Mechanism for an Office Chair

14:

• The mechanism according to claim 13, wherein said spring arrangement includes at least one spring end of a spring element and the adjustment is caused by an alteration of the position of said at least one spring end when the overall position of said spring element remains substantially the same or is altered.

15:

• The mechanism according to claim 13, wherein said spring arrangement includes a spring element and the adjustment is caused by an alteration to the position of said spring element relative to a fixed or at least partially movable, spring end of said spring element.

16:

• The mechanism according to claim 13, wherein said seat support and said base support are arranged such that they do not change their relative position when said movable unit moves.

17:

• The mechanism according to claim 13, wherein at least one of said base support and said seat support includes a linear guide which transmits relative movement to said spring arrangement.

18:

• The mechanism according to claim 13, wherein said spring arrangement includes a spring element and during a relative movement of said movable unit said spring element directly impinges on said movable unit.

19:

• The mechanism according to claim 18, wherein said movable unit drives said spring element during a relative movement of said movable unit.

20:

• The mechanism according to claim 13, wherein said spring arrangement includes a spring element and during a relative movement of the movable unit said spring element indirectly impinges on said movable unit.

21:

• The mechanism according to claim 20, wherein said spring arrangement includes a spring element and during a relative movement of said movable unit said spring element is driven by a transmission unit which cooperates with said movable unit.

22:

• The mechanism according to claim 21, wherein said transmission unit has a lever, a belt, and a plurality of cooperating slotted guides.

23:

• The mechanism according to claim 13, further including a synchronous mechanism, wherein said seat support is rearwardly pivotable in synchronism with said backrest support and said spring arrangement is configured to act on said synchronous mechanism opposite to the synchronous movement of said seat support and said backrest support.

24:

• The mechanism according to claim 13, further including a safety device for preventing an adjustment of said spring arrangement by a weight when said backrest support pivots.