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:
Nov. 23, 1999
Filed:
Apr. 03, 1996
John D Wallace, Newburyport, MA (US);
Shepard D Johnson, Andover, MA (US);
MRS Technology, Inc., Chelmsford, MA (US);
Abstract
A focus shift sensor includes a light source which directs light through a first grating to form a pattern of light. The pattern is directed through the lens which images the pattern at a second grating. The two gratings have different periods such that the second grating generates a pattern of Moire fringes which are projected onto a CCD array. The second grating is preferably tilted with respect to the plane of the image of the pattern from the first grating such that only a portion of the second grating is within the range of focus of the lens. As a result, a pattern of shortened Moire fringes is produced. As the range of focus shifts along the second grating, the Moire fringes move along the CCD array. The movement of the fringes is tracked and the system is adjusted to maintain the location of the focal plane of the lens at a desired location.