U.S. patent application number 10/874545 was filed with the patent office on 2004-12-30 for photodetector for optical encoder.
Invention is credited to Ohkubo, Isamu, Shichi, Koichi.
Application Number | 20040262498 10/874545 |
Document ID | / |
Family ID | 33535261 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040262498 |
Kind Code |
A1 |
Shichi, Koichi ; et
al. |
December 30, 2004 |
Photodetector for optical encoder
Abstract
A photodetector for an optical encoder has plural sets of
segmented photodiodes, each set of which is made by two adjoining
segmented photodiodes capable of coping with a scale slit having a
reference resolution. Output lines of the two adjoining segmented
photodiodes are connected together in each set of the photodiodes.
These output lines are connected to output lines of the
corresponding segmented photodiodes in the other sets. The two
adjoining segmented photodiodes function like one segmented
photodiode, and thereby, the resolution of the applied scale slit
is made 1/2 of the reference resolution. Thus, this photodetector
easily copes with a scale slit having a half resolution of the
reference resolution at low cost only by modification of wiring
without changing any configuration of the segmented
photodiodes.
Inventors: |
Shichi, Koichi;
(Yamatotakada-shi, JP) ; Ohkubo, Isamu;
(Kashiba-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
33535261 |
Appl. No.: |
10/874545 |
Filed: |
June 24, 2004 |
Current U.S.
Class: |
250/214R ;
250/231.13 |
Current CPC
Class: |
H03M 1/485 20130101;
H03M 1/301 20130101; G01D 5/36 20130101 |
Class at
Publication: |
250/214.00R ;
250/231.13 |
International
Class: |
H01L 047/00; G06M
007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2003 |
JP |
P2003-182403 |
Claims
1. A photodetector for an optical encoder constructed by a
plurality of segmented photodiodes which are formed by being
electrically divided on a semiconductor chip, comprising: output
terminals of two or more mutually adjacent segmented photodiodes
electrically connected together.
2. A photodetector for an optical encoder constructed by a
plurality of segmented photodiodes which are formed by being
electrically divided on a semiconductor chip, comprising: two or
more arrays of the plurality of segmented photodiodes arranged in
parallel such that segmented photodiodes in one array are shifted
in relation to segmented photodiodes in another array by one half
an arrangement pitch of the segmented photodiodes to mutually shift
phases of segmented photodiodes between the arrays.
3. The photodetector for an optical encoder as claimed in claim 2,
further comprising: output terminals of two or more adjacent
segmented photodiodes in each of the arrays electrically connected
together.
4. The photodetector for an optical encoder as claimed in claim 1,
wherein, output terminals of two segmented photodiodes located at
both ends in three or more adjacent segmented photodiodes are
electrically disconnected.
5. The photodetector for an optical encoder as claimed in claim 3,
wherein, output terminals of two segmented photodiodes located at
both ends in three or more adjacent segmented photodiodes are
electrically disconnected.
6. The photodetector for an optical encoder as claimed in claim 1,
wherein the electrical connection of the output terminals of the
segmented photodiodes is achieved by adjusting metal wiring with
use of laser trimming.
7. The photodetector for an optical encoder as claimed in claim 1,
wherein the electrical connection of the output terminals of the
segmented photodiodes is achieved by switching means having a
control terminal, and the segmented photodiode of the output
terminals, which are electrically connected, is changed in number
by an external control signal to the control terminal of the
switching means.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This nonprovisional application claims priority under 35
U.S.C. .sctn.119(a) on patent application Ser. No. 2003-182403
filed in Japan on 26 Jun. 2003, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an electrically
multidivided photodetector used for an optical encoder.
[0003] Optical encoders have been used in a wide variety of fields
for controlling the rotational speed, rotational direction,
rotational position and so on of a motor or the like and
controlling the travel speed, movement direction, movement position
and so on of a moving object. For example, reference should be made
to JP 59-40258 A and JP 61-292016 A.
[0004] A disk called a code disk is used for the rotational
control. A thin plate called a scale slit is used for the movement
control. The code disk is provided with optically transparent slits
arranged at prescribed intervals along its circumference, where
optically transparent areas and opaque areas exist alternately
along the circumference of the code disk. On the other hand, the
scale slit is provided with optically transparent slits arranged at
prescribed intervals along its one side, where optically
transparent areas and opaque areas exist alternately along the
above-mentioned side of the scale slit.
[0005] For the rotational control, the rotational amount and the
rotational speed are detected by counting the number of slits of
the rotating code disk by means of a photodetector. For the
movement control, likewise, the movement amount and the travel
speed are detected by counting the number of slits of the moving
scale slit by means of a photodetector. Further, the rotational
direction or the movement direction can also be detected by using
the two kinds of signals having a phase difference of 90 degree,
the signals being formed by the positions of a plurality of
photodiodes constituting the photodetector.
[0006] In the code disk and the scale slit, the opaque areas is
formed by an opaque material such as ink on a board made of a
transparent resin or glass, so that a stripe pattern is formed by
the opaque areas and the transparent slits between the opaque
areas. Otherwise, in some cases, the transparent slit is formed by
providing holes through a metal plate.
[0007] Regarding the configuration of the photodiodes, as shown in
FIGS. 10A and 11A and described in the above-stated patent
documents, one set of photodiodes is constructed by four adjoining
segmented photodiodes Pd1 to Pd4 which are formed on one
semiconductor chip under a electrically separated state. The slit
pitch of the scale slit is made 4-fold of the arrangement pitch of
the segmented photodiodes. Then, one set of the segmented
photodiodes is arranged as shown in FIG. 10A. In some cases, as
shown in FIG. 11A, plural sets of the segmented photodiodes are
arranged in order to level positional variations in the quantity of
light from a light source. Then, outputs of the segmented
photodiodes Pd1 to Pd4 are respectively connected to outputs of the
other corresponding segmented photodiodes as shown in FIG. 11A
(refer to FIG. 6B of JP 61-292016 A).
[0008] Among the photocurrents outputted from the segmented
photodiodes Pd1 to Pd4 when the scale slit moves, a pair of
photocurrents A+(Pd1) and A-(Pd3) and a pair of photocurrents
B+(Pd2) and B-(Pd4), which have a phase difference of 180.degree.
each other as shown in FIGS. 10C and 11C, are inputted to a
comparator (not shown) so that the levels of the input signals are
compared with each other. Consequently, two digital rectangular
waves having a phase difference of 90.degree. are obtained, as
indicated by CHA (a channel A) and CHB (a channel B) in FIGS. 10D
and 11D.
[0009] In the above case, the design value of the resolution of the
photodiodes is determined by the arrangement pitch of the segmented
photodiodes Pd1 to Pd4. Moreover, the slit pitch (resolution) of
the scale slit used for forming two digital rectangular waves,
which have a phase difference of 90.degree., is also limited within
a narrow range centered around a theoretical value based on the
arrangement pitch of the segmented photodiodes Pd1 to Pd4.
[0010] However, the above-stated conventional optical encoder has a
disadvantage as follows. That is, the slit pitch of the code disk
and the scale slit is made 4-fold of the arrangement pitch of the
segmented photodiodes Pd1 to Pd4. Therefore, in the case of a
photodetector for the above-stated conventional optical encoder
constructed by the segmented photodiodes obtained by electrically
quadrisecting one semiconductor chip, it is required to prepare a
semiconductor chip such that the value being 4-fold of the
arrangement pitch of the segmented photodiodes coincides with the
slit pitch (resolution) of the desired code disk or scale slit.
[0011] Moreover, the segmented photodiodes Pd1 to Pd4, which
constitute the photodetector, are arranged in a line in the above
case, and therefore, the slit pitch (resolution) of the code disk
or the scale slit eventually obtained becomes theoretically four
pitches of the segmented photodiodes.
[0012] For the above reasons, the above-stated conventional optical
encoder has the disadvantage that the photodetector must be remade
according to the slit pitch (resolution) of the code disk or the
scale slit every time the required slit pitch (resolution) of the
code disk or the scale slit is changed.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a
photodetector for an optical encoder capable of coping also with
various slit pitches (resolutions) of a code disk or a scale
slit.
[0014] In order to achieve the above-stated object, the present
invention provides a photodetector for an optical encoder
constructed by a plurality of segmented photodiodes which are
formed by being electrically divided on a semiconductor chip,
wherein output terminals of two or more adjacent segmented
photodiodes are electrically connected together.
[0015] According to the above construction, in the case that the
photodetector is regarded as a reference photodetector, and the
resolution of the code disk or the scale slit applied to this
reference photodetector is regarded as a reference resolution, m
(m: integer of not smaller than 2) segmented photodiodes, the
output terminals of which are electrically connected together,
function as one segmented photodiode of the reference
photodetector. Consequently, the resolution of the applied code
disk or scale slit becomes 1/m of the reference resolution.
[0016] The present invention also provides a photodetector for an
optical encoder constructed by a plurality of segmented photodiodes
which are formed by being electrically divided on a semiconductor
chip, wherein two or more arrays of the plurality of segmented
photodiodes are arranged in parallel such that segmented
photodiodes in one array are shifted in relation to segmented
photodiodes in another array by one half an arrangement pitch of
the segmented photodiodes to mutually shift phases of segmented
photodiodes between the arrays.
[0017] According to the above-mentioned construction, in the case
that this photodetector is regarded as a reference photodetector,
and the resolution of the code disk or the scale slit applied to
the reference photodetector is regarded as a reference resolution,
the segmented photodiode of a half width functions as one segmented
photodiode of the reference photodetector. Consequently, the
resolution of the applied code disk or scale slit becomes 2-fold of
the reference resolution.
[0018] In one embodiment of the present invention, output terminals
of two or more adjacent segmented photodiodes in each of the arrays
are electrically connected together.
[0019] According to this embodiment, m segmented photodiodes, the
output terminals of which are electrically connected together,
function as one segmented photodiode in the reference
photodetector. Consequently, the resolution of the applied code
disk or scale slit becomes 2/m of the reference resolution.
[0020] In one embodiment of the present invention, output terminals
of two segmented photodiodes located at both ends in three or more
adjacent segmented photodiodes are electrically disconnected.
[0021] According to this embodiment, a wide constant gap is
provided between segmented photodiodes, the output terminals of
which are electrically connected together to generate an output
signal of one phase. Therefore, influence of a leakage current is
alleviated and thus a signal-to-noise ratio is improved, the
leakage current becoming a noise for a signal current from the
segmented photodiodes that constitute respective phases.
[0022] In one embodiment of the present invention, the electrical
connection of the output terminals of the segmented photodiodes is
achieved by adjusting metal wiring with use of laser trimming.
[0023] According to this embodiment, the resolution of the
photodiodes in the photodetector is set by a simple process of
laser trimming in response to the resolution of an applied code
disk or scale slit.
[0024] In one embodiment of the present invention, the electrical
connection of the output terminals of the segmented photodiodes is
achieved by switching means having a control terminal, and the
segmented photodiodes, the output terminals of which are
electrically connected, is changed in number by an external control
signal to the control terminal of the switching means.
[0025] According to this embodiment, even if the resolution of the
applied code disk or scale slit is variously changed, the setting
of the resolution of the photodiodes in the photodetector is
changed by the external control signal in response to the
resolution of the code disk or the scale slit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0027] FIGS. 1A, 1B, 1C and 1D are diagrams showing arrangement and
wiring of segmented photodiodes, a slit pitch, segmented photodiode
outputs and digitized outputs, respectively, in a photodetector for
a 1/2 resolution optical encoder according to the present
invention;
[0028] FIGS. 2A, 2B, 2C and 2D are diagrams showing the arrangement
and wiring of segmented photodiodes, the slit pitch, the segmented
photodiode outputs and the digitized outputs, respectively, in a
photodetector for a 1/4 resolution optical encoder according to the
present invention;
[0029] FIGS. 3A, 3B, 3C and 3D are diagrams showing the arrangement
and wiring of segmented photodiodes, the slit pitch, the segmented
photodiode outputs and the digitized outputs, respectively, in a
photodetector for a 1/8 resolution optical encoder according to the
present invention;
[0030] FIGS. 4A, 4B, 4C and 4D are diagrams showing the arrangement
and wiring of segmented photodiodes, the slit pitch, the segmented
photodiode outputs and the digitized outputs, respectively, in a
photodetector for a two-fold resolution optical encoder according
to the present invention;
[0031] FIGS. 5A, 5B, SC and 5D are diagrams showing the arrangement
and wiring of segmented photodiodes, the slit pitch, the segmented
photodiode outputs and the digitized outputs, respectively, in a
photodetector for a one-fold resolution optical encoder according
to the present invention;
[0032] FIGS. 6A, 6B, 6C and 6D are diagrams showing the arrangement
and.wiring of segmented photodiodes, the slit pitch, the segmented
photodiode outputs and the digitized outputs, respectively, in a
photodetector for a 2/3-fold resolution optical encoder according
to the present invention;
[0033] FIGS. 7A, 7B, 7C and 7D are diagrams showing the arrangement
and wiring of segmented photodiodes, the slit pitch, the segmented
photodiode outputs and the digitized outputs, respectively, in a
photodetector for a 1/2 resolution optical encoder according to the
present invention, different from FIGS. 1A through 1D;
[0034] FIGS. 8A, 8B, 8C and 8D are diagrams showing the arrangement
and wiring of segmented photodiodes, the slit pitch, the segmented
photodiode outputs and the digitized outputs, respectively, in a
photodetector for a 1/4 resolution optical encoder according to the
present invention, different from FIGS. 2A through 2D;
[0035] FIGS. 9A, 9B, 9C and 9D are diagrams showing the arrangement
and wiring of segmented photodiodes, the slit pitch, the segmented
photodiode outputs and the digitized outputs, respectively, in a
photodetector for a 2/3-fold resolution optical encoder according
to the present invention, different from FIGS. 6A through 6D;
[0036] FIGS. 10A, 10B, 10C and 10D are diagrams showing the
arrangement and wiring of segmented photodiodes, the slit pitch,
the segmented photodiode outputs and the digitized outputs,
respectively, in a conventional photodetector for an optical
encoder; and
[0037] FIGS. 11A, 11B, 11C and 11D are diagrams showing the
arrangement and wiring of segmented photodiodes, the slit pitch,
the segmented photodiode outputs and the digitized outputs,
respectively, in a conventional photodetector for an optical
encoder, different from FIGS. 10A through 10D.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] The present invention will be described in detail below on
the basis of embodiments with reference to the drawings.
[0039] First Embodiment
[0040] The present embodiment is related to a photodetector for an
optical encoder, wherein plural sets of segmented photodiodes, each
set of which is constructed by four adjoining segmented photodiodes
Pd1 to Pd4, are arranged so that the photodetector is capable of
coping with a plurality of resolutions of a scale slit (a thin
plate with slits) by changing the number of sets of the segmented
photodiodes as well as connection between the segmented
photodiodes.
[0041] In the above case, the change of connection between the
segmented photodiodes is achieved by preparing a plurality of kinds
of masks to be used in the forming process of connection wiring and
changing the mask.
FIRST EXAMPLE
[0042] FIGS. 1A to 1D are diagrams of a photodetector for an
optical encoder, which is capable of coping with a scale slit
having a half resolution relative to the resolution of the scale
slit of FIG. 10. FIGS. 1A, 1B, 1C and 1D respectively show
arrangement and wiring of segmented photodiodes, a slit pitch,
segmented photodiode outputs and digitalized outputs.
[0043] In this photodetector, one set of segmented photodiodes is
constructed by a subset of Pd1 to Pd4 and a subset of Pd1' to Pd4',
which are equivalent to two sets of the segmented photodiodes Pd1
to Pd4 shown in FIG. 10 and functions as the segmented photodiodes
Pd1 to Pd4 of FIG. 10. Further, plural sets of the segmented
photodiodes Pd1 to Pd4 and Pd1' to Pd4' are arranged in order to
level variations in the quantity of light from the light source,
similarly to the case of FIG. 11.
[0044] Specifically, two output lines of two adjoining segmented
photodiodes i.e. Pd1 and Pd2; Pd3 and Pd4; Pd1' and Pd2'; and Pd3'
and Pd4' are connected each other. Further, these output lines of
the segmented photodiodes are respectively connected to output
lines of corresponding segmented photodiodes in the other similar
sets of segmented photodiodes, as in the case of FIG. 11.
[0045] With this arrangement, two adjoining segmented photodiode
Pd1 and Pd2; Pd3 and Pd4; Pd1' and Pd2'; and Pd3' and Pd4', the
output lines of which are respectively connected, can be made to
function as one segmented photodiode Pd1, Pd2, Pd3 and Pd4 of FIG.
10. As shown in FIGS. 1A and 1B, the slit pitch of the scale slit
is made 8-fold of the arrangement pitch (PD pitch) of the segmented
photodiodes Pd. That is, the resolution of the scale slit is made
1/2 of the resolution (hereinafter referred to as a reference
resolution) of the conventional scale slit shown in FIG. 10.
[0046] Moreover, plural sets of segmented photodiodes are arranged,
each set of which is constructed by three adjacent subsets of the
segmented photodiodes Pd1 to Pd4 shown in FIG. 10. Output lines of
three adjoining segmented photodiodes in each set are connected
each other. Also, these output lines are respectively connected to
the output lines of the corresponding segmented photodiodes among
the sets of segmented photodiodes so as to have 1/3 of the
reference resolution.
[0047] As described above, according to the present example, the
resolution of the scale slit can be made 1/2 or 1/3 of the
reference resolution only by changing the wiring without changing
the configuration of the segmented photodiodes of FIG. 10.
Therefore, this arrangement can cope with various resolutions of
the scale slit easily at low cost.
SECOND EXAMPLE
[0048] FIGS. 2A to 2D are diagrams of a photodetector for an
optical encoder, which is capable of coping with a scale slit
having a 1/4 resolution of the reference resolution. FIGS. 2A, 2B,
2C and 2D show arrangement and wiring of segmented photodiodes, a
slit pitch, segmented photodiode outputs and digitalized
outputs.
[0049] In the present example, plural sets of segmented photodiodes
are arranged, each set of which is constructed by four adjacent
subsets of the segmented photodiodes Pd1 to Pd4 formed electrically
quadrisected on a semiconductor chip having the same size as that
of the photodetector of FIG. 10. Then, output lines of the four
adjoining segmented photodiodes in each set are connected together.
The four connected output lines in each set are also connected to
four connected output lines of the corresponding segmented
photodiodes in the other sets of segmented photodiodes. Therefore,
the four adjoining segmented photodiodes function as one segmented
photodiode of FIG. 10. Thereby, the resolution of the scale slit
can be made 1/4 of the reference resolution.
[0050] Likewise, as shown in FIGS. 3A to 3D, plural sets of the
segmented photodiodes are arranged, each set of which is
constructed by eight adjacent subsets of the segmented photodiodes
Pd1 to Pd4 of FIG. 10. Then, output lines of the eight adjoining
segmented photodiodes in each set are connected together. The eight
connected output lines in each set are also connected to eight
connected output lines of corresponding segmented photodiodes in
the other sets. With this arrangement, the resolution of the scale
slit is made 1/8 of the reference resolution.
[0051] As described above, in the present embodiment, plural sets
of the segmented photodiodes are arranged, each set of which is
constructed by the number n (n: positive integer) of the adjacent
photodetectors of FIG. 10. Therefore, the slit pitch of the scale
slit can be made 4n-fold of the arrangement pitch of the segmented
photodiodes by connecting together the output lines of the number n
of adjacent segmented photodetectors and connecting together output
lines of the corresponding segmented photodetectors among the sets
thereof.
[0052] In brief, the present embodiment can cope with the scale
slit of which the resolution is 1/n of the reference resolution by
directly using the photodetector for an optical encoder shown in
FIG. 10.
[0053] Second Embodiment
[0054] The present embodiment is related to a photodetector for an
optical encoder where two segmented photodiode arrays are arranged
in parallel, each array being constituted by arranging plural sets
of segmented photodiodes, each set of which is constructed by four
adjoining segmented photodiodes Pd1 to Pd4, and where phases of the
arrays are mutually shifted by one half the arrangement pitch of
the segmented photodiodes Pd. The photodetector for an optical
encoder is capable of coping with a plurality of resolutions of a
scale slit by changing the number of sets of the segmented
photodiodes and changing connection between the segmented
photodiodes.
[0055] In the above case, the change of connection between the
segmented photodiodes is achieved by changing a plurality of kinds
of masks prepared and used in the forming process of connection
wiring.
THIRD EXAMPLE
[0056] FIGS. 4A to 4D show diagrams of the arrangement and wiring
of segmented photodiodes (FIG. 4A), the slit pitch (FIG. 4B), the
segmented photodiode outputs (FIG. 4C) and the digitalized outputs
(FIG. 4D) with relation to a photodetector for an optical encoder
capable of coping with a scale slit of which the resolution is
2-fold of the reference resolution.
[0057] In this photodetector for an optical encoder, a first
segmented photodiode array is formed by arranging in series plural
sets of the segmented photodiodes constructed by the segmented
photodiodes Pd1 to Pd4 shown in FIG. 10 so as to level variations
in the quantity of light from the light source. Likewise, a second
segmented photodiode array is formed by arranging in series plural
sets of the segmented photodiodes constructed by the segmented
photodiodes Pd1 to Pd4 of FIG. 10. Then, the first segmented
photodiode array and the second segmented photodiode array are
arranged in parallel with their phases mutually shifted by one half
the arrangement pitch of the segmented photodiodes.
[0058] Then, with regard to the connection between the segmented
photodiodes, the output lines of every other segmented photodiodes
of the first segmented photodiode array are connected together, and
the output lines of the remaining segmented photodiodes are
connected together. Likewise, the output lines of every other
segmented photodiodes of the second segmented photodiode array are
connected together, and the output lines of the remaining segmented
photodiodes are connected together. Then, the slit length L of the
scale slit is made roughly equal to the total width W of the first
and second segmented photodiode arrays arranged in parallel or
sufficiently long so that incident light is not obstructed.
[0059] Thus, as one set of segmented photodiodes to function as the
segmented photodiodes Pd1, Pd2, Pd3 and Pd4 of FIG. 10, there are
two adjoining segmented photodiodes Pd1 and Pd2 of the first
segmented photodiode array and two adjoining segmented photodiodes
Pd1' and Pd2' of the second segmented photodiode array, which
opposes to the fist segmented photodiode array while being shifted
by one half the arrangement pitch. Therefore, as shown in FIGS. 4A
and 4B, the slit pitch of the scale slit can be made 2-fold of the
arrangement pitch (PD pitch) of the segmented photodiodes Pd. That
is, the resolution of the scale slit can be made 2-fold of the
reference resolution.
[0060] As described above, in the present example, plural sets of
segmented photodiodes are arranged, each set of which is
constructed by a pair of bisected ones of the segmented photodiodes
of the photodetector for an optical encoder shown in FIG. 10, which
are opposed to each other with their phases shifted by one half the
arrangement pitch. Then, the output lines of the corresponding
segmented photodiodes are connected together among the sets of
photodetectors. Further, the slit length L of the scale slit is
made roughly equal to the total width W of the two segmented
photodiodes opposed to each other. Therefore, the resolution of the
scale slit can be made 2-fold of the reference resolution.
[0061] That is, according to the present example, the resolution of
the scale slit can be made 2-fold of the reference resolution by
changing the arrangement and wiring of the segmented photodiodes
without changing the configuration of the segmented photodiodes of
FIG. 10, and this arrangement can cope with various resolutions of
the code disk or the scale slit easily at low cost.
FOURTH EXAMPLE
[0062] The present example is related to a photodetector for an
optical encoder capable of coping with various resolutions of a
scale slit by changing the connection between the segmented
photodiodes of the third example.
[0063] In the photodetector for an optical encoder shown in FIGS.
5A to 5D, the output lines of two segmented photodiodes Pd1 and
Pd1' are connected together, which photodiodes are opposed to each
other with their phases shifted by one half the arrangement pitch
in the first segmented photodiode array and the second segmented
photodiode array as in the case with the third example.
[0064] That is, as one set of segmented photodiodes to function as
the segmented photodiodes Pd1, Pd2, Pd3 and Pd4 of FIG. 10, there
are four adjoining segmented photodiodes Pd1 to Pd4 of the first
segmented photodiode array and four adjoining segmented photodiodes
Pd1' to Pd4' of the second segmented photodiode array, which is
opposed to the first segmented photodiode array while being shifted
by one half the arrangement pitch. Then, these output lines are
connected to the corresponding segmented photodiodes among the sets
of photodetectors.
[0065] In this case, as shown in FIGS. 5A and 5B, the slit pitch of
the scale slit can be made 4-fold of the arrangement pitch of
segmented photodiodes Pd, and the resolution of the scale slit can
be made equal to the reference resolution.
[0066] In the case of a photodetector for an optical encoder as
shown in FIGS. 6A to 6D, output lines of two adjoining segmented
photodiodes Pd1 and Pd2 in the first segmented photodiode array are
connected to a output line of one segmented photodiode Pd1' in the
second segmented photodiode array, and vice versa, Pd1' of which is
opposed to the first segmented photodiode array while being shifted
by one half the arrangement pitch of the two segmented photodiodes
Pd1 and Pd2.
[0067] In the above case, the output lines of two adjoining
segmented photodiodes and one opposite segmented photodiode are
connected together, the selection of which are alternately changed
between the first segmented photodiode array and the second
segmented photodiode array.
[0068] That is, as one set of segmented photodiodes to function as
the segmented photodiodes Pd1, Pd2, Pd3 and Pd4 of FIG. 10, there
are arranged the adjoining six segmented photodiodes in the first
segmented photodiode array and the adjoining six segmented
photodiodes in the second segmented photodiode array, which is
opposed to the first segmented photodiode array while being shifted
by one half the arrangement pitch, as shown in FIG. 6A. Then, these
output lines are connected to the corresponding segmented
photodiodes among the sets of photodetectors.
[0069] In this case, as shown in FIGS. 6A and 6B, the slit pitch of
the scale slit can be made 6-fold of the arrangement pitch of the
segmented photodiodes Pd, and the resolution of the scale slit can
be made 2/3 of the reference resolution.
[0070] In the case of a photodetector for an optical encoder as
shown in FIGS. 7A to 7D, output lines of two adjoining segmented
photodiodes Pd1 and Pd2 of the first segmented photodiode array are
connected to output lines of two segmented photodiodes Pd1' and
Pd2' of the second segmented photodiode array, which are opposed to
the segmented photodiodes Pd1 and Pd2 while being shifted by one
half the arrangement pitch.
[0071] That is, as one set of segmented photodiodes to function as
the segmented photodiodes Pd1, Pd2, Pd3 and Pd4 of FIG. 10, there
are arranged adjoining eight segmented photodiodes of the first
segmented photodiode array and adjoining eight segmented
photodiodes of the second segmented photodiode array, which is
opposed to the first segmented photodiode array while being shifted
by one half the arrangement pitch. Then, these output lines are
connected to the corresponding segmented photodiodes among the sets
of photodetectors.
[0072] In this case, as shown in FIGS. 7A and 7B, the slit pitch of
the scale slit can be made 8-fold of the arrangement pitch of the
segmented photodiodes Pd, and the resolution of the scale slit can
be made 1/2 of the reference resolution.
[0073] In the present embodiment, as described above, plural sets
of segmented photodiodes are adjacently arranged, each set of which
is constructed by two arrays of segmented photodiodes each array of
which having n/2 photodetectors for an optical encoder of FIG. 10
and which are opposed to each other with their phases shifted by
one half the arrangement pitch. The slit length of the scale slit
is made roughly equal to or sufficiently longer than the total
length of two segmented photodiodes that are opposed to each
other.
[0074] Therefore, the slit pitch of the scale slit can be made
2n-fold of the arrangement pitch of the segmented photodiodes by
connecting together the output lines of n segmented photodiodes
opposing each other in each set and connecting together the output
lines of the corresponding segmented photodiodes among the sets of
photodetectors.
[0075] That is, the present embodiment can cope with the scale slit
of which the resolution is 2/n of the reference resolution by
directly using the photodetector for an optical encoder of FIG. 10
and cope with a scale slit of a resolution more various (2-fold)
than that of the first embodiment.
[0076] Third Embodiment
[0077] The present embodiment is related to a photodetector for an
optical encoder in which a wide constant gap is provided between
photodiodes. The wide constant gap is formed by not providing
wiring for the segmented photodiodes located at both ends in the
case that the number of adjoining segmented photodiodes, each of
which generates an output corresponding to one phase and output
lines of which are connected together, is not smaller than three as
shown in FIGS. 2A and 3A in the second example of the first
embodiment.
[0078] In the above case, the change of connection between the
segmented photodiodes for obtaining the gap is achieved by changing
a plurality of kinds of masks prepared to be used in the forming
process of the connection wiring.
FIFTH EXAMPLE
[0079] FIG. 8A shows a photodetector for an optical encoder under
modification of the second example, where the number of segmented
photodiodes is "4", each of which form an output signal
corresponding to one phase as stated in the first embodiment, and
where the segmented photodiodes Pd1 and Pd4 are not wired which are
located at both ends of the segmented photodiodes and only the
output lines of the segmented photodiode Pd2 and Pd3 located inside
are connected together. Further, these output lines are connected
to the corresponding segmented photodiodes among the sets of
photodetectors.
[0080] With this arrangement, a wide constant gap can be obtained
between the segmented photodiodes that constitute each phase.
Thereby, the influence of a leakage current can be reduced to
improve the signal-to-noise ratio, which current becomes a noise
against the signal current from the segmented photodiodes that
constitute respective phases.
[0081] FIG. 9A shows an photodetector for an optical encoder under
modification of the fourth example, where the number of segmented
photodiodes is "3", each of which forms an output signal
corresponding to one phase in the second embodiment, and where two
adjoining segmented photodiodes Pd1 and Pd2 are not wired, which
are located on one segmented photodiode array side among three
segmented photodiodes that constitute each phase (that is, the
photodiodes Pd1 and Pd2 are located outside among three segmented
photodiodes), and only one segmented photodiode Pd1' is wired,
which is located on the other segmented photodiode array side (that
is, the segmented photodiode Pd1' is located inside). Further,
these output lines are connected to the corresponding segmented
photodiodes among the sets of photodetectors.
[0082] Thus, the wide prescribed gap is obtained between the
segmented photodiodes that constitute each phase, and the influence
of crosstalk between phases is reduced, which allows the
signal-to-noise ratio to be improved.
[0083] In the present embodiment, the influence of the noise
component can be reliably reduced by grounding the output terminals
of all the segmented photodiodes that are not wired.
[0084] Moreover, in the second embodiment, the number of segmented
photodiode arrays is "2", which are arranged in parallel with their
phases mutually shifted by one half the arrangement pitch. However,
the present invention is not limited to this. It is also possible
to arrange three or more segmented photodiode arrays in
parallel.
[0085] Moreover, if each example of the first embodiment is
combined with each example of the second embodiment, the combined
arrangement can cope with scale slits of more various
resolutions.
[0086] Moreover, in each of the above-stated embodiments, the
plurality of sets of segmented photodiodes are arranged which
function as the segmented photodiodes Pd1, Pd2, Pd3 and Pd4 of FIG.
10 in order to level variations in the quantity of light from the
light source. However, even one set of the segmented photodiodes
makes it possible to produce the effects intended by the present
invention.
[0087] Moreover, the above-stated embodiments describe as examples
the scale slit having the rectangular slits and the photodetector
having the rectangular segmented photodiodes that conform to the
slits. However, it is needless to say that the present invention
may be applied to the case where a code disk having sectorial slits
and a photodetector for an optical encoder having segmented
photodiodes of a configuration that conforms to the sectorial
slits.
[0088] Moreover, in each of the above-stated embodiments, the
change of connection between the segmented photodiodes is achieved
by changing the mask used in the forming process of the connection
wiring. However, it is also possible to achieve the change of
connection between the segmented photodiodes by adjusting the metal
wiring with use of laser trimming.
[0089] Furthermore, it is also possible to change the arrangement
pitch (resolution) of the photodiode by changing the number of
connected segmented photodiodes with use of switching means having
a control terminal of a transistor or the like. In this case, the
segmented photodiodes, the output lines of which are connected
together, are made switch able, and an external control signal in
accordance with the resolution of the code disk or the scale slit
is used for the switching means at the time of the change of the
number in the photodiodes.
[0090] The invention being thus described, it will be obvious that
the invention may be varied in many ways. Such variations are not
be regarded as a departure from the spirit and scope of the
invention, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of
the following claims.
* * * * *