Abstract:
A lens displacement mechanism using shaped memory alloy (SMA) applied to an auto-focusing lens module is disclosed. The lens displacement mechanism comprising at least one SMA wire. Two opposite ends of the SMA wire are fixed and a longitudinal mid-point of an intermediate movable portion between the two opposite ends is tightened and is fixed on a corresponding hook disposed on an outer edge of the lens so that the intermediate movable portion is tightened between the two opposite ends. When the SMA wire is heated, the intermediate movable portion contracts to pull the hook of the lens for driving the lens to move and slide along with an optical axis so as to achieve auto-focus control. The present lens displacement mechanism is simple in structure and reflow process. Therefore, the present displacement mechanism is suitable to be used in portable camera or mobile phone or PDA, which needs to be small and have easily mass production by SMT.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a lens displacement mechanism using shaped memory alloy (SMA), especially to a lens displacement mechanism that uses SMA to control forward/backward movement of the lens for zooming and such mechanism is applied to an auto-focusing lens module. 
     Portable electronic devices such as digital cameras, mobile phones with camera function, or notebooks available now are generally disposed with auto-focusing (AF) compact camera, so called with auto-focusing lens module inside. The auto-focusing lens module primarily consists of a housing, a lens and a lens displacement mechanism. The lens is consists of a lens holder and a lens group. The lens holder and the lens group are mounted in the housing. The lens displacement mechanism is used for driving the lens in moving along an optical axis or toward/away from an object side by sliding or screw rotation for auto-focus control. A conventional lens displacement mechanism is composed of a piezoelectric motor that is formed by piezoelectric material. However, the general piezoelectric material is unable to endure high temperature of a reflow process. Once a special piezoelectric material that is durable to high temperature is used, the cost is quite expensive. As to another component, a voice coil motor (VCM), it uses magnetic force and includes elastic parts. But, under high temperature of the reflow process, the voice coil motor may be damaged or the magnetic force is reduced. Thus the reflow process is not used while assembling the piezoelectric motor or the voice coil motor. Therefore, this leads to difficulty in mass production. Furthermore, a SMA device formed by shaped memory alloy is used. By its principle of heat contraction and cold expansion, the lens is driven to move. The contraction and expansion amount of the SMA device is about 5%, far more effective than that of general material. Moreover, SMA device is durable to high temperature of the reflow process so that the reflow process can be applied when assembling the auto-focusing lens module. Therefore, the SMA device is practical and the assembling efficiency is improved. 
     Referring to patents of U.S. Pat. No. 5,185,621, U.S. Pat. No. 5,279,123, U.S. Pat. No. 5,459,544, U.S. Pat. No. 6,307,678, U.S. Pat. No. 6,449,434, US2002/0136548, US2007/0058070, US2007/0047938; WO2005/001540; Japan patents JP64-000938, JP09-127398, JP62-067738, JP03-196781, JP2006-329111, JP2005-275270, JP2005-195998, JP2005-156892, JP2004-184775, JP2004-129950, JP2004-069986, JP2004-038058, JP2000-056208; Taiwan patents TWM242178, TW200710464 and so on, all are prior arts relative to SMA devices in lens displacement mechanisms. Although they all use SMA devices as driving sources of lens displacement, the technique or driving way disclosed are different from one another. However, most of them have complicated design and large volume so that they can&#39;t match requirement of compact design of the lens modules. Referring to U.S. Pat. No. 6,449,434, a SMA wire is used. The two ends of the SMA wire is fixed and an intermediate moveable portion is hooked on a pivoted actuator. A projective pin is arranged on the outer edge of the actuator for locking with a slot on an outer edge of the lens holder as a stress point. By heating contraction and cold expansion of the SMA wire, the actuator is driven to pivot at an angle. Synchronously, the projective pin is also pivoted so as to drive the lens holder pivot at an angle. Thus by other element, the lens holder moves so as to achieve focusing. It is found that driving force is from the SMA wire, these prior arts still require some other linkage devices such as actuators, triggers or other leverage with similar functions to drive the lens holder in moving. The linkage device is disposed between the SMA wire and the lens holder so that contraction force of the SMA is converted into driving force for movement of the lens holder through the linkage device. Thus the movement and structure of the lens displacement mechanism are too complicated and this leads to negative effects on design requirements of compact lens module and low cost as well as has disadvantageous in mass production by SMT (Surface-Mount Technology). Therefore, there is still a space for improvement. 
     SUMMARY OF THE INVENTION 
     Therefore, it is a primary object of the present invention to provide a lens displacement mechanism applied to an auto-focusing lens module. At least one shaped memory alloy (SMA) wire is arranged around the lens symmetrically or in equal distance. Two opposite ends of the SMA wire are fixed and a longitudinal mid-point of an intermediate movable portion between the two opposite ends is tightened and is hooked on a corresponding hook disposed on an outer edge of a lens holder so that the intermediate movable portion is tight compared to the two opposite ends. When the SMA wire is heated due to the control current rush-in, the intermediate movable portion contracts so as to pull the hook for driving the lens to move and slide along with the optical axis. Therefore, auto focusing is achieved. 
     It is another object of the present invention to provide a lens displacement mechanism using shaped memory alloy that further includes a recovery spring element disposed on the lens. When the control current is cut off, the SMA wire is cooled and expanded back to original length. Then the recovery spring element provides the lens a recovery force that is opposite to a pulling force of the contracted SMA wire so as to drive the lens back to original place and auto focusing is achieved. 
     It is a further object of the present invention to provide a lens displacement mechanism using shaped memory alloy that includes a guide slot and a corresponding guide rail arranged between the lens and edges of a housing so as to make the lens move and slide stably inside the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment according to the present invention; 
         FIG. 2  is a schematic drawing showing top side of the embodiment in  FIG. 1 ; 
         FIG. 3  is a schematic drawing showing lateral side of the embodiment in  FIG. 1 ; 
         FIG. 4  is a perspective view of another embodiment according to the present invention; 
         FIG. 5  is a schematic drawing showing top side of the embodiment in  FIG. 4 ; 
         FIG. 6  is a schematic drawing showing lateral side of the embodiment in  FIG. 4 ; 
         FIG. 7  is a perspective view of a further embodiment according to the present invention; 
         FIG. 8  is a schematic drawing showing top side of the embodiment in  FIG. 7 ; and 
         FIG. 9  is a schematic drawing showing lateral side of the embodiment in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A lens displacement mechanism using shaped memory alloy of the present invention is applied to an auto-focusing lens module. There is no restriction on shape or structure of a housing or the lens of the lens module. For example, the lens may include either a single lens or lens group having a plurality of lens. The single lens or lens group can be set in a fixing member and then is assembled with a lens holder to form a lens. There is also no limit on the lens holder as long as it can fit with a cover, an inner space, the housing or other components of the lens module. As to number of shape memory alloy (SMA) wires and lens being driven thereby, there is also no restriction. There are many driving ways such as a lens is driven by a SMA wire, a plurality sets of SMA wires drive a lens, or a plurality sets of SMA wires drive a plurality of lenses. 
     Referring to  FIG. 1  to  FIG. 3 , a lens displacement mechanism  1  of the present invention is applied to an auto-focusing lens module  2 . The auto-focusing lens module  2  includes at least a housing  20  for mounting a lens  21  that moves along an optical axis X thereof. There is no restriction on structure or assembling way of the lens  21 . Generally, the lens  21  consists of a lens group  22  having a single lens or a plurality of lenses (such as two lenses) and a lens holder  23 . 
     In the lens displacement mechanism  1 , the lens  21  is driven to slide and move by at least one SMA wire  10  with features of temperature change as well as heat contraction and cold expansion after being conducted. Where the SMA wire  10  is the characteristic of martensite/austenite transformation when the SMA wire  10  is heated by control current rush-in achieving the heating-contracting behavior between austenitic start temperature and austenitic finish temperature, is cooled by current cut-off achieving the cooling-expansion behavior between martensite start temperature and martensite finish temperature. 
     The SMA wire  10  includes two opposite ends  11  and an intermediate moveable portion  12  located between the two opposite ends  11 . The two opposite ends  11  are fixed on somewhere such as a frame  24  surrounding the housing  20  of the auto-focusing lens module  2 . There is no limit on fixing way of the opposite end  11  to the frame  24 . The fixing way can be clipping, adhesion, or welding as long as it&#39;s an easy processing. A longitudinal mid-point  13  of the intermediate moveable portion  12  is tightened and is hooked on a corresponding hook  25 . The hook  25  is disposed on the outer edge of the fixing member of the lens group  22  or the outer edge of the lens holder  23  so as to make the intermediate moveable portion  12  become tight between two opposite ends  11 . In accordance with above structure, when the SMA wire is heated due to the control current rush-in, the intermediate moveable portion  12  of the SMA wire  10  contracts to pull the hook  25  so that the lens  21  is driven to slide and move along the optical axis X. Thus auto focusing is achieved. 
     The number of the SMA wire  10  in the present invention and the way of arranging each SMA wire  10  around the lens  21  are not restricted. The number of the SMA wire  10  may be one, two or four in different embodiments. 
     The First Embodiment 
     Referring to  FIG. 1  to  FIG. 3 , one SMA wire  10  is used in this embodiment. When zooming from tele to wide, the lens  21  is moved away from the image side and towards the object side. While zooming, the lens  21  moves under control of a focus button (not shown in figure). When user presses the focus button, the lens displacement mechanism  1  gets control current passed from electrodes  31 ,  32 . After a control current passing through the SMA wire  10 , joule heat generates due to resistance of the SMA wire  10 . Thus the SMA wire  10  is heated and contracted. Due to linear relationship among the length, temperature and the control current of the SMA wire  10 , displacement of the lens  21  can be controlled according to contraction of the SMA wire  10 . Thus the distance between the lens  21  and an image-forming plane is changed so as to achieve auto focusing. In this embodiment, the SMA wire  10  is made from Nickel-Titanium alloy with diameter of 0.002″. The distance change between the lens  21  and the image forming plane as well as the control current is shown in the table I. 
     
       
         
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
             
             
               
                 Object distance(mm) 
                 70 
                 100 
                 600 
                 1000 
                 infinity 
               
               
                 Move of lens (mm) 
                 0.243 
                 0.167 
                 0.023 
                 0.011 
                 0 
               
               
                 control current (mA) 
                 50 
                 35 
                 20 
                 15 
                 0 
               
               
                   
               
             
          
         
       
     
     There is no restriction on power supply structure and/or electrical connection of the lens displacement mechanism  1  of the present invention. 
     The lens displacement mechanism  1  further includes a recovery spring element  30  such as spring or clip disposed on the lens  21 . When the control current is diminish, the SMA wire  10  is cooled down and expanded back while the recovery spring element  30  provides a recovery force opposite to the pulling force of the contracted SMA wire  10 . That means direction of the recovery force is opposite to displacement direction of the lens  21  pulled by the contraction of the intermediate moveable portion  12  so that the lens  21  turns back to the balance place. As to types of the recovery spring element  30 , it can be compression spring, or extension spring, and there is no restriction on numbers or disposed positions in figures, on top of the lens  21  so as to provide the lens  21  a compression spring force that is in opposite direction to the pulling force of the contracted SMA wire  10 . Or an extension spring is arranged on bottom of the lens  21  for providing the lens  21  an extension spring force opposite to the pulling force of the contracted SMA wire  10  so as to move the lens  21  back to the original place. 
     Furthermore, a set of guide rail device  26  is disposed between the lens  21  and the housing  20 . The guide rail device  26  includes a guide slot  261  and a corresponding guide rail  262  respectively arranged between the housing  20  and the frame  27  close to or connected with the lens  21  so that the lens  21  moves and slides stably inside the housing  20  by the guide rail device  126 . The position and number of the guide rail device  26  have no limits. 
     The Second Embodiment 
     Referring to  FIG. 4  to  FIG. 6 , this embodiment includes two SMA wires  10 . The two SMA wires  10  are arranged symmetrically or in equal distance around the lens  21 . The . driving way and function of each SMA wire  10  is the same with that in the first embodiment. A recovery spring element  30  is disposed on the lens  21  for providing a recovery force in opposite direction to the pulling force of the contracted SMA wire  10  so as to turn the lens  21  back to a balance place. 
     Furthermore, a guide rail device  26  is disposed between the lens  21  and the housing  20 . The guide rail device  26  is arranged on one side between the two SMA wires  10  so that the lens  21  moves and slides stably inside the housing  20  by the guide rail device  26 . 
     Or two guide rail devices  26  are disposed between the lens  21  and the housing  20 . The two guide rail devices  26  are arranged symmetrically in accordance with positions of the two SMA wires  10 . As shown in  FIG. 4  to  FIG. 6 , the two SMA wires  10  are disposed symmetrically while the two guide rail devices  26  are arranged symmetrically (not shown in figure). The two SMA wires  10  and the two guide rail devices  26  may also be arranged next to each other. For example, the two SMA wires  10  are arranged on two adjacent sides of the rectangular frame while the two guide rail devices  26  are disposed on the remaining two adjacent sides. The purpose of disposition of the guide rail device  26  is to make the lens  21  move and slide stably inside the housing  20 . Generally, the two SMA wires  10  of the second embodiment provide better pulling force than one SMA wire  10  of the first embodiment 
     The Third Embodiment 
     Referring to  FIG. 7  to  FIG. 9 , this embodiment includes four SMA wires  10 . The four SMA wires  10  are arranged symmetrically or in equal distance around the lens  21 . For example, the SMA wires  10  respectively are arranged on four sides of the lens  21 . The driving way and function of each SMA wire  10  are the same as those in the second embodiment. Moreover, a recovery spring element  30  is disposed on the lens  21  for providing a recovery force in opposite direction to the pulling force of the contracted SMA wire  10  so as to turn the lens  21  back to balance place. 
     In this embodiment, four SMA wires  10  respectively are disposed on four sides surrounding the lens  21  so as, to provide the lens  21  equipollent contacting and pulling forces. Thus, the lens  21  moves stably inside the housing  20 . Basically, there is no need to add the guide rail devices  26  in this embodiment. Furthermore, once an image quality feedback mechanism is added to control and regulate the four SMA wires  10  for fine adjustment of a tilt of the lens  21 , the image quality is improved. 
     Compared with prior arts, the present invention has following advantages: 
     (1) The SMA wire  10  of the present invention drives the lens  21  to move and slide directly without other linkage device such as actuators and triggers so that structure and movement of the lens are simplified. Thus, requirements of compact lens module and reduced cost are satisfied and this has positive effect on mass production.
 
(2) The present invention can endure high temperature of the reflow process so that is has higher possibility to be mass-produced.
 
(3) The longitudinal mid-point  13  of the intermediate moveable portion  12  of the SMA wire  10  according to the present invention is tightened and hooked on a corresponding hook  25  of the lens  21  so that the SMA wire  10  forms a V-shaped structure and a longer range can be obtained. That means by the same SMA wire  10 , the same SMA wire  10  of the present invention provides the lens  21  larger displacement range. Moreover, a feedback mechanism on the circuit is used to control the length—temperature-resistance of the SMA wire  10  for fine adjustment of displacement of the lens  21 . The focusing position of the lens is controlled precisely.
 
(4) Once at least two SMA wires  10  are arranged symmetrically or in equal distance surrounding the lens  21  as shown in the third embodiment, a suitable image quality feedback mechanism is used so as to control each SMA wire  10  respectively for correcting tilt, yaw or pitch of the lens  21 .
 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.