Patent ID: 6791681
Filing Date: 2004-09-14
Classification: G01N,G11B

Abstract:
An apparatus for determining an existence range of a foreign substance which is present on a surface of an object, comprising:an optical system including a light source for emitting a light beam onto the surface of the object; a movement section for relatively moving the object with respect to the light beam; a light detection section for detecting a light quantity of the light beam reflected by the surface of the object to generate a light detection signal which indicates the light quantity, the light detection section including a first light detection section for generating a first light detection signal and a second light detection section for generating a second light detection signal; a difference signal generation section for generating a difference signal which indicates a difference between the first light detection signal and the second light detection signal; a perimeter signal generation section for comparing the difference signal with a reference value to generate a perimeter signal which indicates a perimeter of the foreign substance, the reference value being an average of the actual light quantity measured under actual conditions in which the apparatus is used; and a foreign substance determination section for determining an existence range of the foreign substance using the perimeter signal.