JP5139891B2 - Imaging system and peripheral monitor device - Google Patents

Description

  The present invention relates to an imaging system and a peripheral monitor device.

  2. Description of the Related Art In recent years, an in-vehicle monitoring device, a security monitoring system, and the like have taken a surrounding situation with a solid-state imaging means such as a CCD camera. When these devices perform photographing, there are cases where light such as infrared rays is continuously irradiated in the photographing direction and the reflected light is photographed. For example, photographing is performed while illuminating infrared rays in front of a moving vehicle. In such a photographing method, there is a problem that an object existing in the vicinity appears bright and an object existing in the distance appears dark. In addition, since light is continuously irradiated, in the case of weather conditions such as fog and rain, the light is reflected by raindrops and the like, and it is difficult to photograph a distant place.

  On the other hand, there is an imaging method using an image intensifier that enhances the light intensity of an incident light image (see, for example, Patent Document 1). When an image intensifier is used, a natural image can be obtained without being affected by light irradiation as compared with the above method. For example, when an image intensifier is used, a road sign that could not be recognized due to reflection of light when shooting with infrared light in front of a moving vehicle using the above method without using an image intensifier Can be recognized.

Patent Document 1 describes an in-vehicle low-field imaging system using an image intensifier. The system described in this document irradiates an object to be imaged with pulsed light, and makes the time interval between the emission timing of the pulsed light and the imaged timing variable according to the distance to the object to be imaged. Thus, even in an environment where the field of view is obstructed, it is possible to recognize an imaging object far away.
US Pat. No. 6,732,123

  In an imaging method using an image intensifier, a gate operation (electronic shutter operation) in which a gate voltage is applied for a short time is adopted, so that a remote imaging object can be suitably used even in weather conditions such as fog and rain. Can shoot. However, with this imaging method, the amount of reflected light obtained from a distant imaging object is extremely small compared to the amount of reflected light obtained from a nearby imaging object, resulting in an image with varying overall brightness.

  The present invention has been made in view of the above-described problems, has an imaging method using an image intensifier, and suppresses variations in light and darkness in an image due to the distance to the imaging object. An object of the present invention is to provide an imaging system and a peripheral monitor device capable of performing the above.

  In order to solve the above-described problems, an imaging system according to the present invention includes a pulse light source that irradiates an imaging target with pulsed light, an imaging device that captures an optical image related to the imaging target using pulsed light, a pulse light source, and an imaging device. The imaging device receives a light image and emits photoelectrons, and performs a gate operation by controlling the potential of the control unit, and a micro-surface that is arranged opposite to the photocathode and multiplies photoelectrons. It has a channel plate and an imaging unit that generates image data based on an electronic image emitted from the micro channel plate, and the control unit generates pulsed light from the pulse light source and raises the potential difference between both ends of the micro channel plate. Are periodically performed, and after the generation of the pulsed light, the gate of the photocathode is within the rising period of the potential difference at both ends. Characterized in that to open the.

  The imaging apparatus provided in the imaging system receives a light image, emits photoelectrons, and performs a gate operation by controlling the potential by a control unit, and a microchannel plate (MCP) that is disposed opposite to the photocathode and multiplies photoelectrons. And so-called image intensifier. This image intensifier can enhance the incident light image with a multiplication factor corresponding to the potential difference between both ends applied to the MCP. In the imaging system described above, the generation of the pulsed light and the rise of the potential difference at both ends of the MCP are performed periodically, and after the generation of the pulsed light and within the rise period of the potential difference at both ends, The imaging object is photographed by the imaging device by opening the gate. It should be noted that the rising period of the potential difference between both ends is an extremely short time such as about 500 nanoseconds. Of these, the gate opening time of the photocathode is, for example, about 300 nanoseconds.

  The time required for the pulsed light to be reflected by the imaging object and returned as an optical image varies depending on the distance from the imaging object to the imaging device, but the imaging object included in the incident light image immediately after the gate is opened is imaged. The imaging object included in the incident light image is closer to the imaging device as the gate opening time elapses. Since the optical image becomes weaker as the imaging object is farther from the imaging device, the light amount of the incident optical image becomes smaller as the gate opening time elapses. However, in the imaging system described above, the gate of the photocathode is opened within the rise period of the potential difference between both ends of the MCP, so that the potential difference between both ends of the MCP monotonously increases while the gate is opened. That is, in the imaging target included in the optical image, the multiplication factor by the image intensifier increases as the distance from the imaging device increases. Therefore, according to the imaging system described above, it is possible to suppress variations in light and darkness in the image due to the distance to the imaging target.

  In addition, the imaging system may be characterized in that the increasing rate of the potential difference between both ends of the microchannel plate during the rising period is variable. For example, when comparing clear weather and rainy weather, the amount of incident light image is relatively large even when the object is far from the imaging system in fine weather, but the pulse light is blocked by rain in rainy weather. The light quantity of the incident light image related to the imaging object far from the imaging system is smaller than that in fine weather. In such a case, by changing the rate of increase of the potential difference between both ends of the rise of the potential difference between both ends of the MCP, that is, by increasing the increase rate of the photomultiplier of the image intensifier, for example, when it is raining, than when clearing, A clearer image can be obtained while suppressing the influence of such imaging conditions.

  In the imaging system, the increasing rate of the potential difference between both ends of the microchannel plate during the rising period of the both ends changes with time, and the timing at which the gate of the photocathode is opened in the control unit is variable. This may be a feature. With such a configuration, the increase width of the light multiplication factor of the image intensifier while the gate is open can be suitably changed according to the imaging condition, so that a clearer image can be obtained while suppressing the influence of the imaging condition.

  The imaging system may be characterized in that the pulse light source has an LED. Thereby, pulsed light can be easily generated.

  A peripheral monitor device according to the present invention is a peripheral monitor device that monitors a surrounding situation, and includes any one of the imaging systems described above. Since the peripheral monitor device includes the above-described imaging system, it is possible to effectively suppress variations in brightness and darkness in the image due to the distance to the imaging target.

  According to the present invention, it is possible to provide an imaging system and a peripheral monitor device that are equipped with an imaging method using an image intensifier and that can suppress variations in brightness and darkness in an image due to the distance to the imaging object. .

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an imaging system and a peripheral monitor device according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(Embodiment)
FIG. 1 is a diagram showing a configuration according to an embodiment of an imaging system according to the present invention. The imaging system 1 according to the present embodiment constitutes a peripheral monitor device that monitors surrounding conditions, such as an in-vehicle monitoring device or a security monitoring system. As shown in FIG. 1, the imaging system 1 includes a pulse light source 2 that irradiates an imaging target (subject) A with pulsed light P, and a light image (mainly reflected light image) B related to the imaging target A by the pulsed light P. And a control unit 4 that controls the pulse light source 2 and the imaging device 3.

  The pulse light source 2 includes a semiconductor light emitting element 5 such as a light emitting diode (LED) or a laser diode (LD), and a lens 6 that expands the pulsed light P emitted from the semiconductor light emitting element 5 in the photographing direction. Yes. The semiconductor light emitting element 5 emits, for example, infrared light as the pulsed light P. As described above, the pulsed light P can be easily generated by having the semiconductor light emitting element 5 that can easily switch between the light emitting state and the non-light emitting state by supplying power, such as the LED or LD. .

The imaging device 3 receives an image intensifier 10 that increases the amount of light of an optical image B incident from the imaging object A, and an imaging unit (CCD) that receives the optical image output from the image intensifier 10 and generates image data. Camera) 11. Further, the imaging device 3 includes a lens 12 that forms an optical image B toward the image intensifier 10, an optical member 13 that propagates the optical image output from the image intensifier 10 to the CCD camera 11, and an image. A voltage source 14 that applies a driving voltage to the intensifier 10 and a gain control unit 15 that controls the magnitude of the driving voltage output from the voltage source 14 are provided. For example, a relay lens or a fiber optic plate (FOP) is suitable as the optical member 13.

  Here, FIGS. 2 and 3 are diagrams showing a detailed configuration of the image intensifier 10. FIG. 2 is a plan view showing the image intensifier 10 in a partially broken view, and FIG. 3 is a cross-sectional view showing a part of the image intensifier 10 shown in FIG. 2 along the line III-III. . In FIG. 3, for the convenience of explanation, the size of each member is slightly changed from the image intensifier 10 of FIG. An image intensifier 10 shown in FIGS. 2 and 3 is a proximity image intensifier in which a photocathode, an MCP (microchannel plate: electron multiplier), and a phosphor screen are placed in proximity within an envelope. is there.

As shown in FIG. 2, the inside of the image intensifier 10 is hermetically sealed at both ends of a substantially hollow cylindrical envelope 20 by a substantially disc-shaped entrance window 30 and a substantially cylindrical exit window 70. Thus, a high vacuum having a pressure of about 1 × 10 ⁻⁸ [Torr] to 1 × 10 ⁻⁶ [Torr] (1.33 × 10 ⁻⁶ [Pa] to 1.33 × 10 ⁻⁴ [Pa]) Is held in. The envelope 20 covers a substantially hollow cylindrical side tube member 21, a substantially hollow cylindrical mold member 22 covering a side portion of the side tube member 21, and a side portion and a bottom portion of the mold member 22. A substantially hollow cylindrical case member 23 is included. In particular, two openings are respectively formed at both ends of the mold member 22. One end of the case member 23 is formed open, and the other end of the case member 23 is formed with an opening in which one opening of the mold member 22 is aligned with the periphery thereof.

On one end side of the mold member 22, an incident window 30 is installed in close contact with the surface around one opening of the mold member 22. A thin-film photocathode 40 is formed in the central region of the vacuum side surface of the entrance window 30. The photocathode 40 receives the light image B and emits photoelectrons e ₁ . The incident window 30 and the photocathode 40 constitute a photocathode 35.

Further, on the other end side of the mold member 22, an emission window 70 is installed in close contact with the other opening of the mold member 22. A thin-film fluorescent screen 60 is formed in the central region of the vacuum side surface of the exit window 70. Further, a disc-shaped MCP 50 is installed between the photocathode 40 and the phosphor screen 60 so as to face the photocathode 40 and the phosphor screen 60 with a predetermined gap therebetween. The MCP 50 is held by the other end portions of electrodes 81 and 82 made of two kinds of conductive members supported by burying one end portion in the side tube member 21, and photoelectrons e ₁ emitted from the photocathode 40. Is multiplied.

  A metal conductive film (not shown) is formed in contact with the photocathode 40 in the peripheral region on the vacuum side surface of the entrance window 30. This conductive film is in contact with an electrode 80 made of a conductive member for joining the side tube member 21 and the entrance window 30. Specifically, one end of the electrode 80 is buried in the mold member 22 and the other end is in contact with the conductive film.

  A metal conductive film (not shown) is formed in contact with the phosphor screen 60 in the peripheral region on the vacuum side surface of the emission window 70. An electrode 83 is provided so as to be in contact with the conductive film. Specifically, one end of the electrode 83 is buried in the mold member 22 and the other end is in contact with the conductive film.

  Four types of lead wires 90 to 93 that are in contact with one end portions of the four types of electrodes 80 to 83 are installed so as to penetrate the mold member 22 and the case member 23 in an airtight manner and protrude to the outside. The other end portions of the lead wires 90 to 93 are electrically connected to the voltage source 14 (see FIG. 1). Therefore, a high voltage is applied from the voltage source 14 to the photocathode 40, the photocathode side surface of the MCP 50, the phosphor screen side back surface, and the phosphor screen 60, respectively.

As shown in FIG. 3, about 200 [V] is set as the potential difference V ₁ between the photocathode 40 and the photocathode side surface of the MCP 50. About 400 [V] to about 900 [V] are variably set as the potential difference V ₂ between the photocathode side surface and the phosphor screen side surface of the MCP 50. About 6 [kV] is set as the potential difference V ₃ between the phosphor screen side surface of the MCP 50 and the phosphor screen 60. As a result, the phosphor screen 60 is located between the gap between the photocathode 40 and the MCP 50, the inside of the channel tube arranged between the electron incident surface and the electron exit surface of the MCP 50, and the gap between the MCP 50 and the phosphor screen 60. Electric fields from the photocathode 40 toward the photocathode 40 are generated.

  The entrance window 30 is a glass face plate formed by processing sapphire into a shape having a substantially flat surface in the central region of each surface on the atmosphere side and the vacuum side. The photocathode 40 is formed by growing gallium arsenide (GaAs) on the entrance window 30. The photocathode 40 is set to a potential of about −150 [V] to about −200 [V] based on the voltage applied from the voltage source 14 via the lead wire 90 and the electrode 80.

  The exit window 70 is a fiber plate configured by converging a large number of optical fibers into a plate shape. The phosphor screen 60 is formed by applying a phosphor to the vacuum side surface of the exit window 70, and is made of, for example, GdO2S2: Tb. The phosphor screen 60 is set to a potential of about 5000 [V] to about 6000 [V] based on the voltage applied from the voltage source 14 via the lead wire 93 and the electrode 83.

  Note that a metal back layer and a low electron reflectivity layer are sequentially laminated on the vacuum side surface of the phosphor screen 60. The metal back layer is formed by depositing Al on the surface of the phosphor screen 60. This metal back layer has a relatively high reflectivity with respect to light incident through the MCP 50 and has a relatively high transmittance with respect to photoelectrons emitted from the MCP 50 and incident. The low electron reflectivity layer is formed by evaporating C, Be or the like on the surface of the metal back layer. This low electron reflectivity layer has a relatively low reflectivity for photoelectrons emitted from and incident on the MCP 50.

  FIG. 4 is a perspective view showing the MCP 50 shown in FIG. As shown in FIG. 4, the MCP 50 includes at least one electron multiplication region 51 formed by converging a plurality of channel tubes 52 in a plate shape, and a glass edge portion 53 surrounding the electron multiplication region 51. And. The pitch of the channel tubes 52 arranged on the electron incident surface and the electron emission surface of the electron multiplying region 51 is about 7.5 [μm] to about 25 [μm] as the distance between the centers of the adjacent channel tubes 52. .

  The photocathode side surface of the MCP 50 is set to the ground potential based on the voltage applied from the voltage source 14 via the lead wire 91 and the electrode 81. The back surface of the MCP 50 on the phosphor screen side is set to a potential of about 400 [V] to about 900 [V] based on the voltage applied from the voltage source 14 via the lead wire 92 and the electrode 82.

When the light image B passes through the entrance window 30 from the outside and enters the photocathode 40, electrons located in the valence band of the photocathode 40 are excited to the conduction band, and the two of the photoimage B are caused by the negative electron affinity action. Photoelectrons e ₁ holding the dimensional position information are emitted into the vacuum. Thus, the photoelectrons e ₁ emitted from the photocathode 40 are accelerated by the electric field generated in the gap between the photocathode 40 and the MCP 50 and enter the electron incident side surface of the MCP 50.

The photoelectrons e ₁ incident on the MCP 50 are accelerated by the electric field generated inside the channel tube 52, move while repeatedly colliding with the wall surface of the channel tube 52, and generate electron-hole pairs each time energy is lost. The electrons generated as the electron-hole pairs repeat the process of generating electron-hole pairs as secondary electrons in the same manner as the photoelectrons e ₁ . Therefore, the photoelectron e ₂ multiplied in comparison with the photoelectron e ₁ is emitted from the phosphor screen side surface of the MCP 50 as an electronic image holding the two-dimensional position information of the optical image B. At this time, the gain of the photoelectron e ₂ with respect to the photoelectron e ₁ reaches about 1 × 10 ³ to about 2 × 10 ⁴ due to the potential difference V ₂ at both ends. Thus, the photoelectrons e ₂ emitted from the MCP 50 are accelerated by the electric field generated in the gap between the MCP 50 and the phosphor screen 60 and enter the phosphor screen 60.

A light image C generated as fluorescence corresponding to the photoelectrons e ₂ incident on the phosphor screen 60 enters the emission window 70. The light image C incident on the emission window 70 in this way is emitted toward the CCD camera 11 through the optical member 13 as an optical image holding the two-dimensional position information of the light image B.

With reference to FIG. 1 again, the configuration of the imaging system 1 according to the present embodiment will be described. The control unit 4 includes an MCP gate circuit 16, a PC gate circuit 17, and a timing circuit 18. The MCP gate circuit 16 is electrically connected to the lead wires 91 and 92 of the image intensifier 10 shown in FIG. 2, and the potential difference V ₂ between both ends of the MCP 50 applied through the electrodes 81 and 82 is determined. Controls gate operation. The PC gate circuit 17 is electrically connected to the lead wire 90 of the image intensifier 10 shown in FIG. 2 and controls the gate operation for the potential of the photocathode 40 applied via the electrode 80. . The timing circuit 18 is electrically connected to each of the MCP gate circuit 16 and the PC gate circuit 17, and the gate open timing at each of the MCP 50 and the photocathode 40 is determined based on the MCP gate circuit 16 and the PC gate circuit 17. A signal for instructing to be output. The timing circuit 18 is electrically connected to the pulse light source 2 and outputs a signal for instructing the pulse light source 2 on the light emission timing of the semiconductor light emitting element 5. Here, the gate operation is to switch the image intensifier 10 between a state for outputting the light image C and a state for not outputting the light image C, and the gate opening means a state for outputting the light image C. Is to do.

Here, FIG. 5 is a timing chart showing (a) transition of potential difference V ₂ at both ends of MCP 50, (b) transition of potential of photocathode 40, and (c) transition of intensity of pulsed light P, respectively. Referring to FIG. 5A, the potential difference V ₂ at both ends of the MCP 50 rises in a periodic period T1, and this rising period T1, that is, the MCP 50 gate open period. The time width of the startup period T1 is, for example, 500 nanoseconds. The peak voltage of the potential difference V ₂ at both ends is, for example, 400 [V]. During the start-up period T1, the potential difference V ₂ at both ends of the MCP 50 monotonously increases, and the increase rate decreases with time in the period.

The image intensifier 10 enhances the incident light image B with a multiplication factor corresponding to the both-end potential difference V ₂ applied to the MCP 50. Here, FIG. 6 is a graph showing the relationship between the both-end potential difference V ₂ applied to the MCP 50 and the multiplication factor (luminance gain) with respect to the incident light image B. As shown in FIG. 6, the multiplication factor of the image intensifier 10 increases in proportion to the exponential function of the potential difference across V _2. Therefore, (see FIG. 5 (a)) during the period T1 to the potential difference across V ₂ of MCP50 increases monotonically, the multiplication factor of the image intensifier 10 also becomes possible to increase monotonically.

Referring to FIG. 5B, the potential of the photocathode 40 is applied as a negative pulse in the periodic period T2, and this period T2 is the gate open period of the photocathode 40. The time width of the period T2 is, for example, 300 nanoseconds. Period T2 is included in the start-up period T1 of the potential difference across V ₂ of MCP50 shown in FIG. 5 (a), the optical image B are captured by the image capturing device 3 only during the period T2. Further, as described above, the potential difference V ₂ at both ends of the MCP 50 monotonously increases during the start-up period T1, so the potential difference V ₂ at both ends of the MCP 50 also increases monotonously during the period T2, and the MCP 50 at the end of the period T2 is increased. the potential difference across V ₂₂ of the larger potential difference across V ₂₁ of MCP50 in the period T2 at the start.

Referring to FIG. 5C, the generation of the pulsed light P from the pulsed light source 2 is periodically performed in accordance with the rising cycle of the both-end potential difference V ₂ of the MCP 50. The gate opening period T2 of the photocathode 40 shown in FIG. 5B is set after the generation of the pulsed light P.

  The time required for the pulsed light P to be reflected by the imaging object and returned as the optical image B varies depending on the distance from the imaging object to the imaging device 3. That is, in the period T2 shown in FIG. 5B, the incident light image B immediately after the gate is opened includes the imaging object closest to the imaging device 3, and the incident light image B includes the imaging device as time passes. 3 includes an object to be imaged far from 3. Since the optical image becomes weaker as the imaging object is farther from the imaging device 3, the light amount of the incident light image B decreases with the passage of time in the period T2.

Therefore, in the imaging system 1 of the present embodiment, by opening the gate of the photocathode 40 in the period T2 in the start-up period T1 of the potential difference across V ₂ of MCP50. As a result, as described above, the potential difference V ₂ at both ends of the MCP 50 monotonously increases while the gate is open, and in the imaging target included in the optical image B, the image intensifier increases as the distance from the imaging device 3 increases. The light multiplication factor by 10 increases. Therefore, according to the imaging system 1 of the present embodiment, variations in brightness and darkness in the image due to the distance to the imaging object can be effectively suppressed.

  7 to 9 are images when the above effects are confirmed by the imaging system 1 according to the present embodiment. FIG. 7 is an image showing a daytime landscape that is a subject of photographing, and shows an approximate distance from the photographing position to the main building. FIG. 8A is a night image acquired as described above by the imaging system 1 according to the present embodiment, and FIG. 8B illustrates gate control in the photocathode 40 and the MCP 50 as in the present embodiment. This is a night image taken without both. 9A is a night image obtained by photographing only an object close to the gate photographing position only by the gate control of the photocathode 40. FIG. 9B is a photograph of only an object far from the gate photographing position. It is a night image. As shown in FIG. 8B, when the gate control is not performed, the light image relating to the object existing near the photographing position becomes brighter, and the light image relating to the object existing relatively far from the photographing position is obtained. It will be dark. On the other hand, in the image (FIG. 8A) obtained by the imaging system 1 of the present embodiment, the brightness variation in the image is suppressed regardless of the distance from the shooting position, and a clear image is obtained.

9A and 9B correspond to the captured image by the imaging system described in Patent Document 1 described above, but according to the imaging system 1 according to the present embodiment, described in Patent Document 1. Unlike the imaging system described above, it is possible to acquire an entire image with uniform brightness instead of obtaining an image of only an object at a specific distance according to the gate opening timing. In addition, since the imaging system described in Patent Document 1 does not include an electron multiplier, if an attempt is made to adjust the amplification factor as in the present embodiment, the voltage applied to the photocathode will be changed. In such a case, the dynamic range becomes extremely narrow. On the other hand, in the imaging system 1 according to the present embodiment, since the electron multiplication factor of the MCP 50 changes exponentially with respect to the potential difference V _{2 at} both ends (see FIG. 6), the dynamic range is widened and the image intensity is increased. The light multiplication factor of the fire 10 can be easily increased.

The imaging system 1 according to the present embodiment preferably further includes the following configuration. FIG. 10 is a timing chart showing (a) transition of the potential difference V ₂ at both ends of the MCP 50, (b) transition of the potential of the photocathode 40, and (c) transition of the intensity of the pulsed light P, respectively. The difference from FIG. 5 which has been already described, the rate of increase in the potential difference across V ₂ at start-up period T1 of the potential difference across V ₂ of MCP50, a timing of the gate opening period T2 of the photocathode 40.

That is, the peak voltage of the both-end potential difference V ₂ in the start-up period T1 shown in FIG. 10A is, for example, 900 [V], which is higher than the above-described 400 [V]. Duration of the rising period T1 because the same (500 nanoseconds) and FIG. 5 (a), the rate of increase in the potential difference across V ₂ at start-up period T1 is larger than the FIG. 5 (a). Further, regarding the gate opening period T2 of the photocathode 40 shown in FIG. 10B, the time width is the same as that in FIG. 5B (300 nanoseconds), but the rising period of the both-end potential difference V ₂ of the MCP 50 The start timing of the period T2 with respect to T1 (FIG. 10 (a)) is earlier than that in FIG. 5 (b).

As shown in FIG. 10A, the increasing rate of the both-end potential difference V ₂ in the start-up period T1 changes with time in the period T1. Specifically, the rate of increase in the potential difference across V ₂ is decreasing with time within the period T1, the rate of increase in the potential difference across V ₂ immediately after the start of the period T1 is large, the increase in the potential difference across V ₂ with time The rate is getting smaller. That is, the start timing of the relative time period T2 to rise period T1 potential difference across V ₂ is accelerated, so that the increment of the potential difference across V ₂ in the period T2 is enlarged. Further, when the increasing rate of the both-end potential difference V ₂ in the start-up period T1 is increased, the increasing rate of the both-end potential difference V ₂ in the period T2 is further increased. Therefore, the difference (V ₂₄ −V ₂₃ ) between the potential difference V ₂₃ at both ends of the MCP 50 at the start of the period T2 and the potential difference V ₂₄ at both ends of the MCP 50 at the end of the period T2 is the difference (V ₂₂ −V) in FIG. ₂₁ ) It is bigger. That is, in the example shown in FIG. 10, the change width of the amplification factor of the image intensifier 10 in the period T2 is larger than that in the form shown in FIG.

Such a form is suitable for imaging conditions in which the optical image B is difficult to reach the imaging device 3, such as rainy weather or heavy fog. Even when the object is far from the imaging system 1 in fine weather, the amount of light of the incident light image B is relatively large. However, in the rainy weather, the pulsed light P and the light image B are blocked by rain. The light quantity of the incident light image B relating to the far object to be imaged becomes smaller than that in fine weather. In such a case, a change is made such that the rate of increase of the potential difference V ₂ at both ends in the rising period T1 of the potential difference V ₂ at the both ends of the MCP 50, that is, the increase rate of the photomultiplier of the image intensifier 10 is larger than that at the time of fine weather in rainy weather. By performing the above in the gain control unit 15, it is possible to obtain a clearer image while suppressing the influence of the imaging condition.

Accordingly, in the control unit 4, the rate of increase in the potential difference across V ₂ of MCP50 in start-up period T1 is preferably variable depending on the imaging conditions. Specifically, it is preferable that the peak voltage of the both-end potential difference V ₂ in the start-up period T1 can be changed in the range including 400 [V] to 900 [V] in the control unit 4. Further, as in the present embodiment, when the increasing rate of the both-end potential difference V ₂ within the start-up period T1 changes with time within the period T1, the control unit 4 starts the start timing (start-up of the period T2). The relative timing at which the gate of the photocathode 40 is opened with respect to the period T1 is preferably variable according to the imaging conditions.

  FIG. 11 is a diagram illustrating changes in the brightness of the light image B and the multiplication factor of the image intensifier 10 according to the distance from the imaging system 1. A curve R1 in the figure indicates attenuation of the light image B due to light diffusion, and a curve R2 indicates attenuation of the light image B due to imaging conditions (rain or fog). A curve R3 in the figure indicates the multiplication factor of the image intensifier 10 in fine weather, and a curve R4 indicates the light multiplication factor of the image intensifier 10 in rainy weather.

  As shown by a curve R1 in FIG. 11, the brightness of the optical image B attenuates exponentially according to the distance from the imaging system 1 due to the diffusion of the pulsed light P and the optical image B itself. In addition, when it is raining or foggy, in addition to this attenuation, it further attenuates exponentially (R2). In the imaging system 1 of the present embodiment, as described above, as the distance from the imaging system 1 increases, the light multiplication factor of the image intensifier 10 increases exponentially (R3, R4). Attenuation due to distance (R1) and attenuation due to imaging conditions (R2) are effectively compensated, and variations in light and darkness in the image can be suppressed regardless of the distance from the shooting position.

(First modification)
FIG. 12 is a diagram for explaining a first modification of the above embodiment, in which (a) transition of the potential difference V ₂ at both ends of the MCP 50, (b) transition of the potential of the photocathode 40, and (c) pulsed light. 6 is a timing chart showing transitions of P intensity. In this modification, the waveform of the potential difference V ₂ at both ends of the MCP 50 (FIG. 12A) is different from that in FIG. 5A, the start time of the period T1 is equal to the start time of the period T2, and the start time of the period T2 The potential difference V ₂ at both ends of the MCP 50 is maintained so as not to drop below the potential difference V _{21 at} the both ends of the MCP 50 (for example, 200 [V]) or a value slightly smaller than V ₂₁ . In this case, since the period T1 can be shortened, the gate operation per unit time can be increased, and a more real-time image can be acquired. The transition of the potential of the photocathode 40 shown in FIG. 12 (b) and the transition of the intensity of the pulsed light P shown in FIG. 12 (c) are those shown in FIG. 5 (b) and FIG. 5 (c), respectively. It is the same.

The potential difference V ₂ at both ends of the MCP 50 in the imaging system 1 may be controlled to a waveform as shown in FIG. 12A by the gain control unit 15 or the MCP gate circuit 16. Even in such a case, the effects according to the above-described embodiment can be suitably obtained.

(Second modification)
FIG. 13 is a diagram for explaining a second modification of the above embodiment, and is a timing chart showing (a) intensity transition of the pulsed light P and (b) potential transition of the photocathode 40, respectively. Although not shown, with respect to the relationship between the transition of the potential of the photocathode 40 of the potential difference across _{V 2} and 13 of MCP50 (b), equal to the relationship shown in FIG. 5 (a) and 5 (b). In this modification, the waveform of the pulsed light P (FIG. 13 (a)) is different from that of FIG. 5 (c), and the rising of the intensity of the pulsed light P is steep and gently decreases. It has become. Further, the gate operation of the photocathode 40 is performed during the emission of the pulsed light P.

  By setting the emission intensity of the pulsed light P to such a shape, the irradiation intensity of the pulsed light P becomes stronger as the imaging object is farther from the imaging system 1 in the obtained image. Therefore, even by irradiation with the pulsed light P, attenuation due to the distance from the imaging system 1 can be compensated, and variations in light and darkness in the image can be more suitably suppressed regardless of the distance from the imaging position.

  The imaging system and the peripheral monitor device according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above-described embodiment, the image intensifier 10 includes the thin-film phosphor screen 60, and the method of capturing the light image emitted from the phosphor screen 60 with the CCD camera 11 is described. Image data may be generated by directly detecting electrons. In the above embodiment, the optical member 13 is disposed between the image intensifier 10 and the CCD camera 11. However, in the imaging apparatus according to the present invention, the components including the photocathode and MCP and the imaging unit are directly connected. It may be combined.

1 is a diagram illustrating a configuration according to an embodiment of an imaging system according to the present invention. FIG. 2 is a plan view showing a partially broken image intensifier 10. It is sectional drawing which shows a part of image intensifier 10 shown in FIG. 2 along a III-III line. FIG. 3 is a perspective view showing a partially broken MCP 50 shown in FIG. 2. 5A is a timing chart showing a transition of a potential difference V ₂ at both ends of the MCP 50, a transition of a potential of the photocathode 40, and a transition of the intensity of the pulsed light P, respectively. 6 is a graph showing a relationship between a potential difference V ₂ applied to the MCP 50 and a multiplication factor (luminance gain) with respect to an incident light image B. It is an image showing a daytime landscape that is a subject of photographing when the effect of the imaging system 1 is confirmed, and shows an approximate distance from the photographing position to a main building. (A) A night image acquired by the imaging system 1. (B) Night image taken without gate control. (A) A night image obtained by photographing only an object close to the gate photographing position only by the gate control of the photocathode 40. (B) A night image obtained by photographing only an object far from the gate photographing position. 5A is a timing chart showing a transition of a potential difference V ₂ at both ends of the MCP 50, a transition of a potential of the photocathode 40, and a transition of the intensity of the pulsed light P, respectively. It is a figure which shows the change of the brightness of the optical image B and the multiplication factor of the image intensifier 10 according to the distance from the imaging system 1. FIG. Is a diagram for explaining a first modification, (a) shows transition of the potential difference across V ₂ of MCP50, (b) transition of the potential of the photocathode 40, and (c) a transition of the intensity of the pulsed light P, respectively It is a timing chart. It is a figure for demonstrating a 2nd modification, (a) The intensity | strength transition of the pulsed light P, (b) It is a timing chart which each shows the transition of the electric potential of the photoelectric surface 40.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Imaging system, 2 ... Pulse light source, 3 ... Imaging device, 4 ... Control part, 5 ... Semiconductor light emitting element, 6, 12 ... Lens, 10 ... Image intensifier, 11 ... CCD camera, 13 ... Optical member, 14 DESCRIPTION OF SYMBOLS ... Voltage source, 15 ... Gain control part, 16 ... MCP gate circuit, 17 ... PC gate circuit, 18 ... Timing circuit, 30 ... Incident window, 35 ... Photocathode, 40 ... Photocathode, 50 ... MCP, 60 ... a phosphor screen, 80 to 83 ... electrode, 90 to 93 ... lead wire, A ... imaged object, B, C ... optical image, P ... pulsed light, V ₂ ... the potential difference across, e _1, e ₂ ... photoelectrons.

Claims (4)

A pulsed light source that irradiates the imaging object with pulsed light;
An imaging device that captures an optical image related to the imaging object by the pulsed light; and
A controller that controls the pulse light source and the imaging device;
The imaging device
A photocathode that receives the optical image and emits photoelectrons and performs a gate operation by potential control by the control unit;
A microchannel plate arranged to face the photocathode and multiplying the photoelectrons,
An imaging unit that generates image data based on an electronic image emitted from the microchannel plate;
The control unit periodically generates pulse light from the pulse light source and raises the potential difference between both ends of the microchannel plate, and after the pulse light is generated, within the rise period of the potential difference between both ends. Opening the gate of the photocathode ,
An imaging system, wherein an increase rate of the potential difference between both ends of the microchannel plate during a rising period is variable . A pulsed light source that irradiates the imaging object with pulsed light;
An imaging device that captures an optical image related to the imaging object by the pulsed light; and
A controller that controls the pulse light source and the imaging device;
The imaging device
A photocathode that receives the optical image and emits photoelectrons and performs a gate operation by potential control by the control unit;
A microchannel plate arranged to face the photocathode and multiplying the photoelectrons,
An imaging unit that generates image data based on an electronic image emitted from the microchannel plate;
The control unit periodically generates pulse light from the pulse light source and raises the potential difference between both ends of the microchannel plate, and after the pulse light is generated, within the rise period of the potential difference between both ends. Opening the gate of the photocathode ,
The rate of increase of the potential difference between both ends within the rising period of the potential difference between both ends of the microchannel plate is time-varying within the period,
The timing of opening the gate of the photocathode in the controller is variable . Wherein the pulsed light source has a LED, an imaging system according to claim 1 or 2. A peripheral monitoring device for monitoring the surrounding situation,
A peripheral monitor device comprising the imaging system according to any one of claims 1 to 3 .