JPH08139985A - Automatic focus control method and circuit, and scanning infrared imager - Google Patents

Abstract

(57) [Summary] [Objective] For example, regarding an automatic focus control method and circuit used in remote sensing, and a scanning infrared imaging device,
The objective is to keep the focus always at infinity during the effective scanning period. [Configuration] In a scanning infrared imaging device, which uses an optical system and a scanning mirror to cause infrared rays from the outside to enter an infrared detector, and the infrared detector extracts an image signal from the incident infrared light, during a scanning mirror invalid scanning period, Insert the reflection means into the optical system, the infrared detector itself emits the radiation, and the infrared detector itself picks up from the infrared rays reflected by the reflection means and returned so that the level of the image signal of the infrared detector itself becomes maximum It is configured to automatically control the distance from the detector.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus control method and circuit used in remote sensing, and a scanning infrared imager.

A scanning infrared imager is used, for example, when remote sensing or remote monitoring is performed by an observation device mounted on an aircraft or an artificial satellite, but it is not affected by fluctuations in ambient temperature or vibrations. , It is necessary to keep the focus of the device at infinity while acquiring the video signal.

[0003]

2. Description of the Related Art FIG. 5 is an overall system diagram of a conventional example, and FIG. 6 is a scanning mirror operation explanatory diagram. The description of FIGS. 5 and 6 will be given below.

In FIG. 5, infrared rays from infinity (which are in a state of parallel light flux because of infinity) pass through a first optical system composed of lenses L ₁ and L ₂ , and an optical path is bent by a scanning mirror 11. Focus through infrared detector 55 through lens L ₃ .

Therefore, the infrared detector converts the infrared signal into an electric signal to take out a video signal, and this signal is sent to the outside through the video amplifier 54 for display. In the infrared detector 55, for example, a plurality of infrared detecting elements are arranged in a line, but a two-dimensional video signal can be obtained by scanning the scanning mirror.

Since the incident parallel rays of infrared rays are radiated as they are from the lenses L ₁ and L ₂ , the afocal lens system and the portion of the lens L _{3 form} the parallel rays on the focal plane. Therefore, it is called an imager lens system.

Further, since the scanning mirror driving portion 4 sends a clock (hereinafter referred to as a driving pulse) to the scanning mirror 11 having a pulse motor (not shown), the pulse motor rotates, and the scanning mirror correspondingly rotates. As shown in 6, the scanning angle linearly changes within a range of ± several degrees.

During the effective scanning period (the period during which a video signal is acquired), the changing speed is, for example, 3 pulses at point a → point.
Scan up to b, but invalid scan period (scanning mirror at initial position a
During the period (return period), for example, the pulse is returned at a faster speed than during one pulse and the effective scanning period. At this time, the phase of the drive pulse is changed to reverse the drive current.

Next, in the adjustment of the focus in the infrared detector 55, the operator finds the focus shift by looking at the displayed image, and the knob 53 in FIG. 5 is rotated manually or by a remote controller to rotate the gear. Here, the screw cut on the outside of the lower lens barrel 52 meshes with the screw cut on the inside of the upper lens barrel 51, so by rotating the gear, the lower lens barrel rotates while the lower lens barrel rotates. Move in and out (see up and down arrows).

As a result, the distance between the lens L ₃ and the infrared detector 55 changes, so that the operator fixed the knob while the displayed image was clearly visible. However, in such a method, the operator needs to focus each time the lens L ₃ (which has the greatest influence on the focus adjustment) deviates from the optimum position due to temperature fluctuations, mechanical deviations, and the like.

[0011]

As described above, the operator finds the defocus by looking at the displayed image, and the lens L ₃
This gap had to be minimized by manually adjusting the spacing between the and infrared detectors.

In particular, when mounted on a vehicle, there is a problem that the number of times of focus adjustment is increased because the focus shifts more frequently due to vibration. It is an object of the present invention to keep the focus always at infinity during the effective scanning period.

[0013]

According to a first aspect of the present invention, a reflecting means is inserted into an optical system during an invalid scanning period of a scanning mirror. Therefore, the infrared detector itself radiates, and the level of the video signal of the infrared detector itself extracted from the infrared rays returned by being reflected by the reflecting means is maximized between the optical system and the infrared detector. The interval is automatically controlled.

According to a second aspect of the present invention, a first optical system for converting an infrared ray from the outside into a parallel luminous flux, and a mirror surface angle linearly changing from θ ₀ to θ ₁ with respect to the infrared ray of the parallel luminous flux. And a second optical system for forming an image of infrared rays of a parallel light flux whose optical path is bent by the scanning mirror section, and an infrared detector for converting the formed infrared rays into an electric signal and extracting a video signal. In the scanning infrared image device having, during the invalid scanning period when the mirror surface angle of the scanning mirror returns from θ ₁ to θ ₀ , a reflection means for reflecting the infrared rays of the incident parallel light flux, and the infrared detector itself emits, An automatic control that automatically controls the interval between the second optical system and the infrared detector so that the level of the video signal of the infrared detector itself extracted from the infrared light reflected by the reflecting means and returned is maximized. Focus control means is provided.

According to a third aspect of the present invention, infrared rays pass through the reflecting means as they are during the effective scanning period of the scanning mirror.
During the invalid scanning period, the infinity reference plate has a structure that reflects infrared rays emitted by the infrared detector itself, and a drive portion that rotates the infinity reference plate in synchronization with the scanning operation of the scanning mirror.

According to a fourth aspect of the present invention, the scanning infrared imager is provided with the automatic focus control circuit, and the focus is always kept at infinity during the effective period of the scanning mirror.

[0017]

In the first aspect of the present invention, the optical system is provided with the reflecting means in addition to the scanning mirror. Here, the reflecting means is, for example, a metal disk provided with a plurality of cutouts, and during the period in which a normal image is to be acquired (effective scanning period), the infrared rays of the incident parallel light flux cutouts. The optical path is bent by the scanning mirror while passing through as it is. However, during the invalid scanning period when the scanning mirror returns to the initial position, it becomes a part of the metal plate, so that the infrared rays are completely reflected.

That is, during the effective scanning period, the cut portion,
During the invalid scanning period, the rotating operation of the reference plate at infinity is synchronized with the oscillating operation of the scanning mirror so that it becomes a metal plate portion. As a result, during the invalid scanning period, the infrared ray detector itself cooled to an extremely low temperature emits the infrared ray, which is reflected by the reflecting means and returned to detect the image signal of itself.

At this time, if it is out of focus, only a part of the returned infrared rays can be detected, and the level of the video signal is lowered. Therefore, the imager lens system L ₃ and infrared ray detection are performed so that this level becomes maximum. The distance to the vessel is automatically controlled.

A second aspect of the present invention is a reflection device for reflecting infrared rays incident on a scanning infrared image device having a first optical system, a scanning mirror section, a second optical system and an infrared detector during an invalid scanning period. Means and automatic focus control means are provided.

Then, the automatic focus control means uses the second optical element so that the level of the video signal of its own extracted from the infrared rays radiated by the infrared detector itself and returned through the reflecting means is maximized. The system is configured to automatically control the distance between the system and the infrared detector.

In the third aspect of the present invention, the reflecting means is composed of the infinity reference plate and the driving portion. According to a fourth aspect of the present invention, the scanning infrared imager is provided with an automatic focus control circuit to keep the focus always at infinity during the effective scanning period of the scanning mirror.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of the essential parts of the first to fourth embodiments of the present invention, and FIG. 2 is a diagram for explaining the operation of FIG. Explanatory diagram of output signal to be sent,
(b) is an explanatory view of an infinity reference plate. FIG. 3 is a configuration diagram of a main part of a reference plate driving part in FIG. 1, and FIG. 4 is a configuration diagram of a main part of a maximum value detection part in FIG.

Here, the lenses L ₁ and L ₂ are the first optical system, the scanning mirror 11 and the scanning mirror driving portion 12 are the constituent portions of the scanning mirror portion 1, the infinity reference plate 21, the reference plate driving portion 22 and the motor. Reference numeral 23 is a component part of the reflection means 2, a maximum value detection part 31, a motor 32, a gear 33.
Is a component of the automatic focus control means 3. In addition, the same reference numerals denote the same objects throughout the drawings.

1 to 4, the parts described in detail above will be briefly described, and the parts of the present invention will be described in detail. First, as shown in FIG. 2 (b), the infinity reference plate 21 which is a constituent element of the reflection means 2 in FIG. 1 is, for example, a mirror-finished metal plate having a diameter of about 10 cm, which is incident during the invalid scanning period. It is composed of a reflection portion 211 that reflects infrared rays and a notch portion 212 that allows the infrared rays that have been incident during the effective scanning period to pass therethrough.

Then, as shown in FIG. 3, the infinity reference plate 21
And an encoder 221 are concentrically attached to the shaft of the motor 23. Now, when the motor 23 rotates, the encoder 221
The reference plate at infinity also rotates, but a pulse corresponding to the number of rotations is sent from the encoder 221 to the frequency dividing portion 226, but the period of this pulse is shorter than the period of the clock from the scanning mirror driving portion 12. .

The frequency dividing portion 226 is of a counter type,
The frequency division ratio m is determined by the application timing of the synchronizing signal from the scanning mirror driving portion (the value of m is set so that the above pulse period is approximately the same as the clock period from the scanning mirror driving portion). The pulse sent by the encoder 221 is frequency-divided by m and sent to the phase detector 225.

Since the clock from the scanning mirror driving section is also added to the phase detector 225, an output corresponding to the phase difference is taken out and applied to the voltage controlled oscillator 223 as a control voltage via the low pass filter 224. .

The voltage-controlled oscillator 223 outputs a pulse whose control voltage is, for example, 0 to the motor 23 via the amplifier 222.
Add to As a result, the rotation speed of the motor is controlled and is always synchronized with the operation of the scanning mirror, and as shown in FIG. 6, it is in the reflective state during the invalid scanning from the effective scanning end position b to the initial position a. .

As described above, the reference plate at infinity is in a reflecting state during the invalid scanning period, and the infrared rays of the parallel light flux passing through the afocal lenses L ₁ and L ₂ shown in FIG. 1 are reflected. . On the other hand, the infrared detector 55 emits infrared rays corresponding to about 80K from the detector itself because it is in an extremely low temperature environment of about 80K, for example.
L ₃ is reflected by the reference plate at infinity via the scanning mirror 11 and again applied to the infrared detector to take out the image signal of itself. Then, this video signal is amplified by a video amplifier,
It is displayed in the display system.

Since the scanning mirror scans as described above, when the center of scanning is reached (the infrared detector is placed at the center of scanning), the infrared detector detects its own infrared rays. Upon reception, a downward image as shown on the right side of Fig. 2 (a) is obtained.

This is because the peripheral portion that is not the center of scanning, for example, the lens barrel or the inside of the apparatus, is at a normal temperature environment (for example,
The temperature of the latter is lower than that of the former because the infrared detector is in a cryogenic environment.

When the focus is not in focus, the infrared rays reflected by the detector itself spread, so that the temperature rises on average and looks like a dotted line. 31 detects and controls the position of the imager lens L ₃ so that the output of the video amplifier becomes maximum.

Here, the maximum value detection part has a structure as shown in FIG. 4, and a part of the output of the input image amplifier is input.
The A / D conversion unit 311 converts it to a digital signal and stores it in the current value register 312 sequentially.

On the other hand, the maximum value register 314 stores the maximum value of the digital signals up to the present, and this maximum value is applied to the comparison portion 313. Therefore, the comparison portion compares the magnitude of the current digital signal and the maximum value at the time when the detector image detection synchronizing signal is applied from the scanning mirror driving portion, and indicates an increase or a decrease according to the comparison result. The signal is sent to the drive polarity generation part 315, and when the comparison result is the output of the current value register> the output of the maximum value register, the maximum value storage command is sent to the maximum register 314 to output the output of the current value register to the maximum value register. Store and update maximum value.

Since the drive polarity generating section 315 generates a drive signal having a polarity corresponding to the input comparison result and applies it to the motor 32 shown in FIG. 1, the motor changes its rotation direction in accordance with the polarity of the drive signal. However, the voltage of the video signal of the infrared detector itself becomes maximum downward, and the focus of the imager lens L ₃ comes to be focused on the infrared detector.

That is, the imager lens is driven so that the image of the infrared detector is maximized, and an infrared image focused at infinity is always obtained as the entire apparatus.

[0038]

As described in detail above, according to the present invention, it is possible to keep the focus always at infinity during the effective scanning period.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram of an embodiment of first to fourth embodiments of the present invention.

2 is an explanatory diagram of the operation of FIG. 1, (a) is an explanatory diagram of an output signal sent by an infrared detector during a valid / invalid scanning period, (b)
FIG. 3 is an explanatory diagram of an infinity reference plate.

FIG. 3 is a main part configuration diagram of a reference plate driving portion in FIG. 1.

FIG. 4 is a main part configuration diagram of a maximum value detection part in FIG. 1.

FIG. 5 is an overall system diagram of a conventional example.

FIG. 6 is an explanatory diagram of a scanning mirror operation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Scanning mirror section 2 Reflecting means 3 Automatic focus control means 11 Scanning mirror 11 12 Scanning mirror drive section 21 Infinity reference plate 22 Reference plate drive section 23, 32 Motor 31 Maximum value detection section 33 Gear

Claims (4)

[Claims] 1. A scanning infrared imager, wherein an infrared ray from the outside is made incident on an infrared detector using an optical system and a scanning mirror, and an image signal is taken out from the incident infrared ray at the infrared detector. During the scanning period, the reflection means is inserted into the optical system, the infrared detector itself emits the radiation, and the level of the image signal of the infrared detector itself extracted from the infrared rays reflected by the reflection means and returned to the maximum level. The automatic focus control method is characterized in that the distance between the optical system and the infrared detector is automatically controlled. 2. A first parallel beam of infrared rays from the outside
Optical system, a scanning mirror section that repeats linearly changing the mirror surface angle from θ ₀ to θ ₁ with respect to the infrared rays of the parallel light flux, and infrared rays of the parallel light flux whose optical path is bent by the scanning mirror section. In the scanning infrared image device having a second optical system for forming an image and an infrared detector for converting the formed infrared light into an electric signal to take out an image signal, the mirror surface angle of the scanning mirror is from θ ₁ to θ _0. During the invalid scanning period, the image signal of the infrared ray detector itself emitted from the infrared ray detector emitted by the reflecting means and the infrared ray detector itself for reflecting the incident infrared ray of the parallel light flux and reflected by the reflecting means. The automatic focus control circuit is provided with an automatic focus control means for automatically controlling the distance between the second optical system and the infrared detector so that the level of (1) is maximized. 3. An infinity reference plate having a structure in which the reflection means allows infrared rays to pass through during the effective scanning period of the scanning mirror, but reflects the infrared rays emitted by the infrared detector itself during the invalid scanning period. 3. The automatic focus control circuit according to claim 2, further comprising: a drive portion for rotating the reference plate at infinity in synchronization with the scanning operation of the scanning mirror. 4. The scanning infrared imager according to claim 1, wherein the automatic focus control circuit is provided, and the focus is always kept at infinity during the effective period of the scanning mirror. Scanning infrared imager.