The robot arm controls the movement of several of the moving joints, and realizes the movement of the other joints by controlling the motor and transmission device. The robot arm has two structures, one is a two-arm structure and the other is a three-arm structure. The two-arm structure refers to the basic structure of the mechanical arm, which is composed of two joints: one is a fixed joint, and the other is a movable joint, which can move on three basic axes, namely the left and right axis, the front and back axis and the upper and lower axis. The three-arm structure means that the robot arm is composed of three joints, which are fixed joints, movable joints and arm joints, and it can move on three basic axes, which are left and right axis, front and back axis and upper and lower axis.