Absolute incremental position encoder and method
First Claim
1. A position encoder comprising:
- a track encoded with a pattern comprising a plurality of unique subsequences, the pattern having alternating dark and light portions wherein both the dark and light portions have widths that vary in accordance with bits of the subsequences;
two or more sensors to detect edges and the widths of the alternating dark and light portions as the track moves; and
a processing element to generate a portion of at least one of the unique subsequences from signals provided by the sensors for use in initially determining an incremental position of the track,wherein the sensors comprise first and second sensors spaced apart approximately one-half their field of view to provide partially overlapping fields of view,wherein the first sensor is to provide a quadrature-phase pick-off signal, the second sensor to provide an in-phase pick-off signal, andwherein the processing element is to generate quadrature pairs from the quadrature-phase and in-phase pick-off signals, is to generate bits of the sequence based on the quadrature pairs, and is to determine an absolute position of the track when a number of bits generated exceed a predetermined number.
1 Assignment
0 Petitions
Accused Products
Abstract
A position encoder uses a track encoded with a pattern of bit-widths in accordance with a sequence. The sequence may be any sequence having unique subsequences, and may be a pseudo-random noise (PRN) sequence such that each N-bit subsequence occurs only once on the track. Sensors detect transitions between the bits and bit-widths as the track moves with respect to the sensors to provide in-phase and quadrature-phase pick-off signals. The pickoff signals are summed and absolute value thresholded. The absolute value thresholded sum signal is sampled when the quadrature pairs are in the “00” or “11” quadrants, and latched when the sum signal goes high to distinguish between wide and narrow bit widths. The latch is shifted into a shift data register for use in determining the position of the encoder track. In the case of a PRN sequence having a length of 2N bits, the position may be an absolute position when the number of valid bits in the shift data register is at least N. The position may be an incremental position when the number of transitions detected is less than N.
18 Citations
20 Claims
-
1. A position encoder comprising:
-
a track encoded with a pattern comprising a plurality of unique subsequences, the pattern having alternating dark and light portions wherein both the dark and light portions have widths that vary in accordance with bits of the subsequences; two or more sensors to detect edges and the widths of the alternating dark and light portions as the track moves; and a processing element to generate a portion of at least one of the unique subsequences from signals provided by the sensors for use in initially determining an incremental position of the track, wherein the sensors comprise first and second sensors spaced apart approximately one-half their field of view to provide partially overlapping fields of view, wherein the first sensor is to provide a quadrature-phase pick-off signal, the second sensor to provide an in-phase pick-off signal, and wherein the processing element is to generate quadrature pairs from the quadrature-phase and in-phase pick-off signals, is to generate bits of the sequence based on the quadrature pairs, and is to determine an absolute position of the track when a number of bits generated exceed a predetermined number. - View Dependent Claims (2, 3)
-
-
4. A position encoder comprising:
-
a track encoded with a pattern comprising a plurality of unique subsequences; sensors to detect the pattern as the track moves; and a processing element to detect a portion of at least one of the unique subsequences from the signals provided by the sensors for use in determining either an absolute or incremental position of the track, wherein the sensors comprise first and second sensors, the first sensor to provide a quadrature-phase pick-off signal, the second sensor to provide an in-phase pick-off signal, wherein the processing element; to generate quadrature pairs from the quadrature-phase and in-phase pick-off signals, to sum the quadrature-phase and in-phase pick-off signals and absolute value threshold the sum to generate a quantized signal, to sample the quantized signal when the quadrature pairs indicate “
00”
, or “
11”
, quadrants,to latch a bit when the sampled quantized signal is high when the quadrature pairs indicate “
00”
or “
11”
quadrants,to shift the latched bit into a data-shift register when a transition through either the “
00”
or “
11”
quadrant occurs, andto determine a position of the track from bits shifted into the data-shift register, the bits shifted into the data-shift register corresponding with a portion of at least one of the unique subsequences. - View Dependent Claims (5, 6, 7, 8)
-
-
9. A method of determining a position of a track encoded with a pattern comprising a plurality of unique subsequences, the pattern having alternating dark and light portions wherein both the dark and light portions have widths that vary in accordance with bits of the subsequence, the method comprising:
-
detecting edges and widths of the alternating dark and light portions as the track moves with two or more sensors; generating a least a portion of the unique subsequences in a bit-by-bit manner from outputs of the sensors; and comparing the generated portion with the pattern to initially determine an incremental position of the track, wherein sensors comprise first and second optical sensors positioned to have partially overlapping fields of view, the method further comprising; providing by the first sensor a quadrature-phase pick-off signal; providing by the second sensor an in-phase pick-off signal; generating quadrature pairs from the pick-off signals for use in generating bits of the sequence; and determining an absolute position of the track when a number of bits generated exceed a predetermined number. - View Dependent Claims (10, 11)
-
-
12. A method of determining a position of a track encoded with a pattern comprising a plurality of unique subsequences, the method comprising:
-
detecting transitions as the track moves with sensors; combining outputs of the sensors to generate a least a portion of the unique subsequences; comparing the generated portion with the pattern to determine either an absolute or incremental position of the track; providing a quadrature-phase pick-off signal with a first sensor and an in-phase pick-off signal with a second sensor; generating quadrature pairs from the quadrature-phase and in-phase pick-off signals; summing the quadrature-phase and in-phase pick-off signals and absolute value thresholding the sum to generate a quantized signal; sampling the quantized signal when the quadrature pairs indicate “
00”
or “
11”
quadrants;latching a bit when the sampled quantized signal is high when the quadrature pairs indicate “
00”
or “
11”
quadrants;shifting the latched bit into a data-shift register when a transition through either the “
00”
or “
11”
quadrant occurs; anddetermining a position of the track from bits shifted into the data-shift register, the bits shifted into the data-shift register corresponding with a portion of at least one of the unique subsequences. - View Dependent Claims (13, 14, 15, 16)
-
-
17. A system comprising:
-
first and second nested gimbals; a first position encoder to determine an angular position of the first gimbal with respect to a base; and a second position encoder to determine an angular position of the second gimbal with respect to the first gimbal, wherein the position encoders have tracks encoded with a pattern of alternating dark and light portions wherein both the light and dark portions of each track have widths that vary in accordance with a sequence comprising a plurality of subsequences, the position encoders further having two or more sensors to detect edges and the widths of the alternating dark and light portions as the tracks move, and wherein a processing element is to determine an incremental positions of the tracks from sensor signals wherein each sensor comprises first and second optical sensors positioned to have partially overlapping fields of view, wherein the first and second sensors of each encoder are spaced apart to provide the partially overlapping fields of view, and wherein the first sensor is to provide a quadrature-phase pick-off signal, the second sensor to provide an in-phase pick-off signal, and wherein the processing element is to generate quadrature pairs from the quadrature-phase and in-phase pick-off signals, is to generate bits of the sequence based on the quadrature pairs, and is to determine an absolute position of the track when a number of bits generated exceed a predetermined number. - View Dependent Claims (18, 19)
-
-
20. A system comprising:
-
first and second nested gimbals; a first position encoder to determine an angular position of the first gimbal with respect to a base; and a second position encoder to determine an angular position of the second gimbal with respect to the first gimbal, wherein the position encoders have tracks encoded with a pattern of bit-widths in accordance with sequence comprising a plurality of subsequences, have sensors to detect the pattern as the tracks move, and have a processing element to determine the positions of the tracks from sensor signals; wherein each of the sensors comprise first and second sensors, the first sensor to provide a quadrature-phase pick-off signal, the second sensor to provide an in-phase pick-off signal, wherein the processing element of each encoder; to generate quadrature pairs from the quadrature-phase and in-phase pick-off signals, to sum the quadrature-phase and in-phase pick-off signals and absolute value threshold the sum to generate a quantized signal, to sample the quantized signal when the quadrature pairs indicate “
00”
or “
11”
quadrants,to latch a bit when the sampled quantized signal is high when the quadrature pairs indicate “
00”
or “
11”
quadrants,to shift the latched bit into a data-shift register when a transition through either the “
00”
or “
11”
quadrant occurs, andto determine a position of the track from bits shifted into the data-shift register, the bits shifted into the data-shift register corresponding with a portion of at least one of the unique subsequences.
-
Specification