Patent ID: 7275790

Claim:
A backrest elevation adjustment assembly for a chair, comprising: an L-shape member, said L-shape member having a horizontal section attached to a seat supporting board of said chair; a multi-step positioning member having a plurality of parallel indented wedging slots, said multi-step positioning member having at least a top raised block in an appropriate location above the topmost wedging slot and at least a bottom raised block in an appropriate location below the bottommost wedging slot; said multi-step positioning member installed in a through opening in a vertical section of said L-shape member; and a sliding member, said sliding member installed around said vertical section of said L-shape member, said sliding member having an inverted hook device with a downward hook, said downward hook constantly pressed toward said wedging slots, said sliding member having a stopping block at an appropriate location above said inverted hook device, said sliding member attached to a backrest supporting board; said sliding member comprising: a body; a cover; a spring; and a pair of sliding plates; wherein a plurality of notches are configured on said body allowing said top and bottom raised blocks to pass through when said sliding member is slid vertically along said vertical section of said L-shape member; said inverted hook device has two axles at an end sticking out horizontally from the inverted hook device's two sides, said inverted hook device is installed on said body by fitting its two axles into two pockets of said body; said spring is installed in an opening between said two axles, and is configured so that the spring constantly delivers a force pushing said inverted hook device's downward hook to extend away from said body and toward said wedging slots; said stopping block is installed in a space above where said inverted hook device is installed; said sliding plates are installed on said body along two inner walls of said body facing each other from the two sides of said L-shape member; and said body and said cover are sealed together to enclose said vertical section of said L-shape member; wherein a user grabs said backrest supporting board and pulls the backrest supporting board upward until said inverted hook device is wedged into an appropriate wedging slot so as to fix said backrest supporting board to a specific vertical position; when said backrest supporting board is pulled to a topmost position, said top raised block pushes said stopping block downward to force said downward hook of said inverted hook device out of said wedging slot and said downward hook is prevented from wedging into said wedging slots; and when said backrest supporting board is dropped to a bottommost position, said bottom raised block raises said stopping block upward to release said downward hook of said inverted hook device and said downward hook is able to wedge into said wedging slots.