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. 24, 1990
Filed:
Jan. 18, 1989
Souji Ichikawa, Sagamihara, JP;
Hideki Oka, Kawasaki, JP;
Naoyoshi Terao, Urawa, JP;
Seiji Sakagami, Kawasaki, JP;
Mitutoyo Corporation, Minato, JP;
Abstract
In a diffraction type optical displacement encoder using a diffractive light source and having a main scale grating and an index scale grating, a light-receiving element receives two rays satisfying a relationship concerning the lengths of light paths at the rays between the light source and the index scale grating, and the width of the light receiving element, wherein the difference between the path length of each ray is approximately equal to an integral multiple of the square of the pitch of the main scale grating divided by the wavelength of the light source, and the width of the light receiving element, measured as the distance between the impingement points of the two rays at the index scale, is integrally related to the difference in ray path lengths and the angle of the impinging rays due to an offsetting of the light-receiving element. In a second aspect of the invention, two light-receiving elements receive two rays satisfying a similar relationship, and a sum of outputs of the respective light-receiving elements is made to be a detection signal. Or, in an optical encoder using a collimated lighting system, an index scale is leaned (inclined) toward a main scale by a predetermined value. With any one of these arrangements, a component of variation in the detection signal due to a geometric image can be offset or integrated to be removed, whereby the dependence of an S/N ratio of the detection signal on the grating gap can be avoided. Furthermore, in a reflection type encoder using a diffusive light source, diffused rays from a point light source is focused by a condensing lens to produce a secondary point light source and this secondary point light source is positioned in a plane where second gratings corresponding to an index scale are formed. With this arrangement, a collimator lens can be dispensed with, so that the encoder can be rendered compact in size. Furthermore, the respective elements can be easily supported and positioned.