EP2661986A1

EP2661986A1 - Chair with swaying resistance

Info

Publication number: EP2661986A1
Application number: EP13166980.6A
Authority: EP
Inventors: Michael Klingstedt; Magnus Berggren
Original assignee: Kinnarps AB
Current assignee: Kinnarps AB
Priority date: 2012-05-09
Filing date: 2013-05-08
Publication date: 2013-11-13
Anticipated expiration: 2033-05-08
Also published as: SE1200283A1; SE537254C2; EP2661986B1

Abstract

The invention relates to an adjustment device for chairs, for adjusting a swaying resistance for a backseat part of a chair. The adjustment device comprises a chair base (10), a backrest part (20) pivotally arranged to the chair base (10) around a pivot shaft (40) and at least one spring element (31, 32) having a first end (31 a, 32a) arranged to the chair base (10) and a second end arranged to the backrest part (20), whereby the spring element (31, 32) has a spring force having a force direction parallel to the direction of the spring element from its first end to its second end, and that the spring element is arranged such that when the backrest part is loaded, the spring element will be loaded. The adjustment device further has a setting mechanism (50, 51) for setting the force of the spring element, whereby the setting mechanism (50, 51) is arranged to move the spring element (31, 32) such that the force direction of the spring element is changed and whereby the setting mechanism (50, 51) is arranged to move the first end (31 a, 32a) of the spring element or the second end (31 b, 32b) of the spring element substantially perpendicular to the force direction of the spring element. The invention further relates to a chair provided with such an adjustment device.

Description

Technical field

The present invention relates to a device for providing a resistance in the backrest and/or the seat of a chair when swaying the chair backwards.

Background art

A chair such as a working chair has a chair base and a backrest part that are pivotally connected to each other via a pivot shaft such that when the user presses its back against the backrest, the backrest part will be pivoted around the pivot shaft such that the backrest is leaned backwards. In addition, the chair has a resistance, for example a so called swaying resistance that resists the movement of the backrest backwards. The swaying resistance may be realized with the aid of one or more springs having one end connected to the chair base and the other end connected to the backrest part of the chair. When the backrest of the chair is pressed backwards, the springs will be extended such that the spring force will resist the movement of the backrest backwards and/or the movement of the seat downwards.
The load of this swaying resistance may be adjusted manually by the user by for example turning a wheel such that the user can achieve a resistance suitable for him/her. The wheel may change the tension of the spring, or rather the position of the spring such that the spring is extended more when the backrest of the chair is bent backwards, when the wheel has been turned in a direction towards increased load. The solutions existing today for changing the load of the swaying resistance requires the user to turn the wheel many rounds to change the load between its extreme positions, and/or that the user has to use a strong force to turn the wheel for changing the load.
To facilitate for a user to change the load of a swaying resistance there is thus a need for easily being able to change the load of the swaying resistance.

Summary of the invention

An object of the present invention is thus to easily and in a smooth way be able to change the load of a swaying resistance in a chair having a swaying resistance.
This object is achieved according to a first aspect of the invention by an adjustment device for chairs for adjusting a swaying resistance of a backrest part of a chair. The adjustment device comprises a chair base, a backrest part pivotally arranged to the chair base around a pivot shaft and at least one spring element with a first end arranged to the chair base and a second end arranged to the backrest part, whereby the spring element has a spring force with a force direction that is parallel to the extension direction of the spring element from its first end to its second end, and that the spring element is arranged such that when the backrest part is loaded such that the backrest part is pivoted in relation to the chair base, the spring element will be loaded. The adjustment device further has a setting mechanism for setting the force of the spring element, which setting mechanism is arranged to move the spring element such that the force direction of the spring element is changed and whereby the setting mechanism is arranged to move the first end or the second end of the spring element in a direction substantially perpendicular to the force direction of the spring element.
Hereby it is possible for a user to change the load of the swaying resistance in an easy way without having to use especially much force.
By changing the position of the first end of the spring element such that the first end of the spring element is moved substantially perpendicular to the extension direction of the spring element, the force that the spring element exerts against the movement will be small, for which reason it will be easier for a user to change the load. Thereby, the user may also change the force of the swaying resistance with relatively high gear without the user having to use too much force. It is thus possible to for example design the setting mechanism such that the user with one revolution or even less than one revolution on a wheel can change the setting of the swaying resistance from its lowest to its highest resistance.
A spring element signifies an element that causes a springy or resilient effect in the direction of the element, such as a mechanical tension spring, a gas spring etc. A chair base signifies the part on which the chair itself is built from, or upon, that is the part of the chair that, when the chair is standing on a floor, does not perform any pivoting movement or similar in relation to the floor. The chair base may also be called the central hub of the chair, or the yoke of the chair. The seat of the chair may be attached to the chair base. The expression the backrest part being loaded signifies that the backrest is pushed backwards such that the backrest part is pivoted in relation to the chair base. The expression the backrest part is loaded such that the spring element is loaded signifies that when the backrest part is pushed backwards/downwards, the spring element will be stretched out.
According to an embodiment, the adjustment device further comprises a spring frame through which the first end of the spring element is arranged to the chair base. The spring frame has a first end part arranged to the first end of the spring element and a second end part pivotally arranged to the chair base. The second end part of the spring element is further pivotally arranged to the chair base in the area where the second end of the spring element is arranged to the backrest part when the backrest part is unloaded.
By using a spring frame arranged with its second end part to the chair base, and by arranging the first end part of the spring frame to the same attachment point as the first end of the spring element, the spring frame will control the movement of the first end of the spring element when changing the force of the spring element. By placing the second end part of the spring frame in the area where the second end of the spring element is arranged to the backrest part, i.e. adjacent to the position where the second end of the spring element is arranged to the backrest part, when the backrest is non-loaded, the spring element will move substantially perpendicular to the extension direction of the spring element. Thereby, it will be easy for a user to change the swaying resistance without having to use much force. In addition, the spring frame makes it possible for the spring to be in a pre-tensioned condition when the back of the chair is unloaded.
According to a second aspect of the invention a chair is concerned, comprising a seat, a backrest, and an adjustment device according to the first aspect of the invention, whereby the seat is arranged to be attached to the chair base and the backrest is arranged to be attached to the backrest part.

Brief description of drawings

The invention is now described, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 is a side view of a working chair comprising an adjustment device according to the invention;
Fig. 2 is a perspective view of a part of a chair having an adjustment device according to an embodiment;
Fig. 3 is a schematic illustration of different spring positions K, L, M and N;
Fig. 4 is a cross-sectional side view of an embodiment of the adjustment device with the backrest part unloaded and with one end of the spring in a first position;
Fig. 5 is a cross-sectional side view of an embodiment of the adjustment device with the backrest part loaded and with the one end of the spring in the first position.
Fig. 6 is a cross-sectional side view of an embodiment of the adjustment device with the backrest part unloaded and with the one end of the spring in a second position.
Fig. 7 is a cross-sectional side view of an embodiment of the adjustment device with the backrest part loaded and with the one end of the spring in the second position.
Fig. 8 is cross-sectional perspective view of an embodiment of the adjustment device with the one end of the spring in the second position.

Description of embodiments

Figure 1 shows a working chair having a seat 1, a backrest 2 and a foot (not shown). The working chair further has an adjustment device having a chair base 10, on which the seat 1 is to be arranged, and a backrest part 20, on which the backrest 2 is to be arranged. For arranging the foot of the chair to the chair base, the chair base has a relatively centrally placed opening 15 (see fig. 2) arranged for receiving the foot of the chair. The backrest part has a horizontal part 20a, which is in a substantially horizontal position when the backrest is unloaded, and a vertical part 20b, which is in a substantially vertical position when the backrest is unloaded. The vertical part 20b is arranged to receive the backrest. The chair base 10 and the backrest part 20 are arranged to each other via a pivot shaft 40, such that when the backrest is loaded backwards, the backrest part 20 will be pivoted around the pivot shaft 40 such that the backrest part 20 is moved downwards and backwards in relation to the chair base 10. This is also illustrated by comparing figure 4 and figure 5, where figure 4 shows the adjustment device when the backrest is unloaded, and figure 5 shows the adjustment device when the backrest is pushed backwards.
The working chair also has two tension springs 31 and 32, respectively, arranged in parallel, the tension springs being arranged to function as a swaying resistance, i.e. resisting the movement of the backrest backwards. The tension springs are arranged on one side each of the opening 15 arranged for receiving the foot of the chair. The tension springs have one first end 31 a, 32a each, the first ends being connected to the chair base 10 via a common spring shaft 13, which is pivotally connected to the chair base 10 via spring frame 14, which first end is attached to the chair base 10. The spring shaft 13 has an extension that is substantially perpendicular to the tension springs. The tension springs have one second end 31 b, 32b each, which second ends are connected to the backrest part 20 via an attachment shaft 23. The attachment shaft 23 has an extension that is substantially perpendicular to the tension springs and it is attached to the backrest part 20. This attachment shaft 23 may be broken, i.e. the attachment shaft of the tension springs may have a common mathematical axis but different physical shafts. The swaying resistance works as follows: when the backrest is pushed backwards, the backrest part is pivoted round the pivot shaft 40, whereby the attachments shaft 23 is moved away from the spring shaft 13 and the tension springs 31, 32 are stretch out. Since the tension springs are stretched out when the backrest is pushed backwards, the springs will provide a resistance against the movement of the backrest backwards. Figure 4 shows one of the tension springs 31 when the backrest is in an unloaded condition. Figure 5 shows the same tension spring 31 when the backrest has been pushed backwards. In figure 5 it is shown how the attachment shaft 23 for the spring 31 has moved downwards and backwards when the backrest has moved backwards.
The resistance provided by the tension springs depends on how much the springs are stretched out in relation to how much the backrest is pushed backwards. Since the tension force in a tension spring is directed in the same direction as the tension spring itself, between its ends, the position of the spring, i.e. the direction of the spring in relation to how the movement between the chair base and the backrest part is performed, to decide which swaying resistance the spring will provide. In other words, where the first and the second end of the tension spring are positioned determines the swaying resistance. This is shown schematically in figure 3. In a first position KM, the first end 31 a of the tension spring 31 is in position K, which means low load, and the second end 31 b of the tension spring is in position M, which means a rest position, i.e. the backrest is in an unloaded position. When the backrest is loaded, the second end 31 b of the tensions spring will move to position N, which means a position where the spring is maximally extended, such that the spring ends up in a second position KN where the spring is more stretched out than in the first position. The first and the second positions are illustrated with broken lines.
By moving the first end 31 a of the spring from position K to position L, the spring will end up in a third position LM when the backrest is unloaded. When the backrest is loaded, the second end 31 b of the tension spring will be moved to position N such that the spring ends up in a fourth position LN where the spring is more stretched out than in the third position. The third and fourth positions are illustrated with continuous lines. As seen in the figure, illustrated by the lines 102 and 104 showing the length of the spring in an unloaded position projected on the length of the spring in the loaded position, the spring will be stretched out more when it is moved from the third position LM to the fourth position LN than when it is moved from the first position KM to the second position KN. Thus a higher swaying resistance is achieved for the spring when the first end of the spring is moved from position K to position L. Generally it can be said that the more parallel the extension direction to the distance the spring is moved when the backrest is loaded, i.e. the distance from M to N in the figure, the higher the swaying resistance.
For this reason the chair has a setting mechanism for changing the load of the swaying resistance, the setting mechanism comprising a control means 50 connected to the pivot shaft 40 (around which the backrest part 20 can move in relation to the chair base 10) and an eccentric 51 arranged on the pivot shaft, which is also bears against the spring shaft 13 of the tension springs. By turning the control means 50 such that the pivot shaft 40 is turned, the eccentric 51 will change position and move the spring shaft 13 of the tension springs. If a user turns the control means in one direction, for example clockwise (illustrated with a "+" in figure 2), the eccentric 51 will move the spring shaft 13 upwards whereby the position of the first ends 31 a, 32a of the tension springs will change such that the swaying resistance is increased. Figure 6 shows the adjustment device positioned to such a higher swaying resistance. Thereby, the tension springs are now positioned such that they have a direction which results in that they are more stretched when the backrest is loaded compared to when the tension spring is positioned as in figure 4. In figure 7, a tension spring is shown positioned as in figure 6, but with the backrest pushed backwards. As can be distinguished when figure 5 and figure 7 are compared, the tension springs are more extended when the backrest is pushed backwards when the spring is in the high-load position (fig. 7) than when the spring is in the low-load position (fig. 5). By turning the control means in the opposite direction, e.g. counterclockwise (illustrated with a "-" in figure 1), the spring shaft 13 will be moved downwards again in a direction towards a position as in figure 5. In this embodiment, the eccentric is positioned on the pivot shaft 40. It is also possible that the eccentric 51 and the control means 50 are positioned on a separate control shaft i.e. separate from the pivot shaft 40. Other embodiments of control means that can provide a movement of the first ends of the tension springs are also possible. In an alternative embodiment, the setting mechanism may be adapted to move the second ends of the tension springs, i.e. the ends attached to the backrest part, instead of the first ends of the tension springs.
However, to change direction of the tension springs to thereby change the swaying resistance by moving the position of the first (or second) ends of the tension springs may result in that a user has to turn the control means with a certain force. To facilitate this movement, the setting mechanism is, according to the invention, arranged such that it moves the first ends of the tension springs substantially perpendicular to the extension direction of the tension springs between their first ends 31 a, 32a and their second ends 31 b, 32b. When the first ends of the tension springs are moved approximately perpendicular to the extension direction of the tension springs, the tension springs will have approximately the same extension before and after the movement. That is, no or a very small force from the tension springs has to be overcome to move the position of the first ends.
According to the invention, the chair has a so called spring frame 14 attached to the chair base 10 to facilitate a substantially perpendicular movement of the first ends 31 a, 32a of the tension springs at adjustment of the swaying resistance. The spring frame 14 has a first end 14a connected to the spring shaft 13, and a second end 14b that is pivotally attached to the chair base 10 via a spring frame shaft 14c. This implies that the spring shaft 13 is connected to the chair base 10 via the spring frame 14. In other words, the first ends 31 a, 32a of the tension springs are connected to the chair base 10 via the spring shaft 13 and further via the spring frame 14 to the spring frame shaft 14c that is pivotally attached to the chair base 10.
When the control means 50 is turned, the eccentric 51 moves the spring shaft 13, the position for the first ends 31 a, 31 b of the tension springs 31, 32 is changed and also the position for the first end 14a of the spring frame. As a result, the spring frame will pivot around the spring frame shaft 14c. Since the spring frame is a solid construction, the spring frame will control the movement of the first ends 31 a, 32a of the springs. Since the spring frame shaft 14c is positioned in the approximately same region as the attachment shaft 23, the tension springs will only be stretched out a very small distance when the position of the first ends of the tension springs is changed, resulting in a small load on the tension springs and easy for a user to change the swaying resistance using the control means 50. The spring frame thus leads to that the tension springs will be moved without being stretched out, or being stretched only a very small distance when the first end of the tension springs are moved in relation to the second ends of the tension springs. The spring frame shaft 14c being in approximately the same region as the attachment shaft 23 of the tension springs in the backrest part may signify that the spring frame shaft 14c has a mathematical axis that is close by the mathematical axis of the attachment shaft 23 of the tension springs. The closer the mathematical axis of the spring frame shaft 14c is to the mathematical axis of the attachment shaft 23, the smaller the force needed for a user to change swaying resistance using the control means. In an advantageous embodiment, the spring frame shaft 14c is concentric with the attachment shaft 23 of the springs. In this case, a user would not feel any resistance from the springs when changing the position of the spring shaft 13 of the springs, and thus the swaying resistance can be very easily changed. Since the tension springs are attached in a spring frame they may have a bias tension, i.e. they may be lightly tensioned in the rest position. Thereby, there is a freedom from play when the load is to be increased from the rest position.
While the solution above has been described with reference to specific embodiments, the description is intended to illustrate the inventive concept and should not be taken as limiting the scope of the invention. For example, the swaying resistance is above realized with tension springs, although, it is within the scope of the invention to use other type of spring elements (having a resistance in their longitudinal direction) such as gas springs etc. In addition, the swaying resistance is realized with two spring elements, although, it is possible to use only one spring element or more than two spring elements. The setting mechanism for adjusting the force of the spring element is in the figures realized as a control means connected to an eccentric, although many other variants of setting mechanisms may be used. The eccentric may for example be a screw or a gas spring which longitudinal extension is controlled by a control means.

Claims

Adjustment device for chairs for adjusting resistance for a backrest part of a chair, the adjustment device comprising:
a chair base (10);

a backrest part (20) pivotally arranged to the chair base (10) around a pivot shaft (40);

at least one spring element (31, 32) having a first end (31 a, 32a) arranged to the chair base (10) and a second end (31 b, 32b) arranged to the backrest part (20), whereby the spring element (31, 32) has a spring force having a force direction parallel to the direction of the spring element from its first end to its second end, and that the spring element is arranged such that when the backrest part is loaded such that the backrest part is pivoted in relation to the chair base, the spring element will be loaded;

a setting mechanism (50, 51) for setting the force of the spring element, whereby the setting mechanism (50, 51) is arranged to move the spring element (31, 32) such that the force direction of the spring element is changed and whereby the setting mechanism (50, 51) is arranged to move the first end (31 a, 32a) of the spring element substantially perpendicular to the force direction of the spring element, characterized in that the first end (31 a, 32a) of the spring element is arranged to the chair base (10) via a spring shaft (13), and that the second end (31 b, 32b) of the spring element is arranged to the backrest part via an attachment shaft (23), whereby the adjustment device further comprises a spring frame (14) having a first end part (14a) arranged to the spring shaft (13) and a second end part (14b) and a spring frame shaft (14c), whereby the second end part (14b) is arranged to the spring frame shaft (14c), whereby the spring shaft (13) is pivotally attached to the chair base (10) via the spring frame shaft (14c) such that the spring shaft is movable parallel to its own extension, and whereby the spring frame shaft (14c) is arranged to the chair base (10) in the area where the attachment shaft (23) is arranged to the backrest part (20), when the backrest part is unloaded.
Adjustment device according to claim 1, wherein the second end part (14b) of the spring frame is pivotally arranged to the chair base (10) in the area where the second end (31 b, 32b) of the spring element is arranged to the backrest part when the backrest part (20) is unloaded.
Adjustment device according to any of claims 1 or 2, wherein the spring frame shaft (14c) and the attachment shaft (23) are concentric when the backrest part is unloaded.
Adjustment device according to any of claims 1 or 2, wherein the spring frame shaft (14c) and the attachment shaft (23) are substantially parallel.
Adjustment device according to any of claims 1 or 2, wherein the spring frame shaft (14c) and the spring shaft (13) are substantially parallel.
Chair comprising a seat (1), a backrest (2), and an adjustment device (4) according to any of the preceding claims, wherein the seat (1) is arranged to be attached to the chair base (10) and the backrest (2) is arranged to be attached to the backrest part (20).