Abstract:
The present invention provides a compact automatic focusing system using a Micro-Electro-Mechanical System (MEMS) unit. The automatic focusing system using the MEMS unit has a small volume and low power consumption, and its operation is very reliable, precise, and fast. The MEMS unit for automatic focusing comprises at least one micromirror, at least one micro-actuator, and at least one micro-converter fabricated on the same substrate by microfabrication technology. By fabricating the micromirror, the micro-actuator, the micro-converter on the same substrate, the volume of the automatic focusing system of the present invention can be greatly reduced. The micro-converter converts the in-plane translation of the micro-actuator to out-of-plane translation of the micromirror to provide a large out-of-plane translation range.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to an automatic focusing device, more particularly, to an automatic focusing device using micro-electro-mechanical system providing compactness, reliability, low power consumption, and fast focusing. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention contrives to provide a reliable compact and slim automatic focusing camera with low power consumption and fast focusing capability for portable devices such as cellular phone camera. 
         [0003]    Most conventional automatic focusing systems perform their automatic focusing by moving one or more lenses using an electro-magnetically driven motor and/or piezo-electrically actuated apparatus. Since the lens or lenses in those systems have a considerable inertia and need to have macroscopic mechanical motions, the automatic focusing systems require a macroscopic actuator generating large actuating force. The macroscopic actuator can cause many problems including bulky size, large power consumption, slow focusing time, and eventually decrease in the probability of the automatic focusing system. The automatic focusing can be performed by moving a sensor, as well. But, it also requires a macroscopic actuator with additional complexity necessary to satisfy electrical connection. For simpler automatic focusing, a movable mirror can be used for the automatic focusing systems. The movable mirror can provide a simple and reliable automatic focusing, but it still requires a macroscopic actuator. 
         [0004]    To apply the automatic focusing system to portable devices such as cellular phone camera, it is very important to reduce volume and power consumption of the automatic focusing system and increase the reliability and focusing speed of automatic focusing function. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention contrives to reduce the volume and the power consumption and increase the reliability and focusing speed of an automatic focusing system.  FIG. 1  shows a conventional automatic focusing system using a mirror translation. An actuator is connected to the mirror such that the mirror moves to adjust focusing. Since the optical system with automatic focusing function requires additional optical components including a mirror and an actuator, the optical system has larger volume than an optical system without automatic focusing function. To apply automatic focusing system to portable devices such as cellular phone camera, it is very important to reduce the volume and power consumption of the automatic focusing system and increase the reliability and focusing speed of automatic focusing function. 
         [0006]    In the present invention, the automatic focusing function is performed by a Micro-Electro-Mechanical System (MEMS) unit. The MEMS unit has a small volume and low power consumption, and its operation is very reliable, precise, and fast. The MEMS unit for automatic focusing includes at least one micromirror and at least one micro-actuator fabricated on the same substrate by microfabrication technology. By fabricating the micromirror and the micro-actuator on the same substrate, the volume of the automatic focusing system of the present invention can be greatly reduced. In general, an actuator used for automatic focusing is required to provide several hundreds micrometer of out-of-plane translation to a mirror. The out-of-plane translation is defined as a translation in the surface normal direction of the substrate while the in-plane translation is defined as a translation in the direction of an axis laying on the substrate surface. The conventional MEMS devices are capable of providing out-of-plane translation to the mirror and have an advantage of adding negligible volume to the optical system. However, they have a limited range in the out-of-plane translation; typically only several micrometers. In order to increase the range of the out-of-plane translation, the present invention preferably comprises at least one micromirror, at least one micro-actuator, and at least one micro-converter, wherein the micro-converter converts the in-plane translation of the micro-actuator to out-of-plane translation of the micromirror. The conventional MEMS device has a larger range in the in-plane translation than in the out-of-plane translation. The micro-converter of the present invention allows large out-of-plane translation by converting the large in-plane translation of the micro-actuator into the large out-of-plane translation of the micromirror. Preferably, the micro-actuator is actuated by electrostatic force. The micro-actuator can be a least one comb-drive using electrostatic force. The comb-drive can generate “coming and going” in-plane motion with a short stroke. The combination of two comb-drives can be used as a micro-actuator, wherein two comb-drives generate in-plane revolution and the in-plane revolution is converted to large linear in-plane translation. Then, the large linear in-plane translation can be converted to the large out-of-plane translation by the micro-converter. The micro-converter comprises at least one beam and at least one hinge. All structures in the MEMS unit including the micromirror, micro-actuator, and the micro-converter can be fabricated on the same substrate by microfabrication technology and the micro-actuator can be controlled by applied voltage. 
         [0007]    The general principle, structure and methods for making the discrete motion control of MEMS device are disclosed in U.S. patent applicaton Ser. No. 10/872,241 filed Jun. 18, 2004, U.S. patent applicaton Ser. No. 11/072,597 filed Mar. 4, 2005, U.S. patent application Ser. No. 11/347,590 filed Feb. 4, 2006, U.S. patent applicaton Ser. No. 11/369,797 filed Mar. 6, 2006, U.S. patent application Ser. No. 11/426,565 filed Jun. 26, 2006, U.S. patent applicaton Ser. No. 11/463,875 filed Aug. 10, 2006, U.S. patent applicaton Ser. No. 11/534,613 filed Sep. 22, 2006, U.S. patent application Ser. No. 11/534,620 filed Sep. 22, 2006, U.S. patent applicaton Ser. No. 11/549,954 filed Oct. 16, 2006, U.S. patent application Ser. No. 11/609,882 filed Dec. 12, 2006, U.S. patent applicaton Ser. No. 11/685,119 filed Mar. 12, 2007, U.S. patent applicaton Ser. No. 11/693,698 filed Mar. 29, 2007, U.S. patent application Ser. No. 11/742,510 filed Apr. 30, 2007, and U.S. patent applicaton Ser. No. 11/762,683 filed Jun. 13, 2007, all of which are incorporated herein by references. 
         [0008]    The portable optical devices have a high demand to provide high quality images while maintaining compactness. When the automatic focusing system uses a single mirror having a large area size, distortion and twisting problems of the mirror can occur, which causes aberration. The present invention provides more robust and reliable automatic focusing system using a plurality of micromirrors. The MEMS unit of the present invention uses a plurality of micromirrors, a plurality of micro-actuators, and a plurality of micro-converters. The micromirrors are configured to have large out-of-plane translations. The micro-actuators are configured to have in-plane motions and make the micromirrors have out-of-plane motions. The micro-converters are configured to provide large out-of-plane motions to the micromirrors by converting the in-plane translations of the micro-actuators into the out-of-plane translations of the micromirrors. The micromirrors, the micro-actuators, and the micro-converters are fabricated on the same substrate by microfabrication technology. A plurality of comb-drives using electrostatic force can be used as in-plane micro-actuators. 
         [0009]    An automatic focusing system as one embodiment of the present invention using an MEMS unit comprises a lens unit, an image sensor, and an MEMS unit. The MEMS unit comprises a plurality of micromirrors having reflective surfaces and configured to have out-of-plane translations, a plurality of micro-actuators configured to have in-plane translations, a plurality of micro-converters configured to convert the in-plane translations of the micro-actuators to the out-of-plane translations of the micromirrors, and a substrate having a control circuitry and supporting the micromirrors, the micro-actuators, and micro-converters. The MEMS unit is positioned between the lens unit and the image sensor and configured to automatically focus an image received from the lens unit to the image sensor by adjusting the out-of-plane translations of the micromirrors. The out-of-plane translations of the micromirrors are adjusted by the control circuitry controlling the in-plane translations of the micro-actuators, wherein the in-plane translations of the micro-actuators are converted to the out-of-plane translations of the micromirrors using the micro-converters, The micromirrors, the micro-actuators, and the micro-converters are fabricated by microfabrication technology on the same substrate in order to reduce the volume of the automatic focusing system. The automatic focusing system of the present invention can have more robust and reliable automatic focusing function by using a plurality of micromirrors. 
         [0010]    The automatic focusing system further comprises an image processor in communication with the image sensor and the control circuit, wherein the image processor uses an algorithm to compare the image quality of the image data from the image sensor with focus criteria and generates a feedback signal for the control circuitry to adjust the out-of-plane translations of the micromirrors. The out-of-plane translations of the micromirrors are adjusted by the control circuitry controlling the in-plane translation of the micro-actuator by using the feedback signal from the image processor 
         [0011]    The fabrication thickness of each micromirror is less than 100 μm. The fabrication thickness of each micro-actuator is less than 100 μm. The fabrication thickness of each micro-converter is less than 100 μm. The micro-actuators are actuated by electrostatic force. The micro-actuator is a comb-drive. 
         [0012]    Each micromirror can be rotatably connected by at least one micro-converter. Instead of being connected rigidly to at least one micro-converter, each micromirror can be supported by at least one micro-converter. Each micro-actuator is rotatably connected by at least one micro-converter. In addition to having a translation, each micromirror can be configured to have a rotation about at least one axis lying on the in-plane by changing the in-plane translations of the micro-actuators. 
         [0013]    Each micromirror is configured to translate at least 100 μm. Each micromirror is configured to translate between 50 μm and 1,000 μm. 
         [0014]    The automatic focusing system further comprises a beam splitter positioned between the lens unit and the MEMS unit. Instead of using the beam splitter, the MEMS unit can be positioned obliquely with respect to an optical axis of the lens unit in the automatic focusing system such that the image received from the lens unit is focused on the image sensor. 
         [0015]    Each micro-converter comprises at least one beam and at least one hinge. 
         [0016]    Each micro-converter comprises a first beam and a second beam. A first end of the first beam is rotatably connected to the micro-actuator and a second end of the first beam is rotatably connected to the micromirror. A first end of the second beam is rotatably connected to the micromirror and a second end of the second beam is rotatably connected to the substrate. In this configuration, the micro-converter can make the micromirror have in-plane translation as well as out-of-plane translation. 
         [0017]    To avoid the in-plane translation of the micromirror, each micro-converter comprises a first beam and a second beam. A first end of the first beam is rotatably connected to the micro-actuator and a second end of the first beam is rotatably connected to a first end of the second beam. A second end of the second beam is rotatably connected to the substrate. In this configuration, the micromirror is supported by a pivot point connecting the second end of the first beam and the first end of the second beam. Each micromirror has at least one flexible member connecting the micromirror and the substrate and providing restoring force to the micromirror. 
         [0018]    The micromirrors are a Micromirror Array Lens. 
         [0019]    The focus (or image) can be shifted by the out-of-plane translations of the micromirrors. The micromirrors are configured to be tilted to compensate focus shift with respect to the image sensor. Also, the Micromirror Array Lens can change its optical axis to compensate focus shift with respect to the image sensor. Alternatively, the image processor can compensate focus shift with respect to the image sensor using a compensation algorithm. 
         [0020]    An automatic focusing system as another embodiment of the present invention using an MEMS unit comprises a lens unit, an image sensor and an MEMS unit. The MEMS comprises a micromirror having reflective surfaces and configured to have out-of-plane translation, at least one micro-actuators configured to have in-plane translation, at least one micro-converter configured to convert the in-plane translation of the micro-actuator to the out-of-plane translation of the micromirror, and a substrate having a control circuitry and supporting the micromirror, the micro-actuator, and the micro-converter. The MEMS unit is positioned between the lens unit and the image sensor and configured to automatically focus an image received from the lens unit to the image sensor by adjusting the out-of-plane translation of the micromirror. The out-of-plane translation of the micromirror are adjusted by the control circuitry controlling the in-plane translation of the micro-actuator, wherein the in-plane translation of the micro-actuator are converted to the out-of-plane translation of the micromirror using the micro-converter, The micromirror, the micro-actuator, and the micro-converter are fabricated by microfabrication technology on the same substrate in order to reduce the volume of the automatic focusing system. The automatic focusing system further comprises an image processor in communication with the image sensor and the control circuit, wherein the image processor uses an algorithm to compare the image quality of the image data from the image sensor with focus criteria and generates a feedback signal for the control circuitry to adjust the out-of-plane translation of the micromirror. The out-of-plane translation of the micromirror is adjusted by the control circuitry controlling the in-plane translation of the micro-actuator by using the feedback signal from the image processor. The micromirror is configured to translate at least 100 μm. The micromirror is configured to translate between 50 μm and 1,000 μm. The micromirror is configured to be tilted to compensate focus shift with respect to the image sensor. Also, the image processor can compensate focus shift with respect to the image sensor using a compensation algorithm. 
         [0021]    An automatic focusing system as another embodiment of the present invention using an MEMS unit comprises a lens unit, an image sensor, and an MEMS unit. The MEMS unit comprises a plurality of micromirrors having reflective surfaces and configured to have out-of-plane translations, a plurality of actuation units configured to move the micromirrors, and a substrate having a control circuitry and supporting the micromirrors and the micro-actuators. The MEMS unit is positioned between the lens unit and the image sensor and configured to automatically focus an image received from the lens unit to the image sensor by adjusting the out-of-plane translations of the micromirrors. The out-of-plane translations of the micromirrors are adjusted by the control circuitry controlling the actuation units. The micromirrors and the actuation units are fabricated by microfabrication technology on the same substrate in order to reduce the volume of the automatic focusing system. The automatic focusing system further comprises an image processor in communication with the image sensor and the control circuit, wherein the image processor uses an algorithm to compare the image quality of the image data from the image sensor with focus criteria and generates a feedback signal for the control circuitry to adjust the out-of-plane translations of the micromirrors. The out-of-plane translations of the micromirrors are adjusted by the control circuitry controlling the in-plane translations of the actuation units by using the feedback signal from the image processor. Each micromirror is configured to translate at least 100 μm. Each micromirror is configured to translate between 50 μm and 1,000 μm. 
         [0022]    The micromirrors are a Micromirror Array Lens. The focus (or image) can be shifted by the out-of-plane translations of the micromirrors. The micromirrors are configured to be tilted to compensate focus shift with respect to the image sensor. The Micromirror Array Lens changes its optical axis to compensate focus shift with respect to the image sensor. The image processor compensates focus shift with respect to the image sensor by using a compensation algorithm. 
         [0023]    Although the present invention is brief summarized herein, the full understanding of the invention can be obtained by the following drawings, detailed description, and appended claims. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0024]    These and other features, aspects, and advantages of the present invention will become better understood with reference to the accompanying drawings, wherein: 
           [0025]      FIG. 1  shows a conventional automatic focusing system using a mirror translation; 
           [0026]      FIG. 2  is a schematic diagram for a compact automatic focusing system using an MEMS unit; 
           [0027]      FIG. 3  is a schematic diagram for one embodiment of an automatic focusing system with an obliquely positioned MEMS unit; 
           [0028]      FIG. 4  is a schematic diagram of a side view of one embodiment of an MEMS unit; 
           [0029]      FIG. 5  is a schematic diagram of a side view of another embodiment of an MEMS unit; 
           [0030]      FIGS. 6A and 6B  are schematic diagrams showing how auto focusing is performed; 
           [0031]      FIG. 7  is a schematic diagram showing how auto focusing is performed when object distance is changed; 
           [0032]      FIG. 8  is a schematic diagram of an auto focusing system performing auto focusing and focus shift compensation; 
           [0033]      FIG. 9A  is a schematic diagram of a side view of one exemplary MEMS unit using a plurality of micromirrors; 
           [0034]      FIGS. 9B and 9C  are schematic diagrams of top views of exemplary arrangements of the micromirrors, micro-actuators, and micro-converters; 
           [0035]      FIG. 10  is a schematic diagram of another exemplary MEMS unit using a plurality of micromirrors; 
           [0036]      FIG. 11A  is a schematic diagram showing how MEMS units are used for auto focusing; 
           [0037]      FIG. 11B  is a schematic diagram showing how a Micromirror Array Lens are used for auto focusing; 
           [0038]      FIG. 11C  is a schematic diagram showing how a Micromirror Array Lens are used for auto focusing and focus shift compensation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]      FIG. 1  shows a conventional automatic focusing system using a mirror translation. The conventional automatic focusing system  11  uses a mirror  12  configured to be actuated by a macroscopic actuator  13 . This automatic focusing system can have many problem including bulky size, large power consumption, slow focusing time, and eventually decrease in portability. 
         [0040]      FIG. 2  is a schematic diagram for a compact automatic focusing system of the present invention using an MEMS unit. The compact automatic focusing system  21  comprises a lens unit  22 , an image sensor  23 , and an MEMS unit. Although the lens unit  22  is illustrated as a single objective lens, those skilled in the art will understand that the lens unit  22  may comprise a plurality of lenses depending upon a particular application. The MEMS unit comprises at least one micromirror  24  having a reflective surface and configured to have out-of-plane translation  25 , at least one actuation unit  26  configured to provide the micromirror  24  with out-of-plane translation  25 , and a substrate  27  having a control circuitry (not shown) and supporting the micromirror  24  and the actuation unit  26 . The micromirror  24  and the actuation unit  26  are fabricated by microfabrication technology on the same substrate  27  in order to reduce the volume of the automatic focusing system  21 . Because the out-of-plane dimension of the micromirror  24  and the actuation unit  26  is typically in order of several micrometers, the volume of the MEMS unit is negligible. The micromirror  24  should reflect incident light  28  into an image sensor  23 . Therefore, the automatic focusing system  21  requires a beam splitter  29 . Because the beam splitter  29  wastes  75 % of the incident light  28 , it is desirable to position the micromirror  25  obliquely with respect to an optical axis of the lens unit  22  instead of using the beam splitter  29 . 
         [0041]      FIG. 3  is a schematic diagram for one embodiment of an automatic focusing system with an obliquely positioned MEMS unit. The automatic focusing system  31  comprises a lens unit  32 , an image sensor  33 , and an MEMS unit. The MEMS unit comprises at least one micromirror  34  having a reflective surface and configured to have out-of-plane translation  35 , at least one actuation unit  36  configured to provide the micromirror  34  with out-of-plane translation  35 , and a substrate  37  having a control circuitry (not shown) and supporting the micromirror  34  and the actuation unit  36 . The MEMS unit is obliquely positioned between the lens unit  32  and the image sensor  33  and configured to automatically focus an image received from the lens unit  32  to the image sensor  33  by adjusting the out-of-plane translation  35  of the micromirror  34  using the actuation unit  36 . 
         [0042]      FIG. 4  is a schematic diagram of a side view of one embodiment of an MEMS unit configured to generate the large out-of-plane translation of a micromirror. The conventional MEMS devices are capable of providing a limited range of out-of-plane translation (typically only several micrometers), while the in-plane translation can be more than several millimeters. To provide the large out-of-plane translation of the micromirror, the present invention uses micro-converters configured to convert large in-plane translation to large out-of-plane translation. The MEMS unit  41  of the present invention comprises at least one micromirror  42  having a reflective surface and configured to have out-of-plane translation  43 A, at least one actuation unit  44  configured to provide the micromirror  42  with out-of-plane translation  43 A, and a substrate  45  having a control circuitry (not shown) and supporting the micromirror  42  and the actuation unit  44 . In order to increase the range of the out-of-plane translation  43 A of the micromirror  42 , the actuation unit  44  of the MEMS unit  41  of the present invention preferably comprises at least one micro-actuator  46  configured to have in-plane translation  43 B and at least one micro-converter  47  configured to convert the in-plane translation  43 B of the micro-actuator  46  to the out-of-plane translation  43 A of the micromirror  42 . Since the micro-actuator  46  can be fabricated to have large in-plane translation  43 B using conventional MEMS technologies (e.g. comb-drive device), the micromirror  42  of the present invention can have large out-of-plan translation  43 A. The out-of-plane translation  43 A of the micromirror  42  is adjusted by the control circuitry controlling the in-plane translation  43 B of the micro-actuator  46 . The micromirror  42 , the micro-actuator  46 , and the micro-converter  47  are fabricated by microfabrication technology on the same substrate  45  in order to reduce the volume of the MEMS unit  41 . 
         [0043]    The micro-converter  47  comprises at least one beam  48 A,  48 B and at least one hinge  48 C to convert the in-plane translation  43 B of the micro-actuator  46  to the out-of-translation  43 A of the micromirror  42 . 
         [0044]    In one embodiment of the present invention, each micro-converter  47  comprises a first beam  48 A and a second beam  48 B. A first end  49 A of the first beam  48 A is rotatably connected to the micro-actuator  46  and a second end  49 B of the first beam  48 A is rotatably connected to the micromirror  42 . A first end  49 C of the second beam  48 B is rotatably connected to the micromirror  42  and a second end  49 D of the second beam  48 B is rotatably connected to the substrate  45 . In this configuration, the micro-converter  47  can make the micromirror  42  have in-plane translation  43 C as well as out-of-plane translation  43 A. 
         [0045]    The MEMS unit can be configured to avoid the unnecessary in-plane translation  43 C of the micromirror  42  as shown in  FIG. 5 .  FIG. 5  is a schematic diagram of a side view of another embodiment of an MEMS unit. The MEMS unit  51  of the present invention comprises at least one micromirror  52  having a reflective surface and configured to have out-of-plane translation  53 A, at least one actuation unit  54  configured to provide the micromirror  52  with out-of-plane translation  53 A, and a substrate  55  having a control circuitry (not shown) and supporting the micromirror  52  and the actuation unit  54 . In order to increase the range of the out-of-plane translation  53 A of the micromirror  52 , the actuation unit  54  of the MEMS unit  51  of the present invention preferably comprises at least one micro-actuator  56  configured to have in-plane translation  53 B and at least one micro-converter  57  configured to convert the in-plane translation  53 B of the micro-actuator  56  to the out-of-plane translation  53 A of the micromirror  52 . Since the micro-actuator  56  can be fabricated to have large in-plane translation  53 B using conventional MEMS technologies (e.g. comb-drive device), the micromirror  52  of the present invention can have large out-of-plan translation  53 A. The out-of-plane translation  53 A of the micromirror  52  is adjusted by the control circuitry controlling the in-plane translation  53 B of the micro-actuator  56 . The micromirror  52 , the micro-actuator  56 , and the micro-converter  57  are fabricated by microfabrication technology on the same substrate  55  in order to reduce the volume of the MEMS unit  51 . 
         [0046]    The micro-converter  57  comprises at least one beam  58 A,  58 B and at least one hinge  58 C to convert the in-plane translation  53 B of the micro-actuator  56  to the out-of-translation  53 A of the micromirror  52 . 
         [0047]    Each micro-converter  57  comprises a first beam  58 A and a second beam  58 B. A first end  59 A of the first beam  58 A is rotatably connected to the micro-actuator  56  and a second end  59 B of the first beam  58 A is rotatably connected to a first end  59 C of the second beam  58 B. A second end  59 D of the second beam  58 B is rotatably connected to the substrate  55 . In this configuration, the micromirror  52  is supported by a pivot point  59 E connecting the second end  59 B of the first beam  58 A and the first end  59 C of the second beam  58 B. Each micromirror  52  has at least one flexible member  55 A connecting the micromirror  52  and the substrate  55  and providing restoring force to the micromirror  52 . The restoring force of the flexible member  55 A makes the tops of the micro-converters  57  be in contact with the bottom of the micromirror  52 . The MEMS unit  51  removes the unnecessary translation of the micromirror  52 . 
         [0048]      FIG. 5  also shows that the MEMS unit is capable of providing the micromirror with rotation as well as large out-of-plane translation. In-plane translations  53 B of a plurality of micro-actuators  56  can make the micromirror  52  have both rotation and translation. The micro-converters  57  convert the in-plane translations  53 B of the micro-actuators  56  to the rotation  53 C and out-of-plane translation  53 A of the micromirror  52 . The micro-micromirror  52  is configured to have a plurality of rotations  53 C and out-of-plane translations  53 A by adjusting an amount of the in-plane translation  53 B of each micro-actuator  56 . 
         [0049]      FIGS. 6A and 6B  are schematic diagrams showing how the auto focusing system of  FIG. 3  performs auto focusing.  FIG. 6A  is a schematic diagram of an auto focusing system  61  using a micromirror  64 , wherein the out-of-plane translation  65  of the micromirror  64  changes the focal plane of the auto focusing system  61 . The lens unit  62  makes its focus at a focal point  68 A without a micromirror. In order to provide auto focusing, a micromirror  64  is disposed obliquely with respect to an optical axis  62 A between the lens unit  62  and the image sensor  63 . The micromirror  64  is configured to have a plurality of displacements from the substrate  67  in the out-of-plane direction. When the micromirror  64  is located at a position  65 A, the focus  68 B is out of the plane of the image sensor  63 . To perform auto focusing, the micromirror  64  is moved to another position  65 B in the out-of-plane direction. Then, the micromirror  64  and the lens unit  62  make a focus  68 C on another focal plane. The position of the focal plane can be adjusted to be on the plane of the image sensor  63  by adjusting the out-of-plane translation  65  of the micromirror  64 . When the focal plane is on the plane of the image sensor  63 , auto focusing is accomplished. 
         [0050]    In order to provide focusing status, the auto focusing system  61  can further comprise an image processor (not shown) in communication with the image sensor  63  and the control circuit. The image processor uses an algorithm to compare the image quality of the image data from the image sensor  63  with focus criteria and generates a feedback signal for the control circuitry to adjust the out-of-plane translation  65  of the micromirror  64 . 
         [0051]    The micromirror  64  is not necessarily aligned with 45 degree to an image side optical axis  62 A. The angle between micromirror  64  and the image side optical axis  62 A can be varied if the geometry permits. 
         [0052]      FIG. 6B  is a schematic diagram of an auto focusing system using a curved micromirror  64 A. Similarly to the micromirror  64  in  FIG. 6A , the position of the focal plane can be adjusted to be on the plane of the image sensor  63  by adjusting the out-of-plane translation of the curved micromirror  64 A. When the focal plane is on the plane of the image sensor  63 , auto focusing is accomplished. 
         [0053]      FIG. 7  is a schematic diagram showing how auto focusing is performed when object distance is changed. When an object is located at a position  79 A, the micromirror  74  is required to have a certain position  75 A in the out-of-plane direction to make a focus  78 D on the plane of the image sensor  73 . When the object moves from the point  79 A to other position  79 B, the micromirror  74  is controlled to have out-of-plane translation  75  from one position  75 A to another position  75 B so that the focus  78 E remains on the plane of the image sensor  73 . Without changing the focal length of the lens unit  72 , the auto focusing system  71  can make its focus on the plane of the image sensor  73 . 
         [0054]    The focus (or image) can be shifted when the out-of-plane translations of the micromirror is used for auto focusing as shown in  FIGS. 6 and 7 . As an example, the auto focusing system in  FIG. 7  is considered. In the auto focusing system of  FIG. 7 , the focus is shifted from  78 D to  78 E due to auto focusing. To compensate this focus shift, the micromirror  74  is configured to have rotation as well as out-of-plane translation.  FIG. 8  is a schematic diagram of an auto focusing system performing auto focusing and focus shift compensation. The lens unit  82  makes its focus  88 A without a micromirror. In order to provide auto focusing and focus shift compensation, a micromirror  84  is disposed obliquely with respect to an optical axis  82 A between the lens unit  82  and an image sensor  83 . The micromirror  84  is configured to have a plurality of displacements from the substrate  87  in the out-of-plane direction  85  and a plurality of rotations  85 C. The micromirror  84  has out-of-plane translation  85  to make its focus on the plane of the image sensor  83  and has rotation  85 C to compensate focus shift. In this case, the focus is changed from  88 A to  88 B. The MEMS unit of the present invention can provide the micromirror  84  with both out-of-plane translation  85  and rotation  85 C as shown in  FIG. 5 . 
         [0055]    When an automatic focusing system uses a single mirror having a large area size, distortion and twisting problems of the mirror can occur, which causes aberration. The MEMS unit of the present invention can provide more robust and reliable automatic focusing system by using a plurality of micromirrors, wherein each micromirror is configured to provide large out-of-plane translation. Each micromirror and its actuation unit can have a configuration shown in  FIG. 4  or  FIG. 5 .  FIG. 9A  is a schematic diagram of a side view of one exemplary MEMS unit using a plurality of micromirrors. The MEMS unit  91  comprises a plurality of micromirrors  92  having reflective surfaces and configured to have out-of-plane translations  93 , a plurality of micro-actuators  94  configured to have in-plane translations  95 , a plurality of micro-converters  96  configured to convert the in-plane translations  95  of the micro-actuators  94  to the out-of-plane translations  93  of the micromirrors  92 , and a substrate  97  having a control circuitry and supporting the micromirrors  92 , the micro-actuators  94 , and micro-converters  96 . The micromirrors  92 , the micro-actuators  94 , and the micro-converters  96  are fabricated by microfabrication technology on the same substrate  97  in order to reduce the volume of the automatic focusing system. Although the MEMS unit  91  comprising a plurality of micromirrors  92  is illustrated by using a plurality of MEMS units  41  of  FIG. 4 , those skilled in the art will understand that the MEMS unit  91  using a plurality micromirrors  92  can be made with any combination of micro-actuators and micro-converters including that of the  FIG. 5  depending upon a particular application. The micro-actuators  94  and the micro-converters  96  that make micromirrors  92  move are disposed over the substrate  97  such that the motion of each micromirror does not interfere with the motions of other micromirrors.  FIGS. 9B and 9C  show schematic diagrams of top views of exemplary arrangements of the micromirrors  92 , micro-actuators  94 , and micro-converters  96 . The point or area  98  on each micromirror  92  can be a connecting pivot point or area of  FIG. 4  or a contacting pivot point or area of  FIG. 5  between the micromirror  92  and the micro-converter  96 . 
         [0056]      FIG. 10  is a schematic diagram of another exemplary MEMS unit using a plurality of micromirrors. The MEMS unit  101  comprises a plurality of micromirrors  102  having reflective surfaces and configured to have out-of-plane translations  103 , a plurality of actuation units  104  configured to provide the micromirrors  102  with out-of-plane translations  103 , and a substrate  105  having a control circuitry (not shown) and supporting the micromirrors  102  and the actuation units  104 . The micromirrors  102  and the actuation units  104  are fabricated by microfabrication technology on the same substrate  105  in order to reduce the volume of the automatic focusing system. Each actuation unit  104  is configured to provide a corresponding micromirror  102  with out-of-plane translation  103 . Each actuation unit  104  comprises a plurality of segmented electrodes  104 A disposed on the substrate surface  105  and electronically coupled to the control circuitry for activating the segmented electrodes  104 A selectively, at least one flexible structure  104 B for connecting the micromirror  102  and the substrate  105  and providing restoring force to the micromirror  102 , and at least one pillar structure  104 C for supporting the flexible structure  104 B and providing connection between the substrate  105  and the flexible structure  104 B. The actuation unit  104  further comprises at least one top electrode plate  104 D disposed underneath the micromirror  102 . The activated segment electrodes  104 A of each actuation unit  104  attract the micromirror  102  in the out-of-plane direction  103 . The top electrode plate  104 D increases the electrostatic force induced between the segmented electrodes  104 A and the top electrode plate  104 D by reducing the electrostatic gap between the electrodes. Also, the structural deformation of the micromirror  102  is reduced by connecting the micromirror  102  to the top electrode plate  104 D using at least one top electrode post  104 E. 
         [0057]    The actuation unit  104  of the present invention can provide the micromirrors  102  with rotation as well. The rotation and translation of each micromirror  102  is controlled by a selected set of activated segmented electrodes  104 A. The MEMS units  91 A,  91 B, and  101  of the present invention provide robust and reliable auto focusing systems by using a plurality of micromirrors, wherein each micromirror is configured to provide large out-of-plane translation. 
         [0058]    The micromirrors of  FIGS. 9B ,  9 C, and  10  are a Micromirror Array Lens forming at least one optical surface profile. The optical surface profile of the Micromirror Array Lens can be fixed or varied during auto focusing. 
         [0059]      FIG. 11A  shows how MEMS units in  FIGS. 9B ,  9 C, and  10  are used for auto focusing. The automatic focusing system  111  comprises a lens unit  112 , an image sensor  113 , and an MEMS unit. The MEMS unit comprises a plurality of micromirrors  114  having reflective surfaces and configured to have out-of-plane translations  115 , a plurality of micro-actuators (not shown) configured to have in-plane translations, a plurality of micro-converters (not shown) configured to convert the in-plane translations of the micro-actuators to the out-of-plane translations  115  of the micromirrors  114 , and a substrate  116  having a control circuitry (not shown) and supporting the micromirrors  114 , the micro-actuators, and micro-converters. The MEMS unit is positioned between the lens unit  112  and the image sensor  113  and configured to automatically focus an image received from the lens unit  112  to the image sensor  113  by adjusting the out-of-plane translations  115  of the micromirrors  114 . The out-of-plane translations  115  of the micromirrors  114  are adjusted by the control circuit controlling the in-plane translations of the micro-actuators, wherein the in-plane translations of the micro-actuators are converted to the out-of-plane translations of the micromirrors using the micro-converters. The micromirrors  114 , the micro-actuators, and the micro-converters are fabricated by microfabrication technology on the same substrate  116  in order to reduce the volume of the automatic focusing system  111 . 
         [0060]    The out-of-plane translations  115  of the micromirrors  114  change the focal plane of the auto focusing system  111 . The lens unit  112  makes its focus at a focal point  117 A without a micromirror. In order to provide auto focusing, an array of the micromirrors  114  are disposed obliquely with respect to an optical axis  112 A between the lens unit  112  and the image sensor  113 . Each micromirror  114  is configured to have a plurality of displacements from the substrate  116  in the out-of-plane direction. When the array of the micromirrors  114  is located at a position  115 A, the focus  117 B is out of the plane of the image sensor  113 . To perform auto focusing, the array of the micromirrors  114  is moved to another position  115 B in the out-of-plane direction  115 . Then, the array of the micromirrors  114  and the lens unit  112  make a focus  117 C on another focal plane. The position of the focal plane can be adjusted to be on the plane of the image sensor  113  by adjusting the out-of-plane translation of the array of the micromirror  114 . When the focal plane is on the plane of the image sensor  113 , auto focusing is accomplished. 
         [0061]    In order to provide focusing status, the auto focusing system  111  can further comprise an image processor (not shown) in communication with the image sensor  113  and the control circuit. The image processor uses an algorithm to compare the image quality of the image data from the image sensor  113  with focus criteria and generates a feedback signal for the control circuitry to adjust the out-of-plane translations  115  of the micromirrors  114 . 
         [0062]    The array of the micromirrors  114  is not necessarily aligned with 45 degree to an image side optical axis  112 A. The angle between the array of the micromirrors  114  and the image side optical axis  112 A can be varied if the geometry permits. 
         [0063]      FIG. 11B  is a schematic diagram showing how a Micromirror Array Lens  114 A are used for auto focusing. Similarly to the array of the micromirrors  114  in  FIG. 11A , the position of the focal plane can be adjusted to be on the plane of the image sensor  113  by adjusting the out-of-plane translation  115  of the Micromirror Array Lens  114 A. When the focal plane is on the plane of the image sensor  113 , auto focusing is accomplished. 
         [0064]    The focus can be shifted when the out-of-plane translation of the micromirror is used for auto focusing as shown in  FIGS. 11A and 11B . The Micromirror Array Lens can compensate focus shift by changing its optical axis.  FIG. 11C  is a schematic diagram showing how a Micromirror Array Lens are used for auto focusing and focus shift compensation. Since the Micromirror Array Lens itself has an ability to change its optical axis, the auto focusing system with the Micromirror Array Lens  114 B can change its focal length by out-of-plane translation  115  of the Micromirror Array Lens  114 B and compensate focus shift by the optical axis change of the Micromirror Array Lens  114 B. Without focus shift compensation, the Micromirror Array Lens  114 B makes its focus at the position  117 C. Using the optical axis change of the Micromirror Array Lens  114 B, the Micromirror Array Lens  114 B makes its focus at the position  117 D, wherein both auto focusing and focus shift compensation are achieved simultaneously. 
         [0065]      FIG. 11D  shows how MEMS units in  FIGS. 9B ,  9 C, and  10  and curved surface mirror in  FIG. 6B  are used for auto focusing. The automatic focusing system  111  comprises a lens unit  112 , an image sensor  113 , and an MEMS unit. The MEMS unit comprises a plurality of micromirrors  114  having curved reflective surfaces and configured to have out-of-plane translations  115 , a plurality of micro-actuators (not shown) configured to have in-plane translations, a plurality of micro-converters (not shown) configured to convert the in-plane translations of the micro-actuators to the out-of-plane translations  115  of the micromirrors  114 , and a substrate  116  having a control circuitry (not shown) and supporting the micromirrors  114 , the micro-actuators, and micro-converters. The MEMS unit is positioned between the lens unit  112  and the image sensor  113  and configured to automatically focus an image received from the lens unit  112  to the image sensor  113  by adjusting the out-of-plane translations  115  of the micromirrors  114 . The out-of-plane translations  115  of the micromirrors  114  are adjusted by the control circuit controlling the in-plane translations of the micro-actuators, wherein the in-plane translations of the micro-actuators are converted to the out-of-plane translations of the micromirrors using the micro-converters. The micromirrors  114 , the micro-actuators, and the micro-converters are fabricated by microfabrication technology on the same substrate  116  in order to reduce the volume of the automatic focusing system  111 . 
         [0066]    The out-of-plane translations  115  of the micromirrors  114  change the focal plane of the auto focusing system  111 . The lens unit  112  makes its focus at a focal point  117 A without a micromirror. In order to provide auto focusing, an array of the micromirrors  114  are disposed obliquely with respect to an optical axis  112 A between the lens unit  112  and the image sensor  113 . Each micromirror  114  is configured to have a plurality of displacements from the substrate  116  in the out-of-plane direction. When the array of the micromirrors  114  is located at a position  115 A, the focus  117 B is out of the plane of the image sensor  113 . To perform auto focusing, the array of the micromirrors  114  is moved to another position  115 B in the out-of-plane direction  115 . Then, the array of the micromirrors  114  and the lens unit  112  make a focus  117 C on another focal plane. The position of the focal plane can be adjusted to be on the plane of the image sensor  113  by adjusting the out-of-plane translation of the array of the micromirror  114  other than by changing the surface profile of the array of the micromirrors  114 . When the focal plane is on the plane of the image sensor  113 , auto focusing is accomplished. 
         [0067]    In order to provide focusing status, the auto focusing system  111  can further comprise an image processor (not shown) in communication with the image sensor  113  and the control circuit. The image processor uses an algorithm to compare the image quality of the image data from the image sensor  113  with focus criteria and generates a feedback signal for the control circuitry to adjust the out-of-plane translations  115  of the micromirrors  114 . 
         [0068]    The array of the micromirrors  114  is not necessarily aligned with 45 degree to an image side optical axis  112 A. The angle between the array of the micromirrors  114  and the image side optical axis  112 A can be varied if the geometry permits. 
         [0069]    The general principle and methods for making the Micromirror Array Lens are disclosed in U.S. Pat. No. 6,970,284 issued Nov. 29, 2005 to Kim, U.S. Pat. No. 7,031,046 issued Apr. 18, 2006 to Kim, U.S. Pat. No. 6,934,072 issued Aug. 23, 2005 to Kim, U.S. Pat. No. 6,934,073 issued Aug. 23, 2005 to Kim, U.S. Pat. No. 7,161,729 issued Jan. 09, 2007, U.S. Pat. No. 6,999,226 issued Feb. 14, 2006 to Kim, U.S. Pat. No. 7,095,548 issued Aug. 22, 2006 to Cho, U.S. patent applicaton Ser. No. 10/893,039 filed Jul. 16, 2004, U.S. patent application Ser. No. 10/983,353 filed Nov. 8, 2004, U.S. patent applicaton Ser. No. 11/076,616 filed Mar. 10, 2005, and U.S. patent applicaton Ser. No. 11/426,565 filed Jun. 26, 2006, all of which are incorporated herein by references. 
         [0070]    Also the general properties of the Micromirror Array Lens are disclosed in U.S. Pat. No. 7,057,826 issued Jun. 6, 2006 to Cho, U.S. Pat. No. 7,173,653 issued Feb. 06, 2007, U.S. Pat. No. 7,215,882 issued May 8, 2007 to Cho, U.S. patent applicaton Ser. No. 10/979,568 filed Nov. 2, 2004, U.S. patent applicaton Ser. No. 11/218,814 filed Sep. 2, 2005, U.S. patent application Ser. No. 11/359,121 filed Feb. 21, 2006, U.S. patent applicaton Ser. No. 11/382,273 filed May 9, 2006, and U.S. patent applicaton Ser. No. 11/429,034 filed May 5, 2006, and its application are disclosed in U.S. Pat. No. 7,077,523 issued Jul. 18,  2006  to Seo, U.S. Pat. No. 7,068,416 issued Jun. 27, 2006 to Gim, U.S. patent applicaton Ser. No. 10/914,474 filed Aug. 9, 2004, U.S. patent application Ser. No. 10/934,133 filed Sep. 3, 2004, U.S. patent applicaton Ser. No. 10/979,619 filed Nov. 2, 2004, U.S. patent application Ser. No. 10/979,624 filed Nov. 2, 2004, U.S. patent applicaton Ser. No. 11/076,688 filed Mar. 10, 2005, U.S. patent applicaton Ser. No. 11/208,114 filed Aug. 19, 2005, U.S. patent application Ser. No. 11/208,115 filed Aug. 19,  2005 , U.S. patent applicaton Ser. No. 11/382,707 filed May 11, 2006, U.S. patent application Ser. No. 11/419,480 filed May 19, 2006, U.S. patent applicaton Ser. No. 11/423,333 filed Jun. 9, 2006, and U.S. patent applicaton Ser. No. 11/933,105 filed Oct. 31, 2007, all of which are incorporated herein by references. 
         [0071]    While the invention has been shown and described with reference to different embodiments thereof, it will be appreciated by those skills in the art that variations in form, detail, compositions and operation may be made without departing from the spirit and scope of the invention as defined by the accompanying claims.