Abstract:
A two-step auto-focusing camera includes a lens unit ( 12 ); a permanent magnet ( 124 ) being fixedly mounted around the lens unit to move with the lens unit; first and second coil seats ( 14, 15 ) with first and second coils ( 145, 155 ) wound thereon being mounted around the lens unit at two opposite sides of the magnet. When electric currents are supplied to the first and second coils, one of the coil seats generates an attraction force to the lens unit, and the other coil seat generates a repulsion force to the lens unit. A flange ( 143, 153 ) extends outwardly from an outer periphery of each coil seat at an end near the magnet to limit the magnet to move between the flanges of the first and second coil seats during movement of the lens unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a drive source of a camera, and more particularly to a drive source of a two-step auto-focusing camera. 
         [0003]    2. Description of Related Art 
         [0004]    Conventionally, an auto-focus structure is used for controlling the telescopic movement of a lens of the camera. Auto-focus structures are used to automatically produce high-quality images with minimum user effort, and as such are important part of a modern camera. 
         [0005]    The auto focus structure of the camera focuses on an object by analysis of the image on an image sensor. The image sensor is either a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor, and is controlled by a central processing unit (CPU) installed inside the digital camera. In the beginning, the lens moves back and forth around its original position (static position). As the lens moves, the CPU compares the image from the lens with the image in the image sensor. Finally, as the lens moves to the position where the image is the clearest the lens stops at that position. In this case, the lens has to be continuously driven back and forth by an annular cam. The annular cam is provided with a lens driving structure and driven to rotate by a stepping motor. The moment the CPU detects the clearest image as the lens moves back and forth, a stop signal is sent to the lens. Therefore, the lens stops in the best focal position (static position). When the lens is moved back to the original position, the annular cam starts to rotate again. Once the lens moves back to its original position, the photo interrupter installed in the lens cylinder uses the shutter at the end of the lens cylinder, to detect the original position of the lens. The shutter will interrupt the light of the penetration-type photo interrupter. The lens stops at the moment when the photo interrupter detects the original position. 
         [0006]    Consequently, the lens in a digital camera auto focus system has to be driven continuously to obtain the clearest positions. However, narrow gaps usually exist between components of the camera when the components are assembled to form the camera, which, in most of cases, results in imprecise and unstable movement of the lens, which may finally result in losing the clearest position to obtain the best image. 
       SUMMARY OF THE INVENTION 
       [0007]    According to a preferred embodiment of the present invention, a two-step auto-focusing camera includes a lens unit; a permanent magnet being fixedly mounted around the lens unit to move with the lens unit; a first coil seat with a first coil wound thereon mounted around the lens unit and being arranged on a side of the permanent magnet; and a second coil seat with a second coil wound thereon mounted around the lens unit and being arranged on an opposite side of the permanent magnet. When electric currents are supplied to the first and second coils, the first and second coil seats create magnetic fields interacting with a magnetic field of the magnet to generate forces for moving the lens unit in the lens mount, the force generated by one of the first and second coil sets and the permanent magnet being attractive, the force generated by the other of the first and second coil sets and the magnet being repulsive. A flange extends outwardly from an outer periphery of each coil seat at an end near the permanent magnet, and the permanent magnet is limited to move between the flanges of the first and second coil seats during movement of the lens unit. 
         [0008]    Other advantages and novel features of the present invention will be drawn from the following detailed description of a preferred embodiment of the present invention with attached drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Many aspects of the present two-step auto-focusing camera can be better understood with reference to the following 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 two-step auto-focusing camera. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views: 
           [0010]      FIG. 1  is an isometric, exploded view of a two-step auto-focusing camera in accordance with a preferred embodiment of the present invention; 
           [0011]      FIG. 2  is an assembled view of  FIG. 1 ; 
           [0012]      FIG. 3  is similar to  FIG. 2 , but showing the two-step auto-focusing camera without a sidewall; 
           [0013]      FIG. 4  shows a cross-sectional view of the two-step auto-focusing camera of  FIG. 2  taken along line IV-IV thereof with a lens unit at its front focal point; and 
           [0014]      FIG. 5  is similar to  FIG. 4 , but showing the lens unit of the two-step auto-focusing camera at its rear focal point. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Referring to  FIGS. 1 through 3 , a two-step auto-focusing camera  10  according to a preferred embodiment of the present invention includes a lens mount  11 , a lens unit  12  received in the lens mount  11 , and a motor (not labeled) for driving the lens unit  12  into telescopic movement. 
         [0016]    The lens mount  11  includes a base  17 , and a sidewall (not labeled) mounted on the base  17 . The base  17  is square-shaped and defines an opening (not labeled) therein. A pair of notches  171  are respectively defined in two neighboring corners of the base  17 . A pair of connecting pins  159  are formed in the notches  171  of the base  17  and extend outwardly therefrom. The sidewall is approximately a hollow regular prism with top and bottom ends thereof being opened, and is constructed by fixedly connecting two U-shaped parts  111 ,  112  together through soldering. A pair of ears  113  are formed at two neighboring corners of the sidewall corresponding to the corners of the base  17  forming the connecting pins  159  thereon and extend downwardly from a bottom end of the sidewall. Each ear  113  has a height approximately the same as that of the base  17 , covering the connecting pins  159  of the base  17  therein when the sidewall is mounted on the base  17 . 
         [0017]    The lens unit  12  is approximately column-shaped, including a barrel  121  and a lens  122  being fixedly mounted in the barrel  121 . The barrel  121  forms an inner thread  126  on an inner surface thereof, and the lens  122  forms an outer thread  136  on an outer surface thereof, which threadedly engages with the inner thread  126  of the barrel  121 . A pair of blocks  127  (only one shown) extend radially and outwardly from an outer surface of the barrel  121  of the lens unit  12  near a bottom end thereof. When the lens unit  12  is received in the lens mount  11 , an interspace (not labeled) is defined therebetween receiving the motor. The motor includes a permanent magnet  124  mounted around the barrel  121  and attached to a middle of the outer surface of the barrel  121 , and upper and lower coil seats  14 ,  15  being arranged at upper and lower sides of the magnet  124 , respectively. 
         [0018]    The coil seats  14 ,  15  are made of magnetizable materials, such as iron. Each of the coil seats  14 ,  15  includes a cylinder  141 ,  151  having an inner diameter approximately the same as an outer diameter of the barrel  121  of the lens unit  12 . Top and bottom flanges  142 ,  153 ,  143 ,  152  are respectively extend from outer peripheries of the cylinders  141 ,  151  at top and bottom ends thereof. The top and bottom flanges  142 ,  153 ,  143 ,  152  are square shaped. Furthermore, the top and bottom flanges  153 ,  143  define cutouts  146 ,  156  in each of the four corners thereof. A pair of grooves  154  are defined in an inner surface of the cylinder  151  of the lower coil seat  15  corresponding to the blocks  127  of the lens unit  12 . A lower baffle  157  extends perpendicularly and upwardly from each cutout  156  of the top flange  153  of the lower coil seat  15 , and an upper baffle  147  extends perpendicularly and downwardly from each cutout  146  of the bottom flange  143  of the upper coil seat  14 . When the coil seats  14 ,  15  are assembled, each upper baffle  147  overlaps with and abuts against a corresponding lower baffle  157 . In this embodiment, the upper baffles  147  are located outside of the lower baffles  157 . The lower baffles  157  are located inside of the upper baffles  147  and are tangential to the barrel  121  of the lens unit  12 . Thus movement of the lens unit  12  is limited by the lower baffles  157 , and thus swing of the lens unit  12  is avoided. Alternatively, the lower baffles  157  can be located on the outside of the upper baffles  147 , and thus the upper baffles  147  abut the lens unit  12  to avoid swing of the lens unit  12 . 
         [0019]    Each coil seat  14 ,  15  forms two mounting pins  148 ,  158  thereon. The mounting pins  148 ,  158  of each coil seat  14 ,  15  extend outwardly from two neighboring baffles  147 ,  157  thereof. The cylinders  141 ,  151  of the upper and lower coil seats  14 ,  15  have upper and lower coils  145 ,  155  wound thereon, respectively, and two ends of each coil  145 ,  155  are respectively wound on the mounting pins  148 ,  158  of the corresponding coil seat  14 ,  15 . When assembled, the lens unit  12  with the magnet  124  is movably received in the lens mount  11 . The upper and lower coil seats  14 ,  15  with upper and lower coils  145 ,  155  wound thereon are received in the interspace formed between the lens unit  12  and the lens mount  11 , and are arranged on the upper and lower sides of the magnet  124 , respectively. The two corners of the coil seats  14 ,  15  having the mounting pins  148 ,  158  are located corresponding to the position of the corners of the base  17  of the lens mount  11  where the connecting pins  159  are formed. The blocks  127  of the lower coil seat  15  engage into the grooves  154  of the lower coil seat  15  to prohibit rotation of the lens unit  12 . The ends of the coils  145 ,  155  wound on the mounting pins  148 ,  158  of the coil seats  14 ,  15  are electrically connected with the connecting pins  159  of the base  17  of the lens mount  11  through soldering. When a power source is electrically connected to the connecting pins  159  of the base  17 , a current is applied to each coil  145 ,  155  through the connecting pins  159 . The coils  145 ,  155  are wound in different directions so that induced magnetic fields established by the two coils  145 ,  155  have polarities opposite to each other to drive the lens mount  11  into movement. 
         [0020]    As shown in  FIG. 4 , assuming the upper side of the magnet  124  is N (north pole), and the lower side of the magnet  124  is S (south pole). The lens unit  12  is at its front focal point A initially. The bottom flange  143  of the upper coil seat  14  abuts the upper side of the magnet  124 , whilst the top flange  153  of the lower coil seat  15  is separated by a space from the lower side of the magnet  124 . The induced magnetic field of the upper coil  145  has polarities opposite to that of the magnet  124 . The top end of the upper coil seat  14  is S, whilst the bottom end of the upper coil seat  14  is N. The induced magnetic field of the lower coil  155  has a similar polarity to that of the magnet  124 . The bottom end of the lower coil seat  15  is S, whilst the top end of the lower coil seat  15  is N. Thus an attractive force is generated between the lower coil seat  15  and the magnet  124 , whilst a repelling force is generated between the upper coil seat  14  and the magnet  124 . The lens unit  12  with the magnet  124  moves downwardly to its rear focal point B (as shown in  FIG. 5 ) from the bottom flange  143  of the upper coil seat  14  to the top flange  153  of the lower coil seat  15 . Since the coil seats  14 ,  15  are made of magnetic material which have residual magnetic force therein after the current is stopped from supplying to the coils  145 ,  155 , no current is needed for holding the lens unit  12  at the rear focal point B after the lens unit  12  is moved to the rear focal point B. 
         [0021]    Conversely, when the lens unit  12  is at the rear focal point B and moves to the front focal point A, the directions of the currents applied to the coils  145 ,  155  are switched. The induced magnetic field of the upper coil  145  has polarities similar to that of the magnet  124 . The top end of the upper coil seat  14  is N, whilst the bottom end of the upper coil seat  14  is S. The induced magnetic field of the lower coil  155  has a polarity substantially opposite to that of the magnet  124 . The bottom end of the lower coil seat  15  is N, whilst the top end of the lower coil seat  15  is S. Attractive force is generated between the upper coil seat  14  and the magnet  124 , and repelling force is generated between the lower coil seat  15  and the magnet  124 . The lens unit  12  with the magnet  124  moves upwardly to its front focal point A from the top flange  153  of the lower coil seat  15  to the bottom flange  143  of the upper coil seat  14  under the attractive force of the upper coil seat  14  and the repelling force of the lower coil seat  15 . Also the upper coil seat  14  provides an attractive force to the magnet  124  to keep the lens unit  12  at its front focal point A after the lens unit  12  reaches the front focal point A and the current is stopped from supplying to the coils  145 ,  155 . During movement of the lens unit  12 , the baffles  147 ,  157  are arranged around the lens unit  12  and are approximately tangential to the lens unit  12 . The flanges  143 ,  153  formed on the upper and lower coil seats  14 ,  15  are capable of limiting the telescopic movement of the lens unit  12 . The lens unit  12  is thus limited to switch between the two flanges  143 ,  153  to obtain the clearest positions which are the front and rear focal points. Thus, the lens unit  12  of the camera  10  can have precise and stable movement for obtaining the clearest position to catch the best image. 
         [0022]    It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, 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.