Abstract:
A camera module includes a positioning plate, a positioning frame, a spring member, a lens holder, and a piezoelectric actuator. The positioning frame is fixed to the positioning plate and defines a positioning through hole. The spring member is disposed on the positioning plate and in a compressed state. The lens holder is received in the positioning through hole and movably engaged with the positioning frame. The piezoelectric actuator is sandwiched between the compressed spring member and the lens holder. The piezoelectric actuator is operable to drive the lens holder to rotate about a central axis of the positioning frame, thereby move along the central axis relative to the positioning frame.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to camera modules and, particularly, to a camera module having a piezoelectric actuator. 
     2. Description of Related Art 
     Recent development trends in the field of camera modules focus on low cost and miniaturization. However, to provide focusing functions, current camera modules typically employ stepper motors or voice coil motors (VCMs), which substantially increase the cost and the size of these camera modules. 
     Therefore, it is desirable to provide a small, inexpensive camera module which has focusing function. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, all the views are schematic. 
         FIG. 1  is an exploded, isometric view of a camera module, according to an exemplary embodiment. 
         FIG. 2  is an assembled, cross-sectional view of the camera module of  FIG. 1 . 
         FIG. 3  is an assembled view of the camera module of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will now be described in detail with reference to the drawings. 
     Referring to  FIG. 1 , a camera module  100 , according to an exemplary embodiment, includes a substrate  10 , a receiving frame  11 , an image sensor  12 , a positioning plate  13 , a spring member  14 , a piezoelectric actuator  15 , a lens holder  16 , a lens barrel  17 , a positioning frame  18 , and a cover  19 . 
     The substrate  10  is a rectangular plate. In this embodiment, the substrate  10  is a printed circuit board. 
     The image sensor  12  is operable to sense incident light and generate electrical signals correspondingly. 
     The receiving frame  11  is a rectangular plate defining a rectangular opening  110  in the center thereof. The height of the receiving frame  11  is larger than that of the image sensor  12 . 
     The positioning plate  13  is rectangular, and defines a circular receiving through hole  130  in the center thereof. 
     The spring member  14  includes a rectangular outer portion  140 , an annular inner portion  142 , and four rectangular connecting portions  144 . One end of each connecting portion  143  is perpendicularly connected to a corresponding side of the outer portion  140 , and the other end is connected to the inner portion  142 . As such, the inner portion  142  is enclosed by the outer portion  140  and held a short distance from the outer portion  140  by the connecting portions  143 . The outer diameter of the inner portion  142  is slightly smaller than the diameter of the receiving through hole  130 . 
     The piezoelectric actuator  15  includes a piezoelectric member  150 , two protecting members  152 ,  154 , and two electrodes  156 . The piezoelectric member  150  and the two protecting members  152 ,  154  are ring-shaped (annular). The piezoelectric member  150  includes a number of polarized piezoelectric segments  158 . In  FIG. 1 , the symbols “+” and “−” represent opposite polarizing directions of the piezoelectric segments  158 . The two electrodes  156  are connected to the piezoelectric segments  158 . The piezoelectric member  150  is thus operable to generate a wave travelling around the circumference thereof, when two voltages having a phase difference of ninety degrees are correspondingly applied to the oppositely polarized piezoelectric segments  158  via the two electrodes  156 . The two protecting members  152 ,  154  are elastic and sandwich the piezoelectric member  150  therebetween in order to protect the piezoelectric member  150 . In practice, the protecting members  152 ,  154  are made of a material with a high coefficient of friction, such as rubber. The outer diameters of the piezoelectric member  150  and the two protecting members  152 ,  154  are substantially equal to the outer diameter of the inner portion  142 . 
     The lens holder  16  is approximately a circular tube in shape. The lens holder  16  defines a first internal screw thread  160  in an inner surface thereof, and a first external screw thread  162  in an outer surface thereof. 
     The lens barrel  17  is approximately a circular tube in shape, and defines a second external screw thread  170  in an outer surface thereof. The outer diameter of the lens barrel  17  is substantially equal to the inner diameter of the lens holder  16 . The lens barrel  17  is structured and arranged to receive lenses. 
     The positioning frame  18  is approximately a short, rectangular tube in shape, and defines a positioning through hole  180  in the center thereof. The positioning frame  18  defines a second internal screw thread  182  in an inner surface thereof which bounds the positioning through hole  180 . The diameter of the positioning through hole  180  is substantially equal to the outer diameter of the lens holder  16 . 
     The cover  19  includes a sidewall  190 , and an upper plate  192  extending from (or mounted on) the sidewall  190 . The cover  19  defines a circular opening  194  in the center of the upper plate  192 . 
     Also referring to  FIGS. 2-3 , in assembly of the camera module  100 , the image sensor  12  is fixed to the center of the substrate  10  and electrically connected to the substrate  10 . The receiving frame  11  is also fixed to the substrate  10  and surrounds the image sensor  12 . The positioning plate  13  is fixed to the receiving frame  11 . The spring member  14  is positioned on the positioning plate  13 , with the outer portion  140  in contact with the positioning plate  13 , and the inner portion  142  coaxially suspended over the receiving through hole  130 . The piezoelectric actuator  15  is fixed to the inner portion  142 , and the electrodes  156  are electrically connected to the substrate  10 . The positioning frame  18  is fixed to the outer portion  140  of the spring member  14  and thus sleeved on the piezoelectric actuator  15 . A lens  20  is received in the lens barrel  17 , and then the lens barrel  17  is screwed into the lens holder  16 . The lens holder  16  is screwed into the positioning through hole  180  of the positioning frame  18 , and presses the piezoelectric actuator  15 . The piezoelectric actuator  15  tightly contacts the inner portion  142 , and the inner portion  142  is pressed into the receiving through hole  130  by the piezoelectric actuator  15 . The cover  19  is covered on the positioning frame  18  and fixed to the positioning plate  13 . The lens barrel  17  is exposed via the opening  194 . The camera module  100  is thus assembled. 
     In operation of the camera module  100 , if the lens barrel  17  needs to move upwards, two driving voltages having a phase difference of ninety degrees are correspondingly applied to the oppositely polarized piezoelectric segments  158  to generate a counterclockwise travelling wave. The counterclockwise travelling wave is transferred to the protecting member  152 , and a friction is generated between the protecting member  152  and the lens holder  16 . As a result, the lens holder  16  rotates counterclockwise around a central axis of the positioning through hole  180 , and thereby simultaneously moves gradually upwards along the second internal screw thread  182 . The pressed inner portion  142  moves upwards accordingly, and applies a counterforce to the piezoelectric actuator  15  to maintain the tight contact between the protecting member  152  and the lens holder  16 . As a result, the lens received in the lens barrel  17  moves upwards with the lens barrel  17  for focusing. In practice, the driving voltages should be high enough such that the friction between the protecting member  152  and the lens holder  16  can overcome the friction between the first external screw thread  162  and the second internal screw thread  182 . 
     If the lens barrel  17  needs to move downwards, opposite driving voltages are applied to the piezoelectric member  150 , and a clockwise travelling wave is generated accordingly. The lens holder  16  is driven to rotate clockwise, and thereby simultaneously moves gradually downwards relative to the positioning frame  18 . Accordingly, the lens received in the lens barrel  17  moves downwards. The piezoelectric actuator  15  and the inner portion  142  are pressed by the lens holder  16  to correspondingly move downwards. 
     It should be understood that the spring member  14  can instead be an elastic ring, which is received in the positioning frame  18  and sandwiched between the lens holder  16  and the positioning plate  13 . 
     While various exemplary and preferred embodiments have been described, it is to be understood that the disclosure is not limited thereto. To the contrary, various modifications and similar arrangements (as would be apparent to those skilled in the art) are intended to also be covered. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.