Four-axis actuator

The invention discloses a four-axis actuator which comprises a central gear driven by a step motor and four driven actuators, wherein the driven actuators are capable of separately moving or stopping moving; each driven actuator comprises a star gear, a ball screw, a ball nut, a ball screw rotation-stopping positioning key, a cylindrical gear friction plate, a friction disc seat, a friction disc, a thrust spring and a ball screw brake, wherein the star gear is meshed with the central gear; the ball screw rotation-stopping positioning key is used for stopping rotation of the ball screw; the ball nut is connected with the ball screw; the cylindrical gear friction plate is fixed to the star gear; the thrust spring is used for pushing the friction disc to be closely connected with the cylindrical gear friction plate; the star gear is used for driving the ball nut to rotate through the cylindrical gear friction plate, the friction disc and the friction disc seat so as to drive the ball screw to move up and down; the ball screw brake after electrification is used for sucking the friction disc to be separated from the cylindrical gear friction plate so as to stop moving of the ball screw. According to the four-axis actuator, the number of actuators is reduced and a main reflection surface of a large radio telescope can be adjusted.