Case study of a tornado in the Upper Rhine valley

An alignment system incudes a sensor device including a pair of a light emitting element and a light receiving element, for detecting an edge of a substrate without contact thereto; a driving device for supporting the substrate and for moving the substrate; and a control device for controlling the driving device so as to position the substrate, wherein the control device controls the driving device so that the sensor device produces an output of a level which is within a predetermined tolerance range with respect to a set level, and wherein the control device is operable to renew the set level at a predetermined timing on the basis of (i) a first output of the sensor device corresponding to an output of the sensor device as produced in a first state in which light from the light emitting element of the sensor device is received by the light receiving element of the sensor device without being blocked and (ii) a second output of the sensor device corresponding to an output of the sensor device as produced in a second state in which the light reception of the light receiving element is completely blocked.