Abstract:
A lens retracting structure includes a housing, an image-forming lens set moveably supported on two parallel guide rods inside the housing, and a driving mechanism for moving the image-forming lens set along the parallel guide rods between a first position and a second position by means of the engagement of a threaded coupling member of the image-forming lens set with a threaded shaft which is rotatably driven by a motor of the driving mechanism.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to image-forming lenses and more particularly, to a lens retracting structure. 
   2. Description of the Related Art 
   Following fast development of high technology, a variety of high-tech products have been intensively used to satisfy different requirements. It is the market trend to develop products having light, thin, short and small characteristics. In order to meet the requirement for a camera having a small characteristic, the size of the image-forming lens set and the related driving mechanism must be made as smaller as possible. Further, in addition to cameras, an image-forming lens set can also be used in other small mobile electronic products such as cellular telephone. 
   The image-forming lens set of a camera or mobile electronic product may be made retractable so as to provide zoom-in and zoom-out functions. An image-forming lens set driving mechanism for this purpose is known using a bevel gear transmission mechanism to move the image-forming lens set between the retracted position and the extended position. This design of driving mechanism has a complicated structure and heavy size, resulting in high manufacturing cost and low movement stability. 
   SUMMARY OF THE INVENTION 
   The present invention has been accomplished under the circumstances in view. It is therefore one object of the present invention to provide a lens retracting structure, which is easy and inexpensive to manufacture. 
   It is another object of the present invention to provide a lens retracting structure, which is highly stable and reliable upon movement. 
   To achieve these objects of the present invention, the lens retracting structure comprises a housing having a guide member therein, an image-forming lens set supported on the guide member inside the housing and movable along the guide member between a first position and a second position reciprocally, and a driving mechanism mounted inside the housing. The image-forming lens set has a threaded coupling member. The driving mechanism has a motor and a transmission device having a shaft rotatable by the motor. The shaft has a threaded actuating portion engaged with the threaded coupling member for driving the image-forming lens set to move along the guide member between the first position and the second position upon rotation of the shaft driven by the motor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of a lens retracting structure according to a preferred embodiment of the present invention. 
       FIG. 2  is a perspective view of the lens retracting structure according to the preferred embodiment of the present invention, showing the lens retracting structure is partially assembled. 
       FIG. 3  is a schematic drawing according to the preferred embodiment of the present invention, showing the image-forming lens set is located at the retracted position. 
       FIG. 4  is a schematic drawing according to the preferred embodiment of the present invention, showing the image-forming lens set is located at the extended position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 2 , a lens retracting structure  100  in accordance with a preferred embodiment of the present invention is shown comprising a housing  10 , a driving mechanism  20 , an image-forming lens set  30 , and a sensor  40 . 
   The housing  10  is comprised of a first cover shell  11  and a second cover shell  12 . The first and second cover shells  11  and  12  are detachably fastened together, having therein positioning backings that define accommodating spaces for receiving the other component parts. 
   The driving mechanism  20  comprises a motor  21 , an electric connector  22 , a connecting member  23 , a transmission device  24 , and a buffering member  25  which is a compression spring in this embodiment. The motor  21  is a mini motor mounted inside the housing  10 , having a driving spur gear  211  fixedly mounted on the output shaft thereof for synchronous rotation with the output shaft of the motor. The electric connector  22  is an electric terminal electrically connected to the motor  21  and partially extending out of the housing  10 . The connecting member  23  is adapted to electrically connect the electric connector  22  to an external control circuit (not shown) for transmitting control signal from the external control circuit to the motor  21  through the electric connector  22 . The transmission device  24  comprises an idler spur gear  241  meshed with the driving spur gear  221  and a shaft  242  pivotally mounted in the housing  10 . The shaft  242  has a shaft body  243 , an actuating portion  244  which is an outer thread formed integrally on the periphery of the shaft body  243 , and a driven spur gear  245  which is fixedly mounted on the lower end of the shaft body  243  and meshed with the idler spur gear  241 , such that the driven spur gear  245  and the shaft  242  can be driven by the motor  21  to rotate through the driving spur gear  211  and the idler spur gear  241 . 
   The image-forming lens set  30  comprises a lens body  31 , a coupling member  32  connected to a side of the periphery of the lens body  31 , and a detected member  34  connected to a lateral side of the coupling member  32 . The lens body  31  is shaped like a barrel and has two longitudinal grooves  311  which extend respectively along two opposite sides of the periphery of the lens body  31  and are sleeved respectively onto two parallel upright guide rods  13  disposed at the first shell  11  of the housing  10  to guide an axial reciprocating motion of the lens body  31  along the upright guide rods  13 . The coupling member  32  has a coupling hole  321  with an inner thread engaged with the actuating portion  244  of the transmission device  24 . The top side of the coupling member  32  is contacted with the buffering member  25  of the driving mechanism  20 . 
   The sensor  40  is mounted inside the housing  10  and electrically connected to an external control circuit, and adapted to detect the position of the detected member  34  of the image-forming lens set  30  and to provide the external control circuit with a signal indicative of the position of the detected member  34 . 
   The operation of the lens retracting structure  100  is outlined hereinafter with reference to  FIGS. 3 and 4 . When moving the lens body  31  from the retracted position as shown in  FIG. 3  to the extended position as shown in  FIG. 4 , drive the external control circuit to input a control signal or power through the connecting member  23  into the connector  22  and then the motor  21 , causing the motor  21  to rotate the driving spur gear  211  through a predetermined angle. During rotation of the driving spur gear  211 , the driven spur gear  245  is synchronously rotated through the idler spur gear  241  such that the actuating portion  244  of the shaft  242  will be rotated at the same time. Because the coupling portion  321  of the coupling member  32  is engaged with the actuating portion  244 , the coupling member  32  is forced to move the image-forming lens set  30  outwards along the guide rods  13  from the first position (the retracted position as shown in  FIG. 3 ) to the second position (the extended position as shown in  FIG. 4 ) during rotation of the shaft  242 . When the lens body  31  reached to the predetermined position, the sensor  40  detects the relative position of the detected member  34  and outputs a corresponding signal to the external control circuit, causing the external control circuit to stop the motor  21 , and therefore the lens body  31  is held in the desired position. During the movement of the lens body  31  the buffering member (spring)  25  is always pressed on the coupling member  32  such that the lens body  31  can move stably. 
   When wishing the change of the lens body  31  from the second position (extended position) to the first position (retracted position), reverse the motor  21  to rotate the shaft  242  in the reversed direction, and therefore the coupling member  32  is forced to move the image-forming lens set  30  inwards along the upright guide rods  13  to the first position. 
   In the above-mentioned preferred embodiment, the driven spur gear  245  is driven by the driving spur gear  211  through the idler spur gear  241 . In fact, the idler spur gear  241  can be eliminated if the driven spur gear  245  is designed to be directly engaged with the driving spur gear  211 . 
   Because the invention uses spur gears to transfer the driving force from the motor to the lens body, the lens body can be stably and smoothly moved between the first position (retracted position) and the second position (extended position). Comparing to other gear structures, spur gears have the advantages of low manufacturing cost. Further, spur gears require less installation space, satisfying small size requirement. 
   Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.