Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-05-04
2003-01-07
Epps, Georgia (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S370150, C348S207990, C348S033000
Reexamination Certificate
active
06504155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an infrared camera and an infrared camera system equipped with the infrared camera and a display unit for displaying image signals obtained by the infrared camera.
2. Description of the Prior Art
Infrared cameras are used for, for example, fire detection, invasion monitoring, and installation monitoring. Furthermore, as shown in
FIG. 7
, an infrared camera C is mounted on a moving object M, such as a vehicle, and is used for detecting an obstacle by obtaining and displaying images representing the front of the moving object M. In addition, an infrared camera C is mounted on the rear or side of a moving object and is used for, for example, detecting a following moving object or a side moving object or obstacle. Moreover, as shown in
FIG. 8
, a removable head-mounted helmet H equipped with an infrared camera C and display unit D for displaying images obtained by the infrared camera C is mounted on the head of a person, such as a firefighter, and is used for, for example, to detect a heat source, such as a fire, by supplying power to the infrared camera C and display unit D using a battery B.
FIG. 9
is a block diagram of a conventional infrared camera. In this figure, M is a subject; 1 is an infrared optical system;
2
is an imaging device located on the image-formed plane of the infrared optical system
1
;
3
is a device-temperature monitor thermally connected to the imaging device
2
;
4
is a direct-current bias power supply connected to the imaging device
2
;
5
is a device output-level setting circuit connected to the imaging device
2
;
6
is a driver circuit connected to the imaging device
2
;
7
is an amplifier connected to the imaging device
2
;
8
is an offset-level setting circuit connected to the amplifier
7
;
9
is a display processing circuit connected to the amplifier
7
;
10
is a sensitivity-correcting data memory connected to the display processing circuit
9
;
11
is a defect-correcting data memory connected to the display processing circuit
9
;
12
is a thermoelectric device thermally connected to the imaging device
2
;
13
is a device operating-temperature setting circuit;
14
is a power-supply circuit connected to the device-temperature monitor
3
, the device operating-temperature setting circuit
13
, and the thermoelectric device
12
. The sensitivity-correcting data memory
10
and defect-correcting data memory
11
are ROMs which have recorded and stored correction data at the time of the test and adjustment of a camera.
15
is a shutter located across an optical path between the infrared optical system
1
and the imaging device
2
;
16
is a timing-generating circuit connected to the driver circuit
6
, the display processing circuit
9
, and the shutter
15
;
17
is a device package for housing the imaging device
2
, the device-temperature monitor
3
, and the thermoelectric device
12
;
18
is an infrared window for transmitting infrared rays;
19
is an enclosure. The space sealed by the device package
17
and the infrared window
18
is held in a vacuum and a conventional technical example of such an implementation method can be found in Japanese Patent National Publication No. Hei 7-508384.
FIG. 10
shows the structure of the imaging device
2
. For the sake of simplicity, it is assumed that the number of pixels for the imaging device
2
is 2×2. In this figure,
20
-
23
are infrared-detecting devices;
24
-
27
are diodes;
28
-
32
are transistors;
33
is a horizontal scanning circuit;
34
is a vertical scanning circuit. The infrared-detecting devices
20
-
23
are, for example, microbolometers having a hollow structure described in Japanese Patent National Publication No. Hei 7-509057.
FIG. 11
shows the structure of the display processing circuit
9
. In this figure,
35
is an A/D converting circuit;
36
is an offset-correcting data memory;
37
is an offset-correcting circuit;
38
is a sensitivity-correcting circuit;
39
is a defect-correcting circuit;
40
is a D/A converting circuit.
Now, the operation will be described. When power is applied, the power-supply circuit
14
supplies the thermoelectric device
12
with power corresponding to the difference between the output of the device-temperature monitor
3
and that of the device operating-temperature setting circuit
13
and stabilizes the temperature of the imaging device
2
at a constant room temperature set by the device operating-temperature setting circuit
13
. This temperature is usually between 20 and 40° C. Next, clock signals generated by the timing-generating circuit
16
are sent to the imaging device
2
via the driver circuit
6
. The horizontal scanning circuit
33
and vertical scanning circuit
34
having received the clock signals supply bias currents depending on the output of the device output-level setting circuit
5
and on the characteristics of the transistor
32
from the direct-current bias power supply
4
to the infrared-detecting devices
20
-
23
, in order, by turning on the transistors
28
-
31
in order. The presence of the diodes
24
-
27
causes a bias current to flow to ground via a selected infrared-detecting device and the transistor
32
. Signals corresponding to the resistance value of each infrared-detecting device are output as a potential difference arising between the transistor
32
and the ground and are amplified by the amplifier
7
and are then input to the display processing circuit
9
.
The shutter
15
is temporarily closed and the output of the infrared-detecting devices
20
-
23
exposed to uniform infrared rays, that is to say, voltage corresponding to dispersion specific to the resistance values of the infrared-detecting devices
20
-
23
is converted to digital signals by the A/D converting circuit
35
and stored into the offset-correcting data memory
36
. Next, the shutter
15
is opened and infrared rays emitted from subject M are collected by the infrared optical system
1
and are transmitted through the infrared window
18
and then image-formed on the infrared-detecting devices
20
-
23
. This causes minute temperature rises in the infrared-detecting devices
20
-
23
of about a few millikelvin corresponding to the intensity of infrared rays emitted from subject M and their resistance values change individually. Under this condition, offset correction is performed in the offset-correcting circuit
37
by subtracting offset-correcting data for each infrared-detecting device.
The sensitivity-correcting data memory
10
stores data regarding dispersion of the sensitivity to a target temperature difference of each infrared-detecting device. Sensitivity correction is performed in the sensitivity-correcting circuit
38
by multiplying stored data for each infrared-detecting device. In addition, the defect-correcting data memory
11
stores the addresses of pixels having a sensitivity outside a prescribed range, that is to say, of defective pixels. The correction of a defective pixel is performed by consecutively using the output for the next pixel on the left side of the defective pixel. After the above correction, signals are converted by the D/A converting circuit
40
to analog video signals, which are output.
A conventional infrared camera has the above structure. Therefore, when it is used at an environment temperature, for example at a temperature below −10° C. or above +60° C., which is widely different from the operating temperature of the imaging device
2
, the amount of heat flowing in or out via thermal resistance between the imaging device
2
and the device package
17
, or via the thermal resistance of the electric connections of the imaging device
2
and the device-temperature monitor
3
increases. This will increase the amount of heat emitted or absorbed by the thermoelectric device
12
for stabilizing the imaging device
2
at a constant temperature, resulting in the drawback of higher dissipation power. Moreover, if the difference between the operating temperature of the ima
Burns Doane , Swecker, Mathis LLP
Harrington Alicia
Mitsubishi Denki & Kabushiki Kaisha
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