Abstract:
A driving system for an SMA based actuator having SMA wires or rods includes a capture module, a determination module, and four drive modules. The capture module captures current position of a lens module from a position sensor. The displacement difference between the current position and a target position is determined. The first drive module can rapidly or slowly increase the current to the SMA, or rapidly or slowly decrease the current to the SMA, causing fast or slow movement of a lens module in one direction or fast or slow movement in the opposite direction, to achieve the desired auto-focus of a camera module.

Description:
FIELD 
       [0001]    The subject matter herein generally relates to shape-memory alloys and functions thereof. 
       BACKGROUND 
       [0002]    With ongoing developments in microcircuitry and multimedia technology, camera modules have become widely used in a variety of consumer electronic devices, such as smart phones, notebook computers, digital cameras, and personal digital assistants (PDAs). A typical camera module includes at least one lens module and an image sensor. In addition, there is a growing demand for developing more camera modules with multiple functions, such as camera modules having auto-focus function. A shape memory alloy (SMA) based actuator utilizing shape-memory alloy is widely used in a camera module to achieve the auto-focus function. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    Implementations of the present technology will now be described, by way of example only, with reference to the attached figures. 
           [0004]      FIG. 1  is a block diagram of an example embodiment of a camera module. 
           [0005]      FIG. 2  is a flowchart showing an auto-focus method of the camera module. 
       
    
    
     DETAILED DESCRIPTION 
       [0006]    It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts have been exaggerated to better illustrate details and features of the present disclosure. 
         [0007]    Several definitions that apply throughout this disclosure will now be presented. 
         [0008]    The term “comprising,” means “including, but not necessarily limited to” and specifically indicates open-ended inclusion or membership in the so-described combination, group, series and the like. The references “a plurality of” and “a number of” mean “at least two.” 
         [0009]    The present disclosure is described in relation to a driving system for an SMA based actuator. The SMA based actuator utilizes wires or rods made of SMA (hereafter “SMA wires”). The driving system includes a capture module, a determination module, a first drive module, a second drive module, a third drive module, and a fourth drive module. The capture module is configured to capture current position of a lens module from a position sensor. The determination module is configured to calculate difference P 0  between the current position and a target position and to determine which range out of a plurality of ranges the difference P 0  may fall into. The first drive module is configured to rapidly increase the current applied to the SMA wires to contract the SMA wires to move the lens module towards the target position when P 0 ≧20μm. The second drive module is configured to rapidly decrease the current applied to extend the SMA wires to move the lens module to the target position when P 0 ≦−20 μm. The third drive module is configured to slowly increase the current applied to the SMA wires to contract the SMA wires to move the lens module to the target position when 0&lt;P 0 &lt;20 μm. The fourth drive module is configured to slowly decrease the current applied to the SMA wires to slowly extend the SMA wires to move the lens module to the target position when −20 μm&lt;P 0 &lt;0. 
         [0010]    The present disclosure is described in relation to a camera module. The camera module includes a lens module, a position sensor, an SMA based actuator, and a driving system. The position sensor is configured to detect the position of lens module. The SMA based actuator utilizes SMA wires and is configured to move the lens module along an optical axis from an initial position to a target position to achieve auto-focus function. The driving system includes a capture module, a determination module, a first drive module, a second drive module, a third drive module, and a fourth drive module. The capture module is configured to capture current position of the lens module from the position sensor. The determination module is configured to calculate difference P 0  between the current position and the target position and to determine which range out of a plurality of ranges the difference P 0  may fall into. The first drive module is configured to rapidly increase the current applied to the SMA wires to contract the SMA wires to move the lens module towards the target position when P 0 ≧20 μm. The second drive module is configured to rapidly decrease the current applied to the SMA wires to extend the SMA wires to move the lens module to the target position when P 0 ≦−20 μm. The third drive module is configured to slowly increase the current applied to the SMA wires to contract the SMA wires to move the lens module to the target position when 0&lt;P 0 &lt;20 μm. The fourth drive module is configured to slowly decrease the current applied to the SMA wires to slowly extend the SMA wires to move the lens module to the target position when −20 μm&lt;P 0 &lt;0. 
         [0011]      FIG. 1  illustrates an example embodiment of a camera module  400 . The camera module  400  can include an SMA based actuator  100 , a position sensor  200 , a lens module  300 , and a driving system  10 . 
         [0012]    A plurality of lenses (not shown) are received in the lens module  300 . The SMA based actuator  100  is configured to move the lens module  300  along an optical axis in the camera module  400  from an initial or current position to a target position, so achieving the auto-focus function. The position sensor  200  is configured to detect the position of lens module  300 . In this embodiment, the position sensor  200  is a Hall sensor. The SMA based actuator  100  includes SMA wires. When a current to the SMA wires is increased, the SMA wires are heated and contract, and the contracted SMA wires move the lens module  300  along the optical axis to the target position. When the current to the SMA wires is decreased, the SMA wires cool and extend, and the extended SMA wires move the lens module  300  along the optical axis to the target position. The driving system  10  is configured to drive the SMA based actuator  100  to move the lens module  300 . 
         [0013]    The driving system  10  can include a capture module  11 , a determination module  12 , a first drive module  131 , a second drive module  132 , a third drive module  133 , and a fourth drive module  134 . 
         [0014]    The capture module  11  is configured to capture the current position of the lens module  300  from the position sensor  200 . The determination module  12  is configured to calculate the difference P 0  between the current position and the target position, to determine which range out of a number of ranges that the difference P 0  may fall into, and to activate the corresponding drive module  131 ,  132 ,  133 , or  134 , to drive the SMA based actuator  100  to move the lens module  300 . When the difference P 0  is a positive number, it represents that the current position of the lens module  300  exceeds the target position of the lens module  300 , and the SMA wires should be shorten to move the lens module  300  along the optical axis to the target position. When the difference P 0  is a negative number, it represents that the current position of the lens module  300  does not reach the target position of the lens module  300 , and the SMA wires should be lengthened to move the lens module  300  along the optical axis to the target position. The ranges are stored in the determination module  12  and include the following formulas: P 0 20 μm, P 0 ≦−20 μm, 0&lt;P 0 &lt;20 μm, −20 μm&lt;P 0 &lt;0, and −5 μm&lt;P 0 &lt;0. In this embodiment, the capture module  11  can be a Bluetooth drive or a WIFI drive which can capture data from external devices. The determination module  12  can be a central processing unit (CPU) which can execute calculation and comparison. The four drive modules  131 ,  132 ,  133 , and  134  can be triggers. 
         [0015]    The first drive module  131  is configured to rapidly increase the current applied to the SMA wires, by 10 mA per second, to rapidly contract the SMA wires to move the lens module  300  to the target position, when the difference P 0  exceeds or is equal to 20 micrometers (P 0 20 μm). 
         [0016]    The second drive module  132  is configured to rapidly decrease the current applied to the SMA wires, by 10 mA per second, to rapidly extend the SMA wires to move the lens module  300  to the target position, when the difference P 0  is less than or is equal to −20 micrometers (P 0 ≦−20 μm). “Rapidly” means increasing the current by over 10 mA per second or decreasing the current by over 10 mA per second. 
         [0017]    The third drive module  133  is configured to slowly increase the current applied to the SMA wires, by 2˜4 mA per second, to slowly contract the SMA wires to move the lens module  300  to the target position, when the difference P 0  is less than 20 micrometers and more than 0 micrometer (0&lt;P 0 &lt;20 μm). 
         [0018]    The fourth drive module  134  is configured to slowly decrease the current applied to the SMA wires, by 2˜4 mA per second, to slowly extend the SMA wires to move the lens module  300  to the target position, when the difference P 0  is more than −20 micrometers and less than 0 micrometer (−20 μm&lt;P 0 &lt;0). “Slowly” means increasing the current by 2˜4 mA per second or decreasing the current by 2˜4 mA per second. 
         [0019]      FIG. 2  shows a flowchart illustrating an auto-focus method  500  of the camera module  400 . The auto-focus method  500  is provided by way of an example, as there are a variety of ways to carry out the method. The auto-focus method  500  described below can be carried out using the configurations illustrated in  FIG. 1 , for example, and various elements of these figures are referenced in explaining auto-focus method  500 . Each block shown in  FIG. 2  represents one or more processes, methods, or subroutines, carried out in the auto-focus method  500 . Additionally, the illustrated order of blocks is by example only and the order of the blocks can change. The auto-focus method  500  can begin at block  502 . 
         [0020]    At block  501 , the current position of the lens module  300  is captured from the position sensor  200 . Block  501  is executed by the capture module  11 . 
         [0021]    At block  502 , the difference P 0  between the current position and the target position is calculated, and whether P 0 20 μm is determined. If P 0 20 μm, the method proceeds to block  503 . If not, the method proceeds to block  504 . Block  502  is executed by the determination module  12 . 
         [0022]    At block  503 , the current applied to the SMA wires is increased by 10 mA per second, causing the SMA wires to rapidly contract to move the lens module  300  to the target position. Block  503  is executed by the first drive module  131 . As block  503  is executed, blocks  501  and  502  are continuously executed. 
         [0023]    At block  504 , whether P 0 20 μm is determined. If P 0 20 μm, the method proceeds to block  505 . If not, the method proceeds to block  506 . Block  504  is executed by the determination module  12 . 
         [0024]    At block  505 , the current applied to the SMA wires is decreased by 10 mA per second, causing the SMA wires to rapidly extend to move the lens module  300  to the target position. Block  505  is executed by the second drive module  132 . As block  505  is executed, blocks  501  and  502  are continuously executed. 
         [0025]    At block  506 , whether 0&lt;P 0 &lt;20 μm is determined. If 0&lt;P 0 &lt;20 μm, the method proceeds to block  507 . If not, the method proceeds to block  509 . Block  506  is executed by the determination module  12 . 
         [0026]    At block  507 , the current applied to the SMA wires is slowly increased by 2˜4 mA per second, causing the SMA wires to slowly contract to move the lens module  300  to the target position. Block  507  is executed by the third drive module  133 . As block  507  is executed, block  508  is also executed. 
         [0027]    At block  508 , whether −5 μm&lt;P 0 &lt;0 is determined. If −5 μm&lt;P 0 &lt;0, the method proceeds to block  510 . If not, the method reverts to block  507 . Block  508  is executed by the determination module  12 . 
         [0028]    At block  509 , whether −20 μm&lt;P 0 &lt;0 is determined. If −20 μm&lt;P 0 &lt;0, the method proceeds to block  510 . Block  509  is executed by the determination module  12 . 
         [0029]    At block  510 , the current applied to the SMA wires is slowly decreased by 2˜4 mA per second, causing the SMA wires to slowly extend to move the lens module  300  to the target position. Block  510  is executed by the fourth drive module  134 . 
         [0030]    The embodiments shown and described above are only examples. Many details are often found in the art such as the other features of a driving system for a shape memory alloy based actuator and a camera module using the driving system. Therefore, many such details are neither shown nor described. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in the matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims. It will therefore be appreciated that the embodiments described above may be modified within the scope of the claims.