Abstract:
A microelectromechanical systems (MEMS) scanner is provided. The MEMS scanner includes: a stationary frame; a first movable stage disposed inside the stationary frame and suspended on the stationary frame so as to pivot and vibrate around a virtual center shaft; a second movable stage disposed inside the first movable stage and suspended on the first movable stage so as to pivot and vibrate around the center shaft; and an actuator providing a driving force used to pivot and vibrate the first movable stage.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims priority from Korean Patent Application No. 10-2007-0107433, filed on Oct. 24, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Apparatuses consistent with the present invention relate to a microelectromechanical systems (MEMS) scanner, and more particularly, to a MEMS scanner in which a mirror is separated from an actuator and is indirectly driven. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, researches on MEMS devices fabricated by semiconductor processes have been actively performed in the technical fields of displays, printers, precision measurement, and precision processing. For example, with regard to a display in which light incident from a light source is scanned in a predetermined screen region and an image is realized, or with regard to a scanner in which light is scanned in a predetermined screen region and reflected light is received and image information is read, a MEMS device has been highlighted for use as an optical scanner. 
         [0006]    In particular, as the printing technology has advanced, high-speed, silentious, and small and light printers are required. Thus, one general solution in this regard is to replace a polygonal mirror and an f-O optical system, which are used in a laser scanning unit (LSU) of a related art printer, with a MEMS scanner and arcsine mirror. In addition, such MEMS scanner can be manufactured to have a small size by silicon semiconductor processes, is suitable for mass production, and the manufacturing costs are low. 
         [0007]    A related art electromagnetic MEMS scanner may be classified into a moving coil type electromagnetic MEMS scanner and a moving magnet type electromagnetic MEMS scanner. In the moving coil type electromagnetic MEMS scanner, a coil is attached to a mirror and a magnet is disposed outside of the mirror. The moving coil type electromagnetic MEMS scanner is suitable for small-sized printers. However, a manufacturing process of the same is complicated, the mirror is deformed by thermal deformation of the coil when it operates, and it is not easy to keep high flatness of a reflection surface. In the moving magnet type electromagnetic MEMS scanner, the magnet is attached to the mirror and the coil is disposed outside of the mirror, a manufacturing process of the same is comparatively simple. However, the mass of an operating portion increases. Thus, the moving magnet type electromagnetic MEMS scanner is not suitable for small-sized printers, and mass eccentricity and stress concentration occur. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a MEMS scanner having an improved structure in which a mirror is separated from an actuator and is indirectly driven. 
         [0009]    According to an aspect of the present invention, there is provided a MEMS scanner comprising: a stationary frame; a first movable stage disposed inside the stationary frame and suspended on the stationary frame so as to pivot and vibrate around a virtual center shaft; a second movable stage disposed inside the first movable stage and suspended on the first movable stage so as to pivot and vibrate around the virtual center shaft; and an actuator providing a driving force used to pivot and vibrate the first movable stage. 
         [0010]    The first movable stage may be directly driven by the actuator and the second movable stage may be indirectly driven by driving the first movable stage. 
         [0011]    A reflection surface from which incident light is reflected may be provided on at least one of an upper surface and a bottom surface of the second movable stage. 
         [0012]    The stationary frame, the first movable stage and the second movable stage may be formed on one silicon substrate as one body. 
         [0013]    The stationary frame and the first movable stage may be connected to each other by at least one first tortional spring disposed therebetween and the first movable stage and the second movable stage may be connected to each other by at least one second tortional spring disposed therebetween. The first tortional spring may have larger rigidity than the second tortional spring. 
         [0014]    The first tortional spring and the second tortional spring may be placed on the center axis and have a shape of a bar extending along the center axis. The first tortional spring may have a larger thickness than the second tortional spring. 
         [0015]    The first tortional spring may have a folded shape. In this case, two first tortional springs may be provided at each of two facing edges of the first movable stage or at each of four edges of the first movable stage. 
         [0016]    The actuator may be an electromagnetic actuator comprising permanent magnets and an electromagnet. 
         [0017]    The permanent magnets may be attached to each of both sides of the bottom surface of the first movable stage. In this case, the permanent magnets may be attached to the first movable stage so that the same magnetic poles point in the same direction. 
         [0018]    The electromagnet may comprise a core and a coil wound around the core, and both ends of the core may face each other and may be spaced apart from each of the permanent magnets by a predetermined distance. 
         [0019]    According to another aspect of the present invention, the actuator may be an electrostatic actuator comprising movable combs and stationary combs. In this case, the stationary combs may be disposed at different heights from those of the moveable combs in a vertical direction so that an electrostatic force is applied to the movable combs in the vertical direction. 
         [0020]    The actuator may further comprise stationary stages disposed under both sides of the first movable stage and supporting the stationary combs. 
         [0021]    The movable combs may protrude from both sides of the first movable stage in a horizontal direction and the stationary combs may protrude from one side of each of the stationary stages in the horizontal direction, and may be disposed not to overlap the movable combs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The above and other aspects of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings, in which: 
           [0023]      FIG. 1  is a perspective view illustrating a MEMS scanner according to an exemplary embodiment of the present invention; 
           [0024]      FIG. 2  is a sectional view of the MEMS scanner taken along line A-A′ of  FIG. 1 , according to an exemplary embodiment of the present invention; 
           [0025]      FIG. 3  illustrates an equivalent system for vibrating a first movable stage and a second movable stage of the MEMS scanner of  FIG. 1 , according to an exemplary embodiment of the present invention; 
           [0026]      FIG. 4  is a perspective view illustrating a MEMS scanner according to another exemplary embodiment of the present invention; 
           [0027]      FIG. 5  is a sectional view of the MEMS scanner taken along line B-B′ of  FIG. 4 , according to an exemplary embodiment of the present invention; 
           [0028]      FIGS. 6 and 7  are plane views illustrating modified examples of the MEMS scanner of  FIG. 1 , according to an exemplary embodiment of the present invention and 
           [0029]      FIG. 8  is a plane view illustrating a modified example of the MEMS scanner of  FIG. 4 , according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0030]    Hereinafter, the present invention will be described in detail by explaining exemplary embodiments of the invention with reference to the attached drawings. Like reference numerals in the drawings denote like elements. 
         [0031]      FIG. 1  is a perspective view illustrating a MEMS scanner according to an exemplary embodiment of the present invention, and  FIG. 2  is a sectional view of the MEMS scanner taken along line A-A′ of  FIG. 1 . 
         [0032]    Referring to  FIGS. 1 and 2 , the MEMS scanner according to an exemplary embodiment of the present invention comprises a stationary frame  110 , a first movable stage  120 , a second movable stage  130 , and an electromagnetic actuator  140 . 
         [0033]    The stationary frame  110  is plate-shaped and has a predetermined thickness. The first movable stage  120  is disposed inside the stationary frame  110 . The first movable stage  120  is suspended on the stationary frame  110  so as to pivot and vibrate around a virtual center shaft C by a predetermined angle. To this end, the stationary frame  110  and the first movable stage  120  may be connected to each other by a first tortional spring  122  disposed therebetween. The first tortional spring  122  may be placed on the virtual center shaft C and may have the shape of a bar extending along the virtual center shaft C. 
         [0034]    The second movable stage  130  is disposed inside the first movable stage  120  and is suspended on the first movable stage  120  so as to pivot and vibrate around the virtual center shaft C at a predetermined angle. To this end, the first movable stage  120  and the second movable stage  130  may be connected to each other by a second tortional spring  132  disposed therebetween. The second tortional spring  132  may be placed on the virtual center shaft C and may have the shape of a bar extending along the virtual center shaft C. 
         [0035]    A reflection surface  135  from which incident light is reflected, that is, a mirror, may be provided on the upper surface of the second movable stage  130 . In addition, as will be described later, the reflection surface  135  may be provided on the bottom surface of the second movable stage  130 . 
         [0036]    The stationary frame  110 , the first movable stage  120 , the second movable stage  130 , the first tortional spring  122  and the second tortional spring  132  may be formed on one silicon wafer as one body. As such, a manufacturing process of the MEMS scanner may be simplified. 
         [0037]    The electromagnetic actuator  140  pivots and vibrates the first movable stage  120  and may comprise permanent magnets  141  and  142 , and an electromagnet  144  disposed therebelow. The permanent magnets  141  and  142  may be attached to two opposite sides of the bottom surface of the first movable stage  120 , respectively. The permanent magnets  141  and  142  may be attached to the first movable stage  120  so that the same magnetic poles, for example, the S poles of the permanent magnets  141  and  142 , point in the same direction, for example, a downward direction. The electromagnet  144  may comprise a core  145  and a coil  146  wound around the middle portion of the core  145 . Two ends  145   a  and  145   b  of the core  145  may face each other and be spaced apart from each of the permanent magnets  141  and  142  by a predetermined distance. 
         [0038]    In the electromagnetic actuator  140  having the above structure, when an alternating current (AC) voltage having a predetermined frequency is applied to the coil  146  from an electric power source  147 , polarities of both ends  145   a  and  145   b  of the core  145  vary according to the direction of current. As such, due to a mutual attraction force or a repulsive force formed between the permanent magnets  141  and  142  and both ends  145   a  and  145   b  of the core  145 , the first movable stage  120  pivots and vibrates around the virtual center shaft C with a predetermined frequency. Pivoting and vibrating of the first movable stage  120  causes pivoting and vibrating of the second movable stage  130  suspended on the first movable stage  120 , as will be described later. In other words, the first movable stage  120  is directly driven by the electromagnetic actuator  140 , and the second movable stage  130  having the reflection surface  135  pivots and vibrates indirectly due to pivoting and vibrating of the first movable stage  120 . 
         [0039]    As described above, in the MEMS scanner illustrated in  FIG. 1 , since a coil, a magnet, or the like is not attached to the second movable stage  130  having the reflection surface  135 , the mass of the second movable stage  130  can be minimized. As such, the size of the second tortional spring  132  supporting the second movable stage  130  can be reduced, and stress to be applied thereto can also be reduced. Thus, the structural reliability of the MEMS scanner can be improved, and the maximum rotation speed of the second movable stage  130  can also be increased. 
         [0040]    The permanent magnets  141  and  142  are attached to the first movable stage  120 , as described above. Thus, the first tortional spring  122  supporting the first movable stage  120  may have sufficiently larger rigidity than the rotation rigidity of the first movable stage  120  so as to prevent a damage that may occur when the permanent magnets  141  and  142  are attached to the first movable stage  120  and to be solid with respect to an external shock or the like. The first tortional spring  122  supporting the first movable stage  120  may have larger rigidity than that of the second tortional spring  132 . Specifically, the width of the first tortional spring  122  may be larger than that of the second tortional spring  132 . As such, the resonant frequency of the first tortional spring  122  is higher than that of the second tortional spring  132 . 
         [0041]    Since a coil, a magnet, or the like is not attached to the second movable stage  130 , the reflection surface  135 , that is, a mirror, may be provided on both the upper surface and the bottom surface of the second movable stage  130 . As such, the number of scanners used in an LSU is reduced by half, the size of the LSU is reduced, and manufacturing costs thereof can be reduced. 
         [0042]      FIG. 3  illustrates an equivalent system for vibrating a first movable stage and a second movable stage of the MEMS scanner of  FIG. 1 . 
         [0043]    As illustrated in  FIG. 3 , the MEMS scanner of  FIG. 1  may be equivalent to a dynamic model having the degree of freedom (DOF) equal to 2. Specifically, the first movable stage  120  and the second movable stage  130 , which are movable elements, may be modeled as mass m 1  and m 2 , respectively, and respective rotation displacement may be indicated by x 1  and x 2 . The first tortional spring  122  and the second tortional spring  132  may be modeled with rotation rigidity k 1  and k 2 , respectively. On the other hand, a damping element of the first movable stage  120  and the second movable stage  130  is small and thus may be neglected. 
         [0044]    Referring to  FIG. 3 , when an external force F is applied to the first movable stage  120  corresponding to mass m 1 , the first movable stage  120  moves by the displacement x 1 . A value which is obtained by multiplying the displacement x 1  of the first movable stage  120  by the rotation rigidity k 2  of the second tortional spring  130  acts as a vibration force on the second movable stage  130  corresponding to mass m 2 . In this case, when a vibration force is applied to the first movable stage  120  with the resonant frequency of the second movable stage  130  through the electromagnetic actuator  140 , the second movable stage  130  having the reflection surface  135  causes resonance and moves by the maximum displacement x 2 . 
         [0045]      FIG. 4  is a perspective view illustrating a MEMS scanner according to another exemplary embodiment of the present invention, and  FIG. 5  is a sectional view of the MEMS scanner taken along line B-B′ of  FIG. 4 . 
         [0046]    Referring to  FIGS. 4 and 5 , the MEMS scanner according to another exemplary embodiment of the present invention comprises a stationary frame  110 , a first movable stage  120 , a second movable stage  130 , and an electrostatic actuator  240 . 
         [0047]    The first movable stage  120  is disposed inside the stationary frame  110  and is suspended by a first tortional spring  122  on the stationary frame  110  so as to pivot and vibrate around a virtual center shaft C by a predetermined angle. The second movable stage  130  is disposed inside the first movable stage  120 , and is suspended by a second tortional spring  132  on the first movable stage  120  so as to pivot and vibrate around the virtual center shaft C by a predetermined angle. A reflection surface  135  on which incident light is reflected, that is, a mirror, may be provided on both the upper surface and the bottom surface of the second movable stage  130 . The stationary frame  110 , the first movable stage  120 , the second movable stage  130 , the first tortional spring  122  and the second tortional spring  132  are the same as those of the MEMS scanner of  FIG. 1 , and thus a detailed description thereof will be omitted. 
         [0048]    The electrostatic actuator  240  pivots and vibrates the first movable stage  120 , and may comprise movable combs  242  provided on the first movable stage  120  and stationary combs  244  formed on stationary stages  246 . The movable combs  242  may protrude from two opposite sides of the first movable stage  120  in a horizontal direction. The stationary stages  246  are disposed under the two opposite sides of the first movable stage  120 , and the stationary combs  244  protrude from two sides of the stationary stages  246  in a horizontal direction, and are disposed not to overlap the movable combs  242 . The stationary combs  244  are disposed at different heights from the moveable combs  242  so that an electrostatic force is applied to the movable combs  242  in a vertical direction. 
         [0049]    In the electrostatic actuator  240  having the above structure, an electrostatic force is applied to the movable combs  242  in a vertical direction according to a difference between voltages applied to the movable combs  242  and the stationary combs  244 , and the first movable stage  120  pivots and vibrates around the virtual center shaft C according to the direction of the electrostatic force. Pivoting and vibrating of the first movable stage  120  causes pivoting and vibrating of the second movable stage  130  suspended on the first movable stage  120 . In other words, the first movable stage  120  may be directly driven by the electrostatic actuator  240 , and the second movable stage  130  having the reflection surface  135  may be indirectly driven by pivoting and vibrating of the first movable stage  120 . 
         [0050]      FIGS. 6 and 7  are plane views illustrating modified examples of the MEMS scanner of  FIG. 1 , and  FIG. 8  is a plane view illustrating a modified example of the MEMS scanner of  FIG. 4 . 
         [0051]    Referring to  FIGS. 6 and 7 , in the MEMS scanner of  FIG. 1 , a first tortional spring  124  connecting the stationary frame  110  and the first movable stage  120  may have a folded shape. Two first tortional springs  124  may be provided at each of two facing edges of the first movable stage  120 , as illustrated in  FIG. 6 , or two first tortional springs  124  may be provided at each of four edges of the first movable stage  120 , as illustrated in  FIG. 7 . 
         [0052]    Referring to  FIG. 8 , even in the MEMS scanner of  FIG. 4 , a first tortional spring  124  connecting the stationary frame  110  and the first movable stage  120  may have a folded shape. Two first tortional springs  124  may be provided at each of four edges of the first movable stage  120  or only at each of two facing edges of the first movable stage  120 . When two first tortional springs  124  are provided at each of four edges of the first movable stage  120 , as illustrated in  FIG. 8 , the movable combs  242  of the electrostatic actuator  240  may be disposed between two first tortional springs  124 . 
         [0053]    As described above, when the first tortional spring  122  has a folded shape, the first movable stage  120  can be more stably and firmly supported such that structural reliability is improved. 
         [0054]    While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.