Surface normal measurement in the end effector of a drilling robot for aviation

Aiming at the robot drilling perpendicularity in aircraft assembly, a surface normal measurement method is presented and a drilling end effector is designed. Four laser ranging sensors are uniformly distributed around the drill to measure the surface normal as four non-coplanar points define a unique circumscribed sphere and the sphere center can be calculated. By this principle, the method measures four points coordinates on the curved surface in the drilling area using four laser ranging sensors. If the four laser ranging sensors are close enough to each other, it is reasonable to assume that the drilling point is on the sphere surface. Therefore, the connection line of the sphere center and the drilling point is the surface normal at the drilling point. The angle θ between the normal and the axis of the drill is calculated and if θ is larger than 0.5 degree, the drilling end effector will adjust the attitude of the drill to make sure θ is smaller than 0.5 degree to meet the requirement in aircraft assembly. A novel adjusting mechanism is designed in the end effector which can keep drill vertex immobile when adjusting drill position. Thus, it is not required to remove the drill vertex to the mark point. Simulation results of three kinds curved surfaces show that the surface normal measurement method is accurate and efficient. Experiments on aviation drilling system results also demonstrate the adjusting mechanism is effective with high accuracy.