Abstract:
In a rear projector for projecting an image from behind a screen, its screen size is variable. In order to permit flexible adaptation to the variation in the screen size, the projector is constructed to permit easy adjustment of a detection device for detecting an image display position or a position indicated on the screen.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rear projector for projecting an image from behind a screen and, more particularly, to a rear projector capable of adapting to different screen sizes. 
     2. Related Background Art 
     With image display apparatus (projectors), there are recent trends toward large screens. For example, the rear projection type image display apparatus is known as one of methods for realizing the large screens. The image display apparatus of this type is constructed to enlargingly project an image formed by an image forming device such as a liquid crystal panel or the like, through a projection lens (projection optical system) onto the backface of the screen (which is a surface on the far side from the user with respect to the screen) and to permit an observer to observe the transmitted image on the other side of the screen. In parallel with the trends toward the large screens of the image display apparatus, image control equipment has been developed for use in controlling an externally connected computer while entering coordinates by direct indication on the screen with an indicator or the like or for use in writing characters, graphics, etc., and has been being mounted on the image display apparatus. 
     The rear projection type image display apparatus heretofore was constructed to project the image onto the screen by use of a reflecting mirror in order to shorten the depth of the housing. The image display apparatus, as illustrated in FIG. 1 (also referring to FIG.  4 ), is set up to project an image from a projection optical system for forming the image and projecting it, onto the reflecting mirror  27  placed on a housing back panel  36  and thus project the image onto the thin screen  30  placed on the front surface of the housing, and the structure consists of two parts, the housing  37  having the projection optical system and the reflecting mirror  27 , and the screen part  32  having the screen  30 . 
     The image control equipment is an image control device comprised of an indicator for generating a light spot and a detection device for detecting the light spot generated by the indicator, and the detection device  26  is placed inside the housing  37 . With these image display device and image control device, the image display position and the image control range for control of image were adjusted in such a manner that the image display position was adjusted relative to the screen part  32  upon installation of the projection optical system and that the position of the image control device was adjusted relative to the screen part  32  upon installation of the detection device. 
     In the housing structure consisting of the screen part  32  and the housing  37 , as in the case of the above conventional image display device illustrated in FIG. 1, however, all the members of the housing  37  must naturally be changed with replacement of the screen part  32  for variation in the screen size. 
     The housings have been increasing their size with increase in the screen size of the image display apparatus and it is also becoming difficult to design the housings with sufficient accuracy in the relation of process accuracy with deflection of the members themselves and cost. This means that with increase in the screen size the displayed image becomes more affected by deviation between relative positions of the projection optical system and the reflecting mirror  27  placed on the back panel  36 , because the increase in the screen size involves a trade-off relation between dimensional accuracy for each member and dimensional accuracy optically required. Part of the image cannot be displayed on the screen in certain cases. It is, however, extremely difficult in terms of the structure to adjust each of the image display position and the detection device  26  after the projection optical system and the detection device  26  have been incorporated in the housing. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is, therefore, to solve the problem in the above conventional apparatus and provide a projector that is capable of flexibly adapting to change of the screen size and that permits easy adjustment of the image display position or the detection device forming the image control device. 
     A projector according to one aspect of the present invention is a projector of a rear projection type for projecting an image from behind a screen, which comprises: 
     a screen part having a screen of a predetermined size; and 
     a main body part having projection means for projecting an image onto the screen, 
     wherein said screen part is replaceable with a screen part having a screen of another size different from said screen of the predetermined size. 
     In the projector according to another aspect of the invention, a projection distance of said projector is variable. 
     In the projector according to another aspect of the invention, said screen part comprises a reflecting mirror behind said screen and said projection means projects the image via the reflecting mirror onto said screen to display the image thereon. 
     In the projector according to another aspect of the invention, said main body part comprises detection means for detecting information indicated on said screen. 
     In the projector according to another aspect of the invention, said information is a position indicated on said screen. 
     In the projector according to another aspect of the invention, said projection means and said detection means are integrally formed. 
     The projector according to another aspect of the invention comprises image control means for detecting the information indicated on said screen, by use of said detection means and changing the image displayed on said screen, based on the information. 
     In the projector according to another aspect of the invention, at least part of said projection means and said detection means is moved to effect positional adjustment of a range in which said projection means projects the image and a detection range in which said detection means can detect the information, on said screen. 
     In the projector according to another aspect of the invention, said main body part comprises a projection optical system for projecting the image and a detection optical system for detecting the information on the screen, and said projection optical system and said detection optical system are integrally formed in a state in which optical axes of said systems are parallel to each other. 
     A projector according to a further aspect of the present invention is a projector of a rear projection type for projecting an image from behind a screen, which comprises: 
     a screen part having a screen of a predetermined size; and 
     a main body part comprising projection means for projecting an image onto the screen and detection means for detecting information on the screen, 
     wherein said projection means and said detection means are integrally formed. 
     In the projector according to another aspect of the invention, said projection means and said detection means are integrally formed so that an optical axis of a projection optical system of said projection means is parallel to an optical axis of a detection optical system of said detection means. 
     The projector according to another aspect of the invention comprises image control means for changing the image displayed on the screen, based on the information detected by use of said detection means. 
     In the projector according to another aspect of the invention, a projection distance of said projector is variable. 
     In the projector according to another aspect of the invention, said screen part comprises a reflecting mirror behind said screen and the image is projected via the reflecting mirror onto said screen to be displayed thereon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a drawing to show the structure of the conventional image display device; 
     FIG. 2 is a drawing to show the overall structure of an adjustment unit in the projector according to an embodiment of the present invention; 
     FIG. 3 is a drawing to show an exploded view of the adjustment unit of FIG. 2; 
     FIG. 4 is a drawing to show the overall structure of the projector in the embodiment of the present invention; 
     FIG. 5 is a diagram for explaining the adjustment structure by the detection device in the embodiment of the present invention; 
     FIG. 6 is a drawing to show another configuration of the projector in the embodiment of the present invention; 
     FIG. 7 is a drawing to show another configuration of the projector in the embodiment of the present invention; 
     FIG. 8 is a drawing to show another configuration of the projector in the embodiment of the present invention; 
     FIG. 9 is a drawing for explaining the function of the detection device; 
     FIG. 10 is a drawing for explaining the adjustment of the position relative to the screen of the projection optical system, and other matter; 
     FIG. 11, FIG. 12, and FIG. 13 are perspective views to explain positioning of the upper and lower housing parts; 
     FIG. 14 is a cross-sectional view for detailing the connection between the upper and lower housing parts; and 
     FIG. 15, FIG. 16, FIG. 17, and FIG. 18 are front views of the image display area, observed at the position ahead of the screen, before positional adjustment thereof relative to the screen. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The projector disclosed in the present embodiment is constructed in such structure that the screen part having the screen of predetermined size can be separated from the main body part having the projection means for projecting the image formed by the image forming device onto the screen, whereby the screen size can readily be changed by simply replacing the screen part with another screen part on the main body part. An example of this structure employed for the housing structure will be described below referring to FIG.  4 . 
     In the same figure, the housing structure of the rear projection type image display device provided with the back mirror is comprised of a lower part (main body part)  28 , in which the projection means can be installed, and an upper part  33 , in which the back mirror  27  is disposed and on which the screen  32  is mounted. The lower part and the upper part are separable from each other. In this structure, the projection means for projecting the image onto the screen and the detection device (detection means)  26  for detecting information indicated on the screen are set in an adjustment unit part  34 , and the adjustment unit part  34  is mounted in the lower part  28 . 
     The adjustment unit part  34  is constructed so that the projection means  1  can be adjusted relative to the lower part  28  in vertical and horizontal directions, rotational directions, tilt directions, etc. and so that the detection device  26  can be adjusted similarly relative to the projection means  1 . 
     Since the housing structure of the rear projection type image display device provided with the back mirror can be separated into the upper part  33  and the lower part  28 , the screen size can be changed by replacing the upper part  33  and the screen part  32  with another set. 
     Further, in the image display device described above, the projection means and the detection device  26  are first set and adjusted in the adjustment unit part  34  and the adjustment unit part  34  therewith is then mounted in the lower part  28 , which can facilitate the adjustment after the projection means has been mounted inside the housing. When the range of adjustment is wide, it becomes feasible to obtain the structure rarely depending upon the mounting of the projection means, the accuracy of the housing, and an error in connection between the upper and lower parts of the housing. 
     In the image display device equipped with the image control device, the detection device inside the image control device has a detection optical system for detecting information on the screen and the projection means inside the main body part has the projection optical system for projecting the image onto the screen or the like. If the optical axis of the detection optical system and the optical axis of the projection optical system are parallel to each other and if the relative distance between them is always kept constant, the information can be detected irrespective of the size of the upper part  33 . In the structure with the adjustment unit part  34 , therefore, the projection means and the detection device  26  can be adjusted before the adjustment unit part  34  is mounted in the housing. Thus there is no need for adjustment of the detection device  26  after the adjustment unit part  34  has been set in the lower part  28 . 
     Next, embodiments of the present invention will be described hereinafter, but, prior thereto, the detection device used in the embodiments will be first described briefly as an example of the detection device. It is a matter of course that the detection device is not limited to this example but can also be selected from a variety of other detection devices. 
     FIG. 9 is an explanatory diagram to show the detection device used in the embodiments. The detection device is mainly comprised of an indicator  31  for forming a light spot on the screen  30  being an image control surface, and a detector for detecting, for example, coordinates of the position of the light spot  35  on the screen  30 . The indicator  31  incorporates a light-emitting element such as a semiconductor laser or an LED for emitting a light beam, an emission control means for activating and controlling the emission, a plurality of control switch means, and a power supply means such as a battery or the like. 
     The emission control means performs control of on/off of emission according to states of the control switches and control of emission with a control signal superimposed by a modulation method. 
     The positional relation between two linear sensors  40 X,  40 Y is determined as illustrated in FIG.  9 . Through a cylindrical lens  90 X,  90 Y as an imaging optical system, an image of the light spot  35  is focused in the form of a line  91 X,  91 Y on each sensor  41 X,  41 Y. These two sensors are placed at exactly right angles, whereby each sensor outputs a signal having a peak at a pixel reflecting an X-coordinate or a Y-coordinate. These two sensors are controlled by sensor control means and their output signals are converted into digital signals by A/D conversion means connected to the sensor control means. The digital signals are sent to a coordinate calculation means to calculate output coordinate values, and the result, together with data such as a control signal or the like from the control signal detection means, is sent through a communication control means to an external control device by a predetermined communication method. 
     In this example, the system concerning the detection, including the cylindrical lenses  90 X,  90 Y and the linear sensors  40 X,  40 Y, is defined as a detection optical system. 
     FIG. 2, FIG. 5, FIG. 9, and FIG. 10 show the structure of the embodiment of the present invention. In these figures, numeral  1  designates the projection means having the projection optical system for enlargingly projecting the image formed by the image forming device not illustrated, onto the screen, and the projection means, together with a projection-optical-system-fixing band (a plate for reinforcing fixing of the projection optical system) of  10 , a projection-optical-system-supporting panel (a plate for reinforcing fixing of the projection optical system) of  9 , and a detection-device-fixing panel of  25 , is fixed to a projection-optical-system-fixing tilt panel A (a plate for fixing the projection optical system) of  3 . The detection device  26  is fixed to the detection-device-fixing panel  25 . A detection-device-substrate-fixing panel  11  is fixed to the projection-optical-system-supporting panel  9 . 
     The above-stated unit consisting of the projection optical system, the projection-optical-system-fixing tilt panel A of  3 , the projection-optical-system-supporting panel  9 , the projection-optical-system-fixing band  10 , the detection-device-substrate-fixing panel  11 , the detection-device-fixing panel  25 , and the detection device  26  is attached to a projection-optical-system-fixing tilt panel B of  2 , and it can be adjusted with an adjustment knob A of  20  in directions K relative to the screen  30  as illustrated in FIG.  10 . The unit is constructed to be adjusted so that the optical axis is incident at right angles in the X-directions to the screen  30 , whereby X-directional trapezoidal distortion can be corrected. 
     A tilt assistance panel A of  8  is attached to the projection-optical-system-fixing tilt panel B of  2  and the projection-optical-system-fixing tilt panel B of  2  is attached to left and right side panels of symbols  4   a ,  4   b . Therefore, the projection means can be adjusted with an adjustment knob B of  6  in directions L relative to the screen  30  as illustrated in FIG. 10 so that the optical axis is incident at right angles in the Y-directions to the screen  30 , whereby Y-directional trapezoidal distortion can be corrected. A tilt assistance panel B of  7  is attached to the left and right side panels of  4   a ,  4   b.    
     Next, the left and right side panels of  4   a ,  4   b  are fixed to a θ-adjustment panel of  21 , and the θ-adjustment panel  21  is arranged to be rotatable relative to a Y-adjustment panel of  22 , whereby rotational adjustment of θ can be effected relative to the screen  30  by adjusting an adjustment knob C of  17 . The θ-adjustment panel  21  is attached to the Y-adjustment panel  22  and the Y-adjustment panel  22  is attached to an X-adjustment panel of  23 . Since the Y-adjustment panel  22  is movable relative to the X-adjustment panel  23  in the Y-directions, the Y-directional position of the image field is corrected relative to the screen  30  by adjustment of an adjustment knob D of  18 . 
     Next, the X-adjustment panel  23  is attached to an adjustment-unit-fixing panel of  24 . Since the X-adjustment panel  23  is movable relative to the adjustment-unit-fixing panel  24  in the X-directions, the X-directional position of the image field is corrected relative to the screen  30  with an adjustment knob E of  19 . Then the adjustment unit denoted by numeral  34  as a whole is positioned and fixed to the housing  28 . 
     Next, as illustrated in FIG. 5, the detection device  26  is attached to the detection-device-fixing panel  25  so that the adjustment in four ways of G, H, I, and J can be effected with respect to the projection optical system. 
     G indicates rotational adjustment for the optical axis of the detection optical system of the detection device, which permits alignment of relative position θ with the projection optical system. 
     H indicates capability of aligning the X-directional relative position of the detection optical system of the detection device  26  with the projection optical system. 
     I indicates capability of adjusting the optical axis of the detection optical system of the detection device  26  relative to the screen  30  to right angles in the X-directions. 
     Therefore, this permits the optical axes of the projection optical system and the detection optical system of the detection device  26  to be positioned relative to the screen  30  at right angles in the X-directions. 
     J indicates capability of adjusting the Y-directional position of the detection optical system of the detection device  26  relative to the projection optical system. Since the adjustment in the directions J permits the optical axis of the detection optical system to be positioned relative to the screen  30  at right angles in the Y-directions, the optical axes of the projection optical system and the detection optical system can be positioned relative to the screen  30  at right angles in the Y-directions. 
     Through these adjustments, as illustrated in FIG. 4, the optical path F of the detection optical system can be matched at A with the optical path B of the projection optical system, and the optical path E of the detection optical system at B with the optical path C of the projection optical system. 
     Further, FIG. 6, FIG. 7, and FIG. 8 show another embodiment of the present invention. In these figures, the housing of the screen part  33  and the housing of the main body  28  are constructed so as to be separable from each other and the housing of the main body  28  including the adjustment unit  34  is adjusted to change the projection distance with variation in the screen size, as illustrated in FIG.  7  and FIG.  8 . This permits common use of the housing of the main body  28  to different screen sizes. 
     Next, positioning of the upper and lower housing parts will be described hereinafter with reference to the drawings. First, FIG. 11, FIG. 12, and FIG. 13 are perspective views to explain the positioning of the upper and lower housing parts, FIG. 14 is a cross-sectional view for detailing the connection between the upper and lower housing parts, and FIG. 15, FIG. 16, FIG. 17, and FIG. 18 show images displayed before the position of the display area is adjusted relative to the screen. 
     In the drawings, numeral  38  designates the display area;  39   a ,  39   b , and  39   c  positioning pins,  42   a  and  42   c  positioning holes;  43  screws for connecting the upper and lower housing parts to each other;  44  washers;  45   a ,  45   b ,  45   c , and  45   d  holes for connection between the upper and lower housing parts;  46   a ,  46   b ,  46   c , and  46   d  pits for connection and fixation between the upper and lower housing parts; and  47   a ,  47   b ,  47   c , and  47   d  holes for connection between the upper and lower housing parts. 
     The first embodiment of positioning between the upper and lower housing parts will first be described with reference to FIG.  11 . In FIG. 11, the positioning holes  42   a ,  42   b  are bored in the upper part  33  and the upper and lower housing parts are set so that the positioning pins  39   a ,  39   b  disposed on the lower part  28  are fitted in the positioning holes  42   a ,  42   b . Then the upper part  33  and the lower part  28  are set in the positioned state relative to each other as illustrated in FIG.  12 . For connection between the upper and lower parts, the connecting screws  43  are put into the respective connection holes  45   a ,  45   b ,  45   c , and  45   d  illustrated in FIG. 11, and are fixed in the fixing pits  46   a ,  46   b ,  46   c , and  46   d  formed in the lower part  28 , thereby connecting and fixing the upper and lower parts  33  and  28  as illustrated in FIG.  12 . Next, the second embodiment of positioning between the upper and lower parts will be described with reference to FIG.  13 . In FIG. 13, a slot for positioning  42   c  is bored in the upper part  33 . The slot is formed such that the positioning pin  39   c  provided on the lower part  28  is so fitted into the slot  42   c  as to allow adjustment of the upper part  33  relative to the lower part  28  in the X-direction of e or f, or in the rotational direction of g or h. However, the upper and lower parts need to be fixed relative to each other in the Y-direction, because change of projection distance results in change of the size of the display area  38 . 
     Adjustment methods will be described hereinafter. First, the image area is displayed on the screen in the structure of FIG.  13 . When the display area  38  has no trapezoidal distortion and when a&lt;b as illustrated in FIG. 15, the upper part  33  is moved in the direction f to meet the condition of a=b. When the display area  38  has no trapezoidal distortion and when a&gt;b as illustrated in FIG. 16, the upper part  33  is moved in the direction e to meet the condition of a=b. 
     When the display area  38  has the trapezoidal distortion of c&gt;d as illustrated in FIG. 17, the upper part  33  is rotated in the direction h to effect correction for the trapezoidal distortion. At this time, correction is made for the trapezoidal distortion, but the correction can change the balance between a and b. Therefore, adjustment is also made in the X-direction to make a=b. When the display area  38  has the trapezoidal distortion of c&lt;d as illustrated in FIG. 18, the upper part  33  is rotated in the direction g to effect correction for the trapezoidal distortion. At this time, correction is made for the trapezoidal distortion, but the correction can change the balance between a and b. Therefore, adjustment is also made in the X-direction to make a=b. Next described is the connection between the upper and lower parts carried out after completion of the correction of the display area  38 . Since the upper part  33  is not always fixed at a constant position relative to the lower part  28 , the holes  47  are bored in the size larger than the holes  45 , as illustrated in FIG.  14 . This is a means for avoiding such hindrance that the upper and lower parts cannot be incorporated with each other in the connection work of the upper and lower parts with the connection screws  43  before the relative positions of the upper and lower parts are determined, e.g., in the state of FIG.  11 . The washers  44  serve as functional assistance for the larger connection holes  47 .