Apparatus for detecting extraneous substances on a glass plate

Claim 1

An apparatus for detecting an extraneous substance on a glass plate, the apparatus comprising a first light projecting system for irradiating the surface of the glass plate with an S-polarized laser beam at a first elevation angle as viewed from the surface thereof under examination for extraneous substance detection, a second light projecting system for irradiating the surface under examination with a P-polarized laser beam at a second elevation angle greater than the first elevation angle, and a light receiving system for receiving scattered light from the surface under examination, which has received laser beams from the first and the second light projecting systems, at a third elevation angle smaller than the first elevation angle, and the light receiving system being arranged so that the normal line to the surface at the laser beam irradiation point is located between the first and second light projecting systems and the light receiving system, wherein a first detection level is defined as a detection level of the scattered light detected in the light receiving system when an extraneous substance having a particle diameter on the surface under examination is irradiated with an S-polarized laser beam, a second detection level is defined as a detection level of the scattered light detected in the light receiving system when the extraneous substance is irradiated, via the glass substrate, with the S-polarized laser beam, with the glass plate being turned upside down, a third detection level is defined as a detection level of the scattered light detected in the light receiving system when the extraneous substance is irradiated with the P-polarized laser beam, and a fourth detection level is defined as a detection level of the scattered light detected in the light receiving system when the extraneous substance is irradiated with the P-polarized laser beam via the glass plate with the glass plate turned upside down; wherein the output level of the P-polarized laser beam is set so that the third and fourth detection levels fall between the first and second detection levels; and wherein when the signal level obtainable by the light receiving system which corresponds to the irradiation of the S-polarized laser beam is greater than the signal level that is obtainable thereby correspondingly to that of the P-polarized laser beam, the extraneous substance is judged to exist on the surface under examination.

Claim 2

An apparatus for detecting an extraneous substance on a glass plate, the apparatus comprising a first light projecting system for irradiating the surface of the glass plate with an S-polarized laser beam at a first elevation angle as viewed from the surface thereof under examination for extraneous substance detection, a second light projecting system for irradiating the surface under examination with a P-polarized laser beam at a second elevation angle greater than the first elevation angle, and a light receiving system for receiving scattered light from the surface under examination, which has received laser beams from the first and the second light projecting systems, at a third elevation angle smaller than the first elevation angle, and the light receiving system being arranged so that the normal line to the surface at the laser beam irradiation point is located between the first and second light projecting systems and the light receiving system, wherein a first detection level is defined as a detection level of the scattered light detected in the light receiving system when an extraneous substance having a particle diameter on the surface under examination is irradiated with an S-polarized laser beam, a second detection level is defined as a detection level of the scattered light detected in the light receiving system when the extraneous substance is irradiated, via the glass substrate, with the S-polarized laser beam, with the glass plate being turned upside down, a third detection level is defined as a detection level of the scattered light detected in the light receiving system when the extraneous substance is irradiated with the P-polarized laser beam, and a fourth detection level is defined as a detection level of the scattered light detected in the light receiving system when the extraneous substance is irradiated with the P-polarized laser beam via the glass plate with the glass plate turned upside down; wherein the output level of the P-polarized laser beam is set so that the third and fourth detection levels fall between the first and second detection levels; and wherein when the signal level obtainable by the light receiving system which corresponds to the irradiation of the S-polarized laser beam is greater than the signal level that is obtainable thereby correspondingly to that of the P-polarized laser beam, the extraneous substance is judged to exist on the surface under examination.