Patent ID: 7062010

Claim:
An apparatus for making a gap between first and second objects, said apparatus comprising: a light introducing unit configured to introduce light to a first entry window formed in the first object; a first detection unit configured to detect a total intensity of light from a first exit window formed in the first object with respect to each of a plurality of values of the gap, the first exit window being at such a position that light would enter through the first entry window of the first object, reflect off the second object, and then enter the first exit window if the gap has a predetermined value; a second detection unit configured to detect a total intensity of light from a second exit window formed in the first object with respect to each of a plurality of values of the gap, the second exit window being at such a position that light would enter through a second entry window of the first object, reflect off the second object, and then enter the second exit window if the gap has the predetermined value; and a positioning mechanism configured to obtain a position of the second object, with respect to a direction of the gap, where the gap has the predetermined value based on a plurality of total intensities of light detected by said first detection unit and a plurality of total intensities of light detected by said second detection unit, and to position the second object at the obtained position, wherein said positioning mechanism is configured to obtain a first position of the second object, with respect to the direction of the gap, where said first detection unit detects the maximum total intensity of light and a second position of the second object, with respect to the direction of the gap, where said second detection unit detects the maximum total intensity of light, and to position the second object at an average position of the first and second positions.