U.S. patent application number 15/637750 was filed with the patent office on 2019-01-03 for contamination and defect resistant optical encoder configuration for providing displacement signal having a plurality of spatial phase detectors arranged in a spatial phase sequence along a direction transverse to the measuring axis.
The applicant listed for this patent is Mitutoyo Corporation. Invention is credited to Shu Hirata, Akihide Kimura, Joseph Daniel Tobiason.
Application Number | 20190003860 15/637750 |
Document ID | / |
Family ID | 64662057 |
Filed Date | 2019-01-03 |
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United States Patent
Application |
20190003860 |
Kind Code |
A1 |
Tobiason; Joseph Daniel ; et
al. |
January 3, 2019 |
CONTAMINATION AND DEFECT RESISTANT OPTICAL ENCODER CONFIGURATION
FOR PROVIDING DISPLACEMENT SIGNAL HAVING A PLURALITY OF SPATIAL
PHASE DETECTORS ARRANGED IN A SPATIAL PHASE SEQUENCE ALONG A
DIRECTION TRANSVERSE TO THE MEASURING AXIS
Abstract
An optical encoder configuration comprises an illumination
portion, a scale, and a photodetector configuration. The
illumination portion transmits source light to a scale which
outputs a periodic scale light pattern to the photodetector
configuration. The photodetector configuration comprises a set of N
spatial phase detectors arranged in a spatial phase sequence along
a direction transverse to the measuring axis comprising two outer
spatial phase detectors at a start and end of the sequence along
the direction transverse to the measuring axis. At least a majority
of the respective spatial phase detectors are relatively elongated
along the measuring axis direction and relatively narrow along the
direction perpendicular to the measuring axis direction, and
comprise periodic scale light receptor areas positioned
corresponding to a respective spatial phase of that spatial phase
detector relative to the periodic scale light pattern, and are
configured to provide a respective spatial phase detector
signal.
Inventors: |
Tobiason; Joseph Daniel;
(Bothell, WA) ; Kimura; Akihide; (Tokorozawa,
JP) ; Hirata; Shu; (Kawasaki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitutoyo Corporation |
Kanagawa-ken |
|
JP |
|
|
Family ID: |
64662057 |
Appl. No.: |
15/637750 |
Filed: |
June 29, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01D 5/38 20130101; G01D
5/34707 20130101; G01D 5/24438 20130101; G01D 5/34761 20130101 |
International
Class: |
G01D 5/347 20060101
G01D005/347 |
Claims
1. A contamination and defect resistant optical encoder
configuration for providing displacement signals, comprising: an
illumination portion that transmits source light to a scale along a
source light path; a scale that extends along a measuring axis
direction, the scale comprising a periodic pattern comprising bars
that are narrow along the measuring axis direction and elongated
along a Y direction perpendicular to the measuring axis direction,
and that are arranged periodically along the measuring axis
direction, the scale inputting the source light along the source
light path and outputting scale light along a scale light path; and
a photodetector configuration that receives a periodic scale light
pattern from the scale along a scale light path, the periodic scale
light pattern displacing past the photodetector configuration
corresponding to a relative displacement between the scale and the
photodetector configuration along the measuring axis direction,
wherein: the photodetector configuration comprises a set of N
spatial phase detectors arranged in a spatial phase sequence along
a direction transverse to the measuring axis, where N is an integer
that is at least 6 and the spatial phase sequence comprises two
outer spatial phase detectors at a start and end of the sequence
along the direction transverse to the measuring axis and an
interior group of spatial phase detectors located between the two
outer spatial phase detectors; at least a majority of the
respective spatial phase detectors are relatively elongated along
the measuring axis direction and relatively narrow along the
direction perpendicular to the measuring axis direction, and
comprise scale light receptor areas that are spatially periodic
along the measuring axis direction and positioned corresponding to
a respective spatial phase of that spatial phase detector relative
to the periodic scale light pattern, and are configured to provide
a respective spatial phase detector signal; and each spatial phase
detector in the interior group is preceded and followed in the
spatial phase sequence by spatial phase detectors that have
respective spatial phases that are different from that spatial
phase detector and different from each other.
2. The contamination and defect resistant optical encoder
configuration of claim 1, wherein the set of N spatial phase
photodetectors comprises at least M subsets of spatial phase
detectors, where M is an integer that is at least 2, and wherein
each of the M subsets includes spatial phase detectors that provide
each of the respective spatial phases included in the set of N
spatial phase photodetectors.
3. The contamination and defect resistant optical encoder
configuration of claim 2, wherein M is at least 3.
4. The contamination and defect resistant optical encoder
configuration of claim 2, wherein M is at least 6.
5. The contamination and defect resistant optical encoder
configuration of claim 2, wherein each of the M subsets of spatial
phase detectors comprises spatial phase detectors that provide the
same respective spatial phases arranged in the same subset spatial
phase sequence.
6. The contamination and defect resistant optical encoder
configuration of claim 5, wherein each subset of spatial phase
detectors comprises 3 spatial phase detectors having respective
spatial phases separated by 120 degrees.
7. The contamination and defect resistant optical encoder
configuration of claim 5, wherein N is at least 8 and each subset
of spatial phase detectors comprises 4 spatial phase detectors
having respective spatial phases separated by 90 degrees.
8. The contamination and defect resistant optical encoder
configuration of claim 1, wherein the photodetector configuration
includes connections configured to combine spatial phase detector
signals corresponding to the same respective spatial phase and to
output each such combination as a respective spatial phase position
signal.
9. The contamination and defect resistant optical encoder
configuration of claim 8, wherein the photodetector configuration
is configured to output 3 spatial phase position signals
corresponding to spatial phases separated by 120 degrees.
10. The contamination and defect resistant optical encoder
configuration of claim 8, wherein the photodetector configuration
is configured to output 4 spatial phase position signals
corresponding to spatial phases separated by 90 degrees.
11. The contamination and defect resistant optical encoder
configuration of claim 1, wherein each of the respective spatial
phase detectors is relatively elongated along the measuring axis
direction and relatively narrow along the direction perpendicular
to the measuring axis direction, and comprises scale light receptor
areas that are spatially periodic along the measuring axis
direction and positioned corresponding to a respective spatial
phase of that spatial phase detector relative to the periodic scale
light pattern, and is configured to provide a respective spatial
phase detector signal.
12. The contamination and defect resistant optical encoder
configuration of claim 1, wherein a dimension YSLRA of the scale
light receptor areas of each of the N spatial phase detectors along
the Y direction is at most 250 micrometers.
13. The contamination and defect resistant optical encoder
configuration of claim 11, wherein a separation distance YSEP
between the scale light receptor areas of each adjacent pair of the
N spatial phase detectors along the Y direction is at most 25
micrometers.
14. The contamination and defect resistant optical encoder
configuration of claim 1, wherein a dimension YSLRA of the scale
light receptor areas of each of the N spatial phase detectors along
the Y direction is at least 5 micrometers.
15. The contamination and defect resistant optical encoder
configuration of claim 1, wherein a dimension YSLRA of the scale
light receptor areas of each of the N spatial phase detectors is
the same along the Y direction.
16. The contamination and defect resistant optical encoder
configuration of claim 15, wherein a separation distance YSEP
between the scale light receptor areas of each adjacent pair of the
N spatial phase detectors is the same along the Y direction.
17. The contamination and defect resistant optical encoder
configuration of claim 1, wherein each of the N spatial phase
detectors comprises a photodetector covered by a spatial phase mask
that blocks the photodetector from receiving the periodic scale
light pattern except through openings included in the spatial phase
mask, wherein the scale light receptor areas comprise areas of the
photodetector that are exposed through the openings in the spatial
phase mask.
18. The contamination and defect resistant optical encoder
configuration of claim 1, wherein each of the N spatial phase
detectors comprises a periodic array of electrically interconnected
photodetector areas that receive the periodic scale light pattern,
wherein the scale light receptor areas comprise the photodetector
areas of the periodic array of photodetectors.
19. The contamination and defect resistant optical encoder
configuration of claim 1, wherein each of the N spatial phase
detectors comprises an even number of scale light receptor areas.
Description
BACKGROUND
Technical Field
[0001] The invention relates generally to precision position or
displacement measurement instruments, and more particularly to an
encoder configuration with signal processing which is resistant to
errors that may be associated with a contaminated or defective
portion of a scale.
Description of the Related Art
[0002] Optical position encoders determine the displacement of a
readhead relative to a scale that includes a pattern that is
detected by the readhead. Typically, position encoders employ a
scale that includes at least one scale track that has a periodic
pattern, and the signals arising from that scale track are periodic
as a function of displacement or position of the readhead along the
scale track. Absolute type position encoders may use multiple scale
tracks to provide a unique combination of signals at each position
along an absolute scale.
[0003] Optical encoders may utilize incremental or absolute
position scale structures. An incremental position scale structure
allows the displacement of a readhead relative to a scale to be
determined by accumulating incremental units of displacement,
starting from an initial point along the scale. Such encoders are
suitable for certain applications, particularly those where line
power is available. In low power consumption applications (e.g.,
battery powered gauges and the like), it is more desirable to use
absolute position scale structures. Absolute position scale
structures provide a unique output signal, or combination of
signals, at each position along a scale, and therefore allow
various power conservation schemes. U.S. Pat. Nos. 3,882,482;
5,965,879; 5,279,044; 5,886,519; 5,237,391; 5,442,166; 4,964,727;
4,414,754; 4,109,389; 5,773,820; and 5,010,655 disclose various
encoder configurations and/or signal processing techniques relevant
to absolute position encoders, and are hereby incorporated herein
by reference in their entirety.
[0004] Some encoder configurations realize certain advantages by
utilizing an illumination source light diffraction grating in an
illumination portion of the encoder configuration. U.S. Pat. Nos.
8,941,052; 9,018,578; 9,029,757; and 9,080,899, each of which is
hereby incorporated herein by reference in its entirety, disclose
such encoder configurations. Some of the configurations disclosed
in these patents may also be characterized as utilizing super
resolution moire imaging.
[0005] In various applications, scale manufacturing defects or
contaminants such as dust or oils on a scale track may disturb the
pattern detected by the readhead, creating errors in the resulting
position or displacement measurements. In general, the size of
errors due to a defect or contamination may depend on factors such
as the size of the defect or contamination, the wavelength of the
periodic pattern on the scale, the size of the readhead detector
area, the relationship between these sizes, and the like. A variety
of methods are known for responding to abnormal signals in an
encoder. Almost all such methods are based on disabling the encoder
signals, or providing an "error signal" to warn the user, or
adjusting a light source intensity to boost low signals, or the
like. However, such methods do not provide a means of continuing
accurate measurement operations despite the abnormal signals that
arise from certain types of scale defects or contamination.
Therefore these methods have limited utility. One known method that
does mitigate the effects of scale contaminants or defects on
measurement accuracy is disclosed in Japanese Patent Application
JP2003-065803 (the '803 application). The '803 application teaches
a method wherein two or more photo detectors output periodic
signals having the same phase, which are each input to respective
signal stability judging means. The signal stability judging means
only outputs signals that are judged to be "normal," and "normal"
signals are combined as the basis for position measurement. Signals
that are "abnormal" are excluded from position measurement
calculations. However, the methods of judging "normal" and
"abnormal" signals disclosed in the '803 application have certain
disadvantages that limit the utility of the teachings of the '803
application.
[0006] U.S. Pat. No. 8,493,572 (the '572 patent) discloses a
contamination and defect resistant optical encoder configuration
which provides a means to select signals from photodetector
elements which are not subject to contamination. However the '572
patent relies on complex signal processing that may be less
desirable in some applications.
[0007] Improved methods for providing accurate measurement
operations that avoid or mitigate abnormal signals that arise from
certain types of scale defects or contamination without the need
for complex signal processing would be desirable.
BRIEF SUMMARY
[0008] A contamination and defect resistant optical encoder
configuration for providing displacement signals is disclosed. The
contamination and defect resistant optical encoder configuration
comprises an illumination portion, a scale, and a photodetector
configuration. The illumination portion transmits source light to
the scale along a source light path. The scale extends along a
measuring axis direction, and comprises a periodic pattern
comprising bars that are narrow along the measuring axis direction
and elongated along a Y direction perpendicular to the measuring
axis direction, and that are arranged periodically along the
measuring axis direction. The scale inputs the source light along
the source light path and outputs scale light along a scale light
path. The photodetector configuration receives a periodic scale
light pattern from the scale along a scale light path. The periodic
scale light pattern displaces past the photodetector configuration
corresponding to a relative displacement between the scale and the
photodetector configuration along the measuring axis direction. The
photodetector configuration comprises a set of N spatial phase
detectors arranged in a spatial phase sequence along a direction
transverse to the measuring axis, where N is an integer that is at
least 6 and the spatial phase sequence comprises two outer spatial
phase detectors at a start and end of the sequence along the
direction transverse to the measuring axis and an interior group of
spatial phase detectors located between the two outer spatial phase
detectors. At least a majority of the respective spatial phase
detectors are relatively elongated along the measuring axis
direction and relatively narrow along the direction perpendicular
to the measuring axis direction, and comprise scale light receptor
areas that are spatially periodic along the measuring axis
direction and positioned corresponding to a respective spatial
phase of that spatial phase detector relative to the periodic scale
light pattern, and are configured to provide a respective spatial
phase detector signal. Each spatial phase detector in the interior
group is preceded and followed in the spatial phase sequence by
spatial phase detectors that have respective spatial phases that
are different from that spatial phase detector and different from
each other.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0009] The foregoing aspects and many of the attendant advantages
will become more readily appreciated as the same become better
understood by reference to the following detailed description, when
taken in conjunction with the accompanying drawings, wherein:
[0010] FIG. 1 is a partially schematic exploded diagram of a
contamination and defect resistant optical encoder configuration
for providing displacement signals.
[0011] FIG. 2 is a partially schematic diagram of a contamination
and defect resistant optical encoder configuration for providing
displacement signals.
[0012] FIG. 3 is a partially schematic diagram of a photodetector
configuration of a contamination and defect resistant optical
encoder configuration.
[0013] FIG. 4A is a schematic diagram of a portion of a
photodetector configuration of a contamination and defect resistant
optical encoder configuration.
[0014] FIG. 4B is a schematic diagram of a portion of a
photodetector configuration of a contamination and defect resistant
optical encoder configuration.
DETAILED DESCRIPTION
[0015] FIG. 1 is a partially schematic exploded diagram of a
contamination and defect resistant optical encoder configuration
100 for providing displacement signals. The encoder configuration
100 comprises a scale grating 110, an illumination portion 120, and
a photodetector configuration 160.
[0016] FIG. 1 shows orthogonal X, Y, and Z directions, according to
a convention used herein. The X and Y directions are parallel to
the plane of the scale grating 110, with the X direction parallel
to a measuring axis direction MA (e.g., perpendicular to elongated
pattern elements of the scale grating 110). The Z direction is
normal to the plane of the scale grating 110.
[0017] In the implementation shown in FIG. 1, the scale grating 110
is a transmissive grating. The scale grating 110 extends along a
measuring axis direction MA, and comprises a periodic pattern
comprising bars that are narrow along the measuring axis direction
MA and elongated along a perpendicular to the measuring axis
direction MA (i.e., the Y direction), and that are arranged
periodically along the measuring axis direction MA.
[0018] The illumination portion 120 comprises an illumination
source 130, a first illumination grating 140, and a second
illumination grating 150. The illumination source 130 comprises a
light source 131, and a collimating lens 132. The light source 131
is configured to output source light 134 to the collimating lens
132. The collimating lens 132 is configured to receive the source
light 134 and output collimated source light 134' to the first
illumination grating 140. The first illumination grating 140
receives the source light 134' and diffracts the source light 134'
toward the second illumination grating 150. The second illumination
grating 150 receives the source light 134' and further diffracts
the source light 134' toward the scale grating 110 along a source
light path SOLP. The scale grating 110 inputs the source light 134'
along the source light path SOLP and outputs scale light comprising
a periodic scale light pattern 135 along a scale light path SCLP to
the photodetector configuration 160. The photodetector
configuration 160 receives the periodic scale light pattern 135
from the scale grating 110 along the scale light path SCLP. The
periodic scale light pattern 135 displaces past the photodetector
configuration 160 corresponding to a relative displacement between
the scale grating 110 and the photodetector configuration 160 along
the measuring axis direction MA. An example of a photodetector
configuration similar to the photodetector 160 is shown in detail
FIG. 3. The photodetector configuration 160 comprises a set of N
spatial phase detectors arranged in a spatial phase sequence along
a direction transverse to the measuring axis direction MA (i.e.,
the Y direction), where N is an integer that is at least 6 and the
spatial phase sequence comprises two outer spatial phase detectors
at a start and end of the sequence along the direction transverse
to the measuring axis and an interior group of spatial phase
detectors located between the two outer spatial phase detectors. In
the implementation shown in FIG. 1, the set of N spatial phase
photodetectors comprises 3 subsets of spatial phase detectors
S.sub.1, S.sub.2, and S.sub.3 that have the same subset spatial
phase sequence.
[0019] At least a majority of the respective spatial phase
detectors are relatively elongated along the measuring axis
direction MA and relatively narrow along the direction
perpendicular to the measuring axis direction MA (i.e., the Y
direction), and comprise scale light receptor areas that are
spatially periodic along the measuring axis direction MA and
positioned corresponding to a respective spatial phase of that
spatial phase detector relative to the periodic scale light
pattern, and are configured to provide a respective spatial phase
detector signal. Each spatial phase detector in the interior group
is preceded and followed in the spatial phase sequence by spatial
phase detectors that have respective spatial phases that are
different from that spatial phase detector and different from each
other.
[0020] In various applications, the photodetector configuration 160
and the illumination portion 120 may be mounted in a fixed
relationship relative to one another, e.g., in a readhead or gauge
housing (not shown), and are guided along the measuring axis
direction MA relative to the scale grating 110 by a bearing system,
according to known techniques. The scale grating 110 may be
attached to a moving stage, or a gauge spindle, or the like, in
various applications.
[0021] It should be appreciated that the contamination and defect
resistant optical encoder configuration 100 is only one example of
a contamination and defect resistant optical encoder configuration
according to the principles disclosed herein. In alternative
implementations, various optical components may be utilized such as
a telecentric imaging system, limiting apertures, and the like. In
alternative implementations, an illumination portion may comprise
only a single illumination grating.
[0022] FIG. 2 is a partially schematic diagram of a contamination
and defect resistant optical encoder configuration 200 for
providing displacement signals. The optical encoder configuration
200 is similar to the encoder configuration 100. Similar references
numbers 2XX in FIG. 2 and 1XX in FIG. 1, may refer to similar
elements unless otherwise indicated by context or description. The
encoder configuration 200 shown in FIG. 2 is a reflective
configuration. Scale 210 is a reflective scale grating.
[0023] FIG. 3 is a partially schematic diagram of a photodetector
configuration 360 of a contamination and defect resistant optical
encoder configuration 300. The contamination and defect resistant
optical encoder configuration 300 may be similar to the
contamination and defect resistant optical encoder configuration
100 or the contamination and defect resistant optical encoder
configuration 200. The photodetector configuration 360 comprises a
set of N spatial phase detectors arranged in a spatial phase
sequence along a direction transverse to the measuring axis
direction MA, where N is an integer that is at least 6 and the
spatial phase sequence comprises two outer spatial phase detectors
at a start and end of the sequence along the direction transverse
to the measuring axis and an interior group of spatial phase
detectors located between the two outer spatial phase detectors. At
least a majority of the respective spatial phase detectors are
relatively elongated along the measuring axis direction MA and
relatively narrow along the direction perpendicular to the
measuring axis direction MA, and comprise scale light receptor
areas that are spatially periodic along the measuring axis
direction MA and positioned corresponding to a respective spatial
phase of that spatial phase detector relative to the periodic scale
light pattern, and are configured to provide a respective spatial
phase detector signal. Each spatial phase detector in the interior
group is preceded and followed in the spatial phase sequence by
spatial phase detectors that have respective spatial phases that
are different from that spatial phase detector and different from
each other.
[0024] In some implementations, the set of N spatial phase
photodetectors may comprise at least M subsets of spatial phase
detectors, where M is an integer that is at least 2, and wherein
each of the M subsets includes spatial phase detectors that provide
each of the respective spatial phases included in the set of N
spatial phase photodetectors. In some implementations, M may be at
least 3. In some implementations, M may be at least 6. In some
implementations, each of the M subsets of spatial phase detectors
may comprise spatial phase detectors that provide the same
respective spatial phases arranged in the same subset spatial phase
sequence. FIG. 3 shows an implementation with M subsets of spatial
phase detectors indicated as S.sub.1 through S.sub.M. The subset
S.sub.1 comprises spatial phase detectors SPD.sub.1A, SPD.sub.1B,
SPD.sub.1C, and SPD.sub.1D. The subset S.sub.2 comprises spatial
phase detectors SPD.sub.2A, SPD.sub.2B, SPD.sub.2C, and SPD.sub.2D.
The subset S.sub.M comprises spatial phase detectors SPD.sub.MA,
SPD.sub.MB, SPD.sub.MC, and SPD.sub.MD. Each of the spatial phase
detectors in FIG. 3 is shown to have K scale light receptor areas.
As an example of scale light receptor areas, the spatial phase
detector SPD.sub.MD is labeled with scale light receptor areas
SLRA.sub.M1 and SLRA.sub.Mk. In some implementations, K may be an
even value.
[0025] In the implementation shown in FIG. 3, the spatial phase
sequence is indicated by spatial phase detectors including
subscript indices A, B, C, and D (e.g., the spatial phase detectors
SPD.sub.1A, SPD.sub.1B, SPD.sub.1C, and SPD.sub.1D). The spatial
phase detectors with subscript indices A and D are the two outer
spatial phase detectors at the start and end of each instance of
the spatial phase sequence. The spatial phase detectors with
subscript indices B and C are the interior groups.
[0026] The spatial phase detectors SPD.sub.1A, SPD.sub.1B,
SPD.sub.1C, and SPD.sub.1D output respective spatial phase detector
signals A.sub.1, B.sub.1, C.sub.1, and D.sub.1. The spatial phase
detectors SPD.sub.2A, SPD.sub.2B, SPD.sub.2C, and SPD.sub.2D output
respective spatial phase detector signals A.sub.2, B.sub.2,
C.sub.2, and D.sub.2. The spatial phase detectors SPD.sub.MA,
SPD.sub.MB, SPD.sub.MC, and SPD.sub.MD output respective spatial
phase detector signals A.sub.M, B.sub.M, C.sub.M, and D.sub.M.
[0027] A contamination and defect resistant optical encoder
configured according to the principles disclosed herein provides a
simple design which may be tolerant to contaminants (e.g.,
wirebonding contamination) which are as large as 100 micrometers
and scale defects which are as large as 300 micrometers.
Contaminants or defects on a scale will typically produce a common
mode error component on adjacent spatial phase detectors which may
be canceled out in signal processing (e.g., quadrature processing).
Spatial phase detectors which are relatively elongated along the
measuring axis direction MA and relatively narrow along the
direction perpendicular to the measuring axis direction MA provide
better resistance to contamination and defects. Signal levels may
change more slowly by decreasing the frequency of the structure of
the spatial phase detectors along the measuring axis direction MA.
Furthermore, such an encoder does not require complex signal
processing to provide tolerance to contamination and defects.
Signals provided by the set of N spatial phase detectors may be
processed according to standard techniques known to one skilled in
the art.
[0028] In some implementations such as the implementation shown in
FIG. 3, N is at least 8 and each subset of spatial phase detectors
may comprise 4 spatial phase detectors having respective spatial
phases separated by 90 degrees. In alternative implementations,
each subset of spatial phase detectors may comprise 3 spatial phase
detectors having respective spatial phases separated by 120
degrees.
[0029] In the implementation shown in FIG. 3, the photodetector
configuration 360 includes connections configured to combine
spatial phase detector signals corresponding to the same respective
spatial phase and to output each such combination as a respective
spatial phase position signal. The photodetector configuration 360
is configured to output 4 spatial phase position signals
corresponding to spatial phases separated by 90 degrees. Spatial
phase signals with the same letter designation (e.g., A.sub.1,
A.sub.2, and A.sub.M) are combined (e.g., summed) to provide
spatial phase signals .SIGMA.A, .SIGMA.B, .SIGMA.C, and .SIGMA.D.
In alternative implementations, a photodetector configuration may
be configured to output 3 spatial phase position signals
corresponding to spatial phases separated by 120 degrees. In either
case, spatial phase position signals may be further utilized to
determine displacement signals, e.g., through quadrature or three
phase signal processing.
[0030] In some implementations, each of the respective spatial
phase detectors may be relatively elongated along the measuring
axis direction MA and relatively narrow along the direction
perpendicular to the measuring axis direction MA, and may comprises
scale light receptor areas that are spatially periodic along the
measuring axis direction MA and positioned corresponding to a
respective spatial phase of that spatial phase detector relative to
the periodic scale light pattern, and may be configured to provide
a respective spatial phase detector signal.
[0031] In some implementations, a dimension YSLRA of the scale
light receptor areas of each of the N spatial phase detectors along
the Y direction may be at most 250 micrometers. In some
implementations, YSLRA may be at least 5 micrometers.
[0032] In some implementations, a separation distance YSEP between
the scale light receptor areas of each adjacent pair of the N
spatial phase detectors along the Y direction may be at most 25
micrometers.
[0033] In some implementations, a dimension YSLRA of the scale
light receptor areas of each of the N spatial phase detectors may
be the same along the Y direction. In some implementations, a
separation distance YSEP between the scale light receptor areas of
each adjacent pair of the N spatial phase detectors may be the same
along the Y direction.
[0034] It should be appreciated that while a large value of N
provides greater robustness to contamination, there is a tradeoff
in that a large value of N may provide smaller signal levels within
each individual spatial phase detector.
[0035] FIG. 4A is a schematic diagram of a portion of a
photodetector configuration 460A of a contamination and defect
resistant optical encoder configuration 400A. For simplicity, FIG.
4A only shows one subset of spatial phase detectors S.sub.1 with
two spatial phase detectors SPD.sub.1A and SPD.sub.1B. It should be
appreciated that the photodetector 460A comprises at least six
spatial phase detectors according to the principles disclosed
herein, but only two are shown for simplicity. In the
implementation shown in FIG. 4A, each of the N spatial phase
detectors (e.g., spatial phase detectors SPD.sub.1A and SPD.sub.1B)
comprises a photodetector (e.g., photodetectors PD.sub.1A and
PD.sub.1B indicated by dashed lines) covered by a spatial phase
mask (e.g., phase masks PM.sub.1A and PM.sub.1B) that blocks the
photodetector from receiving the periodic scale light pattern
except through openings included in the spatial phase mask. In this
case, the scale light receptor areas comprise areas of the
photodetectors (e.g., the photodetectors PD.sub.1A and PD.sub.1B)
that are exposed through the openings in the respective spatial
phase masks (e.g., the spatial phase masks PM.sub.1A and
PM.sub.1B). In the implementation shown in FIG. 4A, the scale light
receptor areas (i.e., the openings) of the phase mask PM.sub.1B are
offset relative to the scale light receptor areas the phase mask
PM.sub.1A along the measuring axis direction MA by 90 degrees. It
should be appreciated that the while the spatial phase masks
PM.sub.1A and PM.sub.1B are schematically illustrated as separate
portions in FIG. 4A, in some implementations, they may be
conveniently constructed with the same material in the same process
to eliminate any potential positioning errors.
[0036] FIG. 4B is a schematic diagram of a portion of a
photodetector configuration 460B of a contamination and defect
resistant optical encoder configuration 400B. For simplicity, FIG.
4B only shows one subset of spatial phase detectors S.sub.1' with
two spatial phase detectors SPD.sub.1A' and SPD.sub.1B'. It should
be appreciated that the photodetector 460B comprises at least six
spatial phase detectors according to the principles disclosed
herein, but only two are shown for simplicity. In the
implementation shown in FIG. 4B, each of the N spatial phase
detectors (e.g., spatial phase detectors SPD.sub.1A' and
SPD.sub.1B') comprises a periodic array of electrically
interconnected photodetector areas that receive the periodic scale
light pattern. In this case, the scale light receptor areas
comprise the photodetector areas of the periodic array of
photodetectors. In the implementation shown in FIG. 4B, the
photodetector areas of the spatial phase detector SPD.sub.1B' are
offset relative to the photodetector areas of the spatial phase
detector SPD.sub.1A' along the measuring axis direction MA by 90
degrees.
[0037] While preferred implementations of the present disclosure
have been illustrated and described, numerous variations in the
illustrated and described arrangements of features and sequences of
operations will be apparent to one skilled in the art based on this
disclosure. Various alternative forms may be used to implement the
principles disclosed herein. In addition, the various
implementations described above can be combined to provide further
implementations. All of the U.S. patents and U.S. patent
applications referred to in this specification are incorporated
herein by reference, in their entirety. Aspects of the
implementations can be modified, if necessary to employ concepts of
the various patents and applications to provide yet further
implementations.
[0038] These and other changes can be made to the implementations
in light of the above-detailed description. In general, in the
following claims, the terms used should not be construed to limit
the claims to the specific implementations disclosed in the
specification and the claims, but should be construed to include
all possible implementations along with the full scope of
equivalents to which such claims are entitled.
* * * * *