JP2008278036A - Infrared camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared camera for preventing the failure of an infrared imaging part due to imaging the image of a high luminance object or a high temperature object. <P>SOLUTION: This infrared camera is provided with: an infrared imaging part for converting received infrared rays of light into an electric signal corresponding to intensity; a shutter mechanism for interrupting the rays of light made incident from the outside to the infrared imaging part; an optical diaphragm mechanism for controlling the diaphragm of the rays of light made incident from the outside to the infrared imaging part; an image signal generation part for generating an image signal by processing a signal acquired by amplifying the electric signal from the infrared imaging part by a first gain, and A/D converting it; and an incident light control signal generation part for amplifying the electric signal from the infrared imaging part by a second gain which is lower than the first gain, and for A/D converting it, and for transmitting an incident light control signal to the shutter mechanism or the optical diaphragm mechanism for interrupting or reducing the rays of light made incident from the outside to the infrared imaging part when the A/D converted infrared signal is turned to be a predetermined threshold or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an infrared camera, and more particularly to an uncooled infrared camera using a thermal infrared imaging element that operates at room temperature.

  Conventionally, this type of infrared camera using a thermal infrared imaging device or the like has been disclosed in, for example, Patent Document 1, and in Patent Document 1, shading due to unnecessary infrared radiation from an infrared optical system or a housing of an apparatus is disclosed. An apparatus that effectively corrects the influence of the above with a shutter provided inside the camera is disclosed.

JP 2005-274301 A

  In this type of conventional infrared camera using a bright optical system, when a high-brightness object such as sunlight or a high-temperature object is imaged, the pixel temperature of the infrared imaging element of the infrared imaging unit becomes high, and the heat-resistant temperature for a long time. There was a problem that the device failed if the state exceeding the value continued.

  An object of the present invention is to provide an infrared camera that prevents a failure of an infrared imaging unit caused by imaging a high-luminance subject or a high-temperature subject.

  The present invention includes an infrared imaging unit that converts received infrared light into an electrical signal corresponding to intensity, a shutter mechanism that blocks light incident on the infrared imaging unit from the outside, and the infrared imaging unit from the outside An optical aperture mechanism for adjusting the aperture of light incident on the image signal, and an image signal generation unit that generates an image signal by processing an A / D-converted signal after amplifying an electrical signal from the infrared imaging unit with a first gain And when the electric signal from the infrared imaging unit is amplified with a second gain lower than the first gain and then A / D converted, and when the A / D converted infrared signal exceeds a predetermined threshold value. An infrared light camera comprising: an incident light control signal generation unit that transmits an incident light control signal to the shutter mechanism or the optical diaphragm mechanism to block or restrict light incident on the infrared imaging unit from the outside It is in.

  According to the present invention, it is possible to provide an infrared camera that prevents a failure of the infrared imaging unit caused by imaging a high-luminance subject or a high-temperature subject.

Embodiment 1 FIG.
FIG. 1 is a diagram showing the configuration of an infrared camera according to Embodiment 1 of the present invention. The infrared camera includes a housing 14, an infrared optical system 1 attached to the housing 14, a thermal infrared imaging unit 4 (hereinafter referred to as an infrared imaging unit), and a shutter 2 provided between the infrared optical system 1 and the infrared imaging unit 4. And an optical aperture 20, a vacuum package 5 for holding the infrared imaging unit 4 in a vacuum state, and an infrared transmission window 3 installed in the infrared incident direction of the vacuum package 5.

  Also, a first preamplifier 6 for amplifying an electrical signal from the infrared imaging unit 4, a first A / D converter 7 for converting an output signal of the first preamplifier 6 into a digital signal, and a first A / D A signal processing circuit 8 that outputs a video output signal (image signal) based on the quantized signal from the converter 7 is included, which is intended to generate an image signal and constitutes an image signal generation unit.

  In addition, a second preamplifier 9 for amplifying an electric signal from the infrared imaging unit 4, a second A / D converter 10 for converting an output signal of the second preamplifier 9 into a digital signal, and a second A / D A level detection circuit 11 for detecting the level of the quantized signal from the converter 10 is included, which is intended to generate an incident light control signal that is a control signal to the shutter 2 and the optical aperture 20. A control signal generation unit is configured.

  Further, a shutter driver 12 for controlling the opening and closing of the shutter 2 and an optical aperture driver 15 for controlling the aperture of the optical aperture 20 by an incident light control signal from the level detection circuit 11 are included. The shutter 2 and the shutter driver 12 constitute a shutter mechanism, and the optical aperture 20 and the optical aperture driver 15 constitute an optical aperture mechanism. Further, a camera control unit 13 that controls the entire infrared camera is included.

  FIG. 2 is a plan view of the infrared imaging unit 4. An infrared imaging element unit 42 in which infrared imaging elements are arranged two-dimensionally (matrix) on a silicon substrate 41 and a pixel output signal readout circuit 43 are formed. .

  FIG. 3 is a perspective view showing the structure of one pixel of the infrared imaging element section 42 in FIG. 2, that is, one infrared imaging element 402. An infrared detector 402a is provided on the silicon substrate 41 so as to be lifted from the substrate by the support legs 402b on both sides. When infrared rays are irradiated, the thermal infrared imaging element 402 absorbs infrared rays and the temperature of the infrared detection unit 402a rises, and the temperature change is converted into a resistance change and detected.

  First, the general operation will be described. In FIG. 1, infrared light incident from the infrared optical system 1 passes through the infrared transmission window 3 and is applied to the infrared imaging unit 4. The irradiated infrared ray is absorbed by the infrared ray detection unit 402a in FIG. 3, and the temperature of the infrared ray detection unit rises. When a resistor such as vanadium oxide is used for the infrared detection unit 402a, the resistance value changes with a change in temperature. Therefore, the change in the resistance value due to the change in temperature is read out as a change in the electrical signal to read a two-dimensional infrared ray. Image information can be obtained.

  Since infrared rays are radiated from all objects at room temperature, even if the shutter 2 is closed, the amount of infrared rays incident on the infrared imaging unit 4 does not become zero. In an infrared camera, it is necessary to perform offset correction by imaging a certain reference plane and subtracting it from the imaging signal. In FIG. 1, the shutter 2 is closed by the control of the shutter driver 12 in accordance with a signal from the camera control unit 13, and the infrared imaging unit 4 at that time passes through the first preamplifier 6 and the first A / D converter 7. The value of the imaging signal obtained in this way is held and stored in the signal processing circuit 8 as an offset correction value, and an operation of subtracting from the raw imaging signal is performed during imaging.

  Further, if the resistance temperature coefficient of the resistor used in the infrared detecting unit 402a shown in FIG. 3 is the same, the temperature rise of the infrared detecting unit 402a is the same. The larger the resistance, the greater the resistance change that can be obtained with the same amount of infrared radiation, and the higher the sensitivity. Therefore, in order to increase the temperature rise, it is effective to minimize the heat escaping from the infrared detecting unit 402a to the silicon substrate 41. For this purpose, the support legs 402b on both sides are designed to increase the thermal resistance as much as possible. The

  Therefore, since the recent high-performance infrared imaging element 402 is designed to reduce the thermal resistance of the support leg 402b and to easily increase the pixel temperature, when a bright optical system is used, When a high-temperature object is viewed directly, there has been a problem that the device malfunctions when the pixel temperature rises to several hundred degrees Celsius. The heat resistance temperature of the infrared imaging element 402 is determined by the melting point of the member being used, the alteration of the member, thermal deformation, and the like. For example, the heat resistance temperature due to the melting point of aluminum used for wiring is about 400 ° C.

  With respect to the present invention, the temperature resolution of a high-sensitivity infrared camera is generally around 0.1 m ° C., and the first preamplifier 6 for generating an image signal with a high S / N ratio is designed to have a high gain (first gain). Has been. For this reason, when a subject having a certain luminance or higher or a certain temperature is imaged, the first A / D converter 7 is saturated and the image is overexposed. On the other hand, the second preamplifier 9 is designed so that the gain (second gain) of the above-mentioned first preamplifier 6 is lower than the gain so that the second A / D converter 10 is not saturated even in high-temperature imaging. Yes.

  Next, an operation for preventing a failure of the infrared imaging device by imaging a high-luminance subject or a high-temperature object will be described. An image signal generation unit including a first preamplifier 6, a first A / D converter 7, and a signal processing circuit 8, and incident light including a second preamplifier 9, a second A / D converter 10, and a level detection circuit 11. Each of the control signal generation units can perform processing with a signal in units of frames including signals from a plurality or all of the infrared imaging elements 402 of the infrared imaging unit 4.

  FIG. 4 is a diagram for explaining the signal processing operation in the level detection circuit 11. In FIG. 4, the vertical axis represents the gradation of the output (infrared signal) quantized by the second A / D converter 10, and the horizontal axis represents the frame number. In this example, 10 bits (1024 gradations) are used as the A / D converter 10. In each frame period, outputs of all pixels, that is, outputs from, for example, all the infrared imaging elements 402 of the infrared imaging element unit 42 in FIG. 2 are displayed. In FIG. 4, five frames are displayed.

  In the third and subsequent frames, a high-luminance subject or a high-temperature subject is imaged, and the output is large in some pixels. A threshold value is set in advance, and when a part of the pixel output exceeds the threshold value, an incident light control signal for closing the shutter 2 is output to the shutter driver 12. If the temperature at which a pixel fails is, for example, 400 ° C., the infrared imaging element is protected by closing the shutter 2 when a high-luminance subject or a high-temperature subject is imaged by setting the threshold value to a temperature lower than that. be able to.

  In the above example, the data for level determination uses the output (infrared signal) of the A / D converter 10 as it is, but the shutter 2 is closed by the level detection circuit 11 in the same manner as the signal processing circuit 8. The value of the infrared signal obtained from the infrared imaging unit 4 through the second preamplifier 9 and the second A / D converter 10 is held and stored as an offset correction value and offset from the raw infrared signal at the time of imaging. An infrared signal subjected to offset correction for subtracting the correction value may be used. The same applies to the following embodiments.

Embodiment 2. FIG.
FIG. 5 is a diagram for explaining the signal processing operation in the level detection circuit 11 in the infrared camera according to Embodiment 2 of the present invention. The configuration of the entire infrared camera is basically the same as that shown in FIG. In the first embodiment described above, after the incident light from the high-luminance subject or the high-temperature subject is incident, the level detection circuit 11 is configured to close the shutter 2 when it is determined that the infrared signal first exceeds the threshold value. In contrast to outputting the light control signal, in this embodiment, after determining that the threshold value is exceeded first, the incident light control signal that closes the shutter 2 when the threshold value is continuously exceeded N frames times. Is output. The number of frames N is set according to a period in which each infrared imaging element 402 can withstand high temperatures. For example, if the period is 1 second, N is set to 30 because it is 30 frames / second in the case of TV synchronization. Accordingly, it is possible to prevent a shutter operation with incident light from a high-luminance or high-temperature subject in a short time so that the infrared imaging element does not break down.

Embodiment 3 FIG.
FIG. 6 is a diagram showing the configuration of an infrared camera according to Embodiment 3 of the present invention. Parts that are the same as or equivalent to those in FIG. The infrared camera in FIG. 6 differs from the first embodiment in that an incident light control signal output from the level detection circuit 11 is input to the optical aperture driver 15. In response to an incident light control signal output from the level detection circuit 11 by detecting incident light from a high-luminance subject or a high-temperature subject, the optical aperture driver 15 drives the optical aperture 20 to a state where the aperture is minimized. The level detection method is the same as that in the first or second embodiment.

It is a figure which shows the structure of the infrared camera by Embodiment 1 of this invention. FIG. 1 is a plan view of the infrared imaging unit. It is a perspective view which shows one infrared image sensor of the infrared image sensor part of FIG. It is a figure for demonstrating the operation | movement of the signal processing in the level detection circuit of the infrared camera by Embodiment 1 of this invention. It is a figure for demonstrating the operation | movement of the signal processing in the level detection circuit of the infrared camera by Embodiment 2 of this invention. It is a figure which shows the structure of the infrared camera by Embodiment 3 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Infrared optical system, 2 Shutter, 3 Infrared transmission window, 4 (thermal type) infrared imaging part, 5 Vacuum package, 6 1st preamplifier, 7 1st A / D converter, 8 Signal processing circuit, 9 2nd Preamplifier, 10 Second A / D converter, 11 Level detection circuit, 12 Shutter driver, 13 Camera control unit, 14 Housing, 15 Optical aperture driver, 20 Optical aperture, 41 Silicon substrate, 42 Infrared imaging device unit, 43 Read Circuit, 402 Infrared imaging device, 402a Infrared detector, 402b Support leg.

Claims (4)

An infrared imaging unit for converting the received infrared light into an electrical signal corresponding to the intensity;
A shutter mechanism for blocking light incident on the infrared imaging unit from the outside;
An optical diaphragm mechanism for adjusting the diaphragm of light incident on the infrared imaging unit from the outside;
An image signal generator for amplifying an electrical signal from the infrared imaging unit with a first gain and then processing an A / D converted signal to generate an image signal;
When the electric signal from the infrared imaging unit is amplified by a second gain lower than the first gain and then A / D converted, and the A / D converted infrared signal becomes equal to or greater than a predetermined threshold, An incident light control signal generation unit that sends an incident light control signal to the shutter mechanism or the optical diaphragm mechanism to block or restrict light incident on the infrared imaging unit from
An infrared camera characterized by comprising:   The infrared imaging unit includes a plurality of infrared imaging elements, and the image signal generation unit and the incident light control signal generation unit perform processing with a signal in units of frames including signals from the plurality of infrared imaging elements of the infrared imaging unit, The infrared camera according to claim 1, wherein the incident light control signal generation unit transmits an incident light control signal when the infrared signal becomes equal to or greater than the threshold value in a plurality of consecutive frames.   The incident light control signal generation unit stores a signal value from the infrared imaging unit when the shutter mechanism is in a blocking state as an offset correction value, and uses a signal obtained by subtracting the offset correction value from the infrared signal. The infrared camera according to claim 1 or 2.   The infrared camera according to any one of claims 1 to 3, wherein the infrared imaging unit is a thermal infrared imaging unit in which a signal output changes due to a temperature change caused by irradiated infrared rays.

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