Patent Publication Number: US-2005128438-A1

Title: Actuator for improvement of resolution

Description:
This application claims priority under 35 U.S.C. 119(a) on Korean Patent Applications No. 89943/2003 filed Dec. 11, 2003; No. 37917/2004 filed May 27, 2004; No. 37918/2004 filed May 27, 2004; No. 39695/2004 filed Jun. 1, 2004; and No. 42293/2004 filed Jun. 9, 2004 all of which are herein incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an actuator for improving the resolution in a projection-type image display device.  
      2. Description of the Related Art  
      Recently, display devices tend to be lightweight, slim and large-sized. Specifically, large-screen display devices have become important in the display fields. With the advent of digital broadcasting, a projection-type display device requires a high resolution.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to an actuator for improving resolution that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
      An object of the present invention is to provide an actuator for effectively improving the resolution of a projection-type display device.  
      Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by reference to the written description and appended drawings of the present application.  
      To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an actuator is provided for improving the resolution in an image display device which includes: a fixing member; a rotating member rotatably coupled to the fixing member; a displacement plate fixed to the rotating member and on which a light is incident; an engaging member formed on the fixing member, for elastically supporting the rotating member; and a driving unit for driving the rotating member.  
      In another aspect of the present invention, the actuator for improving the resolution includes: a fixing member disposed in an optical path; a rotating member rotatably coupled to the fixing member, the rotating member having a rotation center shaft disposed substantially perpendicular to the optical path; a displacement plate fixed to the rotating member; an engaging member for elastically supporting the rotation center shaft; and a driving unit for driving the rotating member.  
      In a further aspect of the present invention, the actuator for improving the resolution includes: a fixing member; a rotating member rotatably coupled to the fixing member; a light transmitting element fixed to the rotating member; an engaging member for elastically supporting the rotating member, thereby allowing free rotation of the rotating member relative to the fixing member; a coil and an iron fragment disposed on both sides of the rotating member; and a dipole magnet disposed on both sides of the fixing member and opposing the coil.  
      In still a further aspect of the present invention, the actuator for improving the resolution includes: a fixing member; a rotating member rotatably coupled to the fixing member; a light transmitting element fixed to the rotating member; a coil and an iron fragment provided at either the fixing member or the rotating member; and a dipole magnet provided at the other of the fixing member or the rotating member.  
      It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory in nature and are not intended to limit the scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein:  
       FIG. 1  is a view illustrating a display device used in conjunction with the resolution improving apparatus of the present invention;  
       FIG. 2  is a view illustrating the display device used in conjunction with the resolution improving apparatus of the present invention;  
      FIGS.  3 ( a )- 3 ( c ) are views illustrating examples of an operation of displacement plate in the display device of  FIGS. 1 and 2  according to the present invention;  
       FIG. 4  is a view illustrating an operation principle of the displacement plate acting as an image displacement unit in the display device of  FIGS. 1 and 2  according to the present invention;  
      FIGS.  5 ( a )- 5 ( c ) and  6 ( a )- 6 ( b ) are views illustrating different examples of a displacement of light projected onto a screen depending on the motion of a displacement plate in the display device according to the present invention;  
      FIGS.  7 ( a ) and  7 ( b ) are respectively, examples of displayable views of a first image and a second image using the display device of  FIGS. 1 and 2  according to the present invention;  
       FIG. 8  is a perspective view of an actuator for improving the resolution of the display device according to the present invention;  
       FIG. 9  is an exploded perspective view of the actuator shown in  FIG. 8 ;  
       FIG. 10  is a bottom exploded perspective view of the rotating member used in the actuator according to the present invention;  
       FIG. 11  is an en exploded perspective view of the fixing member used in the actuator according to the present invention;  
       FIG. 12  is a view of the rotating member containing a coil holder according to the present invention;  
       FIG. 13  is a view showing the use of an iron fragment formed at a side of the rotating member according to the present invention;  
       FIG. 14  is a view illustrating a position of the iron fragment with respect to the magnet; and  
       FIG. 15  is a view of a projection television system containing the resolution improving apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Reference will now be made to detailed embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
      A resolution is the number of pixels per square inch on a display device. That is, the resolution is used as a scale representing precision in displaying an image.  
      In order to improve the resolution, a conventional display device uses a physical method of increasing the number of pixels. However, the present invention improves the resolution by using human&#39;s visual characteristics.  
      According to the present invention, an image can be viewed at a more improved resolution compared with an actual physical resolution, thereby obtaining the same effect that the resolution is physically improved.  
      Although described below in detail, an image signal corresponding to one frame is split into sub images, e.g., a first image signal and a second image signal. The first image signal and the second signal are respectively displayed as a first image and a second image at respective first and second positions of a screen in sequence, such that a viewer feels as if the resolution is improved due to the viewer&#39;s visual characteristics.  
      For example, the first position and the second position on the screen may have a gap below or above a size of one pixel and may be spaced apart in a vertical, horizontal or diagonal direction.  
      Specifically, according to the present invention, an optical path changing unit is used to make the first image and the second image to be displayed respectively, at the first position and the second position of the screen.  
      The optical path changing unit uses a light transmitting element and the optical path is changed depending on the displacement position and displacement angle of the light transmitting element.  
       FIG. 1  is a view of a display device containing a resolution improving apparatus according to an embodiment of the present invention.  
      In  FIG. 1 , there is shown an illuminating system of a projection TV using a reflection-type liquid crystal display (LCD). In the reflection-type illuminating system of a 3 PBS (polarized beam splitter) system shown in  FIG. 1 , a light irradiated from a lamp  1  passes through a condensing lens and is incident on a first dichroic mirror  2 . The first dichroic mirror  2  reflects red and green light R and G and transmits a blue light B.  
      The reflected red and green light R and G are incident on a second dichroic mirror  3 . The second dichroic mirror  3  transmits the red light R to a first PBS  4   a  and reflect the green light G onto a second PBS  4   b.  The blue light B from the first dichroic mirror  2  impinges on a third PBS  4 C, e.g., through a reflecting mirror. As a result, the red, green and blue light R, G and B are respectively incident on the first, second and third PBSs  4   a,    4   b  and  4   c,  which are disposed in front of first, second and third LCD panels  5   a,    5   b  and  5   c,  respectively.  
      The red, green and blue light R, G and B incident on the first, second and third PBSs  4   a,    4   b  and  4   c  are reflected and then incident on the first, second and third LCD panels  5   a,    5   b  and  5   c,  respectively. Phases of the red, green and blue light R, G and B are changed respectively by the first, second and third LCD panels  5   a,    5   b  and  5   c.  Then, the red, green and blue light R, G and B having the changed phases are reflected from the LCD panels  5   a,    5   b  and  5   c  and transmitted respectively through the first, second and third PBSs  4   a,    4   b  and  4   c.    
      Images are displayed on the first, second and third LCD panels  5   a,    5   b  and  5   c, l depending on image signals inputted from a signal processing unit  50 .    
      The red, green and blue images, transmitted through the first, second and third LCD panels  5   a,    5   b  and  5   c  and then through the first, second and third PBSs  4   a,    4   b  and  4   c,  are combined by an X-prism  6 . Then, the combined images pass through a displacement plate  11  and are incident on a projection lens  10 . The images passing through the projection lens  10  are projected onto a screen  12 . All of the components of the illuminating system in  FIG. 1  are operatively coupled.  
      At this point, the displacement plate  11  may be disposed between the X-prism  6  and the projection lens  10 , or between the projection lens  10  and the screen  12 .  
      The displacement plate  11  is a thin-plate shaped element that can transmit light and is movable during the operation of the display device. For example, the position and/or angle of the displacement plate  11  can be moved periodically using mechanical means. A higher resolution can be implemented by changing the position or angle of the displacement plate  11 .  
      In addition, although the illuminating system using the reflection-type LCD, the dichroic mirror and the PBSs is shown in  FIG. 1 , a transmission-type LCD instead of the reflection-type LCD can also be used. A liquid crystal on silicon (LCOS) can also be used as the reflection-type LCD.  
      Further, although three LCD panels are shown in  FIG. 1 , only one LCD panel can also be used and a structure of the optical system can be variously modified.  
      Furthermore, the present invention can be applied to a projector as well as a projection TV.  
      That is, the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.  
       FIG. 2  is a view illustrating a display device according to another embodiment of the present invention. More specifically, a digital light processing (DLP) optical system according to the present invention will be described below in detail with reference to  FIG. 2 .  
      The DLP optical system provides light to be irradiated to a digital micromirror device (DMD)  14  and determines whether to allow respective micromirrors in the DMD  14  to irradiate the light to a screen in an on-state or to irradiate the light to a non-screen in an off-state, depending on image signals, e.g., from a signal processing unit  50 .  
      Referring to  FIG. 2 , the DLP optical system includes a lamp  17 , a rod lens  18 , a color wheel  19 , a condensing lens  13 , a prism  15 , a DMD  14 , a displacement plate  11 , and a projection lens  16 . All of the components of the system are operatively coupled. The lamp  17  generates light and the rod lens  18  transmits the light generated from the lamp  17 . The color wheel  19  separates the white light passing through the rod lens  18  into red, green and blue light. The condensing lens  13  condenses the light passing through the color wheel  19  and the prism  15  reflects the condensed light onto the DMD  14 . The DMD  14  irradiates the impinging light to the displacement plate  11  through the prisms  15 . The displacement plate  11  displaces the light reflected from the DMD  14 , depending on time. As in  FIG. 1 , the position and/or angle of the displacement plate  11  here is moved periodically or as desired using mechanical means. The projection lens  16  magnifies the lights passing through the displacement plate  11  and projects the magnified lights onto a screen  12 .  
      Based on such a structure, the operation of the DLP optical system will be described below. White light emitted from the lamp  17  is focused by an inner curvature of a reflector and the focused light passes through a light tunnel or rod lens  18 .  
      The rod lens  18  is provided by attaching four small and elongated mirrors to one another. The light passing through the rod lens  18  is scattered and reflected such that brightness is uniformly distributed.  
      The brightness of light that will be finally projected onto the screen  12  needs to be uniform. The rod lens  18  performs this function so that it is an important optical element in a projection-type display device.  
      The light passing through the rod lens  18  is then transmitted through the color wheel  19  for the color separation. The color wheel  19  rotates according to a vertical synchronization of the image.  
      Then, the light passes through the condensing lens  13  and is reflected by the prism  15 , so that the light is directed to the DMD  14 . The prism  15  can totally reflect or transmit the light, depending on the incident angle of the light.  
      The light incident on the DMD  14  is redirected toward the screen  12 , depending on the on/off state of the micromirrors of the DMD  14  controlled in response to sampled pixel values. The DMD  14  changes into the on- or off-state depending on the image signals inputted from the signal processing unit  50 . In this manner, a predetermined image is formed.  
      The image reflected from the DMD  14  and directed to the screen  12  passes through the displacement plate  11  and the projection lens  16 . In this course, the image is enlarged and projected onto the large screen  12 .  
      The displacement plate  11  may be disposed between the prism  15  and the projection lens  16 , or between the screen  12  and the projection lens  16 . Also, the displacement plate  11  may be disposed between the DMD  14  and the prism  15 .  
      The light is projected onto different locations on the screen  12  depending on the periodic change in the positions and/or angles of the displacement plate  11 .  
      According to the embodiments of  FIGS. 1 and 2 , the displacement plate  11  may be disposed at a predetermined position between the screen and the image forming unit for forming the image through the R, G and B combination. Depending on how and/or where the displacement plate  11  is positioned, the light can be projected at different locations on the screen  12 .  
      Meanwhile, in the image forming unit shown in  FIGS. 1 and 2 , the image signal corresponding to one frame is separated into the first image signal and the second image signal by the signal processing unit  50 . Then, the first image signal and the second image signal are transformed as the first image and the second image by the R, G and B combination, respectively.  
      In  FIG. 1 , the image forming unit may be provided with the first, second and third LCD panels  5   a,    5   b  and  5   c,  the first, second and third PBSs  4   a,    4   b  and  4   c  and the X-prism  6 .  
      In  FIG. 2 , the image forming unit may be provided with the color wheel  19 , the condensing lens  13  and the DMD  14 .  
      That is, the image signal corresponding to one frame is separated into a plurality of image signals and processed into a plurality of images and then displayed. The image signal corresponding to one frame may be split into “n” image signals and processed into “n” images and then displayed at “n” or less different positions on the screen.  
      According to the present invention, a display time of one image is equal to a time given by dividing the display time of one frame image by the number of images.  
      However, the present invention can make the viewer feel as if the resolution is improved by separating the image signal corresponding to one frame into the first image signal and the second image signal, processing the first image signal and the second image signal into the first image and the second image and then sequentially displaying the first image and the second image at the different positions of the screen.  
      FIGS.  3 ( a )- 3 ( c ) are examples of views illustrating an operation of the displacement plate in the display device, e.g., shown in FIGS.  1  or  2 ) according to the present invention. Particularly,  FIG. 3 ( a ) shows a case where there is no displacement plate  11  or there is no motion/angle of the displacement plate  11 . In this case, the image projected from the prism or the projection lens is displayed at the same position of the screen.  FIG. 3 ( b ) shows the case where the displacement plate  11  is rotated in a counterclockwise direction, and  FIG. 3 ( c ) shows the case wherein the displacement plate  11  is rotated in a clockwise direction.  
      If the displacement plate  11  changes from state (a) to state (b) or (c), the image is refracted while passing through the displacement plate  11 , such that the image is displayed at a different location on the screen. That is, since the displacement plate  11  functions as an optical path changing unit, the projected image is displaced due to the displacement plate  11  and is thus displayed onto a different position of the screen depending on the motion/angle of the displacement plate  11 . The displacement distance of the image displayed on the screen may be less than the size of one pixel. Thus, the displacement plate  11  according to the present invention acts as an image displacement unit to displace the image to be displayed onto different positions of the screen.  
       FIG. 4  is a view illustrating the operation principle of the displacement plate acting as an image displacement unit in the display device according to the present invention.  
      A degree of motion of the light on the screen  12  can be calculated depending on the displacement plate&#39;s thickness T, tilt angle (light incident angle) θ 1  and refractive index n 2 . The displacement plate&#39;s thickness, tilt angle and refractive index can be determined depending on the required motion degree of the light on the screen  12 .  
      The displacement plate&#39;s thickness, tilt angle and refractive index can be derived from Snell&#39;s law given by Equation 1 below.
 
 n   1  sin θ 1   =n   2  sin θ 2   [Equation 1]
          where, n 1  is the refractive index of air;     n 2  is the refractive index of the displacement plate;     θ 1  is the incident angle of light; and     θ 2  is the refraction angle of light.        

      Thus, the optical path difference D between the light passing through the displacement plate  11  can be given by Equation 2 below.  
               D   =       T     cos   ⁢           ⁢     θ   2         ⁢     sin   ⁡     (       θ   1     -     θ   2       )           ⁢     
     ⁢         cos   ⁢           ⁢     θ   2       =     T   x       ,       sin   ⁡     (       θ   1     -     θ   2       )       =     D   x       ,       θ   2     =       sin     -   1       ⁡     (         n   1     ⁢   sin   ⁢           ⁢     θ   1         n   2       )                   [     Equation   ⁢           ⁢   2     ]             
          where T is the thickness of the displacement plate;     n 1  is the refractive index of air;     n 2  is the refractive index of the displacement plate;     θ 1  is the incident angle of light;     θ 2  is the refraction angle of light; and     x is the length of the optical path of the refracted light within the displacement plate.        

      In addition, the optical path difference D between the light passing through the displacement plate  11  determines the displacement of the light actually displayed onto the screen  12 , depending on magnification of the projection lens.  
      It is preferable that the refractive index (n 2 ) of the displacement plate  11  falls within the range of from 1.4 to 2.0. But the invention covers other ranges.  
      In the examples of  FIGS. 1 and 2 , the present invention uses the light transmitting element and the light refraction, e.g., the displacement plate  11 , to make the optical path difference D.  
      A reflection mirror may be used to change the optical path. That is, if the reflection angle of the light is changed, the optical path of the reflected light can be changed depending on the angle of the reflection mirror, as disposed on the optical path.  
      According to the method of changing the optical path using the reflection, the change in the optical path is sensitive to the change in the angle of the reflection mirror, compared with the method of changing the optical path using the light refraction. Therefore, a precise control is required if the reflection is used to change the optical path.  
      According to the present invention, the displacement degree of the image may be more than or less than the size of one pixel. However, since the displacement degree of the image is small, the optical path changing unit must be precisely controlled so that the image projected from the projection lens can be displaced within a small range.  
      Therefore, the optical path changing unit using the light transmitting element, e.g., the displacement plate  11 , has advantages in that it can be easily manufactured and the error probability is greatly reduced.  
      Specifically, as shown in  FIG. 4 , if the light is incident onto the same position of the light transmitting element, such as the displacement plate  11 , the optical path difference D occurs but the traveling direction of the list does not change. On the other hand, in the case of the reflection mirror to change the light path, even if the light is incident onto the same position of the reflection mirror, the traveling direction of the light is changed depending on the angles of the reflection mirror, such that more precise control over the positioning of the reflection mirror and any of the factors is required.  
      FIGS.  5 ( a ) and  6 ( b ) are views illustrating the displacement of light projected onto the screen depending on the motion of the displacement plate in the display device (e.g., shown in FIGS.  1  or  2 ) according to the present invention. In these figures, T and T 1  represent time.  
      Referring to FIGS.  5 ( a )- 5 ( c ), in the display device having a rectangular pixel structure, the displacement plate  11  periodically moves and thus the positioning of the image on the screen  12  moves.  
      Referring to  FIG. 5 ( a ), conventionally an image is displayed at the same corresponding positions on the screen during a predetermined time (T=0−T 1 ). However, referring to FIGS.  5 ( b ) and  5 ( c ), different images are displayed at different positions on the screen at time T=0 and T=T 1 . Thus, a double resolution can be recognized using the same number of pixels.  
      For example, the image signal of one frame is separated into the first and second image signals as discussed above. Then, when the image of one frame is to be displayed, the first and second image signals are displayed in sequence as first and second images of the original image with such images displaced from each other on the screen.  
      In one example, assume that the same image information is displayed during {fraction (1/60)} second in the related art. Now, according to the present invention, the image information is separated into a first image information and a second image information, and then the first image information and the second image information are respectively and sequentially displayed at the first and second positions on the screen, each image information for {fraction (1/120)} of a second.  
      FIGS.  7 ( a ) and  7 ( b ) are respectively exemplary views of a first image and a second image separated from the image corresponding to one frame according to the present invention. As shown in FIGS.  7 ( a ) and  7 ( b ), the image corresponding to one frame can be separated into the first image (e.g., odd data) and the second image (e.g., even data image), and the first image and the second image can be separated depending on the positions of the pixels. The positions at which the first image (odd data) and the second image (even data) are displayed differ from each other and such displacement can be displaced by the displacement plate  11 , as discussed above.  
      Returning to  FIG. 5 ( b ), in this example the display positions of the first image (odd data) and the second image (even data) are displaced from each other in a diagonal direction. That is, at time T=0, the first image (odd data image) of the original image is displayed at a first location on the screen for a certain duration. Then at time T=T 1 , the second image (even data image) of the original image is displayed at a second location on the screen for a certain duration. The second location is displaced from the first location in a diagonal direction. In the example of  FIG. 5 ( c ), the display positions of the first image (odd data) and the second image (even data) are displaced from each other in a horizontal direction. Such displacement can be made by moving the position/angle of the displacement plate or reflection mirror as discussed above.  
      FIGS.  6 ( a ) and  6 ( b ) show the position of an image displayed onto the screen depending on time in a rhombus pixel structure.  
      Referring to  FIG. 6 ( a ), conventionally an image is displayed at the same corresponding position on the screen during a predetermined time (T=0−T 1 ). However, referring to  FIG. 6 ( b ), according to the present invention, different images are displayed at different positions of the screen at time T=0 and T=T 1 . Thus, according to the present invention, a double resolution can be achieved using the same number of pixels. As a variation, the different images may be displayed at the same time.  
      Accordingly, the present invention separates an image into two or more sub images (e.g., odd data image and even data image) and displaces them from each other using an optical path changing unit (e.g., displacement plate or reflecting mirror), such that the displaced sub images are displayed sequentially or in some order on the screen. This increases resolution and has the same visual effect of physically increasing the number of pixels on the display device. This effect is shown as an example in FIGS.  3 ( b ) and  3 ( c ).  
       FIG. 8  is a perspective view of an actuator for improving the resolution of a display device according to the present invention, and  FIG. 9  is an exploded perspective view of the actuator shown in  FIG. 8 .  
       FIG. 10  is a bottom exploded perspective view of a rotating member in the actuator according to the present invention, and  FIG. 11  is an exploded perspective view of a fixing member in the actuator according to the present invention.  
      Referring to FIGS.  8  to  11 , the actuator for improving the resolution of a display device includes a fixing member  20  and a rotating member  30 .  
      The fixing member  20  is disposed in an optical path between an image forming unit and a screen and has a fixing part  21  at a side such that it can fix the actuator. Although a screw hole is shown in the drawings, other members can also be used to fix the actuator within the display device.  
      Thus, the fixing member  20  is firmly fixed to the resolution improving apparatus in the optical path.  
      In addition, a magnet  23  and a yoke  22  are formed at a side of the fixing member  20 . Preferably, the magnet  23  and the yoke  22  can be formed on one side or both sides of the fixing member  20 .  
      The magnet  23  may be a dipole magnet having N and S poles. Also, the magnet  23  may be a monopole magnet or a multipole magnet.  
      The magnet  23  drives the rotating member  30  by using its magnetic field. The yoke  22  forms a passage of the magnetic field for increasing the efficiency of the magnetic field.  
      The rotating member  30  is rotatably coupled to the inside of the fixing member  20 .  
      The rotating member  30  is formed in a rectangular or rhombus shape and surrounds the optical path. The rotating member  30  has a structure suitable for housing the displacement plate  31 .  
      As described above, the displacement plate  31  is a light transmitting element that rotates at a predetermined angle for a short time and changes the position at which an image is displayed.  
      For this purpose, the displacement plate  31  may be disposed perpendicular to the optical path or inclined at a predetermined angle relative to the optical path. Thus, the incident angle of the light incident on the displacement plate is periodically changed.  
      The rotating member  30  includes shafts  32  on both sides and is rotatably connected to the fixing member  20  through shaft inserting grooves  27 . Preferably, the rotating member  30  further includes first and second bearings  33  and  36 . The shaft  32  serves as a rotation center axis of the rotating member  30  or the displacement plate  31 , and the rotation center axis is perpendicular to the optical path.  
      The first bearing  33  is formed in an approximately cylindrical shape and the shaft  32  is inserted into the first bearing  33 . The first bearing  33  is then disposed in the shaft inserting groove  27  of the fixing member  20 .  
      The second bearing  36  makes the outer diameter of the rotating member  30  so large that the rotating member  30  can be caught by an inner surface of the fixing member  20 . That is, the rotating member  30  that is inserted into the fixing member  20  cannot move in a left, lateral direction due to the second bearing  36 . Also, an engaging member, e.g., a leaf spring  24  is formed at the right lateral side of the first bearing  33 , such that the rotating member  30  cannot move in a right lateral direction. The elasticity of the leaf spring  24  secures a proper motion while fixing the rotating member, such that the rotating member  30  can rotate in a smooth manner. In such a state where only one end of the leaf spring  24  is coupled to the fixing member  20 , the leaf spring  24  supports the rotating member  30 .  
      A first cover  25  and a second cover  26  are disposed on upper sides of the first and second bearings  33  and  36  so that the rotating member  30  cannot be released in the upwards direction.  
      The first cover  25  is coupled to the fixing member  20  by two screws, and the second cover  26  is partially coupled to the fixing member  20  by one screw. The covers are provided to secure a proper motion to enable the rotating member  30  to rotate smoothly.  
      The second cover  26  provides a proper elastic force and is similar in operation to the leaf spring  24 .  
      In other words, the second cover  26  serves as an elastic member that can fix the rotating member  30  to the fixing member  20  while securing a desired motion of the rotating member  30 .  
      A coil  35  is provided at one side of the rotating member  30 , that is, at the side opposite to the magnet  23  formed in the fixing member  20 .  
      Referring to  FIG. 12 , in order to easily install the coil  35 , a coil holder  38  is provided at the side of the rotating member  30 , whereby the coil  35  can be supported and fixed by the coil holder  38 . The coil is formed in a rectangular shape or a racetrack shape. Thus, the rotating member  30  can move past the magnet  23  in the direction of the current.  
      Thus, when power is supplied to the coil  35  through a power line  34 , a current flows through the coil  35  and thus an attractive force and a repulsive force are generated due to the interaction with the magnet  23  provided in the fixing member  20 , thereby causing the rotating member  30  to rotate. The rotating member  30  rotates about the rotation center axis in a clockwise or counterclockwise direction depending on the direction of the current applied to the coil  35 .  
      Although not shown, according to another embodiment, a magnet may be provided in the side of the rotating member. In this embodiment, the coil holder is provided in the side of the fixing member opposite to the magnet, and a coil is supported by the coil holder.  
      As shown in  FIG. 10 , the displacement plate  31  is coupled to the rotating member  30 . The displacement plate is positioned on a protrusion  39  formed at the inside of the rotating member  30 , and then fixed by an engaging member  37 . A detail of the shape of the protrusion  39  is shown in  FIG. 9 .  
      In addition, the displacement plate  31  may be injected together with the rotating member  30 . In this case, the displacement plate  31  can be fixed to the rotating member  30  without any additional engaging member  37 .  
      As shown in  FIG. 11 , a stopper  28  is provided at the inside of the fixing member  20  so as to limit the rotational angle of the rotating member  30 . Thus, due to the stopper, the rotational range of the rotating member  30  is limited to be below a predetermined angle due to an external impact or an erroneous operation or an excessive operation.  
      In  FIG. 13 , an iron fragment is provided at a side of the rotating member  30  so as to control the rotating member  30  more accurately. In  FIG. 14 , the iron fragment  40  is shown in more detail.  
      The iron fragment  40  allows the driving member  30  to operate linearly. As shown in  FIG. 14 , the iron fragment  40  is formed in a side of the rotating member  30  and opposing the center of the dipole magnet  23 . That is, the iron fragment  40  can be disposed at the center  41  of the coil  35  or can be bilaterally and symmetrically disposed with respect to the center  41  of the coil  35 .  
      When only one iron fragment  40  is provided, it is disposed at the center  41  of the coil  35 .  
      As shown in  FIG. 13 , when two iron fragments  40  are provided, they are disposed at locations that are bilaterally symmetrical with respect to the center  41  of the coil  35 . That is, the iron fragments  40  are formed in a rectangular or racetrack shape and are disposed at the center of the coil  35  or at locations that are bilaterally symmetrical with respect to the center of the coil  35 .  
      This makes use of the property that the iron fragments  40  move to the center of the magnetic force under the influence of the line of the magnetic force. When the rotating member  30  changes to the location (angle) shown in  FIG. 7  during the iterative location change of the rotating member  30 , the iron fragment  40  can cause the rotating member  30  to change to the accurate location (angle).  
      In another embodiment, the rotating member  30  can rotate by controlling the current by forming the coil  35  and the iron fragment  40  in the fixing member  20  and forming the magnet  23  in the rotating member  30 .  
      The resolution improving apparatus of the present invention is disposed in the optical path of the display device and is rotated due to the interaction of the coil  35  and the magnet  23  depending on the applied control current. Preferably, the rotation range of the rotating member  30  can be set within ±0.75° and can be rotated such that it is periodically disposed at a first location and a second location.  
      The rotating member  30  rotates at least one time while an image signal of one frame is applied, whereby the resolution that the user visually feels can be remarkably improved.  
       FIG. 15  is a view of a projection containing the resolution improving apparatus according to the present invention.  
      Referring to  FIG. 15 , the projection television includes an optical assembly  500  containing the resolution improving apparatus, a reflection mirror for reflecting an image projected on the optical assembly  500 , a screen  400  on which the reflected image is displayed, a front cabinet  300  for supporting the screen  400 , and a back cover  100  for supporting the reflection mirror  200 .  
      In such a projection television, when the resolution improving apparatus is driven, an image of one frame is split into a first image indicated by a solid line and a second image indicated by a dotted line and is displayed at different locations on the screen  400 . In  FIG. 15 , there is exemplarily shown a case where the first image and the second image are displaced up and down.  
      As described above, an image of one frame is split into the first image and the second image and is periodically displayed at different locations on the screen. In this manner, the observer visually feels as if there are a large number of pixels, such that the resolution can be improved using the same number of the pixels. Accordingly, the resolution of a large-sized display device can be effectively improved at a low cost.  
      It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of the present invention provided they come within the scope of the appended claims and their equivalents.