Method and apparatus for absolute optical encoders with reduced sensitivity to scale or disk mounting errors
First Claim
1. An absolute position rotary encoding apparatus comprising:
- a disk having a first code track and a second code track formed on said disk;
a light source for illuminating said code tracks;
a first area array sensor, comprising a pixel matrix having a plurality of rows, configured to receive the light illuminating said code tracks for forming an imaged pattern of a portion of said first and second code tracks simultaneously, the first array sensor being;
adapted to read a first detector line corresponding to a row in the pixel matrix comprising the imaged pattern of the first code track and a second detector line corresponding to a row in the pixel matrix comprising the imaged pattern of the second code track; and
a Field Programmable Gate Array (FPGA)/processor adapted tocompensate for fluctuations in the code tracks, resulting from the disk being inaccurately mounted, by dynamically shifting at least one of said detector lines on the first area array sensor being read, corresponding to a radial shift along a code track on said disk, such that a period length of the imaged pattern along said at least one detector line remains constant; and
numerically calculate an absolute position based on a light distribution of the imaged patterns of incremental and absolute code tracks from the disk.
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Accused Products
Abstract
An absolute optical encoder apparatus for measuring an absolute position comprises an optical disk or scale element (100) having both incremental and absolute code tracks formed thereon. In the embodiment, a photoemitter light source (110, 111) illuminates the tracks onto a CCD area array sensor (115, 116) such that an image is formed from a pixel matrix having of rows and columns. Two detector line rows (410, 420) of the pixel matrix are each read out from the portion of the matrix comprising the incremental and absolute code tracks respectively. Inaccurate mounting of the disk or scale element can cause fluctuations in the period of the code tracks resulting from the rotation of the disk or movement of the scale element. The mounting inaccuracies are compensated for either by matching the spatial frequency by dynamically changing row of detector line read from the incremental image of the code track or by altering the numerical value of the pattern period used in the Fourier phase algorithm. The absolute position is numerically calculated from the imaged code tracks.
27 Citations
23 Claims
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1. An absolute position rotary encoding apparatus comprising:
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a disk having a first code track and a second code track formed on said disk; a light source for illuminating said code tracks; a first area array sensor, comprising a pixel matrix having a plurality of rows, configured to receive the light illuminating said code tracks for forming an imaged pattern of a portion of said first and second code tracks simultaneously, the first array sensor being; adapted to read a first detector line corresponding to a row in the pixel matrix comprising the imaged pattern of the first code track and a second detector line corresponding to a row in the pixel matrix comprising the imaged pattern of the second code track; and a Field Programmable Gate Array (FPGA)/processor adapted to compensate for fluctuations in the code tracks, resulting from the disk being inaccurately mounted, by dynamically shifting at least one of said detector lines on the first area array sensor being read, corresponding to a radial shift along a code track on said disk, such that a period length of the imaged pattern along said at least one detector line remains constant; and numerically calculate an absolute position based on a light distribution of the imaged patterns of incremental and absolute code tracks from the disk. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A Total Station theodolite apparatus used for topographic surveying and mapping includes an optical encoder for measuring angular position in the vertical plane and the horizontal plane and cooperates with a servo-mechanism for automatically tracking a target, said encoder comprising:
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an optical disk having an incremental code track and an absolute code track formed thereon; a photoemitter light source for illuminating said code tracks; a first area array sensor, comprising a pixel matrix having a plurality of rows, configured to receive the light illuminating said code tracks for forming an imaged pattern of a portion of said incremental and absolute code tracks simultaneously, the first array sensor being adapted to read a first detector line corresponding to a row in the pixel matrix comprising imaged pattern of the first code track and a second detector line corresponding to a row in the pixel matrix comprising the imaged pattern of the second code track; and a Field Programmable Gate Array (FPGA)/processor adapted to compensate for fluctuations in the code tracks, resulting from the disk being inaccurately mounted, by dynamically shifting at least one of said detector lines on the area array sensor being read, corresponding to a radial shift along a code track on said disk, such that a period length of the imaged pattern along said at least one detector line remains constant; and numerically calculate an absolute position based on a light distribution of the imaged patterns of incremental and absolute code tracks from the disk; and calculate topographic data and tracking information about the target. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A method of calculating an absolute position with an optical rotary encoder device comprising:
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illuminating with a light source an incremental code track and an absolute code track formed on a disk; imaging a segment of the incremental and absolute code tracks onto a first CCD or CMOS area array sensor for forming an imaged pattern of the code tracks, said area array sensor comprising a pixel matrix having a plurality of rows; reading a first detector line corresponding to a row in the pixel matrix comprising the imaged pattern of the incremental code track; reading a second detector line corresponding to a row in the matrix comprising the imaged pattern of the absolute code track; compensating for fluctuations in the code tracks, resulting from inaccurate mounting of the disk, by selecting suitable first and second detector lines such that a period length of the imaged pattern of the code tracks along the detector lines remains constant; and calculating numerically the absolute position based on light distribution of the imaged patterns of the incremental and absolute code tracks. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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Specification