U.S. patent application number 09/181255 was filed with the patent office on 2001-11-29 for beam position detector having a photodetection unit.
Invention is credited to YAMAZAKI, TAKAAKI, YOSHINO, KEN-ICHIRO.
Application Number | 20010045507 09/181255 |
Document ID | / |
Family ID | 18175399 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010045507 |
Kind Code |
A1 |
YAMAZAKI, TAKAAKI ; et
al. |
November 29, 2001 |
BEAM POSITION DETECTOR HAVING A PHOTODETECTION UNIT
Abstract
A beam position detector, which comprises a photodetection unit
for receiving a laser beam and issuing a signal corresponding to
photodetection amount, wherein said photodetection unit has a first
photoelectric conversion unit and a second photoelectric conversion
unit and width of said first photoelectric conversion unit is
gradually decreased in positive position detecting direction, and
width of said second photoelectric conversion unit is gradually
increased in positive position detecting direction, and scanning
position of the laser beam is detected by comparing the output
value of said first photoelectric conversion unit with the output
value of said second photoelectric conversion unit.
Inventors: |
YAMAZAKI, TAKAAKI;
(TOKYO-TO, JP) ; YOSHINO, KEN-ICHIRO; (TOKYO-TO,
JP) |
Correspondence
Address: |
HENRY C NIELDS
NIELDS & LEMACK
176 E MAIN STREET SUITE 8
WESTBORO
MA
01581
|
Family ID: |
18175399 |
Appl. No.: |
09/181255 |
Filed: |
October 28, 1998 |
Current U.S.
Class: |
250/206.1 |
Current CPC
Class: |
G01C 15/006
20130101 |
Class at
Publication: |
250/206.1 |
International
Class: |
G01C 021/02; G01C
021/24 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 1997 |
JP |
325310/1997 |
Claims
What we claim are:
1. A beam position detector, comprising a photodetection unit for
receiving a laser beam and issuing a signal corresponding to
photodetection amount, wherein said photodetection unit is divided
to divided portions symmetrical to each other by a division line
running perpendicularly with respect to position detecting
direction, said divided portions are further subdivided to a
plurality of subdivided sectors, some of the subdivided sectors of
one of the divided portions and some of the subdivided sectors of
the other of the divided portions constitute a first photoelectric
conversion unit, the rest of the subdivided sectors of one of the
divided portions and the rest of the subdivided sectors of the
other of the divided portions constitute a second photoelectric
conversion unit, and width of said first photoelectric conversion
unit is gradually decreased in positive position detecting
direction, and width of said second photoelectric conversion unit
is gradually increased in positive position detecting
direction.
2. A beam position detector, comprising a photodetection unit for
receiving a laser beam and issuing a signal corresponding to
photodetection amount, wherein said photodetection unit is divided
to divided portions symmetrical to each other by a division line
running perpendicularly with respect to position detecting
direction, said divided portions are further subdivided to a
plurality of subdivided sectors, at least one of the subdivided
sectors of one of the divided portions has a geometrical form
having a part of said division line as a base thereof and having a
portion with width thereof gradually decreased in positive position
detecting direction, and at least one of the subdivided sectors of
the other of the divided portions has said base in common and has a
geometrical form having width thereof gradually decreased in
negative position detecting direction, wherein said geometrical
form having width thereof gradually decreased in positive position
detecting direction of one of the divided portions and said
geometrical forms except the forms having width thereof gradually
decreased in negative position detecting direction of the other of
the divided portions constitute a first photoelectric conversion
unit, said geometrical form with width thereof gradually decreased
in negative position detecting direction of the other of said
divided portions and geometrical forms except the forms having
width thereof gradually decreased in positive position detecting
direction of one of said divided portions constitute a second
photoelectric conversion unit, and width of said first
photoelectric conversion unit is gradually decreased in positive
position detecting direction, and width of said second
photoelectric conversion unit is gradually increased in positive
position detecting direction.
3. A beam position detector according to claim 2, wherein said
division line is further divided so that said base is equal to the
remaining part of said division line except said base.
4. A beam position detector according to claim 2, wherein divided
forms of two divided portions are symmetrical to each other with
respect to said division line.
5. A beam position detector according to claim 2, wherein said
photodetection unit has a symmetrical line running perpendicularly
to said division line and said divided forms are symmetrical to
each other with respect to said symmetrical line.
6. A beam position detector according to claim 2, wherein variation
amount of width of said first photoelectric conversion unit and
variation amount of width of said second photoelectric conversion
unit have higher change ratio near said division line.
7. A beam position detector according to claim 2, wherein the
geometrical form having a part of said division line as a base
thereof and having a portion gradually decreased in position
detecting direction has two divided line segments in the central
portion of said division line divided into four line segments with
equal length as a base thereof.
8. A beam position detector according to claim 2, wherein said
division line is divided into four divided segments with equal
length, and said two divided portions have respectively a
geometrical form having two central divided line segments each as a
base thereof and with width thereof gradually decreased in position
detecting direction and two geometrical forms having a divided line
segment on each side as a base thereof and with width thereof
gradually decreased in position detecting direction, wherein said
first photoelectric conversion unit comprises two geometrical forms
each on one side and having width thereof gradually decreased in
positive position detecting direction of one of the divided
portions and the remaining part of the portion except said two
geometrical forms and having width thereof gradually decreased in
negative position detecting direction of the other of the divided
portions, and said second photoelectric conversion unit comprises
the remaining part of said portion except two geometrical forms
each on one side and having width thereof gradually decreased in
positive position detecting direction of one of said divided
portions and two geometrical forms one on each side and having
width thereof gradually decreased in negative position detecting
direction of the other of the divided portions.
9. A beam position detector according to claim 2, wherein two or
more geometrical forms each having a part of said division line as
a base thereof and having a portion with width thereof gradually
decreased in position detecting direction are formed on each of the
divided portions, said division line is equally divided to sectors
in multiple number of 4, and said geometrical form having a portion
with width thereof gradually decreased in said position detecting
direction has two divided line segments for every two other divided
line segments except the one divided line segment on each end of
said division line as a base thereof.
10. A beam position detector according to claim 2, wherein there
are further provided a signal processing unit for detecting a light
beam incident position based on a signal from said photodetection
unit and a display unit for displaying information relating to
projecting position of the laser beam based on a signal from said
signal processing unit.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a beam position detector
for receiving a laser beam from a rotary laser irradiating
apparatus, which projects the laser beam by rotary irradiation, and
for displaying a photodetecting position.
[0002] In the field of civil engineering and architectural
engineering, a laser survey system is used to form a reference
plane. The laser survey system comprises a rotary laser irradiating
apparatus and a beam position detector, and a laser beam is
projected for rotary scanning from the rotary laser irradiating
apparatus. By the laser beam, a reference plane is formed, and a
scanning position of the laser beam is detected by the beam
position detector.
[0003] Now, description will be given on a laser survey system
referring to FIG. 6.
[0004] In this figure, reference numeral 1 represents a rotary
laser irradiating apparatus, and 2 represents a beam position
detector.
[0005] The rotary laser irradiating apparatus 1 is installed on a
tripod (not shown). The rotary laser irradiating apparatus 1 has a
rotator 3 on its upper portion. From the rotator 3, a laser beam 4
is projected in horizontal direction and is rotated for total
circumferential scanning. On the rotary laser irradiating apparatus
1, an operation panel 9 for defining leveling operation, scanning
speed of the laser beam and range of scanning, etc. and for
operating the rotary laser irradiating apparatus 1 is provided.
[0006] The beam position detector 2 comprises a photodetection unit
5 for detecting the laser beam and a display unit 6 for displaying
a photodetecting position. On each of the lateral ends of the beam
position detector 2, a notch 7 is formed.
[0007] At an irradiating position of the laser beam 4 on wall
surface, for example, the beam position detector 2 is supported.
The photodetection unit 5 detects a passing position when the laser
beam passes through. The display unit 6 notifies that the
irradiating position of the laser beam 4 with respect to the beam
position detector 2 is adequate based on the results of detection
by the photodetection unit 5. If the position is deviated, it
notifies a direction of deviation or a direction to be corrected by
a display pattern 8. In case the position of the beam position
detector 2 is adequate and not deviated, a mark is put using the
notch 7. The mark thus formed serves as an index for a reference
position.
[0008] Next, description will be given on the beam position
detector 2.
[0009] As shown in FIG. 7(A) and FIG. 7(B), the photodetection unit
5 of the beam position detector 2 is divided to a first
photoelectric conversion unit 10 and a second photoelectric
conversion unit 11. The first photoelectric conversion unit 10 and
the second photoelectric conversion unit 11 are both designed in
triangular shape and are at positions of point symmetry to each
other.
[0010] Referring to FIG. 7(A) and FIG. 7(B), description will be
given now on photodetecting status on the photodetection unit 5 and
further on scanning position detecting status of the laser
beam.
[0011] When the laser beam 4 scans over the photodetection unit 5,
lengths L1 and L2 of line segments, along which the laser beam 4
goes across the first photoelectric conversion unit 10 and the
second photoelectric conversion unit 11, vary according to vertical
position of the photodetection unit 5. If the laser beam 4 goes
across the graphical center of the photodetection unit 5, the line
segments are given as: L1=L2. If the scanning position of the laser
beam 4 is deviated from the graphical center of the photodetection
unit 5, e.g. in case it is lower than the graphical center, the
following relationship exists: L1<L2.
[0012] Photodetection amount (or received light quantity) of each
of the first photoelectric conversion unit 10 and the second
photoelectric conversion unit 11 is proportional to the length of
the line segment, along which the laser beam 4 is projected, and
output value of each of the first photoelectric conversion unit 10
and the second photoelectric conversion unit 11 is proportional to
the photodetection amount respectively. By comparing signal level
of relative ratio of the output value from each of the first
photoelectric conversion unit 10 and the second photoelectric
conversion unit 11, it is possible to determine the scanning
position of the laser beam 4 with respect to the photodetection
unit 5. As described above, in case the scanning position of the
laser beam 4 is deviated from and lower than the graphical center
of the photodetection unit 5, and if the first maximum
photodetection amount is compared with the first maximum
photodetection amount, output value from the first photoelectric
conversion unit 10 is lower, and output value from the second
photoelectric conversion unit 11 is higher.
[0013] By comparing the output value of the first photoelectric
conversion unit 10 with that of the second photoelectric conversion
unit 11, it is possible to determine the scanning position of the
laser beam 4. Also, according to the display on the display unit 6
as described above, a position to set the beam position detector 2
is also found.
[0014] As described above, in the beam position detector 2, the
difference of the photodetection amount between the first
photoelectric conversion unit 10 and the second photoelectric
conversion unit 11 (i.e. the difference between the first maximum
photodetection value and the second maximum photodetection value)
is compared, and the scanning position of the laser beam with
respect to the photodetection unit 5 is detected. In this way, by
detecting relative value of the output of the photoelectric
conversion units, it is possible to accurately detect the scanning
position even when intensity of the laser beam itself is low and
regardless of the size of diameter of the laser beam.
[0015] However, as shown in FIG. 8(A), the photodetection unit 5 is
usually placed at retreated position with respect to a
photodetection window 12 of the beam position detector 2. There is
no problem in case the laser beam 4 is projected perpendicularly to
the photodetection unit 5, but if the laser beam 4 enters obliquely
as shown in FIG. 8(A) or FIG. 8(B), a shadow 13 is formed by the
beam position detector 2 itself. In case the laser beam 4 is
scanned with the shadow 13 formed in this way, the second
photoelectric conversion unit 11 does not detect the laser beam 4
in the shadow 13. As a result, the length of line segment of the
laser beam 4 detected by the second photoelectric conversion unit
11 is turned to L2', exempting the portion of the shadow 13, and
this is shorter than the length of the line segment L2, along which
the beam actually is projected. Therefore, this means that relative
value of the photodetection amount extensively varies between the
first photoelectric conversion unit 10 and the second photoelectric
conversion unit 11. This leads to the decrease of the accuracy to
detect the scanning position of the laser beam 4 by the beam
position detector 2.
SUMMARY OF THE INVENTION
[0016] It is an object of the present invention to provide a beam
position detector, by which it is possible to perform accurate
position detection without being influenced by the shadow even when
a laser beam is not projected perpendicularly toward the
photodetection unit.
[0017] To attain the above object, the beam position detector,
according to the present invention comprises a photodetection unit
for receiving a laser beam and issuing a signal corresponding to
photodetection amount, wherein said photodetection unit is divided
to divided portions symmetrical to each other by a division line
running perpendicularly with respect to position detecting
direction, said divided portions are further subdivided to a
plurality of subdivided sectors, some of the subdivided sectors of
one of the divided portions and some of the subdivided sectors of
the other of the divided portions constitute a first photoelectric
conversion unit, the rest of the subdivided sectors of one of the
divided portions and the rest of the subdivided sectors of the
other of the divided portions constitute a second photoelectric
conversion unit, and width of said first photoelectric conversion
unit is gradually decreased in positive position detecting
direction, and width of said second photoelectric conversion unit
is gradually increased in positive position detecting direction.
Also, the present invention provides the beam position detector
comprises a photodetection unit for receiving a laser beam and
issuing a signal corresponding to photodetection amount, wherein
the photodetection unit is divided to divided portions symmetrical
to each other by a division line running perpendicularly with
respect to position detecting direction, the divided portions are
further subdivided to a plurality of subdivided sectors, at least
one of the subdivided sectors of one of the divided portions has a
geometrical form having a part of the division line as a base
thereof and having a portion with width thereof gradually decreased
in positive position detecting direction, and at least one of the
subdivided sectors of the other of the divided portions has the
base in common and has a geometrical form having width thereof
gradually decreased in negative position detecting direction,
wherein the geometrical form having width thereof gradually
decreased in positive position detecting direction of one of the
divided portions and the geometrical forms except the forms having
width thereof gradually decreased in negative position detecting
direction of the other of the divided portions constitute a first
photoelectric conversion unit, the geometrical form with width
thereof gradually decreased in negative position detecting
direction of the other of the divided portions and geometrical
forms except the forms having width thereof gradually decreased in
positive position detecting direction of one of the divided
portions constitute a second photoelectric conversion unit, and
width of the first photoelectric conversion unit is gradually
decreased in positive position detecting direction, and width of
the second photoelectric conversion unit is gradually increased in
positive position detecting direction. Further, the present
invention provides the beam position detector as described above,
wherein the division line is further divided so that the base is
equal to the remaining part of the division line except the base.
Also, the present invention provides the beam position detector as
described above, wherein divided forms of two divided portions are
symmetrical to each other with respect to the division line. The
present invention further provides the beam position detector as
described above, wherein the photodetection unit has a symmetrical
line running perpendicularly to the division line and the divided
forms are symmetrical to each other with respect to a symmetrical
line. The invention further provides the beam position detector as
described above, wherein variation amount of width of the first
photoelectric conversion unit and variation amount of width of the
second photoelectric conversion unit have a higher change ratio
near the division line. The present invention also provides the
beam position detector, wherein the geometrical form having a part
of the division line as a base thereof and having a portion
gradually decreased in position detecting direction has two divided
line segments in the central portion of the division line divided
into four line segments with equal length as a base thereof. The
present invention also provides the beam position detector as
described above, wherein the division line is divided into four
divided segments with equal length, and the two divided portions
have respectively a geometrical form having two central divided
line segments each as a base thereof and with width thereof
gradually decreased in position detecting direction and two
geometrical forms having a divided line segment on each side as a
base thereof and with width thereof gradually decreased in position
detecting direction, wherein the first photoelectric conversion
unit comprises two geometrical forms each on one side and having
width thereof gradually decreased in positive position detecting
direction of one of the divided portions and the remaining part of
the portion except the two geometrical forms and having width
thereof gradually decreased in negative position detecting
direction of the other of the divided portions, and the second
photoelectric conversion unit comprises the remaining part of the
portion except two geometrical forms each on one side and having
width thereof gradually decreased in positive position detecting
direction of one of the divided portions and two geometrical forms
one on each side and having width thereof gradually decreased in
negative position detecting direction of the other of the divided
portions. The present invention further provides the beam position
detector as described above, wherein two or more geometrical forms
each having a part of the division line as a base thereof and
having a portion with width thereof gradually decreased in position
detecting direction are formed on each of the divided portions, the
division line is equally divided to sectors in multiple number of
4, and the geometrical form having a portion with width thereof
gradually decreased in the position detecting direction has two
divided line segments for every two other divided line segment
except the one divided line segment on each end of the division
line as a base thereof. Further, the present invention provides the
beam position detector as described above, wherein there are
further provided a signal processing unit for detecting a light
beam incident position based on a signal from the photodetection
unit and a display unit for displaying information relating to the
projecting position of the laser beam based on a signal from the
signal processing unit. Scanning position of the laser beam is
detected by comparing the output value of the first photoelectric
conversion unit with the output value of the second photoelectric
conversion unit. Even when a shadow is formed on the photodetection
unit, it is formed evenly over the first photoelectric conversion
unit and the second photoelectric conversion unit, and it does not
adversely affect the detection of the center position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a front view of a beam position detector according
to an embodiment of the present invention;
[0019] FIG. 2 is a drawing to explain a first aspect of a
photodetection unit in the beam position detector;
[0020] FIG. 3 is a block diagram of beam position detection of the
beam position detector of the laser survey system;
[0021] FIG. 4(A) and FIG. 4(B) each represents a drawing to show a
second aspect of the photodetection unit in the beam position
detector;
[0022] FIG. 5 is a drawing to explain a third aspect of the
photodetection unit of the beam position detector;
[0023] FIG. 6 is a perspective view of a laser survey system
provided with the beam position detector;
[0024] FIG. 7 represents drawings to show operation of laser beam
position detection of a conventional example. FIG. 7(A) shows
positional relationship of a first photoelectric conversion unit
and a second photoelectric conversion unit, and FIG. 7(B) is a
diagram showing output values from the first photoelectric
conversion unit and the second photoelectric conversion unit;
and
[0025] FIG. 8(A), FIG. 8(B) and FIG. 8(C) each represents a drawing
to explain the case where a shadow is formed in a conventional type
photodetection unit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] In the following, description will be given on embodiments
of the present invention referring to the attached drawings.
[0027] FIG. 1 represents a beam position detector 2 according to
the present invention. In FIG. 1, the same component as in FIG. 6
is referred by the same symbol.
[0028] A photodetection unit 5 to be provided in the beam position
detector 2 is shown in FIG. 2. The photodetection unit 5 is divided
symmetrically in vertical direction. Each of an upper portion and a
lower portion of the photodetection unit 5 is further subdivided
into a plurality of sectors, and the subdivided sectors are
symmetrically arranged in horizontal direction.
[0029] Various divided forms can be designed. Basically, the
photodetection unit, which receives a laser beam and issues a
signal corresponding to the photodetection amount (received light
quantity), is divided symmetrically with respect to a division line
which is approximately in parallel to laser scanning direction, and
the divided portion is further subdivided into a plurality of
sectors. At least one of the subdivided sectors in one of the
divided portions has a geometrical form having a part of the above
division line as its base and with its width gradually decreased in
positive position detecting direction (+y direction in FIG. 2), and
at least one of the subdivided sectors in the other of the divided
portions has a common base with the above form and has a
geometrical form with its width gradually decreased in negative
position detecting direction (-y direction in FIG. 2). The base as
described above is equal in length to the remaining part of the
above division line.
[0030] The form of one of the subdivided sectors with its width
gradually decreased in positive position detecting direction and
the subdivided remaining part of the other of the subdivided
sectors constitute a first photoelectric conversion unit. Further,
the form of the other of the subdivided sectors with its width
gradually decreased in negative position detecting direction and
the remaining part of one of the subdivided sectors constitute a
second photoelectric conversion unit. The width of the first
photoelectric conversion unit is gradually decreased in a positive
direction perpendicular to the division line, and the width of the
second photoelectric conversion unit is gradually increased.
[0031] In the following, description will be given on an aspect of
division shown in FIG. 2.
[0032] First, the division of the upper portion will be
described.
[0033] A horizontal division line 15 dividing the photodetection
unit 5 to upper and lower portions is divided into four equal line
segments. The upper portion of the photodetection unit 5 is divided
to an erected triangle 16 having two divided line segments at the
central portion of the horizontal division line 15 as its base and
the center of the upper side of the photodetection unit 5 as its
vertex, and to inverted trapezoids 17 and 18, which are formed at
left and right of the erected triangle 16 respectively.
[0034] The lower portion of the photodetection unit 5 is
symmetrical to the upper portion. It is divided into three sectors,
i.e. an inverted triangle 19, which has two divided line segments
at the central portion as its base and has the center of the lower
side of the photodetection unit 5 as its vertex, and into erected
trapezoids 20 and 21 formed at left and right of the inverted
triangle 19 respectively.
[0035] The erected triangle 16 and the erected trapezoids 20 and 21
constitute a first photoelectric conversion unit 23 (hatched
portion in the figure), and the inverted triangle 19 and the
inverted trapezoids 17 and 18 constitute a second photoelectric
conversion unit 24(non-hatched portion in the figure).
[0036] Referring to FIG. 3, description will be given on a block
diagram for beam position detection of the beam position
detector.
[0037] A photodetection signal from the first photoelectric
conversion unit 23 is inputted to an amplifier 25. After being
amplified by the amplifier 25, it is inputted to a first peak hold
unit 27. At the first peak hold unit 27, a first maximum
photodetection amount is detected, and the detected first maximum
photodetection value is inputted to an arithmetic unit 29.
[0038] A photodetection signal from the second photoelectric
conversion unit 24 is inputted to an amplifier 26. After being
amplified by the amplifier 26, it is inputted to a second peak hold
unit 28. At the second peak hold unit 27, a second maximum
photodetection value is detected, and the detected second maximum
photodetection value is inputted to the arithmetic unit 29. At the
arithmetic unit 29, the first maximum photodetection value is
compared with the second maximum photodetection value. If there is
a deviation between the two values, one of display patterns 8a or
8c on the display unit 6 is turned on depending upon the condition
of deviation, and a direction is displayed, toward which the beam
position detector 2 should move. In case there is no deviation
between the first maximum photodetection value and the second
maximum photodetection value, a display pattern 8b is turned on,
and it is indicated that scanning position of the laser beam 4 is
adequate.
[0039] In case the laser beam 4 scans over the center of the
photodetection unit 5 in left-right direction (in horizontal
direction), output value from the first photoelectric conversion
unit 23 is made equal to output value from the second photoelectric
conversion unit 24. Further, if the laser beam 4 is moved in
vertical direction (i.e. in position detecting direction) with
respect to the photodetection unit 5, e.g. if it is moved downward
(in negative position detecting direction), the output value of the
first photoelectric conversion unit 23 is increased, and the output
value of the second photoelectric conversion unit 24 is
decreased.
[0040] If it is supposed that output value of the second
photoelectric conversion unit 24 is A, that the output value of the
first photoelectric conversion unit 23 is B, and that the height of
the photodetection unit 5 is L, positional displacement y (in
vertical direction from the center of the photodetection unit 5) of
the laser beam 4 scanning the photodetection unit 5 is given by the
following equation (1):
y=L.times.{A/(A+B)}-L/2
[0041] As described above, the output of the first photoelectric
conversion unit 23 is inputted to the arithmetic unit 29 via the
amplifier 25 and the first peak hold unit 27, and the output from
the second photoelectric conversion unit 24 is inputted to the
arithmetic unit 29 via the amplifier 26 and the second peak hold
unit 28. Then, these values are relatively compared by comparison
arithmetic operation using the arithmetic unit 29. Based on the
comparison arithmetic operation, the display unit 6 is driven.
[0042] It is now assumed that, in the photodetection unit 5 shown
in FIG. 2, a shadow 13 formed by the beam position detector 2
itself covers a portion "W" at right side of the photodetection
unit 5 in the figure. The shadow formed by the beam position
detector 2 runs in parallel to position measuring direction and
perpendicularly to scanning direction of the laser beam 4. Because
the first photoelectric conversion unit 23 and the second
photoelectric conversion unit 24 are symmetrical to each other with
respect to the horizontal division line 15, area of each region
invalidated by the shadow 13 is identical to each other in these
two units, and the condition of invalidation is also identical.
Further, at the central portion, which is the most important in
position detection, output value of the first photoelectric
conversion unit 23 is identical with that of the second
photoelectric conversion unit 24. Thus, regardless of whether the
shadow 13 is present or not, it is possible to accurately detect
the position of the center of the photodetection unit 5.
[0043] In case the scanning position of the laser beam 4 is
deviated from the graphical center of the photodetection unit 5,
e.g. in case it is lower (deviated in negative position detecting
direction) than the graphical center, the ratio of the output of
the second photoelectric conversion unit 24 is increased compared
with the case where the shadow 13 is not formed. However, there is
no change in the direction, in which the beam position detector 2
should be moved, and the display unit 6 is driven, and the display
pattern 8a is turned on. Accordingly, no trouble occurs in the
measurement.
[0044] FIG. 4(A) shows another aspect of the division to the upper
and the lower portions. In the aspect shown in FIG. 4(A), another
photodetection unit is added in horizontal direction to the
photodetection unit 5 shown in FIG. 2.
[0045] Description will be given now on the division of the upper
portion. The horizontal division line 15 dividing the
photodetection unit 5 to upper and lower portions is divided into
eight equal line segments, and its upper side is divided into four
equal line segments. The upper portion of the photodetection unit 5
is divided in such manner that two inverted trapezoids 31 and 32
are formed, each of which has a divided line segment of 1/8 of the
total length of the horizontal division line 15 each at left and
right respectively as its base and has a divided line segment of
1/4 each at left and right of the upper side of the photodetection
unit 5 as its upper side respectively, and that an inverted
trapezoid 33 is formed, which has the line segment of 1/4 at the
central portion of the horizontal division line 15 as its base and
has a divided line segment of 1/2 of the upper side of the
photodetection unit 5 as its upper side. Then, with the inverted
trapezoid 33 therebetween, two erected triangles 34 and 35 are
formed at left and right respectively, each of which has a divided
line segment of 1/4 of the horizontal division line as its base and
has its vertex at a position at 1/4 of total length from each end
of the upper side of the photodetection unit 5. Thus, the upper
portion of the photodetection unit 5 is divided to three inverted
trapezoids 31, 33 and 32 and two erected triangles 34 and 35.
[0046] The lower portion of the photodetection unit 5 is
symmetrical to the upper portion. That is, two erected trapezoids
36 and 37 are formed at left and right of the horizontal division
line 15, each having the divided line segment at 1/8 each at left
and right of the horizontal division line 15 as its upper side and
having the divided line segment at 1/4 at left and right of the
lower side of the photodetection unit 5 as its base. Further, an
erected trapezoid 38 is formed, which has the divided line segment
at 1/4 at the central portion of the horizontal division line 15 as
its upper side and has the divided line segment at 1/2 of the lower
side of the photodetection unit 5 as its base. With the erected
trapezoid 38 therebetween at left and right, two inverted triangles
39 and 40 are formed respectively, each of which has a divided line
segment of 1/4 of the horizontal division line 15 as its upper side
and has a vertex at a position at 1/4 from each of the lower side
of the photodetection unit 5. Thus, the lower portion of the
photodetection unit 5 is divided to three erected trapezoids 36, 38
and 37 and two inverted triangles 39 and 40.
[0047] The two erected triangles 34 and 35 and the three erected
trapezoids 36, 38 and 37 constitute a first photoelectric
conversion unit 23, and the inverted trapezoids 31, 33 and 32 and
the inverted triangles 39 and 40 constitute a second photoelectric
conversion unit 24.
[0048] In the present aspect of division, the number of subdivided
sectors on photodetection surface on the upper and the lower
portions is increased, and this means that the ratio of effective
portion to ineffective portion (i.e. the portion invalidated by the
shadow) is decreased. For example, in case the shadow 13 is formed
in FIG. 4 and if the number of subdivisions is many, the shadow 13
covers not only the inverted trapezoid 32 but also the erected
triangle 35. As a result, not only the output value of the second
photoelectric conversion unit 24 but also the output value of the
first photoelectric conversion unit 23 is decreased. Therefore,
compared with the case where the shadow covers only one of the
second photoelectric conversion unit 24 and the first photoelectric
conversion unit 23, variation of output ratio is reduced, and the
accuracy is improved.
[0049] The aspect of division shown in FIG. 4(B) is the same as
that of FIG. 4(A), while forms of vertical division lines are
different. Specifically, the vertical division lines to divide the
upper portion to the inverted trapezoids 31, 33 and 32 and the
erected triangles 34 and 35 are designed as curved lines. The
closer the vertical division lines approach the horizontal division
line 15, the less a gradient of the line becomes. That is, it is
designed in such manner that the closer it is to the horizontal
division line 15, the more the change ratio of the length of line
segment going across the inverted trapezoids 31, 33 and 32 and the
erected triangles 34 and 35 is increased. By designing in such
manner that the change ratio is increased near the horizontal
division line 15, it is possible to increase accuracy of detection
of the horizontal division line 15, i.e. accuracy of position
detection. The same applies to the lower portion, and detailed
description is not given here.
[0050] The vertical division line is not necessarily a curved line,
and it may be designed as a straight line that is adequately
bent.
[0051] FIG. 5 represents a third aspect of division. The horizontal
division line 15 is divided into four equal line segments, and the
upper portion of the photodetection unit 5 is divided to two
erected triangles 45 and 46, each having a divided line segment of
1/4 of total length of the horizontal division line 15 each at left
and right as its base, and having the center of the upper side of
the photodetection unit 5 as its vertex, an erected triangle 47
having two line segments each being 1/4 of the total length at the
central portion as its base, and two inverted triangles 48 and 49
at the ends. Also, the lower portion is divided to two inverted
triangles 50 and 51 each having a line segment of 1/4 of total
length of the horizontal division line 15 each at left and right as
its base and having the center of the upper side of the
photodetection unit 5 as its vertex, an inverted triangle 52 having
two line segments each being 1/4 of total length of the horizontal
division line at the center as its base, and two erected triangles
53 and 54 each at an end of the horizontal division line 15.
[0052] The two triangles 45 and 46 at left and right, the inverted
triangle 52 at the center, and the two erected triangles 53 and 54
at the ends constitute a first photoelectric conversion unit 23,
and the erected triangle 47, the two inverted triangles 48 and 49
at the ends and the two inverted triangles 50 and 51 constitute a
second photoelectric conversion unit 24.
[0053] Further, the number of divisions of each of the upper and
the lower portions is not limited to 3 divisions or 5 divisions,
but these portions may be divided into 7 or 9 portions, or more.
Also, the horizontal division line 15 need not be horizontal, and
it will suffice as far as it is in parallel to a scanning direction
of the laser beam.
[0054] As described above, it is possible according to the present
invention to attain a superb effect to accurately detect the
position of the laser beam even in case the laser beam obliquely
enters the beam position detector and a shadow is formed on the
photodetection surface.
* * * * *