Abstract:
A camera module lens cap is provided to protect a camera module in a mobile device where the camera module is exposed. The camera module lens cap includes an optically transparent member for positioning adjacent a camera lens, and a housing for carrying the optically transparent member. The housing includes an overhanging lip for engaging a base of the camera module.

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to a camera module lens cap, and in particular, to a lens cap for a camera module of a solid state image sensor. 
       BACKGROUND OF THE INVENTION  
       [0002]    The field of solid state image sensors is well established. CCD and CMOS sensors are found in a large number of devices from digital still cameras to mobile telephones, as well as in laptops, webcams, pointing devices and barcode readers to name but a few. Mobile devices include, but are not limited to, mobile telephones, smart phones, palmtops and personal digital assistants, for example. 
         [0003]    A typical camera module for a solid state image sensor is shown in  FIG. 1 . It includes a base  10 , which can also be called a mount, and a barrel  12 . In this example, the base  10  has a lower pedestal portion and an upper cylindrical portion which encases the barrel  12 . A lens (not shown) is housed within the barrel  12 , and the barrel moves vertically to adjust the focus. The lens  14  focuses incident light onto an image sensing integrated circuit  16 , typically formed by a CMOS process. When packaging the camera module within a mobile device, it is important to protect the module and its components from being damaged by the end user or from entry of dust or other contamination. If the lens is exposed it can be scratched, and if the barrel  12  is exposed, any forces applied to it can make it move and interfere with the correct focusing of the camera module. 
         [0004]    Traditionally, mobile devices have been constructed with a protective cover integrated into the casing to prevent damage and scratching to the camera module. However, with the abovementioned pressures on form factor and for other manufacturing reasons, some manufacturers prefer to omit this cover and leave the module exposed. In this case, a known way of protecting the module from exposure is to provide a circular glass or plastic fixture mounted on top of the barrel, usually fixed in place with an adhesive washer or with a glue material. 
         [0005]    However, this method of protection presents a number of practical disadvantages. The fixture has a low mechanical strength when shear forces are applied, and forces applied to it will translate into the barrel and may move the focus of the module. Adhesive washers are a nonpermanent method, and can be peeled off by an end user. Glue and adhesive tend to be more susceptible to environmental conditioning, and do not perform well in drop tests. Furthermore, circular glass is relatively expensive compared to regular shapes such as squares or rectangles. This is due to the extra steps required to grind the edges, and to the material that is wasted in its manufacture. 
       SUMMARY OF THE INVENTION  
       [0006]    In view of the foregoing background, an object of the present invention is to provide a lens cap for a camera module of a solid state image sensor with a reduced form factor without compromising on the effective packaging of components to ensure robust operation. 
         [0007]    This and other objects, advantages and features in accordance with the present invention are provided by a camera module lens cap comprising an optically transparent member for positioning over a lens, and a housing comprising an overhanging lip that engages with a base of a camera module. 
         [0008]    The housing may comprise a central aperture, and may be circular in shape. The optically transparent member may comprise a square member that may be formed from a glass material. The square member may be fitted to an underside of the housing, and may rest on four corners of the cylindrical portion of the base. 
         [0009]    The optically transparent member and the housing may be a one piece construction, such as being formed as a unitary molded plastic member. The housing may be painted and/or textured on to render it optically opaque. The optically transparent member may be coated with a toughening or a protection material. 
         [0010]    The lip may extend part way down a cylindrical portion of the housing. The lip may also rest on a pedestal portion of the housing. 
         [0011]    The optically transparent portion may be coated with an anti-reflection coating. The housing may comprise apertures on an upper surface for the entry of adhesive. 
         [0012]    The housing may comprise slots on a bottom edge of the lip for locating the cap in a tape and reel carrier. The housing may comprise indents on a top surface for locating the cap in a holder for a glass attachment. Two opposing indents may be provided which have different angles of inclination. 
         [0013]    According to a second aspect, a mobile device comprises a camera module fitted with the lens cap as described above. The camera module lens cap may be loosely fitted with a casing portion of the mobile device. 
         [0014]    Further aspects are directed to providing a mobile telephone, laptop computer, webcam, digital still camera, camcorder, optical mouse and barcode reader that comprises a camera module fitted with the lens cap as described above. These are all types of mobile devices according to the second aspect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]    The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0016]      FIG. 1  illustrates a typical camera module according to the prior art; 
           [0017]      FIG. 2  shows a lens cap according to a first embodiment of the present invention; 
           [0018]      FIG. 3  shows the location of an optically transparent member within the lens cap of  FIG. 2 ; 
           [0019]      FIG. 4  shows an isometric view of the lens cap of  FIG. 2  in position on a camera module; 
           [0020]      FIG. 5  is a cross-sectional view taken across line A-A shown in  FIG. 4 ; 
           [0021]      FIG. 6  is a cut away view showing the location of the optically transparent member within the embodiment of  FIG. 4 ; 
           [0022]      FIG. 7  shows a tape and reel strip for holding lens caps during a manufacturing process according to the present invention; 
           [0023]      FIG. 8  shows a mobile telephone incorporating a camera module provided with the lens cap of  FIG. 2 ; and 
           [0024]      FIG. 9  shows a lens cap according to a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    A first embodiment of a lens cap is illustrated with reference to  FIGS. 2 to 8 . As shown in  FIG. 2 , the lens cap  20  comprises a housing  22  and an optically transparent member  24 . The housing  22  comprises a one piece plastic molding formed from a material such as a liquid crystalline polymer (LCP), and includes an aperture  26  for the transmission of light. The housing  22  further comprises an overhanging lip portion  28 . 
         [0026]    As can be more clearly shown in  FIG. 3 , the optically transparent portion  24  comprises a square piece of optically transparent material, such as an appropriate glass or plastics material. The material is optionally coated with an anti-reflection coating on one or both sides for reducing the incidence of reflections in the images output by the image sensor.  FIG. 3  shows how the square piece  24  is glued into place in the housing  22 . 
         [0027]    The lens cap  20  then covers a camera module  30  as shown in  FIG. 4 . The overhanging lip portion  28  is fixed or attached to the mount  10 . This causes all forces applied to the cap  20  to be transmitted into the mount  10 , thus shielding the barrel  12  and having no effect on the module&#39;s focusing. Also, because the overhanging lip  28  extends downwards, the cap  20  can withstand higher lateral forces as compared with a single piece circular member that is placed or fixed on top of the barrel or module. The overhanging lip  28  can be formed to extend further down the mount than illustrated in order to increase these effects, to any depth until it touches the pedestal portion of the base. An additional advantage of the overhanging design is to prevent dust from entering between the cap and barrel lenses. 
         [0028]    Furthermore, the use of the square glass reduces cost as compared with the use of circular glass, as mentioned above. As can be seen in  FIG. 6 , the square glass can be arranged to sit on the mount in four corners to prevent the glass from being pushed out of the cap by the end user. 
         [0029]    In an example of a process for manufacturing the camera module, the cap  20  is supplied in a tape and reel carrier and then taken out and placed onto a boat carrier, and glue is applied to the underside of the cap and the glass is set in place. The cap  20  is then mounted on the module and glue is applied to the mount. 
         [0030]    The lens cap  20  can be advantageously provided with features to aid this manufacturing process. As seen in  FIG. 2 , two opposing slots  32  are provided on the bottom edge of the overhanging lip  28  which forces the cap  20  in position within a tape and reel cavity such as that shown in  FIG. 7 , by mating with the projections  34  seen in  FIG. 7 . This prevents the cap  20  from turning, thus ensuring consistent location for pick and place machinery used to process the cap  20 . The cap  20  is also provided with slots  36  for locating the cap  20  in a holder for the glass attach step, or to a boat carrier. The surfaces  38  of the slots  36  are angled, and can be formed with different surface textures so that they reflect light differently, and can be distinguished from each other by the pick and place machinery. 
         [0031]    The cap  20  can also be provided with two holes  40  on a top surface for the application of an adhesive for fixing using standard automation equipment and can easily be sealed afterwards to prevent dust or debris entry. The cap  20  can also optionally be provided with a lip on its underside to prevent glue from bleeding into the optical surface. 
         [0032]    A mobile device incorporating a camera module with a lens cap is shown in  FIG. 8 . The cap  20  rather than the module itself is exposed so that the lens is protected, and the focus is not affected when the cap is subjected to forces as described above. 
         [0033]    A lens cap according to a second embodiment is shown in  FIG. 9 . Instead of a two piece plastic housing with glass insert, the cap  42  can be formed from a single piece of molded material, suitably a plastics material. Typically, an optically transparent plastic will be used, and then a portion will be rendered opaque by being painted or textured, leaving an optically transparent section  44  in a central portion. The optically transparent section  44  can then be coated with an anti-reflection coating, and can also be toughened to give it glass-like properties. 
         [0034]    It will be apparent that the cap  42  of the second embodiment shares the same advantages of the cap  20  of the first embodiment. These are directly transferable and so will not be described in detail herein. 
         [0035]    It is to be appreciated that the lens cap could be applied to any camera module, whether or not the module would actually be exposed without the cap, and irrespective of the type of device in which it is used. That is, it is not restricted for use in mobile devices. Examples of mobile devices for which the lens cap could be used include a mobile telephone, laptop computer, webcam, digital still camera, optical mouse or barcode reader. It will be apparent to those skilled in the art on how to incorporate the lens cap into these products without further explanation being needed herein. The exact fit of the module and cap will depend on the topology of a particular device. 
         [0036]    Various improvements and modifications can be made to the above without departing from the scope of the invention.