Chair with adjustable back depth

A chair with an adjustable back depth, comprising a chassis, a seat plate, a back plate, a hinge seat, a pneumatic rod, a trigger piece, a drive piece, a support seat frame, and rocking bars, wherein

• the chassis comprises an accommodating cavity and two support plates arranged at a rear end;
• the hinge seat comprises a hinge cavity and a rod channel communicated with the hinge cavity;
• the support seat frame comprises a bottom hinge cavity and two frame poles, and the two frame poles are hollow, have a front opening, and are communicated with the bottom hinge cavity;
• the rocking bars are arranged between an upper hinge plate and a lower hinge plate;
• a connecting seat is arranged on a rear surface of a back plate;
• the connecting seat has two hinge grooves with rear openings and lower openings;
• the seat plate is fixed to the chassis;
• the hinge seat is arranged in the accommodating cavity;
• inner sides of lower ends of the two frame poles are hinged to a rear hinge hole of the two support plates;
• the lower hinge plate is hinged to a front hinge hole of the two support plates;
• the rocking bars are embedded into the two frame poles;
• outer sides of upper ends of the two frame poles are hinged to a rear end of one of the two hinge grooves;
• the upper hinge plate is hinged to a front end of one of the two hinge grooves;
• a main body of the pneumatic rod is hinged to the bottom hinge cavity;
• a piston rod is hinged to the hinge cavity;
• the trigger piece is hinged to the hinge seat and cooperates with an execution push rod of the pneumatic rod;
• and the drive piece is arranged on the chassis and cooperates with the trigger piece.