Abstract:
An imaging system for a motor vehicle includes a camera housing part and at least one camera module to be mounted to said camera housing part. The camera module has first rotation locking means, the camera housing part has second rotation locking means adapted to cooperate with the first rotation locking means, wherein the first and second rotation locking means cooperate to lock the camera module against rotation relative to the camera housing part.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to European Patent Application 14167380.6. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to an imaging system for a motor vehicle, comprising a camera housing part and at least one camera module to be mounted to the camera housing part. The invention also relates to a method of mounting a camera module to a camera housing part. 
         [0004]    2. Description of Related Art 
         [0005]    In the assembly process of an imaging system for a motor vehicle, the lens objective is usually aligned relative to the image sensor in order to compensate for manufacturing tolerances of the lens objective and tilt or misalignment of the image sensor, which would otherwise lead to a deterioration of the image quality. Once the optimal position and orientation of the lens objective has been determined, it is conventionally fixed relative to the image sensor by a glue joint between the lens objective and the front of the lens holder. However, since the lens objective is usually rotationally symmetrical around the optical axis, a roll angle displacement of the image sensor cannot be corrected by rotating the lens objective relative to the image sensor in the alignment process. Therefore, in particular for stereo systems but also for mono systems, a laborious roll alignment has to be performed during mounting of the camera modules into an external camera housing part by rotating one camera module around its optical axis. 
       SUMMARY 
       [0006]    Generally, in order to handle both mono and stereo camera systems, it is desired to share common production processes as much as possible in order to gain efficiency and throughput, hence a modular approach for the camera eyes. It is also critical to maintain focus over the temperature envelope for any automotive camera. 
         [0007]    The problem underlying the present invention is to provide an imaging system with a camera module which is suited to be used both in mono and stereo systems without modification, and where a laborious roll alignment during mounting of the camera modules into the camera housing part can be avoided. 
         [0008]    The invention solves this object with the features of the independent claims. According to the invention, cooperating first and second rotation locking means are provided at the camera unit and the camera housing part, which cooperate to lock the camera module against rotation relative to the camera housing part. Due to the inventive rotation locking means, the camera module is roll aligned relative to the camera housing part by simply bringing the rotation locking means into cooperation, without any further measures to be taken. According to the invention, therefore, a simple passive alignment of the camera module relative to the camera housing part is provided. 
         [0009]    Preferably the first and second rotation locking means are designed to be fittingly inserted into each other along a linear insertion direction. In a simple embodiment, the rotation locking means comprises bores and pins to be fittingly inserted into the bores. In this case, the pins are preferably hollow to allow engagement of screws for fixing said camera module to said camera housing part. Here, the bores may preferably be through holes in a mounting wall to allow the fixing screws to extend through the bores. Furthermore, the mounting wall advantageously comprises an opening through which light can pass on its way into the camera module. Furthermore, the first rotation locking means is advantageously arranged at the lens holder. 
         [0010]    In a preferred embodiment, the camera housing part comprises at least one contact surface designed to be in planar contact with a surface of the camera module when the camera module is fully inserted in said camera housing part. The planar contact between the surfaces guarantees that the alignment, in particular the tip and tilt angle alignment of the camera module relative to the camera housing part is precisely maintained in the mounted state. 
         [0011]    Preferably the alignment of the lens holder relative to a back plate of the camera module is fixed by a glue joint between the lens holder and the back plate. A roll angle displacement of the image sensor is corrected by rotating the lens holder relative to the back plate holding the image sensor. In other words, the roll alignment can be performed already in the mounting of the camera module, such that the mounted camera module can be fully roll-aligned in itself, and no further roll alignment is required during the mounting of the camera modules into the camera housing part. One and the same type of camera module is suited to be used without modifications in mono as well as in stereo applications. 
         [0012]    Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows a scheme illustrating a vision system; 
           [0014]      FIG. 2  shows a cross-sectional view of a camera module; 
           [0015]      FIG. 3  shows a perspective view of a camera module; 
           [0016]      FIG. 4  shows a top view onto a camera module; 
           [0017]      FIG. 5  shows a perspective view of a camera housing part for a stereo imaging means; 
           [0018]      FIG. 6  shows a rear view of the camera housing part of  FIG. 5 ; 
           [0019]      FIG. 7  shows a perspective view of a camera housing part for a mono imaging means; and 
           [0020]      FIG. 8  shows a rear view of the camera housing part of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Referring now to  FIG. 1 , the vision system  10  is mounted in a motor vehicle and comprises an imaging means  11  for acquiring images of a region surrounding the motor vehicle, for example a region in front of the motor vehicle. The imaging means  11  comprises a camera housing part  96  and one or more optical imaging devices  12 , in particular camera modules, mounted in the camera housing part  96 . The camera housing part  96  comprises one or more receptacles  98  each adapted to receive a camera module  12 . The camera housing part  96  is preferably made of metal, for example of Aluminium, and may be mounted behind a front windshield of a motor vehicle in the region of the rear mirror. 
         [0022]    In one embodiment the imaging means  11  operates in the visible wavelength range. However, infrared cameras may also be possible, where infrared covers near IR with wavelengths below 5 microns and/or far IR with wavelengths beyond 5 microns. In some embodiments the imaging means  11  comprises a plurality of imaging devices  12  in particular forming a stereo imaging means  11 . In other embodiments only one imaging device  12  forming a mono imaging means  11  can be used. Each camera module  12  has one optical path; therefore it can also be called a camera eye. 
         [0023]    The imaging means  11  may be coupled to an image pre-processor, not shown in  FIG. 1 , adapted to control the capture of images by the imaging means  11 , receive the electrical signal containing the image information from the imaging means  11 , warp pairs of left/right images into alignment and/or create disparity images, which per se is known in the art. The image pre-processor may be realized by a dedicated hardware circuit, in particular a Field Programmable Gate Array (FPGA). Alternatively the pre-processor, or part of its functions, can be realized in the electronic processing means  14 . In case of a mono imaging means  11  using only one camera  12  a pre-processor is not needed. 
         [0024]    The image data are provided to an electronic processing means  14  where further image and data processing is carried out by corresponding software. In particular, the image and data processing in the processing means  14  comprises the following functions: identification and classification of possible objects surrounding the motor vehicle, such as pedestrians, other vehicles, bicyclists or large animals; tracking over time the position of identified object candidates in the recorded images; estimation of a collision probability between the vehicle and a detected object; and/or activation or control of at least one driver assistance means  18  depending on the result of said collision probability estimation. The driver assistance means  18  may in particular comprise a display means for displaying information relating to a detected object. However, the invention is not limited to a display means. The driver assistance means  18  may in addition or alternatively comprise a warning means adapted to provide a collision warning to the driver by suitable optical, acoustical and/or haptical warning signals; one or more restraint systems such as occupant airbags or safety belt tensioners, pedestrian airbags, hood lifters and the like; and/or dynamic vehicle control systems such as brakes or steering means. The processing means  14  expediently has access to a memory means  25 . 
         [0025]    The electronic processing means  14  is preferably programmed or programmable and expediently comprises a microprocessor or micro-controller. The electronic processing means  14  can preferably be realized in a digital signal processor (DSP). The electronic processing means  14  and the memory means  25  are preferably realised in an on-board electronic control unit (ECU) and may be connected to the imaging means  11  via a separate cable or a vehicle data bus. In other embodiments the ECU and one or more of the imaging devices  12  can be integrated into a single unit, where a one box solution including the ECU and all imaging devices  12  can be preferred. All steps from imaging, image processing to activation or control of driver assistance means  18  are performed automatically and continuously during driving in real time. 
         [0026]    In a preferred embodiment shown in  FIGS. 2 to 4  the camera module  12  comprises a lens objective  20 , a lens holder  53  holding the lens objective  20 , an image sensor  24  and a back plate  32  holding the image sensor  24 . The lens holder  53  is connected to the back plate  32  by means of a glue joint  80  which may be overall ring-shaped, or for example be composed of a plurality of glue dots. The glue  80  preferably is UV light curable glue. The lens holder  53 , the back plate  32  and the glue joint  80  form a housing  22  which, together with the lens objective  20 , is basically closed in a light tight manner except for an incident light opening  28 . With respect to thermal stability, the lens holder  53  is preferably made of metal, for example Zinc or Zinc alloy. 
         [0027]    The lens holder  53  comprises a tubular part  54  which is preferably cylindrical and extends parallel to the optical axis of the lens objective  20 , and a base part  55  to connect the lens holder  53  to the back plate  32  by the glue joint  80 . The tubular part  54  of the lens holder  53  and the lens objective  20  are arranged concentrically to the optical axis of the lens objective  20 . The lens objective  20  is coaxially held in the tubular part  54  of the lens holder  53  and connected to it via a screw connection. More specifically, the lens holder  53  comprises an inner thread  58  and the lens objective  20  comprises a corresponding outer thread  72  adapted to engage the thread  58  of the lens holder  53 . The lens objective  20  can therefore be screwed into the lens holder  53 . The connection between the lens objective  20  and the lens holder  54  is fixed by glue  81  preferably applied between the threads  58 ,  72 . 
         [0028]    Incident light from an object surrounding the motor vehicle falls through the opening  28  and is focussed by the lens objective  20  in the image plane A of the lens objective  20 . The sensitive plane of the image sensor  24  is advantageously disposed at or in the image plane of the lens objective  20 . The image sensor  24  is preferably a two-dimensional image sensor, in particular an optical sensor having maximum sensitivity in the visible wavelength region, and is adapted to convert incident light into an electrical signal containing image information of the object to be detected. The image sensor  24  may for example be a CCD sensor or a CMOS sensor. The rigid back plate  32  is preferably made of metal, in particular steel. 
         [0029]    The printed circuit board  83  of the invention is preferably a flexible printed circuit board arranged on the sensor side of the back plate  32 . The lens objective  20  comprises a lens barrel  63  and one or more lenses held inside the lens barrel  63 . The lens barrel  63  is preferably made of metal, in particular brass. The outer shape of the lens barrel  63  or the lens objective  20  is generally cylindrical and closely fits the inner cylindrical shape of the tubular part  54  or the lens holder  53  such that the lens objective  20  is closely guided in the lens holder  53 . 
         [0030]    The position of the lens holder  53  is adjusted relative to the position of the back plate  32  along six degrees of freedom, namely in x-y-direction perpendicular to the optical z-axis for bore sight correction, with respect to the tip-tilt angles Θ x , Θ y  adjustment, along the optical z-axis with respect to focus adjustment, and, in particular, with respect to the roll angle Θ z . Due to the glue  80  connection being arranged between the lens holder  53  and the back plate  32 , the camera module  12  is inherently roll-aligned, i.e. aligned with respect to the roll angle Θ z . During an active alignment performed in the mounting of the camera module  12 , it is possible, within certain tolerances, to reference the bore sight of each camera module  12  to its contact surface  95 . 
         [0031]    The lens holder  53  comprises rotation locking means  94  provided on the lens holder  53 , preferably on an upper surface  95  of the base part  55 . The rotation locking means  94  have the form of hollow pins. Preferably each camera module  12  comprises two pins  94  arranged in opposite octants defined by the optical axis of the camera module  12 . This means that the angle defined by the two pins  94  and the optical axis is at least 135°, preferably 180° as seen in  FIGS. 3 and 4 . 
         [0032]    Each receptacle  98  of the camera housing part  96  comprises a mounting wall  101 . In each mounting wall  101  bores  99  are formed which are adapted to fittingly receive a pin  94  of a camera module  12  to be inserted into the receptacle  98 . The bores  99  are preferably through-holes through which screws  103  can be screwed from the front side of the wall  101 , which will be explained later. One of each bores  99  of a receptacle  98  may be oblong along a line connecting the two bores  99  of a receptacle  98  in order to compensate for manufacturing tolerances. In  FIGS. 6 and 8  the left bores  99  of each receptacle  98  are slightly oblong in such manner. Alternative to the design shown in the Figures, pins  94  may be provided at the camera housing part  96  and bores  99  may be provided at the camera module  12 . 
         [0033]    In each mounting wall  101 , preferably an opening  102  is formed through which light can pass on its way to the image sensor  24 . In the mounted state, the base part  55  of camera module  20  with the back plate  32  and the image sensor  24  is arranged on the rear side or mounting side of the mounting wall  101  in the receptacle  98 , while the lens objective  20  and/or the tubular part  54  of the lens holder  53  may extend through the opening  102  to the front side. 
         [0034]    Each mounting wall  101  also preferably comprises at least one contact surface  100  designed to provide an abutment for a surface  95  of the camera module  12 , such that the surface  95  of the camera module  12  and the counter-surface  100  of the receptacle  98  are in planar contact when the camera module  12  is fully received in the receptacle  98 . In the embodiment shown in  FIGS. 6 and 8  each receptacle  98  comprise two contact surfaces  100  on opposite sides of the opening  102 , where in every surface  100  one bore  99  is formed. Alternatively, for example, each receptacle  98  may comprise only one preferably ring shaped contact surface  100  surrounding the opening  102 . 
         [0035]    The surfaces  100  are preferably highly planar, which may be achieved by using machined surfaces  100  if the camera housing part  96  is cast metal, i.e. providing an additional machining step in the manufacturing of the camera housing part  96 . Advantageously all contact surfaces  100  of a camera housing part  96  lie in the same plane, for example all four contact surfaces  100  of the stereo camera housing part  96  shown in  FIG. 6 . 
         [0036]    For mounting a camera module  12  to the camera housing part  96 , the camera module  12  is inserted into the receptacle  98  and the pins  94  of the camera module  12  are simply plugged into the bores  99  of the camera housing part  96  along the pin&#39;s  94  axis from the mounting side of the wall  101 . When the pins  94  of a camera module  12  are fully inserted into the bores  99  of a receptacle  98 , a rotation of the camera module  12  relative to the camera housing part  96  around the optical axis, i.e. a change of the roll angle Θ z  of the camera module  12 , is prevented. Finally, the camera module  12  is fixed to the camera housing part  96  by means of screws  103  which are screwed into the hollow pins  94  through the bores  99  from the non-mounting side of the wall  101 . The screws  103  are preferably self-tapping and the bores  99  are adapted to the size of the screws to allow self-tapping. 
         [0037]    As described above, the pins  94  and bores  99  function to fasten the camera module  12  with fixed roll orientation to the camera housing part  96 . This corresponds to a most simple passive roll alignment, without necessity for any further alignment measure, which is possible since the roll angle Θ z  is inherently fixed in the camera module  12  as described above. 
         [0038]    Furthermore, precise locking of the tip and tilt angles Θ x , Θ y , and also fixing of the z-alignment, of the camera module  12  relative to the camera housing part  96  in the mounted state is achieved by the highly planar contact between the contact surfaces  95 ,  100 . 
         [0039]    As a person skilled in the art will readily appreciate, the above description is meant as an illustration of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.