Abstract: The present invention relates to a jerk arresting mechanism to prevent the back rests of office chairs from unexpected movement such as rebounding and impacting upon users in an undesirable fashion. More generally, the mechanism described positively arrests an acceleration of one part moving relative to another part. This is accomplished in a housing fastened to one of the parts, wherein the mechanism resides, through which a spirally contoured shaft is passed that is connected to the other part. As the acceleration exceeds a predictable threshold, a nut with an outer toothed surface is axially translated relative to the shaft movement and engages a complementarily toothed surface integral with the housing. This engagement stops the rotational and linear movement of both the nut and shaft thereby arresting the movement of the parts relative to each other.

Abstract: A control mechanism for a seat carrier of a chair, especially a swivel chair. A pivotable part is clamped and released by lamellae with rotatably anchored ends. One set of ends is anchored without play; the other, with play. The ends anchored with play are suspended via holes from a clamping bolt which can slide, inside the clamping mechanism, against a spring that clamps the pivotable part. The lamellae are released by a control lever. The clamping bolt is slideably fitted in a pressure sleeve of diameter greater than the holes in the lamellae. The bolt behind the pressure sleeve has a stop that bears against the pressure sleeve during active clamping. On its other side this bolt passes through the wall at which the clamping action takes place. The outside of the clamping bolt, at a distance from this wall, has a mounting for a pressure spring that acts between the bolt and the wall. The pressure spring pushes the bolt outward, thus directing the clamping force to the lamellae.