Indexed optical encoder
First Claim
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1. An optical encoder comprising:
- an optical disk having a diffraction grating track and an index track, the index track being disposed radially inward from the diffraction grating track;
the diffraction grating track having a plurality of equally spaced lines that create an alternating light/dark pattern;
the index track having a pattern with at least two sequences of marks, the at least two sequences being equally spaced about a circumference of the index track, each of the at least two sequences having at least one mark and each of the at least two sequences having a different number of marks from each of the other sequences,wherein the number of marks of a given sequence define the length of the sequence, the length of the sequence being measured in a number of fringes detected in the index track between the start and the end of the sequence as generated by the marks of the sequence,wherein each sequence includes a sequence center at the midpoint between the start and end of the given sequence, wherein each sequence center is angularly spaced apart from each other sequence center about the optical disk and defines a specific angular position about the optical disk, andwherein each sequence is separated from another sequence by a rotational distance.
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Abstract
An optical encoder for measuring rotation is provided. The optical encoder includes an optical disk having a diffraction grating track and an index track. The index track being disposed radially inward from the diffraction grating track. The diffraction grating track having a plurality of equally spaced lines that create an alternating light/dark pattern. The index track includes a pattern with at least two sequences, the at least two sequences being equally spaced about the diameter of the index track, each of the sequences having at least one mark and each of the sequences having a different number of marks from the other sequences.
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Citations
20 Claims
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1. An optical encoder comprising:
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an optical disk having a diffraction grating track and an index track, the index track being disposed radially inward from the diffraction grating track; the diffraction grating track having a plurality of equally spaced lines that create an alternating light/dark pattern; the index track having a pattern with at least two sequences of marks, the at least two sequences being equally spaced about a circumference of the index track, each of the at least two sequences having at least one mark and each of the at least two sequences having a different number of marks from each of the other sequences, wherein the number of marks of a given sequence define the length of the sequence, the length of the sequence being measured in a number of fringes detected in the index track between the start and the end of the sequence as generated by the marks of the sequence, wherein each sequence includes a sequence center at the midpoint between the start and end of the given sequence, wherein each sequence center is angularly spaced apart from each other sequence center about the optical disk and defines a specific angular position about the optical disk, and wherein each sequence is separated from another sequence by a rotational distance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of determining rotational movement, the method comprising:
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providing an encoder disk having a diffraction grating track and an index track, the diffraction grating track having a plurality of equally spaced lines that create an alternating light/dark pattern, the index track having a pattern with a plurality of sequences, the plurality of sequences of marks having sequence centers that are equally spaced about a circumference of the index track, each of the plurality of sequences having at least one mark and each of the plurality sequences having a different number of marks from each of the other sequences, wherein the number of marks of a given sequence define the length of the sequence, the length of the sequence being measured in a number of fringes detected in the index track between the scan and the end of the sequence as generated by the marks of the sequence, wherein each sequence center is angularly spaced apart from each other sequence center about the optical disk and defines a specific angular position about the optical disk, and wherein each sequence is separated from another sequence by a rotational distance; illuminating the encoder disk with light; detecting the light diffracted with a sensor; generating a fringe signal with the sensor; detecting a first edge of a first sequence of the plurality of sequences; determining a first length of the first sequence; determining a first angular position of the encoder disk based at least in part on the first length; detecting a second edge of the second sequence of the plurality of sequences; determining a second length of the second sequence; and determining a second angular position of the encoder disk based at least in part on the second length. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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Specification