According to a second aspect, the present invention relates to a method for the manufacture of a flexible base for a chair intended for compensating irregularities of a substratum.

Background of the Invention A plurality of conventional office chairs most often have a"rigid"base pro- vided with four wheels. In this type of office chairs, it is possible to secure the base by for instance braking/locking two of the wheels, e. g. , the rear wheels. If the sub- stratum is not perfectly plane, one of the wheels will be left hanging in the air, i. e., not be in contact with the substratum. This entails that the braking will not work satisfactory.

The document SE-C2-511 494 discloses a flexible base for a chair solving the above-mentioned problems. This base for a chair can only be equipped with two braked and two unbraked castors. Behind the fixing point of the adjusting device, this chair base has a flexible hinge, enabling adaptation to possible irregularities of the floor. However, certain problems of this chair base remain. If the user is too light, the problem with some of the wheels ending up in the air may remain. On the other hand, if the user is too heavy, the chair base bends too much and may give a feeling of instability. This chair base can not be varied according to the demands on the market, i. e. , vary the number of arms/wheels and/or the num- ber of braked castors.

Summary of the Invention The present invention aims at solving the above-mentioned problems. This is achieved by means of a flexible base for a chair for compensating irregularities of a substratum according to claim 1. The flexible chair base according to the pre- sent invention comprises a front-wheel unit and a rear-wheel unit. The front-wheel unit comprises at least two arms provided with a wheel each and the rear-wheel unit comprises at least two arms provided with a wheel each. The chair base fur-

thermore comprises an adjusting member, the front-wheel unit or the rear-wheel unit being fixedly secured to the adjusting member by means of a clamping mem- ber, which clamps the adjusting member against a seat in said fixedly secured unit. The other unit of the front-wheel unit and the rear-wheel unit is arranged to the adjusting member by means of an axle member in such a way that the other unit is turnable around the axle member arranged perpendicularly in relation to the adjusting member. This enables all of the wheels to be in contact with the sub- stratum also in case of an uneven substratum. An additional advantage of this chair base is that the mobility is effective irrespective of the load that the chair is subjected to.

According to one embodiment, it is an advantage if all of the wheels are not brakeable.

According to another embodiment, it is an advantage if all of the wheels are brakeable/lockable by means of lock members arranged at the wheels.

According to yet another embodiment, it is an advantage if all of the wheels on the front-wheel unit or the rear-wheel unit are brakeable/locleable by means of lock members arranged at the wheels.

In reference to this, it is an advantage if the chair base furthermore com- prises an upper bushing device and a lower bushing device, which co-operate with the clamping member upon clamping the adjusting member against the seat in said fixedly secured unit.

In reference to this, it is an additional advantage if the chair base further- more comprises a sleeve member arranged abutting against the lower bushing device and the hub of the fixed unit at said seat.

In reference to this, it is an advantage if the adjusting member does not abut against a seat in the non-fixedly secured unit.

In reference to this, it is an additional advantage if the adjusting member consists of a cylindrical adjusting device, and in that the clamping member con- sists of a gripping jaw.

In reference to this, it is an advantage if the axle member consists of a tightening screw arranged at the clamping member, which screw constitutes a fixed pivot for the non-fixedly secured unit.

In reference to this, it is an additional advantage if the upper bushing device consists of a bushing, and in that the lower bushing device consists of a snap-in bushing.

In reference to this, it is an advantage if said seats are semi-cylindrical seats.

According to another embodiment, it is an advantage if the adjusting member does not abut against a seat in the non-fixedly secured unit.

In reference to this, it is an advantage if the adjusting member consists of a cylindrical adjusting device, and in that the clamping member consists of a tight- ening screw.

In reference to this, it is an additional advantage if the axle member con- sists of a tightening screw that constitutes a fixed pivot for the non-fixedly secured unit.

In reference to this, it is an advantage if the adjusting member abuts against a seat in the fixedly secured unit by means of projections arranged on the adjusting member.

According to a second aspect of the present invention, the above-men- tioned problems are solved by means of a method for the manufacture of a base for a chair according to claim 16. The method comprises the steps of: manufacturing a front-wheel unit comprising at) east two arms provided with a wheel each ; manufacturing a rear-wheel unit comprising at least two arms provided with a wheel each; - determining if the front-wheel unit or the rear-wheel unit should be fixed; - fixedly securing said fixed unit to an adjusting member included in the chair base by means of a clamping member that clamps the adjusting member against a seat in said fixed unit, and - mounting the other unit of the front-wheel unit and the rear-wheel unit to the adjusting member by means of an axle member in such a way that the other unit is turnable around the axle member arranged perpendicularly in relation to the adjusting member, which enables all of the wheels to be in contact with the substratum, also in the case of an uneven substratum.

According to one embodiment, it is an advantage if the method further- more comprises the step of: - applying lock members to all of the wheels so that these become brake- able/lockable.

According to another embodiment, it is an advantage if the method fur- thermore comprises the step of: - applying lock members to all of the wheels on the front-wheel unit or the rear-wheel unit so that these become brakeable/lockable.

In reference to this, it is an advantage if the method furthermore comprises the steps of: - mounting an upper bushing device and a lower bushing device on the adjusting member, which co-operate with the clamping member upon clamping the adjusting member against the seat in said fixedly secured unit.

In reference to this, it is an additional advantage if the method furthermore comprises the step of: -mounting a sleeve member abutting against the lower bushing device and the hub of the fixed unit to said seat.

In reference to this, it is an advantage if the adjusting member is mounted so that it does not abut against a seat in the non-fixedly secured unit.

In reference to this, it is an additional advantage if the adjusting member consists of a cylindrical adjusting device, and in that the clamping member con- sists of a gripping jaw.

In reference to this, it is an advantage if the axle member consists of a tightening screw arranged at the clamping member, which screw constitutes a fixed pivot for the non-fixedly secured unit.

In reference to this, it is an additional advantage if the upper bushing device consists of a bushing, and in that the lower bushing device consists of a snap-in bushing.

In reference to this, it is an advantage if said seats are semi-cylindrical seats.

The invention will now be more closely explained by the subsequent description of preferred embodiments of the same, reference being made to the appended drawings.

Brief Description of the Drawings Figure 1 shows a perspective view of a flexible base for a chair according to a first embodiment of the present invention; Figure 2 shows a perspective view, partly dismounted, of a part of the chair base shown in Figure 1; Figure 3 shows an enlarged detailed view of a fixed pivot of the chair base shown in Figure 1; Figure 4 shows a side view of the chair base shown in Figure 1; Figure 5 shows a perspective view, partly dismounted, of a part of the chair base shown in Figure 1; Figure 6 is a flow chart of a method for the manufacture of a flexible base for a chair according to the present invention.

Figure 7 shows a perspective view of a flexible base for a chair without wheels according to a second embodiment of the present invention ; Figure 8 shows a perspective view of the front-wheel unit/rear-wheel unit comprised in the chair base shown in Figure 7 ; Figure 9 shows a view from above of the chair base shown in Figure 7; Figure 10 shows a cross-section view of the chair base shown in Figure 9 along the line A-A ; and Figure 11 shows a perspective view of a part of the chair base shown in Figure 7.

Detailed Description of Embodiments of the Present Invention In figures 1-5, different views are shown of the flexible chair base 10 for compensating irregularities of a substratum 12, according to a first embodiment of the present invention. The chair base 10 comprises a front-wheel unit 14 and a rear-wheel unit 16. The front-wheel unit 14 comprises at least two arms 181,....

18n provided with a wheel each 201,..., 20n or support feet. In figures 1-5, only two arms and two wheels are shown for the sake of simplicity, n is an integer and n > 2. The rear-wheel unit 16 comprises at least two arms 221,..., 22m provided with a wheel each 241,..., 24m. In figures 1-5, only two arms and two wheels are shown for the sake of simplicity. m is an integer and m : 2. The chair base 10 fur- thermore comprises an adjusting member 26, which in turn is holder of the chair

seat (not shown in the figures). Before the mounting, the configurations of the units 14,16 in the interface to the adjusting member 26 are identical. In the proper mounting procedure, it is determined which unit 14,16 should be fixed and which should be movable. The cylindrical adjusting member 26 becomes fixedly secured in the fixed unit 14; 16 by means of a clamping member 28, which clamps the adjusting member 26 against a seat 30 in said fixedly secured unit 14 ; 16. The <BR> <BR> other unit 16; 14, i. e. , the movable unit 16 ; 14, is arranged at the adjusting member 26 by means of an axle member 32 arranged perpendicularly in relation to the adjusting member 26. This enables all of the wheels 201, 202, 241, 242 to be in contact with the substratum 12, also in case of an uneven substratum 12.

According to a preferred embodiment of the present invention, the chair base 10 furthermore comprises an upper bushing device 34 and a lower bushing device 36. These co-operate with the clamping member 28 upon clamping the adjusting member 26 against the seat 30 in said fixedly secured unit 14; 16.

According to a preferred embodiment of the present invention, the chair base 10 furthermore comprises a sleeve member 38 abutting against the lower bushing device 36 and the hub 40 of the fixed unit 14; 16 at said seat 30. In this connection, it should be pointed out that the adjusting member 26 does not abut against a seat 30' (not shown explicitly) in the movable unit 16; 14. The seat 30' corresponds to and has similar configuration as the seat 30 shown in Figure 5.

According to a preferred embodiment of the present invention, the adjust- ing member 26 consists of a cylindrical adjusting device 26 and the clamping member 28 consists of a gripping jaw 28.

According to a preferred embodiment of the present invention, the axle member 32 consists of a tightening screw 32 arranged at the clamping mem- ber/gripping jaw 28, which screw constitutes a fixed pivot for the non-fixedly secured unit 14; 16.

According to a preferred embodiment of the present invention, the upper bushing device 34 consists of a bushing 34. The lower bushing device 36 consists of a snap-in bushing 36.

According to a preferred embodiment of the present invention, said seats 30,30'are semi-cylindrical seats 30,30'.

In Figure 6, a flow chart is shown of a method for the manufacture of a flexible base 10 for a chair, intended for compensating irregularities of a substra-

turn 12. The method according to the present invention begins at block 50. The method then continues at block 52 with the step of: manufacturing a front-wheel unit 14 comprising at least two arms 181,..., 18n provided with a wheel each 201,..., 20n. n is an integer and n 2 2. Then, the method continues, at block 54, with the step of: manufacturing a rear-wheel unit 16 comprising at least two arms 221,..., 22m provided with a wheel each 241,..., 24m. The method then continues at block 56 with the step of: determining if the front-wheel unit 14 or the rear-wheel unit 16 should be fixed. Then, the method continues, at block 58, with the step of: fixedly securing said fixed unit 14; 16 to an adjusting member 26 included in the chair base 10 by means of a clamping member 28, which clamps the adjusting member 26 against a seat 30 in said fixed unit 14; 16. The method then continues at block 60 with the step of: mounting the other unit 16; 14 of the front-wheel unit 14 and the rear-wheel unit 16 to the adjusting member 26 by means of an axle member 32 in such a way that the other unit 16 ; 14 is turnable around the axle member 32 arranged perpendicularly in relation to the adjusting member 26. This enables all of the wheels 201,... 20n, 241,..., 24m to be in contact with the substra- tum 12, also in case of an uneven substratum 12. The method is terminated at block 62.

According to a preferred embodiment of the present invention, the method furthermore comprises the steps of: applying lock members ío all of l : he wheels 201,..., 20n, 241,..., 24m so that these become brakeable/lockable.

According to another embodiment of the present the invention, the method furthermore comprises the step of: applying lock members to all of the wheels 201,... 20n, 241,..., 24m on the front-wheel unit 14 or the rear-wheel unit 16, so that the same become brakeable/lockable.

According to a preferred embodiment of the present invention, the method furthermore comprises the step of: mounting an upper bushing device 34 and a lower bushing device 36 on the adjusting member 26, which co-operate with the clamping member 28 upon clamping the adjusting member 26 against the seat 30 in said fixedly secured unit 14; 16.

According to a preferred embodiment of the present invention, the method furthermore comprises the steps of: mounting a sleeve member 38 abutting against the lower bushing device 36 and the hub 40 of the fixed unit 14; 16 to said seat 30.

According to a preferred embodiment of the present invention, the adjust- ing member 26 is mounted so that it does not abut against a seat 30'in the non- fixedly secured unit 14; 16.

In figures 7-11, different views are shown of a second embodiment of the flexible chair base 10"for compensating irregularities of a substratum 12"accord- ing to the present invention. The chair base 10"comprises a front-wheel unit 14" and a rear-wheel unit 16". The front-wheel unit 14"comprises at least two arms 18"1,..., 18"n provided with a wheel each or support feet (not shown in figures 7- 11). In figures 7-11, only two arms are shown for the sake of simplicity. n is an integer and n 2 2. The rear-wheel unit 16"comprises at least two arms 22"1,..., 22"m provided with a wheel each (not shown). In figures 7-11, only two arms are shown for the sake of simplicity. m is an integer and m 2 : 2. The chair base 10"furthermore comprises an adjusting member 26", which in turn is holder of the chair seat (not shown in figures 7-11). Before the mounting, the configurations of the units 14", 16"in the interface to the adjusting member 26" are identical. In the proper mounting procedure, it is determined which unit 14", 16"should be fixed and which should be movable. The cylindrical adjusting member 26"becomes fixedly secured in the fixed unit 14" ; 16" by means of a clamping member 28", which clamps the adjusting member 26"against a seat 30" in said fixedly secured unit 14." ; 16". The other unit 16" ; 14", i. e., the movable unit 16" ; 14", is arranged at the adjusting member 26"by means of an axle member 32"arranged perpendicularly in relation to the adjusting member 26". This enables all of the wheels to be in contact with the substratum, also in case of an uneven substratum. Compare Figure 4, as the two embodiments shown have this property that they compensate irregularities of a substratum.

According to a preferred embodiment of the present invention, all of the wheels are brakeable/lockable by means of lock members (not shown) arranged at the wheels.

According to another embodiment, none of the wheels are brakeable.

According to yet another embodiment, all of the wheels on the front-wheel unit 14"or the rear-wheel unit 16"are brakeable/lockable by means of lock mem- bers (not shown) arranged at the wheels.

According to a preferred embodiment of the present invention, the adjust- ing member 26"does not abut against a seat 30"'in the non-fixedly secured unit 16". Compare Figure 10.

The second embodiment of the flexible chair base 10", which is shown in figures 7-11, has another configuration than the first embodiment of the flexible chair base 10, shown in figures 1-5. This is most clearly seen by looking at figures 10 and 11, which will be described more in detail below.

As is seen in Figure 10, the fixedly secured unit 14"is fastened by means of a clamping member 28", in this case in the form of a tightening screw 28", to the adjusting member 26". In this case, the adjusting member 26"consists of a cylindrical adjusting device 26". Compare Figure 11. Also a spacer 70"is arranged between the tightening screw 28"and the adjusting device 26". A spacer 70"is also arranged between the tightening screw 32"and the adjusting device 26". As is seen in Figure 10, the seat 30"of the fixedly secured unit 14"abuts against a projection 72"of the adjusting device 26". Also compare Figure 11. This entails that the fixedly secured unit 14"is not turnable around the tightening screw 28".

On the other hand, if we turn to the non-fixedly secured unit 16", it is seen from Figure 10 how the seat 30"'of the non-fixedly secured unit 16"does not abut against the adjusting device 26".

This half of the adjusting device 26"comprises no proJedion (oona re Figure 11) corresponding to the projection 72"on the other half of the adjusting device 26". This ensures that the non-fixedly secured unit 16"can be turned around the tightening screw 32".

The flow chart of a method for the manufacture of a flexible base for a chair, shown in Figure 6, is also applicable to the flexible chair base 10"shown in figures 7-11 and described.

The invention is not limited to the shown embodiments, but a plurality of variations are feasible within the scope of the appended claims.