Screw tightening mechanism

The utility model discloses a screw tightening mechanism, which comprises a mounting seat, a controller, a servo motor, a vertical driving device, a transmission shaft, an outer transmission block, an inner transmission block, a screwdriver head fixing seat and a screwdriver head, wherein the servo motor and the vertical driving device are mounted on the mounting seat, the vertical driving device drives the servo motor to slide up and down relative to the mounting seat, the controller is electrically connected with the servo motor, the servo motor drives the transmission shaft to rotate, one of the inner transmission block and the outer transmission block is connected with the lower end of the transmission shaft and rotates along with the transmission shaft, the upper end of the screwdriver head fixing seat is fixedly arranged at the other of the inner transmission block and the outer transmission block, the screwdriver head is detachably and fixedly arranged at the lower end of the screwdriver head fixing seat, the inner transmission block is contained into the outer transmission block and is driven by the outer transmission block to rotate, and the inner transmission block and the outer transmission block can relatively swing. The screw tightening mechanism has the advantage that actual torque in a screw tightening process by the screwdriver head is transferred to the servo motor and then is fed back to the controller, so as to judge whether the actual torque is controlled within a preset range, and whether loosening and slipping the screw appear or not.