Abstract: A resilient leaning position-restoring device for a height-adjustable chair back of an office chair includes a back support unit, a height-adjustable chair back disposed on the back support unit, and a resilient leaning position-restoring device disposed between the back support unit and the chair back. The resilient leaning position-restoring device essentially includes a sliding element slidable along a slot disposed on the back support unit and being pulled downward by a spring. The upper end of the sliding element extends to form a resilient member of an inverted U shape. A lower end of the resilient member is coupled to the chair back. The resilient member maintains the predetermined resilience thereof for supporting the bottom of the chair back while height adjustment of the chair back is underway. The bottom of the chair back lends proper support to the sitter's waist, regardless of an adjusted position of the chair back.

Abstract: An adjustment structure of a chair armrest is provided. The armrest is attached to a chair back through a fastening seat. A releasable fastener provided between the armrest and the fastening seat allows the armrest to be slide vertically and get positioned with respect to the fastening seat. The fastening seat has a guiding groove facing the armrest and the guiding groove is formed with toothed portions. The releasable fastener includes an engaging member for bilaterally engaging with the toothed portions, mutually engageable slanting tooth portions formed on a lever and a driven member assembled to the armrest, respectively, and a screw passing through the engaging member and the guiding groove to be screwingly fixed to the driven member. By pulling the lever upward or downward, the armrest is released to be repositioned or is positioned so that the armrest attached to the chair back can be adjusted in altitude.

Abstract: A resilient lower-back supporting device capable of vertical adjustment along with a backrest of a chair includes a resilient supporting unit pivotally connected between a lower end of the height-adjustable backrest and a supporting element. Configured for resilient extension and retraction, the resilient supporting unit includes an outer supporting rod and an inner supporting rod inserted therein. The two supporting rods are pulled toward each other by a spring provided therebetween. Besides, a spring is provided at an outer end of each supporting rod to bias the resilient supporting unit and the backrest toward a predetermined direction. With the backrest being vertically adjustable, and with the resilient support provided by a lower-back supporting portion at the lower end of the backrest, people of different heights are ergonomically supported especially on the lower back while sitting in the chair and are protected from back pain attributable to a prolonged sitting posture.