JPH0126594B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an infrared imaging device, and more particularly to a clamp level control means for direct current reproduction in a mechanical scanning infrared imaging device.

[Technology background]

In general, direct current reproduction is a widely used technique in visible imaging devices, but its importance becomes even greater in the infrared region or long infrared region. In particular, in the case of FLIR, only the fluctuations in the incident light power are extracted and output, so DC reproduction is essential to obtain faithful infrared images. Conventionally, therefore, a method has been used to apply a clamp based on the output level of the detector when scanning the surface of a field stop located near the actual focal plane in the optical system.

However, in this case, if the temperature of the target in the field of view and the temperature of the field stop are extremely different,
This temperature difference accounts for most of the dynamic range of the amplifier that amplifies the detector output signal, and signal distortion due to saturation is likely to occur for important AC components, so the dynamic range is relatively There was a problem with it being smaller.

[Purpose of the invention]

An object of the present invention is to maintain the temperature difference between a field stop and a target within the field of view small by controlling the temperature of the field stop in a mechanical scanning type infrared imaging device, thereby improving the effective dynamics of the system. The purpose is to provide a means to increase the range.

[Structure of the invention]

The present invention compares the level of the detector output in the field of view and the level relative to the field stop, and automatically controls the temperature of the field stop to minimize the difference. A scanning type infrared imaging device includes a detector for detecting the incident power of infrared rays, a temperature-controllable field stop means disposed near the actual focal plane of an optical system of the detector, and a field stop means for scanning the field stop means. means for outputting the level at the time of detection of the field stop means in the detector output, and means for outputting the level for a selected appropriate area within the field of view of the detector output. and means for controlling the temperature of the field stop means based on the difference between the level at the time of detection of the field stop means and the level for the appropriate area, and means for controlling the temperature of the field stop means based on the signal indicating the period. It is characterized by being equipped with a clamp circuit that clamps to the level when the stop means is detected.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to Examples.

FIG. 1 is a schematic diagram of an infrared imaging device for explaining the principle of the present invention. In the figure, 1 is the object,
2 to 4 are lenses, 5 and 6 are field stops, 7 is a scanning mirror, 8 is a multi-element detector, and 9 is an amplifier group. The multi-element detector 8 is composed of n detection elements as will be described later, and the amplifier group 9 also includes n amplifiers correspondingly, and the outputs of each are represented by ch.1 to ch.n. I'm being ignored.

FIG. 2 shows a scanning screen viewed from the multi-element detector 8 in the apparatus shown in FIG. The multi-element detector 8 is shown as n sensing elements □1, □2, . . . □n arranged vertically in the center of the scanning area. n is usually about 100, and by using the interlaced scanning method, the total number of
You can get 200 scan lines.

In FIG. 1, by swinging or rotating the scanning mirror 7 in the direction of the arrow, the object 1 is scanned in the vertical direction of the figure. This appears in FIG. 2 as a horizontal scan, ie, a scan perpendicular to the array of elements of a multi-element detector. The field stops 5, 6 are placed in the focal plane of the lens 2 and, as shown in FIG. 2, block the field of view at the beginning and end of the scan and are scanned in place of the field of view. The surfaces of these field stops 5, 6 are formed as blackbody surfaces and are used to provide a reference level for the multi-element detector 8.

In this way, a scanned screen as shown in FIG. 2 is obtained.

Next, DC regeneration of the detector output signal will be explained with reference to FIGS. 3a to 3d. For example, the second
If the incident power of the infrared rays incident on the detection element □1 in the figure is as shown in Figure 3a, the output of the amplifier of channel 1 has the DC component cut out and becomes as shown in Figure 3B. If you clamp the output to zero at the same time you are looking at the field stop, you will get a waveform like the one shown in Figure 3c. However, at this time, if the background of the object within the field of view is high temperature, the waveform becomes like the dotted line waveform A in FIG. 3d, and the ratio of effective signals becomes small. Therefore, if the temperature of the field stop is raised to around the average temperature within the field of view, the waveform shown by the solid line B in the same figure will be obtained, and the dynamic range of the amplifier can be effectively utilized. Moreover, the influence of nonlinearity of the sensing element, which becomes noticeable when viewing a large temperature difference, can be reduced, and a screen with better linearity can be obtained.

FIG. 4 is a configuration diagram of an apparatus according to an embodiment of the present invention, which corresponds to the schematic diagram of the infrared imaging device shown in FIG. 1 and shows the detailed configuration.

In FIG. 4, 3 and 4 are lenses, 5 and 6 are field stops, 7 is a scanning mirror, 8 is a multi-element detector, 9 is an amplifier group, 10 is a position detector,
11 is a clamp circuit, 12 is an average circuit, 13 is a sample/hold circuit (S/H), 14 is an integration circuit, 15 is a subtraction circuit, 16 is a temperature controller,
17 and 18 are Peltier elements; 19 is a temperature sensor that detects the temperature of the field stop 6; and 20
indicates a temperature sensor that detects the housing temperature.

Each element shown by 3 to 9 is the same as that shown in FIG. 1 and FIG. 2, so the explanation will be omitted.

The position detector 10 optically detects the rotational position of the scanning mirror 7 and outputs a signal indicating the period during which the field stop 5 or 6 is being scanned.

The clamp circuit 11 is synchronously controlled by the output signal of the position detector 10, and clamps each signal of each amplifier output channel ch.1 to ch.n of the amplifier group 9 to the level of the field stop detection signal.

The averaging circuit 12 is composed of a well-known analog adder, and in the illustrated example, signals of multiple channels ch.m to ch.k, that is, (K-m+1) scanning lines at the center of the screen are observed for level comparison. It has a function to select, add and average each of those signals. Figure 5 shows the channels ch.m to ch.m in the scanning screen.
Indicates the location of ch.k. The averaging circuit 12 over the entire scanning range of these (m-K+1) scanning lines,
The output signals of the respective amplifiers corresponding to each horizontal position are averaged and applied to the sample-and-hold circuit 13 and the integration circuit 14.

The sample hold circuit 13 is the clamp circuit 1
1, it is synchronously controlled by the output signal of the position detector 10, and the output signal level of the averaging circuit 12 while scanning the field stops 5 and 6 is sampled and held. On the other hand, integrating circuit 1
4 is an averaging circuit 12 over the entire horizontal scanning range consisting of the field of view and two field stops.
The output signal of is integrated, that is, averaged on the time axis.

The subtraction circuit 15 subtracts the output signal of the sample-and-hold circuit 13 from the output signal of the integration circuit 14, creates a signal representing the level difference, and feeds it back to the temperature controller 16.

The temperature controller 16 receives the feedback signal applied from the subtraction circuit 15 and the temperature sensor 19.
Based on the field stop temperature and the case temperature detected by and 20, drive signals for the Peltier elements 17 and 18 are generated, and the Peltier elements 17 and 18 are driven.

The Peltier elements 17 and 18 are elements that utilize the Peltier effect, and can be cooled or heated depending on the direction in which the drive current is passed. Any other suitable means for heating or cooling field stops 5 and 6 may be used.

In this manner, the field stop temperature is controlled so that the signal detected from the field stop matches the average signal of the detection signals over the entire scanning range, and the field stop temperature is controlled as shown in waveform B in Figure 3d. You can get a good signal.

In the above embodiment, the average value over the entire screen of several channels in the center of the screen was taken as the standard for adjusting the field stop temperature, but there are several ways to take this standard as shown below. Variations are possible.

(1) Select the optimal scanning line (or multiple lines) depending on the screen. It may be adjusted by the operator, or scanning lines with low autocorrelation (containing complex information) may be automatically selected on the screen.

(2) Control the area to be averaged not only in the vertical direction but also in the horizontal (scanning) direction. This can be easily achieved by taking the average between lines and controlling the temporal range when integrating.

〔Effect of the invention〕

According to the present invention, the average output of important parts of the screen can be made close to zero, so the dynamic range of the entire system can be expanded. Further, the influence of variations between scanning lines (between elements) can be relatively reduced, and a uniform screen can be obtained. Moreover, it has a function of automatic level adjustment for the output of the monitor, and the relatively narrow dynamic range of the monitor can be used effectively.

[Brief explanation of drawings]

Figure 1 is a schematic diagram for explaining the principle of the present invention, Figure 2 is an explanatory diagram of the scanning screen, and Figures 3 a to d.
4 is an explanatory diagram of DC regeneration according to the present invention, FIG. 4 is a configuration diagram of an apparatus according to an embodiment of the present invention, and FIG. 5 is an explanatory diagram showing an example of selected channels to be observed for level comparison. In the figure, 5 and 6 are field stops, 7 is a scanning mirror, 8 is a multi-element detector, 10 is a position detector, and 11
12 is a clamp circuit, 12 is an average circuit, 13 is a sample/hold circuit, 14 is an integration circuit, 15 is a subtraction circuit, 16 is a temperature controller, and 17 and 18 are Peltier elements.

Claims (1)

[Claims] 1 In a mechanical scanning infrared imaging device,
A detector that detects the incident power of infrared rays, a temperature-controllable field stop means placed near the actual focal plane of the optical system of the detector, and synchronization by a signal indicating the scanning period of the field stop means. means for outputting a level when the field stop means is detected in the detector output; means for outputting a level for a selected appropriate area within the field of view of the detector output; and when the field stop means is detected. and means for controlling the temperature of the field stop means based on the difference between the level of the field stop means and the level for the appropriate area, and clamping the detector output signal to the level at the time of detection of the field stop means based on the signal indicative of the period. An infrared imaging device characterized by comprising a clamp circuit.