US 5,965,879 AGranted

Method and apparatus for ultra-high-sensitivity, incremental and absolute optical encoding

AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration

InventorDouglas B. Leviton

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Abstract

An absolute optical linear or rotary encoder which encodes the motion of an object (3) with increased resolution and encoding range and decreased sensitivity to damage to the scale includes a scale (5), which moves with the object and is illuminated by a light source (11). The scale carries a pattern (9) which is imaged by a microscope optical system (13) on a CCD array (17) in a camera head (15). The pattern includes both fiducial markings (31) which are identical for each period of the pattern and code areas (33) which include binary codings of numbers identifying the individual periods of the pattern. The image of the pattern formed on the CCD array is analyzed by an image processor (23) to locate the fiducial marking, decode the information encoded in the code area, and thereby determine the position of the object.

Claims20

Dependent claims

An optical encoder for determining an absolute position of an object, the optical encoder comprising:

a scale having a pattern formed thereon, the pattern having a plurality of periods, each of the plurality of periods including (a) a first portion which is identical for all of the plurality of periods and (b) a second portion which identifies said each of the plurality of periods;
means for causing relative motion between the scale and the object;
means for illuminating the scale;
means for receiving light from the scale, the means for receiving comprising detector means for forming an image of one of the plurality of periods of the pattern which lies within a field of view of the detector means and for outputting signals derived from the image, the field of view defining a fixed coordinate system;
and
analyzing means, receiving the signals from the detector means, for (i) determining a location of the first portion of the one of the plurality of periods within the fixed coordinate system, (ii) decoding the second portion of. the one of the plurality of periods to derive an identity of the one of the plurality of periods;
and (iii) determining the absolute location of the object in accordance with the location of the first portion determined in operation (i) and the identity determined in operation (ii).

4 more elements

Dependencies are inferred from the claim text.