Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1997-03-26
1998-11-24
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356374, G01B 1100
Patent
active
058411348
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application is a 371 of PCT/EP96/03276 Jul. 25, 1996.
The invention is directed to a photoelectric path- and angle-measurement system for measuring the displacement of two objects relative to one another and is suitable for use in path- and angle-measurement systems, for example.
2. Description of the Related Art
Very different constructional types of path- and angle-measurement systems are known from the prior art. In general, these measurement systems have in common that a reference grating divided into a plurality of fields is arranged over the scale or the circular graduation and the rulings in the fields are displaced relative to one another by 1/4 or 1/3 of the ruling period in each case. The photoelectric detectors associated with the fields of the reference grating send signals which are phase-shifted by 90.degree. or 120.degree. and which detect the scale displacement or graduated circle rotation as a function of direction in appropriate electronic equipment.
DE-C-3904898 describes an "optical encoder" which uses a noncollimated light source, a reference grating between the light source and scale grating, and a reference grating between photoreceivers and scale grating. The two reference gratings lie in a plane. The reference grating between the photoreceivers and the scale grating is divided into a plurality of fields. The grating rulings in the fields are displaced relative to one another by 1/4 of the ruling period in each instance. The photoreceivers associated with the reference fields detect signals with phase positions of 0.degree., 90.degree., 180.degree. and 270.degree..
However, the three-grating encoder described above is sensitive to rotation and changes in the spacing of the measurement head from the scale with respect to the phase position of the receiver signals.
Further, there is a known device for measuring displacement and rotation of a body which uses receiver arrangements in matrix form, wherein the reference grating fields are associated with phase-shifted grating lines and are interconnected statistically to compensate for amplitude errors, phase errors and ruling errors.
This arrangement is particularly suitable for transmitted-light measurement systems with collimated illumination, but has relatively high requirements with respect to manufacturing.
OBJECT AND SUMMARY OF THE INVENTION
Based on the prior art described above, the primary object of the present invention is to provide a photoelectric path- and angle-measurement system for measuring the displacement of two objects relative to one another which is not sensitive to changes in distance and rotations of the measurement head relative to the scale and which at the same time enables a very simple and economical construction.
This object is met, according to the invention, in a generic photoelectric path- and angle-measurement system in that the diagonals of the photoreceivers parallel to the diagonal of the photoreceiver matrix and parallel to the optical fringe patterns, and the diagonals of the photoreceivers which do not detect the same phase position and whose diagonals lie adjacent to the diagonal of the photoreceiver matrix are equispaced with respect to one another, wherein the diagonal of the photoreceivers contains the points forming the critical surface points or centroids, in that, further, the photoreceivers which detect the same phase position are electrically interconnected, and in that these signals are fed to an evaluating circuit.
In accordance with a preferred further development of the photoelectric path- and angle-measurement system according to the invention, the light of the light source impinges on the photoreceiver matrix after it has passed through the reference grating and been reflected by the scale grating and passed through the reference grating a second time.
In another advantageous construction of the invention, the optical fringe patterns are produced by adjusting an angle .alpha. between the reference grating and the scale gr
REFERENCES:
patent: 5666196 (1997-09-01), Ishii et al.
Burgschat Reiner
Willhelm Joerg
Carl Zeiss Jena GmbH
Pyo Kevin
Westin Edward P.
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