The detection of a processing deviation in a cluster tool of a wafer processing system is achieved by assigning individual wafers a set of positional coordinates each time the wafer moves within the cluster tool. The housing includes a latching protrusion, and the fixing member includes a latching portion. The first and second lift portions are operable to move the first and second groups of substrates in a first direction independently from each other. The control circuitry then provides control signals to turn on a light emitting component above the output port which is optically connected with the input port. The transfer assembly may include a gear, a belt, a chain or similar devices structured to transfer rotational motion from one component to another.