Elevation-adjustable display screen support arm

An elevation-adjustable display screen support arm, comprising:

• an arm shaft comprising a box-like shaft body defining therein an accommodation chamber and a front opening in communication with said accommodation chamber, and an outer cover fastened to said box-like shaft body and covered over said front opening, said outer cover defining therein an upper opening in communication with said accommodation chamber;
• a balance adjustment mechanism mounted in said accommodation chamber of said box-like shaft body, said balance adjustment mechanism comprising a first sliding tooth rack, a second sliding tooth rack, a gear train meshed between said first sliding tooth rack and said second sliding tooth rack, a tension spring connected between said box-like shaft body and said second sliding tooth rack, and an actuating plate mounted at said second sliding tooth rack and connected to a bottom end of said tension spring;
• and
• a display screen mounting head comprising a body block for supporting a display screen at a front side thereof, a first guideway and a second guideway respectively mounted on two side panels of said box-like shaft body, and a connection panel mounted at an opposing back side of said body block and inserted through said upper opening of said outer cover into the inside of said box-like shaft body and fixedly connected to said first sliding tooth rack, said first guideway and said second guideway;
• wherein when adjusting the elevation of the supported said display screen, said body block of said display screen mounting head is driven to move said first sliding tooth rack in rotating said gear train, causing said gear train to move said second sliding tooth rack in driving said actuating plate to stretch or compress said tension spring, and thus, rotation of said gear train causes said tension spring to provide a corresponding torque that is acted upon said first sliding tooth rack to control upward or downward movement of said display screen mounting head and the supported said display screen in a stepless manner.