Document Type and Number:
Japanese Patent JPS5165958
Kind Code:
A
Abstract:
In a grating measuring system of a basic type originated by DeLang employing a concave mirror-lens main optical system introduced by Dyson, improved separation of the light fluxes of input illumination and output motion-modulated signals is achieved. The arrangement depends upon the fact that in such a system wherein the grating is imaged back on itself so that for every point in the half plane containing the grating surface at one side of the optical axis, there is a conjugate point in the half plane at the other side of the axis. Separation by reason of beam separation is attained by illuminating one half plane and deriving output signals from the other. Further separation is attained from the fact that the concave mirror lies in a so-called "complementary plane" or "Fourier plane" to the object-image plane. Each point in the complementary plane is the focus of all rays originating in the object-image plane in a particular direction. Thus for each of the finite directions corresponding to successive orders of diffraction from the grating, a virtual focus of all of the light in each of the orders is situated in the complementary plane in an array of parallel bright lines. The invention lies in the imaging of this array of output virtual sources on a sensor array by mean of common optics, whereby both space-frequency filtering and perfect registry are maintained, and in large-aperture auxilliary lenses to image both the grating plane and the Fourier plane away from the main imaging structure and the grating for better separation of beams.
Inventors:
FUROMUNTO HOTSUKU
Application Number:
JP12943375A
Publication Date:
June 08, 1976
Filing Date:
October 29, 1975
Export Citation:
Assignee:
LEITZ ERNST GMBH
International Classes:
G01D5/36; G01D5/38; G02B27/00; G02B27/10; G02B27/42; (IPC1-7): G01B7/00; G02B27/00