BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a projection type picture display apparatus in which pictures output from a projection unit are projecting to a back face of a screen to thereby display the pictures. 
     2. Description of the Related Art 
     The prior art is shown FIGS. 7-11. In FIGS. 7-11, “X”, “Y” and “Z” show the Z-axis, Y-axis and Z-axis of the three dimension space. FIG. 7 is a side view showing the inside of a conventional multi-projector. Here, the multi-projector described above means a display apparatus which is designed to display a large display frame (picture) by arranging and stacking plural projection type picture display apparatuses (rear projection type video projectors) vertically and horizontally. In FIG. 7, it is illustrated that two conventional projection type picture display apparatuses  160  are stacked in the vertical direction. 
     As shown in FIG. 7, the projection type picture display apparatus comprises a cabinet (the housing of the projection type picture display apparatus)  101 , a projection unit  102  which is disposed at the rear side in the cabinet  101  and projects an output picture to the front side, a screen  103  provided at the front face of the cabinet  101 , and a position adjusting mechanism  150  for correcting a position of a outline of a picture to be projected from the projection unit  102  to the screen  103 . The projection unit  102  projects an output picture to a back face of the screen. A large display frame can be displayed by combining and using a plurality of projection type picture display apparatuses  160  each having the above structure. In this case, the projection unit  102  is secured to the upper portion of the position adjusting mechanism  160  so that the position thereof is adjustable. 
     FIGS. 8 to  10  are diagrams which conceptually show pictures displayed on the screen  103  while each picture is displaced with respect to the screen  103 . As displacements on the screen  103  exist six kinds of displacements which are a vertical displacement (a displacement in the vertical direction), a horizontal displacement (a displacement in the right-and-left direction), an inclining displacement, a projection magnification displacement, a longitudinal trapezoidal distortion and a lateral trapezoidal distortion, or a combination thereof. 
     In FIG. 8, reference numeral  104   a  represents a picture which is improper in projection magnification to the screen  103  (magnification-improper picture), reference numeral  104   b  represents a picture which is improperly inclined with respect to the screen  103  (improperly-inclined picture), and reference numeral  104   c  represents a picture which is improperly displaced in the vertical and horizontal directions with respect to the screen  103  (vertical/horizontal improper picture). 
     In FIG. 9, reference numeral  104   d  represents a picture in which a longitudinal trapezoidal distortion occurs (longitudinal trapezoidal improper picture), and in FIG. 10 reference numeral  104   e  represents a picture in which a lateral trapezoidal distortion occurs (lateral trapezoidal improper picture). 
     In most cases, Braun tube (CRT) has been mainly applied to the projection unit  102  because the displacements on the screen  103  of the Braun tube can be easily corrected by an electrical circuit. However, in place of the Braun tube, a liquid crystal device or a digital mirror device for which the optical path cannot be electrically corrected have been recently mainly applied to the projection unit  102  because of the tendency of digitalization of pictures. In this case, a position adjusting mechanism  150  is indispensable for the projection unit  102  for which the optical path cannot be electrically corrected. 
     FIG. 11 is a perspective view showing the outlook of a conventional position adjusting mechanism  150 . 
     In FIG. 11, reference numeral  150   a  represents a Y-axis moving plate which can move the projection unit  102  in the Y-axis direction, reference numeral  150   b  represents an Y-axis rotating plate which is rotatable around the Y-axis, reference numeral  150   c  represents a Z-axis rotating plate which is rotatable around the Z-axis, reference numeral  150   d  represents an X-axis rotating plate which is rotatable around the X-axis, reference numeral  150   e  represents a Z-axis moving plate which is movable in the Z-axis direction, and reference numeral  150   f  represents an X-axis moving plate which is movable in the X-axis direction. 
     Next, the position adjusting operation of the conventional picture outlook adjusting mechanism  150  shown in FIG. 11 will be described with reference to FIGS. 7 to  11 . 
     A picture projected from the projection unit  102  is projected onto the screen  103 . At this time, the projection magnification of the picture can be corrected by the adjusting operation of the Z-axis moving plate  150   e . Further, the lateral trapezoidal distortion can be corrected by the Y-axis rotating plate  150   b , and the inclination of the picture can be corrected by the adjustment of the Z-axis rotating plate  150   c . The longitudinal trapezoidal distortion can be also corrected by the adjustment of the X-axis rotating plate  150   d . Still further, the vertical and horizontal position can be corrected by the adjustment of the X-axis moving plate  150   f  and the Y-axis moving plate  150   d.    
     Japanese Laid-open Patent Application No. Hei-8-32907 discloses another prior art, and specifically it discloses a technique of separating one display unit (projection type picture display apparatus) into a front side cabinet and a back side cabinet. 
     As described above, in the conventional projection type picture display apparatuses, six adjusting functions must be adjusted for the position adjusting mechanism  6 , and also six adjusting functions must be provided every adjusting mechanism performing only one adjustment. Therefore, the number of parts of the apparatus and the weight of the apparatus are increased, and the cost is also increased. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been implemented in view of the above circumstances and has an object to provide a projection type picture display apparatus which can reduce the number of parts and the weight. 
     In order to attain the above object, according to the present invention, a projection type picture display apparatus comprising a projection unit for projecting a picture to a back face of a screen and a position adjusting mechanism for supporting the projection unit and for giving six adjusting functions including X, Y, Z directional adjustments for moving the projection unit along X-axis, Y-axis, Z-axis of three dimension space respectively, and X, Y, Z rotational adjustments for rotating the projection unit around X-axis, Y-axis, Z-axis respectively, characterized in that said position adjusting mechanism has an adjusting plate member for performing three adjusting functions of said six adjusting functions. 
     The adjusting plate member performs the three adjusting functions including Z rotational adjustment for rotating the projection unit around Z-axis, X rotational adjustment for rotating the projection unit around X-axis, and Y directional adjustment for moving the projection unit along Y-axis. 
     Further the adjusting plate member has a first support shaft extending in the Y-axis direction, a second support shaft which is disposed so as to be in parallel to said first support shaft and spaced from said first support shaft at a predetermined interval in the Z-axis direction, a third support shaft which is disposed so as to be in parallel to said first support shaft and spaced from said first support shaft at a predetermined interval in the X-axis direction, a first adjusting shaft which is selectively engageable with both of said first and second support shafts or only said second support shaft through a gear switching operation, a second adjusting shaft which is selectively engageable with both said first and third support shafts or only said first support shaft through a gear switching operation, and an adjusting plate is supported on said first, second and third support shafts for supporting the projection unit. 
     Also the adjusting plate member performs said Z rotational adjustment when said first adjusting shaft engages with both said first and second support shaft and said second adjusting shaft engages with said first support shaft but no-engages with said third support shaft, said X rotational adjustment when said first adjusting shaft engages with said second support shaft but no-engages with said first support shaft and said second adjusting shaft engages with said first support shaft but no-engages with said third support shaft, and said Y directional adjustment when said first adjusting shaft engages with both said first and second support shaft and said second adjusting shaft engages with both said second and third support shafts. 
     In the projection type picture display apparatus, one end of said first adjusting shaft has a knurled portion on the outer peripheral portion thereof, and said knurled portion is engaged with a member having a knurled portion on the inner peripheral portion thereof to stop the rotation of said first adjusting shaft. 
     Further the adjusting plate member has a first support shaft extending in the Y-axis direction, a second support shaft which is disposed so as to be in parallel to said first shaft and spaced from said first support shaft at a predetermined interval in the Z-axis direction, a third support shaft which is disposed so as to be in parallel to said first support shaft and spaced from said first support shaft at a predetermined interval in the X-axis direction, and first, second and third motors for adjusting said first, second and third support shafts respectively, and said adjusting plate member has a adjusting plate is supported on said first, second and third support shaft for supporting the projection unit which is equipped with a projection unit for projecting a picture to a screen and an angle-of-view adjusting mechanism for supporting the projection unit so that the position of the projection unit is adjustable and with which the picture projected from the projection unit is projected from the back of the screen, is characterized in that the angle-of-view adjusting mechanism has an adjusting plate for adjusting three degrees of freedom out of six degrees of freedom of the projection unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing a adjusting plate member of a first embodiment of the present invention; 
     FIG. 2 is a cross-sectional view showing a adjusting plate member of the first embodiment of the present invention; 
     FIG. 3 is a plan view showing a gear switching operation of the first embodiment of the present invention; 
     FIG. 4 is a plan view showing the gear switching operation of the first embodiment of the present invention; 
     FIG. 5 is a cross-sectional view showing a lock mechanism of the first embodiment of the present invention; 
     FIG. 6 is a diagram showing a adjusting plate member of a second embodiment of the present invention; 
     FIG. 7 is a diagram showing a projection type picture display apparatus based on a prior art; 
     FIG. 8 is a diagram showing the prior art; 
     FIG. 9 is a diagram showing the prior art; 
     FIG. 10 is a diagram showing the prior art; and 
     FIG. 11 is a diagram showing a position adjusting mechanism based on the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments according to the present invention will be described hereunder with reference to the accompanying drawings. In FIGS. 1,  3 ,  4  and  5 , “X”, “Y” and “Z” show the X-axis, Y-axis and Z-axis of the three dimension space. 
     [First Embodiment] 
     A projection type picture display apparatus according to a first embodiment of the present invention will be described hereunder with reference to the accompanying drawings. 
     FIG. 1 is a perspective view showing a position adjusting mechanism including a adjusting plate member which is a constituent element of the projection type picture display apparatus. In FIG. 1, reference numeral  10  represents a three-axis adjusting plate (corresponding to an adjusting plate), reference numeral  50   f  represents an X-axis moving plate, reference numeral  50   e  represents a Z-axis moving plate and reference numeral  50   b  represents a Y-axis rotating plate. The X-axis moving plate  50   f  for X directional adjustment, the Z-axis moving plate  50   e  for Y directional adjustment and the Y-axis rotating plate  50   b  for Y rotational adjustment (each of these plates corresponds to one adjusting plate) have the same structure as the conventional ones, and they correspond to the X-axis moving plate  150   f , the Z-axis moving plate  150   e  and the Y-axis rotating plate  150   b  described in the prior art. On the adjusting plate  10 , the projection unit same as prior projection unit  102  is supported. 
     The three-axis adjusting plate  10  of this embodiment is designed to be supported by gears  14 ,  15  and  16  in which totally three support bolts  11  (corresponding to a second support shaft),  12  (corresponding to a third support shaft) and  13  (corresponding to a first support shaft) are threaded respectively. 
     The other parts than the position adjusting mechanism in the projection type picture apparatus are designed in the same structure of the conventional projection type picture apparatus, and thus the description thereof is omitted. 
     The three adjusting plate  10  is supported on three bolt  11 ,  12  and  13 . FIG. 2 is a cross-sectional view showing the support portion of one bolt  11  of the three-axis adjusting plate  10 . In FIG. 2, the three-axis adjusting plate  10  is freely rotatably supported by a C ring  17  at the boss portion of the gear (spiral gear)  14 . The gear  14  is internally threaded on the inner periphery thereof, and the support bolt  11  is threaded in the gear  14 . The same construction is applied to the gears  15 ,  16 . 
     Further, in FIG. 1, the gears  14  and  16  are engaged with the gears  22  and  23  fixed to a shaft  20  (corresponding to the first adjusting shaft), and the gears  14  and  16  are rotated in the same direction by rotating the shaft  20 . The gears  15  and  16  are engaged with the gears  24  and  25  fixed to a shaft  21  (corresponding to the second adjusting shaft). 
     One end of the shaft  20  is rotatably supported through a hole  10   a  of the three-axis adjusting plate  10 , and the other end thereof penetrates through an elongated hole  10   b  provided in the three-axis adjusting, plate  10  and then is pivotally supported through a hole  30   a  of a switching lever. A knob  32  is secured to the tip of the other end of the three-axis adjusting plate  10 . Further, one end of the shaft  21  is rotatably supported by a bearing  10   d  provided to the three-axis adjusting plate  10 , and the other end thereof penetrates through an elongated hole  10   c  of the three-axis adjusting plate and then is rotatably supported through a hole  31   a  of a switching lever  31 . 
     By moving the switching lever  30  in the “−X axis direction” (this moving state is referred to as “OFF state”, and the moving state in the opposite direction (“+X axis direction”) is referred to as “ON state”) as shown in FIG. 3, the gear  23  is separated from the gear  16  or no-engages with the gear  16 , and the gear  14  is kept engaged with the gear  22 . 
     Further, as shown in FIG. 4, by moving the switching lever  31  in the “+Z axis direction” (this moving state is referred to as “OFF state”, and the moving state in the opposite direction (“−Z axis direction”) is referred to as “ON state”), the gear  15  is separated from the gear  24  or no-engages with the gear  24 , and only the gear  16  is kept engaged with only the gear  25 . 
     Next, the operation will be described. 
     When the shaft  20  is rotated in the three-axis adjusting plate  10  while the switching levers  30  and  31  are kept in the ON state, the gears (spiral gears)  14 ,  15  and  16  are rotated in the same direction, and the three-axis adjusting plate  10  makes a translating motion in the Y-axis direction along the support bolts  11 ,  12  and  13 . The adjustment function is the Y directional adjustment. Further, when the shaft  20  is rotated under the state that the switching lever  30  is set to the ON state and the switching lever  31  is set to the OFF state, the gears  14  and  16  are rotated, however, the gear  15  is not rotated, so that the three-axis adjusting plate  10  makes a rotational motion around the Z-axis with the gear  15  serving as a fulcrum. This adjustment function is the Z rotational adjustment. Further, when the shaft  20  is rotated under the state that the switching lever  30  is set to the OFF state, only the gear  14  is rotated and thus the three-axis adjusting plate  10  makes a rotational motion around the X-axis with the line connecting the gears  12  and  13  serving as an axis. This adjustment function is the X rotational adjustment. 
     As described above, the three-axis adjusting plate  10  has X-axis rotating, Z-axis rotating and Y-axis moving functions. 
     FIG. 5 is a cross-sectional view showing a lock mechanism for stopping the rotation of the adjusting shaft after adjustments of six degrees of freedom are carried out. As shown in FIG. 5, a knurled portion  20   a  is formed on the outer periphery of one end of the shaft  20  so as to project outwardly from the opening portion  10   a  formed in the frame of the three-axis adjusting plate  10 . When the shaft  20  is pushed in the −Z axis direction, the shaft  20  is engaged with a cap  26  (secured from the outside of the frame of the three-axis adjusting plate  10 ) having a knurled portion  26   a  formed on the inner periphery thereof, the knurled portion  26   a  being engaged with the knurled portion  20   a  of the shaft  20 , whereby the rotation of the shaft  20  is stopped. 
     The projection type picture display apparatus of the presents invention has the three-axis adjusting plate constituting the position adjusting mechanism, and thus it can adjust three degrees of freedom out of six degrees of freedom by using one adjusting plate. Therefore, the number of parts constituting the display apparatus can be reduced with sufficiently keeping the precision of the position adjustment, so that the weight of the display apparatus and the cost thereof can be reduced. 
     Further, only one cap  26  which is required as a stopper for rotation of the adjusting shaft and only one operating knob  32  secured to the end portion of the shaft are sufficient for the three-axis adjusting plate  10 . In addition, the stopping operation of the rotation after the adjustment of the six degrees of freedom can be easily performed by merely pushing the knob  32  when the knurled portion  20   a  of the shaft  20  is engaged with the knurled portion  26   a  of the cap  26 . 
     In the above embodiments, totally three support bolts are provided. However, the above embodiment may be modified so that support bolts are arranged at four corners of the adjusting plate and the engagement states thereof are adjusted by the switching levers in the same manner as the case where the three support bolts are arranged. In this case, the adjustment of three degrees of freedom can be also adjusted by using one adjusting plate. 
     [Second Embodiment] 
     Next, a second embodiment of the present invention will be described with reference to FIG.  6 . 
     FIG. 6 is a perspective view showing a three-axis adjusting plate  10   aa  (corresponding to the adjusting plate) constituting the angle-of-view adjusting mechanism of the projection type picture display apparatus. 
     In FIG. 6, reference numerals  27 ,  28  and  29  represent gears in which support bolts  11 ,  12  and  13  respectively are threaded, reference numerals  40 ,  41  and  42  represent motors (the motor  40  corresponds to a second motor), the motor  41  corresponds to a third motor and the motor  42  corresponds to a first motor), and reference numerals  43 ,  44  and  45  represent gears (worm gears) which are fixed to the rotational shafts and disposed to be engaged with the gears  27 ,  28  and  29 , respectively. Reference numeral  46  represents a control box for controlling the motors  40 ,  41  and  42 . The same elements as or corresponding elements to those of the first embodiment are represented by the same reference numerals. 
     As in the case of the three-axis adjusting plate  10  of the first embodiment, the bolts  11 ,  12  and  13  are threaded in the gears  27 ,  28  and  29  in the three-axis adjusting plate  10   aa  of the second embodiment. The coupling structure of the three-axis adjusting plate  10   aa  and the gears  27 ,  28  and  29  is also the same as the first embodiment. 
     Next, the operation of the second embodiment will be described. 
     When the motors  40 ,  41  and  42  are rotated in the same direction, the gears  27 ,  28  and  29  are moved along the support bolts, and the three-axis adjusting plate  10   aa  makes a translating motion in the Y-axis direction. When only the motor  40  is rotated, the three-axis adjusting plate  10   aa  makes a rotational motion around the X-axis with the line connecting the gears  28  and  29  serving as an axis. When only the motor  41  is rotated, the three-axis adjusting plate  10   aa  makes a rotational motion around the Z-axis with the line connecting the gears  27  and  29  serving as an axis. As described above, the three-axis adjusting plate  10   aa  of the second embodiment has the X-axis rotating, Z-axis rotating and Y-axis translating functions like the first embodiment. 
     As described above, even when the adjustment of three degrees of freedom out of six degrees of freedom is carried out by using the three motors  40 ,  41  and  42 , the adjustment of three degrees of freedom can be carried out by using one adjusting plate, so that the weight and cost of the display apparatus can be reduced. 
     In order to simplify the description, the X-axis translating plate  50   f  and the Z-axis translating plate  50   e  are omitted from the illustration of FIG.  6 . 
     According to the projection type picture display apparatus of the present invention, three adjusting functions of six adjusting functions degrees can be performed by using one adjusting plate member, and the number of parts constituting the display apparatus can be reduced with sufficiently keeping the precision of the position adjustment, so that the weight and cost of the display apparatus can be reduced. 
     Further, according to the projection type picture display apparatus, the stop of the rotation of the adjusting shaft can be carried out by a simple operation of engaging the knurled portion formed at the end portion of the adjusting shaft with the knurled portion fixed to the adjusting plate, and thus stable projection can be performed. 
     Still further, according to the projection type picture display apparatus, even when the first, second and third support shafts provided to the adjusting plate are adjusted by the first, second and third motors, three adjusting functions of six adjusting functions can be performed by one adjusting plate, and the number of parts constituting the display apparatus can be reduced with sufficiently keeping the precision of the position adjustment, so that the weight and cost of the display apparatus can be reduced.
In a projection type picture display apparatus, three degrees of freedom out of six degrees of freedom which are adjusted by an angle-of-view adjusting mechanism are adjusted by using one adjusting plate (three-axis adjusting plate). The adjusting plate on which a projection unit is fixedly supported rotates the projection unit around the X-axis or Z-axis with respect to a screen disposed in parallel to the XY plane and translates the projection unit in the Y-axis direction to adjust three degrees of freedom. The adjusting plate has first, second and third support shafts extending in the Y-axis direction, a first adjusting shaft engageable with the first and second support shafts, and a second adjusting shaft engageable with the first and third support shafts, and adjusts the three degrees of freedom of the projection unit on the basis of the combination of the engagements.