Abstract:
An electromagnetic driving device which is defined with an axis and comprises: a casing, a driven unit and an electromagnetic driving module. The casing has an inner compartment. The driven unit is received in the compartment and is guided by a guiding mechanism such that the driven unit is movable alone the axis inside the casing. The electromagnetic driving module comprises: a plurality of permanent magnets inside the casing, at least one magnetic member fixed to an outer surface of the driven unit, and a coil located between the magnetic member and permanent magnets. When no electric power is provided to the coil, the magnetic forcing between the permanent magnets and magnetic member will result in a friction force to the guiding mechanism, so as to keep the driven unit at its current position inside the compartment.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to an electromagnetic driving device, and more particularly to the electromagnetic driving device that introduces a current magnetic field as a power source to drive an optical focus or zoom lens set, and whose lens set can be positioned by a friction induced by a field of magnets during a power-off state. 
         [0003]    2. Description of the Prior Art 
         [0004]    Referring to  FIG. 1 , an exploded view of a conventional focus lens set is shown. The focus lens set utilizes a mechanical focusing unit  9  including a hi-cost precision driving element  91 . (for example, the step motor, the supersonic motor, the piezoelectric actuator, . . . , etc.) as the power source to drive the carrier  93  of the lens set  92 , and many other transmission elements. Actually, such an arrangement in the conventional focus lens set, structural complication, assembly difficulty, cumbersome appearance and high cost are inevitable. Also, considerable energy consumption is another disadvantage for this type of lens sets. All of the foregoing features make the price of the aforesaid lens set irreducible. 
         [0005]    In the early stage of the photography art, large human labor has been involved in metering, focusing and winding. Inevitably, it can be foreseen that how sorry would be if meeting a human mistake in taking photos in an important scene. Obviously, a quality photographer is the only answer to ensure photographing during such an important scene. Yet, it is well known that no 100% photographer is available anywhere and anytime. In the 50&#39;s and 60&#39;s, a great step has been achieved in the mechanical automation, from which people believe that automation would be the key to the future world. At that time, in the photography art, various developments such as the auto-metering device, the electrical winding apparatus and so on, have convinced people that automation is the future to the photography art. Among these developments, the development in the automatic focusing system who ensures the possibility of rapid photo-taking plays an important part. 
         [0006]    Along with the technology development, conventional photographic apparatus has been progressed both in photographing quality and in the miniaturized appearance. However, the mechanical focusing lens set driven by the step motor hinders a further reduction in occupation of the apparatus 
         [0007]    On the other hand, electromagnetic technology has also been introduced to improve the VCM electronic feedback system in monitoring the bias of the coil, which can replace the conventional step motor and provide a size down in the driving mechanism. Another development of the photography art is to add the photographic function to the other apparatus; for example, the integration of the photographic unit to the mobile phone, the PDA, the notebook computer and so on. All these changes make the current electronic merchandises equipped with a photographic unit that enhances a powerful video application to these aforesaid apparatuses. 
         [0008]    Nevertheless, the aforesaid mobile phone, PDA, notebook computer, and the like portable electronic apparatus all have limitations in the battery capacity. Therefore, in aiming at the future of the photography art, the devotion upon how to design a low-energy-consumed driving device for focus or zoom lens set and how to anchor the lens set while the power is off is definitely welcome to the skilled person in the art. 
       SUMMARY OF INVENTION 
       [0009]    Accordingly, it is a primary object of the present invention to provide an electromagnetic driving device that utilizes a magnetic force to induce a friction force for further hold still a lens module while the power is off, such that a purpose of saving the energy can be achieved. 
         [0010]    The electromagnetic driving device according to the present invention defines a center axis and comprises a casing, a driven unit and an electromagnetic driving module. The casing is a hollow housing having an inner compartment. The driven unit accommodated in the inner compartment can be a lens module and moved along the center axis inside the casing by a guiding mechanism. The electromagnetic driving module is located inside the inner compartment at a position respective to the lens module. 
         [0011]    The electromagnetic driving module further includes a plurality of permanent magnets, at least a magnetic member and a coil located between the magnetic member and the permanent magnets. The magnetic member is mounted at the lens module. The permanent magnets are positioned respective to the magnetic member. In the present invention, while a current is terminated to the coil, a friction force at the friction part of the guiding mechanism which is induced from forcing between the permanent magnets and the magnetic member can be generated to hold still the lens module inside the inner compartment. 
         [0012]    All these objects are achieved by the electromagnetic driving device described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will now be specified with reference to its preferred embodiment illustrated in the drawings, in which: 
           [0014]      FIG. 1  is an exploded view of a conventional focus lens set; 
           [0015]      FIG. 2  is an exploded view of a preferred electromagnetic driving device in accordance with the present invention; 
           [0016]      FIG. 3  a perspective view of the assembly of  FIG. 2 ; 
           [0017]      FIG. 4  is a cross-sectional view along line A-A of  FIG. 3 ; and 
           [0018]      FIG. 5  is a perspective view of  FIG. 3  by removing the casing and the coil. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    The invention disclosed herein is directed to an electromagnetic driving device. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instance, well-known components are not described in detail in order not to unnecessarily obscure the present invention. 
         [0020]    Referring now to  FIG. 2 ,  FIG. 3  and  FIG. 4 , an exploded view, a perspective view and a specific cross-sectional view along line A-A of  FIG. 3  of a preferred electromagnetic driving device  1  in accordance with the present invention are shown, respectively. 
         [0021]    As shown, the electromagnetic driving device  1 , defined along a center axis  5 , includes a casing  11 , a driven unit (preferably, a lens module  13 ), an electromagnetic driving module  15 , a position-sensing module  17  and an image-sensing module  19 . The center axis  5  defines a front direction  51  and a rear direction  52 . The casing  11  further includes an upper cover  111 , a lower cover  112  and at least a guiding mechanism  113  and a skin shield  114 . In this embodiment, the driven unit can be a lens module  13  further including a lens set  131  and a lens carrier  132 . In the other embodiments not shown herein, the driven unit can be an object that is linearly moved within the casing  11 . The electromagnetic driving module  15  further includes a plurality of permanent magnets  151 , at least a magnetic member  152 , a coil  153  and two coil terminals  154 . The position-sensing module  17  further includes a position-sensing terminal  171  and a position sensor  172 . 
         [0022]    The upper cover  111  is a hollow top structure. The skin shield  114  to provide housing between the upper cover  111  and the lower cover  112  is a hollow shell structure having a central penetration hole  1141 . While the upper cover  111  engages with the lower cover  112 , an inner compartment  110  is formed to accommodate thereinside the lens module  13 . As shown, a plurality of receiving slots  1111  for nesting respective permanent magnets  151  is included peripherally to the upper cover  111 . The permanent magnets  151  are further positioned by the skin shield  114  between the upper cover  111  and the lower cover  112 . The lens module  13  inside the inner compartment  110  is to capture the external image through the penetration hole  1141 . 
         [0023]    In the preferred embodiment as shown herein, four permanent magnets  151  and two magnetic members  152  are included. Also, four receiving slots  1111  for receiving respective permanent magnets  151  are located to four lateral sides of the upper cover  111  and are further restrained by the skin shield  114 . The magnetic members  152  are mounted to respective sides of the lens carrier  132 , and each of which is to pair respective permanent magnet  151 . In this embodiment, the magnetic member  152  is made of yoke iron in a thin plate form. As shown, the two magnetic members  152  are located respectively to two neighboring lateral sides of the lens carrier  132 . 
         [0024]    The lens module  13  is located inside the inner compartment  110  in a manner of a center line of the lens module  13  being hold on and moved linearly along the center axis  5  by the guiding mechanism  13 . No rotation is allowed to the lens module  13 . The lens set  131  is mounted in a center of the lens carrier  132 , and is synchronically moved with the lens carrier  132 . Between the upper cover  111  and the lower cover  112 , the guiding mechanism  113  is extended therebetween and engaged therewith to provide the lens module  13  linear motion guiding along the center axis  5  inside the inner compartment  110 . The image-sensing module  19  is engaged behind the lower cover  112  and looks at the lens module  13  in the inner compartment  110  through a center penetration empty  1121  at the lower cover  112 . Both the image-sensing module  19  and the lens module are located at the center axis  5 . The image-sensing module  19  captures images of foreign objects through the penetration hole  1141  of the skin shield  114 . In the present invention, the guiding mechanism  113  can be preferably embodied as a pair of a slim long rod and a corresponding penetration hole or a pair of an extended rack and a corresponding guiding slot. 
         [0025]    As shown in  FIG. 2 , the guiding mechanism  113  includes two guiding rods (labeled as the same  113  in the following description) engaging the corresponding guiding holes  1321  (or slots) located to opposing sides of the lens module  13 . Further, corresponding friction parts  1322  (as shown in  FIG. 5 ) are included to pair the guiding holes or slots  1321 . The friction part  1322  is to provide relevant friction to the contacting guiding rod  113 . The magnitude of the friction is dependent on the material and/or the size of the friction part  1322 . In addition, one end (the upper end) of the guiding rod  113  is fastened to a position terminal  1112  of the upper cover  111 , while another end (the lower end) of the guiding rod  113  is fastened to an engagement terminal  1122  of the lower cover  112 . Upon such an arrangement, two guiding rods  113  can be formed as two axial racks parallel to the center axis  5  inside the inner compartment  110  to mount and slide therealong the lens module  13  via the two guiding holes or slots  1321 . The lens module  13  can be driven by the electromagnetic driving module  15  to slide linearly back and forth along the center axis  5 , and no rotation is allowed to the lens module  15 . 
         [0026]    The coil  153  surrounding the lens module  13  inside the inner compartment  122  is located between the permanent magnets  151  and the magnetic members  152 . By providing predetermined currents with specific phases to cross two terminals  154  of the coil  15  so as to induce corresponding magnetic fields with different directions, the lens carrier  132  in the inner compartment  110  can be driven either forward  51  or backward  52  along the center axis  5 . Thereby, focusing or zooming operation between the lens set  131  and the image-sensing module  19  engaged to rear of the lower cover  112  can be achieved. 
         [0027]    In this embodiment of the present invention, the coil  153  is electrically connected with the two coil terminals  154  located at the outsides of the lower cover  112 . It is defined that the electromagnetic force F 1  is the force to drive the lens module  13  upward after a specific current is applied through the two coil terminals  154 , the magnetic force F 2  is the resultant force induced from the magnetic members  152  and the permanent magnets  151 , and the force F 3  is the weight of the lens module  13 . As shown in  FIG. 5 , for two magnetic members  152  are included and located at two sides of the lens carrier  132  neighboring to the same corner thereof, the resultant magnetic force F 2  from the permanent magnets  151  and the two magnetic members  152  would be the force shown in  FIG. 5  that pulls the lens carrier  132  outwards along a diagonal direction. Accordingly, the force F 2  would induce a relevant friction force F 4  between the guiding rods  113  of the guiding mechanism and the corresponding friction parts  1322 . The magnitude of F 4  is determined by the material and/or the size of the friction part  1322  and also by changing the F 2 . 
         [0028]    When the power on the coil  153  is removed, in order to hold still the position of the lens module  13 , the friction force F 4  between the guiding rods  113  and the corresponding friction parts  1322  must be greater than the weight F 3  of the lens module  13 ; i.e., F 4 &gt;F 3 . On the other hand, in order to move the lens module  13  after the coil  153  is charged, the electromagnetic force F 1  to drive the lens module  13  must be greater than the sum of the friction force F 4  and the weight of the lens module  13 ; i.e., F 1 &gt;F 4 +F 3 . It is noted that the F 1  can be changed by altering the magnetic of the permanent magnets  151  or the coil number of the coil  153 , and the F 2  can be altered by changing the magnetic of the permanent magnets  151  and/or the action area of the magnetic member  152 . Such that states of F 4 &gt;F 3  and F 1 &gt;F 4 +F 3  can be obtained. 
         [0029]    Namely, the electromagnetic driving device  1  of the present invention is to control the electromagnetic force F 1  by altering the current input to the coil terminals  154  of the coil  153 . The lens carrier  132  in the inner compartment  110  can be also moved axially along a specific direction due to the change in the current magnetic field of the coil  153 . For the F 1  can be greater than the sum of F 4  and F 3  (F 1 &gt;F 4 +F 3 ), the lens module  13  can be driven by F 1  and guided by the guiding mechanism  113  to perform forward  51  and backward  52  motion along the center axis  5  so as to process focusing or zooming operation. 
         [0030]    However, in the case that the current input to the coil  153  is removed, the electromagnetic force F 1  would be dead. At this time of terminating the action of the coil  153 , the friction force F 4  between the guiding rods  13  and the friction parts  1322  would be greater than the weight F 3  of the lens module  13  (F 4 &gt;F 3 ), such that the lens module  13  can be hold still by the F 4  and thus energy for further moving the lens module  13  can be avoided. 
         [0031]    In the present invention, the position-sensing module  17  is to detect and calculate the relative position between the lens module  13  and the casing  11 . The position-sensing terminal  171  for detecting the displacement of the lens module  13  in the inner compartment  110  of the casing  11  is mounted on the upper cover  111  at a position respective to the position sensor  172  located at the exterior of the lens module  13 . The position-sensing terminal  171  further has a plurality of metal leads  1711  for connection with the foreign circuitry. 
         [0032]    While the present invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be without departing from the spirit and scope of the present invention.