Abstract:
A camera module includes an integral motor for rotating a lens unit of the camera module within a housing of the camera module. The housing includes a plurality of electromagnetic coils that function as a stator of the motor. The lens unit includes a plurality of ferrite elements and functions as a rotor of the motor. Rotation of the lens unit within the housing causes focal adjustment, such that the motor can be used as a component of an auto-focus system. A method for assembling the camera module is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of copending U.S. Provisional Patent Application No. 60/872,142 filed Dec. 1, 2006 by the same inventors, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to electronic devices, and more particularly to digital camera modules. Even more particularly, the present invention relates to a system for focusing a digital camera module via a stepper motor incorporated therein. 
         [0004]    2. Description of the Background Art 
         [0005]    Digital camera modules are currently being incorporated into a variety of electronic devices. Such camera hosting devices include, but are not limited to, cellular telephones, personal data assistants (PDAs), and computers. The demand for digital camera modules continues to grow as the ability to incorporate the camera modules into host devices expands. Therefore, one design goal of digital camera modules is to make them as small as possible so that they will fit into an electronic device without substantially increasing the overall size of the device. Furthermore, it is also desirable to manufacture such digital camera modules as efficiently and robustly as possible. It is also desirable to manufacture digital camera modules that require minimal user knowledge and effort to operate. Means for achieving these design goals should enhance, or at least preserve, the quality of the image captured by the camera modules. 
         [0006]    Typically, camera modules include multiple focal modes for focusing on images at various distances. For example, known camera modules include multiple modes for focusing images of objects at different distances. Changing from one mode to another requires a change in displacement between a lens and an image capture device within the camera module. This displacement change is facilitated by many different mechanisms known to those skilled in the art. For example, many prior art camera modules include a threaded lens housing that is threaded into and out of an image capture device housing, thereby changing the distance between the lens and the image capture device. Other commonly known focusing devices include cam mechanisms to move the lens with respect to the image capture device. 
         [0007]    In miniature camera modules, prior art focusing methods are typically accomplished manually, because the size limitations prohibit the use of drive motors, cams, gears, and so on. In addition, prior art devices include other disadvantages. For example, some prior art camera modules have only two focal modes, micro and macro. Thus, image quality is sacrificed at intermediate ranges. Another disadvantage is that the user is inconvenienced by having to make sure the camera is in the correct focal mode and/or switching the focal modes. The extremely small size of some camera modules makes manual focal adjustment even more difficult. 
         [0008]    What is needed, therefore, is a camera module that provides many focal modes and/or continuous focal adjustment. What is also needed is a camera module that requires minimal user effort and knowledge to operate. What is also needed is a camera module that can be automatically focused. What is also needed is a camera module that provides focusing flexibility, while remaining relatively small in size. 
       SUMMARY 
       [0009]    The present invention overcomes problems of the prior art by providing a means for incorporating a drive motor into a camera module. The drive motor is suitable for use in even extremely small camera modules, because components of the camera module also serve as components of the motor. 
         [0010]    In one embodiment a camera module includes an image capture device, a lens unit, a housing, an electrical motor, and an adjustment (e.g., focus, zoom, etc.) mechanism. The housing is adapted to receive the lens unit and to position the lens unit with respect to the image capture device. The housing forms a first portion of the electrical motor, and the lens unit forms a second portion of the electrical motor. When the electrical motor is energized, the lens unit rotates within the housing. 
         [0011]    In a particular embodiment, the motor is a stepper motor. The portion of the motor formed by the housing is a stator of the stepper motor, and the portion of the motor formed by the lens unit is a rotor of the stepper motor. The lens unit includes a generally cylindrical body with a plurality of ferrite elements fixed to the cylindrical body. The housing includes a plurality of electrical windings that electromagnetically attract the ferrite elements when energized. 
         [0012]    An example adjustment mechanism includes a plurality of ramps formed on the housing and a plurality of complementary ramps formed on the lens unit. When the lens unit rotates within the housing the adjustment mechanism changes the position of the lens unit with respect to the image capture device. Optionally, the complementary ramps are formed on an annular ring of the lens unit, and the lens unit includes a second adjustment mechanism between another portion of the annular ring and the cylindrical body of the lens unit. The first adjustment mechanism (between the ring and the housing) facilitates focusing by the motor. The second adjustment mechanism (between the ring and the cylindrical body of the lens unit) facilitates a factory focus operation. 
         [0013]    According to another aspect of the invention, a camera focusing motor is provided for use in various types of cameras and/or camera modules. The camera focusing motor includes a stator formed integrally with a housing of the camera and a rotor formed integrally with the lens unit of the camera. The rotor includes a lens barrel of the lens unit and a plurality of ferrite elements embedded in the lens barrel. The stator includes a plurality of electromagnetic coils mounted in the housing. The individual coils are disposed adjacent the periphery of the lens barrel so that the plurality of electromagnetic coils surrounds the lens barrel of the lens unit. Control circuitry selectively energizes the electromagnetic coils to control the rotational movement of the rotor with respect to the stator. Optionally, at least a portion of the control circuitry is included in an integrated image capture device mounted with respect to the housing. In the example shown, the motor functions as a stepper motor. 
         [0014]    A method for assembling a camera module is also disclosed. The method includes providing a housing including a first portion of a motor, providing a housing including a second portion of a motor, and positioning the lens unit with respect to the housing to engage the first portion of the motor with the second portion of the motor. The step of providing the housing with a first portion of the motor includes providing a housing with a plurality of electromagnetic coils fixed thereto. Thus, a stator of the motor is built into the housing. The step of providing the lens unit includes providing a lens unit with a plurality of ferrite elements fixed thereto. Thus, the rotor of the motor is built into the lens unit. In the disclosed example method, the assembled camera module operates as a stepper motor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The present invention is described with reference to the following drawings, wherein like reference numbers denote substantially similar elements: 
           [0016]      FIG. 1  is a perspective view of a camera module; 
           [0017]      FIG. 2  is an exploded perspective view of the camera module of  FIG. 1 ; 
           [0018]      FIG. 3  is a perspective cross-sectional view of the lens barrel shown in  FIG. 1 ; 
           [0019]      FIG. 4  is a perspective view of the camera module housing shown in  FIG. 1 ; 
           [0020]      FIG. 5  is a rear perspective view of the interior of the housing shown in  FIG. 1 ; 
           [0021]      FIG. 6  is a cross-sectional view of the camera module shown in  FIG. 1 ; 
           [0022]      FIG. 7  is flow chart summarizing a method for assembling a camera module; and 
           [0023]      FIG. 8  is a flow chart summarizing another method for assembling a camera module. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The present invention overcomes the problems associated with the prior art, by providing a camera module with a stepper motor incorporated therein. In the following description, numerous specific details are set forth (e.g., material selection) in order to provide a thorough understanding of the invention. Those skilled in the art will recognize, however, that the invention may be practiced apart from these specific details. In other instances, details of well known electrical practices (e.g., stepper motor assembly and control, etc.) and components have been omitted, so as not to unnecessarily obscure the present invention. Such details can be found in references generally known to those skilled in the art. For example, Acarnley, Paul P., Stepping Motors: A Guide to Theory and Practice, 4 th  edition, (IEE Control Engineering Series, 63) provides useful information regarding the operation of stepper motors. That reference is incorporated herein by reference in its entirety. 
         [0025]      FIG. 1  shows a perspective view of an assembled digital camera module  100 . In this particular embodiment, camera module  100  includes a printed circuit board (PCB)  102 , a housing  104 , an actuating ring  106 , and a lens barrel  108 . In this particular embodiment, camera module  100  also includes an autofocus feature wherein lens barrel  108  is vertically displaceable with respect to PCB  102  via an electro-magnetically driven system (e.g., stepper motor). 
         [0026]      FIG. 2  shows a perspective view of camera module  100  exploded along an optical axis  200 . As shown, PCB  102  includes an image capture device  202  affixed thereon. PCB  102  is further affixed to the rear surface of housing  104  so as to provide support to actuating ring  106 . In this particular embodiment, actuating ring  106  is rotatable about optical axis  200 . Lens barrel  108  includes a threaded peripheral surface  204  that threads into a complimentary threaded inner portion  206  of actuating ring  106 . Threads  204  and  206  enable lens barrel  108  to be properly focused with respect to actuating ring  106 . This particular focusing feature is typically carried out during the manufacturing process and is typically only done one time. This is commonly referred to as factory focusing. 
         [0027]    The autofocus feature is different than the factory focusing carried out during the manufacturing of camera module  100 . The autofocus feature enables the focal field to be changed anytime either by the user or automatically by autofocusing means known to those skilled in the art. The autofocus mechanism works using the same principle as a stepper motor. In the center of camera module  100  is lens barrel  108  which includes ferrite elements  208  embedded into it&#39;s peripheral surface. Barrel  108  acts as the “rotor”. Housing  104  includes magnetic windings  210  (electromagnetic coils) that function as a “stator”. As windings  210  are given power (energized), ferrite elements  208  become electromagnetically attracted to windings  210 . As a result, actuation ring  106  and lens barrel  108  (fixed within ring  106  during factory focusing) are rotated in a direction that depends on which of windings  210  are given power. As ring  106  rotates, it slidably contacts a sloped surface  212  of housing  104 , which changes the vertical distance between lens barrel  108  and image capture device  202 . Of course, this vertical distance change between lens barrel  108  and image capture device  202  facilitates the focusing of camera module  100 . 
         [0028]    In this particular embodiment, the control circuitry for the stepper motor is included in image capture device  202 . The power circuitry and electrical interconnections are not shown, so as to not unnecessarily obscure the description invention. However, those skilled in the art will understand that such circuitry would reside on PCB  102  and an electrical interconnection between PCB  102  and housing  104  would be provided in order to route power to windings  210 . 
         [0029]      FIG. 3  shows a cross-sectional perspective view of lens barrel  108 . In this particular embodiment, lens barrel  108  houses a lens assembly  300 . It should be apparent to those skilled in the art that specifications (e.g., prescription, IR filters, fixing means, etc.) of lens assembly  300  are not essential aspects of the present invention and are only shown to provide a better understanding of the present invention. 
         [0030]      FIG. 4  is a top perspective view of housing  104 . In this particular embodiment, housing  104  includes sloped surfaces  212  (ramps) that slidably engage the rear surface (complementary ramps) of actuating ring  106 . As lens barrel  108  is rotated by the electromagnetic force between ferrite elements  208  and windings  210 , sloped surface  212  facilitates the change in distance between lens assembly  300  and image capture device  202 . 
         [0031]      FIG. 5  is a bottom perspective view of housing  104 . This particular figure illustrates how windings  210  are built into the interior of housing  104 . 
         [0032]      FIG. 6  is cross-sectional view of camera module  100 , showing the relative positioning of lens barrel  108  and housing  104  when lens barrel  108  is mounted to housing  104 . Note that the individual windings  210  are each disposed adjacent the periphery of lens barrel  108  such that the plurality of windings  210  surrounds lens barrel  108 . Lens barrel  108  and housing  104  actually form a portion of the electrical motor used to provide focal adjustment. In particular, lens barrel  108  forms a portion of a rotor, and housing  104  actually forms a portion of a stator. 
         [0033]      FIG. 7  is a flow chart summarizing one particular method  700  for assembling a camera module. In a first step  702 , a lens barrel is provided. Next, in a second step  704 , an actuating ring is provided. Then, in a third step  706 , a camera module housing is provided. Next, in a fourth step  708 , the lens barrel is partially thread into the actuating ring. Then, in a fifth step  710 , the actuating ring is placed into the housing and rotated up against a stop for calibration. Next, in a sixth step  712 , with the actuating ring held against the stop, the lens barrel is rotated within the actuating ring until focus is achieved (factory focus). Finally, in a seventh step  714 , the lens barrel is bonded to the actuating ring. 
         [0034]      FIG. 8  is a flow chart summarizing another particular method  800  of assembling a camera module. In a first step  802 , a camera module housing including a first portion of a motor is provided. Then, in a second step  804 , a lens unit including a second portion of the motor is provided. Next, in a third step  806 , the lens unit is mounted to the camera housing to engage the first portion of the motor to the second portion of the motor. Thus, the assembly of a camera module and the assembly of the motor occur simultaneously. 
         [0035]    The description of particular embodiments of the present invention is now complete. Many of the described features may be substituted, altered or omitted without departing from the scope of the invention. For example, alternate lens assemblies may be substituted for lens assembly  300 . As another example, alternate adjustment mechanisms (e.g. threads, grooves, etc.) can be substituted for sloped surface  212 . These and other deviations from the particular embodiments shown will be apparent to those skilled in the art, particularly in view of the foregoing disclosure.