer46around the spring-guide plate44to bias the lower end of the biasing-force transmitting member41backward by storing a reaction force under compression.

The compression spring48is larger in a spring constant than the compression spring28.

In FIGS.4,5and14-17, between the biasing-force transmitting member41in the base6and the front surface of a vertical wall11esuspending from the rear end of the upper portion11aof the base11, the biasing-force adjusting means39is provided.

The biasing-force adjusting means39comprises the biasing-force transmitting member41; a fulcrum member49which can come in contact with and move along the rear surface of the biasing-force transmitting member41vertically; and a moving member50for moving the fulcrum member49along the rear surface of the biasing-force transmitting member41. The biasing-force transmitting member41acts as a lever having as the fulcrum which is a contact point with the fulcrum member49. A biasing force of the second biasing means40exerting the end as the point of effort is reversed. By the base end as the point of action, the connecting rod19and rotary member16are biased in a direction for standing up the backrest10.

A lower surface49aof the fulcrum member49is inclined rightward and upward inFIG. 16, and an upper surface49bis horizontal. Between the upper surface49band the front surface49c, there is formed an inclined surface49dforward and downward. A corner between the inclined surface49dand the front surface49cis a contact portion49ewith the back surface of the biasing-force transmitting member41. The contact portion49emay preferably be arcuate viewed from an axis of the pivot shaft8.

The back of the fulcrum member49vertically slides in a shallow vertical groove51in the middle of the front surface of the vertical wall11eof the base body11.

The lower surface49aof the fulcrum member49is disposed on an upper surface50aof the moving member30as a right triangle. The moving member50horizontally moves inFIG. 16, and the lower surface49aof the fulcrum member49slides along the upper surface of the moving member50, so that the fulcrum member49moves along the groove51vertically.

In order that the fulcrum member49may move down securely with movement of the moving member50rightward, inFIGS. 14 and 15, at the lower part of a back surface49fof the fulcrum member49, there is formed a short recess52in parallel with the lower surface49a, and there is formed a long recess53in parallel with the upper surface50aat the upper part of a back surface50bof the moving member50. In the grooves52,53, a forward and downward upper portion54aand a forward and upward lower portion54bof a leaf spring54engage. The leaf spring54elastically holds a part between the grooves52and53thereby preventing the fulcrum member49from leaving the moving member50.

Minute waves are applied to the lower surface of the fulcrum member49and the upper surface50aof the moving member50to prevent the moving member50from moving horizontally without reason.

However, in order that the upper surface of the moving member50may slide on the lower surface of the fulcrum member49, the ends of the upper portion54aand lower portion54bare elastically deformed to expand vertically so as to allow up-and-down motion of the fulcrum member49over the moving member50in which the waves on the upper surface50aof the moving member50go over the waves on the lower surface49aof the fulcrum member49.

The lower surface of the moving member50slides over the upper surface of the guide member55fixed to the front surface of the lower end of the vertical wall11eof the base11.

At the lower end of the moving member50, a wire-through groove56is formed across the chair, and a closed-loop inner wire37connected to the operating means (later described) runs through the wire-through groove56.

The inner wire57extends sideward beyond the right and left ends of the guide member55from the wire-through groove50into the flexible outer tubes58,58the end of which is mounted to a position spaced from the guide member55.

The other ends of the outer tubes58,58are mounted to the case for the operating means (later described), and the inner wire57pulled out is pushed and pulled axially.

The closed-loop inner wire57and the pair of outer tubes58,58constitute the Bowden cable59.

Above the wire-through groove56, a spring-housing portion60is formed and is continuous with the wire-through groove56. In the middle of the spring-housing portion60, a cylindrical spring retainer61is fixed to the inner wire57. Between the left end face of the spring retainer61and the left end of the spring-housing portion60and between the right end face of the spring retainer61and the right end of the spring-housing portion60, compression springs62,63are provided around the inner wire57.

When the moving member50is unloaded, the moving member50is held at a position such that the right and left compression springs62,63may be balanced with respect to the spring retainer61.

InFIG. 16, when the inner wire57is pulled leftward by the operating means, the moving member50is moved leftward with the leftward motion of the spring retainer61while the left compression spring62is compressed. The fulcrum member49is pushed up on the upper surface50aof the moving member50inFIG. 17.

InFIG. 17, when the inner wire57is pulled rightward by the operating means, the moving member50is moved leftward with rightward motion of the spring retainer61while the compression spring63is compressed, so that the fulcrum member49lowers.

When the backrest10is in an upright position and the front end of the elongate hole43of the spring guide plate44is in contact with the shaft23, the spring guide plate44prevents the lower end of the biasing-force transmitting member41from turning backward further.

The back surface of the biasing-force transmitting member41is parallel with the front surface of the vertical wall11aof the base11, and the fulcrum member49is slightly spaced from the back surface of the biasing-force transmitting member41. Alternatively, the fulcrum member49may preferably be in contact with the back surface of the biasing-force transmitting member41such that the biasing force of the compression spring48does not exerts the fulcrum member49.

Then, the second biasing means4, biasing-force adjusting means39therefor and all the members in the base11will be described on function.

When the backrest10is in the upright position, the right and left rotary member16,16are in a rest position inFIGS. 8,9and12. The rotary member16and backrest10are prevented from turning counterclockwise by contacting the shaft23with the front end of the elongate hole22of the spring guide plate24.

InFIGS. 14 and 15, the biasing-force transmitting member41suspends under the connecting rod19. The lower end of the biasing-force transmitting member41is prevented from further turning backward by contacting the shaft23with the front end of the elongate hole43of the spring-guide plate44.

Hence, the fulcrum member49of the biasing-force adjusting means39can be moved up and down by a weak force.

InFIGS. 9 and 11, the locking device32is usually in a lock state in which the teeth33aof the locking member33aengage with the teeth31of the left rotary member16.

By operating means of the locking device32, the inner wire36is pulled, and the locking member33is moved inward and upward off the rotary member16. The teeth33adisengages from the teeth31of the rotary member16in the unlocking state.

The back of the occupant is leaned over the backrest10, and the backrest10can be reclined backward.

When the backrest10is inclined backward inFIG. 13, the right and left rotary members16,16and connecting rod19turn clockwise around an axis of the pivot shaft8together with the backrest10. The right and left guide plates24,24are pushed up forward with movement of the shafts21,21, and the compression springs28,28are compressed. The reaction force is applied to the rotary members16,16as biasing force of the first biasing means20,20to make the backrest return to the upright position.

With turning of the connecting rod19, the upper end of the biasing-force transmitting member41is turned backward and downward on the contacting portion49eof the fulcrum member19as the fulcrum, and the lower end of the biasing-force transmitting member41is turned forward. The spring guide plate44is pushed up forward via the shaft42, and the reaction force exerts the rotary members16,16as biasing force for the second biasing means to return the backrest10to the upright position.

When the fulcrum member49is in a lower limit inFIG. 18, a distance L1 from the fulcrum to the point of effort L1 is smaller than a distance L2 from the fulcrum to the point of action. Hence, the biasing force of the second biasing means40is slightly transmitted to the rotary members16,16and the backrest10via the connecting rod19. Thus the returning force of the backrest10becomes weak.

InFIG. 19, when the fulcrum member49is raised from the lower limit by ΔL, a distance L3 from the fulcrum P to the point of effort becomes L1+ΔL, and a distance L2−ΔL. A lot of biasing force of the second biasing means40is transmitted to the rotary members16,16and the backrest10. The returning force of the backrest10becomes stronger.

In the biasing-force transmitting member41, the difference between the distance La from the fulcrum P to the point of effort Q and the distance from the fulcrum to the point of action changes twice of a moving distance of the fulcrum member41. By moving the fulcrum member41slightly, biasing force exerting the backrest10can be changed greatly. Hence, the whole device can be made smaller. The biasing force acting on the backrest10can continuously be adjusted.

Because the contact portion49eto the biasing-force transmitting member41is arcuate when viewed axially, the biasing-force transmitting member can be turned smoothly on a contact point with the fulcrum member49. The contact point is moved on the arcuate surface of the contact portion49eof the fulcrum member49depending on a rotary angle of the biasing-force transmitting member41. Wear does not gather locally thereby enhancing durability. By utilizing that the contact point moves with a turning angle of the biasing-force transmitting member41, the biasing force transmitted to the backrest10is increased with backward inclination of the backrest10.

The connecting rod19is coupled above the pivot shaft8of the right and left rotary members16,16. The biasing-force transmitting member41suspends from the connecting rod19, and the second biasing means30is disposed at the lower end of the biasing-force transmitting member41. The biasing-force transmitting member41and the right and left rotary members16,16overlap across the chair. Hence, the right and left rotary members16,16, biasing-force transmitting member41, right and left first biasing means20,20and second biasing means40overlap across the chair and can be housed in a small space.

The backrest10can smoothly be biased in a good balance by a plurality of biasing means. The biasing force exerting the backrest10can effectively be adjusted without losing balance. Furthermore, a plurality of biasing means can be housed in a small space.

Then, how to mount the seat7to the base6will be described with respect toFIGS. 1-3andFIGS. 20-30.

The seat7comprises a seat-holding frame70; a synthetic-resin seat plate71mounted to the seat-holding frame70; and a cushion62mounted to the seat plate71to cover the upper surface and outer circumferential surface of the seat plate71.

The seat-holding frame70is made of rigid synthetic-resin rectangular frame and comprises a pair of guide rods73,73; a front connecting rod74for connecting the front ends of the guide rods73,73to each other; and a back connecting rod75for connecting the back ends of the guide rods73,73.

A pair of elongate holes76,76is formed in the front connecting rod74.

InFIGS. 3,20and21, in the front of the upper surface of the base body11, there is provided a pair of holding plates77,77having an arcuate upper surface having a large curvature. On the holding plate77, the lower surface of the front connecting rod74is disposed on the upper surface. A washer78in which the back part is thicker than the front part is disposed. A bolt79which passes through the washer78, the elongate hole76of the front connecting rod74and holding plate77is engaged on the upper portion11aof the base body11. The front part of the seat-holding frame70slides over the upper arcuate surface of the holding plate77without taking off the upper surface of the base body11.

A recess80formed on the rear end of the holding plate77engages with a projection81on the upper surface of the base body11, thereby preventing the holding plate77from turning around the bolt79.

A pair of downward projections82,82suspending from the rear lower surface of the right and left guide rods73,73of the seat holding frame70is connected to upward projections83,83with a transverse shaft84. With backward inclining of the backrest10, the seat-holding frame70is inclined backward and downward while the back part moves backward and downward and the front part slides backward along the arcuate upper surface of the holding plate77.

InFIG. 22, right and left guide rods73,73of the seat-holding frame70engage with the right and left sides on the lower surface of the seat plate71. There is formed a pair of grooves85,85such that the seat plate71slides along the chair with respect to the guide rods73,73within a certain range.

The right and left grooves85,85are formed slightly inward of the side ends, and the right and left guide rods are spaced inward from the ends of the seat plate71.

InFIGS. 23-27, on inner and outer edges of the groove65, there is provided a plurality of engagement projections88,89which engage with a plurality of outward projections86,87projecting sideward from the side edge of the guide rod73in the groove85.

In this embodiment, a downward projection and an engagement projection88are provided

A longer outward projection86and a longer engagement projection88are provided on the inner edge of the guide rod73and the inner edge of the groove85respectively. Three shorter outward projections87and three shorter engagement projections are provided on the outer edge of the guide rod73and the outer edge of the groove85. When the seat plate71is located from a back limit to a borderline just before a front limit, the outward projections86,87engage with the engagement projections88,89, thereby preventing the guide rod73from leaving the groove85downward. When the seat plate71is located closer to the front limit beyond the borderline, all of the outward projections86,87do not disengage from the engagement projections88,89.

The number, length and space of the outward projections86,87and engagement projections88,89are determined so that the guide rod73may not leave the groove85with engagement of them within a certain moving range. Compared with a case where the outward projections86,87and engagement projections88,89are provided over the whole moving range, the areas of mold drawing holes88a,89afor forming the engagement projections88,89become smaller inFIGS. 23 and 27thereby preventing the seat plate71from decreasing in strength.

On an upper wall of the groove85of the seat plate71, there is provided a downward elastically-engaging portion90which comes in contact with the rear end of the guide rod73to prevent the seat plate71from moving further toward the front limit when the seat plate71reaches to the borderline.

The elastically-engaging portion90is elastically deformed upward to take off a moving path of the guide rod73thereby enabling the seat plate71to move toward the front limit. During the time, the seat plate71is only raised, so that the seat-holding frame70can easily be removed.

In order to attach the seat plate71to the seat-holding frame70, the seat plate71is put over the seat-holding frame70such that the seat plate71is positioned from the borderline to the front limit with respect to the seat holding frame70, and the elastically-engaging portion90is pushed up with the upper surface of the guide rod73of the seat-holding frame70. The seat plate71is moved backward while it pushes over the seat-holding frame70, and each of the guide rods73is positioned forward of the borderline in the groove85.

The guide rod73moves forward of the borderline in the groove85, and the elastically-engaging portion90projects into the moving path of the guide rod73in the groove85. Thereafter, the guide rod73is not able to move backward of the borderline relatively, and the seat plate71does not take off the seat holding frame70.

Operating means of each part will be described.

Longitudinal position adjusting means for the seat plate71to the seat holding frame70will be described.

InFIG. 22, a plurality of slits92is formed in the front part of the right side surface of the seat holding frame70.

InFIGS. 24-26, an operating lever93projects outward and downward of the lower surface of the seat plate71. A shaft94at the upper end of the operating lever93is disposed in the right side of the seat plate71.

An engagement claw95projecting inward of the seat7is provided in the operating lever93. The engagement claw95selectively engages with any one of the slits92of the seat holding frame70, so that the seat plate71is held at a desired position with respect to the seat holding frame70.

Biasing means for biasing the operating lever93in a direction for engaging the engagement claw95with the slit92, but is not shown.

The slits92and the operating lever93constitute seat-longitudinal-position adjusting means91.

Then, locking means100for operating the locking device32will be described.

InFIGS. 2 and 27, the locking means100is disposed at the right end of the seat-holding frame70behind the longitudinal-position-adjusting means91.

InFIG. 27, the locking means100comprises a body101mounted to the lower surface in the middle of the right guide rod73of the seat holding frame70; and an operating lever104pivotally mounted to a case102with a shaft103and projecting from the lower surface of the seat plate71outward and downward.

As mentioned above, the right and left guide rods73,73are spaced from each end of the seat plate71. Thus, the operating lever104can be disposed under the side end of the seat plate104not to project outward, and the lower surface of the seat plate71can be a stopper when the operating lever104is pulled up. Furthermore, while gripping the seat plate71, the operating lever104can be operated thereby enhancing operation capability.

The other end of the outer tube35of the Bowden cable34connected to the locking device32is mounted to the case102of the body101.

The end of the inner wire36pulled out of the outer tube35is mounted to the operating lever104, which is turned upward from the locking position inFIG. 27, so that the inner wire36can be pulled.

In the body101, there is provided a known device in JP2006-136437A that the operating lever104is pulled up from the locking position to an upper operating position drawn by an imaginary line inFIG. 27, held in a lower unlocking position by an imaginary line in returning, pulled up to the operating position again from the position to turn the locking position in returning repeatedly thereafter.

When the operating lever104is in the locking position, the locking member33can be held in the locking position due to balance of the inner and outer compression springs37,38. When the operating lever104is in the unlocking position, the locking member33can be held in the unlocking position due to balance of the inner and outer compression springs37,38.

Thus, when the operating lever104is in the locking position, the backrest10can be constricted, and when the operating lever104is in the unlocking position, the backrest10can be turned freely longitudinally of the chair although a biasing force of the first biasing means20and the second biasing means40acts.

Operating means for the biasing-force adjusting means39will be described with respect toFIGS. 31 to 34.

InFIG. 31, the operating means110is provided on the lower surface of the seat holding frame70.

The operating means110comprises a body case112mounted to the lower surface of the left guide rod73of the seat holding frame70, and having an opening and a window111; a lower cover114which closes the lower opening of the body case112and projects outward of the body case112to form a lower guard113; a rotary member116which is pivotally mounted via a shaft115in the body case112and connected to the moving member50of the biasing-force adjusting means39via the inner wire57of the Bowden cable59to rotate around the shaft115to move the moving member50; and an operating lever117which projects on the outer circumferential surface of the rotary member116through the window111of the body case112and turns within a space between the lower surface of the seat plate71and the lower guard113of the lower cover114.

For attachment of the operating means110, it is useful to space the right and left guide rods73,73inward from the ends of the seat plate71.

The outer end of the lower guard113is positioned right or inward under the outer end of the seat plate71. Thus, the lower guard113cannot project outward from the seat plate71. If the lower guard113projects outward from the seat plate71, the occupant will hand on the upper surface of the lower guard113and loads it, so that the lower cover114does not fall off. Such accident can be prevented.

InFIG. 33, the other ends of a pair of outer tubes58,58of the Bowden cable59are mounted to the body case112respectively.

Because the operating means110is constructed as above, the lower part of the operating lever117can be guarded by the lower guard113of the lower cover114thereby preventing the operating lever117from hitting other material. The operating lever117becomes unlikely to expose outside thereby enhancing its appearance.

On the upper surface of the lower guard113, the indications on the operating lever117such as an isosceles triangle118and “+−” inFIG. 32are applied thereby leading easier understanding on how to operate the operating lever117.

InFIG. 33, the rotary member116is a circular pulley in this embodiment, and a semi-circular notch119is formed on the outer circumferential surface. A circular wire stopper120fixed to the inner wire57wound on the outer circumferential surface of the rotary member116engages in the notch119, so that part of the inner wire57is mounted to the part of the outer circumferential surface of the rotary member116.

The rotary member116can be made to be semi-arcuate or sector-shaped depending on a turning range or may be a cross having a perpendicular arm to the operating lever117, two inner wires being mounted to the end of the arm.

By taking the lower cover114off the structure, the Bowden cable59as connecting means can easily be mounted and removed thereby facilitating assembling and replacement of the connecting means.

In the body case112, there is provided a pressing member122biased toward the outer circumferential surface of the rotary member116with a leaf spring121. A semi-arcuate projection123is provided in the middle of the pressing member122facing the rotary member116. On the outer circumferential surface of the rotary member116facing it, a plurality of recesses124is formed to elastically engage with the projection123at a different rotary position of the rotary member116, thereby applying moderation to the rotating operation of the operating lever117and enhancing operation capability.

The pressing member122has wider portions122b,122bat each end of a base portion122a. The end faces are guided to slide on guide surfaces112a,112afacing each other in the body case112. The upper and lower ends of guide shafts125,125passing through the wider portions122b,122bslides in a pair of elongate holes126,126of the body case112and in a pair of grooves (not shown) in the upper surface of the lower cover114smoothly.

InFIG. 34, the leaf spring121has a U-shaped lower end which engages with an open edge at the lower end of the body case114on the lower cover114. The lower cover114is screwed to the body case112and fixed without special fixing means.

Therefore, fixing means for the leaf spring is not required thereby simplifying the structure and manufacturing them at low cost.

The leaf spring121is inclined at an upper part toward the rotary member116and comes in contact with the pressing member122at the upper end thereby biasing the pressing member122toward the rotary member116.

Then, height adjusting means for the seat will be described.

InFIGS. 3,26and31, the height adjusting means130is pivotally mounted to a holding member131mounted over the left side surface to the lower surface with a shaft132, and comprises an operating lever133projecting outward and downward below the seat133; an end face cam mechanism134on the upper surface at the rear part of the base body11over the column5; and connecting means for connecting the operating lever133to the end-face cam mechanism134.

A mentioned above, the right and left guide rods7373are spaced inward of each end of the seat plate71. Hence, the operating lever133is disposed below the seat plate71not to project outward from the side end of the seat plate71. The lower surface of the seat plate71acts as a stopper for the operating lever133which is pulled up. The operating lever133can be operated with a hand over the seat plate71thereby enhancing operation capability.

InFIGS. 14,15and35-40, the end face cam mechanism134comprises a cylindrical case136on the upper surface at the rear part of the base body11; a rotary member137rotatably disposed in the upper part of the case136; and an elevating member138disposed in the lower part of the case136.

The upper end of a cylindrical portion139of the case136is closed with an upper plate140. A sector-shaped notch141is formed in the upper plate139and cylindrical portion139.

A downward shaft142projects in the middle of the lower surface of the upper plate140. The shaft142is a stepped shaft which comprises an upper larger-diameter shaft142aand a lower smaller-diameter shaft142b.

The larger-diameter shaft142aengages in a larger-diameter hole143in the middle of the rotary member137, and the smaller-diameter shaft142bengages in a smaller-diameter hole144in the middle of the elevating member138.

On the inner surface of the cylindrical portion139, three vertical grooves139aare equally spaced circumferentially. Three projections138aequally spaced on the outer circumferential surface of the elevating member138fit in the vertical grooves139arespectively to slide vertically. The elevating member138is able to slide vertically but cannot rotate with respect to the case136.

On the end face of the rotary member137, there are provided three tilted cam planes145tilted circumferentially. On the end face of the elevating member138, there are provided three tilted cam planes146tilted circumferentially at the same angle as that of the tilted cam planes145.

InFIGS. 14 and 15, the lower surface of the elevating member138is in contact with the upper end of an unlocking pin4awhich projects from the upper end of the gas spring4at the upper part of the telescopic column5and is usually biased upward by biasing means (not shown) for returning the unlocking pin4ain the gas spring4.

On the upper outer circumferential surface of the rotary member137, a wire-engaging portion147is positioned in the notch141.

The connecting means135comprises a Bowden cable150comprising a flexible outer tube148which is attached at one end to the holding member131inFIGS. 3 and 26and at the other end to the upper outer circumferential portion of the case136; and an inner wire149which is disposed in the outer tube148. One end of the inner wire149pulled out of one end of the outer tube149is attached to the operating lever133, and the other end of the inner wire149pulled out of the other end of the outer tube148is wound on the outer circumferential surface of the rotary member137and attached to a wire-attaching portion147.

In the height-adjusting means130, the operating lever133is pulled up from a non-actuating position in a solid line to an actuating position in an imaginary line inFIG. 26to make the inner wire149pulled, and the rotary member137rotates from a position inFIG. 37to a position inFIG. 39. The tilted cam plane145of the rotary member137slides on the tilted cam plane146of the elevating member138, and the elevating member138is pressed down. The unlocking pin4aof the gas spring4is pressed down thereby enabling the column to retract freely.

When the seat7reaches a desired height, a hand gets away from the operating lever133. A returning force of the unlocking pin4aof the gas spring4presses up the elevating member138. With sliding motion of the tilted cam plane146of the elevating member138with the tilted cam plane145of the rotary member137, the rotary member137rotates reversely to the above, the inner wire149is pulled toward the end face cam mechanism134, and the operating lever133returns to the non-actuating position.

FIGS. 41-52illustrate a main part of a chair comprising a variation of the biasing-force adjusting means39. The same numerals are allotted to the same members as those in the foregoing embodiments, and detailed description thereof is omitted.

A fulcrum member151in this embodiment is a roller and a moving mechanism152for moving the fulcrum member151vertically comprises a U-shaped horizontally-moving member153; and a pair of link arms155,155pivotally mounted to right and left upright portions153a,153aof the horizontally-moving member153via right and left support shafts154,154. The distance between the right and left upright portions153aand153ais wider than the biasing-force transmitting member41. When the horizontally-moving member153moves forward, it does not come in contact with the rear end of second biasing means20and the lower end of the biasing-force transmitting member41. In order that the support shafts154also act as a guide shaft for guiding the moving mechanism152longitudinally of the chair, they project from the outer side surface of the link arm155.

The fulcrum member151is pivotally mounted via a pivot shaft157which runs through the link arms155and fulcrum member151between forward portions156aand156aof a U-shaped support member156disposed between facing surfaces of the upper ends of the right and left link arms155. The front faces of the support member151are in sliding contact with the rear surface in the middle of the biasing-force transmitting member41.

The horizontally-moving member153is supported on the upper surface of a support plate159fixed to the upper surface of a rear lower cover158aof the base6so as to move the rear lower part of the second biasing means40. The lower cover158in this embodiment comprises the rear lower cover158aand a front lower cover158binFIG. 43.

In front of the support shaft154of the link arm155, to the right and left upright portions153a,153aof the horizontally-moving member153, guide shafts160,160which project outward are fixed such that the upper end thereof is as high as the upper end of the support shaft154.

On the upper surface of a recessed step158eat the sides of the rear lower cover158a, a pair of L-shaped guide members161,161which comprises a horizontal portion161aand a vertical portion161bare mounted with flat screws162,162engaged in female thread holes163,163of the right and left recessed steps158e. An elongate guide hole164is formed in an upright portion161bof the guide member161.

The right and left support shafts154,154of the right and left link arms155and right and left guide shafts160,160of the horizontally-moving member153fit in the elongate guide holes164,164of the right and left guide members161to move along the chair. The upper ends of the support shaft154and guide shaft160are in sliding contact with the upper ends of the elongate guide holes164. Thus, the horizontally-moving member153to which the link arms155are pivotally mounted can move along the upper surface of the support plate159stably.

The lower ends of the horizontally-moving member153and the right and left link arms155moves along the chair, and the link arms11is tilted. The fulcrum member151and the support member156moves vertically between the biasing-force transmitting member41and the vertical wall11eof the base body11inFIGS. 43 and 44. On the vertical wall11eof the base body11, a U-shaped guide plate165is mounted to prevent wear thereon and to vertically guide the support member156stably.

Between the lower surface of the horizontally-moving member153and the upper surface in the middle of the rear lower cover158a, there is provided a position changing device166for moving a moving mechanism152and stopping it at a certain position.

InFIG. 42andFIGS. 47-52(without the fulcrum member151and support member156), the position changing device166comprises a rack-like stopper member168having a plurality of serrated engagement grooves167; an actuating member170slightly shorter than the stopper member168and having an obtuse V-shaped recess169formed by a pair of tilted planes169a,169ain the middle; a locking member173having a plurality of engagement projections171engagable with the engagement grooves167of the stopper member168and a projection172which engages in the recess169; and a moving member175having a recess174which houses the locking member173to move with the locking member173.

The stopper member168is disposed on the upper surface of a bent portion176aat a left side of a base plate176. By engaging a bolt (not shown) inserted from below of the base plate176in a female thread hole177of the stopper member168, the stopper member168is fixed to slightly project sideward from the inner edge of the bent portion176a.

An upward portion176bis provided at the left side edge of the bent portion176aof the base plate176. Upward projections179,179are formed at the upper end of the upward portion176bto engage engagement holes178,178at a left part of the support plate159. A bent portion176cwhich is higher than the left bent portion176ais formed at a right part of the base plate176. On the upper surface of the bent portion176c, the right part of the support plate158is disposed, and the support plate159is disposed on the upper surface of the base plate176by engaging the upward projection179of the base plate176into the engagement hole178of the support plate159from below inFIG. 45.

InFIG. 42, in the disposed state, the base plate176is housed in a recess158din the middle of the rear lower cover158a. The lower surface of the right bent portion176cof the base plate176and the lower surface of the support plate159are disposed on the right and left recessed step158eof the rear lower cover158a. Four bolts181inserted into through holes180of the right and left steps158efrom below of the rear lower cover158aengage in four female thread holes182of the support plate159, so that the support plate159and base plate176are fixed on the upper surface of the rear lower cover158a.

The actuating member170as above is lower than the stopper member168at the left side end, and engages in a gap183between the upper surface of the base plate176and the lower surface of the stopper member168. The actuating member170is supported on the upper surface of the base plate176to move in parallel with a direction of moving of the horizontally-moving portion153and the moving member175inFIG. 48.

Upward projections170a,170aare provided on the front and rear ends of the actuating member170except the part engaging in the gap183, and to the projections170a,170a, the ends of the inner wires57,57of the Bowden cable59connected to the operating means110are attached. Hence, the actuating member170is moved longitudinally of the chair in parallel with a moving direction of the moving member175.

InFIG. 48, the locking member173is disposed on the upper surface in the middle of the base plate176by the actuating member170so as to be approximately coplanar with the upper surface of the stopper member168. The engagement projections171of the locking member173are slightly longer than the other parts. The whole locking member173can move transversely of the chair perpendicular to the engagement groove167of the stopper member168in the recess174of the moving member175and is housed, limiting the maximum rightward moving amount.

InFIGS. 48 and 49, a compression spring185is housed in a blind hole184of the locking member173. The right end of the compression spring185is pressed onto the inner surface of the recess174of the moving member175. Thus, the locking member173is pressed toward the stopper member168and actuating member170anytime. The engagement projections171of the locking member173engage in the engagement grooves167of the stopper member168anytime.

A wider portion173aof the locking member173slides in a wider recess174aof the recess174. When the locking member173moves rightward against the compression spring185until the right end of the wider portion173acomes in contact with the left end of the wider recess174a, the engagement projections171of the locking member173leave the engagement grooves167of the stopper member168inFIG. 52.

InFIG. 46, the projection172of the locking member173is shorter than the engagement projection171and is formed with the locking member173such that the end projects from the recess174of the moving member175. When the engagement projections171engage with the engagement grooves167of the stopper member173, the position of the projection172is determined to also engage with the recess169of the actuating member170below the engagement projections171of the locking member173inFIG. 50. The end of the projection172is determined to fit with the recess169of the actuating member170.

InFIGS. 42 and 49, the upper end of the moving member175slides in the elongate guide hole186of the support plate159. In this state, the flat screws187are engaged in the female thread holes188of the moving member175and the moving member175is fixed to the lower surface of the right part of the horizontally-moving member153. The lower surface of the right part of the moving member175are in sliding contact with the upper surface of the base plate176and the inner side surface of the bent portion176c. Hence, the moving member175can move with the horizontally-moving member153longitudinally of the chair along the elongate guide hole186of the support plate159and the base plate.

WithFIGS. 43,44and49-52, the biasing-force adjusting means38and position changing device166in the variation will be described on their functions.

FIGS. 49 and 50illustrate non-actuation of the operating means110, the projection172of the locking member173engages in the recess169of the actuating member170, and the engagement projections171of the locking member173engage with the engagement grooves167of the stopper member168. Hence, the moving mechanism152which comprises the horizontally-moving member153fixed to the moving member175and right and left link arms155stop at a predetermined position. InFIG. 43, the fulcrum member151supported by the link arms155stops at a predetermined position, so that a biasing force of the second biasing means40is suitably adjusted via the biasing-force transmitting member41.

In this state, by operating the operating means110, the actuating member170is moved forward (downward inFIG. 49). InFIGS. 51,52, the projection172of the locking member173gradually leaves the recess169and moves rightward by action of the projection172with the tilted surface169ain the recess169of the actuating member170. Thus, the engagement projections171of the locking member173gradually leave the engagement grooves167of the stopper member168and moves rightward until the right side of the wider portion173aof the locking member173comes in contact with the wider recess174aof the recess174. The engagement projections171completely leave the engagement grooves167of the stopper member168.

The locking member173moves rightward against a biasing force of the compression spring185, and a resistant force is slightly applied to the operating means110via the actuating member170and inner wire57. But the biasing force of the compression spring185is small and the operating means can be operated by a weak force.

The wider portion173aof the locking member173comes in contact with the wider recess174aof the recess174, so that the locking member173is hindered from moving rightward. The projection172is prevented from leaving the recess169completely and the projection172is in sliding contact with the rear tilted surface169aanytime. Hence, the operating means110is further operated to move the actuating member170forward, and the projection172is moved forward by the rear tilted surface169aof the recess169, thereby moving the moving mechanism152including the locking member173, moving member175and horizontally-moving member153. The right and left link arms155are inclined and laid. The fulcrum member151rolls along the biasing-force transmitting member41inFIG. 44and moves downward smoothly, thereby adjusting the biasing force of the second biasing means40to be smaller. If the biasing force of the biasing means40should get larger, the operating means110is operated contrary to the above, and the actuating member170may be moved backward.

The fulcrum member151is in sliding contact with the biasing-force transmitting member41connected to the second biasing means40, and the locking member173only moves with the moving member175and horizontally-moving member153while the compression spring185is compressed. A strong resistant force is not applied to the operating means11by the second biasing means40and compression spring185via the actuating member170and inner wire57connected to it. Hence, a biasing force transmitted to the backrest support rod9from the second biasing means40via the biasing-force transmitting means41can be adjusted by operating the operating means110by the same operating force anytime.

By using the biasing-force adjusting means39and position changing device166in this variation, the fulcrum member151is supported by the upper end of the link arm155, and the lower end of the link arm155is moved longitudinally of the chair by the position changing device166, thereby increasing a vertical moving range of the fulcrum member151and increasing an adjustable range of the biasing force of the second biasing means40.

By simple operation that the actuating member170moves longitudinally of the chair with the operating means110, a longitudinal position of the moving member175connected to locking member173, horizontally-moving member153and the lower end of the link arm155can easily be changed. When the actuating member170is stopped, the engagement projections171of the locking member173engage in the engagement grooves167of the stopper member168by a biasing force of the compression spring185, so that the moving member175and horizontally-moving member153can be stopped at a predetermined position.

Furthermore, the engagement projections171of the locking member173selectively engage in the engagement grooves167of the stopper member168thereby increasing a moving stroke of the moving member175, horizontally-moving member153and link arm155.

The engagement projections171of the locking member173engage with the engagement grooves167of the stopper member168within approximately the same plane, and under it, the projection172is in sliding contact with the recess169of the actuating member170within approximately the same plane. The locking member173is housed in the recess174of the moving member175thereby reducing a vertical size of the stopper member168, locking member173and moving member175and a vertical size of the whole position changing device166. Thus the height of the base6in which the position changing device166is installed can be reduced.

The present invention is not limited to the foregoing embodiments. Without departing from the scope of claims, for example, the following variation may be possible.

Instead of the compression spring48in the second biasing means40, a gas spring may be used.

The gas spring may have a locking function and the locking device32may be omitted.

The fulcrum member151in the variation may be a plate without a roller. A contact surface with the biasing-force transmitting member41may be arcuate and the rear surface thereof may be in sliding contact with the vertical wall11eof the base body11. The support member156may thus be omitted.

Without the base plate176in the variation, the stopper member168, actuating member170and locking member173may directly be assembled within the recess158don the upper surface of the rear lower cover158.

Without the support plate159, a sliding surface with which the horizontally-moving member153is in sliding contact may be formed on the upper surface of the rear lower cover158a.