Robotic manipulation of ophthalmic lenses assisted by a dedicated vision system

A robotic system developed to manipulate ophthalmic lenses during the edging process is presented. The robot is assisted by a machine vision system to accurately determine the position and orientation of the lens´ optical center and axis, through the localization of two small fiducial marks on the lens surface. The optimal design of the fiducial marks is investigated in order to minimize their size. It is shown that a regular diamond is the most detectable shape at minimum sizes. Three different camera placement strategies are discussed, taking into account accuracy constraints and calibration requirements. The chosen solution uses a camera attached to the robot end-effector. The robotic system proves to be advantageous with respect to the manual process, substantially improving the final accuracy while maintaining or even reducing the cycle time