Patent Publication Number: US-6707482-B2

Title: Exposure head and producing method for a light guiding member thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exposure head used for an instant printer and so forth. 
     2. Description of the Related Art 
     An instant printer built in an electronic still camera obtains a subject image by exposing an instant film with an exposure head utilizing a semiconductor light source of LEDs, a laser and so forth. Incidentally, the LEDs emit the light of red, green and blue. On the instant film, is recorded a subject obtained through a taking lens. In the case of the exposure head, the light emitted from the LED and the laser is condensed on the instant film by using a lens system of a condenser lens and so forth. Colors are controlled every dot. When the lens system is used for the exposure head, there arises a problem in that the exposure head becomes large. Further, in this instance, an amount of the light is reduced at the time of light transmission. Thus, there arises another problem in that it is required to secure sufficient exposure duration by slowing down a printing speed, in order to gain enough amounts of the light. 
     As to a method for solving the above problems, Japanese Patent Laid-Open Publication No. 10-76706 discloses a small-sized exposure head in which a condenser Lens is not used. This exposure head comprises a light-source portion, a front portion, and a light shielding portion. The front portion is formed with an opening for irradiating exposure light, which is emitted from a semiconductor light source, to a photosensitive material. The light shielding portion is formed with an opening for containing the semiconductor light source. The front portion is adapted to face the photosensitive material. By virtue of this, the light emitted from the light source is directly irradiated to a photosensitive surface of the photosensitive material. In this way, it is possible to form an image by using the high-intensity exposure light whose attenuation is small. 
     However, in the above-mentioned exposure head, the opening formed in the front portion is smaller than the opening formed in the light shielding portion. Due to this, there arises a problem in that the light emitted from the light source can not be efficiently used. As a method for solving this problem, it may be considered to employ a photosensitive material having high sensitivity. However, using the photosensitive material of high sensitivity causes an increase of cost. Meanwhile, since this exposure head does not use a lens system, a depth of focus is shallow. Thus, when a distance between the photosensitive material and the exposure head is long, there arises a problem in that contrast is lowered. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is a primary object of the present invention to provide an exposure head and a producing method therefor in which an amount of light emitted from a light source is efficiently used without using a lens system. 
     It is a second object of the present invention to provide an exposure head and a producing method therefor in which high-quality printing is performed by making a depth of focus deep. 
     In order to achieve the above and other objects, the exposure head according to the present invention comprises a plurality of light emitting elements and a light guiding member for surrounding each of these elements. The light emitting elements are disposed at same intervals to form an image on a photosensitive material. The light guiding member is attached to the light emitting element so as to surround an optical axis thereof. Light of the light emitting element is uniformly applied to a photosensitive surface of the photosensitive material by means of the light guiding member. At the same time, a part of the light of the light emitting element is reflected on an inner wall of the light guiding member. Owing to this, the lights of the adjacent light emitting elements are prevented from overlapping on the surface of the photosensitive material. 
     In a preferred embodiment, the inner wall of the light guiding member has at least two kinds of reflectance, namely low reflectance and high reflectance. A cross section of the light guiding member perpendicular to the optical axis is preferable to be a square shape or a circular shape. The inner wall of the light guiding member is constituted of a first low-reflection area, a high-reflection area, and a second low-reflection area. These areas are arranged from a side of the light emitting element toward the photosensitive material. The light guiding member is preferable to be disposed such that a middle point between the light emitting element and the photosensitive material is positioned within the high-reflection area. 
     In another embodiment, the inner wall of the light guiding member is slanted in an optical-axis direction thereof. The cross section of the light guiding member perpendicular to the optical axis is formed so as to become smaller gradually toward a light irradiation opening. In this instance, a slant angle θ of the inner wall is preferable to be within a range of 1°≦θ≦3°. It is further effective that the inner wall of the light guiding member is formed from a material having the reflectance of 50% or more. 
     As to a producing method for the light guiding member whose inner wall is constituted of at least two kinds of reflectance, there is a method in which masking is performed for the low-reflection area of the light guiding member. Except a portion of masking, plating or deposition is carried out to form the high-reflection area. 
     According to the exposure head of the present invention, it is possible to obtain a large amount of the light without using a condenser lens. Moreover, the light of the light emitting element may be effectively used so that a picture print having high quality may be obtained without using a photosensitive material having high sensitivity. Further, it is possible to realize the exposure head in which the depth of focus is deep. Owing to this, positional management of the photosensitive material may be easily executed, and costs of the printer itself may be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments of the invention when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view showing a front side of an electronic still camera according to the present invention; 
     FIG. 2 is a perspective view showing a rear side of the electronic still camera; 
     FIG. 3 is an explanatory illustration showing an internal structure of the electronic still camera; 
     FIG. 4 is a perspective view showing a structure of a conveying mechanism of an instant film; 
     FIG. 5 is a sectional view showing a structure of an exposure head; 
     FIG. 6 is a flow chart showing a process for producing a reflection case; 
     FIG. 7 is a perspective view showing an LED and the reflection case; 
     FIG. 8 is a graph showing a relationship between an irradiation range of the LED and light-amount distribution of respective positions when an inner wall of the reflection case is formed from only a high-reflection material; 
     FIG. 9 is a graph showing a relationship between the irradiation range of the LED and light-amount distribution of the respective positions when the inner wall of the reflection case is formed from a low-reflection material and the high-reflection material; 
     FIG. 10 is a graph showing another example of a relationship between the irradiation range and the light-amount distribution when the inner wall of the reflection case is formed from only the high-reflection material; 
     FIG. 11 is a graph showing another example of a relationship between the irradiation range and the light-amount distribution when the inner wall of the reflection case is formed from the low-reflection material and the high-reflection material; 
     FIG. 12 is a sectional view showing a structure of the exposure head in a case that the inner wall of the reflection case is slanted in an optical-axis direction; 
     FIG. 13 is a sectional view showing a reflection state of the light emitted from the LED; 
     FIG. 14 is a graph showing the light-amount distribution under a condition that the inner wall of the reflection case is slanted; and 
     FIG. 15 is a perspective view showing the LED and the reflection case. 
    
    
     DETAILED DESCRIPTION OF THE 
     PREFERRED EMBODIMENT (S) 
     FIG. 1 is a perspective view showing a front side of an electronic still camera having a built-in instant printer according to the present invention. The electronic still camera  2  substantially has a parallelepiped shape. A front face of a camera body  3  is provided with a viewfinder window  4 , a taking lens  5  having a zoom function, a release button  6 , a flash window  7 , and a light receiving window  8  for photometry. Moreover, a central portion of the camera body  3  is provided with a film-chamber lid  9 . The camera body  3  is provided with a lock release button  10  disposed at a light-upper portion of the front face thereof. When a film pack is contained or is removed, the lock release button  10  is pressed to open the film-chamber lid  9 . A top face of the camera body  3  is formed with a film outlet  11  (see FIG. 3) which is usually covered with an outlet lid  12 . 
     As shown in FIG. 2, a rear face of the camera body  3  is provided with a power switch  13 , an eyepiece window  14 , a liquid-crystal-display panel (LCD panel)  15 , and an operation panel  16 . The LCD panel  15  displays, in real time, a subject image taken through the taking lens  5 . In other words, the LCD panel  15  constitutes an electric viewfinder. The operation panel  16  includes a mode changing key, a frame selecting key, a print start key, an eraser key for image data, a data input-output key, and so forth. The mode changing key is for changing a photograph mode and a reproduction mode, and the data input-output key is for changing input and output of the image data. Moreover, a lower portion of the camera body  3  is provided with a memory-chamber lid  17  and a battery-chamber lid  18 . The memory-chamber lid  17  is locked in a closed position. When a memory card is contained or is removed, the memory-chamber lid  17  is opened by moving a slider  19  provided on the bottom of the camera body  3 . 
     FIGS. 3 and 4 schematically show arrangement of components of the instant printer. After containing a film pack  20 , the film-chamber lid  9  is closed. In association with this, an exposure head  25  is moved above the film pack  20  so as to be positioned just above an exposure aperture formed in the film pack  20 . Upon instruction of printing, an instant film  21  is exposed with the exposure head  25 . 
     A conveying mechanism for the instant film  21  is constituted of a DC motor  30 , a driving mechanism  31 , a capstan  32 , a pinch roller  33 , and a roller pair  34 . The capstan  32 , the pinch roller  33  and the roller pair  34  are rotated by the DC motor  30  via the driving mechanism  31 . When the DC motor  30  is driven, a well-known claw (not shown) is actuated via the driving mechanism  31  to push the uppermost instant film  21 . A top end of this instant film  21  is advanced to be interposed between the capstan  32  and the pinch roller  33 . Successively, the advanced instant film  21  is conveyed by the above-mentioned components. After that, developer pods of the instant film  21  are broken by the roller pair  34  for permeation of the developer. The developed instant film  21  is discharged through the film outlet  11 . 
     As shown in FIG. 5, the exposure head  25  comprises LEDs  40  to  42  respectively emitting light of each color of R, G and B. Each of the LEDs  40  to  42  has a line shape whose length corresponds to a width of an exposure area of the instant film  21 . The respective LEDs  40  to  42  are disposed so as to lengthen in a main-scanning direction and are arranged in a sub-scanning direction in an order of R, G and B. It is possible to perform the exposure every dot. The respective LEDs  40  to  42  are controlled by a controller (not shown) with respect to a light emitting period and light intensity. Incidentally, the arrangement of the LEDs  40  to  42  is not exclusive to this embodiment. For example, the LEDs of R, G and B may be arranged in matrix (m×n). In this instance, the exposure head is required to be moved in the main-scanning direction at the time of printing. 
     A reflection case  45  is attached to the front of each of the LEDs  40  to  42 . The reflection case  45  is used as a light guiding member and has a square cross section in a crosswise direction relative to an optical axis of the reflection case  45 . One end of the reflection case  45  is an opening facing a photosensitive surface of the instant film  21 . In other words, one end of the reflection case  45  is an irradiation opening  46  through which the light emitted from the LED is applied to the instant film  21 . The reflection cases  45  are arranged in matrix, and the adjacent reflection cases  45  are disposed at a predetermined interval. Incidentally, the cross section of the reflection case  45  is not exclusive to the square shape, but may be a circular shape. 
     A process for producing the reflection case  45  is described below, referring to a flow chart shown in FIG.  6 . The reflection case  45  is formed from plastic which includes a black resin material comprising ABS resin, for example. One side of the reflection case  45  is dipped in a liquid masking material to perform masking. Similarly, masking is performed for the other side of the reflection case  45 . After that, plating or deposition is carried out except the masking portion, using silver, aluminum, and so forth. Finally, the masking materials of both sides are removed. Incidentally, the reflection case  45  may be formed by means of micro-machining and etching. 
     FIG.  8  and FIG. 9 are graphs, each of which shows light-amount distribution of an area irradiated by the LED. Such as shown in FIG. 7, a size of the LED  50  (width W1×depth D1) is 80×80 μm, and a size of the reflection case  45  (width W2×depth D2×height H1) is 100×100×1000 μm. An abscissa line of the graph represents distances from an optical axis of the LED  50 . An ordinate line of the graph represents relative light intensity with the proviso that the maximum amount of the light is set to 1. Meanwhile, in FIGS. 8 and 9, measurement is performed under a condition that a length L is 50 μm, wherein the length L is from the irradiation opening  46  of the reflection case  45  to the photosensitive surface of the instant film  21 . When an inner wall of the reflection case  45  is formed only with a high-reflection area  45   b  (reflectance is 0.9, G 1 =G 3 =0, G 2 =1000 μm), the light-amount distribution becomes normal distribution, such as shown in FIG.  8 . In this instance, since the width W2 of the reflection case  45  is equal to 100 μm, the light amount is considerably observed at the outside of dotted lines in FIG.  8 . In other words, the light applied to the photosensitive surface considerably escapes so that contrast of an image is deteriorated. 
     When the inner wall of the reflection case  45  is formed with a first low-reflection area  45   a  (reflectance is 0.1, G 1 =510 m), the high-reflection area  45   b  (reflectance is 0.9, G 2 =40 μm), and a second reflection area  45   c  (reflectance is 0.1, G 3 =450 μm), the light is applied to the photosensitive surface of the instant film  21  within a range substantially corresponding to the width of the irradiation opening  46  of the reflection case  45 . Thus, a leakage amount of the light is a little so that the contrast of the image is improved. Moreover, since the above-mentioned length L is set to 50 μm, a middle point between the respective LEDs  40  to  42  and the photosensitive surface of the instant film  21  is positioned within the high-reflection area  45   b . Owing to this, it is possible to effectively use the light emitted from the LED. Further, by using the reflection case  45 , it is possible to make the interval of the adjacent LEDs narrower than the height of the reflection case  45 . 
     By the way, the breadths G 1  to G 3  of the reflection areas  45   a  to  45   c  are different in accordance with the size and the light amount of the LED, the size of the reflection case, the reflectance of the reflection area, and the length between the irradiation opening of the reflection case and the photosensitive surface of the instant film. The breadths G 1  to G 3  may be properly changed in accordance with a size of the exposure head. Meanwhile, the reflectance of the first low-reflection area  45   a  is determined so as to be same with that of the second low-reflection area  45   c . However, this is not exclusive. The reflectance maybe properly changed. 
     In the above embodiment, the reflection case  45  is disposed such that the middle point between the respective LEDs  40  to  42  and the photosensitive surface of the instant film  21  is positioned within the high-reflection area  45   b . The middle point, however, may be positioned at a border between the high-reflection area and the low-reflection area. For example, when the sizes of the LED and the reflection case are identical with that of the above embodiment and the length L is set to be equal to 100 μm, the light-amount distribution of the area irradiated by the LED is shown in each of FIGS. 10 and 11. As shown in these drawings, when the inner wall of the reflection case  45  is formed only with the high-reflection area  45   b , the light-amount distribution becomes normal distribution. At this time, a spread of distribution is wider in comparison with the case of 50 μm. Due to this, the leakage amount of the light becomes larger so that the contrast is deteriorated. In the meantime, when the inner wall is constituted of three reflection areas, the irradiation range and the contrast do not change in comparison with the case in that the length L is equal to 50 μm. 
     As to another method in which the light emitted from a plurality of elements disposed at same intervals is uniformly applied to the photosensitive material and the light of the adjacent elements are prevented from overlapping, it is considered that the inner wall of the reflection case is slanted in an optical-axis direction. In this instance, as shown in FIG. 12, the inner wall of the reflection case  55  is inwardly slanted by θ relative to the optical axis. In other words, the reflection case  55  is formed such that a section thereof crosswise to the optical axis is adapted to gradually become small from an LED side toward an irradiation opening  56 . The section of the reflection case  55  may have a circular shape instead of the square shape. In this instance, the inner wall of the reflection case  55  (including a side inner wall and an end inner wall to which the LEDs  57  to  59  are attached) is formed from a material having the high reflectance. The light emitted from each of the LEDs  57  to  59  is reflected inside the reflection case  55  and is applied to a photosensitive surface of the instant film  60  through the irradiation opening  56  which is formed at a position facing the instant film  60 . Incidentally, reference numeral  62  denotes the exposure head. 
     In FIG. 13, light A 1  is emitted from an LED  65  so as to have an angle which is near a right angle relative to the photosensitive material. The light A 1  is reflected on the inner wall of the reflection case and is applied to the photosensitive surface of the photosensitive material through the irradiation opening  56 . In contrast, light A 2  is emitted so as to have an angle which is near a parallel angle relative to the photosensitive material. The light A 2  is repeatedly reflected on the inner wall of the reflection case  55  and is not applied to the photosensitive material. Owing to this, the reflected light of the respective LEDs  57  to  59  may be effectively used. Incidentally, the material of the inner wall of the reflection case  55  is sufficient to have the reflectance of 50% or more. Instead of forming the inner wall of the reflection case  55  from the material having the high reflectance, plating and deposition using silver, aluminum, and so forth may be performed for the inner wall of the reflection case  55 . 
     FIG. 14 is a graph showing examples of the light-amount distribution on the photosensitive surface under a condition that the slant angle θ of the reflection case  55  is changed. An abscissa line of the graph has the origin which coincides with the optical axis of the LED. An ordinate line of the graph represents the normalized light intensity of each position under a condition that the maximum light amount is set to 1. As shown in FIG. 15, the reflection case used in this embodiment has an upper face whose sizes (width W1×depth D1, and height H1) are respectively 100×100 μm, and 1000 μm. Meanwhile, the LED  65  has sizes (width W3×depth D3) are 80×80 μm. The irradiation opening  56  of the reflection case  55  has sizes (width W2×depth D2) which are determined in accordance with the slant angle θ. The slant angles θ are set to four kinds of 0°, 1°, 2° and 2.5°, and the graph in FIG. 14 shows the light-amount distribution of each condition. 
     When the slant angle θ is 0°, the reflection case  55  has a parallelepiped shape. In this instance, such as shown in FIG. 14, the light emitted from the LED  65  becomes normal distribution wherein a dispersion width is long on the photosensitive surface of the photosensitive material. As the slant angles θ are set to 1°, 2° and 2.5°, the dispersion width of the light applied to the photosensitive surface becomes shorter. In other words, a percentage of the applied light becomes large around an intersection of the photosensitive surface and the optical axis of the LED  65 . The light intensity is rapidly lowered in accordance with a separation from the intersection so that the leakage light may be reduced. In view of this, the inner wall of the reflection case  55  is preferable to be formed within a range of the slant angle θ being 1°≦θ≦3°, more preferably, 1°≦θ≦2.5°. By slanting the inner wall of the reflection case  55  within the above range, is effectively used the irradiation light of the LED  65  advancing at an angle being substantially perpendicular to the photosensitive material. The light emitted from the LED  65  at a small angle relative to the photosensitive material is cut out so that a percentage of the leakage light is reduced. Consequently, the contrast between the adjacent pixels may be intensified. 
     In the above embodiment, the present invention is adopted to the exposure head of the instant printer. The present invention, however, may be adopted to an exposure head of a printer using a peculiar photosensitive material, such as disclosed in Japanese Patent Laid-Open Publication No. 10-76706. 
     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.