Abstract:
An exemplary lens module includes a lens barrel ( 10 ), a lens ( 20 ) and a sleeve barrel ( 30 ). The lens barrel includes an adjusting magnet ( 15 ). The lens is mounted in the lens barrel. A part of the lens barrel is slidably mounted in the sleeve barrel, the sleeve barrel includes a positioning magnet group ( 33 ), and the positioning magnet group cooperates with the adjusting magnet to selectably position the lens barrel in at least two different positions in the sleeve barrel.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to lens modules and, more particularly, to a lens module with a magnetic focusing mechanism; the lens module being typically used in an optical device such as a microscope, a camera module, a digital camera module of a portable electronic device, or the like. 
     DESCRIPTION OF RELATED ART 
     With the ongoing development of microcircuitry and multimedia technologies, digital cameras are now in widespread use. In addition, high-end portable electronic devices, such as mobile phones and personal digital assistants (PDAs), are being developed to be increasingly multi-functional. Thus many of these portable electronic devices are now equipped with a digital camera module. These electronic devices enable consumers to enjoy capturing digital pictures anytime and anywhere. Nevertheless, there is increasing consumer demand for very high quality digital pictures. 
     In a typical camera module, the lens module thereof is very important to the quality of the pictures captured by the camera module. Generally, a lens module includes a lens and an image sensing module. Optical image signals are focused by the lens and then received by the image sensing module, whereupon the image sensing module transforms the optical image signals into electronic image signals. When a distance between the lens and the image sensing module is adjusted, the definition of the optical image signals received by the image sensing module is also changed. 
     In a typical lens module with a focusing mechanism, the focusing mechanism generally includes some drivers such as gearings or axles. When the lens module is used to take photos, the focusing mechanism appropriately adjusts the positions of some optical components of the lens module such as the lens and the image sensing module via the drivers. However, the focusing mechanism is liable to suffer from wear because of continual friction between the various parts, whereby the precision of the focusing mechanism is reduced. 
     Therefore, a new lens module is desired in order to overcome the above-described shortcomings. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, a lens module includes a lens barrel, a lens and a sleeve barrel. The lens barrel includes an adjusting magnet. The lens is mounted in the lens barrel. A part of the lens barrel is slidably mounted in the sleeve barrel, the sleeve barrel includes a positioning magnet group, and the positioning magnet group cooperates with the adjusting magnet to selectably position the lens barrel in at least two different positions in the sleeve barrel. 
     Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present lens module. Moreover, in the drawings, like reference numerals designate corresponding parts through out the views. 
         FIG. 1  is a cutaway view of a lens module in accordance with a preferred embodiment of the present invention, showing the lens module in a state in which it is used to take long distance photos. 
         FIG. 2  is similar to  FIG. 1 , but showing the lens module in a state in which it is used to take photos of objects at close range. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail,  FIG. 1  shows a lens module  100  in accordance with a preferred embodiment of the present invention. The lens module  100  includes a lens barrel  10 , a lens  20 , a sleeve barrel  30 , and an image sensing module  40 . The lens  20  is mounted in the lens barrel  10 , and the lens barrel  10  is mounted in the sleeve barrel  30 . The image sensing module  40  is mounted on an end of the sleeve barrel  30 . 
     The lens barrel  10  is a substantially hollow cylinder in shape, and includes an outer surface  101 , a first inner surface  102 , an aperture end  11 , an image sensing end  12 , a front stopper  13 , a back stopper  14 , an adjusting magnet  15 , a first positioning member  16 , and a second positioning member  17 . The image sensing end  12  is located opposite to the aperture end  11 . The lens barrel  10  defines an aperture  111  in a center of the aperture end  11 , and an image sensing opening  121  in a center of the image sensing end  12 . 
     The front stopper  13  is an annular block fixed to the outer surface  101  at the aperture end  11 . The back stopper  14  is an annular block fixed to the outer surface  101  at the image sensing end  12 . The adjusting magnet  15  is an annular permanent magnet, which is secured in an annular recess defined in the lens barrel  10  at the outer surface  101  between the front stopper  13  and the back stopper  14 . Thereby, an outer surface of the adjusting magnet  15  is flush with the outer surface  101 . The south magnetic pole of the adjusting magnet  15  is oriented towards the aperture end  11 , and the north magnetic pole of the adjusting magnet  15  is oriented towards the image sensing end  12 . The first positioning member  16  is an annular ferromagnet, which is secured in an annular recess defined in a back side of the front stopper  13 . The second positioning member  17  is an annular ferromagnet, which is secured in an annular recess defined in a front side of the back stopper  14 . 
     The lens  20  is a typically a round biconvex lens. A peripheral configuration of the lens  20  is shaped to correspond to a shape of the first inner surface  102 , so that the lens  20  can be securely mounted in the lens barrel  10 . 
     The sleeve barrel  30  is substantially a hollow cylinder in shape, and includes a second inner surface  301 , an adjusting end  31 , a mounting end  32 , a positioning magnet group  33 , and a limiting block  34 . The mounting end  32  is located opposite to the adjusting end  31 . The limiting block  34  is located between the mounting end  32  and the adjusting end  31 . The sleeve barrel  30  defines an adjusting opening  311  in a center of the adjusting end  31 . A diameter of the adjusting opening  311  is larger than a diameter of the outer surface  101 , and less than an outer diameter of the front stopper  13 . 
     The positioning magnet group  33  includes a first positioning magnet  331 , a second positioning magnet  332 , a first magnetizer  333 , and a second magnetizer  334 . The first positioning magnet  331  is an annular permanent magnet, which is secured in an annular recess defined in the sleeve barrel  30  at the second inner surface  301  adjacent to the adjusting end  31 . The second positioning magnet  332  is an annular permanent magnet, which is secured in an annular recess defined in the sleeve barrel  30  at the second inner surface  301  adjacent to a back of the limiting block  34 . An inner diameter of the first positioning magnet  331  and an inner diameter of the second positioning magnet  332  are both larger than both the diameter of the outer surface  101  and an outer diameter of the back stopper  14 . The south magnetic pole of the first positioning magnet  331  and the south magnetic pole of the second positioning magnet  332  are both oriented towards the adjusting end  31 . The north magnetic pole of the first positioning magnet  331  and the north magnetic pole of the second positioning magnet  332  are both oriented towards the mounting end  32 . 
     The first magnetizer  333  and the second magnetizer  334  are both annular ferromagnets. The limiting block  34  is an annular protrusion projecting inward from the second inner surface  301 , and is located between the first positioning magnet  331  and the second positioning magnet  332 . An inner diameter of the limiting block  34  is larger than the diameter of the outer surface  101 , and less than the outer diameter of the back stopper  14 . The first magnetizer  333  is installed in the adjusting end  31 , such that an annular back side of the first magnetizer  333  is in contact with the first positioning magnet  331 , and an annular front side of the first magnetizer  333  is exposed at a front face of the adjusting end  31 . The second magnetizer  334  is installed in an annular recess defined in a back side of the limiting block  34 , such that an inner portion of an annular back side of the second magnetizer  334  is exposed at a back face of the limiting block  34 , and an outer portion of the annular back side of the second magnetizer  334  is in contact with the second positioning magnet  332 . 
     The image sensor module  40  includes a base  41  and an image sensor  42 . The image sensor  42  is secured to a front side of the base  41 . 
     In assembly, the lens  20  is coaxially mounted in the lens barrel  10 . In further or alternative embodiments, one or more other lenses can be mounted in the lens barrel  10 . The back stopper  14  is fixed around the outer surface  101  of the lens barrel  10  at the image sensing end  12 . This subassembly is then inserted into the sleeve barrel  30  via the mounting end  32 , so that the aperture end  11  of the lens barrel  10  protrudes out from the adjusting opening  311  of the adjusting end  31  of the sleeve barrel  30 . The front stopper  13  is then fixed around the outer surface  101  at the aperture end  11 . Thus the front stopper  13  is located outside of the sleeve barrel  30 , and the adjusting end  31  and the limiting block  34  are both located between the front stopper  13  and the back stopper  14 . With this configuration, a part of the lens barrel  10  is slidably mounted in the sleeve barrel  30 , the lens barrel  10  can move forward until the back stopper  14  is stopped by the limiting block  34 , and the lens barrel  10  can move rearward until the front stopper  13  is stopped by the adjusting end  31 . When the front stopper  13  is stopped by the adjusting end  31 , the first positioning member  16  comes into contact with the first magnetizer  333 , and the first positioning magnet  331  attracts the first positioning member  16  via the first magnetizer  333 . When the back stopper  14  is stopped by the limiting block  34 , the second positioning member  17  comes into contact with the second magnetizer  334 , and the second positioning magnet  332  attracts the second component  17  via the second magnetizer  334 . Finally, the base  41  of the image sensing module  40  is mounted on the mounting end  32 , so that the image sensor  42  is aligned with the image sensing opening  121 . 
     When the lens module  100  is used to take photos of objects at a long distance, the lens barrel  10  is driven by a driving mechanism (not shown) to move rearward until the front stopper  13  is stopped by the adjusting end  31 . When the front stopper  13  is stopped by the adjusting end  31 , the first positioning member  16  comes into contact with the first magnetizer  333 , and the first positioning magnet  331  attracts the first positioning member  16  via the first magnetizer  333 . In this way, the lens barrel  20  is prevented from moving axially, the lens  20  is located relatively close to the image sensor  42 , and the lens module  100  is capable of taking photos of objects at a long distance. 
     At the same time, the second positioning magnet  332  is located around the adjusting magnet  15 . The south magnetic pole of the adjusting magnet  15  is adjacent to the south magnetic pole of the second positioning magnet  332 , and the north magnetic pole of the adjusting magnet  15  is adjacent to the north magnetic pole of the second positioning magnet  332 . Thus a whole periphery of the adjusting magnet  15  is repulsed by the second positioning magnet  332  towards a center of the second positioning magnet  332 , so that the lens barrel  10  is prevented from coming into contact with the sleeve barrel  30 . As a result, friction between the lens barrel  10  and the sleeve barrel  30  is eliminated, and a working lifetime of the lens module  100  is prolonged. 
     If the lens barrel  10  moves radially from the center of the second positioning magnet  332 , a first side of the adjusting magnet  15  comes closer to the second positioning magnet  332 , and the repulsion between the first side of the adjusting magnet  15  and the second positioning magnet  332  increases. Additionally, an opposite second side of the adjusting magnet  15  moves farther from the second positioning magnet  332 , and the repulsion between the second side of the adjusting magnet  15  and the second positioning magnet  332  decreases. In this way, radial movement of the lens barrel  10  is soon stopped by the increasing repulsion between the first side of the adjusting magnet  15  and the second positioning magnet  332 , and the lens barrel  10  is repulsed back to the center of the second positioning magnet  332  again. When the adjusting magnet  15  is in the center of the second positioning magnet  332 , the repulsion between the adjusting magnet  15  and the second positioning magnet  332  is equal in all radial directions. Thus the lens barrel  10  is suspended in the center of the second positioning magnet  332 . In this way, the lens barrel  10  resists being displaced radially, and remains coaxially positioned in the sleeve barrel  30 . Accordingly, the image sensor  42  remains aligned with the image sensing opening  121  to receive optical image signals focused by the lens  20 . 
     Also referring to  FIG. 2 , when the lens module  100  is used to take photos of objects at a short distance, the lens barrel  10  is driven by the driving mechanism to move forward until the back stopper  14  is stopped by the limiting block  34 . When the back stopper  14  is stopped by the limiting block  34 , the second positioning member  17  comes into contact with the second magnetizer  334 , and the second positioning magnet  332  attracts the second positioning member  17  via the second magnetizer  334 . In this way, the lens barrel  10  is prevented from moving axially, the lens  20  is located far from the image sensor  42 , and the lens module  100  is capable of taking photos of objects at a short distance. 
     At the same time, the first positioning magnet  331  is located around the adjusting magnet  15 . The south magnetic pole of the adjusting magnet  15  is adjacent to the south magnetic pole of the first positioning magnet  331 , and the north magnetic pole of the adjusting magnet  15  is adjacent to the north magnetic pole of the first positioning magnet  331 . Thus a whole periphery of the adjusting magnet  15  is repulsed by the first positioning magnet  331  towards a center of the first positioning magnet  331 , so that the lens barrel  10  is prevented from coming into contact with the sleeve barrel  30 . As a result, friction between the lens barrel  10  and the sleeve barrel  30  is eliminated, and a working lifetime of the lens module  100  is prolonged. 
     If the lens barrel  10  moves radially from the center of the first positioning magnet  331 , the repulsion between the adjusting magnet  15  and the second positioning magnet  331  stops the lens barrel  10  moving radially and repels the lens barrel  10  back to the center of the first positioning magnet  331  again. When the adjusting magnet  15  is in the center of the first positioning magnet  331 , the repulsion between the adjusting magnet  15  and the first positioning magnet  331  is equal in all radial directions. Thus the lens barrel  10  is suspended in the center of the first positioning magnet  331 . In this way, the lens barrel  10  resists being displaced radially, and remains coaxially positioned in the sleeve barrel  30 . Accordingly, the image sensor  42  remains aligned with the image sensing opening  121  to receive optical image signals focused by the lens  20 . 
     Understandably, the above-described magnetic repulsion means that the lens barrel  10  resists being displaced radially, and can remain in a desired correct position in the sleeve barrel  30 . That is, the magnetic repulsion can prevent friction occurring between the lens barrel  10  and the sleeve barrel  30 . 
     In an alternative embodiment, the orientations of the magnetic poles of the adjusting magnet  15 , the first positioning magnet  331  and the second positioning magnet  332  can all be reversed compared to the above-described embodiment. In such alternative embodiment, the south magnetic poles of the adjusting magnet  15 , the first positioning magnet  331  and the second positioning magnet  332  are all oriented towards the image sensing end  12 , and the north magnetic poles of the adjusting magnet  15 , the first positioning magnet  331  and the second positioning magnet  332  are all oriented towards the aperture end  11 . 
     It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.