JPS6177724A - Infrared-ray control device - Google Patents

Abstract

PURPOSE:To expand the substantial input dynamic range, by providing an infrared lens, which forms the image of infrared light on the light receiving surface of an infrared-ray sensor, and providing a stop, which automatically varies the actual aperture area of the infrared lens in correspondence with the amount of incident light. CONSTITUTION:An infrared lens 22 is arranged so as to form an image on the light receiving surface of an infrared-ray sensor 21 utilizing a two-dimensional IR-CCD. A stop 25 is provided at the rear of the infrared lens 22. Said stop 25 is provided with a stopping function (mechanical stop) so that the aperture area of the infrared lens 22 is automatically increased or decreased in correspondence with the amount of infrared rays received from a target 23 (temperature T). Therefore, saturation of the amount of accumulated charge in the accumulating part of the infrared-ray sensor can be prevented beforehand even if the amount of the infrared-rays from the target to be photographed is large, and the substantial input dynamic range can be expanded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a two-dimensional IR-CCD (Infra Red-Charg
The present invention relates to an infrared light control device that can prevent the amount of accumulated charge in the accumulation section of an infrared sensor of eCoupled Devtce from becoming saturated.

[Technical background of the invention]

Generally, IR-COD is one of the infrared light detection elements.
When capturing images of targets emitting infrared light using an infrared imaging device using , the dynamism and power consumption are small. Furthermore, if the aperture of the infrared lens is set on the low temperature side, it will become saturated at high temperatures. As is clear from equation (1) described later, this is generally handled by making the exposure time Δt variable.

C Problems with background technology] However, there are limits to the variation of this Δt.

Furthermore, as is clear from equation (1), λ1 to λ2 are narrowed (that is, an optical bandpass filter is inserted). This means that the signal from the target will also be small, making it impossible to narrow it down too much.

Furthermore, it is possible to prepare various infrared lenses with different aperture diameters (F-numbers) and replace them according to the target, but this is not a good idea as it is cumbersome and expensive to replace. .

On the other hand, a two-dimensional IR-COD detection element used in an infrared sensor has a larger amount of dark current than a general visible COD image detector. This dark current is accumulated in the storage ridge. The number of electrons accumulated in one pixel of the IR-CCD detection element due to the signal from the target is expressed by equation (1).

・・・・・・・・・・・・・・(1) Equation Ko: Lens transmittance Ka: Atmospheric transmittance F: Lens F value (lens focal length is f (m) Lens aperture diameter (crn) When F=-) Sd: Light receiving area of two-dimensional IR-CCD detection element (cnl
) Δt: Photosensitive time (S) η: Quantum efficiency of the sensing element ε Emissivity of two targets C: Speed of light (2,9979X10 (cnlg)
)h Ni blank constant (6,626196X10 (
Jl+))λ: Wavelength (cnt) k: Gel-Raman constant (1,380622X10-23
(JK-1))T: Target temperature λ1. λ! : Cutoff wavelength of the filter of the detection element By the way, when capturing a target through the atmosphere, so-called back-ground noise due to black body radiation due to the temperature of the atmosphere is always mixed in, and this is also converted into electrons in the storage section.
Accumulated.

As described above, the dynamic range of the target amount of electrons stored in the storage section after photoelectric conversion is usually small due to dark current and back-ground noise.

As is clear from the above, when a general infrared lens 22 without an aperture is placed in front of the two-dimensional IR-CCD 21 as shown in FIG. 4, light from the target 23 (temperature T) is When receiving light, back-ground noise 24 due to black body radiation due to atmospheric temperature always mixes within the viewing angle θ. Note that Ka is the transmittance of the atmosphere.

[Purpose of the invention]

This invention was made to eliminate the above-mentioned drawbacks of the conventional technology, and even if the amount of infrared light from the target to be photographed is large, it is possible to prevent the amount of accumulated charge in the accumulation part of the infrared sensor of the two-dimensional IR-COD from saturating. It is an object of the present invention to provide an infrared light control device that can expand the dynamic range of actual input.

[Summary of the invention]

The infrared light control device of the present invention has an infrared lens disposed in front of an infrared sensor using a two-dimensional IR-COD, and automatically adjusts the infrared lens according to the amount of infrared E-mail from the target to be imaged. It is equipped with a mechanical diaphragm mechanism that can increase or decrease the opening area.

[Embodiments of the invention]

Embodiments of the infrared light control device of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of one embodiment. In FIG. 1, an infrared lens 22 is disposed in front of an infrared sensor 21 using a two-dimensional IR-CCD in order to form an image on the light receiving surface of the infrared range 2.

A diaphragm 25 is provided behind this infrared lens 22. The diaphragm 25 has a diaphragm function (mechanical diaphragm) to automatically increase or decrease the aperture area of the infrared lens 22 according to the amount of infrared rays received from the target 23 (tm degrees T).

In Fig. 1, 24 is pack ground noise (T, = 300K), 26 is aperture 25 or Rano noise, θ
is infrared V 7 , e 22 no F, O, V, (Fiel
dof Vievr (viewing angle), φ is the equivalent F of the infrared lens 22 narrowed by the aperture 25, 0. It is V.

Next, the operation of the infrared light control device of the present invention configured as above will be explained. Figure 2 1 (,) shows the relationship between the aperture 25 of the infrared lens 22 in Figure 1 and the thermal noise from the aperture 25, and Figure 2 (b) is a side view of Figure 2 (,). be. In FIGS. 2(a) and 2(b), the same parts as in FIG.

In this invention, when the optical bandpass filter (not shown) is set to a fixed value and the exposure time is set to a fixed value, the dynamic range is expanded from a low temperature to a high temperature target using a mechanical aperture 25. .

In FIG. 1, noise 24 from the pack ground is photoelectrically converted into a two-dimensional IR-COD infrared sensor 21.
The number QB of electrons accumulated in one pixel is expressed by equation (2). However, assuming that the brightness of the infrared lens 22 is F,
When the aperture is stopped down to FB, the equivalent F and O of the infrared lens 22 are
, V are F, and θ becomes ψ at FB.

Q, == [g # (l Km) ・Sd ・Δ1xη
”i+X+(1-cai(2tan-1)Ko
) Ka r Sd rΔt, η, C, h, λ,.

λ2 is the same as equation (1), εB = atmospheric emissivity FB: aperture value (equivalent F value of the lens) T, temperature of the two atmospheres. The number Q of electrons accumulated in one pixel of the infrared sensor 2 of the IR-COD is expressed by equation (3).

Qt:=Sd −Δt・η・tix+ [[C1−w
(2tm-'(2'y)) ) (electron)・
・・・・・・・・・(3) Equation εi: More than the emissivity of the aperture (1 n equation, the number of electrons obtained by equations (2), and (3), plus the electron Q for the dark current.

will be added.

Now, if the storage capacity of one pixel of the infrared sensor 2 of the two-dimensional IR-COD is Qll (electron), then if the aperture FB is switched so that the condition Q8> (QT+QB+Q, +Q, ) is satisfied, saturation is achieved. It is possible to capture images in a wide dynamic range from low to high temperatures.

Below, the target temperature calculated under the following conditions versus the number of electrons converted to the storage section is expressed as F.

is shown in FIG. 3 as a parameter.

Lens transmittance (optical system transmittance) Ko=0.
5 Atmospheric transmittance Ka=0.8 Lens brightness F=1.8 Light receiving area of one pixel of detection element 5d=4.7X10 cm Photosensitivity time Δ to 1ms Quantum efficiency
Emissivity of η = 0.1 target
ε = 1 Emissivity of the atmosphere εB: Emissivity of 1 aperture ε, = 1 Atmosphere, temperature around the measurement system T, = Bandwidth of the optical filter at 300
λ, = 4.4 μm ~ λ, = 4.7 μm 2-dimensional IR-CO
When the area of the accumulation part of the infrared sensor 21 of D is 800 μm, the number of saturated charges (electrons) is 5×106 (
electrons), and the amount of dark current flowing into one pixel storage unit during Δt ” 1 ms converted into charge is 5×105
(electron) (this dark current is a typical IR
- This is a model with a little more than COD).

As shown in FIG. 3, when F=1.8 (fully open aperture), a target close to room temperature 300 can discriminate temperature differences with great sensitivity, but it quickly reaches a saturation level. Once the saturation level is reached, the aperture 25 can be switched to FB=3 to discriminate higher temperature targets. In this example 275 to 715
Up to K, discrimination is possible with F = 1.8-22.

〔Effect of the invention〕

As described above, according to the infrared light control device of the present invention, since the infrared lens has an aperture function that automatically opens and closes the aperture according to the amount of received light, the amount of infrared light from the target to be imaged is However, saturation of the amount of charge stored in the storage section of the infrared sensor can be prevented, and the effective input dynamic range can be expanded.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the configuration of an embodiment of the infrared light control device of the present invention, and Fig. 2 (,) is the relationship between the aperture of the infrared lens and the thermal noise from the aperture in the infrared light control device. FIG. 2(b) is a side view of FIG. 2(a), and FIG. 3 is a cross-sectional view showing the target to be imaged versus the total storage section of the infrared sensor when the aperture in the infrared light control device is switched. A diagram showing the relationship between the number of accumulated electrons and FIG. 4 is a diagram showing the state of incident light on an infrared sensor of an infrared imaging device using a conventional infrared lens. 2 No.. Infrared sensor, 22.. Infrared lens, 23
...Target, 24...Background noise, 25...
・Aperture, 26...Noise from the aperture. Applicant's agent Patent attorney Takehiko Suzue Figure 1 2-'7-' Figure 2 (2) % (b)

Claims (1)

[Claims] An infrared sensor using an infrared charge coupled device, an infrared lens placed in front of the infrared sensor that forms an image of infrared light on the receiving surface of the infrared sensor, and an infrared lens that automatically forms an image according to the amount of incident light. An infrared light control device comprising: an aperture that changes the effective aperture area of the infrared light control device;