Exposure apparatus

Abstract: An exposure apparatus has a color shifter disk (93) which comprises three, B, G, and R, color filters (93B, 93G, 93R) formed by dividing the disk into three sectors and a light shielding member (94) arranged for moving to and from the light path in synchronization with the rotating movement of the color shifter disk (93), the light shielding member (94) advancing into the light path to interrupt the exposure light when a boundary between two adjacent color filters of the color shifter disk runs across the light path and retracting from the light path to pass the exposure light when the boundary between two adjacent color filters of the color shifter disk departs from the light path.

Description: BACKGROUND OF THE INVENTION The present invention relates to an exposure apparatus for use in a photographic printer machine and more specifically, to a digital exposure apparatus equipped with an exposure shutter of PLZT or liquid crystal type. Such an exposure apparatus is provided, as shown in Fig. 10, in which photosensitive papers (not shown) are exposed to three, blue, green, and red (referred to as BGR), colors of light produced by their respective color filters 101, 102, and 103 of a color shifter disk 104 disposed across the light path extending from a light source 105 to a light receiving surface 108 of a bundle of optical fibers 106. While a boundary 107 between two adjacent color filters of the color shifter disk 104 is across the light path, a mixture of their colors falls on the light receiving surface 108 of the optical fiber bundle 106. For this reason, a PLZT shutter (not shown) is kept turned off during the shifting movement of the disk 104. An exposure apparatus of this type is disclosed in EP-A-0 616 248. However, it is not perfectly done to interrupt an intensity of exposure light with the off action of the PLZT shutter and a leakage of the light will be perceived by the photosensitive papers which are thus declined in the quality of printing. Also, it takes a considerable length of time for the boundary 107 between the two filters to pass through the light receiving surface 108 of the optical fiber bundle 106. Accordingly, the shifting movement will be retarded as compared with the exposure time thus discouraging the increase of the quality of printing. The shifting time relative to the exposure time may be shortened by increasing the diameter of the color shifter disk 104 but this is not practical. It is an object of the present invention, in view of the foregoing predicaments, to provide an exposure apparatus capable of eliminating a leakage of the exposure light during the shifting of one color to another and shortening the duration of the shifting for preventing the quality of printing from declining. SUMMARY OF THE INVENTION The exposure apparatus according to the present invention is defined in claim 1. Also, as defined in claim 2, in the exposure apparatus according to claim 1 the light receiving face of the bundle of optical fibers may be formed of an oval configuration. As defined in claim 3, in the exposure apparatus according to claim 1 the light receiving face of the bundle of optical fibers may be formed of a rectangular configuration. As defined in claim 4, in the exposure apparatus according to claim 2 the light receiving face of the bundle of optical fibers may be formed of a fan-shaped configuration which spreads from the center point of the color shifter disk. In the exposure apparatus defined in claim 1, each of the three color filters of the color shifter disk is driven across the light path between the light source and the light receiving face of the bundle of optical fibers to produce B, G, and R modes of exposure light to which the photosensitive material is exposed forming a pattern of dots. When the boundary between two adjacent color filters on the color shifter disk runs across the light path, the light shielding member is advanced into the light path to interrupt the exposure light. As the boundary between two adjacent color filters on the color shifter disk departs from the light path, the light shielding member is retracted from the light path to pass the exposure light. The exposure apparatus of claim 1 allows the light shielding member to blind, in response to the boundary on the color shifter disk running across the light path (during the shifting of one color filter to another), the light receiving face of the bundle of optical fibers which will thus be prevented from receiving any unwanted portion of light or being double exposed. In addition, in the exposure apparatus of claim 1, the light receiving face of the bundle of optical fibers is flattened so that it extends along the boundary of two adjacent color filters of the color shifter disk which runs across the light path. More particularly, the width of the light receiving face of the bundle of optical fibers which extends in the direction of rotation across the boundary on the color shifter disk is shortened without changing the size of the same, thus minimizing the angular movement of the boundary across the light receiving face. As the duration of the boundary crossing the light receiving face of the bundle of optical fibers is decreased without changing the size of the light receiving face, the interval of light shielding will be minimized. In the exposure apparatus of claim 2 the duration of the boundary on the color shifter disk crossing the light receiving face of the bundle of optical fibers is decreased without changing the size of the light receiving face and the interval of blinding with the light shielding member will thus be minimized. In the exposure apparatus of claim 3 the duration of the boundary on the color shifter disk crossing the light receiving face of the bundle of optical fibers is decreased without changing the size of the light receiving face and the interval of blinding with the light shielding member will thus be minimized. The exposure apparatus of claim 4 has the light receiving face of the bundle of optical fibers formed of a fan-shaped configuration which spreads from the center point of the color shifter disk. This allows the boundary to run across the fan-shaped light receiving face with optimum efficiency as its angular movement matches the shape of the light receiving face, thus minimizing further the duration of blinding action of the light shielding member. BRIEF DESCRIPTION Or THE DRAWINGS Fig. 1 is a schematic overall view of a photographic printer machine equipped with an exposure apparatus of the present invention; Fig. 2 is a perspective view showing Embodiment 1 of an exposure apparatus; Fig. 3 is a diagram showing the timing relation in rotating movement between a color shifter disk and a light shielding disk of the embodiment; Fig. 4 is a diagram explaining steps of an exposure process of the embodiment; Fig. 5 is a diagram showing Embodiment 2 of an exposure apparatus; Fig. 6 is a diagram showing Embodiment 3 of an exposure apparatus; Fig. 7 is a diagram showing Embodiment 4 of an exposure apparatus; Fig. 8 is a diagram showing the timing relation in rotating movement between a color shifter disk and a light shielding disk of the last embodiment; Fig. 9 is a diagram showing a modification of the last embodiment; Fig. 10 is a perspective view of a prior art; and Fig. 11 is a diagram showing the timing relation in rotating movement between a color shifter disk and a light shielding disk of the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Fig. 1 is an overall schematic view of a photographic printing machine equipped with an exposure apparatus. As shown, there are provided a magazine 1 for supplying a tape of printing paper 2 as a photosensitive material, a negative exposure station 3 which comprises a light source 31 for emitting an intensity of exposure light through image frames of a negative film 32 and a lens 33, and a line exposure station 4 for reproducing digital images. Also, provided are a development station 5 for subjecting the exposed printing paper to a development process and a transfer mechanism 6 for acting as a conveying means. In action, the printing paper 2 is lengthwisely transferred on a basis of line-by-line and frame-by-frame. The photographic printing machine includes a line exposure controller station (not shown) which serves as a voltage changing means. The line exposure controller station controls the timing of exposure actions in the line exposure station 4 and the timing of transfer actions on the transfer mechanism 6. The line exposure station 4 prints on the printing paper 2 digital images retrieved by a scanner or produced by a separate electronic device such as a computer. The line exposure station 4 includes a PLZT shutter 41 composed of multiple rows of PLZT elements (not shown) extending widthwisely of the printing paper 2. The unshown PLZT elements of the PLZT shutter 41 are joined to a bundle of optical fibers 8. The optical fiber bundle 8 has a proximal end (at light receiving end) thereof located opposite to a PLZT illumination source 9 (described later) for emission of B, G, and R colors of light. The PLZT elements are energized with given amplitudes of voltage corresponding to the modes of light which have passed a color shifter disk 93 rotated in synchronous action. A selected waveform of the exposure light is then allowed to pass from the optical fiber bundle 8. The PLZT illumination source 9 includes a lamp 91 and a mirror tunnel 92 as well as the color shifter disk 93, and is adjacent to the proximal end of the optical fiber bundle 8. The optical fiber bundle 8 comprises a multiplicity of optical fibers having a light receiving end face 81 shaped of a round configuration. The color shifter disk 93 comprises three, B, G, and R, color filters 93B, 93G, and 93R formed as three equal sectors of the disk. Each fan-shaped sector of the filters 93B, 93G, and 93R extends through 120 degrees about the center C1 of the color shifter disk 93. The center C1 of the color shifter disk 93 is coupled to a rotary shaft (not shown) driven by an unshown motor. The color shifter disk 93 is disposed between the mirror tunnel 92 and the light receiving face 81 of the optical fiber bundle 8 so that its filter part comes across the light path extending from the lamp 91 to the light receiving face 81 of the optical fiber bundle 8. In action, while the color shifter disk 93 is rotated, its filters 93B, 93G, and 93R runs across the light path. Accordingly, the light passed through any of the filters 93B, 93G, and 93R is directed to the light receiving face 81 of the optical fiber bundle 8 and transmitted to corresponding PLZT elements of the PLZT shutter 41. During a color shifting interval where the boundary 930 between two adjacent ones of the color filters 93B, 93G, and 93R runs across the light receiving face 81 of the optical fiber bundle 8, the light receiving face 81 is blinded by a light shielding disk 94. The light shielding disk 94 comprises a shielding sector 94A (denoted by the hatching) and a transparent sector 94B. More specifically, the light shielding sector 94A extends through 60 degrees about the center C2 of the light shielding disk 94 while the rest of the disk 94 is the transparent sector 94B. The light shielding disk 94 is identical in the outer diameter to the color shifter disk 93. The light shielding disk 94 is disposed between the color shifter disk 93 and the light receiving face 81 of the optical bundle 8 so that its sector comes across the light path. The center C2 of the light shielding disk 94 is coupled to a rotary shaft (not shown) driven by an unshown motor. In action, the light shielding disk 94 rotates at a speed three times greater than the speed of and reversely of the color shifter disk 93. The movement of the light shielding disk 94 is controlled so that the light shielding sector 94A runs across the light path in synchronization with the boundary 930 of the color shifter disk 93 passing the same. As the light shielding sector 94a runs across the light path, it prevents the light receiving face 81 from receiving the light from the lamp 91 and allows no exposure to the light during the color shifting action. Otherwise, the transparent sector 94B remains across the light path allowing exposure actions. Although the light shielding sector 64A extends through 60 degrees, its 30-degree portion can entirely cover the light receiving face 81 of the optical fiber bundle 8 (Figs. 3(B) and 3(C)). The timing relation between the color shifter disk 93 and the light shielding disk 94 will now be explained referring to Fig. 3, in which the arrows indicate the directions of rotation of the two disks 93 and 94 respectively. (1) When the boundary 930 of the color shifter disk 93 moves into the light path across the light receiving face 81 (at the start of color shifting), the light shielding sector 94A of the light shielding disk 94 is simultaneously advanced to cover the light receiving face 81 (Fig. 3(A)). (2) As the boundary 930 is turned to 10 degrees from the position shown in Fig. 3(A), the light shielding sector 94A rotates 30 degrees to cover the light receiving face 81 entirely (Fig. 3(B)). (3) The boundary is further turned by 10 degrees from the position shown in Fig. 3(B) and the light shielding sector 94A further rotates 30 degrees (Fig. 3(C)). During the interval from Fig. 3(B) to 3(C), the light receiving face 81 remains blinded completely. (4) As the boundary 930 is turned again by 30 degrees from the position shown in Fig. 3(C) departing from the light receiving face 81, the light shielding sector 94A rotates 30 degrees and also departs from the same (Fig. 3(D)). As apparent, the light shielding action is terminated upon the completion of the color shifting. It should be noted that the PLZT shutter 41 remains turned off while the boundary 930 is running across the light receiving face 81 of the optical fiber bundle 8 and is turned on upon the completion of the color shifting with the boundary 930 having departed from the light receiving face 81. Accordingly, when the duration is T in which the boundary 930 runs throughout the light receiving face 81 (i.e. the boundary 930 rotates 30 degrees) with the need of blinding the entire area of the light receiving face 81, it takes a length of time T/3 (Figs. 3(A) and 3(B)) to cover the entire area of the light receiving face 81 with the light shielding sector 94A (or for the light shielding disk 94 to rotate 30 degrees). Also, the duration in which the light receiving face 81 is completely blinded with the light shielding sector 94A is T/3 (Figs. 3(B) and 3(C)). As the result, a leakage of light during the color shifting appears for T-T/3=2T/3. This means the exposure time of the printing paper 2 to the leakage light is reduced to 2/3. In respect to blinding a point (for example, the point a shown in Fig. 3(A)) in the light receiving face 81, the duration of the point being blinded with the light shielding sector 94A is expressed by 2T/3 (Figs. 3(B) to 3(D)). The leakage of light during the color shifting then appears for T-2T/3=T/3. Hence, the exposure time of the printing paper 2 to the leakage light is reduced to 1/3. The main exposure time will be examined. The duration of each of the color filters 93B, 93G, and 93R running across the light receiving face 81 of the optical fiber bundle 8 (i.e. the duration in which the color shifter disk 93 rotates 120 degrees) is (120/20)T=4T. The duration 4T includes a time T required for the color shifting. During the color shifting, the PLZT shutter 41 remains turned off disabling the exposure action. The duration for the exposure action is thus 4T-T=3T. The light shielding sector 94A moves in across the light receiving face 81 upon the boundary 930 running in across the light receiving face 81 and departs from the same upon the boundary 930 leaving the same. Thus, the exposure time will not be affected by the action of the light shielding sector 94A. The main exposure duration and the exposure time to leakage light may be controlled by varying the shape and size of the light shielding sector 94A and the receiving face 81 and/or the timing relation between the color shifter disk 93 and the light shielding disk 94. For example, when the light shielding disk 94 is greater in the outer diameter and higher in the rotating speed than the color shifter disk 93, the leakage of light will be minimized. It is also possible to change the diameter and rotating speed of the color shifter disk 93 and the light shielding disk 94 in accordance with the size of the light receiving face 81 of the optical fiber bundle 8. The exposure to each mode of B, G, and R color lights will be explained referring to Fig. 4. When the B filter moves into the light path, the amplitude of voltage to corresponding PLZT elements is turned to 45 V by the action of the line exposure controller 6. Then, the B mode of light is projected on to the printing paper 2 thus producing a pattern of dots D1, D2..., as shown in Fig. 4(A). After the color shifter disk 93 is rotated again to forward the G filter across the light path, the line exposure controller 6 turns the voltage to PLZT elements to 50 V. Accordingly, the G mode of light falls on the printing paper 2 producing another pattern of dots D1, D3..., as shown in Fig. 4(B). Similarly, when the color shifter disk 93 is further rotated to forward the R filter across the light path, the line exposure controller 6 turns the voltage to PLZT elements to 55 V. Then, the R mode of light is projected on to the printing paper 2 producing a pattern of dots D1..., as shown in Fig. 4(C). After the steps of exposure process, the dot D1 appears consisting of three, B, G, and R, colors, the dot D2 comprises B and R colors, the dot D3 is expressed by G color, and the dot D4 holds no color. While the boundary 930 on the color shifter disk 93 is running across the light receiving face 81 of the optical fiber bundle 8, the light receiving face 81 is blinded by the light shielding sector 94A of the light shielding disk 94. During a series of the exposure actions to B, G, and R modes of light, the printing paper 2 is held at the same location to allow printing of a row of dots extending widthwisely of the printing paper 2. After the steps shown in Fig. 4 is completed, the printing paper 2 is advanced by a distance of one dot size. As the result, the succeeding row of dots on the printing paper 2 is exposed to light at the exposure location, as shown in Figs. 4(D) to 4(F). Also, a series of the exposure actions to the B, G, and R modes of light are carried out in synchronization with the rotating action of the color shifter disk 93 thus producing another row of print dots. After the succeeding row of dots is printed by exposure to the B, G, and R modes of light, the printing paper 2 is further advanced by the distance of one dot size. In this manner of row-by-row printing, the exposure process is implemented lengthwisely of the printing paper 2. The rotating action of the color shifter disk 92 is not limited to one particular means but may be conducted by controlling the number of pulses to a stepping motor. The exposure apparatus of this embodiment is not limited to the use in the photographic printer machine but may be applied to exposure to any other photosensitive materials. In the development station 5, the printing paper 2 exposed to light at the negative exposure station 3 and/or the line exposure station 4 is subjected to a development process and cut into frames. Embodiment 2 An exposure apparatus of this embodiment for use in a photographic printing machine is substantially identical in the construction to that of Embodiment 1, comprising a magazine for supplying a tape of printing paper, a negative exposure station, a line exposure station, a development station, a transfer means for conveying the printing paper lengthwisely on a line-by-line and frame-by-frame basis, and a line exposure controller. Also, a PLZT light source is provided similar to that of Embodiment 1, including a lamp (not shown), a mirror tunnel (not shown), a color shifter disk 93, and a bundle of optical fibers 8 with its proximal end arranged as a light receiving face, but excluding the light shielding disk. As shown in Fig. 5, the light receiving face 81 of the optical fiber bundle 8 is shaped of an oval configuration of which long axis extends along the boundary 930 of the color shifter disk 93 disposed across the light path between the lamp and the light receiving face 81 of the optical fiber bundle 8. It should be noted that the size of the light receiving face 81 remains unchanged as is identical to that of Embodiment 1. The color shifter disk 93 is also identical in the construction to that of Embodiment 1 and will be explained in no more details in which like components are denoted by like numerals. The exposure apparatus of this embodiment allows the boundary 930 of the color shifter disk 93 to perform a smaller angular motion for crossing the light receiving face 81, as shown in Figs. 5(A) to 5(C). In other words, the boundary 930 can cross the light receiving face 81 within a shorter period of time. This will decrease the leakage of light and hardly impair the quality of printing with no use of the light shielding disk of Embodiment 1. Embodiment 3 An exposure apparatus of this embodiment for use in a photographic printing machine is substantially identical in the construction to that of Embodiment 1, comprising a magazine for supplying a tape of printing paper, a negative exposure station, a line exposure station, a development station, a transfer means for conveying the printing paper lengthwisely on a line-by-line and frame-by-frame basis, and a line exposure controller. Also, a PLZT light source is provided similar to that of Embodiment 1, including a lamp (not shown), a mirror tunnel (not shown), a color shifter disk 93, and a bundle of optical fibers 8 with its proximal end arranged as a light receiving face, but excluding the light shielding disk. As shown in Fig. 6, the light receiving face 81 of the optical fiber bundle 8 is shaped of a rectangular configuration of which long side extends along the boundary 930 of two adjacent color filters on the color shifter disk 93 disposed across the light path between the lamp and the light receiving face 81 of the optical fiber bundle 8. It is found that the rectangular light receiving face 81 of the optical fiber bundle 8 is most efficient when its long side is equal to 1/4 of the diameter of the color shifter disk 93. Assuming that the diameter of the color shifter disk 93 is D, the long side of the light receiving face 81 is L, and the area of the light receiving face 81 is A, the angle  of a straight line extending from the center C1 of the color shifter disk 93 and tangent to the rectangular light receiving face 81 is expressed by Equation 1 (Fig. 6): The angle  is minimum when 2L(D/2-L) is maximum. Then, L-D/4 is given. As the angle  is minimized, L1 becomes as small as close to zero, and may be negligible. In this arrangement like Embodiment 2, it is also possible for the boundary 930 to cross the light receiving face 81 within a shorter period of time. This will decrease the leakage of light and hardly impair the quality of printing with no use of the light shielding disk of Embodiment 1. According to the invention, a light shielding disk as that of Embodiment 1 is provided in this embodiment so that the effect of the leakage of light will be further attenuated. Embodiment 4 An exposure apparatus of this embodiment for use in a photographic printing machine is substantially identical in the construction to that of Embodiment 1, comprising a magazine for supplying a tape of printing paper, a negative exposure station, a line exposure station, a development station, a transfer means for conveying the printing paper lengthwisely on a line-by-line and frame-by-frame basis, and a line exposure controller. Also, a PLZT light source is provided similar to that of Embodiment 1, including a lamp (not shown), a mirror tunnel (not shown), a color shifter disk 93, and a bundle of optical fibers 8 with its proximal end arranged as a light receiving face, but excluding the light shielding disk. As shown in Fig. 8, the light receiving face 81 of the optical fiber bundle 8 has a fan-shaped configuration which spreads from the center point of the color shifter disk 93. Assuming that the diameter of the color shifter disk 93 is D, the long side of the light receiving face 81 is L, and the area of the light receiving face 81 is A, the angle  1 of a straight line extending from the center C1 of the color shifter disk 93 and tangent to the fan-shaped light receiving face 81 is expressed by Equation 2 (Fig. 7):  1 = 360A π D 2 If the light receiving face 81 has a fan shape with its proximal part eliminated (Fig. 9) and the distance from the center C1 of the color shifter disk 93 to the inner side of the light receiving face 81 is equal to 1/X of the diameter D of the color shifter disk 93, the angle  2 of a straight line extending from the center C1 of the color shifter disk 93 and tangent to the truncated fan-shaped light receiving face 81 is expressed by Equation 3: With those arrangements, the duration of the boundary 930 running throughout the light receiving face 81 is shortened as shown in Figs. 8(A) to 8(C). Since the fan-shaped light receiving face 81 corresponds exactly to an area defined by an angular movement of the boundary 930 of the color shifter disk 93, the duration is minimized. Accordingly, the leakage of light will be further reduced thus hardly impairing the quality of printing with no use of the light shielding disk of Embodiment 1. According to the invention, a light shielding disk as that of Embodiment 1 is provided in this embodiment so that the effect of the leakage of light will be further attenuated. The shape of the light receiving face of the optical fiber bundle is not limited to those of the embodiments and may be modified for minimizing the width of the light receiving face of the optical fiber bundle which extends in the direction of rotation across the boundary on the color shifter disk without changing the size of the shape.

Claims: An exposure apparatus (4, 9) for exposing a photosensitive material (2), the apparatus including a light source (91), a PLZT or liquid crystal exposure shutter (41), an optical fibre means (8) for transmitting light from said light source (91) to said exposure shutter (41), a rotatable colour shifter disc (93) constituted by a disc (93) divided into three sectors having a blue, a green and a red colour filter (93B, 93G, 93R), respectively, such that when the disc (93) rotates each of the three filters moves sequentially across the light path between the light source and the light receiving face (81) of said optical fibre means (8) thereby producing blue, green and red exposure light for exposing the photosensitive material (2), characterised in that the optical fibre means is an optical fibre bundle (8) and the light receiving face (81) of the bundle of optical fibres (8) is flattened so that it extends along the boundary (930) of two adjacent colour filters of the colour shifter disc (93) which runs across the light path, the apparatus further comprising a rotatable light shielding disc (94) comprising a light shielding sector (94A) and a transparent sector (94B), said shielding sector (94A) and said transparent sector (94B) being arranged for moving sequentially to and from the light path in synchronisation with the rotating movement of the colour shifter disc so that the light shielding sector advances into the light path to interrupt the exposure light when a boundary (930) between two adjacent colour filters (93B, 93G, 93R) of the colour shifter disc (93) runs across the light path and retracts from the light path to pass the exposure light when the boundary between the two adjacent colour filters of the colour shifter disc (93) departs from the light path. An exposure apparatus as claimed in claim 1, wherein the light receiving face (81) of the bundle of optical fibres (8) has an oval shape. An exposure apparatus as claimed in claim 1, wherein the light receiving face (81) of the bundle of optical fibres (8) has a rectangular shape. An exposure apparatus as claimed in claim 1, wherein the light receiving face (81) of the bundle of optical fibres (8) has a fan shape which spreads from the centre point of the colour shifter disc (93).

Inventors: ISHIKAWA MASAZUMI, TANIBATA TOHRU, ISHIKAWA, MASAZUMI, TANIBATA, TOHRU
Applicants: NORITSU KOKI CO LTD, NORITSU KOKI CO., LTD.
Application year: 1995
Main classification: G03B27
IPC codes: G03B27, G03B41, G03B33, G02B26, H04N9, H04N1