A mechanical gripper mechanism for transporting and handling storage devices including a sensor to determine the position of opposing gripper fingers is provided. The gripper mechanism includes a pair of opposing gripper fingers rotatably mounted to a picker frame, each having a distal end adapted to engage a storage device. The gripper mechanism further includes at least one optically detectable indicator associated with the position and movement of the gripper fingers, and an optical sensor positioned to detect at least one of the optically detectable indicators. In one example, the at least one optically detectable indicators are disposed in a curve coupled to a gear associated with rotating the gripper fingers.