Beam position detector having a photodetection unit

Details Beam position detector having a photodetection unit Beam position detector having a photodetection unit

1998-10-28

2002-01-08

Le, Que T. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

C250S208100, C356S004080

Reexamination Certificate

active

06337473

ABSTRACT:

BACKGROUND OF THE INVENTION
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.
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.
Now, description will be given on a laser survey system referring to FIG.
6
.
In this figure, reference numeral
1
represents a rotary laser irradiating apparatus, and
2
represents a beam position detector.
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.
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.
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.
Next, description will be given on the beam position detector
2
.
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.
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.
When the laser beam
4
scans over the photodetection unit
5
, lengths L
1
and L
2
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: L
1
=L
2
. 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: L
1
<L
2
.
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.
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.
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.
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 L
2
′, exempting the portion of the shadow
13
, and this is shorter than the length of the line segment L
2
, 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
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.
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

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