A method for determining if a robot gripper assembly (preferably servo controlled) has acquired a work piece wherein the robot gripper assembly includes at least two opposing fingers comprising the steps of commanding the robot gripper assembly to close the two opposing fingers to a predetermined position to acquire the work piece, the predetermined position being less than or different than the expected work piece dimension; quantifying the movement of the two opposing fingers when the closing step has been completed; comparing the actual position to the predetermined position to determine a position error; and recognizing that a work piece has been acquired by the two opposing fingers if the position error is not zero indicating that the interference of the work piece between the two opposing fingers has prevented the two opposing fingers from achieving the predetermined position.