Patent Publication Number: US-2007098400-A1

Title: Lens module and digital camera module using the same

Description:
BACKGROUND  
      1. Technical Field  
      This invention relates generally to optical imaging apparatuses, and more particularly to lens modules and digital camera modules using the same.  
      2. Related Art  
      Nowadays, digital camera modules are widely accepted for their ease of use, digital image storage, immediate results and image management potential, for example, employed in mobile phones. Commonly, the digital camera modules work at various outdoor environments having different temperatures and humidities, so the reliability of working in the various environments to lens modules of the digital camera modules is one of critical factors to achieve a high imaging quality.  
      A typical lens module of a digital camera module includes a lens barrel, and a first glass lens, an aperture stop, a second glass lens, a spacer and an IR cut filter received in the lens barrel in that order from an object side to an image side of the lens module. Usually, the aperture stop and the spacer are made of either polymer materials (e.g., carisoprodol) or dark-painted copper or brass. However, the polymer materials and dark-painted copper or brass are prone to generate thermal-induced deformations due to their different thermal expansion coefficients comparing with glass. The thermal-induced deformations of the aperture stop and/or spacer may cause tilt, bending, and deformation on their neighboring lenses, which will result in a deteriorated imaging quality of the digital camera modules.  
      What is needed is to provide a lens module and a digital camera module using the same having a better environment-tolerance.  
     SUMMARY  
      A preferred embodiment provides a lens module including: a lens barrel, a lens unit and an aperture stop. The lens barrel includes a receiving part defining a passage therein. The lens unit is made of glass. The aperture stop is made from an iron-nickel based alloy having a thermal expansion coefficient matching with that of glass. The lens unit and the aperture stop are received in the passage of the receiving part in succession order from an object side to an image side of the lens module.  
      In another preferred embodiment, a digital camera module includes a lens module as above described, an image sensor and a holder. The holder defines an opening therein. The receiving part of the lens barrel of the lens module as above described is engaged in the opening. The image sensor is received in the opening and arranged at the image side.  
      Other advantages and novel features will become more apparent from the following detailed description of embodiments when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Many aspects of the present lens module and digital camera module using the same can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present lens module and digital camera module. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1  is a schematic, cross-sectional view of a lens module in accordance with a preferred embodiment; and  
       FIG. 2  is a schematic, cross-sectional view of a digital camera module using the lens module of  FIG. 1 . 
    
    
      The exemplifications set out herein illustrate preferred embodiments, in various forms, and such exemplifications are not to be construed as limiting the scope of the present lens module and digital camera module in any manner.  
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Referring to  FIG. 1 , a lens module  100  in accordance with a preferred embodiment of present invention is shown. The lens module  100  includes a lens barrel  10 , lens units  22 ,  24 , an aperture stop  30 , a spacer  40  and a filter  50 . The lens unit  22 , aperture stop  30 , lens unit  24 , spacer  40  and filter  50  are received and fixed in the lens barrel  10  in succession order from an object side to an image side of the lens module  100 .  
      The lens barrel  10  includes a receiving part  12  and a front part  14 . The receiving part  12  has a cylindrical shape and defines a passage  122  therein. The receiving part  12  usually has an external thread  124  on an outward circumference thereof. The passage  122  is configured for receiving the lens units  22 ,  24 , aperture stop  30 , spacer  40  and filter  50  therein. The front part  14  has a cone-shaped passage  144  defined in a central portion thereof. A diameter of the cone-shaped passage  144  gradually decreases along a direction from the object side to the image side. The cone-shaped passage  144  is connected with the passage  122  of the receiving part  12 . Incident light beams passing through the cone-shaped passage  144  can reach into the passage  122  and incident on the lens units  22 ,  24  and the filter  50 .  
      The lens units  22 ,  24  are usually made of glass and can be aspherical lenses or spherical lenses. The lens unit  22  includes a transparent central region  222  and a peripheral region  224  surrounding the transparent central region  222 . Likewise, the lens unit  24  includes a transparent central region  242  and a peripheral region  244  surrounding the transparent central region  242 .  
      The aperture stop  30  usually is dark-painted annular sheet which has a thickness in the range from 30 to 70 micrometers and an inner diameter in the range from 0.3 to 0.8 micrometers. Preferably, the annular sheet has a thickness in the range from 40 to 60 micrometers and an inner diameter in the range from 0.4 to 0.6 micrometers.  
      The spacer  40  is configured for separating optical elements such as lens unit  24  and filter  50 , and for thereby forming a space therebetween. The spacer  40  generally has a configuration matching with the passage  122  and defines a passage  402  therein. The passage  402  usually has a cone shape having a diameter increasing along the direction for the object side to the image side.  
      The aperture stop  30  and the spacer  40  are made from a material having a thermal expansion coefficient matching with (i.e., similar as) that of glass from which the lens units  22 ,  24  are made. This characteristic of the material can beneficially prevent the neighboring glass lens units  22 ,  24  of the aperture stop  30  and/or the spacer  40  from tilt, bending, and deformation when the lens module  100  working at various different environments. For example, the aperture stop  30  and the spacer  40  are made from an iron-nickel based (FeNi-based) alloy. The FeNi-based alloy may have a tensile strength of 67,000 pounds per square inch (psi) and can be used in a wide temperature range from −40° C. to 85° C. and tolerate a relative humidity in the range from 5% to 90%. In particular, in one embodiment, the FeNi-based alloy is an invar alloy. The invar alloy can be composed of 62.51% iron (Fe), 36% nickel (Ni), 0.25% chromium (Cr), 0.5% manganese (Mn), 0.25% silicon (Si), 0.05% carbon (C), 0.1% aluminum (Al), 0.1% magnesium (Mg), 0.1% zirconium (Zr), 0.1% titanium (Ti), 0.02% phosphorus (P) and 0.02% sulfur (S) by weight; or 58.07˜60.17% iron, 39˜41.1% nickel, 0.05% chromium, 0.6% manganese, 0.02% silicon, 0.05% carbon, 0.02% aluminum, 0.05% cobalt (Co), 0.02% phosphorus and 0.02% sulfur by weight. In another embodiment, the FeNi-based alloy is a kovar alloy (i.e., iron-nickel-cobalt based alloy). The kovar alloy can be composed of 52˜53% iron, 29% nickel, 17% cobalt, and 1˜2% residual composition by weight, the residual composition is selected from the group consisting of magnesium, manganese, silicon, carbon, aluminum, zirconium, titanium, phosphorus, sulfur, and an mixture thereof. For example, the kovar alloy is composed of 52.79% iron, 29% nickel, 17% cobalt, 0.1% magnesium, 0.5% manganese, 0.2% silicon, 0.06% carbon, 0.1% aluminum, 0.1% zirconium, 0.1% titanium, 0.025% phosphorus, and 0.025% sulfur by weight.  
      The filter  50  usually is an infrared (IR) cut filter which includes a glass base and an IR cut coating formed on at least one surface of the glass base member. This IR cut filter can be used to filter infrared rays.  
      Referring to  FIG. 2 , a digital camera module  200  incorporating the above-described lens module  100  is shown. The digital camera module  200  includes the lens module  100  as above described, a holder  60 , a base member  70 , an image sensor  80  and a cover  90 .  
      The holder  60  defines an opening  62  therein. An internal thread  624  is defined on peripheral sidewalls of the opening  62 . The internal thread  624  is engaged together with the external thread  124  of the lens barrel  10  for thereby holding the lens module  100 .  
      The base member  70  is received in the opening  62  of the holder  60 . The base member  70  usually defines a cavity in a surface thereof adjacent to the lens module  100  for receiving the image sensor  80 . In the illustrated embodiment, the base member  70  is made from ceramic.  
      The image sensor  80  is fixed in the base member  70  and configured for detecting optical signals representative of a target image and converting the optical signals into corresponding electronic signals. The image sensor  80  usually is a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) device.  
      The cover  90  is arranged on the base member  70  for covering the opening of the base member  70 . The cover  90  usually is used to protect the image sensor  80  fixed in the base member  70  from contaminations, such as dust and/or water vapor. The cover  90  is usually made of a transparent material, such as transparent glass.  
      In summary, the aperture stop and the spacer in the above described preferred embodiments are made from a material (e.g., FeNi-based alloy) having a thermal expansion coefficient matching with that of glass from which the lens units are made. When such kinds of aperture stop and/or spacer are employed in optical imaging apparatuses such as, lens modules and digital camera modules, they can render the optical imaging apparatuses achieving a better environment-tolerance and then a high imaging quality.  
      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 present invention.