| 摘要 |
An improved seat back height adjustment mechanism for a chair is disclosed. The improved height adjustment mechanism includes a U-shaped mounting bracket having a back wall and two side walls. A longitudinal shaft having a handwheel is rotatably mounted in the bracket between the side walls and spaced from the back wall. A seat back support arm is insertable through the bracket between the shaft and the bracket back wall. A back plate provided with a rack and an adjacent planar surface both extending along the length of the back plate is mounted onto the seat back support arm. In one aspect, the shaft is provided with a pinion for engaging the rack and a multi-sided, symmetrical cam adjacent the pinion for locking the shaft against free rotation. When assembled, the rack and the planar surface of the back plate are aligned with the pinion and cam respectively. When the shaft is rotated via the handwheel, the pinion rotates and engages the rack thereby causing the seat back support arm to be vertically displaced with respect to the mounting bracket. When a planar face of the cam is contiguous with the planar surface of the back plate shaft rotation is resisted thereby locking the height adjustment mechanism.
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