Patent ID: 7593116

Claim:
An apparatus for detecting error in a transfer system, comprising: a test substrate on which a plurality of reflective marks are arranged, the test substrate being transferred on the transfer system; an emitter that generates and radiates a light onto the test substrate; a receiver for receiving reflected light from at least one of the plurality of reflective marks on the test substrate; a controller coupled with the receiver to detect an error in the transfer system based on a reflective time difference of the reflected light received by the receiver, wherein the controller is configured to output the detected error; and a display coupled with the controller that displays the outputted error of the transfer system detected by the controller, wherein the controller measures the reflective time difference when reflective lights are reflected by adjacent reflective marks, and temporarily stores the reflective time difference, wherein the controller compares the temporarily stored reflective time difference with a designated reference reflective time difference to detect an error of the transfer system, wherein if the temporarily stored reflective time difference and the designated reference reflective time difference are substantially the same, the controller determines that the transfer system is a normal state and displays the normal state on the display, and wherein if the temporarily stored reflective time difference is substantially different from the designated reference reflective time difference, the controller determines that the transfer system is in an error state and displays the error state on the display.