Abstract:
A tilt preventing structure for electromagnetic driving device comprises: a casing, a driven object (such as lens module), a guiding mechanism and an electromagnetic driving module. The driven object is received within the casing and is movable along an axial direction. The guiding mechanism is furnished inside the casing and is sleeved with the driven object, so as to guide the driven object to move along the axial direction. The electromagnetic driving module comprises a plurality of magnetic elements mounted on the driven object. The guiding mechanism is made of magnetically susceptible material and is nearby one of the magnetic elements. By means of the magnetic pulling force generated by the nearby magnetic elements, the guiding mechanism is pulled by the force and leans against the driven object, so as to minimize the tilts when the driven object is moving relative to the guiding mechanism.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a tilt preventing structure for an electromagnetic driving device. The tilt preventing structure comprises a guiding mechanism comprising a magnetically susceptible material and a magnet disposed on a lens assembly. The magnet exerts a magnetic attraction force upon the guiding mechanism to reduce a dynamic tilt of the lens assembly during its movement along the guiding mechanism and thereby enable the lens assembly to move steadily. 
     2. Description of the Prior Art 
     Referring to  FIG. 1 , there is shown an exploded perspective view of a conventional zooming or focusing lens. A mechanical-transmission focusing mechanism  9  for use with a conventional focusing lens employs a high-cost precise driving element  91  (such as a stepper motor, an ultrasonic motor, or a piezoelectric actuator) to function as a power source for driving a support  93  having a lens assembly  92  and employs plenty of transmission elements, thereby resulting in a complicated mechanical structure, an intricate and difficult assembly process, an excessive volume, high costs, excessive power consumption, and a lack of price competitiveness. 
     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. 
     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 
     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. 
     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. 
     Furthermore, all conventional lens driving devices are equipped with a guiding mechanism for guiding a lens to perform linear reciprocating displacement in a predetermined direction. To prevent the lens from getting stuck during its movement or proceeding with jerks and jolts, every conventional guiding mechanism always has an appropriate allowance (i.e., clearance) between its movable part and non-movable part (such as an axle hole and an axle). However, the clearance accounts for a slight quiver or a dynamic tilt that occur to the lens while at rest or in motion. The clearance increases with the tolerance of the axle hole to the detriment of the imaging quality of the lens or the precision in the positioning of the lens in motion. Accordingly, there is still room for improvement in the prior art. 
     SUMMARY OF INVENTION 
     It is a primary objective of the present invention to provide a tilt preventing structure for an electromagnetic driving device. The tilt preventing structure comprises a guiding mechanism comprising a magnetically susceptible material and a magnet element disposed on a lens assembly. Magnetic attraction between the guiding mechanism and the magnetic element allows a driven object to abut against the guiding mechanism and further reduces a dynamic tilt of the driven object during its movement along the guiding mechanism. 
     In order to achieve aforementioned objective, the present invention discloses a tilt preventing structure for an electromagnetic driving device, in which the tilt preventing structure is defined with a central axis. The tilt preventing structure comprising: a casing having a receiving space therein, a driven object received in the receiving space and capable of moving within the casing and along the central axis, a guiding mechanism positioned in the receiving space of the casing and connected to the driven object for guiding the driven object to move along the central axis, and an electromagnetic driving module comprising a plurality of magnetic elements coupled to the driven object. Wherein, the guiding mechanism comprises a magnetically susceptible material and is positioned proximate to at least one of the magnetic elements and corresponds in position thereto, such that an adjacent one of the magnetic element exerts a magnetic attraction force upon the guiding mechanism to cause the driven object to abut against the guiding mechanism and thereby reduce a dynamic tilt occurring to the driven object while the driven object is moving along the guiding mechanism. 
     In a preferred embodiment, the electromagnetic driving module further comprises a plurality of coils, the coils being disposed on the casing and corresponding in position to the magnetic elements, respectively, and the magnetic elements being magnets. 
     In a preferred embodiment, the driven object is a lens assembly and comprises a lens support and a lens centrally disposed at the lens support and moving together with the lens support synchronously. 
     In a preferred embodiment, the tilt preventing structure further comprises a lid for positioning the lens support in the receiving space and confining the coils to the casing, wherein the guiding mechanism comprises a guiding rod. 
     In a preferred embodiment, the tilt preventing structure further comprises a frictional element disposed at the lens support and abutting against the guiding rod for producing an appropriate frictional force relative to the guiding rod, the frictional force being larger than a weight of the lens assembly. 
     In a preferred embodiment, the magnetic elements come in threes, attach to the lens support from outside, and correspond in position to three said coils disposed on the casing, respectively. 
     In a preferred embodiment, the electromagnetic driving module further comprises a lead frame and two conductive terminals, wherein the lead frame and two said conductive terminals are coupled to a top side and an outer side of the casing, respectively, electrically connected by a plurality of wires and the coils, respectively, to form a current loop, and clamped together to be fixed between the lid and the casing by means of the lid. 
     In a preferred embodiment, the tilt preventing structure further comprises a position sensing module. The position sensing module further comprises a position sensor and a permanent magnet. The position sensor is coupled to the casing, and is corresponding in position to the permanent magnet coupled to an external periphery of the lens assembly, and is electrically connected to the lead frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be specified with reference to its preferred embodiment illustrated in the drawings, in which: 
         FIG. 1  is an exploded perspective view of a conventional a focusing lens; 
         FIG. 2  is an exploded perspective view of a tilt preventing structure for an electromagnetic driving device of the present invention; 
         FIG. 3  is an assembled perspective view of a tilt preventing structure for an electromagnetic driving device of the present invention; 
         FIG. 4  is an assembled schematic view of a tilt preventing structure for an electromagnetic driving device, without a lid, according to the present invention; 
         FIG. 5A  is a top view of a tilt preventing structure for an electromagnetic driving device, without a lid and a casing, according to the present invention; and 
         FIG. 5B  is a partial enlarged schematic view of a tilt preventing structure for an electromagnetic driving device shown in  FIG. 5A  according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 2  and  FIG. 3 , there are shown an exploded perspective view and an assembled perspective view of a tilt preventing structure for an electromagnetic driving device of the present invention, respectively. As shown in  FIG. 2 , a tilt preventing structure for an electromagnetic driving device  1  is defined with a central axis  5 , and the tilt preventing structure for an electromagnetic driving device  1  comprises a casing  11 , a driven object (a lens assembly  12 ), an electromagnetic driving module  13 , a guiding mechanism  14 , a position sensing module  15 , and a lid  16 . The central axis  5  is defined with two axial directions, namely a front  51  and a rear  52 . The casing  11  is substantially a hollow casing structure that is penetrated and has a receiving space  110  therein. The casing  11  further comprises a top side  111 , a bottom side  112 , an outer side  113 , a plurality of fixing chambers  114 , and an engaging chamber  115 . In this embodiment, the driven object is the lens assembly  12 . The lens assembly  12  further comprises a lens support  121 . A plurality of coupling chambers  1211  is disposed at the external periphery of the lens support  121 . However, in other embodiments not shown in the drawings, the lens assembly  12  can also be another object comprising a lens and capable of being driven to perform forward and backward linear displacement. The electromagnetic driving module  13  further comprises a plurality of magnetic elements  131 , a plurality of coils  132 , a lead frame  133 , and two conductive terminals  134 . The position sensing module  15  further comprises a position sensor  151  and a permanent magnet  152 . 
     The lid  16  is a hollow lid with a through-hole  161  therein. The lid  16  is coupled to the casing  11  so as to cover the casing  11 . The lid  16  and the casing  11  can be coupled together to thereby allow the lens assembly  12  to be positioned in the receiving space  110 . The fixing chambers  114  are disposed at predetermined positions on the periphery of the casing  11 , such that the fixing chambers  114  are engaged with the coils  132 , respectively. The lid  16  further confines the coils  132  to the casing  11 ; meanwhile, the lens assembly  12  in the receiving space  110  can still capture an external image through the through-hole  161 . 
     In a preferred embodiment of the present invention, the magnetic elements  131  come in threes, whereas the coils  132  also come in threes and correspond in position to the magnetic elements  131  respectively. Likewise, it is feasible that the magnetic elements  131  and the coils  132  corresponding thereto come in twos, fours, or any larger numbers. The fixing chambers  114  equal the coils  132  in quantity and are disposed on the outer side  113  of the casing  11 . The coils  132  are received in the fixing chambers  114 , respectively, communicate with the receiving space  110  of the casing  11 , and correspond in position to the magnetic elements  131  in the coupling chambers  1211  at the periphery of the lens support  121 , respectively. In this embodiment, the magnetic elements  131  are permanent magnets. At least one of the magnetic elements  131  is positioned proximate to the guiding mechanism  14  and corresponds in position thereto. The guiding mechanism  14  comprises a magnetically susceptible material. Hence, the adjacent one of the magnetic elements  131  exerts a magnetic attraction force F 2  upon the guiding mechanism  14  to attract the guiding mechanism  14  (and, in particular, attracts a guiding rod  141  comprising a magnetically susceptible material). 
     The lens assembly  12  is positioned in the receiving space  110 . With the guiding mechanism  14 , the middle axis of the lens assembly  12  is aligned with the central axis  5 , and the lens assembly  12  performs linear displacement to a certain extent along the central axis  5  but is prevented from rotating. The lens assembly  12  further comprises a lens (not shown) which is coupled to the center of the lens support  121  and moves together with the lens support  121  synchronously. The guiding mechanism  14  is extendible and coupled to within the casing  11 . The guiding mechanism  14  enables the lens assembly  12  to perform axial linear motion within the receiving space  110 . The guiding mechanism  14  comprises one of a guiding rod or a guiding track. In an embodiment of the present invention, the guiding mechanism  14  comes in the form of two slender guiding rods  141 ,  141 ′ operating in conjunction with a guiding hole  1212  and a guiding groove  1212 ′, respectively, which are penetratingly disposed at the lens support  121 . The guiding mechanism  14  comprising a magnetically susceptible material is manufactured by introducing a magnetically susceptible material, such as yoke powder, into the two guiding rods  141 ,  141 ′ whose manufacturing process is underway, so as to manufacture the two guiding rods  141 ,  141 ′ capable of magnetic susceptibility. 
     In this preferred embodiment as shown in  FIG. 2 , the guiding mechanism  14  comprises the two guiding rods  141 ,  141 ′ (and thus hereinafter referring to the guiding mechanism as guiding rods) coupled to the guiding hole  1212  and the guiding groove  1212 ′ on two diagonal corners of the lens support  121 . A frictional element  4  is disposed at both or one of the guiding hole  1212  and the guiding groove  1212 ′ of the lens support  121  in a manner that the frictional element  4  has a curved surface that abuts against the guiding rod  141  and/or the guiding rod  141 ′ to thereby produce an appropriate frictional force. The strength of the frictional force depends on the material of which the frictional element  4  is made or the size of the frictional element  4 . The upper ends and lower ends of the two guiding rods  141 ,  141 ′ are fixed to coupling ends  1111 ,  1121  of the top side  111  and the bottom side  112  of the casing  11 , respectively. An axial track corresponding in position to the central axis  5  is formed in the receiving space  110 . The axial track enables the lens support  121  to be supported by the two guiding rods  141 ,  141 ′ through the guiding hole  1212  and the guiding groove  1212 ′. The lens support  121  is electromagnetically driven by the electromagnetic driving module  13  to move forward and backward linearly and steadily within the receiving space  110  and in the axial direction of the central axis  5  but is prevented from rotating. 
     Referring to  FIG. 4 , there is shown an assembled schematic view of a tilt preventing structure for an electromagnetic driving device, without a lid, according to the present invention. The lead frame  133  and the two conductive terminals  134  are coupled to the top side  111  and the outer side  113  of the casing  11 , respectively. The lead frame  133  and the two conductive terminals  134  are electrically connected by a plurality of wires  6  and the coils  132 , respectively, to form a current loop. The lead frame  133  and the two conductive terminals  134  are clamped together and thus fixed between the lid  16  and the casing  11  by means of the lid  16 . 
     With the two conductive terminals  134  being connected to the coils  132  and predetermined electrical currents being applied in different directions to produce different magnetic field directions, the magnetic elements  131  are driven to move under the magnetic field. In response to changes in the electrical current and the magnetic field, the lens support  121  can perform axial displacement within the receiving space  110  and in two different directions, that is, moving toward the front  51  or the rear  52  of the central axis  5 . As a result, the lens coupled to the lens support  121  is capable of focusing or zooming. 
     In an embodiment of the present invention, the coils  132  are electrically connected to the two conductive terminals  134  positioned on the outer side  113  of the casing  11 , respectively, by means of the wires  6 . The two conductive terminals  134  produce an electromagnetic force F 1  for driving the lens assembly  12  to move upward as soon as an electrical current is applied to the two conductive terminals  134 . As a result, a magnetic force F 2  is produced between the guiding rod  141  and the magnetic elements  131 . The lens assembly  12  itself produces a gravitational force F 3  (i.e., the weight of the lens assembly). 
     Referring to  FIG. 5A  and  FIG. 5B , there are shown a top view of a tilt preventing structure for an electromagnetic driving device, without a lid and a casing, according to the present invention, and a partial enlarged schematic view of a tilt preventing structure for an electromagnetic driving device shown in  FIG. 5A  according to the present invention. In an embodiment of the present invention, the magnetic elements  131  come in threes. One of the magnetic elements  131  is disposed at the corner in the vicinity of the lens support  121  and positioned proximate to the magnetically susceptible material-containing guiding rod  141  so as to correspond in position thereto. Hence, the adjacent one of the magnetic elements  131  exerts a magnetic attraction force F 2  upon the guiding rod  141 . The magnetic attraction force F 2  exerted by the adjacent one of the magnetic elements  131  upon the guiding rod  141  causes the lens support  121  to move in the direction perpendicular to the central axis  5 . A clearance allowance necessarily exists between the guiding rod  141  and the guiding hole  1212  and the guiding groove  1212 ′ of the lens support  121  in order to preclude the difficulty in the movement of the lens support  121  relative to the guiding rod  141  because of excessive friction between the lens support  121  and the guiding rod  141 . The clearance allowance is a major factor in a slight quiver or a dynamic tilt that occur to the lens support  121  while the lens support  121  is moving relative to the guiding rod  141 . Hence, the magnetic attraction force F 2  draws the guiding hole  1212  and the guiding groove  1212 ′ closer to the guiding rod  141  and thereby reduces a slight quiver or a dynamic tilt that occur to the lens support  121  while the lens support  121  is in motion. 
     In this embodiment, to allow the magnetic element  131  positioned proximate to the guiding rod  141  and corresponding in position thereto to produce the magnetic attraction force F 2  sufficiently in order to attract the guiding rod  141  and thereby eliminate the clearance allowance and prevent a slight quiver or a dynamic tilt, it is necessary for the shortest distance between the guiding rod  141  and the adjacent magnetic element  131  to be preferably less than 5 mm. 
     Referring to  FIG. 5A  and  FIG. 5B , in an embodiment of the present invention, the guiding hole  1212  disposed at one of the corners of the lens support  121  and adapted to accommodate the guiding rod  141  comes in the form of a through-hole with a polygonal inner rim, and the open-style guiding groove  1212 ′ opposite to the guiding hole  1212  is disposed at one of the other corners of the lens support  121  for accommodating the guiding rod  141 ′ of the guiding mechanism. The guiding hole  1212  comes in the form of a through-hole with an octagonal inner rim. Normally, in the absence of any other external attractive force, the guiding hole  1212  is evenly spaced apart from the circumference of the cylindrical guiding rod  141  by a clearance allowance conducive to smooth movement of the lens support  121  relative to the two guiding rods  141 ,  141 ′ through the guiding hole  1212  and the guiding groove  1212 ′. In an embodiment of the present invention, the clearance allowance is extremely small, such that the imaging effect of the focusing or zooming of the lens assembly  12  remains unabated in the absence of a dynamic tilt. 
     Due to the aforesaid clearance allowance, the lens support  121  in motion relative to the two guiding rods  141 ,  141 ′ often quivers slightly—a factor in a dynamic tilt. Hence, the dynamic tilt affects the angle between the lens assembly  12  and an image sensing module corresponding in position to the lens assembly  12 . A large tilt angle between the lens assembly  12  and the image sensing module is likely to cause poor optical (imaging) performance. In case of a high pixel requirement, the deviation of angle between the lens assembly  12  and the image sensing module must be less than 10′ (1°=60′) in order to meet the high pixel requirement. However, according to the prior art, a dynamic tilt angle usually approximates to 10′ (i.e., 0.167°). In view of this, with the tilt preventing structure for an electromagnetic driving device of the present invention, the dynamic tilt angle between the lens assembly  12  in motion and the image sensing module is reduced to less than 6′ (i.e., 0.1°) so as to minimize the adverse effect of a dynamic tilt on imaging and further enable the image sensing module to capture better images. 
     As described earlier, one of the three magnetic elements  131  fixedly disposed in the coupling chambers  1211  at the external periphery of the lens support  121 , respectively, is positioned proximate to the magnetically susceptible guiding rod  141  and correspond in position thereto, and the magnetic element  131  also corresponds in position to one of the coils  132 . For the aforesaid two reasons, in the absence of any power applied to the coils  132 , the guiding hole  1212  of the lens support  121  is driven to move in a first direction  8  perpendicular to the central axis  5  under the magnetic attraction force F 2  and is eventually attached to a semi-side  1411  of the guiding rod  141 , such that the lens support  121  performs a slight displacement to thereby abut against the guiding rod  141 . In an embodiment of the present invention, after the guiding hole  1212  with an octagonal inner rim has been subjected to the magnetic attraction force F 2 , two inner sides  12121 ,  12122  (that is, two inner sides in the vicinity of the magnetic element  131 ) of the guiding hole  1212  abut against the semi-side  1411  of the guiding rod  141 , such that the two inner sides  12121 ,  12122  come into contact with the semi-side  1411  of the guiding rod  141  at linear contact points a, b on the semi-side  1411 , respectively, for enhancing the stability of the movement of the lens support  121 . By contrast, after the guiding hole  1212  with an octagonal inner rim has been subjected to the magnetic attraction force F 2 , two other inner sides  12123 ,  12124  (opposite to the two inner sides  12121 ,  12122 ) of the guiding hole  1212  are not in contact with another semi-side  1412  of the guiding rod  141  but have a clearance allowance larger than the average clearance allowance. Furthermore, the open-style guiding groove  1212 ′ and the guiding rod  141 ′ together prevent the lens support  121  from deviating in a direction perpendicular to the first direction  8 . With the magnetic elements  131  being driven by the plurality of coils  132 , respectively, the lens support  121  is capable of performing axial motion along the central axis  5 . As a result, after the guiding rods  141 ,  141 ′ of the guiding mechanism have provided support for the lens support  121 , the dynamic tilt that might otherwise occur to the lens support  121  in motion is greatly reduced. 
     To keep the lens assembly  12  stationary under the frictional force between the frictional element  4  and the guiding rod  141  of the guiding mechanism in the absence of any power applied to the coils  132 , it is necessary for the frictional force in the axial direction to be larger than the weight of the lens assembly  12 . To enable the powered coils  132  to drive the lens assembly  12  to move, it is necessary for the electromagnetic force F 1  of the lens assembly  12  to be larger than the sum of the frictional force and the gravitational force F 3  of the lens assembly  13 . The electromagnetic force F 1  is adjustable, depending on the magnetic strength of the magnetic elements  131  and the number of turns of the coils  132 . 
     Hence, the tilt preventing structure for an electromagnetic driving device  1  of the present invention not only enables the coils  132  to generate the electromagnetic force F 1  in different directions for moving the magnetic elements  131  corresponding in position thereto when the two conductive terminals  134  apply a predetermined electrical current in different directions to the coils  132 , but also enables the lens support  121  to perform axial displacement in a predetermined direction within the receiving space  110 . The magnetic attraction force F 2  between the guiding rod  141  and the magnetic elements  131  causes the guiding hole  1212  of the lens assembly  12  to abut against the guiding rod  141  and there by enhances the stability of movement of the lens assembly  12  within the receiving space  110  while the guiding hole  1212  of the lens assembly  12  abuts against the guiding rod  141 . As a result, the dynamic tilt angle between the lens assembly  12  and the image sensing module corresponding in position thereto is less than 6′, thereby restricting the tilt arising from motion and enhancing optical imaging. In addition, with the electromagnetic force F 1  being larger than the sum of the frictional force between the guiding rod  141  and the frictional element  4  and the gravitational force F 3  of the lens assembly  12 , the lens assembly  12  can perform displacement and zooming along the central axis  5  and toward the front  51  or the rear  52  under the electromagnetic force F 1  and the auxiliary guidance provided by the guiding mechanism  14 . 
     The electromagnetic force F 1  stops providing a magnetic field as soon as electrical current is no longer supplied to the coils  132 . Since the frictional force between the guiding rod  141  and the frictional element  4  is larger than the gravitational force F 3  of the lens assembly  12 , electrical supply to the coils  132  can be suspended immediately after focusing or zooming is done. The lens assembly  12  is fixed in place by the frictional force, and thus the lens assembly  12  is stationary, thereby manifesting a power saving effect by power suspension and positioning. 
     In another embodiment, it is also feasible that the tilt preventing structure for an electromagnetic driving device  1  of the present invention dispenses with the frictional element  4 . Although a lack of the frictional element  4  prevents the tilt preventing structure for an electromagnetic driving device  1  of the present invention from providing the functionality of power suspension and positioning, it saves the power which will otherwise be required to power the coils  132  and drive the lens support  121  to move. 
     The position sensing module  15  senses and calculates the position of the lens assembly  12  relative to the casing  11 . The position sensor  151  is coupled to the outer side  113  of the casing  11 , positioned in the engaging chamber  115 , adapted to correspond in position to the permanent magnet  152  coupled to a predetermined position at the external periphery of the lens assembly  12 , and adapted to sense the displacement of the lens assembly  12  within the receiving space  110  of the casing  11 . The position sensor  151  can be electrically connected to the lead frame  133  for effectuating connection with an external control circuit.