An industrial robot system includes an end effector connectable to a robot arm, a drive assembly, and a controller. The end effector includes a distal housing, a spindle assembly rotatable about a rotational axis, a drill bit rotatable about the rotational axis, and a sensor assembly. The sensor assembly includes a first light source, a second light source, and a photosensitive array. The first light source produces a first fan of light which is projected as a first line of light on the object surface. The second light source produces a second fan of light, which is projected as a second line of light on the object surface. The photosensitive array detects a first reflection line corresponding to the first line of light and a second reflection line corresponding to the second line of light.