EXPOSURE CONTROL DEVICE

Abstract: An exposure device of a color copying apparatus has a filter holding frame mounting a filter plate (19, 21) provided with color filter layers and a transparent section (26) and a pair of aperture plates (22, 23) for forming a variable aperture. The filter holding frame is movable in one direction perpendicular to an exposure light path to selectively place the filter layer and transparent section into the exposure light path. The aperture plates (22, 23) are movable close to and away from each other in a direction perpendicular to the one direction and the exposure light path so as to vary the size of aperture formed thereby. Between the filter holding frame and the pair of aperture plates (22, 23) there is a mechanism comprising pins and cam grooves for cooperating the filter holding frame and the aperture plates. The cam groove comprises a straight cam section and an inclined section.

Description: Background of the Invention The present invention relates to an exposure control device used in a silver salt photographic type color copying apparatus or a color printer for regulating the amount and components of exposure light. A very early type of exposure device is described in AT-B-29 610. This reference shows a filter holding plate for holding a filter plate comprising a transparent section and a colour filter section which is positioned parallel to the aperture blades and movable in a direction perpendicular to the optical axis. A more recent type of exposure control device which is disclosed in, for example, Japanese Patent Publication No.44-2542 includes two color filter plates and a variable aperture plate both disposed between front and rear groups of a lens system. These color filter plates and variable aperture plate are moved in a direction perpendicular to the optical axis of the lens system so as to regulate the amount and color components of light passed therethrough in order to control the color balance and density of a copy. Each color filter plate includes two color filter sections and a transparent section between the two color filter sections. These two color filter sections have two different colors of three primary colors, namely blue, green and red, or of cyan, magenta and yellow. One of these three colors is used in both color filters. Color originals from which copies are made are generally classified into two, namely color printed materials and color photographic materials. Because of different coloring materials used in these color printed and photographic materials, these two materials have different spectral distributions for three primary colors. As a result, copies of these materials tend to have different color densities and/or color balances. In order to make copies having the same color density and color balance from any one of the two color materials, filters are used according to spectral sensitivities of photosensitive materials used. In addition, it is needed to adjust the color temperature of a light source to that of a photosensitive material to be used. The conventional color copying apparatus with color filter plates to be moved in and out of an optical path are needed to provide a filter adjusting mechanism which is complicated in construction and, therefore, makes the apparatus large. Object of the Invention It is, therefore, an object of the present invention to provide an exposure device with color filter plates and a variable aperture plate which are driven in cooperation with each other so as to be made compact. Summary of the Invention The above and other objects of the present invention are accomplished by providing an exposure device according to claim 1. Brief Description of the Drawings Figure 1 is a fragmentary side view showing a silver salt type copying apparatus embodying the present invention; Figure 2 is a perspective view of the exposure control device of a preferred embodiment of the present invention; Figure 3 is an enlarged cross sectional view of the exposure device of Fig. 2; Figures 4 to 6 are graphs showing a spectral transmittance for yellow, magenta and cyan filter layers, respectively; Figure 7 is a graph showing spectral transmittances for a green reflection type band-pass filter layer and a light balancing filter layer; Figure 8(A) is a diagram illustrating the filter positions of the green reflection type band-pass filter layer and the light balancing filter layer; Figure 8(B) is a diagram illustrating the size of the variable aperture; and Figure 9 is a block diagram showing a exposure control circuit used in connection with the exposure control device of Fig. 2. Detailed Description of the Invention Referring now to Fig 1 shown therein is a silver salt photographic type color copying apparatus embodying the present invention. As shown, a color original 10 from which a color copy is made is moved at a constant speed in a direction shown by an arrow. While the color original is moved, the color original 10 is illuminated with a slit light illumination light emitted from an illumination light source 11 which comprises a lamp 12 and a reflector13. Between the color original 10 and a color photosensitive material 15, there is a lens unit 16 for forming an image of the color original 10 on the color photosensitive material 15 and for regulating three color components and the amount of exposure light passed therethrough so as to make a color copy with a corrected color and density. Specifically, the lens unit 16 has front and rear lens groups 17 and 18; a first filter plate 19, a fixed aperture plate 20 and a second filter plate 21 disposed in this order between the front and rear lens groups 17 and 18; and a pair of aperture plates 22 and 23, and a third filter plate 24 disposed in this order behind the rear lens group 18. The pair of aperture plates 22 and 23 is movable close to and far away from each other so as to form a variable diaphragm. The first filter plate 19, as is shown in detail in Figs. 2 and 3, comprises a transparent glass plate 26 with color filter layers, namely a magenta filter layer 27 and a yellow filter layer 28, coated to its front surface. Between the filter layers 27 and 28 there is left a transparent or non-filter space. The second filter plate 21 also comprises a transparent glass 29 with color filter layers, namely a magenta filter layer 30 and a cyan filter layer 31, coated to its front surface. Between the filter layers 30 and 31 there is also left a transparent space. These filter layers; yellow 28, magenta 27and 30, and cyan 29, have spectral transmittances shown in Figs. 4 through 6, respectively. Since these first and second filter plates 19 and 21 are located close to a pupil of the lens system, the exposure light in the form of a slit line is prevented from being colored even partially. As is shown clearly in Figs 2 and 3, the fixed aperture plate 20 has an aperture opening 20a defined by a center circle. As is known in the art, inks used in ordinary printed matters have a green component having a peak wavelength approximately at 570 nm and, on the other hand, dyes used in photographic prints have a green component having a peak wavelength approximately at 535 nm. For making a same color balance and density of color copies from printed matter and photographic prints as color originals, it is often taken to shift substantially the peak of sensitivity of a color photosensitive material by using a band-pass filter. For example, if the color photosensitive material 15 has a sensitivity distribution for green having a peak approximately at 560 nm, a green reflection band-pass filter is used to cut green light having wavelengths on a relatively longer wavelength side of a green wavelength range so as to shift the peak of sensitivity distribution of the color photosensitive material to approximately 540 nm. Generally, a light balancing filter ( LB filter ) is used as a color conversion filter in color copying apparatus. For this reason, the third filter plate 24 comprises a transparent glass plate 32 with a combination filter layer ( G + LB ) 33 comprising a green reflection band-pass filter layer ( G filter layer ) and a light balancing layer ( LB filter layer ) coated on one surface thereof. These filter layers have spectral transmittances shown in Fig. 7. For the green reflection band-pass filter layer, an interference filter is used to reflect green light having relatively long wavelengths. When using such an interference filter, reflected green light is partially bounced by the rear lens group 18 toward the interferential filter and partially pass therethrough. If the reflected light is repeatedly bounced, it creates ghost images. For avoiding such ghost images, a variable diaphragm comprising the aperture plates 22 and 23 is arranged in front of the green reflection band-pass filter to prevent undesirable light from reaching the green reflection band-pass filter. Behind the lens unit 16, there is a swingable mirror shutter 36 which is placed in the optical path L as is shown by a solid line in Fig. 1 when the color original 10 is measured by light measurement means 37 to detect its density. The swingable mirror shutter 36 is removed out of the optical path L when a copy is made. In an exposure station there are a pressure plate 38 for holding the color photosensitive material 15 flat and a slit mask 39. On upper and lower sides of the exposure station there are pairs of conveyor rollers 40 and 41. There is a photosensitive material magazine 42 contains therein the color photosensitive material 15 in the form of a roll which is withdrawn by means of the conveyor rollers 40 and 41. After exposure, the color photosensitive material 15 is cut off by means of a cutter 43 to a color photosensitive sheet 15A which is sent into a processing section 44 incorporated in the copying apparatus. The color photosensitive sheet 15A is superimposed over a color image-receiving material 45 in the form of sheet in the processing section 44 for diffusion transfer processing. Referring now to Fig. 2 showing a filter driving mechanism, there is a filter frame 50 mounting the first filter plate 19 which is movable in a direction perpendicular to the optical path L. This filter frame 50 is formed with a rack 50a and a straight slot 50b which is engaged by a fixed pin 53. The rack 50a is in mesh with a gear 52 coupled to a stepping motor 51. The second filter plate 21 is mounted by a filter holder 54 which is formed with a rack 54a in mesh with a gear 56 coupled to a stepping motor 55 and a straight slot 54b engaged by a fixed pin 57. The third filter plate 24 is mounted in the filter frame 60 which is formed with a rack 60a and a straight slot 60b engaged by a fixed pin 63. The rack 60a is in mesh with a gear 62 coupled to a stepping motor 61. These filter frames 50, 54 and 60 are independently moved in a direction perpendicular to the optical path L by means of the respective stepping motors 51, 55 and 61 through pin-and-slot engagement. The filter frame 60 for the third filter plate 24 is formed with upper and lower cam slots 64 and 65 slidably engaged with which are pins 66 and 67 of the aperture plates 22 and 23, respectively. Each cam slot 64, 65 has a horizontally extending cam section 64a, 65a for maintaining the aperture plates 22 and 23 away from each other and a inclined cam section 64b, 65b for moving the aperture plates 22 and 23 close to each other. Shown are slots 22a for guiding the aperture plates 22 and 23 to move up and down through pins 68 which, unlike pins 63, 66 and 67, are not fixed. Referring now to Fig. 8A and 8B shown therein is the relationship between the position of the third filter plate 24 and the aperture plates. The stepping motor 61 can make rotational steps between 0 (initial position) and up to m4. When a density measurement is effected, the stepping motor 61 stays at its initial position O and, on the other hand, upon a copy being carried out, the stepping motor 61 makes rotational steps between m2 and m4. While the stepping motor 61 makes rotation through the rotational steps between the initial position O and m1, the third filter plate 24 is placed with its transparent section in the optical path L and the pins 66 and 67 of the aperture plates 22 and 23 stay in the straight cam sections 64a and 65a of the cam slots 64 and 65, respectively; the aperture plates 22 and 23 maintain the maximum size of aperture. When the stepping motor 61 makes more than the number of rotational steps m1, the third filter plate 24 begins to place the combination filter layer ( G + LB ) 33 in the optical path L. Between the numbers of rotational steps m2 and m4 of the stepping motor 61, the third filter plate 24 moves so that the combination filter layer ( G + LB ) 33 is fully placed in the optical path L. Simultaneously with this movement of the third filter plate 24, the inclined cam sections 64b and 65b of the upper and lower cam slots 64 and 65 of the filter frame 60 is slidingly guided by the pins 66 and 67 of the aperture plates 22 and 23, forcing the aperture plates 22 and 23 to move close to each other. Consequently, the aperture plates 22 and 23 decreasingly vary the size of aperture so as to control the amount of exposure light passed therethrough. Reference is now had to Fig. 9 shown therein is an exposure control circuit used in connection with the exposure control device according to the present invention. The light measurement means 37 comprises three light sensors 37a, 37b and 37c for blue, green and red, for detecting three color components of the reflected light from the color original 10, respectively upon the color original being scanned. Outputs from the respective light sensors 37a to 37c are converted into digital signals by means of an A/D converter 71 after being amplified by an amplifier 70. These digital signals, after being transformed into logarithms by a logarithmic transformer 72, are sent to a controller 73 and then memorized in a memory 74. The controller 73, following to the scanning of the color original 12, reads out the data on the three components of the reflected light measured by the light measurement means 37 to calculate needed amounts of color correction and of density correction by using an exposure calculation formula. According to the calculated amount of color correction, the controller 73 causes drivers 75 and 76 to drive the stepping motors 51 and 52, respectively. Simultaneously, the controller 73 causes a driver 77 to drive the stepping motor 61 according to the calculated amount of density correction so as to move the filter frame 60 in order to place the combination filter layer 33 in the optical path and to move the aperture plates 22 and 23 for decreasingly varying the size of aperture. In operation of the exposure control device described above, prior to making a color copy, a color original 10 is scanned to detect three color densities thereof. For a high accuracy of measurement, the first to third filter plates 19, 21 and 24 are located at their initial positions as shown in Figs. 2 and 3 to place their transparent sections in the optical path L. The swingable mirror shutter 36 is moved into the optical path to direct the reflected light from the color original 10 to the light measurement means 37 shown by a solid line in Fig. 1. When the third filter plate 24 is at its initial position, the combination filter layer 33 and the aperture plates 22 and 23 are all out of the optical path L, providing the maximum size of aperture. When the color original 10 is continuously moved down at a constant speed in the direction shown by an arrow shown in Fig. 1 and scanned with a slit line illumination light emitted from the lamp 12 of the illumination light unit 11, the reflection light from each division of the color original 10 travels to the mirror shutter 36 through the lens unit 16 and is reflected and directed by the mirror shutter 36 to the light measurement means 37. As is described previously, the sensors 37a to 37c of the light measurement means 37 detects three color components of the reflected light. Outputs from the sensors 37a to 37c are memorized in the memory 74 after having been subjected to amplification, digital conversion, and logarithmic transformation. After the scanning of the color original 10, the color original 10 is returned to its initial position. The controller 73 reads out the data of the measured components of the reflected light for the divisions of the color original 10 from the memory 74 to calculate correction exposures by color. From the correction exposures for the respective colors, what is common to some correction exposures is extructed as the amount of density correction. The remaining correction exposure is used as the amount of color correction. The controller 73 drives the stepping motor 51 and 55 according to the amount of color correction to force the filter frames 50 and 54 to slide in a direction perpendicular to the optical path L, thereby regulating the color components of light passed therethrough. Simultaneously, the controller 73 drives the stepping motor 61 according to the amount of density correction to force the filter frame 60 in a direction perpendicular to the optical path L, thereby regulating the amount of light passed therethrough. When the stepping motor 51 is driven in the normal direction, the yellow filter layer 28 of the first filter plate 19 is inserted into the optical path L in proportion to the number of rotational steps of the stepping motor 51. On the other hand, when the stepping motor 51 is driven in the reversed direction, the magenta filter layer 27 of the first filter plate 19 is inserted into the optical path L in proportion to the number of rotational steps of the stepping motor 51. In the same way, the stepping motor 55 can selectively insert the cyan and magenta filter layers 31 and 27 into the optical path L in proportional to the number of rotational steps thereof. By the control of rotation of the stepping motors 51 and 55, it is possible to insert various combinations of two filter layers into the optical path L. Specifically, in one case, two same filter layers one individual to each filter plate 19, 21 are placed in the optical path L and, in the other case, two different filter layers are placed in the optical path L. These combinations of filter layers are previously memorizes in the memory 73 and selectively retrieved by the controller 73 so as to control the stepping motors 51 and 55. It will be understood that it is impossible to place simultaneously the three different filter layers, namely magenta, yellow and cyan, in the optical path L in order to regulate the color component of light. However, by varying the size of the aperture formed by the aperture plates 22 and 23, the color component of light can be equivalently regulated. The stepping motor 61 is controlled by the controller 73 to be driven so as to slide the filter frame 60 in a direction to the left as viewed in Fig. 2 according to the amount of density correction. If it is not needed to introduce any density correction, the stepping motor 61 rotates through the rotational steps of m2, the combination filter layer ( G + LB ) 33 of the third filter plate 24 is fully placed in the optical path L. On the other hand, in the case that it is needed to introduce some density correction, the stepping motor 61 rotates through more than the rotational step m2 to vary the size of aperture which is defined by the aperture plates 22 and 23, thereby to regulate the amount of light. After the adjustment of the filter plates 19, 21 and 24, the color original 10 is again moved at a constant speed in the direction shown by the arrow in Fig. 1. The conveyor rollers 40 and 44 are rotated in synchronism with the movement of the color original 10 to withdraw the photosensitive material 15 from the magazine 42 at a constant speed. When a predetermined of time is passed after the cmmencement of the movement of the color original 10, the mirror shutter 36 is turned to be removed out of the optical path L so as to allow the exposing light reflected from the color original 10 in the form of a slit line to the photosensitive material 15 moving in synchronism with the color original 10, thereby exposing the photosensitive material 15. Upon the photosensitive material 15 being exposed with a slit line exposing light, the exposing light reflected from the color original 10 is corrected in color balance by the first and second filter plates 19 and 21 and in the amount of light by the aperture plates 22 and 23. Further, the exposing light is adjusted in color temperature by the LB filter layer of the combination filter layer 33 of the third filter plate 24 and a green component of the exposure light having a relatively long wavelengths is cut by the green reflection band-pass filter layer (G) of the combination filter layer 33 of the third filter plate 24. By using the combination of the four filters, the exposure light is regulated so as to make copies with same image conditions from either of printed and photographic originals. When the whole length of the color original is scanned, the mirror shutter 36 is returned to the position shown by a solid line in Fig. 1 so as to block the optical path L, completing a copy. Following the return of the mirror shutter 36, the exposed part of the photosensitive material 15 is cut off by the cutter 41 to a photosensitive sheet 15A and then sent into the processing section 44 of the apparatus. There, the exposed photosensitive sheet 15A is superimposed over an image-receiving sheet 45 for diffusion transfer processing in a well known manner. After a predetermined time needed to form a diffusion image on the image-receiving sheet 45, the image-receiving sheet 45 is peeled-apart from the photosensitive sheet 15A. Additional details of such a diffusion transfer type color copying apparatus may be obtained by reference to Japanese Patent Unexamined Publication No.59-204042. Although the above embodiment of the present invention has been directed to a diffusion transfer type color copying apparatus, it is to be understood that the present invention may be applicable to various kinds color copying apparatus using silver salt photographic materials such as direct positive photosensitive materials and color printers which making positive images on a photographic paper from negative images. It is to be noted that, in place of moving a color original, the mirror unit may be moved in synchronism with the lens unit so as to scan the color original stationarily placed.

Claims: An exposure control device comprising: a filter plate (24) comprising a transparent section (32) and a colour filter section (33); a filter holding frame (60) movable in a first direction perpendicular to an optical axis (L) for holding said filter plate therein; characterised by a pair of aperture blades (22, 23) arranged in a plane extending perpendicularly to said optical axis (L) such that the blades (22, 23) are movable towards and away from each other in a direction perpendicular to said first direction, thereby forming a variable aperture therebetween; a pair of pins (66, 67) fixed to either one of said filter holding frame (60) and said pair of aperture blades (22, 23); and a pair of cam slots (64, 65) formed in the other one of said filter holding frame (60) and said pair of aperture blades (22, 23) and engaged by said pair of pins (66, 67), each cam slot (64, 65) comprising a first straight cam section (64a, 65a) extending in said first direction and a second cam section (64b, 65b) inclined with respect to said first direction, said first cam section (64a, 65a) being arranged to maintain said pair of aperture blades (22, 23) out of an optical path parallel to said optical axis (L) when said transparent section (32) of said filter plate (24) is positioned in said optical path and when said colour filter section (33) of said filter plate (24) is positioned by a movement thereof in a position fully in said optical path, whereas said second cam section (64b, 65b) moves said pair of aperture blades (22, 23) into said optical path by a further movement of id filter plate (24) in said first direction so as to decrease the distance between said aperture blades to control the amount of light passed therethrough. An exposure control device as defined in claim 1, wherein said filter plate (24) comprises a transparent glass plate forming said transparent section (32) and comprising a colour temperature conversion filter layer (LB) and a green reflection band-pass filter layer (G) overlapping each other, thereby forming said colour filter section of said filter plate (24). An exposure control device as defined in claim 1, wherein said pair of cam slots (64, 65) is formed in said filter holding frame (60). An exposure control device as defined in claim 2, wherein said pair of aperture blades (22, 23) is located in front of said filter holding frame (60). An exposure control device as defined in claim 2, wherein said colour temperature conversion filter (LB) is a light balancing filter.

Inventors: HORIGUCHI, MASASHI, YAKUBO, MINORU
Applicants: FUJI PHOTO FILM CO., LTD.
Application year: 1988
Main classification: G03B7
IPC codes: G03B27, G03G15