Abstract:
Provided is a highly reliable imaging module that can easily carry out optical axis adjustments and focus adjustments while assuring required light shielding performance, and in which malfunctions do not easily occur in solder junctions and the like for imaging elements even under severe temperature environments. An imaging module has, in addition to a lens holding member ( 10 ), an imaging element ( 25 ), and a substrate ( 30 ) on which the imaging element ( 25 ) is mounted, a shielding member ( 40 ) that is for preventing extraneous light from entering the imaging surface of the imaging element ( 25 ) and on which a ring-shaped or notched ring-shaped protrusion ( 51 ) for shielding is provided. The shielding member ( 40 ) is held between the lens holding member ( 10 ) and the substrate ( 30 ) without the protrusion ( 51 ) for shielding coming into contact with another member.

Description:
TECHNICAL FIELD 
     The present invention relates to an imaging module including, as basic configuration elements, a lens, an imaging element to convert light, which becomes incident through the lens, into an electric signal, and a substrate on which the imaging element is mounted, a stereo camera for a vehicle which camera includes a pair of right and left imaging modules, and a light shielding member for an imaging module. 
     BACKGROUND ART 
     Examples of an imaging module including a lens, an imaging element, and a substrate include those disclosed in PTL 1 and PTL 2. 
     The imaging module disclosed in PTL 1 includes a roughly box lid-shaped holder for an imaging element. On a front side of the holder, an opening into which a translucent member such as glass or a filter is attached is formed and on a rear (opening) side thereof, an imaging element is attached. Between the translucent member and the imaging element in the holder, rectangular frame-shaped rubber packing is held in a compressed manner. More specifically, a rectangular ring-shaped light shielding rib is provided in a protruded manner on an outer peripheral side of the rubber packing and a notched rectangular ring-shaped pressing rib is provided in a protruded manner on an inner peripheral side of the light shielding rib in such a manner that the rubber packing has both of a light shielding function and a holding function thereof. Protruded leading ends of the light shielding rib and the pressing rib are pressed against the imaging element. 
     The imaging module disclosed in PTL 2 includes a stepped short-cylindrical pressing member arranged on a substrate in such a manner as to surround an imaging element mounted on the substrate, and an O-ring (sealing member) installed between a flange part, which is provided in a lower outer periphery of the pressing member, and the substrate. The O-ring is pressed against the substrate by the pressing member, whereby air-tightness (and light-shielding property) in the pressing member (space between translucent member and substrate) is secured. 
     On the other hand, recently, it is becoming popular to employ a stereo camera, which includes a pair of right and left imaging modules described above, as a vehicle driving support system to support safe driving of a car (see, for example, PTL 3). 
     The stereo camera calculates a distance to an object by triangulation with a pair of images acquired from the pair of right and left imaging modules and recognizes the object. 
     Specifically, in an environment in a vehicle, it is necessary to perform measurement of a distance to a distant object and recognition thereof accurately and securely since there is an application request for, for example, detecting a leading vehicle, a person, or an obstacle and dealing therewith previously and safely. 
     Moreover, in a case of using the stereo camera in the vehicle driving support system or the like, high reliability is required in addition to downsizing and lowering a price. 
     In the stereo camera, special LSI to perform processing of specifying pixel positions of feature points, which are common in a pair of images, in pixel information included in the images and of calculating the number of pixels deviated between the feature points in the pair of pictures (hereinafter, referred to as parallax) is generally included. 
     For the principle, it is preferable that there is no deviation between the pair of images other than the parallax. Thus, a structure to perform adjustment accurately in such a manner that deviation in an optical characteristic or signal characteristic is not generated and to keep the accuracy is necessary for each imaging module. 
     Also, in order to improve performance of detecting a leading vehicle or the like, it is necessary to accurately calculate feature points common in the pair of images. Thus, it is preferable that luminance values of feature points are the same in a reference imaging module and the other imaging module. 
     Thus, it is preferable that extraneous light other than signal light that becomes incident through a lens does not become incident through a place other than the lens. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Application Laid-Open No. 2011-160365 
     PTL 2: Japanese Patent Application Laid-Open No. 2009-201079 
     PTL 3: Japanese Patent Application Laid-Open No. 2011-123078 
     SUMMARY OF INVENTION 
     Technical Problem 
     Specifically, in a case of a stereo camera, it is necessary to improve relative positional accuracy of right and left imaging modules in order to improve measurement accuracy as described above. However, since it is not possible to realize adequate performance of the stereo camera only by improving mechanical accuracy of a housing or the like, it is necessary to perform a mechanical adjustment in a production process. The mechanical adjustment is operation to adjust a positional relationship between a lens and an imaging element. In a case of the stereo camera, the lens is a reference. Thus, it is necessary to move a position of the imaging element. 
     Also, recently, there are increasing cases of mounting an imaging element to a substrate with solder junction by a BGA. Furthermore, since it is requested to extend a range of tolerant environmental temperature in order to deal with installation in a vehicle, it is preferable that no load is applied to the imaging element or the substrate. 
     However, the imaging module disclosed in PTL 1 includes a structure in which the rubber packing to function as a light shielding member applies a load to the imaging element and durability of solder in a temperature environment in a vehicle is concerned. 
     Also, the imaging module disclosed in PTL 2 includes a structure in which the pressing member and the O-ring which function as light shielding members apply a load to the substrate and durability of the substrate in a temperature environment in a vehicle and deviation of a focus due to a change in a temperature of the substrate are concerned. 
     The present invention is provided in view of the forgoing and is to provide a highly reliable imaging module which can easily carry out optical axis adjustments and focus adjustments while assuring required light shielding performance and in which malfunctions do not easily occur in solder junctions and the like for imaging elements even under severe temperature environments. 
     Solution to Problem 
     In order to achieve the above purpose, an imaging module according to the present invention basically includes a lens, a lens holding member that holds the lens, an imaging element to convert light, which becomes incident through the lens, into an electric signal, and a substrate on which the imaging element is mounted. In addition, the imaging module includes a light shielding member on which a ring-shaped or notched ring-shaped protrusion for light shielding is provided to prevent extraneous light from entering an imaging surface of the imaging element. The light shielding member is held between the lens holding member and the substrate without the protrusion for light shielding coming into contact with the other members. 
     Advantageous Effects of Invention 
     According to the present invention, a structure in which a protrusion for light shielding is not in contact with an imaging element or a substrate is included. With this structure, no load is applied to a solder junction in an imaging element or to a substrate on which the imaging element is mounted and it becomes possible to reduce a malfunction in the solder junction and the like in the imaging element even in an environment with a large temperature change or an environment with high temperature. As a result, it is possible to improve durability and reliability. 
     A problem, configuration, and effect other than what has been described above will be disclosed in the following embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross sectional view illustrating a left imaging module in a stereo camera for a vehicle which camera includes an embodiment of an imaging module according to the present invention on each of right and left sides. 
         FIG. 2  is an enlarged cross sectional view of a main part of the imaging module illustrated in  FIG. 1 . 
         FIG. 3A  is a perspective view of a rear side of a light shielding member used in the embodiment and  FIG. 3B  is a perspective view of a front side thereof. 
         FIG. 4A  is a side view of the light shielding member used in the embodiment and  FIG. 4B  is a cross sectional view thereof. 
         FIG. 5A  is a cross sectional view for describing a solder junction between an imaging element and a substrate in an imaging element assembly used in the embodiment and  FIG. 5B  is a perspective view of a front side thereof. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, embodiments of the present invention will be described with reference to the drawings. 
       FIG. 1  is a cross sectional view illustrating a left imaging module in a stereo camera for a vehicle which camera includes an embodiment of an imaging module according to the present invention on each of right and left sides and  FIG. 2  is an enlarged cross sectional view of a main part of the imaging module illustrated in  FIG. 1 . 
     In an illustrated stereo camera  1 , an illustrated left imaging module  5  and a right imaging module  5  including a configuration substantially identical thereto are mirror-symmetrically included and (main part of) the pair of right and left imaging modules  5  and  5  are respectively assembled to a right end part and a left end part of a stay (housing)  10 , which is a common configuration element, in such a manner as to be separated from each other for a predetermined distance (see PTL 3). 
     In the following, the illustrated left imaging module  5  will be mainly described and an overlapped description of the right imaging module  5  will be omitted. 
     The illustrated imaging module  5  includes a lens unit  15  inserted into and held in a cylindrical mount part  12  provided in the left end part of the stay  10 , an imaging element assembly  20 , a substrate  30  on which (imaging element  25  of) the imaging element assembly  20  is mounted, a holding plate  35  that holds the substrate  30 , and a light shielding member  40  that configures a main characteristic part of an embodiment of the present invention. 
     For example, the lens unit  15  includes a stepped-cylindrical lens holder  16  including a plurality of lenses (not illustrated), a fixture thereof (not illustrated), and the like. A male screw  16   a  provided in a rear end part of the lens holder  16  is screwed to a female screw  12   a  provided in the cylindrical mount part  12 . A center line of the lens unit  15  is an optical axis O. 
     As illustrated in  FIG. 5(A)  and  FIG. 5(B) , the imaging element assembly  20  includes a frame member  21  having a rectangular opening on a front side, a cover glass  23  airtightly fitted to the rectangular opening, and a rectangular plate-like imaging element  25  an outer peripheral part of which is airtightly fixed to a rear side of the frame member  21 . A center part on a front side of the imaging element  25  is an imaging surface  26 . 
     Wiring lines on the imaging element  25  and the substrate  30  are electrically connected to each other by soldering. More specifically, as illustrated in  FIG. 5(A) , the imaging element  25  is mounted on the substrate  30  by junction with a BGA solder ball  27 . 
     The substrate  30  on which the imaging element  25  is mounted in such a manner is fixed to the holding plate  35  with the predetermined number of set screws while an outer periphery thereof is abutted to a ring-shaped protruded part  38  provided in a protruded manner on a planar base body  36  of the holding plate  35 . After an adjustment of a position (position in direction of optical axis O, direction orthogonal to optical axis O, and rotational direction), the holding plate  35  is attached and fixed, with a screw or the like, to an inner peripheral side of a ring-shaped protruded part  13  provided in the left end part of the stay  10 . 
     Here, the adjustment of a position of the holding plate  35  with respect to the stay  10  is performed to adjust a positional relationship between the lens and the imaging element  25 , that is, to place the center of the imaging surface  26  of the imaging element  25  on the optical axis O, to make the imaging surface  26  orthogonal to the optical axis O, to determine a position of the imaging element  25  in a rotational direction, and to make a distance between the imaging surface  26  and the lens a prescribed value. 
     Then, the light shielding member  40  is arranged between a ring-shaped groove  14  provided in a rear part of the cylindrical mount part  12  of the stay  10  and a recessed receiving part with an opening  37  provided in the holding plate  35 . 
     The light shielding member  40  prevents light (extraneous light) other than desired signal light that becomes incident through a lens from entering the imaging surface  26  of the imaging element  25 . As illustrated in  FIG. 3  and  FIG. 4  in addition to  FIG. 1  and  FIG. 2 , the light shielding member  40  includes a ring-shaped base part  41  fitted into the ring-shaped groove  14  of the stay  10  and a top part  42  protruded from the base part  41  in a direction orthogonal thereto (direction of optical axis O and direction toward side of substrate  30 ). In the base part  41 , a semi-oval protrusion  41   a  for positioning which protrusion is used for positioning in a rotational direction with respect to the optical axis O of the lens is provided in a manner protruded outward in a radial direction. Also, at the center of the top part  42 , a rectangular window  44  for limiting an optical path which window is to prevent unneeded light from entering the imaging surface  26  is formed with respect to a path of the light that becomes incident through the lens. 
     Note that the protrusion  41   a  for positioning is fitted into a groove  14   a  for positioning which groove is formed continuously with the ring-shaped groove  14 . The base part  41  is tightly fitted into the ring-shaped groove  14  of the stay  10  and the protrusion  41   a  for positioning is tightly fitted into the groove  14   a  for positioning, whereby positioning of the light shielding member  40  with respect to the stay  10  is performed. The positioning may be performed, for example, by a method of fitting the protrusion  41   a  for positioning into the groove  14   a  for positioning as illustrated in the drawing or a method of forming each of an outer shape of the base part  41  of the light shielding member  40  and that of the ring-shaped groove  14  as a non-circular shape such as a quadrangle. 
     Near an outer peripheral end of the top part  42  of the light shielding member  40 , a triangular or trapezoidal first protrusion  51  for light shielding, which has a rectangular ring shape as a whole and a cross section of which becomes smaller on a leading end side, is provided in a manner protruded toward the substrate  30  (in direction of optical axis O) in such a manner as to surround an outer periphery of a side of the imaging element assembly  20 . Also, in a position which is on an inner peripheral side of the first protrusion  51  for light shielding in the top part  42  and which faces an outer peripheral end of the cover glass  23  of the imaging element assembly  20 , a triangular or trapezoidal second protrusion  52  for light shielding which protrusion has a rectangular ring shape as a whole, a cross section of which protrusion becomes smaller on a leading end side, and which protrusion is much smaller than the first protrusion  51  for light shielding is provided in a manner protruded toward the cover glass  23  (in direction of optical axis O). 
     Between a leading end of the first protrusion  51  for light shielding and the substrate  30 , a predetermined gap S 1  is formed and a height and the like of the first protrusion  51  for light shielding are set in such a manner not to be in contact with the substrate  30  or any other parts. 
     Also, a predetermined gap S 2  is formed between the second protrusion  52  for light shielding and the cover glass  23  of the imaging element assembly  20 . A height and the like of the second protrusion  52  for light shielding are also set in such a manner not to be in contact with the cover glass  23  or any other parts. 
     As a material of the light shielding member  40 , a material with flexibility and elasticity such as silicone rubber is preferably used in such a manner that it becomes possible to deal with a change in a provided space due to a variation in production of the member. 
     Moreover, on each of up, down, right, and left sides of the outer peripheral end of the top part  42  of the base part  41 , a pair of half-barrel-shaped or truncated cone-shaped protrusions  45  for supporting, eight in total, which protrusions become smaller on a leading end side and are provided to hold the light shielding member  40  with pressure between the ring-shaped groove  14  of the stay  10  and the recessed receiving part  37  of the holding plate  35  is equally provided in a manner protruded toward the side of the holding plate  35  (in direction of optical axis O). 
     Here, in order to hold the light shielding member  40  with pressure between the ring-shaped groove  14  of the stay  10  and the recessed receiving part  37  of the holding plate  35 , a size and a shape of each part are set in such a manner that a distance L 2  between (bottom surface of) the ring-shaped groove  14  of the stay  10  to which a front end surface  43  of the base part  41  is pressed and the recessed receiving part  37  of the holding plate  35  to which a leading end surface  46  of the protrusion  45  for supporting is pressed in an assembled state illustrated in  FIG. 2  becomes shorter than a length (natural length) L 1  from the front end surface  43  of the base part  41  to the leading end surface  46  of the protrusion  45  for supporting in a natural state with no load which state is illustrated in  FIG. 4 . 
     Accordingly, when the holding plate  35  is attached and fixed to the stay  10  with a screw or the like, the protrusion  45  for supporting of the light shielding member  40  receives a load in such a manner as to be sandwiched between the ring-shaped groove  14  of the stay  10  and the recessed receiving part  37  of the holding plate  35  and is compressively deformed. The protrusion  45  for supporting is held in the position by the pressure from the members  10  and  35 . In this case, it is preferable that the front end surface  43  which is a surface in contact with the ring-shaped groove  14  of the stay  10  and the leading end surface  46  of the protrusion  45  for supporting which surface is in contact with the recessed receiving part  37  of the holding plate  35  are arranged on a surface orthogonal to the optical axis O and that the protrusion  45  for supporting is compressed in a direction of the optical axis O. 
     On the other hand, specifically, in a case of the stereo camera  1 , a shooting direction of the reference imaging module  5  and that of the other imaging module  5  are preferably the same. Thus, in each of the imaging modules  5 , it is necessary to adjust positions of the lens (optical axis O) and the imaging surface  26 . 
     As described above, in the present embodiment, in a case of attaching and fixing the holding plate  35  (and substrate  30 ) to the stay  10 , a position thereof (position in direction of optical axis O, in direction orthogonal to optical axis O, and in rotational direction) is adjusted. Here, in a case where a surface (which is leading end surface  46  of protrusion  45  for supporting) in contact with the recessed receiving part  37  of the holding plate  35  is too large, the light shielding member  40  is deformed and a position or a shape of the rectangular window  44  for limiting an optical path is changed when the holding plate  35  is moved for adjustment. Thus, even desired light among light that becomes incident through the lens may be blocked. 
     Thus, in order to prevent the light shielding member  40  from being deformed even when the holding plate  35  is moved, it is preferable that the total area of a surface (which is leading end surface  46  of eight protrusions  45  for supporting) in contact with the recessed receiving part  37  of the holding plate  35  is much smaller than the total area of the front end surface  43  of the base part  41  which surface is in contact with the ring-shaped groove  14  of the stay  10  and that the surface in contact with the recessed receiving part  37  of the holding plate  35  has, similarly to the illustrated half-barrel-shaped or truncated cone-shaped protrusion  45  for supporting which protrusion becomes smaller on a leading end side, a shape with which only a leading end is deformed and a position or a shape of the window for limiting an optical path  44  is not changed when a load is applied. 
     Also, it is preferable that an arbitrary space is formed between the protrusion  45  for supporting of the light shielding member  40  and an inner surface of the recessed receiving part  37  of the holding plate  35  in such a manner that the holding plate  35  can be moved for a necessary degree in a direction orthogonal to the optical axis O during the positional adjustment. 
     Next, a function and an effect of the light shielding member  40  will be described. 
     A function necessary for the light shielding member  40  is to prevent undesired extraneous light from entering the imaging surface  26  of the imaging element  25 . For example, as indicated by arrows J and K in  FIG. 2 , it is considered that the extraneous light becomes incident through a path between the stay  10  and the holding plate  35  and a path between the holding plate  35  and the substrate  30 . In order to block the light, for example, the first protrusion  51  for light shielding is provided. 
     Accordingly, it is possible to prevent the light from directly entering the imaging surface  26  of the imaging element  25  and to prevent the extraneous light from entering the imaging surface  26  with the small number of times of reflection. 
     For example, in a case where the extraneous light reaches the imaging surface  26  after ten times of multiple reflection, when a color or material with low reflectivity such as black rubber is used as the light shielding member  40  and reflectivity in one time of reflection is 0.1 times, the extraneous light can be reduced to 0.1 10  times in a case of ten times of reflection. 
     Here, when the first protrusion  51  for light shielding is in contact with the substrate  30  or the cover glass  23 , a higher light-shielding property can be acquired. However, in this case, when there is a contact, for example, with an outer peripheral part of the cover glass  23 , a load is applied to the cover glass  23  especially during assembly or in an environment of high temperature. By the load, a load is applied to the BGA solder ball  27 . Thus, durability of the BGA solder with respect to thermal shock or the like may be decreased. 
     Thus, in the embodiment of the present invention, a structure in which the first protrusion  51  for light shielding is not in contact with the imaging element assembly  20  (imaging element  25 ) or the substrate  30  is included. With this structure, no load is applied to the BGA solder ball  27  of the imaging element  25  or the substrate  30  on which the imaging element  25  is mounted. Thus, even in an environment with a large temperature change or in an environment of high temperature in a vehicle, it is possible to reduce a malfunction in the solder junction  27  and the like of imaging element  25  and to improve durability and reliability. 
     In this case, it is expected that light shielding performance is adequate. As described above, light can be reduced to 0.1 10  times or more. Thus, even when there is a gap S 1  or S 2  between the first protrusion  51  for light shielding and the substrate  30  or the second protrusion  52  for light shielding and the cover glass  23  of the imaging element assembly  20 , the adequate light shielding performance can be secured. 
     Note that when the adequate light shielding performance can be acquired only with the first protrusion  51  for light shielding, the second protrusion  52  for light shielding is not necessarily provided. Only when it is not possible to acquire the adequate light shielding performance only with the first protrusion  51  for light shielding due to a limit or the like in a size or shape of each part, the second protrusion  52  for light shielding may be provided. 
     The second protrusion  52  for light shielding is preferably provided in a position without multiple reflection in which position the light reduced by the first protrusion  51  for light shielding does not reach the imaging surface  26 . As illustrated in the drawing, the second protrusion  52  for light shielding is preferably arranged near the outer peripheral part of the cover glass  23  of the imaging element assembly  20 . However, as described above, similarly to the first protrusion  51  for light shielding, a height or the like of the second protrusion  52  for light shielding is set in such a manner not to be in contact with the imaging element assembly  20  or the substrate  30 . 
     As illustrated in the drawing, the first protrusion  51  for light shielding and the second protrusion  52  for light shielding are preferably ring-shaped (continuous in whole circumference). However, when the adequate light shielding performance can be acquired, a notched ring shape (discontinuous shape) may be employed. 
     The surface in contact with the ring-shaped groove  14  of the stay  10  may be one surface (whole front end surface  43 ) as illustrated in the drawing or may be divided into a plurality of surfaces. Also, the surface in contact with the recessed receiving part  37  of the holding plate  35  may be divided into a plurality of surfaces (leading end surface  46  of eight protrusions  45  for supporting) as illustrated in the drawing or may be one surface (for example, ring-shaped protrusion which becomes thinner on leading end side may be included instead of eight protrusions  45  for supporting). 
     Note that in the above embodiment, the protrusions for light shielding  51  and  52  of the light shielding member  40  are placed near the imaging element assembly  20 . However, for example, the protrusions for light shielding may not be placed near the imaging element assembly  20  and may be placed on an outer peripheral side of the holding plate  35  to block extraneous light in a position far from the imaging element  25 . 
     Also, in the above embodiment, the holding plate  35  that holds the substrate  30  is attached and fixed to the stay  10  after adjustment of a position. However, this is not the limitation. The stay and the holding plate may be integrated (light shielding member is positioned and assembled therebetween before or after integration) and the substrate may be moved with respect to the holding plate in the adjustment of a position. In this case, a protrusion for light shielding of the light shielding member is not in contact with the substrate and the imaging element assembly (imaging element). Thus, similarly to the above embodiment, no load is applied to the BGA solder ball of the imaging element or the substrate on which the imaging element is mounted and it becomes possible to reduce a malfunction in the solder junction and the like of the imaging element even in an environment with a large temperature change or an environment of high temperature. As a result, it is possible to improve durability and reliability. 
     Also, for example, when structural strength (rigidity) of the substrate itself is increased, the holding plate becomes unnecessary. In this case, the substrate also functions as the holding plate and a position is adjusted by moving the substrate with respect to the stay. Even in this case, the protrusion for light shielding of the light shielding member is not in contact with the substrate and the imaging element assembly (imaging element). Thus, an effect similar to that of the above embodiment can be acquired. 
     Note that the present invention is not limited to the above embodiments and various modified examples are included. For example, the above embodiments are described in detail to describe the present invention in an easily-understandable manner. The present invention is not limited to what includes all of the above-described configurations. 
     Also, it is possible to replace a part of a configuration of an embodiment with a configuration of a different embodiment and to add a configuration of a different embodiment to a configuration of an embodiment. 
     Also, with respect to a part of a configuration of each embodiment, a different configuration can be added, deleted, or replaced. 
     REFERENCE SIGNS LIST 
     
         
           1  stereo camera 
           5  imaging module 
           10  stay (lens holding member) 
           12  cylindrical mount part 
           14  ring-shaped groove 
           15  lens unit 
           16  lens holder 
           20  imaging element assembly 
           23  cover glass 
           25  imaging element 
           26  imaging surface 
           27  BGA solder ball 
           30  substrate 
           35  holding plate (substrate holding member) 
           37  recessed receiving part 
           40  light shielding member 
           41  base part 
           42  top part 
           43  front end surface (contact surface) 
           44  rectangular window for limiting optical path 
           45  protrusion for supporting 
           46  leading end surface (contact surface) 
           51  first protrusion for light shielding 
           52  second protrusion for light shielding