Abstract:
Provided is a projection video display device with which a sliding load is minimized while maintaining an adjustment precision in a lens shift mechanism. A lens shift mechanism ( 32 ) which moves a projection lens in a direction which is orthogonal to the optical axis of projected light has a configuration in which mobile bases ( 50, 60 ), which retain the projection lens, slide using a shaft ( 52 ), which is attached on a fixed member ( 4 ) side, as a guide member. A further aspect of the configuration is that a correction screw is inserted from the rear face side of the fixed member ( 4 ) to make contact with the shaft ( 52 ), and optical axis tilt and misalignment of the projection lens are corrected by adjusting the degree of insertion of the correction screw.

Description:
RELATED APPLICATIONS 
     This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2011/073592, filed on Oct. 13, 2011, the disclosures of which Application is incorporated by reference herein. 
     TECHNICAL FIELD 
     The present invention relates to a projection video display device. 
     BACKGROUND ART 
     Projection video display devices such as a liquid crystal projector irradiate a display element such as a liquid crystal panel with light emitted from a light source such as a mercury lamp, and enlarges and projects a video formed by the display element with a projection lens onto a screen. The configuration of an optical system of the device includes an optical unit from irradiation with light emitted from the light source on the liquid crystal panel to formation of the video (hereinafter, referred to as an optical engine) and a projection optical system which enlarges and projects the video formed by the liquid crystal panel with a projection lens. In an optical engine of a color video display device, three liquid crystal panels for three primary colors (RGB) as display elements, a color separation system for irradiation light, and a color synthesis system for respective video colors are provided. Moreover, for adjusting a video-displaying position on the screen, a lens shifting mechanism which can move a projection lens in a direction perpendicular to an optical axis is provided in the projection optical system. 
     The lens shifting mechanism is arranged to move the projection lens in two directions perpendicular to the optical axis of projection light, i.e., a horizontal direction and a vertical direction, and is required to be reduced in size and have high accuracy. In Patent Literature 1, a structure is proposed which aims to downsize the lens shifting mechanism and improve the operability thereof and includes a manual operating portion, which is provided with an arrangement of operating knobs for horizontal direction and vertical direction, and a movement transmission mechanism portion for cutting off a transmitted force at a lens-shift-limit position by means of a clutch mechanism portion. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Application Laid-Open No. 2010-256388 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Conventional lens shifting mechanisms, including the one in Patent Literature 1, incorporate two movable bases for moving a projection lens in two axial directions. Portions between the movable bases and stationary members for supporting them and between the two movable bases are configured to allow opposed contact surfaces to slide (surface sliding). In this case, for preventing a positional displacement between both, the portions are configured such that a pressure contact force of a predetermined magnitude or more is applied to the contact surfaces by means of a spring or the like. Thus, when the movable base is moved, a friction is generated, so that a sliding load is large and smooth adjustment of a lens position is difficult. On the other hand, when the pressure contact force is weakened for reducing the sliding load, positioning of the movable base is not stable, thus degrading the accuracy of lens position adjustment. In this way, it has been difficult to simultaneously achieve reduction in sliding load when the lens is moved and improvement of adjustment accuracy. In addition, correction of tilt of the optical axis of the projection lens or the like is required as another function of the lens shifting mechanism. In that case, it is difficult to incorporate a tilt correction function in the structure in which the movable base is made to surface-slide, and an optical axis correction function has to be provided separately, thus making the device larger. 
     It is an object of the present invention to provide a projection video display device which can reduce a sliding load with maintaining adjustment accuracy in a lens shifting mechanism. 
     Solution to Problem 
     According to the present invention, in a projection video display device which enlarges and projects a video formed by a display element with a projection lens, a lens shifting mechanism is provided which moves the projection lens in a direction perpendicular to an optical axis of projection light, and is configured to make a movable base for holding the projection lens slide by using shafts attached on a fixed member side as guide members. 
     Moreover, it is configured that correction screws are inserted toward the shafts which guide the movable base from a rear side of the fixed member to come into contact with the shafts, and insertion amounts of the correction screws are adjusted, thereby tilt of an optical axis of the projection lens and a position displacement of the projection lens are corrected. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a projection video display device which can reduce a sliding load with maintaining adjustment accuracy in a lens shifting mechanism. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing an entire structure of a projection video display device according to this example. 
         FIG. 2  is a diagram showing an entire structure of an optical system. 
         FIG. 3  is an entire view of a projection optical system  3 . 
         FIG. 4  is an exploded view of the projection optical system  3 . 
         FIG. 5  is an entire view of a lens shifting mechanism  32 . 
         FIG. 6  is an exploded view of the lens shifting mechanism  32 . 
         FIG. 7  is an entire view of a movable base assembly  33 . 
         FIG. 8  is an exploded view of the movable base assembly  33 . 
         FIG. 9  is a diagram showing a power transmission structure of actuators  51  and  61 . 
         FIG. 10  is a diagram showing power transmission to a movable base. 
         FIG. 11  is a diagram showing an optical axis correction mechanism for a projection lens. 
         FIG. 12  is a diagram explaining an operation for correcting an optical axis of the projection lens. 
         FIG. 13  is a diagram explaining how to attach and detach the projection lens. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be described below, referring to the drawings. 
       FIG. 1  is a diagram showing the entire structure of a projection video display device of this example, and shows an internal structure of the display device. In a case  1 , an optical engine  2 , which emits light from a light source and radiates the light onto a liquid crystal panel as a display element to form a video, and a projection optical system  3 , which enlarges and projects the video formed by the liquid crystal panel with a projection lens, are accommodated as an optical system. In addition to those, a power supply unit  6  and a cooling unit  7 , and a video signal circuit, a control circuit, and the like which are not shown are also accommodated. 
       FIG. 2  is a diagram showing the entire structure of the optical system. The optical system includes the optical engine  2  and the projection optical system  3  which both are fixed to a common base  4  and are attached to the case  1 . 
     The optical engine  2  is formed by a light source portion  21 , a color separation optical system  22 , and a color synthesis optical system  23 . A light source such as an ultra-high pressure mercury lamp is used in the light source portion  21 , and emits approximately white light. The color separation optical system  22  separates the approximately white light into light of RGB three primary colors and guides the light of three primary colors to respective liquid crystal panels corresponding thereto. The color synthesis optical system  23  includes R, G, and B liquid crystal panels and a cross dichroic prism, and forms respective videos based on R, G, and B signals and performs color synthesis for those videos. 
     The projection optical system  3  is formed by a projection lens  31  and a lens shifting mechanism  32 . Video light emitted from the color synthesis optical system  23  is enlarged and projected onto a screen or the like by the projection lens  31 . The lens shifting mechanism  32  holds the projection lens  31  and moves it in two axial directions perpendicular to an optical axis (projection direction), i.e., a horizontal direction and a vertical direction. Thus, a position of an image projected onto the screen can be moved and adjusted in the horizontal direction and the vertical direction. 
       FIG. 3  and  FIG. 4  show the projection optical system  3  and an exploded view thereof.  FIG. 3  is the entire view of the projection optical system  3 , and  FIG. 4  is a view when the projection optical system  3  is exploded into the projection lens  31  and the lens shifting mechanism  32 . The lens shifting mechanism  32  is held by the common base  4  and performs a lens shifting operation. 
     As shown in  FIG. 4(   a ), a lens barrel  311  of the projection lens  31  is provided with a flange (projection)  80 . By engagement of this flange  80  with a convex portion  81  provided in the lens shifting mechanism  32 , the projection lens  31  is attached. FIG.  4 ( b ) is a rear view of the projection lens  31 . The projection lens  31  has three flanges  80 , for example, provided on the periphery of the lens barrel  311 . Similarly, three convex portions  81  are provided in the lens shifting mechanism  32 . 
       FIG. 5  and  FIG. 6  show the lens shifting mechanism  32  and an exploded view thereof.  FIG. 5  is the entire view of the lens shifting mechanism  32 , and  FIG. 6  shows a state in which the lens shifting mechanism  32  is exploded into the common base  4 , the movable base assembly  33 , and a base cover  34 . In the following description, a direction of an optical axis of projection light is referred to as Z direction, and the horizontal direction and the vertical direction which are perpendicular thereto are referred to as X direction and Y direction, respectively. 
     The common base  4  includes a fixing frame  41  standing in a central portion and pedestal portions  42  and  43  on both sides thereof. The movable base assembly  33  is mounted on one of the pedestal portion  43  and is fixed to the fixing frame  41 . On the other pedestal portion  42 , the optical engine  2  is mounted. 
     The movable base assembly  33  is a member which can move in X direction and Y direction while holding the projection lens  31 , and is configured by a Y-axis movable base (hereinafter, referred to as a Y base)  50  which is arranged on the common base  4  side and can move in Y direction and an X-axis movable base (hereinafter, referred to as an X base)  60  which is arranged on the projection lens  31  side and can move in X direction, the Y base  50  and the X base  60  being stacked. The Y base  50  is driven in Y direction by an Y-axis actuator  51  attached to a side face of the common base  4 , and the X base  60  is driven in X direction by an X-axis actuator  61  attached to a side face of the Y base  50 . 
     In the movable base assembly  33 , two Y shafts  52  are provided as guide members for making the Y base  50  slide in Y direction, which are a feature of the present invention. These Y shafts  52  are fixed to shaft attaching portions  521  on both side faces of the fixing frame  41  of the common base  4  with retaining metal fittings  522 , thereby the movable base assembly  33  is attached to the common base  4 . The fixing frame  41  is provided with a potentiometer  58  which can detect a moving position of the Y base  50  and an end sensor  59  which can detect a moving end point. Similarly, for detecting a moving position and a moving end point of the X base  60 , the Y base  60  is also provided with a potentiometer  68  and an end sensor  69  (see  FIG. 8 ). 
     The base cover  34  is arranged in front of the movable base assembly  33  and is attached to a cover attaching portion  90  of the common base  4 . When the base cover  34  is attached, a biasing force toward Z direction is applied to the movable base assembly  33 , i.e., a force which presses the movable base assembly  33  against the common base  4  is applied, by means of a leaf spring  91  provided in the base cover  34 , so that rattling of the position in Z direction of the projection lens  31  is eliminated. 
       FIG. 7  and  FIG. 8  show the movable base assembly  33  and an exploded view thereof.  FIG. 7  is an entire view of the movable base assembly  33 , and  FIG. 8  shows a state in which the movable base assembly  33  is exploded into the Y base  50  and the X base  60 . The Y base  50  is driven in Y direction by the Y-axis actuator  51  attached to the common base  4 , while the X base  60  is driven in X direction by the X-axis actuator  61  attached to the Y base  50 . Moreover, cylindrical shafts are employed as guide members for sliding of the respective movable bases  50  and  60 , thereby a sliding load is reduced as compared with a conventional surface-contact sliding and the positioning accuracy (linearity) of each of the movable bases  50  and  60  is improved. 
     The Y base  50  slides in Y direction by using two Y shafts  52  attached to the common base  4  as guide members. In both side faces of the Y base  50 , two shaft holes  53 , through which the Y shafts  52  are arranged to extend, are provided, respectively, for sliding. One of the two Y shafts  52  which is closer to the Y-axis actuator  51  (main shaft) is shown with reference sign  52   a , and the other farther one (sub shaft) is shown with reference sign  52   b . The shaft holes corresponding thereto are shown with reference signs  53   a  and  53   b , respectively. The shaft hole  53   a  for main shaft has a perfectly circular shape having approximately the same diameter as the Y shaft  52   a , and the shaft hole  53   b  for sub shaft has an elliptical shape larger than the diameter of the Y shaft  52   b , so that slight rattling (play) is provided between the shaft hole  53   b  and the Y shaft  52   b . Thus, even when an attached distance between the two Y shafts  52  is not perfectly coincide with a distance between the two shaft holes  53  formed in the Y base  50 , an error between them can be absorbed and the Y base  50  can be made to smoothly slide with a low load. Moreover, because sliding with no rattling is achieved on the main shaft side which receives a driving force from the Y-axis actuator  51 , the positional accuracy (linearity) of the Y base  50  during sliding can be maintained. 
     On the other hand, the X base  60  slide in X direction by using two X shafts  62  arranged along a top side and a bottom side of the Y base  50  as guide members. At the top and bottom sides of the X base  60 , two shaft holes  63  for allowing the X shafts  62  to extend therethrough for sliding are provided. One of the two X shafts  62  which is closer to the X-axis actuator  61  (main shaft) is shown with reference sign  62   a , the other farther one (sub shaft) is shown with reference sign  62   b , and the shaft holes corresponding thereto are shown with reference signs  63   a  and  63   b , respectively. Similarly to the case of the aforementioned Y base  50 , the shaft hole  63   a  for main shaft is formed to be a perfect circle corresponding to the diameter of the X shaft  62   a , and the shaft hole  63   b  for sub shaft is formed to be an elliptical shape larger than the diameter of the X shaft  62   b  to provide slight rattling between the shaft hole  63   b  and the X shaft  62   b . Due to this, the X base  60  can be made to slide smoothly with respect to the Y base  50 , and the positioning accuracy (linearity) of the X base  60  when sliding can be maintained. For detecting a moving position and a moving end point of the X base  60 , a potentiometer  68  and an end sensor  69  are provided in the Y base  50 . 
       FIG. 9  and  FIG. 10  show a power transmission structure of the actuators.  FIG. 9  show entire views of the actuators, and  FIG. 10  show power transmission to the movable base. 
     In  FIG. 9 , (a) shows the Y-axis actuator  51  and (b) shows the X-axis actuator  61 . Each of the Y-axis actuator  51  and the X-axis actuator  61  reduces a rotational force of an electric motor  54 ,  64  with a gear train  55 ,  65  to transmit the reduced rotational force to a lead screw  56 ,  66 , thereby propelling a non-rotating drive nut  57 ,  67  which meshes with the lead screw. To the drive nuts  57  and  67 , the Y base  50  and the X base  60  are connected, respectively, and the Y base  50  and the X base  60  move in Y direction and X direction. Two electric motors  54  and  64  are arranged on both side faces of the lens shifting mechanism  32 , respectively, with rotation axes thereof arranged along Y direction for reducing the outer sizes thereof. In the gear train  55  or  65 , rotation is reduced by using a worm gear  551  or  651  and a worm wheel  552  or  652 , and backlash during movement is eliminated. Moreover, a crown gear  553  is added in the Y-axis gear train  55  for changing a direction of the rotation axis by 90 degrees. Since the sliding load when the movable base  50  or  60  is moved is reduced in this example as described before, a driving power required for the electric motors  54  and  64  is reduced and a small sized motor can be used. 
       FIG. 10  shows the lead screw and the drive nut which perform power transmission to the movable base. Although the lead screw  56  and the drive nut  57  for driving the Y base  50  are shown in this drawing, the lead screw  66  and the drive nut  67  for driving the X base  60  are the same if  FIG. 10  is rotated by 90 degrees. In  FIG. 10 , operations in a case where the side-face direction of the Y base  50  is tilted with respect to the axial direction of the lead screw  56  are shown in (a), (b), and (c) while being compared with one another. 
     First, an operation common to (a) to (c) is described. When the worm wheel  553  rotates, the lead screw  56  which is concentric therewith also rotates and propels the drive nut  57  meshing with the lead screw  56  in Y direction. On the other hand, the Y base  50  is provided with connecting pieces  50   a  which sandwich the drive nut  57  therebetween from both end faces of the drive nut  57  in Y direction (connecting faces). The drive nut  57  pushes the connecting pieces  50   a  to move by moving in Y direction, thereby moving the Y base  50  in Y direction. On the connecting face of the drive nut  57 , a protrusion  57   a  is formed in a central portion so that the drive nut  57  comes into contact with the connecting piece  50   a  on the Y base  50  side at this protrusion  57   a  but does not come into contact at other portions than the protrusion  57 . This protrusion  57   a  is used for stably moving the Y base  50  even if the posture (the side-face direction) of the Y base  50  is tilted, and how to move the Y base  50  is described below. 
       FIG. 10(   b ) shows a case where the axial direction of the lead screw  56  and the side-face direction of the Y base  50  are parallel to each other. In this case, the connecting faces of the drive nut  57  and the connecting pieces  50   a  of the Y base  50  are parallel to each other, and therefore the Y base  50  can smoothly move without the protrusion  57   a . On the other hand,  FIGS. 10(   a ) and ( c ) show cases where the side-face direction of the Y base  50  is tilted with respect to the axial direction of the lead screw  56  in a direction shown with arrow. In those cases, although the connecting pieces  50   a  of the Y base  50  are tilted together, the posture of the drive nut  57  is regulated by the lead screw  56  and cannot be tilted. Thus, the connecting face of the drive nut  57  and the connecting pieces  50   a  are not parallel to each other. If the connecting face of the drive nut  57  is flat, contact with the engaging portion  50   a  is unstable (because an edge portion comes into contact), so that the sliding load becomes larger and smooth moving of the Y base  50  becomes difficult. Thus, the protrusion  57   a  is formed on the connecting face of the drive nut  57 , thereby always making this protrusion  57   a  in contact with the opposed connecting piece  50   a , stabilizing the contact therebetween irrespective of the posture of the Y base  50 , and enabling smooth moving of the Y base  50 . 
       FIG. 11  and  FIG. 12  show correction of the optical axis of the projection lens.  FIG. 11  is a diagram explaining a correction mechanism, and  FIG. 12  is a diagram explaining a correction operation. In optical axis correction, two types of correction, i.e., tilt correction for a lens optical axis and lens position correction in the direction of the optical axis (Z direction) are performed. The former correction, i.e., tilt correction corrects tilt generated by accumulated tolerances after the shifting mechanism is assembled, for suppressing focus imbalance. The latter one, i.e., lens position correction corrects a displacement of the lens position in the direction of the optical axis which is generated by accumulated tolerances after the shifting mechanism is assembled, for making a distance from an image forming surface (a liquid crystal panel surface) to a rear edge of the lens (back focus) appropriate. 
       FIG. 11  is a view of the common base  4  with the lens shifting mechanism  32  mounted thereon, when seen from the rear side (the side on which the optical engine  2  is mounted). At four corners of the fixing frame  41  of the common base  4 , four correction screws  70   a  to  70   d  for optical axis correction are inserted from the rear side. Enlarged views A and B show portions in which the correction screws  70   a  and  70   b  are attached and surrounding portions thereof, respectively. The position at which the correction screw is attached is set to correspond to positions of top and bottom ends of the Y shaft  52  which is the guide member of the lens shifting mechanism  32 . The Y shaft  52  is pressed toward the fixing frame  41  by receiving the biasing force in Z direction from the leaf spring  91  provided in the base cover  34 . The correction screw  70  is pushed into the Y shaft  52  or is pulled back with the Y shaft  52 , thereby the upper end side or the lower end side of the Y shaft  52  which is in contact with the correction screw  70  can be displaced in a projection direction (Z direction). Adjusting the insertion amounts of four correction screws  70   a  to  70   d  can change the tilt or the displacement amount of two Y shafts  52 , so that the tilt and the position of the lens shifting mechanism  32 , i.e., the tilt of the optical axis and the lens position of the projection lens  31  attached to the lens shifting mechanism  32  can be corrected. In this manner, correction of the lens optical axis can be achieved in this example by a simple structure in which the Y shafts  52  introduced as the guide members for the lens shifting mechanism  32  are used and pushed in by means of the correction screws  70 . 
       FIG. 12  shows a specific example of the correction operation. (a) is a lens top view showing an example of tilt correction in the horizontal direction, in which the optical axis (Z-axis) of the projection lens  31  is tilted with respect to a normal state in the horizontal direction (X-axis). In this case, with respect to the lens shifting mechanism  32 , the correction screws  70   c  and  70   d  on the right end side or the correction screws  70   a  and  70   b  on the left end side are pushed in, thereby the direction of the optical axis is corrected to the normal state. (b) is a lens side view showing an example of tilt correction in the vertical direction, in which the lens optical axis (Z-axis) is tilted with respect to the normal state in the vertical direction (Y direction). In this case, the correction screws  70   a  and  70   c  on the upper end side or the correction screws  70   a  and  70   b  on the lower end side are pushed in, thereby correction to the normal state is achieved. (c) is a lens side view showing an example of lens position correction, in which the lens position of the projection lens  31  is displaced from a reference position in the direction of the optical axis (Z direction). In this case, four correction screws  70   a  to  70   d  are pushed in or pulled back, thereby the lens position is corrected to a normal position. 
     In a case where the lens optical axis is tilted in both the horizontal direction and the vertical direction, it is sufficient to perform a combination of the operations of (a) and (b). Also, in a case where both the tilt of the lens optical axis and the displacement of the lens position occur, it is sufficient to perform a combination of the operations of (a) and (c) or (b) and (c). 
       FIG. 13  is a diagram explaining how to attach and detach the projection lens  31 , and shows the X base  60  in  FIG. 8  which has been further exploded. For holding the projection lens  31 , the X base  60  can be divided into an X base main body  601 , a pressing ring  602 , and a lens holder  603 . For holding the projection lens  31 , the X base main body  601  is provided with the concave portions  81  (at three positions) with which the flanges  80  (see  FIG. 4 ) provided on the lens barrel  311  of the projection lens  31  are engaged. Please note that the depth in Z direction of the concave portion  81  is set to be slightly smaller than the width in Z direction of the flange  80 . In the pressure ring  602  and the lens holder  603 , cutout portions  82  and  83  are provided (at three positions, respectively), each of which allows the corresponding flange  80  to pass therethrough when the projection lens  31  is attached or detached. 
     Moreover, a lever  84  for switching between locking and releasing of the held lens is provided in the pressing ring  602 . When the projection lens  31  is attached, the pressing ring  602  is turned by the lever  84  so that a portion other than the cutout portion  82  presses the flange  80  engaged with the concave portion  81 , thereby fixing the projection lens  31  to the X base  60 . In a case of detaching the projection lens  31 , the pressing ring  602  is turned by the lever  84  in an opposite direction to position the cutout portion  82  at the position of the concave portion  81  and release the pressing by the flange  80 , thereby the projection lens  31  can be removed from the X base  60 . 
     As described above, according to this example, a projection video display device can be provided which reduces a sliding load while maintaining adjustment accuracy in a lens shifting mechanism. Moreover, tilt of an optical axis of a projection lens and a displacement of a lens position thereof can be achieved by a simple structure. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  . . . case, 
               2  . . . optical engine, 
               21  . . . light source portion, 
               22  . . . color separation optical system 
               23  . . . color synthesis optical system, 
               3  . . . projection optical system, 
               31  . . . projection lens, 
               32  . . . lens shifting mechanism, 
               33  . . . movable base assembly, 
               34  . . . base cover, 
               4  . . . common base, 
               41  . . . fixing frame, 
               42 ,  43  . . . pedestal portion, 
               50  . . . Y-axis movable base (Y base), 
               50   a  . . . connecting piece, 
               51  . . . Y-axis actuator, 
               52  . . . Y shaft, 
               521  . . . shaft attaching portion, 
               522  . . . pressing metal fitting, 
               53 ,  63  . . . shaft hole, 
               54 ,  64  . . . electric motor, 
               55 ,  65  . . . gear train, 
               551 ,  651  . . . worm gear, 
               552 ,  652  . . . worm wheel, 
               553  . . . crown gear, 
               56 ,  66  . . . lead screw, 
               57 ,  67  . . . drive nut, 
               57   a  . . . protrusion, 
               58 ,  68  . . . potentiometer, 
               59 ,  69  . . . end sensor, 
               60  . . . X-axis movable base (X base), 
               601  . . . X base main body, 
               602  . . . pressing ring, 
               603  . . . lens holder, 
               61  . . . X-axis actuator, 
               62  . . . X shaft, 
               70   a  to  70   d  . . . correction screw, 
               80  . . . flange, 
               81  . . . convex portion, 
               84  . . . lever, 
               90  . . . cover attaching portion, 
               91  . . . leaf spring