Patent ID: 6423978
Filing Date: 2002-07-23
Classification: H01L,Y10S

Abstract:
A disk-shaped object detecting system detecting a disk-shaped object having a circumferential edge, the system comprising:a light emitting element emitting light toward the circumferential edge of the object while being moved across the object with respect to a direction of thickness of the object; a light receiving element receiving the light reflected on the circumferential edge of the object while being moved across the object with respect to the direction of thickness of the object together with the light emitting element, thereby delivering first and second light signals each according to the received light, the light receiving element having two opposite ends, the first and second light signals having a ratio depending upon at what position between the opposite ends the light receiving element receives the light reflected on the circumferential edge of the object, the first and second signals having a magnitude relation which is reversed when the light reflected on the circumferential edge of the object has been moved from one end side to the other end side of the light receiving element; an AND processing section to which the first and second light signals delivered from the light receiving element are supplied, the AND processing section delivering either one of the light signals having a smaller magnitude than the other as an output thereof; and a determining section determining whether the output of the AND processing section has exceeded a predetermined level.