Patent Publication Number: US-6906740-B2

Title: Light emitting array unit and side printing device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light emitting array unit having light emitting elements, and a side printing device. More particularly, the present invention relates to a light emitting array unit having light emitting elements, and a side printing device, which have a simple structure and in which quality in emitting light can be high. 
     2. Description Related to the Prior Art 
     A process of manufacturing photosensitive material, such as photo film, includes a step of side printing for printing information to a side portion of the photosensitive material in a form of a latent image. The information has forms of at least one of letters, numbers, indicia, bar code or the like, and represents a name of the manufacturer, the ISO sensitivity and the like. The latent image is converted to a visible image by developing operation for developing the photosensitive material. At the time of producing photographic prints, the information can be read or checked directly by the naked eye of an operator, or an automatic reader device. 
     JP-A 2-100043 discloses an example of side printing head assembly for side printing to a side portion of the photosensitive material. The side printing head assembly includes a light source, which includes plural LEDs (light emitting diodes) for emitting light of different wavelengths. Optical fibers having a great diameter include an entrance surface, which is opposed to the light source. A plurality of optical fiber bundles having a small diameter is connected to an exit surface of the optical fibers by fiber coupling. Light from the light source is caused to exit through the exit surfaces of the optical fiber bundles. 
     The optical fibers mix up uniformly the colors of light emitted by the LEDs as light source. The optical fiber bundles form shapes of pixels. Exit surfaces of the optical fiber bundles are oriented perpendicularly to feeding of the photosensitive material. In synchronism with feeding of the photosensitive material, the LEDs are driven to emit light selectively. The latent image of the letters, numbers, indicia, bar code or the like is printed to a side portion of the photosensitive material through a lens constituting an optical system for the side reduction. 
     Also, U.S. Pat. No. 4,508,438 (corresponding to JP-A 58-219543) discloses another structure of the side printing head assembly. An LED array includes plural LEDs, is opposed to the photosensitive material, and extends perpendicularly to feeding of the photosensitive material. Each of the LEDs in the LED array corresponds to one of the pixels constituting the latent image, and is connected with an LED driver, and is driven selectively to illuminate according to a pixel position designated in the sequential driving. A pattern is created by sequential driving, and is focused on to the side portion of the photosensitive material by a lens that is an optical system for size reduction. In synchronism with feeding of the photosensitive material, the LEDs are selectively driven one after another, to print the latent image of the letters, numbers, indicia, bar code or the like to the side portion of the photosensitive material. 
     However, the known structure according to the above first document has a shortcoming. The side printing head assembly including the optical fibers has such problems as diminution of the light amount in the optical fiber bundles, a considerably large space of the entire apparatus due to the structural complexity, a high manufacturing cost, and the like. 
     On the other hand, the known structure according to the above second document has a shortcoming. Light beams emitted by adjacent two of the LEDs are mixed at least partially, to cause problems of irregularity in the light amounts between the pixels, irregularity in patterned dots, and other unwanted states of light. Also, the LEDs must be disposed in a very high number per unit area, and causes difficulties in producing a wiring pattern on a printed circuit board. It may be possible to prevent such problems by spreading an interval at which the LEDs are arranged. However, a pitch of pixels in the latent image will be greater, so that the quality in printing will become remarkably low. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems, an object of the present invention is to provide a light emitting array unit having light emitting elements, and a side printing device, in which quality in emitting light can be high, which can be produced easily, and also in which the light emission can be controlled easily. 
     In order to achieve the above and other objects and advantages of this invention, a light emitting array unit for emitting line-shaped light constituted by plural spotted lights arranged in a line is provided. There are N light emitting element arrays disposed substantially in parallel with one another, each of the light emitting element arrays including plural light emitting elements arranged linearly in a first direction and at a pitch P, the light emitting elements being offset between the light emitting element arrays in the first direction by P/N time as much an amount as the pitch. A light guide means guides light emitted by respectively the light emitting elements, to create the line-shaped light. 
     A light emitting array unit for emitting line-shaped light is provided, in which a first light emitting element array includes first to Pth light emitting elements, for emitting a first beam train or train of spotted lights. A second light emitting element array is disposed to extend substantially in parallel with the first light emitting element array, and includes (P+1)th to Qth light emitting elements arranged alternately with the first to Pth light emitting elements for emitting a second beam train. At least one light path changer receives incidence of a selected one of the first and second beam trains, and changes a path of the selected beam train to emit the selected beam train together with a remaining one of the first and second beam trains, the line-shaped light being constituted by the first and second beam trains and being emitted. 
     In a preferred embodiment, the at least one light path changer includes a first light path changer for receiving incidence of the first beam train, and for emitting the first beam train in a predetermined direction. A second light path changer receives incidence of the second beam train, and emits the second beam train in the predetermined direction. 
     The line-shaped light is projected to photosensitive material being fed, and prints information thereon. 
     The first light path changer includes first to Pth reflection surfaces for reflecting first to Pth beams or spotted lights in a predetermined direction, the first to Pth beams being included in the first beam train being incident. The second light path changer includes (P+1)th to Qth reflection surfaces for reflecting (P+1)th to Qth beams in the predetermined direction, the (P+1)th to Qth beams being included in the second beam train being incident. 
     Furthermore, first to Pth photo sensors detect respectively the first to Pth beams or spotted lights, to check operation of the first to Pth light emitting elements. (P+1)th to Qth photo sensors detect respectively the (P+1)th to Qth beams, to check operation of the (P+1)th to Qth light emitting elements. 
     The first and second light path changers include first to Qth prism elements having respectively the first to Qth reflection surfaces. 
     The first to Pth light emitting elements and the (P+1)th to Qth light emitting elements are so arranged that an interval between two adjacent light emitting elements thereof are substantially equal to a width of each of the light emitting elements. 
     An Nth reflection surface included in the first to Qth reflection surfaces reflects part of an Nth beam or spotted beam included in the first to Qth beams, and transmits remaining part of the Nth beam. An Nth photo sensor included in the first to Qth photo sensors is disposed on an extension of a straight line from an Nth light emitting element included in the first to Qth light emitting elements to the Nth reflection surface. 
     The first to Qth light emitting elements are light emitting diodes. 
     The photosensitive material is photo film, and the information is printed to a side portion of the photo film. 
     The first and second light emitting element arrays are opposed to each other, and emit the first and second beam trains toward each other. The first and second light path changers are disposed between the first and second light emitting arrays, and the predetermined direction is crosswise to a straight line extending between the first and second light emitting element arrays. 
     The (P+1)th to Qth reflection surfaces are arranged alternately with the first to Pth reflection surfaces, and are inclined opposite to the first to Pth reflection surfaces. 
     Furthermore, first and second boards have respectively the first and second light emitting element arrays mounted thereon, and being so disposed that the first and second light path changers are disposed therebetween. 
     In another preferred embodiment, furthermore, one board is provided, and has the first and second light emitting element arrays mounted thereon. The first to Pth light emitting elements and the (P+1)th to Qth light emitting elements are arranged in a zigzag arranging form. 
     The first to Pth reflection surfaces and the (P+1)th to Qth reflection surfaces are arranged in a zigzag form defined by moving the zigzag arranging form in parallel. 
     In still another preferred embodiment, each of the first to Qth light emitting elements includes three light emitting diodes for emitting light of respectively red, green and blue colors. 
     In another preferred embodiment, the light emitting array unit is used as a combination of first, second and third light emitting array units for emitting light of respectively red, green and blue colors. 
     According to another aspect of the invention, a side printing device is provided. A red light emitting array unit emits line-shaped light constituted by plural red spotted lights arranged in a line. A green light emitting array unit emits line-shaped light constituted by plural green spotted lights arranged in a line. A blue light emitting array unit emits line-shaped light constituted by plural blue spotted lights arranged in a line. An optical system combines the line-shaped light of three colors, to record a letter, number or indicia photographically in a full-color manner to a side portion of photo film being fed. Each of the red, green and blue light emitting array units includes the above-described construction. 
     The optical system includes two dichroic mirrors for combining the line-shaped light of the three colors, and a lens for projecting the line-shaped light of the three colors being combined on to the photo film. 
     In another preferred embodiment, the optical system includes three lenses for projecting respectively the line-shaped light of the three colors, to combine the three colors of the line-shaped light on to the photo film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent from the following detailed description when read in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective, partially cutaway, illustrating a side printing device; 
         FIG. 2  is an exploded perspective illustrating a light emitting array unit in the side printing device according to the invention; 
         FIG. 3  is an exploded perspective illustrating the light emitting array unit; 
         FIG. 4  is a perspective illustrating light emitting array boards in the light emitting array unit; 
         FIG. 5  is an exploded perspective illustrating arrangement of LEDs, prism elements and photo sensors; 
         FIG. 6  is an explanatory view in side elevation, illustrating a preferred embodiment in which three printing heads are used for full-color printing; 
         FIG. 7  is an explanatory view illustrating another preferred side printing device having three LED array units for three colors; 
         FIG. 8  is a perspective illustrating three illuminating surfaces for the three colors are associated with each one of the light emitting diodes; 
         FIG. 9  is an exploded perspective illustrating a preferred embodiment in which LEDs are arranged in a zigzag manner on one board. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE PRESENT INVENTION 
     In  FIG. 1 , a side printing device  10  is depicted. The side printing device  10  includes a printing head  11 , a controller  12 , a suction drum  13 , a rotary encoder  14  and the like. Photo film  15  as a photosensitive material is positioned, and opposed to the printing head  11 . The printing head  11  includes a lens  16  and a light emitting array unit  18 . The lens  16  is an optical system for reduction of an image size. In the light emitting array unit  18  are disposed exit surfaces  17  arranged in an array for outputting light. See FIG.  2 . 
     The light emitting array unit  18  outputs light through the exit surfaces  17  for forming a latent image  15   a  of information by projecting the light into a side portion of the photo film  15 , in such desired forms as letters, numbers, indicia, bar code or the like. The emitted light is passed through the lens  16 , and projected to the side portion of the photo film  15  for an exposure. Each one of the exit surfaces  17  is associated with one pixel in the latent image  15   a  of the photo film  15 . The light in the line shape is emitted by the light emitting array unit  18  to print one line of the latent image  15   a.    
     The photo film  15  is fed by the suction drum  13  which tightly contacts the photo film  15  by suction. The rotary encoder  14  is connected with the suction drum  13 , and detects a state of feeding the photo film  15 . Each time that the photo film  15  is fed by a predetermined length, one rotational pulse is generated by the rotary encoder  14 . The rotational pulse is sent to the controller  12 , which drives the light emitting array unit  18  in synchronism with feeding of the photo film  15 . The latent image  15   a  is recorded to the photo film  15  one line after another. 
     In  FIG. 3 , the light emitting array unit  18  includes light emitting array boards  21  and  22 , spacer sheets  23  and  24 , a first prism element group  25  as first light path changer, a second prism element group  26  as second light path changer, and opaque blocking partitions  27 . A first light emitting element array  31  is mounted on the light emitting array board  21 . A second light emitting element array  32  is mounted on the light emitting array board  22 . 
     In  FIG. 4 , chips of LEDs (light emitting diodes)  33  as light emitting elements are arranged on the light emitting array board  21  in an array extending perpendicularly to feeding of the photo film  15 , and constitute the first light emitting element array  31 . Each of the LEDs  33  includes an illuminating surface  33   a  for emitting a light beam or spotted light. An interval between the LEDs  33  in the first light emitting element array  31  is approximately equal to a size of each of the LEDs  33 . An array of terminals  21   a  is provided, and operates for connection with the controller  12 . The terminal array  21   a  connects the LEDs  33  to the controller  12  electrically. 
     The second light emitting element array  32  in the light emitting array board  22  includes the LEDs  33  in a manner similar to the first light emitting element array  31 . There is an array of terminals  22   a  in the light emitting array board  22  for connecting the LEDs  33  with the controller  12  electrically. The light emitting array board  22  is structurally equal to the light emitting array board  21 , so that the two boards of only one type are prepared for the purpose of producing the light emitting array unit  18 . 
     The light emitting array boards  21  and  22  are so oriented as to oppose the LEDs  33  to one another on the two arrays. There are spacer sleeves  35  through which screws are inserted. The screws fasten the light emitting array board  21  to the light emitting array board  22  at a predetermined interval. Arrangement of the LEDs  33  is so determined that the LEDs  33  of a first one of the boards are not opposed to the LEDs  33  of the second one of the boards when boards are fastened on each other. 
     In combining the light emitting array boards  21  and  22 , the LEDs  33  included in the second light emitting element array  32  are disposed in alternation with those in the first light emitting element array  31 . In other words, the LEDs  33  in the second light emitting element array  32  are offset from those in the first light emitting element array  31  by an amount equal to the width of the LEDs  33 . Detection openings  36  are formed in the light emitting array boards  21  and  22  and positioned in their portions respectively opposed to the LEDs  33 . 
     In the present embodiment, the arrangement of the LEDs  33  is predetermined so that the contours of the light emitting array boards  21  and  22 , when combined, are opposed exactly to each other without offsetting. However, it may be possible to shape the light emitting array boards  21  and  22  so that the LEDs  33  would opposed directly to one another between those if those were opposed exactly. At the time of combining, the light emitting array boards  21  and  22  are intentionally offset by an amount of one LED so that the LEDs  33  are offset in the array extending direction. 
     The LEDs  33  in the single light emitting array unit have one common color. If the light emitting array unit is for use with motion picture photo film of a color positive type, the LEDs  33  have one of green and blue colors because red is used for the sound track. If the light emitting array unit is for use with motion picture photo film of a color negative type or photo film for still photography, the LEDs  33  have one of orange and yellow colors. If the light emitting array unit is for use with X-ray photo film, the LEDs  33  have one of green and blue colors. 
     In  FIG. 5 , the first and second prism element groups  25  and  26  are right-angle prisms in which entrance surfaces  25   a  and  26   a  receive entry of light, and the exit surfaces  17  output the light after bending a light path of the light by 90 degrees. The second prism element group  26  is structurally the same as the first prism element group  25  except for an orientation in disposition. 
     The first prism element group  25  includes plural prism elements corresponding to the LEDs  33  in the first light emitting element array  31 . The entrance surface  25   a  is opposed to the illuminating surface  33   a  of the LEDs  33  in the first light emitting element array  31 . The first prism element group  25  is oriented to direct the exit surfaces  17  to the front of the light emitting array unit  18 . The second prism element group  26  includes plural prism elements corresponding to the LEDs  33  in the second light emitting element array  32 . The entrance surface  26   a  is opposed to the illuminating surface  33   a  of the LEDs  33  in the second light emitting element array  32 . The second prism element group  26  is oriented to direct the exit surfaces  17  to the front of the light emitting array unit  18 . 
     Inclined reflection surfaces  25   b  and  26   b  are included in the first and second prism element groups  25  and  26  for bending light paths of the light beams or spotted lights. The light emitted by the LEDs  33  of the first and second light emitting element arrays  31  and  32  is bent by the inner reflection surfaces  25   b  and  26   b , and exits through the exit surfaces  17 . As the exit surfaces  17  are aligned in the combination of the first and second prism element groups  25  and  26 , beams of the light or spotted lights from the LEDs  33  are output through the front of the light emitting array unit  18  in a regularly aligned manner. 
     The exit surfaces  17  of the first and second prism element groups  25  and  26  have a sufficient surface roughness in a form of frosted glass to diffuse the light being emitted to the outside. This regulates an amount of light output for each of the pixels by the LEDs  33  as light source. 
     Half mirrors  37  are formed by depositing aluminum or the like on the reflection surfaces  25   b  and  26   b  of the first and second prism element groups  25  and  26 . The light from the LEDs  33  strikes the entrance surfaces  25   a  and  26   a  for entry, and is reflected by the inside of the reflection surfaces  25   b  and  26   b . However, the LEDs  33  are disposed very close to the entrance surfaces  25   a  and  26   a . An angle of incidence of the light from the LEDs  33  relative to the reflection surfaces  25   b  and  26   b  is in a considerably large range. Therefore, no total reflection of the incident light occurs. Part of the incident light passes the reflection surfaces  25   b  and  26   b , and exits from those. The remaining part is reflected by the reflection surfaces  25   b  and  26   b  in a manner of partial reflection. 
     The reflection layer is formed on the reflection surfaces  25   b  and  26   b , which is effective in minimizing a loss of light. Through the reflection layer or the half mirrors  37 , part of the incident light is used for checking operation of the LEDs  33 . 
     The blocking partitions  27  are arranged between the first and second prism element groups  25  and  26 . Light emitted by any one selected among the prism elements is prevented by the blocking partitions  27  from entry into the remaining prism elements. This is effective in preventing occurrence in irregularity in the light amounts between the pixels, irregularity in patterned dots, and other unwanted states of light. In  FIG. 3 , the blocking partitions  27  are depicted with a greater thickness than it has actually for the purpose of understanding by exaggeration. An actual thickness of the blocking partitions  27  is approximately 2 μm. Alternatively, it is possible to form a light-shielding film or layer by aluminum deposition on lateral faces of the first and second prism element groups  25  and  26  instead of disposing the blocking partitions  27 . 
     The spacer sheets  23  and  24  have suitably high resiliency, and are disposed between the inner face of the light emitting array board  21  and the first prism element group  25  and the inner face of the light emitting array board  22  and the second prism element group  26 . The spacer sheet  23  has a thickness associated with a difference between levels of the light emitting array board  21  and the LEDs  33  in a space between the light emitting array board  21  and the first prism element group  25 . The spacer sheet  24  has a thickness associated with a difference between levels of the light emitting array board  22  and the LEDs  33  in a space between the light emitting array board  22  and the second prism element group  26 . 
     The spacer sheets  23  and  24  have a compressible characteristic, and when the light emitting array boards  21  and  22  are combined, are resiliently deformed by pressure of the light emitting array boards  21  and  22  and the prisms. The spacer sheets  23  and  24  contact those tightly, and keep the prisms positioned relative to the array boards. In the present embodiment, both of the spacer sheets  23  and  24  are resilient and compressible. However, only a selected one of the spacer sheets  23  and  24  may be compressible. The remaining one of those may be rigid, and may operate only as a spacer without the tight contact. 
     In  FIG. 5 , the reflection surfaces  25   b  and  26   b  of the first and second prism element groups  25  and  26  are disposed directly above or below the detection openings  36  formed in the light emitting array boards  21  and  22 . In  FIG. 2 , a detection circuit board  40  is mounted on an outer face of the light emitting array boards  21  and  22 . Photo sensors  41  are incorporated in the detection circuit board  40 . Examples of the photo sensors  41  are photo diodes, photo transistors and the like. The photo sensors  41  are positioned on light paths that pass the detection openings  36  and the reflection surfaces  25   b  and  26   b , as the detection circuit board  40  is mounted on each of the light emitting array boards  21  and  22 . 
     The photo sensors  41  output a photoelectric signal upon receiving light. The photoelectric signal is sent from the photo sensors  41  to the controller  12 . The controller  12  monitors the photoelectric signal, and checks whether the LEDs  33  normally emits light. It is to be noted that the LEDs  33  may be inspected as to whether light is output at an intended light amount. Feedback control may be used to adjust the LEDs  33  to emit at a regularized light amount. 
     An input device (not shown) is connected with the controller  12 . Information related to printing is input to the controller  12  by operating the input device. According to the input information, the controller  12  drives the LEDs  33  selectively to emit light beams or spotted lights, so as to record the information to the photo film  15  in a form of the latent image  15   a . A current of driving the LEDs  33  and time of light emission are determined suitably according to photosensitivity and feeding speed of the photo film  15 . 
     The operation of the above construction is described now. The controller  12  is supplied with signals of printing information for printing letters, numbers, indicia, bar codes and the like to a side portion of the photo film  15  as the latent image  15   a . A driving pattern to drive the LEDs  33  is produced in the controller  12  according to the printing information. 
     Then a command signal for starting the side printing device  10  is input. The photo film  15  starts being fed. The rotary encoder  14  outputs a rotational pulse and sends the same to the controller  12 . The controller  12  drives the LEDs  33  selectively in synchronism with feeding of the photo film  15  according to a patterned sequence for driving the LEDs  33  and the rotational pulse. 
     Light beams or spotted lights emitted by the LEDs  33  on the light emitting array board  21  enter the first prism element group  25  through the entrance surface  25   a , and are reflected by the reflection surface  25   b , and exit from the first prism element group  25  through the exit surfaces  17 . Light beams emitted by the LEDs  33  on the light emitting array board  22  enter the second prism element group  26  through the entrance surface  26   a , and are reflected by the reflection surfaces  26   b , and exit from the second prism element group  26  through the exit surfaces  17 . 
     As a result, light emitted by the LEDs  33  on the light emitting array boards  21  and  22  exits through the exit surfaces  17  aligned in the front of the light emitting array unit  18 , passes through the lens  16 , and is projected to the photo film  15  for an exposure in one line. In synchronism with feeding of the photo film  15 , the LEDs  33  are selectively driven, to record information or the latent image  15   a  by projecting beams or spotted lights in an array to the side portion of the photo film  15  one line after another. 
     The exit surfaces  17  are formed in the manner of frosted glass. This form diffuses the light beams or spotted lights exiting through the exit surfaces  17 . Also, the blocking partitions  27  between the first and second prism element groups  25  and  26  operate for blocking light. There occurs no irregularity in the light amounts between the pixels, irregularity in patterned dots, and other unwanted states of light. 
     While the latent image  15   a  is recorded one line after another, part of light output by the LEDs  33  is passed through the half mirrors  37 , and received by the photo sensors  41 . If one of the LEDs  33  operates normally, a corresponding one of the photo sensors  41  outputs a photoelectric signal at a predetermined sufficient level. If one of the LEDs  33  is broken and does not emit light, a corresponding one of the photo sensors  41  does not output a photoelectric signal even while the light emitting array unit operates. 
     The controller  12  checks changes in the photoelectric signal according to timing of driving the LEDs  33 , and monitors a normal state of the LEDs  33  emitting light beams. If abnormality is detected to occur, a sequence for recording the latent image  15   a  is discontinued. An abnormality signal is sent to the external interface. Signal processing at the external interface stops the suction drum  13  from being driven. The feeding of the photo film  15  is stopped. If abnormality is detected, no failing product is made any longer. It is easy to designate positions in the photo film  15  having abnormality. 
     Light paths of light beams or spotted lights emitted by the LEDs  33  are bent by the first and second prism element groups  25  and  26  in a vertical manner, to emit light in a line shape. Then the light emitting array unit  18  can be constructed in a reduced size. Also, it is easy to design a pattern of wiring for driving the LEDs  33 , because the LEDs  33  are arranged at a sufficient interval on the light emitting array boards  21  and  22 . 
     The first and second prism element groups  25  and  26  in the light emitting array unit  18  cause the light beams or spotted lights from the LEDs  33  to exit and travel in one array. It is unnecessary to set changes in the timing of driving the LEDs  33  for the purpose of exposing one line. Thus, it is easy to control light emission of the LEDs  33 . 
     In  FIG. 6 , a side printing device of another preferred embodiment is depicted, including a red printing head  51 , green printing head  52 , and blue printing head  53  each of which is a light emitting array unit. Each of the printing heads  51 - 53  is provided with the lens  16 . To output light of a selected one of three colors from the printing heads  51 - 53 , any suitable one of various methods can be used. For example, LED chips having red, green and blue colors may be used. Alternatively, filters of red, green and blue colors may be combined with LED chips illuminating in a white color. 
     In this construction, the arrays of the light beams or spotted lights emitted by the printing heads  51 - 53  are mixed at points on the surface of the photo film  15 . The proportion in the light amount between the light beam arrays from the printing heads  51 - 53  can be changed to form the latent image  15   a  in full-color recording as desired. 
     In the embodiment of  FIG. 6 , the colors of light are mixed on the surface of the photo film. However, the colors of light may be mixed in a printing head  55  as depicted in FIG.  7 . The printing head  55  includes a red light emitting array unit  56 , a green light emitting array unit  57 , a blue light emitting array unit  58 , dichroic mirrors  59  and  60 , and a lens  61 . Each of the light emitting array units  56 ,  57  and  58  includes LEDs arranged in line. The dichroic mirror  59  lets red light pass, and reflects green light. The dichroic mirror  60  lets red light and green light pass, and reflects blue light. 
     Light axes of the green and blue light emitting array units  57  and  58  for the green and blue colors are set perpendicular to a light axis of the red light emitting array unit  56  for the red color. The dichroic mirror  59  is disposed at an intersection point of the light path of the green light emitting array unit  57  and that of the red light emitting array unit  56 . The dichroic mirror  60  is disposed at an intersection point of the light path of the blue light emitting array unit  58  and that of the red light emitting array unit  56 . When light beams or spotted lights are output by the light emitting array units  56 - 58 , the red, green and blue colors of the light beams are mixed up in the printing head  55 , and projected to the photo film  15  through the lens  61 . 
     It is preferable that part of light emitted by the green and blue light emitting array units  57  and  58  may be received by photo sensors and checked. To this end, pinholes may be formed in the dichroic mirrors  59  and  60  for passing the light. Furthermore, the dichroic mirrors  59  and  60  can have such a characteristic as to pass part of light of the green and blue light emitting array units  57  and  58  in a particular wavelength range. Also, it is possible to add a dichroic mirror for bending a light path of light from the red light emitting array unit  56 . This dichroic mirror may be provided with a structure similar to that of the dichroic mirrors  59  and  60 , so as to monitor light emission of the LED chips. Note that, in order to bend the red light path, a structure other than the dichroic mirror may be used. For example, a half mirror, a mirror with pinholes or the like may be used. 
     In  FIG. 8 , another preferred embodiment is illustrated, in which each of chips of LEDs (light emitting diodes)  62  as light emitting elements has a red illuminating surface  62   a , a green illuminating surface  62   b  and a blue illuminating surface  62   c . Except for the LEDs  62 , elements similar to those in the above embodiments are designated with identical reference numerals. Light beams or spotted lights output by the illuminating surfaces  62   a - 62   c  are mixed by the first and second prism element groups  25  and  26 , and then are applied to the photo film. As a result, the latent image  15   a  can be formed in the full-color recording. 
     In  FIG. 9 , another preferred embodiment is depicted, in which LED chips are disposed in a zigzag manner. Elements similar to those in the above embodiment are designated with identical reference numerals. 
     In the light emitting array unit, a light emitting array board  70  is provided with a first light emitting element array  71  and a second light emitting element array  72  both including the LEDs  33 . The LEDs  33  in the first light emitting element array  71  are offset from those in the second light emitting element array  72  by an amount equal to the width of one LED in the direction of the extension of the arrays. 
     A first prism element group  74  as first light path changer has an entrance surface  74   a , which is opposed to the LEDs  33  of the first light emitting element array  71 . The first prism element group  74  bends a light path of light from the LEDs  33 , and causes the light to exit through the exit surfaces  17 . A second prism element group  75  as second light path changer has such a size that an interval between an inclined reflection surface and the exit surfaces  17  is smaller than that of the first prism element group  74 . An entrance surface  75   a  of the second prism element group  75  is opposed to the LEDs  33  of the second light emitting element array  72 . The exit surfaces  17  of the second prism element group  75  are aligned with those of the exit surfaces  17  of the first prism element group  74 . A light path of light from the LEDs  33  in the second light emitting element array  72  is bent by the second prism element group  75  to output the light through the exit surfaces  17 . 
     Light beams or spotted lights output from the LEDs  33  on the light emitting array board  70  in a zigzag manner enter the first and second prism element groups  74  and  75 , are bent by 90 degrees, and are output as a single array of beams. A difference between lengths of light paths through the first and second prism element groups  74  and  75  is negligible. Thus, it is unnecessary to set changes in the timing of driving the LEDs  33  between the light emitting element arrays  71  and  72  for the purpose of exposing one line. Note that the LEDs  33  may be arranged in three or more arrays instead of the two arrays in the present embodiment. 
     Note that the LED chips are used as light emitting elements. However, other types of light emitting elements may be used. Instead of the prisms, other structures for bending light paths may be used, for example mirrors, half mirror. Furthermore, a light emitting array unit of the invention may be used in an optical printer in which a photosensitive drum can be exposed to record lines by use of light emitted in the linear shape. 
     In the above embodiments, the light paths are bent by the reflection. Alternatively, the light paths may be bent by methods other than the reflection. 
     Also, a light emitting array unit of the invention may be used as linear light source for various uses, for example, indoor illumination of a decorative type. 
     Although the present invention has been fully described by way of the preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those having skill in this field. Therefore, unless otherwise these changes and modifications depart from the scope of the present invention, they should be construed as included therein.