Abstract:
A digital camera module ( 100 ) for a portable electronic device, includes a lens holder ( 20 ), a lens module ( 10 ) axially movably received in the lens holder and at least one position tracking device ( 30 ). Each position tracking device includes a resistor ( 33 ) secured to the holder, a probe ( 31 ) attached to the lens module and slidably contacting with the resistor, and a measuring unit ( 35 ) electrically connecting with the resistor and the probe therebetween in series for measuring a resistance value of the resistor as it changes with the movement of the lens module thus enabling it to detect the position of the lens module.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to digital camera modules, and more particularly to a digital camera module which integrates a position tracking device for tracking a real-time position of a lens module.  
         [0003]     2. Discussion of the Related Art  
         [0004]     Nowadays, digital cameras with an automatic focus (AF) function are widely used. The AF apparatus works by detecting the focusing state of an image-taking lens to find a defocus amount (i.e. the distance by which the camera is out of focus), calculating a movement amount of a focus lens corresponding to the defocus amount, and driving the focus lens to move. However, there is a risk that an actual movement amount of the focus lens driven to move will not be the same as the target movement amount and the focusing accuracy of the digital camera will be affected as a result.  
         [0005]     What is needed, therefore, is a digital camera module with position tracking device which tracks a real-time position of a lens module for improving focusing accuracy.  
       SUMMARY OF THE INVENTION  
       [0006]     In one aspect, a digital camera module for a portable electronic device includes a lens holder, a lens module axially movably received in the lens holder and at least one position tracking device. Each position tracking device includes a resistor secured to the holder, a probe attached to the lens module and slidably contacting with the resistor, and a measuring unit electrically connecting with the resistor and the probe therebetween in series for measuring a resistance value of the resistor as it changes with the movement of the lens module thus enabling it to detect the position of the lens module.  
         [0007]     Other advantages and novel features will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Many aspects of the present digital camera module with a position tracking device 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 digital camera module with a position tracking device. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
         [0009]      FIG. 1  is a schematic, exploded, isometric view of a digital camera module in accordance with a preferred embodiment, without showing a measuring unit; and  
         [0010]      FIG. 2  is an assembled, cross-sectional view of  FIG. 1 , but showing the measuring unit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]     The digital camera module with a position tracking device of the present invention is suitable to use in portable electronic devices, such as cameras, mobile phones, personal digital assistants (PDA), palm computers and so on, which can contain a digital camera module having an AF function therein. Referring to  FIG. 1  and  FIG. 2 , a digital camera module  100  according to a preferred embodiment includes a lens module  10 , a lens holder  20  and a position tracking device  30 . The lens module  10  is received in the lens holder  20  and can be driven to move axially in the lens holder  20 . The position tracking device  30  is used to detect a position of the lens module  10  received in the lens holder  20 .  
         [0012]     The lens module  10  includes a lens barrel  11 , a lens group  13  and an infrared-cut filter (IR-cut filter)  14 . The lens barrel  11  has a first half-opening end  12  and a second opening end (not labeled) opposite to the first end  12 . The lens barrel  11  has a groove  15  defined in an outer peripheral surface (not labeled) of the barrel  11 , axially extending from the second end to the first end  12 . In a central portion of the first end  12 , there is a window  121  for transmitting light beams into the lens barrel  11 . The window  12  includes a transparent board  122  embedded therein, in order to seal the first end  12 , and protect the lens group  13  from dust and/or particle pollution/contamination. It is to be understood that, a focus lens could be embedded in the window  121  instead of the transparent board  122 . The focus lens can converge external light beams into the lens barrel  11  while preventing dust and/or particle pollution/contamination.  
         [0013]     The lens holder  20 , which is a cylinder in shape, includes an inner surface  21  and a receiving chamber  23  defined therein. The inner surface  21  peripherally surrounds the receiving chamber  23 , and has a slot  25  defined therein. The slot  25  communicates with the receiving chamber  23 , and corresponds to the groove  15  of the barrel  11 . The receiving chamber  23  is used to receive the barrel  11  of the lens module  10 , and has a profile slightly larger than that of the barrel  11 .  
         [0014]     The position tracking device  30  includes a probe  31 , a resistor  33 , a measuring unit  35  and a controlling unit (not shown). The probe  31  is made from electric conducting material, and has a pin  311  projecting therefrom. The probe  31  is embedded in and fixed to the groove  15  of the barrel  11 , with the pin  311  extending out of the groove  15 . The resistor  33  is received in the slot  25  and fixed to the lens holder  20 . The measuring unit  35 , such as an ohmmeter, electrically connects with the probe  31  and one end of the resistor  33  therebetween in series. The lens module  10  is received in the receiving chamber  23  of the holder  20 , and the pin  311  of the probe  31  electrically contacts with the resistor  33 . Therefore, the measuring unit  35  measures a resistance value of the resistor  33  between a contact position where the pin  311  contacts with the resistor  33  and the end of the resistor  33  electrically connecting with the measuring unit  35 , which is in association with the movement of the lens module  10  to detect the position of the lens module  10  received in the lens holder  20 . The measuring unit  35  outputs a signal with the resistance value corresponding to the position of the lens module  10 . The controlling unit electrically connects with the measuring unit  35  and receives the signal with the resistance value. The controlling unit calculates the position of the lens module  10  received in the lens holder  20  from the resistance value transmitted from the measuring unit  35 .  
         [0015]     In use of the digital camera module  100 , which is integrated into a portable electronic device, the measuring unit  35  is electrically connected with a power source such as a battery of the portable electronic device in order to supply electrical power. The controlling unit could be a micro controller unit (MCU) of the portable electronic device. When the digital camera module  100  needs to AF, the lens module  10  is driven by an actuator, such as a step motor integrated in the electronic portable device, to axially move in the lens holder  20 . The contact position jointly changes, and the resistance value of the resistor  33  between the contact position and said end of the resistor  33  changes in response to the movement of the lens module  10 . The controlling unit receives the continuously varied signal with the resistance value from the measuring unit  35  and calculates the position of the lens module  10  deriving on the resistance value. Therefore, in this manner the tracking of the position of the lens module  10  received in the lens holder  20  is achieved. If the actual movement amount of the lens module  10 , which is calculated by the controlling unit deriving on the signal output from position tracking device  30 , is unequal to the target movement amount of the lens module  10 , the controlling unit triggers the actuator to drive the lens module  10  until the actual movement amount of the lens module  10  is equal to the target movement amount.  
         [0016]     It is to be understood that the position tracking device  30  could include multiple groups of the probe  31 , the resistor  33  and the measuring unit  35 . The probes  31  can be axially mounted to the lens barrel  11  and spaced from each other. The resistors  33  can be mounted to the lens holder  20 , each resistor  33  contacting with a probe  31 . Each measuring unit  35  can electrically connect with a corresponding probe  31  and a corresponding resistor  33 . The controlling unit electrically connects with the measuring units  35  of each group, and compares the resistance values simultaneously transmitted from the measuring units  35  to estimate whether the lens barrel  11  moves axially or deviates from the axis.  
         [0017]     It is believed that the present embodiments and their advantages will be understood From the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.