The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jul. 25, 1989
Filed:
Feb. 01, 1988
Christiaan H Velzel, Eindhoven, NL;
Henricus M Kessels, Eindhoven, NL;
U. S. Philips Corporation, New York, NY (US);
Abstract
An apparatus for optically scanning a surface, such as the information surface of an optical record carrier. An error in focus of the scanning spot on the surface is detected by providing two gratings in succession in the path of the beam reflected from the surface. The grating periods of the two gratings are related in accordance with the nominal beam divergence at zero focus error, and the grating strips thereof are parallel but offset with respect to each other. A bounding line between detectors in a composite radiation-sensitive detection system extends parallel to the grating strips. An interference pattern of light and dark bands is projected by the second grating on the detection system, such pattern having an intensity distribution which varies with variations in focus error and can be enhanced by an appropriate value of the offset between the two gratings.