Automatic calibration method for robot system

An automatic calibration method for a robot system, comprising:

• providing a ball-rod member including a connection rod and a sphere connected to a first end of the connection rod;
• fixing an opposite second end of the connection rod to an end execution tool mounted on a flange of a robot;
• controlling the robot to move a center of the sphere to a same target point in a plurality of different poses under the guidance of a vision sensor;
• calculating a transformation matrix Ts of the center of the sphere with respect to a center of the flange based on pose data of the robot at the same target point;
• and
• calculating a transformation matrix Tt of a center of the end execution tool with respect to the center of the flange according to a following formula:
• Tt=Ts * Tc,
• wherein Tc is a transformation matrix of the center of the end execution tool with respect to the center of the sphere and is constant.