Abstract:
An illumination device used in a printing head of a printer, which is capable of switching color of light emitted from a light source quickly. The illumination device has a color wheel that includes at least three grass panels having a fan-like shape and switches the color of light by rotating. The grass panels of the color wheel are supported by a circumferential ring at these exterior circumference. Thereby, the grass panels are hard to be damaged even when the color wheel is rotated at a high speed so as to switch the color of light quickly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on Japanese Patent Application No. HEI 10-99651 filed in Japan on Apr. 10, 1998, the content of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an illumination device provided with a rotating panel for switching color of illumination light. 
     2. Description of the Related Art 
     Conventionally, printers have been proposed which are provided with a printing head using a light shutter that comprises, for example, a PLZT. Furthermore, printing heads have been proposed which are provided with an illumination device having a rotating panel to modulate light emitted from a light source into light of each color red (R), green (G) and blue (B) and direct the modulated light to the light shutter. 
     The general construction of a full color printer provided with a PLZT printing head is described below. FIG. 10 briefly shows a partial construction of the full color printer. Part of light emitted from a halogen lamp  21  as a light source is directed to an illumination device  24  by an aluminum pipe  23 . Only a color wheel  11  is shown in the drawing as a rotating panel forming a structural element of the illumination device  24 , and other structural elements which are not illustrated include a drive source for driving the rotation of the color wheel  11 , and a housing for accommodating the color wheel  11 . Reference number  22  refers to a light-transmitting heatproof filter for blocking the heat generated by the halogen lamp  21 . 
     The color wheel  11  of the illumination device  24  is provided with a plurality of glass panels as transparent members sequentially arranged in a direction of rotation of the color wheel  11 . The light emitted from the halogen lamp  21  passes through the pipe  23  and is modulated sequentially to R, G, B by the respective glass panels via the rotation of the color wheel  11 . Details of the construction of the color wheel  11  and the illumination device  24  are described later. 
     Reference number  25  is a fiber bundle comprising a lot of plastic fibers. The light modulated by the illumination device  24  (i.e., color wheel  11 ), is transmitted within the fibers to a polarizer  26 . The fiber bundle  25  has a circular cross section on the color wheel  24  side, and the fibers are arranged in a linear array on the polarizer  26  side. 
     Only the light oscillating in a predetermined direction is transmitted through the polarizer  26 . The light which is transmitted through the polarizer  26  further passes through an integrator  27  to suppress dispersion. A shutter array  28  is a member in which a plurality of PLZT elements as optical shutters is arranged in the form of an array, and these shutters are turned ON and OFF via the application of a voltage to the PLZT elements. The light passing through the shutter array  28  arrives at an analyzer  29 , and only the light oscillating in a predetermined direction passes through the analyzer  29 . The light passing through the analyzer  29  forms an image on a color photographic paper  31  as a recording medium via a lens  30 . A full color image is printed on the photographic paper  31  by regulating an amount of R, G, B light via the shutter array  28 . 
     The color wheel  11  is described below. FIG. 11 is a top view of the color wheel  11 . FIG. 12 is a cross section view on an A-A′ plane in FIG.  11 . Glass panels  1   r ,  1   g  and  1   b  are each 1 mm thick, and are processed such that these have a fan-like shape with an interior angle of 60°. The glass panels  1   r ,  1   g  and  1   b  are optically coated so as to modulate white light transmitted therethrough to R ( 1   r ), G ( 1   g ), B ( 1   b ) light, respectively. That is, the glass panels  1   r ,  1   g  and  1   b  have mutually different light transmitting characteristics. The glass panels  1   r ,  1   g  and  1   b  respectively comprise a pair of elements, for a total of six elements. 
     A top flange  2  and a bottom flange  3  fixedly hold the glass panels  1   r ,  1   g  and  1   b . The top flange  2  and bottom flange  3  made of aluminum both have a disk-like shape. The bottom flange  3  is provided with an opening  3   a  on its center. A wall  3   b  is formed on one side of the bottom flange  3  along a circumferential edge of the opening  3   a.    
     The glass panels  1   r ,  1   g  and  1   b  are locked by the top flange  2  and the bottom flange  3  as described below. The bottom flange  3  is disposed with a surface on which the wall  3   b  is formed facing upward, and the glass panels  1   r ,  1   g  and  1   b  are placed on the bottom flange  3  and abut the wall  3   b , such that like color panels face one another across the center. Then, the top flange  2  is overlaid onto the bottom flange  3  so as to hold the glass panels  1   r ,  1   g  and  1   b  between the two flanges, and the top flange  2  is fixed to the bottom flange  3  via adhesive or screws or the like. 
     By the way, in the full color printer provided with the PLZT printing head of the aforesaid construction, the color wheel  11  must rotate at approximately 12000 rpm to attain a desirable printing speed. When rotating at such a high speed, however, the color wheel  11  is subject to extremely large centrifugal force which rapidly causes damage to the glass panels  1   r ,  1   g  and  1   b.    
     Gaps may be generated at mutual connective regions of the glass panels  1   r ,  1   g  and  1   b  of the color wheel  11  due to measurement discrepancies during manufacture. Light may disadvantageously leak from these gaps, and adversely affect printing. 
     Furthermore, another problem occurs when the color wheel  11  rotates. FIG. 13 is a side section view of a conventional illumination device  24 . The color wheel  11  is accommodated in a dustproof housing  8 . A motor  10  as a drive source is provided in the opening  3   a  of the bottom flange  3  of the color wheel  11  (refer to FIG.  12 ). The color wheel  11  is rotated within the housing  8  via the drive provided by the motor  10 . The light emitted from the halogen lamp  21  (refer to FIG. 10) enters the color wheel  11  through an entrance window (not illustrated) in the housing  8 , passes through the glass panel  1   r  (or  1   g , or  1   b ), and is emitted from an exit window (not illustrated) in the housing  8 . 
     As shown in the drawing, the housing  8  has two mutually opposing surfaces parallel to the rotational plane of the color wheel  11 , i.e., a bottom surface of the housing body  8   a  and the back surface of the housing cover  8   b . The color wheel  11  is disposed within these two surfaces so as to be closer to the housing body  8   a . When the color wheel  11  is rotated, the area near the rotational axis and the area of the exterior circumference have different circumferential speeds, such that an airflow is generated from the center of the color wheel  11  toward the exterior side in a space (B) between the color wheel  11  and the housing body  8   a  (indicated by an arrow  12  in the drawing). 
     The space (B) is subject to a low air pressure condition due to this airflow  12 , which produces a force in a downward direction (indicated by an arrow  14  in the drawing) on the color wheel  11 . The rotational balance of the color wheel  11  is disrupted under the effects of this downward force, and rotational stability is lost. These effects are particularly pronounced when an air motor is used as the drive source. 
     OBJECTS AND SUMMARY 
     An object of the present invention is to eliminate the previously described disadvantages by providing an improved illumination device. 
     Another object of the present invention is to provide an illumination device provided with a rotating panel capable of high-speed rotation. 
     Still another object of the present invention is to provide an illumination device which does not leak light from a rotating panel. 
     Yet another object of the present invention is to provide an illumination device capable of stable rotation of a rotating panel. 
     These objects are attained by providing an illumination device comprising: 
     a rotating panel including a plurality of transparent members having different light transmitting characteristics sequentially arranged in a rotational direction of the rotating panel; and 
     a frame member arranged on an exterior circumference of the rotating panel for supporting the plurality of transparent members. 
     In this illumination device, the transparent members are hard to be damaged even when subjected to centrifugal force via the rotation of the rotating panel because the transparent members are supported by the frame member. 
     In this illumination device, the frame member may be adhered to the transparent members via adhesive. In this case, even when dimension discrepancies occur during the manufacture of the transparent members and the frame member, the looseness is absorbed by the adhesive. 
     These objects are further attained by providing an illumination device comprising: 
     a rotating panel including a plurality of transparent members having different light transmitting characteristics sequentially arranged in a rotational direction of the rotating panel; and 
     a light shield member for sealing between adjacent transparent members. 
     In this illumination device, even when gaps occur at the connective regions between transparent members, light is prevented from leaking by the light shield member. 
     These objects are further attained by providing an illumination device comprising: 
     a rotating panel including a plurality of transparent members having different light transmitting characteristics sequentially arranged in a rotational direction of the rotating panel; and 
     a housing for accommodating the rotating panel, said housing having two mutually opposing surfaces parallel to a rotational plane of the rotating panel, and having an airflow inlet near a rotational axis of the rotating panel on a surface nearer to the rotating panel among the two surfaces. 
     In the space between the rotating panel and the surface nearer to the rotating panel in this illumination device, airflow is generated from the center of the rotating panel toward the exterior side thereof, but there is no change in air pressure in this space because external air inflows to the space from the airflow inlet. 
     In this illumination device, a plurality of the airflow inlets may be disposed at equal intervals on a circumference centered on a position corresponding to a rotational axis of the rotating panel. In this case, air flowing from the airflow inlet is not deflected so as to maintain equal air pressure in the space. 
     In this illumination device, a filter may be provided at the airflow inlet. In this case, external air flowing into the housing is clean because the filter traps dust etc. 
     In this illumination device, the housing also may be provided with an airflow outlet near an exterior circumference of the rotating panel on the surface provided with the airflow inlet. In this case, there is no change in air pressure in the space because exterior air flows into the housing from the airflow inlet, and air inside the housing is discharged from the airflow outlet. 
     In this illumination device, the housing may be provided with a pipe connecting the airflow inlet and the airflow outlet. In this case, there is no change in air pressure in the space because an airflow is generated circulating through the pipe and the space. 
     A plurality of the airflow inlets and the airflow outlets may be arranged at equal intervals on respective circumferences centered on a position corresponding to a rotational axis of the rotating panel. In this case, a constant air pressure is maintained in the space because the inflow and discharge of air from the airflow inlet and the airflow outlet are not deflected. 
     These objects are further attained by providing an illumination device comprising: 
     a rotating panel including a plurality of transparent members having different light transmitting characteristics sequentially arranged in a rotational direction of the rotational panel; and 
     a housing for accommodating the rotating panel, 
     wherein the rotating panel is accommodated in the housing so as to maintain equal distance from two mutually opposing surfaces of the housing parallel to a rotational plane of the rotating panel. 
     In this illumination device, an equal airflow is generated in both spaces between the rotating panel and the two surfaces of the housing, and pressure is hard to be exerted on the rotating panel due to deflection of air pressure because the spacing between the rotating panel and the two surfaces of the housing are equal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: 
     FIG. 1 is a top view of a color wheel of an illumination device of a first embodiment of the invention; 
     FIG. 2 is a side section view of an assembly tool and the color wheel of the illumination device of the first embodiment; 
     FIG. 3 is a top view of a color wheel of an illumination device of a second embodiment of the invention; 
     FIG. 4 is a side section view of the color wheel of the illumination device of the second embodiment; 
     FIG. 5 is a side section view of an illumination device of a third embodiment of the present invention; 
     FIG. 6 is a side section view of an illumination device of a fourth embodiment of the invention; 
     FIGS. 7A and 7B are side section views of modifications of the illumination device of the third and fourth embodiments; 
     FIG. 8 is a side section view of an illumination device of a fifth embodiment of the invention; 
     FIG. 9 is a side section view of an illumination device of a sixth embodiment of the invention; 
     FIG. 10 briefly shows a construction of a full color printer provided with a PLZT printing head; 
     FIG. 11 is a top view of a color wheel of a conventional illumination device; 
     FIG. 12 is a side section view of the color wheel of the conventional illumination device; and 
     FIG. 13 is a side section view of the conventional illumination device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings. In the following description, like structural elements common to the conventional art of FIGS. 10 through 13 are designated by like reference numbers throughout the several drawings, and duplicative descriptions are omitted. 
     FIG. 1 is a top view of a color wheel  11  of an illumination device of a first embodiment of the present invention. FIG. 2 is a section view of the color wheel  11  on an A-A′ plane of FIG. 1, and is a side section view of a tool used for assembling the color wheel  11 . The color wheel  11  of the present embodiment is provided with a circumferential ring  4  as a frame member on an exterior circumference of glass panels  1   r ,  1   g  and  1   b.    
     A method of assembling the color wheel  11  is described below. First, a bottom flange  3  and the circumferential ring  4  are mounted on an assembly tool  40  as shown in FIG.  2 . Then, the glass panels  1   r ,  1   g  and  1   b  are placed on the bottom flange  3 . At this time, the glass panels  1   r ,  1   g  and  1   b  are pressed against the inner side of the circumferential ring  4 , and an epoxy adhesive  5  is loaded between the circumferential ring  4  and the glass panels  1   r ,  1   g  and  1   b  to bond the elements. A top flange  2  is placed on top of the assembly and attached to the bottom flange  3  via screws  6 . At this time, adhesive may also be loaded between the glass panels  1   r ,  1   g  and  1   b  and the flanges  2  and  3 . 
     In the illumination device of the present embodiment, the glass panels  1   r ,  1   g  and  1   b  are hard to be damaged even when a large centrifugal force is generated by a rotation of the color wheel  11  because the glass panels  1   r ,  1   g  and  1   b  are supported by the circumferential ring  4 . Furthermore, even when some looseness is produced by dimensional discrepancies between the circumferential ring  4  and the glass panels  1   r ,  1   g  and  1   b , this looseness is absorbed by the adhesive  5  loaded between the elements. Accordingly, the circumferential ring  4  stably supports the glass panels  1   r ,  1   g  and  1   b , and prevents damage to the glass panels  1   r ,  1   g  and  1   b.    
     When the color wheel of the aforesaid construction was actually rotated by a DC brushless motor, the glass panels were undamaged even at a rotational speed of 12000 rpm. According to the illumination device of the present embodiment, color of illumination light can be switched quickly, and a fast printing speed is the result when used in a printer. 
     FIG. 3 is a top view of a color wheel  11  of an illumination device of a second embodiment of the present invention. FIG. 4 is a section view of the color wheel  11  on an A-A′ plane of FIG.  3 . This color wheel  11  differs from the color wheel of the first embodiment shown in FIGS. 1 and 2 in that light shield sheets  7  are provided as light shield members straddling connective areas  1 ′ between glass panels  1   r ,  1   g  and  1   b . As shown in FIG. 4, the light shield sheets  7  are adhered to the surfaces of the glass panels  1   r ,  1   g  and  1   b  on the bottom flange  3  side. In other aspects of this illumination device are identical to the illumination device (or color wheel) of the first embodiment. 
     In the illumination device of the present embodiment, even when gaps occur in connective areas  1 ′ between the glass panels  1   r ,  1   g  and  1   b , these gaps are filled by the light shield sheets  7 . For this reason, the illumination device of the present embodiment eliminates the disadvantage of the adverse affects on printing caused by light leaking from the color wheel  11 . 
     FIG. 5 is a side section view of an illumination device  24  of a third embodiment of the invention. As shown in the drawing, a housing body  8   a  is provided with airflow inlets  9   a  at positions near a rotational axis of a color wheel  11 . The airflow inlets  9   a  are provided at equal intervals on a circumference centered on a position corresponding to the rotational axis of the color wheel  11 . 
     In the illumination device  24  of this embodiment, a space (B) between the color wheel  11  and the housing body  8   a  is small relative to a space (C) between the color wheel  11  and a housing cover  8   b , such that an airflow (indicated by an arrow  12 ) is generated from the center of the color wheel  11  toward the exterior side in the space (B). However, since airflow inlets  9   a  are provided on the space (B) side, exterior air flows in from the airflow inlets  9   a , and air pressure in the space (B) does not change. Since the airflow inlets  9   a  are provided at equal intervals on the circumference centered on the position corresponding to the rotational axis of the color wheel  11 , the entering airflow is not deflected, and a constant air pressure is maintained in the space (B). 
     FIG. 6 is a side section view of an illumination device  24  of a fourth embodiment of the invention. This illumination device  24  differs from the illumination device  24  of the third embodiment shown in FIG. 5 in that airflow outlets  9   b  are provided at positions in a housing body  8   a  near a circumferential area of a color wheel  11 . The airflow outlets  9   b  are provided at equal intervals in housing body  8   a  on a circumference centered on a position corresponding to a rotational axis of the color wheel  11 . Other structural aspects are identical with those of the illumination device of the third embodiment. 
     In the illumination device  24  of the present embodiment, an airflow (indicated by an arrow  12  in the drawing) is generated from a center of the color wheel  11  toward the exterior side thereof in a space (B) between the color wheel  11  and the housing body  8   a , identical to the airflow in the illumination device  24  of the third embodiment. At this time, exterior air inflow through the airflow inlets  9   a , and the air within the housing  8  is discharged via the airflow outlets  9   b , such that the air pressure in the space (B) does not change. Since the airflow inlets  9   a  and the airflow outlets  9   b  are provided at equal intervals on the circumferences centered on the position corresponding to the rotational axis of the color wheel  11 , the inflowing air and the outflowing air are not deflected, and a constant air pressure is maintained in the space (B). 
     In the illumination devices  24  of the third and fourth embodiments, air filters may be installed in the airflow inlets  9   a  . FIGS. 7A and 7B are respective side section views of devices provided with air filters  13  in the airflow inlets  9   a  of the illumination devices  24  of the third and fourth embodiments. Since this air filters  13  trap the dust in the air entering through the airflow inlets  9   a , the air within the housing  8  is clean, and dirt adhering to the color wheel  11  is greatly suppressed. 
     FIG. 8 is a side section view of an illumination device  24  of a fifth embodiment of the invention. This illumination device  24  differs from the illumination device  24  of the fourth embodiment of FIG. 6 in that connecting pipes  9   c  are provided to connect the airflow inlets  9   a  and the airflow outlets  9   b . Other structural aspects of the device are identical to the illumination device  24  of the fourth embodiment. 
     In the illumination device  24  of the present embodiment, an airflow (indicated by an arrow  12  in the drawing) is generated from a center of a color wheel  11  toward an exterior side thereof in a space between the color wheel  11  and a housing body  8   a , identically to the illumination device  24  of the fourth embodiment. Since this airflow  12  circulates through the connecting pipes  9   c , the air pressure in the space does not change. 
     FIG. 9 is a side section view of an illumination device  24  of a sixth embodiment of the invention. As shown in the drawing, in the illumination device  24  of this embodiment, a color wheel  11  is accommodated within a housing  8  such that a space (B) between the color wheel  11  and a housing body  8   a  and a space (C) between the color wheel  11  and a housing cover  8   b  are identical in size. The housing  8  is provided with a space (D) which is larger than the conventional housing  8  (refer to FIG. 13) on an exterior side of the color wheel  11 . 
     In the illumination device  24  of the present embodiment, an airflow (indicated by an arrow  12  in the drawing) is generated from a center of the color wheel  11  toward the exterior side thereof in the space (B) and space (C), so that a low air pressure condition exists in both space (B) and space (C). Since there is no difference in the air pressure in the space (B) and the space (C), there is no deflection force (indicated by the arrow  14  in FIG. 13) exerted on the color wheel  11  as is the case conventionally. The air in the space (B) and the space (C) moves to the space (D) of the housing  8  via the airflow  12 , and a high air pressure condition exists in the space (D) to maintain a constant low air pressure condition in the spaces (B) and (C). 
     Each of the illumination devices of the first through the sixth embodiments are applied to a full color printer using a PLZT printing head as shown in FIG. 10, and the color of the glass panels  1   r ,  1   g  and  1   b  are designated R, G, B. However, it is naturally possible to use glass panels of other colors. The illumination device of the present invention is an illumination device which sequentially switches color of light, and as such is not only applicable to printers, but also to other devices. 
     As described above, the illumination device of the present invention is provided with a frame member on an exterior circumference of a rotating panel, and, therefore, the rotating panel is supported by the frame member such that transparent members of the rotating panel are hard to be damaged even when a very large centrifugal force is exerted on the rotating panel. For this reason, the rotating panel is capable of high-speed rotation, and allows color of light to be switched rapidly. When adhesive is loaded in gaps between the transparent members and the frame member in the illumination device, any looseness between the members is absorbed by the adhesive. For this reason, the transparent panels are supported stably by the frame member and are hard to be damaged even when a very strong centrifugal force is exerted. 
     In another illumination device of the present invention, a light shield member is provided in a connective region between the transparent panels, so as to block light from leaking from gap in the connective region. In this way, the illumination device prevents light from leaking from the rotating panel. 
     In another illumination device of the invention, a housing is provided with an airflow inlet and an airflow outlet, such that air pressure within the housing does not change even when an airflow is generated within the housing by the rotation of the rotating panel. For this reason, in this illumination device, a deflection force is not exerted on the rotating panel due to a change in air pressure within the housing, thereby providing stable rotation of the rotating panel. Furthermore, since dust is removed from an air flowing into the housing when a filter is provided in the airflow inlet, the air within the housing remains clean, and dirt adhesion to the rotating panel is greatly suppressed. 
     In yet another illumination device of the present invention, the rotating panel is accommodated within the housing so as to maintain the two mutually opposing surfaces of the housing parallel to the rotational plane of the rotating panel at equal distances from the rotating panel, and maintain a uniform low air pressure state on the periphery of the rotating panel. For this reason, a deflection force is not exerted on the rotating panel, and the rotating panel maintains a stable rotation. 
     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the present invention as defined by the appended claims unless they depart therefrom.