Hinge devices for office chairs and an office chair

The present invention relates to hinge devices for office chairs.

More specifically the invention relates to hinge devices for joining a seat and/or a backrest to a carrier frame of said office chair in an articulated, spring-loaded manner. Further, the invention relates to an office chair comprising a hinge device.

Hinge devices of the above type are applied to office chairs in order to adjust the relationship between a seat and/or a backrest to a carrier frame of the chair. Some hinge devices for office chairs involve several mechanical elements in complicated structures, which take up large amounts of space and are, as a consequence, aesthetically unsatisfactory and expensive in manufacture. This is especially the case when the hinge device provides several adjustment possibilities, which is often required in working chairs. Further, many hinge devices of the prior art are difficult to assemble, and broken parts of the devices may similarly be difficult to replace.

In an office chair applied with a hinge device of the described type in order to improve the comfort of the user, the user is able to ad- just the angle of the seat and/or the backrest, forwards and backwards. The chair may provide a "weightless" function such that the chair's seat and/or backrest dynamically follow the movement of the user when he leans forwards and backwards. An easy adjustment with many positions is to be preferred since the user will often change sitting positions many times during a day, and since a more or less precise adjustment of the chair position is of great ergonomic importance.

Several hinge devices have been developed or may be applied for office chairs. However, very often hinge devices of the prior art only have very limited settings of adjustment of the seat and/or backrest an- gle. The relevant desired angle adjustments should be small, the angle between the extreme backward and forward positions of e.g. the backrest typically being about 30°. If a prior art hinge device is provided with stepless adjustment of the seat angle, adjustment of the angle is typically still to a rather large extent carried out in steps because of me- chanical insufficiencies of the hinge device when operating within small

angles.

In some prior art office chairs it is possible to lock the chair in one or more positions between the extreme backward and forward positions. Prior art hinge devices applied for office chairs are typically rather large in size, which is expensive and aesthetically unappealing. It is important in the construction of office chairs that the user's knees are raised as little as possible when the user leans backwards. To achieve this the fulcrum for tilting the seat must be positioned as close to the front end of the seat as possible or the seat should perform some kind of compensating movement. If the hinge device is large, the fulcrum can typically not be placed very close to the front edge of the seat.

It is a distinct wish that one type of office chair should fit many different people. Accordingly, it should be possible to adjust the chair ac- cording to individual needs and body weights. Thus, there exists a need for pretensioning of the spring force between the seat and/or backrest and the carrier frame. Preferably, it should be possible to readily change the pretension of the spring force both during manufacture of the chair and especially by a user sitting on the chair. DE 44 24 096 Al discloses a hinge device for an office chair, the hinge device comprising two helical springs and two leaf springs. When a user sits on the chair seat the springs are compressed to provide a spring force on the seat and backrest of the chair, the backrest being fixed to the seat. The leaf springs are provided centrally in the hinge de- vice, abutting the respective inwards ends of the helical springs. The outwards ends of the helical springs abut respective abutment elements, the position of which may be adjusted against or away from the helical springs in order to pretension these. The pretensioning is carried out by means of threaded rods engaging inner threads of the abutment ele- ments.

It is the object of the present invention to provide a hinge device as described in the introduction, which overcomes or lessens the above-described drawbacks of the prior art.

To meet this object the invention provides in a first aspect a hinge device for an office chair, more specifically for joining a seat

and/or a backrest to a carrier frame of said office chair in an articulated, spring-loaded manner, comprising an abutment element abutting one end of a spring element, c h a r a c t e r i z e d in that it comprises a first sliding element comprising said abutment element and adapted to tension said spring element by means of a sliding movement of said first sliding element and thereby said abutment element of said sliding element against or away from said spring element on articulation of said seat and/or said backrest in relation to said carrier frame such as to provide a spring tension between said seat and/or said backrest in relation to said carrier frame, the position of said abutment element being adjustable in relation to the position of the remaining part of said first sliding element such as to adjust a pretension of said spring element. With the hinge device according to the first aspect of the present invention a standard hinge device may be applied to an office chair or a type of office chair used by different people of different weights and preferences. Since the abutment element can be adjusted independently of the sliding element, it is possible to adjust the pretensioning of the spring element in an easy manner, both at the production facility and by a user. This is possible without reducing the sliding motion interval of the sliding element, the maximum angle of movement of the seat and/or backrest in relation to the carrier frame thus remaining constant during pretensioning of the spring element. The hinge device according to the first aspect of the invention may be produced as a low-weight device that may be easily mounted in an aesthetically appealing manner. A high degree of freedom of design is provided when choosing the mounting position of the device. Further, the hinge device can be manufactured with low costs and be easily as- sembled from its parts by placing the elements in the proper order from end openings of the hinge device, the spring element not having to be pretensioned during assembly. Any broken parts making up the hinge device may similarly be easily replaced.

The hinge device can be manufactured with a small cross- section and overall size, rendering the hinge device of the present inven-

tion a practical and aesthetically attractive solution in many cases.

In a preferred embodiment of the hinge device according to the first aspect of the invention said first sliding element and said first actuating element comprise mutually abutting surfaces, said first actuating element being adapted to actuate said sliding movement of said first sliding element by means of cooperation between said abutting surfaces. Preferably, said sliding element is slidable in an axial direction of said hinge device and retained against rotation about its axis; more preferably, said actuating element is rotatable about its axis, but retained against movement in an axial direction of said hinge device.

In another preferred embodiment said hinge device comprises a second actuating element and a second sliding element directly or indirectly abutting another end of said spring element such as to provide an oppositely directed function similar to said first actuating element and said first sliding element. This provides a stronger and more stable (symmetric) distribution of forces. In such a double system only the first sliding element need to be connected to an individually adjustable abutment element. The second sliding element may directly abut the spring without compromising the symmetric distribution of forces on the hinge device. Furthermore, only one single spring is necessary although it may be purposeful to provide e.g. two or more helical springs embedded in each other.

In another preferred embodiment the position of said abutment element in relation to the position of said first sliding element is adjust- able by means of a pretensioning member preferably extending through said first actuating element from one end of said hinge device. This provides an effective, compact device. Preferably, said pretensioning member is a pretensioning rod axially secured to said sliding element, said pretensioning rod comprising an outer thread cooperating with an inner thread of said abutment element such that said spring element is pre- tensioned on rotation of said pretensioning rod, friction between said inner and outer threads preferably providing a friction lock between said pretensioning rod and said abutment element. These features provide for a low-cost solution, which is easy to manipulate. More preferably, said pretensioning rod at one end is connected rotationally, but axially

locked, to a locking means in the form of a locking rod such as to form a trough-going member extending substantially from one end of said hinge device to the other. Even more preferably said spring element comprises a helical spring, said through-going member extending through an inte- rior cavity of said helical spring, this making the device even more compact. In a preferred development said locking rod is connected with a locking member adapted to optionally lock and release said seat and/or said backrest in relation to said carrier frame via locking engagement with said second sliding element. Thereby, it is possible for a user to lock the office chair in a desired angle between the seat and/or backrest and the carrier frame. The locking means may provide the possibility of locking the chair in none, one or more intermediate positions as well as one or both extreme positions. In a further development of the locking rod of the hinge device a handle for activation of said locking rod is provided at an end of said hinge device in order to provide an easy means for locking the chair in a desired position by a user sitting in the chair.

In yet another preferred embodiment a similar handle for actuation of said adjustment of the pretension of said spring element is provided at an end of said hinge device, making it easy to quickly adjust the pretension of the spring to fit the desired purpose. Preferably, the handle for actuating the locking rod and the handle for actuating the pretension- ing of the spring device are provided at opposite sides of the office chair. In a second aspect the invention provides a hinge device for an office chair, more specifically for joining a seat and/or a backrest to a carrier frame of said office chair in an articulated, spring-loaded manner, said hinge device comprising a spring element, c h a r a c t e r i z e d in that said hinge device further comprises a first actuating element and a first sliding element, said first sliding element and said first actuat- ing element comprising mutually abutting ends with a number of mutually corresponding cams, said first actuating element being adapted to actuate a sliding movement of said first sliding element against or away from said spring element on articulation of said seat and/or said backrest in relation to said carrier frame by means of cooperation between said cams of said

abutting ends, whereby said first spring element spring-loads said seat and/or said backrest in relation to said carrier frame.

The hinge device according to the second aspect of the invention provides an interaction between a sliding element and an actuating element such that when a seat and/or a backrest articulate in relation to a carrier frame of an office chair, the actuating element actuates a sliding movement of the separate sliding element. If, for example, the spring element is a helical spring, and the sliding element abuts one end of the helical spring, the sliding element compresses or elongates the spring on said articulation. Compressing/elongating a spring element typically provides a far more effective and stable spring force than for example rotating one end of the helical spring wire in relation to the other end. Further, the lifetime of the spring element may be considerably extended, the articulation of the seat and/or backrest of the office chair are natural and stepless and noise is reduced.

The hinge device according to the second aspect of the invention provides a tool for efficiently transforming a rotational movement into an axial movement, thereby making it possible to apply common spring means for providing the desired spring force. It may be produced as a low-weight device that may be easily mounted in an aesthetically appealing manner. A high degree of freedom is provided when choosing the mounting position of the device.

Further, the hinge device can be manufactured with low costs and be easily assembled from its parts by placing the elements in the proper order from end openings of the hinge device, the spring element not having to be pretensioned during assembly. Any broken parts making up the hinge device may similarly be easily replaced. The hinge device provides for a simple and truly stepless adjustment of the angle between the backrest/seat and the carrier frame. A user may readily carry out such adjustment and it is possible to provide locking means such as to lock the chair in a number of intermediate and/or extreme positions. With proper spring-loading a "weightless" functionality can furthermore be achieved.

The hinge device can be manufactured with a small cross- section and overall size compared to prior art hinge devices with similar

qualities, rendering the hinge device of the present invention a practical and aesthetically attractive solution in many cases.

When applying the hinge device to an office chair it is possible to construct the chair such that the user's knees are raised very little when the user leans backwards because of the freedom provided in positioning of the device in relation to the seat of the chair.

In a preferred embodiment of the hinge device according to the second aspect of the invention an opposite end of said first actuating element abuts an end of a rotationally and axially locked support ele- ment, said mutually abutting ends between said first actuating element and said support element comprising a number of mutually corresponding cams such as to extend said offsetting of said abutment element of said first sliding element against said spring element. This embodiment is in fact a gearing of the hinge device having the effect that a specific angular movement between the seat and/or the backrest in relation to the carrier frame provides for a larger spring force between the said components because the sliding element is moved a farther distance against the spring element. Also, a softer and smoother movement is provided. If desired, further gearing may similarly be provided in the form of further actuating and sliding elements provided in series in the hinge device. Such gearing may have the positive effect that a smaller or less strong spring device is necessary.

In another embodiment the hinge device according to the second aspect of the invention comprises a second actuating element and a second sliding element directly or indirectly abutting another end of said spring element such as to provide an oppositely directed function similar to said first actuating element and said first sliding element.

The hinge device according to the second aspect of the invention may comprise the features of any of the above embodiments relat- ing to the first aspect of the invention, gaining the specific advantages of the said individual embodiments.

In another preferred embodiment said first sliding element is slidable in an axial direction of said hinge device and retained against rotation about its axis. In a development of this embodiment said first ac- tuating element is rotatable about its own axis and slidable in said axial

direction of said hinge device, said sliding movement of said first sliding element against or away from said spring element being carried out by rotation of said first actuating element in relation to said first sliding element. In another preferred embodiment said hinge device further comprises a tubular enclosure, which retains said first sliding element against rotation about its axis with respect to said carrier frame, but permits it to slide in an axial direction of said hinge device.

In a third aspect the invention provides an office chair compris- ing a backrest, a seat and a carrier frame, said office chair further comprising a hinge device for joining said seat and/or said backrest to said carrier frame in an articulated, spring-loaded manner by means of a spring element of said hinge device, c h a r a c t e r i z e d in that said hinge device comprises a sliding element and an actuating element, said sliding element and said actuating element comprising mutually abutting surfaces, said actuating element being adapted to actuate said sliding element to slide against or away from said spring element on articulation of said seat and/or said backrest in relation to said carrier frame by rotation of said actuating member in relation to said sliding element and thus cooperation between said abutting surfaces, whereby said spring element spring-loads said seat and/or said backrest in relation to said car- rier frame.

The office chair according to the third aspect of the invention provides an interaction between a sliding element and an actuating element such that when the seat and/or the backrest articulate in relation to said carrier frame, the actuating element actuates a sliding movement of the separate sliding element. If, for example, the spring element is a helical spring, and the sliding element abuts one end of the helical spring, the sliding element compresses or elongates the spring on said articulation. Compressing/elongating a spring element typically provides a far more effective and stable spring force than for example rotating one end of the helical spring wire in relation to the other end. Further,

the lifetime of the spring element may be considerably extended, the articulation of the seat and/or backrest of the office chair are natural and stepless and noise is reduced.

The office chair according to the third aspect of the invention may be produced with a small, low-weight hinge device that may be easily mounted in an aesthetically appealing manner. A high degree of freedom is provided when choosing the mounting position of the device.

Further, the hinge device and thereby the office chair can be manufactured with low costs and be easily assembled from its parts by placing the elements in the proper order from end openings of the hinge device, the spring element not having to be pretensioned during assembly. Any broken parts making up the hinge device may similarly be easily replaced. The hinge device provides for a simple and truly stepless adjustment. A user may readily carry out such adjustment. With proper spring-loading a "weightless" functionality can furthermore be achieved.

The hinge device can be manufactured with a very small cross- section and overall size, rendering the office chair a practical and aesthetically attractive solution.

The office chair may be constructed such that the user's knees are raised very little when the user leans backwards because of the freedom provided in positioning of the hinge device in relation to the seat of the chair.

The hinge device according to the third aspect of the invention may furthermore be provided with a hinge device according to the first aspect of the invention.

In a preferred embodiment of the office chair according to the third aspect of the invention said mutually abutting surfaces of said sliding element and said actuating element comprise mutually corresponding outer and inner threads or form ends of said elements comprising a number of mutually corresponding cams.

If said hinge device of said office chair further comprises the features of any of the above embodiments relating to the first or second aspect of the invention, the chair gains the specific advantages of the individual embodiments. The invention will be explained in detail in the following by

means of examples of embodiments with reference to the schematic drawing, in which

Fig. 1 is a sectional view of a first embodiment of a hinge device for an office chair according to the third aspect of the invention; Fig. Ia is a sectional view of a development of the hinge device according to Fig. 1;

Fig. 2 is a sectional view of a second embodiment of a hinge device for an office chair according to the third aspect of the invention;

Fig. 3 is a perspective view of a third embodiment of a hinge device for an office chair according to the third aspect of the invention, the third embodiment being according to the first aspect of the invention;

Fig. 4 is a cross-sectional view of the hinge device according to Fig. 3 taken along line IV-IV; Fig. 5 shows perspective views of a threaded rod and a threaded tube of the hinge device according to Fig. 3;

Fig. 6a shows a cross-sectional view of a locking rod of the hinge device of Fig. 3 taken along line IV-IV of Fig. 4;

Fig. 6b shows a cross-sectional view of a locking bushing of the hinge device of Fig. 3 taken along line IV-IV of Fig. 4;

Fig. 6c shows the locking rod of Fig. 6a in an unlocked position in the locking bushing of Fig. 6b;

Fig. 6d is a cross-sectional view similar to Fig. 6c, but with the locking rod in a locked position in the locking bushing; Fig. 7 is a perspective view of a first embodiment of an office chair according to the third aspect of the invention provided with a hinge device according to Fig. 3;

Fig. 8 is an enlarged perspective view of the hinge device according to Fig. 3 implemented in the office chair according to Fig. 7; Fig. 9 is a side view of the office chair according to Fig. 7;

Fig. 10 is a side view showing two possible seating positions of a second embodiment of an office chair according to the third apect of the invention with a hinge device according to Fig. 3;

Fig. 11 is a side view showing another two possible seating posi- tions of the office chair of Fig. 10;

Fig. 12 is a side view showing two possible seating positions of a third embodiment of an office chair according to the third aspect of the invention provided with a hinge device according to Fig. 3;

Fig. 13 is a side view showing another two possible seating posi- tions of the office chair of Fig. 12;

Fig. 14 is a perspective view of a fourth embodiment of a hinge device for use in an office chair according to the third aspect of the invention, this fourth embodiment being according to the first and second aspects of the invention; Fig. 15 is a cross-sectional view of the hinge device according to

Fig. 14 taken along line XV-XV;

Fig. 16 is a perspective view of the hinge device according to Fig. 14 with some parts removed and the hinge device in a first, non- loaded position; and Fig. 17 is a perspective view corresponding to Fig. 16 with the hinge device in a second, loaded position.

Similar or equivalent parts of different embodiments are provided with similar reference numerals.

Fig. 1 shows a first embodiment of a hinge device H for an office chair according to the third aspect of the invention with a section through its centre along its vertical axis. At the right end of the hinge device H a first sliding element in the form of a first threaded rod 2 with an outer thread and a first actuating element in the form of a first threaded tube 3 with a corresponding inner thread extend in the axial di- rection of the hinge device H, the threaded rod 2 being fitted in the threaded tube 3. A spring element in the form of a helical spring 7 extends in the axial direction of the hinge device H, abutting at one end against and preferably being attached to the threaded rod 2. At the other end of the helical spring 7 an end stop 7a is provided, the helical spring 7 preferably being attached to this at its other end. The end stop 7a is fixed to a connecting rod 7b extending axially through the hinge device H.

The hinge device H is connected to one of a seat and/or a backrest and a carrier frame of an office chair (not shown) by means of a first arm 13 and to the other of said seat and/or backrest and said car-

rier frame by means of a second arm 33, the arms 13, 33 and thereby the seat and/or the backrest and the carrier frame being joined in an articulated, spring-loaded manner. The second arm 33 is fixed to the threaded rod 2, and the first arm 13 is secured to the threaded tube 3 and the connecting rod 7b. The arms 13, 33 do not, in the embodiment shown, form part of the hinge device H.

Fig. 2 shows a second embodiment of a hinge device according to the invention in a configuration very similar to the embodiment of Fig. 1. In Fig. 2 the hinge device H is modified such that the second arm 33 is connected to a sliding element in the form of threaded tube 3, and the first arm 13 is connected to an actuating element in the form of threaded rod 2.

In both the first and the second embodiment the helical spring 7 is provided such that axial movement of the threaded rod 2 and the threaded tube 3 in their corresponding threads with respect to each other provides a spring force exerted by the second arm 33 on the first arm 13 and thereby between the seat and/or backrest and the carrier frame of the office chair. The helical spring 7 is compressed or extended as the threaded rod 2 (Fig. 1) or the threaded tube 3 (Fig. 2) engages the helical spring 7 at its left end. The spring force is exerted as a torque forcing the arms 33, 13 away from each other or against each other around the axis of the hinge device H. Further, the said axial movement forces the arms away from each other or against each other in the axial direction of the hinge device H. In the embodiment of the hinge device according to Figs 3 and 4 only the rotational spring force (torque) is applied; the arms will not move against or away from each other in the axial direction of the hinge device H.

Fig. Ia shows a development of the hinge device according to Fig. 1. In this case the second arm 33 replaces the end stop 7a. The arm 33 is fixed to the connecting rod 7b. The connecting rod 7b retains the threaded rod 2 against rotation about its axis but permits it to slide in its axial direction. This is preferably achieved by splining the threaded rod 2 to the connecting rod 7b. This configuration prevents relative axial movement of the arms 13, 33. However, the arms are still rotationally spring-loaded in relation to each other. As a further advantage, this de-

velopment allows for the threaded tube to extend in the complete length of the hinge device H in order to function as a housing of the other parts of the hinge device, including the spring element. The thread of such housing would only need to be applied at one end of the hinge device H. A second set of threaded rod and threaded tube could be provided at the other end of the hinge devices of the embodiments of Figs. 1, Ia and 2 dependent on the field of application of the hinge device. Providing only one set makes the hinge device shorter in its axial direction. Figs 3 and 4 show a third embodiment of a hinge device H according to the first aspect of the invention applying the same abutment (and preferably attachment) of a sliding element in the form of a threaded tube 3 against a spring element 7 as the second embodiment described in the above in relation to Fig. 2. A similar connection to said seat and/or backrest and said carrier frame as the second embodiment is also applied. The hinge device H is suitable for joining these in an articulated manner such as to form an office chair according to the third aspect of the invention as is shown in the three embodiments of Figs 7-9, 10-11 and 12-13, respectively. Referring to Figs 3 and 4 the hinge device H comprises a tubular enclosure 1 (cf. Fig. 4) with an axis and an axial direction, the tubular enclosure 1 being removed in Fig. 3 in order to reveal interior parts of the hinge device H. The tubular enclosure 1 has a small diameter of for example about 4 cm. At the right end of the tubular enclosure 1 a first actuating element in the form of a first threaded rod 2 and the first sliding element in the form of the threaded tube 3 extend in the axial direction of the tubular enclosure 1, the threaded rod 2 being fitted in the threaded tube 3 such that the threaded surfaces of these abut each other, this corresponding to the embodiment described in relation to Fig. Ia in the above.

In Fig. 3 the threaded tube 3 has been removed to render the threaded rod 2 visible. At the other end of the tubular enclosure 1 an equivalent second actuating element in the form of a threaded rod 4 with an opposite thread is similarly fitted in a second threaded sliding element in the form of a second threaded tube 5 equivalent to the first threaded

tube 3. The two sets of threaded rods 2, 4 and tubes 3, 5 do not necessarily have the same dimensions. However, this is the case in the embodiment shown and is also preferred. Between the respective threaded rods 2, 4 and threaded tubes 3, 5 a spring element in the form of a heli- cal spring 7 extends in the axial direction of the tubular enclosure 1. It may also comprise a second or further helical springs. The threaded tube 3 abuts against one end of the helical spring 7 in area 9 and an abutment element 10 abuts against the other end of the helical spring 7. The threaded rods 2, 4 are thus adapted to actuate the threaded tubes 3, 5, respectively, to slide against or away from the helical spring 7 on articulation of a seat and/or a backrest in relation to a carrier frame of an office chair to which the hinge device H is applied. This is done by rotation of the threaded rods 2, 4 in relation to the threaded tubes 3, 5 and thus cooperation between the abutting threaded surfaces, whereby the helical spring 7 spring-loads the seat and/or backrest in relation to the carrier frame.

End plugs 11, 12 are provided at each end of the tubular enclosure 1, thus limiting the axial movement of the threaded tubes 3, 5 in the direction away from the spring element 7. An arm 13 is fixed to the threaded rod 2, and an arm 14 is fixed to the threaded rod 4, the arm 14 being equivalent to the first arm 13. The arms 13, 14 are thus rotatably positioned in relation to the tubular enclosure 1, but axially fixed in relation to the tubular enclosure 1. The tubular enclosure 1 is fixed, for example at its mid-point, to another object. Between the end plugs 11, 12 and the arms 13, 14, respectively, friction members 11a, 12a are provided to ensure a smoother movement of the two articulated objects in relation to each other. Between the end plugs 11, 12 and the friction members 11a, 12a, respectively, arm connectors 13a, 14a are provided. The arm connectors 13a, 14a are fixed to the respective arms 13, 14 and are rotatable in relation to the end plugs 11, 12. The threaded rods 2, 4 are hollow, allowing for a through-going member 15 to extend centrally through the tubular enclosure 1 along its axis from one end plug 11 to the other 12, the ends of the through-going member 15 being fixed to respective handles 16, 17 forming the outermost ends of the hinge device H.

Referring still to Figs 3 and 4 the threaded rod 2 and the threaded tube 3 are shown enlarged and in perspective in Fig. 5. The threaded rod 4 and the threaded tube 5 of the opposite end of the tubular enclosure 1 are elements similar to these but with an opposite helical angle. The threaded tubes 3, 5 are splined into splinings 3b, 5b of the wall of the tubular enclosure 1 by means of projections, the threaded tubes 3, 5 thus being retained against rotation about the axial direction with respect to the tubular enclosure 1, but being slidable in the axial direction. The threaded rods 2, 4 are retained against movement in the axial direction by means of the end plugs 11, 12, but are able to rotate about the axis of the tubular enclosure 1. The threaded rods 2, 4 are provided with outer threads 2a, 4a corresponding to inner threads 3a, 5a of the threaded tubes 3, 5. In Fig. 5 the inner threads of the threaded tubes 3, 5 are visible from the outside; this is not the case in Figs 3 and 4. The threads 2a, 3a are right-handed in the embodiment shown, and the threads 4a, 5a are left-handed.

When the end plugs 11, 12, the threaded rods 2, 4 and the arms 13, 14, which are all fixed together, rotate about the axis of the tubular enclosure 1, the threaded tubes 3, 5 are thus urged to move in the axial direction towards or away from the spring element 7 depending on the direction of rotation. This is caused by movement of the threaded tubes 3, 5 in the corresponding threads 2a, 4a of the threaded rods 2, 4. The position of the helical spring 7 between the threaded tubes 3, 5 provides, via the abutment elements 9, 10, compression or release of the helical spring 7, providing a spring force to be exerted by said seat and/or backrest and said carrier frame. The angle between these will thus increase or decrease depending on the direction of movement of the threaded tubes 3, 5. The helical angle of the threaded rods 2, 4 and the threaded tubes 3, 5 is about 50° in the embodiment shown. Part of the through-going member 15, more specifically a threaded locking rod 18 provides, together with a locking bushing 19, locking means for locking the axial movement of the threaded tube 3. Fig. 6a shows a cross-sectional view through the locking rod 18 along the line IV-IV of Fig. 4, and Fig. 6b shows a cross-section through the locking bushing 19, with only the internal periphery shown, along the

line IV-IV of Fig. 4. With reference to Fig. 6a the locking rod 18 has a circular-cylindrical cross-sectional profile, from which peripheral sections 20, 21 have been cut off along chords 20, 21 to the circular cross- section of the locking rod 18 on each side of this. On the remaining pe- riphery the locking rod 18 is provided with an outer thread 22. The locking bushing 19 is provided with a corresponding inner thread 23. In Figs 6c and 6d the locking rod 18 is shown within the locking bushing 19 in an unlocked and a locked position, respectively. When the hinge device H is assembled, the threaded rod 2 is in a rotationally unlocked state in the situation shown in Fig. 6c, the axial movement of the threaded tube 3 thus being in an unlocked state. When adjusting the angle between the said two objects during use, said angle is adjusted to a preferred position, after which the hinge device H may be locked in said preferred position by rotating the locking rod 18 90° to the state shown in Fig. 6d, the thread 22 engaging the thread 23. In the embodiment shown this rotation can be easily carried out by the user by means of rotation of the handle 16 at the right hand end of the tubular enclosure 1. Preferably means for letting the locking rod 18 click into position at said 90° increments (not shown) are provided in the hinge device H. Since the through-going member 15 (i.e. pre-tensioning rod 25) is axially locked to the threaded tube 5 by means of clip 27, 28, axial movement of the locking rod 18 of the through-going member 15 is twice the axial movement of each of the threaded tubes 3, 5. This provides for twice as many locking points. The number of locking points may be varied by varying the thread pitch. Preferably, a large number of locking positions are provided.

A spacing member 8 is positioned rotationally locked, abutting the threaded tube 3 by means of the locking bushing 19 and extending towards the centre of the hinge device H. The spacing member 8 com- prises an interior thread 8a at its left-hand end in Figs 3 and 4 for engaging the exterior thread of the threaded locking rod 18. By rotating the handle 16 and thus the threaded locking rod 18 it is thus possible to axially move the spacing member 8 towards or away from the centre of the hinge device H. Since the spacing member 8 functions as a stop for the axial movement of the threaded tube 3, the angle of movement be-

tween the extreme positions of said two objects can thus be controlled by means of the handle 16. The handle 16 must be rotated at least a full 360° before a noticeable change in the angle of movement between the extreme positions of said two objects is achieved. Preferably limitation means are provided to influence the user such that he will intuitively rotate the locking rod 18 in one direction for locking the threaded tubes 3, 5 and in the other direction for releasing the threaded tubes 3, 5 as opposed to locking and releasing by rotating the rod 18 in the same direction. This has the advantage that no noticeable change in the angle of movement between the extreme positions of said two objects is provided when locking or releasing the locking rod 18.

Still referring to Figs 3 and 4, other parts of the through-going member 15, more specifically two pretensioning rods 24, 25, provide a pretensioning member for pretensioning the spring element 7. This is useful when applying the hinge device H in an office chair as shown in Figs 7-9 to preset a standard hinge device H to users of different weights. The pretensioning rod 24 is rotationally locked to the pretensioning rod 25 by means of connecting member 26. The abutment element 10 is rotationally locked to the tubular enclosure 1 by means of projections projecting into the splinings 5b of the tubular enclosure 1 and is provided with internal threads engaging external threads of the rod 25. The pretensioning rod 24 is connected to a second handle 17 at the left end of the tubular enclosure 1. By rotation of the handle 17 the abutment part 10 engages the external threads of pretensioning rod 25 pulling the abutment part 10 away from or against the threaded tube 3 dependent on the direction of rotation of the handle 17. Thus, the abutment element 10 is made adjustable in relation to the threaded tube 5, providing an extension or compression of the helical spring 7 and thereby a pretensioning of the helical spring 7. Further, the second han- die 17 comprises a hole 17a for receiving a tool (not shown) for pretensioning of the spring means 7 before the chair reaches the end user, e.g. during assembly of the hinge device H. The pitch of the internal threads of the abutment member 10 and of the external threads of the pretensioning rod 25 is suitably small such that a friction lock between said pretensioning rod 25 and said abutment element 10 is provided at all

times when the pretensioning rod is not intentionally rotated. The pre- tensioning rod 25 and the locking rod 18 are axially locked to each other by means of assembly 25a. They may however rotate in relation to each other by means of assembly 25a, making the pretensioning and the locking of the hinge device H two independent systems.

The tubular enclosure 1 and/or the threaded rods 2, 4 are preferably hydroformed or extruded from stainless steel; the threaded tubes 3, 5 are preferably moulded. They may, however, be manufactured in any suitable way. The tubular enclosure is not necessarily circular- cylindrical. It may be provided with any suitable shape, e.g. with a quadratic, rectangular or an elliptic cross-section.

Figs 7-9 show the hinge device H of Figs 3 and 4 applied to adjustably connect a seat 29 of a first embodiment of an office chair or a swivel chair according to the third aspect of the invention and a centre column 30 of a carrier frame carrying the seat 29. The carrier frame further comprises a foot 31 provided at the bottom end of the centre column 30 and a backrest 32 connected to the seat 29. The tubular enclosure 1 of the hinge device H is connected to the centre column 30 by means of an arm 33. Preferably the arm 33 engages the tubular enclo- sure 1 on the splinings 3b, 5b to provide a stronger rotational lock of the arm 33 to the tubular enclosure 1. Further, the tubular enclosure 1 of the hinge device H abuts on the central part of the seat 29 and, by means of arms 13, 14, is connected to the backward part of the seat 29.

Referring to Figs 3 and 4 and Figs 7-9, with a proper pretension- ing of the spring element 7 provided by activation of the handle 17 an upward spring-induced torque will be applied to the seat 29 and the backrest 32. A user sitting in the chair, wanting to adjust the seat 29 and backrest 32 in order to assume a more upward-leaning sitting position unlocks the locking means 18, 19 by means of the handle 16, slightly relieves his weight on the seat 29 until a new, preferred sitting position is assumed and then again locks the locking means 18, 19. A more backward-leaning position may similarly be assumed by increasing the weight of the user as opposed to relieving it. The locking means 18, 19 may also remain unlocked, the spring-load thus providing for dy- namic support of the user when sitting in and shifting between different

working positions. The user may thus shift his position forwards or backwards while at all times being supported by the spring force exerted on the seat. Further, the maximum angle between the seat 29 and the backrest 32 may be adjusted by rotating the handle 16 as described in the above such that the tilting back of the backrest 32 may be delimited or extended.

As mentioned in the above, pretensioning of the spring to fit users of different weights or with different preferences can be achieved by use of the pretensioning means 24, 25 and the abutment part 10 acti- vated by the handle 17.

Figs 10 and 11 show a second embodiment of an office chair according to the invention with a hinge device H according to Figs 1 and 2. The foot of the chair is not shown. In this embodiment the hinge device H is mounted in proximity of the centre column 30 and connected to a backrest 32 via two arms, of which only one arm 13 is shown. The arms are provided on each side of a seat 29 of the chair. A first joint 34 connects the seat 29 and the backrest 32. The arm 13 is connected to the backrest 32 at a point near or right beneath a horizontal centre line through the backrest 32. The hinge device H is further connected via an arm 33, and a second joint 35, which constitutes the fulcrum for tilting the seat, near the front part of the seat 29 to the seat 29. The position of said fulcrum thus causes that the user's knees are not raised very much when the user leans backwards.

This configuration of the chair provides for a first adjustment possibility illustrated in Fig. 10 and a second adjustment possibility illustrated in Fig. 11. Fig. 10 shows the chair in the unlocked position of the locking means 18, 19 of the hinge device H as described in the above. This provides a dynamic adjustment of the seat and backrest allowing the user to dynamically change his seating position between an upward position and a backward position, the difference between these being about 25° as shown. The seat 29 is also tilted backwards along with the backrest 32, albeit with a smaller angle of about 6.8°. Typically, preferred seating positions involve a larger angle of the backrest 32 than of the seat 29. When designing the hinge device H the dimensions of the ele-

ments of the hinge device H may be varied to allow for variations of the mechanical properties of the hinge device H. For example power transmission may be varied by increasing the diameters of the threaded rods 2, 4 and the threaded tubes 3, 5 allowing for a longer spring deformation of the spring element. As another example the length of the spring member 7 and the tubular enclosure 1 may be varied to a high degree to correspond to different designs of an office chair. The position of the hinge device H in the plane of the drawing may also be varied in order to change the geometrical relationship between the angle of the seat 29 and the angle of the backrest 32. If, for example, the hinge device H is moved to the left in the figures, the backrest 32 will move relatively more than the seat 29.

In Fig. 11 the locking means 18, 19 of the hinge device H are in the locked position, and the joint 35 may slide up and down in rail 35a. This allows for a forward tilt of the seat 29 of about 5° in the embodiment shown, the corresponding movement angle of the backrest being about 2° as shown. Adjusting the position and rotation of rail 35a may vary the relationship between these angles. The angle adjustment of the backrest may, when adjusting the position of the joint 35, be entirely eliminated with proper arrangement of the rail 35a.

Figs 12 and 13 show a third embodiment of an office chair according to the third aspect of the invention applying a hinge device H according to Figs 3 and 4. The third embodiment corresponds essentially to the second embodiment of the office chair according to the invention, the description of the second embodiment applying also to the third (Fig. 12 corresponding to Fig. 10, and Fig. 13 corresponding to Fig. 11) with the following exception. The arm 13 of the chair of the third embodiment has been given a backwardly curved shape in order to avoid disturbance of the user of the chair. The three different embodiments of an office chair described in the above may be provided with other adjustment means than the ones described, such as means for sliding the seat 29 forwards and backwards and means for independent adjustment of the seat 29 and the backrest 32. Such further adjustment means are well known to the person skilled in the art. In general, an office chair applying a hinge device according to

the first and second aspects of the invention may be constructed differently from the embodiments described in the above. The hinge device H may for example provide adjustment of the seat 29 alone, the backrest 32 being directly connected to the rod 30 of the chair, or the backrest 32 may be left out entirely. The roles of the tubular enclosure 1 and the threaded rod 2 in the spring-loading of the seat 29 and the backrest 32 may be inverted; in the first embodiment (Figs 7-9), e.g., the tubular enclosure 1 may be connected to the seat 29 while the threaded rod 2 of the hinge device H is connected to the carrier frame instead. In general more than one hinge device may be applied to a single office chair.

Figs 14 to 17 show different views of a fourth embodiment of a hinge device H, this hinge device H being according to the first and second aspects of the invention. Fig. 14 is a perspective view of the hinge device H, and Fig. 15 is a cross-sectional view of the embodiment ac- cording to Fig. 14 taken along line XV-XV. Fig. 16 shows the hinge device H in a first, non-loaded position, and Fig. 17 shows the hinge device H in a second, loaded position. In the loaded position of Fig. 17 one could imagine that a user is sitting in an office chair in which the hinge device H has been applied. The hinge device H of Figs 14 to 17 may be applied, similar to the hinge device of Figs 3 and 4, to the three embodiments of the office chair according to the third aspect of the invention with comparable result, the general function, purpose and most of the components of the third and fourth embodiments being essentially identical. However, in the present embodiment the interaction between sliding elements and actuating elements has been varied as will be explained in the following. Similar to the third embodiment the hinge device H according to the fourth embodiment comprises two oppositely positioned sets of oppositely working sliding elements 3', 5' and actuating elements 2', 4', these being mounted on two oppositely positioned slide rods 42, 43. The variations with respect to the hinge device according to the third embodiment will be explained in the following with regards to the left end of the hinge device H in the figures, i.e. with regards to the sliding element 5' and the actuating element 4' mounted on the slide rod 42. The actuating element 4' is a generally tubular and circular-

cylindrical element, which on its two ends comprises a number of cams 4'a, 4'b, the cams 4'a, 4'b being shaped as triangular projections with one inclining end surface and one end surface extending axially with the hinge device H, said projections being positioned in a zigzag pattern. Both end surfaces extend substantially linearly from the remaining part of the actuating element 4'. The cams may be shaped differently in other embodiments, they may e.g. take other polygonal shapes, such as tetragonal, and the surfaces may be more or less curved.

In both the unloaded position of Fig. 16 and the loaded position of Fig. 17 the inclined surfaces of the cams 4'a directed towards the centrally positioned helical spring 7 of the hinge device H abut correspondingly shaped surfaces of corresponding cams 5'a of coaxially positioned sliding element 5'. Correspondingly, the inclined surfaces of the cams 4'b directed away from the helical spring 7 abut correspondingly shaped sur- faces of corresponding cams 40a of a coaxially positioned support element 40. A similar support element 41 is positioned at the other end of the hinge device H. In the unloaded position of Fig. 16 the cam surfaces normal to the respective elements (support element 40, actuating element 4' and sliding element 5') also abut each other such as to form a stop for the angular movement of a seat/backrest in relation to a carrier frame of an office chair to which the hinge device H has been applied.

Both the sliding element 5' and the support element 40 are shaped as generally tubular and circular-cylindrical elements with diameters corresponding to the diameter of the actuating element 4'. The end of the support element 40 opposite the end provided with cams 40a abuts end plug 12, and the end of the sliding element 5' opposite the end provided with cams 5'a is secured to pretensioning rod 25 by means of clips 27, 28.

The slide rod 42 is fixed to the arm 14 as was the threaded rod 3 in the embodiment of Figs 3 and 4. The actuating member 4' comprises inwards facing longitudinal projections mating with corresponding outwards facing longitudinal projections of the slide rod 42 (these projections of the slide rod 43 are visible in Figs. 14 and 15). The actuating member 4' is thus rotationally fixed to the slide rod 42 and thus the arm 14 and is further axially slidable. The support element 40 is axially

locked between the arm connector 14a and end plug 12 and the actuating element 4', and the sliding element 5' is axially slidable. Both the support element 40 and the sliding element 5' are rotationally locked to the tubular enclosure 1 by means of projections 40b and 5'b splined into splinings 5b of tubular enclosure 1. The inwards facing surfaces of the support element 40 and the sliding element 5' are thus smooth such as to not mate with the said projections of the slide rod 42.

As was the threaded rod 4 in the embodiment of Figs 3 and 4, the actuating element 4' of the present embodiment is to be connected to a seat/backrest of an office chair. Thus, when a user puts pressure on the seat/backrest, the actuating element 4' rotates, the cams 4'a, 4'b sliding with their inclining surfaces on the corresponding surfaces of cams 40a of the support element 40 and cams 5'a of the sliding element 5'. Sliding on the cams 40a makes the actuating element 4' slide in the axial direction towards the sliding element 5'. Similarly, sliding on the cams 4'a makes the sliding element 5' slide in the same direction, the sliding element 5' being pushed towards the helical spring 7. Since the sliding element 5' is connected to abutment element 10 via the preten- sioning rod 25, the helical spring 7 is compressed. The actuating element 4' is thus adapted to actuate a sliding movement of the sliding element 5' against or away from the helical spring 7 on articulation of a seat/backrest in relation to a carrier frame by means of cooperation between the cams 40a, 4'a, 4'b, 5'a, whereby the helical spring spring-loads the seat/backrest in relation to the carrier frame. The same general function can be achieved without the support element 40, the distance travelled in the axial direction by the sliding element 5' however being halved. Equivalently, one or more further actuating elements/sliding elements may be provided in series in the axial direction such as to provide further gearing. The tubular enclosure 1 and/or the slide rods 42, 43 are preferably hydroformed or extruded from stainless steel; the support elements 40, 41, the actuating elements 2', 4' and the sliding elements 3', 5' are preferably moulded.

The pretensioning system of the present embodiment is virtually identical to the embodiment of Figs 3 and 4, and the description of said

system can be applied, mutatis mutandis, to the present embodiment.

A combination of the embodiment of Figs 3 and 4 and the present embodiment of Figs 14 to 17 lies within the scope of the present invention. In such a combination the threaded tube 5 of the hinge device H of Figs 3 and 4 might function as a further actuating element with cams abutting corresponding cams of a sliding element positioned coaxi- ally with the threaded tube 5 towards the spring element 7. This solution would thus provide gearing means to the embodiment of Figs 3 and 4.