METHOD FOR DETECTING FOREIGN MATTER ON OBJECT, DEVICE FOR DETECTING FOREIGN MATTER ON OBJECT, AND OPTICAL DISC APPARATUS

摘要

A foreign matter detector comprises light signal detecting means (1), foreign matter detecting means (2a to 2h), and foreign matter judging means (3). The light signal detecting means (1) applies a light spot on the surface of an object to be inspected while scanning the light spot in a predetermined direction, receives light reflected from the surface of the object, and generates a light detection signal (HF) corresponding to the amount of light reflected. The foreign matter detecting means (2a to 2h) generates, from the light detection signal (HF), foreign matter detection signals (C) corresponding to the first and last portions, in the scanning direction, of the foreign matter adhering to the object. The foreign matter signal is determined as a signal representing the difference between the light detection signal (HF) and a delay signal (HF1) produced by delaying the light detection signal (HF) by a predetermined time. The foreign matter judging means generates from the foreign matter detection signal (C) a foreign matter judgment signal (H) representing the area where a foreign matter is present.