JPS6040228B2 - infrared monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an infrared monitoring device that images a surrounding scene as a thermal image using an array of infrared detectors arranged linearly in a direction perpendicular to a scanning direction.

Fig. ' is a diagram showing the basic configuration of an infrared monitoring device using a conventional photoconductive detector. 2
Incident infrared light 4 that enters from the surroundings is imaged by a light receiving optical system 1 onto an infrared detector array 2 to which a bias current is supplied from a bias power supply 5.

Note that the infrared detector row herein means a row of photoconductive infrared detectors. Therefore, one infrared detector in the infrared detector array 2 can detect a thermal image within the vertical field of view determined by the focal length of the light receiving optical system 1 and the size of the infrared detector by rotating the mount 3. Scanning is performed using one scanning line. The output of this one infrared detector corresponds to a video signal of one scanning line in a normal imaging device such as a television camera, and the output of each detector in the infrared detector row 2 is amplified by the front direct amplifier 6. If they are later arranged one after another, a video signal similar to the video signal in a television is obtained, and by supplying this signal to the image display 7 a thermal image of the scene around the infrared monitoring device is obtained. In FIG. 1, a multiplexer 8 has the function of converting the video signals sent in parallel from the infrared detector array 2 into serial video signals convenient for the image display 6. By monitoring the image displayed on the image display 6, the operator of this infrared monitoring device can learn about changes in ambient temperature, the approach of abnormal objects, and the like. The number of infrared detectors in the infrared detector array 2 in Fig. 1 is equal to the number of scanning lines scanning the surrounding actual scene, and the amount of information in the displayed image increases as the number of scanning lines increases. situation can be more easily understood.

For this reason, the number of infrared detectors is usually tens to hundreds. On the other hand, focusing on two infrared detectors in the infrared detector array, the sensitivity of the first detector is R1, the sensitivity of the second detector is R2, and the received light power of the first detector is P.
1. If the received light power of the second detector is P2, the outputs SI and S2 of the first detector and the second detector are respectively expressed by the following equations. SI:RIPI
...'1}S2=R is 2
...■The brightness difference △B of the image displayed on the image display is
Using the gain G of the amplifier provided for each detector and the constant K determined by the image display, it is expressed as follows.

△B=KGSI-KGS2 KG{P1 (RI-R2) ten (PI-P2) R2}.
...[3] It is desirable that the brightness difference △B of the image displayed on the image display is determined only by the magnitude of the received light power, and the second term in equation 3' represents this effect. .

On the other hand, the first term represents the brightness difference caused by the difference in sensitivity between the detectors. The reason why the first term can be ignored compared to the second term is "R Aoben 2"[IP;. P21
---When the condition [4} holds true, for powder at room temperature, IPI-P2l<PI, so the difference in sensitivity between each detector must be limited to an extremely small value. It won't happen.

However, with the current manufacturing technology for infrared detectors, it is difficult to satisfy the condition of equation 4) for many detectors as described above. Therefore, in the displayed image of the conventional device, horizontal stripe-like brightness unevenness occurs due to uneven sensitivity of the detector.
In addition, in the scanning method of an infrared monitoring device as shown in Fig. 1, when monitoring the entire circumference of the device, there is an invalid scanning period, so-called retrace period, as in raster scanning performed with a television camera, etc. Therefore, the infrared detector always receives signal light from the outside. Therefore, the amplifier provided for each detector must be a DC amplifier that also amplifies DC signals. However, compared to AC amplifiers that only amplify alternating current, DC amplifiers
Due to poor gain stability, the brightness of the entire displayed image or between scan lines varies. In order to eliminate these drawbacks, this invention makes infrared light incident on an infrared detector from a reference infrared light source as necessary, and changes the bias current for each detector using the output of the infrared detector at that time. It is equipped with a circuit that allows this to occur, and uses the following principle.

The sensitivity R of the photoconductive detector is expressed as follows using the sensitivity Ro per unit bias current and the bias current lb. R=Ro×lb...
■Therefore, if you change the bias current, the sensitivity will change proportionally, so even if Ro is different for each detector, if you set the bias current appropriately for each detector, you can R has the same value for all detectors, making it possible to satisfy the condition of equation '4-.

Hereinafter, this invention will be explained in detail using the drawings.
FIG. 2 is a diagram showing an embodiment of the invention.

The device shown in FIG. 2 has two operating modes: a sensitivity correction mode in which the difference in sensitivity between the detectors in the infrared detector array 2 is detected and corrected, and an imaging mode in which the surrounding actual scene is imaged in green.
The operator gives an instruction to the sensitivity correction multiplexer 9 to instruct the sensitivity correction mode as necessary, and the sensitivity correction multiplexer 9 switches the operation mode to the imaging mode when the correction is completed. In the sensitivity correction mode, the blade rotation signal 11 is given from the sensitivity correction multiplexer 9 to the motor 0, and the rotary plate 12, which is provided in front of the infrared detector row 2 and consists of two blades with different emissivities, is rotated. do.

A blade synchronization signal 13 indicating which of the two blades of the rotating plate is in front of the infrared detector row 2 is supplied from the motor 10 to the sensitivity correction multiplexer 9. 9 detects the difference in sensitivity between each detector based on this blade synchronization signal 13 and the output of the front layer amplifier 6 provided for each detector in the infrared detector row 2. Sensitivity correction multiplexer 9
gives a bias current 14 to each detector based on the detected sensitivity difference between the detectors.

Appropriate bias current 14 is provided for each detector;
When the sensitivities of all the detectors in the infrared detector array 2 become equal, the operating mode of the device is switched from the sensitivity correction mode to the imaging mode. In the imaging mode, the blades of the rotary plate 12 are fixed at a position where they do not block the incident infrared light 4, and the bias current 14 is held at its final value in the sensitivity correction mode. Further, the sensitivity correction multiplexer 9 converts the video signals sent in parallel from the infrared detector array 2 into a serial format, and supplies the converted video signals to the image display 7 as a multiplexed video signal 15. FIG. 3 is a diagram showing the relationship between the rotary plate 12 and the infrared detector row 2.

The rotating plate 12 needs to have a material and structure that improves temperature uniformity, and is composed of a first blade 16 that has a high infrared emissivity and a second blade 17 that has a different emissivity from the first blade. be done. In addition, the emissivity of these two blades reduces the reflection of infrared rays from other parts, so
It is desirable that both values be close to 1. The size and position of the blades of the rotary plate 12 are such that when the blades come in front of the infrared detector array 2, the blades sufficiently cover the field of view of each detector. Therefore, when the blade comes in front of the infrared detector row 2, all the detectors receive the same amount of infrared light, which is the same amount as when the second blade 17 comes in front.
It is different when the blade 16 is closed forward. FIG. 4 is a diagram showing an example of the configuration of a sensitivity correction multiplexer.

When the operator specifies the sensitivity correction mode, the mode setting circuit 18 generates a blade rotation signal 11 and a mode setting signal 19. The digital memory 20 is for digitizing and storing the value of the bias current 14 to be supplied to each detector, and the stored contents are reset in the initial state. The multiplexing circuit 21 selects one of the many detectors based on the detector designation signal 23 given from the detector designation circuit 22, and multiplexes the preconverting amplifier output 24 corresponding to that detector. Output as signal 15. The voltage correction circuit 25 detects the difference when the sensitivity of the detector designated by the detector designation circuit 22 differs from a preset value based on the multiplexed video signal 15 and the blade synchronization signal 13, and converts it into a digital signal. The memory contents 26 of the memory 20 are modified and sent back to the digital memory 2 as write contents 28 together with a write signal 27. Note that the write signal 27 is a signal for putting the digital memory 20 into a write state, and the stored contents of the digital memory 20 do not change during a period when this signal is not applied. The information stored in the digital memory 20 is modified during multiple rotations of the rotary plate, and a completion signal 29 is generated when the modification of the contents corresponding to one detector is completed. Based on this completion signal 29, the detector designation circuit 22 designates the next detector. The sample-and-hold signal 30 is transmitted by a sample-and-hold circuit 31 corresponding to a designated detector to a digital-to-analog converter 32.
Digital memory 20 converted into an analog quantity by
is generated by the detector designation circuit 22 in order to sample and hold the contents of . In addition, the sample/hold circuit 3
After passing through a low-pass filter 33 provided to stabilize the output of sample-and-hold circuit 31, the output of sample-and-hold circuit 31 becomes bias current 14. When the contents of the digital memory 20 have been corrected for all detectors, the detector designation circuit 22 generates a correction completion signal 34, and the operating mode is switched from the sensitivity correction mode to the imaging mode. FIG. 5 is a diagram showing an example of the configuration of the voltage correction circuit.

The multiplexed video signal 15 is supplied to two sample-and-hold circuits 36a and 36b after passing through a low-pass filter 35 provided to reduce noise. Based on the blade synchronization signal 13, the blade synchronization signal separation circuit 37 selects the first blade when the first blade is in front of the infrared detector row.
A blade synchronization signal 38 is generated, and a second blade synchronization signal 39 is generated when the second blade is in front of the infrared detector array. Two sample and hold circuits 36a, 36b
samples and holds the multiplexed video signal 15 based on the first blade synchronization signal 38 and the second blade synchronization signal 39, and its output becomes a first blade level 40 and a second blade level 41.

The sensitivity of each detector in the infrared detector array determines the difference between the first blade level 40 and the second blade level 41, and if all the detectors have the same sensitivity, this difference will also be constant. The subtractor 42a determines the difference between the first predetermined level 40 and the second predetermined level 41, and the difference between this difference and a predetermined reference value 43 is determined again by the subtractor 42b and becomes an error signal 44. This error signal 44 passes through a coefficient multiplier 45 having a predetermined attenuation coefficient, and then is applied to an analog-to-digital converter 46 to become a digitized error signal 47. Digital adder 48 adds memory contents 26 and digitized error signal 47 to generate write contents 28. The blade synchronization signal separation circuit 37 generates a blade completion signal 49 at the timing when this write content 28 is generated, the mode setting signal 19 indicates that the sensitivity correction mode is in operation, and the blade completion signal 49 is generated. AND gate 5 generates a write signal 27 when Further, the discriminator 51 generates a completion signal 29 when the absolute value of the digitized error signal 47 becomes less than or equal to a certain value. FIG. 6 is a diagram showing the phase relationship of the main signals in the voltage correction circuit, including the multiplexed video signal 15, the first blade synchronization signal 38, the second blade synchronization signal 39, the flade completion signal 49, the first blade level 40, The relationship between the second plaid level 41 is shown.

FIG. 7 is a diagram showing a configuration example of a detector designation circuit.
A signal from an internal clock 53 and a completion signal 29 are input to the digital switch 52, and when the mode setting signal 19 indicates that the sensitivity correction mode is in operation, the completion signal 29 is input, and the completion signal 29 is input to the digital switch 52. If so, a signal from the internal clock 53 is output. The digital counter 54 is reset in the initial state, and the counter input 55 increments the number of the designated detector in order to generate the detector designation signal 23. Decoder 56 decodes detector designation signal 23 and supplies sample and hold signal 30 to the signal line corresponding to each detector. Further, when the mode setting signal 19 indicates that the sensitivity correction mode is in operation and the digital counter 54 generates a signal 57 indicating that all the detectors have been processed, the AND gate 58 outputs the correction completion signal 34. In addition, the above is a rotating plate with two different infrared emissivities.
Although the description has been made using a device having two blades, the number of blades is not limited to two, and the same effect can be obtained by using a method similar to the method described above if there is a plurality of blades.

Furthermore, when there is only one blade, the same effect can be expected by regarding that blade as the first blade and setting the second blade level to an appropriate DC level. Furthermore, if the temperature of each blade of the rotary plate is changed, the amount of infrared radiation will change for each blade without changing the emissivity, so the same effect as described above can be obtained by the same method. Further, in the above, a preset value was used as a reference value to be compared with the difference between the first plate level and the second plate level, but instead of this, the first plate level and the second plate level in all detectors By determining the difference between the two and using this average value as a reference value, the operating time of the sensitivity correction mode can be shortened.

Also, in the above explanation, we explained how to digitize all the bias current values and store them in memory.
If a common offset value is given to all detectors, and only the increment/decrement corresponding to each detector from that value is stored in digital memory, the memory capacity required for bias current setting accuracy can be reduced. I can do it.

Furthermore, although the above explanation deals with the case of correcting the variation in sensitivity between each detector in an infrared detector array, there is a case where a front layer amplifier is provided for each detector and the gain is different for each detector. However, the variation can be corrected using the method explained above.

Further, although the infrared monitoring device having an array of infrared detectors arranged in a direction perpendicular to the scanning direction has been described above, the present invention is not limited to this. It may also be applied to an optical monitoring device using a detector. As described above, in the infrared monitoring device according to the present invention, a highly uniform infrared image can be obtained by having a circuit that automatically corrects sensitivity differences between a plurality of infrared detectors.

[Brief explanation of the drawing]

Fig. 1 shows the basic configuration of an infrared monitoring device using a conventional photoconductive detector, Fig. 2 shows an embodiment of the present invention, and Fig. 3 shows a rotating plate and an infrared detector array. FIG. 4 is a diagram showing a configuration example of a sensitivity correction multiplexer,
FIG. 5 is a diagram showing an example of the configuration of the voltage correction circuit, and FIG. 6 is a diagram showing the phase relationship of the main signals in the voltage correction circuit.
FIG. 7 is a diagram showing an example of the configuration of a detector designation circuit.
2 is a light receiving optical system, 2 is an infrared detector array, 8 is a multiplexer, 9 is a sensitivity correction multiplexer, 12 is a rotary plate, 22 is a detector designation circuit, and 25 is a voltage correction circuit. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Completed diagram

Claims (1)

[Claims] 1 A photoconductive infrared detector array and a light receiving optical system arranged linearly in a direction perpendicular to the scanning direction, and a combination of the above infrared detector array and light receiving optical system with the direction of the infrared detector array as an axis. In an infrared monitoring device that has a frame that scans the surrounding scene by rotating it and obtains a thermal image of the surrounding scene, the rotating plate having a plurality of blades each having a different amount of infrared radiation is used as the infrared detector array. The rotary plate is rotated according to the operator's needs, and when the different blades of the rotary plate rotate to the front of the infrared detector array, The bias current applied to each photoconductive infrared detector in the infrared detector array is controlled so that the difference in the output of the stationary amplifier becomes the same value for all detectors with respect to the corresponding blade, and this current control When the control is completed, the rotation of the rotary plate is stopped at a position where the blades do not block the field of view of the infrared detector array, and the value of the bias current applied to each photoconductive infrared detector is maintained at the value at the time of completion of control. An infrared monitoring device characterized by: