JP2009302943A - Dome type camera, and method for manufacturing dome cover - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dome type camera for suppressing the generation of aberration, and for improving picture quality in horizontal photographing, and to provide a method for manufacturing a dome cover to be used for the same. <P>SOLUTION: This dome type camera is provided with a camera 3 for imaging the image of an object through a lens 3a and a dome cover 2 covering the camera 3 in which the optical axis of the lens 3a is offset to a dome zenith side from the center of the dome. The dome cover 2 has a refractive index gradient in which a refractive index becomes smaller as a tilt angle made by the optical axis of the lens 3a becomes larger from the direction of the dome zenith. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a dome type camera in which a camera is accommodated in a dome cover and a method for manufacturing a dome cover used for the dome type camera.

  In a conventional dome type camera, for example, as described in FIG. 1 of Patent Document 1, the dome cover and the lens are arranged so that the lens optical axis of the camera is offset toward the dome zenith side from the center of the dome housing the camera. This arrangement eliminates the occurrence of so-called vignetting, which is caused by the camera casing or the like entering a part of the shooting range, so that shooting in a direction parallel to the mounting plane is possible. However, if the lens optical axis of the camera is offset toward the dome zenith side with respect to the dome center, an aberration caused by the dome cover occurs, and this aberration may deteriorate the image quality.

  FIG. 6 is a diagram for explaining the optical relationship when the lens optical axis of the camera is offset from the dome center to the dome zenith side, and shows a side view of the dome portion. The inner wall of the dome cover, the lens in the camera, etc. are indicated by broken lines. In FIG. 6, the lens 100 accommodated in the dome cover 101 is disposed so as to face the horizontal direction. The optical axis 102 of the lens 100 is offset in the dome zenith direction with respect to the center 103 of the dome cover 101. Light rays 104 and 105 parallel to the optical axis 102 of the lens 100 are light rays that enter the vicinity of the upper end and the vicinity of the lower end of the lens 100.

  When the optical axis 102 of the lens 100 is offset to the dome top side, the incident angles of the light beams 104 and 105 with respect to the outer surface of the dome cover 101 are different from each other as shown in FIG. Here, the optical path length d ′ of the light beam 105 incident from the vicinity of the lower end of the lens 100 is longer than the optical path length d of the light beam 104 incident from the vicinity of the upper end of the lens 100 at the dome cover 101 portion. Here, the optical path length in the dome cover 101 part (cover passing part) is the length of the thickness part in the cover in the optical path.

  Thus, when the optical axis 102 of the lens 100 is offset to the dome zenith side, the optical path lengths d and d ′ of the light rays 104 and 105 incident on the lens 100 are different from each other depending on the dome cover 101, and the dome cover 101 is an optical system. It functions as an asymmetric optical system member constituting a part of the lens and causes aberration. This aberration increases as the tilt angle from the zenith direction increases, and the image quality deteriorates. The problem due to this aberration is not remarkable in a dome type camera using a low magnification lens, but it cannot be ignored with the recent spread of cameras having a high magnification zoom function.

  As a solution to the above-mentioned problems, there is a dome type camera described in Patent Document 2, for example. This camera is configured such that the thickness of the dome cover increases as the tilt angle from the dome zenith direction increases. With this configuration, even when shooting in a direction with a large tilt angle, the optical path difference in the thickness portion of the dome cover of the light passing through the upper and lower ends of the lens is reduced, and the image quality is improved. Can do.

  In addition, when manufacturing a dome cover having a different wall thickness at such a specific location, uneven molding is likely to occur. Therefore, it is necessary to use a special manufacturing method as described in Patent Document 3, for example. This patent document 3 suppresses occurrence of partial molding unevenness in a manufactured dome cover by injecting molten resin into a cavity from a gate port provided at a position corresponding to the zenith portion of the dome cover.

JP 2000-244783 A (2nd page, FIG. 1) Japanese Patent Laying-Open No. 2005-300659 JP 2007-160734 A

  In a conventional dome type camera, when the lens optical axis of the camera is offset to the dome zenith side in order to enable horizontal shooting, the optical path for the wall thickness of the dome cover depends on the incident position of the light beam parallel to the lens optical axis. There was a problem that the image quality deteriorates due to the difference and aberration.

  Further, as in Patent Document 2, if the thickness of the dome cover is increased as the tilt angle from the dome zenith direction is increased, the optical path difference can be reduced. When the thickness is changed, molding unevenness is likely to occur, and there is a problem that it is necessary to perform a special process for reducing the molding unevenness.

  For example, as in Patent Document 3, when molten resin is injected into the cavity from a gate port provided at a position corresponding to the zenith portion of the dome cover, it is possible to suppress partial molding unevenness in the dome cover. However, when the gate opening is at the dome zenith, the gate mark remains at the zenith, which causes a problem that the image quality at the zenith deteriorates.

  The present invention has been made in order to solve the above-described problems. A dome-type camera capable of suppressing the occurrence of aberration and improving the image quality in horizontal shooting, and a method of manufacturing a dome cover used therefor The purpose is to obtain.

  A dome type camera according to the present invention includes a camera that captures an image of an object through a lens, and a dome cover that covers the camera and in which the optical axis of the lens is offset from the center of the dome to the dome zenith side. In the type camera, the dome cover has a refractive index gradient in which the refractive index decreases as the tilt angle formed by the optical axis of the lens increases from the dome zenith direction.

  A method for manufacturing a dome cover according to the present invention is the method for manufacturing a dome cover for a dome type camera, wherein a temperature gradient is set in the injection mold when the resin material for the dome cover is injected into the injection mold. By forming a density gradient in the resin material, a dome cover having a refractive index gradient that decreases as the tilt angle formed by the optical axis of the lens increases is formed.

  According to the present invention, the dome cover is provided with a refractive index gradient in which the refractive index decreases as the tilt angle from the dome zenith direction increases, so that it passes through both ends of the lens even when photographing in a direction with a large tilt angle. There is an effect that the optical path difference of the light beam is reduced and the image quality can be improved.

  Further, according to the present invention, the dome cover having the refractive index gradient is formed by setting the temperature gradient in the injection mold and giving the resin material the density gradient, so that the dome having the refractive index gradient is formed. There is an effect that the cover can be easily manufactured.

Embodiment 1 FIG.
FIG. 1 is a front view of a dome type camera according to Embodiment 1 of the present invention. In FIG. 1, the dome type camera 1 according to the first embodiment includes a main body 1 a and a dome covered with a dome cover 2. The main body 1a is attached to an attachment target site such as a ceiling by the attachment part 5. Further, the main body 1 a is provided with a pan / tilt mechanism 4 of the camera 3, and the camera 3 is attached to the pan / tilt mechanism 4. The pan / tilt mechanism 4 rotates the lens 3a of the camera 3 in the pan and tilt directions with respect to the main body 1a. The pan / tilt mechanism 4 may be motor-driven or manual.

  The camera 3 is configured by assembling a plurality of lenses 3a in a lens barrel and incorporating an image sensor such as a CCD behind the lens barrel. As shown in FIG. 1, the dome cover 2 has a hemispherical shape and is attached to the main body 1 a so as to cover the pan / tilt mechanism 4 in which the camera 3 is installed. The dome cover 2 is made of polycarbonate or acrylic and is transparent.

  The optical axis of the lens 3 a is offset to the zenith side of the dome cover 2 with respect to the center of the dome cover 2 (that is, the center of the hemisphere). An offset amount A shown in FIG. 1 indicates an offset when the optical axis of the lens 3a is horizontal. The offset amount is the length of a perpendicular line drawn from the center of the dome cover 2 (horizontal position a1) to the optical axis (horizontal position a2) of the lens 3a, and changes according to the direction of the lens 3a. By offsetting the optical axis of the lens 3a in this way, it is possible to perform forward shooting with the camera 3 without being blocked by the main body 1a even when the lens 3a is oriented in the horizontal direction.

  The angle formed between the zenith direction of the dome cover 2 and the optical axis of the lens 3a is defined as a tilt angle. Here, the tilt angle when the optical axis of the lens 3a faces the zenith of the dome cover 2 is 0 degree. Further, the tilt angle when the optical axis of the lens 3a is oriented in the horizontal direction of the dome cover 2 is 90 degrees. In the following, the case where the dome-type camera 1 is installed downward on the ceiling will be described as an example, so that the tilt angle becomes 0 degree when the lens 3a faces directly below.

  FIG. 2 is a view for explaining the optical relationship of the dome type camera in FIG. 1, and schematically shows a side surface of the dome portion. As in FIG. 6, the inner wall of the dome cover 2 and the lens 3a in the camera 3 are indicated by broken lines. In FIG. 2, light rays that are parallel to the optical axis (horizontal position a2) of the lens 3a and enter the vicinity of the upper end and the lower end of the lens 3a are referred to as an upper light ray 6a and a lower light ray 6b, respectively.

  In the example of FIG. 2, the lens 3a of the camera 3 is oriented in the horizontal direction and the tilt angle is 90 degrees. In the first embodiment, the refractive index of the dome cover 2 changes according to the tilt angle. In addition, the intersection of the perpendiculars drawn from the center 7a of the dome cover 2 to the dome cover 2 is the zenith 7b of the dome cover 2.

When the refractive index in the passage portion of the upper light beam 6a in the dome cover 2 is n and the refractive index in the passage portion of the lower light beam 6b is n ′, the optical path lengths of the upper light beam 6a and the lower light beam 6b in consideration of these refractive indexes. L and L ′ can be expressed by the following formula (1). However, d is the optical path length in the thickness part of the dome cover 2 of the upper light beam 6a, and d 'is the optical path length in the thickness part of the dome cover 2 of the lower light beam 6b.

The optical path length d of the upper light beam 6a and the optical path length d 'of the lower light beam 6b described above can be expressed by the following equation (2). Here, Rout is the outer surface radius of the dome cover 2, Rin is the inner surface radius of the dome cover 2, and θ2 is the refraction angle of the lower light ray 6b at the thickness portion of the dome cover 2.

The incident angle of the lower light ray 6b to the surface of the dome cover 2 is θ1, the incident angle of the upper light ray 6a to the surface of the dome cover 2 is θ3, and the refraction angle of the upper light ray 6a at the thickness portion of the dome cover 2 is θ4. Assuming that the offset amount of the upper ray 6a with respect to the center 7a is h and the offset amount of the lower ray 6b is h ′, the following relational expression (3) is established.

  As shown in FIG. 2, the upper light beam 6 a is incident substantially perpendicular to the cover surface of the dome cover 2. On the other hand, the lower light beam 6 b is incident on the cover surface of the dome cover 2 with an inclination. If the dome thickness is uniform and the refractive index is constant as in the prior art, the optical path length d of the upper light beam 6a at the thickness portion of the dome cover 2 becomes less than the lower light beam 6b due to the angle difference of the incident angle. It becomes shorter than the optical path length d ′ and an optical path difference occurs.

  Therefore, in the first embodiment, a refractive index gradient that reduces the refractive index in the thickness portion of the dome cover 2 is provided in accordance with the tilt angle of the lens 3a of the camera 3, so that the angle difference between the incident angles is increased. Compensates for the accompanying change in optical path length. By doing so, the optical path length d of the upper light beam 6a and the optical path length d 'of the lower light beam 6b in the thickness portion of the dome cover 2 become substantially equal, and aberrations due to the optical path difference can be reduced.

In order to eliminate the optical path difference between the upper light beam 6a and the lower light beam 6b, L = L ′ may be used. Therefore, the refractive index n, n ′ is refracted so that the refractive indexes n and n ′ satisfy the following relational expression (4). Set the rate gradient. That is, a refractive index gradient is formed so that the refractive index at the thickness portion of the dome cover 2 decreases from the zenith 7b of the dome cover 2 to the horizontal plane including the center 7a of the dome cover 2.

Next, the operation will be described.
In the dome type camera 1, the lens 3 a of the camera 3 can be rotated in the tilt direction by the pan / tilt mechanism 4.
(1) When the lens 3a faces the zenith 7b direction of the dome cover 2 (tilt angle is 0 degree)
In this case, since the dome cover 2 is rotationally symmetric, if the lens 3a faces in the direction of the zenith 7b of the dome cover 2, the optical path in the thickness portion of the dome cover 2 between the light rays incident on both ends of the lens 3a. There is no difference. Accordingly, no aberration occurs in the thickness portion of the dome cover 2, and the camera 3 can obtain a good quality image.

(2) When the lens 3a is oriented horizontally (tilt angle is 90 degrees)
As described above, the dome cover 2 according to the first embodiment has a refractive index at the thickness portion of the dome cover 2 from the zenith 7b of the dome cover 2 to the horizontal plane including the center 7a of the dome cover 2. A smaller refractive index gradient is provided. That is, as the tilt angle from the direction of the dome zenith 7b increases, the refractive index in the thickness portion of the dome cover 2 decreases.

  As shown in FIG. 2, when the lens 3a is oriented horizontally, the vicinity of the upper end of the lens 3a is far from the zenith 7b of the dome cover 2 and the tilt angle with respect to the zenith 7b direction of the dome cover 2 is large. The refractive index n in the thickness portion of 2 is small. On the other hand, in the vicinity of the lower end of the lens 3a, the refractive index n 'in the thickness portion of the dome cover 2 is large because it is close to the zenith 7b of the dome cover 2 and the tilt angle with respect to the zenith 7b direction of the dome cover 2 is small.

  The refractive index gradient is set so that the optical path lengths d and d 'of the upper light beam 6a and the lower light beam 6b in the thickness portion of the dome cover 2 are substantially equal using the above equation (4). Therefore, the aberration caused by the optical path difference between the upper light beam 6a and the lower light beam 6b in the thickness portion of the dome cover 2 is reduced, and a high-quality image can be obtained even when the image is taken in the horizontal direction.

  As described above, the dome type camera 1 according to the first embodiment has the lens 3a regardless of whether the lens 3a is photographed in the direction of the dome zenith 7b or the dome is directed in the horizontal direction of the dome. The optical path difference in the thickness portion of the dome cover 2 of the light beams 6a and 6b passing near both ends is small. Further, even when the lens 3a is facing an arbitrary direction between the direction of the dome zenith 7b and the horizontal direction of the dome, the optical path difference is similarly reduced, so that the aberration is small and a high-quality image can be obtained.

  As described above, according to the first embodiment, as the tilt angle from the direction of the dome zenith 7b is increased, the refractive index gradient is reduced so that the refractive index in the thickness portion of the dome cover 2 is reduced. Even in the case of shooting in a direction in which the lens is large, it is possible to reduce the optical path difference in the thickness portion of the dome cover 2 of the light beam passing through both ends of the lens 3a, and to improve the image quality of the shot image. .

Embodiment 2. FIG.
In the second embodiment, as shown in the first embodiment, the dome cover having a refractive index gradient in which the refractive index in the thickness portion of the dome cover 2 decreases as the tilt angle from the direction of the dome zenith 7b increases. A method for producing 2 will be described.

  FIG. 3 is a cross-sectional view showing an injection mold for a dome cover used in the dome camera according to the present invention. As shown in FIG. 3, the injection mold 8 according to the second embodiment includes an upper mold 9a and a lower mold 9b that are opened and closed vertically. When the upper mold 9a and the lower mold 9b are combined (closed state), a cavity 10 corresponding to the shape of the dome cover 2 is formed between the upper mold 9a and the lower mold 9b. The upper mold 9 a and the lower mold 9 b are provided with cooling medium flow paths 11-1 to 11-5 and 12 for circulating a cooling medium (cooling water or cooling oil) around the inner wall surface serving as the cavity 10. It is done.

  In manufacturing the dome cover 2 by injection molding, the upper mold 9a and the lower mold 9b of the injection mold 8 are closed (combined) to form the cavity 10. Further, the temperature of the cooling medium flowing through the cooling medium flow paths 11-1 to 11-5 and 12 is adjusted to provide a temperature gradient around the cavity 10 (inner wall surface of the cavity 10) of the injection mold 8. . In this state, molten resin is injected into the cavity 10 through a gate port (not shown) provided in the injection mold 8 and is taken out after being cured. The gate opening is not provided at a position corresponding to at least the dome zenith. Thereby, the gate mark does not remain at the zenith, and the image quality of the dome zenith is not deteriorated.

The above-mentioned temperature gradient is set by the method shown below, for example.
First, the relationship between the refractive index and the density of a substance can be expressed by the Lorentz-Lawrence formula shown in the following formula (5). Here, n is the refractive index of the target substance, d is the density of the target substance, M is the molecular weight of the target substance, N is the number of mole molecules of the target substance, and α is the polarizability of the target substance.

Since the number N of mole molecules, the polarizability α, and the molecular weight M are constants, the refractive index n can be expressed by the following formula (6) using the density d as a parameter.

  Using the above equation (6), the refractive index gradient set in advance for improving the image quality is replaced with the density distribution of the target substance (the resin material of the dome cover 2), and the injection molding metal is used to obtain the density distribution. The gradient of the mold temperature of the mold 8 is set.

  FIG. 4 is a diagram showing the relationship between the density of the dome cover molding material and the refractive index. The density of the polycarbonate resin and the acrylic resin generally used for molding the dome cover 2 and the refractive index at this density, the above formula The K value in (6) is shown. The K value is a value calculated from the general physical property values of the polycarbonate resin and the acrylic resin, and both are 1 or less.

  FIG. 5 is a graph showing the result of calculating the refractive index change when the density of the polycarbonate resin and the acrylic resin is increased or decreased by about 10% with respect to the general physical property value using the K value in FIG. As is apparent from FIG. 5, it is understood that the refractive index of the polycarbonate resin or acrylic resin used for the dome cover 2 also increases monotonically as the density increases.

  Therefore, as the tilt angle from the zenith direction of the dome cover 2 increases, that is, from the zenith 7b of the dome cover 2 to the horizontal plane including the center 7a of the dome cover 2, the density of the resin material of the dome cover 2 gradually increases. By providing a lower gradient, a refractive index gradient that reduces the refractive index in the thickness portion of the dome cover 2 can be provided.

  The density gradient of the dome cover 2 as described above can be set by giving a gradient to the mold temperature at the time of manufacture. That is, if the curing temperature of the resin that is the dome cover molding material is different, the amount of shrinkage of the resin changes accordingly, and a density distribution is obtained.

  Specifically, with reference to FIG. 3, the cooling medium channel 11-3 located near the portion corresponding to the vicinity of the zenith of the dome cover 2 in the cavity 10 circulates the cooling medium so that the temperature becomes the lowest. As the tilt angle from the zenith direction of the dome cover 2 increases, a medium having a temperature higher than that of the cooling medium flow path 11-3 is circulated through the cooling medium flow paths 11-2 and 11-4. A medium having the highest temperature is circulated in 11-1 and 11-5.

  By doing so, the temperature gradient (as the tilt angle from the dome zenith direction increases) on the inner wall surface of the cavity 10 corresponding to the zenith 7b from the dome cover 2 to the horizontal plane including the center 7a of the dome cover 2. A temperature gradient at which the temperature increases) is set. By curing the molten resin in this state, the dome cover 2 can have a refractive index gradient in which the refractive index decreases as the tilt angle from the dome top direction increases.

  As described above, according to the second embodiment, when the resin material of the dome cover 2 is injected into the injection mold 8, the temperature increases as the tilt angle increases from the zenith direction of the dome cover 2. The gradient is set in the injection mold 8 and the resin material is cured with a density gradient. In this way, the dome cover 2 having a refractive index gradient that decreases as the tilt angle formed by the optical axis of the lens 3a increases can be easily manufactured.

  The dome type camera according to the present invention can improve the image quality with a wider field of view than the conventional dome type camera, and is useful as, for example, a surveillance camera.

It is a front view of the dome type camera by Embodiment 1 of this invention. It is a figure for demonstrating the optical relationship of the dome shape camera in FIG. It is sectional drawing which shows the metal mold | die for injection molding of the dome cover used for the dome shape camera by this invention. It is a figure which shows the relationship between the density of a dome cover molding material, and a refractive index. It is a graph which shows the result of having calculated the refractive index change when the density of polycarbonate resin and an acrylic resin increased / decreased about 10% with respect to the general physical property value using K value in FIG. It is a figure for demonstrating the optical relationship at the time of offsetting the lens optical axis of a camera from the dome center to the dome zenith side.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Dome type camera, 1a main body part, 2 dome cover, 3 camera, 3a lens, 4 pan tilt mechanism, 5 attachment part, 6 optical axis, 6a upper ray, 6b lower ray, 7a center, 7b zenith, 8 injection molding gold Mold, 9a Upper mold, 9b Lower mold, 10 cavity, 11-1 to 11-5, 12 Cooling medium flow path, 100 lens, 101 dome cover, 102 optical axis, 103 center, 104 upper light beam, 105 lower light beam.

Claims (2)

In a dome type camera provided with a camera that images an object through a lens, and a dome cover that covers the camera and the optical axis of the lens is offset from the dome center to the dome zenith side,
The dome cover has a refractive index gradient in which a refractive index decreases as a tilt angle formed by an optical axis of the lens increases with respect to a dome zenith direction. In the manufacturing method of the dome cover of the dome type camera of Claim 1,
A refractive index that decreases the refractive index as the tilt angle formed by the optical axis of the lens increases by setting a temperature gradient in the injection mold and giving the molding resin material a density gradient along with this temperature gradient. A method of manufacturing a dome cover, comprising forming a dome cover having a gradient.

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