Abstract: A servo mechanism for a seat part arranged on a support frame for travel in a longitudinal direction in synchronism with an adjustment of a back rest part from a normal position to several predetermined reclined positions, includes a scissor-type articulated lever assembly which is connected to the seat part and the support frame. The articulated lever assembly includes several articulated lever elements. A spring assembly progressively applies a spring force upon the scissor-type articulated lever assembly such that a relative change in angular disposition between the lever elements applies a substantially constant force upon the seat part in every position of the seat part, whereby a relatively great longitudinal travel distance of the seat part is accompanied by a short spring travel during the spring force application.

Abstract: The invention relates to a chair, especially an office or work chair or similar, whereon a back-rest part (15) can be placed in an inclined position from an initial or rest position via a first axis of rotation (12). A seating part (14) performs a longitudinal displacement around a second axis of rotation (20) and an inclined displacement around a third axis of rotation (11) in a synchronous manner with respect to the inclined movement of the back-rest part (15). A return device (13) is provided for returning the back-rest part (15) and/or seating part (14) to the initial position or rest position. The office chair (1) comprises a carrier frame (5) which disposed centrically on the leg frame (2) and which supports in a stationary manner the first axis of rotation (12) on the centre of the leg frame, said axis of rotation remaining at a constant, predetermined distance above the seating part (14) in the rest position and in all inclined positions of the back-rest part (15).

Abstract: A servo mechanism for a seat part arranged on a support frame for travel in a longitudinal direction in synchronism with an adjustment of a back rest part from a normal position to several predetermined reclined positions, includes a scissor-type articulated lever assembly which is connected to the seat part and the support frame. The articulated lever assembly includes several articulated lever elements. A spring assembly progressively applies a spring force upon the scissor-type articulated lever assembly such that a relative change in angular disposition between the lever elements applies a substantially constant force upon the seat part in every position of the seat part, whereby a relatively great longitudinal travel distance of the seat part is accompanied by a short spring travel during the spring force application.