Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1998-04-28
2001-06-19
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S577000, C250S231100, C356S249000, C356S139100, C033S366230
Reexamination Certificate
active
06248989
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tilt detecting device provided with an electric bubble tube, and in particular, to a tilt detecting device provided with a light transmission type electric bubble tube.
In case an equipment such a survey instrument is to be installed, which must be placed at a horizontal position, an electric bubble tube is used to detect tilting of the equipment. Description is given now on a conventional type tilt detecting device provided with the electric bubble tube, referring to FIG.
3
.
An electric bubble tube
1
comprises a light source
2
, a photoelectric conversion element (photodetector element)
3
, a photoelectric conversion element (photodetector element)
4
, and a bubble tube
5
, and tilt is detected according to a signal from the electric bubble tube
1
.
The light source
2
is placed under the bubble tube
5
in such a manner that the optical axis of the light source
2
runs perpendicularly to the axis of the bubble tube
5
. On the other side of the bubble tube
5
opposite to the light source
2
, a pair of photodetector elements
3
and
4
are arranged at symmetrical positions with respect to the optical axis of the light source
2
, the two elements being separated from each other by a predetermined spacing.
The light source
2
is driven by a light source driving unit
6
, and detection light
7
emitted from the light source
2
passes through the bubble tube
5
and reaches the photodetector elements
3
and
4
. Each of the photodetector elements
3
and
4
outputs detected photodetection electric current corresponding to the amount of detected light to a tilt detection control unit
19
. The tilt detection control unit
19
comprises a differential amplifier
8
and a control arithmetic unit
9
. The differential amplifier
8
amplifies a difference of electric current values of output signals from the photodetector elements
3
and
4
, performs current-voltage conversion, and outputs the result to the control arithmetic unit
9
. The control arithmetic unit
9
processes the signal from the differential amplifier
8
and calculates a tilt angle.
The detection light
7
emitted from the light source
2
transmits a portion containing only liquid
10
of the bubble tube
5
, but, in a portion containing an air bubble
11
, it is reflected by boundary surface between the air bubble
11
and the liquid
10
, and it is blocked. Therefore, amount of the detection light
7
entering the photodetector elements
3
and
4
varies according to the position of the air bubble
11
. Because the position of the air bubble
11
moves according to tilting, tilt is detected by finding a difference between the amount of the light received from the photodetector element
3
and that of the photodetector element
4
.
The tilt detecting device as described above is mounted in various types of survey instrument, e.g. a laser survey instrument. In the following, description will be given on general features of a laser survey instrument provided with a tilt detecting device referring to FIG.
4
and FIG.
5
.
In a laser survey instrument, a laser beam having directivity is projected in a horizontal direction, and an irradiation plane is formed by rotary irradiation. A photodetection unit (not shown) is positioned on the rotary irradiation plane so as to receive and detect the laser beam and the position of irradiation plane. Thus, a reference line or a reference plane can be obtained.
In the figure, reference numeral
14
represents a laser beam emitter. The laser beam emitter
14
is supported in such a manner that it can be tilted in all directions, and a rotator
15
rotatable around the optical axis of the laser beam emitter
14
is mounted on its head. On the laser beam emitter
14
, electric bubble tubes
16
and
17
as described above are mounted, and these bubble tubes run perpendicularly to two different horizontal directions. Further, a vertical tilt sensor
18
is disposed. The tilt sensor
18
, the electric bubble tubes
16
and
17
, and the tilt detection control unit
19
constitute together a tilt detecting device.
The rotator
15
deflects an emitted laser beam
21
toward a horizontal direction, and it is rotated by a scanning motor
22
, thus projecting the laser beam
21
by rotary irradiation.
Arms
23
and
24
(the arm
24
is not shown in the figure) are extended from the laser beam emitter
14
in two different horizontal directions running perpendicularly to each other. Tip of each of the arms
23
and
24
engages with a tilt mechanism.
The tilt mechanism comprises two sets of tilt driving units
25
and
26
(the tilt driving unit
26
is not shown) mounted with respect to the arms
23
and
24
respectively, and a tilt control unit (not shown) for controlling the tilt driving units
25
and
26
. Each of the tilt driving units
25
and
26
comprises a screw
27
extending in the direction of the optical axis of the laser beam emitter
14
, a nut
28
screwed with the screw
27
and in contact with tip of the arms
23
or
24
, and a tilt adjusting motor
32
for turning the screw
27
via gears
30
and
31
. In the figure, reference numeral
29
represents a focus adjusting device, which adjusts focal point of the laser beam
21
by moving a condenser lens
33
arranged in an optical path of the laser beam emitter
14
in the direction of the optical axis.
As shown in
FIG. 4
, the tilt detection control unit
19
comprises the differential amplifier
8
where photodetection signals from the photodetector elements
3
and
4
are inputted, and the control arithmetic unit
9
, which issues a control signal based on the signal from the differential amplifier
8
. Based on the control signal from the control arithmetic unit
9
, a driving circuit
34
drives the tilt adjusting motor
32
, and the optical axis of the laser beam emitter
14
is adjusted to a vertical direction or to a predetermined angle.
When the laser beam
21
is projected in a horizontal direction from the rotator
15
and the rotator
15
is rotated by the scanning motor
22
, an irradiation plane is formed. By setting the scanning position of the laser beam
21
to a predetermined position using a photodetection device, a reference plane can be obtained.
When the reference plane is obtained, the operating position in wide range can be easily determined. For example, this is applied in the setting of window position in interior operation of construction works or for land grading in civil engineering works.
However, the conventional type tilt detecting device as described above has the following disadvantages:
(1) Because the amount of light emitted from the light source
2
is temperature-dependent, the amount of emitted light varies when ambient temperature changes. This leads to the change of sensitivity in the angle detection and makes it difficult to perform accurate the angle detection.
(2) When external light enters, the difference of light amount entering the photodetector elements
3
and
4
at left and right is offset and is outputted from the differential amplifier
8
. This makes it difficult to perform accurate the tilt angle detection.
(3) Because offset and drift of the differential amplifier
8
are outputted as error, the tilt angle detection with high accuracy cannot be achieved. To perform the detection at high accuracy, it is necessary to use an amplifier with smaller values of offset and drift in the differential amplifier
8
. This means the use of expensive components and higher cost.
(4) Dark current is present in the photodetector elements
3
and
4
, and this emerges in the output as offset of the differential amplifier
8
. Because dark current is highly dependent on temperature, output of the detector is changed due to temperature fluctuation, and this leads to inaccurate detection of tilt angle.
(5) It is possible to increase S/N ratio by increasing the amount of the light emitted from the light source
2
and to reduce the influence of drift and offset. However, to avoid the influence of d
Kabushiki Kaisha Topcon
Le Que T.
Luu Thanh X.
Nields & Lemack
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