Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-06-08
2001-08-21
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S231140
Reexamination Certificate
active
06278107
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical reader for a high-resolution optical coder used in particular to determine the angular position of one object relative to another.
Optical coders are known from the prior art which allow measuring the angular position of two objects that may be in relative motion by means of interferometry. Such a device is known from the European patent applications 262,349 and 419,701 in the form of a disk fitted along a peripheral annulus with angular graduations allowing to diffract in a first instance a light beam from a light source. Once diffracted, the light beam enters a prism deflecting it to a read-unit diametrically opposite the light source. Before reaching the read unit, the light beam again crosses the disk and is diffracted a second time by the angular graduation. The beam is also totally reflected on the prism's side faces, thereby producing interferences.
An optic pickup is further known from the French patent 2,666,145 and in particular acts as a speed detector or a position detector of a rotating or translating element. This pickup comprises a coding element fitted with reflecting surfaces of defined geometry and a transducer comprising an optical emitter and an optical detector. The speed of the coding element is sensed on account of the light-beam reflections on the particular surfaces of the coding element. These surfaces are bounded at least in part by a conical surface, that is a parabola, an ellipse or a hyperbola. Because of the manufacture of the coding element, this pickup requires high-accuracy machining ands thus entails large costs and high fragility.
SUMMARY OF THE INVENTION
Accordingly the objective of the present invention is to palliate the drawbacks of the prior art by means of an optical reader for a high-resolution optical coder simple in design and maintenance, where, without resort to interferometry, improvement is achieved in the accuracy of object location.
This objective is attained in that the optical reader of a high-resolution optical coder comprises means to emit a light beam and means to detect this light beam, a disk of which the angular position is to be determined, reflecting means to deviate the beam from the emitter and the diffraction means on the coding disk toward the detection means and in that it is characterized by the beam emitting and detecting means being situated in one plane which is parallel to the coder disk, this disk being situated between the plane containing the emitting and detecting means on one hand and on the other the reflecting means, these reflecting means comprising at least two reflecting surfaces each subtending a given angle with the plane containing the detecting and emitting means, where the emitting and detecting means are aligned along a disk radius.
In another feature of the invention, the angle subtended between the reflecting surfaces and the plane containing the emitting and detecting means is 45°.
In another feature of the invention, the emitting and detecting means are configured in such manner that the optical path of the light beam crosses the coder disk at least once and the diffraction means at least once.
In another feature of the invention, the reflecting surfaces consist of mirrors and/or prisms and/or of polished surfaces of a solid body.
In another feature of the invention, at least one reflecting surface is of a given, non-planar topology and preferably is selected from the concave shapes.
In another feature of the invention, the two reflecting surfaces are non-planar and designed so that the beam reflected by the second reflecting surface toward the detector shall be collimated.
In another feature of the invention, the beam-emitting means comprise at least one emitter each of which is associated with a detector constituting the light-beam detecting means.
In another feature of the invention, the light-beam emitting means and detecting means are configured in such a way that they are aligned along a geometric half-line apart from the disk's axis of symmetry.
In another feature of the invention, the light beam emitted by the emitter means is contained in a plane perpendicular to the plane containing the emitting and detecting means and the axis of symmetry of the coder disk.
In another feature of the invention, the diffraction means comprise a reticle stationary relative to the disk and comprising a diaphragm opposite the emitting means and one or more apertures opposite the detectors.
REFERENCES:
patent: 3512006 (1970-05-01), Haller
patent: 3983391 (1976-09-01), Clemons
patent: 4247769 (1981-01-01), Warner
patent: 4334430 (1982-06-01), Hansen et al.
patent: 36 09 211 (1987-09-01), None
patent: 1198517 (1970-07-01), None
patent: 60-031016 (1985-02-01), None
patent: WO 80/01416 (1980-07-01), None
Codechamp
Lee John R.
Nixon & Vanderhye P.
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