JPH0552658A - Infrared radiation image pickup device - Google Patents

Abstract

PURPOSE:To make a detecting element output always maximum, being not influenced by the readout time interval of the stored charge of the CCD detecting element, in an infrared radiation image pickup device, which reflects optical power from an image pickup scene by means of a mirror, and converts it into the charge by means of the CCD detecting element, while scanning controls the mirror based on a scanning angle command value varying linearly at a certain angular velocity. CONSTITUTION:A circuit is provided and the circuit superimposes a waveform, which flattens the scanning angle variation during a readout time interval of the stored charge of a detecting element, on a scanning angle command value based on an image pickup sampling clock which synchronizes with the starting point of the readout time interval. When a master clock, which is used for the generation of the scanning angle command value, is available as the image pickup sampling clock, a corrected scanning angle command value is generated by using stored memory in the superimposed form of the waveform to flatten the scanning angle variation during the readout time interval, instead of the superimposing circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared imaging device,
In particular, the present invention relates to an infrared imaging device that controls optical scanning of a mirror based on a scanning angle command value that linearly changes at a constant angular velocity, reflects optical power from an imaging scene on the mirror, and converts the optical power into charges by a CCD detection element. Is.

The infrared image pickup device, as schematically shown in FIG. 5, includes an image pickup scene 31, a lens 32 and a mirror 30.
A two-dimensional information of the imaging scene 31 is typically obtained by two-dimensionally scanning the mirror 30 with the optical power incident on a single detection element (one of the reference numerals 34).

In such an infrared imaging device, when the number of sensing elements that can be continuously formed increases to 50 to 180, they are arranged in one row (this row is called a linear array) and the rows are arranged in a row. Two-dimensional information of the captured scene 34 is acquired by optically scanning in one vertical direction.

In the detector for utilizing the "atmosphere window" of 10 μm band (referred to as a wavelength region having a high atmospheric transmittance and usable for electromagnetic wave propagation), a two-dimensional array of detector elements is still in trial production. Since it is a stage, linear array type detectors are the mainstream, but the photoelectric conversion method is obtained by accumulating the induced charge and PC (Photo-Conductive) type detector that utilizes the change in electrical conductivity. PV (P
There is a hoto-Voltaic type detector.

In the former method, a bias current is passed through each element to read the change in electrical conductivity as a voltage signal, so the number of sensing elements is limited by the heat generated by the bias power, and there is a limit of about 200 sensing elements. Requires separate amplifier for output. The latter allows signals to be read out in series by transferring charges using a CCD, does not generate heat due to bias power, and requires only one output amplifier, thus increasing the number of sensing elements of several hundred at present. There is room. Therefore, the mainstream of linear array type detectors is currently shifting to IR (infrared) CCDs using PV type.

[0006]

2. Description of the Related Art As described above, a linear array type CCD has come to be used as a detector in the 10 .mu.m band, and as an optical scanning means in the direction perpendicular to the detector element array, it is shown in FIG. Like the mirror 30 that rotates in the middle of the optical axis
Is generally used to change the angle of arrival of the light beam incident on the sensing element array (thus, the azimuth at which an image is instantaneously captured with one element width) is changed.

6 and 7 show a control circuit of the mirror 30 of the infrared imaging device shown in FIG. 5, of which FIG. 6 shows a circuit for generating a scanning angle command value for the mirror 30. Reference numeral 7 denotes a circuit for automatically controlling the mirror 30 based on this scanning angle command value.

First, FIG. 6 shows the mirror angle θ shown in FIG.
The temporal change of _SCN × 2 (or imaging azimuth angle θ _in ) is a linear scanning angle command value in one field period as shown in the characteristic diagram of FIG. 8, that is, a scanning angle command value that changes linearly at a constant angular velocity. The sync signal generator 12 generates a sync signal of one field width from the field sync signal based on the master clock generated by the oscillator 11 and supplies the sync signal to the counter 13.

In this counter 13, the synchronization signal generator 12
During receiving the synchronization signal as a reset signal from the counts master clock providing the ROM14 the count value as an address signal, the mirror angle theta _SCN × corresponding in ROM14 the address signal as time data in FIG. 8 2 (or the imaging azimuth θ _in ) is stored in advance, and therefore the mirror angle θ _SCN × 2 (or the imaging azimuth θ
_Since the data of ( _in ) is read out and given to the D / A converter 15, the D / A converter 15 also outputs a linear scanning angle command value as shown in FIG. 8 based on the master clock.

This scanning angle command value is sent to the automatic control circuit shown in FIG. 7, and the angular deviation from the scanning angle detected by the angle sensor 26 for detecting the actual scanning angle of the mirror 30 is sent to the gain amplifier 21. It is converted into a proportional servo signal and sent to the integration circuit 22 to become an error integration signal, which are added together to form a PI control signal.

Further, this PI control signal becomes a PID servo signal by subtracting the signal obtained by differentiating the scanning angle from the sensor 26 by the differentiating circuit 23, and the current is obtained by the galvanometer 25 which drives the mirror 30. By driving the galvanometer 25 after amplification by the power amplifier 24 by the difference from the driving current value of, the mirror 30 is rotated to a desired scanning angle.

[0012]

As described above, when the CCD detector is scanned with the characteristics as shown in FIG.
The imaging direction changes momentarily even while the electric charge obtained by converting the received optical power by the detection element is accumulated (detection element integration time).

Since the scanning angle command value has a continuous linear characteristic, as shown in FIG. 9 (a), the watching angle of the sensing element (the angle at which the sensing element instantaneously sees it with respect to the size of the target object). It is a range, and the change in it is unreadable. Instantaneous view) Δω
The [rad] is from the state of the solid line shown in the figure (a state in which 100% CCD output is obtained at the start of charge accumulation shown in Fig. 6 (b)) to the state of the dotted line (50 at the end of charge accumulation shown in Fig. 6 (b)). % CCD
In the case of the camera, the optical axis is moving during exposure, that is, the camera shake occurs and blurring occurs.

The change in the image pickup direction due to scanning is within 1 pixel, and although it does not cause visible blurring, the sharpness of the edge is blunted, which causes deterioration of the MTF which leads to a reduction in the recognition distance.

That is, the amplitude ratio (MTF) τ _sc (f) of the output signal to the input signal of the spatial frequency f [cycle / rad]
Is expressed as τ _sc (f) = sin (π ・ Δω ・ f) / (π ・ Δω ・ f). For example, when the sensing element integration time is taken only for the time of angular scanning equal to the instantaneous visual field Δω, The signal amplitude of the video frequency (the one gray-scale cycle in which the grayscale of brightness changes for each instantaneous visual field is completed in two instantaneous visual fields, and the highest spatial frequency that can be imaged is 0.5 [cycle] / instantaneous visual field). This is 63.7% of the signal amplitude of a sufficiently low spatial frequency.

Therefore, according to the present invention, while controlling the scanning of the mirror based on the scanning angle command value that linearly changes at a constant angular velocity, the optical power from the imaged scene is reflected by the mirror and the charge is charged by the CCD detection element. It is an object of the present invention to make it possible to always maximize the output of a detection element in an infrared imaging device that converts the detection signal into the above, without being affected by the reading time interval of the charge accumulated in the CCD detection element.

[0017]

SUMMARY OF THE INVENTION In the present invention, as shown in principle in FIG.
The circuit 1 is provided for superimposing a waveform for flattening the change of the scanning angle of the accumulated charge during the reading time interval on the basis of the imaging sampling clock synchronized with the start time of the reading time interval.

Further, in the present invention, when the master clock for generating the scanning angle command value can be used as the imaging sampling clock, the scanning angle change during the reading time interval is used instead of the superposition circuit. The corrected scanning angle command value can be generated by using the memory that stores the flattening waveform in a superimposed manner.

Further, in the present invention, the above-mentioned superposed waveforms have a sawtooth shape having an inclination opposite to the scanning angle command value.

[0020]

[Action] In the prior art described above, the mirror angle changes the effective scanning period which has been varied at a constant angular velocity, the reading time interval (integration time) of the stored charge, as shown in FIG. 2 in the present invention each tau _SMPL In the superimposing circuit 1, the scanning angle change (increment of the nominal image pickup direction) corresponding to the time is changed into a stepwise change.

The difference in the scanning waveform is that the scanning angle command value to be input to the scanner for driving the mirror 30 is directed from the simple sawtooth wave with fine eyes (the interval is equal to the scanning angle corresponding to the accumulated charge reading interval). However, it can be realized simply by changing to a sawtooth wave in which the sawtooth waves having the opposite slopes and the same inclination are superimposed.

As described above, according to the present invention, by superimposing the scanning waveforms as shown in FIG. 2, the contribution of the change of the imaging direction during the integration time of the sensing element to the MTF deterioration is reduced, and the MTF is improved and the image is sharpened. Can be improved.

[0023]

FIG. 3 is a block diagram showing an embodiment of an infrared image pickup device according to the present invention. In this embodiment, the waveform superimposing circuit 1 synchronizes with the start time of the charge accumulation time interval of the sensing element. The buffer 2 for inputting the "imaging sampling clock", the delay line 3 for delaying the output signal of the buffer 2 by a predetermined time, the inverter 4 for inverting the output signal of the delay line 3, and the buffer 2
For inputting the output signal of the inverter and the output signal of the inverter 4
Sawtooth wave generation for generating a signal having the same inclination angle but opposite polarity of the sawtooth wave signal of the D / A converter 15 described in the conventional example from the output signal of the ND gate 5 and the NAND gate 5. Resistor R1, which constitutes a circuit (CR circuit)
R2 (R1 << R2), diode D1, capacitor C1, buffer 7 for receiving the output signal of the sawtooth wave generation circuit with high impedance, scan angle command value from D / A converter 15, and buffer It is composed of resistors R3 to R5 and an operational amplifier 8 which form an adder for adding the output signal of the No. 7 output signal. The other structure is similar to that of the conventional example shown in FIG.

In such an embodiment, the integration time constant depending on the values of the resistor R1 and the capacitor C1 of the CR circuit is D /
The resistance R of the adder should be the same as the slope a of the sawtooth wave output from the A converter 15 but to have a sawtooth wave with a reverse polarity slope a '.
The resistor R4 is adjusted so that 3 to R5 are a '(R5 / R4) = a (R5 / R3). In practice, the waveform of the terminal TP1 shown in the figure is observed with an oscilloscope or the like, and the resistor R4 is adjusted so that the "nominal imaging direction area" becomes flat.

When this is added to the original scanning waveform, it is constant during the period corresponding to the sensing element integration time,
A scanning angle command value (see FIG. 2) in which the transition increases stepwise is generated.

If the corrected scanning angle command value is used as the command angle of the conventional galvanometer-scanner control circuit shown in FIG. 7, a scanning waveform close to that shown in FIG. 2 can be obtained.

FIG. 4 shows a modification of the embodiment shown in FIG. 3. In this embodiment, when the master clock can be used as the imaging sampling clock, R
A step-like change can be incorporated in advance in the OM 14, and the hardware is the same as that of the conventional configuration of FIG. 6, and the corrected scanning angle command value can be obtained by a simpler circuit. ..

[0028]

As described above, according to the infrared image pickup device of the present invention, a waveform for flattening the change of the scanning angle during the reading time interval of the charge accumulated in the sensing element is read with respect to the scanning angle command value. A circuit for superimposing on the basis of the imaging sampling clock synchronized with the start time of the time interval is provided, or when the master clock for generating the scanning angle command value can be used as the imaging sampling clock, the superimposing circuit Instead, the memory is stored in such a manner that waveforms for flattening the change of the scanning angle during the reading time interval are stored and the corrected scanning angle command value is generated to read the accumulated charge of the sensing element. A scanning waveform that maintains the nominal imaging azimuth during the time interval is obtained, and the incident luminous flux azimuth is kept constant while accumulating the charges generated by photoelectric conversion. Can, MT by the scanning of the charge storage
It is possible to prevent the deterioration of F and improve the sharpness of the image.

The ratio of the time during which the image is picked up in the nominal image pickup direction to the read time interval of the accumulated charge of the detecting element is set to x%, and the integrated value of the optical power incident at other times is in the vicinity thereof. Assuming that it is equal to the integrated value of the average optical power from the scene, the signal amplitude of the highest video frequency becomes x% of the signal amplitude of a sufficiently low spatial frequency, and the time taken to capture the nominal imaging direction is 64%. If the above can be maintained, the effect of MTF improvement can be obtained.

Further, in reality, since the step width is about one instantaneous visual field, there is a contribution to signal transmission similar to scanning at a constant angular velocity even during a step-like change period.
Even if the scanning waveform is slightly corrugated, the effect of improving the MTF is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration principle of an infrared imaging device according to the present invention.

FIG. 2 is a diagram showing a working principle of the infrared imaging device according to the present invention.

FIG. 3 is a block diagram showing an embodiment of an infrared imaging device according to the present invention.

FIG. 4 is a block diagram showing another embodiment of the infrared imaging device according to the present invention.

FIG. 5 is a diagram showing a schematic configuration of a general infrared imaging mechanism.

FIG. 6 is a block diagram showing a configuration of a conventional example.

FIG. 7 is a block diagram showing an automatic control unit of a mirror in the present invention and a conventional example.

FIG. 8 is a graph showing a temporal change of a mirror angle (imaging azimuth angle) in a conventional example.

FIG. 9 is a graph for explaining the problems of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Waveform superposition circuit 30 Mirror 31 Imaging scene 34 Detection element In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. The optical power from the imaged scene is reflected by the mirror (30) while controlling the scanning of the mirror (30) based on a scanning angle command value that linearly changes at a constant angular velocity, and CC
In the infrared image pickup device for converting into electric charge by the D detection element (34), a waveform for flattening the change of the scanning angle during the read time interval of the accumulated electric charge of the detection element (34) is set to the scanning angle command value. Imaging sampling synchronized with the start of the readout time interval
An infrared imaging device comprising a circuit (1) for superimposing based on a clock. 2. When a master clock for generating the scanning angle command value can be used as the imaging sampling clock, a waveform for flattening the scanning angle change during the reading time interval is used instead of the superimposing circuit. The infrared imaging device according to claim 1, wherein a corrected scanning angle command value is generated by using a memory stored in a superimposed form. 3. The waveform according to claim 1, wherein the waveform has a sawtooth shape having an inclination opposite to the scanning angle command value.
The infrared imaging device according to.